The rheology of interactions between leukocytes, platelets and the vessel wall in thrombo-inflammation.

Leukocytes and platelets must adhere to the wall of blood vessels to carry out their protective functions in inflammation and haemostasis. Recruitment is critically dependent on rheological variables (wall shear rate and stress, red cell aggregation and haematocrit) which affect delivery to the vessel wall as well as velocities and forces experienced there. Leukocyte recruitment is efficient only up to wall shear rates of about 300 s-1 and usually restricted to low-shear post-capillary venules in inflammation. Being smaller, platelets experience lower velocities and shear forces adjacent to the wall and can adhere at much higher shear rates for haemostasis in arteries. In addition, we found quite different effects of variations in haematocrit or red cell aggregation on attachment of neutrophils or platelets, which also assist their separate recruitment in venules or arteries. However, it has become increasingly evident that inflammatory and thrombotic responses may occur together, with platelets promoting the adhesion and activation of neutrophils and monocytes. Indeed, it is 30 years since we demonstrated that platelets could cause neutrophils to aggregate in suspension and, when attached to a surface, could support selectin-mediated rolling of all leukocytes. Thrombin-activated platelets could further induce neutrophil activation and immobilisation. In some conditions, platelets could bind to intact endothelial monolayers and capture neutrophils or monocytes. Subsequently, we found that extracellular vesicles released by activated platelets (PEV) fulfilled similar functions when deposited on surfaces or bound to endothelial cells. In murine models, platelets or PEV could act as bridges for monocytes in inflamed vessels. Thus, leukocytes and platelets are rheologically adapted for their separate functions, while novel thrombo-inflammatory pathways using platelets or PEV may underlie pathogenic leukocyte recruitment.

Coarse-grained simulations of von Willebrand factor adsorption to collagen with consequent platelet recruitment.

A multimeric glycoprotein of blood plasma-Von Willebrand factor (VWF)-mediates platelet adhesion to the fibrillar collagen of the subendothelial matrix if the blood vessel walls are damaged. The adsorption of VWF to collagen is thus essential for the initial stages of platelet hemostasis and thrombosis, as it plays a role of a molecular bridge between the injury and platelet adhesion receptors. Biomechanical complexity and sensitivity to the hydrodynamics are inherent in this system, therefore, modern computational methods supplement experimental studies of biophysical and molecular mechanisms that underlie platelet adhesion and aggregation in the blood flow. In the present paper, we propose a simulation framework for the VWF-mediated platelet adhesion to a plane wall with immobilized binding sites for VWF under the action of shear flow. VWF multimers and platelets are represented in the model by particles connected by elastic bonds and immersed in a viscous continuum fluid. This work complements the scientific field by taking into account the shape of a flattened platelet, but keeping a compromise between the detail of the description and the computational complexity of the model.

A Multiscale Model for Shear-Mediated Platelet Adhesion Dynamics: Correlating In Silico with In Vitro Results.

Platelet adhesion to blood vessel walls is a key initial event in thrombus formation in both vascular disease processes and prosthetic cardiovascular devices. We extended a deformable multiscale model (MSM) of flowing platelets, incorporating Dissipative Particle Dynamics (DPD) and Coarse-Grained Molecular Dynamics (CGMD) describing molecular-scale intraplatelet constituents and their interaction with surrounding flow, to predict platelet adhesion dynamics under physiological flow shear stresses. Binding of platelet glycoprotein receptor Ibα (GPIbα) to von Willebrand factor (vWF) on the blood vessel wall was modeled by a molecular-level hybrid force field and validated with in vitro microchannel experiments of flowing platelets at 30 dyne/cm2. High frame rate videos of flipping platelets were analyzed with a Semi-Unsupervised Learning System (SULS) machine learning-guided imaging approach to segment platelet geometries and quantify adhesion dynamics parameters. In silico flipping dynamics followed in vitro measurements at 15 and 45 dyne/cm2 with high fidelity, predicting GPIbα-vWF bonding and debonding processes, distribution of bonds strength, and providing a biomechanical insight into initiation of the complex platelet adhesion process. The adhesion model and simulation framework can be further integrated with our established MSMs of platelet activation and aggregation to simulate initial mural thrombus formation on blood vessel walls.

[Platelet adhesion mediated by von Willebrand factor in patients with premature coronary artery disease].

Aim    To study platelet adhesion mediated by von Willebrand factor (VWF) in patients with premature ischemic heart disease (IHD).Material and methods    This study enrolled 58 patients with stable IHD, including 45 men younger than 55 years with the first manifestation of IHD at the age of <50 years and 13 women younger than 65 years with the first manifestation of IHD at the age of <60 years. The control group consisted of 33 patients, 13 men younger than 55 years and 20 women younger than 65 years without IHD. Platelet adhesion to the collagen surface at the shear rate of 1300 s-1 was studied by evaluating the intensity of scattered laser light from the collagen-coated optical substrate in a flow chamber of a microfluidic device after 15-min circulation of whole blood in the chamber. Decreases in platelet adhesion after addition to the blood of monoclonal antibodies (mAb) to platelet receptors glycoproteins Ib (GPIb) to inhibit the receptor interaction with VWF were compared for patients of both groups. Results    In patients with premature IHD, the decrease in platelet adhesion following the platelet GPIb receptor inhibition was significantly less than in patients of the control group (74.8 % (55.6; 82.7) vs. 28.9 % (-9.8; 50,5), p <0.001). For the entire sample, the median decrease in platelet adhesion following the GPIb receptor inhibition was 62.8 % (52.2; 71.2). With an adjustment for traditional risk factors of IHD, a decrease in platelet adhesion of >62.8% after blocking GPIb receptors increased the likelihood of premature IHD (OR=9.84, 95 % CI: 2.80-34.59; p <0.001).Conclusion    Blocking the interaction of GPIb receptors with VWF in patients with premature IHD and increased shear rate induced a greater decrease in platelet adhesion than in patients without this disease. This suggested that an excessive interaction of VWF with platelets might contribute to the pathogenesis of premature IHD.

Human Blood Platelets Adsorption on Polymeric Materials for Liquid Biopsy.

Platelets are emerging as a promising source of blood biomarkers for several pathologies, including cancer. New automated techniques for easier manipulation of platelets in the context of lab-on-a-chips could be of great support for liquid biopsy. Here, several polymeric materials were investigated for their behavior in terms of adhesion and activation of human platelets. Polymeric materials were selected among the most used in microfabrication (PDMS, PMMA and COC) and commercial and home-made resins for 3D printing technology with the aim to identify the most suitable for the realization of microdevices for human platelets isolation and analysis. To visualize adherent platelets and their activation state scanning, electron microscopy was used, while confocal microscopy was used for evaluating platelets' features. In addition, atomic force microscopy was employed to further study platelets adherent to the polymeric materials. Polymers were divided in two main groups: the most prone to platelet adhesion and materials that cause few or no platelets to adhere. Therefore, different polymeric materials could be identified as suitable for the realization of microdevices aimed at capturing human platelets, while other materials could be employed for the fabrication of microdevices or parts of microdevices for the processing of platelets, without loss on surfaces during the process.

[Main Factors Influencing the Platelet Spreading].

OBJECTIVE: To explore the main factors of platelet spreading and provide the foundation for related research. METHODS: Platelets (2×107/ml) were draw from C57BL/6J mouse and kept at 22 ℃ for 1-2 hours. Platelets (2×107/ml) were were allowed to adhere and spread on the fibrinogen-coated slides, after staining F-actin in platelets, the platelets were observed with the confocal microscopy. The effects of different concentrations of fibrinogen (10 µg/ml, 30 µg/ml, 100 µg/ml) and kinds of agonists ï¼»thrombin(0.01,0.05,0.1 U/ml), ADP（5,10,20 µmol/L）, U46619（0.125,0.25,0.5 µmol/L）］ on platelets were analyzed. The platelet spreading was successful if the spreading rate was higher after treated with agonists. RESULTS: Compared to the group which coated with 10 µg/ml and 100 µg/ml fibrinogen, the platelet density is optimal when coated with 30 µg/ml fibrinogen. In addition, under the stimulation of thrombin, ADP and U46619, the spreading rate of platelets showed a certain concentration-dependent increasing. CONCLUSION: The platelet spreading is easily influenced by various factors, the platelet spreading can be induced successfully at 0.1 U/ml thrombin, 20 µmol/L ADP and 0.5 µmol/L U46619 on the slide coated with 30 µg/ml fibrinogen.

Regulation of Human Platelet Adhesion with Ascorbic Acid.

Morphofunctional characteristics of human platelets in the presence of 0.1-5 mM ascorbic acid were studied. The platelet ability to form lamellae and the preservation of granules in platelets in suspension and during adhesion were evaluated. Ascorbic acid in concentrations of 0.1-1 mM induced no visible changes in platelet structure and did not affect their adhesion activity, but suppressed lamella growth and degranulation in adherent platelets in a dose-dependent manner. The maximum preservation of granules was revealed in the presence of 0.5 mM ascorbic acid (55% in 1 h from the moment of adhesion). In the presence of 2-5 mM ascorbic acid, spontaneous activation and degranulation of platelets was observed. Thus, ascorbic acid is capable of both suppressing and stimulating platelet activity. In concentrations of 0.5-1 mM ascorbic acid can be used to stabilize granules in adherent platelets.

GPIb-IX-V and platelet clearance.

Platelet adhesion to the site of vascular damage is a critical early step in hemostasis. The platelet glycoprotein (GP) Ib-IX-V plays a key role in this step via its interaction with immobilized von Willebrand Factor (VWF). In addition to its well-known role in adhesion, GPIb-IX-V is critical for platelets' survival in circulation and plays an important role in the regulation of platelet clearance. Several mechanisms of platelet clearance work in concert to maintain a normal platelet count and ensure that circulating platelets are functionally viable via removal of senescent or activated platelets. Furthermore, dysregulation of platelet clearance underlies several bleeding disorders. GPIb-IX-V is central to many physiological mechanisms of platelet clearance including clearance via glycan receptors, clearance of VWF-platelet complexes, and fast clearance of transfused platelets. GPIb-IX-V dependent clearance also underlies thrombocytopenia in several bleeding disorders, including von Willebrand disease (VWD) and immune thrombocytopenia. This review will cover physiological and pathological mechanisms of platelet clearance, focusing on the role of GPIb-IX-V.

The voltage-gated K+ channel Kv1.3 modulates platelet motility and α2ß1 integrin-dependent adhesion to collagen.

Kv1.3 is a voltage-gated K+-selective channel with roles in immunity, insulin-sensitivity, neuronal excitability and olfaction. Despite being one of the largest ionic conductances of the platelet surface membrane, its contribution to platelet function is poorly understood. Here we show that Kv1.3-deficient platelets display enhanced ADP-evoked platelet aggregation and secretion, and an increased surface expression of platelet integrin αIIb. In contrast, platelet adhesion and thrombus formation in vitro under arterial shear conditions on surfaces coated with collagen were reduced for samples from Kv1.3-/- compared to wild type mice. Use of collagen-mimetic peptides revealed a specific defect in the engagement with α2ß1. Kv1.3-/- platelets developed significantly fewer, and shorter, filopodia than wild type platelets during adhesion to collagen fibrils. Kv1.3-/- mice displayed no significant difference in thrombus formation within cremaster muscle arterioles using a laser-induced injury model, thus other pro-thrombotic pathways compensate in vivo for the adhesion defect observed in vitro. This may include the increased platelet counts of Kv1.3-/- mice, due in part to a prolonged lifespan. The ability of Kv1.3 to modulate integrin-dependent platelet adhesion has important implications for understanding its contribution to normal physiological platelet function in addition to its reported roles in auto-immune diseases and thromboinflammatory models of stroke.

Main Factors Influencing the Platelet Spreading / 中国实验血液学杂志

OBJECTIVE@#To explore the main factors of platelet spreading and provide the foundation for related research.@*METHODS@#Platelets (2×107/ml) were draw from C57BL/6J mouse and kept at 22 ℃ for 1-2 hours. Platelets (2×107/ml) were were allowed to adhere and spread on the fibrinogen-coated slides, after staining F-actin in platelets, the platelets were observed with the confocal microscopy. The effects of different concentrations of fibrinogen (10 μg/ml, 30 μg/ml, 100 μg/ml) and kinds of agonists ［thrombin(0.01,0.05,0.1 U/ml), ADP（5,10,20 μmol/L）, U46619（0.125,0.25,0.5 μmol/L）］ on platelets were analyzed. The platelet spreading was successful if the spreading rate was higher after treated with agonists.@*RESULTS@#Compared to the group which coated with 10 μg/ml and 100 μg/ml fibrinogen, the platelet density is optimal when coated with 30 μg/ml fibrinogen. In addition, under the stimulation of thrombin, ADP and U46619, the spreading rate of platelets showed a certain concentration-dependent increasing.@*CONCLUSION@#The platelet spreading is easily influenced by various factors, the platelet spreading can be induced successfully at 0.1 U/ml thrombin, 20 μmol/L ADP and 0.5 μmol/L U46619 on the slide coated with 30 μg/ml fibrinogen.

Ultrastructural Study of Platelet Behavior and Interrelationship in Sprouting and Intussusceptive Angiogenesis during Arterial Intimal Thickening Formation.

Platelets in atherosclerosis, bypass stenosis, and restenosis have been extensively assessed. However, a sequential ultrastructural study of platelets in angiogenesis during the early phases of these lesions has received less attention. Our objective was the study of platelets in angiogenesis and vessel regression during intimal thickening (IT) formation, a precursor process of these occlusive vascular diseases. For this purpose, we used an experimental model of rat occluded arteries and procedures for ultrastructural observation. The results show (a) the absence of platelet adhesion in the de-endothelialized occluded arterial segment isolated from the circulation, (b) that intraarterial myriad platelets contributed from neovessels originated by sprouting angiogenesis from the periarterial microvasculature, (c) the association of platelets with blood components (fibrin, neutrophils, macrophages, and eosinophils) and non-polarized endothelial cells (ECs) forming aggregates (spheroids) in the arterial lumen, (d) the establishment of peg-and-socket junctions between platelets and polarized Ecs during intussusceptive angiogenesis originated from the EC aggregates, with the initial formation of IT, and (e) the aggregation of platelets in regressing neovessels ('transitory paracrine organoid') and IT increases. In conclusion, in sprouting and intussusceptive angiogenesis and vessel regression during IT formation, we contribute sequential ultrastructural findings on platelet behavior and relationships, which can be the basis for further studies using other procedures.

The Proteoglycan Biglycan Modulates Platelet Adhesion and Thrombus Formation in a GPVI-Dependent Manner.

BACKGROUND: Vascular injury induces the exposure of subendothelial extracellular matrix (ECM) important to serve as substrate for platelets to adhere to the injured vessel wall to avoid massive blood loss. Different ECM proteins are known to initiate platelet adhesion and activation. In atherosclerotic mice, the small, leucine-rich proteoglycan biglycan is important for the regulation of thrombin activity via heparin cofactor II. However, nothing is known about the role of biglycan for hemostasis and thrombosis under nonatherosclerotic conditions. METHODS: The role of biglycan for platelet adhesion and thrombus formation was investigated using a recombinant protein and biglycan knockout mice. RESULTS: The present study identified biglycan as important ECM protein for the adhesion and activation of platelets, and the formation of three-dimensional thrombi under flow conditions. Platelet adhesion to immobilized biglycan induces the reorganization of the platelet cytoskeleton. Mechanistically, biglycan binds and activates the major collagen receptor glycoprotein (GP)VI, because reduced platelet adhesion to recombinant biglycan was observed when GPVI was blocked and enhanced tyrosine phosphorylation in a GPVI-dependent manner was observed when platelets were stimulated with biglycan. In vivo, the deficiency of biglycan resulted in reduced platelet adhesion to the injured carotid artery and prolonged bleeding times. CONCLUSIONS: Loss of biglycan in the vessel wall of mice but not in platelets led to reduced platelet adhesion at the injured carotid artery and prolonged bleeding times, suggesting a crucial role for biglycan as ECM protein that binds and activates platelets via GPVI upon vessel injury.

The Effects of Micro-vessel Curvature Induced Elongational Flows on Platelet Adhesion.

The emerging profile of blood flow and the cross-sectional distribution of blood cells have far reaching biological consequences in various diseases and vital internal processes, such as platelet adhesion. The effects of several essential blood flow parameters, such as red blood cell free layer width, wall shear rate, and hematocrit on platelet adhesion were previously explored to great lengths in straight geometries. In the current work, the effects of channel curvature on cellular blood flow are investigated by simulating the accurate cellular movement and interaction of red blood cells and platelets in a half-arc channel for multiple wall shear rate and hematocrit values. The results show significant differences in the emerging shear rate values and distributions between the inner and outer arc of the channel curve, while the cell distributions remain predominantly uninfluenced. The simulation predictions are also compared to experimental platelet adhesion in a similar curved geometry. The inner side of the arc shows elevated platelet adhesion intensity at high wall shear rate, which correlates with increased shear rate and shear rate gradient sites in the simulation. Furthermore, since the platelet availability for binding seems uninfluenced by the curvature, these effects might influence the binding mechanics rather than the probability. The presence of elongational flows is detected in the simulations and the link to increased platelet adhesion is discussed in the experimental results.

Complex Interaction of Platelets, von Willebrand Factor and Leukocytes, in Whole Blood at High Shear Rates Is Mediated by Platelet GPIIb/IIIa Receptor.

We studied the contribution of von Willebrand factor (vWF) into blood cell adhesion to collagen-coated surfaces in whole blood of healthy volunteers. Adhesion of blood cells to collagen I was measured at shear rate of 2300 sec-1. The interaction of platelet GPIIb/IIIa receptor with vWF was blocked with monoclonal anti-GPIIb/IIIa antibodies. The degree of cell adhesion was quantified by measuring the intensity of scattered light after 15-min perfusion: in samples with blocked GPIIb/IIIa it decreased to 0.39±0.13 V vs 0.06±0.03 V in control samples (p=0.002). Under a fluorescence microscope, intensively stained structures consisting of vWF, platelets, and leukocytes attached to the collagen surface were observed. After blockade of GPIIb/IIIa, these structures were absent. Leukocyte recruitment at high shear rates is a time-dependent process sensitive to complex interaction of vWF, leukocytes, and platelets, in which the platelet GPIIb/IIIa receptor is essential.

Intercellular Interactions in Peripheral Venous Blood in Practically Healthy Residents of High Latitudes.

The paper presents the results of studying the immunological parameters of 369 people who were practically healthy at the time of the survey, 298 women and 71 men, of which 216 people are living in the European North of the Russian Federation (173 women and 43 men) and 153 are residents of the Arctic (125 women and 28 men). The study was carried out in the morning (08:00-10:00 am). The study included the determination of the aggregation of erythrocytes, platelets, neutrophilic granulocytes, lymphocytes, hemogram study, hematological analysis, enzyme immunoassay, and flow cytometry. Statistical processing of the obtained data was carried out using the Statistica 7.0 software package (StatSoft, USA). It was found that the activity of aggregation of cells of peripheral venous blood in Arctic residents is 1.5-1.7 times higher than that in people living in more favourable climatic conditions. The frequency of registration of aggregation of erythrocytes and platelets is actually 2 times higher than the aggregation of leukocytes. Aggregation of erythrocytes is associated with an increase in the concentrations of transferrin and receptors for this transport protein. The frequency of detection of platelet aggregation is accompanied by an increase in transferrin concentrations; in cases of aggregation of nonnuclear blood cells, the content of NO2 in the blood serum is increased. Aggregation of neutrophilic granulocytes and lymphocytes is associated with an increase in the content of free adhesion molecules. Aggregation of erythrocytes and platelets is in evidence when it is necessary to trigger reactions of changes in the hemodynamics of microcirculation to increase the efficiency of oxygen and trophic supply of tissues. The adhesion of leukocytes to the endothelium determines the secretion of biologically active substances that contribute to a change in microcirculation and an increase in the migration of leukocytes into tissues for the implementation of phagocytic and cytolytic functions.

In Vitro Measurements of Shear-Mediated Platelet Adhesion Kinematics as Analyzed through Machine Learning.

Platelet adhesion to blood vessel walls in shear flow is essential to initiating the blood coagulation cascade and prompting clot formation in vascular disease processes and prosthetic cardiovascular devices. Validation of predictive adhesion kinematics models at the single platelet level is difficult due to gaps in high resolution, dynamic morphological data or a mismatch between simulation and experimental parameters. Gel-filtered platelets were perfused at 30 dyne/cm2 in von Willebrand Factor (vWF)-coated microchannels, with flipping platelets imaged at high spatial and temporal resolution. A semi-unsupervised learning system (SULS), consisting of a series of convolutional neural networks, was used to segment platelet geometry, which was compared with expert-analyzed images. Resulting time-dependent rotational angles were smoothed with wavelet-denoising and shifting techniques to characterize the rotational period and quantify flipping kinematics. We observed that flipping platelets do not follow the previously-modeled modified Jefferey orbit, but are characterized by a longer lift-off and shorter reattachment period. At the juncture of the two periods, rotational velocity approached 257.48 ± 13.31 rad/s. Our SULS approach accurately segmented large numbers of moving platelet images to identify distinct adhesive kinematic characteristics which may further validate the physical accuracy of individual platelet motion in multiscale models of shear-mediated thrombosis.

Estrogen activates endothelial exocytosis.

Estrogen therapy is used to treat patients with post-menopausal symptoms, such as hot flashes and dyspareunia. Estrogen therapy also decreases the risk of fractures from osteoporosis in post-menopausal women. However, estrogen increases the risk of venous thromboembolic events, such as pulmonary embolism, but the pathways through which estrogen increase the risk of thromboembolism is unknown. Here, we show that estrogen elicits endothelial exocytosis, the key step in vascular thrombosis and inflammation. Exogenous 17ß-estradiol (E2) stimulated endothelial exocytosis of Weibel-Palade bodies (WPBs), releasing von Willebrand factor (vWF) and interleukin-8 (IL-8). Conversely, the estrogen antagonist ICI-182,780 interfered with E2-induced endothelial exocytosis. The ERα agonist propyl pyrazole triol (PPT) but not the ERß agonist diarylpropionitrile (DPN) induced vWF release, while ERα silencing counteracted vWF release by E2, suggesting that ERα mediates this effect. Exocytosis triggered by E2 occurred rapidly within 15 min and was not inhibited by either actinomycin D or cycloheximide. On the contrary, it was inhibited by the pre-treatment of U0126 or SB203580, an ERK or a p38 inhibitor, respectively, suggesting that E2-induced endothelial exocytosis is non-genomically mediated by the MAP kinase pathway. Finally, E2 treatment enhanced platelet adhesion to endothelial cells ex vivo, which was interfered with the pre-treatment of ICI-182,780 or U0126. Taken together, our data show that estrogen activates endothelial exocytosis non-genomically through the ERα-MAP kinase pathway. Our data suggest that adverse cardiovascular effects such as vascular inflammation and thrombosis should be considered in patients before menopausal hormone treatment.

Arterial Platelet Adhesion in Atherosclerosis-Prone Arteries of Obese, Insulin-Resistant Nonhuman Primates.

Background Platelet-endothelial interactions are thought to contribute to early atherogenesis. These interactions are potentiated by oxidative stress. We used in vivo molecular imaging to test the hypothesis that platelet-endothelial interactions occur at early stages of plaque development in obese, insulin-resistant nonhuman primates, and are suppressed by NADPH-oxidase-2 inhibition. Methods and Results Six adult rhesus macaques fed a Western-style diet for a median of 4.0 years were studied at baseline and after 8 weeks of therapy with the NADPH-oxidase-2-inhibitor apocynin (50 mg/kg per day). Six lean control animals were also studied. Measurements included intravenous glucose tolerance test, body composition by dual-energy X-ray absorptiometry, carotid intimal medial thickness, carotid artery contrast ultrasound molecular imaging for platelet GPIbα (glycoprotein- Ibα) and vascular cell adhesion molecule-1, and blood oxidative markers on mass spectrometry. Compared with lean controls, animals on a Western-style diet were obese (median body mass: 16.0 versus 8.7 kg, P=0.003; median truncal fat: 49% versus 20%, P=0.002), were insulin resistant (4-fold higher insulin-glucose area under the curve on intravenous glucose tolerance test, P=0.002), had 40% larger carotid intimal medial thickness (P=0.004), and exhibited oxidative signatures on proteomics. In obese but not lean animals, signal enhancement on molecular imaging was significantly elevated for GPIbα and vascular cell adhesion molecule-1. The signal correlated modestly with intimal medial thickness but not with the degree of insulin resistance. Apocynin significantly (P<0.01) reduced median signal for GPIbα by >80% and vascular cell adhesion molecule-1 signal by 75%, but did not affect intimal medial thickness, body mass, or intravenous glucose tolerance test results. Conclusion In nonhuman primates, diet-induced obesity and insulin resistance leads to platelet-endothelial adhesion at early atherosclerotic lesion sites, which is associated with the expression of pro-inflammatory adhesion molecules. These responses appear to be mediated, in part, through oxidative pathways.

Computer Simulation of Platelet Adhesion around Stent Struts in the Presence and Absence of Tissue Defects around Them.

AIM: To predict platelet accumulation around stent struts in the presence or absence of tissue defects around them. METHODS: Computer simulations were performed using virtual platelets implementing the function of the three membrane proteins: glycoprotein (GP) Ibα, GPIIb/IIIa, and GPVI. These platelets were perfused around the stent struts implanted into the vessel wall in the presence or absence of tissue defects around them using within the simulation platform. The number of platelets that adhered around stent struts was calculated by solving the blood flow using Navier-Stokes equation along with the adhesion of membrane protein modeled within the platform. RESULTS: Platelet accumulation around stent struts occurred mostly at the downstream region of the stent strut array. The majority of platelets adhered at the downstream of the first bend regardless of the tissue defect status. Platelet adhesion around stent struts occurred more rapidly in the presence of tissue defects. CONCLUSION: Computer simulation using virtual platelets suggested a higher rate of platelet adhesion in the presence of tissue defects around stent struts.

The basement membrane protein nidogen-1 supports platelet adhesion and activation.

The core structure of the extracellular basement membrane is made up of self-assembling networks of collagen and laminin which associate with each other through the bridging adapter proteins including the sulfated monomeric glycoprotein nidogen. While collagen and laminin are known to support platelet adhesion and activation via ß1 integrins and glycoprotein (GP) VI, respectively, whether nidogen contributes to platelet activation and hemostasis is unknown. In this study, we demonstrate that recombinant human nidogen-1 supports platelet adhesion and stimulates platelet activation in a phospholipase-C γ-2 (PLCγ2), Src and Syk kinase-dependent manner downstream. Platetet adhesion to nidogen-1 was inhibited by blocking the platelet receptors GPVI and ß1 integrins. Platelet adhesion to nidogen-1 activated the IκB kinase (IKK) complex, while pharmacological inhibition of IKK blocked platelet spreading on nidogen. Taken together our results suggest that nidogen may play a redundant role in hemostasis by activating platelets downstream of GPVI.