A critical role of thrombin/PAR‐1 in ADP‐induced platelet secretion and the second wave of aggregation. Issue 5 (15th May 2013)

• Record Type: Journal Article
• Authors: Jiang, L.; Xu, C.; Yu, S.; Liu, P.; Luo, D.; Zhou, Q.; Gao, C.; Hu, H.
• Is Part Of: Journal of thrombosis and haemostasis. Volume 11:Issue 5(2013)
• Page Start: 930
• Page End: 940
• Publication Date: 2013-05-15
• Subjects: Thrombosis -- Periodicals; Hemostasis -- Periodicals; Blood coagulation disorders -- Periodicals; 616.1
• DOI: 10.1111/jth.12168
• Languages: English
• ISSNs: 1538-7933

Abstract

<abstract abstract-type="main" id="jth12168-abs-0001"> <title>Summary</title> <sec id="jth12168-sec-0001" sec-type="section"> <title>Background</title> <p>The stable or second wave of platelet aggregation often observed in ADP‐stimulated platelet‐rich plasma (PRP) with an artificially lowered extracellular calcium level has been attributed to enhanced thromboxane A<sub>2</sub> (TXA<sub>2</sub>) generation and inhibition of ectonucleotidase activity. However, the role of thrombin in ADP‐induced platelet secretion and the second wave of aggregation is unknown.</p> </sec> <sec id="jth12168-sec-0002" sec-type="section"> <title>Objectives and Methods</title> <p>We employed aggregometry, flow cytometry, immunoblotting and ELISA to determine whether and how thrombin participates in ADP‐induced platelet secretion and the second wave of aggregation.</p> </sec> <sec id="jth12168-sec-0003" sec-type="section"> <title>Results</title> <p>ADP induces a phosphoinositide 3‐kinase (PI3K) pathway‐dependent thrombin generation, presumably resulting from the cleavage of α<sub>II</sub><sub>b</sub>β<sub>3</sub>‐associated prothrombin. Generated thrombin subsequently activates protease‐activated receptor‐1 (PAR‐1) and mediates dense granule secretion and the second wave of platelet aggregation in ADP‐stimulated citrated PRP. Thus, ADP‐induced dense granule secretion and the second wave of platelet aggregation in PRP were similarly and non‐additively blocked by thrombin inhibitor hirudin, PAR‐1 antagonist SCH‐79797 or PI3K inhibitor wortmannin. Moreover, ADP stimulation caused the dissociation of prothrombin from α<sub>II</sub><sub>b</sub>β<sub>3</sub> and an increased plasma thrombin level; both were prevented by wortmannin. Furthermore, the wortmannin‐inhibited second wave of platelet aggregation by ADP was restored by a subaggregation concentration of PAR‐1 activating peptide SFLLRN. Blocking TXA<sub>2</sub> production with indomethacin or restoring extracellular calcium to physiological concentration did not influence this thrombin/PAR‐1 dependence.</p> </sec> <sec id="jth12168-sec-0004" sec-type="section"> <title>Conclusions</title> <p>A PI3K‐dependent thrombin generation and the resultant PAR‐1 activation serve as an indispensable mechanism to relay the platelet activation process induced by ADP.</p> </sec> </abstract>