Attenuated Muscle Regrowth with Age is Not Associated with Differences in Anabolic and Catabolic Pathways

Abstract

The ability to recover muscle size after disuse is attenuated at old age. We hypothesized that anabolic and catabolic pathways were altered with aging thereby inhibiting the regrowth response. Male Fisher344/Brown Norway rats at 6 (young) and 32 (old) months of age were divided into 3 groups: ambulatory controls, hindlimb suspended (HS) for 2 weeks and HS followed by two weeks reloading (RE). Soleus muscle weight and muscle fiber cross sectional area decreased with HS and recovered to control in young, but not old rats. mRNA abundance of protein degradation marker MAFbx and autophagy markers Atg5 and Atg7 increased with HS and were restored to control with RE in soleus muscle of young and old rats. Similarly, phosphorylated GSK3β was decreased with atrophy induced by HS and returned to control upon reloading in both ages. In contrast, no changes in phsophorylated p70s6kinase were observed at either age. We conclude that changes in anabolic and catabolic pathways associated with alterations in muscle size are similar in soleus muscles of young and old rats, suggesting that factors external to muscle may play a role in the attenuated muscle regrowth response in the aged. Funding NIH AG28925