胰岛素及格列齐特治疗2型糖尿病大鼠肝脏脂质沉积的机制探讨

Insulin and gliclazide therapies improve liver lipid deposition in type 2 diabetic rats

目的:探讨胰岛素及格列齐特治疗2型糖尿病对大鼠肝脏脂质沉积的影响及机制。方法:制备高脂及链脲佐菌素诱导的2型糖尿病大鼠模型,随机分为糖尿病组、胰岛素组和格列齐特组,并设正常对照组。通过肝脏油红O染色观察其肝细胞脂质沉积情况;ELISA检测血清脂联素水平;实时荧光定量PCR检测肝脏脂联素受体1(AdipoR1)mRNA表达;Western blotting检测肝脏腺苷酸活化蛋白激酶(AMPK)、磷酸化的腺苷酸活化蛋白激酶(Thr172p-AMPK)、固醇调节因子结合蛋白1c(SREBP-1c)、磷酸化的固醇调节因子结合蛋白1c(Ser372p-SREBP1-1c)、乙酰辅酶A羧化酶(ACC)、磷酸化的乙酰辅酶A羧化酶(Ser79p-ACC)和免疫球蛋白结合蛋白(BiP)的表达。结果:糖尿病组肝细胞脂质沉积较正常对照组明显增多,胰岛素和格列齐特治疗后肝细胞脂质沉积明显改善。胰岛素治疗后,血清脂联素的水平及肝脏AdipoR1 mRNA水平较糖尿病组和正常对照组显著升高(P<0.01),而格列齐特治疗后两者水平恢复至正常对照组水平。Western blotting结果显示,糖尿病大鼠与正常对照组比较,肝脏Thr172p-AMPK/AMPK和Ser372p-SREBP-1c/SREBP-1c和Ser79p-ACC/ACC表达明显降低(P<0.01),BiP表达明显升高(P<0.01)。胰岛素治疗后,Thr172p-AMPK/AMPK和Ser372p-SREBP-1c/SREBP-1c显著升高(P<0.01),Ser79p-ACC/ACC和BiP蛋白表达恢复至正常对照组水平。而格列齐特治疗后Thr172p-AMPK/AMPK和Ser372pSREBP-1c/SREBP-1c恢复至正常对照组水平,BiP蛋白表达显著下降(P<0.01),Ser79p-ACC/ACC与糖尿病组比较无明显改善。结论:胰岛素和格列齐特治疗均能通过激活脂联素-AMPK减轻2型糖尿病大鼠肝脏的脂质沉积。但两者作用的分子机制有所不同。胰岛素激活AMPK,通过抑制SREBP-1c表达、直接磷酸化SREBP-1c抑制SREBP-1c入核等短期和长期的作用以及抑制内质网应激影响SREBP-1c,减少脂质合成;而格列齐特仅通过磷酸化的短期作用和抑制内质网应激对SREBP-1c产生影响,且对脂肪酸氧化无作用。

AIM：To investigate the effect of insulin and gliclazide therapies on the liver fat accumulation in type 2 diabetic rats .METHODS：A high-fat diet plus low-dose streptozotocin was implemented to establish a type 2 diabetic rat model, and the rats were randomly divided into diabetes mellitus （DM） group, diabetic rats treated with insulin （ INS） group, diabetic rats treated with gliclazide per os （ PO） group, and normal control （ NC） group.The diabetic rats in INS group and PO group were given insulin and gliclazide for 3 weeks, respectively.The changes of the liver fatty were evaluated with oil red O staining .Fasting plasma adiponectin concentration was measured by ELISA .The expression of adiponectin receptor 1 （ AdipoR1 ） was detected by real-time PCR.The protein levels of AMP-activated protein kinase （AMPK）, phosphorylated AMPK on threonine 172 （ Thr172p-AMPK）, sterol regulatory element-binding protein 1c＆amp;nbsp;（SREBP-1c）, phosphorylated SREBP-1c on serine 372 （Ser372p-SREBP-1c）, acetyl-CoA carboxylase （ACC）, phospho-rylated ACC on serine79 （Ser79p-ACC） and immunoglobulin-binding protein （BiP） in the liver homogenate were deter-mined by Western blotting .RESULTS：Compared with the normal rats , in DM group, the presence of cytoplasmic lipid deposits was confirmed by oil red O staining .In INS group, these changes were significantly lower than those in DM group . Similar results were obtained in PO group .Insulin therapy significantly increased the plasma concentration of diponectin and liver tissue levels of AdipoR1 compared with DM group.At the same time, these 2 indicators returned to normal levels after gliclazide therapy .Thr172p-AMPK/AMPK, Ser372p-SREBP-1c/SREBP-1c and Ser79p-ACC/ACC expression ratios were significantly reduced in DM group compared with control values .The expression of BiP was increased on the contrary . After insulin therapy, Thr172p-AMPK/AMPK and Ser372p-SREBP-1c/SREBP-1c were significantly increased, and Ser79p-ACC/ACC and BiP returned to the normal levels .After gliclazide treatment, Thr172p-AMPK/AMPK and Ser372p-SREBP-1c/SREBP-1c returned to the normal levels , the expression ratio of Ser79p-ACC/ACC had no significant improve-ment compared with DM group , and the expression of BiP significantly declined .CONCLUSION： Both the insulin and gliclazide therapies reduce the lipid deposition in the liver of rats with type 2 diabetes by activating AMPK , but the extent and mechanism are not the same.In insulin therapy, AMPK restrains the expression of SREBP-1c directly, increases the phosphorylation of SREBP-1c, and affects SREBP-1c by inhibiting the endoplasmic reticulum stress .Gliclazide treatment, which has no effect on the lipid oxidation , reduces lipid deposition in the liver only through the phosphorylation of SREBP-1c and the suppression of the endoplasmic reticulum stress .