As part of the research on the molecular mechanisms that impact AAV vector expression in pathological muscle, the group of Sofia Benkhelifa-Ziyyat (research project leader/AIM) and Stéphanie Lorain (currently project leader/AFM) from the Institute’s Myology Centre for Research evaluated the impact of the necrosis-regeneration process on AAV vector expression efficiency in Duchenne muscle.
This study was conducted in a mouse model of myofibers regenerated by intramuscular injection of cardiotoxin (CTX), a myonecrotic agent that induces muscle regeneration, in wild-type mice as well as in the mdx mouse, a mouse model of Duchenne muscular dystrophy (DMD).
The authors showed that the expression of a reporter gene is drastically reduced at the transcriptional and protein level in CTX-regenerated muscles as well as in the muscles of the mdx mouse compared to wild-type muscles, while the viral genomes are well present in the myofibre nuclei. This expression defect is maintained over time as it is observed when AAV injection is performed 10 months after muscle regeneration.
These results were reproduced with AAV-U7ex23 vectors coding for the therapeutic U7 transgene allowing the skipping of exon 23 of the dystrophin gene in mdx mice. This transgene shows the same expression defect as the reporter transgene with two times less exon skipping in the regenerated muscles of the CTX and mdx mouse models than in the muscles of wild-type mice.
The results obtained demonstrate, for the first time, that the process of muscle necrosis-regeneration participates in the low expression efficiency of AAV vectors in dystrophic muscle, which could limit their therapeutic effectiveness. In order to improve the clinical use of these vectors, ongoing studies conducted by Sofia Benkhelifa-Ziyyat’s group will establish how the molecular events affecting the therapeutic efficacy of AAV vectors can be overcome in pathological muscle.
Mollard A, Peccate C, Forand A, Chassagne J, Julien L, Meunier P, Guesmia Z, Marais T, Bitoun M, Piétri-Rouxel F, Benkhelifa-Ziyyat S, Lorain S. Muscle regeneration affects Adeno Associated Virus 1 mediated transgene transcription. Sci Rep. 2022 Jun 11;12(1):9674. doi: 10.1038/s41598-022-13405-9. PMID: 35690627; PMCID: PMC9188557.