Significance: Diabetes is a global epidemic with 48 million people affected in USA, and the prevalence is expected to increase to 63 million by 2045. The disease represents a significant public health problem. Diabetes within the Veterans Health Administration (VHA) poses a significant challenge because the estimated prevalence of diabetes among its enrolled patients is as high as 25%, substantially higher than the general population. Diabetes is the third most common VHA diagnosis and accounted for 25% of pharmacy costs and over 1.7 million hospital bed days. Diabetic retinopathy, a microvascular complication of diabetes is the leading cause of vision loss in middle-aged adults. Despite the use of therapeutics targeting the vascular endothelial growth factor (VEGF), about two thirds of patients do not recover vision, and the effect is transient, needing repeated intravitreal injections of drugs. Rationale: Chronic inflammation in retina plays a major role in BRB alteration resulting in vascular leakage. Our preliminary work presents novel evidence that there is increased influx of monocytes and activation of microglia in the retina in diabetes. The goal of this research proposal is to determine what factors are secreted by the activated microglia and how those factors interact with vascular cells leading to alteration of the BRB. Hypothesis: Activated microglia in the diabetic retina secrete factors that affect pericyte-endothelial interactions leading to BRB alteration. Aims: 1) Determine effect of microglia depletion on the retinal vasculature and structure in the context of diabetic retinopathy, 2a) Identify and prioritize “candidate genes” by analyzing the core transcriptional signatures of activated retinal microglia in an animal model of diabetes in relationship to blood-retinal barrier alteration. 2b) Validate the role of “microglial candidate genes” on endothelial cell permeability and blood retinal barrier alteration in diabetes and 3) Test the druggability of the functionally validated candidate genes using an off-patent small molecule library in cell culture models and a diabetic animal model. Design: In this research proposal, next generation sequence (NGS) technology will be utilized to investigate the molecular basis of alteration of the BRB in diabetes. This research will address a critical scientific gap by identifying molecular mediators beyond VEGF that alter the BRB. Relevance: The findings may help in development of novel biomarkers and improved therapeutic strategies targeting these molecules in both type 1 and 2 diabetes patients that may prevent vision loss in those who poorly respond to anti-VEGF drugs. Our approach is innovative because this proposal introduces an innovative strategy that targets the mechanisms of stabilizing the initial step of microglia dysfunction in diabetes, a critical upstream event for the development of diabetic macular edema.