Resveratrol improves palmitic acid-induced insulin resistance via the DDIT4/mTOR pathway in C2C12 cells

The present study aimed to establish a model of palmitic acid (PA)-induced insulin resistance (IR) in C2C12 cells and to determine the mechanism underlying how resveratrol (RSV) improves IR. C2C12 cells were divided into the control (CON), PA, PA + RSV, PA + RSV + DNA damage-inducible transcript 4 (DDIT4)-small interfering (si)RNA and PA + RSV + MHY1485 (mTOR agonist) groups. Glucose contents in culture medium and triglyceride contents in cells were determined. Oil red O staining was performed to observe the pathological changes in the cells. Reverse transcription-quantitative PCR and western blotting were conducted to evaluate the mRNA and protein expression levels, respectively, of DDIT4, mTOR, p70 ribosomal protein S6 kinase (p70S6K), insulin receptor substrate (IRS)-1, PI3K, AKT and glucose transporter 4 (GLUT4). Compared with in the CON group, glucose uptake was decreased, cellular lipid deposition was increased, phosphorylated (p)-IRS-1, p-mTOR and p-p70S6K protein expression levels were increased, and p-PI3K, p-AKT, GLUT4 and DDIT4 protein expression levels were decreased in the PA group. By contrast, compared with in the PA group, culture medium glucose content and cellular lipid deposition were decreased, p-PI3K, p-AKT, GLUT4 and DDIT4 protein expression levels were increased, p-IRS-1 protein expression levels were decreased, and mTOR and p70S6K mRNA and protein expression levels were decreased in the PA + RSV group. Compared with in the PA + RSV group, DDIT4 protein and mRNA expression levels were reduced in the PA + RSV + DDIT4-siRNA group, but showed no change in the PA + RSV + MHY1485 group. Following transfection with DDIT4-siRNA or treatment with MHY1485, the effects of RSV on improving IR and lipid metabolism were weakened, mTOR and p70S6K protein expression levels were upregulated, p-PI3K, p-AKT and GLUT4 protein expression levels were down-regulated, p-IRS-1 protein expression levels were upregulated, and culture medium glucose content and cellular lipid deposition were increased. In conclusion, RSV may improve PA-induced IR in C2C12 cells through the DDIT4/mTOR/IRS-1/PI3K/AKT/GLUT4 signaling pathway, as well as via improvements in glucose and lipid metabolism.