YAP在大脑皮层星形胶质细胞分化和增殖中的作用及其机制

Astrocytes emerge as a major type of glial cells for a wide variety of functions in the central nervous system (CNS). However, the molecular mechanism underlying of neocortical astrogliogenesis remains unclear. Our previous data has shown that ①transcript factor Yes-Associated Protein (YAP) specifically was highly expressed in neural stem cells and astrocytes;②YAP Nestin-CKO displayed the reduced number of neocortical astrocytes;③YAP knockout resulted into the reduction of Smad1 level and astrocyte differentiation induced by BMP-2;④YAP knockout resulted into the reduction of astrocyte proliferation. Based on these preliminary data, we propose our hypothesis: During the nervous development, YAP is involved in the neocortical astrogliogenesis through promotion of astrocyte differentiation and proliferation. To further test this hypothesis, firstly, we will further confirm the phenotypes, the reduction of cortical astrocytes in several YAP conditional knockout mice. Secondly, we will examine the roles and mechanisms of YAP in the astrocyte differentiation and proliferation. Finally, we will examine whether crossing Smad1 transgenic mice can rescue the phenotypes, the reduction of cortical astrocytes in YAP Nestin-CKO mice. This study will help for us to understand the roles and mechanisms of YAP pathways in astrocytes, and provide new insights for the neocortical astrogliogenesis.

星形胶质细胞是大脑中最主要的胶质细胞，然而，其产生的机制不清楚。我们预实验发现：①转录因子Yes-Associated Protein（YAP）高表达于神经干细胞和星形胶质细胞；②YAP Nestin-CKO敲除小鼠皮层星形胶质细胞减少；③YAP敲除导致Smad1下降和BMP2诱导星形胶质细胞分化减少；④YAP敲除导致星形胶质细胞增殖减少。由此设想：在大脑发育中，YAP促进星形胶质细胞分化和增殖，参与皮层星形胶质细胞产生。拟将采用多种条件性基因敲除小鼠、细胞和生化等手段，明确YAP敲除导致皮层星形胶质细胞减少的表型；其次，阐明YAP在星形胶质细胞分化和增殖中作用及其机制；最后，通过杂交Smad1转基因小鼠，阐明过表达Smad1是否能rescue YAP Nestin-CKO小鼠皮层星形胶质减少的表型。本研究将首次深入阐明YAP在星形胶质细胞中的功能，为皮层星形胶质细胞产生提供新的分子机制。

星形胶质细胞是大脑内最主要的胶质细胞，产生和功能的异常与多种神经系统疾病相关。然而，星形胶质细胞分化和增殖机制尚不清楚。在发育过程中，Hippo/YAP通路调节器官大小，本课题采用条件性基因敲除小鼠、细胞、分子生化等技术手段，系统地阐明了该信号通路在星形胶质细胞发育及其相关神经疾病中作用及其机制，主要发现如下：1）在大脑发育过程中YAP特异高表达于神经干细胞和星形胶质细胞；YAP通路促进皮层神经干细胞分化为星形胶质细胞，同时促进星形胶质细胞局部增殖，参与皮层星形胶质细胞产生；2）YAP促进星形胶质细胞分化的分子机制如下：BMP-2通过Neogenin/RhoA通路激活皮层神经干细胞中YAP信号，促进YAP入核，与p-Smad1/5/8形成符合体，稳定BMP-2/Smad通路，促进星形胶质细胞分化；3）YAP促进星形胶质细胞局部增殖分子机制如下：bFGF刺激星形胶质细胞，通过RhoA信号通路激活YAP，促进YAP入核，其实CRM1基因转录，CRM1表达增加，促进p27从细胞核转运至细胞浆，解除p27的细胞周期抑制功能，从而促进星形胶质细胞的增殖；4）在脊髓损伤过程中，星形胶质细胞中YAP表达升高，入核被激活，主要依赖于Hippo通路；条件性敲除星形胶质细胞YAP不影响脊髓的正常发育和小鼠的正常运动功能，但抑制脊髓损伤后神经再生，不利于运动功能恢复，主要是由于星形胶质细胞增殖减少引起的胶质疤痕形成减少导致的。我们这些研究结果不仅阐明了YAP通路在中枢神经系统发育中促星形胶质细胞产生的功能，而且也为大脑皮层星形胶质细胞分化和局部增殖中提供新的分子机制，同时为脊髓损伤中胶质疤痕形成提供新的分子机制。