Résumé :
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DM1 is caused by the expansion of a CTG repeat in the 3’untranslated region (3’-UTR) of a protein kinase (DMPK), which map to 19q13.3. There is accumulating evidence that the CTG repeat causes titration and sequestration of specific RNA-binding proteins that create a gain-of-function mutation. Together these results indicate that the targeting of mutant DMPK transcripts could be a major approach for the development of a gene therapy for DM1. The proof of principle regarding this approach was originally demonstrated in human DM1 cells. We have shown that ribozyme and antisense RNAs restore a normal behavior to DM1 myoblasts as shown by an increase in the ability of DM1 myoblasts to fuse, the restoration in the uptake of glucose and in the normal splicing of insulin receptor mRNAs and the decrease in the levels of CUG binding proteins in nuclear extracts. To determine if ribozyme and/or antisense RNAs can target mutant DMPK transcript in vivo, we examined the effect of a single intramuscular injection of AAV2/6 producing antisense RNA or ribozyme on hDMPK RNA levels, in a DM1 mouse model carrying 500 CTG repeats. The levels of mutant transcripts were decreased by 55 ± 20 and 38 ± 19 % by expression of antisense RNAs or ribozymes, one month after a single intramuscular injection. This effect was maintained for at least 4 months after the injection. The decreased levels in mutant DMPK transcripts were associated with a 30% increase in muscle volume recovery, as determined by MRI. We also showed that restoration in muscle volume needs the targeting of more than 40% of mutant DPK RNAs. No toxic effects were observed. This is the first demonstration of efficiency of a RNA-based gene therapy for DM1.
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