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

描述(申请人提供)：阿尔茨海默病(AD)大脑的特征是两种类型的蛋白质聚集体，神经原纤维缠结(NFT)，由过度磷酸化的tau组成，以及淀粉样斑块，由淀粉样蛋白(A�，A�)组成。临床上，阿尔茨海默病患者的记忆和其他认知功能呈进行性下降。最近的证据表明，可溶性A�是记忆丧失的初始触发因素；然而，A�导致认知功能下降的分子机制仍然不清楚。在我们的初步研究中，我们已经确定雷帕霉素的哺乳动物靶点(MTOR)是A�、tau与认知功能下降之间的潜在分子联系。此外，我们还发现A-�寡聚体增加了�-2肾上腺素能受体(�-2AR)介导的mTOR信号转导。为了确定mTOR信号与A�、tau和认知功能下降之间的机制联系，提出了三个具体目标：具体目标1将验证A�寡聚体的积累通过�2ARs介导的机制增加mTOR活性的假说。MTOR在调节蛋白质动态平衡方面起着关键作用，因此，揭示导致其在AD发病机制中失控的分子途径将有助于更好地了解该病的发病机制。在这里，我们将剖析将A�积累与�2ARs/mTOR信号变化联系起来的分子途径。具体目标2将测试A�诱导的mTOR信号增加进一步增加A�病理并加剧认知功能下降的假设。我们的初步数据显示，在3xTg-AD和Tg2576小鼠中，mTOR信号增加。此外，我们还发现，用选择性mTOR抑制剂雷帕霉素降低mTOR信号，可以挽救6月龄3xTg-AD小鼠的早期神经病理和行为表型。越来越多的证据表明，雷帕霉素可能具有mTOR非依赖性作用。为了直接解决mTOR在AD中的作用，我们将使用一种遗传方法，并在Tg2576小鼠的大脑中敲除mTOR。具体目标3将检验mTOR信号的增加直接导致tau病理的假设。我们的初步数据显示，在3xTg-AD小鼠中恢复mTOR信号足以减少A�和tau病理。然而，这些小鼠的tau病理高度依赖于A�水平，因此，恢复mTOR信号对tau病理的影响是由mTOR和tau之间的直接相互作用介导的，还是仅仅由于A�水平的下降所致，仍有待确定。使用过度表达野生型tau的小鼠模型，我们将使用遗传学和药理学方法来减少mTOR信号，并测试mTOR信号和tau病理之间的机制联系。总体而言，提出的具体目标将阐明A�、tau和认知下降之间的潜在分子途径。识别导致认知功能下降的途径可能会指向新的治疗靶点。

DESCRIPTION (provided by applicant): The Alzheimer disease (AD) brain is characterized by two types of protein aggregates, neurofibrillary tangles (NFTs), comprised of hyperphosphorylated tau, and amyloid plaques, comprised of amyloid-� (A�). Clinically, AD patients show a progressive deterioration of memory and other cognitive functions. Recent evidence points to soluble A� as an excellent candidate for the initial trigger of memory loss; however, the molecular mechanisms underlying A� -induced cognitive decline remain elusive. In our preliminary studies, we have identified the mammalian target of rapamycin (mTOR) as a potential molecular link between A�, tau and cognitive decline. Additionally, we show that A� oligomers increase mTOR signaling, an event mediated by the �2 adrenergic receptors (�2ARs). To identify the mechanistic link between mTOR signaling and A�, tau and cognitive decline, three Specific Aims are proposed: Specific Aim 1 will test the hypothesis that the accumulation of A� oligomers increases mTOR activity by a mechanism mediated by �2ARs. mTOR plays a key role in regulating protein homeostasis; thus, unveiling the molecular pathways leading to its deregulation in AD will lead to a better understanding of the disease pathogenesis. Here we will dissect the molecular pathways that link the A� accumulation to changes in �2ARs/mTOR signaling. Specific Aim 2 will test the hypothesis that the A� -induced increase in mTOR signaling further increases A� pathology and exacerbates cognitive decline. Our preliminary data show that mTOR signaling is increased in 3xTg-AD and Tg2576 mice. Additionally, we show that reducing mTOR signaling with rapamycin, a selective mTOR inhibitor, rescues the early neuropathological and behavioral phenotypes in 6-month-old 3xTg-AD mice. Growing evidence shows that rapamycin may have mTOR-independent effects. To directly address the role of mTOR in AD, we will use a genetic approach and knockout mTOR in the brain of the Tg2576 mice. Specific Aim 3 will test the hypothesis that the increase in mTOR signaling directly contributes to the tau pathology. Our preliminary data show that restoring mTOR signaling in the 3xTg-AD mice suffices to reduce A� and tau pathology. However, the tau pathology in these mice is highly dependent on A� levels; therefore, it remains to be established whether the effects of restoring mTOR signaling on tau pathology are mediated by a direct interaction between mTOR and tau or are simply due to a decrease in A� levels. Using a mouse model overexpressing wild type tau, we will use genetic and pharmacological approaches to decrease mTOR signaling and test the mechanistic link between mTOR signaling and tau pathology. Overall, the proposed Specific Aims will elucidate the underlying molecular pathways linking A�, tau and cognitive decline. The identification of the pathways that lead to cognitive decline may point to new therapeutic targets.