辛伐他汀对2型糖尿病认知功能障碍的保护作用及其机制研究

Protective Effect and Mechanism of Simvastatin on Cognitive Dysfunction in Type 2 Diabetes Mellitus

背景 2型糖尿病(T2DM)是常见的代谢紊乱性内分泌疾病,以高血糖为特征,长期高血糖状态可引起认知功能损害,表现为记忆和学习障碍、定向障碍、执行力障碍等。与T2DM常见并发症相比,关于中枢神经系统并发症的研究较少。目的观察辛伐他汀对T2DM大鼠学习记忆能力的影响,探讨哺乳动物雷帕霉素靶蛋白(mTOR)/p70核糖体蛋白S6激酶(p70S6K)信号通路在辛伐他汀改善认知功能中的作用。方法于2016年9月采用随机数字表法将120只健康雄性SD大鼠分为对照组(40只)、糖尿病组(40只)和辛伐他汀组(40只),糖尿病组和辛伐他汀组采用腹腔注射链脲佐菌素分别成功制备T2DM大鼠模型38、37只;辛伐他汀组大鼠采用辛伐他汀灌胃,对照组和糖尿病组大鼠灌胃等体积0.9%氯化钠溶液。饲养至32周行Morris水迷宫实验评估大鼠的记忆能力;显微镜下观察各组大鼠海马组织结构的改变,行Western blotting对mTOR、p70S6K、tau、丙二醛(MDA)、谷胱甘肽(GSH)表达水平进行分析。结果糖尿病组和辛伐他汀组大鼠空腹血糖均高于对照组,体质量均低于对照组(P<0.01)。糖尿病组和辛伐他汀组第2、3、4、5天的逃避潜伏期均长于对照组(P<0.05);辛伐他汀组第2、3、4、5天的逃避潜伏期均短于糖尿病组(P<0.05)。显微镜观察显示,糖尿病组海马神经元数量减少,且排列紊乱,细胞膜皱褶,胞核缺失,细胞器减少;辛伐他汀组海马神经元细胞结构大致正常,数量略减少。糖尿病组和辛伐他汀组的p-mTOR/mTOR、p-p70S6K/p70S6K、p-tau/t-tau均高于对照组(P<0.01);辛伐他汀组的p-mTOR/mTOR、p-p70S6K/p70S6K、p-tau/t-tau均低于糖尿病组(P<0.01)。糖尿病组和辛伐他汀组的MDA/β-actin、GSH/β-actin均高于对照组(P<0.01);辛伐他汀组的MDA/β-actin、GSH/β-actin均低于糖尿病组(P<0.01)。结论辛伐他汀能够改善T2DM大鼠认知功能,可能与mTOR/p70S6K信号通路的抑制和氧化应激产物生成减少有关。

Background Type 2 diabetes mellitus(T2DM) is a common endocrine and metabolic disorder characterized by hyperglycemia. Long-term hyperglycemia can cause cognitive impairment,including memory and learning impairment, orientation impairment,executive impairment and so on. Compared with common complications of T2DM,there is less research on the complications of central nervous system. Objective To observe the effect of simvastatin on learning and memory capacity in rats with T2DM and to determine the role of the mammalian target of rapamycin(mTOR)/p70 ribosomal protein S6 kinase(p70S6K) pathway in the improvement in cognitive function induced by simvastatin.Methods In September 2016,120 healthy male Sprague-Dawley(SD) rats were divided into the control group,diabetic group and simvastatin group(n=40,respectively).T2DM rat models were successfully established in the diabetic group(n=38) and the simvastatin group(n=37) by intraperitoneal injection of streptozotocin.Rats in the simvastatin group were given simvastatin intragastrically.Rats in the control group and diabetic group were administered an equal volume of 0.9% sodium chloride solution intragastrically.After 32 weeks of feeding,the rats were subjected to a Morris water maze test to evaluate memory capacity.Changes in the hippocampal formation in each group were observed under a microscope.Western blotting was performed to analyze the expression of mTOR,p70S6K,tau,malondialdehyde(MDA),and glutathione(GSH) protein.Results Compared with the control group,rats in the diabetic group and simvastatin group were characterized by higher fasting blood glucose and lower body weight(P<0.01).The escape latencies of rats in the diabetic and simvastatin groups were longer on the 2 nd,3 rd,4 th,and 5 th day than in the control group(P<0.05);while the escape latencies on the 2 nd,3 rd,4 th,and 5 th days in the simvastatin group were shorter than those in the diabetic group(P<0.05).Microscopic observations showed that hippocampal neurons in the diabetic group were reduced,showed disordered arrangement,membrane folds,missing nuclei,and reduced organelles;while the hippocampal neurons in the simvastatin group were approximately normal in structure and slightly reduced in number.The p-mTOR/mTOR,p-p70S6K/p70S6K,and p-tau/t-tau in the diabetic and simvastatin groups were significantly higher than those in the control group(P<0.01);while these levels in the simvastatin group were lower than those in the diabetic group(P<0.01).The MDA/β-actin and GSH/β-actin in the diabetic group and simvastatin group were significantly higher than those in the control group(P<0.01);while these levels in the simvastatin group were lower than those in the diabetic group(P<0.01).Conclusion The improvement in cognitive function in T2DM rats administered simvastatin may be related to inhibition of the mTOR/p70S6K signaling pathway and reduced generation of oxidative stress.