Characterization of autosomal dominant retinitis pigmentosa-associated rhodopsin missense mutations in Xenopus laevis rod photoreceptors

Retinitis pigmentosa (RP) is an inherited retinal disease that causes progressive vision loss due to retinal degeneration. RP has at least three associated clinical classes, each with differing disease presentations in patients. One subclass is sector RP, which is less severe than typical RP and has only one or two affected retinal quadrants. Due to the asymmetric phenotype, sector RP is hypothesized to be exacerbated by light exposure. Over a third of autosomal dominant RP (adRP) cases are associated with mutations in rhodopsin (RHO), which encodes the visual pigment in rod photoreceptors. Over 200 mutations have been identified as pathogenic; however, the pathogenic mechanisms associated with most mutations is unknown. Well-studied mutations include P23H RHO, which causes misfolding of RHO and undergoes ER stress-related cell death, and T4K RHO, which is partially glycosylation-deficient and causes a photoactivation-induced toxicity mechanism. These mutations cause the same disease but have contrasting characteristics regarding pathogenic mechanisms, highlighting the potential variability of cellular consequences in RHO-associated adRP. In this thesis, I aimed to characterize uncharacterized RHO mutations and their associated pathogenic mechanisms by generating transgenic Xenopus laevis models of RP. We identified and described a novel RHO mutation associated with sector RP and created an experimental paradigm to characterize mutations in vivo. This was applied to another 26 uncharacterized mutations, where we evaluated RHO localization, retinal degeneration, RHO glycosylation, and effects of photoactivation on retinal degeneration. The majority of the mutations investigated caused retinal degeneration in our models. We further identified that all but two mutations (P23H and S176F) are predominantly trafficked to the rod outer segment. Several sector RP-associated mutations caused light-dependent degeneration, which aligns with published data; however, we identified a group of sector RP mutations that caused light-independent degeneration and abnormal RHO multimerization. Overall, we propose new classifications of RHO mutations based on pathogenic mechanisms described in vivo. We identified a set of sector RP-associated mutations that activate novel pathogenic mechanisms. A variety of mechanisms should be considered when developing and evaluating RHO-associated RP treatment options.