Corticosteroids prevent pathological angiogenesis yet compromise reparative vascular remodeling in the retina
Tissue inflammation is often broadly associated with cellular damage, yet sterile inflammation also plays critical roles in beneficial tissue remodeling. In the central nervous system (CNS), this is observed through a predominantly innate immune response in retinal vascular diseases such as age-related macular degeneration, diabetic retinopathy and retinopathy of prematurity. Here we set out to elucidate the dynamics of the immune response during progression and regression of pathological neovascularization in retinopathy. In a mouse model of oxygen-induced retinopathy, we report that broad spectrum corticosteroid drugs such as dexamethasone suppress initial formation of pathological pre-retinal neovascularization in early stages of disease, yet blunt successive waves of reparative inflammation and hence prevent beneficial vascular remodeling. Using genetic depletion of distinct components of the innate immune response, we demonstrate that CX3C chemokine receptor 1 (CX3CR1)-expressing microglia contribute to angiogenesis. Conversely, myeloid cells expressing Lyz-M (lysozyme 2) are recruited to sites of damaged blood vessels and pathological neovascularization where they partake in a reparative process that ultimately restores circulatory homeostasis to the retina. Hence, the Janus-faced properties of anti-inflammatory drugs should be considered when treating retinal vascular disease and particularly in stages associated with persistent neovascularization.