Autophagic Clearance of Aberrant Tau: Biochemical and Therapeutic Implications

描述（由申请人提供）：细胞内错误折叠的蛋白质包涵体是许多神经退行性疾病的标志。参与清除异常或过时细胞蛋白的两种蛋白水解途径，泛素-蛋白酶体系统（UPS）和自噬-溶酶体系统（A-LS）中的任何一种功能障碍都可能是疾病发展的基础。巨噬（自噬）是溶酶体系统的一种主要降解途径，在去除太大的细胞器和蛋白质聚集体或不能被伴侣蛋白展开从而无法被UPS降解的蛋白质聚集体中起着重要作用。自噬体的形成和溶酶体的清除之间存在平衡，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最终阶段至关重要。A-LS已被证明在清除错误折叠、易于聚集的蛋白质(如？-synuclein和huntingtin。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物种，但随着更大的tau聚集物的积累，该系统变得不堪重负。我们设想，A-LS随后被上调，以补偿失去的UPS活动并清除聚集物，但最终两个系统都失灵，导致病理加速和衰退。tau积累之间的关系，UPS和A-LS之间的相互作用，以及相关药物操作对与人类tau病相关的结果测量的影响将在三个具体目标中进行评估。目的1将检查UPS、AL-S和来自4R牛头病变患者的人组织中tau积累之间的相互作用，并将比较两种经过修饰以表达自噬标记物的4R牛头病变小鼠模型。小鼠模型将使我们能够操纵自噬途径的组成部分，进一步研究与UPS的相互作用，通过特异性检查特定泛素化形式的蛋白质发生了什么，以确认自噬充足性在体内牛头病进展中的重要性。Aim 2将使用上述动物模型中的原代神经元来测试特定途径功能障碍的影响（自噬空泡异常运输导致自噬通量失败）及其对tau病的影响，以及激活a - ls或降低过度磷酸化tau水平的化合物是否能改善病理表型。目的3将确定NCGC/NIH（国家化学和遗传中心）使用MLPCN（分子文库探针中心网络）鉴定的化合物，以减少亨廷顿蛋白聚集和细胞死亡，是否是可用于治疗tau病的可行的自噬增强剂。总的来说，这些研究将深入了解清除途径之间的关系，它们如何以及何时失败，以及靶向自噬的药物作为治疗性干预的影响

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.