Epigenetic component of the APOE gene in Alzheimer's disease

描述（由申请人提供）： 本研究旨在从表观遗传学角度阐明载脂蛋白E基因（APOE）在阿尔茨海默病（AD）中的作用。拟议的实验将确定APOE β 4等位基因的表观遗传特征与AD的生物学改变之间是否存在因果关系。 APOE的β 4等位基因是AD最公认的遗传危险因素。对APOE在AD中作用的主流研究主要集中在apoE蛋白及其结构和功能的亚型特异性差异上。这种方法产生了广泛和宝贵的见解和假设。然而，apoE 4在AD中发挥其有害作用的确切机制仍不清楚。例如，apoE 4蛋白对中枢神经系统具有明显的有害作用，但这些作用并不能完全解释AD发病和进展的年龄相关方面。多年来，独立的研究表明，除了apoE蛋白亚型外，APOE的其他生物学效应可能导致总体AD风险。在过去的五年里，我的实验室一直在研究载脂蛋白E基因，试图确定可能对AD产生这种新的生物学效应的其他功能元件。最近，我们在APOE的β 4等位基因外显子中发现了一个很好的候选者。我们的初步研究表明，这个外显子是嵌入在一个真实的CpG岛（CGI）是高度甲基化的人死后脑（PMB），并表现出转录增强子活性。我们的工作提供了证据表明，这种APOE CGI可以以细胞类型、DNA甲基化（DNAm）和β 4等位基因特异性方式差异调节APOE基因座的基因表达。目前，尚不清楚APOE的CGI和DNAm是否具有任何影响AD风险的关键生物学功能或后果。 基于这一证据，我们假设APOE的β 4等位基因是APOE CGI的一个关键因素，它是表观遗传学标记的，调节APOE基因座上多个基因的表达，并与其蛋白产物产生协同效应，增加一个人患AD的风险。这项工作的短期目标是评估APOE CGI和AD风险之间的表观基因型-表型相关性，并确定APOE CGI的DNAm是否是β 4等位基因和AD风险之间强关联信号的组成部分。我们的研究的具体目标将调查这一整体范式的几个组成部分。目的1将检测PMB各种组织中APOE CGI的DNA m谱，以确定β 4等位基因和AD疾病特异性差异甲基化区域。DNA m的这种差异有很大的潜力作为一类新的AD生物标志物，其中监测表观遗传学改变可能指示疾病进展。目的二是考察DNAm对APOE CGI增强子活性的影响。将评价APOE CGI的DNAm水平与AD相关基因的RNA表达水平之间的相关性。此外，结果将按APOE CGI的β 2/β 3/β 4等位基因分层，以确定β 4等位基因的特异性作用。目的3将探索APOE CGI的调控机制和蛋白结合特性，以确定其功能核心区域并鉴定相关结合蛋白，从而更全面地了解β 4等位基因在AD风险中的作用。 在我们目前对APOE-4等位基因和AD风险之间联系的理解中存在一些关键的空白;填补这些空白构成了这项建议的基础。本文提出的研究将确定一个新的范式载脂蛋白E基因的作用，在AD。该项目的结果还将提供有关AD表观遗传影响和调节性质的基本新知识。反过来，这项工作应该为AD的干预和预防新策略提供重要的见解。

DESCRIPTION (provided by applicant): The present study aims to elucidate the role of the apolipoprotein E gene (APOE) in Alzheimer's disease (AD) from a novel epigenetic perspective. The proposed experiments will determine if a causal connection exists between epigenetic characteristics of the APOE �4 allele and the biological alterations responsible for AD. The �4 allele of APOE is the most recognized genetic risk factor for AD. Mainstream research into the role of APOE in AD has primarily focused on the apoE protein and isoform-specific differences in its structure and function. That approach has generated broad and valuable insights and hypotheses. However, the precise mechanism by which the apoE4 exerts its detrimental effect in AD remains obscure. For example, the apoE4 protein has clear detrimental effects on the central nervous system, yet these effects do not fully account for the age-related aspects of AD onset and progression. Over the years, independent studies have suggested that other biological effects of APOE, besides the apoE protein isoforms, may contribute to overall AD risk. My laboratory has been studying the APOE gene for the past five years in an attempt to identify additional functional elements that might contribute such novel biological effects to AD. Recently, we have identified an excellent candidate in the �4 allele-carrying exon of APOE. Our preliminary studies show that this exon is imbedded in an authentic CpG island (CGI) that is highly methylated in human postmortem brain (PMB), and exhibits transcriptional enhancer activity. Our work provides evidence that this APOE CGI can differentially modulate expression of genes at the APOE locus in a cell type-, DNA methylation- (DNAm), and �4 allele- specific manner. Currently, it is unknown if this CGI and DNAm of APOE have any critical biological functions or consequences that impact AD risk. Based on this evidence, we hypothesize that the �4 allele of APOE is a critical element of the APOE CGI, which is epigenetically marked, modulates the expression of multiple genes at the APOE locus, and exerts a synergistic effect with its protein product to increase a person's risk for AD. The short-term goal of this work is to assess the epigenotype-phenotype correlations between the APOE CGI and the risk of AD, and to determine if DNAm of the APOE CGI is an integral element of the strong association signal between the �4 allele and the risk of AD. The specific aims of our study will investigate several components of this overall paradigm. Aim 1 will examine the DNAm profile of the APOE CGI, in various tissues of PMB, to identify �4 allele- and AD disease- specific differentially methylated regions. Such differences in DNAm have great potential to serve as a new class of AD biomarkers, in which monitoring epigenetic alterations might indicate disease progression. Aim 2 will inspect the effects of DNAm on the enhancer activity of the APOE CGI. Correlations between DNAm levels of the APOE CGI and RNA expression levels of AD-associated genes will be evaluated. Additionally, the results will be stratified by the �2/�3/�4 alleles of the APOE CGI to determine the specific effects of the �4 allele. Aim 3 will explore the regulatory mechanisms and protein binding properties of the APOE CGI to determine its functional core region and identify relevant binding proteins, which will provide a more comprehensive view of the �4 allele's role in AD risk. A number of key gaps exist in our current understanding of the link between the APOE �4 allele and AD risk; filling these gaps forms the basis for this proposal. The studies proposed herein will define a new paradigm of APOE gene action in AD. Results from this project will also provide fundamental new knowledge regarding the nature of epigenetic influence and regulation in AD. In turn, this work should provide crucial insights for new strategies of intervention and prevention for AD.