Platelet interaction with the vessel wall

Role and therapeutic potential of gelsolin in atherosclerosis

Atherosclerosis is the major pathophysiological basis of a variety of cardiovascular diseases and has been recognized as a lipid-driven chronic inflammatory disease. Gelsolin (GSN) is a member of the GSN family. The main function of GSN is to cut and seal actin filaments to regulate the cytoskeleton and participate in a variety of biological functions, such as cell movement, morphological changes, metabolism, apoptosis and phagocytosis. Recently, more and more evidences have demonstrated that GSN is Closely related to atherosclerosis, involving lipid metabolism, inflammation, cell proliferation, migration and thrombosis. This article reviews the role of GSN in atherosclerosis from inflammation, apoptosis, angiogenesis and thrombosis.

Does Exercise Influence the Susceptibility to Arterial Thrombosis? An Integrative Perspective

Arterial thrombosis is the primary cause of death worldwide, with the most important risk factors being smoking, unhealthy diet, and physical inactivity. However, although there are clear indications in the literature of beneficial effects of physical activity in lowering the risk of cardiovascular events, exercise can be considered a double-edged sword in that physical exertion can induce an immediate pro-thrombotic environment. Epidemiological studies show an increased risk of cardiovascular events after acute exercise, a risk, which appear to be particularly apparent in individuals with lifestyle-related disease. Factors that cause the increased susceptibility to arterial thrombosis with exercise are both chemical and mechanical in nature and include circulating catecholamines and vascular shear stress. Exercise intensity plays a marked role on such parameters, and evidence in the literature accordingly points at a greater susceptibility to thrombus formation at high compared to light and moderate intensity exercise. Of importance is, however, that the susceptibility to arterial thrombosis appears to be lower in exercise-conditioned individuals compared to sedentary individuals. There is currently limited data on the role of acute and chronic exercise on the susceptibility to arterial thrombosis, and many studies include incomplete assessments of thrombogenic clotting profile. Thus, further studies on the role of exercise, involving valid biomarkers, are clearly warranted.

Increased Platelet Aggregation in Children and Adolescents with Sleep-disordered Breathing

Rationale: Sleep-disordered breathing (SDB) is associated with increased vascular resistance in children and adults. Persistent increased vascular resistance damages vascular endothelial cells-a marker of which is increased platelet activation.Objectives: This study compared whole-blood impedance platelet aggregation in children with clinically diagnosed SDB warranting adenotonsillectomy and healthy control subjects.Methods: Thirty children who had SDB warranting intervention clinically diagnosed by experienced pediatric otolaryngologists were recruited from adenotonsillectomy waitlists, and 20 healthy children from the community underwent overnight polysomnography to determine SDB severity (obstructive apnea-hypopnea index). Snoring frequency was collected from parents. In the morning, a fasting blood sample was taken, and whole-blood platelet aggregation was measured.Measurements and Main Results: Children with SDB exhibited increased platelet aggregation to TRAP (thrombin receptor-activating peptide) (children with SDB = 114.8 aggregation units [AU] vs. control subjects = 98.0 AU; P < 0.05) and COL antibody (96.7 vs. 82.2 AU; P < 0.05) and an increased trend in ADP antibody (82.3 vs. 69.2 AU; P < 0.07) but not aspirin dialuminate (82.1 vs. 79.5 AU; P > 0.05). No significant association was observed between either the obstructive apnea-hypopnea index and any aggregation parameter, but parental report of snoring was positively associated with TRAP aggregation (Kendall's τ-c = 0.23; P < 0.05).Conclusions: The finding of increased platelet aggregation is consistent with endothelial damage. This suggests that the profile of cardiovascular changes noted in adults with SDB may also occur in children with SDB.

Thrombin-like serine protease, antiquorin from Euphorbia antiquorum latex induces platelet aggregation via PAR1-Akt/p38 signaling axis

Plant latex proteases (PLPs) are pharmacologically essential and are integral components of traditional medicine in the management of bleeding wounds. PLPs are known to promote blood coagulation and stop bleeding by interfering at various stages of hemostasis. There are a handful of scientific reports on thrombin-like enzymes characterized from plant latices. However, the role of plant latex thrombin-like enzymes in platelet aggregation is not well known. In the present study, we attempted to purify and characterize thrombin-like protease responsible for platelet aggregation. Among tested plant latices, Euphorbia genus latex protease fractions (LPFs) induced platelet aggregation. In Euphorbia genus, E. antiquorum LPF (EaLPF) strongly induced platelet aggregation and attenuated bleeding in mice. The purified thrombin-like serine protease, antiquorin (Aqn) is a glycoprotein with platelet aggregating activities that interfere in intrinsic and common pathways of blood coagulation cascade and alleviates bleeding and enhanced excision wound healing in mice. In continuation, the pharmacological inhibitor of PAR1 inhibited Aqn-induced phosphorylation of cPLA₂, Akt, and P38 in human platelets. Moreover, Aqn-induced platelet aggregation was inhibited by pharmacological inhibitors of PAR1, PI3K, and P38. These data indicate that PAR1-Akt/P38 signaling pathways are involved in Aqn-induced platelet aggregation. The findings of the present study may open up a new avenue for exploiting Aqn in the treatment of bleeding wounds.

Mechanistic Actions of microRNAs in Diabetic Wound Healing

Wound healing is a complex biological process that is impaired under diabetes conditions. Chronic non-healing wounds in diabetes are some of the most expensive healthcare expenditures worldwide. Early diagnosis and efficacious treatment strategies are needed. microRNAs (miRNAs), a class of 18-25 nucleotide long RNAs, are important regulatory molecules involved in gene expression regulation and in the repression of translation, controlling protein expression in health and disease. Recently, miRNAs have emerged as critical players in impaired wound healing and could be targets for potential therapies for non-healing wounds. Here, we review and discuss the mechanistic background of miRNA actions in chronic wounds that can shed the light on their utilization as specific wound healing biomarkers.

The role of platelets in bleeding in patients with thrombocytopenia and hematological disease

This review evaluates the role of platelets in bleeding risk among patients with hematological disease and thrombocytopenia. Platelets are pivotal in primary hemostasis, and possess non-hemostatic properties involved in angiogenesis, tissue repair, inflammation and metastatis. Also, platelets safeguard vascular integrity in inflamed vessels. Overall, bleeding risk depends on the underlying disease, and patients with cancer and platelet count <6-10 × 109/L have a markedly increased bleeding risk, while the platelet count does not correlate with bleeding risk at higher platelet counts. Other factors might affect platelet properties and thus bleeding risk, for example, drugs, low hematocrit, coagulation system impairments or transfusion of dysfunctional donor platelets. For patients with leukemia and immune thrombocytopenia, reduced platelet activation, platelet aggregation, or thrombopoiesis, reflected by the reduced presence of reticulated platelets, are associated with bleeding phenotype. However, mechanistic insight into the cause of reduced platelet function in different thrombocytopenic conditions is sparse, except for some inherited platelet disorders. Promising tools for platelet function studies in thrombocytopenia are flow cytometry and biomarker studies on platelet constituents. An important message from this current paper is that bleeding risk assessment must be tailored to specific patient populations and cannot be applied broadly to all patients with thrombocytopenia.

Long noncoding RNA MEG3 prevents vascular endothelial cell senescence by impairing miR-128-dependent Girdin downregulation

Long noncoding RNAs (lncRNAs) are commonly associated with various biological functions, in which the function of lncRNA maternally expressed gene 3 (MEG3) has been identified in various cancers. Strikingly, an association between MEG3 with microRNAs (miRNAs), mRNAs, and proteins has been reported. This study investigates the role of MEG3 in vascular endothelial cell (VEC) senescence. Expression of Girdin and miR-128 was monitored in the blood vessel samples of young and old mice/healthy volunteers, along with the measurement of human umbilical vein endothelial cells (HUVECs). The relationship between MEG3/Girdin and miR-128 was determined and verified. Loss- and gain-of-function approaches were applied to analyze the regulatory effects of MEG3 on platelet phagocytosis and lipoprotein oxidation of HUVEC membrane. In addition, the effect of MEG3 on HUVEC senescence was evaluated by detection of the reactive oxygen species, telomerase activity, and telomere length. To further analyze the MEG3-mediated regulatory mechanism, miR-128 upregulation and inhibition were introduced into the HUVECs. Downregulated Girdin and upregulated miR-128 were found in the blood vessels of old individuals and old mice, as well as in senescent HUVECs. MEG3 downregulation was found to be capable of inhibiting Girdin but enhancing miR-128 expression. It was also indicated to inhibit platelet phagocytosis and reduce telomerase activity and telomere length, while enhancing lipoprotein oxidation and reactive oxygen species production, which ultimately contributed in preventing and protecting HUEVCs from senescence. These findings provide evidence supporting that MEG3 leads to miR-128 downregulation and Girdin upregulation, which promotes platelet phagocytosis, thus protecting VECs from senescence.

Influential factors and clinical significance of an atypical presentation of posterior reversible encephalopathy syndrome in patients with eclampsia

BACKGROUND AND PURPOSE

Posterior reversible encephalopathy syndrome (PRES) is a clinical and radiologic entity for which eclampsia is one of the most common predisposing conditions. Despite the imaging changes typically reported, the predisposing factors and clinical implications of atypical presentations have yet to be fully clarified.

METHODS

A total of 56 patients with PRES were selected for study. Demographic, clinical, and laboratory data were analyzed, focusing on atypical presentations of PRES. Multiple logistic regression was applied to identify factors impacting such atypical presentations, and functional outcomes were assessed upon patient discharge.

RESULTS

Overall, 22 of the 56 patients (39.3%) displayed features of atypical PRES. By multiple logistic regression, headache (OR = 5.39; 95% CI, 1.24-23.51; p = 0.025) and frequent convulsions (OR = 4.41; 95% CI, 1.09-17.91; p = 0.038) proved to be independent factors associated with atypical PRES. Ultimately, outcomes of 18 patients were gauged as poor, based on the modified Rankin Scale (mRS). Logistic regression indicated that visual disturbances (OR = 9.02; 95% CI, 1.37-59.35; p = 0.02), frequent convulsions (OR = 9.47; 95% CI, 1.67-53.63; p = 0.01), and restricted diffusion on imaging (OR = 11.96; 95% CI, 1.76-81.11; p = 0.01) were independently associated with poor outcomes in patients with eclampsia-related PRES.

CONCLUSION

Headache and frequent convulsions are independently associated with atypical presentations of PRES. If present, restricted diffusion may help in predicting poor outcomes of such patients upon discharge.

The primary haemostasis is more preserved in thrombocytopenic patients with liver cirrhosis than cancer

: In thrombocytopenia, differences in haemostatic capacity may explain discrepancies in bleeding risk between patients with cancer and patients with liver cirrhosis. The objective was to compare the haemostatic capacity in different thrombocytopenic patient populations. We evaluated platelet aggregation using impedance aggregometry (Multiplate Analyzer), von Willebrand factor antigen (VWF:Ag), VWF:ristocetin-cofactor activity (VWF:RCo), activated partial thromboplastin time (aPTT), coagulation factor VIII, fibrinogen, and thrombin generation in adult hospitalized patients with platelet count less than 80 × 10/l. Patients either had liver cirrhosis (n = 28), or cancer (n = 169; n = 49 had haematological cancer) with no difference among patients with liver cirrhosis and cancer. Median platelet count was 48 × 10/l [interquartile range (IQR) 32-63 × 10/l]. Median platelet aggregation was higher in patients with cirrhosis than cancer, 416 AU × min (IQR 257-676) versus 145 AU × min (IQR 50-326) for collagen-induced platelet aggregation, P < 0.001. There was no difference in activated partial thromboplastin time (aPTT), coagulation factor VIII, or thrombin generation between the patient groups. Fibrinogen activity was higher in patients with cancer compared with patients with cirrhosis [12.5 μmol/L (IQR 9.9-16.5) versus 7.2 μmol/l (IQR 5.6-10.2)], P < 0.003. Patients with liver cirrhosis had a more preserved primary haemostasis compared with patients with cancer.

Engulfment of platelets delays endothelial cell aging via girdin and its phosphorylation

Endothelial cells are critical in angiogenesis and maintain the homeostasis of the blood‑brain barrier (BBB). Platelets (PLTs) are essential in vascular biology, including angiogenesis. The present study aimed to investigate the effect of PLTs on the aging of endothelial cells. Human brain microvascular endothelial cells (HBMECs) and human astrocytes were co‑cultured to mimic the BBB. Transmission electron microscopy was used to observe the engulfment of PLTs. Confocal microscopy was used to observe the co‑localization of PLTs, girders of actin filament (girdin) and phosphorylated (p‑)girdin. Senescence‑associated β‑galactosidase (β‑gal) staining, 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide and flow cytometry were performed to examine the cell senescence, viability and apoptosis, respectively. Transwell assays were performed to examine cell invasion and migration. Western blot analysis was performed to detect the expression of girdin, AKT and p‑AKT. PLTs delayed senescence, and promoted the viability and resistance to apoptosis of the HBMECs. Cell invasion and migration were enhanced by PLTs. In addition, girdin and p‑girdin were essential to the engulfment of HBMECs to PLTs. Mechanically, the inhibition of AKT signals reversed the effect of PLTs on HBMECs by increasing the activity of β‑gal, decreasing the cell viability, and inhibiting the invasion and migration of the HBMECs. The engulfment of PLTs assisted in delaying the aging of endothelial cells via girdin and p‑girdin, in which the AKT signal was involved. The present study indicated a potential strategy for delaying endothelial cell aging in the treatment of central nervous system diseases.

Light transmission aggregometry using pre-coated microtiter plates and a Victor X5 plate reader

BACKGROUND

Light transmission aggregometry (LTA) can be performed with microtiter plates (96-well LTA). When conducting LTA, an agonist is added to platelet-rich plasma and the sample is shaken for minutes after which absorbance readings are done. Platelet aggregation is detected as decrease in absorbance. However, the classical method is cumbersome and therefore microtiter plates can be used for concomitant testing of multiple samples. Furthermore, it would be convenient to prepare the plate in advance of platelet aggregation testing. Aim: The aim of the present study was to establish a simplified 96-well LTA protocol, where plates were pre-coated with agonists and stored at -80 C until use.

RESULTS

We developed and validated a protocol for 96-well LTA using a Victor X5 plate reader and pre-coated microtiter plates. The minimum requirement of platelet-rich plasma was 45 μL per sample and the sample platelet count should not be below 100 x109/L. Optimal absorbance reading was 595 nm wavelengths. Platelet aggregation results were higher at 37°C than at room temperature. Platelet adherence to wells after stimulation was observed; it was not avoided by pre-coating of the wells with gelatin. A range of up to 7 concentrations for each agonist (collagen, arachidonic acid, adenosine diphosphate, thrombin receptor-activating peptide and protease-activated receptor-4) was tested concomitantly. A transient rise in platelet aggregation was observed after 2 minutes of shaking in some samples with low agonist concentration, and platelet aggregation was optimal after 10 minutes of shaking for samples with high agonist concentration. Plates could be stored at -80°C for 15 days without significant change in the platelet aggregation results.

CONCLUSION

The 96-well LTA is suitable for platelet aggregation testing and a range of agonist concentrations can be concomitantly tested.

Wound healing: time to look for intelligent, 'natural' immunological approaches?

There is now good evidence that cytokines and growth factors are key factors in tissue repair and often exert anti-infective activities. However, engineering such factors for global use, even in the most remote places, is not realistic. Instead, we propose to examine how such factors work and to evaluate the reparative tools generously provided by 'nature.' We used two approaches to address these objectives. The first approach was to reappraise the internal capacity of the factors contributing the most to healing in the body, i.e., blood platelets. The second was to revisit natural agents such as whey proteins, (honey) bee venom and propolis. The platelet approach elucidates the inflammation spectrum from physiology to pathology, whereas milk and honey derivatives accelerate diabetic wound healing. Thus, this review aims at offering a fresh view of how wound healing can be addressed by natural means.

Potential influences of complement factor H in autoimmune inflammatory and thrombotic disorders

Complement system homeostasis is important for host self-protection and anti-microbial immune surveillance, and recent research indicates roles in tissue development and remodelling. Complement also appears to have several points of interaction with the blood coagulation system. Deficiency and altered function due to gene mutations and polymorphisms in complement effectors and regulators, including Factor H, have been associated with familial and sporadic autoimmune inflammatory - thrombotic disorders, in which autoantibodies play a part. These include systemic lupus erythematosus, rheumatoid arthritis, atypical haemolytic uremic syndrome, anti-phospholipid syndrome and age-related macular degeneration. Such diseases are generally complex - multigenic and heterogeneous in their symptoms and predisposition/susceptibility. They usually need to be triggered by vascular trauma, drugs or infection and non-complement genetic factors also play a part. Underlying events seem to include decline in peripheral regulatory T cells, dendritic cell, and B cell tolerance, associated with alterations in lymphoid organ microenvironment. Factor H is an abundant protein, synthesised in many cell types, and its reported binding to many different ligands, even if not of high affinity, may influence a large number of molecular interactions, together with the accepted role of Factor H within the complement system. Factor H is involved in mesenchymal stem cell mediated tolerance and also contributes to self-tolerance by augmenting iC3b production and opsonisation of apoptotic cells for their silent dendritic cell engulfment via complement receptor CR3, which mediates anti-inflammatory-tolerogenic effects in the apoptotic cell context. There may be co-operation with other phagocytic receptors, such as complement C1q receptors, and the Tim glycoprotein family, which specifically bind phosphatidylserine expressed on the apoptotic cell surface. Factor H is able to discriminate between self and nonself surfaces for self-protection and anti-microbe defence. Factor H, particularly as an abundant platelet protein, may also modulate blood coagulation, having an anti-thrombotic role. Here, we review a number of interaction pathways in coagulation and in immunity, together with associated diseases, and indicate where Factor H may be expected to exert an influence, based on reports of the diversity of ligands for Factor H.

A constitutive model for developing blood clots with various compositions and their nonlinear viscoelastic behavior

The mechanical properties determine to a large extent the functioning of a blood clot. These properties depend on the composition of the clot and have been related to many diseases. However, the various involved components and their complex interactions make it difficult at this stage to fully understand and predict properties as a function of the components. Therefore, in this study, a constitutive model is developed that describes the viscoelastic behavior of blood clots with various compositions. Hereto, clots are formed from whole blood, platelet-rich plasma and platelet-poor plasma to study the influence of red blood cells, platelets and fibrin, respectively. Rheological experiments are performed to probe the mechanical behavior of the clots during their formation. The nonlinear viscoelastic behavior of the mature clots is characterized using a large amplitude oscillatory shear deformation. The model is based on a generalized Maxwell model that accurately describes the results for the different rheological experiments by making the moduli and viscosities a function of time and the past and current deformation. Using the same model with different parameter values enables a description of clots with different compositions. A sensitivity analysis is applied to study the influence of parameter variations on the model output. The relative simplicity and flexibility make the model suitable for numerical simulations of blood clots and other materials showing similar behavior.

The role of antiplatelet medications in angiogram-negative subarachnoid hemorrhage

BACKGROUND

The use of antiplatelet medications has greatly expanded and this has been associated with an increased rate of complications after aneurysmal subarachnoid hemorrhage (SAH). The influence of antiplatelet medications on outcomes after non-aneurysmal SAH is unknown.

OBJECTIVE

To analyze the frequency and impact on outcome of antiplatelet medication use among patients with angiogram-negative SAH.

METHODS

An analysis of patients within the Columbia University SAH Outcomes Project database was performed. All patients who underwent catheter cerebral angiography after presenting with nontraumatic SAH between 1996 and 2013 were included. Outcomes were assessed by using the modified Rankin Scale.

RESULTS

A total of 1351 patients underwent catheter angiography for evaluation of SAH. Of these, 173 (13%) were designated angiogram-negative. The fraction of patients presenting with angiogram-negative SAH as well as the frequency of antiplatelet use among these patients significantly increased during the study period. Antiplatelet use was more commonly associated with angiogram-negative SAH than with angiogram-positive SAH (27% vs 14%, P = .001). At 14 days after presentation, poor outcome was significantly more frequent among patients who took antiplatelet agents than among those who did not (38% vs 20%, P = .017). This effect was also seen after multivariate analysis (odds ratio, 2.58; P = .034), although no difference was observed by 12 months (P > .05).

CONCLUSION

Antiplatelet medication use is associated with poor early, but not late, outcomes after angiogram-negative SAH. Corresponding increased rates of antiplatelet medication use and angiogram-negative SAH may be related. Additional studies are needed to confirm this association.

Phagocytosis of platelets enhances endothelial cell survival under serum deprivation

Platelets are key players in fundamental processes of vascular biology, such as angiogenesis, tissue regeneration, and tumor metastasis. However, the underlying mechanisms remain unclear. In this study, some tumor vascular endothelial cells were positively stained by antiplatelet antibodies. Further investigation revealed that platelets were taken up by endothelial cells in vitro and in vivo. Human umbilical vascular endothelial cells were rendered apoptotic under conditions of serum deprivation. However, endothelial apoptosis was suppressed and cell viability was enhanced when platelets were added to the cultures. Endothelial survival was paralleled by an upregulation of phosphorylated Akt and p70 S6K. In conclusion, this study demonstrated that platelets can be phagocytosed by endothelial cells, and the phagocytosed platelets could suppress endothelial apoptosis and promote cell viability level. The mechanism underlying this process involves the activation of Akt signaling.

Raynaud's phenomenon: from molecular pathogenesis to therapy

Raynaud's phenomenon (RP) is a well defined clinical syndrome characterized by recurrent episodes of digital vasospasm triggered by exposure to physical/chemical or emotional stress. RP has been classified as primary or secondary, depending on whether it occurs as an isolated condition (pRP) or is associated to an underlying disease, mainly a connective tissue disease (CTD-RP). In both cases, it manifests with unique "triple" (pallor, cyanosis and erythema), or "double" color changes. pRP is usually a benign condition, while sRP can evolve and be complicated by acral digital ulcers and gangrene, which may require surgical treatment. The pathogenesis of RP has not yet been entirely clarified, nor is it known whether autoantibodies have a role in RP. Even so, recent advances in our understanding of the pathophysiology have highlighted novel potential therapeutic targets. The aim of this review is to discuss the etiology, epidemiology, risk factors, clinical manifestations, recently disclosed pathogenic mechanisms underlying RP and their correlation with the available therapeutic options, focusing primarily on pRP and CTD-RP.

Elevated circulating levels of tissue factor-positive microvesicles are associated with distant metastasis in lung cancer

PURPOSE

Microvesicles (MV) in the blood stream are associated with distant metastasis in cancer. Platelet or endothelial cell-related MV actively participate in thrombogenesis, which is an important step in cancer metastasis. This study investigated the correlations between MV levels of platelet-poor plasma and distant metastasis in lung cancer.

METHODS

Platelet-poor plasma from 44 treatment-naive lung cancer (23 with distant metastasis) and 19 normal subjects was used to determine the levels of glycoprotein Iβ (CD42) + platelet MV (PMV), P-selectin (CD62P) + PMV, VE-cadherin (CD144) + endothelial MV (EMV), tissue factor (CD142) + MV, thrombin-antithrombin complex and vascular endothelial growth factor (VEGF).

RESULTS

The level of CD142 + MV was significant (odds ratio 5.86, 95 % confidence interval 1.31-38.3) in predicting distant metastasis in lung cancer, and a cutoff value of 2.668 (after logarithm transformation) in the ROC curve had a specificity of 90 % and a sensitivity of 59 %. The presence of distant metastasis showed a significant correlation between CD144 + EMV and VEGF, but not between CD144 + EMV and CD42 + PMV or CD62P + PMV in lung cancer subjects.

CONCLUSIONS

The finding of CD142 + MV in platelet-poor plasma may be useful for suggesting distant metastasis in lung cancer. In addition to thrombogenesis, interaction between VE-cadherin and VEGF may be needed for successful metastasis in lung cancer.

Native high density lipoproteins (HDL) interfere with platelet activation induced by oxidized low density lipoproteins (OxLDL)

Platelets and lipoproteins play a crucial role in atherogenesis, in part by their ability to modulate inflammation and oxidative stress. While oxidized low density lipoproteins (OxLDL) play a central role in the development of this disease, high density lipoproteins (HDL) represent an atheroprotective factor of utmost importance. As platelet function is remarkably sensitive to the influence of plasma lipoproteins, it was the aim of this study to clarify if HDL are able to counteract the stimulating effects of OxLDL with special emphasis on aspects of platelet function that are relevant to inflammation. Therefore, HDL were tested for their ability to interfere with pro-thrombotic and pro-inflammatory aspects of platelet function. We are able to show that HDL significantly impaired OxLDL-induced platelet aggregation and adhesion. In gel-filtered platelets, HDL decreased both the formation of reactive oxygen species and CD40L expression. Furthermore, HDL strongly interfered with OxLDL-induced formation of platelet-neutrophil aggregates in whole blood, suggesting that platelets represent a relevant and sensitive target for HDL. The finding that HDL effectively competed with the binding of OxLDL to the platelet surface might contribute to their atheroprotective and antithrombotic properties.

High precision platelet releasate definition by quantitative reversed protein profiling--brief report

OBJECTIVE

Platelet activation and subsequent protein release play an important role in healthy hemostasis and inflammatory responses, yet the identity and quantity of proteins in the platelet releasate are still debated. Here, we present a reversed releasate proteomics approach to determine unambiguously and quantitatively proteins released from activated platelets.

APPROACH AND RESULTS

Isolated platelets were mock and fully stimulated after which the released proteins in the supernatant were removed. Using high-end proteomics technology (2D chromatography, stable isotope labeling, electron transfer dissociation, and high collision dissociation fragmentation) allowed us to quantitatively discriminate the released proteins from uncontrolled lysis products. Monitoring the copy numbers of ≈ 4500 platelet proteins, we observed that after stimulation via thrombin and collagen, only 124 (<3%) proteins were significantly released (P<0.05). The released proteins span a concentration range of ≥ 5 orders, as confirmed by ELISA. The released proteins were highly enriched in secretion tags and contained all known factors at high concentrations (>100 ng/mL, eg, thrombospondin, von Willebrand factor, and platelet factor 4). Interestingly, in the lower concentration range of the releasate many novel factors were identified.

CONCLUSIONS

Our reversed releasate dataset forms the first unambiguous, in depth repository for molecular factors released by platelets.