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 TGFbeta1 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-1beta.
Methods: BEAS-2B and primary normal human bronchial epithelial cells were stimulated with TGFbeta1 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-1beta. Results were analyzed using non-parametric statistical tests.
Results: Treatment of BEAS-2B or primary human bronchial epithelial cells with TGFbeta1 significantly reduced the expression level of the epithelial adherence junction protein E-cadherin. TGFbeta1 then markedly induced mesenchymal marker proteins such as collagen I, tenascin C, fibronectin and alpha-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 pre-treatment did not significantly alter the TGFbeta1 induced transition but IL-1beta enhanced the transition.
Conclusion: Our results indicate, that TGFbeta1 can induce mesenchymal transition in the bronchial epithelial cell line and primary cells. Since asthma has been strongly associated with increased expression of TGFbeta1 in the airway, epithelial to mesenchymal transition may contribute to the contractile and fibrotic remodeling process that accompanies chronic asthma.