Liver Regeneration as a Model for Angiogenesis

描述（由申请人提供）：血管生成是新血管从现有血管中萌发的过程，并要求血管内壁的特化常驻细胞内皮细胞（ECs）根据特定信号在空间和时间上增殖、迁移和分化。另一方面，血管生成直到最近才成为成人组织中血管生长的另一种机制，它是骨髓来源的循环EC前体（ECPs）归巢和移植到新生血管区域的结果。已知这两种情况在生长、损伤和修复的非常不同的条件下都发生在肝脏血管中，但每种情况的程度和它们在每种情况下进行的机制是完全未知的。该提案的总体目标是确定在肝脏环境下诱导血管生成与血管生成血管生长的特定生长因子信号事件，并确定随后诱导EPC募集和/或肝特异性窦状内皮细胞（SEC）开窗形态分化的微环境。两种临床相关的肝修复模式使我们能够在空间和时间上详细描述生长因子信号事件，并评估大鼠的窦状动脉超微结构和肝脏特异性SEC功能。目的1：在70%肝部分切除术（PHx）后，将在肝窦表面检查生长因子和微环境相互作用，因为在PHx术后96小时前，在没有EC增殖的情况下，肝细胞开始大量增殖，导致无血管肝灶。随后，SEC在这些无血管实质团簇中的增殖和浸润，以及正常肝脏结构的重建，为评估生理性血管生成提供了一个很好的模型。AIM II：血管生成和血管生成事件将使用异体肝移植模型（双杂交株和雌性到雄性移植，非GFP到GFP大鼠）同时进行检查，以确定SEC的来源（宿主vs移植物），并确定受体和供体参与SEC植入和/或增殖的程度。移植前，肝脏在冷缺血条件下储存18小时，移植后（热再灌注），大部分SEC立即从窦表面脱落。值得注意的是，在24小时内，SEC衬里几乎完全重新填充，至少部分来自ECPs，但微血管重塑、形态和功能改变在随后的几天内发生。对这两种系统的比较分析将阐明相似和不同的生长因子信号机制以及控制这些事件的微环境的作用，并可能导致治疗的优化，这将反映基于损伤的肝脏新生血管的具体要求。

DESCRIPTION (provided by applicant): Angiogenesis is the process whereby new blood vessels sprout from existing vessels and requires that the specialized resident cells lining the vasculature, the endothelial cells (ECs), proliferate, migrate and differentiate spatially and temporally in response to specific signals. Vasculogenesis, on the other hand, has only recently emerged as an alternative mechanism of blood vessel growth in adult tissues and is the result of homing and engraftment of circulating EC precursors (ECPs) of bone marrow origin to areas of neovascularization. Both events are known to occur within the liver vasculature under very different conditions of growth, injury and repair, but the extent of each and the mechanisms by which they proceed in each case is completely unknown. The overall goal of this proposal is to determine the specific growth factor signaling events that induce angiogenic versus vasculogenic blood vessel growth in the context of liver and determine the subsequent microenvironmental milieu that induces EPC recruitment and/or differentiation of the liver-specific sinusoidal endothelial cell (SEC) fenestrated morphotype. Two paradigms of clinically-relevant liver repair allow us to spatially and temporally detail the growth factor signaling events and evaluate sinusoidal ultrastructure and liver-specific SEC function in the rat. AIM I: Growth factor and microenvironmental interactions will be examined at the sinusoidal surface following 70% partial hepatectomy (PHx) since there is initially extensive hepatocyte proliferation in the absence of EC proliferation until 96 hr post-PHx, resulting in avascular hepatic foci. Subsequent proliferation and infiltration of the SEC into these avascular parenchymal clusters and reestablishment of the normal hepatic architecture provides a well-timed model for evaluating physiological angiogenesis. AIM II: Angiogenic and vasculogenic events will be examined concurrently using an allogeneic liver transplant model (dual cross strain and female to male transplants, non-GFP to GFP rats) to ascertain the source of SEC (host vs. graft) and determine extent of recipient and donor involvement in SEC engraftment and/or proliferation. Prior to transplantation, livers are stored under cold, ischemic conditions for 18 h, and upon transplantation (warm reperfusion), a majority of the SEC slough off immediately from the sinusoidal surface. Remarkably, within 24 hr, the SEC lining has nearly completely repopulated at least partially from ECPs, but microvascular remodeling, morphological and functional modification occurs over subsequent days. Comparative analysis of these two systems will elucidate both similar and dissimilar growth factor signaling mechanisms and the role of the microenvironment that control these events and potentially lead to optimization of therapies that will reflect the specific requirements for injury based liver neovascularization.