Enhanced levels of soluble CD40 ligand exacerbate platelet aggregation and thrombus formation through a CD40-dependent tumor necrosis factor receptor-associated factor-2/Rac1/p38 mitogen-activated protein kinase signaling pathway.
OBJECTIVE
CD40 ligand is a thromboinflammatory molecule that predicts cardiovascular events. Platelets constitute the major source of soluble CD40 ligand (sCD40L), which has been shown to influence platelet activation, although its exact functional impact on platelets and the underlying mechanisms remain undefined. We aimed to determine the impact and the signaling mechanisms of sCD40L on platelets.


RESULTS
sCD40L strongly enhances platelet activation and aggregation. Human platelets treated with a mutated form of sCD40L that does not bind CD40, and CD40(-/-) mouse platelets failed to elicit such responses. Furthermore, sCD40L stimulation induces the association of the tumor necrosis factor receptor-associated factor-2 with platelet CD40. Notably, sCD40L primes platelets through activation of the small GTPase Rac1 and its downstream target p38 mitogen-activated protein kinase, which leads to platelet shape change and actin polymerization. Moreover, sCD40L exacerbates thrombus formation and leukocyte infiltration in wild-type mice but not in CD40(-/-) mice.


CONCLUSIONS
sCD40L enhances agonist-induced platelet activation and aggregation through a CD40-dependent tumor necrosis factor receptor-associated factor-2/Rac1/p38 mitogen-activated protein kinase signaling pathway. Thus, sCD40L is an important platelet primer predisposing platelets to enhanced thrombus formation in response to vascular injury. This may explain the link between circulating levels of sCD40L and cardiovascular diseases.
Laboratory of Thrombosis and Hemostasis, Montreal Heart Institute, Montreal, Quebec, Canada.
Daniel
D
Yacoub
Ahmed
A
Hachem
Jean-François
JF
Théorêt
Marc-Antoine
MA
Gillis
Walid
W
Mourad
Yahye
Y
Merhi
D000199:Actins / Q000097:blood; D000818:Animals; D001792:Blood Platelets / Q000201:enzymology* / Q000276:immunology; D019013:CD40 Antigens / Q000097:blood* / Q000235:genetics; D023201:CD40 Ligand / Q000097:blood* / Q000235:genetics; D048430:Cell Shape; D004195:Disease Models, Animal; D005260:Female; D006801:Humans; D007962:Leukocytes / Q000276:immunology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009154:Mutation; D009479:Neuropeptides / Q000097:blood; D010974:Platelet Aggregation; D011994:Recombinant Proteins / Q000097:blood; D015398:Signal Transduction; D047992:TNF Receptor-Associated Factor 2 / Q000097:blood*; D013927:Thrombosis / Q000097:blood* / Q000201:enzymology / Q000276:immunology; D013997:Time Factors; D048051:p38 Mitogen-Activated Protein Kinases / Q000097:blood*; D020744:rac GTP-Binding Proteins / Q000097:blood; D020830:rac1 GTP-Binding Protein / Q000097:blood*
D000199:Actins; D019013:CD40 Antigens; D009479:Neuropeptides; C107953:RAC1 protein, human; C484602:Rac1 protein, mouse; D011994:Recombinant Proteins; D047992:TNF Receptor-Associated Factor 2; D023201:CD40 Ligand; D048051:p38 Mitogen-Activated Protein Kinases; D020744:rac GTP-Binding Proteins; D020830:rac1 GTP-Binding Protein