PS1调控线粒体动态平衡和线粒体功能的机制研究

Mitochondrial dysfunction is a prominent and early feature of Alzheimer's disease (AD). Mitochondria are dynamics organelles that undergo continual fission and fusion events which serve crucial physiological function. Our recent studies demonstrated that an altered balance in mitochondrial fission and fusion was likely an important mechanism leading to mitochondrial and neuronal dysfunction in AD. Mutations in presenilins (PS) cause early-onset familial form of AD (FAD). PS1 is found in mitochondria and mutant PS1 affects mitochondrial function and transport. Our preliminary studies revealed that PS1 knockout (KO) primary neurons demonstrated significant changes in mitochondria dynamics which could be prevented by co-expression of wild-type PS1, but not FAD-causing PS1 mutant, suggesting that presenilins are involved in the regulation of mitochondrial dynamics which may be impaired by PS1 FAD mutations. Most importantly, we further found that PS1 physically interacted with DLP1, a key regulator of both mitochondrial fission and distribution. These studies suggest that a detailed investigation into the potential direct role of PS1 in mitochondrial dynamics is warranted. Amyloid-β (Aβ) peptides are major of components of senile plaques in AD. And, calcium dyshomeostasis has been implicated as an early manifestation of this devastating disease. In addition to its crucial role in Aβ production, PS1 has been found to regulate calcium release from endoplasmic reticulum (ER). The activity of DLP1 is subject to tight regulation through phosphorylation/dephophoayrlation by Cyclin-dependent kinase 1 (CDK1), calcineurin and Cyclic AMP-dependent protein kinase A (PKA). Our preliminary studies found altered phosphorylation of DLP1 in AD brain and AD models. Therefore, these studies suggest that PS1 may also regulate mitochondrial dynamics and function indirectly through Aβ and calcium signaling. Overall, based on our novel findings, we hypothesize that FAD-associated PS1 mutants cause impaired regulation of mitochondrial dynamics through either specific direct interaction with DLP1 or indirect effect of which causes mitochondrial dysfunction and redistribution which adversely affects neuronal functions including causing synaptic abnormalities in AD. To begin to address this hypothesis, the following specific aims will be pursued: 1) to determine the effect of FAD-associated PS1 mutants on mitochondria dynamics; 2) to determine whether PS1-DLP1 interaction directly mediates the effects of FAD-associated PS1 mutants on mitochondrial dynamics; and 3) to determine whether Aβ and calcium signaling indirectly mediates the effects of FAD-associated PS1 mutants on mitochondrial dynamics. By focusing on PS1/DLP1 interaction, calcium signaling and DLP1 phosphorylation, this study will begin to reveal the underlying mechanisms by which AD-associated PS1 induces mitochondrial abnormalities, and likely lead to novel therapeutic targets. Additionally, since calcium-dependent calcineurin plays an important role in mediating Aβ-induced synaptic dysfunction and memory defects, the study of calcineurin-dependent DLP1 dephosphorylation will likely link two important deficits (i.e., calcium dyshomeostasis and mitochondrial dysfunction) involved in AD. Similarly, ectopic re-expression of cell cycle-related proteins including CDK1 were reported in AD neurons, CDK1-dependent DLP1 phosphorylation will also establish a new link between aberrant cell cycle and mitochondrial dysfunction. In addition, as increasing evidence supports a critical role of abnormal mitochondrial dynamics in other neurodegenerative diseases such as Parkinson’s disease and Huntington’s disease, the proposed study will have broader implications in the field of neurodegeneration.

线粒体功能异常是老年痴呆症（AD）的早期和显著特征之一，但是其中的机制仍不清楚。线粒体的分裂和融合对其功能至关重要。我们最近的研究发现线粒体分裂和融合异常导致AD中线粒体和突触功能异常。早老素蛋白（Presenilins, PS）突变可导致早发家族性AD（FAD）。前期结果显示敲除PS1会导致线粒体的形态、分布和运动显著改变，表达野生型PS1可逆转此异常，而表达FAD相关的突变PS1却无法逆转PS1敲除引起的缺陷。此结果提示与FAD相关的PS1突变可导致线粒体动态平衡的异常。我们还发现1）PS1与调控线粒体分裂和分布的关键蛋白DLP1蛋白相互作用。2）在AD病人和AD模型中，DLP1的磷酸化水平显著改变。在此基础上我们将利用细胞和动物模型深入研究FAD相关突变PS1对线粒体动态平衡和功能的影响，阐明突变PS1通过线粒体异常引发AD的分子机制，寻找潜在治疗AD的药物靶点。

阿尔兹海默病（AD）是世界范围内流行最为广泛的神经退行性疾病，线粒体障碍是其重要的病理特征，而PS1突变是导致此疾病的基因之一。PS1与线粒体的功能的关系以及在AD发病中的作用仍未有明确的报道。本课题旨在阐明PS1对线粒体的影响极其具体机制。通过本课题的研究，我们发现1）PS1定位于线粒体基质中，其与线粒体内膜的多个蛋白具有相互作用，并参与线粒体功能的调控，在维持线粒体内膜和嵴的形态稳定发挥重要作用。如果PS1异常，线粒体功能也将受损，进而影响细胞功能-包括mtDNA损伤修复、细胞生长、凋亡。对于PS1功能的深入研究将为我们进一步理解阐明AD的发病机制具有重要意义，同时为治疗AD提供新的治疗靶点。2）同时我们还发现调控线粒体动态平衡的蛋白Drp1能通过影响微管蛋白的乙酰化调控微管的稳定性，从而影响神经元的生长发育。这对于我们深入理解Drp1蛋白的功能提供了新的方向。并且Drp1在AD等神经退行性疾病中也有改变，也是潜在的药物靶点，深入理解Drp1的生物学功能对于研究开发临床药物具有重要意义。