Altered proteasome function and subunit composition in aged muscle.

Myofibrillar protein degradation is mediated through the ubiquitin-proteasome pathway. To investigate if altered proteasome activity plays a role in age-related muscle atrophy, we examined muscle size and proteasome function in young and aged F344BN rats. Significant age-related muscle atrophy was confirmed by the 38% decrease in cross-sectional area of type 1 fibers in soleus muscle.