Women with COPD from biomass smoke have reduced serum levels of biomarkers of angiogenesis and cancer, with EGFR predominating, compared to women with COPD from smoking

Comparative study of cigarette smoke, Klebsiella pneumoniae, and their combination on airway epithelial barrier function in mice

BACKGROUND

The airway epithelium acts as a physical barrier to protect pulmonary airways against pathogenic microorganisms and toxic substances, such as cigarette smoke (CS), bacteria, and viruses. The disruption of the structural integrity and dysfunction of the airway epithelium is related to the occurrence and progression of chronic obstructive pulmonary disease.

PURPOSE

The aim of this study is to compare the effects of CS, Klebsiella pneumoniae (KP), and their combination on airway epithelial barrier function.

METHODS

The mice were exposed to CS, KP, and their combination from 1 to 8 weeks. After the cessation of CS and KP at Week 8, we observed the recovery of epithelial barrier function in mice for an additional 16 weeks. To compare the epithelial barrier function among different groups over time, the mice were sacrificed at Weeks 4, 8, 16, and 24 and then the lungs were harvested to detect the pulmonary pathology, inflammatory cytokines, and tight junction proteins. To determine the underlying mechanisms, the BEAS-2B cells were treated with an epidermal growth factor receptor (EGFR) inhibitor (AG1478).

RESULTS

The results of this study suggested that the decreased lung function, increased bronchial wall thickness (BWT), elevated inflammatory factors, and reduced tight junction protein levels were observed at Week 8 in CS-induced mice and these changes persisted until Week 16. In the KP group, increased BWT and elevated inflammatory factors were observed only at Week 8, whereas in the CS + KP group, decreased lung function, lung tissue injury, inflammatory cell infiltration, and epithelial barrier impairment were observed at Week 4 and persisted until Week 24. To further determine the mechanisms of CS, bacteria, and their combination on epithelial barrier injury, we investigated the changes of EGFR and its downstream protein in the lung tissues of mice and BEAS-2B cells. Our research indicated that CS, KP, or their combination could activate EGFR, which can phosphorylate and activate ERK1/2, and this effect was more pronounced in the CS + KP group. Furthermore, the EGFR inhibitor AG1478 suppressed the phosphorylation of ERK1/2 and subsequently upregulated the expression of ZO-1 and occludin. In general, these results indicated that the combination of CS and KP caused more severe and enduring damage to epithelial barrier function than CS or KP alone, which might be associated with EGFR/ERK1/2 signaling.

CONCLUSION

Epithelial barrier injury occurred earlier, was more severe, and had a longer duration when induced by the combination of CS and KP compared with the exposure to CS or KP alone, which might be associated with EGFR/ERK signaling.

Angiogenesis, Lymphangiogenesis, and Inflammation in Chronic Obstructive Pulmonary Disease (COPD): Few Certainties and Many Outstanding Questions

Chronic obstructive pulmonary disease (COPD) is characterized by chronic inflammation, predominantly affecting the lung parenchyma and peripheral airways, that results in progressive and irreversible airflow obstruction. COPD development is promoted by persistent pulmonary inflammation in response to several stimuli (e.g., cigarette smoke, bacterial and viral infections, air pollution, etc.). Angiogenesis, the formation of new blood vessels, and lymphangiogenesis, the formation of new lymphatic vessels, are features of airway inflammation in COPD. There is compelling evidence that effector cells of inflammation (lung-resident macrophages and mast cells and infiltrating neutrophils, eosinophils, basophils, lymphocytes, etc.) are major sources of a vast array of angiogenic (e.g., vascular endothelial growth factor-A (VEGF-A), angiopoietins) and/or lymphangiogenic factors (VEGF-C, -D). Further, structural cells, including bronchial and alveolar epithelial cells, endothelial cells, fibroblasts/myofibroblasts, and airway smooth muscle cells, can contribute to inflammation and angiogenesis in COPD. Although there is evidence that alterations of angiogenesis and, to a lesser extent, lymphangiogenesis, are associated with COPD, there are still many unanswered questions.