Project 2: Tau metabolism: Quantifying tau half-life and secretion

摘要 肌萎缩侧索硬化症可能由家族性机制发生，其中MAPT基因突变占主导地位 遗传性致额颞叶变性(FTLD-tau)或由MAPT 单倍型与疾病风险增加相关(例如进行性核上性麻痹和皮质基底细胞麻痹 退化)。MAPT突变和风险单倍型已被认为是疾病发病的驱动因素 通过含有3-微管结合结构域重复序列(3R Tau)、4R tau或两者的蛋白形式。然而， 特定的tau形式(蛋白形式)对tau毒性的贡献以及tau病发生的机制 人们对此仍然知之甚少。我们假设MAPT突变驱动tau聚集和神经元 通过改变tau代谢和几个潜在调节节点之一的整体蛋白平衡而导致功能障碍。 在初步研究中，我们已经证明了诱导的多能干细胞来源的神经元表达MAPT 与同基因的对照神经元相比，突变显示tau周转率的变化，我们观察到了差异。 在突变神经元中特定tau蛋白形式的周转。表达MAPT突变的神经元表现为 溶酶体结构扩大和溶酶体酶的继发性升高，溶酶体的标志是 无法正确地将其内容降级。对突变等位基因的纠正足以恢复这些 溶酶体缺陷。这表明tau动力学的改变可能是由于内溶酶体缺陷所致。 路径。因此，MAPT突变驱动转位症的一个统一特征是通过被破坏的蛋白稳定。 这项研究的目的是扩展我们的初步发现，以定义通过 Tau蛋白形式扰乱了tau病的蛋白平衡。我们假设特定的tau蛋白形式就足够了 破坏蛋白稳定，改变tau半衰期和分泌，导致tau在体内蓄积。 脆弱的大脑区域。为了验证这一假设，我们将确定MAPT突变和 遗传修饰物破坏tau的动力学，以及蛋白平衡受损如何影响tau的分泌。我们还将 创建系统的遗传相互作用图，以阐明MAPT突变、改变 在tau代谢途径中，以及相关的治疗靶点。总而言之，这项研究将揭示小说 由特定tau蛋白形式驱动的tau病的潜在机制以及治疗学 旨在阻止特定的tau蛋白形式影响病理事件。项目2将与 管理核心(核心A)、大分子结构(核心B)、基因组学和转录学核心(核心 C)和项目1，以解决总的假设，即适当的tau代谢需要精确的， 分子伴侣、辅助伴侣和溶酶体蛋白酶的协同作用。牛磺酸代谢和 本项目产生的变异数据库(TMVdb)和Tau多基因风险评分(TPRS)将是一个 对于更广泛的科学界来说，这是无价的资源。

ABSTRACT Tauopathies may occur by familial mechanisms in which mutations in the MAPT gene are dominantly inherited causing frontotemporal lobar degeneration (FTLD-tau) or by sporadic mechanisms in which MAPT haplotypes are associated with increased disease risk (e.g. progressive supranuclear palsy and corticobasal degeneration). MAPT mutations and risk haplotypes have been proposed to drive disease pathogenesis through proteoforms that contain 3-microtubue binding domain repeats (3R tau), 4R tau, or both. However, the contribution of specific tau forms (proteoforms) to tau toxicity and the mechanisms by which tauopathies occur remains poorly understood. We hypothesize that MAPT mutations drive tau aggregation and neuronal dysfunction by altering tau metabolism and overall proteostasis at one of several potential nodes of regulation. In preliminary studies, we have shown that induced pluripotent stem cell derived-neurons expressing MAPT mutations exhibit changes in tau turnover compared to isogenic, control neurons, and we observed differences in the turnover of specific tau proteoforms in mutant neurons. Neurons expressing MAPT mutations exhibit enlarged lysosomal structures and secondary elevation of lysosomal enzymes, markers of lysosomes that are unable to properly degrade their contents. Correction of the mutant allele was sufficient to restore these lysosomal defects. This suggests that altered tau kinetics may be due to defects in the endolysosomal pathway. Thus, a unifying feature by which MAPT mutations drive tauopathy is through disrupted proteostasis. The objective of this study is to extend our preliminary findings to define the nodes and mechanisms by which tau proteoforms disrupt proteostasis in tauopathies. We hypothesize that specific tau proteoforms are sufficient to destabilize proteostasis, alter tau half-life and secretion, and to result in the accumulation of tau in vulnerable brain regions. To test this hypothesis, we will determine the extent to which MAPT mutations and genetic modifiers disrupt tau kinetics and how impaired proteostasis impacts tau secretion. We will also generate a systematic genetic interaction map to elucidate connections between MAPT mutations, alterations in the tau metabolism pathway, and associated therapeutic targets. Together, this study will reveal novel mechanisms underlying tauopathy that are driven by specific tau proteoforms and whether therapeutics designed to block specific tau proteoforms impact pathologic events. Project 2 will work synergistically with the Administration Core (Core A), Macromolecular Structure (Core B), Genomics and Transcriptomics Cores (Core C) and Project 1 to address the overall hypothesis that proper tau metabolism requires the precise, coordinated action of molecular chaperones, co-chaperones and lysosomal proteases. Tau Metabolism and Variant database (TMVdb) and Tau Polygenic Risk Score (TPRS) generated from this project will be an invaluable resource for the broader scientific community.