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

描述（由申请人提供）：本申请旨在研究胚胎发育过程中Ah受体（AHR）调控的基因-环境相互作用及其在成人疾病中的影响。人类暴露于器官氯化Ah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死亡率最为突出。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配体在人体中发挥作用的分子机制仍有待确定。我们建议确定这些机制，并提供AHR、胎儿暴露于二恶英和心血管疾病之间因果关系的生物学测试。我们的直接目标是：(i)确定小鼠在发育过程中暴露于TCDD或Ahr基因消融是否会导致与成年期生理缺陷相关的心脏变化；（ii）评估这些变化是否源于正常心脏特异性发育表观遗传程序的改变；（iii）表征基因-基因-环境相互作用，这种相互作用加剧了由调节心脏发育的基因突变引起的已知单倍蛋白充足性导致的心脏病；（iv）使用计算工具建立变异心脏表观遗传程序、基因表达调控变化和子宫内TCDD暴露之间的因果关系。我们发现，在发育过程中，AHR协调了一个复杂的调控目标网络，负责实现和维持心脏稳态。该网络的关键是Nkx2-5，编码心脏同源盒转录因子，该因子位于心脏发育所必需的多个基因的遗传上游。Nkx2-5在小鼠胚胎干细胞和分化小鼠胚胎中受到tcdd依赖性AHR激活的抑制。在人类和小鼠中，NKX2.5多态性导致与先天性心脏畸形相关的NKX2-5单倍功能不全，独立流行病学研究表明，先天性心脏畸形与母亲在怀孕期间暴露于二恶英和多氯联苯有关。我们建议探索这样一种假设，即在发育过程中暴露于二恶英将内源性AHR功能重定向为毒性/适应性反应，从而抑制NKX2-5及其靶基因的表达，破坏心肌细胞分化，概括人类因NKX2.5单倍不全导致的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，也是成人心脏功能不全的主要原因。这项工作的结果将确定

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.