Regulation of the NAD + ‐dependent histone deacetylase Sirt1 in conditions of muscle use and disuse

Abstract

Caloric restriction promotes longevity in mammals. This effect is mediated by the NAD+-dependent histone deacetylase Sirt1, which is sensitive to metabolic alterations and interacts with the regulatory protein of mitochondrial biogenesis PGC-1α. Conditions of muscle use and disuse such as endurance training and denervation are known to produce alterations in mitochondrial biogenesis as well as energy metabolism. To determine whether Sirt1 is regulated under those conditions, Sirt1 deacetylase activity was evaluated in muscles of rats subjected to chronic electrical stimulation for 7 days (10 Hz; 3 hrs/day), or denervation for 14 days. Mitochondrial biogenesis was determined by measuring the protein expression of PGC-1α and cytochrome c, and COX enzyme activity. Sirt1 activity was measured using a fluorimetric deacetylation assay and its reliability was assessed as a function of sample protein concentration, incubation time, and inhibitor (nicotinamide) concentration. In chronically-stimulated extensor digitorum longus (EDL) muscle, PGC-1α, cytochrome c and COX enzyme activity were increased by 30–50% compared to non-stimulated muscle. In denervated EDL, those markers of mitochondrial biogenesis were decreased to the same extent (30–50%) compared to the control muscle. In contrast, Sirt1 activity was increased by 20% and 76% in chronically-stimulated and denervated EDL, respectively. Our data suggest that 1) SIRT1 and PGC-1α expression are independently regulated, and 2) mitochondrial biogenesis and SIRT1 function are involved in separate metabolic pathways in conditions of muscle use and disuse. Support from CIHR.