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.