Project 3: Roles of Tau Levels, Sequence and Interactors in Neural Network Dysfunction of Alzheimer's Disease

项目3-摘要 Tau与阿尔茨海默病(AD)和许多其他脑部疾病有关。然而，目前还不确定tau如何 导致神经元功能障碍和变性，部分原因是实验模型没有优化到 在与疾病相关的情况下，比较不同tau物种的相对致病性。MAPT的突变，即 编码tau的基因，导致额颞叶变性(FTLD)而不是AD。相比之下，稀有的A152T Tau基因的变异会增加患这两种疾病的风险。这些联系值得进一步探讨，尤其是 作为表达FTLD-突变体tau的模型，tau被广泛用于研究tau在AD中的作用和开发新的AD治疗方法。 临床阿尔茨海默病发病前，脑内淀粉样蛋白b(Ab)多肽异常积聚，许多AD 患者至少有一个载脂蛋白(Apo)E4等位基因，这是AD最重要的遗传风险因素。因此， 我们将建立新的小鼠模型，将人类抗体和apoE4的表达与接近生理水平结合起来 与大多数AD患者一样，人类tau基因是(1)野生型，(2)携带A152T替换，从而增加AD 风险，或(3)携带P301S突变，导致FTLD，并被广泛用于过度表达模型。 新模型的全面功能、病理和转录分析，与 项目1、2和4以及核心B应该会对这些tau物种的不同影响及其 在痴呆症发病机制中的作用。我们假设，增加AD风险或导致FTLD的tau物种 它们对神经元和神经网络的完整性和功能的影响不同，特别是当它们结合在一起时 带有β和apoE4。直到我们知道哪些形式的tau在不同的条件下最具致病性，最 在我们看来，治疗tau的务实方法是部分降低总体tau水平，这是很好的耐受性。 而且在传统型号中也有好处。因此，我们将使用tau靶向反义寡核苷酸(Aso)。 为了(1)确定减少人类tau是否可以减少神经网络功能障碍，神经退行性变和 共同表达人抗体和载脂蛋白E4的模型中的认知衰退，(2)确定了这一过程的最佳时机 干预，以及(3)揭示tau最关键的共同致病机制。我们假设ASO- 介导性tau减少不仅会减少一个或多个新模型中tau的病理改变，还会减少突触。 缺陷、神经网络功能障碍和认知缺陷，尽管它不太可能减少淀粉样蛋白沉积 或斑块相关的小胶质细胞增多症。这项实验应该有助于确定何时必须开始降低tau。 相对于认知缺陷的出现，它在与AD相关的情况下具有治疗益处。单人- 核/单细胞转录分析将用于识别特定细胞类型的基因表达变化 以及可能介导tau致病效应或tau有益效应的新的分子和细胞机制 牛磺酸减少量。这些分析还将帮助项目1和项目2区分 载脂蛋白E4和抗体依赖或不依赖于tau，并可以识别新的分子和细胞机制， 在不存在或存在与AD相关的共病原体的情况下，介导tau序列特异性效应。

PROJECT 3 – SUMMARY Tau contributes to Alzheimer’s disease (AD) and many other brain diseases. However, it is uncertain how tau causes neuronal dysfunction and degeneration, in part because experimental models are not optimized to compare the relative pathogenicity of different tau species in disease-relevant contexts. Mutations in MAPT, the gene encoding tau, cause frontotemporal lobar degeneration (FTLD) instead of AD. In contrast, the rare A152T variant of tau increases risk for both types of diseases. These associations merit further exploration, especially as models expressing FTLD-mutant tau are widely used to study tau in AD and to develop novel AD treatments. Clinical AD onset is preceded by abnormal accumulations of amyloid-b (Ab) peptides in brain, and many AD patients have at least one apolipoprotein (apo) E4 allele, the most important genetic risk factor for AD. Therefore, we will generate new mouse models combining human Ab and apoE4 expression with near-physiological levels of human tau that is (1) wildtype, as in most AD patients, (2) carries the A152T substitution, which increases AD risk, or (3) bears the P301S mutation, which causes FTLD and is widely used in overexpression models. Comprehensive functional, pathological, and transcriptomic analyses of the new models, in collaboration with Projects 1, 2, and 4 and Core B, should yield new insights into differential effects of these tau species and their roles in the pathogenesis of dementia. We hypothesize that tau species that increase AD risk or cause FTLD differ in their effects on the integrity and function of neurons and neural networks, especially when combined with Aβ and apoE4. Until we know which forms of tau are most pathogenic in different conditions, the most pragmatic therapeutic approach to tau in our view is partial reduction of overall tau levels, which is well tolerated and has benefits in conventional models. We will therefore use tau-targeting antisense oligonucleotides (ASOs) to (1) determine whether reducing human tau can diminish neural network dysfunction, neurodegeneration and cognitive decline in models co-expressing human Ab and apoE4, (2) define the optimal timing for this intervention, and (3) reveal the most critical co-pathogenic mechanisms of tau. We hypothesize that ASO- mediated tau reduction will diminish not only tau pathology in one or more of the new models, but also synaptic deficits, neural network dysfunction, and cognitive deficits, even though it is unlikely to reduce amyloid deposition or plaque-associated microgliosis. This experiment should help determine when tau reduction must be initiated relative to the onset of cognitive deficits for it to have therapeutic benefits in AD-relevant contexts. Single- nucleus/single-cell transcriptomic analyses will be used to identify cell-type-specific gene expression changes and novel molecular and cellular mechanisms that may mediate pathogenic effects of tau or beneficial effects of tau reduction. These analyses will also help Projects 1 and 2 distinguish between pathogenic mechanisms of apoE4 and Ab that do or do not depend on tau and could identify novel molecular and cellular mechanisms that mediate tau sequence-specific effects in the absence or presence of AD-relevant co-pathogens.