Background: Antithrombin (AT) is an endogenous protein of the serpin superfamily involved in regulation of the proteolytic activity of the serine proteases of the coagulation system. AT is known to exhibit anti-inflammatory and cardioprotective properties when it binds to distinct heparan sulfate proteoglycans (HSPGs) on vascular endothelial cells. The energy sensor AMP-activated protein kinase (AMPK) plays an important cardioprotective role during myocardial ischemia and reperfusion (I/R). The objective of this study was to investigate whether the cardioprotective signaling function of AT against I/R injury is mediated through the AMPK pathway.
Methods and Results: The cardioprotective activities of wild-type (WT) AT and its two recombinant derivatives, one having high affinity and the other no affinity for heparin, were evaluated in an acute I/R (20 min/4 h) injury model in which the left anterior descending coronary artery (LAD) was occluded. The serpin derivatives were given 5 min before reperfusion. The results showed that AT-WT can activate the protective AMPK signaling pathway in both in vivo and ex vivo conditions. Blocking AMPK activity abolished the cardioprotective function of AT against I/R injury. The AT derivative having high affinity for heparin was more effective in activating AMPK, but the derivative lacking any affinity for heparin was inactive in eliciting AMPK-dependent cardioprotective activity. The activation of AMPK by AT inhibited the inflammatory c-Jun N-terminal protein kinase (JNK) pathway during I/R. Further studies revealed that the AMPK activity of AT also modulates cardiac substrate metabolism by increasing glucose oxidation but inhibiting fatty acid oxidation during I/R.
Conclusions: These results suggest that AT binds to vascular HSPGs to invoke a cardioprotective function by triggering cardiac AMPK activation, thereby attenuating JNK inflammatory signaling pathways and modulating substrate metabolism during I/R.