Preservation of visual function in an animal model of retinal degeneration using CRISPR/Cas9 gene editing

Aims: Inherited Retinal Disorders represent a difficult target for gene therapy. This study exploits the possibility of using CRISPR/Cas9-based gene editing in photoreceptor progenitors to prevent cell death. We performed all the experiments on Rd10 mice, which carry a point mutation on a gene associated with human Retinitis Pigmentosa (RP). Methods: First, we tested the efficiency of the editing system (composed of gRNA, Cas9, and DNA repair template) in Rd10-derived neural progenitor cells. Later we delivered the constructs to the retina of Rd10 pups via sub-retinal injection followed by electroporation. We attempted the treatment either at an early (P3) or at a late (P8) stage of photoreceptor differentiation. To confirm functional recovery, we assessed the visual acuity using the Optomotor test at P30, P60, and P90. Besides, we recorded the cortical visually evoked potentials at P90. Results: We could detect GFP expression in the photoreceptor layer starting from 2 days after electroporation. The treated eye retained a higher visual acuity compared to the control eye in all the treated groups for all the time points tested (despite a slight decrease at P90). Furthermore, we observed a partial preservation of the light-evoked response in the visual cortex of both the treated groups. The results are statistically significant when compared to data obtained from sham and control mice. Conclusions:Our study strongly suggests a positive effect of the CRISPR­/Cas9-based therapy on photoreceptor survival in the RP model. DNA sequencing and ERGs measurements on explanted treated retinas might support these findings.