TGF-β1 induced epithelial to mesenchymal transition (EMT) in human bronchial epithelial cells is enhanced by IL-1β but not abrogated by corticosteroids

Background: Chronic persistent asthma is characterized by ongoing airway inflammation and airway remodeling. The processes leading to airway remodeling are poorly understood, and there is increasing evidence that even aggressive anti-inflammatory therapy does not completely prevent this process. We sought to investigate whether TGF beta(1) stimulates bronchial epithelial cells to undergo transition to a mesenchymal phenotype, and whether this transition can be abrogated by corticosteroid treatment or enhanced by the pro-inflammatory cytokine IL-1 beta. Methods: BEAS-2B and primary normal human bronchial epithelial cells were stimulated with TG beta(1) and expression of epithelial and mesenchymal markers assessed by quantitative real-time PCR, immunoblotting, immunofluorescence microscopy and zymography. In some cases the epithelial cells were also incubated with corticosteroids or IL-1 beta. Results were analyzed using non-parametric statistical tests. Results: Treatment of BEAS-2B or primary human bronchial epithelial cells with TGF beta(1) significantly reduced the expression level of the epithelial adherence junction protein E-cadherin. TGF beta(1) then markedly induced mesenchymal marker proteins such as collagen I, tenascin C, fibronectin and a-smooth muscle actin mRNA in a dose dependant manner. The process of mesenchymal transition was accompanied by a morphological change towards a more spindle shaped fibroblast cell type with a more motile and invasive phenotype. Corticosteroid pretreatment did not significantly alter the TGF beta(1) induced transition but IL-1 beta enhanced the transition. Conclusion: Our results indicate, that TGF beta(1) can induce mesenchymal transition in the bronchial epithelial cell line and primary cells. Since asthma has been strongly associated with increased expression of TGF beta(1) in the airway, epithelial to mesenchymal transition may contribute to the contractile and fibrotic remodeling process that accompanies chronic asthma.