CAMKKβ/AMPK-α1 pathway regulates phosphorylation of cytoskeletal targets in thrombin-stimulated human platelets

Background. Platelet activation requires sweeping morphological changes, supported by contraction and remodelling of platelet actin cytoskeleton. In various other cell types, AMP-activated protein kinase (AMPK) controls the phosphorylation state of cytoskeletal targets. Objective. We hypothesized that AMPK is activated during platelet aggregation and contributes to the control of cytoskeletal targets. Results. We found that AMPK-α1 was mainly activated by thrombin and not by other platelet agonists in purified human platelets. Thrombin activated AMPK-α1 ex vivo via a Ca2+/calmodulin-dependent kinase kinase β (CAMKKβ)-dependent pathway. Pharmacological inhibition of CAMKKβ blocked thrombin-induced platelet aggregation and counteracted thrombin-induced phosphorylation of several cytoskeletal proteins, namely, regulatory myosin light chains (MLC), cofilin and vasodilator-stimulated phosphoprotein (VASP), three key elements involved in actin cytoskeleton contraction and polymerization. Platelets isolated from mice lacking AMPK-α1 exhibited reduced aggregation in response to thrombin, associated with a defect in MLC, cofilin and VASP phosphorylation and actin polymerization. More importantly, we show for the first time that AMPK pathway was activated in platelets of patients undergoing major cardiac surgery, in a heparin-sensitive manner. Conclusion. AMPK-α1 is activated by thrombin in human platelets. It controls phosphorylation of key cytoskeletal targets and actin cytoskeleton remodelling during platelet aggregation