Gene-Environment Interactions in the Fetal Origin of Adult Cardiac Disease

描述(由申请人提供)：本申请旨在研究在胚胎发育过程中由ah受体(AHR)调控的基因-环境相互作用及其在成人疾病中的后果。人体接触器官氯化受体配体，如二恶英，在流行病学上与许多毒理学结果和疾病有关，其中发育异常和心血管疾病的死亡是突出的。虽然普遍的科学证据表明，这些结果是由AHR激活介导的，但AHR配体在人类中发挥作用的分子机制仍未确定。我们建议确定这些机制，并对AHR、胎儿暴露于二恶英和心血管疾病之间的因果关系进行生物学测试。我们目前的目标是：(I)确定小鼠发育过程中暴露于TCDD或去除AhR基因是否会导致与成年生活中生理缺陷相关的心脏变化；(Ii)评估这些变化是否源于对正常心脏特定发育表观遗传计划的修改；(Iii)表征因调控心脏发育的基因突变而导致已知单倍素充足而加剧心脏病的基因-基因-环境相互作用；(Iv)利用计算机工具建立不同的心脏表观遗传程序、基因表达调控变化和子宫内暴露TCDD之间的因果关系。我们发现，AHR在发育过程中协调一个复杂的调控靶点网络，负责实现和维持心脏动态平衡。在这个网络中的关键是Nkx2-5，它编码一种心脏同源框转录因子，它位于心脏发育所必需的多个基因的上游。Nkx2-5在小鼠ES细胞和分化小鼠胚胎中被TCDD依赖的AHR激活抑制。在人类和小鼠中，NKX2.5基因多态性导致与先天性心脏畸形相关的NKX2-5单倍体功能不全，在独立的流行病学研究中，这种畸形与母亲在怀孕期间接触二恶英和多氯联苯有关。我们提出的假设是，在发育过程中暴露于二恶英会将内源性AHR功能重定向毒性/适应性反应，从而抑制NKX2-5及其靶基因的表达，并扰乱心肌细胞分化，重述由NKX2.5单倍体功能不全导致的人类先天性心脏畸形和成人心脏病。先天性心脏病是人类最常见的出生缺陷类型，是新生儿/婴儿死亡的主要原因，也是成人心功能不全的主要来源。这项工作的结果将确定 AHR在心脏发育和调节子宫毒性和心脏病中的作用，表征在子宫内暴露于环境因素TCDD如何影响心脏发育的表观遗传程序，并确定可能加剧心脏病易感性的基因-环境相互作用。

DESCRIPTION (provided by applicant): This application is directed at the study of gene-environment interactions regulated by the Ah receptor (AHR) during embryonic development and at their consequences in adult disease. Human exposure to organ chlorinated Ah receptor ligands, such as dioxin, has been epidemiologically associated with a number of toxicological outcomes and diseases, of which developmental abnormalities and mortality from cardiovascular disease are preeminent. While prevailing scientific evidence suggests that these outcomes are mediated by AHR activation, the molecular mechanisms by which AHR ligands exert their effects in humans remain to be identified. We propose to identify these mechanisms and to provide a biological test of the causal connection between AHR, fetal exposure to dioxin and cardiovascular disease. Our immediate objectives are, (i) to determine if developmental exposure of mice to TCDD or ablation of the Ahr gene causes cardiac changes associated with physiological deficits in adult life; (ii) to assess if these changes result from modifications to he the normal heart-specific developmental epigenetic program; (iii) to characterize gene-gene-environment interactions that exacerbate cardiac disease resulting from known haploin sufficiency caused by mutations in genes that regulate cardiac development; and (iv) to use computational tools to build causal relationships between variant cardiac epigenetic programs, gene expression regulatory changes, and TCDD exposure in utero. We have found that the AHR coordinates a complex regulatory target network during development responsible for attainment and maintenance of cardiac homeostasis. Key in this network is Nkx2-5, coding for a cardiac homeobox transcription factor that lies genetically upstream of multiple genes essential for heart development. Nkx2-5 is repressed by TCDD-dependent AHR activation in mouse ES cells and in differentiating mouse embryos. In humans and mice, NKX2.5 polymorphisms cause NKX2-5 haploinsufficiency associated with congenital cardiac malformations which, in independent epidemiologic studies have been associated with maternal exposure to dioxins and polychlorinated biphenyls during pregnancy. We propose to explore the hypothesis that exposure to dioxin during development redirects endogenous AHR functions towards toxic/adaptive responses that depress expression of NKX2-5 and its target genes and disrupt cardiomyocyte differentiation, recapitulating the congenital cardiac malformations and adult cardiac disease resulting from NKX2.5 haploinsufficiency in humans. Congenital cardiac disease is the most common type of human birth defect, the leading cause of neonatal/infant mortality, and a major source of adult cardiac insufficiency. Results from this work will establish the role of AHR in cardiac development and in mediating in utero toxicity and heart disease, characterize how in utero exposure to an environmental agent, TCDD, affects the epigenetic programing of heart development, and identify gene-environment interactions that may aggravate heart disease susceptibility.