Redox-sensitive activation of REDD1 in diabetic retinopathy

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Project Summary Diabetic retinopathy (DR) is a leading cause of vision loss, yet much remains unknown regarding the molecular events that cause this pervasive complication. Diabetes promotes expression of the stress response protein regulated in development and DNA damage 1 (REDD1) in the retina, which has been implicated in visual deficits in both preclinical models and diabetic patients. REDD1 protein expression is increased in the retina of rodent models of type 1 and type 2 diabetes, and REDD1 deletion prevents the development of diabetes-induced retinal pathology and functional deficits in vision. Intravitreal administration of a siRNA targeting the REDD1 mRNA has also demonstrated promise for improving visual function in patients with diabetic macular edema. Together these findings provide strong support that REDD1 plays an important role in the functional deficits in vision that are caused by diabetes. The objective here is to address two critical unresolved basic research questions related to the role of REDD1 in DR. The proposed studies will investigate why retinal REDD1 protein expression is increased by diabetes. We will also explore the molecular events downstream of REDD1 to determine how it contributes to visual impairment. The rationale is that an understanding of the molecular events that lead to increased REDD1 protein content, as well as those that are responsible for its deleterious effects on vision, may identify molecular targets for improved therapeutic strategies that provide interventions early in the preclinical and non-proliferative stages of DR. The central hypothesis is that diabetes suppresses REDD1 protein degradation in the retina to promote oxidative stress, inflammation, and subsequent retinal pathology. Aim 1 will investigate a molecular switch in the REDD1 protein that is potentially activated by diabetes, leading to reduced REDD1 degradation. The proposed studies will use in vivo SNAP-tagging to define the biochemical events that regulate REDD1 degradation in the retina of diabetic mice. Aim 2 will build on recent evidence from our laboratory supporting that REDD1 acts as a dominant governor of the nuclear factor erythroid-2-related factor 2 (Nrf2) antioxidant response. We predict that diabetes prevents a proper antioxidant response in the retina by promoting Nrf2 nuclear exclusion via REDD1-dependent activation of glycogen synthase kinase 3 (GSK3). Aim 3 will investigate a role for REDD1 in retinal inflammation, as REDD1 was recently shown to promote atypical activation of nuclear factor kappa B (NF-κB) by directly interacting with and sequestering inhibitor of κB (IκB). It is well established that oxidative stress and inflammation are crucial factors in the development and progression of the complications that cause visual impairment. The proposed studies are designed to identify and characterize specific molecular events that contribute to the development of retinal oxidative stress and inflammation in type 1 and type 2 diabetes by addressing key knowledge gaps related to a cutting-edge therapeutic target. To do so, we will explore the entirely novel concept that non-enzymatic post-translational modification of the REDD1 protein is a shared mechanism for improper activation of Nrf2 and NF-κB in DR.