Airway epithelial cell apoptosis and inflammation in COPD, smokers and nonsmokers

Abstract

We hypothesised that primary bronchial epithelial cells (PBECs) from subjects with chronic obstructive pulmonary disease (COPD) respond differently to Pseudomonas aeruginosa lipopolysaccharide (LPS) after cigarette smoke extract (CSE) exposure than PBECs obtained from smokers without airflow obstruction and nonsmokers. PBECs from 16 COPD subjects, 10 smokers without airflow obstruction and nine nonsmokers were cultured at air-liquid interface. Cultures were incubated with CSE prior to stimulation with P. aeruginosa LPS. Interleukin (IL)-6 and IL-8 were measured by ELISA and Toll-like receptor (TLR)-4 expression by fluorescence-activated cell sorter. Activation of nuclear factor (NF)-κB was determined by Western blotting and ELISA, and MAPK and caspase-3 activity by Western blotting. Apoptosis was evaluated using Annexin-V staining and the terminal transferase-mediated dUTP nick end-labelling methods. Constitutive release of IL-8 and IL-6 was greatest from the COPD cultures. However, CSE pretreatment followed by P. aeruginosa LPS stimulation reduced IL-8 release from COPD PBECs, but increased it from cells of smokers without airflow obstruction and nonsmokers. TLR-4 expression, MAPK and NF-κB activation in COPD cultures were reduced after CSE treatment, but not in the smokers without airflow obstruction or nonsmoker groups, which was associated with increased apoptosis. CSE attenuates inflammatory responses to LPS in cells from people with COPD but not those from nonsmoking individuals and those who smoke without airflow obstruction.

Keywords: Airway inflammation; chronic obstructive pulmonary disease; cigarette smoking; epithelial cell biology; infections in COPD; smoking and health.