Increased expression of protease-activated receptor-2 (PAR2) and PAR4 in human coronary artery by inflammatory stimuli unveils endothelium-dependent relaxations to PAR2 and PAR4 agonists

Abstract

Protease-activated receptor (PAR)1 and PAR2 are expressed on vascular endothelial cells and mediate endothelium-dependent relaxation in several species, and PAR4 agonists cause similar responses in rat aortas. To date, only PAR1 has been reported to mediate relaxation of human arteries despite endothelial cell expression of both PAR1 and PAR2 in these tissues. Because inflammatory stimuli increase PAR2 expression in human endothelial cells in culture, the present study investigated the effect of similar stimuli on PARs in human isolated coronary arteries (HCAs). In HCA ring segments suspended for isometric tension measurements, the selective PAR1-activating peptide, TFLLR (0.01 to 10 μmol/L), caused endothelium-dependent relaxation of precontracted preparations. Little or no change in vascular tension was elicited by either the PAR2- or PAR4-activating peptides, SLIGKV and GYPGQV, respectively (up to 100 μmol/L). Exposure of HCAs to interleukin (IL)-1α (1 ng/mL, 12 hours) or tumor necrosis factor-α (3 nmol/L, 12 hours) did not affect PAR1 expression but increased PAR2 and PAR4 mRNA levels by ≈5- and 4-fold, respectively, as determined by quantitative polymerase chain reaction. Similar IL-1α treatment did not affect TFLLR-induced relaxations but revealed significant endothelium-dependent relaxations to SLIGKV (100 μmol/L, 61.4±6.7%) and GYPGQV (100 μmol/L, 34.8±6.4%). These studies are the first to demonstrate functional PAR2 and PAR4 in human arteries in situ. The selective upregulation of PAR2 and PAR4 expression and the increased vascular response in HCAs after exposure to inflammatory stimuli suggest a role for these endothelial receptors during inflammation.