NO inhibits arterial injury after vascular procedures via adventitial stem cells

描述（由申请人提供）：新生内膜增生是导致血管介入失败的重要问题。导致新生内膜增生的经典动脉损伤反应描述了涉及内膜和中膜的过程，相对缺乏外膜的参与。然而，外膜不再被认为是动脉壁的简单结构组成部分。在过去的十年中，研究表明，来自外膜的许多细胞类型积极调节并促进新生内膜增生的发展，包括驻留和循环外膜干细胞和祖细胞。我们和其他人已经证明，NO是一种有效的抑制剂，通过调节不同方面的经典动脉损伤反应的新生内膜增生。然而，很少有人知道NO如何影响动脉壁外膜层损伤后。我们最近评估了整个动脉壁对损伤和暴露于NO的细胞反应。有趣的是，虽然NO阻止了新生内膜增生的发展并延迟了中膜的再增殖，但我们惊讶地发现NO实际上增加了外膜中的细胞结构。这种细胞构成的增加不是由于血管平滑肌细胞、成纤维细胞、肌成纤维细胞或炎性细胞的增加，而实际上可能是由于Sca 1+祖细胞等的增加。因此，考虑到外膜在调节动脉损伤反应中的重要作用，干细胞和祖细胞在此过程中的作用的最新发现，以及我们的初步数据，我们假设NO通过调节损伤后驻留和循环外膜干细胞和祖细胞的募集和表型分化来抑制新生内膜增生。此外，我们假设NO支持外膜干细胞和祖细胞分化为内皮样细胞，促进外膜新生血管形成。为了研究这些假设，我们的具体目标是：1）在体内表征NO对动脉损伤后的Sca 1+、CD 34+和flk-1+外膜干细胞和祖细胞群的影响; 2）在体外确定NO对Sca 1+、CD 34+和flk-1+外膜细胞群的影响;和3）在体内操作Sca 1+、CD 34+和flk-1+外膜细胞群，以确定NO介导的动脉损伤后新生内膜增生的抑制是否依赖于这些外膜细胞群。本提案中描述的创新研究将导致我们如何看待NO的外膜和血管生物学的变化，并提供一种新的机制，NO通过该机制调节新生内膜增生，这将导致开发新的策略来预防血管介入后的新生内膜增生和再狭窄。

DESCRIPTION (provided by applicant): Neointimal hyperplasia is a significant problem that results in the failure of vascular interventions. The classic arterial injury response that leads to the development of neointimal hyperplasia describes processes involving the intima and media with a relative lack of involvement of the adventitia. However, the adventitia is no longer considered a simple structural component of the arterial wall. In the last decade, research has shown that many cell types from the adventitia actively regulate and contribute to the development of neointimal hyperplasia, including resident and circulating adventitial stem and progenitor cells. We, and others, have demonstrated that NO is a potent inhibitor of neointimal hyperplasia through regulating different aspects of the classic arterial injury response. However, little is known about how NO affects the adventitial layer of the arterial wall following injury. We have recently assessed the cellular response throughout the arterial wall to injury and exposure to NO. Interestingly, while NO prevents the development of neointimal hyperplasia and delays repopulation of the media, we were surprised to find that NO actually increases cellularity in the adventitia. This increase in cellularity is not due to an increase in vascular smooth muscle cells, fibroblasts, myofibroblasts, or inflammatory cells, but may in fact be due to an increase in Sca1+ progenitor cells, among others. Thus, given the important role of the adventitia in regulating the arterial injury response, recent discoveries of the role of stem and progenitor cells in this process, and our preliminary data, we hypothesize that NO inhibits neointimal hyperplasia by regulating recruitment and phenotypic differentiation of resident and circulating adventitial stem and progenitor cells following injury. Furthermore, we hypothesize that NO supports differentiation of adventitial stem and progenitor cells into endothelial-like cells, contributing to adventitial neovascularity. To investigate these hypotheses, our specific aims are: 1) to characterize the effect of NO on Sca1+, CD34+, and flk-1+ adventitial stem and progenitor cell populations following arterial injury in vivo; 2) to determine the effect of NO on Sca1+, CD34+, and flk-1+ adventitial cell populations in vitro; and 3) to manipulate Sca1+, CD34+, and flk-1+ adventitial cell populations in vivo to determine if NO-mediated inhibition of neointimal hyperplasia following arterial injury is dependent on these adventitial cell populations. The innovative studies described in this proposal will result in a change in how we think about the adventitia and the vascular biology of NO, and provide a novel mechanism by which NO regulates neointimal hyperplasia that will lead to the development of new strategies to prevent neointimal hyperplasia and restenosis following vascular interventions.