Endothelial Cell Biology Unit, School of Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, UK.
Exp Cell Res. 2012 Nov 1;318(18):2297-311. doi: 10.1016/j.yexcr.2012.06.023. Epub 2012 Jul 11.
Vascular endothelial growth factor A (VEGF-A) is an essential cytokine that regulates endothelial function and angiogenesis. VEGF-A binding to endothelial receptor tyrosine kinases such as VEGFR1 and VEGFR2 triggers cellular responses including survival, proliferation and new blood vessel sprouting. Increased levels of a soluble VEGFR1 splice variant (sFlt-1) correlate with endothelial dysfunction in pathologies such as pre-eclampsia; however the cellular mechanism(s) underlying the regulation and function of sFlt-1 are unclear. Here, we demonstrate the existence of a biphasic stress response in endothelial cells, using serum deprivation as a model of endothelial dysfunction. The early phase is characterized by a high VEGFR2:sFlt-1 ratio, which is reversed in the late phase. A functional consequence is a short-term increase in VEGF-A-stimulated intracellular signaling. In the late phase, sFlt-1 is secreted and deposited at the extracellular matrix. We hypothesized that under stress, increased endothelial sFlt-1 levels reduce VEGF-A bioavailability: VEGF-A treatment induces sFlt-1 expression at the cell surface and VEGF-A silencing inhibits sFlt-1 anchorage to the extracellular matrix. Treatment with recombinant sFlt-1 inhibits VEGF-A-stimulated in vitro angiogenesis and sFlt-1 silencing enhances this process. In this response, increased VEGFR2 levels are regulated by the phosphatidylinositol-3-kinase and PKB/Akt signaling pathways and increased sFlt-1 levels by the ERK1/2 signaling pathway. We conclude that during serum withdrawal, cellular sensing of environmental stress modulates sFlt-1 and VEGFR2 levels, regulating VEGF-A bioavailability and ensuring cell survival takes precedence over cell proliferation and migration. These findings may underpin an important mechanism contributing to endothelial dysfunction in pathological states.
血管内皮生长因子 A（VEGF-A）是一种调节内皮功能和血管生成的重要细胞因子。VEGF-A 与内皮细胞受体酪氨酸激酶（如 VEGFR1 和 VEGFR2）结合，触发包括细胞存活、增殖和新血管芽生在内的细胞反应。可溶性 VEGFR1 剪接变体（sFlt-1）水平的升高与子痫前期等病理状态下的内皮功能障碍相关；然而，sFlt-1 的调节和功能的细胞机制尚不清楚。在这里，我们使用血清剥夺作为内皮功能障碍的模型，证明内皮细胞中存在双相应激反应。早期阶段的特征是高 VEGFR2:sFlt-1 比值，在晚期阶段发生逆转。其功能后果是短期增加 VEGF-A 刺激的细胞内信号。在晚期阶段，sFlt-1 被分泌并沉积在细胞外基质中。我们假设，在应激下，内皮细胞中 sFlt-1 水平的升高会降低 VEGF-A 的生物利用度：VEGF-A 处理诱导细胞表面的 sFlt-1 表达，而 VEGF-A 沉默抑制 sFlt-1 锚定到细胞外基质。用重组 sFlt-1 处理可抑制 VEGF-A 刺激的体外血管生成，而 sFlt-1 沉默则增强这一过程。在这种反应中，VEGFR2 水平的增加受磷脂酰肌醇-3-激酶和 PKB/Akt 信号通路调节，而 sFlt-1 水平的增加则受 ERK1/2 信号通路调节。我们得出结论，在血清剥夺期间，细胞对外界环境应激的感知调节 sFlt-1 和 VEGFR2 水平，调节 VEGF-A 的生物利用度，确保细胞存活优先于细胞增殖和迁移。这些发现可能为病理状态下内皮功能障碍的一个重要机制提供依据。
