Abstract 1029: Protease-activated Receptor-2 Modulates Mitogenesis in Human Vascular Smooth Muscle Cells by a Peroxisome Proliferator-activated Receptor-γ-dependent Pathway
Protease-activated receptor-2 (PAR-2) is a G-protein-coupled receptor that is activated by trypsin and factor-Xa, but not by thrombin. It plays an important role in inflammation by regulating prostaglandin production and exerts mitogenic effects in vascular smooth muscle cells (SMC), similar to the thrombin receptor PAR-1. However, evidence accumulates that PAR-2 may also function antagonistic to PAR-1 and may inhibit mitogenesis. Prostaglandin (PG) J2, which converts from the prostaglandin D2 synthase (PGDS) product PGD2, inhibits mitogenesis via activation of the peroxisome proliferator-activated receptor-γ (PPAR-γ). This study describes that activation of PAR-2 in human SMC has antimitogenic effects via a PPAR-γ-dependent mechanism. Human SMC were explanted from aorta and mammary artery. Specific peptides were used to activate PAR1 (PAR1-AP) and PAR2 (PAR2-AP). DNA synthesis was determined by [3H]-thymidine incorporation, Akt (protein kinase B) phosphorylation by Western blotting, lipocalin-type and hematopoietic (L-/H-) PDGS by RT-PCR. While PAR1-AP caused a dose-dependent increase in DNA synthesis, PAR2-AP (0.3–300 μmol/L each) caused only a minor mitogenic response. When PAR1 or PAR2 were activated prior to stimulation of DNA synthesis with fetal calf serum (FCS), PAR1-AP caused further increase in mitogenesis. In contrast, activation of PAR2 caused a significant reduction of DNA synthesis (3% FCS: 44±4%, 10% FCS: 35±7% inhibition). This inhibitory effect of PAR2-AP was reversed by the non-selective cyclooxygenase (COX) inhibitor diclofenac (1.5 μmol/L), by the COX-1 inhibitor SC-560 (1 μmol/L), and by the PPAR-γ specific inhibitor GW9662 (1 μmol/L). COX-2 selective inhibitors did not affect the antimitogenic action of PAR2. Furthermore, PAR2-AP attenuated FCS-induced phosphorylation of Akt after 8–16 hours of stimulation. RNA for both L- and H-PGDS, which can increase the PPAR-γ activating PGJ2, was expressed in these cells. The antimitogenic effect of PAR-2 activation was mimicked by troglitazone, which activates PPAR-γ. These data suggest that PAR-2 can modulate mitogenesis in human vascular SMC via increased COX-1-dependent PGJ2 production and activation of PPAR-γ.