PTEN, Cell Cycle and Neurofibrillary Degeneration

描述(申请人提供)：在阿尔茨海默病(AD)中，神经原纤维缠结(NFT)的出现和选定脑区的大量神经元死亡/丢失被广泛认为是两个主要特征。虽然在几种神经退行性疾病中，NFT与细胞死亡是一致的，尤其是在AD中，但导致这种慢性神经细胞丢失的分子机制仍然不清楚。细胞周期标记物的异位表达，表明异常的细胞周期重入，已被报道与转基因(TG)小鼠和人类AD脑中的神经元死亡有关。因此，“细胞周期假说”被提出，认为这些细胞周期事件(CCE)在这种毁灭性疾病的发展过程中起着中心致病作用，并代表着第一步。这个模型是对“淀粉样蛋白假说”的补充。然而，缺乏CCES致病作用的直接证据，上游调控因素也是未知的。基于核PTEN调控神经细胞周期的发现，我们现在确定抑癌基因PTEN是调控有丝分裂后神经元CCE的上游因子。此外，这种细胞周期调节功能在空间上与PTEN在PI3激酶-Akt信号通路中的经典作用是分开的，PI3激酶-Akt信号通路主要由细胞质蛋白介导。PTEN(尤其是核PTEN)的缺失在Tg小鼠和人类疾病脑中AD相关区域都被发现，与CCES相关。我们推测，这种核PTEN的缺失是CCES的早期致病因素之一，慢病毒携带的核PTEN基因转移不仅可以阻断CCES，还可以阻止随后的神经变性。本文提出的研究将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，提出了四个具体的目标：1)定量分析轻度认知障碍(MCI)和AD脑中PTEN/PACK T谱和CCES；2)定量分析AD三重TG小鼠模型中PTEN/PAKT水平及其激酶活性；3)研究三重TG模型中CCES的早期可能原因；4)评估慢病毒介导的核PTEN在治疗三重TG小鼠模型CCES和神经退行性变中的有效性。这项工作将有助于未来设计新的治疗干预措施，不仅旨在缓解症状，而且还旨在改善疾病机制。除了治疗外，这项研究还可能有助于验证CCES作为疾病诊断的早期标志物。公共卫生相关性：我们的目标是验证两个新概念，即异常的细胞周期事件是AD的重要疾病机制之一，以及慢病毒传递的中枢神经系统核PTEN基因转移可以在AD小鼠模型中预防这些事件。一旦这些概念得到验证，这项工作将对探索一类新的细胞周期抑制剂在未来AD的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.