DESCRIPTION (provided by applicant): Diabetic retinopathy (DR) is a sight threatening disease with few therapeutic options. Low-grade chronic inflammation in the retina [1-8] and inadequate vascular repair due to compromised function of the bone marrow (BM)-derived circulating angiogenic cells (CACs) [9-12] contribute to progression of retinal vascular pathology. A number of hyperglycemia- and dyslipidemia- activated pathways promoting the increase of pro-inflammatory cytokines, pro-inflammatory lipids and pro-angiogenic factors leading to retinal endothelial cell and CAC dysfunction have been identified [2-4, 6, 9, 10, 13-25]. Dysregulation of these pathways is hypothesized to involve microRNAs (miRNAs). These small non-coding RNAs anneal imperfectly to target genes and simultaneously control translation and transcription [26]. Several miRNA classes have been shown to contribute to diabetes and diabetic complications [27, 28], including diabetic retinopathy [29]. Studies during the previous funding period identified miR-15a as a key regulator of both pro-inflammatory and pro-angiogenic pathways. miR-15a accomplishes these tasks through direct binding and inhibition of the central enzyme in the sphingolipid pathway, acid sphingomyelinase (ASM), and inhibition of VEGF-A. Based on these data, we hypothesize that miRNAs represent therapeutic targets for prevention and treatment of DR by simultaneously regulating pro-inflammatory and pro-angiogenic pathways in the retina and CACs. We will address the role of miR-15a in DR with the following Specific Aims. Specific aim 1: To test the hypothesis that the decrease in miR-15a observed in diabetes contributes to increased ASM activity and VEGF-A production leading to pro- inflammatory changes, increased permeability and endothelial dysfunction in the retina. Specific aim 2: To test the hypothesis that decrease in miR-15a in diabetes leads to ASM activation and ceramide production resulting in decreased membrane fluidity of bone marrow-derived CACs. Decreased membrane fluidity results in entrapment of progenitor cell in the bone marrow and reduced repair function due to impaired migration and extravasation capacity. Manipulation of miR-15a to simultaneously control sphingolipid metabolism and pro-angiogenic pathways through direct regulation of ASM and VEGF-A production in the diabetic retina and BM should provide a unique and effective "combination therapy" approach that will add to the pharmacological armamentarium of drug therapies for diabetic retinopathy.