甲状腺功能异常大鼠大脑皮层Alzheimer病样tau蛋白异常修饰

Alzheimer-like Hyperphosphorylation of Tau in Cerebral Cortex of Rats with Abnormal Thyroid Status

目的探讨甲状腺功能亢进及减低状态大鼠大脑皮层tau蛋白部分位点磷酸化水平的变化。方法雌性Wistar大鼠分别以甲状腺片及丙基硫氧嘧啶片灌胃4周造模成甲状腺机能亢进组(甲亢组)及甲状腺机能减低组(甲减组),温度计记录大鼠直肠温度,葡萄糖氧化酶法检测血糖,放免法检测血浆游离T3(FT3)、游离T4(FT4)及促甲状腺激素(TSH)。Western blot法分析大脑皮层内总tau蛋白、tau蛋白上部分位点(Ser199、Thr205、Thr212、Ser214、Ser396及Ser422)的磷酸化水平,免疫组化SP法分析tau蛋白Ser396/404位点上磷酸化水平。结果甲亢组大鼠直肠温度显著高于对照组,而甲减组显著低于对照组。甲亢组血糖水平显著高于对照组,而甲减组与对照组比较则显著下降。3组大鼠海马回总tau蛋白无差异,但在检测磷酸化位点Ser199、Thr212、Ser214、Ser396及Ser422的磷酸化程度上甲减组都显著高于甲亢组及对照组,而后两组磷酸化水平无显著差异。tau蛋白在Ser396/404位点上免疫组化检测结果显示甲减组大鼠海马CA3区大量阳性表达细胞,而其他两组在此区呈弱阳性表达。结论①甲状腺功能减低大鼠大脑皮层tau蛋白呈Alzheimer样过度磷酸化改变。②低代谢可能参与了甲状腺功能减低大鼠tau过度磷酸化的形成。③甲状腺功能亢进时虽代谢率及体温都升高,但不影响大脑皮层tau蛋白磷酸化状态。

Objective To study the changes in hyperphosphorylation of tau in cerebral cortex in rats with hyperthyroidism or hypothyroidism. Methods Wistar female rats were randomly divided into 3 groups： hyperthyroidism group, hypothyroidism group and control group. The rats in hyperthyroid group were treated with thyroid at a dose of 0.8 mg/（kg·d） for 4 weeks, and those in hypothyroid group with tapazole at a dose of 0.6 mg/（kg·d） for 4 weeks. The rectal temperature of rats was recorded. The plasma FTa, FT4 and TSH levels were measured by RIA method, and the blood glucose by glucose-oxidase method. Total tau level and the phosphorylation level of tau at individual phosphorylation sites （Ser199, Thr205, Thr212, Ser214, Ser396 and Ser422） were detected by Western blot. The expression of Tau [pS396/404-] was determined by immunohistochemical assay. Results The rectal temperature and glucose levels in hyperthyroid group were significantly higher than in control group. But in hypothyroid group, these two targets were significantly lower than in control group. Neither hyperthyroid nor hypothyroid changed the total level of tau protein in the cortex of rats. However, Tau was found to be hyperphosphorylated at several alzheimer disease （AD）-related phosphorylation sites （Ser199, Thr212, Ser214, Ser396 and Ser422） in hypothyroid group. The expression of phosphorylated tau was modestly increased in CA3 sector of hippocampus in hypothyroid group as compared with that in hyperthyroid and control groups. Conclusion ① tau protein in cortex was hyperphosphorylated in hy- pothyroid rats; ② tau hyperphosphorylation in hypothyroid status may be caused by low metabolism;③ High temperature and glucose metabolism in hyperthyroid status may not change the phosphorylation of tau protein.