Disease modeling and pharmacological rescue of autosomal dominant Retinitis Pigmentosa associated with RHO copy number variation

Abstract

Retinitis pigmentosa (RP), a heterogenous group of inherited retinal disorder causes slow progressive vision loss with no effective treatments available. Mutations in the rhodopsin gene (RHO), account for ∼40% cases of autosomal dominant RP (adRP). In this study, we describe the disease characteristics of the first ever reported mono-allelic copy number variation (CNV) in RHO as a novel cause of adRP. We (1) show advanced retinal degeneration in a male patient (late 60s) harboring four transcriptionally active intact copies of rhodopsin, (2) recapitulated the clinical phenotypes using retinal organoids, and (3) assessed the utilization of a small-drug like molecule, Photoregulin3 (PR3), as a clinically viable strategy to target and modify disease progression in RP patient associated with RHO-CNV. Patient retinal organoids showed the survival of photoreceptors with rudimentary outer segments, where rod photoreceptors displayed stunted outer segments with semi-occasional elongated cilia-like projections (microscopy); increased RHO mRNA expression (qRT-PCR and bulk RNA-sequencing); along with elevated levels and mislocalization of rhodopsin protein (RHO) within the cell body of rod photoreceptors (western blotting and immunohistochemistry) over the extended (300-days) culture time period. Lastly, we utilized PR3 to target NR2E3, an upstream regulator of RHO, to effectively alter the RHO expression and observed a partial rescue of RHO protein localization from the cell body to the inner/outer segments of rod photoreceptors in patient organoids. These results provided a proof-of-principle for personalized medicine and suggest that RHO expression requires a precise control. Taken together, this study supports the clinical data indicating that adRP due to RHO-CNV develops due to a dominant negative gain of function.