Treatment of autosomal dominant retinitis pigmentosa caused by RHO-P23H mutation with high-fidelity Cas13X in mice

Mutations in Rhodopsin (RHO) gene commonly cause autosomal dominant retinitis pigmentosa (adRP) without effective therapeutic treatment so far. Compared with genomic DNA-targeting CRISPR-Cas9 system, Cas13 edits RNA for therapeutic applications, avoiding the risk of causing permanent changes in the genome. In particular, a compact and high-fidelity Cas13X (hfCas13X) recently has been developed to degrade targeted RNA with minimal collateral effects and could also be packaged in a single adeno-associated virus for efficient in vivo delivery. In this study, we engineered single-guide RNA for hfCas13X to specifically knock down human mutant Rhodopsin transcripts RHO-P23H with minimal effect on wild-type transcripts. Moreover, treatment with hfCas13X alleviated the adRP progression in both RHO-P23H overexpression-induced and humanized hRHOP23H/WT mouse models. Our study indicates the potential of hfCas13X in treating adRP caused by RHO mutations and other genetic diseases.

CRISPR genome surgery in a novel humanized model for autosomal dominant retinitis pigmentosa

Mutations in rhodopsin (RHO) are the most common causes of autosomal dominant retinitis pigmentosa (adRP), accounting for 20% to 30% of all cases worldwide. However, the high degree of genetic heterogeneity makes development of effective therapies cumbersome. To provide a universal solution to RHO-related adRP, we devised a CRISPR-based, mutation-independent gene ablation and replacement (AR) compound therapy carried by a dual AAV2/8 system. Moreover, we developed a novel hRHOC110R/hRHOWT humanized mouse model to assess the AR treatment in vivo. Results show that this humanized RHO mouse model exhibits progressive rod-cone degeneration that phenocopies hRHOC110R/hRHOWT patients. In vivo transduction of AR AAV8 dual vectors remarkably ablates endogenous RHO expression and overexpresses exogenous WT hRHO. Furthermore, the administration of AR during adulthood significantly hampers photoreceptor degeneration both histologically and functionally for at least 6 months compared with sole gene replacement or surgical trauma control. This study demonstrates the effectiveness of AR treatment of adRP in the human genomic context while revealing the feasibility of its application for other autosomal dominant disorders.

High-resolution photoreceptor imaging analysis of patients with autosomal dominant retinitis pigmentosa (adRP) caused by HK1 mutation

PURPOSE

The hexokinase 1 (HK1) gene encodes one of the four human hexokinases that play essential roles in glucose metabolism. Recently, several cases of E847K mutation in the HK1 gene were reported to cause inherited retinal dystrophy. The purpose of this study was to identify the phenotypical characteristics of patients with a recurrent E847K mutation in the HK1 gene.

METHODS

Three generations of one family with autosomal dominant retinitis pigmentosa were examined. Whole exome sequencing was performed on the DNA. Fundus imaging by an adaptive optics fundus camera was used to obtain high-resolution photoreceptor images.

RESULTS

Fundus examination of the proband showed degeneration of the mid-peripheral retina, and SD-OCT images showed an absence of the ellipsoid zone (EZ) and interdigitation zone (IZ) in the parafovea and more peripherally. SD-OCT images of the mother of the proband showed an absence of the EZ and IZ, and fundus autofluorescence images showed hypo-autofluorescence surrounding the macular region. One daughter of the proband had only mild night blindness, however, the density of the cone photoreceptors was reduced in the parafoveal region. Whole exome sequencing identified a heterozygous variant, E847K, in the HK1 gene. This variant was found to co-segregate with the disease in three family members.

CONCLUSIONS

Although the systemic phenotypes were found to be associated with the HK1 mutations, only the E847K mutation can cause a non-syndromic photoreceptor degeneration. Our study strengthened the hypothesis that the amino acid E847 might play a critical role in the maintenance of the morphology and function of the photoreceptors.

Disease Progression in Patients with Autosomal Dominant Retinitis Pigmentosa due to a Mutation in Inosine Monophosphate Dehydrogenase 1 (IMPDH1)

Purpose

Mutations in the inosine monophosphate dehydrogenase 1 (IMPDH1) gene are a common cause of inherited retinal degeneration (IRD). Due to species- and tissue-dependent expression of IMPDH1, there are no appropriate models of human IMPDH1 disease. Therefore, a limited understanding remains of disease expression and rates of progression for IMPDH1-related IRD.

Methods

We evaluated semiautomated kinetic and chromatic static perimetry, spectral-domain optical coherence tomography (SD-OCT), and ultra-wide field fundus images with autofluorescence in a cohort of 12 patients (ages 11–58 at first visit). Ten patients had longitudinal data for which rates of progression were estimated.

Results

Visual acuities were relatively stable over time and the photoreceptors within the central retina remained intact. Perifoveal photoreceptor loss measured over a period of years coincided with visual fields, which were constricted and progressed over time in all patients. Rod sensitivity showed a similar pattern of defect to that of the kinetic perimetry and the autofluorescence ultra-wide field imaging. Full-field electroretinograms were severely reduced and the dark-adapted rod and mixed responses were extinguished at earlier visits than the light-adapted cone responses.

Conclusions

There was variability in disease severity at the first visit, but results show that the peripheral retina is more susceptible to the deleterious consequences of an IMPDH1 mutation. Given the pattern of degeneration and the alternatively spliced isoforms of IMPDH1, potential interventions may consider targeting the periphery early in disease, modulating transcript expression, and/or preserving central vision at late stages of the disease.

Translational Relevance

These results inform clinical prognosis and offer evidence strategies toward therapeutic intervention.

Calpain Activation Is the Major Cause of Cell Death in Photoreceptors Expressing a Rhodopsin Misfolding Mutation

The majority of mutations in rhodopsin (RHO) cause misfolding of the protein and has been linked to degeneration of photoreceptor cells in the retina. A lot of attention has been set on targeting ER stress for the development of new therapies for inherited retinal degeneration caused by mutations in the RHO gene. Nevertheless, the cell death pathway activated by RHO misfolded protein is still debated. In this study, we analyzed the retina of the knock-in mouse expressing the P23H misfolded mutant RHO. We found persistent unfolded protein response (UPR) during degeneration. Interestingly, long-term stimulation of the PERK branch of ER stress had a protective effect by phosphorylating nuclear factor erythroid 2-related factor 2 (NRF2) transcription factor, associated with antioxidant responses. Otherwise, we provide evidence that increased intracellular calcium and activation of calpains strongly correlated with rod photoreceptor cell death. By blocking calpain activity, we significantly decreased the activation of caspase-7 and apoptosis-inducing factor (AIF), two cell death effectors, and cell demise, and effectively protected the retina from degeneration caused by the P23H dominant mutation in RHO.