MYOCARDIALIZATION AND EPICARDIALIZATION OF CUSHION TISSUE

在发育中的心脏中，隔膜和瓣膜的形成是至关重要的形态发生事件，使最初的单个胚胎心管发育成复杂的四腔心脏，支持两种不同的血液循环。这种发展包括心内膜缓冲层的重塑，以及(2)心外膜化，即心外膜来源的细胞迁移到缓冲组织中。初步数据表明，任何一个过程的扰动都可能导致心脏畸形，包括发育中的流出道（OFT）和房室（AV）功能。本项目AIM 1中提出的研究旨在解决心肌化是房室连接处节段性和间隔性排列的“驱动力”这一总体工作假设。本研究的具体目标是：(1)阐明tgf β在心肌化调控中的作用，并验证对流出道tgf β信号通路的扰动将导致心肌化的扰动，从而导致双出口右心室（DORV）和双进口左心室（DILV）等特定先天性畸形的假设；(2)心肌化诱导的线性曲率重构导致房室管向右扩张，从而连接右心房和右心室。本应用的AIM 2中提出的研究重点是心外膜来源细胞（EPDCs）在瓣膜间隔形态发生中的作用。这里的中心工作假设是EPDCs在心内膜缓冲的间充质细胞转化、增殖和分化的调节中起关键作用。研究的具体目的是：(1)验证房室瓣膜的正常发育依赖于EPDCs及时迁移到心内膜缓冲组织的假设；(2)验证EPDCs通过局部抑制心内膜细胞向间充质细胞的转化和增殖以及促进分化来调节心内膜缓冲形成的假设。对这些目标的追求将进一步推进我们对正常心脏发育背后的分子和细胞事件的认识，并将对导致先天性心脏病的过程及其缓冲组织的作用产生新的见解。

The formation of septa and valves in the developing heart are crucial morphogenetic events that allow the initially single, embryonic cardiac tube to develop into a complex 4-chambered heart, supporting two different blood circulations. This development involves remodeling of the endocardial cushions, and (2) epicardialization, the migration of epicardially derived cells into the cushion tissues. Preliminary data indicate that perturbation of either process can lead to cardiac malformations involving the developing outflow tract (OFT) and atrioventricular (AV) function. The studies proposed in AIM 1 of this project are designed to address the overall working hypothesis that myocardialization is the "driving force" of segmental and septal alignment of the AV junction. The specific goals in this aim are (1) to elucidate the role of TGFbeta in the regulation of myocardialization and to test the hypothesis that perturbation TGFbeta signaling pathways in the outflow tract will lead to perturbation of myocardialization resulting in a specific set of congenital malformations including double outlet right ventricle (DORV) and double inlet left ventricle (DILV), and (2) to describe the myocardialization-induced remodeling of the linear curvature leading to the rightward expansion of the atrioventricular canal resulting in the connection between right atrium and right ventricle. The studies proposed in AIM 2 of this application focus on the role of epicardial derived cells (EPDCs) in valvuloseptal morphogenesis. The central working hypothesis here is that EPDCs play a crucial role in the regulation of mesenchymal cell transformation, proliferation, and differentiation of the endocardial cushions. The specific goals to be studied are (1) to test the hypothesis that proper development of the atrioventricular valves relies on timely regulated immigration of EPDCs into the endocardial cushion tissues, and (2) to test the hypothesis that EPDCs regulate endocardial cushion formation by local inhibition of endocardial-to-mesenchymal cell transformation and proliferation, and by promotion of differentiation. Pursuit of these aims will further advance our knowledge of the molecular and cellular events that underlie normal cardiac development, and will lead to new insights in the processes that can cause congenital heart disease and the role of the cushion tissues therein.