title: Mitofusin 2 (Mfn2): a key player in insulin-dependent myogenesis in vitro.
abstract: We have previously shown that mitochondrial activity increases in response to insulin in differentiating muscle cells. Moreover, the protein kinase kinase/extracellular-signal-regulated kinase (MAPKK/ERK-MEK) inhibitor PD98059 accelerates insulin-mediated myogenesis, whereas the phosphatidylinositol 3-kinase (PI3-K) inhibitor LY294002 or blockade of mitochondrial respiration abrogates insulin-mediated myogenesis. Our present study focuses on the mitochondrial transmembrane protein, hyperplasia suppressor gene/mitofusin2 (HSG/Mfn2), which regulates both mitochondrial fusion (as demonstrated by perinuclear mitochondria clustering) and insulin-dependent myogenesis in vitro. Increased mitochondrial length and interconnectivity are not observed after the inhibition of PI3-K activity with LY294002. Insulin induces Mfn2 and subunits I and IV of cytochrome-c oxidase (MTCOI and NCOIV) in L6 myoblasts. Inhibition of the MEK-dependent signalling pathway elevates the Mfn-2 protein level. The molecular mechanism of this phenomenon is unknown, although immunoprecipitation studies indicate that, during insulin-mediated myogenesis, Ras protein (an upstream activator of the MAPK/ERK1/2 cascade) interacts with HSG/Mfn2 in muscle cells. Interaction of Ras with Mfn2 continues unless insulin is present and is reduced after PD98059 co-treatment indicating that insulin-mediated myogenesis is increased by the inhibition of MEK, most probably by the lack of mitogenic signals opposing muscle differentiation. We conclude that insulin-mediated myogenesis depends on PI3-K activity, which stimulates mitochondrial activity and the extensive fusion of mitochondria. We further suggest that insulin stimulates the expression of Mfn2 protein, which in turn binds to Ras and inhibits the MEK-dependent signalling pathway. At the same time, the PI3-K-dependent signalling pathway is boosted, mitochondrial respiration increases and the rate of myogenesis is accelerated.
authors.affiliation: Department of Physiological Sciences, Faculty of Veterinary Medicine, Warsaw Agricultural University, Nowoursynowska 159, 02-776 Warsaw, Poland.
authors.forename: Patrycja
authors.initials: P
authors.lastname: Pawlikowska
authors.forename: Barbara
authors.initials: B
authors.lastname: Gajkowska
authors.forename: Arkadiusz
authors.initials: A
authors.lastname: Orzechowski
mesh_terms: D000818:Animals; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D042967:Electron Transport Complex I / Q000096:biosynthesis; D003576:Electron Transport Complex IV / Q000096:biosynthesis; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D020558:GTP Phosphohydrolases / Q000096:biosynthesis*; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D008565:Membrane Proteins / Q000096:biosynthesis*; D051379:Mice; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D024101:Mitochondrial Proteins / Q000096:biosynthesis*; D009025:Morpholines / Q000494:pharmacology; D032446:Myoblasts / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051381:Rats
chemical_list: D002867:Chromones; D004791:Enzyme Inhibitors; D005419:Flavonoids; D007004:Hypoglycemic Agents; D007328:Insulin; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D009025:Morpholines; D000081082:Phosphoinositide-3 Kinase Inhibitors; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D003576:Electron Transport Complex IV; D020558:GTP Phosphohydrolases; C488751:Mfn2 protein, mouse; C489710:Mfn2 protein, rat; D042967:Electron Transport Complex I; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one