The kinetics of αIIbβ3 activation determines the size and stability of thrombi in mice: implications for antiplatelet therapy.
Two major pathways contribute to Ras-proximate-1-mediated integrin activation in stimulated platelets. Calcium and diacyglycerol-regulated guanine nucleotide exchange factor I (CalDAG-GEFI, RasGRP2) mediates the rapid but reversible activation of integrin αIIbβ3, while the adenosine diphosphate receptor P2Y12, the target for antiplatelet drugs like clopidogrel, facilitates delayed but sustained integrin activation. To establish CalDAG-GEFI as a target for antiplatelet therapy, we compared how each pathway contributes to thrombosis and hemostasis in mice. Ex vivo, thrombus formation at arterial or venous shear rates was markedly reduced in CalDAG-GEFI(-/-) blood, even in the presence of exogenous adenosine diphosphate and thromboxane A(2). In vivo, thrombosis was virtually abolished in arterioles and arteries of CalDAG-GEFI(-/-) mice, while small, hemostatically active thrombi formed in venules. Specific deletion of the C1-like domain of CalDAG-GEFI in circulating platelets also led to protection from thrombus formation at arterial flow conditions, while it only marginally increased blood loss in mice. In comparison, thrombi in the micro- and macrovasculature of clopidogrel-treated wild-type mice grew rapidly and frequently embolized but were hemostatically inactive. Together, these data suggest that inhibition of the catalytic or the C1 regulatory domain in CalDAG-GEFI will provide strong protection from athero-thrombotic complications while maintaining a better safety profile than P2Y12 inhibitors like clopidogrel.
Cardeza Foundation for Hematologic Research and Department of Medicine, Thomas Jefferson University, Philadelphia, PA, USA.
Moritz
M
Stolla
Lucia
L
Stefanini
R Claire
RC
Roden
Massiel
M
Chavez
Jessica
J
Hirsch
Teshell
T
Greene
Timothy D
TD
Ouellette
Sean F
SF
Maloney
Scott L
SL
Diamond
Mortimer
M
Poncz
Donna S
DS
Woulfe
Wolfgang
W
Bergmeier
D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism; D000077144:Clopidogrel; D005260:Female; D005434:Flow Cytometry; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D006487:Hemostasis; D007700:Kinetics; D008297:Male; D008643:Mesentery / Q000098:blood supply; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D018482:Muscle, Skeletal / Q000098:blood supply; D010975:Platelet Aggregation Inhibitors / Q000627:therapeutic use; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D058925:Receptors, Purinergic P2Y12 / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013927:Thrombosis / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism*; D013988:Ticlopidine / Q000031:analogs & derivatives / Q000627:therapeutic use
D020662:Guanine Nucleotide Exchange Factors; C548577:P2ry12 protein, mouse; D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; C485927:Rasgrp2 protein, mouse; D058925:Receptors, Purinergic P2Y12; D049452:Green Fluorescent Proteins; D000077144:Clopidogrel; D013988:Ticlopidine