中国族裔的早老因子突变对钙信号调控的影响及其诱发遗传性阿尔茨海默症的研究

Alzheimer's disease (AD) is a common form of dementia that is affecting 30 million people worldwide and the number of affected individuals will be quadruple by 2050. The etiology of AD is unknown. The "amyloid hypothesis" of AD postulates that the accumulation of beta-amyloid plaques triggers neuron atrophy and death which is the most well-accepted molecular mechanism that describes the initiation of AD. Nevertheless, accumulating evidence suggests disrupted intracellular calcium homeostasis may play an early role on the etiology of AD. The inherited cases of familial AD (FAD) caused by the mutation of presenilins (PS1, PS2) share the same neuropathological hallmarks including the deposition of amyloid-plaques and tangles with the sporadic one.Their consistent phenotypes suggest they may share the same pathophysiological origins. PS is the catalytic subunit of gamma-secretase responsible for the cleavage of amyloid precursor protein (APP) to beta-amyloid. Mutations in PS not only alter gamma-secretase-mediated APP cleavage, but also disrupt the intracellular calcium homeostasis.Thus, insights into the molecular mechanisms and cellular functions of mutant PS in FAD, particularly its role in intracellular calcium regulations, are likely to provide important clues into the etiology of AD. .In 2008, we discovered a molecular interaction between PS and inositol trisphosphate receptor (IP3R) where mutation PS exerted stimulatory effect on the IP3R channel activity, thus disrupted the calcium regulations and induced AD. The PS1 mutations (PS1-V97L and PS1-A136G) in Chinese pedigree were identified in 2002. Current major research activities are mainly focused on the regulation of cellular apoptosis, glucose uptake and the insulin-like growth factor-1 cellular protection mechanisms by the PS. However, the effect of these Chinese-specific PS mutations on the intracellular calcium regulation remains unknown. Therefore, we will employ molecular biology, biochemistry, single-cell calcium imaging and electrophysiological techniques to investigate the effect of PS1-V97L and PS1-A136G on cellular calcium homeostasis and their role in AD pathogenesis. Results from this proposal will provide unique insights into the molecular link between disrupted calcium and AD pathogenesis and suggest novel targets for therapeutic interventions.

阿尔茨海默症（AD）是最常见的脑退化病，全球有三千多万患者，而患病人数正不断增加，其发病机理至今仍未完全清楚。除了经典的"淀粉样蛋白沉积"学说，细胞钙离子失调也被证明是诱发AD的潜在原因。而早老因子（PS）突变导致的遗传性AD，与慢性AD有着相同的病理特征，这为研究慢性AD提供了一个良好的模型。PS突变不仅会增加淀粉样蛋白的生成及沉积，亦会扰乱细胞的钙信号平衡。因此探讨PS的细胞功能，特别是在钙离子信号传递中的作用，将有助于揭示该病症的成因。2008年，我们发现变种PS跟三磷酸肌醇受体相互作用，增加其钙离子通道活性，从而扰乱钙信号平衡，引发AD。中国族裔的PS突变（V97L及A136G）于2002年已被鉴定，然而它们对细胞钙离子调控影响的研究仍未展开。我们会以分子生物、膜片钳及钙成像技术探讨中国族裔的变种PS对细胞钙离子调控的影响及其引发AD的机理。本研究将会为AD的治疗提供新靶点和思路。

阿尔茨海默症（Alzheimer’s disease）是最常见的脑退化病，但其具体成因及发病机理⾄今仍未确定。慢性阿尔茨海默症与早⽼因⼦（presenilin, PS1 及PS2）突变导致的早发及遗传性阿尔茨海默症（familial Alzheimer’s disease，FAD）有着相同的病理特征，包括脑部淀粉样斑块（amyloid-plaques）的沉积和神经元纤维缠结（neurofibrillary tangles）。由此推测，慢性与早发性阿尔茨海默症的成因及发病机理可能相同，⽽探讨早⽼因⼦的功能及其基因突变对细胞机能的影响就显得⾮常重要，因为它将有助于揭⽰该病症的成因。.越来越多的研究显⽰，早⽼因⼦会导致钙离⼦调控的失衡，而钙失衡可能是阿尔茨海默症的发病诱因，因为钙离子调控了几乎所有的䐉神经元生理工能。本课题以分⼦⽣物、膜⽚钳电⽣理、荧光钙成像及⽣物化学技术去探讨中国族裔的早⽼因⼦突变对细胞钙离⼦调控的影响。我们的研究结果揭⽰了早⽼因⼦突变会增加内钙释出，同时减低库容性外钙流⼊，导致细胞钙讯号失衡。增加内钙释出，会加剧Abeta42 淀粉样蛋⽩⽣成，⽽减弱库容性钙流⼊会导致神经棘痿缩。这两点可能是早⽼因⼦导致阿尔茨海默症的发病诱因。早⽼因⼦突变引发的钙讯号失衡是恒守表型，缺陷性的钙讯号特点或许可⽤作诊断的指标，去建⽴新速检测阿尔海默⽒病的诊断⽅法。再者，而三磷酸肌醇受体和STIM1 影响了细胞钙平衡，这两个蛋⽩可成为治疗阿尔海默⽒症的靶点。通过抑制这些蛋⽩或可以纠正细胞钙讯号失衡，改善阿尔海默⽒症的病征。