Vascular endothelial growth factor increases endothelial cell permeability in vitro

Purpose. Vascular endothelial growth factor (VEGF) is upregulated in retinal glia during hypoxia, but it is constitutively expressed only by the pigment epithelium in healthy adult retinas. VEGF increases vessel permeability to plasma proteins in vivo. Thus, it may have a role in inducing and maintaining the enhanced permeability of the choriocapillaris endothelium which abuts the pigment epithelium. Methods. We tested this hypothesis and analyzed mechanisms of VEGF-induced permeability alterations using early passage cultures of bovine retinal microvascular endothelial cells and bioassays for permeability, transcellular electrical resistance (TER), and morphology. Results. VEGF treatment induced a rapid and statistically significant increase in permeability to horseradish peroxidase (HRP, 40 kDa) and socium fluorescein (SF, 0.4 KDa). The rate of increase in HRP permeability (66%) was three times that of SF (22%). TER was not affected. Gross morphology of the treated cultures was not altered as indicated by actin localization or scanning electron microscopy. High resolution analysis suggested that the vesicles/fenestrations of the VEGF-treated cells were larger and more abundant as compared with controls. Conclusions. VEGF induces an increase in endothelial cell permeability The large HRP protein is thought to cross primarily via vesicles and fenestrations, whereas the small SF molecule crosses by both paracellular and transcellular routes. Taken with the lack of change in TER and apparent increase in vesicles/fenestrations, these data suggest that VEGF acts by altering transcellular permeability through fenestrations and vesicles.