Transgenic Models of Ah Receptor Action

描述（由申请人提供）：芳烃受体（AHR）是一种配体激活的转录因子，可介导多环芳烃（PAHs）、卤代二恶英（“二恶英”）、-二苯并呋喃、-联苯（PCBs）和-二苯基醚的生物效应。由于AHR信号在大量环境污染物的急性毒性、致畸和致癌性中的核心作用，有关AHR信号的机制信息被监管机构用来确定这些污染物的可接受暴露水平。该提案的首要假设是，至少存在三种不同的AHR信号通路，它们对人类种群和脊椎动物物种具有毒理学意义。我们提出，这三种途径可以通过它们对靶细胞群中转录谱的独特影响来区分，这些途径可以根据它们对AHR部分激活的依赖、它们的细胞背景以及它们通过AHREs增强子元件对基因表达的影响来进一步定义。本提案的目标是确定反映暴露于激动剂及其诱导的毒性反应的生物标志物。我们将通过在新型重组小鼠模型的肝细胞和内皮细胞区室中鉴定低亲和力和高亲和力的AHREs来实现这一目标。为此，我们提出了以下具体目标：具体目标1：在胚胎干细胞中使用基因靶向来产生来自配体反应版本Ahr的重组等位基因。特异性目的2：证明AHR的细胞表达和浓度的重要性。具体目标3：使用基因组方法对高亲和力和低亲和力的AHRE电池进行分类。具体目标4：提供环境AHR激动剂可以刺激内源性AHR通路的证据。我们提出，这项工作的结果将提供新的模型，为人类二恶英毒性的机制提供信息，表征毒性的DNA特征，并测试一个新的假设，即发育毒性是由内源性AHR通路的干扰引起的。总的来说，这些研究将为更准确和信息丰富的人类风险评估奠定基础。

DESCRIPTION (provided by applicant): The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that mediates the biological effects of polycyclic aromatic hydrocarbons (PAHs), halogenated-dioxins ("dioxins"), - dibenzofurans, -biphenyls (PCBs), and -diphenylethers. Because of its central role in acute toxicity, teratogenesis and carcinogenesis of a large number of environmental contaminants, mechanistic information about AHR signaling is used by regulatory agencies to establish acceptable exposure levels for these pollutants. The overarching hypothesis of this proposal is that at least three distinct AHR signaling pathways exist that are of toxicological significance to human populations and vertebrate species in general. We propose that these three pathways can be distinguished by their unique impacts on transcriptional profiles within target cell populations and that these pathways can be further defined based upon their dependence on fractional activation of the AHR, by their cellular context, and their influence on gene expression through enhancer elements known as AHREs. The goal of this proposal is to identify biomarkers that reflect exposure to agonists and their induced toxic responses. We will accomplish this through the identification of low and high affinity AHREs in the hepatocyte and endothelial cell compartments of novel recombinant mouse models. To these ends, we propose the following specific aims: Specific Aim 1: Use gene targeting in ES cells to generate recombinant alleles derived from a ligand responsive version of Ahr. Specific Aim 2: Demonstrate the importance of the cellular expression and concentration of AHR. Specific Aim 3: Classify the high and low affinity AHRE batteries using genomic approaches. Specific Aim 4: Provide evidence that environmental AHR agonists can stimulate the endogenous AHR pathway. We propose that the results of this effort will provide new models that will inform the mechanism of dioxin toxicity in humans, characterize DNA signatures of toxicity, and test a novel hypothesis that developmental toxicity arises from interference with the endogenous AHR pathway. Collectively these studies will set the stage for more accurate and informative risk assessment in man. PUBLIC HEALTH RELEVANCE: This project aims to understand the mechanisms of AHR-mediated transcriptional activation which leads to the adaptive, toxic, and developmental consequences of dioxin exposure and to search for biomarkers that are predictive of these disparate outcomes. These experiments will allow more relevant assessments of AHR-mediated dioxin toxicity as well as generate biomarkers predictive for relevant endpoints of dioxin exposure.