Caloric restriction attenuates apoptosis in larger type II fibers with aging

Abstract

Apoptosis has been implicated in the age‐related decline in skeletal muscle mass known as sarcopenia. Similarly, an attenuation of apoptosis is thought to contribute to the attenuation of sarcopenia by caloric restriction (CR). On this basis, we examined markers of apoptotic activation in cross‐sections of gastrocnemius muscle (Gas) from young adult (YA) and senescent (SEN) ad libitum fed (AL) and CR rats. Although CR markedly attenuated Gas atrophy (27% vs 51% for CR vs AL) and fiber atrophy (26% vs 40% in CR vs AL) with aging, CR did not affect the proportion of nuclei that were TUNEL positive (1.9±0.2% vs 3.0±0.2% for AL vs CR, respectively). Similarly, the number of TUNEL positive nuclei per 100 fibers was not different in SEN CR (11.0±1.1) vs SEN AL (8.3±0.8). On a fiber type basis, type IIa (58%) and IIb/x (51%) fibers exhibited more atrophy with aging in AL than type I fibers (31%), whereas fiber atrophy was less severe and more uniform among fiber types in CR (21%, 11% and 25% for type I, IIa and IIb/x, respectively). Interestingly, whereas fibers with TUNEL positive nuclei were larger than the mean for both type IIa and IIb/x in SEN AL, this was not the case for CR. Collectively, these results suggest that the apoptosis of nuclei in larger type II fibers of AL may contribute to their greater atrophy with aging and that this process may be attenuated by CR.