Inhibition of airway epithelial-to-mesenchymal transition and fibrosis by kaempferol in endotoxin-induced epithelial cells and ovalbumin-sensitized mice

Chronic airway remodeling is characterized by structural changes within the airway wall, including smooth muscle hypertrophy, submucosal fibrosis and epithelial shedding. Epithelial-to-mesenchymal transition (EMT) is a fundamental mechanism of organ fibrosis, which can be induced by TGF-beta. In the in vitro study, we investigated whether 1-20 mu M kaempferol inhibited lipopolysaccharide (LPS)-induced bronchial EMT in BEAS-2B cells. The in vivo study explored demoting effects of 10-20mg/kg kaempferol on airway fibrosis in BALB/c mice sensitized with ovalbumin (OVA). LPS induced airway epithelial TGF-beta 1 signaling that promoted EMT with concurrent loss of E-cadherin and induction of a-smooth muscle actin (alpha-SMA). Nontoxic kaempferol significantly inhibited TGF-beta-induced EMT process through reversing E-cadherin expression and retarding the induction of N-cadherin and alpha-SMA. Consistently, OVA inhalation resulted in a striking loss of epithelial morphology by displaying myofibroblast appearance, which led to bronchial fibrosis with submucosal accumulation of collagen fibers. Oral administration of kaempferol suppressed collagen deposition, epithelial excrescency and goblet hyperplasia observed in the lung of OVA-challenged mice. The specific inhibition of TGF-beta entailed epithelial protease-activated receptor-1 (PAR-1) as with 20 mu M kaempferol. The epithelial PAR-1 inhibition by SCH-79797 restored E-cadherin induction and deterred alpha-SMA induction, indicating that epithelial PAR-1 localization was responsible for resulting in airway EMT. These results demonstrate that dietary kaempferol alleviated fibrotic airway remodeling via bronchial EMT by modulating PAR1 activation. Therefore, kaempferol may be a potential therapeutic agent targeting asthmatic airway constriction.