Nuclear co-repressor (NCoR) is required to maintain insulin sensitivity in C₂ C₁₂ myotubes

Nuclear co-repressor (NCoR) regulates peripheral insulin sensitivity; however, its role in modulating insulin sensitivity in skeletal muscle remains elusive. Present study investigated protein expression and effect of NCoR on insulin sensitivity in murine skeletal muscle cell line C₂ C₁₂ . Myotubes as compared to myoblasts of C₂ C₁₂ cells were found to be more sensitive in response to insulin as increase in insulin-stimulated phosphorylation of AKT at serine 473 residue (pAKT^S473 ) was significantly higher in myotubes. Incidentally, reduced protein level of NCoR coincided with differentiation of myoblasts into myotubes of C₂ C₁₂ cells. However, insulin stimulation per se failed to affect protein level of NCoR either in myoblasts or myotubes of C₂ C₁₂ cells. To assess the role of NCoR on insulin sensitivity, NCoR was transiently knocked down using siRNA in myotubes of C₂ C₁₂ . In fact, transient silencing of NCoR led to significant reduction in insulin-stimulated pAKT^S473 and impaired glucose uptake. This observation is in contrast to published studies where NCoR has been reported to negatively regulate insulin signaling cascade. Furthermore, transient silencing of NCoR failed to improve insulin sensitivity in chronic hyperinsulinemia-induced insulin-resistant model of C₂ C₁₂ cells. Importantly, inhibition of lysosomal protein degradation pathway using ammonium chloride restored protein level of NCoR but failed to increase glucose uptake in serum-starved C₂ C₁₂ myotubes. Collectively, data from present study show differential protein level of NCoR under different cell state (myoblast and myotubes) of C₂ C₁₂ cells and NCoR proves to be vital for maintaining insulin sensitivity in C₂ C₁₂ myotubes.