A novel method for automated assessment of megakaryocyte differentiation and proplatelet formation.

Transfusion of platelet concentrates represents an important treatment for various bleeding complications. However, the short half-life and frequent contaminations with bacteria restrict the availability of platelet concentrates and raise a clear demand for platelets generated ex vivo. Therefore, in vitro platelet generation from megakaryocytes represents an important research topic. A vital step for this process represents accurate analysis of thrombopoiesis and proplatelet formation, which is usually conducted manually. We aimed to develop a novel method for automated classification and analysis of proplatelet-forming megakaryocytes in vitro. After fluorescent labelling of surface and nucleus, MKs were automatically categorized and analysed with a novel pipeline of the open source software CellProfiler. Our new workflow is able to detect and quantify four subtypes of megakaryocytes undergoing thrombopoiesis: proplatelet-forming, spreading, pseudopodia-forming and terminally differentiated, anucleated megakaryocytes. Furthermore, we were able to characterize the inhibitory effect of dasatinib on thrombopoiesis in more detail. Our new workflow enabled rapid, unbiased, quantitative and qualitative in-depth analysis of proplatelet formation based on morphological characteristics. Clinicians and basic researchers alike will benefit from this novel technique that allows reliable and unbiased quantification of proplatelet formation. It thereby provides a valuable tool for the development of methods to generate platelets ex vivo and to detect effects of drugs on megakaryocyte differentiation.

Secretome of apoptotic peripheral blood cells (APOSEC) attenuates microvascular obstruction in a porcine closed chest reperfused acute myocardial infarction model: role of platelet aggregation and vasodilation.

Although epicardial blood flow can be restored by an early intervention in most cases, a lack of adequate reperfusion at the microvascular level is often a limiting prognostic factor of acute myocardial infarction (AMI). Our group has recently found that paracrine factors secreted from apoptotic peripheral blood mononuclear cells (APOSEC) attenuate the extent of myocardial injury. The aim of this study was to determine the influence of APOSEC on microvascular obstruction (MVO) in a porcine AMI model. A single dose of APOSEC was intravenously injected in a closed chest reperfused infarction model. MVO was determined by magnetic resonance imaging and cardiac catheterization. Role of platelet function and vasodilation were monitored by means of ELISA, flow cytometry, aggregometry, western blot and myographic experiments in vitro and in vivo. Treatment of AMI with APOSEC resulted in a significant reduction of MVO. Platelet activation markers were reduced in plasma samples obtained during AMI, suggesting an anti-aggregatory capacity of APOSEC. This finding was confirmed by in vitro tests showing that activation and aggregation of both porcine and human platelets were significantly impaired by co-incubation with APOSEC, paralleled by vasodilator-stimulated phosphoprotein (VASP)-mediated inhibition of platelets. In addition, APOSEC evidenced a significant vasodilatory capacity on coronary arteries via p-eNOS and iNOS activation. Our data give first evidence that APOSEC reduces the extent of MVO during AMI, and suggest that modulation of platelet activation and vasodilation in the initial phase after myocardial infarction contributes to the improved long-term outcome in APOSEC treated animals.

Camostat Mesylate Versus Lopinavir/Ritonavir in Hospitalized Patients With COVID-19-Results From a Randomized, Controlled, Open Label, Platform Trial (ACOVACT).

Background: To date, no oral antiviral drug has proven to be beneficial in hospitalized patients with COVID-19. Methods: In this randomized, controlled, open-label, platform trial, we randomly assigned patients ≥18 years hospitalized with COVID-19 pneumonia to receive either camostat mesylate (CM) (considered standard-of-care) or lopinavir/ritonavir (LPV/RTV). The primary endpoint was time to sustained clinical improvement (≥48 h) of at least one point on the 7-category WHO scale. Secondary endpoints included length of stay (LOS), need for mechanical ventilation (MV) or death, and 29-day mortality. Results: 201 patients were included in the study (101 CM and 100 LPV/RTV) between 20 April 2020 and 14 May 2021. Mean age was 58.7 years, and 67% were male. The median time from symptom onset to randomization was 7 days (IQR 5-9). Patients in the CM group had a significantly shorter time to sustained clinical improvement (HR = 0.67, 95%-CI 0.49-0.90; 9 vs. 11 days, p = 0.008) and demonstrated less progression to MV or death [6/101 (5.9%) vs. 15/100 (15%), p = 0.036] and a shorter LOS (12 vs. 14 days, p = 0.023). A statistically nonsignificant trend toward a lower 29-day mortality in the CM group than the LPV/RTV group [2/101 (2%) vs. 7/100 (7%), p = 0.089] was observed. Conclusion: In patients hospitalized for COVID-19, the use of CM was associated with shorter time to clinical improvement, reduced need for MV or death, and shorter LOS than the use of LPV/RTV. Furthermore, research is needed to confirm the efficacy of CM in larger placebo-controlled trials. Systematic Review Registration: [https://clinicaltrials.gov/ct2/show/NCT04351724, https://www.clinicaltrialsregister.eu/ctr-search/trial/2020-001302-30/AT], identifier [NCT04351724, EUDRACT-NR: 2020-001302-30].

Comparative proteomics reveals unexpected quantitative phosphorylation differences linked to platelet activation state.

There is a need to assess platelet activation in patients with thrombotic disorders. P-selectin and activated integrin αIIbß3 are usually quantified by flow cytometry to measure platelet activation. Monitoring changes in vasodilator-stimulated phosphoprotein (VASP) phosphorylation is an established method to determine the platelet-reactivity status. To study disruptions of platelet reactivity more comprehensively, we compared the human non-secretory platelet proteome after in-vitro -activation and -inhibition with their respective untreated controls using unbiased fluorescence two-dimensional differential in-gel electrophoresis. The non-secretory platelet proteome was more severely affected during inhibition than during activation. Strikingly, while VASP reached a 1.3-fold increase in phosphorylation levels in inhibited platelets, other protein kinase A targets showed several-fold stronger inhibition-induced phosphorylation levels, including LIM and SH3 domain protein 1 (6.7-fold), Src kinase-associated phosphoprotein 2 (4.6-fold), and Ras-related protein Rap1b (4.1-fold). Moreover, phosphorylation of integrin-linked protein kinase (ILK) and pleckstrin (PLEK) species was associated with P-selectin surface expression. The discrimination power between activation and inhibition was more pronounced for dephosphorylated ILK (3.79 Cohen's d effect size) and phosphorylated PLEK (3.77) species than for P-selectin (2.35). These data reveal new insights into the quantitative changes of the platelet reactivity proteome and suggest powerful alternatives to characterise their activation and inactivation potential.

Intravenous immunoglobulins induce CD32-mediated platelet aggregation in vitro.

BACKGROUND: Intravenous immunoglobulins (IVIg) and cytomegalovirus immunoglobulins (CMVIg) are currently finding increased acceptance in clinical states of high immune activity and in transplant recipients. A rare side-effect of their application is intravascular thrombosis, which is thought to be related to pre-existing hyperviscosity. In a previous study we have shown that rabbit antithymocyte globulin causes platelet aggregation in vitro via the Fc IgG receptor (CD32). OBJECTIVES: To investigate if IVIg and CMVIg have the potential to cause CD32-dependent platelet aggregation. METHODS: The influence of CMVIg or IVIg on platelets pre-incubated with or without monoclonal antibody AT10 was studied in an aggregometer. Expression of platelet surface activation marker CD62P was determined by fluorescence-activated cell sorting analysis and presence of soluble CD40L (sCD40L) was evaluated by enzyme-linked immunosorbent assay. All in vitro experiments were performed using platelet concentrates from the blood bank, at therapeutic concentrations of immunoglobulins. Results Incubation of platelets with CMVIg and IVIg markedly induced platelet aggregation, and increased expression of CD62P and secretion of sCD40L. The capacity of CMVIg and IVIg to induce platelet aggregation was completely abrogated by adding the blocking antibody AT10 directed against the low-affinity Fc IgG receptor (CD32). CONCLUSIONS: Our results suggest that CMVIg and IVIg solutions with activating Fc domains are able to bind CD32 on platelets and cause platelet aggregation in vitro. These results indicate a mechanism by which in vivo intravascular thrombosis may be explained and suggest caution with concomitant use of packed platelets and IVIg in autoimmune diseases in the clinical setting.

Androgen receptor dampens tissue factor expression via nuclear factor-κB and early growth response protein 1.

Essentials Androgen deprivation increases the rate of venous thromboembolism in prostate cancer patients. We characterized androgen receptor-mediated tissue factor regulation in prostate epithelial cells. Androgen receptor is dampening tissue factor expression in prostate epithelial cells. Androgen deprivation could enhance tissue factor expression and raise venous thromboembolism rates. SUMMARY: Background Prostate cancer is one of the leading causes of cancer death in men. Advanced prostate cancer is usually treated by androgen deprivation therapy (ADT), which is aimed at reducing circulating testosterone levels to reduce cancer growth. There is growing evidence that ADT can increase the rate of venous thromboembolism (VTE) in prostate cancer patients. The tissue factor (TF) gene is one of the most important mediators of coagulation and VTE, but, so far, there are limited data on androgen receptor (AR)-mediated TF gene expression. Objectives To characterize AR-mediated TF regulation in vitro and in vivo. Methods We used the androgen-dependent prostate cancer cell lines LNCaP and MyC-CaP to test whether TF expression is regulated by AR. Furthermore, we cloned the TF gene promoter into a luciferase reporter vector to identify the transcription factor-binding sites that mediate TF regulation downstream of AR. Finally, we used castration experiments in mice to characterize AR-mediated TF regulation in vivo. Results TF is directly regulated by AR. In LNCaP cells, nuclear factor-κB signaling and EGR1 mediate TF expression. By using castration experiments in mice, we could detect upregulation of TF and early growth response protein 1 mRNA and protein expression in prostate epithelial cells. Conclusion AR is crucial for dampening TF expression, which could be important for increased TF expression and TF-positive microvesicle release in androgen-deprived prostate cancer patients.

Myeloid but not epithelial tissue factor exerts protective anti-inflammatory effects in acid aspiration-induced acute lung injury.

Essentials Tissue factor (TF) represents a central link between hemostasis and inflammation. We studied the roles of myeloid and airway epithelial TF in acid-caused acute lung injury (ALI). TF on myeloid cells displays a non-coagulatory role regulating the inflammatory response in ALI. Airway epithelial TF contributes to hemostatic functions, but is dispensable in ALI pathogenesis. SUMMARY: Introduction Acute lung injury (ALI) is a life-threatening condition characterized by damaged alveolar-capillary structures and activation of inflammatory and hemostatic processes. Tissue factor (TF) represents a crucial link between inflammation and coagulation, as inflammatory mediators induce myeloid TF expression, and TF initiates extrinsic coagulation. Objective As pulmonary inflammation stimulates TF expression and TF modulates immune responses, we aimed to elucidate its impact on ALI. In particular, we wanted to distinguish the contributions of TF expressed on airway epithelial cells and TF expressed on myeloid cells. Methods Mice with different cell type-specific TF deficiency and wild-type littermates were intratracheally treated with hydrochloric acid, and leukocyte recruitment, cytokine levels, thrombin-antithrombin (TAT) complexes and pulmonary protein-rich infiltrates were analyzed. Results Our data demonstrate that a lack of epithelial TF did not influence acute responses, as bronchoalveolar neutrophil accumulation 8 h after ALI induction was unaltered. However, it led to mild, prolonged inflammation, as pulmonary leukocyte and erythrocyte numbers were still increased after 24 h, whereas those in wild-type mice had returned to basal levels. In contrast, myeloid TF was primarily involved in regulating the acute phase of ALI without affecting local coagulation, as indicated by increased bronchoalveolar neutrophil infiltration, pulmonary interleukin-6 levels, and edema formation, but equal TAT complex formation, 8 h after ALI induction. This augmented inflammatory response associated with myeloid TF deficiency was confirmed in vitro, as lipopolysaccharide-stimulated TF-deficient alveolar macrophages released increased levels of chemokine (C-X-C motif) ligand 1 and tumor necrosis factor-α as compared with wild-type macrophages. Conclusion We conclude that myeloid TF dampens inflammation in acid-induced ALI.

Smoking alters circulating plasma microvesicle pattern and microRNA signatures.

Circulating plasma microvesicles (PMVs) and their microRNA content are involved in the development of atherosclerosis and could serve as biomarkers for cardiovascular disease (CVD) progression. However, little is known on how smoking influences the levels of PMVs and microRNA signatures in vivo. Therefore, we aimed to investigate the effects of smoking on circulating PMV levels and CVD-related PMV-derived microRNAs in young, healthy smokers. Twenty young (10 female, 10 male; 25 ± 4 years) healthy smokers (16 ± 6 cigarettes per day for 8 ± 4 years) and age- and sex-matched controls were included in this study. While complete blood count revealed no differences between both groups, smoking significantly enhanced intracellular reactive oxygen species in platelets and leukocytes as well as platelet-leukocyte aggregate formation. Total circulating PMV counts were significantly reduced in smokers, which could be attributed to decreased platelet-derived PMVs. While the number of endothelial PMVs remained unaffected, smoking propagated circulating leukocyte-derived PMVs. Despite reduced total PMVs, PMV-derived microRNA-profiling of six smoker/control pairs revealed a decrease of only a single microRNA, the major platelet-derived microRNA miR-223. Conversely, miR-29b, a microRNA associated with aortic aneurysm and fibrosis, and RNU6-2, a commonly used reference-RNA, were significantly up-regulated. Smoking leads to alterations in the circulating PMV profile and changes in the PMV-derived microRNA signature already in young, healthy adults. These changes may contribute to the development of smoking-related cardiovascular pathologies. Moreover, these smoking-related changes have to be considered when microRNA or PMV profiles are used as disease-specific biomarkers.

Apolipoprotein B100 danger-associated signal 1 (ApoBDS-1) triggers platelet activation and boosts platelet-leukocyte proinflammatory responses.

Low-density lipoproteins (LDL), occurring in vivo in both their native and oxidative form, modulate platelet function and thereby contribute to atherothrombosis. We recently identified and demonstrated that 'ApoB100 danger-associated signal 1' (ApoBDS-1), a native peptide derived from Apolipoprotein B-100 (ApoB100) of LDL, induces inflammatory responses in innate immune cells. Platelets are critically involved in the development as well as in the lethal consequences of atherothrombotic diseases, but whether ApoBDS-1 has also an impact on platelet function is unknown. In this study we examined the effect of ApoBDS-1 on human platelet function and platelet-leukocyte interactions in vitro. Stimulation with ApoBDS-1 induced platelet activation, degranulation, adhesion and release of proinflammatory cytokines. ApoBDS-1-stimulated platelets triggered innate immune responses by augmenting leukocyte activation, adhesion and transmigration to/through activated HUVEC monolayers, under flow conditions. These platelet-activating effects were sequence-specific, and stimulation of platelets with ApoBDS-1 activated intracellular signalling pathways, including Ca2+, PI3K/Akt, PLC, and p38- and ERK-MAPK. Moreover, our data indicates that ApoBDS-1-induced platelet activation is partially dependent of positive feedback from ADP on P2Y1 and P2Y12, and TxA2. In conclusion, we demonstrate that ApoBDS-1 is an effective platelet agonist, boosting platelet-leukocyte's proinflammatory responses, and potentially contributing to the multifaceted inflammatory-promoting effects of LDL in the pathogenesis of atherothrombosis.

Efficient phagocytosis of periodontopathogens by neutrophils requires plasma factors, platelets and TLR2.

BACKGROUND: Periodontitis represents a chronic infection of supportive dental tissues by distinct gram-negative bacteria. It is characterized by chronic and local inflammation as well as transient bacteremia with frequently occurring infections at distant sites. OBJECTIVES: The present work aimed to clarify the role of platelets and plasma factors in neutrophil interactions with the periodontopathogens A. actinomycetemcomitans and P. gingivalis. METHODS: Phagocytosis, cell-cell interactions and activation of platelets and neutrophils in response to periodontopathogens were analyzed by flow cytometry, confocal microscopy and bacteria survival assay. Plasma factors, platelet signaling pathways and receptors involved in platelet-neutrophil-bacteria interactions were determined. The role of platelet and neutrophil TLR2 in phagocytosis was further evaluated in a murine TLR2 knockout model. RESULTS: In the presence of plasma neutrophil-mediated clearance of periodontopathogens is doubled due to opsonisation of bacteria. Platelets, which become activated by periodontopathogens, further enhance clearance of bacteria by 20%, via direct interaction with neutrophils. Plasma factors (e.g. CD14) are required for platelet activation, which is mainly TLR2 dependent and results in PI3K/Akt activation. In a murine TLR2 knockout model we prove that platelet TLR2 is important for formation of platelet-neutrophil aggregates and enhanced phagocytosis of periodontopathogens. In contrast, neutrophil TLR2 is not involved in platelet-neutrophil aggregate formation but is required for efficient phagocytosis. CONCLUSIONS: These data indicate that efficient elimination of periodontopathogens by neutrophils involves a complex interplay of plasma factors as well as platelets and requires functional TLR2. By enhancing neutrophil activation platelets contribute to immune defense but may also foster inflammation.

Thrombospondin-1: a unique marker to identify in vitro platelet activation when monitoring in vivo processes.

BACKGROUND: Measuring platelet activation in patients has become a potent method to investigate pathophysiological processes. However, the commonly applied markers are sensitive to detrimental influences by in vitro platelet activation during blood analysis. OBJECTIVES: Protein isoforms of platelet-derived thrombospondin-1 (TSP-1) were investigated for their potential to identify in vitro platelet activation when monitoring in vivo processes. METHODS: TSP-1 was determined in plasma, serum or supernatant of purified platelets by ELISA and immunoblotting and was compared with standard markers of platelet activation. A collective of 20 healthy individuals and 30 cancer patients was analyzed. RESULTS: While in vitro platelet degranulation led to a selective increase in the 200-kDa full-length molecule, an in vivo process involving platelet activation such as wound healing resulted in the predominant rise of the 140-kDa TSP-1 protein. The physiological ratio of circulating TSP-1 variants was determined and a cut-off level at 1.0 was defined to identify plasma samples with artificial in vitro platelet activation exceeding the cut-off level. In contrast, cancer patients known to frequently exhibit increased in vivo activation of platelets presented with a significantly decreased ratio of TSP-1 variants as compared with healthy volunteers. CONCLUSIONS: In comparison to standard platelet markers, TSP-1 constitutes a sensitive and stable parameter suited to monitor in vitro platelet activation. The analysis of TSP-1 protein isoforms further offers a valuable tool to reliably discriminate between in vitro and in vivo effects, to exclude variability introduced during blood processing and improve clinical monitoring.