Placenta growth factor upregulates VE-cadherin expression in microvascular endothelial cells

Purpose: We have previously reported that placenta growth factor (PlGF) plays an important role in the maintenance and remodelling of newly-formed vessel networks. The aim of this study was to determine if PlGF can regulate endothelial cell permeability and if this occurs through modulation of VE-cadherin. Methods: Retinal microvascular endothelial cells (BRMEC) were obtained from bovine eyes. Cultures were treated with 100ng/ml of either VEGF, PlGF or the VEGF:PlGF heterodimer for 0min, 5min, 1hr, 12hr and 24hr. Endothelial permeability was determined by monitoring transendothelial electrical resistance and FITC-dextran flux. Expression of VE-cadherin at both mRNA and protein level was determined using a combination of QRT-PCR, Western blotting and immunofluorescence staining. Results: As previously reported VEGF increased BRMEC permeability. A significant increase in permeability was noted as early as 5 min after addition of VEGF. By contrast, PlGF significant reduced permeability demonstrating a decrease in both transepithelial resistance and dextran flux. The VEGF:PlGF heterodimer had no significant effect on permeability. These results were consistent with the QRT-PCR data which showed a rapid (by 5 minutes post exposure) increase in VE-cadherin mRNA expression in cultures exposed to VEGF while mRNA levels were significantly reduced below those of controls in PlGF treated cells. Similarly, immunostaining demonstrated that VEGF causes a rapid decrease in VE-cadherin expression between endothelial cells after 5-minuntes treatment, whereas PlGF greatly increased VE-cadherin expression. The VEGF:PlGF heterodimer did not cause detectable changes in VE-cadherin expression between endothelial cells. Unexpectedly, Western blotting showed that overall expression of VE-cadherin did not change until 12 hours after addition of either VEGF or PlGF. After 12 hours, VEGF inhibited VE-cadherin expression, whereas PlGF increased VE-cadherin expression. This delay is likely to be due to both relocation and the phosphorylation status of VE-cadherin. Conclusions: PlGF reduces interendothelial permeability by upregulating VE-cadherin expression in microvascular endothelial cells. This is further confirmation that PlGF plays a critical role in pathological angiogenesis