| Popis: |
Leber congenital amaurosis (LCA) comprises a genetically heterogeneous group of early-onset retinal disorders characterized by severe loss of vision in the first years of life. Approximately 30% of LCA patients harbor mutations in the CEP290 gene, which codes for a centrosomal protein involved in ciliogenesis and ciliary trafficking in the photoreceptors. While AAV-mediated gene therapy is showing promise in clinical trials for RPE65-associated LCA, the size of CEP290 exceeds the limit for efficient packaging in AAV. Thus, alternative approaches to treat CEP290 associated LCA are needed. Here, we report a gene editing approach in which the CRISPR/Cas9 system is used to modify the endogenous CEP290 locus and restore normal function of the gene.The most common mutation in CEP290 is the IVS26 c. 2991+1655 A>G mutation. This point mutation in intron 26 of the gene generates a novel splice donor, resulting in aberrant splicing and the inclusion of an extra 128bp cryptic exon into the coding sequence of the transcript. Using the S. aureus CRISPR/Cas9 system, we employed a dual-cut approach in which two gRNAs are used to induce a pair of double strand breaks and excise the region of DNA containing the mutation. We screened gRNA pairs in primary fibroblasts derived from LCA patients harboring homozygous IVS26 mutations and identified pairs capable of generating targeted deletions with high efficiency. Using qRT-PCR, we showed that deletion of the mutation results in increased expression of wildtype CEP290 and concomitant decrease in expression of the aberrantly spliced mutant RNA species. Genome-wide specificity profiling allows for assessment of potential off-target modifications induced by the gRNAs and informs selection of optimal gRNA pairs for further study. Assays to assess ciliogenesis, as well as molecular characterization of gene editing in patient-derived photoreceptor precursor cells, demonstrate phenotypic correction in the relevant cell population. The use of the S. aureus CRISPR/Cas9 system enables efficient packaging of the Cas9 gene, as well as two gRNA genes, into a single AAV vector and provides a method for delivery of this system into patient photoreceptors. |
