IL-22 contributes to TGF-β1-mediated epithelial-mesenchymal transition in asthmatic bronchial epithelial cells

BACKGROUND Allergic asthma is characterized by airway inflammation in response to antigen exposure, leading to airway remodeling and lung dysfunction. Epithelial-mesenchymal transition (EMT) may play a role in airway remodeling through the acquisition of a mesenchymal phenotype in airway epithelial cells. TGF-β1 is known to promote EMT; however, other cytokines expressed in severe asthma with extensive remodeling, such as IL-22, may also contribute to this process. In this study, we evaluated the contribution of IL-22 to EMT in primary bronchial epithelial cells from healthy and asthmatic subjects. METHODS Primary bronchial epithelial cells were isolated from healthy subjects, mild asthmatics and severe asthmatics (n=5 patients per group). The mRNA and protein expression of epithelial and mesenchymal cell markers and EMT-associated transcription factors was evaluated following stimulation with TGF-β1, IL-22 and TGF-β1+IL-22. RESULTS Primary bronchial epithelial cells stimulated with TGF-β1 underwent EMT, demonstrated by decreased expression of epithelial markers (E-cadherin and MUC5AC) and increased expression of mesenchymal markers (N-cadherin and vimentin) and EMT-associated transcription factors. IL-22 alone had no effect on epithelial or mesenchymal gene expression. However, IL-22+TGF-β1 promoted the expression of some EMT transcription factors (Snail1 and Zeb1) and led to a more profound cadherin shift, but only in cells obtained from severe asthmatics. CONCLUSION The impact of IL-22 on airway epithelial cells depends on the cytokine milieu and the clinical phenotype of the patient. Further studies are required to determine the molecular mechanism of IL-22 and TGF-β1 cooperativity in driving EMT in primary human bronchial epithelial cells.