House Dust Mites Induce Production of Endothelin-1 and Matrix Metalloproteinase-9 in Keratinocytes via Proteinase-Activated Receptor-2 Activation

<b><i>Background:</i></b> Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by skin barrier dysfunction and abnormal immune response. House dust mites (HDM) are a major source of allergens, some of which have cysteine and serine protease activities. Keratinocytes stimulated by HDM-derived proteases have been suggested to contribute to the pathogenesis of AD by producing various cytokines. However, whether keratinocytes contribute to the induction of pruritus in AD, especially by producing pruritus-related mediators upon stimulation with HDM-derived proteases, has not been fully elucidated. <b><i>Methods:</i></b> We examined whether the production of endothelin-1 (ET-1), matrix metalloproteinase (MMP)-2, and MMP-9 in keratinocytes can be induced by stimulation with <i>Dermatophagoides farinae</i> extracts, and if so, whether pretreatment with a protease inhibitor or proteinase-activated receptor-2 (PAR-2) antagonist affects the production of these mediators in keratinocytes. <b><i>Results:</i></b> Although MMP-2 levels were undetectable in the culture supernatants, the production of ET-1 and MMP-9 was increased upon stimulation with HDM extracts in a concentration- and time-dependent manner and suppressed by pretreatment of HDM extracts with serine protease inhibitor, but not with cysteine protease inhibitor. Mite-derived serine proteases also induced ET-1 and MMP-9 production in a concentration- and time-dependent manner. Moreover, pretreatment with a PAR-2 antagonist inhibited the production of ET-1 and MMP-9 in keratinocytes. <b><i>Conclusion:</i></b> These results suggest that the activation of PAR-2 on keratinocytes by HDM-derived serine proteases induces the production of ET-1 and MMP-9, and may contribute to the induction of pruritus in AD.