G protein-coupled receptor regulation of transcriptional mechanisms in the retinal vasculature.

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PROJECT SUMMARY Retinal vascular dysfunction leads to visual impairment and loss of vision, a phenomenon that occurs in retinopathy of prematurity (ROP), diabetic retinopathy (DR) and neovascular age-related macular degeneration (AMD). Injury of the retinal endothelial cell (REC) initiates a series of pathogenetic events that ultimately lead to accelerated progression of retinal diseases. How REC injury leads to transcriptional changes that determine whether the retinal vascular function is restored or leads to pathological changes is not known. Sphingosine 1-phosphate (S1P), a blood-borne lipid mediator that signals via G protein-coupled S1P receptors (S1PR1-5). The applicant’s laboratory discovered the first S1PR and worked out its functional roles in vascular barrier maintenance, development/ maturation, anti-inflammatory processes, cell survival and endothelial/ pericyte interactions. Although two FDA-approved S1PR-targeted drugs are efficacious in the treatment of multiple sclerosis, retinal blistering and macular edema are dose-limiting adverse effects due to the impairment of retinal barriers. We recently showed that S1PR signaling suppresses vascular endothelial growth factor (VEGF)-induced AP-1 transcription factor activity and permits Norrin/Wnt/ß-catenin-dependent REC gene expression, thus leading to retinal REC specialization. Among the AP-1 factors, JunB protein expression is most prominently regulated by S1PR signaling, an event needed for optimal vascular network expansion and formation of deep retinal vascular plexus. The central hypothesis of the proposal is that REC S1PR signaling establishes JunB transcription factor gradients and permits the REC organotypic specialization mechanisms. In this manner, attenuated S1PR signaling axis drives poorly functional retinal vascular network and vasoproliferative ROP. In this proposal, the first specific aim will elucidate mechanisms and consequences of S1PR sculpting of JunB transcription factor gradients in REC. Second, how S1PR signaling in the REC promotes organotypic specialization by enabling efficient Norrin/Wnt/ß-catenin-dependent signal transduction and gene expression will be conducted. Specific focus will be on omega-3 fatty acid transporter (MFSD2A) and iron transporter (TFRC). The relevance of these mechanisms in the mouse models of ROP will be addressed in specific aim 3. These studies are anticipated to enhance our understanding of basic mechanisms of retinal vascular development, specialization and disease in the retina and ultimately lead to approaches that tame retinal disorders by targeting the S1P lipid signaling axis and to provide S1PR inhibitors with fewer side effects.