Platelet Formation Research Articles

Rectifying the impairment of immune thrombocytopenia plasmas through photobiomodulation

<p>Immune thrombocytopenia (ITP) is an autoimmune hemorrhage disorder. The first-line treatment of this disorder is corticosteroids, followed by thrombopoietin (TPO) receptor agonists such as Nplate, and/or splenectomy. Yet, the extended usage of corticosteroids or the expensive Nplate, coupled with the implications of splenectomy, raises concerns due to the array of associated side effects and an escalated vulnerability to subsequent complications. The current investigation shows that while anti-platelet antibodies and ITP plasmas hinder megakaryocyte differentiation and maturation and impair proplatelet and platelet formation in ex vivo culture of umbilical cord human CD34+ stem cells (cHSCs), low-level laser (LLL) treatment or photobiomodulation (PBM) effectively mitigates these detrimental impacts. PBM reinstated megakaryocyte differentiation and maturation, bolstering proplatelet and platelet formation in the presence of auto-platelet antibodies or ITP plasmas. The mitigating effects of PBM appear to pivot on its capacity to uphold cellular mitochondrial functionality and rectify the mitochondrial impairments engendered by anti-platelet antibodies or ITP plasmas. These findings underscore the potential of PBM as a safe and cost-efficient alternative for the management of a specific subset of ITP patients.</p>

Rectifying the impairment of immune thrombocytopenia plasmas through photobiomodulation

<p>Immune thrombocytopenia (ITP) is an autoimmune hemorrhage disorder. The first-line treatment of this disorder is corticosteroids, followed by thrombopoietin (TPO) receptor agonists such as Nplate, and/or splenectomy. Yet, the extended usage of corticosteroids or the expensive Nplate, coupled with the implications of splenectomy, raises concerns due to the array of associated side effects and an escalated vulnerability to subsequent complications. The current investigation shows that while anti-platelet antibodies and ITP plasmas hinder megakaryocyte differentiation and maturation and impair proplatelet and platelet formation in ex vivo culture of umbilical cord human CD34+ stem cells (cHSCs), low-level laser (LLL) treatment or photobiomodulation (PBM) effectively mitigates these detrimental impacts. PBM reinstated megakaryocyte differentiation and maturation, bolstering proplatelet and platelet formation in the presence of auto-platelet antibodies or ITP plasmas. The mitigating effects of PBM appear to pivot on its capacity to uphold cellular mitochondrial functionality and rectify the mitochondrial impairments engendered by anti-platelet antibodies or ITP plasmas. These findings underscore the potential of PBM as a safe and cost-efficient alternative for the management of a specific subset of ITP patients.</p>

Genistin: A Novel Estrogen Analogue Targeting ERβ to Alleviate Thrombocytopenia.

Thrombocytopenia, a prevalent hematologic challenge, correlates directly with the mortality of numerous ailments. Current therapeutic avenues for thrombocytopenia are not without limitations. Here, we identify genistin, an estrogen analogue, as a promising candidate for thrombocytopenia intervention, discovered through AI-driven compound library screening. While estrogen's involvement in diverse biological processes is recognized, its role in thrombopoiesis remains underexplored. Our findings elucidate genistin's ability to enhance megakaryocyte differentiation, thereby augmenting platelet formation and production. In vivo assessments further underscore genistin's remedial potential against radiation-induced thrombocytopenia. Mechanistically, genistin's efficacy is attributed to its direct interaction with estrogen receptor β (ERβ), with subsequent activation of both ERK1/2 and the Akt signaling pathways membrane ERβ. Collectively, our study positions genistin as a prospective therapeutic strategy for thrombocytopenia, shedding light on novel interplays between platelet production and ERβ.

A novel GATA1 variant p.G229D causing the defect of procoagulant platelet formation

IntroductionGATA1 is one of the master transcription factors in hematopoietic lineages development which is crucial for megakaryocytic differentiation and maturation. Previous studies have shown that distinct GATA1 variants are associated with varying severities of macrothrombocytopenia and platelet dysfunction. ObjectiveTo determine the underlying pathological mechanisms of a novel GATA1 variant (c. 686G > A, p. G229D) in a patient with recurrent traumatic muscle hematomas. MethodsComprehensive phenotypic analysis of the patient platelets was performed. Procoagulant platelet formation and function were detected using flow cytometry assay and thrombin generation test (TGT), respectively. The ANO6 expression was measured by qPCR and western blot. The intracellular supramaximal calcium flux was detected by Fluo-5N fluorescent assay. ResultsThe patient displayed mild macrothrombocytopenia with defects of platelet granules, aggregation, and integrin αIIbβ3 activation. The percentage of the procoagulant platelet formation of the patient upon the stimulation of thrombin plus collagen was lower than that of the healthy controls (40.9 % vs 49.0 % ± 5.1 %). The patient platelets exhibited a marked reduction of thrombin generation in platelet rich plasma TGT compared to the healthy controls (peak value: ∼70 % of the healthy controls; the endogenous thrombin potential: ∼40 % of the healthy controls). The expression of ANO6 and intracellular calcium flux were impaired, which together with abnormal granules of the patient platelets might contribute to defect of procoagulant platelet function. ConclusionsThe G229D variant could lead to a novel platelet phenotype characterized by defective procoagulant platelet formation and function, which extended the range of GATA1 variants associated platelet disorders.

Precise Control of Two-Dimensional Hexagonal Platelets via Scalable, One-Pot Assembly Pathways Using Block Copolymers with Crystalline Side Chains.

Crystallization-driven self-assembly (CDSA) of block copolymers (BCPs) in selective solvents provides a promising route for direct access to two-dimensional (2D) platelet micelles with excellent uniformity, although significant limitations also exist for this robust approach, such as tedious, multistep procedures, and low yield of assembled materials. Herein, we report a facile strategy for massively preparing 2D, highly symmetric hexagonal platelets with precise control over their dimensions based on BCPs with crystalline side chains. Mechanistic studies unveiled that the formation of hexagonal platelets was subjected to a hierarchical self-assembly process, involving an initial stage of formation of kinetically trapped spheres upon cooling driven by solvophobic interactions, and a second stage of fusion of such spheres to the 2D nuclei to initiate the lateral growth of hexagonal platelets via sequential particle attachments driven by thermodynamically ordered reorganization of the BCP upon aging. Moreover, the size of the developed 2D hexagonal platelets could be finely regulated by altering the copolymer concentration over a broad concentration range, enabling scale-up to a total solids concentration of at least 6% w/w. Our work reveals a new mechanism to create uniform 2D core-shell nanoparticles dictated by crystallization and particle fusion, while it also provides an alternative facile strategy for the design of soft materials with precise control of their dimensions, as well as for the scalability of the derived nanostructures.

Cytotoxic Stress Transiently Increases the Contribution of Platelet-Biased Hematopoietic Stem Cells to Platelet Production

While hematopoietic stem cells (HSCs) and megakaryocyte (Mk)/platelet lineages exhibit substantial phenotypic and transcriptional overlap, direct Mk production from HSCs is still under investigation. In particular, the hypothesis that specific HSC clones might facilitate rapid megakaryopoiesis and their physiological roles are yet to be elucidated. Previous clonal studies using either single cell transplantations (Yamamoto, Cell 2013; Carrelha, Nature 2018) or barcoding assays (Pei, Cell Stem Cell 2020; Rodriguez-Fraticelli, Nature 2020) have identified subsets of HSCs with Mk-biased output, designated as Mk-biased HSCs or platelet-biased HSCs (P-HSCs), in contrast to multi-lineage HSCs (MUL-HSCs) with balanced output. Moreover, P-HSCs exhibit up-regulated platelet-lineage gene expression and chromatin accessibility, and they generate platelets at a faster rate than MUL-HSCs, pointing towards a direct platelet formation pathway (Rodriguez-Fraticelli, Nature 2020; Meng, 2023 Nat Cell Biol). Notably, under inflammatory stress, direct Mk progenitor (MkP) production and Mk formation from HSCs have been shown to accelerate (Haas, Cell Stem Cell, 2015; Morcos, Nat Commun 2022), suggesting that P-HSCs could drive rapid platelet production during hematopoietic emergencies. To probe this premise, we re-analysed previously published RNA-seq data on HSC subtypes and discovered that the gene Vldlr is markedly expressed in MUL-HSCs relative to P-HSCs. We subsequently created a Vldlr-Cre transgenic mouse model for lineage tracing of platelet production from MUL-HSCs and P-HSCs. Flow cytometry analysis across the HSC-MPP2-preMegE-MkP-platelet developmental sequence revealed a notable increase in the percentages of Tomato- HSCs and platelets, in comparison to MPP2-preMegE-MkP, suggesting that Tomato- HSCs significantly bypass the conventional MPP2-preMegE-MkP pathway in platelet formation. Transplantation of labelled and non-labelled HSCs confirmed that Vldlr-Cre predominantly labelled MUL-HSCs, whilst Tomato- HSCs were rich in P-HSCs and largely generated Tomato- platelets, implying that platelets derived from the direct P-HSC pathway can be identified as Tomato- through Vldlr-Cre lineage tracing. We exploited this model to examine the distinct roles of classical and direct pathways during emergency thrombopoiesis, induced by either antibody-mediated platelet depletion mimicking immune thrombocytopenia or a cytotoxic drug 5-fluorouracil (5-FU) that causes severe hematopoietic disruption. Both interventions precipitated a significant decrease in platelet counts, as previously demonstrated. However, the proportion of Tomato- platelets did not change during platelet recovery following antibody intervention, while the percentage of Tomato- platelets rose up to four-fold in early recovery stage following 5-FU treatment, suggesting an acceleration of the direct pathway under this stressor. The percentage of Tomato- platelets returned to baseline following platelet count normalization. Further analysis of bone marrow progenitors post-intervention revealed that the proportion of Tomato- MkP was maintained during recovery from antibody treatment but significantly expanded after 5-FU treatment. Nevertheless, the fraction of Tomato- HSCs remained unaltered under both interventions, indicating that neither reagent selectively activates P-HSCs or MUL-HSCs. We hypothesize that the 5-FU treatment, by significantly eliminating bone marrow progenitors, permits P-HSCs to rapidly replenish the MkP pool and platelets due to their faster platelet formation kinetics, whereas progenitors are not affected by the antibody, leaving both pathways to contribute to platelet recovery. In summary, our findings suggest that P-HSCs provide a fast-track for platelet formation, enabling them to contribute to platelet recovery more rapidly following progenitor depletion induced by cytotoxic stress.

Newly Identified Roles for PIEZO1 Mechanosensor in Controlling Normal Megakaryocyte Development and in Primary Myelofibrosis

Introduction: Mechanisms through which mature megakaryocytes (Mks) and their progenitors sense the bone marrow extracellular matrix (ECM) to promote lineage differentiation in health and disease are still partially understood. We found PIEZO1, a mechanosensitive cation channel, to be expressed in Mks. Human mutations in PIEZO1 have been described to be associated with blood cell disorders. Primary Myelofibrosis (PMF) is a Chromosome Philadelphia-negative Myeloproliferative Neoplasm (MPN), characterized by altered stiffer ECM and megakaryocytosis, often driven by the gain-of-function mutation in JAK2 V617F. Here, we study a role for PIEZO1 in megakaryopoiesis and proplatelet formation under normal physiological conditions and in the context of PMF. Methods: Bone marrow Mks from C57BL/6J control and myelofibrotic mice carrying the human JAK2 V617F+ mutation, or Mks derived from stem cells of patients carrying the same mutation were analyzed at mRNA and protein levels for Piezo1 expression. Effects of Piezo1 activation or inhibition on Mk maturation and ploidy were assessed by flow cytometry, and proplatelet formation by fluorescent microscopy. Human peripheral blood samples from PMF patients, diagnosed according to established criteria, or healthy individuals were used to compare the two categories for Piezo1 relative expression on mRNA and protein levels and platelet biogenesis. Mk-specific double knockout mice of Piezo1/2 were generated to compare platelet counts under normal conditions or bone marrow ablation with 5-FU challenge. Culture of mouse and human Mks in different 3D microenvironments was used to demonstrate in vitro association of Piezo1 expression levels with different ECM stiffness substrates. Results: Mouse Mks express PIEZO1 and negligible levels of PIEZO2. Pharmacological activation of mouse PIEZO1 increases the number of immature CD41 + Mks, while the number of mature CD41 +CD42 + Mks and Mk ploidy level are reduced. Piezo1/2 knockout mice show an increase in Mk size and platelet count, both at basal state and upon marrow regeneration. Similarly, in human samples, PIEZO1 is expressed during megakaryopoiesis. Its pharmacological activation reduces Mk size, ploidy, maturation, and proplatelet development. Resulting effects of PIEZO1 activation on Mks resemble the profile in PMF. Intriguingly, Mks derived from PMF mice bearing the Jak2 V617F mutation show significantly elevated PIEZO1 expression, compared to wild-type controls. Pharmacological activation of PIEZO1 in these cells significantly augments the number of immature CD41 + Mks, and sharply reduces the number of mature CD41 +CD42 + cells and ploidy level. Accordingly, Mks isolated from bone marrow aspirates of JAK2 V617FPMF patients show increased PIEZO1 expression compared to Essential Thrombocythemia. Additionally, PIEZO1 was overexpressed in 3D culture of human and mouse Mks in stiffer microenvironments as compared to softer ones and liquid medium. Most importantly, PIEZO1 expression in bone marrow Mks is inversely correlated with patient platelet count. The ploidy, maturation, and proplatelet formation of Mks from JAK2 V617FPMF patients are rescued upon PIEZO1 inhibition with GsMTx4. Discussion: Our data show that PIEZO1 might serve as a break of Mk maturation and platelet formation in physiology, and its upregulation in PMF Mks might contribute to aggravating some hallmarks of the disease. Our finding that inhibition of PIEZO1 activity partially rescues the aberrant Mk phenotype associated with PMF suggests that GsMTx4 holds potential as a therapeutic strategy to mitigate the pathological effects observed in Mk development in PMF patients.

A Cytochrome c Variant Enhances Megakaryocytic Maturation

Mutations in genes which play a role in the processes of megakaryopoiesis and platelet production cause thrombocytopenia. Five pathogenic variants in the gene encoding cytochrome c ( CYCS) associated with mild autosomal dominant thrombocytopenia have been reported. The role of cytochrome c in megakaryopoiesis and platelet formation is unknown, and it is unclear how mutations in cytochrome c cause thrombocytopenia. The goal of this project is to understand how CYCS mutations cause thrombocytopenia. We are using the human leukemic K562 cell line as a model system to study the impact of CYCS mutations on megakaryocyte differentiation and mitochondrial function. One of the CYCS pathogenic variants (c.145T>C; p.Tyr49His) was introduced into K562 cells using the CRISPR-Cas9 base-editing method. K562 cells have three copies of CYCS-containing chromosome 7 and we isolated CYCS WT/WT/WT, CYCS WT/WT/Y49H, CYCS WT/Y49H/Y49H, CYCS Y49H/Y49H/Y49H clonal lines, confirmed by sequencing and mass spectrometry. K562 cells undergo megakaryocyte differentiation in response to PMA. We monitored the expression of megakaryocyte markers CD61 and CD41a by flow cytometry in response to PMA in all clonal lines. The K562- CYCS Y49H/Y49H/Y49H line showed faster maturation compared to all other clonal lines and the parental K562 cells. We assessed mitochondrial function using the Seahorse XFe96 Analyzer. Our results show that the mutation does not impact mitochondrial respiratory function. Finally, we have introduced the Y49H mutation into WTC11 iPSCs. Investigations of the impact of the Y49H variant on apoptosis showed that there is no significant differences in apoptosis between WT and the clonal line carrying the Y49H variant. Our results suggest that the pathogenic c.145T>C; p.Tyr49His CYCS variant enhances megakaryocyte maturation.

HDAC Inhibitor CS014 Attenuates Thrombosis Alone and in Combination with Rivaroxaban without Increased Risk of Bleeding

Introduction: Targeting the human platelet for prevention of occlusive thrombotic events remains an active area of research due to the high incidence of myocardial infarction and stroke due to platelet-rich thrombotic clots. While, many patients taking FXa anticoagulant therapy require further inhibition of thrombosis, dual therapy including anticoagulant plus antiplatelet drugs result in an increased risk for bleeding. The current study sought to determine if a histone deacetylase (HDAC) inhibitor, either alone or in combination with the FXa inhibitor rivaroxaban, is able to effectively inhibit platelet and fibrin formation at the site of vascular injury without causing a significant increase in the bleeding risk in mice. Methods and Results: Thrombosis and bleeding models in the mouse were assessed in the presence of the HDAC inhibitors valproic acid (VPA) or the newly developed HDAC inhibitor, CS014. Both CS014 and VPA significantly, dose-dependently inhibit platelet accumulation and fibrin formation at the site of a vascular injury using the laser-induced cremaster thrombosis assay model. Further, to determine if CS014 has the potential to be used in conditions where an anticoagulant is already on board, mice were dosed for 5 days with rivaroxaban alone or in combination with CS014 and were assessed for prevention of laser-induced thrombosis in the cremaster arteriole. Both rivaroxaban and CS014 alone cause significant attenuation of clot formation. To determine if the combination results in an increased risk for bleeding, blood from mice treated with CS014 or rivaroxaban alone, or in combination was assessed for coagulation activity and clot strength using thromboelestography (TEG). Rivaroxaban was found to significantly delay onset of clotting in TEG whereas CS014 did not show any delay in coagulation or clotting with TEG. In combination CS014 was not observed to cause any additional delay in clotting time or decrease in maximal clot strength compared to rivaroxaban alone. Finally, a tail vein bleeding assay was conducted to determine if CS014 alone or in combination with rivaroxaban result in an increased risk for bleeding. Neither CS014 alone, rivaroxaban alone, or the combination of CS014 plus rivaroxaban resulted in increased bleeding time in the resected tail experiment. Conclusions: The data presented here suggests that while CS014 and rivaroxaban are each effective antithrombotic agents, they work well together to minimize clot formation without altering coagulation or clotting compared to rivaroxaban alone. Hence, CS014 has the potential to enrich the toolbox of anticoagulant therapies in patients with a high risk of thrombotic events.

Bone Marrow CD8 + Tissue-Resident Memory T Cell Promote B Cell Differentiation and Inhibit Platelet Production in Patients with Immune Thrombocytopenia

Immune thrombocytopenia (ITP) is a prevalent autoimmune disease in which enhanced anti-platelet T cell activity and dysfunction of CD8 + T cells are involved(Audia et al., 2013; Semple & Freedman, 1991). Persistent secretion of antibodies by long-lived plasma cells and memory B cells in the bone marrow contributes to ITP pathogenesis (Roeser, Lazarus, & Mahevas, 2023). However, the role of memory T cells, especially tissue-resident memory T cells (TRM), in ITP remains underexplored. TRM develop in specific tissues and play crucial role in local immunity. TRM exert their effects through mechanisms including the induction of local humoral responses, contributing to autoimmune diseases such as systemic lupus erythematosus and rheumatoid arthritis (Chang et al., 2021; Gu, Song, Roh, Jung, & Kim, 2021). Bone marrow contains one of the largest pools of memory CD8 + T cells. However, the involvement of bone marrow TRM in ITP pathogenesis remains poorly understood. In this study, we observed a significantly higher proportion of CD8 + TRM (CD8 +CD45RA -CD45RO +CD69 +) in the bone marrow of ITP patients compared to healthy controls. However, no significant differences were observed in CD4 + TRM, CD8 + TCM and CD8 + TEM between the two groups. CD8 + TRM from ITP patients exhibited increased levels of IFN-γ, NLRP3, IL-1β, TNF-α, and decreased levels of IL-10 compared to those from healthy controls. Furthermore, CD8 + TRM proportions were significantly higher in glucocorticoid responders than non-responders, suggesting a potential role of CD8 + TRMs in mediating glucocorticoid therapeutic effects. Transcriptome sequencing revealed upregulated genes, including IGLC2, ASAP2, HIST2H2AA4, IGLV2-11, C1QA, ATP5MC1, IL5RA, and CYC1, and downregulated genes, including CCR9, HSPE1P18, RGCC, and ITGAE, in TRM cells from ITP patients compared to controls. GO/KEGG analysis of the top 500 upregulated genes highlighted pathways associated with B cell-associated immunity. To explore the effect of TRM on B cells, bone marrow CD19 + B cells were co-cultured with autologous TRM or memory T cells without TRM (TM) in the presence of IgM, and the proportion of memory B cells (CD19 +CD27 +CD38 -) and plasma cells (CD19 -CD24 -CD38 +) were measured by flow cytometry. The supernatants were collected, and cytokines and IgG level were tested by ELISA. Results showed that TRMs from ITP patients promoted the differentiation of memory B cells and IgG antibody production compared with those from healthy controls. However, no significant difference was observed in the proportion of naive B cells and plasma cells between the two groups. TRM, but not TM augmented B cell differentiation into memory B cells or plasma cells both in ITP patients and healthy controls. Additionally, TRM-primed B cells showed a stronger effect on antibody production and resulted in a higher level of IgG in supernatant compared with TM primed B cells. In line with these findings, the levels of B cell activating factor (BAFF), a proliferation inducing ligand (APRIL), and sCD40L, which were critical cytokines for B cell survival and differentiation, were significantly higher in supernatants from ITP patients than those from healthy controls. Moreover, the levels of BAFF, APRIL and CD40L in co-culture system with TRM were significantly increased compared to the system with TM, providing insights into the impact of TRM on B cell differentiation and function. To further investigate the role of TRM in regulating platelet production in ITP patients, we cocultured TRM with CD34 +cells in the presence of thrombopoietin (TPO), stem cell factor (SCF) and interleukin (IL)-3. Results showed that TRM did not suppress the production of CD41 + megakaryocytes from CD34 + cells, but reduced megakaryocyte apoptosis and increased the percentage of polyploidy (≥4N) megakaryocytes compared with TM. Additionally, TRM inhibited reticulated platelet formation and platelet production. Notably, dexamethasone (DXM) modulation alleviated certain suppressive effects on platelet production. In summary, our findings reveal the involvement of impaired bone marrow CD8 + TRM in the pathogenesis of ITP through the promotion of B cell differentiation and inhibition of platelet production. These results shed new light on the potential of immune therapy targeting TRM in the management of ITP.

Mitochondrial Fission Protein Drp1 Regulates Platelet Function

Background: Mitochondria in platelets contribute to platelet function and are altered by diseases that involve dysregulated hemostasis or thrombosis. Mitochondrial integrity, governed by its size, number and distribution is modulated by fusion and fission proteins. Pharmacological inhibition of the mitochondrial fission protein Dynamin-related protein 1 (Drp1) has been shown to inhibit granule release in human platelets and impair thrombus formation in a murine model of thrombosis. However, the mitochondrial roles for Drp1 in platelet function are still largely unknown. Objective: To determine the mitochondrial roles of Drp1 in regulating platelet function. Methods: PF4-Cre mediated MK/platelet specific Drp1 null mice (Drp1 -/-) were used. Platelet morphology in Drp1 -/- and wild type (WT) platelets was analyzed by confocal microscopy. Procoagulant platelet formation (PS +ve platelets) after thrombin and the GPVI agonist convulxin (THR+CVX) stimulation was measured using Annexin V staining. Mitochondrial potential (ΔΨm) and mass at baseline and after stimulation was measured using TMRM and mitotracker green. Washed platelet activation in WT and Drp1 -/- platelets in response to convulxin was measured by flow cytometry. Platelet cytoplasmic calcium transients were measured using FURA-2AM after stimulation with THR+CVX. Phosphorylation of Drp1 (pDrp1 S616) in washed WT platelets in response to dual agonist THR+CVX was measured by western blotting. Results: Drp1 -/- platelets were bigger in size than WT platelets as measured by microscopy and had increased mitochondrial mass as determined by flow cytometry. Absence of Drp1 reduced activation of the αIIb/β3 fibrinogen binding receptor (P=0.035; n=5-6 per group) and reduced alpha granule release (P=0.025; n=5-6 per group) in response to CVX.Dual agonist stimulation resulted in reduced PS +ve platelets in Drp1 -/- compared to WT platelets (P=0.0035; n=7 per group). Since depolarization precedes PS exposure, we measured ΔΨm using TMRM in resting and dual agonist stimulated WT and Drp1 -/- platelets. No difference in ΔΨm was observed in resting Drp1 -/- vs WT platelets whereas, stimulated Drp1 -/- platelets exhibited significantly higher ΔΨm (P=0.038; n=4 per group) than stimulated WT platelets. Interestingly, in response to dual agonists, Drp1 -/- platelets also showed a significant increase (P<0.001) in cytoplasmic calcium transients than WT platelets. Western blot analyses of washed WT platelets stimulated with dual agonist showed phosphorylation of Drp1 at S616 (S616), indicating Drp1 activation. Conclusion: These findings highlight a role for Drp1 in murine platelet mitochondrial function, GPVI activation, and procoagulant platelet formation.

Study prognostic significance of low platelet count in newborn admitted in neonatal intensive care unit (NICU) at tertiary care center

One of the most frequent haematological abnormalities found in new-borns is Thrombocytopenia. In neonates admitted to ICUs, thrombocytopenia develops in 18–35 % of all patients. With decreasing gestational age and birth weight, the incidence are increasing. Platelets are formed by megakaryocytes and are present in the bloodstream for 5–7 days. Platelets are known as regulators of haemostasis and thrombosis. Platelets become active in the blood resulting vascular injury. Thrombopoiesis is the formation of platelets in the Bone marrow. Thrombopoietin is the main regulator of thrombopoiesis. Thrombopoietin affects most aspects of the production of platelets. The process of Thrombopoiesis is caused by the breakdown of proplatelets (mature megakaryocyte membrane pseudopodia projections). Aim is to assess the prevalence, causes, treatment modalities, and prognostic outcomes of thrombocytopenia in neonates. Research design was carried out in the Department of paediatrics and neonatology, Government Medical College, Surat from October 2020 to April 2022. Data were collected from MRD section. Platelet numbers were estimated from whole blood EDTA sample taken from neonates for routine medical management. Data were analysed for Age, Sex, Intraventricular haemorrhage, other bleeding manifestation, Necrotising enterocolitis, Sepsis, Fungal infection & final outcome. Out of 1265 neonates admitted to the NICU at Department of paediatrics and neonatology, GMC, Surat 450 neonates were found to have thrombocytopenia. Male neonates are more significantly affected than female neonates. The early platelets drop even without the later development of thrombocytopenia is an early indicator of poor outcome and major morbidities, mainly infection.

Human platelets and megakaryocytes express the BPIFB4 protein and their stimulation with the recombinant Longevity-associated variant LAV-BPIFB4 displays anti-aggregating activity

Abstract Platelets are not only the main players in primary haemostasis and cardiovascular disease, but recent advances attribute them a key role in immune defence mechanisms via the release of plasma mediators of potential clinical relevance. The bactericidal/permeability-increasing fold-containing family B, member 4 (BPIFB4) belongs to a family protein participating in the innate mechanism of host defence. It is a secreted protein and its plasma levels inversely correlated with COVID-19 and coronary artery disease (CAD) severity and the degree of carotid stenosis and intima media thickness in human patient cohorts. Interestingly, Long Living Individuals (LLIs) displayed high BPIFB4 circulating levels and an enrichment of the 4 SNPs missense haplotype at BPIFB4 locus, the Longevity-Associated Variant (LAV). LAV-BPIFB4 genotype correlate with higher BPIFB4 plasma levels and the transfer of LAV-BPIFB4 gene delayed major age-related diseases, mainly rescuing the immunesenescence and the endothelial and cardiac dysfunctions, yet the critical assessment of the BPIFB4 protein as a platelet release product is lacking. Herein we observed BPIFB4 release by calcium activated human platelets, a process that is amplified in LAV allele carriers donors. Furthermore, LAV gene transfer resulted in an enhanced protein enrichment in bone marrow megakaryocyte precursor cells and in a more efficient process of platelets formation in vitro. At functional level, LAV genotype was mimicked by the rhLAV-BPIFB4 platelet stimulation that induced endogenous BPIFB4 release similarly to calcium stimuli. In a small cohort of treatment-naive patients with type 2 diabetes, while ADP and Collagene agonist stimulation induced high aggregation, the co-treatment with the rhLAV-BPIFB4 significantly reduced the activation capacity of patients’ platelets. Accordingly, an administration of rhLAV-BPIFB4 24 hours before tromboembolism induction partly protected from mortality in a murine model of lethal pulmonary thromboembolism in vivo. As a result of reduced platelets’ activation, lower level of circulating leukocyte-platelets aggregates (LPA) was found in rhLAV-BPIFB4-treated mice compared to control. In summary, our data report for the first time that both, human platelets and megakaryocytes, can express BPIFB4 and unravel a novel rhLAV-BPIFB4 therapeutic action in platelet iperaggregation and thrombocytopenia.

ABCC4 impacts megakaryopoiesis and protects megakaryocytes against 6-mercaptopurine induced cytotoxicity

The role of ABCC4, an ATP-binding cassette transporter, in the process of platelet formation, megakaryopoiesis, is unknown. Here, we show that ABCC4 is highly expressed in megakaryocytes (MKs). Mining of public genomic data (ATAC-seq and genome wide chromatin interactions, Hi-C) revealed that key megakaryopoiesis transcription factors (TFs) interacted with ABCC4 regulatory elements and likely accounted for high ABCC4 expression in MKs. Importantly these genomic interactions for ABCC4 ranked higher than for genes with known roles in megakaryopoiesis suggesting a role for ABCC4 in megakaryopoiesis. We then demonstrate that ABCC4 is required for optimal platelet formation as in vitro differentiation of fetal liver derived MKs from Abcc4-/- mice exhibited impaired proplatelet formation and polyploidization, features required for optimal megakaryopoiesis. Likewise, a human megakaryoblastic cell line, MEG-01 showed that acute ABCC4 inhibition markedly suppressed key processes in megakaryopoiesis and that these effects were related to reduced cAMP export and enhanced dissociation of a negative regulator of megakaryopoiesis, protein kinase A (PKA) from ABCC4. PKA activity concomitantly increased after ABCC4 inhibition which was coupled with significantly reduced GATA-1 expression, a TF needed for optimal megakaryopoiesis. Further, ABCC4 protected MKs from 6-mercaptopurine (6-MP) as Abcc4-/- mice show a profound reduction in MKs after 6-MP treatment. In total, our studies show that ABCC4 not only protects the MKs but is also required for maximal platelet production from MKs, suggesting modulation of ABCC4 function might be a potential therapeutic strategy to regulate platelet production.

Abstract 12411: Fatty Acid Saturation Status in Murine High Fat Diets Modulates Platelet Reactivity

Introduction: We have recently shown that membrane fatty acids are key modulators of megakaryocyte differentiation and platelet formation. In obesity, patients have an altered plasma lipid composition, which coincides with enhanced platelet responsiveness to activation. However, the mechanism underlying this platelet phenotype remains unknown. Hypothesis: We hypothesized that the obese plasma lipidome alters the composition of the megakaryocyte membrane, which ultimately leads to the generation of hyper-reactive platelets. Aim: To investigate the impact of high fat diets with different fatty acid compositions on megakaryocyte development and platelet reactivity. Results: Mice were fed chow or high fat diets enriched in either saturated fatty acids (50% SFAs) or polyunsaturated fatty acids (50% PUFAs, omega-6-enriched). Neither high fat diet resulted in changes in megakaryocyte numbers, but both caused a significant increase in the size of bone marrow megakaryocytes, suggesting diet-derived lipid uptake into megakaryocytes. When examining platelet reactivity, we found that mice fed the SFA-enriched high fat diet exhibited increased expression of the active form of integrin αIIbβ3 (JON/A) in resting platelets and that both JON/A and P-selectin expression were significantly decreased after platelets were stimulated with ADP and the thromboxane A 2 analogue U46619. In contrast, platelets from mice fed the PUFA omega-6-enriched high fat diet had no differences in platelet reactivity compared to mice fed normal chow. Conclusions: Our data reveal that dietary fatty acid saturation status affects platelet reactivity, consistent with previous human studies showing variability in platelet reactivity in obese individuals. Further explorations will elucidate if plasma and/or platelet lipid content may be an indicator of risk for thrombosis or cardiovascular disease.

Abstract 16055: Marantic Endocarditis - A Rare Paraneoplastic Presentation of Ovarian Carcinoma

Introduction: Nonbacterial thrombotic endocarditis (NBTE) or Marantic endocarditis, involves formation of sterile platelet & fibrin thrombi on undamaged cardiac valves & adjacent endocardium. The vegetation is associated with embolization. Case presentation: A middle-aged female without cardiac history presented to the ED with blurred vision & fatigue for 3 days. The patient was afebrile with a BP of 183/97mmHg. Physical examination showed decreased visual acuity in the left eye. The EKG was normal. The patient underwent a CT scan brain that showed suspicion of bilateral occipital strokes. MRI brain revealed multiple small acute infarcts in the bilateral cerebral hemispheres & cerebellum. Blood cultures were negative. Telemetry did not show atrial fibrillation. Given a suspicion of cardioembolic stroke, the patient underwent a transesophageal echocardiogram (TEE) which demonstrated a trileaflet aortic valve (AV) with abnormal irregular thickening of leaflets, concerning for vegetation & moderate-severe aortic regurgitation (AR). figure 1. Our patient was diagnosed with marantic endocarditis based on TEE & serial negative cultures. Apixaban was started. Further workup of the patient revealed bilateral pulmonary emboli. Abdominal imaging revealed a pelvic mass, ultimately diagnosed as clear-cell ovarian cancer. Interval TEE at 3 months demonstrated complete resolution of vegetations with preserved cusp motion & mild AR. A shared decision was made to continue lifelong anticoagulation. Discussion: NBTE commonly involves mitral & AV. Risk factors include trauma, circulating immune complexes, hypercoagulability, malignancy & acute inflammation. Symptoms result from embolization, valve dysfunction, or impaired cardiac function. It is based on imaging after ruling out infectious etiologies. Management is anticoagulation & valve replacement with the treatment of the underlying etiology. Valve replacement prevents future embolic complications.

RUNX1 Haplodeficiency Reduces Platelet Endocytosis of Albumin and Fibrinogen and Impairs Megakaryocyte Intracellular Trafficking

Introduction:RUNX1 is a major hematopoietic transcription factor that regulates megakaryopoiesis and platelet formation and function. Germline RUNX1 haplodeficiency (RHD) is characterized by thrombocytopenia, impaired platelet function and granule deficiencies. Our previous studies in a patient with RUNX1 mutation showed that platelet albumin and fibrinogen were decreased (Sun et al, Blood 103: 948-54, 2004) .Human platelet α-granules contain numerous proteins, some synthesized (e.g., PF4 and VWF) and others (e.g., fibrinogen, albumin and IgG) are incorporated by endocytosis, a process poorly understood in platelets/megakaryocytes (MK). Methods: To understand the mechanisms leading to the decreased platelet albumin and fibrinogen, we performed studies on endocytosis in platelets from RHD patients, megakaryocytic HEL cells and MK differentiated from CD34 + hematopoietic stem and progenitor cells (HSPCs). We studied endocytosis of fluorescent-labeled albumin, fibrinogen and IgG in platelet suspensions (0-90 min) and in PMA-treated megakaryocytic HEL cells (up to 24 hrs) using flow cytometry and immunofluorescence microscopy, and assessed proteins linked to endocytosis. Results:Platelet uptake of albumin, fibrinogen and IgG was time- and concentration dependent. Uptake of all 3 was decreased in two patients (father and daughter) with RHD (c.352-1 G>T) (mean fluorescent intensity <50% of normal). In HEL cells, uptake of albumin and fibrinogen was time- and concentration-dependent. On siRNA RUNX1 knockdown (KD), uptake/retention of albumin and fibrinogen over 24 hrs was increased compared to control siRNA cells. Caveolin-1 and flotillin-1, two caveolae-associated membrane proteins linked to endocytosis, and LAMP2 (linked to lysosomal trafficking) and RAB11 (linked to recycling endosomes) were increased on RUNX1 KD on immunoblotting. Caveolin -1 downregulation (siRNA) in RUNX1-deficient HEL cells abrogated the increase in uptake of albumin, but not fibrinogen. At 30 min, in control cells albumin was strongly colocalized with caveolin-1 on immunofluorescence studies. This colocalization was abolished on CAV-1 KD. With RUNX1 KD there was a decrease in colocalization with caveolin-1, and an increase with flotillin-1 both at 30 (Figure 1a) and 120 min. Thus, RUNX1 KD alters endocytosis and trafficking of albumin from caveolin-1 to flotillin-1 bearing vesicles. In experiments where HEL cells were incubated in medium without albumin for 24 hours, cell albumin decreased over time in both control cells and RUNX1-deficient cells with lower levels in the latter. LAMP2 levels were increased on RUNX1 KD, which may provide a mechanism (lysosomal degradation) for this. With respect to fibrinogen, at 30 or 120 min, there was no colocalization of fibrinogen with caveolin-1 or flotillin-1, indicating fibrinogen uptake is not caveolin-dependent. In control cells, there was low/moderate fibrinogen colocalization with RAB11 (marker for recycling endosomes); this was markedly increased with RUNX1 KD (Figure 1b), along with increased RAB11 level on immunoblotting, suggesting that RUNX1 KD is associated with altered fibrinogen trafficking towards recycling endosomes. Recently, IFITM3 has been implicated in platelet fibrinogen uptake in nonviral sepsis. We found HEL cell IFITM3 was increased on RUNX1 KD; however, IFITM3 siRNA KD did not decrease fibrinogen uptake. We studied endocytosis in in vitro differentiated MKs for 12 days from human CD34 + HSPCs; upon lentiviral shRNA KD of RUNX1 the uptake of albumin and fibrinogen was increased compared to control cells . Conclusions: We provide the first evidence that 1) platelet endocytosis of albumin and fibrinogen is impaired in RHD and 2) RUNX1-deficient megakaryocytic cells have enhanced endocytosis but defective trafficking of albumin and fibrinogen, mediated by distinct mechanisms, and associated with increases in caveolin 1, flotillin-1, RAB11, LAMP2 and IFITM3. These studies provide new insights into mechanisms governing endocytosis by platelets and MKs relevant to the α-granule deficiencies in RHD.

Circulating Platelets in Thrombotic Antiphospholipid Syndrome Display High Procoagulant Activity and Surface Complement Deposition: Correlation with Thrombotic Risk

Background Antiphospholipid syndrome (APS) is characterized by circulating antiphospholipid antibodies (aPL) accompanied by arterial and/or venous thrombosis, and/or recurrent pregnancy loss. It commonly affects young women in whom it dramatically increases their risk of myocardial infarction, ischemic stroke, deep vein thrombosis and pulmonary embolism. Although the thrombotic risk associated with aPL is established, the underlying mechanisms are still incompletely defined and there are no definitive predictive biomarkers. As a result the management of APS involves indefinite anticoagulation. Increased activation of vascular cells, including platelets is considered to underlie the pathogenesis of APS, and may be mediated in some cases by complement. There is a considerable crosstalk between platelets and complement at various levels during thrombosis. First, activated complement proteins stimulate platelets through their cognate receptors on the platelet surface, and genetic deficiency of complement proteins in mice leads to decreased platelet responsiveness. Second, platelets secrete complement proteins into the medium upon activation. Third, agonist-stimulated platelets contribute to activation of both the classical and alternative pathways of the complement cascade. Hence, we sought to investigate the association between the complement-platelet axis and the prothrombotic pathology observed in APS. Methods Venous blood was drawn from patients with APS and healthy controls, and washed human platelets were prepared by differential centrifugation. Platelets either remained unstimulated or were treated with thrombin (0.1, 0.25, 0.5 U/ml) for 5 min and then labelled with FITC-PAC1, PE-anti-CD62P antibody, Alexa Fluor 488-anti-C4d conjugate, PE-Annexin V, Mitotracker Red, MitoSOX Red, Fluo4-AM, Rhod2-AM, Cell Event Green Caspase 3/7 detection reagent and FITC-IETD-FMK for 30 min in the dark, and then analyzed by flow cytometry to measure integrin activation, P-selectin expression (α-granule secretion), complement C4d binding, phosphatidylserine (PS) exposure, mitochondrial membrane potential, mitochondrial ROS, cytosolic calcium, mitochondrial calcium, caspase 3/7 activity (apoptosis) and caspase 8 activity (extrinsic apoptosis pathway), respectively. Platelet markers were correlated with complement binding and clinical characteristics of APS patients including number of thrombotic events and circulating levels of aPL. Results Thrombin-induced platelet integrin activation and P-selectin expression were identical in APS patients and healthy controls. However, platelets isolated from APS patients had significantly higher procoagulant activity (PS exposure) as well as complement C4d binding in both unstimulated and thrombin-stimulated states compared to healthy controls. There was a strong positive correlation between platelet PS exposure and C4d binding in APS patients, but not healthy individuals, suggesting a role for complement activation in formation of procoagulant platelets in APS. A subset of APS patients with high platelet procoagulant activity (PS exposure > mean + 2SD observed in healthy individuals) had lower mitochondrial membrane potential and increased mitochondrial calcium transients compared to healthy individuals, suggesting mitochondrial permeability transition pore (mPTP)-driven PS exposure. Another subset of APS patients with PS exposing platelets showed caspase activation indicating apoptosis. Platelet PS exposure and C4d binding correlated strongly with the number of thrombotic events as well as levels of circulating aPL, which identifies complement-induced procoagulant platelets as predictors and possible underlying mechanisms for thrombosis in APS. Conclusion Our preliminary studies suggest that PS-exposing platelets are generated in APS by multiple mechanisms including agonist-induced mPTP formation and apoptosis-associated caspase activation. Platelet PS exposure in APS is positively correlated with C4d binding, suggesting a role for complement activation in driving platelet procoagulant activity. Complement activation and PS exposure on platelets are strong predictors of thrombotic risk in APS and could serve as promising targets for novel antithrombotic agents in APS management.

Use of heated tobacco products (IQOS) causes an acute increase in arterial stiffness and platelet thrombus formation

Background and aimsHeated tobacco products (HTPs) are novel alternative tobacco products being promoted as an alternative to cigarettes. To evaluate the impact of HTP use on vascular function, we investigated the effects of a brief HTP usage on arterial stiffness and platelet thrombus formation in healthy volunteers. MethodsIn a randomised crossover study, twenty-four healthy young adults with occasional tobacco use smoked the HTP IQOS 3 Multi (Phillip Morris Int.) and “no-exposure” was used as a control, with a wash-out period of at least one week in-between. Arterial stiffness was assessed through pulse wave velocity and pulse wave analysis. Blood samples, collected at baseline and 5 min following exposure, were analysed with the Total-Thrombus-formation analysis system evaluating platelet and fibrin-rich thrombus formation tendency. ResultsHTP exposure caused immediate heightened pulse wave velocity (+0.365 m/s, 95% CI: +0.188 to 0.543; p = 0.004) and enhanced augmentation index corrected to heart rate (+6.22%, 95% CI: +2.33 to 10.11; p = 0.003) compared to the no-exposure occasion. Similarly, blood pressure and heart rate transiently increased immediately following HTP inhalation. Platelet thrombus formation significantly increased following HTP exposure (area under the curve +59.5, 95% CI: +25.6 to 93.4; p < 0.001) compared to no-exposure. No effect was seen on fibrin-rich thrombus formation following HTP-exposure. ConclusionsBrief HTP use in healthy young adults had immediate adverse effects on vascular function resulting in increased arterial stiffness and platelet thrombus formation, known risk factors for the development of atherosclerosis. Further research is needed to address long term health impacts.

The serum lipid profiles in immune thrombocytopenia: Mendelian randomization analysis and a retrospective study

BackgroundImmune thrombocytopenia (ITP) is an autoimmune hemorrhagic disease characterized by increased platelet destruction and impaired thrombopoiesis. The changes in platelet indices depend on the morphology and volume of platelets. Serum lipids have been found to affect platelet formation and activity in certain diseases, thus inducing the corresponding variation of platelet indices.MethodsMendelian randomization (MR) analysis was performed based on databases. The clinical data from 457 ITP patients were retrospectively collected and analyzed, including platelet indices, serum lipids, hemorrhages and therapeutic responses.ResultsMR analysis showed low high-density-lipoprotein-cholesterol (HDL-C), low apolipoprotein A-1, high triglyceride (TG) and high apolipoprotein B (ApoB) caused high platelet distribution width (PDW); high low-density-lipoprotein-cholesterol (LDL-C) increased mean platelet volume (MPV). In ITP, there were positive correlations between platelet count with TG, PDW with HDL-C and ApoB, and plateletcrit with TG and non-esterified fatty acid, and the correlation had gender differences. Bleeding scores were negatively correlated with cholesterol and LDL-C. LDL-C and homocysteine were risk factors for therapeutic responses.ConclusionsSerum lipids, especially cholesterol were tightly correlated with platelet indices, hemorrhage and therapeutic effects in ITP patients. These results provide clinical references for the management of serum lipids, and highlight the necessity to further explore the relationship between lipids and pathogenesis of ITP.Trial registrationNo: NCT05095896, October 14, 2021, retrospectively registered.