Molecular interplay between Aβ, tau and mTOR: Mechanisms of neurodegeneration

 描述(申请人提供)：汇聚的数据表明，在阿尔茨海默病(AD)中，淀粉样蛋白β(Aβ)和tau的积累会导致记忆和其他认知功能的进行性恶化。然而，将Aβ和tau的积累与认知缺陷联系起来的分子途径仍然难以捉摸。在当前的资助周期中，我们已经证明了哺乳动物雷帕霉素靶标(MTOR)在人类AD病例的神经元和星形胶质细胞中以及在AD动物模型中都是过度活跃的。我们发现，减少mTOR信号通过恢复蛋白质合成的缺陷和增加Aβ和tau的周转来改善小鼠的AD样病理。此外，我们的初步数据表明，过度活跃的mTOR信号通过促进坏死性下垂(一种程序性的坏死形式)而导致AD的神经退行性变。这一新颖而令人兴奋的发现可能回答了一个关键但尚未解决的问题：AD中细胞丢失的机制是什么。这一应用的总体假设是，过度活跃的mTOR通过破坏神经元和神经胶质细胞中的蛋白质稳态而导致细胞丢失，从而参与AD的发病。为此，我们提出了三个具体目标。特定目的1将验证以下假设：mTOR下游效应分子S6K1过度活跃，通过改变蛋白质翻译参与AD的发病。我们的初步数据表明，S6K1多动是AD突触和认知障碍的一种先前未知的机制。的确，减少S6K1的过度活动改善了3xTg-AD小鼠的AD样病理。在这里，我们将使用互补的方法来剖析mTOR/S6K1下游与AD发病机制的联系。《特殊目的2》将验证这一假说，即过度活跃的mTOR通过促进坏死性下垂而导致AD的神经退行性变。我们的初步数据表明，坏死性下垂是一种程序性的坏死形式，有助于AD的神经变性。与我们的假设一致，来自文献的数据表明mTOR在调节坏死性下垂方面起着关键作用。为了验证我们的假设，我们将系统地调节具有不同水平mTOR活性的动物和细胞中的坏死信号。具体目标3将验证星形胶质细胞中过度活跃的mTOR导致Aβ积聚、认知功能障碍和神经退行性变的假设。我们的初步数据显示，mTOR在AD小鼠和人类AD病例的星形胶质细胞中都是高活性的。这是非常令人兴奋的，不仅因为mTOR调节星形胶质细胞的清道夫功能，还因为激活的星形胶质细胞已知会分泌可能导致坏死性下垂的有毒因子。我们将使用新开发的遗传工具在AD动物模型和从人类AD病例中分离的人原代星形胶质细胞中修改mTOR。综上所述，本申请中提出的实验将确定mTOR、Aβ和tau积累以及神经退化和认知缺陷之间的机制联系。此外，鉴于mTOR信号在衰老中的作用，我们的结果可能揭示衰老促进AD发展的新机制。阐明这些机制可能会确定几个新的假定治疗靶点。

 DESCRIPTION (provided by applicant): Converging data suggest that in Alzheimer's disease (AD), the accumulation of amyloid-β (Aβ) and tau leads to a progressive deterioration of memory and other cognitive functions. However, the molecular pathways linking the buildup of Aβ and tau to cognitive deficits remain elusive. During the current grant cycle, we have shown that the mammalian target of rapamycin (mTOR) is hyperactive in neurons and astrocytes of human AD cases and in animal models of AD. We found that reducing mTOR signaling improved AD-like pathology in mice by restoring deficits in protein synthesis and by increasing Aβ and tau turnover. Furthermore, our preliminary data suggest that hyperactive mTOR signaling contributes to neurodegeneration in AD by facilitating necroptosis, a programmed form of necrosis. This novel and exciting finding may answer a key, and yet unresolved question: which mechanisms govern cell loss in AD. The overall hypothesis of this application is that hyperactive mTOR contributes to AD pathogenesis by disrupting protein homeostasis in neurons and glia leading to cell loss. To this end, we propose three Specific Aims. Specific Aim 1 will test the hypothesis that hyperactive S6K1, a downstream effector of mTOR, contributes to AD pathogenesis by altering protein translation. Our preliminary data implicate S6K1 hyperactivity as a previously unidentified mechanism underlying synaptic and cognitive deficits in AD. Indeed, reducing S6K1 hyperactivity improves AD-like pathology in 3xTg-AD mice. Here we will use complementary approaches to dissect the mechanisms downstream of mTOR/S6K1 that link this pathway to AD pathogenesis. Specific Aim 2 will test the hypothesis that hyperactive mTOR contributes to neurodegeneration in AD by facilitating necroptosis. Our preliminary data indicate that necroptosis, a programmed form of necrosis, contributes to neurodegeneration in AD. Consistent with our hypothesis, data from the literature show that mTOR plays a key role in regulating necroptosis. To test our hypothesis, we will systematically modulate necroptotic signals in animals and cells with different levels of mTOR activity. Specific Aim 3 will test the hypothesis that hyperactive mTOR in astrocytes contributes to Aβ accumulation, cognitive dysfunction, and neurodegeneration. Our preliminary data show that mTOR is hyperactive in astrocytes of AD mice as well as of human AD cases. This is extremely exciting not only because mTOR regulates the scavenger functions of astrocytes but also because activated astrocytes are known to secrete toxic factors that may induce necroptosis. We will use newly developed genetic tools to modified mTOR in animal models of AD and in human primary astrocytes isolated from human AD cases. Taken together, the experiments proposed in this application will identify the mechanistic links among mTOR, Aβ and tau accumulation, as well as neurodegeneration and cognitive deficits. Furthermore, given the role of mTOR signaling in aging, our results may unveil new mechanisms by which aging contributes to the development of AD. Elucidating these mechanisms will likely identify several novel putative therapeutic targets.