Endoglin Regulates Endothelial Survival and Capillary Tube Stability

具体目标 内皮细胞中转化生长因子超家族信号转导调控 血管生成和血管形态形成的基本成分，包括 细胞增殖，毛细血管形成。转化生长因子-β超家族配体发挥其作用 内皮细胞特异性转化生长因子受体复合体ALK1的调节作用 (I型受体)和endoglin(辅受体)，以及普遍存在的I型转化生长因子-β 受体Alk5激活典型的Smad1/5/8和Smad2/3通路， 分别进行了分析。转化生长因子-β配体也通过非Smad信号通路，如MAPK 和PI3K/Akt，尽管潜在的机制仍不清楚。的关键作用 Endoglin和ALK1在内皮细胞转化生长因子信号转导中的作用受其突变的支持 导致人类血管疾病遗传性出血性毛细血管扩张症(HHT1 2)血管生成缺陷所致的胚胎致死表型 或ALK1在小鼠中被靶向删除，并通过endoglin的表达上调 在炎症和肿瘤诱导的血管生成过程中。虽然重要的生物学作用 对于endoglin的研究已经确立，endoglin在血管中发挥作用的分子基础 生物学的特征仍然很差。这里采用的是体外血管生成试验。 准确研究endoglin何时及如何调控内皮细胞毛细血管出芽 和管子的形成。比较endoglin缺失和野生型内皮细胞 Enoglin对血管内毛细血管的稳定性有不同的调节作用。 对其生理上相关的高亲和力配体转化生长因子-β和骨形态发生蛋白-9的反应。 具体地说，转化生长因子β导致毛细血管发芽和管状结构的退化， 主要是通过抑制依赖于endoglin的Akt信号。相反，内联 增强Akt信号对BMP-9的响应，促进毛细血管稳定。这些 结果归因于endoglin和 支架/运输蛋白，GIPC，因为破坏了它们的相互作用而取消了这种 内生素依赖效应。鉴于我最近报告了Smad的增强 1/5/8通过GIPC和endoglin发送信号，在 AKT和依赖于endoglin的Smad 1/5/8信号，我建议对其进行研究。 最后，我发现了内源性endoglin和Akt之间的一种新的相互作用，这是一个发现 这可能会产生内源性生物学的新方面。根据这些初步数据，我 提出以下假设：endoglin与GIPC联合促进 BMP-9依赖Akt激活稳定内皮毛细血管的血管生成 同时通过依赖转化生长因子β抑制Akt信号和细胞来破坏毛细血管的稳定 生存机制。这一假设将在目标中得到解决。 概述了两个具体的目标。

Specific Aims Transforming growth factor (TGF-¿) superfamily signaling in endothelial cells regulates essential components of angiogenesis and vascular morphogenesis, including proliferation and capillary tube formation. TGF-¿ superfamily ligands exert their regulatory effects through the endothelial cell specific TGF-¿ receptor complex, ALK1 (type I receptor) and endoglin (co-receptor), along with the ubiquitous type I TGF-¿ receptor, ALK5, to activate the canonical Smad 1/5/8 and Smad 2/3 pathways, respectively. TGF-¿ ligands also signal through non-Smad pathways such as MAPKs and PI3K/Akt, although the underlying mechanisms remain obscure. A critical role for endoglin and ALK1 in TGF-¿ signaling in endothelial cells is supported by their mutation resulting in the human vascular disease, hereditary hemorrhagic telangiectasia (HHT1 and 2), embryonic lethal phenotype due to defects in angiogenesis when either endoglin or ALK1 is targeted for deletion in mice, and by the elevated expression of endoglin during inflammation and tumor-induced angiogenesis. While important biological roles for endoglin have been established, the molecular basis for endoglin function in vascular biology remains poorly characterized. Here in vitro angiogenesis assays were employed to investigate precisely when and how endoglin regulates endothelial capillary sprouting and tube formation. Comparison of endoglin-null and wild type endothelial cells revealed that endoglin differentially regulates the stability of capillary sprouts and tubes in response to its physiologically relevant high-affinity ligands, TGF-¿ and BMP-9. Specifically, TGF-¿ resulted in regression of the capillary sprouts and tube structures, primarily through suppression of endoglin-dependent Akt signaling. Conversely, endoglin enhanced Akt signaling in response to BMP-9 to promote capillary stability. These outcomes are attributed to the association between endoglin and the scaffolding/trafficking protein, GIPC, since disrupting their interaction abrogated such endoglin-dependent effects. Given that I recently reported the enhancement of Smad 1/5/8 signaling through GIPC and endoglin, there exists a potential crosstalk between Akt and endoglin-dependent Smad 1/5/8 signaling, which I propose to investigate. Lastly, I discovered a novel interaction between endogenous endoglin and Akt, a finding that will likely yield new facets of endoglin biology. Based upon these preliminary data, I propose the following hypothesis: Endoglin associates with GIPC to promote angiogenesis by stabilizing endothelial capillaries via BMP-9-dependent Akt activation while destabilizing capillaries via TGF-¿-dependent suppression of Akt signaling and cell survival mechanisms. This hypothesis will be addressed by the objectives outlined in two specific aims.