title: Skeletal muscle hypertrophy and atrophy signaling pathways.
abstract: Skeletal muscle hypertrophy is defined as an increase in muscle mass, which in the adult animal comes as a result of an increase in the size, as opposed to the number, of pre-existing skeletal muscle fibers. The protein growth factor insulin-like growth factor 1 (IGF-1) has been demonstrated to be sufficient to induce skeletal muscle hypertrophy. Over the past few years, signaling pathways which are activated by IGF-1, and which are responsible for regulating protein synthesis pathways, have been defined. More recently, it has been show that IGF-1 can also block the transcriptional upregulation of key mediators of skeletal muscle atrophy, the ubiquitin-ligases MuRF1 and MAFbx (also called Atrogin-1). Further, it has been demonstrated recently that activation of the NF-kappaB transcription pathway, activated by cachectic factors such as TNFalpha, is sufficient to induce skeletal muscle atrophy, and this atrophy occurs in part via NF-kappaB-mediated upregulation of MuRF1. Further work has demonstrated a trigger for MAFbx expression upon treatment with TNFalpha--the p38 MAPK pathway. This review will focus on the recent progress in the understanding of molecular signalling, which governs skeletal muscle atrophy and hypertrophy, and the known instances of cross-regulation between the two systems.
authors.affiliation: Regeneron Pharmaceuticals, 777 Old Saw Mill River Road, Tarrytown, NY 10591-6707, USA. david.glass@regeneron.com
authors.forename: David J
authors.initials: DJ
authors.lastname: Glass
mesh_terms: D005786:Gene Expression Regulation; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D006801:Humans; D006984:Hypertrophy / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008954:Models, Biological; D009124:Muscle Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology*; D009133:Muscular Atrophy / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D044843:SKP Cullin F-Box Protein Ligases / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000378:metabolism; D000070584:Tripartite Motif Proteins; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D015854:Up-Regulation; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D038362:Glycogen Synthase Kinase 3; D007334:Insulin-Like Growth Factor I; D009124:Muscle Proteins; D016328:NF-kappa B; D019869:Phosphatidylinositol 3-Kinases; D011494:Protein Kinases; D044843:SKP Cullin F-Box Protein Ligases; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors; D000070584:Tripartite Motif Proteins; D044767:Ubiquitin-Protein Ligases; D048051:p38 Mitogen-Activated Protein Kinases; C440907:FBXO32 protein, human; C440908:TRIM63 protein, human; C546842:MTOR protein, human