Cellular aging of skeletal muscle: telomeric and free radical evidence that physical inactivity is responsible and not age.

Abstract
Telomeres play an essential role in maintaining chromosomal integrity in the face of physiological stressors. Although, the age-related shortening of telomere length (TL) in highly proliferative tissue, is predominantly due to the replication process, the mechanism for telomere shortening in skeletal muscle, which is minimally proliferative, is unclear. By studying TL in both the upper and lower limbs of the young (Y), old-mobile (OM), and old-immobile (OI) and by virtue of the bipedal nature of human locomotion, which declines with age, it may be possible to elucidate the mechanism responsible for cellular aging of skeletal muscle. With this approach, we revealed that TL (~15 kb) in arm skeletal muscle is unaffected by age. In contrast TL fell progressively in the legs across the young (~15 kb), the old mobile (~13 kb), and old immobile (~11 kb). Interestingly, there was a reciprocal rise in leg muscle free radical across these groups that was correlated with TL (r=0.7), with no such relationship in the arm (r=0.09). Our results document that chronologic age, per se, does not affect cellular aging of skeletal muscle, but reveals that physical inactivity, likely mediated by free radicals, has a profound effect upon this process.
PMID: 24708050