Posttranslational processing of tau: function & dysfunc.

描述（由申请人提供）：Tau是一种微管相关蛋白，在阿尔茨海默病（AD）的发病机制中起关键作用。位点特异性磷酸化调节tau功能，在AD中，脑tau异常磷酸化，功能受损，异常断裂并以丝状结构积累，这些事件可能损害神经元功能。虽然很明显，所有这些tau蛋白的变化都发生在阿尔茨海默病的大脑中，但事件的顺序及其对阿尔茨海默病神经元细胞死亡的贡献尚未明确描述。我们的长期目标是充分阐明导致tau蛋白异常翻译后加工的病理过程序列，以及这些事件如何损害AD大脑中的神经元存活，以便开发有效的治疗方法。该项目的目的是确定tau特异性位点的磷酸化如何影响tau-微管相互作用、tau寡聚化、tau与分子伴侣的相互作用（以及其功能状态），以及通过泛素-蛋白酶体系统的tau周转。本应用的中心假设是，糖原合成酶激酶3 （GSK3）起关键作用的一系列tau磷酸化事件，最初导致微管结合受损，随后与半胱天酶切割一起导致tau聚集。这些过程破坏了伴侣调节tau功能和周转的能力，最终导致细胞毒性增加。这些研究的基本原理是，一旦知道特定的翻译后过程如何对tau功能产生负面影响并导致神经元功能障碍和死亡，那么就可以确定治疗阿尔茨海默病的治疗靶点。这个项目的目标将通过测试假设的三个具体目标来实现：(1) tau关键位点的磷酸化会损害tau功能，增加tau-tau相互作用，并在tau促进细胞死亡过程中发挥核心作用；(2)tau的caspase切割增加了其自我结合的倾向，降低了细胞存活率，并且这些影响会因tau上特定位点的磷酸化而加剧；(3)伴侣蛋白和E3泛素连接酶CHIP控制tau构象和蛋白酶体靶向。这些相互作用是由位点特异性的tau磷酸化调节的，而被半胱天冬酶切割的tau会积累，因为它不再是蛋白酶体系统的有效底物。总的来说，这些重要而及时的研究将清楚地定义位点特异性磷酸化，caspase切割以及伴侣和泛素-蛋白酶体系统对tau病理变化的影响，这些变化有助于阿尔茨海默病的疾病过程。

DESCRIPTION (provided by applicant): Tau is a microtubule-associated protein that plays a pivotal role in the pathogenesis of Alzheimer's disease (AD). Site-specific phosphorylation regulates tau function and in AD brain tau is abnormally phosphorylated, is functionally impaired, is abnormally cleaved and accumulates as filamentous structures, events that likely impair neuronal function. Although it is clear that all these changes in tau take place in AD brain, the sequence of events and their contribution to neuronal cell death in Alzheimer's disease has not been clearly delineated. Our long range goal is to fully elucidate the sequence of pathological processes that result in aberrant posttranslational processing of tau and how these events compromise neuronal survival in AD brain so that effective therapeutics can be developed. The objective of this project is to determine how the phosphorylation of specific sites on tau affect tau-microtubule interactions, tau oligomerization, tau interaction with molecular chaperones (and thus its functional state), and tau turnover through the ubiquitin-proteasome system. The central hypothesis of this application is that a cascade of tau phosphorylation events in which glycogen synthase kinase 3 (GSK3) plays a key role, initially results in impaired microtubule binding and subsequently, in conjunction with caspase-cleavage, results in tau aggregation. These processes disrupt the ability of chaperones to regulate tau function and turnover and ultimately result in increased cellular toxicity. The rationale for these studies is that once it is known how specific posttranslational processes negatively impact tau function and contribute to neuronal dysfunction and death, then therapeutic targets for the treatment of Alzheimer's disease can be identified. The objectives of this project will be accomplished through three Specific Aims that test the hypotheses: (1) that phosphorylation of key sites on tau impairs tau function, increases tau-tau interactions and plays a central role in tau's facilitation of cell death processes, (2) that caspase cleavage of tau increases its propensity to self-associate and decrease cell survival, and that these effects are exacerbated by phosphorylation of specific sites on tau, and (3) that chaperones and the E3 ubiquitin ligase CHIP control tau conformation and proteasome targeting, that these interactions are regulated by site-specific tau phosphorylation and that tau cleaved by caspases accumulates because it is no longer an efficient substrate of the proteasome system. Overall these are important and timely studies that will clearly define the role of site-specific phosphorylation, caspase cleavage and the impact of chaperones and the ubiquitin-proteasome system on pathological changes in tau that contribute to the disease processes in Alzheimer's disease.