Ambient glucose levels qualify the potency of insulin myogenic actions by regulating SIRT1 and FoxO3a in C₂C₁₂ myocytes

Abstract

Nedachi T, Kadotani A, Ariga M, Katagiri H, Kanzaki M. Ambient glucose levels qualify the potency of insulin myogenic actions by regulating SIRT1 and FoxO3a in C 2C12 myocytes. Am J Physiol Endocrinol Metab 294: E668-E678, 2008. First published January 29, 2008 doi:10.1152/ajpendo.00640.2007.-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 2C12 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 ϩ -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 sirtinoldependent 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 2C12 myocytes.forkhead box O; differentiation SKELETAL MUSCLE CELLS have provided a useful model for exploring the molecular mechanisms involved in cellular differentiation (13), and insulin and insulin-like growth factors (IGFs) have been implicated in the process of myogenesis by activating the IRS-PI 3-kinase signaling pathway (7,22,25,53) that also serves as a pivotal intracellular signal for exerting metabolic actions in mature skeletal muscle (9). However, despite our general understanding of the effects of ambient glucose levels on insulin responsiveness with regard to metabolic actions in skeletal muscle cells (37), the possible interrelationship between glucose and insulin acting on myogenesis remains to be clarified.Skeletal muscle differentiation is a well-organized process governed by muscle-specific transcription factors belonging to the MyoD family, such as MyoD and myogenin (42), and the myocyte enhancer factor-2 (MEF2) family, such as MEF2A and MEF2C (35). In addition to these muscle-specific transcription factors, positively regulating myogenesis, the f...

Glucose deprivation attenuates sortilin levels in skeletal muscle cells

“…Similarly, suppression of myogenesis under hypoglycemic conditions appears to be mediated by sortilin. In addition, it has been shown that the glucose-restricted condition inhibits skeletal myoblast differentiation [18], and the overexpression of sortilin in C2C12 cells significantly stimulated myogenic differentiation [7]. These results together with the present findings suggest that sortilin is an important intermediate molecule for glucose-dependent regulation of myogenic differentiation.…”

“…C2C12 myoblasts were induced to differentiate in low glucose differentiation medium (LG-DM: DMEM containing 5mM glucose + 2% CS) or high glucose differentiation medium (HG-DM: DMEM containing 22.5mM glucose + 2% CS). In our experimental conditions, we had confirmed that the C2C12 myoblasts became hypoglycemic within 24h in LG-DM but not in HG-DM [18]. After inducing differentiation, sortilin expression was examined every 24h.…”

“…1A). It was demonstrated that the C2C12 cell differentiation was inhibited under LG-DM [18]. To exclude the possibility that the enhanced sortilin levels under HG-DM (compared to under LG-DM) may be dependent on the degree of differentiation, we next investigated whether the expression of sortilin is reversibly regulated by glucose in fully differentiated C2C12 myotubes.…”

Hexosamines stimulate apoptosis by altering SIRT1 action and levels in rodent pancreatic -cells

“…Several studies have reported increased SIRT1 protein levels (Balestrieri et al 2008, Kanfi et al 2008, Nedachi et al 2008) and nuclear accumulation (Nedachi et al 2008) under conditions of low glucose concentrations. In line with this, a report showed that glucosamine reduced SIRT1 protein expression in HepG2 cells (Sun et al 2007).…”

“…SIRT1 was shown to impact on cell survival through physical binding with p53, HSF1, Hif-2a, FOXO, and Ku70 (Dioum et al 2009, Westerheide et al 2009, Gagarina et al 2010 and reviewed in Yamamoto et al (2007). Importantly, SIRT1 and its yeast homolog SIR2 appear to be very sensitive to changes in cellular glucose content such as those occurring upon caloric restriction (Lin et al 2000, Cohen et al 2004, Nisoli et al 2005, Civitarese et al 2007, Chen et al 2008, Kanfi et al 2008, Nedachi et al 2008. In cultured pancreatic b-cells, overexpression of Sirt1 was shown to protect against cytokine toxicity (Lee et al 2009).…”