Analysis of the relationship between Amyloid β protein and cholesterol in Alzheimer's disease.

阿尔茨海默病（AD）是老年人最常见的神经退行性疾病之一。家族性阿尔茨海默病已知是由β淀粉样蛋白前体（APP）、早老素1或2的突变引起的，尽管这些原因相对不常见。但这些遗传风险因素在所有阿尔茨海默病病因中所占比例不到2%，其余都是散发性阿尔茨海默病。β淀粉样蛋白（Aβ）是阿尔茨海默病大脑中异常积累的蛋白质之一。长期以来，人们一直认为Aβ纤维的形成和沉积与AD的神经发病机制有关。APP的异常加工和a β的升高可能在遗传性和散发性AD的发病机制中起主要作用。我们研究了APP、a β和胆固醇之间的关系，以寻找胆固醇可能在APP的分裂中发挥作用的证据。我们通过转染野生型、瑞典型和鸟取型（D678N）突变的APP，制备了APP过表达的CHO细胞和npc1缺陷的CHO （nCHO）细胞。npc1在尼曼-皮克病C型中存在缺陷，缺乏细胞内转运和维持胆固醇的稳态。我们分析了细胞内胆固醇的数量、合成和酯化，但过量的APP没有直接影响。然后，我们用铝、低密度脂蛋白和氧化应激两种细胞外刺激来测定不同细胞内胆固醇背景下细胞内APP水平和Aβ产量。APP、Aβ与铝没有关系，但nCHO细胞对铝的敏感性高于正常细胞。过量LDL暴露诱导nCHO细胞β-分泌酶裂解APP，提示产生Aβ。CHO细胞氧化应激时细胞内APP水平降低，而nCHO细胞不受影响。膜nCHO中脂质较少，可防止细胞膜受到氧化攻击。胆固醇稳态的破坏可能会加速和增加AD的风险。

Alzheimer's disease (AD) is one of the most frequent neurodegenerative disorders in elder people. Familial AD is known to be caused by mutations in the amyloid β protein precursor (APP), Presenilin 1 or 2, though these causes of AD are relatively uncommon. But those genetic risk factors account for less than 2% of all AD causes, remaining are sporadic AD.Amyloid β protein (Aβ) is one of the abnormally accumulated proteins in AD's brain. Aβ fibril formation and deposition long have been linked to the neuropathogenesis of AD. And abnormal processing of APP and increase in Aβ may play a major role in the pathogenesis of the hereditary forms and also that of sporadic AD.We investigate the relationship between APP, Aβ and cholesterol to find the evidence that cholesterol may play a role in the cleavage of APP. We made APP-overexpressed CHO cells and npc1 defected CHO (nCHO) cells by transfect the wild type, Swedish and Tottori (D678N) type mutated APP. Npc1 is defected in Niemann-Pick disease type C, which has lack in intracellular transport and maintenance of homeostasis of cholesterol. We analyzed intracellular quantity, synthesis and esterification of cholesterol, but excess APP had no effects directly. Then we determined intracellular APP levels and production Aβ in different intracellular cholesterol background using both cells with extracellular stimulation of Aluminum, LDL and oxidative stress.Despite no relationship APP, Aβ and Aluminum, more sensitive against Aluminum in nCHO cells compared normal cells. Exposure of excess LDL induced the cleavage of APP by β-secretase in nCHO cells, which indicated Aβ production. Intracellular APP levels on the oxidative stress were decreased in CHO cells but not affected in nCHO. Fewer lipids in nCHO of membrane in nCHO may prevent the oxidative attack against cell membrane.The disruption of cholesterol homeostasis might accelerate and strengthen the risks in AD.