title: Ambient glucose levels qualify the potency of insulin myogenic actions by regulating SIRT1 and FoxO3a in C2C12 myocytes.
abstract: Nutrition availability is one of the major environmental signals influencing cell fate, such as proliferation, differentiation, and apoptosis, often functioning in concert with other humoral factors, including insulin. Herein, we show that low-serum-induced differentiation of C(2)C(12) myocytes is significantly hampered under low glucose (LG; 5 mM) compared with high glucose (HG; 22.5 mM) conditions, concurrently with nuclear accumulation of SIRT1, an NAD(+)-dependent deacetylase, and FoxO3a, both of which are implicated in the negative regulation of myogenesis. Intriguingly, insulin appears to exert opposite actions, depending on glucose availability, with regard to the regulation of SIRT1 and FoxO3a abundance, which apparently contributes to modulating the potency of insulin's myogenic action. Namely, insulin exerts a potent myogenic effect in the presence of sufficient glucose, whereas insulin is unable to exert its myogenic action under LG conditions, since insulin evokes massive upregulation of both SIRT1 and FoxO3a in the absence of sufficient ambient glucose. In addition, the hampered differentiation state under LG is significantly restored by sirtinol, a SIRT1 inhibitor, whereas insulin abolished this sirtinol-dependent restoration, indicating that insulin can function as a negative as well as a positive myogenic factor depending on glucose availability. Taken together, our data reveal the importance of ambient glucose levels in the regulation of myogenesis and also in the determination of insulin's myogenic potency, which is achieved, at least in part, through regulation of the cellular contents and localization of SIRT1 and FoxO3a in differentiating C(2)C(12) myocytes.
authors.affiliation: Division of Biomaterials, Tohoku University Biomedical Engineering Research Organization, Tohoku University, Sendai, Japan.
authors.forename: Taku
authors.initials: T
authors.lastname: Nedachi
authors.forename: Akito
authors.initials: A
authors.lastname: Kadotani
authors.forename: Miyako
authors.initials: M
authors.lastname: Ariga
authors.forename: Hideki
authors.initials: H
authors.lastname: Katagiri
authors.forename: Makoto
authors.initials: M
authors.lastname: Kanzaki
mesh_terms: D000818:Animals; D001798:Blood Proteins / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D004357:Drug Synergism; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D007004:Hypoglycemic Agents / Q000378:metabolism* / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000378:metabolism; D018482:Muscle, Skeletal / Q000166:cytology; D032446:Myoblasts / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D056564:Sirtuin 1; D037761:Sirtuins / Q000235:genetics / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases
chemical_list: D001798:Blood Proteins; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D005947:Glucose; D007004:Hypoglycemic Agents; D007328:Insulin; D019869:Phosphatidylinositol 3-Kinases; D011494:Protein Kinases; D056564:Sirtuin 1; D037761:Sirtuins; D058570:TOR Serine-Threonine Kinases; C474033:FoxO3 protein, mouse; C546843:mTOR protein, mouse; C470545:Sirt1 protein, mouse