Autophagic flux and oxidative capacity of skeletal muscles during acute starvation

Abstract

Autophagy is an important proteolytic pathway in skeletal muscles. The roles of muscle fiber type composition and oxidative capacity remain unknown in relation to autophagy. The diaphragm (DIA) is a fast-twitch muscle fiber with high oxidative capacity, the tibialis anterior (TA) muscle is a fast-twitch muscle fiber with low oxidative capacity, and the soleus muscle (SOL) is a slow-twitch muscle with high oxidative capacity. We hypothesized that oxidative capacity is a major determinant of autophagy in skeletal muscles. Following acute (24 h) starvation of adult C57/Bl6 mice, each muscle was assessed for autophagy and compared with controls. Autophagy was measured by monitoring autophagic flux following leupeptin (20 mg/kg) or colchicine (0.4 mg/kg/day) injection. Oxidative capacity was measured by monitoring citrate synthase activity. In control mice, autophagic flux values were significantly greater in the TA than in the DIA and SOL. In acutely starved mice, autophagic flux increased, most markedly in the TA, and several key autophagy-related genes were significantly induced. In both control and starved mice, there was a negative linear correlation of autophagic flux with citrate synthase activity. Starvation significantly induced AMPK phosphorylation and inhibited AKT and RPS6KB1 phosphorylation, again most markedly in the TA. Starvation induced Foxo1, Foxo3, and Foxo4 expression and attenuated the phosphorylation of their gene products. We conclude that both basal and starvation-induced autophagic flux are greater in skeletal muscles with low oxidative capacity as compared with those with high oxidative capacity and that this difference is mediated through selective activation of the AMPK pathway and inhibition of the AKT-MTOR pathways.

Adiponectin Stimulates Autophagy and Reduces Oxidative Stress to Enhance Insulin Sensitivity During High-Fat Diet Feeding in Mice

“…An important and novel focus of our study, therefore, was the analysis of skeletal muscle autophagy (9)(10)(11)(12)14,15). First, increased LC3-II and decreased p62 levels indicated that HFD induced autophagy in skeletal muscle (25).…”

“…Other studies have demonstrated that adiponectin reduced oxidative stress by downregulating NADPH oxidase by inactivating the phosphorylation of p47 phox , the regulatory subunit of NADPH oxidase (23). Many studies have now established an important crosstalk between oxidative stress and autophagy (24), although the significance in terms in skeletal muscle metabolism (9)(10)(11)(12)14,15) requires further investigation.…”

“…Another mouse model of stimulus-deficient autophagy, the BCL2 AAA mice, which contain knock-in mutations in BCL2 phosphorylation sites (Thr69Ala, Ser70Ala, and Ser84Ala) that prevent autophagy activation, showed altered glucose metabolism during acute exercise and impaired chronic exercise-mediated protection against HFD-induced glucose intolerance (10). Others have reported activation of autophagy in skeletal muscle in response to exercise and caloric restriction (11)(12)(13)(14). The ability to induce autophagy has been shown to deteriorate with aging in skeletal muscle (15).…”

Metabolic effects of fasting on human and mouse blood in vivo

“…We next sought to determine autophagic flux 16 by inhibiting the final steps of autophagy using intraperitoneal leupeptin injections. 37,38 In conditions in which mice received leupeptin during the last 2 h of the experiment, starvation did cause LC3B lipidation, both in leukocytes (Fig. 5A, D, G) and hepatocytes ( Fig.…”

Cachexia in chronic obstructive pulmonary disease: new insights and therapeutic perspective

“…Interestingly, the respiratory muscles of COPD patients show an opposite fibre type shift compared with limb muscles, that is, towards more type I fibres 47, 48. This will have implications for the expression levels of constituents of atrophy signalling pathways 22, 49. Increased catabolic signalling through FOXO and NF‐κB can induce gene expression of key factors in both the ubiquitin proteasome system (UPS)50, 51 and the autophagy lysosome pathway 33, 52…”