Retinoids in Vision

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ABSTRACT A substantial proportion of retinal degenerative diseases are known to be associated with either defects in the retinoid (visual) cycle or abnormalities in retinal clearance. Thanks to painstaking biochemical reconstitution studies supported by genetically engineered animal models and genetic/phenotypic studies of humans with specific blinding diseases, a molecular understanding of the retinoid cycle and phototransduction pathway in the mammalian retina has advanced considerably over the past few years. Nevertheless, many important details regarding chemical transformations of retinal and its derivatives are not well defined and many proteins involved in 11-cis-retinal regeneration still await structural, biochemical and functional characterization. Understanding the fundamental biochemical processes underlying these diseases is essential for the development of effective therapeutics. This proposal aims to significantly improve our knowledge of molecular transformations within the retinoid cycle in vivo and then test the efficacy of novel chemical compounds that could prevent or modulate retinal degeneration. First, we will identify next-generation all-trans-retinal trapping agents. We posit that all-trans-retinal and adduct toxicity could be lowered by rapidly and reversibly forming a Schiff base with a test compound and that novel compounds identified from our structural studies could achieve this objective. To support this project, structures of the retinoid isomerase (RPE65) and lecithin:retinol acyl transferase (LRAT) determined in our laboratory will be critical. Second, we will clarify the role of RDH10 in the eye by using a cell-specific knockout of this gene. Achieving this aim will advance our understanding of the specificities of the whole RDH family aided by the crystal structure of a homologous RDH recently obtained in our laboratory. Improved characterization of the molecular specificity of the RDH family should allow us to identify additional visual cycle modulators. Third, we will test cell-specific 9-cis-retinal delivery to cones through the use non-isomerizable-locked retinal analogs that selectively bind rod opsin. We have already demonstrated that mechanism-based pharmacological interventions can restore vision in otherwise incurable genetic retinal degenerations and further improvements are possible. Finally, we will apply RNA-guided genome editing strategies to combat inherited retinal degenerative disorders driven by loss of retinoid cycle activity.