HMOX1 and pulmonary emphysema: Among these, HMOX1 or HO‐1, the inducible isoform responding to various stimuli in the environment, was confirmed to play a pivotal role in protecting against mucus hypersecretion 8, emphysema 9, 10, 11, airway inflammation 12, which were the main characteristics of COPD, in a series of studies.