Summary
Antithrombin (AT) is a 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
heparan sulfate proteo - glycans (HSPGs) on vascular cells. AMP-activated protein
kinase (AMPK) plays an important cardioprotective role during myocardial ischaemia
and reperfusion (I/R). To determine whether the cardioprotective signaling function
of AT is mediated through the AMPK pathway, we evaluated the cardioprotective activities
of wild-type AT and its two derivatives, one having high affinity and the other no
affinity for heparin, in an acute I/R injury model in C57BL/6J mice in which the left
anterior descending coronary artery was occluded. The serpin derivatives were given
5 minutes before reperfusion. The results showed that AT-WT can activate AMPK 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 and in limiting infraction, but the derivative lacking affinity
for heparin was inactive in eliciting AMPK-dependent cardioprotective activity. 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 induced by AT also modulates
cardiac substrate metabolism by increasing glucose oxidation but inhibiting fatty
acid oxidation during I/R. These results suggest that AT binds to HSPGs on heart tissues
to invoke a cardioprotective function by triggering cardiac AMPK activation, thereby
attenuating JNK inflammatory signalling pathways and modulating substrate metabolism
during I/R.