Cigarette smoke and TGF-beta activate distinct repair processes in a proximal airway model

Asthma and Chronic Obstructive Pulmonary Disease (COPD) are characterized by different airways remodeling processes that occur at different anatomical sites. In asthma, large and small airways are altered structurally, with loss of epithelial cells. In COPD, there is a peribronchiolar fibrosis. Here, we investigated mechanisms underlying these epithelial remodeling processes in a proximal airways model using primary bronchial epithelial cells differentiated at the air-liquid interface and exposed to cigarette smoke, as main risk factor of the COPD, and TGF-β, as main growth factor involved in epithelial remodeling of asthma and COPD. E-cadherin, mesenchymal proteins (vimentin, fibronectin), ZEB1, NOTCH1, JAGGED1, HES1 and markers of cellular differentiation (FOXJ1, MUC5AC, SCGB1A1, TP63) were assessed. Our results showed that cigarette smoke: decreased E-cadherin and mesenchymal proteins, increased ZEB1 at 6h but decreased it at 24h, decreased NOTCH1/JAGGED1/HES1 and FOXJ1 and TP63. Instead, TGF-β: decreased E-cadherin but increased mesenchymal proteins, increased ZEB1, NOTCH1/JAGGED1 and TP63. When cells were exposed to the combination of cigarette smoke and TGF-β, the effect of cigarette smoke dominated. These data suggest that cigarette smoke induces initial steps of the epithelial-mesenchymal transition (EMT) which is next inhibited and accompanied by dedifferentiation of epithelial cells with a depletion of basal cells; the loss of NOTCH1 function could be associated with a failure to repair the damage. In contrast, our findings with TGF-β1 are in line with an abnormal repair response, characterized by EMT and an increase of basal cells, which is overruled by concomitant exposure to cigarette smoke.