Kinetics of placenta growth factor/vascular endothelial growth factor synergy in endothelial hydraulic conductivity and proliferation.

Vascular endothelial growth factor (VEGF) was originally discovered as vascular permeability factor because of its ability to increase microvascular permeability to plasma proteins. Since then, it has been shown to induce proliferation and migration in endothelial cells. Placenta growth factor (PlGF) is a member of the VEGF family of growth factors, but has little or undetectable mitogenic activity on endothelial cells. Intriguingly, however, PlGF was able to potentiate the action of low concentrations of VEGF on endothelial cell growth and macromolecule permeability in vitro. Here we show that PlGF can potentiate the effects of VEGF on the hydraulic conductivity of certain endothelial cells and that the duration of pretreatment with PlGF determines the resulting response. Hydraulic conductivity (Lp) was calculated from the water flux across the monolayer of human umbilical vein endothelial cells (HUVECs) or bovine aortic endothelial cells (BAECs). After 2 h of exposure to VEGF(165), the Lp of BAEC monolayers increased threefold, but the Lp of HUVEC monolayers did not increase. PlGF alone induced a small (63%) increase in Lp in BAECs, but not in HUVECs. BAEC, but not HUVEC, monolayers exposed first to PlGF and then to VEGF exhibited a seven- to eightfold increase in Lp. This enhancement in BAEC Lp could be observed for 4 h after the administration of PlGF. PlGF also potentiated the effect of VEGF on BAEC proliferation. Thus, augmentation of VEGF action by PlGF depends on the duration of PlGF exposure and on the origin of endothelial cells. Copyright 2001 Academic Press.