Exosome-mediated propagation of pathogenic tau protein

阿尔茨海默病（AD）是痴呆症的最常见原因，目前影响超过530万人 美国人，但缺乏有效的治疗。神经元缠结是AD的标志，主要包括 磷酸化tau蛋白聚集体。在症状前阶段抑制tau蛋白的传播将 可能为AD提供一种新的预防性治疗方法。然而，分子和细胞 tau的突触传播机制在很大程度上是未知的。外泌体被认为是重要的 tau扩散的载体; AD患者脑脊液外泌体部分中存在tau蛋白 患者提供了强有力的证据，表明这种机制是AD病理生理学的一个重要方面， 人类 我们假设与突触并列的小胶质细胞通过吞噬作用促进tau蛋白的扩散， 外泌体中tau蛋白的分泌，以及AD脑中所见的淀粉样蛋白沉积增强了tau蛋白的传播。 通过小胶质细胞活化以及炎性细胞因子和tau蛋白的共分泌，我们最近的研究有力地证明了小胶质细胞有效地吞噬tau聚集体，然后将它们转移到神经元 通过外泌体（Asai H等人，Nat Neurosci 2015）。我们的工作将由新颖的小鼠模型提供动力， 概括了tau蛋白的传播：立体定向注射腺相关病毒载体， 神经元特异性P301 L tau蛋白进入内侧内嗅皮质表明，抑制外泌体合成或 小神经胶质细胞的耗竭显著减少了tau在体内向齿状回的传播。支持这一 证据，我们表明立体定向注射来自小胶质细胞的含tau蛋白的外泌体成功地扩散， 在野生型小鼠中，tau蛋白进入齿状回的齿状颗粒细胞。这种方法将使我们能够模拟tau 使用从人脑组织和非转基因小鼠分离的外来体进行繁殖。该项目将集中于表征外泌体分泌在tau蛋白沿着增殖中的作用。 使用这些新的小鼠模型解剖学连接的神经网络，具有三个特定目的：1） 表征从人AD脑分离的外泌体tau的组成和繁殖特性， 2）为了确定小胶质细胞或其他细胞类型占外泌体分泌的比例， tau传播，以及3）为了确定外泌体tau传播如何诱导神经生理学和神经病理学的变化， 在新的tau繁殖小鼠模型体内的形态学异常。 我们预计，从这一建议中获得的结果将导致一个全新的范例， 延缓AD和其他tau蛋白病的疾病进展，如额颞叶痴呆和慢性 创伤性脑病此外，建议的小鼠模型将具有更广泛的应用，包括 突触核蛋白病（帕金森病和路易体痴呆）和朊病毒病，因为α-突触核蛋白和 朊病毒也通过外泌体传播。

Alzheimer's disease (AD) is the most common cause of dementia, currently affecting over 5.3 million Americans, yet lacks an effective therapy. Neurofibrillary tangles are a hallmark of AD and primarily consist of phosphorylated tau protein aggregates. Suppressing the spread of tau during the pre-symptomatic stage will potentially provide a novel preventive therapeutic approach to AD. However, the molecular and cellular mechanism of the synaptic propagation of tau is largely unknown. Exosomes are thought to be important vehicles for the spread of tau; the presence of tau proteins in the exosome fraction of cerebrospinal fluid in AD patients provides strong evidence that this mechanism is an important aspect of the pathophysiology of AD in humans. We hypothesize that microglia apposed to synapses facilitate the spread of tau via phagocytosis and secretion of tau in exosomes, and that amyloid deposition as seen in the AD brain enhances the propagation of tau through microglial activation and co-secretion of inflammatory cytokines and tau protein. Our recent studycogently demonstrate that microglia efficiently phagocytize tau aggregates and then transfer them to neurons via exosomes (Asai H et al, Nat Neurosci 2015). Our work will be powered by novel mouse models that recapitulates tau propagation: The stereotactic injection of an adeno-associated viral vector expressing neuron-specific P301L tau into the medial entorhinal cortex shows that inhibition of exosome synthesis or depletion of microglia dramatically reduces tau propagation to the dentate gyrus in vivo. To support this evidence, we showed that stereotactic injection of tau-containing exosomes from microglia successfully spread tau into dentate granular cells of dentate gyrus in wild type mice. This approach will enable us to model tau propagation using exosomes isolated from human brain tissues and non-transgenic mice. This project will focus on characterizing the role of exosomal secretion in the propagation of tau along anatomically connected neural networks using these novel mouse models with three specific aims: 1) To characterize the composition and propagation property of exosomal tau isolated from human AD brain and its potential for the propagation, 2) To determine microglia or other cell types account for exosome secretion for tau propagation, and 3) To determine how exosomal tau propagation induces neurophysiological and morphological abnormality in novel tau propagation mouse models in vivo. We anticipate that the results obtained from this proposal will lead to an entirely novel paradigm for delaying the progression of disease in AD and other tauopathies, such as frontotemporal dementia and chronic traumatic encephalopathy. Additionally, the proposed mouse models will have a wider application, including synucleinopathies (Parkinson's disease and Lewy body dementia) and prion diseases, since α-synuclein and prion also spreads via exosomes.