AD中钙离子内稳态失衡调控GRK5膜质转移影响Tau蛋白异常磷酸化的机制研究

G protein-coupled receptor kinase 5 (GRK5) is a typical silk threonine protein kinase. Previous research found that GRK5-deficient mice developed axonal swelling and behavioral cognitive impairment,which is consistent with the phenomenon of axonal injury in early onset of AD, but the mechanism is unknown. The preliminary results of our group found that GRK5 could regulate the phosphorylation of Tau protein through influencing the GSK3β, then trigger axonal transport disorders and ultimately contributed to AD. In addition,for the first time our group found a new phenomenon that GRK5 show the age-related membranous metastasis in AD mouse model, as well as the study on GRK5 functional SNP loci, we proposed that the steady-state imbalance of Ca ion in AD lead to the occurrence of membrane metastasis of GRK5, and thus promote the phosphorylation of Tau protein, and ultimately affect the function of axon. In the present study, we will verify our scientific hypothesis by GRK5 knockout mice, GRK5KO-APP/PS1 hybrid transgenic mice and the results will for the first time, validate the new pathogenesis of Ca2+/CaM-GRK5-GSK3β-Tau-AD, which will provide the new mechanism and the support for the potential new target of AD, and it will also associate the steady-state imbalance in calcium ion theory of AD with Tau protein theory of AD through GRK5, enrich the pathogenesis of AD.

G蛋白偶联受体激酶5（GRK5）是典型的丝苏氨酸蛋白激酶，前期研究发现GRK5缺陷小鼠出现轴突肿胀现象并伴有行为认知障碍，与AD早期轴突损伤现象符合，但机制不明。课题组前期机制研究证实GRK5通过GSK3β调控Tau蛋白磷酸化、引发轴突转运障碍并最终对AD有贡献。另外课题组首次发现GRK5在AD中出现与年龄相关的膜质转移的新现象，并在GRK5功能性SNP位点研究中得到启示，最终提出‘AD中钙离子稳态失衡导致GRK5出现膜质转移、进而促进Tau蛋白磷酸化、最终影响轴突功能’的科学假设，本课题拟通过GRK5敲除小鼠、GRK5KO-APP/PS1杂交转基因小鼠作为动物模型验证此假说，研究结果将首次验证Ca2+/CaM-GRK5-GSK3β-Tau-AD的全新致病通路，为其作为AD的潜在靶点提供新机制和支持，也将AD的Ca离子内稳态失衡学说与Tau蛋白学说通过GRK5联系起来，丰富AD的发病机制。

GRK5是G蛋白偶联受体（GPCR）激酶家族的一员，与心脏和神经系统疾病密切相关。前期研究表明GRK5与脑神经功能和神经退行性疾病密切相关。然而，GRK5在大脑中的生物学功能以及GRK5缺失对与神经退行性疾病相关的认知功能障碍的影响尚不清楚。在本项目中，我们证实了海马中GRK5减少的小鼠表现出认知障碍和一些阿尔茨海默病（AD）相关的分子病理，如显著的神经元损伤和丢失，tau蛋白磷酸化增强，以及海马中Aβ肽水平的增加。从机制上讲，我们观察到GRK5主要定位于小胶质细胞中，在维持小胶质细胞的形态和功能方面发挥着重要作用。GRK5的缺失引起了小胶质细胞形态的变化和促炎症相关基因的增加，提示了GRK5维持小胶质细胞平衡的可能机制，其缺失可能诱发小胶质细胞功能缺陷，并引起一些与AD相关的分子发病机制。通过海马组织的转录分析显示，在GRK5缺陷的小鼠中，神经活性配体-受体相互作用和TNF信号的变化非常明显，可能是GRK5抑制后引发小鼠AD样认知障碍的重要调控途径。另外，在P301S的tau小鼠中的结果证实过量表达GRK5并没有明显改善tau蛋白的过度磷酸化现象和小鼠的AD样认知行为障碍。相反，GRK5的过表达会引起一定的炎症反应并会造成小鼠在压力状态下的抑郁样行为。总之，这些研究结果进一步明确了GRK5的缺失或者异常过量表达都会对小鼠的脑内神经和免疫系统造成损害，证实了GRK5在维持小鼠正常认知功能中的重要作用，加深了人们对GRK5参与AD认知障碍的理解并为未来的AD药物研发提供了积极的参考。