Intact platelet membranes, not platelet-released microvesicles, support the procoagulant activity of adherent platelets (original) (raw)
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Thrombosis and Haemostasis, 2007
Platelet microparticles (PMPs) aresmallv esiclesr eleasedfrom blood platelets upon activation. Thep rocoagulant activity of PMPs has been previously mainlycharacterized by their ability to bindcoagulation factors VIII and Va in reconstructedsystems. It canbesupposed that PMPs can contribute to the development of thromboticcomplicationsinthe pathologic statesassociated with the increase of theirbloodconcentration. In this study, we compared procoagulant properties of calcium ionophore A23187-activatedplatelets and PMPs using several in-vitromodelso fh emostasis. Surface densitieso fp hosphatidylserine, CD61, CD62P and factor Xb oundp er surfacea reau nit were determinedb yf lowc ytometry.Theyw ere2 .7-,8.4-,4.3-,and 13-foldhigher forPMPsthan foractivatedplatelets,respectively.
Platelets [Working Title], 2020
There are two well-known subpopulations of activated platelets: proaggregatory and procoagulant. Procoagulant platelets represent a subpopulation of activated platelets, which are morphologically and functionally distinct from pro-aggregatory ones. Although various names have been used to describe these platelets in the literature (CoaT, CoaTed, highly activated, ballooned, capped, etc.), there is a consensus on their phenotypic features including exposure of high levels of phosphatidylserine (PSer) on the surface; decreased aggregatory and adhesive properties; support of active tenase and prothrombinase complexes; maximal generation by co-stimulation of glycoprotein VI (GPVI) and protease-activated receptors (PAR). In this chapter, morphologic and functional features of procoagulant platelets, as well as the mechanisms of their formation, will be discussed.
Intravascular tissue factor initiates coagulation via circulating microvesicles and platelets
The FASEB Journal, 2003
Although tissue factor (TF), the principial initiator of physiological coagulation and pathological thrombosis, has recently been proposed to be present in human blood, the functional significance and location of the intravascular TF is unknown. In the plasma portion of blood, we found TF to be mainly associated with circulating microvesicles. By cell sorting with the specific marker CD42b, platelet-derived microvesicles were identified as a major location of the plasma TF. This was confirmed by the presence of full-length TF in microvesicles acutely shedded from the activated platelets. TF was observed to be stored in the α-granules and the open canalicular system of resting platelets and to be exposed on the cell surface after platelet activation. Functional competence of the blood-based TF was enabled when the microvesicles and platelets adhered to neutrophils, as mediated by P-selectin and neutrophil counterreceptor (PSGL-1, CD18 integrins) interactions. Moreover, neutrophil-secreted oxygen radical species supported the intravascular TF activity. The pools of platelet and microvesicle TF contributed additively and to a comparable extent to the overall blood TF activity, indicating a substantial participation of the microvesicle TF. Our results introduce a new concept of TF-mediated coagulation crucially dependent on TF associated with microvesicles and activated platelets, which principally enables the entire coagulation system to proceed on a restricted cell surface. Key words: lipopolysaccharide • platelet rich plasma • superoxide dismutase • catalase • microparticles T wo principal events that are initiated after disrupture of the endothelial barrier are thought to mark the initiation of hemostasis. Blood platelets adhere to subendothelial collagen providing a provisional, mechanically unstable closure of the vessel perforation. Concomitantly, the coagulation process is started. This is mainly due to the formation of an initiator complex between tissue factor (TF), an integral cell membrane protein predominantly
2016
Objective—The goal of this study was to define and characterize the subpopulation of platelets capable of regulating the functional interactions of factors Va (FVa) and Xa (FXa) on the thrombin-activated platelet surface. Methods and Results—Flow cytometric analyses were used to define and characterize platelet subpopulations. At a concentration of thrombin known to elicit maximal platelet activation, platelet-derived FVa release, and prothrombinase assembly/function, only a subpopulation of platelets was positive for FVa and FXa binding. An additional subpopulation bound lower levels of FVa but little, if any, FXa. Fluorescence microscopy analyses confirmed these data. Phenotypically, platelets capable of binding FXa were more highly reticulated and demonstrated significantly increased expression of several key adhesion molecules, including P-selectin, glycoprotein Ib, and integrins IIb and 3. This platelet subpopulation was also defined by the expression of a nondissociable, membr...
Biomaterials, 2000
Procoagulant (activated) platelets provide a site for assembly of the prothrombinase complex which can rapidly convert prothrombin into thrombin (a potent inducer of clot formation). Previously, we reported that adhesion of platelets to surfaces preadsorbed with blood plasma caused them to become procoagulant. In the present study we investigated the e!ect of adsorbed adhesion proteins ("brinogen (Fg), "bronectin (Fn), von Willebrand factor (vWF) and vitronectin (Vn)) on the procoagulant activity of adherent platelets. Adsorbed Fn, vWF and Fg promoted platelet adhesion in the following order: Fn(vWF"Fg. However, these proteins promoted platelet activation (thrombin generation per adherent platelet) in the following order: Fg(Fn(vWF. Adsorption with a series of dilutions of normal plasma, serum, and plasmas de"cient in or depleted of von Willebrand factor (de-vWF), "bronectin (de-Fn), vitronectin (de-Vn), or both vitronectin and "bronectin (de-VnFn) resulted in varied platelet adhesion, but little di!erence in platelet activation. However, preadsorption with dilute de-vWF plasma induced lower procoagulant activity than normal plasma. Preadsorption with normal plasma resulted in higher levels of platelet activation than preadsorption with Fg, suggesting that adsorption of plasma proteins other than Fg caused the high levels of activation observed for plasma preadsorbed surfaces.
2000
Factor V (FV) present in platelet ␣-granules has a significant but incompletely understood role in hemostasis. This report demonstrates that a fraction of platelets express very high levels of surface-bound, ␣-granule FV on simultaneous activation with 2 agonists, thrombin and convulxin, an activator of the collagen receptor glycoprotein VI. This subpopulation of activated platelets represents 30.7% ؎ 4.7% of the total population and is referred to as convulxin and thrombin-induced-FV (COAT-FV) platelets. COAT-FV platelets are also observed on activation with thrombin plus collagen types I, V, or VI, but not with type III. No single agonist examined was able to produce COAT-FV platelets, although ionophore A23187 in conjunction with either thrombin or convulxin did generate this population. COAT-FV platelets bound annexin-V, indicating exposure of aminophospholipids and were enriched in young platelets as identified by the binding of thiazole orange. The functional significance of COAT-FV platelets was investigated by demonstrating that factor Xa preferentially bound to COAT-FV platelets, that COAT-FV platelets had more FV activity than either thrombin or A23187activated platelets, and that COAT-FV platelets were capable of generating more prothrombinase activity than any other physiologic agonist examined. Microparticle production by dual stimulation with thrombin and convulxin was less than that observed with A23187, indicating that microparticles were not responsible for all the activities observed. These data demonstrate a new procoagulant component produced from dual stimulation of platelets with thrombin and collagen. COAT-FV platelets may explain the unique role of ␣-granule FV and the hemostatic effectiveness of young platelets. (Blood. 2000;95:1694-1702)
Antiplatelet Agents Inhibit the Generation of Platelet-Derived Microparticles
Frontiers in Pharmacology, 2016
Platelet microparticles (PMPs) contribute to thrombogenesis but the effects of antiplatelet drugs on PMPs generation is undefined. The present study investigated the cellular events regulating PMPs shedding, testing in vitro platelet agonists and inhibitors. Platelet-rich plasma from healthy subjects was stimulated with arachidonic acid (AA), U46619, collagen type-I (10 and 1.5 µg/mL), epinephrine, ADP or TRAP-6 and pre-incubated with acetylsalicylic acid (ASA, 100 and 10 µmol/L), SQ-29,548, apyrase, PSB-0739, or eptifibatide. PMPs were detected by flow-cytometry using CD61 and annexin-V as fluorescent markers. Platelet agonists induced annexin V-positive PMPs shedding. The strongest response was to high concentration collagen. ADPtriggered PMPs shedding was dose-independent. ASA reduced PMPs induced by AA-(645, 347-2946 vs. 3061, 446-4901 PMPs/µL; median ad range, n = 9,
Deep Vein Thrombosis-Role of Platelet Derived Micro particles in Coagulation
https://www.ijrrjournal.com/IJRR\_Vol.7\_Issue.6\_June2020/Abstract\_IJRR0017.html, 2020
Introduction: Several parameters may help in identification of DVT. Though the most important diagnosis of DVT is by compression Ultrasound but there are several other parameters as D Dimer, P-selectin which may help in identification of DVT. Platelets are one of the important factor which may be altered in patients with DVT. We wanted to look into the status of Platelet Derived Micro particles (PDMP), Methods: A total of 10 patients and 10 controls were included in the study. We included all acute DVT patients as confirmed by duplex scan and excluded those patients who were on antiplatelet or anticoagulants. Isolation of platelet derived microparticles was done after blood sampling with 2 ml of blood collected in blue top sodium citrate vials from each case and control were sent to Biochemistry laboratory and studied within 1-2 hrs.Agonist induced conformational change in integrin αβ results in high affinity binding of fibrinogen to platelet surface. PAC-1 antibody specifically recognizes open conformation of αβ. Therefore, PAC-1 antibody was used to study the effect of agonist on integrin activation. Results: Among all 10patients (6 males and 4 females). 8 patients were in age group 20-39 years. Platelet derived microparticles are 3-4 times raised as compared to healthy individual. Median number of platelet derived microparticles of all cases was 4461.5/105 platelet cells and median number of platelet derived microparticles of all controls was 1868.0/105 platelet cells. Conclusion: Mean number of PDMPs in each case with control which showed that mean number of microparticles were significantly raised in cases (4.09±1.2 vs 3.06±0.5; p=0.029).