In Vivo Application of an RNAi Strategy for the Selective Suppression of a Mutant Allele

Gene therapy for dominantly inherited diseases with small interfering RNA (siRNA) requires mutant allele-specific suppression when genes in which mutation causes disease normally have an important role. We previously proposed a strategy for selective suppression of mutant alleles; both mutant and wild-type alleles are inhibited by most effective siRNA, and wild-type protein is restored using mRNA mutated to be resistant to the siRNA. Here, to prove the principle of this strategy in vivo, we applied it to our previously reported anti–copper/zinc superoxide dismutase (SOD1) short hairpin RNA (shRNA) transgenic (Tg) mice, in which the expression of the endogenous wild-type SOD1 gene was inhibited by more than 80%. These shRNA Tg mice showed hepatic lipid accumulation with mild liver dysfunction due to downregulation of endogenous wild-type SOD1. To rescue this side effect, we generated siRNA-resistant SOD1 Tg mice and crossed them with anti-SOD1 shRNA Tg mice, resulting in the disappearance of lipid accumulation in the liver. Furthermore, we also succeeded in mutant SOD1-specific gene suppression in the liver of SOD1G93A Tg mice, a model for amyotrophic lateral sclerosis, using intravenously administered viral vectors. Our method may prove useful for siRNA-based gene therapy for dominantly inherited diseases. Amyotrophic lateral sclerosis (ALS) is a progressive fatal, neurodegenerative disease caused by the degeneration of motor neurons. Although ALS lacks a clear genetic cause, approximately 20% of familial ALS cases are associated with mutations in the superoxide dismutase (SOD1) gene. In this study, Kubodera et al. examine a novel therapeutic strategy for this disease in a mouse model of ALS wherein they use a single intravenous injection of AAV8 vector to knock down the mutant SOD1 allele using small hairpin RNA (shRNA) while simultaneously expressing functional wild-type SOD1 cDNA.