Changes in the activin A‐myostatin‐follistatin system within bone and muscle of aging mice

The activin A‐myostatin‐follistatin system is thought to play an important role in the regulation of muscle and bone mass, but changes in the relative levels of these factors in muscle and bone with age are not well understood. We investigated age‐related changes in the activin A‐myostatin‐follistatin system using femoral bone marrow aspirates from young (12 months) and aged (24 months) mice, and soleus and extensor digitorum longus (EDL) muscles from these same animals. Bone marrow supernatant samples were analyzed using ELISA, and muscle samples were analyzed using real‐time PCR and ELISA. Results indicate that myostatin levels were significantly (+75%) increased in mouse bone marrow with age, whereas levels of activin A and follistatin did not differ significantly between young and aged mice. Myostatin and activin A levels were not significantly altered with age in either soleus or EDL, however follistatin levels decreased by ~30% in mouse EDL with age. These findings suggest that age‐associated loss of muscle mass in the predominantly fast‐twitch EDL muscle may be due in part to declining levels of follistatin. Funding for this research was provided by the Congressionally Directed Medical Research Programs (USAMRAA).