Role of Nrf2 in retinal vascularization and ROP

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Project Summary/Abstract Retinopathy of prematurity (ROP) is one of the leading causes of blindness in the pediatric population in the U.S. and worldwide. A pivotal aspect of early ROP is a delay/arrest in physiologic retinal vascular development with a component of hyperoxia-induced vascular attenuation. The retinal avascularity and consequent hypoxia in turn leads to production of pro-angiogenic growth factors including VEGF which stimulates blinding pathologic retinal neovascularization. Promotion of physiologic revascularization is therefore highly desirable in ROP as well as other ischemic retinopathies, providing an approach for intervening earlier in ischemic disease. An important driving concept in revascularization of ischemic retina is the retinal milieu which can create either a hostile or favorable environment for blood vessels to re-grow into the ischemic zone. Emerging evidence suggests that multiple retinal cell types, including neuronal elements such as retinal ganglion cells, participate in shaping this environment. Evidence also implicates a major role for Muller cells and myeloid elements including microglia. The transcription factor Nrf2 is an endogenous stress-response factor that offers protection against oxidative stress and inflammation, two major facets of the ischemic retina. Importantly, Nrf2 is amenable to pharmacologic modulation to enhance its action. Our lab has identified Nrf2 as a highly promising positive regulator of revascularization in the ischemic retina using an experimental model of oxygen-induced retinopathy (OIR). We have found that Nrf2-deficient mice exhibit markedly increased retinal avascularity and pathologic neovascularization in oxygen-induced retinopathy. We have also found a key aspect of Nrf2 to be its regulation of the non-vascular elements of the retina, programming the retina to favor beneficial revascularization. We demonstrated that Nrf2 reprograms the ganglion cells to promote revascularization, in part by suppressing RGC production of the anti-angiogenic Semaphorin 6A. It is of great interest to gain further insights into retinal cell types modulated by Nrf2, including Muller cells and myeloid cells, as well as to identify additional molecules that are targeted by Nrf2 in its reprogramming of the retinal response to ischemia in OIR. This can provide critical knowledge to guide development of Nrf2 as a therapeutic strategy for treating OIR and other ischemic retinopathies. We propose to: (1) Determine the importance of Muller and myeloid cell Nrf2 in oxygen-induced retinopathy using conditional Nrf2 knockout mice; (2) Elucidate important guidance molecule systems modulated by Nrf2 in oxygen-induced retinopathy; and (3) Investigate a new therapeutic strategy of Nrf2 activation as a treatment for oxygen-induced retinopathy. We anticipate that these aims will allow us to develop Nrf2 targeting as a new clinical strategy for treating ROP as an earlier stage of disease compared to current options.