Proteinase-activated receptor-1 is an anti-inflammatory signal for colitis mediated by a type 2 immune response

Activation of colonic proteinase activated receptor-1 (PAR1) provokes colonic inflammation and increases mucosal permeability in mice. The mechanism of inflammation is not neurogenic like in the paw of rats but depends on PAR1-mediated activation monocytic cells. PAR1 activation in the colon increases the release of lymphocyte T helper-1 (TH1) cytokines. Moreover, PAR1 expression is increased in biopsies from patients with inflammatory bowel disease, and its activation during TH1-mediated colitis in mice increases all of the hallmarks of inflammation.

This study aimed to characterize the effects of PAR1 activation in oxazolone-mediated colitis, involving a TH2 cytokine profile.

Intracolonic administration of oxazolone increased myeloperoxidase activity, damage score, and interleukin (IL)-4, IL-10, tumor necrosis factor alpha, and IL-1beta mRNA expression but lowered interferon-gamma mRNA expression, indicating colonic inflammation of a TH2 profile. The concurrent intracolonic administration of a PAR1 agonist in oxazolone-treated mice inhibited colitis, resulting in a reduction of myeloperoxidase activity, damage score, and inflammatory cytokine mRNA expression. Using PAR1-deficient mice, we confirmed that the anti-inflammatory effects of PAR1 agonists were mediated by PAR1. Moreover, in PAR1-deficient mice or in mice treated with a PAR1 antagonist, oxazolone-induced colitis was exacerbated, showing an endogenous modulatory role for PAR1 in this TH2 cytokine profile of colitis.

Thus, as opposed to a previously shown proinflammatory role for PAR1 in a TH1 cytokine-mediated colitis, our new data show anti-inflammatory role for PAR1 activation in the setting of TH2 cytokine colitis model.