Human Molecular Genetics Advance Access originally published online on April 1, 2008
Human Molecular Genetics 2008 17(14):2084-2100; doi:10.1093/hmg/ddn107
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Therapeutic benefit derived from RNAi-mediated ablation of IMPDH1 transcripts in a murine model of autosomal dominant retinitis pigmentosa (RP10)
1 The Ocular Genetics Unit, Department of Genetics, Trinity College Dublin, Dublin 2, Ireland 2 Genetics Department, Fundacion Jimenez Diaz-CIBERER, Madrid, Spain
* To whom correspondence should be addressed. Tel: +353 18962486; Fax: +353 18963848; Email: lawrenct{at}tcd.ie
Received February 15, 2008; Accepted March 29, 2008
Mutations within the inosine 5'-monophosphate dehydrogenase 1 (IMPDH1) gene cause the RP10 form of autosomal dominant retinitis pigmentosa (adRP), an early-onset retinopathy resulting in extensive visual handicap owing to progressive death of photoreceptors. Apart from the prevalence of RP10, estimated to account for 5–10% of cases of adRP in United States and Europe, two observations render this form of RP an attractive target for gene therapy. First, we show that while recombinant adeno-associated viral (AAV)-mediated expression of mutant human IMPDH1 protein in the mouse retina results in an aggressive retinopathy modelling the human counterpart, expression of a normal human IMPDH1 gene under similar conditions has no observable pathological effect on retinal function, indicating that over-expression of a therapeutic replacement gene may be relatively well tolerated. Secondly, complete absence of IMPDH1 protein in mice with a targeted disruption of the gene results in relatively mild retinal dysfunction, suggesting that significant therapeutic benefit may be derived even from the suppression-only component of an RNAi-based gene therapy. We show that AAV-mediated co-expression in the murine retina of a mutant human IMPDH1 gene together with short hairpin RNAs (shRNA) validated in vitro and in vivo, targeting both human and mouse IMPDH1, substantially suppresses the negative pathological effects of mutant IMPDH1, at a point where, in the absence of shRNA, expression of mutant protein in the RP10 model essentially ablates all photoreceptors in transfected areas of the retina. These data strongly suggest that an RNAi-mediated approach to therapy for RP10 holds considerable promise for human subjects.