Cardiac Conduction System Development

描述(由申请人提供)：有节奏的心跳需要心脏传导系统的适当发展。这种特殊的心脏组织由不同的亚成分组成，包括起搏的窦房结(SA)、快速传导的结间道(INT)、慢传导的房室结(AV)、房室束和快速传导的浦肯野纤维。在人类中，INT和房室结的组织缺陷可能分别是房颤和房室传导阻滞的原因，从而导致显著的心血管并发症和死亡率。关于这些不同的导电元件是如何被诱导、图案化并集成到一个完整的CCS网络中的，人们知之甚少。我们以前已经证明，血管细胞因子内皮素(ET)来源于心内膜和动脉内皮细胞，并诱导心室肌细胞分化为快速传导的浦肯野纤维。然而，诱导和模式化其他CCS亚成分的机制，如INT和AV-Node，在很大程度上仍然难以捉摸。我们的初步数据表明，内皮素转换酶-1(ECE1)和G蛋白偶联ET受体(ETRs)在鸡胚胎心脏的心房中都有表达，ECE1是从其前体产生具有生物活性的ET所必需的。此外，一组独特的由快速传导浦肯野纤维表达的基因出现在心房内ECE1阳性的心内膜细胞上。相反，尽管ECE1和ET前体表达最高，但在房室连接处没有检测到快导细胞类型的基因。重要的是，我们发现ETR在房室交界处不表达。这些数据提出了两个中心假设：(1)快速传导的心房INT和室浦肯野系统具有共同的特征，并通过共同的诱导信号的活动而产生；(2)房室交界处缺乏ETR抑制了心肌细胞对ET信号的反应性，从而创建了一个没有快速传导细胞分化的区域。这项提议将在实验上验证这些假说，并将为鉴定INT特有的细胞(目标1)、胚胎心房肌细胞对诱导信号做出反应并进入快速传导细胞命运的能力(目标2)以及在胚胎心脏中产生一个没有快速传导细胞分化的区域的分子机制(目标3)提供第一个分子基础。这项研究的结果将作为理解正常和异常INT形成的基础，并为解决仅限于房室连接的慢传导细胞分化的机制奠定基础。与公共卫生相关：传导缺陷，包括房颤和房室传导阻滞，在美国影响着数百万人，但目前的治疗方法仅限于药物治疗、射频消融和植入性设备。缺乏有效的治疗选择是导致心律失常疾病继续流行的原因。这项拟议的研究将探索调控这些必要心脏组织形成的分子机制，并可能为未来的治疗方法提供基础。

DESCRIPTION (provided by applicant): Rhythmic heartbeat requires the proper development of the cardiac conduction system. This specialized cardiac tissue consists of distinct subcomponents, including the pacemaking sinoatrial (SA) node, fast conducting internodal tract (INT), slow conducting atrioventricular (AV) node, AV-bundles, and fast conducting Purkinje fibers. In human, a defect in the organization of the INT and AV-node can be a cause of atrial fibrillation and AV block, respectively, with consequent significant cardiovascular morbidity and mortality. Little is known about how these distinct conducting elements are induced, patterned, and integrated into a complete CCS network. We have previously shown that the vascular cytokine endothelin (ET) is derived from endocardial and arterial endothelial cells and induce ventricular myocytes to differentiate into fast conducting Purkinje fibers. However, mechanisms that induce and pattern other CCS subcomponents, such as the INT and AV-node, remain largely elusive. Our preliminary data show that endothelin converting enzyme-1 (ECE1), which is necessary for production of biologically active ET from its precursor, and G protein-coupled ET-receptors (ETRs) are both expressed in the atrium of the embryonic chick heart. Furthermore, a unique set of genes that are expressed by fast conducting Purkinje fibers occurs along ECE1-positive endocardial cells in the atrium. By contrast, no fast conducting cell-type genes are detected at the AV-junction despite the highest expression of ECE1 as well as ET-precursor. Importantly, we have found that ETR expression is absent at the AV-junction. These data lead to the two central hypotheses: (1) Fast conducting atrial INT and ventricular Purkinje systems share common features and arise through the activity of a common inducing signal; and (2) The absence of ETRs at the AV-junction suppresses the responsiveness of myocytes to ET signal, thereby creating a zone free of fast conducting cell differentiation. This proposal will test these hypothesis experimentally and will provide the first molecular basis for identifying cells unique to the INT (Aim 1), the ability of embryonic atrial myocytes to respond to inductive signals and enter a fast conduction cell fate (Aim 2), and molecular mechanisms that generate a zone free of fast conducting cell differentiation in the embryonic heart (Aim 3). The outcome of this study will serve as the basis for the understanding of normal and aberrant INT formation and for addressing a mechanism that defines slow conduction cell differentiation exclusively to the AV-junction. PUBLIC HEALTH RELEVANCE: Conduction defects, including atrial fibrillation and AV-block, affect millions people in the US, but current treatments are limited to pharmacotherapy, radiofrequency ablation, and implantable devices. The lack of effective treatment options contributes to the continued prevalence of arrhythmic disease. The proposed study will explore the molecular mechanisms that regulate formation of these essential cardiac tissues and may provide a basis for future therapeutic approaches.