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Modelling and rescue of RP2 Retinitis Pigmentosa using iPSC Derived Retinal Organoids

ABSTRACT: Mutations in RP2 lead to a severe form of X-linked retinitis pigmentosa (XLRP). RP2 functions as a GTPase activating protein (GAP) for the small GTPase ARL3, which is essential for cilia function and for photoreceptor development and maintenance. The mechanisms of RP2 associated retinal degeneration in humans are poorly understood, and genetically engineered animal models of RP2 XLRP present with differing retinal phenotypes and slow degeneration suggesting potential species differences. Here, we developed CRISPR gene edited isogenic RP2 knock-out (RP2 KO) induced pluripotent stem cells (iPSC) and RP2 patient derived iPSC to produce 3D retinal organoids as a human retinal disease model. The isogenic RP2 KO retinal organoids and two unrelated RP2 patient iPSC lines produced retinal organoids with a defined photoreceptor cell layer (ONL) containing rod and cone photoreceptors. Strikingly the RP2 KO and RP2 patient derived organoids showed a thinning of the ONL by 180 days (D180) of culture, which was associated with a spike in cell death in the ONL at D150 of differentiation. RNA sequencing confirmed induction of cell death pathways in the RP2 null organoids at this stage. Photoreceptor cell death and ONL thinning was attributed to cells undergoing terminal rod cell differentiation characterized by reduced RHO expression and fewer rhodopsin immunoreactive photoreceptors. Gene augmentation with a human RP2 transgene in an AAV2/5 vector efficiently transduced RP2 KO organoids and led to high levels of RP2 expression in both rods and cones. Importantly, the viral transduction significantly increased ONL thickness and restored rhodopsin expression, suggesting rescue of the RP2 degeneration phenotype. These data show that 3D retinal organoids can be used to model molecular defects associated with inherited retinal disease, photoreceptor cell death and also to test potential therapies targeted to prevent photoreceptor degeneration.

ORGANISM(S): Homo sapiens

PROVIDER: GSE148300 | GEO | 2020/07/08

REPOSITORIES: GEO

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Project description:Retinal degeneration is the leading cause of irreversible blindness. Retinitis pigmentosa (RP) is a genetically heterogenous group of diseases. In the United States, approximately one in 4000 individuals is affected. RP begins with the loss of night vision due to the loss of rod photoreceptor cells. The disease progresses slowly with the loss of peripheral vision, and eventually leads to complete debilitating and irreversible blindness. The first mutation associated with human RP was identified in the gene encoding rhodopsin, the G-protein coupled receptor of rod photoreceptor cells. Mutations within the rhodopsin gene account for significant portion of RP cases. Specifically, mutations of the proline at residue 347 in rhodopsin have been linked to human RP. We are fortunate to have access to the P347S rhodopsin mutant mice. These mice represent an excellent transgenic mouse model of retinal degeneration. The P347S rhodopsin mutation is one of the best studied mutations, yet the mechanism by which the mutation causes degeneration is still unknown. One study has demonstrated that galectin-1 plays a role in degeneration of neuronal processes (1) and another study has shown that expression level of galectin-3 is elevated in retinas of patients with age-related macular degeneration. These studies in conjunction with the availibility of the P347S mutant mice have provided impetus to examine the pathogenesis of retinal degeneration in the context of the possible role of glycans and glycan-binding proteins. The time course of photoreceptor degeneration in the P347S mouse model has been carefully studied. In these mice, degeneration is barely detectable at 1 month of age, yet biochemical evidence suggests that the rod photoreceptor cells have already begun to die. At 4 months of age, approximately half of the rod photoreceptor cells have degenerated. To distinguish involvement of glycogens at the various stages of retinal degeneration, we have collected retinas of wild type and the mutant mice at four time points (1, 2, 3, and 4 months of age). This will allow us to identify the genes that target early, mid- and late stages of the retinal degeneration process. Thus we request the analysis of total 24 samples as specified below: Age Group (months) Mice No of samples at each time point 1 Wild type 3 2 Wild type 3 3 Wild type 3 4 Wild type 3 1 P347S 3 2 P347S 3 3 P347S 3 4 P347S 3 Total 24.

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Modelling and rescue of RP2 Retinitis Pigmentosa using iPSC Derived Retinal Organoids

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