Soluble EphB4 regulates choroidal endothelial cell function and inhibits laser-induced choroidal Neovascularization

PURPOSE. The purpose of this study was to evaluate the effect of a soluble monomeric form of the EphB4 extracellular domain (sEphB4) on choroidal endothelial cell (CEC) migration and tube formation and on experimental laser-induced choroidal neovascularization (CNV). METHODS. EphrinB2 and EphB4 expression in CECs was investigated by Western blot analysis and immunohistochemistry. Effects of sEphB4 ( 0.5 - 3 mu g/mL) on CEC migration were evaluated with a modified Boyden chamber assay. Tube formation was assayed in CEC cultures in collagen gel. CNV was induced in rats by laser photocoagulation. The effects of intravitreal injection of sEphB4 on CNV development were evaluated at day 14 by fluorescein angiography ( FA), confocal volumetric analysis of isolectin-B4 labeled flatmounts, and histologic examination of CNV membranes. RESULTS. CEC cells express both EphB4 and EphrinB2, according to Western blot analysis. Immunohistochemical sections of rat eye showed immunoreactivity for both EphB4 and EphrinB2 in the choroidal endothelium. sEphB4 reduced CEC migration in response to vascular endothelial growth factor ( P < 0.01). Similarly, sEphB4 inhibited CEC tube formation in a dose-dependent manner. EphB4, and to a lesser extent EphrinB2, were detected on vascular channels within laser-induced CNV membranes. Intravitreal injection of sEphB4 inhibited laser-induced CNV formation. CNV membranes showed a reduction in leakage score ( P < 0.05), and membrane volumes were reduced in size ( P < 0.05). Histologic analysis revealed that vascularity was reduced in sEphB4-treated membranes. CONCLUSIONS. Recombinant soluble monomeric EphB4 exerts an inhibitory effect on choroidal angiogenesis in vitro and in vivo. It should be further evaluated for its potential as a novel therapy for CNV.