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Dynamic changes in the mouse skeletal muscle proteome during denervation-induced atrophy.

ABSTRACT: Loss of neuronal stimulation enhances protein breakdown and reduces protein synthesis, causing rapid loss of muscle mass. To elucidate the pathophysiological adaptations that occur in atrophying muscles, we used stable isotope labelling and mass spectrometry to quantify protein expression changes accurately during denervation-induced atrophy after sciatic nerve section in the mouse gastrocnemius muscle. Additionally, mice were fed a stable isotope labelling of amino acids in cell culture (SILAC) diet containing 13C6-lysine for 4, 7 or 11 days to calculate relative levels of protein synthesis in denervated and control muscles. Ubiquitin remnant peptides (K-ε-GG) were profiled by immunoaffinity enrichment to identify potential substrates of the ubiquitin-proteasomal pathway. Of the 4279 skeletal muscle proteins quantified, 850 were differentially expressed significantly within 2 weeks after denervation compared with control muscles. Moreover, pulse labelling identified Lys6 incorporation in 4786 proteins, of which 43 had differential Lys6 incorporation between control and denervated muscle. Enrichment of diglycine remnants identified 2100 endogenous ubiquitination sites and revealed a metabolic and myofibrillar protein diglycine signature, including myosin heavy chains, myomesins and titin, during denervation. Comparative analysis of these proteomic data sets with known atrogenes using a random forest approach identified 92 proteins subject to atrogene-like regulation that have not previously been associated directly with denervation-induced atrophy. Comparison of protein synthesis and proteomic data indicated that upregulation of specific proteins in response to denervation is mainly achieved by protein stabilization. This study provides the first integrated analysis of protein expression, synthesis and ubiquitin signatures during muscular atrophy in a living animal.

SUBMITTER: Lang F

PROVIDER: S-EPMC5536905 | biostudies-other | 2017 Jul

REPOSITORIES: biostudies-other

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Project description:Ubiquitination is a posttranslational protein modification that has been shown to have a range of effects, including regulation of protein function, interaction, localization, and degradation. We have previously shown that the muscle-specific ubiquitin E3 ligase, ASB2β, is downregulated in models of muscle growth and that overexpression ASB2β is sufficient to induce muscle atrophy. To gain insight into the effects of increased ASB2β expression on skeletal muscle mass and function, we used liquid chromatography coupled to tandem mass spectrometry to investigate ASB2β-mediated changes to the skeletal muscle proteome and ubiquitinome, via a parallel analysis of remnant diGly-modified peptides. The results show that viral vector-mediated ASB2β overexpression in murine muscles causes progressive muscle atrophy and impairment of force-producing capacity, while ASB2β knockdown induces mild muscle hypertrophy. ASB2β-induced muscle atrophy and dysfunction were associated with the early downregulation of mitochondrial and contractile protein abundance and the upregulation of proteins involved in proteasome-mediated protein degradation (including other E3 ligases), protein synthesis, and the cytoskeleton/sarcomere. The overexpression ASB2β also resulted in marked changes in protein ubiquitination; however, there was no simple relationship between changes in ubiquitination status and protein abundance. To investigate proteins that interact with ASB2β and, therefore, potential ASB2β targets, Flag-tagged wild-type ASB2β, and a mutant ASB2β lacking the C-terminal SOCS box domain (dSOCS) were immunoprecipitated from C2C12 myotubes and subjected to label-free proteomic analysis to determine the ASB2β interactome. ASB2β was found to interact with a range of cytoskeletal and nuclear proteins. When combined with the in vivo ubiquitinomic data, our studies have identified novel putative ASB2β target substrates that warrant further investigation. These findings provide novel insight into the complexity of proteome and ubiquitinome changes that occur during E3 ligase-mediated skeletal muscle atrophy and dysfunction.

Project description:BackgroundSkeletal muscle atrophy is a pathological condition that contributes to morbidity in a variety of conditions including denervation, cachexia, and aging. Muscle atrophy is characterized as decreased muscle fiber cross-sectional area and protein content due, in part, to the proteolytic activities of two muscle-specific E3 ubiquitin ligases: muscle RING-finger 1 (MuRF1) and muscle atrophy F-box (MAFbx or Atrogin-1). The nuclear factor-kappa B (NF-κB) pathway has emerged as a critical signaling network in skeletal muscle atrophy and has become a prime therapeutic target for the treatment of muscle diseases. Unfortunately, none of the NF-κB targeting drugs are currently being used to treat these diseases, likely because of our limited knowledge and specificity, for muscle biology and disease. The cellular inhibitor of apoptosis 1 (cIAP1) protein is a positive regulator of tumor necrosis factor alpha (TNFα)-mediated classical NF-κB signaling, and cIAP1 loss has been shown to enhance muscle regeneration during acute and chronic injury.MethodsSciatic nerve transection in wild-type, cIAP1-null and Smac mimetic compound (SMC)-treated mice was performed to investigate the role of cIAP1 in denervation-induced atrophy. Genetic in vitro models of C2C12 myoblasts and primary myoblasts were also used to examine the role of classical NF-κB activity in cIAP1-induced myotube atrophy.ResultsWe found that cIAP1 expression was upregulated in denervated muscles compared to non-denervated controls 14 days after denervation. Genetic and pharmacological loss of cIAP1 attenuated denervation-induced muscle atrophy and overexpression of cIAP1 in myotubes was sufficient to induce atrophy. The induction of myotube atrophy by cIAP1 was attenuated when the classical NF-κB signaling pathway was inhibited.ConclusionsThese results demonstrate the cIAP1 is an important mediator of NF-κB/MuRF1 signaling in skeletal muscle atrophy and is a promising therapeutic target for muscle wasting diseases.

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Dynamic changes in the mouse skeletal muscle proteome during denervation-induced atrophy.

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