[Effects of muscle derived-IL-6 on insulin resistance of skeletal muscle cells and its mechanisms].

Objective: To study the effects of exogenous calcium-load on promoting muscle-derived IL-6 secretion, and regulating AMPK and p38MAPK signal pathway to improve insulin resistance.

Methods: C2C12 cell lines and palmitic acid-induced insulin resistance C2C12 cell lines were selected as the experimental objects. Preliminary experiment was aimed to determinate the glucose concentrations of culture solutions and observe contraction status of cells under microscope following different calcium concentrations culture 24 h. In the first official experiment, cells were divided into four groups: control group (A group, normal culture solution), IR group(B group, 0.6 mmol/L palmitic acid culture cells 24 h), 1 000 ng/ml IL-6 culture IR B group cells 48 h(IL-6+IR group) and IL-6 shRNA culture A group cells (IL-6shRNA group). In the second official experiment, cells were divided into three groups: IR group(A group), 100 μmol/L CaCl culture IR group cells 48 h(CaCl+IR group) and 100 μmol/L CaCl and IL-6shRNA co- culture IR group cells 48 h(CaCl+IL-6shRNA+IR group). The expression levels of GLUT4 mRNA and IL-6 mRNA were measured by real-time PCR, the protein expression levels of p-AMPK, p-p38MAPK, p-IRS-1 and p-PI-3K were measured by Western blot.

Results: Preliminary experiment results showed that compared with 0 μmol/L CaCl group, the glucose concentrations were decreased significantly after cells treated with CaCl, at different concentrations. The cell contractions were observed under microscope and the cell contraction was most obvious treated with 100 μmol/L CaCl. The first official experiment results showed that compared with IR group, the contents of p-AMP-activated protein kinase(p-AMPK), p-insulin receptor substrate 1(p-IRS-1), p-phosphoinositide-3 kinase(p-PI-3K), the expression level of glucose transporter 4(GLUT4) mRNA and the glucose uptake of IL-6+IR group were increased significantly(＜0.05 or ＜0.01), the p-p38MAPK protein expression level was decreased significantly (＜0.01) ; Compared with control group, the expression levels of p-AMPK, P-IRS-1, p-PI-3K, the expression level of GLUT4 mRNA and the glucose uptake of IL-6shRNA group were decreased significantly (＜0.05 or ＜0.01), the p-p38MAPK protein expression level was increased significantly (＜0.01). The second official experiment results showed that compared with IR group, the expression levels of p-AMPK, P-IRS-1, p-PI-3K, the level of GLUT4 mRNA of CaCl+IR group were increased significantly (＜0.05 or ＜0.01), the p-p38MAPK protein expression level was decreased significantly (＜0.01); Compared with CaCl+IR group, the contents of p-AMPK, P-IRS-1, p-PI-3K, the expression level of GLUT4 mRNA and the glucose uptake of CaCl+IL-6 shRNA+IR group were decreased significantly (＜0.05 or ＜0.01), the p-p38MAPK protein expression level was increased significantly (＜0.01).

Conclusion: Exogenous Ca-load can stimulate muscle cells contraction, and exercise-induced IL-6 improves insulin resistance by activating AMPK, PI-3Kand inhibiting p38MAPK signal pathway.