Proteomic and bioinformatic analysis of differentially expressed proteins in denervated skeletal muscle

The aim of this study was to improve our understanding and the current treatment of denervation-induced skeletal muscle atrophy. We used isobaric tags for relative and absolute quantification (iTRAQ) coupled with two-dimensional liquid chromatography-tandem mass spectrometry (2DLC-MS/MS) to identify the differentially expressed proteins in the tibialis anterior (TA) muscle of rats at 1 and 4 weeks following sciatic nerve transection. A total of 110 proteins was differentially expressed and was further classified using terms from the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases to unravel their molecular functions. Among the differentially expressed metabolic enzymes involved in glycolysis, Krebs cycle and oxidative phosphorylation, alpha- and beta-enolase displayed an increased and decreased expression, respectively, which was further validated by western blot analysis and immunohistochemistry. These findings suggest that the enolase isozymic switch during denervation-induced muscle atrophy is the reverse of that occurring during muscle maturation. Notably, protein-protein interaction analysis using the STRING database indicated that the protein expression of tumor necrosis factor receptor:associated factor-6 (TRAF6), muscle ring-finger protein 1 (MuRF1) and muscle atrophy F-box (MAFBx) was also upregulated during denervation-induced skeletal muscle atrophy, which was confirmed by western blot analysis. TRAF6 knockdown experiments in L6 myotubes suggested that the decreased expression of TRAF6 attenuated glucocorticoid-induced myotube atrophy. Therefore, we hypothesized that the upregulation of TRAF6 may be involved in the development of denervation-induced muscle atrophy, at least in part, by regulating the expression of MAFBx and MuRF1 proteins. The data from the present study provide valuable insight into the molecular mechanisms regulating denervation-induced muscle atrophy.