Exercise training attenuates age-induced changes in apoptotic signaling in rat skeletal muscle

The aging process in skeletal muscle is characterized by a loss of myocytes and reduction in cross-sectional area of the remaining myocytes, particularly in Type II (fast-twitch) muscle fibers. In multinucleated skeletal muscle, apoptosis may contribute to both fiber atrophy and loss of muscle fibers. Recent evidence suggests that the mitochondrial Bcl-2 family pathway may be a target of aging. Here the authors demonstrated that aging increased DNA fragmentation, cleaved caspase-3, and pro-apoptotic Bax in rat skeletal muscle. Twelve weeks of treadmill exercise training increased anti-apoptotic Bcl-2, while markedly reducing DNA fragmentation, and cleaved caspase-3, Bax, and Bax/Bcl-2 ratio in the white gastrocnemius and soleus muscles of old rats. Upstream anti-apoptotic NF-kappaB activity decreased in aging skeletal muscle, and increased with exercise training. Regulation of NF-kappaB activity with aging and exercise was not related to changes in NF-kappaB subunit protein levels. Instead, changes in post-translational activation of NF-kappaB occurred as a function of altered phosphorylation of IkappaB. These results indicate that treadmill exercise training attenuates fiber atrophy and pro-apoptotic signaling in aging skeletal muscle.