NOX4 and chronic obstructive pulmonary disease: Since TGF-β signaling plays a pivotal role in airway modeling of chronic pulmonary diseases including COPD, pulmonary fibrosis, and asthma, which also interacted with NOX4 signaling [17, 37], the expression of TGF-β in ASM of small airway was determined by IHC and immunoblotting assays.