House dust mite-derived serine protease upregulates gene expression of interleukin-33 in canine keratinocytes via protease-activated receptor-2

Background The involvement of interleukin (IL)-33 produced by keratinocytes has been suggested in the pathogenesis of canine atopic dermatitis (cAD). House dust mite (HDM)-derived proteases induce the production of various cytokines and chemokines in keratinocytes via protease-activated receptor-2 (PAR-2); however, their effects on IL-33 mRNA expression in canine keratinocytes have not been determined. Hypothesis/Objective To clarify whether HDM-derived proteases induce IL-33 mRNA expression in canine keratinocytes via PAR-2. Methods and materials Expression of IL-33 mRNA was quantified by real-time PCR in a cell line of canine progenitor epidermal keratinocytes (CPEK) stimulated with Dermatophagoides farinae (Der f) whole body extract, Der f pre-treated with cysteine protease and serine protease inhibitors, and trypsin. Trypsin and Der f-mediated IL-33 mRNA expression also was measured in CPEK cells treated with a PAR-2 antagonist. Results Der f enhanced IL-33 mRNA expression in CPEK cells in incubation time- and dose-dependent manners. Der f pre-treated with a serine protease inhibitor, and not a cysteine protease inhibitor, abrogated an increase in IL-33 mRNA expression in CPEK cells. Trypsin also enhanced IL-33 mRNA expression in CPEK cells. Trypsin-mediated IL-33 mRNA expression was completely abolished by a PAR-2 antagonist, while Der f-mediated IL-33 mRNA expression was partially and significantly diminished by it. Conclusions and clinical relevance Der f-derived serine protease upregulated IL-33 mRNA expression in CPEK cells at least in part via PAR-2. These findings suggest that HDM may be involved in the development of (C)AD by increasing IL-33 mRNA expression in keratinocytes.