Biomedical subjects

Meinrad Gawaz

Publications and source records attributed to Meinrad Gawaz.

At least 19 recordsLinked to original sources

PubMed2026

Targeting ACKR3/CXCR7 enhances platelet anticoagulant acylcarnitines and modulates procoagulant function.

Targeting ACKR3/CXCR7 regulates enzymatic generation of prothrombotic lipids while favoring antithrombotic lipids that inhibit platelets through the AC-cAMP-PKA pathway in coordination with prostacyclin IP receptor. This investigation validated the effect of CXCR7 in modulating nonenzymatic lipid (per)oxidation, platelet response to lipoproteins, mitochondrial metabolism, and procoagulant functions. CXCR7 agonist VUF11207 preserved mitochondrial membrane integrity, counteracted activation-induced mitochondrial superoxide generation, and reduced nonenzymatic lipid (per)oxidation. Moreover, it regulated lipoprotein-induced platelet adhesion to thrombogenic matrices, degranulation, αIIbβIII-integrin activation, aggregation, and thrombotic responses by reducing lipoprotein uptake through CD36 and ApoER2. CXCR7 ligation triggered the activation of AMP-dependent kinaseSer-172 and prompted AMPK-mediated inhibitory phosphorylation of acetyl-coenzyme A carboxylaseSer-79 to foster lipolysis over lipogenesis. Consequently, the AMPKSer-172-ACCSer-79 pathway increased generation of anticoagulant FXa-inhibitory long-chain acylcarnitines (LC-CAR) in platelets of healthy subjects and patients with coronary artery disease. Enrichment of intraplatelet LC-CARs was not attributable to dysregulated mitochondrial respiration because VUF11207 improved maximal respiration, spare respiratory capacity, and ATP-linked respiration in thrombin-activated platelets, suggesting sustained mitochondrial metabolism. Exerting a 2-pronged effect on procoagulant function, VUF11207 downregulated phosphatidylserine exposure on activated platelets and reduced FX/FXa binding, while platelet-derived anticoagulant LC-CARs regulated thrombin generation. VUF11207 administration reduced thrombus formation, platelet degranulation, αIIbβIII-integrin activation, procoagulant activity, and circulating platelet-leukocyte aggregates in murine venous thrombosis model, also decreased plasma procoagulant lipids derived from platelet cyclooxygenase-1 and 12-lipooxygenase (LOX), and leukocyte 5/15-LOX, decreased thromboinflammatory mediators (IL-1β, IL-6, IFN-γ, TNF-α, and MCP-1), and increased plasma LC-CAR levels. Therefore, pharmacological targeting of CXCR7 could regulate (non)enzymatic lipid processing and promote anticoagulant LC-CAR generation to limit platelet-driven thrombotic propensity and hypercoagulability, also replenish reduced levels of circulatory LC-CARs in patients with STEMI and VTE.

Humans↗

PubMed2005

Platelet adhesion via glycoprotein IIb integrin is critical for atheroprogression and focal cerebral ischemia: an in vivo study in mice lacking glycoprotein IIb.

BACKGROUND: The platelet glycoprotein (GP) IIb/IIIa integrin binds to fibrinogen and thereby mediates platelet aggregation. Here, we addressed the role of GP IIb for platelet adhesion and determined the relevance of platelet GP IIb for the processes of atherosclerosis and cerebral ischemia-reperfusion (I/R) injury. METHODS AND RESULTS: GP IIb(-/-) mice were generated and bred with ApoE(-/-) animals to create GP IIb(-/-)ApoE(-/-) mice. Platelet adhesion to the mechanically injured or atherosclerotic vessel wall was monitored by in vivo video fluorescence microscopy. In the presence of GP IIb, vascular injury and early atherosclerosis induced platelet adhesion in the carotid artery (CA). In contrast, platelet adhesion was significantly reduced in the absence of GP IIb integrin (P<0.05). To address the contribution of platelet GP IIb to atheroprogression, we determined atherosclerotic lesion formation in the CA and aortic arch (AA) of GP IIb(+/+)ApoE(-/-) or GP IIb(-/-)ApoE(-/-) mice. Interestingly, the absence of GP IIb attenuated lesion formation in CA and AA, indicating that platelets, via GP IIb, contribute substantially to atherosclerosis. Next, we assessed the implication of GP IIb for cerebral I/R injury. We observed that after occlusion of the middle cerebral artery, the cerebral infarct size was drastically reduced in mice lacking GP IIb compared with wild-types. CONCLUSIONS: These findings show for the first time in vivo that GP IIb not only mediates platelet aggregation but also triggers platelet adhesion to exposed extracellular matrices and dysfunctional endothelial cells. In a process strictly involving GP IIb, platelets, which are among the first blood cells to arrive at the scene of endothelial dysfunction, contribute essentially to atherosclerosis and cerebral I/R injury.

Animals↗

PubMed2005

Retroviral infection and selection of culture-derived platelets allows study of the effect of transgenes on platelet physiology ex vivo and on thrombus formation in vivo.

UNLABELLED: Background- We recently reported the development of culture-derived (CD) platelets with the aim to express any protein of interest in these platelets. We now report a specific protocol of retroviral infection into the progenitor cells and subsequent selection, which allows to generate large amounts of highly homogenous transgene-expressing CD platelets and to study transgene function rapidly and reliably at large-scale ex vivo and in vivo settings. METHODS AND RESULTS: After retroviral infection and selection, the activation-dependent expression profile of surface markers, aggregation, and granule release were investigated. The function of transgene-expressing CD platelets, the precursor cells of which had been retrovirally infected, compared well to noninfected CD platelets or freshly isolated platelets. Hence, the retroviral infection protocol did not alter platelet physiology. In contrast, adenoviral infection of precursors to CD platelets resulted in marked functional alterations that obviated their use in analytic experiments. Additionally, sufficient amounts of selected CD platelets were generated to warrant intravenous injections into living mice. This approach permitted study of their adhesive profile at endothelial lesions and their effect on thrombus formation in vivo by intravital videofluorescence microscopy. CONCLUSIONS: The novel selection method allowed us to produce recombinant transgene-expressing platelets in sufficient amounts to study genetically modified platelets in vitro and in vivo.

Adenoviridae↗

PubMed2005

Platelet degranulation is associated with progression of intima-media thickness of the common carotid artery in patients with diabetes mellitus type 2.

BACKGROUND: Platelets play a key role in atherogenesis and thromboembolic complications in patients with type 2 diabetes. METHODS AND RESULTS: We prospectively examined the relationship between systemic platelet activation and progression of carotid wall thickness within 1 year in 105 patients with type 2 diabetes. The intima-media thickness (IMT) of the common carotid artery was measured bilaterally at study entry and after 1 year. Platelet activation was assessed with the use of immunologic markers of platelet activation (CD62P, CD63, and CD40L) and flow cytometry. The prevalence for progression of atherosclerotic carotid disease in this population was 55.2%. We found that platelet degranulation (CD63 and CD40L) correlated with progression of IMT within 1 year (CD63: r=0.231, P=0.022; CD40L: r=0.230, P=0.029). Diabetic patients with progression of IMT had a significantly increased expression of CD63 compared with patients with stable carotid disease (mean intensity of immunofluorescence; median, interquartile range: 17.1 [12.4, 25.8] versus 11.9 [7.7, 19.8]; P=0.004). Multivariate logistic regression analysis revealed that degranulation of platelet CD63 is a predictor for progression of IMT independently of classical cardiovascular risk factors and hemoglobin A1c in diabetic patients (P=0.017). CONCLUSIONS: Enhanced systemic platelet degranulation is associated with progression of carotid artery disease in type 2 diabetes.

Aged↗

PubMed2005

[The coagulation cascade--clinical implications].

The coagulation system is a cascade of complex, interacting steps, that can selectively be inhibited in distinct ways. Thus, various therapeutic options are offered, concerning primary hemostasis, which results in formation of a platelet-rich thrombus, as well as secondary hemostasis, resulting in fibrin formation. For patients with coronary artery disease, who have to undergo percutaneous coronary intervention (PCI), a sufficient anticoagulant strategy is essential for prevention of ischemic events, due to the activated state of the coagulation system of these patients. Next to antiplatelet therapy, unfractionated heparin (UFH) is a well-established concomitant intravenous therapy during PCI. Also low-molecular-weight heparins (LMWH) are increasingly used in this setting due to their favorable pharmacodynamic properties. The exact value of these substances in comparison to UFH is not completely evaluated yet.

Anticoagulants↗

PubMed2005

Non-invasive imaging of glycoprotein VI binding to injured arterial lesions.

Glycoprotein VI (GPVI) is the major platelet collagen receptor and plays a critical role in the process of thrombosis at sites of atherosclerotic lesions. This study evaluates the feasibility of radiolabeled soluble GPVI to identify injured arterial lesions. Radiolabeling was carried out using the iodogen method and resulted in the radioiodinated GPVI in radiochemical yields between 97-100%. The biodistribution of [(125)I]GPVI was determined in normal mice and demonstrated a blood clearance halftime of approximately 5.5 hours. Vascular lesions were induced in the carotid artery in wild type and ApoE(-/-)mice. Immediately after injury radioiodinated GPVI was injected intravenously. Binding of [(123)I]GPVI to carotid lesions was assessed by szintigraphic in vivo imaging. Carotid arteries were explanted for ex vivo autoradiography and histological characterization of the lesion. In vivo and ex vivo imaging revealed substantial accumulation of radioiodinated GPVI in the injured artery wall, with a ratio of lesion to control vessel of 3:1 and 7:1, respectively. Because GPVI is the critical collagen receptor that mediates platelet adhesion to vascular lesions, soluble radiolabeled GPVI may be an agent for non-invasive imaging of thrombogenic thus, vulnerable atherosclerotic plaques.

Animals↗

PubMed2005

Plasminogen and matrix metalloproteinase activation by enzymatically modified low density lipoproteins in monocytes and smooth muscle cells.

Protease activity promotes the progression and rupture of atherosclerotic plaques. LDL has been described to become enzymatically modified within the vessel wall yielding an atherogenic moiety (E-LDL). We studied the effect of E-LDL on the activation of plasminogen and matrix metalloproteinases (MMPs) in monocytes and vascular smooth muscle cells (VSMCs) as well as on MMP activation during cellular interactions. Human monocytes, monocytic MonoMac6 cells and human VSMCs were incubated with human native LDL (n-LDL) or E-LDL for 24 hours. E-LDL in contrast to n-LDL induced substantial activation of the plasminogen activation system as well as of the MMP system in monocytic cells, as measured by enhanced cell surface expression of the urokinase receptor (uPAR),the extracellular matrix metalloproteinase Inducer (EMMPRIN) and the membrane type-1 MMPs (MT1-MMP,MMP-14), as well as by secretion of active uPA, and of MMP-9. Consistently, E-LDL-treated monocytes exhibited increased transmigration through "matrigel", which was specifically abrogated by the MMP inhibitor galardin or the plasmin inhibitor aprotinin. In VSMCs, E-LDL induced MMP-1 and MMP-2 secretion. Moreover, monocyte incubation with supernatants of E-LDL-treated (but not n-LDL-treated) VSMCs strongly induced MMP-9 in monoytes, which was inhibited by blocking mAb anti-TNF-alpha. Together, enzymatical modification of LDL allows a direct activation of MMP expression in monocytes and VSMCs, and indirectly promotes the induction of paracrine, cytokine-mediated intercellular activation processes. There by, E-LDL may contribute to atheroprogression, inflammation and plaque rupture.

Arteriosclerosis↗

PubMed2004

Generation of functional culture-derived platelets from CD34+ progenitor cells to study transgenes in the platelet environment.

The possibility of evaluating the function of transgenes in platelets requires the generation of platelets from nucleated progenitor cells in vitro. In this article, we provide effective culture conditions for generating functional culture-derived (CD) human and mouse platelets from CD34(+) progenitor cells that allow expression of any foreign protein of interest. We have evolved an effective cytokine cocktail (thrombopoietin, stem cell factor, interleukin [IL]-1beta, IL-6) that induces a high yield of CD platelets and optimal shedding from cultivated megakaryocytes generated from CD34(+) progenitor cells. CD platelets showed similar functional and morphological characteristics compared with isolated blood platelets, including surface expression of platelet antigens (CD41, CD42, CD62P), aggregation, release of granule constituents (P-selectin, platelet factor 4, serotonin). Moreover, transmission electron microscopy revealed the presence of typical alpha- and dense granules and dense tubular system in CD platelets. Additionally, we showed that stable transgene expression in CD platelets can be performed through infection of CD34(+) progenitor cells using adenoviral vectors. Thus, we describe a methodology that enables studying functional consequences of transgenes of interest in the natural environment of platelets that may impose substantial impact on potential future platelet research and therapeutic target evaluation. The full text of this article is available online at http://circres.ahajournals.org.

Adenoviridae↗

PubMed2004

A randomized trial comparing myocardial salvage achieved by coronary stenting versus balloon angioplasty in patients with acute myocardial infarction considered ineligible for reperfusion therapy.

OBJECTIVES: We assessed myocardial salvage achieved by reperfusion with percutaneous coronary interventions (PCI) and compared stenting with balloon angioplasty (PTCA) in patients with acute myocardial infarction (AMI) ineligible for thrombolysis. BACKGROUND: A substantial proportion of patients with AMI are currently considered ineligible for thrombolysis, and reperfusion treatment is frequently not recommended for them. It is not known whether these patients benefit from PCI. METHODS: The Stent or PTCA for Occluded Coronary Arteries in Patients with Acute Myocardial Infarction Ineligible for Thrombolysis (STOPAMI-3) trial, a randomized, open-label study, included 611 patients with AMI who were ineligible for thrombolysis (lack of ST-segment elevation on the electrocardiogram, late presentation >12 h after symptom onset, and contraindications to thrombolysis). Patients were randomly assigned to receive either coronary artery stenting (n = 305) or PTCA (n = 306). Scintigraphic myocardial salvage index (proportion of the initial myocardial perfusion defect that was salvaged by reperfusion) was the primary end point of the study. RESULTS: A considerable myocardial salvage was achieved with both stenting and PTCA. In patients assigned to receive stenting, the median size of the salvage index was 0.54 (25th and 75th percentiles, 0.29 and 0.87), as compared with a median of 0.50 (25th and 75th percentiles, 0.26 and 0.82) in the group assigned to receive PTCA (p = 0.20). Mortality at six months was 8.2% in the group of patients assigned to receive stenting and 9.2% in the group of patients assigned to receive PTCA (p = 0.69). CONCLUSIONS: Patients with AMI who are currently considered ineligible for thrombolysis by conventional guidelines may greatly benefit from primary PCI. The benefit seems to be comparable when a strategy of stenting is compared with a strategy of PTCA in these patients.

Angioplasty, Balloon, Coronary↗

PubMed2004

Role of platelets in coronary thrombosis and reperfusion of ischemic myocardium.

Platelet-dependent thrombus formation is a key event in the pathogenesis of acute myocardial infarction (AMI). Platelets mediate both thrombotic occlusion of the entire epicardial coronary artery and also accumulate in the microcirculation resulting in impairment of microcirculation and provoking myocardial ischemia during reperfusion. In the past, our understanding of platelet function in myocardial infarction (MI) and reperfusion has extended substantially resulting in development of novel and clinically effective treatment strategies. This review summarizes the mechanisms of coronary thrombosis and consequences of platelet accumulation in reperfused myocardium. Basic pathophysiological mechanisms of platelet adhesion and secretion are reviewed first, followed by the description of the molecular steps involved in platelet-mediated thrombus formation around an atherosclerotic plaque. Next, the role of platelets in inflammation is summarized with the focus on platelet-endothelium and platelet-leukocyte interactions.

Animals↗

PubMed2004

A clinical trial of abciximab in elective percutaneous coronary intervention after pretreatment with clopidogrel.

BACKGROUND: Whether the glycoprotein IIb/IIIa inhibitor abciximab is beneficial in patients undergoing elective percutaneous coronary intervention after pretreatment with clopidogrel is unknown. METHODS: We enrolled 2159 patients with coronary artery disease who underwent a percutaneous coronary intervention: 1079 patients were randomly assigned in a double-blind manner to receive abciximab and 1080 patients to receive placebo. All patients were pretreated with a 600-mg dose of clopidogrel at least two hours before the procedure. The primary end point of the trial was the composite of death, myocardial infarction, and urgent target-vessel revascularization within 30 days after randomization. RESULTS: The incidence of the primary end point was 4 percent (45 patients) in the abciximab group, as compared with 4 percent (43 patients) in the placebo group (relative risk, 1.05; 95 percent confidence interval, 0.69 to 1.59; P=0.82). Most adverse events were myocardial infarctions: the incidence was 4 percent (40 patients) in the abciximab group and 4 percent (41 patients) in the placebo group (P=0.91). Twelve patients (1 percent) in the abciximab group and eight patients (1 percent) in the placebo group had major bleeding complications (P=0.37). Profound thrombocytopenia occurred in 10 patients (1 percent) in the abciximab group but in none in the placebo group (P=0.002). CONCLUSIONS: Our data suggest that in patients at low-to-intermediate risk who undergo elective percutaneous coronary intervention after pretreatment with a high loading dose of clopidogrel, abciximab is associated with no clinically measurable benefit within the first 30 days.

Abciximab↗

PubMed2004

Antiplatelet effects of a 600 mg loading dose of clopidogrel are not attenuated in patients receiving atorvastatin or simvastatin for at least 4 weeks prior to coronary artery stenting.

AIMS: To test prospectively whether the antiplatelet effect of a 600 mg loading dose of clopidogrel is attenuated in patients receiving atorvastatin and simvastatin for at least 4 weeks prior to coronary artery stenting. METHODS AND RESULTS: Blood samples were obtained at least 2 h after receiving 100 mg aspirin and 600 mg clopidogrel and prior to coronary stenting from 90 patients without statin therapy and 90 patients with statin (atorvastatin and simvastatin) therapy for at least 4 weeks. Maximal and residual platelet aggregation was evaluated with optical aggregometry in response to ADP (5 and 20 micromol/l). Surface expression of IIb/IIIa (CD61) and P-selectin (CD62) was assessed with whole blood flow-cytometry at baseline and following stimulation (5 and 20 micromol/l ADP). Inhibition of ADP-induced platelet aggregation was not impaired in the presence of concomitant statin therapy. Moreover, patients with and without statin therapy did not differ in respect to all flow-cytometric parameters obtained. CONCLUSION: The antiplatelet effect of a high, 600 mg loading dose of clopidogrel is not diminished in patients receiving atorvastatin and simvastatin for at least 4 weeks prior to coronary stenting.

Aged↗

PubMed2004

Surface expression of collagen receptor Fc receptor-gamma/glycoprotein VI is enhanced on platelets in type 2 diabetes and mediates release of CD40 ligand and activation of endothelial cells.

Diabetes is associated with an enhanced collagen-mediated platelet activation that contributes significantly to thromboischemic complications. In this study, the platelet collagen receptor glycoprotein VI (GPVI) was studied in 385 patients with type 2 diabetes. Surface expression of the platelet Fc receptor that forms a functional complex with GPVI was significantly increased in patients with diabetes compared with those without diabetes (P = 0.02). Fc receptor expression correlated with GPVI expression and was found to be independently associated with diabetes (r = 0.529, P < 0.001). Stimulation of GPVI through a specific anti-GPVI monoclonal antibody significantly enhanced surface expression of CD40L (P = 0.006). Because CD40L is a potent platelet-derived cytokine that is involved in thrombosis and atherosclerosis, we evaluated the effect of GPVI-mediated release of CD40L on activation of endothelial cells. Coincubation of GPVI-stimulated platelets resulted in substantial enhanced endothelial surface expression of CD62P, alphavbeta3, and intercellular adhesion molecule 1 (P < 0.05) and secretion of monocyte chemoattractant protein 1 of cultured human umbilical vein endothelial cells (P < 0.01). These results suggest that the function of collagen receptor GPVI is altered in type 2 diabetes and may play an important role in atherothrombotic complications. Inhibition of GPVI may be a promising pharmacological target in the treatment of high-risk diabetic patients.

Blood Platelets↗

PubMed2003

Soluble glycoprotein VI dimer inhibits platelet adhesion and aggregation to the injured vessel wall in vivo.

Platelet-collagen interactions play a fundamental role in the process of arterial thrombosis. The major platelet collagen receptor is the glycoprotein VI (GPVI). Here, we determined the effects of a soluble dimeric form of GPVI on platelet adhesion in vitro and in vivo. We fused the extracellular domain of GPVI with the human immunoglobulin Fc domain. The soluble dimeric form of GPVI (GPVI-Fc) specifically bound to immobilized collagen. Binding of GPVI-Fc to collagen was inhibited competitively by soluble GPVI-Fc, but not control Fc lacking the external GPVI domain. GPVI-Fc inhibited the adhesion of CHO cells that stably express human GPVI and of platelets on collagen and attenuated thrombus formation under shear conditions in vitro. To test the effects of GPVI-Fc in vivo, arterial thrombosis was induced in the mouse carotid artery, and platelet-vessel wall interactions were visualized by intravital fluorescence microscopy. Infusion of GPVI-Fc but not of control Fc virtually abolished stable arrest and aggregation of platelets following vascular injury. Importantly, GPVI-Fc but not control Fc, was detected at areas of vascular injury. These findings further substantiate the critical role of the collagen receptor GPVI in the initiation of thrombus formation at sites of vascular injury and identify soluble GPVI as a promising antithrombotic strategy.

Animals↗

PubMed2003

Cytomegalovirus infection status predicts progression of heart-transplant vasculopathy.

BACKGROUND: Transplant vasculopathy (TVP) is the most common cause of death and retransplantation after heart transplantation. Human cytomegalovirus (HCMV) infection has been linked to atherosclerosis and to the development of TVP. A prospective study evaluating the relation between CMV infection and progression of TVP is lacking thus far. The purpose of the present study was to investigate the influence of CMV infection status on the progression of TVP within 1 year. METHODS: We enrolled 103 consecutive heart-transplant recipients who underwent routine cardiac catheterization and intracoronary ultrasound examination at study entry and after 1 year. Plaque progression determined by quantitative intracoronary ultrasound was used to define the severity of disease at baseline and at 1-year follow-up. At study entry, HCMV infection status was evaluated by immunological assays and reverse-transcriptase polymerase chain reaction (RT-PCR). RESULTS: HCMV immunoglobulin (Ig)G/IgM seropositivity was found in 34 (33%) of transplant recipients, 11 of whom were HCMV PCR positive. The HCMV-positive group showed more advanced, calcified lesions (64.7% vs. 27.5%, P=0.002), and the maximal plaque thickness was significantly different from the HCMV IgG/IgM-negative group (median [quartile] 1.36 [0.85, 1.88] vs. 1.05 [0.58, 1.34], P=0.02). In a logistic regression model, we demonstrate that HCMV IgG/IgM positivity is a predictor for the progression of TVP independent of cardiovascular risk factors, inflammatory markers, and platelet activation (P=0.038). In addition, HCMV PCR positivity even increases the risk for accelerated TVP (P=0.017) and, consecutively, transplant failure. CONCLUSIONS: HCMV infection status in transplant patients detects patients with increased risk for transplant failure caused by TVP.

Cytomegalovirus Infections↗

PubMed2003

Effects of statins on platelet inhibition by a high loading dose of clopidogrel.

BACKGROUND: Recent studies suggested that some HMG-CoA reductase blockers might inhibit the antiplatelet activity of clopidogrel. Therefore, we analyzed how various statins together with a high loading dose of clopidogrel (600 mg) affect platelet aggregation. METHODS AND RESULTS: Seventy-seven patients with stable angina scheduled for elective coronary stenting were studied. Patients were randomized to receive atorvastatin, fluvastatin, lovastatin, pravastatin, simvastatin (each 20 mg), cerivastatin (0.3 mg), or placebo, plus a high loading dose of 600 mg of clopidogrel. ADP-induced platelet aggregation (5 and 20 micromol/L) was determined before and 2 and 4 hours after first clopidogrel administration. All patients were taking aspirin (100 mg/d) regularly. We found that none of the statins significantly influenced inhibition of platelet aggregation by clopidogrel. CONCLUSIONS: Concomitant use of statins with clopidogrel does not significantly inhibit antiplatelet activity, at least when clopidogrel is administered at a high loading dose of 600 mg.

Aged↗

PubMed2003

G13 is an essential mediator of platelet activation in hemostasis and thrombosis.

Platelet activation at sites of vascular injury is essential for primary hemostasis, but also underlies arterial thrombosis leading to myocardial infarction or stroke. Platelet activators such as adenosine diphosphate, thrombin or thromboxane A(2) (TXA(2)) activate receptors that are coupled to heterotrimeric G proteins. Activation of platelets through these receptors involves signaling through G(q), G(i) and G(z) (refs. 4-6). However, the role and relative importance of G(12) and G(13), which are activated by various platelet stimuli, are unclear. Here we show that lack of Galpha(13), but not Galpha(12), severely reduced the potency of thrombin, TXA(2) and collagen to induce platelet shape changes and aggregation in vitro. These defects were accompanied by reduced activation of RhoA and inability to form stable platelet thrombi under high shear stress ex vivo. Galpha(13) deficiency in platelets resulted in a severe defect in primary hemostasis and complete protection against arterial thrombosis in vivo. We conclude that G(13)-mediated signaling processes are required for normal hemostasis and thrombosis and may serve as a new target for antiplatelet drugs.

Animals↗

PubMed2003

Novel role of the membrane-bound chemokine fractalkine in platelet activation and adhesion.

Chemokines released by the endothelium have proaggregatory properties on platelets. Fractalkine, a recently discovered membrane-bound chemokine with a transmembrane domain, is expressed in vascular injury; however, the effects of fractalkine on platelets have not yet been investigated. Blood was taken from healthy Wistar-Kyoto rats and the expression of the fractalkine receptor on platelets was demonstrated. The modulation of surface expression of P-selectin was assessed by flow cytometry. P-selectin expression was significantly enhanced by in vitro stimulation with recombinant rat fractalkine compared with baseline levels. Selectively inhibiting the function of recombinant fractalkine by an antagonizing antibody or the disruption of the G-protein-coupled intracellular signaling cascade of the fractalkine receptor by pertussis toxin (PTX) completely prevented fractalkine-mediated platelet activation. Preincubation with apyrase significantly attenuated the fractalkine-induced degranulation. In a flow chamber model of platelet adhesion, stimulation with fractalkine significantly enhanced platelet adhesion to collagen and fibrinogen. Similar to P-selectin expression, enhanced adhesion could be prevented by the antagonizing antibody or preincubation of platelets with PTX. Fractalkine, which is overexpressed in atherosclerosis and vascular injury, contributes to platelet activation and adhesion and hence is likely to play a pathophysiologically important role for increased thrombogenesis in vascular diseases.

Analysis of Variance↗