MYOCARDIALIZATION AND EPICARDIALIZATION OF CUSHION TISSUE

心脏发育中隔膜和瓣膜的形成是关键的形态发生事件，使最初单一的胚胎心管发育成一个复杂的四腔心脏，支持两种不同的血液循环。这种发展包括心内膜垫的重塑，和(2)心外膜化，即心外膜来源的细胞迁移到垫层组织中。初步数据表明，这两个过程中的任何一个过程的扰动都可能导致心脏畸形，涉及发育中的流出道(OFT)和房室(AV)功能。本项目目标1中提出的研究旨在解决整体工作假说，即心肌化是房室交界处节段和间隔对齐的“驱动力”。本研究的具体目的是(1)阐明转化生长因子β(TGFbeta)在心肌化调节中的作用，并验证这样一种假说：流出道中TGFbeta信号通路的紊乱将导致心肌化的紊乱，从而导致一系列特殊的先天性畸形，包括双出口右心室(DORV)和双入口左心室(DILV)；以及(2)描述心肌化诱导的线曲重构导致房室管向右扩张，从而导致右心房和右室之间的连接。在本申请的AIM 2中提出的研究重点是心外膜衍生细胞(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在调节心内膜垫间充质细胞的转化、增殖和分化中起着至关重要的作用。要研究的具体目标是：(1)检验房室瓣的正常发育依赖于EPDCs及时调节移入心内膜垫组织的假说；(2)检验EPDCs通过局部抑制心内膜到间充质细胞的转化和增殖以及促进分化来调节心内膜垫形成的假说。对这些目标的追求将进一步促进我们对构成正常心脏发育基础的分子和细胞事件的了解，并将导致对可能导致先天性心脏病的过程以及其中缓冲组织的作用的新的见解。

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.