Inhibition of NOX4 attenuates muscle damage and mitochondrial dysfunction in inflammatory myopathy.

BACKGROUND: Idiopathic inflammatory myopathy (IIM) is a chronic autoimmune disorder characterized by muscle inflammation and weakness. If a muscle is already damaged, muscle strength often fails to restore with current treatments. Although, NADPH oxidase 4 (NOX4) is the main source of reactive oxygen species (ROS) and has been suggested to contribute to the pathogenesis of various disease by inducing ROS production and mitochondrial dysfunction, its role in IIM has not been fully explained. METHODS: Primary myoblasts from IIM patients and non-myopathic controls, as well as human skeletal muscle cells (SkMCs), were cultured under inflammatory conditions induced by interleukin (IL)-15, IL-6, and interferon-gamma (IFN-γ). NOX4 inhibitors, GKT137831 and GLX351322, were administered prior to cytokine stimulation. The effects of NOX4 inhibition were assessed in vitro and in vivo using a C protein-induced myositis (CIM) mouse model. RESULTS: IIM-derived myoblasts showed impaired myotube formation and elevated NOX4 expression compared to controls. Cytokine stimulation for SkMCs recapitulated key features of inflammatory myopathy, increased NOX4 and myoblast determination protein 1 (MyoD) expression. Treatment with NOX4 inhibitors reduced NOX4 and MyoD levels, restored myotube differentiation, and normalized the elevated oxygen consumption rate (OCR) associated with mitochondrial dysfunction. In the CIM model, NOX4 inhibition significantly reduced muscle inflammation (p < 0.05), preserved muscle mass (p < 0.001), increased cross-sectional area (CSA, p < 0.0001), and improved grip strength (p < 0.01). CONCLUSIONS: We showed that NOX4 is associated with muscle damage in IIM and suggest that its inhibition may have novel therapeutic effect for mitigating muscle damage and disease progression in IIM.