Platelet CD40L Modulates Thrombus Growth Via Phosphatidylinositol 3-Kinase beta, and Not Via CD40 and I kappa B Kinase alpha

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 alpha(IIb)beta(3) activation and a-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 Pik3cb(R/R) platelets or by inhibiting phosphatidylinositol 3-kinase beta(PI3K beta). Addition of CD40L also enhanced collagen-induced Akt phosphorylation, which was again antagonized by absence or inhibition of PI3K beta. Finally, platelets from Chuk1(A/A)Apoe(-/-)mice deficient in I kappa B kinase alpha (IKK alpha), implicated in CD40 signaling to nuclear factor (NF)kappa B, showed unchanged responses to CD40L in aggregation or thrombus formation. Conclusions-Under atherogenic conditions, CD40L enhances collagen-induced platelet-platelet interactions by supporting integrin alpha(IIb)beta(3) activation, secretion and thrombus growth via PI3K beta, but not via CD40 and IKK alpha/NF kappa B. This role of CD40L exceeds the no more than modest role of CD40 in thrombus formation.