前期研究发现老龄GRK5基因缺陷（GRK5KO）小鼠出现了AD样早期的病理改变-轴突转运缺陷，形态学表现为海马内出现了肿胀轴突丛（SACs），但其超微结构本质及其形成机制尚不清楚。我们还发现GSK-3β活性及磷酸化的KLC水平在老龄GRK5-/-小鼠海马内升高。而GSK-3β活性增高据认为可致tau过度磷酸化，并可磷酸化KLC使其与它转运的货物分离而致轴突转运障碍。据此我们提出了"GRK5基因缺陷致GSK-3β活性增高介导AD轴突转运缺陷"的假说。本项目拟用免疫电镜、激光共聚焦、体内受体阻断等方法，研究GRK5-/-小鼠海马内SACs出现和积累与年龄的相关性及其超微结构本质；观察GSK-3β激活在GRK5缺陷导致的海马内tau和KLC畸变磷酸化中的作用；探讨GRK5缺陷引起GSK-3β活性升高的机制。可望阐明GRK5缺陷引起AD样早期病理改变的分子机制，为早期AD防治提供新的药物作用靶点。

Axonal transport defects is one of the early common pathologic features for Alzheimer's Desease (AD) and neurodegenerative diseases, and it also might be the contributing factor of AD. In our previous study, it has been showed that aged G-protein coupled receptor kinase-5 (GRK5) knockout mice (GRK5KO) displayed mild cognitive impairment associated with increased swollen axonal clusters (SACs) in hippocampus. However, the ultrastructural features and the pathogenesis mechanism of hippocampal SACs have yet to be elucidated. Our recent study indicated that the activity of glycogen synthase kinase-3(GSK-3) β and the level of phosphorylated kinesin light chain (KLC) were increased in the hippocampus of aged GRK-/- mice. It was reported that the elevation of GSK3 β activity could lead to hyperphosphorylation of tau, and GSK3β could also phosphorylate KLC and trigger the chaperone-dependent dissociation of kinesin-1 from its cargo, eventually leading to axonal transport defects. Based on these evidences, we hypothesize that elevation of GSK3β induced by GRK5 deficiency can cause AD-like axonal transport deficits. In this proposal, the relationship between the development as well as build-up of hippocampal SACs and the age of GRK5-/- mice will be investigate, and the ultrastructural features of SACs will be examined by immune electron miscroscopy. The role of activation of GSK-3β in the abberant phosphorylation of tau and KLC will be evaluated. And the mechanism that GRK5 deficiency induced the elevation of GSK3β activity will be determined. If our hypothesis is correct, it will help us to reveal the intimate relationship with GRK5 deficiency and early AD-like pathological changes, and provide a new drug target for the prevention and treatment of early AD.