Multiple roles for protease-activated receptor-2 in gastric mucosa

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Abstract
Protease-activated receptor-2 (PAR-2), a G-protein-coupled receptor, is activated by proteolytic unmasking of the N-terminal cryptic tethered ligand. In gastric mucosa, activation of PAR-2 expressed by sensory neurons triggers release of CGRP and tachykinins, leading to mucus secretion via activation of CGRP1 and NK2 receptors, respectively. The PAR-2 agonist reveals mucosal cytoprotective effects in several gastric injury models. Further, PAR-2 activation inhibits gastric acid secretion, independently of sensory neurons or prostanoid formation. The PAR-2 agonist also induces increase in gastric mucosal blood flow, an effect being independent of endogenous CGRP or NO. Endothelium-derived hyperpolarizing factor (EDHF) appears to be involved in the PAR-2-mediated enhancement of mucosal blood flow. In contrast, mucosal chief cells are abundant in immunoreactive PAR-2, and PAR-2 stimulation triggers pepsinogen secretion. Taken together, primarily, PAR-2 plays protective roles in gastric mucosa through multiple mechanisms. Considering PAR-2-mediated pepsinogen secretion, PAR-2 might function as a double-edged sword in gastric mucosa.