Attenuation of VEGFR-2 Expression by sFlt-1 and Low Oxygen in Human Placenta

Abstract

Vascular endothelial growth factor receptor 2 (VEGFR-2), the primary receptor for VEGF, is crucial for normal endothelial function. sFlt-1, a truncated and soluble form of VEGFR-1 which binds and inhibits VEGF, is increased in preeclampsia and is positively regulated by low oxygen. Here, we investigated the effects of sFlt-1 and hypoxia on VEGFR-2 expression and signaling in the human placenta. VEGFR-2 transcript and protein levels were significantly decreased in preeclamptic placentae compared to controls (1.82 and 1.85 fold, respectively). An inverse correlation was observed for VEGFR-2 and sFlt-1 levels in both singleton and twin placentae from patients with preeclampsia. Immunofluorescence analyses revealed co-localization of VEGFR-2 and sFlt-1 in placental vasculature and co-immunoprecipitation analyses confirmed VEGFR-2 and sFlt-1 interaction only in preeclamptic placentae compared to age-matched controls. VEGFR-2 transcript and protein levels from explants cultured in 3% O2 were significantly decreased compared to those incubated at 20% O2 (5.9 and 12.47 fold, respectively). Also, VEGFR-2 transcript levels were significantly decreased in early first trimester placentae (low oxygen environment) compared to late first trimester placentae (2.05 fold). We next explored whether sFlt-1 directly affects VEGFR-2 expression. Treatment of first trimester placental explants with sFlt-1 resulted in significantly decreased levels of VEGFR-2 (2.03 fold) and downstream signaling proteins phospho-ERK (1.60 fold) and phospho-Akt (1.64 fold). Our findings show a novel hypoxia-induced and PE-related down-regulation of VEGFR-2 in the human placenta. sFlt-1, which is known to be increased in hypoxic conditions and PE, directly attenuates VEGFR-2 expression and signaling. A direct interaction between sFlt-1 and VEGFR-2 may represent an important mechanism in VEGFR-2 regulation, inhibition of VEGFR-2-mediated processes in placentation and a novel platform to examine the onset of preeclampsia.

2-Methoxyestradiol regulates VEGFR-2 and sFlt-1 expression in human placenta

“…Recently, we reported that both sFlt-1 and hypoxia attenuated VEGFR-2 levels in human placenta [5]. Previous findings have shown that sFlt-1 expression is mediated by hypoxia and the transcription factor HIF-1a [3].…”

“…However, VEGFR-2 is also expressed in the trophoblast layer in human placenta, hypothesized to play a role in trophoblast transformation into invasive intravascular trophoblasts [4]. Recently, we determined another pathway for sFlt-1-dependent vascular dysfunction through a direct and inhibitory interaction with VEGFR-2 [5], suggesting an intricate regulatory system between sFlt-1 and VEGFR-2, the disruption of which may suggest further pathways of vascular and trophoblast dysfunction in PE.…”

“…Previously, we observed VEGFR-2 expression mainly in the cytotrophoblast layer and to a lesser extent the vasculature of first trimester placentae [5]. To address the cell-specific effects of 2-ME on first trimester placental villous explants, we cultured HMVECs maintained at 20% O 2 and performed western analysis of cells treated with 0.5 mM 2-ME overnight against untreated control cells (Fig.…”

Microvascular endothelial cells from preeclamptic women exhibit altered expression of angiogenic and vasopressor factors

“…An increase in local sFlt1 may act in a paracrine/autocrine manner, exacerbating the effects of circulating sFlt1, but may also be part of a physiologic mechanism that participates in vessel repair (32). In addition, we previously reported that increased levels of sFlt1 may reduce VEGFR2 expression by direct heterodimer formation (30). Decreased expression of VEGFR2 may substantially affect a spectrum of cellular functions, including proliferation and apoptosis (5).…”

sFLT-1 inhibits proliferation, migration, and invasion of colorectal cancer SW480 cells through vascular mimicry formation suppression

“…sFLT-1, which is mainly produced by trophoblast cells and vascular endothelial cells, is supposed sFLT-1 inhibits proliferation, migration, and invasion of colorectal cancer SW480 cells through vascular mimicry formation suppression to be a major angiogenesis inhibitor with strong anti-angiogenic effect. 3,4 In this study, we applied the colon cancer SW480 cell line which has high VM-forming ability to investigate the effect of sFLT-1 on VM formation.…”