脑缺血后神经自救的内源性机制：凋亡神经元来源外泌体促进神经再生

Cerebral ischemia leads to poor prognosis. Mechanistically, the dead neurons couldn’t be replaced due to that the neurogenesis from endogenous neural stem cells and precursors is insufficient, which ultimately results in irreversible loss of neurons. It is of paramount importance to develop novel neuroprotective therapies to boost neurogenesis. It is well established that exosomes are one of the key mediators for cellular communication and apoptotic cells, including neurons, can release abundant exosomes. We have revealed that there is neurogenesis in ischemic cortex, and the delivery of miR-124 by exosomes can promote neurogenesis significantly. Furthermore, the ischemic preconditioning can upregulate miR-124 in the infarct region. All these results suggest that apoptotic neurons release exosomes carrying miR-124 as SOS signal to promote neurogenesis post ischemia, and that ischemic preconditioning exerts its protective role by the amplification of this self-repair mechanism. The proposed project would confirm the intrinsic SOS mechanism of exosomes derived from apoptotic neurons by the intervention of exosome secretion. We would next focus on clarifying the protective effects of neuronal miR-124 ferried by exosomes in ischemic preconditioning. The current proposal would highly possible reveal a novel intrinsic SOS mechanism mediated by exosomes in cerebral ischemia, which would provide a promising therapeutic strategy for neuroprotection and neuroremodeling via promoting neurogenesis.

缺血性脑卒中预后不良，其细胞学机制是神经元再生能力有限，缺血后凋亡神经元得不到理想修复。寻找增强神经元再生的策略对改善缺血性脑卒中具有重要意义。外泌体是细胞间信息交流的新机制，凋亡神经元可以分泌外泌体。我们前期研究发现脑缺血后皮质损伤区具有一定程度神经元再生，而采用外泌体携带miR-124可显著促进损伤区局部神经前体细胞向神经元分化。另一方面，缺血预处理显著增加损伤区miR-124表达。综上，我们推测凋亡神经元可能通过分泌携带miR-124的外泌体促进神经再生，缺血预处理可能通过增强该内源性自救机制改善缺血性脑卒中预后。本项目拟通过干预外泌体分泌关键基因，在动物水平明确凋亡神经元释放外泌体促进神经再生的作用和机制；在此基础上通过预缺血模型探讨神经元外泌体miR-124在缺血预处理脑保护中的作用及机制。本项目有望发现以凋亡神经元外泌体促进缺血后神经再生的自救途径，为靶向增强该途径提供新思路。

本研究综合运用体外培养神经细胞的凋亡模型、小鼠脑缺血模型、外泌体途径干预及递送策略，系统性观察了外泌体及其关键组分在脑缺血后的作用机制，探讨了脑缺血后新的生物疗法，取得以下发现：1）发现在体建立小鼠外泌体抑制策略后，小鼠脑缺血后神经细胞外泌体分泌受到抑制，同时神经修复及功能恢复情况较非抑制组有显著差异；2）通过原代培养神经元及胶质细胞，发现神经元外泌体中miR-124含量显著高于胶质细胞外泌体；3）建立神经细胞凋亡模型，发现凋亡神经元分泌的外泌体可以调节神经干细胞向神经元分化，而抑制外泌体分泌将拮抗该作用；4）发现神经生长因子可以上调miR-124，通过修饰外泌体递送神经生长因子可以发挥抗凋亡、促神经再生的保护性作用，进而减轻小鼠缺血后脑损伤。本项目探讨了外泌体途径在脑缺血后神经细胞应答及促进神经再生中的作用，更深入的揭示了脑组织的修复机制与潜能。通过外泌体靶向递送关键性神经保护因子改善脑缺血预后，为治疗脑缺血提供了生物新疗法。