CARDIOVASCULAR REMODELING MEDIATED BY RXRa RECEPTORS

与心内膜垫组织的形成和重塑相关的心血管缺陷在美国每年占先天性心脏病的很大比例[1.2]。整合了增殖、分化和凋亡过程的分子机制对管状心脏适当重塑形成四腔器官的作用尚不清楚。与心内膜垫组织向瓣膜结构重塑相关的复杂过程涉及心肌、内皮、间充质、神经脊和心外膜来源的多种细胞系。重塑事件，如上皮到间质的转化，以缓冲组织和心肌化的流出道和房室管是这些过程的精确协调的结果。维甲酸X受体α基因敲除(RXRpha-KO)小鼠模型在阐明这些关系和帮助确定先天性心脏缺陷的原因方面显示出相当大的希望。在胚胎发育的第13.5天，RXRpha-KO胚胎表现出类似于人类先天性心脏病的心内膜融合组织和脑室畸形的频谱[3.5]。初步证据表明，RXRpha-KO胚胎心脏的增殖减少，细胞凋亡增加。此外，在RXRpha-KO胚胎中，我们发现心脏中转化生长因子-β2的mRNA和蛋白水平升高。因此，我们的假设是，RXRα在流出道垫组织、房室管和心室肌的重构过程中整合了增殖、分化和凋亡的过程，并且转化生长因子-β2以RXRα依赖的方式参与了这些过程。这一建议的具体目的是：1)检验圆锥干和房室垫上皮细胞向间充质细胞转化是RXRα依赖的假设。Ii)确定RXRα在圆锥干和脑室间隔过程中的增殖和凋亡过程中的作用。Iii)验证以下假设：在心脏发生过程中RXRpha表达中断会导致心脏缺陷，这种缺陷是TGFbeta2依赖的。

Cardiovascular defects associated with the formation and remodeling of endocardial cushion tissue accounts for a large proportion of congenital heart disease in the United States each year [1.2]. The molecular mechanisms integrating the processes of proliferation, differentiation, and apoptosis for proper remodeling of the tubular heart to form the four- chambered organ is not clear. The complex processes associated with remodeling of endocardial cushion tissue into valvular structures involves multiple cell lineages of myocardial, endothelial, mesenchymal, neural crest, and epicardial origins. Remodeling events such as epithelial-to- mesenchymal transformation to cushion tissue and myocardialization in the outflow tract and atrioventricular canal are the result of a precise coordination of these processes. The retinoid X-receptor alpha knockout (RXRalpha-KO) mouse model shows considerable promise at clarifying these relationships and aiding in the determination of the causes of congenital heart defects. At embryonic day (E) 13.5, RXRalpha-KO embryos display a spectrum of endocardial fusion tissue and ventricular chamber malformations analogous to human congenital heart defects [3.5]. Preliminary evidence indicates there is a reduced proliferation and increased apoptosis in RXRalpha-KO embryonic hearts. Moreover,, in RXRalpha-KO embryos, we found elevated levels of TGF-beta2 mRNA and protein in the heart. Thus, our hypothesis is that RXRalpha functions to integrate the processes of proliferation, differentiation, and apoptosis during remodeling of cushion tissue in the outflow tract, AV canal, and ventricular myocardium and that TGF-beta2 contributes to these processes in an RXRalpha-dependent manner. The Specific Aims of this proposal are: 1) To test the hypothesis that epithelial-to-mesenchymal cell transformation in the conotruncal and atrioventricular cushions is RXRalpha-dependent. II) To determine the role of RXRalpha in the processes of proliferation and apoptosis during septation of the conotruncus and ventricular chambers. III) To test the hypothesis that disruption of RXRalpha expression during cardiogenesis results in cardiac defects that are TGFbeta2 dependent.