0358: Differential AMP-activated protein kinase (AMPK) activation in platelets, in response to various agonists. Comparison between human and murine platelets

Abstract

AMPK is activated during platelet aggregation and controls the phosphorylation state of key cytoskeletal targets. CaMKKβ is responsible for thrombin-induced AMPK activation. Substantial differences have been observed between human and murine platelets. This study aims to bring out the differences in AMPK signalling pathway between human and murine platelets. Only α1 catalytic subunit of AMPK is present in human platelets. Thrombin induces a dramatic AMPKα1 activation and subsequent acetyl-CoA carboxylase (ACC) phosphorylation, while thromboxane A2 (U46619) and collagen exert a marginal effect on both enzymes. ADP has no effect at all. These differences cannot be entirely related to a lower calcium production in response to U46619, collagen and ADP. Indeed, U46619 increases calcium with a similar extent than thrombin while it does not modify ACC phosphorylation. PAR1 but not PAR4-activating peptide reproduces the effect of thrombin on ACC. In addition, inhibition of CaMKKβ/AMPKα1 activation blunts platelet aggregation in response to thrombin and does not affect the response upon stimulation by the other agonists. Murine platelets express AMPKα1 and AMPKα2. AMPK can be activated either by thrombin or U46619 or collagen but not by ADP. The absence of AMPKα1 blocks ACC phosphorylation induced by the three agonists. It mainly inhibits the thrombin-induced platelet aggregation but also significantly reduces aggregation in response to U46619 and collagen. The absence of AMPKα2 does not affect the increase in ACC phosphorylation, whatever the agonist used. AMPKα1 is the sole catalytic subunit of AMPK expressed in human platelets and is activated by thrombin through PAR1. Murine platelets contain both catalytic subunits although α1 plays a predominant role. In mice, thrombin is not the predominant AMPK activator probably because of the difference in the type of PAR expression. Signalling events of mouse platelets can diverge from those of human platelets.