The Role of Vascular Flt-1 in Endothelial-Pericyte Interactions

描述（由申请人提供）：血管形成需要一组内皮细胞对信号输入有异质反应。在发育过程中，内皮细胞对血管内皮生长因子(VEGF)-A信号的反应存在差异，从而形成网络扩张所需的表型。与肿瘤发生或糖尿病视网膜病变等病理状况相关的血管异常发育可能部分是由于内皮细胞异质性丧失所致。VEGF受体Flt-1 （VEGFR-1）通过可溶性异质异构体（sFlt-1）的异质表达促进网络形成，进而在空间上调节VEGF信号，为新生血管芽提供局部发芽指导（Chappell et al, 2009）。内皮细胞在血管发育中的表型异质性可能对血管发育的其他方面很重要，例如内皮细胞与血管周围细胞（周细胞）的相互作用。周细胞为成熟血管提供结构稳定性，内皮-周细胞相互作用的扰动有助于

DESCRIPTION (provided by applicant): Blood vessel formation requires a group of endothelial cells with heterogeneous responses to signaling inputs. During development, endothelial cells respond differentially to vascular endothelial growth factor (VEGF)-A signaling to adopt phenotypes required for network expansion. Abnormal vascular development associated with pathological conditions such as tumorigenesis or diabetic retinopathy likely results in part from loss of regulated endothelial heterogeneity. VEGF receptor Flt-1 (VEGFR-1) contributes to network formation via heterogeneous expression of the soluble isoform (sFlt-1) that in turn spatially regulates VEGF signaling to provide local sprout guidance to emerging vessel sprouts (Chappell et al, 2009). Phenotypic heterogeneity of endothelial cells in developing vessels is likely important for other aspects of vascular development, such as endothelial interactions with perivascular cells known as pericytes. Pericytes provide structural stability to maturing vessels, and perturbations in endothelial-pericyte interactions contribute to vascular pathologies. Thus, it is intriguing to speculate that endothelial phenotypic heterogeneity is modulated by Flt-1 regulation of VEGF signaling, and that aspects of this heterogeneity facilitate proper endothelial-pericyte interactions. One primary objective of this study therefore is to investigate how Flt-1 spatially regulates endothelial cell heterogeneity to establish proper vascular morphogenesis in vivo. Vascular morphology will be observed in developing mouse retinas with mosaic flt-1 expression via use of flt-1 conditional deletion mice. In vivo and in vito observations will then be used to generate a computational model for Flt-1 activity in regulating the phenotypic heterogeneity of endothelial cells and overall vessel morphology. In addition, the role of Flt-1 in spatially regulating endothelial-pericyte associations will be explored with in viro assays. In embryonic stem (ES) cell-derived vessels, VEGF signaling will be perturbed via genetic manipulation of flt-1 expression. Endothelial-pericyte interactions will be evaluated to characterize the spatial regulation of pericyte recruitment and investment. To assess the effect of altered spatial distribution of flt-1 expression on endothelial-pericyte interactions, mosaic vessels composed of wild-type (WT) and flt-1 mutant cells will be evaluated for pericyte investment. A computational model simulating how Flt-1 promotes vessel endothelial cell heterogeneity to regulate pericyte-endothelial cell interactions will be created as a tool to understand the biological consequences of disruptions in flt-1 expression (e.g. tumor setting). Observations from in vitro experiments will guide the construction and testing of this in silico model. Lastly, the mechanisms by which Flt-1 regulates pericyte-endothelial interactions in vivo will be characterized. Retinal vasculature from developing flt-1 conditional deletion mice will be evaluated for mosaic flt-1 expression and investment of pericytes. Simulations generated by the computer model for Flt-1 regulation of pericyte associations will provide a means for interpreting, analyzing, and advancing experimental observations and approaches.