HMOX1 and chronic obstructive pulmonary disease: Interestingly, an experimental study showed that irisin ameliorated emphysema in a CS-induced model of COPD in mice, in which irisin played an anti-oxidative role through nuclear factor erythroid 2-related factor 2 (Nrf2, a transcription factor with antioxidant properties) and heme oxygenase-1 (HO-1, an antioxidant in the antioxidant pathway) (80).