Mast cell chymase affects the functional properties of primary human airway fibroblasts: Implications for asthma.

BACKGROUND: Mast cells (MCs) have a profound impact on allergic asthma. Under such conditions, MCs undergo degranulation, resulting in the release of exceptionally large amounts of MC-restricted proteases. However, the role of these proteases in asthma is only partially understood. OBJECTIVES: We sought to test our hypothesis that MC proteases can influence the functionality of human lung fibroblasts (HLFs). METHODS: Primary HLFs were treated with MC chymase or tryptase, followed by assessment of parameters related to fibroblast function. RESULTS: HLFs underwent major morphologic changes in response to chymase, showing signs of cellular contraction, but were refractory to tryptase. However, no effects of chymase on HLF viability or proliferation were seen. Chymase, but not tryptase, had a major impact on the output of extracellular matrix-associated compounds from the HLFs, including degradation of fibronectin and collagen-1, and activation of pro-matrix metalloprotease 2. Further, chymase induced the release of various chemotactic factors from HLFs. In line with this, conditioned medium from chymase-treated HLFs showed chemotactic activity on neutrophils. Transcriptome analysis revealed that chymase induced a proinflammatory gene transcription profile in HLFs, whereas tryptase had minimal effects. CONCLUSIONS: Chymase, but not tryptase, has a major impact on the phenotype of primary airway fibroblasts by modifying their output of extracellular matrix components and by inducing a proinflammatory phenotype.

Targeting integrin α5ß1 ameliorates severe airway hyperresponsiveness in experimental asthma.

Treatment options are limited for severe asthma, and the need for additional therapies remains great. Previously, we demonstrated that integrin αvß6-deficient mice are protected from airway hyperresponsiveness, due in part to increased expression of the murine ortholog of human chymase. Here, we determined that chymase protects against cytokine-enhanced bronchoconstriction by cleaving fibronectin to impair tension transmission in airway smooth muscle (ASM). Additionally, we identified a pathway that can be therapeutically targeted to mitigate the effects of airway hyperresponsiveness. Administration of chymase to human bronchial rings abrogated IL-13-enhanced contraction, and this effect was not due to alterations in calcium homeostasis or myosin light chain phosphorylation. Rather, chymase cleaved fibronectin, inhibited ASM adhesion, and attenuated focal adhesion phosphorylation. Disruption of integrin ligation with an RGD-containing peptide abrogated IL-13-enhanced contraction, with no further effect from chymase. We identified α5ß1 as the primary fibronectin-binding integrin in ASM, and α5ß1-specific blockade inhibited focal adhesion phosphorylation and IL-13-enhanced contraction, with no additional effect from chymase. Delivery of an α5ß1 inhibitor into murine airways abrogated the exaggerated bronchoconstriction induced by allergen sensitization and challenge. Finally, α5ß1 blockade enhanced the effect of the bronchodilator isoproterenol on airway relaxation. Our data identify the α5ß1 integrin as a potential therapeutic target to mitigate the severity of airway contraction in asthma.