内嗅皮层来源谷氨酸诱导小胶质细胞活化在MCAO后海马突触损伤中的作用及机制

Middle cerebral artery occlusion (MCAO) is the most common cause for ischemic stroke which is a risk factor for both vascular dementia and Alzheimer's disease. Neuropathological changes have been observed in the non-ischemic regions such as hippocampus. However, the mechanism underlying MCAO-induced secondary hippocampal injury remains unclear. Our recent study has shown that the glutamatergic synaptic connection between entorhinal cortex and hippocampus plays an important role in the initiation of pathological changes in the hippocampus following MCAO. Excessive glutamate released from entorhinal cortex initiated the pathological changes in the hippocampus. It is becoming increasingly clear that microglia influences major aspects of synapse development, plasticity and function and is closely associated with learning and memory. Microglia can be activated by glutamate via direct receptor binding or chemokine released from injured neurons. It is reasonable to propose that glutamate-induced microglia activation may participate in secondary hippocampal changes. Therefore, we will explore the role of microglial activation in synaptic dysfunction and cognitive impairment following MCAO and the role of CX3CL1/CX3CR1 signaling pathway in microglial activation and synaptic dysfunction. The influence of microglial activation on synaptic formation and function will further be examined in the cultured cells. This study may help guide the development of new therapies for synaptic dysfunction.

大脑中动脉阻塞（MCAO）是缺血性脑卒中最常见原因，存活患者常出现认知障碍。海马与学习记忆密切相关，MCAO后位于非缺血区的海马出现继发性损伤，具体机制尚不清楚。申请者前期结果发现，内嗅皮层来源的谷氨酸能纤维投射是造成MCAO后海马继发性损伤的结构基础。谷氨酸可直接与其受体结合激活小胶质细胞，也可诱导神经元释放CX3CL1等趋化因子间接活化小胶质细胞。小胶质细胞通过调节突触可塑性可影响学习记忆过程。本项目拟在动物模型中观察内嗅皮层来源谷氨酸对MCAO后海马小胶质细胞活性的影响、及其与海马突触损伤的关系，在细胞水平探讨小胶质细胞影响神经元突触形成和电活动的分子机制，并进一步用特异性药物干预和基因工程技术，验证内嗅皮层来源谷氨酸诱导的小胶质细胞活化及CX3CL1/CX3CR1介导的细胞因子信号通路在MCAO后海马突触损伤和学习记忆下降中的作用，为探索缺血性脑卒中后认知障碍的防治提供理论依据。

脑卒中是现阶段我国居民的首位致死病因，其中60%-80%为缺血性脑卒中，大脑中动脉阻塞（middle cerebral artery occlusion,MCAO）是最常见的原因。缺血性脑卒中也是发生认知功能障碍的危险因素，严重妨碍患者日常生活。MCAO除导致缺血区神经元的原发性损伤外，非缺血区的海马也会出现继发性损伤。由于海马与学习记忆密切相关，这种远隔效应可能是脑卒中后认知功能障碍的重要原因。因此，本项目基于内嗅皮层-海马间存在的谷氨酸能纤维投射，在动物模型中观察内嗅皮层来源谷氨酸对MCAO后海马小胶质细胞活性变化的影响及其与海马继发性损伤的关系，在细胞共培养模型中进一步研究小胶质细胞影响神经元活性及功能的分子机制。本研究结果显示: 缺血后海马小胶质细胞主要向M1型极化，预先切断来源于内嗅皮层的纤维投射可减轻缺血后海马区神经元损伤及小胶质细胞的活化, 谷氨酸通过CX3CL1/CX3CR1信号介导小胶质细胞的极化，抑制小胶质细胞的活化可改善缺血后的认知功能。因此，调控小胶质细胞的极化是减轻脑损伤后继发性神经元损伤的极具潜力的治疗靶点。近年来，血管紧张素受体抑制剂在中枢神经系统疾病中的作用也逐渐受到关注。本项目也进一步证实血管紧张素受体抑制剂替米沙坦可调控多种刺激因素诱导的小胶质细胞的极化，这也为调控脑损伤后小胶质细胞极化的干预措施提供了新思路。此外，本研究也证实脑损伤后的炎症反应具有性别差异，而雌激素膜受体GPER激动剂G1调控小胶质细胞极化的效应也具有性别差异，这也为临床雌激素及相关受体激动剂的应用提供了实验基础。