Both G protein-coupled and immunoreceptor tyrosine-based activation motif receptors mediate venous thrombosis in mice

Role of platelet count in a murine stasis model of deep vein thrombosis

Platelets are core components of thrombi but their effect on thrombus burden during deep vein thrombosis (DVT) has not been fully characterized. We examined the role of thrombopoietin-altered platelet count on thrombus burden in a murine stasis model of DVT. To modulate platelet count compared to baseline, CD1 mice were pretreated with thrombopoietin antisense oligonucleotide (THPO-ASO, 56% decrease), thrombopoietin mimetic (TPO-mimetic, 36% increase), or saline (within 1%). Thrombi and vein walls were examined on postoperative days (POD) 3 and 7. Thrombus weights on POD 3 were not different between treatment groups (p = .84). The mean thrombus weights on POD 7 were significantly increased in the TPO-mimetic cohort compared to the THPO-ASO (p = .005) and the saline (p = .012) cohorts. Histological grading at POD 3 revealed a significantly increased smooth muscle cell presence in the thrombi and CD31 positive channeling in the vein wall of the TPO-mimetic cohort compared to the saline and THPO-ASO cohorts (p < .05). No differences were observed in histology on POD 7. Thrombopoietin-induced increased platelet count increased thrombus weight on POD 7 indicating platelet count may regulate thrombus burden during early resolution of venous thrombi in this murine stasis model of DVT.

How Protein Depletion Balances Thrombosis and Bleeding Risk in the Context of Platelet's Activatory and Negative Signaling

Platelets are small cell fragments that play a crucial role in hemostasis, requiring fast response times and fine signaling pathway regulation. For this regulation, platelets require a balance between two pathway types: the activatory and negative signaling pathways. Activatory signaling mediators are positive responses that enhance stimuli initiated by a receptor in the platelet membrane. Negative signaling regulates and controls the responses downstream of the same receptors to roll back or even avoid spontaneous thrombotic events. Several blood-related pathologies can be observed when these processes are unregulated, such as massive bleeding in activatory signaling inhibition or thrombotic events for negative signaling inhibition. The study of each protein and metabolite in isolation does not help to understand the role of the protein or how it can be contrasted; however, understanding the balance between active and negative signaling could help develop effective therapies to prevent thrombotic events and bleeding disorders.

Role of Platelets and Their Interaction with Immune Cells in Venous Thromboembolism

Venous thromboembolism (VTE) represents a significant global health challenge, ranking as the third leading cause of cardiovascular-related mortality. VTE pervades diverse clinical specialties, posing substantial risks to patient well-being and imposing considerable economic strains on health care systems. While platelets have long been recognized as pivotal players in hemostasis, emerging evidence underscores their multifaceted immune functions and their capacity to engage in crosstalk with other immune cells, such as neutrophils, thereby fostering immune-related thrombosis. Notably, investigations have elucidated the pivotal role of platelets in the pathogenesis of VTE. This review provides a comprehensive overview of platelet physiology, encompassing their activation, secretion dynamics, and implications in VTE. Moreover, it delineates the impact of platelet interactions with various immune cells on the initiation and progression of VTE, explores the correlation between platelet-related laboratory markers and VTE, and elucidates the role of platelets in thrombosis regression.

Interactions between integrin α9β1 and VCAM-1 promote neutrophil hyperactivation and mediate poststroke DVT

ABSTRACT

Venous thromboembolic events are significant contributors to morbidity and mortality in patients with stroke. Neutrophils are among the first cells in the blood to respond to stroke and are known to promote deep vein thrombosis (DVT). Integrin α9 is a transmembrane glycoprotein highly expressed on neutrophils and stabilizes neutrophil adhesion to activated endothelium via vascular cell adhesion molecule 1 (VCAM-1). Nevertheless, the causative role of neutrophil integrin α9 in poststroke DVT remains unknown. Here, we found higher neutrophil integrin α9 and plasma VCAM-1 levels in humans and mice with stroke. Using mice with embolic stroke, we observed enhanced DVT severity in a novel model of poststroke DVT. Neutrophil-specific integrin α9-deficient mice (α9fl/flMrp8Cre+/-) exhibited a significant reduction in poststroke DVT severity along with decreased neutrophils and citrullinated histone H3 in thrombi. Unbiased transcriptomics indicated that α9/VCAM-1 interactions induced pathways related to neutrophil inflammation, exocytosis, NF-κB signaling, and chemotaxis. Mechanistic studies revealed that integrin α9/VCAM-1 interactions mediate neutrophil adhesion at the venous shear rate, promote neutrophil hyperactivation, increase phosphorylation of extracellular signal-regulated kinase, and induce endothelial cell apoptosis. Using pharmacogenomic profiling, virtual screening, and in vitro assays, we identified macitentan as a potent inhibitor of integrin α9/VCAM-1 interactions and neutrophil adhesion to activated endothelial cells. Macitentan reduced DVT severity in control mice with and without stroke, but not in α9fl/flMrp8Cre+/- mice, suggesting that macitentan improves DVT outcomes by inhibiting neutrophil integrin α9. Collectively, we uncovered a previously unrecognized and critical pathway involving the α9/VCAM-1 axis in neutrophil hyperactivation and DVT.

Venous thromboembolism: diagnostic advances and unaddressed challenges in management

PURPOSE OF REVIEW

This review summarizes recent advances in developing targeted diagnostics for venous thromboembolism (VTE) and unaddressed knowledge gaps in patient management. Without addressing these critical data needs, the morbidity in VTE patients will persist.

RECENT FINDINGS

Recent studies investigating plasma protein profiles in VTE patients have identified key diagnostic targets to address the currently unmet need for low-cost, confirmatory, point-of-care VTE diagnostics. These studies and a growing body of evidence from animal model studies have revealed the importance of inflammatory and vascular pathology in driving VTE, which are currently unaddressed targets for VTE therapy. To enhance the translation of preclinical animal studies, clinical quantification of thrombus burden and comparative component analyses between modeled VTE and clinical VTE are necessary.

SUMMARY

Lead candidates from protein profiling of VTE patients' plasma offer a promising outlook in developing low cost, confirmatory, point-of-care testing for VTE. Additionally, addressing the critical knowledge gap of quantitatively measuring clinical thrombi will allow for an array of benefits in VTE management and informing the translatability of experimental therapeutics.

Composition of thrombi in zebrafish: similarities and distinctions with mammals

BACKGROUND

Blood clots are primarily composed of red blood cells (RBCs), platelets/thrombocytes, and fibrin. Despite the similarities observed between mammals and zebrafish, the composition of fish thrombi is not as well known.

OBJECTIVES

To analyze the formation of zebrafish blood clots ex vivo and arterial and venous thrombi in vivo.

METHODS

Transgenic zebrafish lines and laser-mediated endothelial injury were used to determine the relative ratio of RBCs and thrombocytes in clots. Scanning electron and confocal microscopy provided high-resolution images of the structure of adult and larval clots. Adult and larval thrombocyte spreading on fibrinogen was evaluated ex vivo.

RESULTS

RBCs were present in arterial and venous thrombi, making up the majority of cells in both circulations. However, bloodless mutant fish demonstrated that fibrin clots can form in vivo in the absence of blood cells. Scanning electron and confocal microscopy showed that larval and adult zebrafish thrombi and mammalian thrombi look surprisingly similar externally and internally, even though the former have nucleated RBCs and thrombocytes. Although adult thrombocytes spread on fibrinogen, we found that larval cells do not fully activate without the addition of plasma from adult fish, suggesting a developmental deficiency of a plasma activating factor. Finally, mutants lacking αIIbβ3 demonstrated that this integrin mediates thrombocyte spreading on fibrinogen.

CONCLUSION

Our data showed strong conservation of arterial and venous and clot/thrombus formation across species, including developmental regulation of thrombocyte function. This correlation supports the possibility that mammals also do not absolutely require circulating cells to form fibrin clots in vivo.

Quantitative proteomics based bioactive proteins discovery and quality control of medicinal leeches

ETHNOPHARMACOLOGICAL RELEVANCE

Leech, a classical traditional Chinese medicine for promoting blood circulation and removing blood stasis, is mainly used in the clinical treatment of cardiovascular and cerebrovascular diseases. The discovery of activity proteins or peptides in the dead and dried medicinal leech is an important task with great challenges.

AIM OF THE STUDY

The aim of this study was to provide a basic proteome profile and help further discover active proteins and quality control for medicinal leeches, which would also provide insight into the research of animal medicines.

MATERIALS AND METHODS

Seventeen batches of dried medicinal leeches covering three species were collected from medicinal markets, which were authenticated by DNA barcoding. Then the proteome of different species leeches was profiled to reveal the significantly different proteins using label-free proteomics. The characteristic peptides were screened out based on biological pathways analysis, which were further absolutely quantified using the developed stable isotope-labeled based parallel reaction monitoring method.

RESULTS

Seventeen batches of leech materials were Whitmania pigra Whitman (WP), Whitmania laevis Whitman (WL) and Poecilobdella manillensis Lesson (PM), respectively. A total of 1,035 proteins (452 in WP, 425 in WL and 158 in PM) were identified. Among them, 90 overlapping proteins were mainly concentrated in diverse metabolic pathways and primarily localized in the cytoplasm and mitochondrial inner membrane, which mainly related to ATP binding, catalytic activity and structural molecular activity. In total of 51 uniquely expressed proteins (21 in WP, 23 in WL and 7 in PM), associated with multiple key signaling pathways, including Rap1, cGMP-PKG, PI3K-Akt, Wnt and HIF-1, etc., relevant to treating cardiovascular diseases, diabetes, cancer and even a variety of neurodegenerative diseases. Three proteins with potential bioactivities, including Neurohemerythrin, Hirudin and Eglin C, were selected as the quality makers and then quantified based on the characteristic peptides.

CONCLUSIONS

This work profiled the proteome of three species of leeches, and addressed potential active proteins of the medicinal leech, which would help to provide the potential molecular mechanisms involved in disease treatment. The proteomics-based approach developed in this work is not only useful for the discovery of proteins with potential bioactivities but also helpful for the bioactivity relevant quality control of animal medicines.

CD14 Blockade Does Not Improve Outcomes of Deep Vein Thrombosis Following Inferior Vena Cava Stenosis in Mice

Background

Neutrophil-mediated persistent inflammation and neutrophil extracellular trap formation (NETosis) promote deep vein thrombosis (DVT). CD14, a co-receptor for toll-like receptor 4 (TLR4), is actively synthesized by neutrophils, and the CD14/TLR4 signaling pathway has been implicated in proinflammatory cytokine overproduction and several aspects of thromboinflammation. The role of CD14 in the pathogenesis of DVT remains unclear.

Objective

To determine whether CD14 blockade improves DVT outcomes.

Methods

Bulk RNA sequencing and proteomic analyses were performed using isolated neutrophils following inferior vena cava (IVC) stenosis in mice. DVT outcomes (IVC thrombus weight and length, thrombosis incidence, neutrophil recruitment, and NETosis) were evaluated following IVC stenosis in mice treated with a specific anti-CD14 antibody, 4C1, or control antibody.

Results

Mice with IVC stenosis exhibited increased plasma levels of granulocyte colony-stimulating factor (G-CSF) along with a higher neutrophil-to-lymphocyte ratio and increased plasma levels of cell-free DNA, elastase, and myeloperoxidase. Quantitative measurement of total neutrophil mRNA and protein expression revealed distinct profiles in mice with IVC stenosis compared to mice with sham surgery. Neutrophils of mice with IVC stenosis exhibited increased inflammatory transcriptional and proteomic responses, along with increased expression of CD14. Treatment with a specific anti-CD14 antibody, 4C1, did not result in any significant changes in the IVC thrombus weight, thrombosis incidence, or neutrophil recruitment to the thrombus.

Conclusion

The results of the current study are important for understanding the role of CD14 in the regulation of DVT and suggest that CD14 lacks an essential role in the pathogenesis of DVT following IVC stenosis.

Mice expressing nonpolymerizable fibrinogen have reduced arterial and venous thrombosis with preserved hemostasis

ABSTRACT

Elevated circulating fibrinogen levels correlate with increased risk for both cardiovascular and venous thromboembolic diseases. In vitro studies show that formation of a highly dense fibrin matrix is a major determinant of clot structure and stability. Here, we analyzed the impact of nonpolymerizable fibrinogen on arterial and venous thrombosis as well as hemostasis in vivo using FgaEK mice that express normal levels of a fibrinogen that cannot be cleaved by thrombin. In a model of carotid artery thrombosis, FgaWT/EK and FgaEK/EK mice were protected from occlusion with 4% ferric chloride (FeCl3) challenges compared with wild-type (FgaWT/WT) mice, but this protection was lost, with injuries driven by higher concentrations of FeCl3. In contrast, fibrinogen-deficient (Fga-/-) mice showed no evidence of occlusion, even with high-concentration FeCl3 challenge. Fibrinogen-dependent platelet aggregation and intraplatelet fibrinogen content were similar in FgaWT/WT, FgaWT/EK, and FgaEK/EK mice, consistent with preserved fibrinogen-platelet interactions that support arterial thrombosis with severe challenge. In an inferior vena cava stasis model of venous thrombosis, FgaEK/EK mice had near complete protection from thrombus formation. FgaWT/EK mice also displayed reduced thrombus incidence and a significant reduction in thrombus mass relative to FgaWT/WT mice after inferior vena cava stasis, suggesting that partial expression of nonpolymerizable fibrinogen was sufficient for conferring protection. Notably, FgaWT/EK and FgaEK/EK mice had preserved hemostasis in multiple models as well as normal wound healing times after skin incision, unlike Fga-/- mice that displayed significant bleeding and delayed healing. These findings indicate that a nonpolymerizable fibrinogen variant can significantly suppress occlusive thrombosis while preserving hemostatic potential in vivo.

Intravital Imaging of Thrombosis Models in Mice

Intravital microscopy is a powerful tool to study thrombosis in real time. The kinetics of thrombus formation and progression in vivo is studied after inflicting damage to the endothelium through mechanical, chemical, or laser injury. Mouse models of atherosclerosis are also used to induce thrombus formation. Vessels of different sizes and from different vascular beds such as carotid artery or vena cava, mesenteric or cremaster arterioles, can be targeted. Using fluorescent dyes, antibodies, or reporter mouse strains allows to visualize key cells and factors mediating the thrombotic processes. Here, we review the latest literature on using intravital microscopy to study thrombosis as well as thromboinflammation following transient middle cerebral artery occlusion, infection-induced immunothrombosis, and liver ischemia reperfusion.

Loss of P2Y1 receptor desensitization does not impact hemostasis or thrombosis despite increased platelet reactivity in vitro

BACKGROUND

The hemostatic plug formation at sites of vascular injury is strongly dependent on rapid platelet activation and integrin-mediated adhesion and aggregation. However, to prevent thrombotic complications, platelet aggregate formation must be a self-limiting process. The second-wave mediator adenosine diphosphate (ADP) activates platelets via Gq-coupled P2Y1 and Gi-coupled P2Y12 receptors. After ADP exposure, the P2Y1 receptor undergoes rapid phosphorylation-induced desensitization, a negative feedback mechanism believed to be critical for limiting thrombus growth.

OBJECTIVE

The objective of this study was to examine the role of rapid P2Y1 receptor desensitization on platelet function and thrombus formation in vivo.

METHODS

We analyzed a novel knock-in mouse strain expressing a P2Y1 receptor variant that cannot be phosphorylated beyond residue 340 (P2Y1340-0P), thereby preventing the desensitization of the receptor.

RESULTS

P2Y1340-0P mice followed a Mendelian inheritance pattern, and peripheral platelet counts were comparable between P2Y1340-0P/340-0P and control mice. In vitro, P2Y1340-0P/340-0P platelets were hyperreactive to ADP, showed a robust activation response to the P2Y1 receptor-selective agonist, MRS2365, and did not desensitize in response to repeated ADP challenge. We observed increased calcium mobilization, protein kinase C substrate phosphorylation, alpha granule release, activation of the small GTPase Rap1, and integrin inside-out activation/aggregation. This hyperreactivity, however, did not lead to increased platelet adhesion or excessive plug formation under physiological shear conditions.

CONCLUSION

Our studies demonstrate that receptor phosphorylation at the C-terminus is critical for P2Y1 receptor desensitization in platelets and that impaired desensitization leads to increased P2Y1 receptor signaling in vitro. Surprisingly, desensitization of the P2Y1 receptor is not required for limiting platelet adhesion/aggregation at sites of vascular injury, likely because ADP is degraded quickly or washed away in the bloodstream.

[Recent research on platelet-leukocyte aggregates and their role in the pathogenesis of Kawasaki disease]

Activated platelets may interact with various types of leukocytes such as monocytes, neutrophils, dendritic cells, and lymphocytes, trigger intercellular signal transduction, and thus lead to thrombosis and synthesis of massive inflammatory mediators. Elevated levels of circulating platelet-leukocyte aggregates have been found in patients with thrombotic or inflammatory diseases. This article reviews the latest research on the formation, function, and detection methods of platelet-leukocyte aggregates and their role in the onset of Kawasaki disease, so as to provide new ideas for studying the pathogenesis of Kawasaki disease.

Decreased Platelet Reactivity and Function in a Mouse Model of Human Pancreatic Cancer

Cancer patients have increased thrombosis and bleeding compared with the general population. Cancer is associated with activation of both platelets and coagulation. Mouse models have been used to study the dysregulation of platelets and coagulation in cancer. We established a mouse model of pancreatic cancer in which tissue factor-expressing human pancreatic tumors (BxPC-3) are grown in nude mice. Tumor-bearing mice have an activated coagulation system and increased venous thrombosis compared to control mice. We also showed that tumor-derived, tissue factor-positive extracellular vesicles activated platelets ex vivo and in vivo. In this study, we determined the effect of tumors on a platelet-dependent arterial thrombosis model. Unexpectedly, we observed significantly reduced carotid artery thrombosis in tumor-bearing mice compared to controls. In addition, we observed significantly increased tail bleeding in tumor-bearing mice compared to controls. These results suggested that the presence of the tumor affected platelets. Indeed, tumor-bearing mice exhibited a significant decrease in platelet count and an increase in mean platelet volume and percentage of reticulated platelets, findings that are consistent with increased platelet turnover. Levels of the platelet activation marker platelet factor 4 were also increased in tumor-bearing mice. We also observed decreased platelet receptor expression in tumor-bearing mice and reduced levels of active αIIb/β3 integrin in response to PAR4 agonist peptide and convulxin in platelets from tumor-bearing mice compared with platelets from control mice. In summary, our study suggests that in tumor-bearing mice there is chronic platelet activation, leading to thrombocytopenia, decreased receptor expression, and impaired platelet adhesive function.

Predictive factors on postoperative venous thromboembolism after minimally invasive colorectal cancer surgery: a retrospective observational study

BACKGROUND

Venous thromboembolism (VTE) is a serious and preventable postoperative complication. However, the predictive significance of perioperative biochemical parameters for VTE after minimally invasive colorectal cancer surgery remains unclear.

METHODS

A total of 149 patients undergoing minimally invasive colorectal cancer surgery were collected between October 2021 and October 2022. Biochemical parameters related to preoperative and postoperative day 1, day 3, and day 5 were collected, including D-Dimer, mean platelet volume (MPV), and maximum amplitude (MA) of thromboelastography (TEG). Receiver operating characteristic (ROC) curves were used to explore the predictive powers of meaningful biochemical parameters for postoperative VTE, and calibration curves were used to assess predictive accuracy.

RESULTS

The overall cumulative incidence of VTE was 8.1% (12/149). The preoperative and postoperative day 3 D-Dimer, postoperative day 3, and day 5 MPV, and postoperative day 1, day 3, and day 5 TEG-MA was significantly higher in the VTE group than in the non-VTE group (P < 0.05). The results of both the ROC curve and the calibration curve indicated that these meaningful D-Dimer, MPV, and TEG-MA had moderate discrimination and consistency for postoperative VTE.

CONCLUSIONS

D-Dimer, MPV, and TEG-MA may predict postoperative VTE in patients undergoing minimally invasive surgery for colorectal cancer at specific times in the perioperative period.

Immunothrombosis and the Role of Platelets in Venous Thromboembolic Diseases

Venous thromboembolism (VTE) is the third leading cardiovascular cause of death and is conventionally treated with anticoagulants that directly antagonize coagulation. However, recent data have demonstrated that also platelets play a crucial role in VTE pathophysiology. In the current review, we outline how platelets are involved during all stages of experimental venous thrombosis. Platelets mediate initiation of the disease by attaching to the vessel wall upon which they mediate leukocyte recruitment. This process is referred to as immunothrombosis, and within this novel concept inflammatory cells such as leukocytes and platelets directly drive the progression of VTE. In addition to their involvement in immunothrombosis, activated platelets can directly drive venous thrombosis by supporting coagulation and secreting procoagulant factors. Furthermore, fibrinolysis and vessel resolution are (partly) mediated by platelets. Finally, we summarize how conventional antiplatelet therapy can prevent experimental venous thrombosis and impacts (recurrent) VTE in humans.

Fibrinogen and Factor XIII in Venous Thrombosis and Thrombus Stability

As the third most common vascular disease, venous thromboembolism is associated with significant mortality and morbidity. Pathogenesis underlying venous thrombosis is still not fully understood. Accumulating data suggest fibrin network structure and factor XIII-mediated crosslinking are major determinants of venous thrombus mass, composition, and stability. Understanding the cellular and molecular mechanisms mediating fibrin(ogen) and factor XIII production and function and their ability to influence venous thrombogenesis and resolution may inspire new anticoagulant strategies that target these proteins to reduce or prevent venous thrombosis in certain at-risk patients. This article summarizes fibrinogen and factor XIII biology and current knowledge of their function during venous thromboembolism.