脂联素对自发性2型糖尿病大鼠肝脏脂代谢的影响

目的 探讨脂联素(APN)对自发性2型糖尿病大鼠肝脏脂代谢的影响及其分子信号机制.方法 自发性2型糖尿病大鼠20只(糖尿病组),同系健康对照鼠10只(对照组).于8、32和40周分批处死.检测不同鼠龄空腹血糖、血浆胰岛素和血脂水平.肝组织甘油三酯(TG)、胆固醇(TC)含量以酶法检测,反转录-PCR检测肝组织乙酰辅酶A羧化酶(AAC)和同醇调节元件结合蛋白-1( SREBP-1) mRNA水平,ELISA法检测血浆和肝组织内APN蛋白水平.免疫沉淀后行Western印迹法检测肝组织胰岛素受体底物-2磷酸化( py-I RS2)表达水平.结果 32周开始糖尿病组大鼠表现出明显的胰岛素抵抗和脂代谢紊乱特征.糖尿病组大鼠肝组织TG和TC含量随鼠龄增加有增高趋势,显著高于对照组40周TG( 1.88±0.11) mmol/L比(0.51±0.07) mmol/L,TC (0.94±0.17)比(0.69±0.14) mmol/L,P＜0.01].糖尿病组大鼠肝组织AAC和SREBP-1 mRNA水平在各鼠龄均显著高于对照组(P＜0.05).糖尿病组大鼠血浆APN水平在8周龄显著低于对照组(2.38±0.23)ng/ml比(3.1±0.17) ng/ml,P＜0.05],随鼠龄增加而升高32周(1.51±0.05) ng/ml比(2.84±0.34) ng/ml,40周(1.24±0.04) ng/ml比(2.64±0.49) ng/ml,P＜0.01].肝组织APN在不同鼠龄均显著低于对照组8、32和40周分别为(2.24±0.18) μg/g比(2.68±0.13) μg/g,(2.04±0.19)μg/g比(2.51 ±0.14) μg/g,(1.76±0.12) μg/g比(2.47±0.21) μg/g,P＜0.05].肝组织py-IRS2表达水平显著低于同龄对照组(P＜0.05).肝组织APN水平与py-IRS2呈正相关(r=0.542,P＜0.001),与肝组织ACC、SREBP-1mRNA、TG、TC含量呈负相关(r=-0.431,- 0.396,-0.353,-0.349,P＜0.05).结论 APN可能通过调控糖尿病大鼠肝脏IRS-2磷酸化水平影响肝组织的胰岛素信号通路,调节肝脏的脂代谢功能.

Regulation of hepatic lipid metabolism by adiponection via IRS-2 phosphorylation in OLETF rats

Objective To explore the effect and mechanism of adiponectin on hepatic lipid metabolism in Otsuka Long Evans Tokushima fatty (OLETF) rats.Methods Twenty male OLETF rats and 10 male Long-Evans Tokushima (LETO) rats were sacrificed at 8,32 or 40-week old to examine the fasting blood glucose,plasm insulin,adiponectin and blood lipid profile.The levels of triglyceride,cholesterol,adiponectin,phosphotyrosine of IRS-2,acetyl-coenzyme A carboxylase and sterol regulatory element-binding protein 1 (SREBP-1) mRNA in liver tissue were determined by chemical enzymatic assay,enzyme-linked immunosorbent assay (ELISA) or Western blot.Results Higher insulin level,lower insulin sensitivity index and deteriorated lipid metabolism was observed in OLETF rats since 32-week age. ACC (acetyl coenzyme A carboxylase) and SREBP-1 mRNA expression,lowered plasma adiponectin (OLETF vs LETO:8weeksage,2.38±0.23 vs3.1 ±0.17,P＜0.05; 32 weeks age,1.51±0.05 vs2.M±0.34,P＜0.01; 40 weeks age,1.24±0.04 vs 2.64 ±0.49 ng/ml,P＜0.01) and liver tissue (8,32 or40 weeksage,2.24±0.18 vs 2.68 ±0.13,2.04±0.19 vs 2.51 ±0.14,1.76±0.12 vs 2.47 ±0.21 μg/grespectively,P ＜ 0.05) as well as elevated triglyceride (TG) (40 weeks age,TG 1.88 ± 0.11 vs 0.51 ±0.07 mmol/L,P ＜ 0.01 ) and cholesterol (40 weeks age,total cholesterol 0.94 ± 0.17 vs 0.69 ± 0.14mmol/L,P ＜0.01 ) and lowered IRS-1 ( insulin receptor substrate 1 ) tyrosin phosphorylation in liver tissue in OLETF rats were observed.The hepatic adiponectin was positively correlated with the level of py-IRS2 and inversely with those of hepatic ACC,SREBP-1 mRNA,triglyceride and cholesterol ( r =- 0.431,- 0.396,-0.353,-0.349,P ＜0.05).Conclusion Adiponectin may affect the signaling pathway of hepatic insulin via tyrosin phosphorylation of IRS-2.It is involved in the regulation of hepatic lipid metabolism.