COX-1 mediates IL-33-induced extracellular signal-regulated kinase activation in mast cells: Implications for aspirin sensitivity.

Abstract

Classical FcεRI-induced mast cell (MC) activation causes synthesis of arachidonic acid (AA)-derived eicosanoids (leukotriene [LT] C₄, prostaglandin [PG] D₂, and thromboxane A₂), which mediate vascular leak, bronchoconstriction, and effector cell chemotaxis. Little is known about the significance and regulation of eicosanoid generation in response to nonclassical MC activation mechanisms. We sought to determine the regulation and significance of MC-derived eicosanoids synthesized in response to IL-33, a cytokine critical to innate type 2 immunity. We used an ex vivo model of mouse bone marrow-derived mast cells and an IL-33-dependent in vivo model of aspirin-exacerbated respiratory disease (AERD). IL-33 potently liberates AA and elicits LTC₄, PGD₂, and thromboxane A₂ production by bone marrow-derived mast cells. Unexpectedly, the constitutive function of COX-1 is required for IL-33 to activate group IVa cytosolic phospholipase A₂ with consequent AA release for synthesis of all eicosanoids, including CysLTs. In contrast, COX-1 was dispensable for FcεRI-driven CysLT production. Inhibition of COX-1 prevented IL-33-induced phosphorylation of extracellular signal-related kinase, an upstream effector of cytosolic phospholipase A₂, which was restored by exogenous PGH₂, implying that the effects of COX-1 required its catalytic function. Administration of a COX-1-selective antagonist to mice completely prevented the generation of both PGD₂ and LTC₄ in a model of AERD in which MC activation is IL-33 driven. MC-intrinsic COX-1 amplifies IL-33-induced activation in the setting of innate type 2 immunity and might help explain the phenomenon of therapeutic desensitization to aspirin by nonselective COX inhibitors in patients with AERD.