Differential regulation of myofibrillar proteins in skeletal muscles of septic mice.

Vanessa Moarbes,Laurent Huck,Theodoros Vassilakopoulos,Philippe Leblanc,Sabah N A Hussain,Dominique Mayaki,Basil J Petrof

doi:10.14814/phy2.14248

Abstract

Sepsis elicits skeletal muscle atrophy as a result of decreased total protein synthesis and/or increased total protein degradation. It is unknown how and whether sepsis differentially affects the expression of specific myofibrillar proteins in respiratory and limb muscles. In this study, we measured the effects of sepsis myofibrillar mRNAs and their corresponding protein levels in the diaphragm (DIA) and tibialis anterior (TA) muscles in a murine cecal ligation and perforation (CLP) model of sepsis. Male mice (C57/BL6j) underwent CLP‐induced sepsis. Sham‐operated mice were subjected to the same surgical procedures, except for CLP. Mice were euthanized 24, 48, or 96 h postsurgery. Transcript and protein levels of autophagy‐related genes, ubiquitin E3 ligases, and several myofibrillar genes were quantified. Sepsis elicited transient fiber atrophy in the DIA and prolonged atrophy in the TA. Atrophy was coincident with increased autophagy and ubiquitin E3 ligase expression. Myosin heavy chain isoforms decreased at 24 h in the DIA and across the time‐course in the TA, myosin light chain isoforms decreased across the time‐course in both muscles, and troponins T and C as well as tropomyosin decreased after 24 and 48 h in both the DIA and TA. α‐Actin and troponin I were unaffected by sepsis. Sepsis‐induced decreases in myofibrillar protein levels coincided with decreased mRNA expressions of these proteins, suggesting that transcriptional inhibition is involved. We hypothesize that sepsis‐induced muscle atrophy is mediated by decreased transcription and enhanced degradation of specific myofibrillar proteins, including myosin heavy and light chains, troponin C, troponin T, and tropomyosin.

Highlights

An important manifestation of severe sepsis in critically ill patients is the development of skeletal muscle weakness and atrophy (Callahan and Supinski, 2009)
The most important findings of this study are that: (1) the DIA develops transient atrophy, lasting 24 h post-initiation of sepsis, whereas the tibialis anterior (TA) develops sustained atrophy, persisting for 96 h, (2) atrophy in both muscles is associated with increased expression of ubiquitin E3 ligases and autophagy-related genes; (3) sepsis elicits time-dependent and muscle- and protein-specific effects on myofibrillar protein
Levels, with myosin light chain (MLC) isoforms decreasing throughout the time course of sepsis in both the DIA and TA, myosin heavy chain (MHC) isoforms decreasing early in sepsis in the DIA and throughout the time course in the TA, troponins T and C and tropomyosin decreasing after 24 and 48 h of sepsis in both the DIA and TA, and a-Actin and troponin I remaining unaffected by sepsis; and (4) sepsis-induced decreases in myofibrillar protein levels coincide with decreased mRNA expressions of these proteins, suggesting that transcriptional inhibition is involved

Summary

Introduction

An important manifestation of severe sepsis in critically ill patients is the development of skeletal muscle weakness and atrophy (Callahan and Supinski, 2009). Protein degradation is accomplished via four metabolic systems: the calpain, caspase-3, ubiquitin-proteasome (UPS), and autophagy-lysosome (ALP) pathways. The calpain, caspase, and UPS pathways are responsible for degrading myofibrillar proteins into smaller peptides. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.

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