The Role Of JNK During The Effect Of Skeletal Muscle Adiponectin On Expression Of GLUT4in Skeletal Muscle

Background: Adiponectin (adiponectin,ApN) is first found as an adipocytokinepredominantly synthesized and secreted by adipose tissue.It plays a fundamental role incounteracting inflammation,regulating systemic energy and insulin sensitivity.Untilrecently, it was thought that adipocytes were the only site of adiponectin synthesis andsecretion.However, several studies have now uncovered the potential for adiponectinproduction by skeletal muscle cells. We have demonstrated that adiponectin isexpressed in mouse skeletal muscles and differentiated L6myotubes，which then hasimportant and beneficial autocrine effect in exerting local metabolic effects, at least inpart via enhancing fatty acid oxidation and insulin sensitivity.However,the mechanismof the control of adiponectin production in skeletal muscle and the functionalsignificance of such production in skeletal muscle insulin resistance is not veryclear.c-Jun N-terminal kinase(JNK),which is a member of the mitogen-activated proteinkinase family(MAPK),can exert effects on the low-grade inflammation and has beenproved to be involved in the insulin signaling pathway via phosphorylating insulinreceptor substrate-1(IRS-1) at Ser307.The AMP-activated protein kinase(AMPK) is thekey molecule in adiponectin signaling pathway,and the MAPK/JNK is the downstreamsignaling molecule of the AMPK.However, the role of JNK during the effect of skeletalmuscle adiponectin on expression of GLUT4in skeletal muscle is not very clear.Objective: To establish palmitic acid-induced insulin resistance model in rat L6muscle cells, and initially explore the role of JNK during the effect of skeletal muscleadiponectin on expression of GLUT4in skeletal muscle. Methods: After cell culture and inducing differentiation, rat L6muscle cell wascultured by different concentration of palmitic acid for different time respectively. Theconcentration of glucose remained in each group was measured by Glucose Test Kitrespectively, and then observed the effects of different concentration of palmitic acid onglucose uptake in rat L6muscle cells. Therewith judge whether the insulin resistancemodel was established or not. Then the cells can be divided into four groups, which arethe NC group (control group); IR group (insulin resistance model group);IR+SP600125group(add the JNK blocker SP600125in the insulin resistance model group); IR+PIOgroup(add pioglitazone in the insulin resistance model group). Then the expressionlevels of the APN, p-JNK and GLUT4of the four groups were measured by theWestern blot method.Results:1、Under the same CO2concentration and the same temperature, whenincubated in0.4mmol/L palmitic acid for12~36h,or in0.6and0.8mmol/L palmiticacid for8~24h, the concentration of glucose remained in PA group was significantlyhigher than in NC group (P<0.05), which suggests that the glucose transport of PAgroup was significantly lower than normal group. On the account of this, the insulinresistance model was established.2、Compared with NC group, The expression of APNand GLUT4in IR group was significantly lower (P<0.05);the expression of p-JNK inIR group was significantly higher (P<0.05). Compared with IR group, The expressionof APN and GLUT4in IR+PIO group was significantly higher (P<0.05), Theexpression of p-JNK was significantly lower (P<0.05); Compared with IR group, Theexpression of APN in IR+SP600125group was significantly higher (P<0.05), Theexpression of p-JNK was significantly lower(P<0.05),however, The expression ofGLUT4in IR+SP600125group had no statistical significance (P>0.05). Conclusion:1. The insulin resistance model of rat L6muscle cells can be builtedthrough certain concentration and time of the PA stimulation.The mechanism mayinvolve the phosphorylation of JNK.2. L6muscle cells can secrete and expressadiponectin. The signal pathway of JNK act as a negative adjustment factor mediatingthe secretion of adiponectin which expressed by skeletal muscle.3. JNK signal pathwaymay not be involved in the mechanism that adiponectin which secreted by the L6muscle cells can effect the expression of GLUT4under insulin stimulating.4.Pioglitazone can enhance the expression of adiponectin secreted by L6muscle cells andGLUT4.To suppress the JNK signal pathways maybe the one of the possible mechanismthat pioglitazone improves the sensitivity of insulin.