Autophagic Clearance of Aberrant Tau: Biochemical and Therapeutic Implications

描述（由申请人提供）：错误折叠蛋白质的细胞内包涵体是许多神经退行性疾病的标志。参与清除异常或废弃细胞蛋白的两种蛋白水解途径中的任一种的功能障碍，即泛素-蛋白酶体系统（UPS）和自噬-溶酶体系统（A-LS），可能是疾病发展的基础。大自噬（Macroautophagy，自噬）是溶酶体系统的主要降解途径，在去除过大的细胞器和蛋白质聚集体中起重要作用，或者不能被伴侣蛋白解折叠，因此不能被UPS降解。自噬体形成和溶酶体清除之间存在平衡，不受损害的囊泡运输，异型细胞器融合和溶酶体功能对于自噬体降解的终末阶段至关重要。A-LS已被证明在清除错误折叠的、易聚集的蛋白质（如？突触核蛋白和亨廷顿蛋白。一般来说，我们假设UPS在疾病早期被上调以清除错误折叠的tau种类，但随着tau聚集体的积累，系统变得不堪重负。我们设想A-LS然后被上调以努力补偿失去的UPS活性并清除聚集体，但最终两个系统都失败，导致加速的病理和衰退。将在三个特定目标中评估tau蓄积、UPS和A-LS之间的相互作用以及相关药理学操作对与人类tau病变相关的结局指标的影响之间的关系。目的1将检查来自4 R tau蛋白病患者的人组织中UPS、AL-S和tau蛋白积累之间的相互作用，并将与两种已被修饰以表达自噬标记物的4 R tau蛋白病小鼠模型进行比较。小鼠模型将使我们能够操纵自噬途径的组成部分，以进一步研究与UPS的相互作用，具体检查特定泛素化形式的蛋白质发生了什么，以确认自噬充分性在体内tau蛋白病进展中的意义。目的2将使用来自上述动物模型的原代神经元来测试特定途径中功能障碍的影响（自噬空泡的异常转运导致自噬通量失败）及其对tau蛋白病的影响，以及激活A-LS或降低过度磷酸化tau水平的化合物是否改善病理表型。目标3将鉴定NCGC/NIH（国家化学和遗传中心）使用MLPCN（分子库探针中心网络）鉴定的减少亨廷顿蛋白聚集体和细胞死亡的化合物是否是可用于治疗tau蛋白病的可行的自噬增强剂。累积起来，这些研究将增加对清除途径之间关系的了解，如何以及何时失败，以及靶向自噬作为tau蛋白病治疗干预的药物的影响。 公共卫生相关性：统称为tau蛋白病的几种神经退行性疾病包括作为病理学的一部分的称为神经元缠结的细胞内包涵体。虽然我们不知道缠结是如何形成的，或者确切地说是什么类型的tau（错误折叠，过度磷酸化，寡聚或聚集的tau）导致细胞功能障碍，但清除异常，错误折叠的tau蛋白可能会减缓疾病进展并可能治愈或稳定疾病。提出的研究旨在更好地了解病理性tau如何通过两种清除途径中的任一种-泛素-蛋白酶体清除途径或自噬清除途径从细胞中清除。使用小鼠tau蛋白病模型，我们将研究这些系统如何以及何时失败;它们彼此之间的关系，异常细胞转运功能的后果;以及增强自噬清除的新型候选药物在tau蛋白病小鼠模型中是否有效。

DESCRIPTION (provided by applicant): Intracellular inclusions of misfolded proteins are the hallmark of many neurodegenerative diseases. Dysfunction of either of the two proteolytic pathways involved in clearing abnormal or obsolete cellular proteins, the ubiquitin-proteasome system (UPS) and the autophagic-lysosomal system (A-LS) may underlie the development of the disease. Macroautophagy (autophagy), a major degradative pathway of the lysosomal system, plays a significant role in the removal of organelles and protein aggregates that are too large, or that cannot be unfolded by chaperone proteins and that are consequently unable to be degraded by the UPS. An equilibrium exists between autophagosome formation and clearance by lysosomes, and uncompromised vesicular trafficking, heterotypic organelle fusion and lysosomal function are critical for the terminal stages of autophagosomal degradation. The A-LS has been shown to play an important role in the clearance of misfolded, aggregate-prone proteins such as ?-synuclein and huntingtin. In general, we hypothesize that the UPS is upregulated to clear misfolded tau species early during the disease, but the system becomes overwhelmed as larger aggregates of tau accumulate. We envisage that the A-LS is then upregulated in an effort to compensate for the lost UPS activity and to clear the aggregates but ultimately both systems fail resulting in accelerated pathology and decline. The relationship between the accumulation of tau, the interplay between the UPS and A-LS, and the effect of relevant pharmacologic manipulations on outcome measures of relevance to human tauopathy will be assessed in three specific aims. Aim 1 will examine the interplay between the UPS, AL-S and tau accumulation in human tissue from patients with 4R tauopathies and will compare to two mouse models of 4R tauopathy that have been modified to express an autophagic marker. The mouse models will allow us to manipulate components of the autophagic pathways to further study the interplay with the UPS, with specific examination of what happens to specific ubiquitinated forms of proteins to confirm the significance of autophagic sufficiency in tauopathy progression in vivo. Aim 2 will use primary neurons from the aforementioned animal models to test the impact of dysfunction in a particular pathway (abnormal transport of autophagic vacuoles leading to failure of autophagic flux) and its impact on tauopathy, and whether compounds that activate A-LS or reduce the levels of hyperphosphorylated tau ameliorate the pathological phenotype. Aim 3 will identify if compounds identified by NCGC/NIH (National Chemical and Genetic Center) using the MLPCN (Molecular Library Probes Center Network) to reduce huntingtin aggregates and cell death are viable autophagic enhancers that can be used to treat tauopathy. Cumulatively, these studies will add insight into the relationship between clearance pathways, how and when they fail, and the impact of drugs that target autophagy as a therapeutic intervention for the tauopathies PUBLIC HEALTH RELEVANCE: Several neurodegenerative diseases known collectively as the tauopathies include, as part of the pathology, intracellular inclusions known as neurofibrillary tangles. Although we do not know how tangles form, or exactly what type of tau (misfolded, hyperphosphorylated, oligomeric or aggregated tau) causes the cell to become dysfunctional, but it is likely that clearing abnormal, misfolded tau proteins will attenuate disease progression and possibly cure, or stabilize the disease. Studies proposed aim to understand better how pathological tau is removed from the cell through either of the two clearance pathways - the ubiquitin-proteasome clearance pathway, or the autophagic clearance pathway. Using mouse models of tauopathy, we will examine how and when these systems fail; their relationship to each other, the consequence of abnormal cellular transport function; and whether novel drug candidates that enhance autophagic clearance are efficacious in a mouse model of tauopathy.