Description:
<jats:p>A growing body of evidence suggests that vitamin D may affect muscle mass and function, especially in older people. The aim was to investigate the effect of 1,25(OH)<jats:sub>2</jats:sub>‐vitamin D<jats:sub>3</jats:sub> (1,25OHD) combined or not with anabolic factors, insulin and leucine (Leu), on protein fractional synthesis rate (FSR) and its intracellular regulating pathways in mouse C2C12 myotubes. After differentiation, myotubes were cultured in 1,25OHD solutions at 0 or 10nM for 72h. Cells were then treated for 30min by L‐[1‐<jats:sup>13</jats:sup>C]valine in presence or not of Leu (5mM) and insulin (100nM), and FSR was determined by measuring tracer enrichments in free amino acids and proteins. Protein expression and phosphorylation of Akt/mTOR‐dependent pathway were measured by western blot. mRNA level of insulin receptor (IR) and vitamin D receptor (VDR) was determined by qPCR. ANOVA was used for statistical analysis. 1,25OHD alone stimulates protein FSR (p<0.05). When combined with 1,25OHD, the stimulation of protein FSR by Leu and insulin was further increased by 14% (p<0.05). Akt/mTOR‐dependent pathway was activated by Leu and insulin and this was further increased by 1,25OHD (p<0.05). IR and VDR mRNA and protein expression were also increased by 1,25OHD (p<0.05). To conclude, 1,25OHD sensitizes the Akt/mTOR‐dependent pathway to the stimulating effect of insulin and Leu resulting in a further activation of protein synthesis in C2C12 myotubes.</jats:p>