Ataxin-3对阿尔茨海默病Cdk5信号通路的调控及机理研究

Alzheimer's disease (AD) is the most common neurodegenerative disorder among old people. Recent studies show that the dysregulation of cyclin-dependent kinase 5 (Cdk5) is a linking event between the major AD neuropathological markers: amyloid plaques, tau hyperphosphorylation and synaptic and neuronal loss, thus contributing significantly to AD pathogenesis by amyloid-independent mechanism. However, how exactly Cdk5 is regulated needs further study. Recently, for the first time we identify Cdk5 as a novel binding partner of ataxin-3, a specific deubiquitinating enzyme (DUB). Moreover, a direct interaction between ataxin-3 and Cdk5 is observed, indicating that they may interact functionally. Our present study focuses on the role of ataxin-3 in the regulation of Cdk5 and its downstream substrates and the underlying molecular mechanisms by using interdisciplinary approaches combining biochemistry, molecular and cell biology. In the meantime, we will investigate whether ataxin-3 can affect the neuronal apoptosis mediated by activated Cdk5, thus being involved in the development of AD. The effect of Cdk5 on ataxin-3 will be determined as well. Given that deubiquitinating enzymes offer significant advantages as therapeutic targets within the ubiquitin enzymatic pathway because of their cell-type and substrate-specificity, they might provide attractive targets for the design of novel therapeutics to treat AD. Our research will also contribute to a better understanding of the involvement of DUB in AD pathology.

阿尔茨海默病(AD)是老年人中最常见的神经系统退行性疾病。研究显示Cdk5在Aβ非依赖的AD发病机制中起关键作用，其活性调控异常与AD主要病理特征, 包括老年斑的形成、tau蛋白高度磷酸化以及神经突触丢失都密切相关，但目前Cdk5自身调控机制尚不明确。我们前期的工作首次发现Cdk5是去泛素化酶ataxin-3的结合伙伴，并且证实二者之间存在直接相互作用，提示它们可能在功能上相互调节。本项目拟采用生化、分子和细胞技术着重分析ataxin-3对Cdk5及其下游底物的调控及可能的分子机理，研究ataxin-3是否影响由Cdk5激活介导的神经细胞凋亡，从而参与AD的病理发生，同时还将探讨Cdk5对ataxin-3的调控作用。鉴于去泛素化酶在泛素酶解通路中具有细胞种类和底物特异性，更适宜作为治疗靶标，因此，本研究将为AD药物的设计提供新靶点，并对探讨去泛素化酶在AD病理发生中的作用具有重要意义。

Cdk5是脯氨酸限定性丝氨酸-苏氨酸蛋白激酶，主要在神经系统中表达，并且只有与其特异激活因子p35/p39结合后才具有生物活性。由于Cdk5活性调控异常与阿尔茨海默病（AD）的三个主要病理特征，包括老年斑的形成、tau蛋白高度磷酸化以及神经突触丢失都密切相关，因此在Aβ非依赖的AD发病机制中起关键性作用，但目前关于其自身的调控机制尚不明确，并且关于去泛素化酶对Cdk5的调控的研究也未见报道。由于我们在前期的研究工作中发现MJD家族去泛素化酶ataxin-3与Cdk5存在直接相互作用,首次将去泛素化酶与Cdk5关联起来，因此本项目主要采用了生化、分子和细胞技术较为深入地研究了ataxin-3对Cdk5及其下游作用底物在刺激作用前后的调控变化及分子机理，同时还研究了Cdk5对ataxin-3的调节作用,并检测了ataxin-3对Cdk5激活介导的神经细胞凋亡的影响。本项目基本完成了既定目标。我们发现ataxin-3通过与Cdk5直接相互作用，二者在功能上相互调节。ataxin-3可直接去泛素化Cdk5，并主要进行K63位去泛素化修饰，ataxin-3的缺失可导致Cdk5下游底物之一tau蛋白的磷酸化降低，ATX-3调节SNP及Aβ（1-42）诱导的Cdk5激活介导的细胞凋亡。同时Cdk5也可磷酸化ataxin-3，并且在氧化损伤引起的ataxin-3入核过程中起重要作用。这些结果将有助于阐明Cdk5在AD发病机制信号通路中自身的调控机制，进而揭示ataxin-3在AD病理发生中的作用，也对AD药物的研发具有显著的指导意义。