Glycoprotein VI Expression Research Articles

Abstract 3094: Traditional Chinese Medicine Buyang Huanwu Decoction Regulates The Platelet Gpvi And Its Downstream Protein Signaling Pathways,inhibiting Thrombosis And Preventing Cardiovascular Disease.

Background: Coronary heart disease Qi-Deficiency and Blood Stasis Syndrome will lead to the body of platelets disorders, blood viscosity, conducive to the formation of thrombosis, Buyang Huanwu Decoction (BYHWD) is a classic Chinese medicine treatment of Qi-Deficiency and Blood Stasis Syndrome. Platelet glycoprotein VI (GPVI) plays a crucial role in collagen-induced activation and aggregation of platelets. GPVI has become the focus of new approaches to antithrombotic therapy. Methods: After 6 weeks of irregular sleep deprivation in rats with syndrome of deficiency of qi and blood stasis formed, the coronary heart disease model was established by ligation of the left anterior descending coronary artery in rats. The dosage of 1 mL/100 g was given by intragastric administration for 14 days after operation. Results: The purpose of this study was to investigate the effects of BYHWD on platelet granule secretion and platelet function in vitro. We found that BYHWD can significantly reduce the platelet aggregation induced by ADP and collagen, significantly reduce the median expression of CD62p and the ratio of activated platelets, and reduce the concentration of fluorescent calcium ions in platelets. Under the electron microscope observation found that under the action of BYHWD, the ultrastructure of rat platelets pseudopodia reduced, aggregation reduced, rat coronary inner wall platelets, thrombus mass adhesion reduced, and the inner wall was smoother. In addition, BYHWD can regulate GPVI and its downstream proteins. Compared with the coronary heart disease group with syndrome of blood stasis, BYHWD can significantly reduce the expression of GPVI. Significantly reduced the expression of Syk, CALDAG-GEFI, significantly reduced the expression of IP 3 and significantly reduced the degree of PLCγ 2 of rats. Decreased the degranulation reaction of the rat blood, significantly decreased the level of TXA 2 , 5-HT in the rat blood, and significantly decreased the content of the rat blood COX-1 in the rat serum. Conclusion: Therefore, BYHWD can regulate GPVI and its downstream protein signaling pathways, reduce platelet over-activation, degranulation reaction, thereby inhibiting thrombosis, protecting heart function and preventing cardiovascular disease.

Increase in Total Protein Level of Bruton's Tyrosine Kinase in Myeloproliferative Neoplasms

Myeloproliferative neoplasms (MPNs), including polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF), are characterized by atherosclerosis and cardiovascular risk. The mechanisms that connect MPNs with atherothrombosis remain elusive. It is known that atherosclerotic plaque causes Glycoprotein VI (GPVI)-dependent platelet activation and hence activation of bruton kinase (Btk) and that Btk inhibitors in vivo and ex vivo suppress GPVI-mediated paltelet activation. Aim of this study is to measure the levels of GPVI and Btk. In addition, we measured the CXCL12 as marker of atherothrombosis. We studied 25 JAK2V617F positive MPNs patients (WHO criteria) (mean age 58 years) including PV 12, ET 8, and PMF 5. We measured platelet count by automated analyzer, GPVI by flow cytometry, total Btk (T-Btk) protein by immunoblot and total CXCL12 (T-CXCL12) protein by ELISA. All patients had thrombocytosis (630±40x109/L) and allele burden ≥ 50%. We found high GPVI expression (mean fluorescence intensity (MFI) 20±5.8) and high T-Btk (mean value 1.0) as well as high T-CXCL12 (15±2 μg/ml). A positive correlation there was between GPVI and Btk. We further investigated Btk mRNA tran script levels using RT-PCR assay in triplicate from each samples and found mean values ≥ 1.0. On the basis of these results the use of GPVI- and Btk- inhibiting agents as atherothrombosis-focused antiplatelet drugs is conceivable. Therefore, clinical trials are eagerly awaited.

The Subtilisin-Like Protease Furin Regulates Hemin-Dependent Ectodomain Shedding of Glycoprotein VI.

Hemolysis results in release of free hemoglobin and hemin liberation from erythrocytes. Hemin has been described to induce platelet activation and to trigger thrombosis. We evaluated the effect of hemin on platelet function and surface expression of the platelet collagen receptor glycoprotein VI (GPVI). Isolated platelets were stimulated with increasing concentrations of hemin. We found that hemin strongly enhanced platelet activation, aggregation, and aggregate formation on immobilized collagen under flow. In contrast, we found that surface expression of GPVI was significantly reduced upon hemin stimulation with high hemin concentrations indicating that hemin-induced loss of surface GPVI does not hinder platelet aggregation. Loss of hemin-induced surface expression of GPVI was caused by shedding of the ectodomain of GPVI as verified by immunoblotting and is independent of the GPVI or CLEC-2 mediated ITAM (immunoreceptor-tyrosine-based-activation-motif) signaling pathway as inhibitor studies revealed. Hemin-induced GPVI shedding was independent of metalloproteinases such as ADAM10 or ADAM17, which were previously described to regulate GPVI degradation. Similarly, concentration-dependent shedding of CD62P was also induced by hemin. Unexpectedly, we found that the subtilisin-like proprotein convertase furin controls hemin-dependent GPVI shedding as shown by inhibitor studies using the specific furin inhibitors SSM3 and Hexa-D-arginine. In the presence of SSM3 and Hexa-D-arginine, hemin-associated GPVI degradation was substantially reduced. Further, SSM3 inhibited hemin-induced but not CRP-XL-induced platelet aggregation and thrombus formation, indicating that furin controls specifically hemin-associated platelet functions. In summary, we describe a novel mechanism of hemin-dependent GPVI shedding and platelet function mediated by furin.

Evaluation of the effect of eltrombopag therapy on the platelet collagen receptor glycoprotein VI (GPVI) expression and soluble GPVI levels in young patients with immune thrombocytopenia

BackgroundPlatelet glycoprotein VI (GPVI) receptor is essential for platelet adhesion and aggregation. Eltrombopag is as an effective treatment for chronic immune thrombocytopenia (ITP); yet, its effect on platelet function is not fully characterized.AimThis prospective study investigated the effect of eltrombopag therapy on platelet function through assessment of GPVI receptor expression and soluble GPVI levels among pediatric patients with persistent or chronic ITP.MethodsThirty-six children and adolescents with persistent or chronic ITP were divided equally into two groups either to receive eltrombopag therapy or the standard of care. All patients were followed-up for 12 months with assessment of bleeding score and complete blood count (CBC). Evaluation of GPVI expression using flow cytometry and measurement of its soluble form by ELISA was done at baseline and at 6 months.ResultsITP patients on eltrombopag had significantly lower bleeding score after 6 months of therapy while the quality of life has significantly improved. Platelet count was significantly increased throughout the study. GPVI expression by flow cytometry and soluble GPVI levels were significantly increased after eltrombopag therapy. After 12 months, ITP patients on eltrombopag were able to maintain a good quality of life and low bleeding score.ConclusionOur data suggest that eltrombopag, through its effect on the GPVI receptor expression and its soluble form, might reduce bleeding manifestations and improve the quality of life of chronic and persistent ITP children independent of its effect on the platelet count.

Treatment of congenital thrombocytopenia and decreased collagen reactivity in G6b-B–deficient mice

AbstractMice lacking the immunoreceptor tyrosine-based inhibition motif-containing co-inhibitory receptor G6b-B (Mpig6b, G6b knockout, KO) are born with a complex megakaryocyte (MK) per platelet phenotype, characterized by severe macrothrombocytopenia, expansion of the MK population, and focal myelofibrosis in the bone marrow and spleen. Platelets are almost completely devoid of the glycoprotein VI (GPVI)-FcRγ-chain collagen receptor complex, have reduced collagen integrin α2β1, elevated Syk tyrosine kinase activity, and a subset has increased surface immunoglobulins. A similar phenotype was recently reported in patients with null and loss-of-function mutations in MPIG6B. To better understand the cause and treatment of this pathology, we used pharmacological- and genetic-based approaches to rescue platelet counts and function in G6b KO mice. Intravenous immunoglobulin resulted in a transient partial recovery of platelet counts, whereas immune deficiency did not affect platelet counts or receptor expression in G6b KO mice. Syk loss-of-function (R41A) rescued macrothrombocytopenia, GPVI and α2β1 expression in G6b KO mice, whereas treatment with the Syk kinase inhibitor BI1002494 partially rescued platelet count but had no effect on GPVI and α2β1 expression or bleeding. The Src family kinase inhibitor dasatinib was not beneficial in G6b KO mice. In contrast, treatment with the thrombopoietin mimetic romiplostim rescued thrombocytopenia, GPVI expression, and platelet reactivity to collagen, suggesting that it may be a promising therapeutic option for patients lacking functional G6b-B. Intriguingly, GPVI and α2β1 expression were significantly downregulated in romiplostim-treated wild-type mice, whereas GPVI was upregulated in romiplostim-treated G6b KO mice, suggesting a cell intrinsic feedback mechanism that autoregulates platelet reactivity depending on physiological needs.

GPVI expression is linked to platelet size, age, and reactivity

AbstractPlatelets within one individual display heterogeneity in reactivity, size, age, and expression of surface receptors. To investigate the combined intraindividual contribution of platelet size, platelet age, and receptor expression levels on the reactivity of platelets, we studied fractions of large and small platelets from healthy donors separated by using differential centrifugation. Size-separated platelet fractions were perfused over a collagen-coated surface to assess thrombus formation. Multicolor flow cytometry was used to characterize resting and stimulated platelet subpopulations, and platelet age was determined based on RNA and HLA-I labeling. Signal transduction was analyzed by measuring consecutive phosphorylation of serine/threonine-protein kinase Akt. Compared with small platelets, large platelets adhered faster to collagen under flow and formed larger thrombi. Among the large platelets, a highly reactive juvenile platelet subpopulation was identified with high glycoprotein VI (GPVI) expression. Elevated GPVI expression correlated with high HLA-I expression, RNA content, and increased platelet reactivity. There was a stronger difference in Akt phosphorylation and activation upon collagen stimulation between juvenile and older platelets than between large and small platelets. GPVI expression and platelet reactivity decreased throughout platelet storage at 22°C and was better maintained throughout cold storage at 4°C. We further detected higher GPVI expression in platelets of patients with immune thrombocytopenia. Our findings show that high GPVI expression is a feature of highly reactive juvenile platelets, which are predominantly found among the large platelet population, explaining the better performance of large platelets during thrombus formation. These data are important for studies of thrombus formation, platelet storage, and immune thrombocytopenia.

Targeting Platelet GPVI Plus rt-PA Administration but Not α2β1-Mediated Collagen Binding Protects against Ischemic Brain Damage in Mice.

Platelet collagen interactions at sites of vascular injuries predominantly involve glycoprotein VI (GPVI) and the integrin α2β1. Both proteins are primarily expressed on platelets and megakaryocytes whereas GPVI expression is also shown on endothelial and integrin α2β1 expression on epithelial cells. We recently showed that depletion of GPVI improves stroke outcome without increasing the risk of cerebral hemorrhage. Genetic variants associated with higher platelet surface integrin α2 (ITGA2) receptor levels have frequently been found to correlate with an increased risk of ischemic stroke in patients. However until now, no preclinical stroke study has addressed whether platelet integrin α2β1 contributes to the pathophysiology of ischemia/reperfusion (I/R) injury. Focal cerebral ischemia was induced in C57BL/6 and Itga2−/− mice by a 60 min transient middle cerebral artery occlusion (tMCAO). Additionally, wild-type animals were pretreated with anti-GPVI antibody (JAQ1) or Fab fragments of a function blocking antibody against integrin α2β1 (LEN/B). In anti-GPVI treated animals, intravenous (IV) recombinant tissue plasminogen activator (rt-PA) treatment was applied immediately prior to reperfusion. Stroke outcome, including infarct size and neurological scoring was determined on day 1 after tMCAO. We demonstrate that targeting the integrin α2β1 (pharmacologic; genetic) did neither reduce stroke size nor improve functional outcome on day 1 after tMCAO. In contrast, depletion of platelet GPVI prior to stroke was safe and effective, even when combined with rt-PA treatment. Our results underscore that GPVI, but not ITGA2, is a promising and safe target in the setting of ischemic stroke.

Diacylglycerol kinase ζ is a negative regulator of GPVI-mediated platelet activation

AbstractDiacylglycerol kinases (DGKs) are a family of enzymes that convert diacylglycerol (DAG) into phosphatidic acid (PA). The ζ isoform of DGK (DGKζ) has been reported to inhibit T-cell responsiveness by downregulating intracellular levels of DAG. However, its role in platelet function remains undefined. In this study, we show that DGKζ was expressed at significant levels in both platelets and megakaryocytes and that DGKζ-knockout (DGKζ-KO) mouse platelets were hyperreactive to glycoprotein VI (GPVI) agonists, as assessed by aggregation, spreading, granule secretion, and activation of relevant signal transduction molecules. In contrast, they were less responsive to thrombin. Platelets from DGKζ-KO mice accumulated faster on collagen-coated microfluidic surfaces under conditions of arterial shear and stopped blood flow faster after ferric chloride–induced carotid artery injury. Other measures of hemostasis, as measured by tail bleeding time and rotational thromboelastometry analysis, were normal. Interestingly, DGKζ deficiency led to increased GPVI expression on the platelet and megakaryocyte surfaces without affecting the expression of other platelet surface receptors. These results implicate DGKζ as a novel negative regulator of GPVI-mediated platelet activation that plays an important role in regulating thrombus formation in vivo.

Significant Hypo-Responsiveness to GPVI and CLEC-2 Agonists in Pre-Term and Full-Term Neonatal Platelets and following Immune Thrombocytopenia.

Neonatal platelets are hypo-reactive to the tyrosine kinase-linked receptor agonist collagen. Here, we have investigated whether the hypo-responsiveness is related to altered levels of glycoprotein VI (GPVI) and integrin α2β1, or to defects in downstream signalling events by comparison to platelet activation by C-type lectin-like receptor 2 (CLEC-2). GPVI and CLEC-2 activate a Src- and Syk-dependent signalling pathway upstream of phospholipase C (PLC) γ2. Phosphorylation of a conserved YxxL sequence known as a (hemi) immunotyrosine-based-activation-motif (ITAM) in both receptors is critical for Syk activation. Platelets from human pre-term and full-term neonates display mildly reduced expression of GPVI and CLEC-2, as well as integrin αIIbβ3, accounted for at the transcriptional level. They are also hypo-responsive to the two ITAM receptors, as shown by measurement of integrin αIIbβ3 activation, P-selectin expression and Syk and PLCγ2 phosphorylation. Mouse platelets are also hypo-responsive to GPVI and CLEC-2 from late gestation to 2 weeks of age, as determined by measurement of integrin αIIbβ3 activation. In contrast, the response to G protein-coupled receptor agonists was only mildly reduced and in some cases not altered in neonatal platelets of both species. A reduction in response to GPVI and CLEC-2, but not protease-activated receptor 4 (PAR-4) peptide, was also observed in adult mouse platelets following immune thrombocytopenia, whereas receptor expression was not impaired. Our results demonstrate developmental differences in platelet responsiveness to GPVI and CLEC-2, and also following immune platelet depletion leading to reduced Syk activation. The rapid generation of platelets during development or following platelet depletion is achieved at the expense of signalling by ITAM-coupled receptors.

Expression of Platelet Collagen Receptor Glycoprotein VI in Coronary Heart Disease: Interaction between Platelets and Endothelial Cells.

1) To investigate the expression of platelet collagen receptor glycoprotein VI (GPVI) on the surface of platelets in patients with coronary heart disease (CHD). 2) To investigate the expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) on the surface of endothelial cells after exposure to subjects' platelets. Platelets were extracted from blood samples of 97 subjects including 43 with acute coronary syndrome (ACS), 21 with stable angina pectoris (SAP), and 33 serving as controls in which CHD was excluded. Using flow cytometry, we measured the expression of GPVI and platelet degranulation markers CD62P and CD63. In addition we quantified expression of endothelial cell ICAM-1 and VCAM-1. A higher expression of platelet GPVI was observed in ACS compared with SAP and control groups. The expression level of platelet GPVI significantly correlated with CD62P and CD63 in the CHD population (r = 0.713 and 0.615, both p < 0.01). Significantly higher ICAM-1 expression was observed in endothelial cells after interaction with platelets from the ACS population. In the CHD subjects, the surface expression of platelet GPVI correlated with the level of ICAM-1 in endothelial cells (r = 0.371, p < 0.05). Platelet GPVI associated with platelet activation and endothelial inflammation is a vital index for predicting CHD occurrence and severity.

Platelets and Arterial Thrombosis: Evolving Role of Platelet Gpvi as an Antithrombotic Drug Target

Acute coronary syndrome is one of the leading causes of mortality and morbidity worldwide. Although the recent advancements in existing anti-platelet therapeutics have significantly reduced the burden of cardiovascular deaths but owing to their global impact on primary haemostasis, their clinical benefits are often limited by bleeding risk. Recent developments in the understanding of platelet biology have placed platelet-collagen interaction at the critical position in the sequence of events during arterial thrombosis. Thus there is considerable interest in developing novel therapeutic strategies against platelet collagen receptor glycoprotein VI (GPVI) because not only its selective blockade or deficiency holds promise for the reduced risk of bleeding complications as evidenced in mice and humans, but also the exclusive expression of GPVI on platelets and megakaryocytes offers to prevent the adverse off-target effects of antithrombotic drugs. The present review summarizes recent developments in understanding of platelet functions during arterial thrombosis and structural and functional attributes of platelet GPVI to identify it as a novel antithrombotic drug target. Moreover, it also emphasises on the development of GPVI antagonists using various experimental approaches as well as their prospective use in cardiovascular disorders.

Investigating the role of rare genetic variants of GP6 gene in platelet function

BackgroundThrombus formation in the arteries is a major risk factor for myocardial infarction and stroke. Platelets are involved in blood homoeostasis because of their ability to form thrombi after the interaction with collagen. Glycoprotein VI (GPVI) in complex with the Fc receptor γ chain forms the major collagen receptor on the platelet membrane. Clustering of the receptor on collagen or collagen-related peptides (CRP-XL) triggers the kinase activity of GPVI which leads to various platelet responses that can be measured in vitro. We aimed to identify and characterise differences in GPVI expression and function in individuals with rare GPVI phenotypes with a view to uncover potentially causal genetic variants. In addition, we tested the hypothesis that individuals with both extremely low GPVI expression and responses to CRP-XL could have previously undescribed genomic sequence variation in the GP6 gene, which encodes the GPVI protein receptor. MethodsWe measured surface glycoprotein expression in 506 healthy individuals with flow cytometry using an anti-GPVI monoclonal antibody. Total glycoprotein expression was measured with western blotting using rabbit anti-GPVI polyclonal antibodies. Flow cytometry was used to measure platelet surface expression of GPVI. Thrombus formation was assessed by perfusing heparinised blood over a collagen-coated glass slide followed by calculation of the area covered by thrombi. FindingsTwo individual showed significantly reduced expression of GPVI, impaired responses to CRP-XL, but normal responses to ADP. The low platelet expression level of GPVI in these two individuals was not balanced by an increase in plasma GPVI, ruling out a metalloproteinase-dependent shedding effect. Sequencing the promoter and the exons of GP6 in these two individuals showed a non-synonymous single nucleotide polymorphism (SNP) in exon 4 of the GP6 gene in each person—in one, a S195N substitution, which is a rare deleterious mutation, and in the other, a previously undocumented SNP in the same region leading to a P194T substitution. Studies in this latter individual, together with three siblings and a son, showed a range of expression levels consistent with their GP6 haplotype status, with no expression from the variant-containing allele. Carriers of the rare variant showed a relatively mild reduction in thrombus formation compared with controls. InterpretationOur screening of GPVI-related phenotypes has identified deficiencies in this important platelet receptor in a pedigree of healthy individuals. Their lack of obvious bleeding problems can partly be explained by the observation that alternative activation pathways (thrombin receptors, ADP receptors) function well in the whole-blood flow cytometry assay and would compensate in normal haemostasis. Further investigations to uncover the mechanisms giving rise to the lack of GPVI expression from this allele are continuing. FundingWellcome Trust, NHS Blood and Transplant.

An adenine insertion in exon 6 of human GP6 generates a truncated protein associated with a bleeding disorder in four Chilean families

Glycoprotein VI (GPVI), 60-65kDa, is a major collagen receptor on platelet membranes involved in adhesive and signaling responses. Mice lacking GPVI have impaired platelet response to collagen and defective primary adhesion and subsequent thrombus formation. Complete or partial deficiency of GPVI in humans is a rare condition presenting as a mild bleeding disorder. The defect in most of the reported patients is acquired and associated with other diseases. To date, only two patients have been characterized at the molecular level who carry different compound heterozygous mutations in the GP6 gene. To report four unrelated patients from non-consanguineous families who presented with mucocutaneous bleeding. They had absent platelet aggregation and (14) C-5-HT secretion with collagen, convulxin and collagen-related peptide. Flow cytometry and immunofluorescence-confocal microscopy showed an absence of GPVI in non-permeabilized platelets. All the patients had an adenine insertion in exon 6 (c.711_712insA), changing the reading frame and generating a premature 'stop codon' in site 242 of the protein. The mutation predicts the synthesis of the truncated protein before the trans-membrane domain, corresponding to a band of ≈49kDa observed in western blots and in permeabilized platelets by immunofluorescence. Platelet mRNA from all the patients was sequenced and contained the corresponding adenine insertion. Heterozygous relatives had no pathological bleeding, normal response to collagen and convulxin and intermediate membrane expression of GPVI. The identification of four unrelated homozygous patients with an identical defect suggests that inherited GPVI deficiency is more frequent than previously suspected, at least in Chile.

CD148 enhances platelet responsiveness to collagen by maintaining a pool of active Src family kinases.

We have previously shown that the receptor-like protein tyrosine phosphatase (PTP) CD148 is essential for initiating glycoprotein VI (GPVI) signaling in platelets. We proposed that CD148 does so by dephosphorylating the C-terminal inhibitory tyrosine of Src family kinases (SFKs). However, this mechanism is complicated by CD148-deficient mouse platelets having a concomitant reduction in GPVI expression. To investigate the effect of CD148 on GPVI signaling independent of the decrease in GPVI expression and to further establish the molecular basis of the activatory effect of CD148 and downregulation of GPVI. CD148-deficient mouse platelets were investigated for functional and biochemical defects. The DT40/NFAT-lucifierase reporter assay was used to analyze the effect of CD148 on GPVI signaling. CD148-SFK interactions and dephosphorylation were quantified using biochemical assays. CD148-deficient mouse platelets exhibited reduced collagen-mediated aggregation, secretion and spreading in association with reduced expression of GPVI and FcR gamma-chain and reduced tyrosine phosphorylation. The phosphorylation status of SFKs suggested a global reduction in SFK activity in resting CD148-deficient platelets. Studies in a cell model confirmed that CD148 inhibits GPVI signaling independent of a change in receptor expression and through a mechanism dependent on tyrosine dephosphorylation. Recombinant CD148 dephosphorylated the inhibitory tyrosines of Fyn, Lyn and Src in vitro, although paradoxically it also dephosphorylated the activation loop of SFKs. CD148 plays a critical role in regulating GPVI/FcR gamma-chain expression and maintains a pool of active SFKs in platelets by directly dephosphorylating the C-terminal inhibitory tyrosines of SFKs that is essential for platelet activation.

Platelet glycoprotein VI (GPVI) for early identification of acute coronary syndrome in patients with chest pain

Background Platelet glycoprotein VI (GPVI) is elevated in patients with acute coronary syndrome (ACS), stroke and associated with acute coronary events. GPVI may be helpful to distinguish an imminent ACS from non-coronary (NC) causes in patients with chest pain who were transferred to chest pain unit, before the myocardial necrosis is evident with classical biomarkers. Methods Based on the findings of our previous studies, we consecutively examined 1004 patients with chest pain in a prospective study design. ACS was found in 416 (41.4%), stable angina pectoris (SAP) in 233 (23.2%), and NC causes of chest pain (hypertension, musculoskeletal disease, pulmonary embolism, myocarditis, cardiophobia) in 355 patients (35.4%). Platelet surface expression of GPVI was measured by flow cytometry. Results Patients with ACS showed significantly enhanced GPVI expression levels compared to patients with SAP or NC causes of chest pain (ACSvs.SAP(mean fluorescence intensity (MFI) ± SD):18.9 ± 7.4vs.17.9 ± 9.5;P = 0.028;ACSvs.NC:15.4 ± 6.9;P = 0.002). Elevated GPVI expression was associated with ACS independent of markers of myocardial necrosis like troponin and creatine kinase-MB. Patients with an elevated GPVI expression (MFI ≥ 18.6) had a poorer clinical outcome than patients with baseline GPVI expression in regard to composite cumulative survival that included myocardial infarction, stroke, and cardiovascular death at three months (Log rank;P = 0.025). Discussion Platelet GPVI surface expression is enhanced in patients at risk for an ACS and is an early marker for imminent acute coronary events in patients with chest pain.

Glycoprotein VI for diagnosis of acute coronary syndrome when ECG is ambiguous

BackgroundThe purpose of the study was to test whether an elevated surface expression of platelet collagen receptor glycoprotein VI (GPVI) is an appropriate marker for the diagnosis of the acute coronary syndrome (ACS), especially when the electrocardiogram (ECG) is ambiguous. MethodsBetween 2007 to 2008, we consecutively evaluated 378 patients with ACS and ambiguous ECG on hospital admission. In all patients, GPVI surface expression was determined by flow cytometry. In addition, the myocardial necrosis markers troponin-I (Tn-I) and creatine kinase-MB (CKMB) were measured. ResultsWe found that in patients with ACS and unclear ECG in whom GPVI levels (mean fluorescence intensity (MFI) ≥18.6) were elevated, the relative risk for ACS was 2.6-fold enhanced. Binary logistic regression analysis revealed that an elevated platelet GPVI level is indicating an ACS independent of biomarkers of myocardial necrosis including Tn-I, creatine kinase (CK), CKMB (GPVI: p=0.011; Tn-I: p=0.180; CKMB: p=0.250; CK: p=0.127). Patients with evident T-wave inversion and/or ST-depression showed a strong association between ACS and GPVI expression. ConclusionsPlatelet GPVI surface expression is enhanced in patients with ACS with unclear ECG findings and is strongly associated with myocardial ischemia. Additional to the classical markers of myocardial necrosis Tn-I and CK, GPVI is an early biomarker for the diagnosis of ACS, especially when the ECG is ambiguous.

Glycoprotein VI as a prognostic biomarker for cardiovascular death in patients with symptomatic coronary artery disease

Platelets play a critical role in arterial thrombosis, acute coronary syndrome (ACS) and stroke. Platelet collagen receptor glycoprotein VI (GPVI) is associated with acute coronary events and a poor clinical outcome. Between January 2006 and March 2009, we evaluated 2,213 consecutive patients in a prospective study design, who presented with chest pain. Among 1,819 patients (82.2%) who underwent coronary angiography, 1,652 patients (90.8%) showed a coronary and 167 patients (9.2%) a non-coronary origin of chest pain. 901 patients (54.5%) presented with an ACS, 751 (45.5%) with a stable angina pectoris. Clinical outcome was performed by a predefined structured telephone interview after a 3-month follow-up (92.8%:1,533 of 1,652 patients). Kaplan-Meier analysis for cumulative event-free survival revealed that patients with a elevated baseline GPVI expression had a poorer clinical outcome for cardiovascular death than patients with decreased GPVI levels (log rank; P = 0.040). These results were paralleled in composite cumulative survival that included myocardial infarction, stroke, and cardiovascular death (log rank; P = 0.002). Relative risk of cardiovascular death was found at 1.41 (95% CI 1.08-1.85) for platelet GPVI, 1.64 (95% CI 1.31-2.05) for brain natriuretic peptide, 1.16 (95% CI 0.81-1.64) for troponin-I and 1.33 (95% CI 0.97-1.82) for C-reactive protein. Patients with CAD presenting increased levels of platelet GPVI had a poorer outcome and may profit from a dual antiplatelet therapy. Thus, GPVI may be a useful prognostic tool for adverse cardiovascular events. Future studies should substantiate GPVI for its potential role of risk prediction and consider its prognostic value to improve risk stratification.

Expression of platelet glycoprotein VI is associated with transient ischemic attack and stroke

Platelet collagen receptor glycoprotein VI (GPVI) contributes significantly to platelet adhesion and thrombus formation. We aimed to investigate GPVI in patients presenting with symptoms of acute cerebrovascular disease and to define GPVI as biomarker for acute stroke. We consecutively evaluated 205 patients, who admitted the stroke unit with symptoms for stroke. Surface expression of the platelet activation markers (GPVI, CD62P, GPIb) was determined by two-color whole blood flow cytometry. Patients with transient ischemic attack (TIA) (n = 18; 8.8%) as well as with stroke (n = 133; 64.9%) showed a significantly enhanced GPVI expression (mean fluorescence intensity +/- SD) on admission compared to patients with non-ischemic (NI) events (n = 54; 26.3%) (TIA: 20.9 +/- 7.1 vs. NI: 16.2 +/- 3.9; P = 0.002; stroke: 20.4 +/- 5.7 vs. NI; P = 0.002). Neither CD62P nor GPIb surface expression showed a significant difference. Logistic regression analysis revealed that on admission GPVI was associated with stroke independent of conventional laboratory markers such as C-reactive protein, blood glucose, and creatine kinase. Using a receiver operating characteristic curve on GPVI, we have determined the cut off value of 18.2 for stroke. Thus, patients with enhanced GPVI expression levels (>or=18.2) had a 2.4-fold relative risk for stroke. Patients with elevated platelet GPVI expression level had a poorer clinical outcome in cumulative event-free survival for stroke, myocardial infarction, and cerebro-/cardiovascular death at 3-month follow-up (log rank; P = 0.045). These findings indicate that platelet GPVI surface expression is significantly enhanced in patients with TIA and stroke compared to patients with NI events. Determination of platelet-specific GPVI may be useful as an early biomarker for cerebral ischemia.

Regulation of platelet glycoprotein VI (GPVI) surface expression and of soluble GPVI in patients with atrial fibrillation (AF) and acute coronary syndrome (ACS)

The platelet collagen receptor glycoprotein VI (GPVI) mediates platelet adhesion to subendothelial matrix and thrombus formation in acute coronary syndrome (ACS). This study examined patients with both ACS and stable coronary artery disease (CAD), which presented with atrial fibrillation (AF) and sinus rhythm (SR). We evaluated 992 patients with acute or stable CAD, and determined platelet surface expression of GPVI using flow cytometry. Seventy-eight patients presented with nonvalvular persistent AF. After 1:1 propensity score matching 156 matched cases with 78 pairs were obtained. Patients with AF and ACS showed a significantly decreased GPVI expression compared to patients with ACS and SR, whereas patients with stable angina pectoris (SA) presented with low level activation and no significant difference between SR and AF [mean fluorescence intensity (MFI) for ACS (SR Vs. AF): 20 +/- 6.3 Vs. 17.7 +/- 4.4; P = 0.023; SA (SR Vs. AF): 18.8 +/- 9.4 Vs. 18.1 +/- 6.1; P = 0.649]. In contrast, soluble GPVI was increased in ACS and AF accordingly [plasma GPVI (ng/ml) for ACS (SR Vs. AF): 1.4 +/- 0.8 Vs. 1.9 +/- 1.1; P = 0.038; SA (SR Vs. AF): 0.9 +/- 0.4 Vs. 1.1 +/- 0.5; P = 0.127]. Platelet GPVI surface expression is decreased in patients with AF and ACS compared to patients with SR and ACS. Nonvalvular AF is related to indices of chronic platelet activation and might be responsible for a down-regulation of GPVI receptor density on platelets, while soluble GPVI was increased in ACS and AF accordingly.

Influence of platelet count on the expression of platelet collagen receptor glycoprotein VI (GPVI) in patients with acute coronary syndrome

Platelets play a key role in the development of an acute coronary syndrome (ACS) and contribute to cardiovascular events. Platelet collagen receptor glycoprotein VI (GPVI) contributes significantly to platelet adhesion and thrombus formation in ACS. We consecutively investigated both the platelet count and the platelet surface expression of GPVI in 843 patients with a symptomatic coronary artery disease verified by coronary angiography. Four hundred fourteen patients presented with stable angina pectoris and 429 patients with ACS. Platelet surface expression of GPVI and CD62P was determined by flow cytometry and platelet count with a coulter counter, plasmatic soluble GPVI was measured by ELISA. Platelet GPVI expression in patients with ACS was compared to platelet count. Patients with ACS showed significantly elevated GPVI expression levels in the first and second quartiles of platelet count compared to patients with higher platelet count [mean fluorescence intensity (MFI) +/- standard deviation): 1(st) vs. 4(th): 20.44 +/- 6.1 vs. 18.62 +/- 3.7; p=0.012; 2(nd)vs.3(rd):21.2+/-8.5vs.18.76+/-3.7;P=0.03; 2(nd)vs.4(th): 21.2+/-8.5vs.18.62+/-3.7;P=0.004], which was paralleled in trend for the CD62P expression [MFI: 1(st) vs. 4(th): 11.2 +/- 6.8 vs. 12.3 +/- 9; p=0.057; 2(nd) vs. 3(rd): 16.3 +/- 16 vs.12.7 +/- 5.3; p=0.138; 2(nd) vs. 4(th): 16.3 +/- 16 vs.11 +/- 4.4; p=0.043]. In a subgroup of 48 patients with ACS, determination of soluble GPVI showed similar results [plasma GPVI (ng/ml): 1(st)vs.4(th): 1.6 +/- 0.6 vs. 1.2 +/- 0.4; p=0.046; 1(st) vs. 3(rd): 1.6 +/- 0.6 vs. 1.1 +/- 0.5; p=0.038; 2(nd) vs. 3(rd): 1.9 +/- 0.8 vs. 1.1 +/- 0.5; p=0.04; 2(nd) vs. 4(th): 1.9 +/- 0.8 vs. 1.2 +/- 0.4; p=0.056]. Thus, a lower platelet count comes along with a higher GPVI surface expression and plasma concentration in patients with ACS, which potentially reflects increased activation and enhanced recruitment of platelets to the site of vascular injury.