• Hideaki Kouzaki, Koji Matsumoto, Hirotaka Kikuoka, Tomohisa Kato, Ichiro Tojima, Shino Shimizu, Hirohito Kita, and Takeshi Shimizu.
• 1 Department of Otorhinolaryngology, Shiga University of Medical Science, Otsu, Shiga, Japan; and.
• Am. J. Respir. Crit. Care Med. 2017 Mar 15; 195 (6): 737-747.

RationaleCystatin A and SPINK5 are endogenous protease inhibitors (EPIs) that may play key roles in epithelial barrier function.ObjectivesTo investigate the roles of EPIs in the pathogenesis of chronic rhinosinusitis (CRS).MethodsWe examined the expression of cystatin A and SPINK5 in the nasal epithelial cells of patients with CRS. Additionally, the in vitro effects of recombinant EPIs on the secretion of the epithelial-derived cytokines IL-25, IL-33, and thymic stromal lymphopoietin in airway epithelial cells, and the in vivo effects of recombinant EPIs in the nasal epithelium of mice exposed to multiple airborne allergens (MAA) were examined.Measurements And Main ResultsCompared with control subjects and patients with noneosinophilic CRS, patients with eosinophilic CRS showed significantly lower protein and mRNA expression of cystatin A and SPINK5 in the nasal epithelium. Allergen-induced production of IL-25, IL-33, and thymic stromal lymphopoietin in normal human bronchial epithelial cells was inhibited by treatment with recombinant cystatin A or SPINK5. Conversely, the production of these cytokines was increased when cystatin A or SPINK5 were knocked down with small interfering RNA. Chronic MAA exposure induced goblet cell metaplasia and epithelial disruption in mouse nasal epithelium and decreased the tissue expression and nasal lavage levels of cystatin A and SPINK5. Intranasal instillations of recombinant EPIs attenuated this MAA-induced pathology.ConclusionsCystatin A and SPINK5 play an important role in protecting the airway epithelium from exogenous proteases. The preservation of EPIs may have a therapeutic benefit in intractable airway inflammation, such as eosinophilic CRS.

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