Inhibition of agonist-induced p42 and p38 mitogen-activated protein kinasephosphorylation and CD40 ligand/P-selectin expression by cyclic nucleotide-regulated pathways in human platelets

Platelet activation and adhesion to endothelial cells and extracellular mat rix proteins are crucial events in the development of arterial cardiovascul ar diseases. Platelet activation is initiated by stimulation of intracellul ar signaling cascades, including the p42 mitogen-activated protein kinase ( MAPK) and p38 MAPK pathways, followed by major changes in the platelet cyto skeleton and expression and activation of platelet surface receptors, such as P-selectin (CD62P) and CD40 ligand (CD40L). Activated platelets directly bind to vascular endothelial cells via CD40L/CD40 interactions and induce inflammatory reactions that initiate or aggravate atherosclerotic Lesions. The aim of this study was to investigate effects of two known platelet inhi bitors-the cAMP-elevating prostaglandin E-1 (PG-E-1) and the cGMP-elevating sodium nitroprusside (SNP)-on platelet p42 MAPK and p38 MAPK activation as well as on surface expression of CD62P and CD40L. MAPK activation was anal yzed by Western blot experiments using phosphorylation-specific antibodies, and surface CD40L and CD62P expression was determined by flow cytometry an alysis. PG-E, and SNP strongly inhibited p42 and p38 MAPK phosphorylation a s well as CD40L and CD62P expression in response to thrombin, a thromboxane A, analog, and ADP. These data indicate that adenosine and guanosine 3',5' -cyclic monophosphate-dependent protein kinases not only inhibit platelet p athways leading to activation and aggregation, but also those resulting in enhanced surface expression of protein ligands involved in inflammation. Ex pression of CD40L and CD62P was found to be independent of MAPK activation, since it was not inhibited by specific MAPK inhibitors. inhibition of plat elet-induced inflammatory responses including CD62P- and CD40L-mediated int eraction of platelets with leukocytes and endothelial cells, respectively, is suggested to be an important component of the long-term vasoprotective e ffects of cyclic nucleotide-elevating prostaglandins and NO donors. (C) 200 0 Elsevier Science Inc.