House Dust Mite–Promoted Epithelial-to-Mesenchymal Transition in Human Bronchial Epithelium

Abstract

The molecular basis of airway remodeling and loss of epithelial integrity in asthma is still undefined. We aimed to establish if exposure of human bronchial epithelium (16HBE cells) to asthma-related stimuli can induce epithelial-to-mesenchymal transition (EMT), a key process in tissue repair and remodeling associated with loss of intercellular contacts. We studied the effects of fibrogenic cytokine TGF-beta and protease-containing aeroallergen house dust mite (HDM) on mesenchymal and epithelial markers, cytoskeleton organization, and activation of beta-catenin-driven reporter TopFLASH. TGF-beta alone up-regulated vimentin and fibronectin, modestly down-regulated E-cadherin, but did not affect cytokeratin. HDM alone did not affect these markers, but promoted stress fibers. Importantly, when added to TGF-beta-primed epithelium, HDM induced E-cadherin internalization, enhanced beta-catenin-dependent transcription, and down-regulated cytokeratin. Regarding the underlying mechanisms, the stimuli together induced sustained myosin light chain phosphorylation, which was crucial for E-cadherin internalization and beta-catenin-dependent transcription. Previously, we showed that HDM signals through the epidermal growth factor receptor (EGFR). Accordingly, inhibition of EGFR prevented TGF-beta/HDM-induced mesenchymalization. TGF-beta facilitated uncoupling of EGFR from E-cadherin, its negative regulator, and prolonged EGFR signaling. Thus, we show that HDM promotes EMT in TGF-beta-primed epithelium. Analysis of primary epithelium appears consistent with this phenotypic change. We propose that TGF-beta secretion and dysregulated EGFR signaling may increase epithelial vulnerability to allergens and trigger the induction of EMT, a hitherto unrecognized contributor to airway remodeling in asthma.

Take the Wnt out of the inflammatory sails: modulatory effects of Wnt in airway diseases

“…This synergistically leads to a higher expression of the mesenchymal markers fibronectin and vimentin. 70 These observations suggest that Wnt/β-catenin and TGF-β are important mediators for the induction of structural changes triggered by EMT in the airways of asthma patients following repeated allergen exposure. Given the so far limited amount of data, further confirmation of these findings would strengthen this concept.…”

“…Repetitive or persistent exposure of the airway epithelium by allergen contact, air pollutants, cigarette smoke, or cycles of infection leads to chronic inflammation. This epithelial damage can be directly induced by proteolytic activity of allergens, [68][69][70] histamine, 71 or pollen. 72 Exposure and stress of the epithelium leads to the production of different cytokines, which induce certain immune responses, and can also be involved in aberrant or uncontrolled tissue repair.…”

“…90,91 Different reports suggest that EMT is linked to airway remodeling in asthma. 70,92 Interestingly, EMT is regulated by the Wnt/β-catenin and the noncanonical Wnt signaling pathway. [93][94][95] Also in the lung, Wnt signaling is involved in the regulation of EMT.…”

“…A potential option for the future could be the reactivation of signaling pathways that are active during lung development to induce epithelial repair in the damaged areas similar to the Wnt/β-catenin pathway. 70,105,106 In human lung samples of patients with COPD, a reduction of nuclear β-catenin is detectable. 64 In addition, decreased Wnt/β-catenin activation has been described in different murine models of emphysema and treatment with LiCl attenuated airspace enlargement and prevents the development of emphysema.…”

Characterisation of cell adhesion in airway epithelial cell types using electric cell-substrate impedance sensing

“…All culture media were supplemented with 100 U?mL -1 penicillin and 100 mg?mL -1 streptomycin. PBECs from bronchial brushings in asthma, COPD and healthy control subjects were obtained and cultured as described previously [10][11][12]. Cells were cultured in hormonally supplemented bronchial epithelial growth medium (BEGM; Lonza, Walkersville, MD, USA), in flasks coated with collagen and fibronectin [13], and used for experiments at passage 2.…”