Ab0149 the Expression and Regulation of Nox4 in Damaged Myoblasts in Inflammatory Myopathy

Abstract

BackgroundIdiopathic inflammatory myopathy (IIM) is a rare autoimmune disease characterized by proximal muscle weakness, elevated muscle enzymes, inflammation in the muscle. If the muscle is already damaged in IIM, it may not regain full strength even after treatment. Also the mechanisms that contribute to muscle weakness in myositis are currently unknown. Nox is the main source of ROS production in various cells types, and is also the source of mitochondria ROS. Excessive expression of Nox4 is characteristic of sclerosis, fibrosis, and cardiac related diseases, and it had been reported that knock down of Nox4 lowers the production of superoxide and hydrogen peroxide. However, the effect of Nox4 in myositis has not been reported.ObjectivesWe investigated the expression and role of Nox4 in damaged myoblasts of myositis.MethodsMyoblasts were isolated from IIM patients who underwent muscle biopsy in Seoul National University Hospital between February 2019 and February 2021. Skeletal muscle cell(SMC) was purchased. Myoblasts and SMCs were treated with cytokine mixture {interferon gamma(IFN-γ), interleukin(IL)-6, IL-15} or PBS for 30 minutes. The expression of Nox4, MyoD and myosin heavy chain(MYH) in myoblast and myotube was analysed by Western blot. For inhibition of Nox4, GKT137831(inhibitor of Nox4) was treated before the cytokine stimulation.ResultsMyoblasts from IIM patients did not differentiate into myotubes like healthy myoblasts suggesting impaired muscle regeneration. Myoblasts from IIM patients express higher level of Nox4 compared to healthy myoblasts. When treated with cytokine mixture(IFN-r, IL-6, IL-15), healthy myoblasts or SMC mimicked inflammatory myositis and showed increased expression of Nox4 and decreased expression of MYH similar to myositis phenotype. Nox4 inhibitor suppressed Nox4 expression and MyoD overexpression in inflammatory myoblasts.ConclusionWe showed that Nox4 expression is increased in myoblasts from IIM patients and is associated with impaired muscle regeneration. Nox4 inhibition attenuated Nox4 and MyoD overexpression in inflamed myoblasts.References[1]Bi Y, Lei X, Chai N,et al.NOX4: a potential therapeutic target for pancreatic cancer and its mechanism.J Transl Med19, 515 (2021)[2]Rayavarapu S, Coley W, Kinder T.B.,et al.Idiopathic inflammatory myopathies: pathogenic mechanisms of muscle weakness.Skeletal Muscle3, 13 (2013)[3]Dalakas MC, Hohlfeld R. Polymyositis and dermatomyositis.Lancet. 2003 Sep 20;362(9388):971-82.[4]Piera-Velazquez S, Makul A, Jiménez SA. Increased expression of NAPDH oxidase 4 in systemic sclerosis dermal fibroblasts: regulation by transforming growth factor β.Arthritis Rheumatol. 2015 Oct;67(10):2749-58.Acknowledgements:NIL.Disclosure of InterestsNone Declared.