Mechanotransduction in Neointimal Hyperplasia Formation in Arteriovenous Grafts

描述(由申请人提供)：移植静脉吻合口狭窄是用于血液透析的动静脉移植物(AVGs)失败的主要原因。目前，还没有明显预防或治疗原发AVGNH的临床治疗方法。动脉血流直接进入静脉的分流极大地改变了静脉的血液动力学。因此，AVG的NH敏感部位的流体剪应力(FSS)和壁周向应力(WCS)发生了明显的变化。我们认为这些血流动力学改变是动静脉曲张静脉吻合口NH发生的主要原因。本课题旨在了解动静脉曲张发展过程中的血流动力学规律。AVG环境中的详细FSS和WCS尚未完全了解。我们将使用最先进的基于图像的计算力学来表征这些应力，并将这些数据应用于设计实验来描绘机械转导路径。我们将集中讨论两个受体酪氨酸激酶(RTK)，血管内皮生长因子受体(VEGFR)和血小板衍生生长因子受体(PDGFR)在NH发病机制中的作用；以及II)转录因子E26-1(ETS-1)作为RTK激活的主要效应因子，导致NH形成的作用。我们的建议是基于我们的初步发现：在猪AVG模型中，VEGFR、PDGFR和ETS-1在NH易感部位上调；ii)RTK抑制剂Sunitinib抑制ETS-1的表达 3)在颈动脉球囊损伤的大鼠模型和自然动静脉瘘的小鼠模型中，ETS-1抑制可减少NH的形成。我们的假设如下：1)RTK和ETS-1的激活是由AVG吻合口旁静脉段FSS和WCS的增加启动的，FSS和WCS分别是由于血流增加和管壁扩张所致。2)VEGFR和PDGFR分别是血管内皮细胞和平滑肌细胞的主要机械感受器，它们分别介导FSS和WCS激活Ets-1。Iii)RTK激活和Ets-1激活是AVG中NH形成的关键事件。有三个具体目标：i)在猪模型中了解AVG NH易感部位和NH抵抗部位的力学环境差异。Ii)在灌流静脉培养模型中，确定增加FSS或WCS是否会增强RTK和ETS-1的激活，并随后促进NH的形成。Iii)探讨RTK和ETS-1是否介导了猪AVG模型中NH的形成。描述依赖RTK和Ets-1的机械转导途径，并探索这些途径在NH形成中的作用是新的。这一结果有可能广泛应用于其他血流改变的血管病理情况，包括房室瘘。该灌流器官培养系统可用于相关流动条件下的药物治疗研究。

DESCRIPTION (provided by applicant): Stenosis at the graft-vein anastomosis due to neointimal hyperplasia (NH) is the predominant cause of failure of arteriovenous grafts (AVGs) used for hemodialysis. Currently, there are no clinical therapies that significantly prevent or tret primary AVG NH. Shunting of arterial blood flow directly into the vein greatly alters the hemodynamics in the vein. Consequently, the fluid shear stress (FSS) and wall circumferential stress (WCS) at the NH-susceptible sites of AVGs are markedly altered. We propose that these hemodynamic changes are major contributors to NH development at the venous anastomosis of AVGs. This project aims to understand the hemodynamic regulation of NH development in AVGs. Detailed FSS and WCS in the AVG setting are not yet fully understood. We will use state-of-the-art image-based computational mechanics to characterize these stresses, and apply these data to design experiments to delineate mechanotransduction pathways. We will focus on i) the roles of two receptor tyrosine kinases (RTKs), vascular endothelial growth factor receptor (VEGFR) and platelet-derived growth factor receptor (PDGFR), as major mechanosensors in the pathogenesis of NH; and ii) the role of the transcription factor E twenty-six-1 (Ets-1) as the primary effector activated by RTK, leading to NH formation. Our proposal is based on our preliminary findings that i) VEGFR, PDGFR and Ets-1 are up-regulated in NH-susceptible sites in a porcine AVG model; ii) the RTK inhibitor sunitinib inhibits Ets-1 expression and NH development in a perfused vein organ culture model; iii) NH formation is reduced by Ets-1 inhibition in a rat model of carotid artery balloon injury and a mouse model of native arteriovenous fistula. Our hypotheses are as follows: i) The activation of RTK and Ets-1 is initiated by increases in FSS and WCS, as a result of increased blood flow and wall distention respectively, at the juxta-anastomotic vein segment of the AVG. ii) VEGFR and PDGFR are the primary mechanosensors in vascular endothelial cells and smooth muscle cells, respectively, that mediate Ets-1 activation by FSS and WCS. iii) RTK activation followed by Ets-1 activation is a critical event in NH formation in the AVG. There are three Specific Aims: i) Understand differences in the mechanical environment between the NH- susceptible and NH-resistant sites of AVG in a porcine model. ii) Determine in a perfused vein culture model whether increased FSS or WCS enhances RTK and Ets-1 activation and subsequently NH formation. iii) Explore whether RTK and Ets-1 mediate NH formation in a porcine AVG model. Delineation of the RTK- and Ets-1-dependent mechanotransduction pathways and exploration of the roles of these pathways in NH formation is novel. The results have the potential for broad applications in other vascular pathological conditions where there is altered blood flow, including AV fistulas. The perfused organ culture system can be used to investigate pharmacological therapies under relevant flow conditions.