Abstract
In retinitis pigmentosa, loss of cone photoreceptors leads to blindness, and preservation of cone function is a major therapeutic goal. However, cone loss is thought to occur as a secondary event resulting from degeneration of rod photoreceptors. Here we report a genome editing approach in which adeno-associated virus (AAV)-mediated CRISPR/Cas9 delivery to postmitotic photoreceptors is used to target the Nrl gene, encoding for Neural retina-specific leucine zipper protein, a rod fate determinant during photoreceptor development. Following Nrl disruption, rods gain partial features of cones and present with improved survival in the presence of mutations in rod-specific genes, consequently preventing secondary cone degeneration. In three different mouse models of retinal degeneration, the treatment substantially improves rod survival and preserves cone function. Our data suggest that CRISPR/Cas9-mediated NRL disruption in rods may be a promising treatment option for patients with retinitis pigmentosa.
Highlights
In retinitis pigmentosa, loss of cone photoreceptors leads to blindness, and preservation of cone function is a major therapeutic goal
Expression cassettes of SpCas[9] and single guide RNA (sgRNA) were delivered by two separate associated virus (AAV) vectors (Fig. 1a)
Therapeutic genome editing has long been considered an ideal strategy for permanent correction of genetic defects and is advancing rapidly since the advent of CRISPR/Cas[9] technology[40]
Summary
Loss of cone photoreceptors leads to blindness, and preservation of cone function is a major therapeutic goal. For RP caused by a dominant mutation, inactivation of the mutant allele has been evaluated in disease models using ribozymes[8] and RNA interference[9], and by transcriptional repression using zinc fingerbased approaches[10,11] Though encouraging, these genespecific approaches appear to be less practical due to extensive heterogeneity in the genetic defects underlying inherited eye disorders. Ablation of Nrl in adult rods leads to loss of rod features and acquisition of cone characteristics This results in a improved survival in the presence of rod-specific gene mutations, presumably preventing secondary cone loss[14]. This proof-of-principle study was conducted in Nrl-floxed mouse lines using inducible Cre-mediated gene knockout (KO), which is not a practical therapeutic approach. In vivo delivery of CRISPR/ Cas[9] to postmitotic photoreceptors, which is therapeutically more relevant for a majority of patients with inherited retinal degeneration, has not been reported
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