α2肾上腺素-钾-钙通路在右美托咪定抑制七氟烷介导Tau蛋白过度磷酸化致发育期神经损伤中的作用

Repeated or lengthy use (>3 hours), of general anesthetic and sedation drugs during surgeries or procedures in children younger than 3 years or in pregnant women during their third trimester may affect the development of children’s brains. Animal experiments have proved that repeated sevoflurane anesthesia in the early postnatal period of rats may cause nerve damage and decline in long-term learning and memory, which may be related to abnormal expression of Tau protein. My previous study in Professor Zhongcong Xie’Lab of Harvard University found that: Anesthesia with sevoflurane for three days increased the expression of AT8 (Tau PS-202 and Tau PT-205) and decreased the expression of PSD-95 in the hippocampus and induced cognitive impairment in young mice;but retreatment of dexmedetomidine, a 2-adrenergic receptor agonist, inhibited sevoflurane-induced upregulation of AT8 and down-regulation of PSD-95 in the hippocampus and cognitive impairment in young mice. We hypothesized that dexmedetomidine inhibited sevoflurane-induced Tau phosphorylation in young mice. We aimed to determine the mechanism of dexmedetomidine against sevoflurane-induced Tau phosphorylation：Which activates the α2 adrenergic system, increasing intracellular potassium ion concentration, antagonizing the increase of intracellular calcium induced by sevoflurane, thereby reducing Tau phosphorylation induced by anesthetics.We will validate the hypothesis by Anesthesia model in young mice, Primary hippocampal neuron model, Spectrum analysis, Electronic speculum, whole-cell patch clamp technique and Calcium imaging. The project will reveal new mechanisms of long-term cognitive impairment in infants caused by general anesthesia and provide an innovative approach to prevent the toxicity of inhaled anesthetic with intravenous anesthetics.

研究显示3岁以下小儿反复接受全身麻醉可能会影响神经发育。动物实验证实大鼠出生早期多次七氟烷麻醉会引起远期认知功能减退，这与Tau蛋白异常表达有关。本人在哈佛大学谢仲淙教授实验室研究发现：三次七氟烷麻醉后，幼鼠海马中Tau蛋白磷酸化水平AT8明显增加，PSD-95明显下降，小鼠远期认知功能减退，而预先给予右美托咪定处理可预防小鼠远期认知功能障碍及Tau蛋白磷酸化。我们推测右美托咪定抑制七氟烷介导的发育期大脑Tau蛋白过度磷酸化改善了远期认知功能，其机制可能是α2肾上腺素系统的激活通过提高细胞内钾离子的浓度来拮抗七氟烷引起的钙离子浓度升高，从而减轻麻醉药引起的Tau蛋白过度磷酸化。本研究将通过幼鼠多次麻醉模型及原代海马神经元模型、质谱分析、电镜、全细胞膜片钳技术、钙成像等方法验证这一假说。本项目将揭示全身麻醉所致婴幼儿期远期认知功能障碍的新机制并且提供用静脉麻醉药预防吸入麻醉药毒性的创新方法。

研究显示3岁以下小儿接受多次全身麻醉后处理问题的速度和精细运动的协调性显著下降，并且执行能力和阅读等的相关问题明显增多。动物实验证实小鼠出生早期多次七氟烷麻醉会引起远期认知功能减退，这与Tau蛋白异常表达有关。本项目在此基础上研究了右美托咪定是可以改善新生小鼠多次七氟烷麻醉引起的认知功能减退，其改善认知功能减退是否通过激动α2肾上腺素受体抑制幼鼠多次接受七氟烷麻醉介导的Tau蛋白过度磷酸化，明确α2肾上腺素受体在右美托咪定改善Tau蛋白磷酸化中的作用并探讨其可能的机制。本项目还探讨了这是右美托咪定特有的还是整个α2肾上腺素受体均有的特性。另外，本项目还探讨了七氟烷引起的EEG的改变及GABA受体在其引起毒性中的作用。结果发现右美托咪定改善了幼鼠多次七氟烷麻醉引起的远期认知功能障碍，其作用和右美托咪定减轻七氟烷引起的幼鼠海马区 Tau 蛋白磷酸化及远期突触丢失有关，α2肾上腺素受体拮抗剂抑制了右美托咪定减轻的七氟烷引起的Tau蛋白磷酸化，并且抑制了认知功能的改善。而其他的α2肾上腺素受体激动剂如可乐定也可以减轻七氟烷引起的幼鼠海马区 Tau 蛋白磷酸化并改善远期认知功能，这种保护作用同样可以被α2肾上腺素受体拮抗剂所抑制。这提示激动α2肾上腺素受体系统可能能够抑制发育期神经毒性，为预防发育期神经毒性奠定了理论基础。