The repeated necrosis/regeneration cycles in dystrophic muscles may limit the impact of Duchenne muscular dystrophy (DMD) therapies utilizing adeno-associated virus (AAV), a new study published in Scientific Reports found.

During the study, AAV genomes were found to be properly localized in the nucleus of wild-type (WT) mice with muscles regenerated after damage with cardiotoxin (CTX) injection and in the DMD mouse model, mdx. However, transcription appeared to be impaired in both groups compared to WT mice indicating that the regeneration process common to both may impair the efficacy of AAV-based treatments.

“Muscle regeneration alters AAV transduction through a long-term reduction of the transgene transcription which may be involved in the transduction defect occurring in the dystrophic muscle,” the authors said.


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The decreased transgene expression in WT+CTX was present both when AAV therapy was administered 3 weeks after CTX treatment and 42 weeks after CTX treatment, indicating that the regeneration-related effects may be irreversible.

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Two different AAV1 viral vectors were tested during the study including one encoding the murine secreted alkaline phosphatase (mSeAP) protein and one encoding the therapeutic transgene U7ex23 designed to skip the nonsense mutation in the dystrophin exon 23 of mdx mice. Transduction of both vectors was drastically reduced compared to WT muscles (only 5% to 18% of WT expressed transcripts).

“Altogether, similar AAV1 transduction defects described for both mSeAP and U7ex23 transgenes in CTX regenerated and mdx muscles highlight that muscle regeneration limits the efficiency of AAV-based therapy,” the authors said.

The progressive restoration of muscle tissue following myofiber necrosis tends to generate fibers that are centronucleated and leads to larger muscle mass. Larger muscle masses were observed in the WT+CTX and mdx mice compared to WT, which could cause a decrease in viral genome due to dilution, but this would not have accounted for the drastic reduction in transduction observed during the study, they said.

No major difference in transcription was observed during the study between different muscle fiber types. The regeneration impact on transcription was slightly for the mSeAP transgene than the U7ex32 (7% transcripts per viral genome vs 30%) which may be partly explained by silencing of the cytomegalovirus promoter.

Reference

Mollard A, Peccate C, Forand A, et al. Muscle regeneration affects adeno associated virus 1 mediated transgene transcription. Sci Rep. 2022;12(1):9674. doi:10.1038/s41598-022-13405-9