Age-related macular degeneration (AMD) is the leading cause of blindness in elderly people. The disease starts with dysfunction of the retinal pigment epithelium (RPE) and formation of drusen, and will further progress to chronic inflammation in the sub-RPE space, geographic atrophy and choroidal neovascularization (CNV). Despite the recent progresses in genetic research and clinical treatment of exudative AMD, its etiology is largely unclear and currently there is no effective cure for dry AMD. We have recently developed an animal model of AMD using knockout mice deficient of nuclear factor erythroid 2-related factor 2 (Nrf2). The Nrf2-/- mice developed AMD-like retinal pathology including age-dependent RPE degeneration, spontaneous CNV and sub-RPE deposit of complement-related proteins. In our preliminary studies, we further demonstrated that Nrf2 is an important regulator of RPE autophagy and macrophage activation. We found that Nrf2-deficient RPE cells had increased accumulation of autophagic vacuoles and lipofuscin in vivo, indicating less efficient degradation by lysosome. Substantially more severe RPE pathology was developed in Nrf2-/- mice in a chronic toxicity model using chloroquine, an inhibitor of lysosome function and RPE autophagy. With differential gene expression assay, we identified Nramp1 as a downstream gene of Nrf2 with novel functions of controlling autophagosome formation. In a model of experimental CNV, Nrf2-/- mice showed significantly increased lesion size and macrophage infiltration than the wild type mice received the same treatment. When co-cultured with RPE, Nrf2-/- macrophages showed more robust pro-inflammatory responses than the wild type cells. Based on these findings, we hypothesize that Nrf2 is an essential regulator of multiple protective mechanisms against age-dependent RPE dysfunction and subsequent CNV. Using Nrf2-/- mice as an established model, experiments will be performed to further examine the mechanisms of RPE degeneration and to explore the roles of chronic inflammation mediated by infiltrating macrophages.
Specific Aim 1 will determine whether Nrf2 regulates RPE autophagy by Nramp1-dependent mechanisms.
Specific Aim 2 will determine whether inhibiting RPE autophagy will accelerate the development of AMD-related pathology in Nrf2-/- mice, and examine the functional interactions between RPE autophagy pathway and exosomal protein export.
Specific Aim 3 will determine whether Nrf2 regulates polarized macrophage activation in experimental CNV. Results from these studies will reveal new mechanisms of the pathobiology of AMD and further define Nrf2 as a molecular target for intervention.
This project will use a newly developed mouse model of age-related macular degeneration (AMD) to examine the essential roles of nuclear factor erythroid 2-related factor 2 (Nrf2) in protecting the outer retina from age-related degeneration and associated immune responses. Results from the proposed studies can expand our knowledge on the molecular etiology of AMD and facilitate the design of better interventional agents that protect against vision loss in elderly people.
