PTEN, Cell Cycle and Neurofibrillary Degeneration

描述（由申请人提供）：在阿尔茨海默病（AD）中，在选定的脑区域中出现神经元缠结（NFT）和大量神经元死亡/损失被广泛接受为两个主要标志。虽然NFT与几种神经退行性疾病（称为tau蛋白病）中的细胞死亡同时发生，并且最显著的是在AD中，但导致神经元细胞的这种慢性损失的分子机制仍然不清楚。细胞周期标志物的异位表达，表明异常的细胞周期折返，已被报道与神经元死亡在转基因（Tg）小鼠和人类AD脑。因此，提出了一个“细胞周期假说”，即这些细胞周期事件（CCE）起着重要的致病作用，并代表了这种毁灭性疾病发展的第一步。该模型补充了“淀粉样蛋白假说”。然而，没有直接的证据证明CCEs的致病作用，上游调控因素也未知。我们现在确定肿瘤抑制基因PTEN作为一个上游因素，在有丝分裂后的神经元的基础上，我们的发现，核PTEN调节神经细胞周期的CCE。此外，这种细胞周期调节功能在空间上与PTEN在PI 3激酶-Akt信号传导途径中的经典作用分离，所述经典作用主要由细胞质蛋白介导。在与CCE相关的Tg小鼠和人类患病脑中的AD相关区域中发现了PTEN（特别是核PTEN）的缺失。我们推测，这种核PTEN的丢失是CCEs的早期致病因素之一，慢病毒递送的核PTEN基因转移不仅可以阻断CCEs，还可以阻止随后的神经变性。本文提出的研究旨在验证细胞周期假说，并在AD小鼠模型中检查核PTEN。为实现这一目标，提出了四项具体目标：1）定量分析轻度认知障碍（MCI）和AD脑中的PTEN/pAkt谱和CCE 2）分析AD的三重Tg小鼠模型中的pAkt水平及其激酶活性3）研究三重Tg模型中的CCE的早期可能原因和4）评估慢病毒治疗的有效性。在治疗三重Tg小鼠模型中的CCE和神经变性中递送核PTEN。这项工作将有助于未来设计新的治疗干预措施，不仅旨在减轻疼痛，而且还旨在改善疾病机制。除了治疗，这项研究还可能有助于验证CCE作为疾病诊断的早期标志物。公共卫生相关性：我们的目的是验证两个新的概念，即异常的细胞周期事件是AD的重要疾病机制之一，慢病毒递送的核PTEN基因转移在CNS中可以防止这些事件在AD小鼠模型。一旦这些概念得到验证，这项工作将对探索新一类细胞周期抑制剂在未来AD预防和治疗策略中产生重大影响。

DESCRIPTION (provided by applicant): In Alzheimer's disease (AD), the appearance of neurofibrillary tangles (NFTs) and massive neuronal death/loss in selected brain regions are widely accepted as the two major hallmarks. Although NFTs are coincident with cell death in several neurodegenerative diseases, known as tauopathies, and most notably in AD, the molecular mechanisms leading to this chronic loss of neuronal cells is still not understood. Ectopic expression of cell cycle markers, indicating aberrant cell cycle reentry, has been reported to be associated with neuronal death in both transgenic (Tg) mouse and human AD brains. Hence, a "cell cycle hypothesis" was proposed that these cell cycle events (CCEs) play a central causative role and represent the first step in the development of this devastating disease. This model complements the "amyloid hypothesis". However, direct proof of a causative role for CCEs is lacking and the upstream regulatory factors are unknown. We now identify the tumor suppressor PTEN as an upstream factor governing the CCEs in post-mitotic neurons based on our finding that nuclear PTEN regulates the neuronal cell cycle. Moreover, this cell cycle regulatory function is spatially separated from the classic role of PTEN in the PI3 kinase-Akt signaling pathway, which is mediated primarily by the cytoplasmic protein. Loss of PTEN (nuclear PTEN, in particular) was found in AD-relevant regions in both Tg mice and human diseased brains which correlated with CCEs. We speculate that this loss of nuclear PTEN is one of the early causative factors in CCEs and that lentivirus-delivered nuclear PTEN gene transfer may not only block CCEs but also halt subsequent neurodegeneration. Studies proposed herein will aim to validate the cell cycle hypothesis and examine nuclear PTEN in an AD mouse model. Four specific aims are proposed to achieve this goal: 1) Quantitative analysis of PTEN/pAkt profiles and CCEs in mild cognitive impairment (MCI) and AD brains 2) Profile the pAkt level and its kinase activity in the triple Tg mouse model of AD 3) To investigate an early possible cause for CCEs in the triple Tg model and 4) To assess the effectiveness of lentivirus-delivered nuclear PTEN in treating CCEs and neurodegeneration in the triple Tg mouse model. This work will be instrumental to the future design of new therapeutic interventions, not only aiming at symptom-relief but also at disease-modifying mechanisms. Besides therapy, this study may also help validate CCEs as an early marker for disease diagnosis. PUBLIC HEALTH RELEVANCE: We aim to validate two new concepts that aberrant cell cycle events are one of the important disease mechanisms in AD and that lentivirus-delivered nuclear PTEN gene transfer in CNS can prevent these events in an AD mouse model. This work should have great impact on exploring a new class of cell cycle inhibitors in future preventive and treatment strategies of AD once these concepts are validated.