Farm dust inhibits epithelial-to-mesenchymal transition in airway epithelial cells exposed to pro-fibrotic mediators after injury

Growing up on a traditional farm is associated with protection against wheezing, allergies and asthma. This protective farm effect is confirmed by studies that show that farm dust extract (FD) improves epithelial barrier function in primary bronchial epithelial cells (PBEC) and enhances repair in co-cultures of PBEC and macrophages. Epithelial-to-mesenchymal transition (EMT) contributes to normal repair at epithelial surfaces. However, during ongoing inflammation and repetitive injury, EMT may persist and contribute to excessive extracellular matrix deposition and airway remodeling. We therefore investigated whether FD exposure modulates EMT in a model of mechanical epithelial injury, in which a pro-fibrotic mediator cocktail (FC) is added to increase EMT. To this end, circular wounds were made in differentiated PBEC cultures that were first pretreated with FD for 24h and subsequently cultured in presence or in absence of FD and FC (TGF-β1, lysophosphatidic acid, PDGF-AB, and TNF-α). Wound closure was monitored for 48h and cells were harvested for immunofluorescence and gene expression analysis. We observed that FC-exposure significantly increased wound closure after 29h (89% in FC-exposed cultures versus 67% in controls), and protein and/or gene expression of EMT-markers (vimentin [26-fold], fibronectin [184-fold] and PAI-1 [22-fold]). FD significantly inhibited FC-induced expression of EMT-markers (p < 0.001), without affecting wound closure in presence and absence of FC. Collectively, this study showed that FD prevents EMT but does not affect wound closure, suggesting a protective effect of FD against processes associated with airway remodeling.