CHOLESTEROL EFFECTS ON HUMAN ApoE AND APP INTERACTIONS

该项目建议测试一种假设，即载脂蛋白E和胆固醇以异构体依赖的方式改变Abeta的沉积，而载脂蛋白E4等位基因以显性模式起作用。淀粉样前体蛋白(APP)的罕见突变是一些早发性常染色体显性阿尔茨海默病(AD)的原因。AD易感基因载脂蛋白(Apo)E基因座的异构体差异影响晚发AD的发病年龄，可能影响15%-50%的病例。在人类中，有三种主要的载脂蛋白E亚型，命名为APOE2，E3和E4，它们只有一个氨基酸不同。载脂蛋白E具有维持胆固醇和脂肪动态平衡的功能。APOE亚型还直接或间接地与APP相互作用，调节与AD病理相关的Abeta沉积的程度。目前的人体研究表明，高胆固醇会增加患阿尔茨海默病的风险。动物研究表明，胆固醇对脑内APP和apoE代谢以及Abeta沉积有显著影响，并提示主要环境因素(如饮食脂肪和胆固醇)可能会改变AD的病理。我们有转基因动物模型来验证这一假设，人载脂蛋白E靶向替换小鼠，人载脂蛋白E转基因小鼠和人APPV717F转基因小鼠。将在基础和高胆固醇条件下测量载脂蛋白E亚型特异性启动子对脑载脂蛋白E水平的影响。AD相关的病理将通过将apoE靶向替代动物与携带人类APP突变的小鼠杂交来检查，使用Abeta沉积和APP代谢作为终点。最后，建立人类常见杂合子APOE3/4的动物模型的能力将使测试人类载脂蛋白E亚型的显性正效应或显性负效应成为可能。对可能调节APP和apoE的饮食因素进行建模将促进对影响AD发生和发展的环境和遗传相互作用的理解。

This project proposes to test the hypothesis that apoE and cholesterol modify Abeta deposition in an isoform-dependent fashion with the apoE4 allele acting in a dominant mode. Rare mutations in amyloid precursor protein (APP) are responsible for some cases of early onset autosomal dominant Alzheimer's disease (AD). Isoform differences at the AD susceptibility gene apolipoprotein (apo) E locus affect age of onset for late on-set AD, and may influence from 15-50% of all cases. In humans, there are three major apoE isoforms designated apoE2, E3, and E4 that differ by a single amino acid. ApoE functions to maintain cholesterol and fat homeostasis. ApoE isoforms also interact either directly or indirectly with APP to modulate the extent of Abeta deposition associated with one dimension of AD pathology. Current human studies suggest that high cholesterol increases the risk of AD. Animal studies reveal significant effects of cholesterol on APP and apoE metabolism in the brain, and on Abeta deposition, and suggest a major environmental (i.e. dietary fat and cholesterol) may modify AD pathology. We have transgenic animal models to test this hypothesis, human apoE targeted replacement mice, human apoE transgenic mice and the human APPV717F transgenic mouse. ApoE isoform-specific promoter effects on brain apoE levels will be measured under basal and high cholesterol conditions. AD-related pathology will be examined by crossing the apoE targeted replacement animals to mice bearing a human APP mutation using Abeta deposition and APP metabolism as endpoints. Finally, the ability to create animal models of the common human heterozygote, APOE3/4, will allow testing for dominant-positive or dominant-negative effects of human apoE isoforms. Modeling dietary factors that may modulate APP and apoE will advance the understanding of environmental and genetic interactions that influence the onset and progression of AD.