Pentatricopeptide repeat protein targeting CUG repeat RNA ameliorates RNA toxicity in myotonic dystrophy type 1 mice
Myotonic dystrophy type1 (DM1) is an autosomal dominant multi-systemic disorder caused by the expansion of a CTG triplet repeat in the 3-prime untranslated region of the dystrophia myotonica protein kinase (DMPK). It results in the transcription of toxic RNAs that contain expanded CUG repeats (CUGexp). Splicing factors, such as MBNL1, are sequestered by CUGexp, thereby disrupting the normal splicing program that is essential for various cellular functions. The pentatricopeptide repeat (PPR) proteins, originally found in plants, regulate RNA in their organelles by binding in a sequence-specific manner. In the present study, we designed PPR proteins that specifically bind to the hexamer of the CUG repeat RNA (CUG-PPRs) and showed that the CUG-PPR1 could ameliorate RNA toxicity induced by CUGexp in DM1 model cells. A single systemic delivery of the recombinant adeno-associated virus (AAV9) containing CUG-PPR1 demonstrated long-term therapeutic effects on myotonia in DM1 model mice in correlation with the restoration of splicing activity. These results suggest that systemic delivery of a CUG-specific PPR molecule via AAV9 represents an effective option for treating DM1. Furthermore, this study demonstrates the general potential of PPR molecules to target pathogenic RNA sequences associated with other RNA-mediated disorders.