Therapeutic impact of systemic AAV-mediated RNA interference in a mouse model of myotonic dystrophy

Authors:

• Darren R. Bisset,
• Ewa Agnieszka Stępniak-Konieczna,
• Maja Zavaljevski,
• Jessica Wei,
• Gregory T. Carter,
• Michael D. Weiss,
• Joel R. Chamberlain

Abstract

RNA interference (RNAi) offers a promising therapeutic approach for dominant genetic disorders that involve gain-of-function mechanisms. One candidate disease for RNAi therapy application is myotonic dystrophy type 1 (DM1), which results from toxicity of a mutant mRNA. DM1 is caused by expansion of a CTG repeat in the 3' UTR of the DMPK gene. The expression of DMPK mRNA containing an expanded CUG repeat (CUG ^exp ) leads to defects in RNA biogenesis and turnover. We designed miRNA-based RNAi hairpins to target the CUG ^exp mRNA in the human a-skeletal muscle actin long-repeat (HSA ^LR ) mouse model of DM1. RNAi expression cassettes were delivered to HSA ^LR mice using recombinant adeno-associated viral (rAAV) vectors injected intravenously as a route to systemic gene therapy. Vector delivery significantly reduced disease pathology in muscles of the HSA ^LR mice, including a reduction in the CUG ^exp mRNA, a reduction in myotonic discharges, a shift toward adult pre-mRNA splicing patterns, reduced myofiber hypertrophy and a decrease in myonuclear foci containing the CUG ^exp mRNA. Significant reversal of hallmarks of DM1 in the rAAV RNAi-treated HSA ^LR mice indicate that defects characteristic of DM1 can be mitigated with a systemic RNAi approach targeting the nuclei of terminally differentiated myofibers. Efficient rAAV-mediated delivery of RNAi has the potential to provide a long-term therapy for DM1 and other dominant muscular dystrophies.