The toxin and hypoxia pathways in cardiogenesis

描述（由申请方提供）：已使用体外试验和细胞培养系证明了毒素和缺氧诱导因子应答（HIF）途径之间对共同异源二聚体伴侣Arnt/HIF 1b的竞争。越来越多的证据表明，这些途径在心血管发育的关键阶段起作用，包括冠状动脉血管的早期发育。毒素TCDD是毒素途径中AhR（芳香烃受体）的原型激动剂，可导致冠状血管的异常发育，并可能是TCDD诱导的扩张型心肌病的基础。我们的研究结果确定了流出道心肌作为心脏组织，其在与心肌细胞凋亡、VEGFR 2表达、HIF-1a核定位和冠状动脉血管内皮前体积累相一致的阶段和部位具有最低的氧分压（大多数缺氧）。此外，这种缺氧对于心脏的正常发育至关重要。当同时受到这两种压力时，正常发育期间的低氧张力和毒素暴露，在这个阶段和位点的分子和细胞事件可能特别容易受到信号分子如Arnt/HIF 1b的竞争，导致基因表达不平衡和发育异常。我们的工作假设是，毒素通路的激活将干扰正常的HIF信号和心脏发生所需的HIF诱导的基因表达。我们将比较在正常缺氧的鸟类胚胎心脏区域中，有和没有TCDD暴露的HIF反应基因的表达。我们还将通过病毒转染干扰卵内心肌细胞中的HIF 1a结合来特异性破坏HIF信号传导，并将心脏和冠状动脉血管表型与TCDD处理的胚胎进行比较。该分析有望揭示正常心脏和冠状血管发育的机制以及心脏毒性的病因。

DESCRIPTION (provided by applicant): Competition between the toxin and hypoxia inducible factor responsive (HIF) pathways for a common heterodimer partner Arnt/HIF1b has been demonstrated using in vitro assays and cell culture lines. Evidence is accumulating that these pathways act at critical stages of cardiovascular development including early development of the coronary vasculature. The toxin TCDD, the prototypical agonist for AhR (aryl hydrocarbon receptor) of the toxin pathway, causes abnormal development of the coronary vascular that precedes and may be the basis for TCDD-induced dilated cardiomyopathy. Our findings identify the outflow tract myocardium as the cardiac tissue with the lowest oxygen tension (most hypoxic) at stages and site coincident with cardiomyocyte apoptosis, VEGFR2 expression, nuclear localization of HIF-1a, and accumulation of endothelial precursors of the coronary vasculature. Furthermore, this hypoxia is critical for normal cardiac development. When simultaneously subjected to both stresses, low oxygen tension during normal development and toxin exposure, the molecular and cellular events at this stage and site may be particularly susceptible to competition for signaling molecules such as Arnt/HIF1b resulting in imbalanced gene expression and abnormal development. Our working hypothesis is that activation of the toxin pathway will interfere with normal HIF signaling and HIF-induced gene expression required for cardiogenesis. We will compare the expression of HIF responsive genes with and without TCDD exposure in normally hypoxic cardiac regions of the avian embryo. We will also specifically disrupt HIF signaling by interfering with HIF1a binding in cardiomyocytes in ovo by viral transfection and compare cardiac and coronary vascular phenotypes to that of TCDD-treated embryos. This analysis would be expected to uncover the mechanisms of normal cardiac and coronary vascular development as well as the etiology of cardiotoxicity.