Inhibition of the Nuclear Receptor RORγ and Interleukin-17A Suppresses Neovascular Retinopathy Involvement of Immunocompetent Microglia

Objective-Although inhibitors of vascular endothelial growth factor (VEGF) provide benefit for the management of neovascular retinopathies, their use is limited to end-stage disease and some eyes are resistant. We hypothesized that retinoic acid-related orphan nuclear receptor gamma (ROR gamma) and its downstream effector, interleukin (IL)-17A, upregulate VEGF and hence are important treatment targets for neovascular retinopathies. Approach and Results-Utilizing a model of oxygen-induced retinopathy, confocal microscopy and flow cytometry, we identified that retinal immunocompetent cells, microglia, express IL-17A. This was confirmed in primary cultures of rat retinal microglia, where hypoxia increased IL-17A protein as well as IL-17A, ROR gamma, and tumor necrosis factor-a mRNA, which were reduced by the ROR gamma inhibitor, digoxin, and the RORa/ROR gamma inverse agonist, SR1001. By contrast, retinal macroglial Mller cells and ganglion cells, key sources of VEGF in oxygen-induced retinopathy, did not produce IL-17A when exposed to hypoxia and IL-1 beta. However, they expressed IL-17 receptors, and in response to IL-17A, secreted VEGF. This suggested that ROR gamma and IL-17A inhibition might attenuate neovascular retinopathy. Indeed, digoxin and SR1001 reduced retinal vaso-obliteration, neovascularization, and vascular leakage as well as VEGF and VEGF-related placental growth factor. Digoxin and SR1001 reduced microglial-derived IL-17A and Mller cell and ganglion cell damage. The importance of IL-17A in oxygen-induced retinopathy was confirmed by IL-17A neutralization reducing vasculopathy, VEGF, placental growth factor, tumor necrosis factor-a, microglial density and Mller cell, and ganglion cell injury. Conclusions-Our findings indicate that an ROR gamma/IL-17A axis influences VEGF production and neovascular retinopathy by mechanisms involving neuroglia. Inhibition of ROR gamma and IL-17A may have potential for the improved treatment of neovascular retinopathies.