Functional Assessment of the Locus for Atrial Fibrillation on Chromosome 4q25

简介(申请人提供)：房颤(AF)是最常见的心律失常，影响着200多万美国人，与中风、痴呆症、心力衰竭和死亡的风险增加有关。房颤的许多常见危险因素已经被确定，在过去的五年里，有越来越多的数据支持基因对房颤的贡献。房颤的遗传位点和突变主要在离子通道蛋白中被描述，尽管这些变异是房颤的罕见原因。房颤仍有一个重要的、但无法解释的遗传基础。冰岛人的一项全基因组关联研究(GWAS)发现了Chr 4q25上的一个房颤易感区域。使用来自另外四个中心的3508名房颤受试者和12173名参照性受试者，我们最近进行了重复和荟萃分析证实了这些发现。因此，最初的GWAS、复制和荟萃分析都证明了Chr 4q25和AF之间有令人信服的关联。在LD区块中没有已知的包含这些SNP的基因；然而，最接近的基因是房颤的有力候选基因。PITX2是一种转录因子，在决定左右不对称以及左心房和肺静脉的发育方面起着关键作用。肺静脉内的异位电灶引发纤颤活动，是用于治疗房颤的导管消融术的靶点。最近的研究表明，高度保守的基因间DNA的短区域经常被发现与转录因子相邻，并通过作为组织特异性增强子来调节基因功能。鉴于LD区缺乏任何与房颤相关的基因，以及左房和肺静脉发育所必需的相邻候选基因，我们假设与房颤相关的SNPs通过高度保守的增强子来调节PITX2的活性。在初步研究中，我们对与房颤相关的LD区块中的增强子元件进行了初步筛选。我们已经确定了一个这样的元素，并发现在LD中带有这种增强子的SNP会增加房颤的独立风险。我们建议通过以下具体目标扩展这项工作：目的1.确定与房颤相关的SNPs是否调节Chr 4q25基因座的基因表达。目的：鉴定和鉴定房颤患者Chr 4q25基因座上保守的非编码增强子。使用体内斑马鱼模型系统快速识别保守的非编码增强子。2B。进行PITX2活性转录调控因子的体外筛选。2C。使用哺乳动物表达系统表征所鉴定的转录调控元件。识别该基因变异导致房颤的机制将为我们进一步了解这种常见心律失常的发病机制、危险分层和治疗方式提供机会。 公共卫生相关性：房颤是最常见的心律异常，会增加中风和死亡的风险。遗传学研究已经确定了房颤的易感区域，但该区域的遗传变异导致房颤的机制尚不清楚。我们建议在斑马鱼、细胞系和小鼠中筛选这一易感区域，以寻找可能导致心房颤动的功能元件。

DESCRIPTION (provided by applicant): Atrial fibrillation (AF) is the most common arrhythmia affecting over 2 million Americans, and is associated with an increased risk of stroke, dementia, heart failure and death. Many common risk factors for AF have been identified, and in the past five years there have been increasing data supporting a genetic contribution to AF. Genetic loci and mutations for AF have been described predominately in ion channel proteins, though these variants are rare causes of AF. There remains a significant, but unexplained genetic basis for AF. A genome-wide association study (GWAS) in Icelanders has identified a susceptibility region for AF on Chr 4q25. Using 3,508 subjects with AF and 12,173 referent subjects from four additional centers, we have recently performed a replication and meta-analysis confirming these findings. Thus, the initial GWAS, replication, and meta-analysis have all demonstrated a convincing association between Chr 4q25 and AF. There are no known genes in the LD block containing these SNPs; however, the closest gene is a strong candidate gene for AF. PITX2 is a transcription factor that has a critical role in determining left-right asymmetry, and the development of the left atrium and pulmonary veins. Ectopic electrical foci within the pulmonary veins initiates fibrillatory activity and is the target of catheter ablation procedures used to treat AF. Recent studies have demonstrated that short regions of highly conserved intergenic DNA are often found adjacent to transcription factors and regulate gene function by acting as tissue specific enhancers. Given the lack of any genes in the LD block associated with AF, and an adjacent candidate gene necessary for left atrial and pulmonary vein development, we hypothesize that the SNPs associated with AF regulate PITX2 activity via highly conserved enhancers. In preliminary studies, we have performed an initial screen for enhancer elements in the LD block associated with AF. We have identified one such element, and found that SNPs in LD with this enhancer confer an independent risk for AF. We propose to extend this work through the following specific aims: Aim 1. To determine if the SNPs associated with AF regulate gene expression at the Chr 4q25 locus. Aim 2. To identify and characterize conserved non-coding enhancers at the Chr 4q25 locus for AF by: 2A. Using an in vivo zebrafish model system to rapidly identify conserved non-coding enhancers. 2B. Performing an in vitro screen for transcriptional regulators of PITX2 activity. 2C. Characterizing the identified transcriptional regulatory elements using a mammalian expression system. Identification of mechanism by which variation at this locus leads to AF will provide an opportunity to advance our understanding of the pathogenesis, risk stratification, therapeutic modalities for this common arrhythmia. PUBLIC HEALTH RELEVANCE: Atrial fibrillation is the most common abnormality of the heart rhythm and increases the risk of stroke and death. Genetic studies have identified a region of susceptibility for atrial fibrillation, but the mechanism by which genetic variation in this area leads to atrial fibrillation is unknown. We propose to screen this region of susceptibility in zebrafish, cell lines, and mice for functional elements that may lead to atrial fibrillation.