Endoplasmic Reticulum Stress Mediate High-fat Diet And Palmitic Acid-induced Insulin Resistance In Skeletal Muscle And Interventional Effects Of Fenofibrate

Objective: To observe the effect of high-fat diet(HFD) on skeletal muscle of female SD rats, and investigate whether the interventional effects of fenofibrate on high-fat diet and palmitic acid-induced insulin resistance(IR) in skeletal muscle are related to endoplasmic reticulum stress(ERS) both in vivo and vitro tests.Methods: Female SD rats were randomly subjected to a standard control diet(SCD) or high-fat diet(HFD) for 20 weeks, then the HFD group was divided into high-fat diet group and high-fat diet group treated with fenofibrate(HFD+FF, 30mg·kg-1·d-1) by gavage for another 8 weeks. Body weight was measured every week. The serum levels of triglyceride(TG), total cholesterol(TC), low density lipoprotein-cholesterol(LDL-C), and high density lipoprotein-cholesterol(HDL-C) were detected. The insulin resistance(IR) was analyzed by Glucose tolerance test(GTT) and insulin tolerance test(ITT). The m RNA expression of peroxisome proliferator-activated receptor α(PPARα), glucose regulated protein 78(GRP78), inositol requiring enzyme1α(IRE1α) and eukaryotic initiation factor 2α(e IF2α) were analysed by Real-time RT-PCR respectively. Western-blot was used to detected the protein expression of GRP78 and CHOP. C2C12 myotubes were divided into normal control group(NC), model group(palmitic acid, PA), postive control drug group(tunicamycin,TM) and treatment group(fenofibric acid, FA +PA). the m RNA expression of GRP78, CHOP, IRE1α and e IF2α were assessed by RT-PCR, the protein expression of GRP78 and CHOP were detected by Western-blot and immune respectively. Insulin-stimulated phosphorylation of protein kinase B(PKB)/v-ak t murine thymoma viral oncogene homologue 1(Akt) were also analyzed to detect changes of insulin sensitivity in C2C12.Results: 1.The results of GTT and ITT showed that comparing to rats in SCD group, the insulin sensitivity of rats in HFD group was decreased, while fenofibrate intervention significantly improved the insulin sensitivity and insulin resistance. 2.Comparing with rats in SCD group, HFD group showed increased body weight, higher serum levels of TG and TC and lower serum levels of HDL-C, while fenofibrate intervention significantly improved high-fat diet induced obesity, decreased the serum level of TC and TG, and increased the serum level of HDL-C. 3.The expression of ERS markers GRP78, CHOP, IRE1α and e IF2α were upregulated in skeletal muscle of rats of HFD group compared with rats in SCD group. However, fenofibrate treatment significantly increased expression of PPARα, decreased expression of GRP78, CHOP, IRE1α and e IF2α in HFD+FF group. 4.Incubation of myotubes with palmitic acid or tunicamycin significantly increased expression of ERS markers GRP78, CHOP, IRE1α and e IF2α. Meanwhile, insulin-stimulated phosphorylation of Akt was inhibited obviously. Pre-incubation with FA markedly inverted PA-induced ERS and insulin-stimulated phosphorylation of Akt.Conclusion: High-fat diet(HFD) for 20 weeks successfully induced the model of hyperlipidemia rats with insulin resistance, fenofibrate(fenofibric acid) has obvious effects of decreasing body weight, regulating blood lipid disorder and improving insulin sensitivity, which may be related with reduced expression of GRP78, CHOP, IRE1α and e IF2α in ERS.