# Protective role of protease-activated receptor-2 in anaphylaxis model mice

## TL;DR

This study shows that protease-activated receptor-2 (PAR-2) protects against anaphylaxis by reducing nitric oxide production, with tryptase acting as its ligand.

## Contribution

The study identifies a protective role of PAR-2 in anaphylaxis through its interaction with mast cell tryptase.

## Key findings

- PAR-2 deficiency worsened anaphylaxis symptoms like hypothermia and hypotension.
- PAR-2 deficiency increased eNOS expression and phosphorylation in anaphylactic lungs.
- Tryptase is likely the ligand for PAR-2 in anaphylaxis, as its absence negated the effect of PAR-2 antagonists.

## Abstract

Anaphylaxis is a severe life-threatening hypersensitivity reaction induced by mast cell degranulation. Among the various mediators of mast cells, little is known about the role of tryptase. Therefore, we aimed to elucidate the role of protease-activating receptor-2 (PAR-2), a receptor activated by tryptase, in murine anaphylactic models using PAR-2-deficient mice and newly generated tryptase-deficient mice. Anaphylaxis was induced by IgE-dependent and IgE-independent mast cell degranulation in mice. PAR-2 deficiency exacerbated the decrease in body temperature and hypotension during anaphylaxis; however, the number of skin mast cells, degree of mast cell degranulation, and systemic and local vascular hyperpermeability were comparable in PAR-2 knockout and wild-type mice. Nitric oxide, which is produced by endothelial nitric oxide synthase (eNOS), is an indispensable vasodilator in anaphylaxis. In the lungs of anaphylactic mice, PAR-2 deficiency promoted eNOS expression and phosphorylation, suggesting a protective effect of PAR-2 against anaphylaxis by downregulating eNOS activation and expression. Based on the hypothesis that the ligand for PAR-2 in anaphylaxis is mast cell tryptase, tryptase-deficient mice were generated using CRISPR-Cas9. In wild-type mice, the PAR-2 antagonist exacerbated the body temperature drop due to anaphylaxis; however, the effect of the PAR-2 antagonist was abolished in tryptase-deficient mice. These results suggest that tryptase is a possible ligand of PAR-2 in anaphylaxis and that the tryptase/PAR-2 pathway attenuates the anaphylactic response in mice.