Differential regulation of protein degradation pathways in the ventilatory and limb muscles in response to sepsis

Abstract

Background & Aims: Sepsis triggers skeletal muscle weakness and atrophy. Muscle atrophy has been attributed to increased proteolysis. In this study, we evaluated the differential regulation of the autophagy and proteasome proteolytic pathway in the ventilatory and limb muscles of septic mice. Methods: Adult male C57/Bl6 mice underwent cecal ligation and perforation (CLP group) or sham procedures (Sham group). The diaphragm (DIA) and tibialis anterior (TA) muscles were examined after 24, 48 and 96h of the surgical procedure. Fiber diameter, autophagy and proteasome pathways were evaluated using immunostaining, immunoblotting, qPCR and electron microscopy. Results: Sepsis triggered transient atrophy (24h) in the DIA and sustained (24, 48 and 96h) atrophy in the TA and significantly induced autophagy in the two muscles with peak values detected after 24 and 48h of sepsis in the DIA and TA, respectively. Upregulation of ULK1, PI3KC3, BNIP3, PARKIN and SQSTM1 proteins were also observed in muscles of septic animals. Biphasic (24 and 96h) upregulation of Atrogin-1, MuRF-1 and Musa1 mRNA was observed in muscles of septic animals. Sepsis also decreased AKT and mTOR activation and upregulated AMPK phosphorylation. Conclusions: We conclude that sepsis triggers transient atrophy in the DIA and more sustained atrophy in the TA muscle and that this atrophy is mediated by enhanced autophagy and proteasome proteolytic activities. We also conclude that sepsis-induced activation of the autophagy pathway is mediated through inhibition of the AKT and mTOR pathways and activation of the AMPK pathway.