title: Platelet P2Y12 receptors enhance signalling towards procoagulant activity and thrombin generation. A study with healthy subjects and patients at thrombotic risk.
abstract: Activated platelets participate in arterial thrombosis by forming aggregates and potentiating the coagulation through exposure of procoagulant phosphatidylserine. The function of the two receptors for ADP, P2Y(1) and P2Y(12), is well-established in aggregation, but is incompletely understood in the platelet procoagulant response. We established that, in PRP from healthy subjects, ADP accelerated and potentiated tissue factor induced thrombin generation exclusively via stimulation of P2Y(12) and not via P2Y(1) receptors. The P2Y(12) receptors also mediated the potentiating effect of PAR-1 stimulation on thrombin generation. Furthermore, ADP enhanced in a P2Y(12)-dependent manner the Ca(2+) response induced by thrombin, which was either added externally or generated in-situ. This ADP effect was in part dependent of phosphoinositide 3-kinase and was paralleled by increased phosphatidylserine exposure. In PRP from (young) patients with either stroke or type-II diabetes, platelet-dependent thrombin generation was similarly enhanced byADP or SFLLRN as in healthy subjects. In PRP from stroke patients of older age, the P2Y(12)-mediated contribution to thrombin generation was variably reduced by two weeks of clopidogrel medication. Remaining P2Y(12) activity after medication correlated with remaining P2Y(12)-dependent P-selectin exposure, i.e. Ca(2+)-dependent secretion, likely due to incomplete antagonism of P2Y(12) receptors. Together, these results indicate that physiological platelet agonists amplify phosphatidylserine exposure and subsequent thrombin generation by release of ADP and P2Y(12)-receptor stimulation. This P2Y(12) response is accomplished by a novel Ca(2+) signalling pathway. It is similarly active in platelets from control subjects and patients at thrombotic risk. Finally, the thrombogram method is useful for measuring incomplete P2Y(12) inhibition with clopidogrel.
authors.affiliation: Department of Biochemistry, University of Maastricht, P.O. Box 616, 6200 MD Maastricht, The Netherlands.
authors.forename: Paola E J
authors.initials: PE
authors.lastname: van der Meijden
authors.forename: Marion A H
authors.initials: MA
authors.lastname: Feijge
authors.forename: Peter L A
authors.initials: PL
authors.lastname: Giesen
authors.forename: Maya
authors.initials: M
authors.lastname: Huijberts
authors.forename: Lisette P M
authors.initials: LP
authors.lastname: van Raak
authors.forename: Johan W M
authors.initials: JW
authors.lastname: Heemskerk
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000328:Adult; D000368:Aged; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling; D016022:Case-Control Studies; D000077144:Clopidogrel; D003924:Diabetes Mellitus, Type 2 / Q000097:blood; D006801:Humans; D066298:In Vitro Techniques; D008565:Membrane Proteins / Q000097:blood*; D008875:Middle Aged; D010718:Phosphatidylserines / Q000097:blood; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D018048:Receptors, Purinergic P2 / Q000097:blood*; D058925:Receptors, Purinergic P2Y12; D020521:Stroke / Q000097:blood; D013917:Thrombin / Q000096:biosynthesis*; D013927:Thrombosis / Q000097:blood* / Q000209:etiology*; D013988:Ticlopidine / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D008565:Membrane Proteins; C548576:P2RY12 protein, human; D010718:Phosphatidylserines; D010975:Platelet Aggregation Inhibitors; D018048:Receptors, Purinergic P2; D058925:Receptors, Purinergic P2Y12; D000244:Adenosine Diphosphate; D000077144:Clopidogrel; D013917:Thrombin; D013988:Ticlopidine