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，并且在AD脑中tau异常磷酸化，功能受损，异常切割并积累为丝状结构，这可能损害神经元功能的事件。虽然很明显tau蛋白的所有这些变化都发生在AD脑中，但事件的顺序及其对阿尔茨海默病中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的顺序，以及这些事件如何影响AD脑中神经元的存活，以便开发有效的治疗方法。该项目的目的是确定tau蛋白上特定位点的磷酸化如何影响tau蛋白-微管相互作用、tau蛋白寡聚化、tau蛋白与分子伴侣的相互作用（从而影响其功能状态）以及tau蛋白通过泛素-蛋白酶体系统的周转。本申请的中心假设是其中糖原合酶激酶3（GSK 3）起关键作用的tau磷酸化事件的级联，最初导致微管结合受损，随后与半胱天冬酶切割结合，导致tau聚集。这些过程破坏了分子伴侣调节tau功能和周转的能力，并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蛋白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。本项目的目标将通过检验假设的三个具体目标来实现：（1）tau上关键位点的磷酸化损害tau功能，增加tau-tau相互作用，并在tau促进细胞死亡过程中起核心作用，（2）tau的半胱天冬酶裂解增加其自缔合倾向并降低细胞存活，并且这些作用通过tau上的特定位点的磷酸化而加剧，以及（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调节的特异性tau磷酸化和被半胱天冬酶切割tau积累，因为它不再是蛋白酶体系统的有效底物。总的来说，这些都是重要和及时的研究，将明确定义位点特异性磷酸化，半胱天冬酶切割的作用和分子伴侣和泛素-蛋白酶体系统对tau蛋白病理变化的影响，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.