Genetic modifiers of APOE-related risk for AD

项目概要（APOE U19项目5） 最重要的阿尔茨海默病（AD）风险基因是载脂蛋白E（APOE）。APOE 4与 风险呈剂量依赖性增加，而APOE 2与风险呈剂量依赖性降低相关， 相对于APOE 3/3，发病年龄延迟（AAO）。基于人群的研究表明，APOE 4/4 与APOE 3/3纯合子中约10%相比，纯合子在85岁时具有约60%的AD终生风险。 尽管对AD易感性有这种强烈的影响，但即使在一年内，AAO也存在巨大的变化（几十年）。 单一APOE基因型。我们假设，在人类群体中，有风险和保护性等位基因， 在单个APOE基因型中通过在相同级联事件中起作用而修饰AAO的基因， 修改AD风险和APOE下游的AAO（关于ApoE的详细描述，请参见总体部分 Cascade Hypothesis）。在这个项目中，我们将分析公开的数据，以确定基因， APOE 4携带者和APOE 3/3纯合子的AD风险。初步分析发现， TREM 2变体作为APOE 3/3纯合子中AAO的修饰剂和罕见的EIF 2B 3变体作为AAO的修饰剂 APOE 4携带者ApoE是一种主要在星形胶质细胞中表达的分泌型载脂蛋白。然而，在这方面， APOE表达在小胶质细胞和其他巨噬细胞亚群中高度上调，特别是在 对衰老或患病大脑中的组织损伤和脂质过载的反应，其方式至少部分地 依赖于TREM 2。这与AD特别相关，因为遗传研究表明， 常见的风险等位基因在髓样/小胶质细胞增强子中特异性富集，表明 APOE基因型及其遗传修饰物对AD风险和AAO的影响可能是通过影响小胶质细胞介导的。 细胞功能我们假设APOE基因型及其遗传修饰因子通过以下途径改变AD风险/AAO： 调节小胶质细胞功能，特别是对衰老和疾病中脑组织损伤的反应。到 为了解决这一假设，我们将使用等基因hiPSC衍生的小胶质细胞（iMGL）来评估 APOE基因型及其遗传修饰物（TREM 2 R47 H和EIF 2B 3 S404 A）对小胶质细胞功能的影响 体外和移植同基因hiPSC衍生的造血祖细胞（iHPC）到小鼠中， 评估APOE基因型及其遗传修饰物（TREM 2 R47 H & EIF 2B 3 S404 A）对 AD小鼠脑中的小胶质细胞功能。该项目将与Cores C、E合作执行 和G，涉及整个U19项目的目标2、4和6。项目5将确定新的AAO改性剂 AD在不同APOE风险背景的背景下，并确定这些分子的后果 新的风险基因对小胶质细胞功能的体外和体内研究。这样，项目5连同项目2-4， 将深入了解ApoE在小胶质细胞中的功能，从而确定新的治疗靶点， AD和生成独特的资源/数据，通过核心A与科学界共享。

PROJECT SUMMARY (APOE U19 Project 5) The most important Alzheimer’s disease (AD) risk gene is apolipoprotein E (APOE). APOE4 is associated with a dose dependent increase in risk, while APOE2 is associated with a dose dependent decrease in risk and delayed age at onset (AAO), relative to APOE3/3. Population-based studies have demonstrated that APOE4/4 homozygotes have ~60% life-time risk for AD by age 85 yrs compared to ~10% in APOE3/3 homozygotes. Despite this strong effect on AD susceptibility, there is huge variation (several decades) in AAO even within a single APOE genotype. We hypothesize that in human populations there are both risk and protective alleles in genes that modify AAO within a single APOE genotype by acting within the same cascade of events that modify AD risk and AAO downstream of APOE (see Overall section for detailed description of the ApoE Cascade Hypothesis). In this project we will analyze publicly available data to identify genes that modify AD risk in APOE4 carriers and APOE3/3 homozygotes. Preliminary analyses have identified rare TREM2 variants as modifiers of AAO in APOE3/3 homozygotes and rare EIF2B3 variants as modifiers of AAO in APOE4 carriers. ApoE is a secreted apolipoprotein that is primarily expressed in astrocytes. However, APOE expression is highly upregulated in subpopulations of microglia and other macrophages, particularly in response to tissue damage and lipid overload in the aged or diseased brain, in a manner that is at least in part dependent on TREM2. This is of particular relevance to AD because genetic studies have demonstrated that common risk alleles are specifically enriched in myeloid/microglial enhancers, suggesting that the effects of APOE genotype and its genetic modifiers on AD risk and AAO may be mediated by their effects on microglial cell function. We hypothesize that APOE genotype and its genetic modifiers alter AD risk/AAO through modulation of microglial cell function, particularly in response to brain tissue damage in aging and disease. To address this hypothesis we will use isogenic hiPSC-derived microglia (iMGL) to assess the impact of APOE genotype and its genetic modifiers (TREM2 R47H & EIF2B3 S404A) on microglial cell function in vitro and transplantation of isogenic hiPSC-derived hematopoietic progenitor cells (iHPCs) into mice to assess the impact of APOE genotype and its genetic modifiers (TREM2 R47H & EIF2B3 S404A) on microglial cell function in AD mouse brains. This project will be performed in collaboration with Cores C, E and G and addresses aims 2, 4 and 6 of the overall U19 project. Project 5 will identify novel modifiers of AAO of AD in the context of different APOE risk backgrounds and determine the molecular consequences of these novel risk genes on microglial function in vitro and in vivo. In so doing, Project 5, together with Projects 2-4, will provide insight into ApoE function in microglia leading to the identification of novel therapeutic targets for AD and generation of unique resources/data to be shared with the scientific community through Core A.