Erythropoietin regulates ischemia–induced retinal neovascularization

Abstract

Abstract: : Purpose: Erythropoietin (Epo) stimulates the formation of red blood cells by preventing apoptotic death of Epo–responsive erythroid precursor cells and by stimulating their proliferation and differentiation. Recently, Epo has been reported to play a role in pathologic angiogenesis. In this study, we investigated Epo expression and its regulation in ischemic retina during neovascularization and vitreous fluid in eyes with proliferative diabetic retinopathy. Methods: Seven–day–old (P7) C57BL/6J mice were exposed to 75 % oxygen for 5 days and then returned to room air at P12 to produce ischemia–induced retinal neovascularization. Epo mRNA expression was analyzed by using real–time PCR. A solution containing soluble Epo receptor (sEpo–R), soluble vascular endothelial growth factor (VEGF) receptor 1(Flt–1)–Fc chimera (sFlt–1–Fc), or both fusion proteins was injected into the vitreous of one eye on P12 and P14 and neovascular nuclei was counted at P19. Fifty–six samples of vitreous fluid (40 in eyes with proliferative diabetic retinopathy and 16 in eyes with nondiabetic ocular disease) were collected at vitrectomy. Epo and VEGF concentrations in the vitreous fluids were measured by using ELISA. Results: Epo mRNA was increased gradually from 12 hours after return to the room air in the retina of ischemia–induced angiogenesis model and the observed increase was peaked at P17. Intraocular injection of sEpo–R, sFlt–1–Fc, and both proteins reduced retinal neovascularization in a murine model of retinal ischemia. The mean magnitude of inhibition was 41%, 47%, and 68% by injection of sEpo–R (62.5 ng), sFlt–1–Fc (250 ng) and both, respectively. The mean vitreous levels of Epo was significantly higher in eyes with proliferative diabetic retinopathy (589.1 ± 602.5 mIU/ml) than in eyes with nondiabetic ocular diseases (43.7 ± 38.9 mIU/ml). Conclusions: Epo expression was up–regulated in the ischemic retina and in the vitreous fluids of patients with proliferative diabetic retinopathy. It is suggested that Epo may have a role in ischemic ocular angiogenesis.

Keywords: retinal neovascularization • ischemia • diabetic retinopathy