Irisin secreted from muscle by exercise ameliorates emphysema of cigarette smoke-induced COPD in mice

Background: Chronic Obstructive Pulmonary Disease (COPD) is a pulmonary disease caused by long-term inhalation exposure of harmful substances, mainly cigarette smoke. Oxidative stress is considered as one of the important mechanisms of COPD. Irisin is a kind of myokine secreted from muscle by exercise. Recent studies have shown that irisin acts defensively against oxidative stress via Nrf2, a transcription factor responsible for antioxidant capacity. In this study, we examined emphysema suppression effect of exercise in mice. Methods: Mice were divided into three groups: control, smoking, and exercise+smoking. All mice in smoking and exercise+smoking groups were exposed to cigarette smoking for 60 minutes per session once a day. All mice in exercise+smoking group were adapted to treadmill for 30 minutes per session once a day. After 12 weeks intervention, serum irisin concentration, expression of Nrf2 mRNA and protein in lung homogenate, number of inflammatory cells in bronchoalveolar lavage fluid (BALF), and Mean Liner Intercept (MLI) in lung tissue were examined. Results: Serum irisin concentration and expression of Nrf2 (mRNA and protein) in lung homogenate were significantly elevated in exercise+smoking group compared to control group and smoking group. Proportion of neutrophils in BALF was significantly lower in exercise+smoking group than that in smoking group. MLI was significantly smaller in exercise+smoking group than that in smoking group. Conclusions: Our results suggested that irisin secreted from muscle by exercise might act defensively against oxidative stress via Nrf2, and ameliorate emphysema in lung. Exercise-irisin axis might be a novel target for COPD treatment.