Platelet PI3Kß and GSK3 regulate thrombus stability at a high shear rate.

ABSTRACT

Class IA phosphoinositide 3-kinase ß (PI3Kß) is considered a potential drug target in arterial thrombosis, which is a major cause of death worldwide. Here we show that a striking phenotype of mice with selective p110ß deletion in the megakaryocyte lineage is thrombus instability at a high shear rate, which is an effect that is not detected in the absence of p110α in platelets. The high shear rate-dependent thrombus instability in the absence of p110ß is observed both ex vivo and in vivo with the formation of platelet emboli. Moreover, PI3Kß is required for the recruitment of new platelets to a growing thrombus when a pathological high shear is applied. Treatment of human blood with AZD6482, a selective PI3Kß inhibitor, phenocopies p110ß deletion in mouse platelets, which highlights the role of the kinase activity of p110ß. Within the growing platelet thrombus, p110ß inactivation impairs the activating phosphorylations of Akt and the inhibitory phosphorylation of GSK3. In accord with these data, pharmacologic inhibition of GSK3 restores thrombus stability. Thus, platelet PI3Kß is not essential for thrombus growth and stability at normal arterial shear but has a specific and critical role in maintaining the integrity of the formed thrombus on elevation of shear rate, suggesting a potential risk of embolization on treatment with PI3Kß inhibitors.