CD40L Priming of Platelets via NF-κB Activation is CD40- and TAK1-Dependent.

Background-CD40 ligand (CD40L) is a thromboinflammatory molecule that predicts cardiovascular events. CD40L is a strong activator of nuclear factor kappa B (NF-kappa B) in platelets that primes and enhances platelet activation in response to thrombotic stimuli. In addition to its classical receptor CD40, CD40L binds alpha IIb beta 3, alpha 5 beta 1, and alpha M beta 2 in various cell types. However, the function of the different CD40L receptors on platelets remains unexplored. The present study aims to identify the receptors of CD40L, involved in platelet NF-kappa B activation, their downstream signaling and their implication in platelet aggregation. Methods and Results-We showed that platelets express CD40, alpha IIb beta 3, and alpha 5 beta 1 and release CD40L in response to sCD40L stimulation. sCD40L alone dose-dependently induced platelet NF-kappa B activation; this effect was absent in CD40(-/-) mouse platelets and inhibited by the CD40 blockade, but was unaffected by the alpha IIb beta 3 or alpha 5 beta 1 blockade in human platelets. sCD40L/CD40 axis activates transforming growth factor-beta-activated kinase 1 upstream of NF-kappa B. In functional studies, sCD40L alone did not affect platelet aggregation but potentiated the aggregation response in the presence of suboptimal doses of thrombin; this effect was abolished by CD40, transforming growth factor-beta-activated kinase 1, and NF-kappa B inhibitors. Conclusions-CD40L primes platelets via signaling pathways involving CD40/transforming growth factor-beta-activated kinase 1/NF-kappa B, which predisposes platelets to enhanced activation and aggregation in response to thrombotic stimuli.