The effect of neutrophil serine proteases on human nasal epithelial cell barrier function

Background The neutrophil serine proteases neutrophil elastase (NE), cathepsin G (CG), and proteinase 3 (PR3) are implicated in the regulation of inflammatory conditions. Pseudomonas aeruginosa elastase (PE), also a serine protease, has been found to behave similarly to NE and has been proposed to assist the pathogen in evading the host immune response. The effect of serine proteases on human nasal epithelial barrier function requires further investigation to better understand the pathophysiology of inflammatory conditions. Methods Purified human neutrophil serine proteases and PE were applied to primary human nasal epithelial cells grown at air-liquid interface (HNEC-ALI) cultures from 6 patients. Barrier integrity and function was assessed via transepithelial electrical resistance (TER), permeability assays, immunofluorescence of Zona occludens-1 (ZO-1), and ciliary beat frequency (CBF) measurements. Cytotoxicity assays were employed to assess cell viability. Interleukin 6 (IL-6) and IL-8 enzyme-linked immunosorbent assay (ELISA) assessed cytokine release from HNEC-ALI. Results The application of serine proteases showed detrimental effects on HNEC-ALI barrier integrity. Reduction in TER occurred with NE, CG, and PE with increased paracellular permeability with NE, CG, PR3, and PE. Discontinuous tight junctions with reduction in ZO-1 expression were identified using immunofluorescence. Neutrophil serine proteases were not toxic cells to the HNECs and had no detrimental effects on the CBF. Conclusion Serine proteases derived from neutrophils and from P. aeruginosa showed detrimental effects on the mucosal barrier integrity with increased permeability, allowing for potential bacterial invasion. This finding may further assist in understanding the pathophysiology present in chronic inflammatory airway diseases.