DUX4 reduction and muscle function improvement by subcutaneous delivery of gapmer antisense oligonucleotides.

Facioscapulohumeral muscular dystrophy (FSHD) is caused by aberrant expression of double homeodomain protein 4 (DUX4). The disease has no effective treatment. Previously we demonstrated effective DUX4 knockdown in vitro and in vivo using 2'-O-methoxyethyl (2'MOE) and locked nucleic acid (LNA) gapmer antisense oligonucleotides delivered via intramuscular injections. This study aimed to evaluate in vivo efficacy of the gapmers via systemic delivery using mouse models expressing DUX4 at different levels. First, we injected the gapmers subcutaneously to FLExDUX4 mice at 20 mg/kg twice a week for 10 weeks. Results showed significant reduction in DUX4 mRNA and improved muscle function, assessed by grip strength. Muscle fibrosis and circulating TGFβ1 levels were significantly reduced, approaching baseline level. A dose-dependent DUX4 reduction was observed in 2'MOE gapmer treated. In the ACTA1-MCM;FLExDUX4 model, where DUX4 expression was induced by tamoxifen (5 mg/kg), treatment with 2'MOE gapmers effectively reduced DUX4, improved muscle function, and decreased inflammation. These findings highlight the therapeutic potential of gapmer-based DUX4 reduction, leading to phenotypic improvement and restoration of muscle function in FSHD mouse models.