胶质细胞激抑失衡联动超突触NMDA受体过激与阿尔茨海默病的研究

Abstract It is normally accepted that astrocyte can be activated by microglia in one-way manner. Recently, some evidences revealed that astrocyte may alleviate neurotoxic effects induced by activated microglia; meanwhile, our preliminary experiment demonstrated the activation of microglia can be improved in astrocyte condition medium, which suggest a mutual activation-inhibition action between microglia and astrocyte. Based on the opinion that the activation disequilibration of microglia is a trigger of Alzheimer’s disease (AD) which proposed in our executing National Natural Science Fund, we hypothesized that the imbalance between microglia-astrocyte’s activation-inhibition (activate-restraint disequilibration) play a key role to drive activation disequilibration of microglia and result in AD pathological exacerbate in the present application. Furthermore, on account of the studies which shown astrocyte was the exclusive resource of D-serine, a coagonist of NMDA receptor, we speculated that activate-restraint disequilibration associated extrasynaptic NMDA receptor over-activation maybe the central part in inducing AD neuron damage. To carry out the hypotheses, the interaction between microglia and astrocyte, the timing change of activation of extrasynaptic NMDA receptor and AD pathology character have been analyzed using spontaneous AD animal with primary glial cell culture experiments,in aim to disclose the associations between activate-restraint disequilibration-extrasynaptic NMDA receptor and AD pathological process, and provide a point in cell balance-regulation mechanism to explain AD.

传统研究认为：星形胶质细胞单向接受活化小胶质细胞信息而激活，新近研究指出星形胶质细胞可削弱小胶质细胞神经毒效应；同时，申请人预实验也发现星形胶质细胞条件培养液可缓解小胶质细胞过激，提示胶质细胞激活抑制作用的交互性。在申请人在研国基项目提出小胶质细胞激活转变失衡是阿尔茨海默病（AD）发展启动因素的观点基础上，本申请进一步提出:星形-小胶质细胞间的激(活)抑（制）失衡是诱导小胶质细胞活化失衡推动AD病理关键环节的假设，并基于星形胶质细胞是脑内NMDA受体共激动剂D-丝氨酸唯一来源的实验发现，认为:激抑失衡联动超突触NMDA受体过激又可能是造成AD神经元损伤的主要原因。为验证上述假说，研究拟采用自发AD动物和体外实验，以星形-小胶质细胞交互作用，超突触NMDA受体激活动态变化与AD病理时程关系等为评价指标，揭示激抑失衡-超突触NMDA受体与AD疾病平衡发展的联动，阐释AD发生的细胞平衡调控机制。

阿尔茨海默病（Alzheimer's disease，AD）是一种多发于老年期或老年前期的慢性神经退行性疾病，小胶质细胞和星形胶质细胞介导的中枢神经炎症是AD发生的重要促进因素。传统研究多认为，病理条件下小胶质细胞过度激活释放白细胞介素（interleukin，IL）-1等促炎因子诱导神经炎症反应，并后续单向活化星形胶质细胞协同加剧神经元损伤。而研究发现，星形胶质细胞是中枢多种神经保护及调控分子如胶质细胞源性神经营养因子（glial cell-derived neurotrophic factor，GDNF）的重要来源，且星形胶质细胞的存在可以缓解小胶质细胞过度激活，提示胶质细胞间作用并非单向协同，星形和小胶质细胞间可能存在双向互动。基于上述认识，并结合突触和超突触N-甲基-D-天冬氨酸 (N-methyl-D-aspartic acid，NMDA)受体不同的功能性（突触NMDA 受体激活发挥神经元保护作用，超突触NMDA受体激活诱导神经元损伤）及星形胶质细胞释放D-丝氨酸是NMDA受体级联激活关键步骤的研究，本项目提出：星形-小胶质细胞间的激活抑制双向失衡（激抑失衡）是诱导小胶质细胞过激推动AD 病理的关键环节，而激抑失衡联动超突触NMDA受体过激又可能是造成AD神经元损伤的重要原因。. 本项目应用自发AD 模型小鼠(senescence-accelerated mice P8, SAM P8)及体外胶质细胞培养，发现：1）伴随AD病变发展，中枢GDNF等表达减少而IL-1等表达增多，表现小胶质细胞M1型（损伤型）活化增强而星形胶质细胞功能失常现象；2）星形胶质细胞限制小胶质细胞向M1型活化，而GDNF沉默则削弱星形胶质细胞限制小胶质细胞M1型活化的效应； 3）星形胶质细胞功能失常伴随D-丝氨酸释放增多及超突触NMDA受体过激，增强内质网应激信号介导的海马神经元凋亡丢失。. 项目证实：星形-小胶质细胞双向互作，星形胶质细胞功能失常，小胶质细胞M1型活化增强，促发胶质细胞间激活-抑制失平衡，诱导超突触NMDA受体过激，启动内质网应激信号介导细胞凋亡，加剧AD病理。.