Signaling role of CD36 in platelet activation and thrombus formation on immobilized thrombospondin or oxidized low-density lipoprotein.

BACKGROUND AND OBJECTIVE: Platelets abundantly express glycoprotein CD36 with thrombospondin-1 (TSP1) and oxidized low-density lipoprotein (oxLDL) as proposed ligands. How these agents promote platelet activation is still poorly understood. METHODS AND RESULTS: Both TSP1 and oxLDL caused limited activation of platelets in suspension. However, immobilized TSP1 and oxLDL, but not LDL, strongly supported platelet adhesion and spreading with a major role of CD36. Platelet spreading was accompanied by potent Ca(2+) rises, and resulted in exposure of P-selectin and integrin activation, all in a CD36-dependent manner with additional contributions of α(IIb) ß(3) and ADP receptor stimulation. Signaling responses via CD36 involved activation of the protein tyrosine kinase Syk. In whole blood perfusion, co-coating of TSP1 or oxLDL with collagen enhanced thrombus formation at high-shear flow conditions, with increased expression on platelets of activated α(IIb) ß(3), P-selectin and phosphatidylserine, again in a CD36-dependent way. CONCLUSIONS: Immobilized TSP1 and oxLDL activate platelets partly via CD36 through a Syk kinase-dependent Ca(2+) signaling mechanism, which enhances collagen-dependent thrombus formation under flow. These findings provide novel insight into the role of CD36 in hemostasis.

CD36 as a multiple-ligand signaling receptor in atherothrombosis.

The glycoprotein CD36, also known as glycoprotein IIIb/IV or FAT, is expressed on the surface of platelets, monocytes, microvascular endothelial cell, smooth muscle cells, cardiomyocytes and other cells of the cardiovascular system. In spite of its abundant presence, CD36 has remained for long a mysterious protein with a poorly understood role. In this paper, we review how CD36 can affect cellular responses by interaction with a variety of ligands, in particular thrombospondin-1, oxidized lipoproteins and fatty acids. Furthermore, given the structure of CD36 with two transmembrane domains and short cytoplasmic tails, we consider how this receptor can induce intracellular signaling, likely in junction with other cellular receptors or associated proteins in the membrane. Current literature points to activation of Src-family and mitogen-activated protein kinases, as well as to activation of the NFκB and Rho pathways. The new insights make CD36 attractive as a therapeutic target to suppress platelet and monocyte/macrophage function and thereby atherothrombosis.

Complementary roles of platelets and coagulation in thrombus formation on plaques acutely ruptured by targeted ultrasound treatment: a novel intravital model.

BACKGROUND: Atherothrombosis is a major cause of cardiovascular events. However, animal models to study this process are scarce. OBJECTIVES: We describe the first murine model of acute thrombus formation upon plaque rupture to study atherothrombosis by intravital fluorescence microscopy. METHODS: Localized rupture of an atherosclerotic plaque in a carotid artery from Apoe(-/-) mice was induced in vivo using ultrasound. Rupture of the plaque and formation of localized thrombi were verified by two-photon laser scanning microscopy (TPLSM) in isolated arteries, and by immunohistochemistry. The thrombotic reaction was quantified by intravital fluorescence microscopy. RESULTS: Inspection of the ultrasound-treated plaques by histochemistry and TPLSM demonstrated local damage, collagen exposure, luminal thrombus formation as well as intra-plaque intrusion of erythrocytes and fibrin. Ultrasound treatment of healthy carotid arteries resulted in endothelial damage and limited platelet adhesion. Real-time intravital fluorescence microscopy demonstrated rapid platelet deposition on plaques and formation of a single thrombus that remained subocclusive. The thrombotic process was antagonized by thrombin inhibition, or by blocking of collagen or adenosine diphosphate receptor pathways. Multiple thrombi were formed in 70% of mice lacking CD40L. CONCLUSIONS: Targeted rupture of murine plaques results in collagen exposure and non-occlusive thrombus formation. The thrombotic process relies on platelet activation as well as on thrombin generation and coagulation, and is sensitive to established and novel antithrombotic medication. This model provides new possibilities to study atherothrombosis in vivo.