Inhibition of vascular endothelial growth factor (VEGF) is sufficient to completely restore barrier malfunction induced by growth factors in microvascular retinal endothelial cells.

Abstract

Deregulated expression of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF) or insulin-like growth factor-1 (IGF-1) is associated with the pathogenesis of diabetic retinopathy. The VEGF(165)-induced increase in permeability of retinal endothelial cells (REC), probably resulting in diabetic macular oedema (DME), could be completely restored by the VEGF-binding Fab fragment ranibizumab in vitro. We investigated whether bFGF and IGF-1 as single factors or in combination with VEGF(165) influence permeability and tight junctions in immortalised bovine REC (iBREC) and if these effects could be restored by inhibition of VEGF. As a measure of changes in cellular permeability, transendothelial electrical resistance (TER) was monitored during long-term treatment of iBREC with growth factors in the absence or presence of ranibizumab or KRN951 (an inhibitor of VEGF receptors). Expression of claudin-1, as an indicator of functional tight junctions, was assessed by western blot analysis. Whereas VEGF(165) decreased TER and expression of claudin-1 in a concentration-dependent manner, long-term treatment of iBREC with 10-100 ng/ml bFGF or/and IGF-1 did not. Changes in claudin-1 expression or TER, induced by 25 ng/ml VEGF(165), were slightly enhanced by bFGF and/or IGF-1 and were accompanied by a slightly increased secretion of VEGF. Complete reversion of these effects was achieved by prolonged treatment with ranibizumab and partly by exposure to KRN951. Our findings indicate that VEGF(165), but not IGF-1 or bFGF, is mainly responsible for changes in cellular permeability observed in REC. This supports VEGF targeting as a therapeutic concept for DME.