Hippo通路对星形胶质细胞xCT的调控在缺血性脑中风中的作用和机制

Astrocytes are key players in the process of ischemic brain injury. Excitotoxic neuronal cell death can be initiated by glutamate extruded from astrocytes via xCT, an amino acid transporter that imports L-cystine and exports L-glutamate. However, the mechanism underlying xCT expression in astrocytes following ischemic stroke is still unknown. In our preliminary data, we found YAP knockdown in primary astrocytes increased the mRNA and protein levels of xCT. Moreover, loss of YAP in astrocytes aggravated brain injury after stroke, indicating that YAP might play important roles in ischemic stroke. Here, we aim to: (1) elucidate the molecular mechanism of YAP on the regulation of xCT expression in astrocytes; (2) define the role of loss of YAP in astrocytes in the middle cerebral artery occlusion (MCAO)-induced brain injury; (3) determine whether YAP-regulated expression of xCT is MST1 dependent and explore the neuro-protective effects of MST1 inhibitor in astrocytes following ischemic stroke. Together, we aim to understand the novel mechanism of Hippo pathway in astrocytes following stoke, with the implication of novel therapeutic avenue for cerebral ischemia diseases.

星形胶质细胞在脑缺血后的神经损伤中发挥着重要的作用，星型胶质细胞过度表达xCT能够引起谷氨酸回收受阻并加剧神经元的死亡，然而xCT在星形胶质细胞中的调控及其对脑缺血所致神经损伤中的作用尚不清楚。我们的前期工作发现在星形胶质细胞中敲降YAP能够增加xCT的mRNA和蛋白表达水平，利用星形胶质细胞特异性敲除YAP的小鼠诱导急性脑缺血模型，发现其中风表型加重。在此基础上，本项目拟采用分子、细胞生物学技术，利用小鼠急性脑缺血模型，主要进行以下几个方面的探讨：（1）阐明YAP对星形胶质细胞xCT的转录调控机制；（2）揭示星形胶质细胞特异性敲除YAP对缺血性脑卒中引起神经损伤的机理；（3）探讨MST1对YAP介导的xCT调控的影响以及MST1抑制剂对脑卒中的神经保护作用，进一步阐明星形胶质细胞中Hippo通路在缺血性脑卒中发生中的新机制，为脑中风疾病的发生、发展和诊治提供理论基础。

在缺血性脑卒中发生过程中，伴随着兴奋毒性引起的脑水肿，然而水肿相关蛋白AQP4主要表达于增殖的星形胶质细胞中，随着星形胶质细胞的增生，伴随着神经炎症和水肿的发生，进而加重脑卒中的疾病发展进程。我们前期研究发现，Hippo通路可通过调控神经炎症参与缺血性脑卒中，然而，缺血性脑卒中引起的脑水肿相关机制还不清楚。因此我们研究了Hippo通路在缺血性脑卒中所致脑水肿中的作用，我们发现MST1可直接磷酸化YY1 T214位点，并维持YY1的蛋白稳定性，进而影响水肿相关蛋白AQP4蛋白和mRNA的表达。并且敲除MST1可保护缺血引起的脑水肿可能是通过YY1-AQP4通路实现的。此外，我们还发现Hippo通路中的另外一个关键分子YAP也参与缺血所致星形胶质细胞的增殖，但是否影响脑水肿还有待进一步的研究。本项目为缺血性脑卒中引起的脑水肿的发病机理提供一定的理论依据，并为将来开发MST1抑制剂作为神经保护药提供线索。