Molecular Regulation of Vein Graft Adapation

描述（由申请人提供）：静脉移植物成功长期适应动脉环境而无过度内膜增厚的机制仍不完全清楚。Ephrin-Eph途径的几个成员最近被描述为血管身份的发育特异性关键决定因素，其中Ephrin-B2配体是动脉的胚胎决定因素，Eph-B4受体是静脉的胚胎决定因素。我们最近在人类和大鼠中发现，Eph-B4表达减少和静脉特性丧失与静脉移植物适应过程中内膜增厚相关，并且VEGF-A是内膜增厚的上游抑制剂。此外，我们发现在人类和大鼠静脉移植物适应过程中血管保护蛋白Nogo-B的量增加。然而，目前尚未确定成人血管特异性基因中是否存在可塑性，Ephrin-Eph通路是否在静脉移植物适应动脉环境期间起机械作用，或者Nogo-B是否与Eph-B4信号通路相关。我们提出了令人兴奋的新数据：1）在静脉移植物适应的小鼠模型中，Eph-B4基因表达和免疫反应蛋白的减少与内膜增厚相关; 2）我们可以在体内操纵Eph-B4信号传导以直接测试Eph-B4在小鼠静脉移植物适应中的作用; 3）Nogo-B抑制静脉移植物适应期间的内膜增厚;和4）Nogo-B蛋白在用针对VEGF-A的siRNA处理的静脉移植物中增加，连接Nogo-B途径与VEGF-A-Eph-B4途径。我们假设，静脉特异性基因表达减少，而动脉特异性基因表达不同时导致内膜过度增厚，最终导致静脉移植失败。我们将通过以下具体目标来测试我们的假设：目标I。确定Eph-B4信号传导是否在静脉移植物适应过程中介导内膜增厚。Aim II.确定VEGF-A抑制内膜增厚是否通过调节血管特性和Eph-B4表达介导。Aim III.确定Nogo-B在静脉移植物适应过程中的血管保护作用是否通过Eph-B4功能调节介导。这些研究是创新的，因为以前没有在小鼠中进行静脉移植物身份的分析，并且以前没有在成人中证明Eph-B4通路的可塑性。在这些研究完成后，我们期望确定Eph-B4在静脉移植物适应中的作用，并确定通过改变血管特性来限制静脉移植物适应期间内膜增厚的策略是否将是人体临床试验的新方法。

DESCRIPTION (provided by applicant): The mechanisms of successful long-term vein graft adaptation to the arterial environment without excessive intimal thickening are still not completely understood. Several members of the Ephrin-Eph pathway have recently been described as developmentally specified critical determinants of vessel identity, with Ephrin- B2 ligand an embryonic determinant of arteries and Eph-B4 receptor an embryonic determinant of veins. We have recently shown in both humans and rats that diminished Eph-B4 expression and loss of venous identity is associated with intimal thickening during vein graft adaptation, and that VEGF-A is an upstream inhibitor of intimal thickening. In addition, we showed increased amounts of the vasculoprotective protein Nogo-B during both human and rat vein graft adaptation. However, it is currently not established whether plasticity exists in vessel specification genes in adults, whether the Ephrin-Eph pathway plays a mechanistic role during vein graft adaptation to the arterial environment, or whether Nogo-B is linked to Eph-B4 signaling pathways. We present our exciting new data that: 1) diminished Eph-B4 gene expression and immunoreactive protein is associated with intimal thickening in the mouse model of vein graft adaptation; 2) we can manipulate Eph-B4 signaling in vivo to directly test the role of Eph-B4 in vein graft adaptation in mice; 3) Nogo-B inhibits intimal thickening during vein graft adaptation; and 4) Nogo-B protein is increased in vein grafts treated with siRNA directed against VEGF-A, linking the Nogo-B pathway with the VEGF-A-Eph-B4 pathway. We hypothesize that decreased expression of venous specification genes without concomitant expression of arterial specification genes leads to excessive intimal thickening, and ultimately vein graft failure. We will test our hypothesis with the following specific aims: Aim I. To determine whether Eph-B4 signaling mediates intimal thickening during vein graft adaptation. Aim II. To determine whether VEGF-A inhibition of intimal thickening is mediated by regulation of vessel identity and Eph-B4 expression. Aim III. To determine whether the vasculoprotective effects of Nogo-B during vein graft adaptation are mediated by regulation of Eph-B4 function. The studies are innovative in that analyses of vein graft identity have not been previously performed in mice, and plasticity of the Eph-B4 pathway has not been previously demonstrated in adults. At the completion of these studies, we expect to identify a role for Eph-B4 in vein graft adaptation and to determine whether strategies to limit intimal thickening during vein graft adaptation by altering vessel identity will be a novel approach for a human clinical trial.