title: Glycogen synthase kinase-3β is required for the induction of skeletal muscle atrophy.
abstract: Skeletal muscle atrophy commonly occurs in acute and chronic disease. The expression of the muscle-specific E3 ligases atrogin-1 (MAFbx) and muscle RING finger 1 (MuRF1) is induced by atrophy stimuli such as glucocorticoids or absence of IGF-I/insulin and subsequent Akt signaling. We investigated whether glycogen synthase kinase-3β (GSK-3β), a downstream molecule in IGF-I/Akt signaling, is required for basal and atrophy stimulus-induced expression of atrogin-1 and MuRF1, and myofibrillar protein loss in C(2)C(12) skeletal myotubes. Abrogation of basal IGF-I signaling, using LY294002, resulted in a prominent induction of atrogin-1 and MuRF1 mRNA and was accompanied by a loss of myosin heavy chain fast (MyHC-f) and myosin light chains 1 (MyLC-1) and -3 (MyLC-3). The synthetic glucocorticoid dexamethasone (Dex) also induced the expression of both atrogenes and likewise resulted in the loss of myosin protein abundance. Genetic ablation of GSK-3β using small interfering RNA resulted in specific sparing of MyHC-f, MyLC-1, and MyLC-3 protein levels after Dex treatment or impaired IGF-I/Akt signaling. Interestingly, loss of endogenous GSK-3β suppressed both basal and atrophy stimulus-induced atrogin-1 and MuRF1 expression, whereas pharmacological GSK-3β inhibition, using CHIR99021 or LiCl, only reduced atrogin-1 mRNA levels in response to LY294002 or Dex. In conclusion, our data reveal that myotube atrophy and myofibrillar protein loss are GSK-3β dependent, and demonstrate for the first time that basal and atrophy stimulus-induced atrogin-1 mRNA expression requires GSK-3β enzymatic activity, whereas MuRF1 expression depends solely on the physical presence of GSK-3β.
authors.affiliation: Department of Respiratory Medicine, School for Nutrition, Toxicology and Metabolism (NUTRIM), Maastricht University Medical Centre (MUMC), Maastricht, the Netherlands.
authors.forename: Koen J P
authors.initials: KJ
authors.lastname: Verhees
authors.forename: Annemie M W J
authors.initials: AM
authors.lastname: Schols
authors.forename: Marco C J M
authors.initials: MC
authors.lastname: Kelders
authors.forename: Céline M H
authors.initials: CM
authors.lastname: Op den Kamp
authors.forename: Jos L J
authors.initials: JL
authors.lastname: van der Velden
authors.forename: Ramon C J
authors.initials: RC
authors.lastname: Langen
mesh_terms: D000818:Animals; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D007334:Insulin-Like Growth Factor I / Q000037:antagonists & inhibitors; D018021:Lithium Chloride / Q000494:pharmacology; D051379:Mice; D009025:Morpholines / Q000494:pharmacology; D009124:Muscle Proteins / Q000096:biosynthesis; D018482:Muscle, Skeletal / Q000187:drug effects / Q000201:enzymology*; D009133:Muscular Atrophy / Q000188:drug therapy / Q000201:enzymology*; D032446:Myoblasts / Q000187:drug effects / Q000201:enzymology* / Q000502:physiology; D018995:Myosin Heavy Chains / Q000096:biosynthesis; D018994:Myosin Light Chains / Q000096:biosynthesis; D011725:Pyridines / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000378:metabolism; D044843:SKP Cullin F-Box Protein Ligases / Q000096:biosynthesis; D015398:Signal Transduction / Q000187:drug effects; D000070584:Tripartite Motif Proteins; D044767:Ubiquitin-Protein Ligases / Q000096:biosynthesis
chemical_list: C473711:Chir 99021; D002867:Chromones; D004791:Enzyme Inhibitors; D009025:Morpholines; D009124:Muscle Proteins; D018994:Myosin Light Chains; D011725:Pyridines; D011743:Pyrimidines; D034741:RNA, Small Interfering; D000070584:Tripartite Motif Proteins; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D007334:Insulin-Like Growth Factor I; D003907:Dexamethasone; C486691:Fbxo32 protein, mouse; D044843:SKP Cullin F-Box Protein Ligases; C499084:Trim63 protein, mouse; D044767:Ubiquitin-Protein Ligases; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D038362:Glycogen Synthase Kinase 3; D018995:Myosin Heavy Chains; D018021:Lithium Chloride