Colocalization of neuropilin-1 and Flk-1 in retinal neovascularization in a mouse model of retinopathy

PURPOSE. TO investigate the mechanisms of the development of retinal neovas cularization, the localizations of vascular endothelial (VEGF) receptors Fl k-1 and neuropilin (NP)-1 mRNAs were examined. METHODS, The model of retinopathy of prematurity (ROP) was produced by isch emia-induced ocular neovascularization, by exposing postnatal day-7 mice to 75% oxygen for 5 days and then returning them to room air for 5 days. Reti nal neovascularization was visualized by injection of fluorescein-dextran. Expression of Flk-1 and NP-I mRNAs were examined by in situ hybridization w ith flatmount and serial sections of the retina. The localization of NP-I w as also confirmed by immunohistochemistry. Blood vessel patterns were chara cterized by immunohistochemical localization of von Willebrand factor (vWF) . RESULTS. Flatmount in situ hybridization showed intense expression of NP-1 and Flk-1 mRNAs colocalized in the area of neovascularization. In situ hybr idization of serial sections of the retina revealed that expression of Flk- 1 and NP-1 was restricted to neovascularized vessels of the retina from ROP mice. CONCLUSIONS. The restricted expression of Flk-1 and NP-1 on neovascularized vessels suggests that these molecules may play important roles in retinal neovascularization. This is the first report of the colocalization of NP-1 and Flk-1 on neovascularized vessels of the retina from ROP mice.