Investigating the role of Type I Interferon Signaling on Muscle Disease using mouse models

Objective Dysregulated type I interferon (IFN) signaling contributes to autoimmune myositis pathogenesis. We investigated the therapeutic effects of JAK inhibitors in two mouse models. We also examined how type I IFNs affect muscle vasculature. Methods Myositis was induced in MHC class I transgenic (HT) female mice at day 21. Mice were randomized into four groups (n=10‐11/group): baricitinib (10 mg/kg), tofacitinib (20 mg/kg), vehicle, and healthy controls. Outcomes included survival, weight, muscle strength, histopathology, and IFN stimulated gene expression. To model IFNβ overexpression, C57BL/6 mice received AAV9‐tMCK‐IFNβ and were treated with vehicle or tofacitinib (40 mg/kg/day) for 10 weeks (n=8‐13/group). Results Tofacitinib—but not baricitinib—significantly reduced IFN scores in severe myositis mice (p<0.05). Survival differed across groups (overall log‐rank p<0.01), with untreated‐ and baricitinib‐treated HT mice showing shorter survival than BL/6 controls, while tofacitinib‐treated mice did not differ from controls. IFNβ overexpression induced muscle inflammation (p<0.01), reduced grip strength (p<0.0001), and increased the IFN score (p<0.0001) and H2Kb (p<0.0001) expression. Conclusion Tofacitinib reduced the IFN signature, and survival in this group did not differ significantly from healthy controls, whereas untreated‐ and baricitinib‐treated HT mice showed shorter survival; functional improvement was not observed. Our results also show that type I IFN signaling contributes to muscle inflammation and weakness, making it a key driver of muscle damage and thereby reinforcing its potential as a therapeutic target.