House dust mite induces Sonic hedgehog signaling that mediates epithelial-mesenchymal transition in human bronchial epithelial cells

Epithelial-mesenchymal transition (EMT) provides a valuable source of fibroblasts that produce extracellular matrix in airway walls. The Sonic hedgehog (SHH) signaling pathway plays an essential role in regulating tissue turnover and homeostasis. SHH is strikingly upregulated in the bronchial epithelia during asthma. Snail1 is a major target of SHH signaling, which regulates EMT and fibroblast motility. The present study was designed to ascertain whether the combination of house dust mite (HDM) and transforming growth factor β1 (TGF-β1) could induce EMT via the SHH signaling pathway in human bronchial epithelial cells (HBECs). HBEC cultures were treated with HDM/TGF-β1 for different periods of time. The involvement of SHH signaling and EMT biomarkers was evaluated by quantitative real-time PCR, western blotting and immunofluorescence staining. Small-interfering RNA (siRNA) for glioma-associated antigen-1 (Gli1) or cyclopamine was used to inhibit SHH signaling in HBECs. HBECs stimulated by HDM/TGF-β1 exhibited morphological features of EMT. E-cadherin (an epithelial marker) was decreased after a 72-h exposure to HDM/TGF-β1 compared to that in the control cells, and the expression of type I collagen and FSP1 (mesenchymal markers) was increased. HDM/TGF-β1 activated the SHH signaling pathway in HBECs, which led to Gli1 nuclear translocation and the transcriptional activation of Snail1 expression. Moreover, gene silencing or the pharmacological inhibition of Gli1 ameliorated EMT. In summary, these findings suggest that HDM/TGF-β1 may induce EMT in HBECs via an SHH signaling mechanism. Inhibition of SHH signaling may be a novel therapeutic method for preventing airway remodeling in asthma.