AQP4介导的胶质淋巴系统在慢性应激中的变化及其对脑内α-syn清除的影响

The glymphatic system (GS) is a brain-wide cerebrospinal fluid-interstitial fluid exchange system dependent on the water channel aquaporin-4 (AQP4) polarized on astrocyte endfeet, which is proposed to account for the clearance of abnormal proteins and metabolites from the brain. Many studies support that chronic stress, a risk factor for Parkinson's disease (PD), can lead to the aggregation of α-synuclein (α-syn) and accelerate the neurodegeneration of PD brain. However, the exact mechanism remains largely unclear. In the brain of PD patients and model animals, wild-type or mutant α-syn is continually secreted into the interstitial fluid. It is possible that the secreted α-syn is also cleared by the proposed glymphatic system. According to our preliminary studies, we hypothesized that chronic stress would damage the glymphatic function, reduce the removal of α-syn from the brain, and then exacerbate the symptom of PD. In the present project, we will focus on the following three aims by using the transgenic mice with over-expression of human A53T mutant α-synuclein and the primary cultured astrocytes in vitro. 1. To study the effects of chronic stress on the GS and the correlation between GS and PD progression. 2. To determine the roles of chronic stress on the expression and localization of pavavascular AQP4 and its mechanism. 3. To identify some medications which can improve the function of the AQP4 mediated glymphatic system in the brain. To our best knowledge, there has been no report to elaborate the influence of chronic stress on the GS during the progression of PD by far. Our project will try to answer the question, and also try to find a new treatment for PD by enhancing the glymphatic function.

胶质淋巴系统（Glymphatic System, GS）是由星形胶质细胞终足处水孔蛋白4（AQP4）介导的脑脊液-脑组织液交换流动系统，发挥着清除脑组织液中代谢产物的作用。慢性应激可导致脑内α-突触核蛋白（α-syn）聚集加重帕金森病（PD）症状，但其机制尚不清楚。根据前期实验结果，我们认为分泌到细胞外的α-syn可通过GS清除出脑，而慢性应激会损害GS功能减慢脑内α-syn的清除加剧PD病变。本课题将以高表达人类α-syn A53T的转基因小鼠为研究对象并结合原代细胞培养研究以下3个问题：1.慢性应激是否降低PD模型鼠脑内GS功能及其和PD病变的相关性；2.慢性应激影响血管周隙AQP4表达和极性分布的分子机制；3.从已有的抗应激药物中寻找能够提高AQP4介导的GS功能的药物。国内外目前尚无关于慢性应激对PD脑内GS功能影响的报道，我们的研究具有较强的探索性并有望为PD找到新的治疗措施。

胶质淋巴系统是由星形胶质细胞终足处水孔蛋白4（AQP4）介导的脑脊液-脑组织液交换流动系统，发挥着清除脑组织中致病蛋白和代谢产物的作用。慢性应激可导致脑内α-突触核蛋白（α-syn）聚集加重帕金森病（PD）症状，但其机制尚不清楚。围绕这一主题，我们首先研究了慢性应激（包括成年期和新生期应激）对AQP4表达、极性分布和对胶质淋巴系统功能的影响及其分子机制，接着研究了胶质淋巴系统在脑内α-syn清除中所起的作用、AQP4基因敲除对脑内α-syn聚集、多巴胺能神经元损伤和PD样行为学的影响，我们也研究了α-syn高表达对AQP4表达、极性分布和对胶质淋巴系统功能的影响。我们做出如下主要发现：慢性应激（成年期或者新生期应激）会导致AQP4表达降低和极性分布异常，导致胶质淋巴系统功能受损，其机制是通过激活糖皮质激素受体信号通路，新生期应激也可能和抑制PDGF-B的表达有关，通过使用糖皮质激素受体抑制剂米非司酮或者补充PDGF-B可改善慢性应激导致的胶质淋巴系统功能受损；通过采用AQP4敲除小鼠和使用抑制剂乙酰唑胺，我们发现胶质淋巴系统发挥着清除脑内α-syn的作用，胶质淋巴系统功能受损（如AQP4敲除小鼠）会加重α-syn的聚集、多巴胺能神经元受损和PD样行为学症状，脑内A53T-α-syn高表达（A53T转基因小鼠和AAV注射小鼠）会导致AQP4表达减少、失去极性分布和胶质淋巴系统功能受损。胶质淋巴系统和脑内α-syn之间的这种互作会形成恶性循环不断加快PD的进展，因此改善胶质淋巴系统的功能具有加快清除α-syn的作用，有望成为PD治疗的新靶点。另外，我们也开发出一种新的方法-荧光酶标仪法来定量测定胶质淋巴系统功能，与传统的荧光示踪法相比更高效和准确，值得推广应用。我们也首次使用荧光显微光学断层扫描（fMOST）技术来三维展示小鼠全脑胶质淋巴系统，并解析出其脑区差异性等结构特征。总之，我们的研究从胶质淋巴系统也就是脑脊液-脑组织液交换流动这个崭新的角度来揭示慢性应激和PD的发病机制，提出了提高胶质淋巴系统功能将有望成为治疗PD等神经退行性疾病的有效途径。

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