Abstract 189: The Cardioprotective Effect of Activated Protein C is Separate From its Anticoagulant Activity
Background: Activated protein C (APC) is a natural plasma serine protease that down-regulates the clotting and inflammatory pathways. In the latter pathway, APC is known to prevent ischemic/reperfusion injury by an unknown mechanism. Here, we investigated the molecular mechanism responsible for the APC's cardioprotective effect.
Methods and Results: FVB/NJ mice were subjected to 20 min ischemia via left coronary artery occlusion followed by 3 hr reperfusion. APC was injected via tail vein (0.2 μg/g) 5 min before reperfusion. Myocardial infarction (MI) was significantly reduced in the APC group (14.4 ± 2.1% vs. 30.9 ± 2.9% saline control, infarct area/area at risk, n=4–5 per group, p<0.05). To determine whether the anticoagulant or the anti-inflammatory signaling activity of APC contributes to its cardioprotective effect, two APC mutants were generated possessing either signaling (APC-2Cys) or anticoagulant activity (APC-E170A). APC-2Cys decreased MI (18.4 ± 1.7%, n=4, p<0.05 vs. saline), but APC-E170A had no effect (27.8 ± 2.8%, n=4, p=NS vs. saline), suggesting that the cardioprotective effect of APC is due to its signaling activity. Intriguingly, APC augmented the activation of AMP-activated protein kinase (AMPK) in ischemic hearts. Moreover, the cardioprotection of APC was abrogated in AMPKα2 KO mice, suggesting that AMPK plays a key role in mediating the APC's cardioprotection against ischemic injury. To further address whether the APC-AMPK cascade can modulate substrate metabolism in the ischemic heart, isolated WT hearts (n=4 each group) were subjected to 10 min global ischemia followed by 30 min reperfusion with or without APC treatment in an ex vivo perfused system. The results demonstrated that APC augments the glucose uptake in the ischemic heart when compared to the control group (0.64 ± 0.04 vs. 0.52 ± 0.02 μmol/min/g, p<0.05). Moreover, APC significantly improved the post-ischemic left ventricular contractile function (78 ± 7% vs. 51 ± 7% of baseline, p<0.05 vs. control group).
Conclusions: APC protects against myocardial ischemic injury by triggering AMPK signaling pathway. Thus, APC derivatives possessing only signaling activity may be developed as therapeutic drugs for treating ischemic heart diseases with no risk of bleeding.
- © 2010 by American Heart Association, Inc.