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Circulation Research Apr 2024While platelets have well-studied hemostatic functions, platelets are immune cells that circulate at the interface between the vascular wall and white blood cells. The...
BACKGROUND
While platelets have well-studied hemostatic functions, platelets are immune cells that circulate at the interface between the vascular wall and white blood cells. The physiological implications of these constant transient interactions are poorly understood. Activated platelets induce and amplify immune responses, but platelets may also maintain immune homeostasis in healthy conditions, including maintaining vascular integrity and T helper cell differentiation, meaning that platelets are central to both immune responses and immune quiescence. Clinical data have shown an association between low platelet counts (thrombocytopenia) and immune dysfunction in patients with sepsis and extracorporeal membrane oxygenation, further implicating platelets as more holistic immune regulators, but studies of platelet immune functions in nondisease contexts have had limited study.
METHODS
We used in vivo models of thrombocytopenia and in vitro models of platelet and monocyte interactions, as well as RNA-seq and ATAC-seq (assay for transposase-accessible chromatin with sequencing), to mechanistically determine how resting platelet and monocyte interactions immune program monocytes.
RESULTS
Circulating platelets and monocytes interact in a CD47-dependent manner to regulate monocyte metabolism, histone methylation, and gene expression. Resting platelet-monocyte interactions limit TLR (toll-like receptor) signaling responses in healthy conditions in an innate immune training-like manner. In both human patients with sepsis and mouse sepsis models, thrombocytopenia exacerbated monocyte immune dysfunction, including increased cytokine production.
CONCLUSIONS
Thrombocytopenia immune programs monocytes in a manner that may lead to immune dysfunction in the context of sepsis. This is the first demonstration that sterile, endogenous cell interactions between resting platelets and monocytes regulate monocyte metabolism and pathogen responses, demonstrating platelets to be immune rheostats in both health and disease.
Topics: Mice; Animals; Humans; Monocytes; Thrombocytopenia; Blood Platelets; Immunity; Sepsis; Platelet Activation
PubMed: 38456277
DOI: 10.1161/CIRCRESAHA.123.323662 -
Platelets Dec 2023Platelets play many roles in the vasculature ensuring proper hemostasis and maintaining integrity. These roles are facilitated, in part, by cargo molecules released from...
Platelets play many roles in the vasculature ensuring proper hemostasis and maintaining integrity. These roles are facilitated, in part, by cargo molecules released from platelet granules via oluble SF ttachment rotein eceptor (SNARE) mediated membrane fusion, which is controlled by several protein-protein interactions. Chaperones have been characterized for t-SNAREs (. Munc18b for Syntaxin-11), but none have been clearly identified for v-SNAREs. α-Synuclein has been proposed as a v-SNARE chaperone which may affect SNARE-complex assembly, fusion pore opening, and thus secretion. Despite its abundance and that it is the only isoform present, α-synuclein's role in platelet secretion is uncharacterized. In this study, immunofluorescence showed that α-synuclein was present on punctate structures that co-stained with markers for α-granules and lysosomes and in a cytoplasmic pool. We analyzed the phenotype of α-synuclein mice and their platelets. Platelets from knockout mice had a mild, agonist-dependent secretion defect but aggregation and spreading were unaffected. Consistently, thrombosis/hemostasis were unaffected in the tail-bleeding, FeCl carotid injury and jugular vein puncture models. None of the platelet secretory machinery examined, . the v-SNAREs, were affected by α-synuclein's loss. The results indicate that, despite its abundance, α-synuclein has only a limited role in platelet function and thrombosis.
Topics: Animals; Mice; alpha-Synuclein; Blood Platelets; Cytoplasmic Granules; Exocytosis; Mice, Knockout; Platelet Activation; Protein Isoforms; SNARE Proteins; Thrombosis
PubMed: 37927048
DOI: 10.1080/09537104.2023.2267147 -
Frontiers in Pharmacology 2023Thromboembolism resulting from platelet dysfunction constitutes a significant contributor to the development of cardiovascular disease. Sirtuin 6 (SIRT6), an essential...
Thromboembolism resulting from platelet dysfunction constitutes a significant contributor to the development of cardiovascular disease. Sirtuin 6 (SIRT6), an essential NAD-dependent enzyme, has been linked to arterial thrombosis when absent in endothelial cells. In the present study, we have confirmed the presence of SIRT6 protein in anucleated platelets. However, the precise regulatory role of platelet endogenous SIRT6 in platelet activation and thrombotic processes has remained uncertain. Herein, we present compelling evidence demonstrating that platelets isolated from SIRT6-knockout mice (SIRT6) exhibit a notable augmentation in thrombin-induced platelet activation, aggregation, and clot retraction. In contrast, activation of SIRT6 through specific agonist treatment (UBCS039) confers a pronounced protective effect on platelet activation and arterial thrombosis. Moreover, in platelet adoptive transfer experiments between wild-type (WT) and SIRT6 mice, the loss of SIRT6 in platelets significantly prolongs the mean thrombus occlusion time in a FeCl-induced arterial thrombosis mouse model. Mechanistically, we have identified that SIRT6 deficiency in platelets leads to the enhanced expression and release of proprotein convertase subtilisin/kexin type 9 (PCSK9), subsequently activating the platelet activation-associated mitogen-activated protein kinase (MAPK) signaling pathway. These findings collectively unveil a novel protective role of platelet endogenous SIRT6 in platelet activation and thrombosis. This protective effect is, at least in part, attributed to the inhibition of platelet PCSK9 secretion and mitogen-activated protein kinase signaling transduction. Our study provides valuable insights into the intricate interplay between SIRT6 and platelet function, shedding light on potential therapeutic avenues for managing thrombotic disorders.
PubMed: 38186648
DOI: 10.3389/fphar.2023.1268708 -
Haematologica Jul 2023Integrins are heterodimeric transmembrane receptors composed of α and β chains, with an N-terminal extracellular domain forming a globular head corresponding to the... (Review)
Review
Integrins are heterodimeric transmembrane receptors composed of α and β chains, with an N-terminal extracellular domain forming a globular head corresponding to the ligand binding site. Integrins regulate various cellular functions including adhesion, migration, proliferation, spreading and apoptosis. On platelets, integrins play a central role in adhesion and aggregation on subendothelial matrix proteins of the vascular wall, thereby ensuring hemostasis. Platelet integrins belong either to the β1 family (α2β1, α5β1 and α6β1) or to the β3 family (αIIbβ3 and αvβ3). On resting platelets, integrins can engage their ligands when the latter are immobilized but not in their soluble form. The effects of various agonists promote an inside-out signal in platelets, increasing the affinity of integrins for their ligands and conveying a modest signal reinforcing platelet activation, called outside-in signaling. This outside-in signal ensures platelet adhesion, shape change, granule secretion and aggregation. In this review, we examine the role of each platelet integrin in hemostatic plug formation, hemostasis and arterial thrombosis and also beyond these classical functions, notably in tumor metastasis and sepsis.
Topics: Humans; Blood Platelets; Integrins; Ligands; Hemostasis; Platelet Glycoprotein GPIIb-IIIa Complex; Thrombosis; Platelet Aggregation
PubMed: 36700400
DOI: 10.3324/haematol.2022.282136 -
Frontiers in Immunology 2023
Topics: Humans; COVID-19; Platelet Activation
PubMed: 37818358
DOI: 10.3389/fimmu.2023.1285355 -
Circulation Research Jan 2024
Topics: Mitochondrial Dynamics; Blood Platelets; Megakaryocytes; Hemostasis; Platelet Activation
PubMed: 38236952
DOI: 10.1161/CIRCRESAHA.123.323867 -
Journal of Thrombosis and Haemostasis :... Aug 2023The response of platelets to activating stimuli and pharmaceutical agents varies greatly within the normal population. Current platelet function tests are used to...
BACKGROUND
The response of platelets to activating stimuli and pharmaceutical agents varies greatly within the normal population. Current platelet function tests are used to measure end-point levels of platelet activation without taking the speed at which platelets activate into account, potentially missing vital metrics to characterize platelet reactivity.
OBJECTIVES
To identify variability, to agonists and among individuals, in platelet activation kinetics and assess the impact of this on thrombus formation.
METHODS
We have developed a bespoke real-time flow cytometry assay and analysis package to measure the rate of platelet activation over time using 2 parameters of platelet activation, fibrinogen binding and P-selectin exposure.
RESULTS
The rate of platelet activation varied considerably within the normal population but did not correlate with maximal platelet activation, demonstrating that platelet activation rate is a separate and novel metric to describe platelet reactivity. The relative rate of platelet response between agonists was strongly correlated, suggesting that a central control mechanism regulates the rate of platelet response to all agonists.
CONCLUSION
For the first time, we have shown that platelet response rate corresponds to thrombus size and structure, wherein faster responders form larger, more densely packed thrombi at arterial, but crucially not venous, shear. We have demonstrated that the rate of platelet activation is an important metric in stratifying individual platelet responses and will provide a novel focus for the design and development of antiplatelet therapy, targeting high-shear thrombosis without exacerbating bleeding at low shear.
Topics: Humans; Platelet Activation; Thrombosis; Blood Platelets; Platelet Function Tests; Arteries; Platelet Aggregation
PubMed: 37085037
DOI: 10.1016/j.jtha.2023.03.044 -
Platelets Dec 2023Arterial tonometry and vascular calcification measures are useful in cardiovascular disease (CVD) risk assessment. Prior studies found associations between tonometry...
Arterial tonometry and vascular calcification measures are useful in cardiovascular disease (CVD) risk assessment. Prior studies found associations between tonometry measures, arterial calcium, and CVD risk. Activated platelets release angiopoietin-1 and other factors, which may connect vascular structure and platelet function. We analyzed arterial tonometry, platelet function, aortic, thoracic and coronary calcium, and thoracic and abdominal aorta diameters measured in the Framingham Heart Study Gen3/NOS/OMNI-2 cohorts ( = 3,429, 53.7% women, mean age 54.4 years ±9.3). Platelet reactivity in whole blood or platelet-rich plasma was assessed using 5 assays and 7 agonists. We analyzed linear mixed effects models with platelet reactivity phenotypes as outcomes, adjusting for CVD risk factors and family structure. Higher arterial calcium trended with higher platelet reactivity, whereas larger aortic diameters trended with lower platelet reactivity. Characteristic impedance (Zc) and central pulse pressure positively trended with various platelet traits, while pulse wave velocity and Zc negatively trended with collagen, ADP, and epinephrine traits. All results did not pass a stringent multiple test correction threshold ( < 2.22e-04). The diameter trends were consistent with lower shear environments invoking less platelet reactivity. The vessel calcium trends were consistent with subclinical atherosclerosis and platelet activation being inter-related.
Topics: Female; Male; Humans; Calcium; Pulse Wave Analysis; Blood Pressure; Platelet Activation; Atherosclerosis
PubMed: 37609998
DOI: 10.1080/09537104.2023.2238835 -
Journal of Veterinary Internal Medicine 2023Dual antithrombotic treatment (DAT) with clopidogrel and rivaroxaban sometimes is prescribed to cats with hypertrophic cardiomyopathy at risk of thromboembolism. To...
BACKGROUND
Dual antithrombotic treatment (DAT) with clopidogrel and rivaroxaban sometimes is prescribed to cats with hypertrophic cardiomyopathy at risk of thromboembolism. To date, no studies have evaluated their combined effects on platelet function.
OBJECTIVES/HYPOTHESIS
Evaluate the safety of DAT in healthy cats and compare, ex vivo, platelet-dependent thrombin generation and agonist-induced platelet activation and aggregation in cats treated with clopidogrel, rivaroxaban, or DAT. We hypothesized that DAT would safely modulate agonist-induced platelet activation and aggregation more effectively than single agent treatment.
ANIMALS
Nine apparently healthy 1-year-old cats selected from a research colony.
METHODS
Unblinded, nonrandomized ex vivo cross-over study. All cats received 7 days of rivaroxaban (0.6 ± 0.1 mg/kg PO), clopidogrel (4.7 ± 0.8 mg/kg PO), or DAT with defined washout periods between treatments. Before and after each treatment, adenosine diphosphate (ADP)- and thrombin-induced platelet P-selectin expression was evaluated using flow cytometry to assess platelet activation. Platelet-dependent thrombin generation was measured by fluorescence assay. Platelet aggregation was assessed using whole blood impedance platelet aggregometry.
RESULTS
No cats exhibited adverse effects. Of the 3 treatments, only DAT significantly decreased the number of activated platelets (P = .002), modulated platelet activation in response to thrombin (P = .01), dampened thrombin generation potential (P = .01), and delayed maximum reaction velocity (P = .004) in thrombin generation. Like clopidogrel, DAT inhibited ADP-mediated platelet aggregation. However, rivaroxaban alone resulted in increased aggregation and activation in response to ADP.
CONCLUSION AND CLINICAL IMPORTANCE
Treatment combining clopidogrel and rivaroxaban (DAT) safely decreases platelet activation, platelet response to agonists, and thrombin generation in feline platelets more effectively than monotherapy with either clopidogrel or rivaroxaban.
Topics: Cats; Animals; Clopidogrel; Rivaroxaban; Platelet Aggregation Inhibitors; Thrombin; Ticlopidine; Cross-Over Studies; Aspirin; Blood Platelets; Platelet Aggregation; Adenosine Diphosphate
PubMed: 37208839
DOI: 10.1111/jvim.16727 -
Blood Sep 2023von Willebrand factor (VWF) mediates primary hemostasis and thrombosis in response to hydrodynamic forces. We previously showed that high shear promoted self-association...
von Willebrand factor (VWF) mediates primary hemostasis and thrombosis in response to hydrodynamic forces. We previously showed that high shear promoted self-association of VWF into hyperadhesive strands, which can be attenuated by high-density lipoprotein (HDL) and apolipoprotein A-I. In this study, we show that low-density lipoprotein (LDL) binds VWF under shear and enhances self-association. Vortexing VWF in tubes resulted in its loss from the solution and deposition onto tube surfaces, which was prevented by HDL. At a stabilizing HDL concentration of 1.2 mg/mL, increasing concentrations of LDL progressively increased VWF loss, the effect correlating with the LDL-to-HDL ratio and not the absolute concentration of the lipoproteins. Similarly, HDL diminished deposition of VWF in a post-in-channel microfluidic device, whereas LDL increased both the rate and extent of strand deposition, with both purified VWF and plasma. Hypercholesterolemic human plasma also displayed accelerated VWF accumulation in the microfluidic device. The initial rate of accumulation correlated linearly with the LDL-to-HDL ratio. In Adamts13-/- and Adamts13-/-LDLR-/- mice, high LDL levels enhanced VWF and platelet adhesion to the myocardial microvasculature, reducing cardiac perfusion, impairing systolic function, and producing early signs of cardiomyopathy. In wild-type mice, high plasma LDL concentrations also increased the size and persistence of VWF-platelet thrombi in ionophore-treated mesenteric microvessels, exceeding the accumulation seen in similarly treated ADAMTS13-deficient mice that did not receive LDL infusion. We propose that targeting the interaction of VWF with itself and with LDL may improve the course of thrombotic microangiopathies, atherosclerosis, and other disorders with defective microvascular circulation.
Topics: Mice; Humans; Animals; von Willebrand Factor; Lipoproteins, LDL; Thrombosis; Hemostasis; Platelet Adhesiveness; ADAMTS13 Protein
PubMed: 37506337
DOI: 10.1182/blood.2023019749