Autocrine and Paracrine Effects of VEGF‐A on PLGF in an In Vitro Model of the Vessel Wall

Abstract

Placenta growth factor (PLGF) and vascular endothelial growth factor-A (VEGF-A) are important regulators of both physiological and pathological vascular remodeling. PLGF mediates these effects by activation and recruitment of monocytes to the vessel wall, while VEGF-A primarily acts upon endothelial cells (EC) inducing their proliferation and migration. We previously reported that human coronary EC primarily express PLGF, while human coronary smooth muscle cells (SMC) primarily express VEGF-A. In the vasculature, EC and SMC are in close proximity to each other. Thus, in study we tested the hypothesis that EC VEGF-A and/or PLGF production influences SMC VEGF-A and/or PLGF expression, and vice versa. EC and SMC were cultured on either side of a porous Transwell insert. SMC were cultured either on the bottom of the well (no cell-cell interaction) or on the opposite side of the insert (some cell-cell interaction). In both instances, coculture of EC and SMC increased PLGF in media relative to EC monoculture (~58%, n=5 p<0.01), but decreased VEGF-A in media compared to SMC monoculture (~72% n=5, p<0.01). Next, EC monolayers were treated with 100 ng/ml of exogenous VEGF-A or VEGF-E (a VEGFR-2 selective isoform). VEGF-A had no significant effect on PLGF. However, VEGF-E increased secreted PLGF (~30%, n=5, p<0.01). PLGF siRNA treatment of SMC increased secreted VEGF (~85% n=5, p<0.001) in SMC, suggesting an inhibitory effect of PLGF on VEGF expression. Furthermore, coculture of PLGF siRNA treated SMC with EC resulted in an increase in secreted PLGF compared to untreated cells (~25% n=5, p<0.05). The available evidence suggests that signaling between EC and SMC contributes to differential expression of PLGF and VEGF-A. Support: R01 HL084494 (PL).