Fox genes in arterial-venous endothelial cell identity

描述(申请人提供)：在成人循环系统中，动脉和静脉在解剖学上是不同的，以前人们认为动脉和静脉内皮细胞的分化是由于血压和血流方向等血液动力学因素的影响而产生的。然而，最近的证据表明，动脉和静脉的规范/分化是由活跃的循环开始之前的遗传机制控制的。这一事件发生在血管重塑之前，动脉和静脉的规范/分化受损导致血管重塑失败。尽管已有研究表明多种信号系统如血管内皮生长因子、Notch和eaffin信号通路参与了这一过程，但转录因子如何调控这些基因表达的分子机制仍有待阐明。我们之前已经证明，编码密切相关的Fox转录因子Foxc1和FOXC2的两个基因在重叠的血管内皮细胞和间充质细胞中表达。缺乏Foxc1或FOXC2的胚胎，以及大多数复合杂合子，在早产或围产期死亡时都会出现类似的异常表型，包括心血管系统的缺陷。复合Foxc1；FOXC2纯合子比单一纯合子死亡更早，缺陷也更严重。最重要的是，复合纯合子存在动静脉畸形和血管重塑失败，在复合纯合子的内皮细胞中，Notch信号基因和ewitinB2下调。这些数据导致了一个中心假设，即Foxc1和FOXC2在动静脉细胞命运决定/分化过程中发挥着剂量依赖的、相互作用的作用。这项资助的目标之一是测试FOXC蛋白是否作用于血管内皮生长因子信号的下游，以调节动脉-静脉特性(目标1)。将通过(A)分析与Tie2-Cre小鼠杂交的内皮细胞中Foxc1和FOXC2的条件复合突变，以及(B)Tie2-Foxc转基因小鼠与复合Foxc1；FOXC2突变(AIMS 2)杂交的救援实验来检验所提出的假设。最终确定在动静脉分化过程中受foxc1和foxc2调控的直接靶基因(S)(目标3)。阐明Foxc1/c2在血管发育过程中发挥作用的分子机制将有助于我们了解基因如何协同控制哺乳动物的心血管发育，并有助于更好地理解人类先天缺陷。

DESCRIPTION (provided by applicant): Arteries and veins are anatomically distinct within the adult circulatory system, and it was previously thought that the differentiated identities of arterial and venous endothelial cells arose in response to hemodynamic forces such as blood pressure and the direction of blood flow. However, recent evidence suggests that the specification/differentiation of arteries and veins is governed by genetic mechanisms before the active onset of circulation. This event occurs before remodeling of blood vessels, and impaired specification/differentiation of arteries and veins leads to failure to remodel blood vessels. Although it has been shown that several signaling systems such as the VEGF, Notch, and ephrin signaling pathways are involved in this process, molecular mechanisms of how transcription factors function to regulate expression of such genes remain to be elucidated. We have previously shown that the two genes encoding closely related Fox transcription factors, Foxc1 and Foxc2, are expressed in overlapping populations of cells contributing to the endothelial and mesenchymal cells of the blood vessels. Embryos lacking either Foxc1 or Foxc2, and most compound heterozygotes, die pre or perinatally with similar abnormal phenotypes, including defects in the cardiovascular system. Compound Foxc1; Foxc2 homozygotes die earlier and with much more severe defects than single homozygotes alone. Most importantly, compound homozygotes have arteriovenous malformations and the failure of blood vessels to remodel, and in the endothelial cells of compound homozygotes Notch signaling genes and ephrinB2 are downregulated. These data lead to the central hypothesis that Foxc1 and Foxc2 play dose-dependent, interactive roles in the process of arterial-venous cell fate determination/differentiation. One of the goals of this grant is to test whether Foxc proteins act downstream of VEGF signaling to regulate arterial-venous identity (Aim 1). The proposed hypothesis will be tested by (a) analyzing conditional compound mutants of Foxc1 and Foxc2 in endothelial cells crossed with Tie2-Cre mice and (b) rescue experiments in which Tie2-Foxc transgenic mice are crossed with compound Foxcl; Foxc2 mutants (Aims 2). Finally, direct target gene(s) regulated by Foxc1 and Foxc2 in the process of specification/differentiation of arteries and veins will be identified (Aim 3). Elucidating the molecular mechanisms of how Foxcl/c2 function during vascular development will significantly contribute to our knowledge of how genes cooperate to control mammalian cardiovascular development and will lead to a better understanding of human congenital defects.