Tang K, Zhao J, Xie J, Wang J. Decreased miR-29b expression is associated with airway inflammation in chronic obstructive pulmonary disease. Am J Physiol Lung Cell Mol Physiol 316: L621-L629, 2019. First published January 17, 2019; doi: 10.1152/ajplung.00436. 2018.-Chronic obstructive pulmonary disease (COPD) is a common chronic airway inflammatory disease. MicroRNAs are shown to be involved in the regulation of inflammation. We investigated the role of microRNA-29b (miR-29b) in the airway inflammation in COPD. The expression of miR-29b in the lung and plasma was examined. The target of miR-29b, bromodomain protein 4 (BRD4), was predicted by online algorithms and verified in human bronchial epithelial (HBE) cells. The expression of BRD4, interleukin (IL)-8, and IL-6 in the lung was also examined. The role of miR-29b in the inflammatory cytokine expression of airway epithelial cells was studied using an in vitro model system. In total, 60 subjects were recruited, including 10 nonsmokers, 24 smokers, and 26 patients with COPD. Both lung and plasma miR-29b are decreased in patients with COPD, and miR-29b expression levels are correlated with pulmonary function and inflammation. BRD4 is increased in the lung of patients with COPD and is correlated with miR-29b and IL-8 expression. miR-29b regulates cigarette smoke extract (CSE)-induced IL-8 expression by targeting BRD4 in HBE cells. The antioxidant N-acetylcysteine prevents CSE-induced miR-29b downregulation and BRD4 and IL-8 upregulation. Our findings indicate that miR-29b may participate in the airway inflammation in COPD by regulating inflammatory cytokine expression through targeting BRD4, plasma miR-29b may serve as a biomarker for disease severity in COPD, and oxidative stress may contribute to the decrease of miR-29b induced by cigarette smoke.