Molecular signaling in aortic valve development and congenital aortic valve defect

摘要 正常的主动脉瓣是三尖瓣，具有三个小叶，其在移植过程中来源于多个细胞系。 胚胎发生主动脉瓣的结构是由基因控制的，瓣膜中的单个细胞- 形成场会根据位置和环境线索来完善它们的命运和功能。遗传 改变细胞-细胞和细胞-环境信号的突变可以破坏发育过程， 导致异常主动脉瓣，例如二叶主动脉瓣（BAV）。影响约2%的 在美国一般人群中，BAV是最常见的先天性心脏病。三分之二融合 在胚胎发生过程中，一个小叶或一个小叶的缺失导致各种BAV亚型。出生后， 超过一半的BAV患者发展为钙化性主动脉瓣疾病，且无有效药物，而BAV亚型 有各种心脏并发症，决定了疾病的结局。关于International Bicuspid Aortic 正在建立瓣膜联盟（BAVCon），以确定人类、动物模型中BAV的遗传原因 的BAV是迫切需要阐明形态和细胞机制的人BAV，以及 控制主动脉瓣模式的分子信号，以确定疾病的治疗靶点 预防为此，我们已经产生了两种具有不同信号传导缺陷的BAV小鼠模型， 异常小叶在第一个模型中，敲除瓣膜内皮细胞（VECs）中的Notch受体1（Notch 1）， 概括了最常见的人类BAV亚型-左和右冠状动脉小叶的融合，其主要是 通过上皮细胞向间充质细胞转化而衍生自VEC。该模型还显示，NOTCH 1- 来自VEC的TNF α信号传导控制瓣膜间充质细胞（VMC）的凋亡。在第二种模式中，删除 VECs中SRY盒转录因子17（Sox 17）导致一种罕见但更严重的BAV类型-缺乏 非冠状动脉瓣叶，其中VMC主要来自第二心脏野（SHF）-衍生 在心肌细胞中，图案化缺陷与VEC-VMC PDGFB信号传导减少有关。基于 根据这些发现，我们假设协调的VEC-VMC信号控制正常的主动脉瓣模式， 在受影响细胞的起源和位置的背景下，它们的破坏导致各种BAV亚型。我们将 在两个目标中测试这个假设。目标1计划在正常情况下揭示协调的VEC-VMC信号网络 主动脉瓣图案化和识别在各种BAV亚型中被破坏的信号传导事件。Aim 2设计 揭示PDGF信号在正常主动脉瓣模式中的功能，并将其作为一个例子， 说明一个中断的信号事件如何改变细胞的命运和功能，导致一个特定的BAV。成功 这些目标的实现将为BAV的发病机制提供新的见解，具有广泛的意义， 先天性心脏瓣膜病

ABSTRACT The normal aortic valve is tricuspid with three leaflets derived from multiple cell lineages during embryogenesis. Aortic valve patterning is genetically controlled where individual cells in the valve- forming field refine their fates and functions in response to positional and environmental cues. Genetic mutations that alter cell-cell and cell-environmental signals can disrupt the developmental process, leading to anomalous aortic valve, for example, bicuspid aortic valve (BAV). Affecting ~2% of the general population in US, BAV is the most common congenital heart defect. Fusion of two of three leaflets or absence of one leaflet during embryogenesis results in various BAV subtypes. After birth, over half of BAV patients develop calcific aortic valve disease with no effective medicine, while BAV subtypes have varied cardiac complications, which decide the disease outcome. With the International Bicuspid Aortic Valve Consortium (BAVCon) being established to identify the genetic causes of BAV in humans, animal models of BAV are critically needed to elucidate morphogenic and cellular mechanisms of human BAV, as well as molecular signals that control aortic valve patterning in order to identify therapeutic targets for disease prevention. To this end, we have generated two mouse models of BAV with distinct signaling defects and anomalous leaflets. In the first model, knocking out notch receptor 1 (Notch1) in valve endocardial cells (VECs) recapitulates the most common human BAV subtype – fusion of left and right coronary leaflets, which are mainly derived from VECs by epithelial to mesenchymal transformation. This model also reveals that the NOTCH1- TNFa signaling from VECs controls apoptosis of valve mesenchymal cells (VMCs). In the second model, deleting SRY-box transcription factor 17 (Sox17) in VECs results in a rare but more severe type of BAV – absence of non-coronary leaflet, of which VMCs arise predominantly from the second heart field (SHF)-derived cardiomyocytes, and the patterning defect is associated with reduced VEC-VMC PDGFB signaling. Based on these findings, we hypothesize that coordinated VEC-VMC signals control normal aortic valve patterning and their disruption leads to various BAV subtypes, in the context of the origin and location of affected cells. We will test this hypothesis in two Aims. Aim 1 is planned to reveal coordinated VEC-VMC signal networks during normal aortic valve patterning and identify signaling events that are disrupted in various BAV subtypes. Aim 2 is designed to uncover the functions of PDGF signaling in normal aortic valve patterning as well as use it as an example to illustrate how a disrupted signaling event can alters cell fate and function, leading to a specific BAV. Successful accomplishment of these Aims will provide new insights into BAV pathogenesis, with a broad implication in congenital heart valve disease.