PDK1 regulates platelet activation and arterial thrombosis

Abstract

The effects of phosphoinositide-dependent protein kinase 1 (PDK1), amaster kinase in the phosphoinositide 3-kinase/Akt pathway, on platelet activation are unknown. Accordingly, platelet-specific PDK1-deficient mice were characterized to elucidate the platelet-related function(s) of PDK1. We found that PDK1 deficiency caused mild thrombocytopenia. The aggregation of PDK1-/- platelets was diminished in response to low levels of thrombin, U46619, and adenosine 5′-diphosphate. Further results demonstrated that PDK1 regulates thrombin-induced platelet activation by affecting αIIbβ3-mediated outside-in signaling. This result provided an explanation for the diminished spreading of PDK1-/- platelets on immobilized fibrinogen (Fg) and the decreased rate of clot retraction in platelet-rich plasma (PRP) containing PDK1-/- platelets. PDK1 deficiency diminished agonist-induced Akt Ser473 phosphorylation and thoroughly abolished Akt Thr308 and Gsk3b Ser9 phosphorylation in response to agonist treatment and platelet spreading, respectively. A Gsk3β inhibitor fully restored the aggregation of PDK1 -/- platelets in response to low levels of thrombin, normal spreading of PDK1-/- platelets on Fg, and normal clot retraction in PRP containing PDK1-/- platelets. Those results indicated that Gsk3β is one of the major downstream effectors of PDK1 in thrombininduced platelet activation and αIIbβ3-mediated outside-in signaling. In addition, in vivo data demonstrated that PDK1 is an important regulator in arterial thrombosis formation. © 2013 by The American Society of Hematology.