High levels of HtrA4 detected in preeclamptic circulation may disrupt endothelial cell function by cleaving the main VEGFA receptor KDR

Systemic endothelial dysfunction is a key characteristic of preeclampsia (PE), which is a serious disorder of human pregnancy. We have previously reported that high-temperature requirement factor (Htr)A4 is a placenta-specific protease that is secreted into the maternal circulation and significantly up-regulated in PE, especially early-onset PE. We have also demonstrated that high levels of HtrA4 detected in the early onset PE circulation induce endothelial dysfunction in HUVECs. In the current study, we investigated whether HtrA4 could cleave the main receptor of VEGFA, the kinase domain receptor (KDR), thereby inhibiting VEGFA signaling. We first demonstrated that HtrA4 cleaved recombinant KDR in vitro. We then confirmed that HtrA4 reduced the level of KDR in HUVECs and inhibited the VEGFA-induced phosphorylation of Akt kinase, which is essential for downstream signaling. Further functional studies demonstrated that HtrA4 prevented the VEGFA-induced tube formation in HUVECs and dose-dependently inhibited the VEGFA-induced angiogenesis in explants of mouse aortic rings. These data strongly suggest that high levels of HtrA4 in the maternal circulation could cleave the main receptor of VEGFA in endothelial cells to induce a wide-spread impairment of angiogenesis. Our studies therefore suggest that HtrA4 is a potential causal factor of early onset PE.