Abstract 3510: PAR1(1–26): The Putative Signal Peptide of Protease-Activated Receptor 1 Confers Potent Protection From Myocardial Ischemia and Reperfusion Injury Through a Gi-Protein Signaling Pathway
Background The Protease-Activated Receptor 1 (PAR1) is activated by the proteolytic release of the N-terminal 41 amino acids. Exogenously administered PAR1(1– 41) peptides protect against myocardial ischemia and reperfusion injury in the rat. In the present study, we determined whether PAR1(1–26), the putative signal peptide of PAR1 contains the functional domain of PAR1(1– 41).
Methods and Results We assessed the protective role of a synthesized PAR1(1–26) peptide in an in vivo rat model of myocardial regional ischemia and reperfusion injury (n=6/group). PAR1(1–26) (0.01–10 μg/kg) treatment immediately before ischemia reduced infarct size from 58±1% to 13±1% area at risk (p<0.01) at an optimal dose of 10 μg/kg. Treatment with PAR1(1–26) after the onset of reperfusion decreased infarct size to 22±1% area at risk (p<0.01). We then explored the survival pathways known to be up-regulated by pharmacologic cardioprotectants. Inhibition of Gi proteins (pertussis toxin), PI3K/Akt (Wortmannin), nitric oxide synthase (NOS; L-NMA), soluble guanylyl cyclase (sGC; ODQ) and sarcolemmal and mitochondrial KATP channels (5-HD, and HMR 1098) abolished the infarct sparing effects of PAR1(1–26). Atractyloside, a mitochondrial permeability transition pore (mPTP) opener also negated PAR1(1–26) cardioprotection. The inhibitors and opener alone had no effect on infarct size. Furthermore, pre-ischemic treatment with PAR1(1–26) increased Akt and endothelial NOS phosphorylation at the time of reperfusion. After 120 min reperfusion, NO levels increased 1.4-fold and cyclic GMP levels increased 4.5-fold in PAR1(1–26) treated hearts when compared to control as detected by NO chemiluminescence and a cyclic GMP assay kit (p<0.05).
Conclusions A single treatment of PAR1(1–26) either before or after ischemia protected against ischemia and reperfusion injury. This protection required a Gi protein mediated pathway which included Akt, NOS, sGC, KATP channels and mPTP, the end effector of the preconditioning pathway. This suggests a potential therapeutic role of PAR1(1–26) in the treatment of ischemia and reperfusion injury.