Activation of the GP IIb-IIIa complex induced by platelet adhesion to collagen is mediated by both alpha2beta1 integrin and GP VI.
alpha2beta1 integrin, CD36, and GP VI have all been implicated in platelet-collagen adhesive interactions. We have investigated the role of these glycoproteins on activation of the GP IIb-IIIa complex induced by platelet adhesion to type I fibrillar and monomeric collagen under static conditions. In the presence of Mg2+, platelet adhesion to fibrillar collagen induced activation of the GP IIb-IIIa complex and complete spreading. Anti-alpha2beta1 integrin and anti-GP VI antibodies inhibited the activation of the GP IIb-IIIa complex by about 40 and 50%, respectively, at 60 min although minimal inhibitory effects on adhesion were seen. Platelet spreading was markedly reduced by anti-alpha2beta1 integrin antibody. The combination of anti-alpha2beta1 integrin with anti-GP VI antibody completely inhibited both platelet adhesion and activation of the GP IIb-IIIa complex. Anti-CD36 antibody had no significant effects on platelet adhesion, spreading, and the activation of the GP IIb-IIIa complex at 60 min. Aspirin and the thromboxane A2 receptor antagonist SQ29548 inhibited activation of the GP IIb-IIIa complex about 30% but had minimal inhibitory effect on adhesion. In the absence of Mg2+, there was significant activation of the GP IIb-IIIa complex but minimal spreading was observed. Anti-GP VI antibody completely inhibited adhesion whereas no effect was observed with anti-alpha2beta1 integrin antibody. Anti-CD36 antibody partially inhibited both adhesion and the activation of the GP IIb-IIIa complex. Platelet adhesion to monomeric collagen, which requires Mg2+ and is exclusively mediated by alpha2beta1 integrin, resulted in partial activation of the GPIIb-IIIa complex and spreading. No significant effects were observed by anti-CD36 and anti-GP VI antibodies. These results suggest that both alpha2beta1 integrin and GP VI are involved in inside-out signaling leading to activation of the GP IIb-IIIa complex after platelet adhesion to collagen and generation of thromboxane A2 may further enhance expression of activated GP IIb-IIIa complexes.
Nakamura
T
T
Otsuka America Pharmaceutical Inc., Rockville, Maryland 20850, USA.
Kambayashi
J
J
Okuma
M
M
Tandon
N N
NN
D000818:Animals; D000906:Antibodies / Q000378:metabolism; D001241:Aspirin / Q000494:pharmacology; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D018955:CD36 Antigens / Q000276:immunology; D002448:Cell Adhesion / Q000187:drug effects; D003094:Collagen / Q000378:metabolism*; D006736:Horses; D006801:Humans; D016023:Integrins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D010980:Platelet Membrane Glycoproteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D038981:Receptors, Collagen
D000906:Antibodies; D018955:CD36 Antigens; D016023:Integrins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D010980:Platelet Membrane Glycoproteins; D038981:Receptors, Collagen; C098341:platelet membrane glycoprotein VI; D003094:Collagen; D001241:Aspirin