Aging alters the reduction of pro-apoptotic signaling in response to loading-induced hypertrophy

This study tested the hypothesis that loading decreased apoptosis in skeletal muscle in an aging-dependent fashion. One wing of young and aged Japanese quails was loaded for 7 or 21 days to induce hypertrophy. The contralateral wing served as the intra-animal control. Loading increased fast-twitch quail patagialis muscle mass by 28 and 49%, after 7 or 21 days of loading, respectively in young adult birds. Muscle mass was not elevated after 7 days of loading, but increased by 29% after 21 days of loading in aged birds. Seven days of loading reduced DNA fragmentation and cytosolic accumulation of cytochrome c in muscles from young birds but not in muscles from aged birds. ARC protein content was lower and H2O2 content was higher in muscles from aged birds following 7 days of loading. The mitochondria-free cytosolic protein fraction from muscles loaded for 7 days had 41 and 29% lower AIF content than control muscles in young and aged birds, respectively. XIAP, an apoptotic suppressor protein increased after 7 days of loading in muscles from young adult but not aged birds. Our results suggest that loading suppresses pro-apoptotic signaling in quail muscle but aging delays or attenuates these anti-apoptotic changes.