Acceleron Pharma to Present ACE-011 Preclinical Data at the Annual Meeting of the American Society for Bone and Mineral Research; Preclinical Data Demonstrates Dual Activity of ACE-011.

CAMBRIDGE, Mass. -- Acceleron Pharma, Inc., a biopharmaceutical company involved in the development of regenerative therapeutics, announced that it will present preclinical data highlighting the anabolic bone activity of ACE-011, the company's lead drug candidate and a novel treatment for bone loss, at the Annual Meeting of the American Society for Bone and Mineral Research (ASBMR).

Scott Pearsall, Ph.D., Director of Preclinical Pharmacology at Acceleron will present the data during the ASBMR's Concurrent Oral Session 15, Osteoporosis-Treatment II, on Sunday September 17, 2006 from 10:00 - 11:30 AM in Ballroom B of the Philadelphia Convention Center.

About ACE-011

ACE-011, a novel bone anabolic agent currently in phase 1 clinical trials, is a protein therapeutic based on the activin receptor IIA. In numerous preclinical models of bone loss, ACE-011 has demonstrated beneficial effects on both trabecular and cortical bone. ACE-011 increased bone mineral density, improved bone architecture, increased the mineral apposition and bone formation rates and improved bone mechanical strength. These effects have been demonstrated in therapeutic models of bone loss in which ACE-011 has stimulated bone formation - a significant unmet medical need that is underserved by current treatments for bone loss. ACE-011 is based on technology exclusively licensed from the Salk Institute.

About Bone Loss

Bone loss is recognized as a disease with significant clinical concerns for patients and economic challenges to society. Osteoporosis is the most common bone disease in humans and, according to the National Osteoporosis Foundation, 10 million Americans are estimated to have the disease and almost 34 million more are estimated to have osteopenia or low bone mass, placing them at increased risk for osteoporosis. Osteoporosis is responsible for more than 1.5 million fractures annually and direct expenditures for hip fractures alone is estimated to cost society more than $18 billion. Bone loss and weakening is also present in other diseases, such as multiple myeloma which is the second most common hematologic malignancy with approximately 50,000 patients in the U.S. currently living with the disease. In multiple myeloma, the malignant cells cause bone lesions which weaken the bone, resulting in pain and increasing the risk of fractures in the bone.

About Acceleron Pharma

Acceleron is a privately held biopharmaceutical company that is focused on developing and commercializing regenerative therapeutics. The company's scientific platform is based on its unique position to harness the clinical potential of naturally-occurring tissue growth factors to treat diseases with significant unmet medical need. The company's lead program is being developed to reverse bone loss in diseases such as osteoporosis and cancer. Additionally, the company has therapeutic programs in the areas of muscle growth, angiogenesis and metabolic diseases. Acceleron utilizes proven biotherapeutic technologies and capitalizes on the company's internal GMP manufacturing capability to rapidly and efficiently advance therapeutics from its R&D platform to create a range of drug products. The investors in Acceleron are Advanced Technology Ventures, Flagship Ventures, OrbiMed Advisors, Polaris Ventures, Sutter Hill Ventures and Venrock Associates.