Simultaneous expression of Vascular Endothelial Growth Factor (VEGF) and its receptors in epiretinal membranes

Purpose. VEGF is a potent angiogenic endothelial cell mitogen and vascular permeability-enhancing glycoprotein. These activities are mediated through two tyrosine kinase receptors, flt-1 and flk-1, which have been specifically localized to endothelial cells. VEGF has been implicated in the development of ocular neovascularization and therefore we hypothesized that VEGF and its receptors would be present in vascularized epiretinal membranes (ERMS), but not in avascular ERMS. Methods. ERMS from patients with proliferative diabetic retinopathy, proliferative vitreoretinopathy, idiopathic ERMS or ERMS resulting from other causes (n=43) were obtained during pars plana vitrectomy, fixed for 1 hr in 2% paraformaldehyde, and frozen after gradually increasing the sucrose concentration to 20% over 2 hrs. Sections were immunohistochemically stained for VEGF, flt-1 or flk-1. For controls, the primary antibody was pre-incubated with the appropriate control peptide. Results. VEGF was demonstrated to some extent in 88% of the ERMs with and without neovascularization, flt-1 was found in 71% and flk-1 was visualized in 62%. Many of the cells that stained for flt-1 and/or flk-1 had morphologic features of RPE or retinal glia. Pre-incubation of the primary antibodies with control peptides eliminated the staining. Most ERMS contained both VEGF and its receptors and the probability of having one isoform of VEGF receptor was significant (p=0.013) if the other type was present. Conclusions. VEGF and its receptors were co-localized in most ERMS, regardless of whether or not they were vascularized suggesting that VEGF may act as an autocrine growth stimulator in ERMS. The findings also suggest that VEGF may exert its mitogenic or other undefined effects on cell types other than endothelial cells, such as RPE cells or retinal glia, that express VEGF receptors.