Abstract 68: PAR2 Activation at Reperfusion Salvages myocardium via ERK 1/2 Pathway in in vivo Rat Hearts
Protease activated receptor-2 (PAR2), a seven transmembrane G protein coupled receptor, is expressed on endothelial cells and cardiomyocytes, and overexpressed in these cells under pathological conditions. However the role of PAR2 in in vivo myocardial ischemia-reperfusion has not yet been determined.
Objective: This study tested the hypothesis that 1) PAR2 activation with the specific PAR2 agonist peptide (PAR2 AP) SLIGRL reduces myocardial infarct size following ischemia - reperfusion in vivo, and 2) this cardioprotection involves the ERK 1/2 signaling pathway.
Methods: Rats were randomly assigned to one of 8 groups with 30 minutes left coronary artery (LCA) occlusion followed by 3 hours reperfusion:
control with equal volume of saline;
Vehicle (DMSO), 300 μl/ Kg 10 minutes before reperfusion;
PAR2 AP: 1mg/ kg intravenously 5 minutes before reperfusion;
scrambled peptide: 1mg/kg 5 minutes before reperfusion;
the ERK 1/2 inhibitor PD 98059 (PD) alone, 0.3 mg/kg 10 minutes before reperfusion;
the PI3-K inhibitor Ly 294002 (Ly) alone, 0.3 mg/kg 10 minutes before reperfusion;
PD + PAR2 AP: PD 0.3 mg/kg 5 minutes before PAR2 AP;
Ly + PAR2 AP: Ly 0.3 mg/kg 5 minutes before PAR2 AP.
Infarct size was determined by TTC, presented as a percentage of the area at risk (AN/AAR). In a separate set of experiments for Western blot analysis, rats were subjected to 30 minutes LCA occlusion and 5 minutes reperfusion with no treatment (sham), control, scrambled peptide and PAR2 AP to quantify phosphorylation of Akt and ERK 1/2 in the AAR myocardium.
Results: PAR2 AP significantly reduced infarct size compared to control (36 ± 2%* vs 53 ± 1%) and scrambled peptide had no effect on infarct size (53 ± 3%). Western blot analysis demonstrated that PAR2 AP administration significantly increased phosphorylation of ERK 1/2 in AAR myocardium at 5 minutes reperfusion, but not phosphorylation of Akt. Accordingly, the infarct size sparing effect of PAR2 AP was abolished by PD 98059 ( PAR2 AP: 36 ± 2% vs PD + PAR2 AP: 50 ± 1%, p < 0.05) but not by Ly294002 (PAR2 AP: 36 ± 2% vs Ly + PAR2 AP: 38 ± 3%, p > 0.05).
Conclusions: Specific PAR2 activation is cardioprotective in the in vivo rat heart ischemia-reperfusion model, and this protection involves the ERK 1/2 pathway. * = p< 0.05 vs Control