Interactions between stem cells and the microenvironment in vivo.

The National Institute of Neurological Disorders and Stroke (NINDS), the National Institute on Drug Abuse (NIDA), the National Institute of Deafness and Other Communication Disorders (NIDCD), the National Institute of Alcohol Abuse and Alcoholism (NIAAA), and the National Institute on Aging (NIA) invite applications for studies on the cellular and molecular signaling between the local environment within organisms and stem and progenitor cells that are either introduced as transplants or are normally resident within host tissues and organs. The objective of this initiative is to promote a thorough exploration and characterization of the bi-directional communication between multipotent cells and the three-dimensional local milieu or niche that they encounter in vivo under normal and compromised states, such as with aging or following injury, disease, or drug exposure. Of particular interest is the rigorous characterization of how interactions with localized cues in space and time regulate stern cell survival, migration, replication, and "plasticity" in the nervous system and other parts of the body. Projects that address comparisons between the responses of stem cells within niches in the developing and mature or aging nervous system in vivo, or in host microenvironments modified by injury, disease, or by exposure to drugs and alcohol would also be directly relevant to this program announcement with set-aside (PAS), as are studies to compare different classes of stem cells or progeny at progressively more advanced stages of differentiation when placed in the same sites in vivo.

Unlike organs such as the skin and the gut that self-renew throughout lift, the nervous system in adult mammals is restricted in its ability to replace neurons and glia that have been lost through injury, disease, alcohol and drug abuse, or even advancing age. Stem cell research offers enormous potential for treating many congenital, developmental, psychiatric, and degenerative diseases of the nervous system for which there are no treatments or cures. Under the appropriate tissue culture conditions, a variety of multipotent cells appear to acquire many properties of neurons and glia--a first step toward developing cell replacement therapies for neurological dysfunction. The discovery, of endogenous stem cells, residing either within the nervous system or in other tissues raises the possibility that these intrinsic systems may be harnessed to restore defective cells and functions. In both cases, the expectation is that, when exposed to the optimal microenvironment in vivo, endogenous or transplanted stem cells will differentiate in a manner appropriate to the local brain region, and integrate with the existing circuits in the nervous system. The past decade has seen enormous progress in our understanding of the specific requirements of stem cells to proliferate and differentiate along specified lineages. This progress has been made possible by the discovery of a myriad of growth factors and substrate conditions followed by careful testing in culture. Unfortunately, the behavior of cells in tissue culture does not adequately predict how these same cells will behave when transplanted into the living host where multiple known and unknown factors converge to influence the biological process. We do not know the whole spectrum of factors present in vivo that influence cell fate. Effective use of stem and progenitor cells for therapeutic purposes hinges on their ability to thrive, integrate, and function in a biologically meaningful manner in vivo without causing adverse events. Therefore the next stage in developing cell restoration therapy requires understanding how the newly generated cells will behave within the host.

Recent reports indicate that the "niche" or local microenvironment that a stem cell encounters governs its behavior and fate. For example, adult neural stem cells produced neurons when transplanted into the neurogenic zone of the hippocampus, but produced astrocytes in the environment of the spinal cord. Further investigation showed that a specific component of the local environment, the regional astrocytes from the hippocampus were capable of instructing these stem cells to adopt a neuronal fate in vitro. In addition to regional differences within the nervous system, the microenvironment encountered by a stem cell may vary as a function of age of the host organism. Similarly, alteration of the niche by injury, drugs or other circumstances is likely to affect the ability of transplanted stem cells to survive, differentiate and integrate into existing neural circuitry. Understanding these changes will be important in making decisions about the use of cell replacement therapies in very young or elderly patients, in patients with a history of alcohol or drug usage, or suffering from injury or other neurological conditions.

Transplanted cells can act to influence and change host cells in their vicinity. Stem cells may release agents that alter the activity or resiliency of damaged host cells. These dynamic interactions are inevitable as living cells and tissue contact, react and respond to each other in time and space. Teasing out and understanding these interactions poses a major challenge that must be faced in order to develop realistic cell replacement therapies and enhance normal tissue regeneration.

This PAS is intended to promote studies that establish and identify the nature and action of microenvironmental cues in the nervous system that regulate stem cell fate. It specifically targets cellular, molecular, and genetic mechanisms that act in vivo to influence stem cell survival, homing/migration, adhesion, differentiation, plasticity, and tumorigenicity in both the central and peripheral nervous systems. Applications that only propose in vitro studies will not be responsive to this initiative.

The following examples illustrate areas that are of high interest; other innovative projects are also encouraged. These examples of research approaches are not meant to be all-inclusive or restrictive. Plans for data and/or reagent sharing and promulgation of results will be integral to the applications. Approaches include 1) identification, localization, and comparison of known or novel cues within the developing, adult, and aging nervous system that influence the mitotic potential, cell cycle and differentiation of stem and progenitor cells along specific lineages; 2) characterization of the cell-extrinsic and cell-intrinsic signaling pathways and components involved in transducing the action of local cues on stem and progenitor cells in vivo; 3) investigation of the causal relationship between site-specific changes of endogenous cues resulting from injury, disease, exposure to alcohol, drugs of treatment or abuse, and any resulting alterations of stem cell activity; 4) evaluation of the effects of external factors such as stress, exercise, or an enriched versus impoverished living conditions on the microenvironment within the host organism, and how these changes in microenvironment influence the behavior of stem cells at different periods throughout the life span of the organism; 5) investigation of local cellular interactions that determine and maintain the structural and functional integration of progenitor cells into the host nervous system and existing circuitry; 6) development of assays facilitating the discovery of novel endogenous signals that modulate stem cell behavior and fate, as well as signals generated by stem cells that regulate components of the local host tissue. These may include the development of measures (physiological, behavioral, neurochemical, imaging) to evaluate the integration and function of progenitor cells in the developing, adult, and aging nervous system; and 7) assessment of the short and long-term local effects of the interactions between the immune system and glial reactions gendered in response to the infiltration of stem cells and their progeny in the host.

The NIDA is interested in how drugs of abuse and factors such as stress andenvironment affect the behavior of stein cells and the functional consequences of such alterations, which might be related to the cognitive impairments, developmental deficits, neuroadaption and addictive behaviors seen in drug abuse. The NIDCD is particularly interested in stem cell research targeting the various peripheral components of the auditory, olfaction, and gustatory systems. The NIAAA is interested in how alcohol exposure alters the biochemical environment of tissues, thus interfering with the capacity of stein cells to establish contact, differentiate and function in target tissue. The NIA is interested in stem cell research and neurogenesis in the aging nervous system with emphasis on basic neurobiology, motor and sensory systems, integrative neurobiology, cognition, and the dementias of aging, particularly Alzheimer disease.

This PAS will use the NIH Exploratory/ Developmental Grant (R21) and the Research Project Grant (R01) award mechanisms. As an applicant, you will be solely responsible for planning, directing, and executing the proposed project. The proposed project period during which the research will be conducted should adequately reflect the time required to accomplish the stated goals and should be no more than five years for R01 grants. Support for the R21 grants is limited to two years with a cumulative maximum of $275,000 direct costs requested for both years. For further information on the R21 mechanism, including institute-specific information, see http://grants.nih.gov/grants/guide/ pa-files/PA-03-107.html.

This PAS uses just-in-time concepts. It also uses the modular as well as the nonmodular budgeting formats; see http://grants.nih. gov/grants/funding/modular/modular.htm. Specifically, if you are submitting an application with direct costs in each year of $250,000 or less, use the modular format. Otherwise follow the instructions for nonmodular research grant applications. More information on this PAS is available at http://grants2.nih.gov/grants/guide/ pa-files/PAS-03-172.html

The participating ICs have set aside a total of $2 million dollars per year to support this initiative. The amount and timing of awards paid from set aside funds will depend on the overall scientific merit of the applications and the availability of funds throughout the duration of this solicitation (two years). Because the nature and scope of the proposed research will vary from application to application, it is anticipated that the size and duration of each award will also vary. Although the financial plans of the IC(s) provide support for this program, awards pursuant to this PAS are contingent upon the availability of funds and the receipt of a sufficient number of meritorious applications.

Contact: Arlene Y. Chiu, Repair and Plasticity Program, NINDS, 301-496-1447, e-mail: [e-mail]; Geraline C. Lin, Division of Neuroscience and Behavioral Research, NIDA, 301-435-1305, e-mail: [e-mail]; Barry Davis, Taste and Smell Program, NIDCD, 301-402-3464, e-mail: [e-mail]; Sam Zakhari, Division of Basic Research, NIAAA, 301-443-0799, e-mail: [e-mail]; or Bradley C. Wise, Neuroscience and Neuropsychology of Aging Program, NIA, 301-496-9350, e-mail: [e-mail]. Reference: PAS No. PAS-03-172