糖尿病大鼠海马组织内Tau蛋白磷酸化水平和糖原合成激酶-3β活性增高

Tau protein phosphorylation levels and glycogen synthase kinase-3βactivities were increased in hippocampus of rats with type 1 or type 2 diabetes

目的研究1型及2型糖尿病对海马组织内Tau蛋白部分位点磷酸化水平的影响,并探讨其作用机制。方法同月龄Wistar大鼠,分为对照组(CTL)、1型(T1DM)及2型(T2DM)糖尿病模型组。葡萄糖氧化酶法检测血糖,放免法检测血浆胰岛素,Western blot分析海马内总Tau以及Tau蛋白上部分位点(pSer199、pThr212、pSer214、pSer396及pSer422)的磷酸化水平。γ32P标记的ATP和特异性底物肽检测海马内胰岛素信号传导系统中的关键酶糖原合成激酶-3β(GSK-3β)活性。结果T1DM及T2DM组血糖水平显著高于CTL组(P<0.001);T2DM组血浆胰岛素水平显著高于CTL组(P<0.001),而T1DM组显著低于CTL组(P<0.01);T2DM组胰岛素抵抗指数显著高于T1DM及CTL组(P<0.001)。T1DM及T2DM组大鼠海马组织内总Tau蛋白水平与CTL比较无显著差异,但阿尔茨海默病相关的Tau蛋白磷酸化位点pS199、pT212及pS396在T1DM及T2DM组都呈现过度磷酸化状态。同时,GSK-3β活性在这两种糖尿病大鼠模型的海马组织内明显增高(P<0.01,P<0.001)。结论糖尿病大鼠海马组织内Tau蛋白部分位点磷酸化水平增高。胰岛素信号系统功能低下而导致传导途径中GSK-3β活性上调,这可能是引起大鼠海马内Tau蛋白磷酸化的一个主要原因。

Objective To investigate the phosphorylation level of tau in hippocampus of type 1 and type 2 diabetic rats, and its possible mechanism. Methods The models of type 1 （T1DM） and type 2 diabetes （T2DM） were made. The plasma insulin and the plasma glucose levels were tested by RIA and glucose-oxidase methods respectivly. The indexes of insulin resistance were calculated by HOMA-IR. Total tau protein and phosphorylation levels （pSer199,pThr212, pSer214, pSer396 and pSer422） of tau were analyzed by Western blot. The activity of glycogen synthase kinase -3β（GSK-3β）, a key component of insulin signal transduction pathway and a known tau kinase, in hippocampus of rats was examined by γ^32 P-ATP and its specific substrate. Results Plasma glucose was significantly higher in T1DM and T2DM group than that in CTL group, and the plasma insulin was significantly higher in T2DM group but lower in T1DM group than that in CTL group. Insulin resistance, which was calculated by HOMA-IR, was significantly higher in T2DM than in T1DM and CTL group. Tau protein is hyperphosphorylated at several Alzheimer disease （AD）-related phosphorylation sites （Ser199, Thr212 and Ser396 ）. The activity of GSK-3β also significantly increased in the brains of both diabetic models. Conclusion Type 1 and type 2 diabetes increase the risk of AD by downregulation of insulin signal transduction and the consequent upregulation of GSK- 3β, which leads to hyperphosphorylation of tau protein.