Gene therapy in animal models of autosomal dominant retinitis pigmentosa

Abstract

Gene therapy for dominantly inherited genetic disease is more difficult than gene-based therapy for recessive disorders, which can be treated with gene supplementation. Treatment of dominant disease may require gene supplementation partnered with suppression of the expression of the mutant gene either at the DNA level, by gene repair, or at the RNA level by RNA interference or transcriptional repression. In this review, we examine some of the gene delivery approaches used to treat animal models of autosomal dominant retinitis pigmentosa, focusing on those models associated with mutations in the gene for rhodopsin. We conclude that combinatorial approaches have the greatest promise for success.

Figure 1

Human rhodopsin illustrating sites of known mutations or deletions. This figure is based on an illustration at RetNet.

Figure 2

Improvement of electroretinography (ERG) response by single AAV injection of normal mouse rhodopsin cDNA (WT Rho) in P23H transgenic mice [89]. Bars represent the average of five scotopic ERG scans at 0 dB (2.6 cd (cd)-s/m²) a-wave response. A: and b-wave response. B: at 1 month and 6 months post injection. ERG amplitudes of 1 month uninjected P23H eyes were set as 100%. A: Compared with that of corresponding contralateral eyes, injection of AAV-Rho demonstrated a significant increase in a-wave amplitudes at both 1 month (122%) and 6 months (90%) time points. (*p<0.05, n=6). B: Compared with contralateral eyes, injection of WT Rho demonstrated the same significant increase in b-wave amplitudes as that of a-wave response at both 1 month (122%) and 6 months (90%) time points. (*p<0.05, ** p<0.005, n=6). Although injection injury can induce protective cytokines such as CNTF, this effect peaks within a few days of injection and is complete before the first measurements were made.

Figure 3

Gene suppression. A: Zinc finger artificial transcription factors (ZF-ATF) use suppressor transcription factors to silence gene transcription. B: Zinc finger nucleases (ZFN) causes a double-stranded break leading to correction of the mutation through recombination. C: miRNA and shRNA degrade the endogenous target transcript while sparing the introduced resistant mRNA (hardened) with an altered sequence. D: Ribozymes catalytically cleave the target transcript, but insertion of a guanosine at the target site dramatically reduces cleavage of the hardened target.