Age-related deficit in load-induced skeletal muscle growth.
The growth response of ankle flexor and extensor muscles to two models of increased loading, functional overload (FO) and hind-limb reloading following hind-limb suspension, was measured by wet weight in Fisher 344-Brown Norway rats at ages ranging from 6 to 30 months. In response to FO, there was a 40% decrease in absolute growth of the plantaris beginning in middle age. Interestingly, the growth response to FO of 30-month old rats maintained on a 40% calorie-restricted diet improved by more than twofold relative to 30-month old rats on a normal chow diet. Recovery of muscle mass upon reloading following disuse was significantly impaired (reduced 7-16%) in predominantly fast, but not slow, muscles of 30-month relative to 9-month old rats. Initial investigation of the Akt signaling pathway following FO suggests a reduction or delay in activation of Akt and its downstream targets in response to increased loading in old rats.
Hwee
Darren T
DT
Department of Neurobiology, Physiology, and Behavior, University of California, Davis, 95616, USA.
Bodine
Sue C
SC
D000222:Adaptation, Physiological; D000367:Age Factors; D000375:Aging / Q000502:physiology*; D000818:Animals; D031204:Caloric Restriction; D006614:Hindlimb / Q000502:physiology; D019417:Hindlimb Suspension / Q000502:physiology; D008297:Male; D023421:Models, Animal; D024510:Muscle Development / Q000502:physiology; D009124:Muscle Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000254:growth & development*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D015398:Signal Transduction / Q000502:physiology; D016474:Weight-Bearing / Q000502:physiology*
D009124:Muscle Proteins; D051057:Proto-Oncogene Proteins c-akt