Nrf2 deficiency in muscle attenuates experimental autoimmune myositis-induced muscle weakness

Idiopathic inflammatory myopathies (IIMs) are systemic autoimmune diseases characterised by muscle weakness. Although multiple physiological and pathological processes are associated with IIMs, T-lymphocyte infiltration into muscle plays a key role in the development and exacerbation of IIMs. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a key transcription factor that regulates inflammatory responses; therefore, muscle Nrf2 may serve an important role in the development of IIMs. In this study, we demonstrated that experimental autoimmune myositis (EAM) causes loss of muscle mass and function in oxidative and glycolytic muscles in C57BL/6 mice. EAM increased CD4+ and CD8+ T-lymphocyte infiltration, as well as interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha) mRNA expression in oxidative soleus and glycolytic extensor digitorum longus muscles, along with elevated chemokine mRNA levels (i.e. CCL3, CCL5, CXCL9, CXCL10 and CXCL16). IFN-gamma and TNF-alpha treatments increased the mRNA expression levels of these chemokines in C2C12 myotubes. EAM also increased phosphorylated Nrf2 at Ser40 in soleus and glycolytic white vastus lateralis muscle. Although the expression of several chemokines was affected by Nrf2 activation following tert-butylhydroquinone treatment or Keap1 knockdown, CCL5 mRNA expression significantly increased in C2C12 myotubes and mouse skeletal muscle. Moreover, muscle-specific Nrf2 knockout in mice attenuates EAM-induced loss of muscle mass and function, which was associated with the inhibition of CCL5 mRNA expression, CD8+ T-lymphocyte infiltration and IFN-gamma mRNA expression. Collectively, these findings reveal that regulating Nrf2 activity is a promising therapeutic approach for treating IIM-mediated muscle weakness. imageKey points Experimental autoimmune myositis (EAM) causes loss of muscle mass and function. Loss of muscle mass and function in EAM were associated with increased chemokine mRNA expression (i.e. CCL3, CCL5, CXCL9, CXCL10 and CXCL16), T-lymphocyte infiltration and inflammatory cytokine mRNA expression (i.e. IFN-gamma and TNF-alpha) in the skeletal muscle. EAM activated Nrf2 in muscle and increased Nrf2 activity in vivo and in vitro increased CCL5 mRNA expression. Muscle-specific Nrf2 knockout in mice attenuated EAM-induced muscle weakness by inhibiting CCL5 mRNA expression, CD8+ T-lymphocyte migration and IFN-gamma mRNA expression in muscles. These results provide further evidence for the potential therapeutic targeting of Nrf2 to mitigate EAM-induced muscle weakness. figure legend Experimental autoimmune myositis (EAM) induces significant CD4+ and CD8+ T-lymphocyte infiltration into the skeletal muscle, accompanied by increased expression of interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha) mRNA, along with elevated levels of chemokine mRNA, such as CCL5. IFN-gamma and TNF-alpha are known to upregulate CCL5 mRNA expression. Additionally, EAM enhances phosphorylated Nrf2 levels in muscle tissue. Activation of Nrf2, achieved through tert-butylhydroquinone treatment or Keap1 KD, leads to a significant increase in CCL5 mRNA expression in C2C12 myotubes and mouse skeletal muscle. Moreover, studies involving muscle-specific Nrf2 knockout mice have demonstrated that Nrf2 deficiency attenuates the loss of muscle mass and function induced by EAM. This protective effect is associated with the inhibition of CCL5 mRNA expression, reduced CD8+ T-lymphocyte infiltration, and decreased IFN-gamma mRNA expression in the skeletal muscle. These findings collectively highlight that modulating Nrf2 activity could be a promising therapeutic strategy for mitigating EAM-mediated muscle weakness and preserving muscle function. image