Journal of Thrombosis and Haemostasis

Objective: Rare STAB2 loss-of-function variants emerged in population studies as being associated with elevated venous thromboembolism (VTE) risk. STAB2 encodes the cell-surface scavenger receptor stabilin-2, and reduced stabilin-2 function might increase VTE risk via elevated plasma levels of its ligands, including von Willebrand factor (VWF) and coagulation factor VIII (FVIII). Approach and Results: A 13-year-old patient with dependency on parenteral nutrition had experienced episodes of central venous catheter-related thrombosis, including the complete thrombotic occlusion of the deep pelvic veins, and pulmonary embolism. Exome sequencing for increased VTE risk identified a homozygous STAB2 splice-site variant and its effect on splicing was characterized in fibroblast-derived RNA and in a minigene splicing system. Plasma VWF, FVIII, and fibrinogen and serum hyaluronic acid (HA) levels were determined. Immunohistochemistry was performed on liver biopsy tissue. The STAB2 splice-site variant caused aberrant STAB2 mRNA splicing. The patient's healthy mother and one healthy sibling were also homozygous for the STAB2 splice-site variant but had no history of VTE. Plasma FVIII levels and VWF activity were elevated in all three, and VWF antigen was elevated in two homozygous individuals. Strikingly, approximately 1000-fold elevated HA levels were observed in all three homozygous individuals. Stabilin-2 immunohistochemistry on a liver biopsy from the proband's mother revealed no detectable signal, whereas control human liver showed strong labelling of liver sinusoidal endothelial cells. The STAB2 splice-site variant thus results in loss of detectable stabilin-2 protein. Conclusion: To current knowledge, this is the first family-based report of stabilin-2 deficiency with markedly elevated circulating HA, VWF, and FVIII levels in humans. These findings support impaired stabilin-2-dependent ligand clearance as a thrombosis susceptibility state with incomplete penetrance. The data are consistent with a significant role for stabilin-2 in circulating HA clearance in humans, but do not establish elevated HA itself as a cause of VTE.

Background: Growing evidence suggests persistent thrombotic endothelial damage (together with elevated (fibrinaloid) microclot complexes (FMCs)) and immune dysfunction in the pathophysiology of Long COVID. Recently we proposed that there are different FMC phenotypes. Here we seek to determine the nature of these FMCs and aggregates in platelet-poor plasma (PPP) by using different markers, as well as thromboelastography (TEG) to assess for hypercoagulability of samples. Material and Methods: Whole-blood and PPP from control (n=19) and Long COVID (n=20) participants were assessed by thromboelastography. FMCs were quantified by imaging flow cytometry of Thioflavin-T (ThT)-stained PPP, 10X diluted PPP, and resuspended PPP pellets. The resuspended pellets were separately stained with a CD62P-PE antibody or Hoechst 33342 to label aggregates and FMCs containing amyloid, platelet, and nuclear material. ThT and CellMask Red were co-stained for confocal microscopy. ThT and myeloperoxidase (MPO), and ThT, Congo Red, and Hoechst were co-stained for fluorescence and polarized microscopy. Whole-blood smears were imaged by scanning electron microscopy (SEM). Results: Long COVID samples showed pronounced hypercoagulability in both whole blood and PPP, with shortened R, K and TMRTG and elevated alpha-angle and MRTG, but unchanged MA and TTG, indicating altered clotting kinetics. Persistence of this phenotype in PPP implicates soluble plasma constituents. ThT-positive FMCs were significantly increased in Long COVID across undiluted, diluted, and resuspended pellet samples; counts were processing-sensitive and a substantial ThT-positive population remained in the supernatant after centrifugation, indicating heterogeneity in density. Across probes, leukocyte material was the most abundant, then platelet material, and ThT-positive FMCs were the least abundant, with the three populations exhibiting unique morphology and occupying distinct size domains. Platelet-derived material was significantly elevated in Long COVID, whereas nuclear material was not. Co-stained samples subject to confocal, fluorescence, and polarized microscopy imaging showed that FMCs are heterogeneous, including events positive for ThT, CellMask, Hoechst, MPO, and Congo Red, and also a distinct subset of membrane-free, ThT-only events. Conclusion: In this Long COVID cohort, plasma is characterised by hypercoagulability and an increased burden of ThT-positive FMCs that are numerically minor relative to, and morphologically distinct from, aggregates and amyloidogenic FMCs marked with platelet- and leukocyte-derived material. The increased burden of platelet debris in PPP is likely indicative of persistent platelet activity. The existence of membrane-free, ThT-only FMCs, in addition to FMCs associated with cellular material, confirms an amyloid-dominated FMC population. Furthermore, positive Congo Red signal further confirms the amyloid nature of FMCs in PPP.

ADAMTS13 (a multidomain metalloproteinase) cleaves von Willebrand factor (VWF), thereby preventing the accumulation of ultra-large VWF multimers that promote platelet-rich thrombus formation. Severe ADAMTS13 deficiency causes thrombotic thrombocytopenic purpura (TTP). In immune-mediated TTP (iTTP), anti-ADAMTS13 autoantibodies inhibit ADAMTS13 activity, often by targeting non-catalytic domains that mediate substrate recognition. We developed ADAMTS13 mimetics by fusing the ADAMTS13 metalloproteinase domain to anti-human VWF A2 domain antibodies, aiming to replace native substrate-recognition domains with antibody-mediated substrate targeting while removing major autoantibody-targeted ADAMTS13 domains. The resulting mimetics bound to the recombinant VWF A2 domain and showed proteolytic activity toward both the recombinant VWF A2 domain and FRETS-VWF73 substrate. Kinetic analysis showed that the mimetics had not only lower kcat values than ADAMTS13 but also lower Km values, thereby maintaining overall catalytic efficiency. Importantly, ADAMTS13 mimetics retained VWF A2-cleaving activity in the presence of a spacer domain-directed anti-ADAMTS13 autoantibody both in vitro and in vivo. In an iTTP mouse model, ADAMTS13 mimetics prevented recombinant VWF-induced thrombocytopenia, whereas the parental anti-VWF A2 domain antibody did not. Platelet-preserving activity was also observed in ADAMTS13-deficient mice. In further analyses, some mimetics showed reduced binding to a conformationally restricted VWF A2 domain, resulting in reduced cleavage activity. Antibody binding correlated with platelet recovery in the iTTP mouse model, suggesting that epitope accessibility and antibody-mediated positioning contribute to in vivo activity. These findings demonstrate that antibody-mediated substrate targeting can reconstitute the VWF-cleaving activity of the ADAMTS13 metalloproteinase domain and suggest that ADAMTS13 mimetics represent a potential therapeutic approach for iTTP.

Syk is a non-receptor type protein-tyrosine kinase (PTK), which is associated with platelets surface receptors, glycoprotein VI (GPVI) and C-type lectin-like receptor II-type (CLEC-2). Syk is also expressed in most hematopoietic lineage cells and other cells, such as fibroblasts and neuronal cells. Syk has two tandem SH2 motifs and a C-terminal kinase domain, which are interrupted by interdomains A and B containing multiple tyrosine residues playing a regulatory role upon phosphorylation. This study aims to evaluate the role of Y130 in Syk signaling in platelets. Syk(Y130F) knock-in (KI) mice we generated using the CRISPR-Cas9 technique represent the first in-vivo model harboring this mutation. Using this system, we compared the platelet signaling and responses in wild-type (WT) and Syk(Y130F) littermates. Platelets from homozygous Syk(Y130F) mice showed a decrease in functional responses after activation with CRP, a GPVI agonist, and CLEC-2 crosslinking compared to WT littermates with no significant differences in responses to PAR-4 or purinergic receptor agonists. Key signaling events triggered via both GPVI and CLEC-2, including phosphorylation LAT and PLC-2, were also reduced in Syk(Y130F) platelets at low agonist concentrations. Consistent with these findings, the time to occlusion in the FeCl3 injury model and bleeding time in the tail bleeding assay were significantly enhanced in Syk(Y130F) mice compared to WT littermates. Thus, phosphorylation of Syk Y130 enhances GPVI- and CLEC-2-mediated signaling and functional responses in platelets affecting thrombosis and hemostasis.

Increased platelet microparticle (PMP) levels in individuals with risk factors for cardiovascular disease correlate with clinical outcomes in these patient groups. PMPs promote thrombosis through enhancing platelet aggregation and binding to the sub-endothelial matrix following vascular injury. Thus, PMPs behave as soluble ligands and adhesive substrates for platelets, and may drive cardiovascular disease progression. Nitric oxide (NO) is released continually from the endothelium as a potent regulator of platelet activation that is crucial to the balance between haemostasis and thrombosis. However, it is unknown if NO regulates PMP-induced platelet activation. In this study we isolated platelets and PMPs from whole blood and measured their interactions in adhesion assays and by flow cytometry. Platelet activation was analysed by ELISA for ADP and thromboxane-B2; both secondary platelet agonists released by activated platelets which enhance thrombosis. The affinity upregulation of the principal platelet integrin receptor responsible for platelet aggregation, integrin IIb{beta}3, was measured using the antibody PAC-1. Our data show that PMP induced platelet adhesion was associated with, and partially dependent upon, platelet ADP release, TxA2 production and IIb{beta}3 upregulation. Crucially, NO dose-dependently reduced these events through cGMP dependent signalling. This is the first report that NO signalling can regulate PMP induced platelet activation and may open an avenue of exploration for clinically targeting PMP driven cardiovascular disease processes.

BACKGROUND: The transport and storage conditions of thawed plasma are not strictly regulated by the FDA and applying red blood cell transport standard of 1-10 degrees Celcius to recently thawed plasma often results in high discard rates. This study evaluated the extended 120-hour (5-day) coagulation factor stability and sterility of thawed plasma frozen within 24 hours (PF24) following a 6-hour transport cooler simulation. STUDY DESIGN AND METHODS: Fourteen PF24 units (8 group O, 6 group B) were thawed at 30-37 degrees Celcius and assigned as control (n=7, direct 1-6 degrees Celcius refrigeration) or experiment (n=7) units. Experiment units were held at room temperature for 30 minutes, stored in validated transport coolers for 6 hours, and then transferred to 1-6 degrees Celcius refrigeration. Measurements of temperature, prothrombin time (PT), Factor V (FV) activity, and Factor VIII (FVIII) activity were conducted at 0-, 6-, 24-, and 120-hour post-thaw. Sterility testing was performed at 0-hour and 120-hour using automated aerobic and anaerobic blood cultures. RESULTS: No statistically significant differences were observed between control and experiment units at 120-hour for mean PT (15.09 vs. 15.16 seconds, p = .44), FV activity (81.14 vs. 74.57%, p = .23), or FVIII activity (61.86 vs. 53.00%, p = .22). Delta analysis (120h-0h) confirmed equivalent factor decay rates between groups. All bacterial cultures showed no growth at 120-hour. CONCLUSION: A 6-hour cooler time of thawed PF24 does not accelerate coagulation factor degradation or compromise sterility over an extended 5-day shelf life. These findings validate flexible inventory return policies, allowing blood banks to reduce product waste.

Cytosolic phospholipase A2 (cPLA2), encoded by PLA2G4A plays a crucial role in platelet activation through thromboxane A2 biosynthesis. Defects in this pathway can lead to bleeding disorders; however, the precise role of cPLA2 in Glanzmann thrombasthenia (GT) or GT-like syndromes remains poorly understood. The current study emerged from a fortuitous discovery of novel PLA2G4A variants, p.Asp455Val (D455V) and p.Glu119Lys (E119K), among 3 GT patients from two unrelated families in south India. We envisaged a hypothesis to identify a hitherto unknown role of cPLA2 that could be attributed to GT-like bleeding symptoms in these patients. An extensive computational workflow, including variant classification, conservation analysis, stability prediction, molecular docking, molecular dynamics simulations, principal component analysis, and binding free energy (MMPBSA) calculations, were employed to assess mutation-induced alterations in the cPLA2 protein. The current findings depicted that both variants affected conformational dynamics, ligand recognition patterns, and local interaction networks, without causing any drastic global structural destabilization. In particular, the D455V partially disrupted the catalytic domain, potentially reducing substrate (PAPC) stabilization and hampering interactions with catalytic products. Likewise, the E119K variant partially affected the C2 domain, potentially altered electrostatic interactions and enhanced regional flexibility, which may compromise product (AA) stabilization. Further analyses revealed mutation-induced changes in collective motions, protein-ligand interactions, solvent accessibility, and secondary structural elements. Overall, our findings promote the hypothesis that both E119K and D455V variants may partially alter phospholipid-associated interactions, and cPLA2-mediated downstream signaling. Moreover, this study underscores cPLA2 as a potential modifier of platelet function and bleeding severity.

Background: Stroke incidence is declining in older adults but rising in younger populations. Circulating plasma proteins are promising biomarkers of vascular disease, yet their causal role in early-onset stroke (EOS) remains unclear. We used proteome-wide Mendelian randomization (MR) to identify proteins causally associated with EOS and its subtypes. Methods: We conducted two-sample MR using protein quantitative trait loci from 54,219 UK Biobank participants and summary-level association results from up to 11,114 EOS cases (onset <60 years) and 435,540 controls in the Early-Onset Stroke Consortium. Variants within {+/-}200 kb of protein-coding genes associated with protein levels (p [&le;]1x10-5) were clumped for linkage disequilibrium and used as instrumental variables. Causal effects were estimated using inverse-variance weighted MR, with sensitivity analyses to assess robustness. Stroke subtypes were defined using TOAST criteria. Results: Among 1,041 proteins tested, 11 were significantly associated with EOS after multiple testing correction. Genetically predicted higher levels of proteins encoded by ABO, F11, F7, MLN, BTD, MEP1B, and VAMP8 increased EOS risk (ORs ~1.05-1.32 per SD), whereas higher levels of proteins encoded by FN1, GRK5, EHBP1, and FCN2 were protective. Eight additional proteins showed subtype-specific associations. Key signals converged on coagulation and thromboinflammatory pathways, particularly ABO, F11, and F7, with consistent evidence across analyses. Cross-trait analyses demonstrated overlap with late-onset stroke, venous thromboembolism, and cardiometabolic risk factors, supporting shared biological mechanisms. Drug-target mapping highlighted Factor XI as a leading therapeutic target, supported by existing inhibitors (e.g., abelacimab, milvexian). Conclusions: This large-scale proteome-wide MR study identified multiple plasma proteins with likely causal roles in EOS, implicating coagulation, platelet activation, extracellular matrix remodeling, and immune pathways in disease etiology. These findings highlight biologically plausible biomarkers and prioritize druggable targets, particularly Factor XI, for prevention of EOS and demonstrate the value of proteogenomic approaches for uncovering disease mechanisms and informing precision prevention strategies.

Thrombostasin is a cysteine-free anticoagulant protein produced by the horn fly Haematobia irritans, featuring an unusual stretch of seven consecutive aspartate residues within the polypeptide sequence. Here, we report the first chemical synthesis of native thrombostasin and a hepta-glutamate analogue, together with assessment of their thrombin inhibitory and anticoagulant activity.

Type 2B von Willebrand disease (VWD) is characterized by missense variants in exon 28 of the von Willebrand factor (VWF) gene that encodes the VWF-A1 domain. These missense mutations result in single amino acid residue substitutions that cause activation of VWF-A1 and promote spontaneous interaction with platelet GPIba;. Importantly, enhanced VWF clearance has been shown to play a key pathogenic role in >90% patients with Type 2B VWD. Although this VWF clearance occurs via mechanisms that are independent of VWF-platelet complex formation, the biological mechanisms responsible for the increased clearance of type 2B VWD variants remain poorly understood. In this study, we investigated a series of different type 2B amino acid substitutions within the VWF-A1 domain (R1306W, R1308C, W1313C and R1379L). We demonstrate that these variants all exhibit significantly increased macrophage binding. In part, the enhanced macrophage interactions are mediated via increased binding of type 2B VWD variants to LRP1 extracellular cluster II and IV. Our findings further demonstrate that the K1405-K1408 lysine cluster in the VWF-A1 domain plays a key role in enabling enhanced LRP1 interactions for type 2B VWD variants. In addition, we show that type 2B VWF variants demonstrate significantly enhanced interaction with the macrophage MGL receptor. Finally, and importantly from a clinical perspective, we demonstrate that the increase in macrophage binding for type 2B variants is significantly attenuated in the presence of BT200. Collectively, our findings have direct translational relevance with respect to the clinical heterogeneity and treatment of type 2B VWD.

Syndecans are transmembrane proteoglycans that regulate angiogenesis through both their glycosaminoglycan chains and core proteins. While roles for all four mammalian syndecans in new blood vessel formation are well established, it has more recently emerged that their extracellular core proteins contain discrete bioactive regulatory sequences capable of influencing cellular processes, including angiogenesis. We previously demonstrated that the syndecan-3 (SDC3) ectodomain possesses anti-angiogenic activity independent of its heparan sulphate chains. Here, we identified and characterised a novel anti-angiogenic sequence within the SDC3 ectodomain. Using recombinant truncation mutants, endothelial migration assays and peptide mapping, we localised activity to a discrete region of the extracellular domain and subsequently defined a conserved minimal nine amino acid peptide, QM111, that retained full biological activity. QM111 inhibited endothelial cell migration and angiogenic sprouting in both rat aortic ring and mouse choroidal explant models. Intrinsic disorder analysis revealed that QM111 resides within a region of comparatively reduced disorder, consistent with other syndecan regulatory sequences. This supports the concept that syndecan ectodomains contain conserved functional modules embedded within intrinsically disordered extracellular domains. QM111 did not induce inflammatory chemokine production, exhibited no detectable cytotoxicity, and retained substantial stability in human serum and vitreous humour. Finally, QM111 displayed anti-angiogenic activity comparable to the previously described syndecan-2-derived peptide QM107, with combination treatment producing more robust inhibition of angiogenesis. These findings identify QM111 as a novel endogenous anti-angiogenic peptide and support the concept that syndecan ectodomains are reservoirs of biologically active regulatory sequences with therapeutic potential. The work further establishes syndecan-derived peptides as a promising platform for the development of next-generation anti-angiogenic therapies.

Snake venom metalloproteinases (SVMPs) are major drivers of pathology following viper envenomation and represent important targets for the development of next-generation recombinant antivenoms. PIII SVMPs are among the most potent haemorrhagic toxins and contain disintegrin-like (Dis) and cysteine-rich (C-rich) accessory domains. Despite their biomedical importance, the mechanistic roles of these accessory domains in substrate recognition and catalysis remain poorly understood. We produced recombinant full-length and domain-deletion variants of two functionally distinct PIII SVMPs: the broadly proteolytic, cytotoxic cPIII and the highly specific prothrombin activator Ecarin. Proteins were expressed as latent zymogens in insect cells, auto-activated by Zn2+, and analysed using enzymatic, blood clotting, and cell-based assays. Progressive removal of the C-rich and Dis domains reduced zymogen auto-activation and markedly diminished catalytic activity in both toxins. In cPIII, domain deletion caused a stepwise loss of proteolytic and cytotoxic activity without altering substrate preference. In Ecarin, removal of the accessory domains strongly impaired prothrombin activation, and thus plasma clotting, demonstrating a critical role in substrate recognition. Conversely, deletion of the C-rich domain increased fibrinogenolytic activity, revealing a substrate-dependent gatekeeping function. Deglycosylation showed that N-linked glycans modulate SVMP activity in a construct-dependent manner. Recombinant Ecarin closely recapitulated the biochemical properties of the native venom-derived toxin. Our data support a model in which PIII SVMP accessory domains enhance substrate positioning and catalytic efficiency while selectively restricting access to non-cognate substrates. These findings establish accessory-domain-mediated substrate recognition as a key determinant of SVMP function, informing rational antivenom design.

Background aimsThe development of next-generation therapies for sickle cell disease (SCD) and beta thalassemia (beta thal), including fetal globin-inducing small molecules and gene therapy approaches, depends on patient-derived CD34+ hematopoietic stem and progenitor cells (HSPCs) for discovery and preclinical validation, but commercial vendors stock only healthy donor material and disease-specific banks hold limited inventories. Recent US Food and Drug Administration and National Institutes of Health guidance favoring human cell-based methods over animal testing underscores the value of authentic patient cells. Methods: Over 14 months we recovered, purified, and biobanked CD34+ HSPCs from clinical apheresis product waste and mobilized peripheral blood (PB) otherwise discarded after clinical procedures, using immunomagnetic selection adapted for hemoglobinopathy specimens; a microfluidic technology was evaluated separately. We quantified yield and purity for bead-selected material and cell number and viability for the microfluidic pilot; engraftment was tested in NBSGW mice. Results: Immunomagnetic selection recovered a median of 4.71 x 106 CD34+ cells from just 1 to 2 mL of apheresis product waste, comparable to the 6.0 x 106 cells from a 10 to 40 fold larger volume of PB waste, with similar purity across sources and diagnoses. Because apheresis product waste is far more concentrated, it reaches equivalent yields without the density-gradient steps required for PB waste, approximately halving processing time. Recovered cells engrafted NBSGW mice, confirming preserved repopulating capacity. The microfluidic pilot (two patients, 11 specimens) recovered 2.17 x 106 CD34+ cells per specimen at greater than 90% viability and purity. Conclusions: A center with existing apheresis infrastructure can reproducibly recover, bank, and distribute research-grade patient CD34+ HSPCs, addressing a recognized gap in the hemoglobinopathy pipeline. HighlightsO_LIClinical apheresis waste is used to generate a single-center biobank of high-quality, research-grade CD34+ HSPCs from patients with sickle cell disease and beta-thalassemia. C_LIO_LIConcentrated apheresis waste matches large-volume PB waste in CD34+ yield and purity. C_LIO_LIMicrofluidic enrichment recovers CD34+ cells at >90% viability and purity across 2 patients. C_LIO_LIRecovered CD34+ HSPCs engraft mice and form erythroid cells, preserving function. C_LI

The long-standing ambiguity surrounding whether platelets are cells or particles has hindered a unified understanding of their biology. In this study, we characterized the morphology of platelet-like particles (PLPs) using nanoparticle tracking analysis, transmission electron microscopy, and immunofluorescence. Notably, we observed that platelets can be endocytosed by living cells. We also indicate that platelets express the canonical extracellular vesicles (EVs) markers CD9, CD63, CD81, and TSG101. Our results demonstrate that platelets share six key similarities with EVs--in size, morphology, surface markers, function, biogenesis, and mode of action--leading us to propose a novel classification. Our findings suggest that platelets fulfill the current minimal criteria for EVs, raising the possibility that they could be conceptually viewed as a specialized EVs subset rather than conventional blood cells. Adopting this EVs-centric perspective could broaden the current conceptual framework for EVs and offer an alternative lens for interpreting platelet functions, which may in turn help guide future translational research and clinical exploration.

BackgroundNeutrophil extracellular traps (NETs) contribute to immunothrombosis and arterial thrombosis. Mechanisms underlying myocardial infarction after SARS-CoV-2 vaccination remain poorly understood. ObjectivesTo investigate histopathologic and immunothrombotic features of coronary thrombi in patients with ST-elevation myocardial infarction (STEMI) after SARS-CoV-2 vaccination. MethodsWe performed a retrospective matched cohort study including patients with STEMI undergoing primary percutaneous coronary intervention between January 2021 and March 2023. Coronary thrombi obtained by aspiration were analyzed by histopathology, immunohistochemistry, and confocal microscopy for NET detection. Vaccinated and unvaccinated patients were matched by age and sex. Associations between vaccination status and thrombus characteristics were assessed after adjustment for SARS-CoV-2 serologic status. ResultsAmong 44 matched patients (23 vaccinated and 21 unvaccinated), NETs were identified in 14 vaccinated patients (61%) and 5 unvaccinated patients (24%; P = .01). Vaccination was associated with increased odds of NET-positive thrombi after adjustment for SARS-CoV-2 serology (odds ratio, 5.1; 95% CI, 1.36-19.45; P = .02). No associations were observed between vaccination and polymorphonuclear cell density, fibrin deposits, plaque fragments, or anti-platelet factor 4 staining. Among patients vaccinated within 100 days before STEMI, NET-positive thrombi were associated with shorter intervals between vaccination and myocardial infarction (median [IQR], 25 [11-64] vs 57 [40-84] days; P = .02). ConclusionsSARS-CoV-2 vaccination was associated with increased NET presence in coronary thrombi from patients with STEMI, suggesting a potential NET-mediated immunothrombotic mechanism independent of classical vaccine-induced immune thrombotic thrombocytopenia.

Background: Venous thromboembolism (VTE), which encompasses deep vein thrombosis (DVT) and pulmonary embolism (PE), is a frequent disease associated with thrombus formation and vein wall remodeling. Hence, fibrosis might result from endothelial-to-mesenchymal transition (EndMT), characterized by the loss of endothelial markers and the acquisition of mesenchymal markers. In chronic thromboembolic pulmonary hypertension, transforming growth factor (TGF{beta}), the most potent inducer of EndMT, impairs thrombus resolution. However, the molecular mechanisms implicated in TGF[beta] signaling in the context of VTE are unknown. We hypothesized that epigenetic processes regulate the TGF{beta} signaling pathway in endothelial cells promoting EndMT and vascular fibrosis. Aims: To determine if the histone deacetylase 6 (HDAC6) regulates the TGF{beta} signaling pathway in endothelial cells promoting EndMT and delays venous thrombosis. Methods: To study the role of HDAC6 in EndMT, endothelial cells were treated with a pharmacological inhibitor (TCS20b) and incubated with TGF{beta} and thrombin for 2, 3, and 5 days. Real time PCR and Western blot were performed to analyze endothelial and mesenchymal marker expression and TGF{beta} signaling. An experimental model of VTE was used to study the role of HDAC6 on thrombus size overtime. Animals were treated or not with a specific HDAC6 inhibitor (tubastatin A) for 7 to 21 days. Analysis of RNAseq data sets publicly available were used to confirm our main results. Within group and treatment differences were analyzed using two-way ANOVA and Tukeys multiple comparisons. Results: Expression of the mesenchymal markers, calponin and transgelin, was increased by TGF{beta} and thrombin. Interestingly these changes were inhibited in presence of TCS20b. TGF{beta} mediated these effects through ERK1/2 and HDAC6 activation. Inhibition of HDAC6 in vivo reduced thrombus size 7 days after surgery compared to controls. This was associated with reduced expression of the EndMT marker transgelin in endothelial cells compared to the control animals. We found that FN1-EDA expression was associated with EndMT and regulated by HDAC6 in vitro. This marker was also associated with thrombosis in the RNAseq data set that we analyzed and potentially in patients with recurrent DVT. Conclusion: We found that HDAC6 regulates EndMT in venous thrombosis and impairs thrombus resolution. HDAC6 also regulates expression FN1-EDA that appears to be a strong marker associated with DVT and DVT recurrence. Thus, HDAC6 might represent an attractive therapeutic target for patients with a high risk of recurrent VTE.

Platelet-leukocyte aggregates (PLAs) are a proposed interface between coagulation and immune regulation, but their distribution across leukocyte subsets beyond monocytes and neutrophils, and their behavior in acute disorders of immune regulation, such as sepsis and severe trauma, remain largely undefined. The study of thromboimmune mechanisms in these acute conditions has relied heavily on murine sepsis models, whose species differences in platelet and leukocyte biology limit translation to human disease. Direct measurement in human whole blood is needed yet reported PLA frequencies vary widely because quantification is highly sensitive to sample handling. Here we present a robust, minimally manipulative 27-color spectral flow cytometry protocol that allows simultaneous deep immunophenotyping and classification of PLAs across >40 leukocyte subpopulations. In healthy donors, PLA frequency ranged from 1.7% on memory CD4 T cells to over 50% on monocyte subsets, with monocytes contributing 25% of all PLAs. We also found novel platelet-binding leukocyte populations, including Th9 and Th22 CD4+ T cells. Optimization identified anticoagulant choice, centrifugation conditions, dilution, and sample processing time as key determinants of reproducible measurement; PLA quantification was validated by imaging flow cytometry. In a small validation cohort of sepsis and trauma patients, the assay recapitulated established immunophenotypic features of critical illness, including neutrophilia and myeloid-derived suppressor cells (MDSC) expansion, and quantified PLAs within each subset. This protocol provides a reference framework for studying thromboinflammation and other dysregulated immune response diseases directly in human blood, and a foundation for further studies, defining the mechanisms and clinical relevance of platelet-leukocyte interactions in disease.

Disintegrins are snake venom toxins that bind integrins and modulate platelet aggregation and cell migration. Isolation from venom often yields insufficient quantities for comprehensive study, making recombinant expression essential for detailed toxin characterisation. Here, we produced and characterised four disintegrins from Echis coloratus and Echis ocellatus in Escherichia coli. These homologous proteins contain distinct integrin-binding motifs: EcDis_RGD, EoDis_RGD, EcDis_KGD, and EcDis_VGD. Functional activities were evaluated using human platelet aggregation and endothelial cell scratch wound-healing assays. RGD-containing disintegrins exhibited the strongest inhibition of platelet aggregation, with EcDis_RGD showing the highest potency. The EcDis_KGD disintegrin inhibited platelet aggregation less potently, whereas EcDis_VGD showed no detectable activity in our assays. In endothelial cells, EcDis_RGD disintegrin markedly impaired cell migration, while EoDis_RGD displayed weaker anti-migratory activity. Neither KGD- nor VGD-containing disintegrins significantly affected wound closure. EoDis_RGD exhibited similar antiplatelet activity to the native, venom-purified disintegrin ocellatusin, validating our recombinant expression strategy. However, the corresponding PII-SVMP preparation displayed reduced inhibitory activity, consistent with incomplete generation of fully mature disintegrins species. Our findings demonstrate the importance of both integrin-binding motif identity and surrounding sequence context in determining disintegrin function, and support further use of recombinant toxins in toxinology and as therapeutic lead molecules.

Mechanical circulatory support essential for managing severe heart failure frequently triggers bleeding complications, driven by shear stress-induced over-proteolysis of von Willebrand factor (VWF) by ADAMTS13. Inhibiting ADAMTS13 presents a rationale to treat this condition, known as acquired von Willebrand syndrome (AVWS). However, conventional therapeutic strategies remain limited due to the risk of triggering thrombotic thrombocytopenic purpura. Here we show that HA10, a humanized anti-ADAMTS13 antibody, preserves a residual level of ADAMTS13 activity above the thrombosis-associated threshold. Multimodal structural and biophysical analyses--including NMR, SAXS, and SANS--revealed that HA10 bound to the disintegrin-like domain of ADAMTS13, dynamically competing with VWF while leaving 10- 20% residual enzymatic activity. The therapeutic efficacy and safety of HA10 were verified in non-human primate models of AVWS. Our findings establish a novel paradigm of enzymatic calibration rather than complete blockade, offering a mechanistically targeted and safe therapeutic approach for cardiovascular bleeding.

Background: Immunothrombosis is increasingly recognized in large-vessel-occlusion acute ischemic stroke (LVO-AIS), yet most biomarker studies infer thrombus biology from circulating neutrophil extracellular trap (NET) markers or from pre-defined thrombus subtypes. We prospectively studied 160 patients with anterior-circulation LVO-AIS treated with mechanical thrombectomy to determine whether intrathrombus NETosis markers identify thrombus phenotypes with distinct clinical trajectories, and whether plasma NETosis biomarkers reflect the molecular composition of thrombi. Methods: Thrombi underwent quantitative histopathology and immunohistochemistry for citrullinated histone H3 (CitH3), neutrophil elastase (NE) and CD61. Thrombi were analyzed without prior etiological or histological stratification, and intrathrombus markers were dichotomized at cohort medians (CitH3 6.62%, NE 3.95%, CD61 23.09%) to define internally standardized candidate phenotypes. Associations with thrombus composition, collateral circulation (Tan 2-3), 3-month functional independence (modified Rankin Scale 2 or less) and long-term mortality were assessed by correlation analyses and progressively adjusted multivariable models, with cross-compartment correlations corrected by the Benjamini-Hochberg false discovery rate (FDR). Results: Intrathrombus markers defined prognostically distinct phenotypes: CD61 tracked functional recovery, NE preserved collateral circulation and CitH3 long-term survival, each remaining significant after multivariable adjustment. Circulating NE, myeloperoxidase and leukocyte count instead tracked the macroscopic red-blood-cell-fibrin composition of retrieved thrombi. Cross-compartment concordance was limited: after FDR correction the only significant plasma-thrombus association was an inverse correlation between plasma cell-free DNA and intrathrombus NE, and no intrathrombus marker correlated positively with its circulating counterpart. Conclusions: Local immunothrombotic signatures therefore provide clinically relevant information not captured by plasma markers, and median-defined intrathrombus thresholds represent hypothesis-generating cutoffs for external validation and NET-targeted treatment stratification.