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Signaling Pathways in Cardiac Myocyte Apoptosis.

1. Introduction

Cell survival and death are fundamental for organ development, tissue homeostasis, and disease pathogenesis. Based on morphological manifestations, cell death was initially classified into three categories by Schweichel and Merker: type I (apoptosis) that is associated with cell fragmentation and heterophagy, type II (autophagic cell death) that is characterized by massive cytoplasmic vacuolization, and type III (necrosis) that is characterized by plasma membrane rupture and organelle swelling [1]. Since Kerr and colleagues introduced the concept of "apoptosis" to the scientific community in 1972 [2], the knowledge regarding this specific type of cell death has expanded tremendously. The original definition of apoptosis was based on morphological characteristics including chromatin condensation, nuclear fragmentation, cell shrinkage, and shedding of vacuoles (apoptotic bodies) that are eventually cleared via phagocytosis in vivo. However, with the substantial progress in the molecular mechanisms underlying cell death in the past decade, the Nomenclature Committee on Cell Death (NCCD) recently recommended defining various types of cell death based on their distinct biochemical characteristics [3]. In this regard, apoptosis is defined as a caspase-dependent, genetically controlled form of cell death [3]. This definition indicates that apoptosis is a biological process that can be modulated by genetic or pharmacologic interventions. In addition to apoptosis, multiple forms of regulated cell death exist, such as autophagic cell death that is associated with lipidation of microtubuleassociated protein light chain 3 (LC3) and degradation of sequestosome 1 (SQSTM1, also known as p62) [4] and necroptosis that is dependent on receptor-interacting protein kinases 1 and 3 (RIPK1/RIPK3) [5]. Interested readers are referred to the above review articles that discuss each cell death modality more comprehensively. Here we focus on the apoptotic form of cell death.

Apoptosis is initiated and executed through two major signaling pathways: the intrinsic and extrinsic pathways. Intrinsic apoptosis pathway (also named as mitochondrial apoptosis pathway) is triggered by intracellular stress such as oxidative stress, calcium overload, and DNA damage, leading to Bax/Bak-dependent mitochondrial outer membrane permeabilization (MOMP) and release of cytochrome c from mitochondria into cytosol (Figure 1). Cytosolic cytochrome c and apoptotic protease-activating factor 1 (Apaf-1) then form apoptosome and result in activation of caspase 9. By contrast, extrinsic apoptosis is initiated by extracellular stress signals including tumor necrosis factor-[alpha] (TNF-[alpha]), Fas ligand (FasL), and TNF-related apoptosis inducing ligand (TRAIL) through binding to their individual death receptors TNF-[alpha] receptor 1 (TNFR1), Fas, and TRAIL receptor 1/2 (TRAILR1/2), respectively. Death receptors then recruit Fasassociated death domain (FADD) and procaspase 8 into the death-inducing signaling complex (DISC), leading to caspase 8 activation (Figure 1). The activated initiator caspase 9 or 8 further induces activation of the effector caspases 3, 6, and 7, resulting in cleavage of essential cellular substrates and eventually apoptotic death of the cell.

Apoptosis is essential during heart development and has long been linked to a number of cardiovascular diseases such as ischemic heart disease, reperfusion injury, chemotherapy-induced cardiomyopathy, and heart failure [6]. Significant apoptosis was detected in embryonic heart at the time of outflow tract shortening [7], and inhibition of apoptosis using the pan-caspase inhibitor zVAD-fmkor adenoviral mediated expression of X-linked inhibitor of apoptosis protein resulted in excessive outflow tract above the base of the ventricles [8], indicating that apoptosis is required for morphogenesis of the outflow tract myocardial tissue. Although apoptosis appears to be dispensable for physiological homeostasis in normal adult heart, it can lead to cardiomyocyte loss that is associated with life-threatening cardiac dysfunction in multiple pathological settings [9,10]. Therefore, modulation of apoptosis is a promising therapeutic strategy for cardiovascular diseases.

Cardiac myocytes, which represent ~85% of total heart mass, are the major contracting cells in the heart. In the past decade, major progress has been made toward understanding the apoptosis mechanisms in cardiomyocytes. We feel that a comprehensive review of these new discoveries is urgently needed in the field. In this review, we will summarize the signaling pathways that regulate cardiomyocyte apoptosis, highlight important new findings, and discuss potential future directions of research.

2. PI3K/Akt Pathway

PI3K/Akt signaling pathway is activated following stimulation with various growth factors, cytokines, and hormones. Upon ligand binding, growth factor receptors, which are a group of receptor tyrosine kinases (RTKs), undergo dimerization and association with the regulatory subunit (p85) of PI3K, leading to activation of the catalytic subunit (p110, Figure 1). PI3K then converts phosphatidylinositol bisphosphate (PIP2) to phosphatidylinositol trisphosphate (PIP3), which recruits Akt to the plasma membrane, where it is activated through dual phosphorylation by PDK1 at Thr308 and by mTORC2 at Ser473. The role of Akt in myocardial biology has been extensively described by us in a previous review article [11]. Here we briefly summarize the recent findings about this pathway in regulation of apoptosis in cardiomyocytes.

The PI3K/Akt pathway was initially shown to be strongly activated by insulin and insulin-like growth factor 1 (IGF-1) and mediates its antiapoptotic effects in cardiomyocytes since blockade of this pathway by a specific PI3K inhibitor wortmannin, dominant-negative PI3K, or dominant-negative Akt dramatically inhibited the cytoprotective effect of insulin and IGF-1 [12, 13]. PI3K/Akt-mediated protection against apoptosis is associated with phosphorylation and inactivation of the BH3-only proapoptotic protein BAD (Figure 1) [13]. In vivo gene transfer of myristoylated Akt (myr-Akt), a membrane-localized constitutively active Akt1 mutant, also increased sarcolemmal Glut-4 expression and enhanced myocyte glucose uptake and glycolysis which may help maintain energy production in the oxygen-deprived ischemic heart [14]. Intriguingly, while acute moderate Akt1 activation is cardioprotective [12,14,15], chronic extensive activation of Akt1 in a cardiac-specific myr-Akt transgenic mice is deleterious during ischemia/reperfusion (I/R) due to feedback inhibition of PI3K activity through downregulation of insulin receptor substrate-1 (IRS-1) and IRS-2 [16]. These findings suggest that the timing and dose of activation are crucial for the effect of Akt on heart protection in vivo.

Subcellular localization of Akt also modulates its biological function likely through altering access to distinct substrates. Physiological importance of nuclear Akt was originally proposed based on the observation that the cardioprotective hormone estrogen is associated with increased nuclear phospho-Akt (Ser473) in human hearts and cultured cardiomyocytes [17]. Overexpression of nuclear-targeted Akt protected against myocardial I/R injury and cardiomyocyte apoptosis without phosphorylating typical cytoplasmic Akt substrates [18]. The myocardial target of nuclear Akt identified so far includes forkhead transcription factors [17], zyxin [19], and Pim1 [20]. Mitochondrial translocation of Akt was also documented in cardiomyocytes following treatment with leukemia inhibitory factor (LIF) [21]. At mitochondria, Akt phosphorylates hexokinase-II at Thr473 to protect outer membrane integrity through a mechanism that is still largely unclear [22].

Both Akt family members Akt1 and Akt2 are abundantly expressed in the heart. It has been shown that Akt2 also plays a cardioprotective role as genetic deficiency of Akt2 exaggerated cardiomyocyte apoptosis in response to ischemic injury [23]. The importance of the PI3K/Akt pathway in cardiomyocyte survival is further supported by its involvement in cardioprotection conferred by hypoxic preconditioning [24, 25], 17beta-estradiol [26], leukemia inhibitory factor (LIF) [27], neuregulin-1 [28], adrenomedullin [29], kallikrein [30], isoflurane [31], clusterin [32], tanshinone IIA [33], urotensin II [34], apoptosis regulator through modulating IAP expression (ARIA) [35], and glucagon-like peptide 1 (GLP1) [36].

2.1. PTEN. In contrast to PI3K, the dual protein/lipid phosphatase and tensin homologue (PTEN) dephosphorylates PIP3 to generate PIP2 and thus inhibits Akt activation. It has been shown that adenoviral expression of PTEN in neonatal rat cardiomyocytes led to caspase 3 activation and apoptosis [37]. Conversely, inactivation of PTEN by cardiac-specific deletion of PTEN gene or overexpression of a catalytically inactive PTEN mutant attenuated myocyte apoptosis in response to I/R injury or [[beta].sub.1]-AR stimulation [38, 39]. PTEN activity is positively regulated by direct interaction with the regulatory subunit (p85) of PI3K [40]. Indeed, expression of a p85 mutant lacking the PTEN binding site inhibited PTEN activity and cell death following simulated ischemia and reperfusion [41]. PTEN activation is observed in cardiomyocytes expressing a cleaved (and constitutively active) mutant of Rho-associated coiled-coil protein kinase 1 (ROCK1) and may contribute to ROCK1-dependent apoptosis [42].

2.2. PHLPP. Akt activity can be inhibited by PH domain leucine-rich repeat protein phosphatase (PHLPP), a protein phosphatase 2C(PP2C) family member that selectively dephosphorylates Akt at Ser473. Knockout of PHLPP-1 potentiated Akt phosphorylation at Ser473 and reduced infarct size in response to I/R challenge [43]. A most recent study revealed that PHLPP-1 expression is increased with aging, and an increase in PHLPP-1 expression exacerbated hypoxia/reoxygenation-induced apoptosis [44]. Similarly, Akt can also be dephosphorylated by PHLPP-2, which is activated by isoproterenol and forskolin through a cyclic AMP(cAMP-) independent mechanism [45]. However, its role in cardiomyocyte apoptosis has not been studied yet.

2.3. GSK-3. Ischemic preconditioning-induced, Akt-dependent phosphorylation and inactivation of its downstream target glycogen synthase kinase-3 (GSK-3) were initially speculated to confer cardioprotection because both preconditioning and pretreatment with GSK-3 inhibitors reduced infarct size to a similar extent [46]. These findings were supported by transgenic studies showing that cardiac-specific expression of either GSK-3[beta] or GSK-3[alpha] potentiated myocyte apoptosis, albeit through distinct mechanisms [47,48]. Conversely, cardiac-specific deficiency of GSK-3[beta] significantly inhibited myocyte apoptosis after myocardial infarction (MI) [49]. Although global deletion of GSK-3a exacerbated apoptosis after MI [50], following up studies revealed that cardiomyocyte-specific conditional deletion of GSK-3a reduced apoptosis by decreasing the Bax/Bcl-2 ratio [51]. The discrepancy is likely caused by secondary and compensatory effects associated with germline somatic gene deletion. Surprisingly, a most recent study revealed that conditional deletion of cardiac GSK-3[alpha]/GSK-3[beta] in adult mice resulted in ventricular dysfunction and dilation within 2 weeks through a mechanism involving DNA damage and mitotic catastrophe [52]. Collectively, these studies indicate that transient and partial inhibition of GSK-3 is cardioprotective, but complete loss of GSK-3 leads to dilated cardiomyopathy.

2.4. Piml. An important downstream target of myocardial Akt signaling has been demonstrated to be Pim1, a serinethreonine kinase that is robustly upregulated following treatment with the cardioprotective growth factor IGF-1 through an Akt-dependent mechanism [20]. Inhibition of Pim1 activity by genetic ablation of Pim1 or expression of a dominantnegative, kinase-dead Pim1 mutant (K67M) exacerbated cardiomyocyte apoptosis, whereas transgenic expression of Pim1 markedly reduced infarct size in mice [20, 53]. Further indepth studies revealed that cardiac-specific Pim1 expression increased levels of the prosurvival proteins Bcl-2 and Bcl-xl, which antagonized mitochondrial damage induced by oxidative stress and the proapoptotic truncated Bid protein [54]. Pim1-dependent inhibition of apoptosis has been implicated in cardioprotection induced by postconditioning and vitamin B1 stimulation [55, 56], supporting a critical role of Pim1 in regulation of cardiomyocyte survival following pathological challenge.

2.5. FoxO1. Akt phosphorylates the FoxO family transcription factors, resulting in their nuclear export and degradation in the cytosol through the ubiquitin-proteasome pathway [57]. FoxO has long been viewed as proapoptotic through transcriptional induction of proteins involved in intrinsic and extrinsic apoptosis pathways including Bim, BAD, Bnip3, FasL, and TRAIL [57]. Interestingly, overexpression of FoxO1 in cardiomyocytes did not seem to result in apoptosis under basal conditions but significantly induced expression of autophagy-related genes LC3 and Atg12 and enhanced autophagy [58, 59]. Following MI, however, cardiac-specific deficiency of FoxO1 decreased heart function and increased myocyte apoptosis, an effect that is associated with reduced expression of autophagy genes [60]. In addition, FoxO1 may also protect against apoptosis by forming a transcriptional complex with Yes-associated protein (YAP) and inducing expression of antioxidant genes catalase and manganese superoxide dismutase (MnSOD) [60, 61]. Moreover, another FoxO family member, FoxO3a, has also been shown to inhibit cardiomyocyte apoptosis and confers cardioprotection by inducing expression of apoptosis repressor with caspase recruitment domain (ARC), which attenuated oxidative stress-triggered sarcoplasmic reticulum [Ca.sup.2+] release [62]. A most recent study showed that knockdown of FoxO1 that is exported from the nuclei following Apelin-13 stimulation exaggerated apoptosis, suggesting that cytosolic FoxO1 may directly inhibit apoptosis through a transcription activity-independent mechanism [63].

3. MAPK Pathway

Mitogen-activated protein kinases (MAPKs) are evolutionarily conserved serine/threonine kinases that regulate cell behavior including survival, growth, and differentiation by altering protein function and gene expression in response to specific extracellular cues. Extracellular signals act through cell surface receptors such as RTKs and G protein-coupled receptors (GPCRs), leading to successive phosphorylation and activation of a three-layered hierarchical model including MAPK kinase kinase (MAPKKK), MAPK kinase (MAPKK), and MAPK. Three main families of MAPKs have been extensively investigated in regulation of cardiomyocyte apoptosis: extracellular signal-regulated kinase 1/2 (ERK1/2 or p44/42), c-Jun N-terminal kinases (JNK), and the p38 isoforms.

3.1. ERK1/2. ERK1/2 is activated following growth factor stimulation or integrin clustering, and activation of ERK1/2 primarily leads to cell growth and survival (Figure 1). ERK1/2 may also be activated by hydroxyl radicals through Ras/Raf-1 MAPKKK, but activation of ERK in this context is still protective as treatment with a selective ERK inhibitor PD98059 exacerbated hydrogen peroxide- ([H.sub.2][O.sub.2]-) induced cardiomyocyte apoptosis [64]. Indeed, while all three MAPKs are activated following daunomycin treatment and hypoxia/reoxygenation, only inhibition of ERK1/2 further potentiated cardiomyocyte apoptosis, suggesting a prosurvival role of the ERK1/2 kinases [65, 66]. Interestingly, doxorubicin-induced persistent ERK1/2 activation and nuclear translocation contributed to apoptosis in H9c2 cells and neonatal rat cardiomyocytes [67]. Inactivation of ERK1/2 by transgenic expression of a dominant-negative Raf-1, the MAPKKK upstream of ERK1/2, potentiated development of cardiomyocyte apoptosis following aortic constriction [68]. Mice deficient in cardiac Raf-1 exhibited spontaneous myocyte apoptosis as early as 3 weeks of age and heart dysfunction later in life [69]. Transgenic mice expressing a constitutively active MEK1, the major MAPKK directly phosphorylating and activating ERK1/2, inhibited I/R-induced cardiomyocyte apoptosis [70]. A more direct evidence of ERK-dependent cardioprotection was from the observation that myocytes were sensitized to apoptosis following pathological insult in both global and cardiac-specific ERK2 knockout mice [70,71]. Activation of ERK1/2 has been shown to mediate the antiapoptotic function of various molecules including [alpha]1-adrenergic receptor [72], urotensin II [34], and sialyltransferase7A [73]. However, much less is known about the mechanism(s) underlying ERK1/2-mediated protection against myocyte apoptosis.

3.2. Stress Activated Protein Kinases (SAPKs). In contrast to ERK1/2, JNK and p38 are stress activated protein kinases (SAPKs) that respond predominantly to environmental stress signals such as hypoxia, heat, inflammatory cytokines, and DNA-damaging agents. Inhibition of JNK protected against I/R-induced cardiomyocyte apoptosis in vitro and in vivo [74, 75]. Mitochondrial but not cytosolic JNK was phosphorylated upon [H.sub.2][O.sub.2] stimulation, leading to mitochondrial outer membrane permeabilization and cytochrome c release [76]. JNK-dependent activation of the mitochondrial apoptosis pathway is associated with decreased BAD phosphorylation at Ser112 [77, 78]. Inactivation of JNK contributed to the antiapoptotic effect of macrophage migration inhibitory factor (MIF) and a Curcumin analog [78, 79]. While mice deficient in JNK1/2 were shown to be resistant to I/Rinduced apoptosis, cardiac-specific transgenic mice expressing MKK7, the MAPKK for JNK kinases, were also protected from I/R injury [77]. Although somewhat surprising, the latter finding was consistent with previous reports revealing a protective role of JNK activation during nitric oxideor hypoxia/reoxygenation-induced cardiomyocyte apoptosis [80-82], possibly by phosphorylating Akt at Thr450, thus priming Akt for full activation [83], or by competing with procaspase 9 to bind Apaf-1 and abrogating apoptosome formation [84]. These contradictory results indicate that the role of JNK signaling in apoptosis is likely context dependent and much more complicated than initially thought.

Earlier studies revealed that treatment with the p38 MAPK inhibitor SB203580 attenuated myocyte apoptosis induced by anthracycline and hypoxia/reoxygenation both in vitro and in vivo, indicating a detrimental role of p38 [65, 66, 85, 86]. These findings were later corroborated by using genetic approaches to inactivate p38 in mouse heart. For example, heterozygous disruption of p38[alpha] drastically reduced infarct size after I/R challenge [87]. Cardiomyocyte apoptosis and cardiac dysfunction following I/R were also attenuated by p38 inactivation in transgenic mice expressing a dominant-negative p38[alpha] mutant, a dominant-negative MKK6 (the MAPKK upstream of p38) mutant, or MAPK phosphatase-1 (MKP-1, a phosphatase that dephosphorylates and inactivates p38 and JNK) [88, 89]. Cardioprotection by p38 inhibition was associated with an increase in the expression of the prosurvival Bcl-2 family members Bcl-2/Bcl-xl [88, 89]. Although p38 is activated by short repeated cycles of simulated ischemia/reoxygenation termed ischemic preconditioning, preconditioned heart actually exhibited lower p38 activity and was protected against injury during sustained ischemia [90, 91], likely through p38-dependent feedback upregulation of MKP-1 [92]. Inhibition of p38 activity has been proposed as a central mechanism underlying cardioprotection mediated by postconditioning [93], estrogen [94], and quercetin [95].

4. Integrin/FAK

Integrins are transmembrane heterodimers of [alpha] and [beta] subunits that physically link extracellular matrix (ECM) to intracellular actin cytoskeleton. In addition to maintaining cell adhesion capability and tissue integrity, integrins also transmit outside mechanical signals into the cell (outsidein signaling). Israeli-Rosenberg et al. recently provided a detailed review of integrins' multiple functions in cardiac myocytes [96] and hence we will only focus on their regulation of apoptosis signals.

The dominant [beta] subunit in heart is [beta]1 integrin, which forms a heterodimer with [alpha]1, [alpha]5, or [alpha]7 to predominantly bind ECM components collagen, fibronectin, or laminin, respectively. Global homozygous loss of [beta]1 integrin, as well as embryonic cardiac-specific knockout of [beta]1 integrin ([beta]1 [integrin.sup.flox/flox]]/Nkx2.5.sup.Cre/+]), was embryonically lethal [97-99]. However, the [beta]1 integrin heterozygous knockout mice developed into adulthood and were more vulnerable to cardiac dysfunction and myocyte apoptosis upon induction of MI or stimulation with the [beta]1 adrenergic receptor agonist isoproterenol [100, 101], suggesting that [beta]1 integrin protects myocyte against apoptosis in these settings. It is noteworthy that pressure overload did not appear to unmask the antiapoptotic role of [beta]1 integrin in acute ([beta]1 [integrin.sup.flox/flox]/[alpha].sub.MHC] Mer-Cre-Mer) or chronic myocyte-specific knockout models ([beta]1 [integrin.sup.flox/flox]/[Mlc2v.sup/Cre/+]) [102, 103]. The fact that acute or chronic ablation of [beta]1 integrin in cardiomyocytes depressed ventricular contractility and blunted hypertrophic response without inducing apoptosis indicates that [beta]1 integrin may protect the heart via additional mechanisms that are independent of its role in apoptosis inhibition. Nonetheless, it would still be interesting to evaluate whether cardiac-specific depletion of [beta]1 integrin modulates responses to I/R or [beta] adrenergic signaling-induced apoptosis, especially with the exciting observation that overexpression of integrin [alpha]7[beta]1D attenuated I/R injury and promoted cardiomyocyte survival [104].

Since integrins do not have an intracellular kinase domain, integrin-dependent signal transduction requires cytosolic kinases including focal adhesion kinase (FAK). Based on earlier studies demonstrating that myocyterestricted deletion of FAK exacerbated myocardial I/R injury [105], we demonstrated that cardiac-specific activation of FAK protected cardiomyocytes from I/R-induced apoptosis by enhancing NF-[kappa]B-dependent transcription of the prosurvival Bcl-2 family members Bcl-2 and Bcl-xl and X-linked inhibitor of apoptosis (XIAP, Figure 1) [106]. In addition, FAK also confers protection against anthracycline doxorubicininduced cardiomyopathy and myocyte apoptosis through increasing mRNA stability of the cyclin-dependent kinase (CDK) inhibitor (CDKI) p21 [107]. Our findings that p21 levels were inversely correlated with mitochondrial vulnerability and expression of the BH3-only protein Bim following doxorubicin treatment suggested that mitochondrial apoptosis pathway was inhibited by FAK/p21. Exactly how p21 regulates Bim expression in cardiomyocytes warrants further investigation.

5. TNF-[alpha]/NF-[kappa]B

Tumor necrosis factor-[alpha] (TNF-[alpha]), a 17 kDa proinflammatory cytokine generated after cleavage of the 26 kDa transmembrane protein pro-TNF-[alpha] by TNF-[alpha] converting enzyme (TACE), is secreted from resident mast cells and macrophages within minutes of myocardial I/R injury through a mechanism that is dependent on oxidative stress [108]. While cardiacrestricted expression of a nonsecretable transmembrane TNF-[alpha] mutant led to concentric hypertrophy, expression of the secreted wild-type TNF-[alpha] using the same strategy resulted in ventricular dilation [109], which is likely caused by primary activation of the extrinsic apoptosis pathway and subsequent t-Bid-dependent secondary activation of the intrinsic mitochondrial apoptosis pathway [110], caspase-dependent desmin cleavage and mislocalization [111], and NF-[kappa]B-dependent transcriptional suppression of sarcoplasmic reticulum [Ca.sup.2+]-ATPase 2a protein (SERCA2a) [112]. Consistently, global deficiency of TNF-[alpha] reduced inflammatory cell infiltration and cardiac rupture after permanent ischemia or I/R injury [113, 114]. The fact that deletion of TNF-[alpha] receptor 1 (TNFR1), but not TNFR2, protected the heart against I/R injury suggested that the detrimental effect of TNF-[alpha] was likely mediated by TNFR1 [115, 116]. Indeed, studies from an independent group revealed that knockout of TNFR1 attenuated apoptosis and suppressed activation of NF-[kappa]B, p38, and JNK2 in a permanent ligation model, while deletion of TNFR2 augmented apoptosis and enhanced activation of NF-[kappa]B and p38, suggesting that activation of TNFR1 and TNFR2 mediates detrimental and beneficial signals, respectively [117].

Given the divergent roles of TNFR1 and TNFR2, it is not surprising that TNF-[alpha] may exert cytoprotection in some context [118, 119]. It has been shown that TNF-[alpha] protected against myocardial I/R injury through TNF receptor-associated factor 2- (TRAF2-) dependent activation of NF-[kappa]B [120], leading to enhanced transcription of prosurvival Bcl-2 and c-IAP1 [121], transcriptional silencing of the death gene Bnip3 [122], or expression of keratin 8 and keratin 18 [123]. Moreover, inactivation of NF-[kappa]B by deletion of NF-[kappa]B essential modulator (NEMO)/inhibitor of kB kinase (IKK)[gamma] led to spontaneous ventricular dilation that is associated with exaggerated apoptosis and decreased expression of Bcl-xl [124]. It is noteworthy that the protective role of NF-[kappa]B may only be limited in cases where the activation of NF-[kappa]B is acute and transient, as persistent NF-[kappa]B activation by cardiomyocyte-specific expression of a constitutively active IKK2 led to inflammatory dilated cardiomyopathy, a phenotype that is associated with enhanced activation of the IFNstimulated gene 15 (ISG15) pathway, and could be reversed by in vivo expression of the endogenous NF-[kappa]B inhibitor I-kBa [125]. Chronic NF-[kappa]B p65 activation in the remote myocardium after permanent ligation has been linked to exacerbated apoptosis and myocardial dilation and dysfunction [126], and cardiomyocyte-restricted NF-[kappa]B inhibition in transgenic mice expressing the nonphosphorylatable I-kBa (S32A, S36A) or I-kBa (S32A, S36A, and Y42F) or the p65deficient mice conferred cardioprotection [126-128].

In addition to the Rel subfamily members (p65/RelA, RelB, and c-Rel) that contain a transcriptional activating domain (TAD), NF-[kappa]B family transcription factors also consist of a "NF-[kappa]B" subfamily (p50 and p52) without a TAD. The role of p50 in regulation of cardiomyocyte apoptosis has been controversial based on data generated from global p50 knockout mice, with deleterious [129, 130] and protective [131] effects being reported. The discrepancy may be explained by the fact that p50 can activate transcription when dimerization with p65 occurs but may also serve as an endogenous NF-[kappa]B inhibitor when it forms a p50/p50 homodimer [132].

6. GPCR

G protein-coupled receptors (GPCRs), the largest gene family in the genome, are conserved seven transmembrane receptors that have been extensively targeted for drug therapy. Ligand binding to GPCR induces dissociation of the G protein subunits G[beta][gamma] with G[[alpha].sub.s], G[[alpha].sub.i], [[alpha].sub.q], or [[alpha].sub.11/12], leading to divergent physiological responses. Dissociated G[beta][gamma] targets GPCR kinase 2 (GRK2) to the membrane and promotes GPCR desensitization. GRK2-mediated desensitization of adiponectin receptor 1 exacerbated ventricular remodeling after MI [133]. GRK2 was also localized to mitochondria following ischemic injury to induce opening of the mitochondrial permeability transition pore (mPTP) and cell death [134]. Consistently, depletion of GRK2 in cardiomyocytes suppressed cardiomyocyte apoptosis and I/R injury [135]. The best investigated cardiac GPCRs include G[[alpha].sub.s]- and G[[alpha].sub.1]-coupled [beta]-adrenergic receptors ([beta]-ARs); Gaq-coupled [alpha]1AR, endothelin receptors, and angiotensin receptors; and G[[alpha].sub.i]-coupled [[alpha].sub.2]-AR and adenosine receptors [136].

The predominant forms of cardiac ARs are [beta]1-AR (~70%), [beta]2-AR (~20%), and [alpha]1-AR (-10%) [137]. Stimulation of [beta]-ARs induces Gas-mediated activation of adenylyl cyclase, leading to production of cAMP and activation of cAMP-dependent protein kinase (PKA, see below for details). Adult rat cardiomyocytes treated with [beta]-AR agonists isoproterenol or norepinephrine underwent apoptosis that can be inhibited by [beta]1-AR antagonist but was potentiated by [beta]2-AR antagonist, suggesting a detrimental role of the Gas-coupled [beta]1-AR and a beneficial role of the Garcoupled [beta]2-AR [138, 139]. Stimulation of [beta]1-AR induced cardiomyocyte apoptosis by activation of PKA [140], calcineurin [141], [Ca.sup.2+]/calmodulin kinase II (CaMKII) [142], and reactive oxygen species-dependent synthesis of TNF-[alpha] [143], whereas stimulation of [beta]2-AR suppressed cardiomyocyte apoptosis by activation of the PI3K/Akt pathway [144-146]. Consistently, transgenic mice selectively expressing [beta]1-AR-associated G protein Gas in the heart displayed aging-related cardiomyopathy due to increased myocyte apoptosis [147], while cardiacspecific inhibition of the [beta]2-AR-associated G[[alpha].sub.i]; by transgenic expression of G[[alpha].sub.i] inhibitor peptide provoked apoptosis and exacerbated myocardial I/R injury [148]. However, it is noteworthy that stimulation of [beta]2-AR by isoproterenol has also been associated with enhanced apoptosis via PKA-mediated activation of p38 MAPK in some contexts [149, 150]. A possible explanation is that isoproterenol may promote cell survival or death in a dose-dependent fashion via activation of distinct pathways: treatment with low-dose isoproterenol enhances cell survival by increasing ERK1/2mediated expression of Bcl-2, while stimulation with high concentration of isoproterenol leads to cell death through PKA-dependent downregulation of Bcl-2 [140]. Interestingly, chronic [beta]1-AR stimulation by transgenic expression of [beta]1-AR or by isoproterenol injection also resulted in necrotic myocyte death that is dependent on mammalian Ste20-like kinase 1 (Mst1) [151].

Stimulation of [alpha]1-AR with the [alpha]1-AR agonist phenylephrine protected against cardiomyocyte apoptosis induced by a number of pathological stimuli such as isoproterenol [152], hypoxia [153], and doxorubicin [154]. By contrast, cardiomyocytes deficient in [alpha]1-AR were more susceptible to stress-induced apoptosis [155]. Cardiac myocytes express two [alpha]1-AR protein subtypes, [alpha]1A-AR and [alpha]1B-AR, in a ratio of 2-4:1 [137]. Vulnerability caused by [alpha]1-AR deletion was rescued by reintroduction of a1A-AR but not a1B-AR through activation of ERK [72]. Intriguingly,[alpha] sustained supraphysiological activation of a1A-AR (66-fold increase) provoked apoptosis and induced premature death of animals [156]. These results are in agreement with previous observation that while expression of the wild-type a subunit of Gq leads to Akt activation and cytoprotection [157], expression of a constitutively active Gp[alpha].sub.q] subunit (GqQ209L) paradoxically reduced Akt activity and induced apoptosis due to exhaustion of cellular PIP2 pool caused by hyperactivation of phospholipase C [beta] (PLC[beta], Figure 1) [158]. Under stress conditions such as pregnancy which may further enhance G[[alpha].sub.q] activity, cardiac-specific expression of wild-type G[[alpha].sub.q] induced apoptosis through a ROCK1-dependent mechanism [159]. Taken together, these studies indicate that moderate activation of the [alpha]1A-AR/G[[alpha].sub.q]/ERK pathway is cardioprotective.

The role of endothelin-1 receptor in cardiomyocyte apoptosis has been controversial. Early in vitro studies suggested that stimulation with endothelin-1 protected against isoproterenol-induced cardiomyocyte apoptosis through endothelin type A receptor ([ET.sub.A]R) but not type B receptor [160]. However, treatment with the [ET.sub.A]R antagonist attenuated myocyte apoptosis in cultured cells [161] and in animal models of MI [162], I/R [163], or doxorubicin-induced cardiomyopathy [164], indicating that endogenous endothelin-1 and [ET.sub.A]R are proapoptotic under these conditions. Mice deficient in cardiac endothelin-1 exhibited decreased hypertrophy and increased apoptosis following transverse aortic constriction [165], whereas cardiac-specific deletion of [ET.sub.A]R attenuated cold stress-induced hypertrophy and apoptosis [166]. The discrepancy may be caused by differences in dose and timing of drugs and/or pathological insults.

It is known that angiotensin II induces cardiomyocyte apoptosis via angiotensin type 1 receptor (AT1R) but not AT2R [167-169]. Indeed, prolonged activation of cardiac AT1R resulted in increased hypertrophy, fibrosis, and apoptosis [170]. AT1R-mediated apoptosis has been attributed to Ga12/13-induced activation of JNK and p38 MAPK [171], leading to HSF1 acetylation and IGF-IIR expression [172]. Angiotensin II-induced apoptosis can be repressed by activation of the Garcoupled A1 and A3 adenosine receptors [173], which mediates survival signaling through the PI3K/Akt and MEK/ERK1/2 pathways [174,175].

7. Hippo Pathway

The Hippo signaling cascade is an evolutionarily conserved pathway fundamental in organ size control through regulation of cell proliferation, apoptosis, and differentiation. The multifaceted roles of Hippo pathway in cardiovascular development and disease have recently been covered in an excellent review [176]. Mst1, an ortholog of Drosophila Hippo, is ubiquitously expressed serine/threonine kinase that has been intensively investigated in enhancing apoptosis in the cardiac settings. Myocardial Mst1 is activated by caspasemediated cleavage or phosphorylation in response to pathological stimuli that induce genotoxic and oxidative stress [177]. The Sadoshima group has demonstrated that cardiacspecific transgenic expression of a dominant-negative Mst1 mutant (K59R) reduced TUNEL labeling and DNA laddering following I/R or permanent ligation, suggesting that Mst1 is necessary for I/R or MI-induced apoptosis [177, 178]. They further showed that cardiomyocyte-restricted expression of Mst1 was sufficient to induce apoptosis and dilated cardiomyopathy [177]. Mst1 phosphorylates Beclin1 at Thr108, leading to sequestration of Bcl-2/Bcl-xl by phospho-Beclin1 and release of Bax to induce apoptosis [179]. Most recent studies revealed that Mst1 may directly phosphorylate Bcl-xl at Ser14, thereby inhibiting Bcl-xl/Bax interaction and inducing Bax activation and apoptotic death of cardiomyocytes [180, 181]. It is noteworthy that although [Mst.sup.1-/-] or [Mst2.sup.-/-] mice developed normally, homozygous disruption of both Mst1 and Mst2 led to increased apoptosis in embryos, a secondary response to placental functional defects in these mice [182]. These findings suggest that Mst1 and Mst2 kinases are necessary for early mouse development.

Activation of Mst1 by oxidative stress requires the scaffold protein Ras-association domain family 1 isoform A (Rassf1A), which binds mitochondrial K-Ras through its Ras-association (RA) domain and Mst1 through a Salvador/Rassf/Hippo (SARAH) domain [180]. Cardiomyocytespecific Rassf1A transgenic mice exhibited enhanced Mst1 phosphorylation, increased apoptosis, and impaired cardiac function after pressure overload [183]. Systemic ablation of Rassf1A reduced myocyte apoptosis but unexpectedly induced fibrosis and cardiac dysfunction following pressure overload through enhanced secretion of TNF-[alpha] by cardiac fibroblasts [183]. Indeed, cardiac-specific disruption of Rassf1A inhibited cardiomyocyte apoptosis and preserved LV ejection function after pressure overload [183]. It is most recently shown that I/R-induced Mst1 activation is mediated by neurofibromin 2 (NF2, Merlin), a 4.1, ezrin, radixin, moesin (FERM) domain-containing protein responsible for membrane and actin cytoskeleton association [184]. Cardiacspecific deletion of NF2 protected against I/R injury through activation of the YAP transcription factor, a main effector of the Hippo pathway [184]. In contrast, mTOR pathway negatively regulates Mst1 kinase activity through mTORC2dependent phosphorylation of Mst1 at Ser438 in the SARAH domain, leading to decreased homodimerization and activity [185]. Cardiac-specific deletion of Rictor, a major mTORC2 component, induced Mst1 activation and provoked apoptosis both at baseline and in response to pressure overload, leading to cardiac dysfunction and dilation [185].

Active Mst1 directly binds and phosphorylates large tumor suppressors 1/2 (Lats1/2), leading to their activation [176]. It has been shown that knockdown of Lats2 inhibited Mst1-induced apoptosis, indicating that Lats2 mediates the proapoptotic effect of Mst1 [186]. Moreover, cardiac-specific transgenic expression of dominant-negative Lats2 suppressed apoptosis induced by transverse aortic constriction [186].

Lats1/2 kinases phosphorylate and inactivate the transcription coactivator YAP through 14-3-3-mediated cytoplasmic retention and casein kinase-dependent degradation [176]. Heterozygous disruption of YAP in cardiomyocytes increased apoptosis after chronic MI in vivo, whereas overexpression of YAP protected cultured cardiomyocytes against [H.sub.2][O.sub.2]-induced apoptosis [187], likely through transcriptional upregulation of antioxidant genes catalase and MnSOD [61]. Cardiac-specific transgenic expression of a constitutively active, nuclear-localized YAP mutant (S112A) decreased apoptosis 7 days after experimental MI [188]. However, cardiac-specific expression of the YAP (S127A) mutant that has been associated with increased nuclear localization mitigated myocardial injury due to enhanced cardiomyocyte proliferation without decreasing apoptosis at 5 weeks after MI, indicating that YAP may regulate other cellular behaviors beyond its antiapoptotic role in the heart [189].

8. Small GTPases

Activities of the small GTPases Rho, Rac, and Cdc42 are regulated by guanine exchange factors (GEFs) and GTPaseactivating proteins (GAPs) downstream of a variety of extracellular and transmembrane molecules such as hormones, growth factors, and GPCRs. RhoA, a Rho subfamily GTPase, has been extensively studied in cardiac pathophysiology. Earlier studies revealed that supraphysiological expression of RhoA leads to heart failure and activation of the mitochondrial apoptosis pathway due to increased Bax expression [190, 191]. In contrast, moderately increased expression of RhoA was cardio protective against myocyteapoptosis in vitro and I/R damage in vivo via activation of multiple prosurvival kinases including Rho kinase, FAK, PI3K/Akt, and PKD [192, 193]. The beneficial role of RhoA was further supported by the observation that cardiac-specific deletion of endogenous RhoA exacerbated I/R injury [193] and that pharmacological inhibition of RhoA led to caspase 3 activation and apoptosis [194].

A major RhoA effector Rho-associated coiled-coil protein kinase 1 (ROCK1) is cleaved by caspase 3 into a 130 kDa fragment upon apoptosis induction. When expressed in cardiomyocytes, the truncated ROCK1 by itself induced caspase 3 activation and apoptosis in vitro and myocardial fibrosis in vivo [42, 195]. Interestingly, global deficiency of ROCK1 also inhibited myocyte apoptosis, and transgenic expression of ROCK1 enhanced apoptosis following pressure overload or in a pathological hypertrophy mouse model overexpressing Gaq [42, 159]. Although not always identical [196], ROCK2 appears to play a similar deleterious role to ROCK1 in apoptosis, as cardiac-specific knockout of ROCK2 reduced oxidative stress, myocyte hypertrophy, and apoptosis following angiotensin II infusion or transverse aortic constriction by inducing expression of four-and-a-half LIM-only protein2 (FHL2) [197].

Recent studies suggested that the small GTPase Rac plays a detrimental role in cardiomyocyte apoptosis. In a cardiomyocyte-specific Rac1 knockout model generated by breeding [Rac1.sup.flox/flox] mice with [alpha]-MHC-cre mice, deficiency of Rac1 reduced hyperglycemia-induced mitochondrial ROS production and myocardial dysfunction [198]. Further in vitro and in vivo studies revealed that overexpression of dominant-negative Rac1 or treatment with a Rac1 inhibitor blocked high glucose-induced cardiomyocyte apoptosis and improved heart function in type 2 diabetic db/db mice [198]. Early pioneering studies showed that cardiac-specific transgenic expression of Rac1 resulted in myocardial hypertrophy or dilation depending on temporal windows of expression [199]. In a similar transgenic mouse model, expression of the corn Rac gene led to superoxide generation and caspase activation upon Thyroxin treatment [200]. The observation that Rac-induced apoptosis can be blocked by administration of an antioxidant indicates that oxidative stress plays a causal role in apoptosis in these animals [200].

Another small GTPase, Cdc42, has also been implicated in inhibition of cardiomyocyte apoptosis. Pressure overload activates Cdc42, which acts as a negative feedback mechanism to inhibit hypertrophy through activation of JNK [201]. Cardiac-specific deletion of Cdc42 ([Cdc42.sup.flox/flox]/[alpha]-[MHC.sup.Cre/+]) aggravated apoptosis after transverse aortic constriction and may have contributed to hypertrophy decompensation in this model [201].

9. PKC

Protein kinase C (PKC) family consists of at least 12 isoforms that mediate hypertrophy and survival signaling in response to growth factors and hormones. Activation of PKC is preceded by phosphorylation of the activation segment by PDK1 and phosphorylation of the hydrophobic motif by mTORC2 [202]. Based on the signals required for their enzymatic activation, PKC isoforms can be divided into conventional PKCs ([alpha], [beta] and [gamma]) that are calcium and phospholipid dependent, novel PKCs ([delta], [epsilon], [etra] and [theta]) that are calcium independent but phospholipid dependent, and atypical PKCs ([zeta], [lambda]) that are calcium and phospholipid independent. These isoforms appear to have distinct functions as PKC[alpha] but not PKC[beta]; [delta] or [epsilon] is sufficient and necessary for cardiomyocyte hypertrophy through activation of ERK1/2 [203]. Mice lacking PKC[alpha] exhibited enhanced cardiac contractility and were resistant to heart failure after chronic pressure overload or MI [204]. Interestingly, combined deficiency of PKC[delta] and PKC[epsilon] enhanced pressure overload-induced cardiac hypertrophy likely through disinhibition of ERK1/2 [205]. It is also known that overexpression of dominant-negative PKC[epsilon] but not other isoforms induced apoptosis in cultured primary cardiomyocytes, suggesting that PKC[epsilon] is required to maintain cell viability [203]. One potential mechanism underlying PKC[epsilon]-mediated protection is by inhibiting calcium-sensing receptor (CaR), a GPCR necessary for [Ca.sup.2+] release from the ER [206]. PKC[epsilon] may also inhibit apoptosis by phosphorylating Connexin-43 at Ser262 and inhibit interaction between Connexin-43 and Kir6.1, a pore-forming subunit of ATP-sensitive potassium channels [207]. Another PKC isoform, PKC[theta], has been shown to be protective based on the observation that global deletion of PKC0 led to p38/JNK activation and ventricular dilation after pressure overload, and [PKC[theta].sup.-/-] cardiomyocytes were more susceptible to apoptosis upon stimulation with PE and hypoxia [208]. Treatment with PKC inhibitor chelerythrine or BIM-1 abolished fibroblast growth factor-2 (FGF-2) mediated protection against DOX-induced apoptosis, suggesting that PKC activation is an important prosurvival mechanism downstream of FGF-2 [209]. Interestingly, treatment with Ly333531, a specific PKC[beta] inhibitor, attenuated mitochondrial depolarization and apoptosis in response to alcohol and advanced glycation end product, indicating a proapoptotic role of PKC[beta] [210, 211].

10. PKA

Cyclic AMP-dependent protein kinase (PKA), the first protein kinase with its amino acid sequence and crystal structure being defined [212, 213], has served as the prototypical kinase for the entire eukaryotic protein kinase superfamily (kinome). The inactive PKA holoenzyme is a heterotetrameric complex composed of 2 regulatory and 2 catalytic subunits [214]. Upon hormone stimulation and GPCR activation, the [alpha] subunit of G protein binds adenylyl cyclase (AC) to convert ATP into cAMP, which then associates with the regulatory subunits and changes its conformation, eventually leading to release and activation of the catalytic subunit of PKA. In cardiac myocytes, PKA is best known for its role in mediating [beta]-AR-induced contraction through phosphorylation of proteins involved in excitationcontraction coupling, such as L-type [Ca.sup.2+] channels, ryanodine receptor, phospholamban, and cardiac troponin I [215]. Activation of PKA leads to feedback inhibition of its activity by enhancing phosphodiesterase 3B- (PDE3B-) dependent cAMP degradation into AMP and PI3K p110[gamma]-dependent AR internalization [216]. This negative feedback mechanism likely explains earlier observation that chronic stimulation of [beta]1-AR induced cardiac myocyte apoptosis through a PKA-independent mechanism that involves the [Ca.sup.2+]/calmodulin kinase II (CaMKII) [142]. It has been reported most recently that reduced [beta]1-AR content on the membrane and decreased PKA activity in the cytoplasm and myofilaments account for impaired myocardial contractility in the diabetic mice [217].

In addition to enhancing contraction, PKA has also been implicated in other biological processes in cardiomyocytes, such as inhibition of hypertrophy [218] and potentiation of apoptosis [219]. Specifically, activation of PKA by catecholamine treatment or deletion of the PKA regulatory subunit I[alpha] (PKARI[alpha]) induced apoptosis by repressing the prosurvival function of myocyte enhancer factor 2 (MEF2) [218, 220] or by enhancing CREB-binding protein (CBP) and c-Myc-dependent transcription of Bim [219]. Moreover, hypoxia/reoxygenation-induced apoptosis is mediated by downregulation of PKARI[alpha] and consequent activation of p90 ribosomal S6 Kinase 1 (RSK1) [221]. In consistence with these findings, knockdown of the cAMP-hydrolyzing PDE3A was sufficient to induce apoptosis in cultured primary cardiac myocytes [222], possibly through PKA-dependent stabilization of inducible cAMP early repressor (ICER) [223]. Angiotensin II or isoproterenol stimulation induced PDE3A downregulation and myocyte apoptosis, which was completely blocked by overexpression of PDE3A, suggesting a critical role of PDE3A-dependent PKA inactivation in protection against apoptosis [222]. Similar to PDE3A, another isoform, PDE4D, appears to be cardioprotective as mice deficient in PDE4D developed cardiac dysfunction and accelerated heart failure following MI [224]. Intriguingly, cardioprotective roles of PKA have also been reported. For example, transient (30 min) treatment with nitrite induced PKA activation, leading to mitochondrial fusion and cytoprotection through phosphorylation of Drp1 at Ser655 [225]. Most recently, Lin28-induced inhibition of apoptosis in a diabetic cardiomyopathy model was shown to be abolished by pretreatment with a PKA inhibitor H89 [226]. These findings suggest that the role of PKA in apoptosis regulation is context dependent.

11. Cell Cycle Regulators

Mammalian cardiomyocytes exit the cell cycle and become terminally differentiated shortly after birth. However, expression of the cell cycle regulatory machinery including cyclin-dependent kinases (CDKs) and CDK inhibitors (CDKIs) persists into adulthood [227]. The catalytic activity of CDKs requires interaction with cyclins, which are regulatory proteins that also control substrate specificity. Emerging evidence indicates that both CDKs and CDKIs are multifaceted proteins with functions beyond cell cycle regulation [228]. For example, overexpression of dominant-negative CDK2 blocked apoptosis of cardiomyocytes in response to hypoxia stimulation, suggesting that activation of CDK2 is necessary for hypoxia-induced apoptosis [229, 230]. The underlying mechanism was believed to be the fact that CDK2-dependent hyperphosphorylation of retinoblastoma protein (Rb) disrupted Rb-E2F interaction, leading to E2F-mediated transcription of proapoptotic genes [230]. Interestingly, Rb hyperphosphorylation was not mediated by CDK4/6, and overexpression of dominant-negative CDK4/6 failed to protect against hypoxia-induced apoptosis [230]. These data are in agreement with recent findings that the early G1 phase cyclin D:CDK4/6 complex enhanced Rb-E2F interaction by monophosphorylating Rb, whereas late G1 phase cyclinE:CDK2 complex abolished Rb-E2F binding through Rb hyperphosphorylation, which were then maintained by the S phase cyclin A:CDK2 and M phase cyclin B:CDK1 complexes through S, G2, and M phases [231]. Indeed, protein level of cyclin A is gradually increased in response to hypoxia stimulation, and ectopic expression of cyclin A induced apoptosis in cultured cardiomyocytes [229]. Suppression of cyclin A-associated kinase activity by the CDKI p21 mediates the antiapoptotic effect of nitric oxide [232].

The E2F family transcription factors, usually sequestered and inhibited by Rb protein through Rb-E2F interaction, are classified into transcription activators (E2F1, E2F2, and E2F3A) and repressors (E2F3B and E2F4-8). E2F family members are best known for their role in G1-S transition but are also important regulators of apoptosis. Adenoviral delivery of E2F1 to primary rat cardiomyocytes evoked DNA synthesis and p53-independent apoptosis that is associated with activation of CDK1/2 and CDK4/6 and downregulation of CDKIs p21 and p27 [233, 234]. E2F1-induced activation of the intrinsic apoptosis pathway has been attributed to transcriptional upregulation of its target gene Bnip3 [235], which is necessary for I/R-induced apoptosis [236] and doxorubicin-induced necrosis [237]. Consistently, E2F1 null mice were protected against I/R-induced cardiomyocyte apoptosis with decreased expression of Bnip3 [238]. It is noteworthy that the expression of classical E2F1 target genes including caspase 3 and Apaf-1 was not reduced in E2F1 null mice either during development or after I/R injury [238,239]. By contrast, the transcription repressor subfamily member E2F4 was able to inhibit transcription of proapoptotic genes E2F1 and Apaf-1 and antagonize hypoxia-induced cardiomyocyte death [240].

Based on their structure and CDK specificity, CDKIs are classified into the INK4 family CDKIs ([p16.sup.INK4a] (Cdkn2a), [p15.sup.INK4b] (Cdkn2b), [p18.sup.INK4c] (Cdkn2c), and [p19.sup.INK4d] (Cdkn2d)) that inhibit CDK4/6 activity by competing with cyclin D to bind CDK4/6 and the Cip/Kip family CDKIs ([p21.sup.Cip1] (Cdkn1a), [p27.sup.Kip1] (Cdkn1b), and [p57.sup.Kip2] (Cdkn1c)) that associate with both cyclins and CDKs and interfere with the activities of cyclin D-, E-, A-, and B-CDK complexes. Consistent with the finding that activation of CDK4/6 is not required for hypoxia-induced apoptosis, overexpression of the CDK4/6-targeting CDKI p16 did not inhibit cardiomyocyte apoptosis in response to hypoxia stimulation [230]. In contrast, the Cip/Kip family CDKIs have been shown to play a critical role in regulating apoptosis. For example, protein levels of p21 are decreased in hypoxicor doxorubicin-challenged cardiomyocytes [107, 229], and overexpression of p21 protected against hypoxia-induced apoptosis, an effect that may be independent of its CDK inhibitory function [230]. Using gain- and loss-of-function approaches, we recently showed that p21 represses expression of the proapoptotic BH3-only protein Bim and antagonizes doxorubicin-induced cardiomyocyte apoptosis [107]. p21 has also been implicated in mediating protection against oxidative stress downstream of the mitochondrial helicase, TWINKLE [241]. There is evidence that another Cip/Kip family member p27 is also protective in cardiac myocytes as p27 deficient mice exhibited increased apoptosis and infarct size following MI [242]. MI-induced cardiomyocyte apoptosis was attenuated by intravenous delivery of p27 fused with transactivator of transcription (TAT) to facilitate transport across plasma membrane [242]. The beneficial effect of p27 was mediated, at least in part, by activation of autophagy [243]. Interestingly, mice deficient in p21 or p27 have also been shown to be protected from some pathological conditions [244, 245]. This discrepancy may be explained by the fact that the mice used in these studies are germline knockout animals and thus many types of cells were affected instead of one single cell type. In agreement with the early observation that mice deficient in p57 displayed increased apoptosis in the heart and died shortly after birth [246], cardiac-specific transgenic expression of p57 attenuated ex vivo I/R injury [247], indicating a cardioprotective role of p57.

12. Jagged/Notch Signaling

Notch signaling regulates embryonic cell fate determination and adult tissue homeostasis through local cell-cell interactions. Mammalian cells express five Notch ligands (Deltalike1, Delta-like3, Delta-like4, Jagged1, and Jagged2) and four Notch receptors (Notch1-4). Upon binding with the ligand on the signal sending cells, the single-pass transmembrane Notch receptors on the signal receiving cells undergo proteolytic cleavage by [gamma]-secretase, leading to translocation of the Notch intracellular domain (NICD) into the nuclei and transcription of downstream target genes (Figure 1). Myocardial Notch1 levels are decreased with postnatal development but are reactivated following injury [248]. Activation of Notch1 in the heart by either transgenic expression or intramyocardial injection augmented antiapoptotic signaling Akt and Bcl2 and improved cardiac performance following MI [248, 249]. Ischemia pre/postconditioning-dependent protection against apoptosis is mediated by Notch1 activation [250,251]. Cardiac-specific deletion of Notch1 increased the number of apoptotic cardiomyocytes following hemodynamic overload [252]. Interestingly, cardiac-specific Notch1 deletion did not affect post-MI cardiac repair possibly due to compensation by Notch2 and Notch3 [253]. Indeed, inactivation of Notch signaling by a y-secretase inhibitor dramatically induced apoptosis, which was fully rescued by ectopic expression of the activated Notch1 NICD [254, 255]. Lentivirus-mediated overexpression of Notch3 has also been shown to protect cardiomyocytes from I/R-induced apoptosis [256]. It is noteworthy that Notch2-induced cell cycle progression resulted in DNA damage checkpoint activation and cell cycle arrest at G2/M in neonatal cardiomyocytes (postnatal day 5) [257]. Release of these cells from cell cycle arrest by treatment with caffeine (an inhibitor of ataxia-telangiectasia mutated (ATM) and ATM and Rad-3 related (ATR) kinases) dramatically induced an 87-fold increase in apoptosis [257]. Intramyocardial injection of the Notch1 ligand Jagged1 induced Notch1 activation and protected against I/R injury [258]. In contrast to full length Jagged1, the cleaved Jagged1 intracellular domain (J1ICD) inhibits Notch signaling through binding with NICD and promoting its degradation [259]. Cardiacspecific J1ICD transgenic mice exhibited decreased Notch activity, alleviated cardiac hypertrophy, and apoptosis in response to pressure overload [260]. Whether the inhibition of apoptosis is a direct effect of J1ICD or a secondary response to reduced hypertrophy is not clear at this point.

13. Calcineurin/CaMKII

Calcium signaling as a second messenger system regulates a number of biological processes in cardiac myocytes including excitation-contraction coupling and cell survival and death. Intracellular calcium ions ([Ca.sup.2+]) bind the calcium sensor calmodulin (CaM) in the cytosol and activate the [Ca.sup.2+]/CaM-dependent phosphatase calcineurin (also known as protein phosphatase 2B or PP2B) and the [Ca.sup.2+]/CaM-dependent kinase II (CaMKII), leading to changes in cell behavior. It is known that calcineurin binds [Ca.sup.2+]/CaM with high affinity (Kd = 2.8 x [10.sup.-11] M) and is activated by moderate levels of [[Ca.sup.2+]], whereas CaMKII is relatively insensitive to [Ca.sup.2+] signals ([K.sub.d] = 3.4 x [10.sup.-8] M) and is predominantly activated by a large elevation of [[Ca.sup.2+]] [261].

Cardiac calcineurin is best known for its prohypertrophic role through dephosphorylation of nuclear factor of activated T cells (NFAT), leading to its nuclear translocation and transcription of hypertrophic genes. Interestingly, persistent activation of calcineurin also protected against apoptosis (Figure 1) [262], and depletion of calcineurin A[beta] augmented apoptosis through an NFAT-dependent mechanism in murine models of I/R injury [263] or dilated cardiomyopathy [264]. Moreover, calcineurin activation inhibited hydrogen peroxide-induced apoptosis [265], and selective inhibition of calcineurin-dependent NFAT activity induced apoptosis after treatment with phenylephrine [266], suggesting that calcineurin/NFAT is antiapoptotic in these settings, likely through upregulation of [alpha]-crystallin B [267]. However, cardiac-specific transgenic expression of a dominant-negative mutant of calcineurin attenuated cardiomyocyte apoptosis induced by isoproterenol infusion [141]. In this regard, calcineurin has been shown to induce apoptosis by dephosphorylation and subsequent activation of the proapoptotic protein BAD [268] and apoptosis signal-regulating kinase 1 (ASK1) [269] or by repressing AMPactivated protein kinase- (AMPK-) dependent autophagy [270]. Further investigations are needed to address the inconsistence between these studies.

Despite the fact that CaMKII[beta]B, the predominant nuclear isoform of CaMKII, has been shown to antagonize doxorubicin-induced cardiotoxicity [271], the majority of studies indicate a detrimental role of CaMKII in the heart. For example, activation of CaMKII is both sufficient and necessary for [beta]1-AR-dependent cardiomyocyte apoptosis [142, 272]. Deletion of CaMKII[delta], the predominant cardiac isoform of CaMKII, attenuated ventricular dilation and myocyte apoptosis following transverse aortic constriction and delayed transition to heart failure [273]. The mechanisms underlying CaMKII-mediated apoptosis have been attributed to direct phosphorylation of calcineurin at Ser197 [274] and subsequent repression of calcineurin/NFAT signaling [275], enhancing voltage-gated [Ca.sup.2+] channel- (Cav1.2-) dependent calcium overload [276], or phosphorylation of mitochondrial [Ca.sup.2+] uniporter (MCU) at Ser57/Ser92 and increasing MCU current, leading to mPTP opening and cell death [277]. In addition, activation of CaMKII also contributes to myocardial I/R injury through promoting inflammatory signaling mediated by NF-[kappa]B [278] and chemokine (C-C motif) ligand 3 (CCL3) [279]. Intriguingly, CaMKII inhibition with a small-molecule inhibitor KN-93 or the CaMKII inhibitory peptide not only protected myocytes against apoptosis but also inhibited necrosis following myocardial I/R injury [280]. Indeed, a most recent study revealed that phosphorylation and oxidation of CaMKII mediate regulated necrosis downstream of RIPK3 [281].

Two decades have passed since the first observation of myocyte apoptosis in human heart failure caused by ischemic heart disease or idiopathic dilated cardiomyopathy [282-285]. Cardiomyocyte apoptosis was later shown to be present in human immunodeficiency virus cardiomyopathy [286] and heart transplants [287] and following retrograde cardioplegia [288]. Growing evidence suggests that augmented myocyte apoptosis plays a causal role in heart failure pathogenesis, since induction of apoptosis by caspase 8 activation in mice to ~10-20% of the levels observed in failing human heart resulted in lethal dilated cardiomyopathy, which can be fully rescued by administration of a pan-caspase inhibitor [289]. However, to date, no drug that specifically blocks apoptotic pathways has been approved by the US Food and Drug Administration in the treatment of heart disease.

Erythropoietin (EPO), a hematopoietic hormone that can activate the PI3K/Akt, MAPK, PKC, and NF-[kappa]B antiapoptotic pathways, has been shown to be cardioprotective in a variety of MI and I/R animal studies and small clinical trials [290-292]. However, larger randomized phase II trials REVEAL [293] and HEBE III [294, 295] failed to show any significant improvement in heart function and, instead, EPO treatment was associated with an increase in infarct size among older patients. Based on these findings, the effectiveness of EPO in the treatment of coronary artery disease has been questioned [296-298].

Experimental studies revealed that ischemic pre/postconditioning protects against cardiomyocyte apoptosis by activation of PI3K/Akt [24,25,46], Pim1 [55,56], and Notch1 [248,249] and inhibition of p38 [89,90,93]. Due to its clinical relevance and feasibility, postconditioning has been evaluated in more clinical trials and has been shown to reduce infarct size in patients with acute ST-segment elevation myocardial infarction (STEMI) [299, 300]. Interestingly, ischemic postconditioning in the heart also ameliorated acute kidney injury in patients with non-ST-segment elevation myocardial infarction [301]. It has also been reported that postconditioning did not seem to improve myocardial reperfusion [302, 303] or even showed a nonsignificant increase in infarct size in STEMI patients [304]. The discrepancymaybe explained by differences in enrollment criteria, timing of treatment and evaluation, and endpoint selection. More rigorously designed clinical trials are warranted to further clarify the effect of postconditioning in STEMI patients.

15. Conclusions and Perspectives

Our knowledge regarding mechanisms underlying cardiomyocyte apoptosis has expanded enormously in the past decade with rapid advances in molecular techniques. We sincerely apologize to researchers whose work could not be covered. A plethora of genes and signaling pathways as reviewed above have been suggested to either promote or suppress cell death in the pathogenesis of heart disease. However, given the scale of human genome and the complexity of disease progression, it is very likely that a number of important apoptosis-regulating genes remain unidentified. High-throughput genome-wide screening coupled with in vitro/in vivo studies will greatly facilitate the discovery of novel drug target in apoptosis-associated heart disease.

Despite the fact that a large number of caspase inhibitors have been developed, none of them has been proved to be successful in clinical trials. A key explanation is that caspase inhibitors block apoptosis at late stages when severe damage such as mitochondrial outer membrane permeabilization has been executed and at this point the cells are committed to die. As a result, treatment with caspase inhibitors often leads to a morphologic shift from apoptotic to necrotic cell death and rarely confers long-term cytoprotection. Therefore, we believe that future intervention procedures should target upstream events at early stages of apoptosis to preserve mitochondrial function and to truly prevent cell death.

Competing Interests

The authors declare that they have no competing interests.

Acknowledgments

This work was supported by NIH Grant R00HL119605 (to Zhaokang Cheng) and WSU College of Pharmacy.

http://dx.doi.org/10.1155/2016/9583268

References

[1] J. U. Schweichel and H. J. Merker, "The morphology of various types of cell death in prenatal tissues," Teratology, vol. 7, no. 3, pp. 253-266,1973.

[2] J. F. Kerr, A. H. Wyllie, and A. R. Currie, "Apoptosis: a basic biological phenomenon with wide-ranging implications in tissue kinetics," British Journal of Cancer, vol. 26, no. 4, pp. 239-257, 1972.

[3] L. Galluzzi, J. M. Bravo-San Pedro, I. Vitale et al., "Essential versus accessory aspects of cell death: recommendations of the NCCD 2015," Cell Death and Differentiation, vol. 22, no. 1, pp. 58-73, 2015.

[4] Y. Liu and B. Levine, "Autosis and autophagic cell death: the dark side of autophagy," Cell Death and Differentiation, vol. 22, no. 3, pp. 367-376, 2015.

[5] T. Vanden Berghe, A. Linkermann, S. Jouan-Lanhouet, H. Walczak, and P. Vandenabeele, "Regulated necrosis: the expanding network of non-apoptotic cell death pathways," Nature Reviews Molecular Cell Biology, vol. 15, no. 2, pp. 135-147, 2014.

[6] A. Haunstetter and S. Izumo, "Apoptosis: basic mechanisms and implications for cardiovascular disease," Circulation Research, vol. 82, no. 11, pp. 1111-1129, 1998.

[7] M. Watanabe, A. Choudhry, M. Berlan et al., "Developmental remodeling and shortening of the cardiac outflow tract involves myocyte programmed cell death," Development, vol. 125, no. 19, pp. 3809-3820, 1998.

[8] M. Watanabe, A. Jafri, and S. A. Fisher, "Apoptosis is required for the proper formation of the ventriculo-arterial connections," Developmental Biology, vol. 240, no. 1, pp. 274-288, 2001.

[9] G. Kung, K. Konstantinidis, and R. N. Kitsis, "Programmed necrosis, not apoptosis, in the heart," Circulation Research, vol. 108, no. 8, pp. 1017-1036, 2011.

[10] M. Chiong, Z. V. Wang, Z. Pedrozo et al., "Cardiomyocyte death: mechanisms and translational implications," Cell Death and Disease, vol. 2, no. 12, article e244, 2011.

[11] M. A. Sussman, M. Volkers, K. Fischer et al., "Myocardial AKT: the omnipresent nexus," Physiological Reviews, vol. 91, no. 3, pp. 1023-1070, 2011.

[12] Y. Fujio, T. Nguyen, D. Wencker, R. N. Kitsis, and K. Walsh, "Akt promotes survival of cardiomyocytes in vitro and protects against ischemia-reperfusion injury in mouse heart," Circulation, vol. 101, no. 6, pp. 660-667, 2000.

[13] R. Aikawa, M. Nawano, Y. Gu et al., "Insulin prevents cardiomyocytes from oxidative stress-induced apoptosis through activation of PI3 kinase/Akt," Circulation, vol. 102, no. 23, pp. 2873-2879, 2000.

[14] T. Matsui, J. Tao, F. del Monte et al., "Akt activation preserves cardiac function and prevents injury after transient cardiac ischemia in vivo," Circulation, vol. 104, no. 3, pp. 330-335, 2001.

[15] T. Matsui, N. Li, J. C. Wu et al., "Phenotypic spectrum caused by transgenic overexpression of activated Akt in the heart," Journal of Biological Chemistry, vol. 277, no. 25, pp. 22896-22901, 2002.

[16] T. Nagoshi, T. Matsui, T. Aoyama et al., "PI3K rescues the detrimental effects of chronic Akt activation in the heart during ischemia/reperfusion injury," The Journal of Clinical Investigation, vol. 115, no. 8, pp. 2128-2138, 2005.

[17] D. Camper-Kirby, S. Welch, A. Walker et al., "Myocardial Akt activation and gender: increased nuclear activity in females versus males," Circulation Research, vol. 88, no. 10, pp. 1020-1027, 2001.

[18] I. Shiraishi, J. Melendez, Y. Ahn et al., "Nuclear targeting of Akt enhances kinase activity and survival of cardiomyocytes," Circulation Research, vol. 94, no. 7, pp. 884-891, 2004.

[19] T. Kato, J. Muraski, Y. Chen et al., "Atrial natriuretic peptide promotes cardiomyocyte survival by cGMP-dependent nuclear accumulation of zyxin and Akt," Journal of Clinical Investigation, vol. 115, no. 10, pp. 2716-2730, 2005.

[20] J. A. Muraski, M. Rota, Y. Misao et al., "Pim-1 regulates cardiomyocyte survival downstream of Akt," Nature Medicine, vol. 13, no. 12, pp. 1467-1475, 2007.

[21] S. Miyamoto, A. N. Murphy, and J. H. Brown, "Akt mediates mitochondrial protection in cardiomyocytes through phosphorylation of mitochondrial hexokinase-II," Cell Death & Differentiation, vol. 15, no. 3, pp. 521-529, 2008.

[22] D. J. Roberts, V. P. Tan-Sah, J. M. Smith, and S. Miyamoto, "Akt phosphorylates HK-II at Thr-473 and increases mitochondrial HK-II association to protect cardiomyocytes," Journal of Biological Chemistry, vol. 288, no. 33, pp. 23798-23806, 2013.

[23] B. DeBosch, N. Sambandam, C. Weinheimer, M. Courtois, and A. J. Muslin, "Akt2 regulates cardiac metabolism and cardiomyocyte survival," Journal of Biological Chemistry, vol. 281, no. 43, pp. 32841-32851, 2006.

[24] H. Tong, W. Chen, C. Steenbergen, and E. Murphy, "Ischemic preconditioning activates phosphatidylinositol-3-kinase upstream of protein kinase C," Circulation Research, vol. 87, no. 4, pp. 309-315, 2000.

[25] T. Uchiyama, R. M. Engelman, N. Maulik, and D. K. Das, "Role of Akt signaling in mitochondrial survival pathway triggered by hypoxic preconditioning," Circulation, vol. 109, no. 24, pp. 3042-3049, 2004.

[26] R. D. Patten, I. Pourati, M. J. Aronovitz et al., "17[beta]-Estradiol reduces cardiomyocyte apoptosis in vivo and in vitro via activation of phospho-inositide-3 kinase/Akt signaling," Circulation Research, vol. 95, no. 7, pp. 692-699, 2004.

[27] S. Negoro, H. Oh, E. Tone et al., "Glycoprotein 130 regulates cardiac myocyte survival in doxorubicin-induced apoptosis through phosphatidylinositol 3-kinase/Akt phosphorylation and Bcl-xL/caspase-3 interaction," Circulation, vol. 103, no. 4, pp. 555-561, 2001.

[28] R. Fukazawa, T. A. Miller, Y. Kuramochi et al., "Neuregulin1 protects ventricular myocytes from anthracycline-induced apoptosis via erbB4-dependent activation of PI3-kinase/Akt," Journal of Molecular and Cellular Cardiology, vol. 35, no. 12, pp. 1473-1479, 2003.

[29] H. Yin, L. Chao, and J. Chao, "Adrenomedullin protects against myocardial apoptosis after ischemia/reperfusion through activation of Akt-GSK signaling," Hypertension, vol. 43, no. 1, pp. 109-116, 2004.

[30] H. Yin, L. Chao, and J. Chao, "Kallikrein/kinin protects against myocardial apoptosis after ischemia/reperfusion via Akt-glycogen synthase kinase-3 and Akt-bad-14-3-3 signaling pathways," The Journal of Biological Chemistry, vol. 280, no. 9, pp. 80228030, 2005.

[31] M. Jamnicki-Abegg, D. Weihrauch, P. S. Pagel et al., "Isoflurane inhibits cardiac myocyte apoptosis during oxidative and inflammatory stress by activating Akt and enhancing Bcl-2 expression," Anesthesiology, vol. 103, no. 5, pp. 1006-1014, 2005.

[32] H.-O. Jun, D.-H. Kim, S.-W. Lee et al., "Clusterin protects H9c2 cardiomyocytes from oxidative stress-induced apoptosis via Akt/GSK-3[beta] signaling pathway," Experimental and Molecular Medicine, vol. 43, no. 1, pp. 53-61, 2011.

[33] H.-J. Hong, J.-C. Liu, P.-Y. Chen, J.-J. Chen, P. Chan, and T.-H. Cheng, "Tanshinone IIA prevents doxorubicin-induced cardiomyocyte apoptosis through Akt-dependent pathway," International Journal of Cardiology, vol. 157, no. 2, pp. 174-179, 2012.

[34] Y.-L. Chen, S.-H. Loh, J.-J. Chen, and C.-S. Tsai, "Urotensin II prevents cardiomyocyte apoptosis induced by doxorubicin via Akt and ERK," European Journal of Pharmacology, vol. 680, no. 1-3, pp. 88-94, 2012.

[35] Y. Kitamura, M. Koide, Y. Akakabe et al., "Manipulation of cardiac phosphatidylinositol 3-kinase (PI3K)/Akt signaling by apoptosis regulator through modulating IAP expression (ARIA) regulates cardiomyocyte death during doxorubicin-induced cardiomyopathy," Journal of Biological Chemistry, vol. 289, no. 5, pp. 2788-2800, 2014.

[36] Y. Ying, H. Zhu, Z. Liang, X. Ma, and S. Li, "GLP1 protects cardiomyocytes from palmitate-induced apoptosis via Akt/ GSK3b/b-catenin pathway," Journal of Molecular Endocrinology, vol. 55, no. 3, pp. 245-262, 2015.

[37] G. Schwartzbauer and J. Robbins, "The tumor suppressor gene PTEN can regulate cardiac hypertrophy and survival," Journal of Biological Chemistry, vol. 276, no. 38, pp. 35786-35793, 2001.

[38] H. Ruan, J. Li, S. Ren et al., "Inducible and cardiac specific PTEN inactivation protects ischemia/reperfusion injury," Journal of Molecular and Cellular Cardiology, vol. 46, no. 2, pp. 193-200, 2009.

[39] R. Seqqat, X. Guo, K. Rafiq et al., "Beta1-adrenergic receptors promote focal adhesion signaling downregulation and myocyte apoptosis in acute volume overload," Journal of Molecular and Cellular Cardiology, vol. 53, no. 2, pp. 240-249, 2012.

[40] R. B. Chagpar, P. H. Links, M. C. Pastor et al., "Direct positive regulation of PTEN by the p85 subunit of phosphatidylinositol 3-kinase," Proceedings of the National Academy of Sciences of the United States of America, vol. 107, no. 12, pp. 5471-5476, 2010.

[41] X. Zhu, Z.-H. Shao, C. Li et al., "TAT-protein blockade during ischemia/reperfusion reveals critical role for p85 PI3K-PTEN interaction in cardiomyocyte injury," PLoS ONE, vol. 9, no. 4, Article ID e95622, 2014.

[42] J. Chang, M. Xie, V. R. Shah et al., "Activation of Rhoassociated coiled-coil protein kinase 1 (ROCK-1) by caspase-3 cleavage plays an essential role in cardiac myocyte apoptosis," Proceedings of the National Academy of Sciences of the United States of America, vol. 103, no. 39, pp. 14495-14500, 2006.

[43] S. Miyamoto, N. H. Purcell, J. M. Smith et al., "PHLPP-1 negatively regulates Akt activity and survival in the heart," Circulation Research, vol. 107, no. 4, pp. 476-484, 2010.

[44] Y. Xing, W. Sun, Y. Wang, F. Gao, and H. Ma, "Mutual inhibition of insulin signaling and PHLPP-1 determines cardioprotective efficiency of Akt in aged heart," Aging, vol. 8, no. 5, pp. 873-888, 2016.

[45] M. H. Gao, A. Miyanohara, J. R. Feramisco, and T. Tang, "Activation of PH-domain leucine-rich protein phosphatase 2 (PHLPP2) by agonist stimulation in cardiac myocytes expressing adenylyl cyclase type 6," Biochemical and Biophysical Research Communications, vol. 384, no. 2, pp. 193-198, 2009.

[46] H. Tong, K. Imahashi, C. Steenbergen, and E. Murphy, "Phosphorylation of glycogen synthase kinase-3[beta] during preconditioning through a phosphatidylinositol-3-kinase--dependent pathway is cardioprotective," Circulation Research, vol. 90, no. 4, pp. 377-379, 2002.

[47] S. Hirotani, P. Zhai, H. Tomita et al., "Inhibition of glycogen synthase kinase 3[beta] during heart failure is protective," Circulation Research, vol. 101, no. 11, pp. 1164-1174, 2007.

[48] P. Zhai, S. Gao, E. Holle et al., "Glycogen synthase kinase-3[alpha] reduces cardiac growth and pressure overload-induced cardiac hypertrophy by inhibition of extracellular signal-regulated kinases," The Journal of Biological Chemistry, vol. 282, no. 45, pp. 33181-33191, 2007.

[49] K. C. Woulfe, E. Gao, H. Lal et al., "Glycogen synthase kinase-3[alpha] regulates post-myocardial infarction remodeling and stress-induced cardiomyocyte proliferation in vivo," Circulation Research, vol. 106, no. 10, pp. 1635-1645, 2010.

[50] H. Lal, J. Zhou, F. Ahmad et al., "Glycogen synthase kinase-3[alpha] limits ischemic injury, cardiac rupture, post-myocardial infarction remodeling and death," Circulation, vol. 125, no. 1, pp. 65-75, 2012.

[51] F. Ahmad, H. Lal, J. Zhou et al., "Cardiomyocyte-specific deletion of Gsk3[alpha] mitigates post-myocardial infarction remodeling, contractile dysfunction, and heart failure," Journal of the American College of Cardiology, vol. 64, no. 7, pp. 696-706, 2014.

[52] J. Zhou, F. Ahmad, S. Parikh et al., "Loss of adult cardiac myocyte GSK-3 leads to mitotic catastrophe resulting in fatal dilated cardiomyopathy," Circulation Research, vol. 118, no. 8, pp. 1208-1222, 2016.

[53] J. A. Muraski, K. M. Fischer, W. Wu et al., "Pim-1 kinase antagonizes aspects of myocardial hypertrophy and compensation to pathological pressure overload," Proceedings of the National Academy of Sciences of the United States of America, vol. 105, no. 37, pp. 13889-13894, 2008.

[54] G. A. Borillo, M. Mason, P. Quijada et al., "Pim-1 kinase protects mitochondrial integrity in cardiomyocytes," Circulation Research, vol. 106, no. 7, pp. 1265-1274, 2010.

[55] C. Penna, M. G. Perrelli, S. Raimondo et al., "Postconditioning induces an anti-apoptotic effect and preserves mitochondrial integrity in isolated rat hearts," Biochimica et Biophysica Acta (BBA)--Bioenergetics, vol. 1787, no. 7, pp. 794-801, 2009.

[56] R. G. Katare, A. Caporali, A. Oikawa, M. Meloni, C. Emanuel, and P. Madeddu, "Vitamin B1 analog benfotiamine prevents diabetes-induced diastolic dysfunction and heart failure through Akt/Pim-1-mediated survival pathway," Circulation: Heart Failure, vol. 3, no. 2, pp. 294-305, 2010.

[57] X. Zhang, N. Tang, T. J. Hadden, and A. K. Rishi, "Akt, FoxO and regulation of apoptosis," Biochimica et Biophysica Acta, vol. 1813, no. 11, pp. 1978-1986, 2011.

[58] A. Sengupta, J. D. Molkentin, and K. E. Yutzey, "FoxO transcription factors promote autophagy in cardiomyocytes," Journal of Biological Chemistry, vol. 284, no. 41, pp. 28319-28331, 2009.

[59] H. J. Evans-Anderson, C. M. Alfieri, and K. E. Yutzey, "Regulation of cardiomyocyte proliferation and myocardial growth during development by FOXO transcription factors," Circulation Research, vol. 102, no. 6, pp. 686-694, 2008.

[60] A. Sengupta, J. D. Molkentin, J.-H. Paik, R. A. DePinho, and K. E. Yutzey, "FoxO transcription factors promote cardiomyocyte survival upon induction of oxidative stress," The Journal of Biological Chemistry, vol. 286, no. 9, pp. 7468-7478, 2011.

[61] D. Shao, P. Zhai, D. P. Del Re et al., "A functional interaction between Hippo-YAP signalling and FoxO1 mediates the oxidative stress response," Nature Communications, vol. 5, article no. 3315, 2014.

[62] D. Lu, J. Liu, J. Jiao et al., "Transcription factor Foxo3a prevents apoptosis by regulating calcium through the apoptosis repressor with caspase recruitment domain," Journal of Biological Chemistry, vol. 288, no. 12, pp. 8491-8504, 2013.

[63] F. Boal, A. Timotin, J. Roumegoux et al., "Apelin-13 administration protects against ischaemia/reperfusion-mediated apoptosis through the FoxO1 pathway in high-fat diet-induced obesity," British Journal of Pharmacology, vol. 173, no. 11, pp. 1850-1863, 2016.

[64] R. Aikawa, I. Komuro, T. Yamazaki et al., "Oxidative stress activates extracellular signal-regulated kinases through Src and Ras in cultured cardiac myocytes of neonatal rats," The Journal of Clinical Investigation, vol. 100, no. 7, pp. 1813-1821,1997.

[65] W. Zhu, Y. Zou, R. Aikawa et al., "MAPK superfamily plays an important role in daunomycin-induced apoptosis of cardiac myocytes," Circulation, vol. 100, no. 20, pp. 2100-2107,1999.

[66] T.-L. Yue, C. Wang, J.-L. Gu et al., "Inhibition of extracellular signal-regulated kinase enhances ischemia/reoxygenationinduced apoptosis in cultured cardiac myocytes and exaggerates reperfusion injury in isolated perfused heart," Circulation Research, vol. 86, no. 6, pp. 692-699, 2000.

[67] J. Liu, W. Mao, B. Ding, and C.-S. Liang, "ERKs/p53 signal transduction pathway is involved in doxorubicin-induced apoptosis in H9c2 cells and cardiomyocytes," American Journal of Physiology--Heart and Circulatory Physiology, vol. 295, no. 5, pp. H1956-H1965, 2008.

[68] I. S. Harris, S. Zhang, I. Treskov, A. Kovacs, C. Weinheimer, and A. J. Muslin, "Raf-1 kinase is required for cardiac hypertrophy and cardiomyocyte survival in response to pressure overload," Circulation, vol. 110, no. 6, pp. 718-723, 2004.

[69] O. Yamaguchi, T. Watanabe, K. Nishida et al., "Cardiac-specific disruption of the c-raf-1 gene induces cardiac dysfunction and apoptosis," The Journal of Clinical Investigation, vol. 114, no. 7, pp. 937-943, 2004.

[70] D. J. Lips, O. F. Bueno, B. J. Wilkins et al., "MEK1-ERK2 signaling pathway protects myocardium from ischemic injury in vivo," Circulation, vol. 109, no. 16, pp. 1938-1941, 2004.

[71] S. Ulm, W. Liu, M. Zi et al., "Targeted deletion of ERK2 in cardiomyocytes attenuates hypertrophic response but provokes pathological stress induced cardiac dysfunction," Journal of Molecular and Cellular Cardiology, vol. 72, pp. 104-116, 2014.

[72] Y. Huang, C. D. Wright, C. L. Merkwan et al., "An [alpha]1A-adrenergic-extracellular signal-regulated kinase survival signaling pathway in cardiac myocytes," Circulation, vol. 115, no. 6, pp. 763-772, 2007.

[73] D. Zhang, L. Zhu, C. Li et al., "Sialyltransferase7A, a Klf4-responsive gene, promotes cardiomyocyte apoptosis during myocardial infarction," Basic Research in Cardiology, vol. 110, no. 3, 2015.

[74] D. Hreniuk, M. Garay, W. Gaarde, B. P. Monia, R. A. Mckay, and C. L. Cioffi, "Inhibition of C-Jun N-terminal kinase 1, but not c-Jun N-terminal kinase 2, suppresses apoptosis induced by ischemia/reoxygenation in rat cardiac myocytes," Molecular Pharmacology, vol. 59, no. 4, pp. 867-874, 2001.

[75] C. Ferrandi, R. Ballerio, P. Gaillard et al., "Inhibition of c-Jun Nterminal kinase decreases cardiomyocyte apoptosis and infarct size after myocardial ischemia and reperfusion in anaesthetized rats," British Journal of Pharmacology, vol. 142, no. 6, pp. 953-960, 2004.

[76] H. Aoki, P. M. Kang, J. Hampe et al., "Direct activation of mitochondrial apoptosis machinery by c-Jun n-terminal kinase in adult cardiac myocytes," Journal of Biological Chemistry, vol. 277, no. 12, pp. 10244-10250, 2002.

[77] R. A. Kaiser, Q. Liang, O. Bueno et al., "Genetic inhibition or activation of JNK1/2 protects the myocardium from ischemiareperfusion-induced cell death in vivo," Journal of Biological Chemistry, vol. 280, no. 38, pp. 32602-32608, 2005.

[78] D. Qi, X. Hu, X. Wu et al., "Cardiac macrophage migration inhibitory factor inhibits JNK pathway activation and injury during ischemia/reperfusion," The Journal of Clinical Investigation, vol. 119, no. 12, pp. 3807-3816, 2009.

[79] Y. Pan, Y. Wang, Y. Zhao et al., "Inhibition of JNK phosphorylation by a novel curcumin analog prevents high glucoseinduced inflammation and apoptosis in cardiomyocytes and the development of diabetic cardiomyopathy," Diabetes, vol. 63, no. 10, pp. 3497-3511, 2014.

[80] P. Andreka, J. Zang, C. Dougherty, T. I. Slepak, K. A. Webster, and N. H. Bishopric, "Cytoprotection by Jun kinase during nitric oxide-induced cardiac myocyte apoptosis," Circulation Research, vol. 88, no. 3, pp. 305-312, 2001.

[81] C. J. Dougherty, L. A. Kubasiak, H. Prentice, P. Andreka, N. H. Bishopric, and K. A. Webster, "Activation of c-Jun N-terminal kinase promotes survival of cardiac myocytes after oxidative stress," Biochemical Journal, vol. 362, no. 3, pp. 561-571, 2002.

[82] A.-M. Engelbrecht, C. Niesler, C. Page, and A. Lochner, "p38 and JNK have distinct regulatory functions on the development of apoptosis during simulated ischaemia and reperfusion in neonatal cardiomyocytes," Basic Research in Cardiology, vol. 99, no. 5, pp. 338-350, 2004.

[83] Z. Shao, K. Bhattacharya, E. Hsich et al., "c-Jun N-terminal kinases mediate reactivation of Akt and cardiomyocyte survival after hypoxic injury in vitro and in vivo," Circulation Research, vol. 98, no. 1, pp. 111-118, 2006.

[84] T. H. Tran, P. Andreka, C. O. Rodrigues, K. A. Webster, and N. H. Bishopric, "Jun kinase delays caspase-9 activation by interaction with the apoptosome," Journal of Biological Chemistry, vol. 282, no. 28, pp. 20340-20350, 2007.

[85] X. L. Ma, S. Kumar, F. Gao et al., "Inhibition of p38 mitogenactivated protein kinase decreases cardiomyocyte apoptosis and improves cardiac function after myocardial ischemia and reperfusion," Circulation, vol. 99, no. 13, pp. 1685-1691,1999.

[86] Y. J. Kang, Z.-X. Zhou, G.-W. Wang, A. Buridi, and J. B. Klein, "Suppression by metallothionein of doxorubicin-induced cardiomyocyte apoptosis through inhibition of p38 mitogenactivated protein kinases," The Journal of Biological Chemistry, vol. 275, no. 18, pp. 13690-13698, 2000.

[87] K. Otsu, N. Yamashita, K. Nishida et al., "Disruption of a single copy of the p38[alpha] MAP kinase gene leads to cardioprotection against ischemia-reperfusion," Biochemical and Biophysical Research Communications, vol. 302, no. 1, pp. 56-60, 2003.

[88] R. A. Kaiser, O. F. Bueno, D. J. Lips et al., "Targeted inhibition of p38 mitogen-activated protein kinase antagonizes cardiac injury and cell death following ischemia-reperfusion in vivo," Journal of Biological Chemistry, vol. 279, no. 15, pp. 15524-15530, 2004.

[89] J. Ren, S. Zhang, A. Kovacs, Y. Wang, and A. J. Muslin, "Role of p38a MAPK in cardiac apoptosis and remodeling after myocardial infarction," Journal of Molecular and Cellular Cardiology, vol. 38, no. 4, pp. 617-623, 2005.

[90] S. Sanada, M. Kitakaze, P. J. Papst et al., "Role of phasic dynamism of p38 mitogen-activated protein kinase activation in ischemic preconditioning of the canine heart," Circulation Research, vol. 88, no. 2, pp. 175-180, 2001.

[91] A. T. Saurin, J. L. Martin, R. J. Heads et al., "The role of differential activation of p38-mitogen-activated protein kinase in preconditioned ventricular myocytes," FASEB Journal, vol. 14, no. 14, pp. 2237-2246, 2000.

[92] J.-H. Hu, T. Chen, Z.-H. Zhuang et al., "Feedback control of MKP-1 expression byp38," Cellular Signalling, vol. 19, no. 2, pp. 393-400, 2007.

[93] H.-Y. Sun, N.-P. Wang, M. Halkos et al., "Postconditioning attenuates cardiomyocyte apoptosis via inhibition of JNK and p38 mitogen-activated protein kinase signaling pathways," Apoptosis, vol. 11, no. 9, pp. 1583-1593, 2006.

[94] K. K. Jin, A. Pedram, M. Razandi, and E. R. Levin, "Estrogen prevents cardiomyocyte apoptosis through inhibition of reactive oxygen species and differential regulation of p38 kinase isoforms," Journal of Biological Chemistry, vol. 281, no. 10, pp. 6760-6767, 2006.

[95] C. Li, T. Wang, C. Zhang, J. Xuan, C. Su, and Y. Wang, "Quercetin attenuates cardiomyocyte apoptosis via inhibition of JNK and p38 mitogen-activated protein kinase signaling pathways," Gene, vol. 577, no. 2, pp. 275-280, 2016.

[96] S. Israeli-Rosenberg, A. M. Manso, H. Okada, and R. S. Ross, "Integrins and integrin-associated proteins in the cardiac myocyte," Circulation Research, vol. 114, no. 3, pp. 572-586,2014.

[97] R. Fassler and M. Meyer, "Consequences of lack of integrin gene expression in mice," Genes and Development, vol. 9, no. 15, pp. 1896-1908,1995.

[98] L. E. Stephens, A. E. Sutherland, I. V. Klimanskaya et al., "Deletion of beta 1 integrins in mice results in inner cell mass failure and peri-implantation lethality," Genes and Development, vol. 9, no. 15, pp. 1883-1895, 1995.

[99] M. Ieda, T. Tsuchihashi, K. N. Ivey et al., "Cardiac fibroblasts regulate myocardial proliferation through integrin signaling," Developmental Cell, vol. 16, no. 2, pp. 233-244, 2009.

[100] P. Krishnamurthy, V. Subramanian, M. Singh, and K. Singh, "Deficiency of integrins results in increased myocardial dysfunction after myocardial infarction," Heart, vol. 92, no. 9, pp. 1309-1315, 2006.

[101] P. Krishnamurthy, V. Subramanian, M. Singh, and K. Singh, "[beta]1 integrins modulate [beta]-adrenergic receptor-stimulated cardiac myocyte apoptosis and myocardial remodeling," Hypertension, vol. 49, no. 4, pp. 865-872, 2007.

[102] R. Li, Y. Wu, A. M. Manso et al., "[[beta]1 integrin gene excision in the adult murine cardiac myocyte causes defective mechanical and signaling responses," American Journal of Pathology, vol. 180, no. 3, pp. 952-962, 2012.

[103] S.-Y. Shai, A. E. Harpf, C. J. Babbitt et al., "Cardiac myocyte-specific excision of the [beta]1 integrin gene results in myocardial fibrosis and cardiac failure," Circulation Research, vol. 90, no. 4, pp. 458-464, 2002.

[104] H. Okada, N. C. Lai, Y. Kawaraguchi et al., "Integrins protect cardiomyocytes from ischemia/reperfusion injury," Journal of Clinical Investigation, vol. 123, no. 10, pp. 4294-4308, 2013.

[105] Z. S. Hakim, L. A. DiMichele, M. Rojas, D. Meredith, C. P. Mack, and J. M. Taylor, "FAK regulates cardiomyocyte survival following ischemia/reperfusion," Journal of Molecular and Cellular Cardiology, vol. 46, no. 2, pp. 241-248, 2009.

[106] Z. Cheng, L. A. DiMichele, Z. S. Hakim, M. Rojas, C. P. Mack, and J. M. Taylor, "Targeted focal adhesion kinase activation in cardiomyocytes protects the heart from ischemia/reperfusion injury," Arteriosclerosis, Thrombosis, and Vascular Biology, vol. 32, no. 4, pp. 924-933, 2012.

[107] Z. Cheng, L. A. DiMichele, M. Rooas, C. Vaziri, C. P. Mack, and J. M. Taylor, "Focal adhesion kinase antagonizes doxorubicin cardiotoxicity via [p21.sup.Cip1]," Journal of Molecular and Cellular Cardiology, vol. 67, pp. 1-11, 2014.

[108] S. Gilles, S. Zahler, U. Welsch, C. P. Sommerhoff, and B. F. Becker, "Release of TNF-[alpha] during myocardial reperfusion depends on oxidative stress and is prevented by mast cell stabilizers," Cardiovascular Research, vol. 60, no. 3, pp. 608-616, 2003.

[109] A. Diwan, Z. Dibbs, S. Nemoto et al., "Targeted overexpression of noncleavable and secreted forms of tumor necrosis factor provokes disparate cardiac phenotypes," Circulation, vol. 109, no. 2, pp. 262-268, 2004.

[110] S. B. Haudek, G. E. Taffet, M. D. Schneider, and D. L. Mann, "TNF provokes cardiomyocyte apoptosis and cardiac remodeling through activation of multiple cell death pathways," The Journal of Clinical Investigation, vol. 117, no. 9, pp. 2692-2701, 2007.

[111] P. Panagopoulou, C. H. Davos, D. J. Milner et al., "Desmin mediates TNF-[alpha]-induced aggregate formation and intercalated disk reorganization in heart failure," Journal of Cell Biology, vol. 181, no. 5, pp. 761-775, 2008.

[112] C.-T. Tsai, C.-K. Wu, J.-K. Lee et al., "TNF-[alpha] down-regulates sarcoplasmic reticulum [Ca.sup.2+] ATPase expression and leads to left ventricular diastolic dysfunction through binding of NF-[kappa]B to promoter response element," Cardiovascular Research, vol. 105, no. 3, pp. 318-329, 2015.

[113] N. Maekawa, H. Wada, T. Kanda et al., "Improved myocardial ischemia/reperfusion injury in mice lacking tumor necrosis factor-[alpha]," Journal of the American College of Cardiology, vol. 39, no. 7, pp. 1229-1235, 2002.

[114] M. Sun, F. Dawood, W.-H. Wen et al., "Excessive tumor necrosis factor activation after infarction contributes to susceptibility of myocardial rupture and left ventricular dysfunction," Circulation, vol. 110, no. 20, pp. 3221-3228, 2004.

[115] M. P. Flaherty, Y. Guo, S. Tiwari et al., "The role of TNF-[alpha] receptors p55 and p75 in acute myocardial ischemia/reperfusion injury and late preconditioning," Journal of Molecular and Cellular Cardiology, vol. 45, no. 6, pp. 735-741, 2008.

[116] Y. Monden, T. Kubota, T. Inoue et al., "Tumor necrosis factora is toxic via receptor 1 and protective via receptor 2 in a murine model of myocardial infarction," American Journal of Physiology-Heart and Circulatory Physiology, vol. 293, no. 1, pp. H743-H753, 2007.

[117] T. Hamid, Y. Gu, R. V. Ortines et al., "Divergent tumor necrosis factor receptor-related remodeling responses in heart failure: role of nuclear factor-xB and inflammatory activation," Circulation, vol. 119, no. 10, pp. 1386-1397, 2009.

[118] K. M. Kurrelmeyer, L. H. Michael, G. Baumgarten et al., "Endogenous tumor necrosis factor protects the adult cardiac myocyte against ischemic-induced apoptosis in a murine model of acute myocardial infarction," Proceedings of the National Academy of Sciences of the United States of America, vol. 97, no. 10, pp. 5456-5461, 2000.

[119] T. Kubota, M. Miyagishima, C. S. Frye et al., "Overexpression of tumor necrosis factor-[alpha] activates both anti- and pro-apoptotic pathways in the myocardium," Journal of Molecular and Cellular Cardiology, vol. 33, no. 7, pp. 1331-1344, 2001.

[120] J. S. Burchfield, J.-W. Dong, Y. Sakata et al., "The cytoprotective effects of tumor necrosis factor are conveyed through tumor necrosis factor receptor-associated factor 2 in the heart," Circulation: Heart Failure, vol. 3, no. 1, pp. 157-164, 2010.

[121] A. Misra, S. B. Haudek, P. Knuefermann et al., "Nuclear factor-kB protects the adult cardiac myocyte against ischemia-induced apoptosis in a murine model of acute myocardial infarction," Circulation, vol. 108, no. 25, pp. 3075-3078, 2003.

[122] J. Shaw, T. Zhang, M. Rzeszutek et al., "Transcriptional silencing of the death gene BNIP3 by cooperative action of NF-[kappa]B and histone deacetylase 1 in ventricular myocytes," Circulation Research, vol. 99, no. 12, pp. 1347-1354, 2006.

[123] S. Papathanasiou, S. Rickelt, M. E. Soriano et al., "Tumor necrosis factor-[alpha] confers cardioprotection through ectopic expression of keratins K8 and K18," Nature Medicine, vol. 21, no. 9, pp. 1076-1084, 2015.

[124] P. Kratsios, M. Huth, L. Temmerman et al., "Antioxidant amelioration of dilated cardiomyopathy caused by conditional deletion of NEMO/IKKy in cardiomyocytes," Circulation Research, vol. 106, no. 1, pp. 133-144, 2010.

[125] H. J. Maier, T. G. Schips, A. Wietelmann et al., "Cardiomyocytespecific IkB kinase (IKK)/NF-[kappa]B activation induces reversible inflammatory cardiomyopathy and heart failure," Proceedings of the National Academy of Sciences of the United States of America, vol. 109, no. 29, pp. 11794-11799, 2012.

[126] T. Hamid, S. Z. Guo, J. R. Kingery, X. Xiang, B. Dawn, and S. D. Prabhu, "Cardiomyocyte NF-[kappa]B p65 promotes adverse remodelling, apoptosis, and endoplasmic reticulum stress in heart failure," Cardiovascular Research, vol. 89, no. 1, pp. 129-138, 2011.

[127] X. Q. Zhang, R. Tang, L. Li et al., "Cardiomyocyte-specific p65 NF-[kappa]B deletion protects the injured heart by preservation of calcium handling," American Journal of Physiology--Heart and Circulatory Physiology, vol. 305, no. 7, pp. H1089-H1097, 2013.

[128] M. Brown, M. McGuinness, T. Wright et al., "Cardiac-specific blockade of NF-[kappa]B in cardiac pathophysiology: differences between acute and chronic stimuli in vivo," American Journal of Physiology--Heart and Circulatory Physiology, vol. 289, no. 1, pp. H466-H476, 2005.

[129] S. Kawano, T. Kubota, Y. Monden et al., "Blockade of NF-[kappa]B improves cardiac function and survival after myocardial infarction," American Journal of Physiology--Heart and Circulatory Physiology, vol. 291, no. 3, pp. H1337-H1344, 2006.

[130] S. Frantz, K. Hu, B. Bayer et al., "Absence of NF-/cB subunit p50 improves heart failure after myocardial infarction," The FASEB journal, vol. 20, no. 11, pp. 1918-1920, 2006.

[131] L. Timmers, J. K. Van Keulen, I. E. Hoefer et al., "Targeted deletion of nuclear factor kB p50 enhances cardiac remodeling and dysfunction following myocardial infarction," Circulation Research, vol. 104, no. 5, pp. 699-706, 2009.

[132] J. W. Gordon, J. A. Shaw, and L. A. Kirshenbaum, "Multiple facets of NF-[kappa]B in the heart: to be or not to NF-[kappa]B," Circulation Research, vol. 108, no. 9, pp. 1122-1132, 2011.

[133] Y. Wang, E. Gao, W. B. Lau et al., "G-protein-coupled receptor kinase 2-mediated desensitization of adiponectin receptor 1 in failing heart," Circulation, vol. 131, no. 16, pp. 1392-1404, 2015.

[134] M. Chen, P. Y. Sato, J. K. Chuprun et al., "Prodeath signaling of G protein-coupled receptor kinase 2 in cardiac myocytes after ischemic stress occurs via extracellular signal-regulated kinase-dependent heat shock protein 90-mediated mitochondrial targeting," Circulation Research, vol. 112, no. 8, pp. 1121-1134, 2013.

[135] Q. Fan, M. Chen, L. Zuo et al., "Myocardial ablation of G protein-coupled receptor kinase 2 (GRK2) decreases ischemia/ reperfusion injury through an anti-intrinsic apoptotic pathway," PLoS ONE, vol. 8, no. 6, Article ID e66234, 2013.

[136] N. C. Salazar, J. Chen, and H. A. Rockman, "Cardiac GPCRs: GPCR signaling in healthy and failing hearts," Biochimica et Biophysica Acta--Biomembranes, vol. 1768, no. 4, pp. 1006-1018, 2007.

[137] T. D. O'Connell, B. C. Jensen, A. J. Baker, and P. C. Simpson, "Cardiac alpha1-adrenergic receptors: novel aspects of expression, signaling mechanisms, physiologic function, and clinical importance," Pharmacological Reviews, vol. 66, no. 1, pp. 308-333, 2014.

[138] C. Communal, K. Singh, D. B. Sawyer, and W. S. Colucci, "Opposing effects of [[beta].sub.1]-and [[beta].sub.2]-adrenergic receptors on cardiac myocyte apoptosis: role of a pertussis toxin-sensitive G protein," Circulation, vol. 100, no. 22, pp. 2210-2212,1999.

[139] M. Zaugg, W. Xu, E. Lucchinetti, S. A. Shafiq, N. Z. Jamali, and M. A. Q. Siddiqui, "[beta]-Adrenergic receptor subtypes differentially affect apoptosis in adult rat ventricular myocytes," Circulation, vol. 102, no. 3, pp. 344-350, 2000.

[140] S.-Y. Shin, T. Kim, H.-S. Lee et al., "The switching role of [beta]- adrenergic receptor signalling in cell survival or death decision of cardiomyocytes," Nature Communications, vol. 5, article 5777, 2014.

[141] S. Saito, Y. Hiroi, Y. Zou et al., "[beta]-adrenergic pathway induces apoptosis through calcineurin activation in cardiac myocytes," Journal of Biological Chemistry, vol. 275, no. 44, pp. 34528-34533, 2000.

[142] W.-Z. Zhu, S.-Q. Wang, K. Chakir et al., "Linkage of [[beta].sub.1]-adrenergic stimulation to apoptotic heart cell death through protein kinase A-independent activation of [Ca.sup.2+]/calmodulin kinase II," The Journal of Clinical Investigation, vol. 111, no. 5, pp. 617-625, 2003.

[143] Y.-C. Fu, C.-S. Chi, S.-C. Yin, B. Hwang, Y.-T. Chiu, and S.-L. Hsu, "Norepinephrine induces apoptosis in neonatal rat cardiomyocytes through a reactive oxygen species-TNF[alpha]-caspase signaling pathway," Cardiovascular Research, vol. 62, no. 3, pp. 558-567, 2004.

[144] W.-Z. Zhu, M. Zheng, W. J. Koch, R. J. Lefkowitz, B. K. Kobilka, and R.-P. Xiao, "Dual modulation of cell survival and cell death by [[beta].sub.2]-adrenergic signaling in adult mouse cardiac myocytes," Proceedings of the National Academy of Sciences of the United States of America, vol. 98, no. 4, pp. 1607-1612, 2001.

[145] W. Zhang, N. Yano, M. Deng, Q. Mao, S. K. Shaw, and Y.T. Tseng, "[beta]-Adrenergic receptor-PI3K signaling crosstalk in mouse heart: elucidation of immediate downstream signaling cascades," PLoS ONE, vol. 6, no. 10, Article ID e26581, 2011.

[146] A. Chesley, M. S. Lundberg, T. Asai et al., "The [beta]2-adrenergic receptor delivers an antiapoptotic signal to cardiac myocytes through G(i)-dependent coupling to phosphatidylinositol 3'kinase," Circulation Research, vol. 87, no. 12, pp. 1172-1179,2000.

[147] Y.-J. Geng, Y. Ishikawa, D. E. Vatner et al., "Apoptosis of cardiac myocytes in Gsa transgenic mice," Circulation Research, vol. 84, no. 1, pp. 34-42, 1999.

[148] B. R. DeGeorge Jr., E. Gao, M. Boucher et al., "Targeted inhibition of cardiomyocyte Gi signaling enhances susceptibility to apoptotic cell death in response to ischemic stress," Circulation, vol. 117, no. 11, pp. 1378-1387, 2008.

[149] M. Zheng, S.-J. Zhang, W.-Z. Zhu, B. Ziman, B. K. Kobilka, and R.-P. Xiao, [beta]2-adrenergic receptor-induced p38 MAPK activation is mediated by protein kinase A rather than by G; or G[beta][gamma] in adult mouse cardiomyocytes," Journal of Biological Chemistry, vol. 275, pp. 40635-40640, 2000.

[150] J. G. Burniston, L.-B. Tan, and D. F. Goldspink, "[beta]2-adrenergic receptor stimulation in vivo induces apoptosis in the rat heart and soleus muscle," Journal of Applied Physiology, vol. 98, no. 4, pp. 1379-1386, 2005.

[151] G. J. Lee, L. Yan, D. E. Vatner, and S. F. Vatner, "Mst1 inhibition rescues [beta]-adrenergic cardiomyopathy by reducing myocyte necrosis and non-myocyte apoptosis ratherthan myocyte apoptosis," Basic Research in Cardiology, vol. 110, 2015.

[152] E. Iwai-Kanai, K. Hasegawa, M. Araki, T. Kakita, T. Morimoto, and S. Sasayama," [alpha]- and [beta]-adrenergic pathways differentially regulate cell type-specific apoptosis in rat cardiac myocytes," Circulation, vol. 100, no. 3, pp. 305-311,1999.

[153] H. Zhu, S. McElwee-Witmer, M. Perrone, K. L. Clark, and A. Zilberstein, "Phenylephrine protects neonatal rat cardiomyocytes from hypoxia and serum deprivation-induced apoptosis," Cell Death & Differentiation, vol. 7, no. 9, pp. 773-784, 2000.

[154] A. Aries, P. Paradis, C. Lefebvre, R. J. Schwartz, and M. Nemer, "Essential role of GATA-4 in cell survival and drug-induced cardiotoxicity," Proceedings of the National Academy of Sciences of the United States of America, vol. 101, no. 18, pp. 6975-6980, 2004.

[155] T. D. O'Connell, P. M. Swigart, M. C. Rodrigo et al., "Nr Adrenergic receptors prevent a maladaptive cardiac response to pressure overload," The Journal of Clinical Investigation, vol. 116, no. 4, pp. 1005-1015, 2006.

[156] H. Chaulet, F. Lin, J. Guo et al., "Sustained augmentation of cardiac [alpha]1A-adrenergic drive results in pathological remodeling with contractile dysfunction, progressive fibrosis and reactivation of matricellular protein genes," Journal of Molecular and Cellular Cardiology, vol. 40, no. 4, pp. 540-552, 2006.

[157] A. L. Howes, S. Miyamoto, J. W. Adams, E. A. Woodcock, and J. H. Brown, "G[alpha]q expression activates EGFR and induces Akt mediated cardiomyocyte survival: dissociation from G[alpha]q mediated hypertrophy," Journal of Molecular and Cellular Cardiology, vol. 40, no. 5, pp. 597-604, 2006.

[158] A. L. Howes, J. F. Arthur, T. Zhang et al., "Akt-mediated cardiomyocyte survival pathways are compromised by Gaqinduced phosphoinositide 4,5-bisphosphate depletion," Journal of Biological Chemistry, vol. 278, no. 41, pp. 40343-40351, 2003.

[159] J. Shi, Y.-W. Zhang, Y. Yang, L. Zhang, and L. Wei, "ROCK1 plays an essential role in the transition from cardiac hypertrophy to failure in mice," Journal of Molecular and Cellular Cardiology, vol. 49, no. 5, pp. 819-828, 2010.

[160] M. Araki, K. Hasegawa, E. Iwai-Kanai et al., "Endothelin-1 as a protective factor against beta-adrenergic agonist-induced apoptosis in cardiac myocytes," Journal of the American College of Cardiology, vol. 36, no. 4, pp. 1411-1418, 2000.

[161] A. Ren, X. Yan, H. Lu et al., "Antagonism of endothelin-1 inhibits hypoxia-induced apoptosis in cardiomyocytes," Canadian Journal of Physiology and Pharmacology, vol. 86, no. 8, pp. 536-540, 2008.

[162] E. 0ie, O. P. F. Clausen, A. Yndestad, H. K. Grogaard, and H. Attramadal, "Endothelin receptor antagonism attenuates cardiomyocyte apoptosis after induction of ischemia in rats," Scandinavian Cardiovascular Journal, vol. 36, no. 2, pp. 108-116, 2002.

[163] S. Tamareille, M. Terwelp, J. Amirian et al., "Endothelin-1 release during the early phase of reperfusion is a mediator of myocardial reperfusion injury," Cardiology, vol. 125, no. 4, pp. 242-249, 2013.

[164] S. Bien, A. Riad, C. A. Ritter et al., "The endothelin receptor blocker bosentan inhibits doxorubicin-induced cardiomyopathy," Cancer Research, vol. 67, no. 21, pp. 10428-10435, 2007.

[165] X.-S. Zhao, W. Pan, R. Bekeredjian, and R. V. Shohet, "Endogenous endothelin-1 is required for cardiomyocyte survival in vivo," Circulation, vol. 114, no. 8, pp. 830-837, 2006.

[166] Y. Zhang, L. Li, Y. Hua et al., "Cardiac-specific knockout of [ET.sub.A] receptor mitigates low ambient temperature-induced cardiac hypertrophy and contractile dysfunction," Journal of Molecular Cell Biology, vol. 4, no. 2, pp. 97-107, 2012.

[167] I. Goldenberg, E. Grossman, K. A. Jacobson, V. Shneyvays, and A. Shainberg, "Angiotensin II-induced apoptosis in rat cardiomyocyte culture: a possible role of AT1 and AT2 receptors," Journal of Hypertension, vol. 19, no. 9, pp. 1681-1689, 2001.

[168] Q. N. Diep, M. El Mabrouk, P. Yue, and E. L. Schiffrin, "Effect of [AT.sub.1] receptor blockade on cardiac apoptosis in angiotensin IIinduced hypertension," American Journal of Physiology--Heart and Circulatory Physiology, vol. 282, no. 5, pp. H1635-H1641, 2002.

[169] H. Sugino, R. Ozono, S. Kurisu et al., "Apoptosis is not increased in myocardium overexpressing type 2 angiotensin II receptor in transgenic mice," Hypertension, vol. 37, no. 6, pp. 1394-1398, 2001.

[170] J. F. X. Ainscough, M. J. Drinkhiil, A. Sedo et al., "Angiotensin II type-1 receptor activation in the adult heart causes blood pressure-independent hypertrophy and cardiac dysfunction," Cardiovascular Research, vol. 81, no. 3, pp. 592-600, 2009.

[171] M. Nishida, S. Tanabe, Y. Maruyama et al., "G[alpha]12/13- and reactive oxygen species-dependent activation of c-Jun NH2-terminal kinase and p38 mitogen-activated protein kinase by angiotensin receptor stimulation in rat neonatal cardiomyocytes," The Journal of Biological Chemistry, vol. 280, no. 18, pp. 18434-18441, 2005.

[172] C.-Y. Huang, W.-W. Kuo, Y.-L. Yeh et al., "ANG II promotes IGF-IIR expression and cardiomyocyte apoptosis by inhibiting HSF1 via JNK activation and SIRT1 degradation," Cell Death and Differentiation, vol. 21, no. 8, pp. 1262-1274, 2014.

[173] I. Goldenberg, A. Shainberg, K. A. Jacobson, V. Shneyvays, and E. Grossman, "Adenosine protects againts angiotensin II-induced apoptosis in rat cardiocyte cultures," Molecular and Cellular Biochemistry, vol. 252, no. 1-2, pp. 133-139, 2003.

[174] R. Germack, M. Griffin, and J. M. Dickenson, "Activation of protein kinase B by adenosine A1 and A3 receptors in newborn rat cardiomyocytes," Journal of Molecular and Cellular Cardiology, vol. 37, no. 5, pp. 989-999, 2004.

[175] R. Germack and J. M. Dickenson, "Adenosine triggers preconditioning through MEK/ERK1/2 signalling pathway during hypoxia/reoxygenation in neonatal rat cardiomyocytes," Journal of Molecular and Cellular Cardiology, vol. 39, no. 3, pp. 429-442, 2005.

[176] Q. Zhou, L. Li, B. Zhao, and K.-L. Guan, "The hippo pathway in heart development, regeneration, and diseases," Circulation Research, vol. 116, no. 8, pp. 1431-1447, 2015.

[177] S. Yamamoto, G. Yang, D. Zablocki et al., "Activation of Mst1 causes dilated cardiomyopathy by stimulating apoptosis without compensatory ventricular myocyte hypertrophy," The Journal of Clinical Investigation, vol. 111, no. 10, pp. 1463-1474, 2003.

[178] M. Odashima, S. Usui, H. Takagi et al., "Inhibition of endogenous Mst1 prevents apoptosis and cardiac dysfunction without affecting cardiac hypertrophy after myocardial infarction," Circulation Research, vol. 100, no. 9, pp. 1344-1352, 2007.

[179] Y. Maejima, S. Kyoi, P. Zhai et al., "Mst1 inhibits autophagy by promoting the interaction between beclin1 and Bcl-2," Nature Medicine, vol. 19, no. 11, pp. 1478-1488, 2013.

[180] D. P. Del Re, T. Matsuda, P. Zhai et al., "Mst1 promotes cardiac myocyte apoptosis through phosphorylation and inhibition of Bcl-xL," Molecular Cell, vol. 54, no. 4, pp. 639-650, 2014.

[181] M. Nakamura, P. Zhai, D. P. Del Re, Y. Maejima, and J. Sadoshima, "Mst1-mediated phosphorylation of Bcl-xL is required for myocardial reperfusion injury," JCI Insight, vol. 1, no. 5, 2016.

[182] S. Oh, D. Lee, T. Kim et al., "Crucial role for Mst1 and Mst2 kinases in early embryonic development of the mouse," Molecular and Cellular Biology, vol. 29, no. 23, pp. 6309-6320, 2009.

[183] D. P. Del Re, T. Matsuda, P. Zhai et al., "Proapoptotic Rassf1A/ Mst1 signaling in cardiac fibroblasts is protective against pressure overload in mice," The Journal of Clinical Investigation, vol. 120, no. 10, pp. 3555-3567, 2010.

[184] T. Matsuda, P. Zhai, S. Sciarretta et al., "NF2 activates hippo signaling and promotes ischemia/reperfusion injury in the Heart-Novelty and significance," Circulation Research, vol. 119, no. 5, pp. 596-606, 2016.

[185] S. Sciarretta, P. Zhai, Y. Maejima et al., "mTORC2 regulates cardiac response to stress by inhibiting MST1," Cell Reports, vol. 11, no. 1, pp. 125-136, 2015.

[186] Y. Matsui, N. Nakano, D. Shao et al., "Lats2 is a negative regulator of myocyte size in the heart," Circulation Research, vol. 103, no. 11, pp. 1309-1318, 2008.

[187] D. P. Del Re, Y. Yang, N. Nakano et al., "Yes-associated protein isoform 1 (Yap1) promotes cardiomyocyte survival and growth to protect against myocardial ischemic injury," Journal of Biological Chemistry, vol. 288, no. 6, pp. 3977-3988, 2013.

[188] M. Xin, Y. Kim, L. B. Sutherland et al., "Hippo pathway effector Yap promotes cardiac regeneration," Proceedings of the National Academy of Sciences of the United States of America, vol. 110, no. 34, pp. 13839-13844, 2013.

[189] Z. Lin, A. von Gise, P. Zhou et al., "Cardiac-specific YAP activation improves cardiac function and survival in an experimental murine MI model," Circulation Research, vol. 115, no. 3, pp. 354-363, 2014.

[190] V. P. Sah, S. Minamisawa, S. P. Tam et al., "Cardiac-specific overexpression of RhoA results in sinus and atrioventricular nodal dysfunction and contractile failure," The Journal of Clinical Investigation, vol. 103, no. 12, pp. 1627-1634,1999.

[191] D. P. Del Re, S. Miyamoto, and J. H. Brown, "RhoA/Rho kinase up-regulate Bax to activate a mitochondrial death pathway and induce cardiomyocyte apoptosis," Journal of Biological Chemistry, vol. 282, no. 11, pp. 8069-8078, 2007.

[192] D. P. Del Re, S. Miyamoto, and J. H. Brown, "Focal adhesion kinase as a RhoA-activable signaling scaffold mediating akt activation and cardiomyocyte protection," Journal of Biological Chemistry, vol. 283, no. 51, pp. 35622-35629, 2008.

[193] S. Y. Xiang, D. Vanhoutte, D. P. Del Re et al., "RhoA protects the mouse heart against ischemia/reperfusion injury," Journal of Clinical Investigation, vol. 121, no. 8, pp. 3269-3276, 2011.

[194] P. A. J. Krijnen, J. A. Sipkens, J. W. Molling et al., "Inhibition of Rho-ROCK signaling induces apoptotic and non-apoptotic PS exposure in cardiomyocytes via inhibition of flippase," Journal of Molecular and Cellular Cardiology, vol. 49, no. 5, pp. 781-790, 2010.

[195] X. Yang, Q. Li, X. Lin et al., "Mechanism of fibrotic cardiomyopathy in mice expressing truncated Rho-associated coiled-coil protein kinase 1," The FASEB Journal, vol. 26, no. 5, pp. 2105-2116, 2012.

[196] J. Shi, X. Wu, M. Surma et al., "Distinct roles for ROCK1 and ROCK2 in the regulation of cell detachment," Cell Death and Disease, vol. 4, no. 2, article no. e483, 2013.

[197] R. Okamoto, Y. Li, K. Noma et al., "FHL2 prevents cardiac hypertrophy in mice with cardiac-specific deletion of ROCK2," FASEB Journal, vol. 27, no. 4, pp. 1439-1449, 2013.

[198] E. Shen, Y. Li, Y. Li et al., "Rac1 is required for cardiomyocyte apoptosis during hyperglycemia," Diabetes, vol. 58, no. 10, pp. 2386-2395, 2009.

[199] M. A. Sussman, S. Welch, A. Walker et al., "Altered focal adhesion regulation correlates with cardiomyopathy in mice expressing constitutively active rac1," The Journal of Clinical Investigation, vol. 105, no. 7, pp. 875-886, 2000.

[200] M. T. Elnakish, M. D. H. Hassona, M. A. Alhaj et al., "Rac-induced left ventricular dilation in thyroxin-treated zmracd transgenic mice: role of cardiomyocyte apoptosis and myocardial fibrosis," PLoS ONE, vol. 7, no. 8, Article ID e42500, 2012.

[201] M. Maillet, J. M. Lynch, B. Sanna, A. J. York, Y. Zheng, and J. D. Molkentin, "Cdc42 is an antihypertrophic molecular switch in the mouse heart," The Journal of Clinical Investigation, vol. 119, no. 10, pp. 3079-3088, 2009.

[202] L. R. Pearce, D. Komander, and D. R. Alessi, "The nuts and bolts of AGC protein kinases," Nature Reviews Molecular Cell Biology, vol. 11, no. 1, pp. 9-22, 2010.

[203] J. C. Braz, O. F. Bueno, L. J. De Windt, and J. D. Molkentin, "PKCa regulates the hypertrophic growth of cardiomyocytes through extracellular signal-regulated kinase1/2 (ERK1/2)," Journal of Cell Biology, vol. 156, no. 5, pp. 905-919, 2002.

[204] Q. Liu, X. Chen, S. M. Macdonnell et al., "Protein kinase Ca, but Not PKC[beta] or PKC[gamma], regulates contractility and heart failure susceptibility: implications for ruboxistaurin as a novel therapeutic approach," Circulation Research, vol. 105, no. 2, pp. 194-200, 2009.

[205] M. Song, S. J. Matkovich, Y. Zhang, D. J. Hammer, and G. W. Dorn II, "Combined cardiomyocyte PKCS and PKCe gene deletion uncovers their central role in restraining developmental and reactive heart growth," Science Signaling, vol. 8, no. 373, article ra39, 2015.

[206] S. Dong, Z. Teng, F.-H. Lu et al., "Post-conditioning protects cardiomyocytes from apoptosis via PKCe-interacting with calcium-sensing receptors to inhibit endo(sarco)plasmic reticulum-mitochondria crosstalk," Molecular and Cellular Biochemistry, vol. 341, no. 1-2, pp. 195-206, 2010.

[207] A. A. Waza, K. Andrabi, and M. U. Hussain, "Protein kinase C (PKC) mediated interaction between conexin43 (Cx43) and K+(ATP) channel subunit (Kir6.1) in cardiomyocyte mitochondria: implications in cytoprotection against hypoxia induced cell apoptosis," Cellular Signalling, vol. 26, no. 9, pp. 1909-1917, 2014.

[208] R. Paoletti, A. Maffei, L. Madaro et al., "Protein kinase C[theta] is required for cardiomyocyte survival and cardiac remodeling," Cell Death and Disease, vol. 1, no. 5, article e45, 2010.

[209] J. Wang, M. W. Nachtigal, E. Kardami, and P. A. Cattini, "FGF-2 protects cardiomyocytes from doxorubicin damage via protein kinase C-dependent effects on efflux transporters," Cardiovascular Research, vol. 98, no. 1, pp. 56-63, 2013.

[210] Y. Wang, J. Zhao, W. Yang et al., "High-dose alcohol induces reactive oxygen species-mediated apoptosis via PKC-[beta]/p66Shc in mouse primary cardiomyocytes," Biochemical and Biophysical Research Communications, vol. 456, no. 2, pp. 656-661,2015.

[211] L. Zhang, D. Huang, D. Shen et al., "Inhibition of protein kinase C [beta]II isoform ameliorates methylglyoxal advanced glycation endproduct-induced cardiomyocyte contractile dysfunction," Life Sciences, vol. 94, no. 1, pp. 83-91, 2014.

[212] S. Shooi, D. C. Parmelee, R. D. Wade et al., "Complete amino acid sequence of the catalytic subunit of bovine cardiac muscle cyclic AMP-dependent protein kinase," Proceedings of the National Academy of Sciences of the United States of America, vol. 78, no. 2, pp. 848-851, 1981.

[213] D. R. Knighton, J. H. Zheng, L. F. Ten Eyck et al., "Crystal structure of the catalytic subunit of cyclic adenosine monophosphate-dependent protein kinase," Science, vol. 253, no. 5018, pp. 407-414, 1991.

[214] S. S. Taylor, R. Ilouz, P. Zhang, and A. P. Kornev, "Assembly of allosteric macromolecular switches: lessons from PKA," Nature Reviews Molecular Cell Biology, vol. 13, no. 10, pp. 646-658,2012.

[215] Y. K. Xiang, "Compartmentalization of [beta]-adrenergic signals in cardiomyocytes," Circulation Research, vol. 109, no. 2, pp. 231-244, 2011.

[216] A. Perino, A. Ghigo, E. Ferrero et al., "Integrating cardiac PIP3 and cAMP signaling through a PKA anchoring function of p110y," Molecular Cell, vol. 42, no. 1, pp. 84-95, 2011.

[217] L. B. Bockus and K. M. Humphries, "CAMP-dependent protein kinase (PKA) signaling is impaired in the diabetic heart," Journal of Biological Chemistry, vol. 290, no. 49, pp. 2925029258, 2015.

[218] J. Backs, B. C. Worst, L. H. Lehmann et al., "Selective repression of MEF2 activity by PKA-dependent proteolysis of HDAC4," Journal of Cell Biology, vol. 195, no. 3, pp. 403-415, 2011.

[219] Y. Y. Lee, D. Moujalled, M. Doerflinger et al., "CREB-binding protein (CBP) regulates [beta]-adrenoceptor ([beta]-AR)-mediated apoptosis," Cell Death and Differentiation, vol. 20, no. 7, pp. 941-952, 2013.

[220] N. L. Estrella, A. L. Clark, C. A. Desjardins, S. E. Nocco, and F. J. Naya, "MEF2D deficiency in neonatal cardiomyocytes triggers cell cycle re-entry and programmed cell death in vitro," The Journal of Biological Chemistry, vol. 290, no. 40, pp. 24367-24380, 2015.

[221] X. Gao, B. Lin, S. Sadayappan, and T. B. Patel, "Interactions between the regulatory subunit of type I protein kinase a and p90 ribosomal s6 kinase1 regulate cardiomyocyte apoptosiss," Molecular Pharmacology, vol. 85, no. 2, pp. 357-367, 2014.

[222] B. Ding, J.-I. Abe, H. Wei et al., "Functional role of phosphodiesterase 3 in cardiomyocyte apoptosis: implication in heart failure," Circulation, vol. 111, no. 19, pp. 2469-2476, 2005.

[223] B. Ding, J.-I. Abe, H. Wei et al., "A positive feedback loop of phosphodiesterase 3 (PDE3) and inducible cAMP early repressor (ICER) leads to cardiomyocyte apoptosis," Proceedings of the National Academy of Sciences of the United States of America, vol. 102, no. 41, pp. 14771-14776, 2005.

[224] S. E. Lehnart, X. H. Wehrens, S. Reiken et al., "Phosphodiesterase 4D deficiency in the ryanodine-receptor complex promotes heart failure and arrhythmias," Cell, vol. 123, no. 1, pp. 25-35, 2005.

[225] C. K. Pride, L. Mo, K. Quesnelle et al., "Nitrite activates protein kinase A in normoxia to mediate mitochondrial fusion and tolerance to ischaemia/reperfusion," Cardiovascular Research, vol. 101, no. 1, pp. 57-68, 2014.

[226] S. Sun, M. Zhang, J. Lin et al., "Lin28a protects against diabetic cardiomyopathy via the PKA/ROCK2 pathway," Biochemical and Biophysical Research Communications, vol. 469, no. 1, pp. 29-36, 2016.

[227] P. Ahuja, P. Sdek, and W. R. MacLellan, "Cardiac myocyte cell cycle control in development, disease, and regeneration," Physiological Reviews, vol. 87, no. 2, pp. 521-544, 2007.

[228] A. Besson, S. F. Dowdy, and J. M. Roberts, "CDK inhibitors: cell cycle regulators and beyond," Developmental Cell, vol. 14, no. 2, pp. 159-169, 2008.

[229] S. Adachi, H. Ito, M. Tamamori-Adachi et al., "Cyclin A/cdk2 activation is involved in hypoxia-induced apoptosis in cardiomyocytes," Circulation Research, vol. 88, no. 4, pp. 408-414, 2001.

[230] L. Hauck, G. Hansmann, R. Dietz, and R. Von Harsdorf, "Inhibition of hypoxia-induced apoptosis by modulation of retinoblastoma protein-dependent signaling in cardiomyocytes," Circulation Research, vol. 91, no. 9, pp. 782-789, 2002.

[231] A. M. Narasimha, M. Kaulich, G. S. Shapiro, Y. J. Choi, P. Sicinski, and S. F. Dowdy, "Cyclin D activates the Rb tumor suppressor by mono-phosphorylation," eLife, vol. 2014, no. 3, Article ID e02872, 2014.

[232] Y. Maejima, S. Adachi, H. Ito, K. Nobori, M. Tamamori-Adachi, and M. Isobe, "Nitric oxide inhibits ischemia/reperfusioninduced myocardial apoptosis by modulating cyclin Aassociated kinase activity," Cardiovascular Research, vol. 59, no. 2, pp. 308-320, 2003.

[233] R. Agah, L. A. Kirshenbaum, M. Abdellatif et al., "Adenoviral delivery of E2F-1 directs cell cycle reentry and p53- independent apoptosis in postmitotic adult myocardium in vivo," Journal of Clinical Investigation, vol. 100, no. 11, pp. 2722-2728,1997.

[234] R. Von Harsdorf, L. Hauck, F. Mehrhof, U. Wegenka, M. C. Cardoso, and R. Dietz, "E2F-1 overexpression in cardiomyocytes induces downregulation of [p21.sup.CIP1] and [p27.sup.KIP1] and release of active cyclin-dependent kinases in the presence of insulin-like growth factor I," Circulation Research, vol. 85, no. 2, pp. 128-136, 1999.

[235] N. Yurkova, J. Shaw, K. Blackie et al., "The cell cycle factor E2F-1 activates Bnip3 and the intrinsic death pathway in ventricular myocytes," Circulation Research, vol. 102, no. 4, pp. 472-479, 2008.

[236] A. Diwan, M. Krenz, F. M. Syed et al., "Inhibition of ischemic cardiomyocyte apoptosis through targeted ablation of Bnip3 restrains postinfarction remodeling in mice," The Journal of Clinical Investigation, vol. 117, no. 10, pp. 2825-2833, 2007.

[237] R. Dhingra, V. Margulets, S. R. Chowdhury et al., "Bnip3 mediates doxorubicin-induced cardiac myocyte necrosis and mortality through changes in mitochondrial signaling," Proceedings of the National Academy of Sciences of the United States of America, vol. 111, no. 51, pp. E5537-E5544, 2014.

[238] E. Angelis, P. Zhao, R. Zhang, J. I. Goldhaber, and W. R. MacLellan, "The role of E2F-1 and downstream target genes in mediating ischemia/reperfusion injury in vivo," Journal of Molecular and Cellular Cardiology, vol. 51, no. 6, pp. 919-926, 2011.

[239] J. Zhang, N. Bahi, A. M. Zubiaga, J. X. Comella, M. Llovera, and D. Sanchis, "Developmental silencing and independency from E2F of apoptotic gene expression in postmitotic tissues," FEBS Letters, vol. 581, no. 30, pp. 5781-5786, 2007.

[240] D. Dingar, F. Konecny, J. Zou, X. Sun, and R. von Harsdorf, "Anti-apoptotic function of the E2F transcription factor 4 (E2F4)/p130, a member of retinoblastoma gene family in cardiac myocytes," Journal of Molecular and Cellular Cardiology, vol. 53, no. 6, pp. 820-828, 2012.

[241] J. L. O. Pohjoismaki, S. L. Williams, T. Boettger et al., "Overexpression of Twinkle-helicase protects cardiomyocytes from genotoxic stress caused by reactive oxygen species," Proceedings of the National Academy of Sciences of the United States of America, vol. 110, no. 48, pp. 19408-19413, 2013.

[242] F. Konecny, J. Zou, M. Husain, and R. von Harsdorf, "Postmyocardial infarct p27 fusion protein intravenous delivery averts adverse remodelling and improves heart function and survival in rodents," Cardiovascular Research, vol. 94, no. 3, pp. 492-500, 2012.

[243] X. Sun, A. Momen, J. Wu et al., "P27 protein protects metabolically stressed cardiomyocytes from apoptosis by promoting autophagy," Journal of Biological Chemistry, vol. 289, no. 24, pp. 16924-16935, 2014.

[244] J. Terrand, B. Xu, S. Morrissy, T. N. Dinh, S. Williams, and Q. M. Chen, "[p21.sup.WAF1/Cip1/Sdi1] knockout mice respond to doxorubicin with reduced cardiotoxicity," Toxicology and Applied Pharmacology, vol. 257, no. 1, pp. 102-110, 2011.

[245] N. Zhou, Y. Fu, Y. Wang et al., "P27kip1 haplo-insufficiency improves cardiac function in early-stages of myocardial infarction by protecting myocardium and increasing angiogenesis by promoting IKK activation," Scientific Reports, vol. 4, article no. 5978, 2014.

[246] Y. Yan, J. Frisen, M.-H. Lee, J. Massague, and M. Barbacid, "Ablation of the CDK inhibitor p57Kip2 results in increased apoptosis and delayed differentiation during mouse development," Genes and Development, vol. 11, no. 8, pp. 973-983,1997.

[247] S. A. Haley, T. Zhao, L. Zou, J. E. Klysik, J. F. Padbury, and L. K. Kochilas, "Forced expression of the cell cycle inhibitor p57Kip2 in cardiomyocytes attenuates ischemia-reperfusion injury in the mouse heart," BMC Physiology, vol. 8, article 4, 2008.

[248] N. A. Gude, G. Emmanuel, W. Wu et al., "Activation of Notchmediated protective signaling in the myocardium," Circulation Research, vol. 102, no. 9, pp. 1025-1035, 2008.

[249] P. Kratsios, C. Catela, E. Salimova et al., "Distinct roles for cellautonomous notch signaling in cardiomyocytes of the embryonic and adult heart," Circulation Research, vol. 106, no. 3, pp. 559-572, 2010.

[250] X.-L. Zhou, L. Wan, Q.-R. Xu, Y. Zhao, and J.-C. Liu, "Notch signaling activation contributes to cardioprotection provided by ischemic preconditioning and postconditioning," Journal of Translational Medicine, vol. 11, article 251, 2013.

[251] B. Yu and B. Song, "Notch 1 signalling inhibits cardiomyocyte apoptosis in ischaemic postconditioning," Heart Lung and Circulation, vol. 23, no. 2, pp. 152-158, 2014.

[252] A. Croquelois, A. A. Domenighetti, M. Nemir et al., "Control of the adaptive response of the heart to stress via the Notchl receptor pathway," Journal of Experimental Medicine, vol. 205, no. 13, pp. 3173-3185, 2008.

[253] Y. Li, Y. Hiroi, S. Ngoy et al., "Notch1 in bone marrow-derived cells mediates cardiac repair after myocardial infarction," Circulation, vol. 123, no. 8, pp. 866-876, 2011.

[254] C. Collesi, L. Zentilin, G. Sinagra, and M. Giacca, "Notch1 signaling stimulates proliferation of immature cardiomyocytes," Journal of Cell Biology, vol. 183, no. 1, pp. 117-128, 2008.

[255] W. Ge and J. Ren, "mTOR-STAT3-notch signalling contributes to ALDH2-induced protection against cardiac contractile dysfunction and autophagy under alcoholism," Journal of Cellular and Molecular Medicine, vol. 16, no. 3, pp. 616-626, 2012.

[256] M. Zhang, C. Wang, J. Hu et al., "Notch3/Akt signaling contributes to OSM-induced protection against cardiac ischemia/ reperfusion injury," Apoptosis, vol. 20, no. 9, pp. 1150-1163,2015.

[257] V. M. Campa, R. Gutierrez-Lanza, F. Cerignoli et al., "Notch activates cell cycle reentry and progression in quiescent cardiomyocytes," Journal of Cell Biology, vol. 183, no. 1, pp. 129-141, 2008.

[258] H. Pei, Q. Yu, Q. Xue et al., "Notch1 cardioprotection in myocardial ischemia/reperfusion involves reduction of oxidative/ nitrative stress," Basic Research in Cardiology, vol. 108, article 373, 2013.

[259] M.-Y. Kim, J. Jung, J.-S. Mo et al., "The intracellular domain of Jagged-1 interacts with Notch1 intracellular domain and promotes its degradation through Fbw7 E3 ligase," Experimental Cell Research, vol. 317, no. 17, pp. 2438-2446, 2011.

[260] M. Metrich, A. Bezdek Pomey, C. Berthonneche, A. Sarre, M. Nemir, and T. Pedrazzini, "Jagged1 intracellular domainmediated inhibition of Notch1 signalling regulates cardiac homeostasis in the postnatal heart," Cardiovascular Research, vol. 108, no. 1, pp. 74-86, 2015.

[261] J. J. Saucerman and D. M. Bers, "Calmodulin mediates differential sensitivity of CaMKII and calcineurin to local [Ca.sup.2+] in cardiac myocytes," Biophysical Journal, vol. 95, no. 10, pp. 4597-4612, 2008.

[262] L. J. De Windt, H. W. Lim, T. Taigen et al., "Calcineurinmediated hypertrophy protects cardiomyocytes from apoptosis in vitro and in vivo: an apoptosis-independent model of dilated heart failure," Circulation Research, vol. 86, no. 3, pp. 255-263, 2000.

[263] O. F. Bueno, D. J. Lips, R. A. Kaiser et al., "Calcineurin A[beta] gene targeting predisposes the myocardium to acute ischemiainduced apoptosis and dysfunction," Circulation Research, vol. 94, no. 1, pp. 91-99, 2004.

[264] J. Heineke, K. C. Wollert, H. Osinska et al., "Calcineurin protects the heart in a murine model of dilated cardiomyopathy," Journal of Molecular and Cellular Cardiology, vol. 48, no. 6, pp. 1080-1087, 2010.

[265] T. Kakita, K. Hasegawa, E. Iwai-Kanai et al., "Calcineurin pathway is required for endothelin-1-mediated protection against oxidant stress-induced apoptosis in cardiac myocytes," Circulation Research, vol. 88, no. 12, pp. 1239-1246, 2001.

[266] W. T. Pu, Q. Ma, and S. Izumo, "NFAT transcription factors are critical survival factors that inhibit cardiomyocyte apoptosis during phenylephrine stimulation in vitro," Circulation Research, vol. 92, no. 7, pp. 725-731, 2003.

[267] N. Bousette, S. Chugh, V. Fong et al., "Constitutively active calcineurin induces cardiac endoplasmic reticulum stress and protects against apoptosis that is mediated by [alpha]-crystallin-B," Proceedings of the National Academy of Sciences of the United States of America, vol. 107, no. 43, pp. 18481-18486, 2010.

[268] H. G. Wang, N. Pathan, I. M. Ethell et al., "[Ca.sup.2+]-induced apoptosis through calcineurin dephosphorylation of BAD," Science, vol. 284, no. 5412, pp. 339-343,1999.

[269] Q. Liu, B. J. Wilkins, Y. J. Lee, H. Ichijo, and J. D. Molkentin, "Direct interaction and reciprocal regulation between ASK1 and calcineurin-NFAT control cardiomyocyte death and growth," Molecular and Cellular Biology, vol. 26, no. 10, pp. 3785-3797, 2006.

[270] H. He, X. Liu, L. Lv et al., "Calcineurin suppresses AMPK-dependent cytoprotective autophagy in cardiomyocytes under oxidative stress," Cell Death and Disease, vol. 5, no. 1, article no. e997, 2014.

[271] G. H. Little, A. Saw, Y. Bai et al., "Critical role of nuclear calcium/calmodulin-dependent protein kinase II[beta]B in cardiomyocyte survival in cardiomyopathy," The Journal of Biological Chemistry, vol. 284, no. 37, pp. 24857-24868, 2009.

[272] W. Zhu, A. Y.-H. Woo, D. Yang, H. Cheng, M. T. Crow, and R.P. Xiao, "Activation of CaMKIISC is a common intermediate of diverse death stimuli-induced heart muscle cell apoptosis," The Journal of Biological Chemistry, vol. 282, no. 14, pp. 10833-10839, 2007.

[273] H. Ling, T. Zhang, L. Pereira et al., "Requirement for [Ca.sup.2+]/ calmodulin-dependent kinase II in the transition from pressure overload-induced cardiac hypertrophy to heart failure in mice," Journal of Clinical Investigation, vol. 119, no. 5, pp. 1230-1240, 2009.

[274] S. M. MacDonnell, J. Weisser-Thomas, H. Kubo et al., "CaMKII negatively regulates calcineurin-NFAT signaling in cardiac myocytes," Circulation Research, vol. 105, no. 4, pp. 316-325, 2009.

[275] M. M. Kreusser, L. H. Lehmann, S. Keranov et al., "Cardiac CaM kinase II genes S and y contribute to adverse remodeling but redundantly inhibit calcineurin-induced myocardial hypertrophy," Circulation, vol. 130, no. 15, pp. 1262-1273, 2014.

[276] O. M. Koval, X. Guan, Y. Wu et al., "CaV1.2 [beta]-subunit coordinates CaMKII-triggered cardiomyocyte death and afterdepolarizations," Proceedings of the National Academy of Sciences of the United States of America, vol. 107, no. 11, pp. 4996-5000, 2010.

[277] M.-L. A. Joiner, O. M. Koval, J. Li et al., "CaMKII determines mitochondrial stress responses in heart," Nature, vol. 491, no. 7423, pp. 269-273, 2012. [278] H. Ling, C. B. B. Gray, A. C. Zambon et al., "[Ca.sup.2+]/calmodul-independent protein kinase II S mediates myocardial ischemia/ reperfusion injury through nuclear factor-xb," Circulation Research, vol. 112, no. 6, pp. 935-944, 2013.

[279] M. Weinreuter, M. M. Kreusser, J. Beckendorf et al., "CaM Kinase II mediates maladaptive post-infarct remodeling and pro-inflammatory chemoattractant signaling but not acute myocardial ischemia/reperfusion injury," EMBO Molecular Medicine, vol. 6, no. 10, pp. 1231-1245, 2014.

[280] M. Viia-Petroff, M. A. Salas, M. Said et al., "CaMKII inhibition protects against necrosis and apoptosis in irreversible ischemiareperfusion injury," Cardiovascular Research, vol. 73, no. 4, pp. 689-698, 2007.

[281] T. Zhang, Y. Zhang, M. Cui et al., "CaMKII is a RIP3 substrate mediating ischemia- and oxidative stress-induced myocardial necroptosis," Nature Medicine, vol. 22, no. 2, pp. 175-182, 2016.

[282] J. Narula, N. Haider, R. Virmani et al., "Apoptosis in myocytes in end-stage heart failure," New England Journal of Medicine, vol. 335, no. 16, pp. 1182-1189, 1996.

[283] G. Olivetti, R. Abbi, F. Quaini et al., "Apoptosis in the failing human heart," New England Journal of Medicine, vol. 336, no. 16, pp. 1131-1141,1997.

[284] A. Saraste, K. Pulkki, M. Kallajoki et al., "Cardiomyocyte apoptosis and progression of heart failure to transplantation," European Journal of Clinical Investigation, vol. 29, no. 5, pp. 380-386, 1999.

[285] J. Narula, P. Pandey, E. Arbustini et al., "Apoptosis in heart failure: release of cytochrome c from mitochondria and activation of caspase-3 in human cardiomyopathy," Proceedings of the National Academy of Sciences of the United States of America, vol. 96, no. 14, pp. 8144-8149,1999.

[286] C. Twu, N. Q. Liu, W. Popik et al., "Cardiomyocytes undergo apoptosis in human immunodeficiency virus cardiomyopathy through mitochondrion- and death receptor-controlled pathways," Proceedings of the National Academy of Sciences of the United States of America, vol. 99, no. 22, pp. 14386-14391, 2002.

[287] C. Cristobal, J. Segovia, L. A. Alonso-Pulpon, E. Castedo, J. A. Vargas, and J. C. Martinez, "Apoptosis and acute cellular rejection in human heart transplants," Revista Espanola de Cardiologia, vol. 63, no. 9, pp. 1061-1069, 2010.

[288] T. Vahasilta, M. Malmberg, A. Saraste et al., "Cardiomyocyte apoptosis after antegrade and retrograde cardioplegia during aortic valve surgery," Annals of Thoracic Surgery, vol. 92, no. 4, pp. 1351-1357, 2011.

[289] D. Wencker, M. Chandra, K. Nguyen et al., "A mechanistic role for cardiac myocyte apoptosis in heart failure," The Journal of Clinical Investigation, vol. 111, no. 10, pp. 1497-1504, 2003.

[290] R. Latini, M. Brines, and F. Fiordaliso, "Do non-hemopoietic effects of erythropoietin play a beneficial role in heart failure?" Heart Failure Reviews, vol. 13, no. 4, pp. 415-423, 2008.

[291] E. Lipsic, P. van der Meer, A. A. Voors et al., "A single bolus of a long-acting erythropoietin analogue darbepoetin alfa in patients with acute myocardial infarction: a randomized feasibility and safety study," Cardiovascular Drugs and Therapy, vol. 20, no. 2, pp. 135-141, 2006.

[292] M. Ferrario, E. Arbustini, M. Massa et al., "High-dose erythropoietin in patients with acute myocardial infarction: a pilot, randomised, placebo-controlled study," International Journal of Cardiology, vol. 147, no. 1, pp. 124-131, 2011.

[293] S. S. Najjar, S. V. Rao, C. Melloni et al., "Intravenous erythropoietin in patients with ST-segment elevation myocardial infarction: REVEAL: a randomized controlled trial," JAMA, vol. 305, no. 18, pp. 1863-1872, 2011.

[294] A. A. Voors, A. M. S. Belonje, F. Zijlstra et al., "A single dose of erythropoietin in ST-elevation myocardial infarction," European Heart Journal, vol. 31, no. 21, pp. 2593-2600, 2010.

[295] M. L. Fokkema, L. Kleijn, P. Van Der Meer et al., "Long term effects of epoetin alfa in patients with ST- elevation myocardial infarction," Cardiovascular Drugs and Therapy, vol. 27, no. 5, pp. 433-439, 2013.

[296] P. Van Der Meer and D. J. Van Veldhuisen, "Acute coronary syndromes: the unfulfilled promise of erythropoietin in patients with MI," Nature Reviews Cardiology, vol. 8, no. 8, pp. 425-426, 2011.

[297] A. Messori, V. Fadda, D. Maratea, and S. Trippoli, "Erythropoietin in patients with acute myocardial infarction: no proof of effectiveness or proof of no effectiveness?" Clinical Cardiology, vol. 36, no. 10, pp. E39-E40, 2013.

[298] M. L. Fokkema, P. van der Meer, S. V. Rao et al., "Safety and clinical outcome of erythropoiesis-stimulating agents in patients with ST-elevation myocardial infarction: a meta-analysis of individual patient data," American Heart Journal, vol. 168, no. 3, pp. 354-362.e2, 2014.

[299] F. Xue, X. Yang, B. Zhang et al., "Postconditioning the human heart in percutaneous coronary intervention," Clinical Cardiology, vol. 33, no. 7, pp. 439-444, 2010.

[300] F. Thuny, O. Lairez, F. Roubille et al., "Post-conditioningreduces infarct size and edema in patients with ST-segment elevation myocardial infarction," Journal of the American College of Cardiology, vol. 59, no. 24, pp. 2175-2181, 2012.

[301] S. Deftereos, G. Giannopoulos, V. Tzalamouras et al., "Renoprotective effect of remote ischemic post-conditioning by intermittent balloon inflations in patients undergoing percutaneous coronary intervention," Journal of the American College of Cardiology, vol. 61, no. 19, pp. 1949-1955, 2013.

[302] J.-Y. Hahn, Y. B. Song, E. K. Kim et al., "Ischemic postconditioning during primary percutaneous coronary intervention: the effects of postconditioning on myocardial reperfusion in patients with st-segment elevation myocardial infarction (POST) randomized trial," Circulation, vol. 128, no. 17, pp. 1889-1896, 2013.

[303] J.-Y. Hahn, C. W. Yu, H. S. Park et al., "Long-term effects of ischemic postconditioning on clinical outcomes: 1-year followup of the POST randomized trial," American Heart Journal, vol. 169, no. 5, pp. 639-646, 2015.

[304] G. Tarantini, E. Favaretto, M. P. Marra et al., "Postconditioning during coronary angioplasty in acute myocardial infarction: the POST-AMI trial," International Journal of Cardiology, vol. 162, no. 1, pp. 33-38, 2012.

Peng Xia, Yuening Liu, and Zhaokang Cheng

Department of Pharmaceutical Sciences, Washington State University College of Pharmacy, PBS 323, 205 E. Spokane Falls Blvd., P.O. Box 1495, Spokane, WA 99210-1495, USA

Correspondence should be addressed to Zhaokang Cheng; zhaokang.cheng@wsu.edu

Received 19 September 2016; Accepted 20 November 2016

Academic Editor: Adrienne Lester King

Caption: Figure 1: Schematic representation of the signaling pathways that regulate apoptosis in mammalian cardiac myocytes. AC, adenylyl cyclase; CaMKII, [Ca.sup.2+]/CaM-dependent kinase II; cAMP, cyclic adenosine monophosphate; Cyt c, cytochrome c; DAG, diacylglycerol; E2F1, E2F transcription factor 1; ECM, extracellular matrix; ERK, extracellular signal-regulated kinase; FADD, Fas-associated death domain; FAK, focal adhesion kinase; GPCR, G protein-coupled receptor; IP3, inositol 1,4,5-trisphosphate; MEK1, mitogen-activated protein kinase 1; Mst1, mammalian Ste20-like kinase 1; NICD, Notch intracellular domain; PI3K, phosphoinositide 3-kinase; PIP2, phosphatidylinositol bisphosphate; PIP3, phosphatidylinositol trisphosphate; PLC[beta], phospholipase C PKA, cyclic AMP-dependent protein kinase; PKC, protein kinase C; RTK, receptor tyrosine kinase. Gray arrows indicate activation; red blocked lines indicate inhibition.
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Title Annotation:Review Article
Author:Xia, Peng; Liu, Yuening; Cheng, Zhaokang
Publication:BioMed Research International
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Date:Jan 1, 2017
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