Platelet CD40L Modulates Thrombus Growth Via Phosphatidylinositol 3-Kinase β, and Not Via CD40 and IκB kinase α
Objective—To investigate the roles and signaling pathways of CD40L and CD40 in platelet–platelet interactions and thrombus formation under conditions relevant for atherothrombosis.
Approach and Results—Platelets from mice prone to atherosclerosis lacking CD40L (Cd40lg−/−Apoe−/−) showed diminished αIIbβ3 activation and α-granule secretion in response to glycoprotein VI stimulation, whereas these responses of CD40-deficient platelets (Cd40−/−Apoe−/−) were not decreased. Using blood from Cd40lg−/−Apoe−/− and Cd40−/−Apoe−/− mice, the glycoprotein VI-dependent formation of dense thrombi was impaired on atherosclerotic plaque material or on collagen, in comparison with Apoe−/− blood. In all genotypes, addition of CD40L to the blood enhanced the growth of dense thrombi on plaques and collagen. Similarly, CD40L enhanced glycoprotein VI–induced platelet aggregation, even with platelets deficient in CD40. This potentiation was antagonized in Pik3cbR/R platelets or by inhibiting phosphoinositide 3-kinase β. Addition of CD40L also enhanced collagen-induced Akt phosphorylation, which was again antagonized by absence or inhibition of phosphoinositide 3-kinase β. Finally, platelets from Chuk1A/AApoe−/− mice deficient in kinase IκB kinase α, implicated in CD40 signaling to nuclear factor κB, showed unchanged responses to CD40L in aggregation or thrombus formation.
Conclusions—Under atherogenic conditions, CD40L enhances collagen-induced platelet–platelet interactions by supporting integrin αIIbβ3 activation, secretion and thrombus growth via phosphoinositide 3-kinase β, but not via CD40 and IκB kinase α/nuclear factor κB. This role of CD40L exceeds the no more than modest role of CD40 in thrombus formation.
- Received December 9, 2014.
- Accepted April 15, 2015.
- © 2015 American Heart Association, Inc.