Saturated Fatty Acids-induced Muscle Insulin Resistance And The Mechanism Of Contraction-increased GLUT4Translocation

Objective:To explore the effect and mechanism of saturated fatty acids on insulin action and the mechanism of contraction-increased GLUT4translocation in skeletal muscle cells.Methods:In part1, we treated L6-GLUT4myc and C2C12-GLUT4myc skeletal muscle cells with palmitate, then cell surface GLUT4myc levels were measured by enzyme-linked immnosorbent assay (ELISA) to investigate the effect of palmitate on insulin-stimulated GLUT4myc translocation. Phosphorylation of protein kinase B (Akt) was detected by Western blotting.In part2, we further detected the phosphorylation of JNK and insulin receptor substrate1(IRS1) by Western blotting. Then, using protein kinase C inhibitors (bisindolylmaleimide I, BIM), cell surface GLUT4myc levels were measured by ELISA and the phosphorylation of Akt were detected by Western blotting.In part3, we treated C2C12-GLUT4myc skeletal muscle cells with electric pulse stimulation (EPS) to investigate the effect of electric stimulateion on GLUT4myc translocation. Then, the roles of AMPK, CaMKK and CaMKⅡin EPS-stimulated GLUT4myc translocation were explored by using Compound C, STO-609, KN93and CN21.Results:We treated L6-GLUT4myc skeletal muscle cells and C2C12-GLUT4myc skeletal muscle cells with palmitate. Both of them have the consistent results. Insulin-stimulated GLUT4myc translocation was decreased by palmitic acid and the level of phosphorylation of Akt was also decreased. There were no changes in the levels of JNK and IRS1phosphorylation. There is no difference between groups with or without n/cPKC inhibitor BIM. BIM-1did not reverse insulin resistant caused by palmitic acid.In C2C12-GLUT4myc skeletal muscle cells, electric pulse stimulation stimulated GLUT4myc translocation, this was inhibted by Compound C, STO-609, KN93and CN21.Conclusion:1. Palmitic acid directly causes insulin resistance in skeletal muscle cells, and PKC or JNK may not involve in the mechanism, or their effect are very small.2. Electric Pulse stimulation stimulates GLUT4myc translocation, and its mechanism may involve AMPK, CaMKK and CaMK Ⅱ.