The role of erythropoietin in physiological angiogenesis of the mouse retina

Background: Diabetic retinopathy (DR) is a prevalent microvascular complication and it is characterized by increased vascular permeability, ischemia and neovascularization. Angiogenesis is modulated by growth factors such as vascular endothelial growth factor and angiopoietin-2. Recently, it is found that erythropoietin, besides neuroprotection, has angiogenic effects and its level is highly elevated in vitreous fluid of patients with proliferative diabetic retinopathy. However, the role of erythropoietin in physiological angiogenesis of the retina and its cooperation with angiopoietin 2 remains unclear.

Aim: The study investigated the effects of erythropoietin on the physiological angiogenesis of the mouse retina.

Methods: C57Bl/6 wild type and angiopoietin 2 transgenic mice were intraperitoneally injected at postnatal day P1, P3, P5, P7 and P9 with human recombinant erythropoietin at doses of 256 IU/kg. Retinae at P10 were stained with isolectin B4, NG2 and Iba1 antibodies, respectively. Angiogenic parameters of retinal vasculatures were analyzed using a Leica confocal microscope TCS SP2 system.

Results: Erythropoietin promoted the outgrowth of the deep vessels by 21% (*p < 0.05) and increased pericytes recruitment in the superficial and deep layer by 23% and by 42%, respectively (*p < 0.05). Microglial number was reduced in the superficial layer of retinal vessel (27%, *p < 0.05), but increased in the deep layer (60%, ***p < 0.001). Microglia located in front of tip cells and acted as a bridge to connect neighboring sprouts. Angiogenic activity was elevated in the deep layer of the retinal vascular plexus, especially with cooperation of angiopoietin 2.

Conclusion: Erythropoietin promotes the development and maturation of the retinal vasculature.