Expression of vascular endothelial growth factor and its receptor (KDR/flk-1) mRNA in experimental choroidal neovascularization

Abstract

Purpose. Vascular endothelial growth factor (VEGF) is an angiogenic peptide that has been suggested to be important in the pathogenesis of choroidal neovascularization. We investigated the transcription of VEGF and its receptor KDR/flk-1 genes during the development of experimentally induced choroidal neovascularization. Methods. Rat VEGF or KDR cDNA was inserted in PGEM or pBluescript to prepare antisense or sense riboprobes. Multiple krypton laser burns were applied to the posterior pole of pigmented rat eyes according to a previously described protocol which produces choroidal neovascularization. At intervals of up to 4 weeks after photocoagulation, the eyes were removed and cut into thin sections. The sections were subjected to in situ hybridization with digoxigenin (DIG)-labeled single-strand rat VEGF and KDR cDNA riboprobes. Results. In normal adult rat retinas, VEGF and KDR mRNA expression was mainly observed in the ganglion cell and the inner nuclear layers. During the development of neovascularization, VEGF and KDR mRNAs were detected in retinal pigment epithelial-like cells, fibroblast-like cells and endothelial cells in neovascular lesions. The level of expression was strongest at 1 week after photocoagulation in lasered lesions, and decreased by 4 weeks after photocoagulation. Conclusions. Our findings demonstrate that expression of VEGF and its receptor KDR may play a role in the formation of experimentally induced choroidal neovascularization. In this study, VEGF and its receptor were co-localized, suggesting that an autocrine and/or paracrine mechanism may be operative.