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

摘要 Tau病可通过家族机制发生，其中MAPT基因中的突变占主导地位。 遗传引起额颞叶变性（FTLD-tau）或通过散发机制，其中MAPT 单倍型与增加的疾病风险相关（例如进行性核上性麻痹和皮质基底动脉硬化）。 退化）。已经提出MAPT突变和风险单倍型驱动疾病发病机制 通过含有3-微管结合结构域重复（3R tau）、4 R tau或两者的蛋白形式。但 特异性tau形式（蛋白形式）对tau毒性的贡献以及tau病变发生的机制 仍然知之甚少。我们假设MAPT突变驱动tau蛋白聚集， 通过改变tau代谢和在几个潜在的调节节点之一的总体蛋白质稳态来实现功能障碍。 在初步研究中，我们已经表明，诱导多能干细胞衍生的神经元表达MAPT， 与同基因的对照神经元相比，突变表现出tau蛋白周转的变化，我们观察到了差异， 在突变神经元中特定tau蛋白形式的周转中。表达MAPT突变的神经元表现出 溶酶体结构扩大和溶酶体酶的继发性升高， 无法正确降解其内容物。突变等位基因的校正足以恢复这些 溶酶体缺陷这表明tau蛋白动力学的改变可能是由于内溶酶体的缺陷， 通路因此，MAPT突变驱动tau蛋白病的统一特征是通过破坏蛋白质稳态。 本研究的目的是扩展我们的初步研究结果，以确定节点和机制， tau蛋白形式破坏tau蛋白病中的蛋白稳态。我们假设特定的tau蛋白形式足以 使蛋白质稳态不稳定，改变tau半衰期和分泌，并导致tau在细胞中的积累， 脆弱的大脑区域为了验证这一假设，我们将确定MAPT突变和 遗传修饰剂破坏tau动力学以及受损的蛋白质稳态如何影响tau分泌。我们还将 生成系统的遗传相互作用图谱，以阐明MAPT突变、改变之间的联系 以及相关的治疗靶点。总之，这项研究将揭示新的 由特定的tau蛋白形式驱动的tau蛋白病的潜在机制以及治疗方法是否 其被设计为阻断特定的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）、基因组学和转录组学核心（核心 C）和项目1以解决适当的tau代谢需要精确的， 分子伴侣、辅伴侣和溶酶体蛋白酶的协调作用。Tau代谢和 从该项目生成的变体数据库（TMVdb）和Tau多基因风险评分（TPRS）将是一个 为广大科学界提供了宝贵的资源。

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.