scholarly journals Functional enhancement of platelet activation and aggregation by erythrocytes: role of red cells in thrombosis

Author(s):  
Gabrielle E Brown ◽  
Leslie S. Ritter ◽  
Paul F. McDonagh ◽  
Zoe Cohen

Platelets expose phosphatidylserine (PS), a component of the prothrombinase complex, on the outer surface of the plasma membrane when activated. [ref 1] The prothrombinase complex catalyzes the conversion of prothrombin to thrombin, and it has been demonstrated that an increase in PS exposure is correlated with an increase in thrombin generation by platelets. [refs 2,3] Similarly, erythrocyte (RBC) activation, or eryptosis, is also characterized by PS exposure on the plasma membrane. [ref 4] Although PS exposure on RBCs is considered a signal for splenic macrophage destruction, eryptosis may allow RBCs to contribute to thrombosis.[ref 4] The aims of this study were to determine whether the addition of RBCs to platelets increased functional platelet aggregation and coagulation properties. A ratio of 4 RBCs to 1 platelet (4:1) was evaluated for aggregation and coagulation compared to platelet control. Platelet aggregation and coagulation properties were evaluated with impedance aggregometry and thromboelastography, respectively. The 4:1 experimental group had significant increases in aggregation and coagulation relative to the platelet control. These results indicate that RBCs increase platelet aggregation and coagulation properties. This suggests that RBCs play a role in diseases traditionally thought of as associated solely via dysregulated platelet activation.

Author(s):  
Gabrielle E Brown ◽  
Leslie S. Ritter ◽  
Paul F. McDonagh ◽  
Zoe Cohen

Platelets expose phosphatidylserine (PS), a component of the prothrombinase complex, on the outer surface of the plasma membrane when activated. [ref 1] The prothrombinase complex catalyzes the conversion of prothrombin to thrombin, and it has been demonstrated that an increase in PS exposure is correlated with an increase in thrombin generation by platelets. [refs 2,3] Similarly, erythrocyte (RBC) activation, or eryptosis, is also characterized by PS exposure on the plasma membrane. [ref 4] Although PS exposure on RBCs is considered a signal for splenic macrophage destruction, eryptosis may allow RBCs to contribute to thrombosis.[ref 4] The aims of this study were to determine whether the addition of RBCs to platelets increased functional platelet aggregation and coagulation properties. A ratio of 4 RBCs to 1 platelet (4:1) was evaluated for aggregation and coagulation compared to platelet control. Platelet aggregation and coagulation properties were evaluated with impedance aggregometry and thromboelastography, respectively. The 4:1 experimental group had significant increases in aggregation and coagulation relative to the platelet control. These results indicate that RBCs increase platelet aggregation and coagulation properties. This suggests that RBCs play a role in diseases traditionally thought of as associated solely via dysregulated platelet activation.


Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 1141-1141
Author(s):  
Satish Babu Cheepala ◽  
Kazumasa Takenaka ◽  
Tamara I. Pestina ◽  
Carl W. Jackson ◽  
Schuetz John

Abstract Abstract 1141 Cyclic nucleotides have an important role in platelet aggregation and the role of phosphodiesterases in regulating their concentration is well known. Currently it is unknown if plasma membrane cyclic nucleotide export proteins regulate cyclic nucleotide concentrations in platelets. The ATP-binding cassette transporter, ABCC4 functions as a cyclic nucleotide exporter that is highly expressed in platelets. However, its role as a cyclic nucleotide transporter in platelets is unknown, because it was reportedly localized intracellularly in the platelet dense granules. This original report (Jedlitschky, Tirschmann et al. 2004) evaluated ABCC4 localization by immune-fluorescence of platelets after attachment to collagen coated coverslips. However, collagen attachment activates platelets causing mobilization and fusion of alpha and dense granules to the plasma membrane, thus rendering conditions that distinguish between plasma membrane and dense granules almost impossible. To resolve this problem we isolated the platelets under conditions that minimize activation during isolation. Subsequently, these platelets membranes were labeled with the cell impermeable biotinylating agent (EZ-Link Sulfo-NHS-LC-LC Biotin). Analysis of total platelet lysate detected the dense granule marker, P-selectin and Abcc4. However, after precipitation of the plasma membrane with streptavidin-beads, we detected only Abcc4. This indicates Mrp4 is at the plasma membrane. We confirmed Abcc4 localization by confocal microscopy on platelets that were treated with a monoclonal antibody specific to Abcc4. Evidence that Abcc4 regulates cyclic nucleotide levels under basal conditions was then provided by the findings that Abcc4-null platelets have elevated cyclic nucleotides. We further used the Abcc4-null mouse model to explore the role of Abcc4 in platelet biology. The Abcc4-null mouse does not have any change in the platelet or dense granules number compared to the wild type mouse. Platelet activation in vivo can be initiated by interaction with collagen through the GPVI receptor that is expressed at the plasma membrane of the platelets. At the molecular level, the initiation of platelet activation by collagen results in an increase in the cyclic nucleotide concentration and phosphorylation of vasodilator-stimulated phosphoprotein (VASP) which can attenuate aggregation. To determine the Abcc4 role in this process we exposed Abcc4-null platelets to collagen and discovered that these platelets have impaired activation in response to collagen. However, Abcc4-null platelets activated by thrombin or ADP, which activate either G-coupled PAR receptors or P2Y12 receptor respectively, show an aggregation profile almost identical to wildtype platelets, thus indicating the defect in Abcc4-null platelet aggregation is specific to the collagen initiated pathway. To understand the basis for the impaired aggregation of Abcc4-null platelets, we examined VASP phosphorylation after collagen treatment, and discovered that the cyclic nucleotide dependent phosphorylation of VASP (Ser 157) is elevated in the Abcc4-null platelets. These results strongly suggest that Abcc4-null platelets have impaired GPVI activation by collagen due to elevated cyclic nucleotide concentrations. Based on these studies we conclude that Abcc4 plays a critical role in regulating platelet cyclic nucleotide concentrations and its absence or perhaps inhibition (by drugs) impairs the aggregation response to collagen. Because many antiplatelet drugs are potent inhibitors of Abcc4 (e.g., Dipyridamole and Sildenafil) these findings have strong implications for not just the development of antiplatelet drugs, but also for understanding the role of Abcc4 in regulating intracellular nucleotide levels. Jedlitschky, G., K. Tirschmann, et al. (2004). “The nucleotide transporter MRP4 (ABCC4) is highly expressed in human platelets and present in dense granules, indicating a role in mediator storage.” Blood 104(12): 3603–10. This work was supported by NIH and by the American Lebanese Syrian Associated Charities (ALSAC). Disclosures: No relevant conflicts of interest to declare.


Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 1063-1063
Author(s):  
Satish B. Cheepala ◽  
Kazumasa Takenaka ◽  
Tamara I. Pestina ◽  
Carl W. Jackson ◽  
John D. Schuetz

Abstract Abstract 1063 Platelet activation is a highly regulated process, and cyclic nucleotide mediated signaling pathways are crucial to effective platelet activation. Vascular injury produces, exposed collagen which binds circulating platelets through the platelet's “collagen” receptor, GPVI, resulting in the activation of guanyly/adenlyl cyclases. These interactions result in the rapid alterations in the cyclic nucleotide concentration inside the platelets leading to activation of protein kinase A and G signaling pathways to modulate platelet function. While, ABCC4 functions as a plasma membrane transporter for cyclic nucleotides its contribution to platelet activation has been obscured because it was reportedly as primarily intracellular in the platelets dense granules. This original report (Jedlitschky, Tirschmann et al. 2004) evaluated ABCC4 localization by immune-fluorescence of platelets attached to collagen coated coverslips. However, attachment via collagen produces platelet activation leading to mobilization and fusion of alpha and dense granules to the plasma membrane, thus under these conditions distinguishing between plasma membrane and dense granules is not possible. We resolved this problem by labeling quiescent platelets with a cell impermeable biotinylating agent (EZ-Link Sulfo-NHS-LC-LC Biotin). Isolation of membrane and internal fraction demonstrated that of over ninety percent of Abcc4 localizes to the plasma membrane. Furthermore, confocal microscopy of platelets stained with specific antibodies against Abcc4 confirmed Abcc4 localization to the plasma membrane. We extended these studies to the Abcc4- knockout (KO) mouse model. The Abcc4- KO mouse does not have any change in the number of platelet or dense granules compared to the wild type mouse. Platelet activation in vivo can be initiated by interaction with collagen through the GPVI receptor that is expressed at the plasma membrane of the platelets. At the molecular level, the initiation of platelet activation by collagen results in an increase in the cyclic nucleotide concentration leading to activation of signaling cascade through protein kinase A or G. Expose of Abcc4-KO platelets to collagen and revealed impaired activation in response to collagen. However, Abcc4-KO platelets activated by either thrombin or ADP (which activate either G-coupled PAR receptors or P2Y12 receptor respectively) shows an aggregation profile almost identical to wildtype platelets, thus indicating the defect in Abcc4 -KO platelet aggregation is specific to the collagen pathway. To understand the basis for the impaired collagen aggregation of Abcc4-KO platelets, we investigated the collagen receptor (GPVI) signaling pathway in Abcc4-KO platelets. Interestingly, in the Abcc4-KO platelets after the platelet activation with collagen, cyclic nucleotide dependent phosphorylation of VASP through protein kinase A or G at Ser-157 or Ser-239 respectively is reduced compared to the wildtype. Notably, Abcc4-KO platelets had reduced GPVI surface expression that correlated with the reduced phosphorylation of VASP after collagen stimulation. The similar, protein levels of Syk and Plcg2, (downstream signaling molecules of GPVI signaling pathway), in the Abcc4 wildtype and KO platelets implies that GPVI expression is the primary defect in Abcc4 deficiency. These results suggest that Abcc4 plays a crucial role in regulating cyclic nucleotides in response to GPVI activation by collagen. These findings suggest ABCC4/Mrp4 loss of function or inhibition (by drugs) may disrupt platelet aggregation under conditions of vascular injury. As, many antiplatelet drugs are potent inhibitors of Abcc4 (e.g., Dipyridamole and Sildenafil) these conclusions have strong implications for not just the development of antiplatelet drugs, but also for further exploring the role of Abcc4 in regulating intracellular nucleotide levels and platelet biology. Disclosures: No relevant conflicts of interest to declare.


1981 ◽  
Author(s):  
M Yamamoto ◽  
K Watanabe ◽  
Y Ando ◽  
H Iri ◽  
N Fujiyama ◽  
...  

It has been suggested that heparin caused potentiation of aggregation induced by ADP or epinephrine. The exact mechanism of heparin-induced platelet activation, however, remained unknown. In this paper, we have investigated the role of anti-thrombin III ( AT ) in heparin-induced platelet activation using purified AT and AT depleted plasma. When ADP or epinephrine was added to citrated PRP one minute after addition of heparin ( 1 u/ml, porcine intestinal mucosal heparin, Sigma Co. USA ), marked enhancement of platelet aggregation was observed, compared with the degree of aggregation in the absence of heparin. However, in platelet suspensions prepared in modified Tyrode’s solution, heparin exhibited no potentiating effect on platelet aggregation induced by epinephrine or ADP. Potentiation of epinephrine- or ADP-induced platelet aggregation by heparin was demonstrated when purified AT was added to platelet suspensions at a concentration of 20 μg/ml. AT depleted plasma, which was prepared by immunosorption using matrix-bound antibodies to AT, retained no AT, while determination of α1-antitrypsinα2- macroglobulin and fibrinogen in AT depleted plasma produced values which corresponded to those of the original plasma when dilution factor was taken into account. The activities of coagulation factors were also comparable to those of the original plasma. Heparin exhibited potentiating effect on ADP- or epinephrine-induced aggregation of platelets in original plasma, but no effect in AT depleted plasma. When purified AT was added back to AT depleted plasma at a concentration of 20 μg/ml, potentiation of platelet aggregation by heparin was clearly demonstrated.Our results suggest that effect of heparin on platelet aggregation is also mediated by anti-thrombin III.


2020 ◽  
Vol 21 (11) ◽  
pp. 3932 ◽  
Author(s):  
Preeti Kumari Chaudhary ◽  
Sanggu Kim ◽  
Youngheun Jee ◽  
Seung-Hun Lee ◽  
Kyung-Mee Park ◽  
...  

Platelet G protein-coupled receptors (GPCRs) regulate platelet function by mediating the response to various agonists, including adenosine diphosphate (ADP), thromboxane A2, and thrombin. Although GPCR kinases (GRKs) are considered to have the crucial roles in most GPCR functions, little is known regarding the regulation of GPCR signaling and mechanisms of GPCR desensitization by GRKs in platelets. In this study, we investigated the functional role of GRK6 and the molecular basis for regulation of specific GPCR desensitization by GRK6 in platelets. We used GRK6 knockout mice to evaluate the functional role of GRK6 in platelet activation. Platelet aggregation, dense- and α-granule secretion, and fibrinogen receptor activation induced by 2-MeSADP, U46619, thrombin, and AYPGKF were significantly potentiated in GRK6−/− platelets compared to the wild-type (WT) platelets. However, collagen-related peptide (CRP)-induced platelet aggregation and secretion were not affected in GRK6−/− platelets. Interestingly, platelet aggregation induced by co-stimulation of serotonin and epinephrine which activate Gq-coupled 5HT2A and Gz-coupled α2A adrenergic receptors, respectively, was not affected in GRK6−/− platelets, suggesting that GRK6 was involved in specific GPCR regulation. In addition, platelet aggregation in response to the second challenge of ADP and AYPGKF was restored in GRK6−/− platelets whereas re-stimulation of the agonist failed to induce aggregation in WT platelets, indicating that GRK6 contributed to P2Y1, P2Y12, and PAR4 receptor desensitization. Furthermore, 2-MeSADP-induced Akt phosphorylation and AYPGKF-induced Akt, extracellular signal-related kinase (ERK), and protein kinase Cδ (PKCδ) phosphorylation were significantly potentiated in GRK6−/− platelets. Finally, GRK6−/− mice exhibited an enhanced and stable thrombus formation after FeCl3 injury to the carotid artery and shorter tail bleeding times, indicating that GRK6−/− mice were more susceptible to thrombosis and hemostasis. We conclude that GRK6 plays an important role in regulating platelet functional responses and thrombus formation through selective GPCR desensitization.


2020 ◽  
Vol 2020 ◽  
pp. 1-6
Author(s):  
Giusy Tiseo ◽  
Elena Cavarretta ◽  
Arianna Forniti ◽  
Cristina Nocella ◽  
Sebastiano Sciarretta ◽  
...  

Background. Although preclinical studies highlighted the potential role of NADPH oxidase (NOX) in sepsis, only few studies evaluated the oxidative stress in patients with sepsis and septic shock. The objective of the study is to appraise the oxidative stress status and platelet function in patients with sepsis and septic shock compared to healthy controls. Methods and Results. Patients with sepsis or septic shock admitted to the hospital Policlinico Umberto I (Sapienza University, Rome) underwent a blood sample collection within 1 hour from admission. Platelet aggregation, serum thromboxane B2 (TxB2), soluble NOX2-derived peptides (sNox2-dp), and hydrogen peroxide breakdown activity (HBA) were measured and compared to those of healthy volunteers. Overall, 33 patients were enrolled; of these, 20 (60.6%) had sepsis and 13 (39.4%) septic shock. Compared to healthy controls ( n = 10 , age 67.8 ± 3.2 , male 50%), patients with sepsis and septic shock had higher platelet aggregation (49% (IQR 45-55), 60% (55.75-67.25), and 73% (IQR 69-80), respectively, p < 0.001 ), higher serum TxB2 (77.5 (56.5-86.25), 122.5 (114-131.5), and 210 (195-230) pmol/L, respectively, p < 0.001 ), higher sNox2-dp (10 (7.75-12), 19.5 (17.25-21), and 33 (29.5-39) pg/mL, respectively, p < 0.001 ), and lower HBA (75% (67.25-81.5), 50% (45-54.75), and 27% (21.5-32.5), respectively, p < 0.001 ). Although not statistically significant, a trend in higher levels of serum TxB2 and sNox2-dp in patients who died was observed. Conclusions. Patients with septic shock exhibit higher Nox2 activity and platelet activation than patients with sepsis. These insights joined to better knowledge of these mechanisms could guide the identification of future prognostic biomarkers and new therapeutic strategies in the scenario of septic shock.


Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 3904-3904
Author(s):  
Samantha Baldassarri ◽  
Alessandra Bertoni ◽  
Paolo Lova ◽  
Stefania Reineri ◽  
Chiara Sarasso ◽  
...  

Abstract 2-Arachidonoylglycerol (2-AG) is a naturally occurring monoglyceride that activates cannabinoid receptors and meets several key requisites of an endogenous cannabinoid substance. It is present in the brain and hematopoietic cells, including macrophages, lymphocytes and platelets. 2-AG is released from cells in a stimulus-dependent manner and is rapidly eliminated by uptake into cells and enzymatic hydrolysis in arachidonic acid and glycerol. 2-AG might exert a very fine control on platelet function either through mechanisms intertwining with the signal transduction pathways used by platelet agonists or through mechanisms modulating specific receptors. The aim of this study was to define the role of 2-AG in human platelets and characterize the mechanisms by which it performs its action. Platelets from healthy donors were isolated from plasma by differential centrifugations and gel-filtration on Sepharose 2B. The samples were incubated with 2-AG (10–100 μM) under constant stirring in the presence or absence of various inhibitors. Platelet aggregation was measured by Born technique. We have found that stimulation of human platelets with 2-AG induced irreversible aggregation, which was significantly enhanced by co-stimulation with ADP (1–10 μM). Furthermore, 2-AG-dependent platelet aggregation was completely inhibited by ADP scavengers, aspirin, and Rho kinase inhibitor, as well as by antagonists of the 2-AG receptor (CB2), of the ADP P2Y12 receptor, and of the thromboxane A2 receptor. We further investigated the role of endocannabinoids on calcium mobilization. Intracellular [Ca2+] was measured using FURA-2-loaded platelets prewarmed at 37°C under gentle stirring in a spectrofluorimeter. 2-AG induced rapid increase of cytosolic [Ca2+] in a dose-dependent manner. This effect was partially blocked by ADP scavengers and CB2 receptor antagonists. Furthermore, 2-AG-induced [Ca2+] mobilization was totally suppressed by aspirin or the thromboxane A2 receptor antagonist. These results suggest that 2-AG is able to trigger platelet activation, and that this action is partially mediated by CB2 receptor and ADP. Furthmore, 2-AG-dependent platelet activation is totally dependent on thromboxane A2 generation.


Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 112-112
Author(s):  
Aleksandra Stojanovic ◽  
Matvey Gorovoy ◽  
Tatyana Voyno-Yasenetskaya ◽  
Xiaoping Du

Abstract LIM Kinase (LIMK)-1 is a member of the LIMK family of serine-threonine protein kinases that phosphorylates actin-binding protein cofilin and regulates actin cytoskeleton organization. LIMK1 is expressed in many cell types including platelets but the exact role of LIMK1 in platelet function remains unclear. To determine the role of LIMK1 in platelet activation, wild type or LIMK1 knockout mouse platelets were stimulated with platelet agonists. Platelet aggregation and granule secretion were analyzed. Integrin-dependent second wave of platelet aggregation induced by von Willebrand factor (VWF) in the presence of VWF activator botrocetin was abolished in LIMK1 knockout platelets. In contrast, platelet aggregation in response to the agonist peptide of protease-activated receptor-4 (PAR4, thrombin receptor), ADP and collagen was either not affected or enhanced in LIMK1 knockout platelets in comparison with wild type mouse platelets. Thus, LIMK appears to play an important role in platelet activation stimulated by VWF binding to its platelet receptor, glycoprotein Ib-IX complex (GPIb-IX) but had no stimulatory effect on or negatively regulate the GPIb-IX-independent platelet activation pathways mediated by PAR-4, ADP receptors and collagen receptors. To determine whether ligand binding to GPIb-IX stimulates LIMK activation and function, platelets were stimulated with VWF in the presence of either ristocetin or botrocetin, and immunoblotted with antibodies specifically recognizing phosphorylated LIMK1 (Serine 505) or cofilin (Serine 3). VWF induced phosphorylation of LIMK1 and LIMK substrate cofilin. Thus, VWF indeed stimulates LIMK1 activation and function. An important physiological role of GPIb-IX in platelets is to mediate platelet adhesion to subendothelial-bound VWF under shear stress at sites of vascular injury. To determine whether LIMK1 is important in platelet adhesion, we investigated whether LIMK1 knockout affected platelet adhesion to VWF-coated surfaces. LIMK1 knockout platelets are defective in mediating stable platelet adhesion to vWF under shear stress, suggesting that LIMK1 plays an important role in GPIb signaling and GPIb-IX-mediated integrin activation that is required for stable platelet adhesion under shear stress. Importantly, LIMK1 knockout mice showed significant delay in the formation of occlusive thrombus following FeCl3-induced carotid artery injury in comparison with wild type mice, indicating that the role of LIMK1 in GPIb-IX-mediated platelet activation is important in in vivo thrombosis. Together, our study reveals that LIMK1 plays an important role in GPIb-IX-mediated platelet activation and arterial thrombosis in vitro and in vivo.


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