NOX4 and chronic obstructive pulmonary disease: In view of the functions of NOX4 in ROS production and ASM hyperplasia and hypertrophy in COPD airway remodeling, as well as the contribution of TGF-β in the disruption of oxidant/antioxidant balance in ASM cells, we hypothesized that TGF-β induces intracellular ROS production in ASM cells through a mechanism by upregulating NOX4, substantially leading to ASM hyperplasia and hypertrophy.