Alternaria‐induced barrier dysfunction of nasal epithelial cells: role of serine protease and reactive oxygen species

Background Upper airway barrier dysfunction has been associated with chronic rhinosinusitis and allergic rhinitis. Alternaria is commonly found in nasal secretion and plays a role in the pathogenesis of airway diseases. The aim of this study was to investigate the effects of Alternaria on the junctional complex of nasal epithelial cells. Methods Air‐liquid interface nasal epithelial cultures from the inferior turbinate of septal surgery patients were stimulated with Alternaria alternate. Production of intracellular reactive oxygen species (ROS) and transepithelial resistance (TER) was measured. The expression of tight junction (TJ) and adherens junction (AJ) molecules was determined using real‐time reverse transcriptase‐polymerase chain reaction, Western blot analysis, and confocal microscopy. Protease activity in Alternaria was determined using protease inhibitors and heat inactivation. Results Alternaria enhanced the production of ROS and reduced the TER. Alternaria decreased the messenger RNA and protein expression of TJs (zonula occludens‐1, occludin, and claudin‐1), but did not influence the AJ molecule. When Alternaria was pretreated with serine protease inhibitor and heat inactivation, ROS, TER, and TJ molecule expression returned to their nonstimulated levels. Conclusion Serine protease in Alternaria altered nasal epithelial barrier function. Intracellular ROS induced by Alternaria may influence the barrier function of nasal epithelial cells and enhance the inflammatory process of nasal mucosa.