Crosstalk between Platelet and Bacteria: A Therapeutic Prospect

2019 ◽  
Vol 25 (38) ◽  
pp. 4041-4052
Author(s):  
Vivek K. Yadav ◽  
Pradeep K. Singh ◽  
Vishnu Agarwal ◽  
Sunil K. Singh
Keyword(s):  
Platelet Activation ◽  
Molecular Mechanisms ◽  
Thrombus Formation ◽  
Critical Role ◽  
Direct Interaction ◽  
Vascular Wall ◽  
Cardiovascular Complications ◽  
Bacterial Cells ◽  
Platelet Surface ◽  
Wide Range

Platelets are typically recognized for their roles in the maintenance of hemostasis and vascular wall repair to reduce blood loss. Beyond hemostasis, platelets also play a critical role in pathophysiological conditions like atherosclerosis, stroke, thrombosis, and infections. During infection, platelets interact directly and indirectly with bacteria through a wide range of cellular and molecular mechanisms. Platelet surface receptors such as GPIbα, FcγRIIA, GPIIbIIIa, and TLRs, etc. facilitate direct interaction with bacterial cells. Besides, the indirect interaction between platelet and bacteria involves host plasma proteins such as von Willebrand Factor (vWF), fibronectin, IgG, and fibrinogen. Bacterial cells induce platelet activation, aggregation, and thrombus formation in the microvasculature. The activated platelets induce the Neutrophil Extracellular Traps (NETs) formation, which further contribute to thrombosis. Thus, platelets are extensively anticipated as vital immune modulator cells during infection, which may further lead to cardiovascular complications. In this review, we cover the interaction mechanisms between platelets and bacteria that may lead to the development of thrombotic disorders. Platelet receptors and other host molecules involved in such interactions can be used to develop new therapeutic strategies to combat against infection-induced cardiovascular complications. In addition, we highlight other receptor and enzyme targets that may further reduce infection-induced platelet activation and various pathological conditions.

scholarly journals High Mobility Group Box 1 enhances ADP-mediated platelet activation by increasing platelet surface P2Y12 localization

2021 ◽  
Author(s):  
Deirdre Nolfi-Donegan ◽  
Gowtham Annarapu ◽  
Lisa Maurer ◽  
Cheryl Hillery ◽  
Sruti Shiva
Keyword(s):  
Platelet Activation ◽  
Cross Talk ◽  
Molecular Mechanisms ◽  
Thrombus Formation ◽  
High Mobility ◽  
Vascular Diseases ◽  
Human Platelets ◽  
Cellular Level ◽  
High Mobility Group ◽  
Platelet Surface

Thrombosis and inflammation are intimately linked and synergistically contribute to the pathogenesis of a number of vascular diseases. On a cellular level, while the platelet is central to thrombus formation as well as an active mediator of inflammation, the molecular mechanisms of cross-talk between thrombosis and inflammation remain elusive. High-Mobility Group Box 1 protein (HMGB1) is an inflammatory regulator that also stimulates platelet activation through its interaction with toll-like receptor 4 (TLR4). However, it remains unclear whether cross-talk between HMGB1 and traditional thrombotic agonists exists to modulate platelet activation. Using isolated human platelets, we tested whether HMGB1 treatment affects platelet activation mediated by traditional agonists. We found that HMGB1 enhances ADP-mediated platelet activation, but not platelet activation stimulated by thrombin or collagen. Further, inhibition of the canonical ADP purinergic P2Y12 receptor attenuates HMGB1-dependent platelet activation. Mechanistically, we discovered that HMGB1 activates platelet surface TLR4 to release ADP from the platelet and concomitantly increase the localization of P2Y12 on the platelet membrane. These data demonstrate that ADP-dependent P2Y12 activation contributes to HMGB1 mediated platelet activation, while HMGB1 primes platelets for an enhanced activation response to ADP. These novel findings further our understanding of thrombo-inflammatory signaling and provide new insight for therapeutic P2Y12 inhibition.

GPIb-dependent platelet activation is dependent on Src kinases but not MAP kinase or cGMP-dependent kinase

Blood ◽  
2004 ◽  
Vol 103 (7) ◽  
pp. 2601-2609 ◽  
Author(s):  
Stuart J. Marshall ◽  
Yotis A. Senis ◽  
Jocelyn M. Auger ◽  
Robert Feil ◽  
Franz Hofmann ◽  
...  
Keyword(s):  
Map Kinase ◽  
Platelet Activation ◽  
Map Kinases ◽  
Thrombus Formation ◽  
Critical Role ◽  
Rabbit Model ◽  
Guanosine Monophosphate ◽  
Src Kinases ◽  
Aggregate Formation ◽  
No Donor

Abstract Glycoprotein Ib-IX-V (GPIb-IX-V) mediates platelet tethering to von Willebrand factor (VWF), recruiting platelets into the thrombus, and activates integrin αIIbβ3 through a pathway that is dependent on Src kinases. In addition, recent reports indicate that activation of αIIbβ3 by VWF is dependent on protein kinase G (PKG) and mitogen-activated protein (MAP) kinases. The present study compares the importance of these signaling pathways in the activation of αIIbβ3 by GPIb-IX-V. In contrast to a recent report, VWF did not promote an increase in cyclic guanosine monophosphate (cGMP), while agents that elevate cGMP, such as the nitrous oxide (NO) donor glyco–SNAP-1 (N-(β-D-glucopyranosyl)-N2-acetyl-S-nitroso-D,L-penicillaminamide) or the type 5 phosphosdiesterase inhibitor, sildenafil, inhibited rather than promoted activation of αIIbβ3 by GPIb-IX-V and blocked aggregate formation on collagen at an intermediate rate of shear (800 s-1). Additionally, sildenafil increased blood flow in a rabbit model of thrombus formation in vivo. A novel inhibitor of the MAP kinase pathway, which is active in plasma, PD184161, had no effect on aggregate formation on collagen under flow conditions, whereas a novel inhibitor of Src kinases, which is also active in plasma, PD173952, blocked this response. These results demonstrate a critical role for Src kinases but not MAP kinases in VWF-dependent platelet activation and demonstrate an inhibitory role for cGMP-elevating agents in regulating this process.

scholarly journals Time-Course Proteomic Analysis of Pseudomonas putida KT2440 during Mcl-Polyhydroxyalkanoate Synthesis under Nitrogen Deficiency

Polymers ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 748 ◽  
Author(s):  
Justyna Możejko-Ciesielska ◽  
Agnieszka Mostek
Keyword(s):  
Pseudomonas Putida ◽  
Proteomic Analysis ◽  
Cellular Response ◽  
Time Course ◽  
Molecular Mechanisms ◽  
Nitrogen Deficiency ◽  
Growth Stages ◽  
Bacterial Cells ◽  
Pseudomonas Putida Kt2440 ◽  
Wide Range

Medium-chain-length polyhydroxyalkanoates (mcl-PHAs) have gained great attention as a new green alternative to petrochemical-derived polymers. Due to their outstanding material properties they can be used in a wide range of applications. Pseudomonas putida KT2440 is a metabolically versatile producer of mcl-polyhydroxyalkanoates. Although the metabolism of polyhydroxyalkanoate synthesis by this bacterium has been extensively studied, the comparative proteome analysis from three growth stages of Pseudomonas putida KT2440 cultured with oleic acid during mcl-PHA synthesis has not yet been reported. Therefore; the aim of the study was to compare the proteome of Pseudomonas putida KT2440 at different time points of its cultivation using the 2D difference gel electrophoresis (2D-DIGE) technique. The analyses showed that low levels of a nitrogen source were beneficial for mcl-PHA synthesis. Proteomic analysis revealed that the proteins associated with carbon metabolism were affected by nitrogen starvation and mcl-PHA synthesis. Furthermore, the induction of proteins involved in nitrogen metabolism, ribosome synthesis, and transport was observed, which may be the cellular response to stress related to nitrogen deficiency and mcl-PHA content in bacterial cells. To sum up; this study enabled the investigators to acquire a better knowledge of the molecular mechanisms underlying the induction of polyhydroxyalkanoate synthesis and accumulation in Pseudomonas putida KT2440 that could lead to improved strategies for PHAs in industrial production.

DETECTION OF ACTIVATED PLATELETS IN WHOLE BLOOD BY FLOW CYTOMETRY

1987 ◽  
Author(s):  
S J Shattil ◽  
J A Hoxie ◽  
M Cunningham ◽  
C S Abrahms ◽  
J O’Brien ◽  
...  
Keyword(s):  
Flow Cytometry ◽  
Monoclonal Antibodies ◽  
Platelet Activation ◽  
Whole Blood ◽  
Thrombus Formation ◽  
Membrane Surface ◽  
White Blood Cells ◽  
Color Flow ◽  
Platelet Surface ◽  
Activated Platelets

Platelets may become activated in a number of clinical disorders and participate in thrombus formation. We have developed a direct test for activated platelets in whole blood that utilizes dual-color flow cytometry and requires no washing steps. Platelets were distinguished from erythrocytes and white blood cells in the flow cytometer by labeling the platelets with biotin-AP1, an antibody specific for membrane glycoprotein lb, and analyzing the cells for phycoerythrin-streptavidin fluorescence. Membrane surface changes resulting from platelet activation were detected with three different FITC-labeled monoclonal antibodies: 1) PAC1, an antibody specific for the fibrinogen receptor on activated platelets; 2) 9F9, which binds to the D-domain of fibrinogen and detects platelet-bound fibrinogen; and 3) S12, which binds to an alpha-granule membrane protein that associates with the platelet surface during secretion. Unstimulated platelets demonstrated no PAC1, 9F9, or S12-specific fluorescence, indicating that they did not bind these antibodies. Upon stimulation with agonists, however, the platelets demonstrated a dose-dependent increase in FITC-fluorescence. The binding of 9F9 to activated platelets required fibrinogen. Low concentrations of ADP and epinephrine, which induce fibrinogen receptors but little secretion, stimulated near-maximal PAC1 or 9F9 binding but little S12 binding. On the other hand, a concentration of phorbol myristate acetate that evokes full platelet aggregation and secretion induced maximal binding of all three antibodies. When blood samples containing activated and non-activated platelets were mixed, as few as 0.8% activated platelets could be detected by this technique. There was a direct correlation between ADP-induced FITC-PAC1 binding and binding determined in a conventional 125I-PAC1 binding assay (r = 0.99; p < 0.001). These studies demonstrate that activated platelets can be reliably detected in whole blood using activation-dependent monoclonal antibodies and flow cytometry. This method may be useful to assess the degree of platelet activation and the efficacy platelet inhibitor therapy in thrombotic disorders.

Regulated Shedding of sema4D from the Platelet Surface Produces a Bioactive Second Messenger in Thrombotic Disorders.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 1641-1641
Author(s):  
Li Zhu ◽  
Wolfgang Bergmeier ◽  
Jie Wu ◽  
Hong Jiang ◽  
Nana Yeboah ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Platelet Activation ◽  
Transmembrane Domain ◽  
Thrombus Formation ◽  
Active Form ◽  
Extracellular Domain ◽  
Human Platelets ◽  
Biologically Active ◽  
Western Blots ◽  
Platelet Surface

Abstract Proteins that are expressed on the platelet surface can participate in contact-dependent signaling events which modulate thrombus formation or, after being shed from the platelet surface, serve as bioactive messengers that affect the function of nearby cells. Here we show for the first time that platelets express the class IV semaphorin known as sema4D or CD100, and that platelet activation causes the regulated shedding of the sema4D extracellular domain in a biologically-active form. Sema4D is a glycosylated 150 kDa disulfide-linked homodimer that has previously been implicated in interactions between T-cells and B-cells. Platelet activation by collagen, thrombin or PMA causes a transient increase in sema4D surface expression peaking at 15 min, followed by a complete loss of expression over 30–60 minutes. These events are accompanied by the release of the sema4D exodomain as a 130 kDa fragment, leaving a 25–30 kDa transmembrane and cytoplasmic domain fragment that is retained by the platelets. The cleavage event required to produce these fragments is inhibited by metalloprotease inhibitors and abolished in platelets from chimeric mice lacking the metalloprotease known as ADAM17 or TACE (TNF alpha converting enzyme). Incubation of recombinant sema4D with ADAM17 identified a single cleavage site just outside the predicted transmembrane domain. Western blots show that human platelets express ADAM17 in both its immature (zymogen) and mature (active) forms, and indicate that at least some of the ADAM17 is located on the platelet surface. ADAM17-dependent cleavage of sema4D does not require platelet aggregation, but the rate is accelerated when aggregation is allowed to occur and slowed when aggregation is prevented. Under both sets of conditions, cleavage of sema4D occurs to a greater extent and more rapidly than the ADAM17-dependent cleavage of GP Ib alpha, suggesting that there is a hierarchy of proteolytic events when platelets are activated. In terms of biological impact, the shedding of sema4D following platelet activation raises the possibility that the soluble extracellular domain of sema4D serves as a bioactive messenger. Two receptors for sema4D have been identified previously: CD72, which is present on lymphocytes where it regulates the activity of the tyrosine phosphatase, SHP-1, and plexin-B1, which is expressed in endothelial cells. Western blots suggest that both of these receptors are expressed on human platelets and show that SHP-1 is associated with CD72 in resting, but not activated platelets. Taken together, these results demonstrate that sema4D undergoes regulated ADAM17-dependent shedding when platelets are activated, and suggest that this results in the production of a bioactive form of the molecule that can affect responses in nearby platelets, lymphocytes and endothelial cells at sites of thrombosis.

LPS Stimulates Platelet Secretion and Promotes Platelet Aggregation Via TLR4/MyD88 and the cGMP-Dependent Protein Kinase Pathway.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 3658-3658
Author(s):  
Guoying Zhang ◽  
Emily Welch ◽  
Asrar B. Malik ◽  
Xiaoping Du ◽  
Zhenyu Li
Keyword(s):  
Platelet Aggregation ◽  
Protein Kinase ◽  
Platelet Activation ◽  
Thrombus Formation ◽  
Critical Role ◽  
Atp Release ◽  
Dependent Protein Kinase ◽  
Cgmp Dependent Protein Kinase ◽  
Dependent Protein ◽  
Platelet Secretion

Abstract Bacterial lipopolysaccharide (LPS) induces rapid thrombocytopenia, hypotension and sepsis. Although growing evidence suggests that platelet activation plays a critical role in LPS-induced thrombocytopenia and tissue damage, the mechanism of LPS-mediated platelet activation is unclear. Here we show that LPS stimulated platelet secretion of dense and alpha granules as indicated by ATP release and P-selectin expression, and thus enhanced platelet activation induced by low concentrations of platelet agonists. Platelets express components of the LPS receptor-signaling complex, including Toll-like receptor (TLR4), CD14, MD2, and MyD88. The effect of LPS on platelet activation was abolished by an anti-TLR4 blocking antibody or TLR4 knockout. Furthermore, LPS-induced potentiation of platelet aggregation and FeCl3-induced thrombus formation were abolished in MyD88 knockout mice. Importantly, TLR4 mediates LPS-induced cGMP elevation and the stimulatory effect of LPS on platelet aggregation was also abolished by inhibitors of nitric oxide synthase (NOS) and the cGMP-dependent protein kinase (PKG). Thus, LPS promotes platelet secretion and aggregation through a TLR4/MyD88 and cGMP/PKG-dependent pathway.

STIM1 Deficiency Results In Impaired Platelet Procoagulant Activity and Protection From Arterial Thrombosis

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 485-485
Author(s):  
Firdos Ahmad ◽  
Lucia Stefanini ◽  
Timothy Daniel Ouellette ◽  
Teshell K Greene ◽  
Stefan Feske ◽  
...  
Keyword(s):  
Platelet Activation ◽  
Conflicts Of Interest ◽  
Thrombus Formation ◽  
Critical Role ◽  
Phosphatidyl Serine ◽  
Flow Chamber ◽  
Procoagulant Activity ◽  
Static Conditions

Abstract Abstract 485 Platelet activation is a central event in thrombosis and hemostasis. We recently demonstrated that most aspects of platelet activation depend on synergistic signaling by two signaling modules: 1) Ca2+/CalDAG-GEFI/Rap1 and 2) PKC/P2Y12/Rap1. The intracellular Ca2+ concentration of platelets is regulated by Ca2+ release from the endoplasmic reticulum (ER) and store-operated calcium entry (SOCE) through the plasma membrane. Stromal interaction molecule 1 (STIM1) was recently identified as the ER Ca2+ sensor that couples Ca2+ store release to SOCE. In this study, we compared the activation response of platelets lacking STIM1−/− or CalDAG-GEFI−/−, both in vitro and in vivo. To specifically investigate Ca2+-dependent platelet activation, some of the experiments were performed in the presence of inhibitors to P2Y12. The murine Stim1 gene was deleted in the megakaryocyte/platelet lineage by breeding Stim flox/flox mice with PF4-Cre mice (STIM1fl/fl). STIM1fl/fl platelets showed markedly reduced SOCE in response to agonist stimulation. aIIbβ3 activation in STIM1fl/fl platelets was significantly reduced in the presence but not in the absence of the P2Y12 inhibitor, 2-MesAMP. In contrast, aIIbb3 activation was completely inhibited in 2-MesAMP-treated CalDAG-GEFI−/− platelets. Deficiency in STIM1, and to a lesser extent in CalDAG-GEFI, reduced phosphatidyl serine (PS) exposure in platelets stimulated under static conditions. PS exposure was completely abolished in both STIM1fl/fl and CalDAG-GEFI−/− platelets stimulated in the presence of 2-MesAMP. To test the ability of platelets to form thrombi under conditions of arterial shear stress, we performed flow chamber experiments with anticoagulated blood perfused over a collagen surface. Thrombus formation was abolished in CalDAG-GEFI−/− blood and WT blood treated with 2-MesAMP. In contrast, STIM1fl/fl platelets were indistinguishable from WT platelets in their ability to form thrombi. STIM1fl/fl platelets, however, were impaired in their ability to express PS when adhering to collagen under flow. Consistently, when subjected to a laser injury thrombosis model, STIM1fl/fl mice showed delayed and reduced fibrin generation, resulting in the formation of unstable thrombi. In conclusion, our studies indicate a critical role of STIM1 in SOCE and platelet procoagulant activity, but not in CalDAG-GEFI mediated activation of aIIbb3 integrin. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Receptor-interacting protein kinase 3 promotes platelet activation and thrombosis

2017 ◽  
Vol 114 (11) ◽  
pp. 2964-2969 ◽  
Author(s):  
Yiwen Zhang ◽  
Jian Zhang ◽  
Rong Yan ◽  
Jingluan Tian ◽  
Yang Zhang ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Protein Kinase ◽  
Platelet Activation ◽  
Thrombus Formation ◽  
Critical Role ◽  
In Vivo Model ◽  
Clot Retraction ◽  
Interacting Protein ◽  
Bone Marrow Derived Cells

Previous studies have shown that receptor-interacting protein kinase 3 (RIP3) is involved in many important biological processes, including necroptosis, apoptosis, and inflammation. Here we show that RIP3 plays a critical role in regulating platelet functions and in vivo thrombosis and hemostasis. Tail bleeding times were significantly longer in RIP3-knockout (RIP3−/−) mice compared with their wild-type (WT) littermates. In an in vivo model of arteriole thrombosis, mice lacking RIP3 exhibited prolonged occlusion times. WT mice repopulated with RIP3−/− bone marrow-derived cells had longer occlusion times than RIP3−/− mice repopulated with WT bone marrow-derived cells, suggesting a role for RIP3-deficient platelets in arterial thrombosis. Consistent with these findings, we observed that RIP3 was expressed in both human and mice platelets. Deletion of RIP3 in mouse platelets caused a marked defect in aggregation and attenuated dense granule secretion in response to low doses of thrombin or a thromboxane A2 analog, U46619. Phosphorylation of Akt induced by U46619 or thrombin was diminished in RIP3−/− platelets. Moreover, RIP3 interacted with Gα13. Platelet spreading on fibrinogen and clot retraction were impaired in the absence of RIP3. RIP3 inhibitor dose-dependently inhibited platelet aggregation in vitro and prevented arterial thrombus formation in vivo. These data demonstrate a role for RIP3 in promoting in vivo thrombosis and hemostasis by amplifying platelet activation. RIP3 may represent a novel promising therapeutic target for thrombotic diseases.

scholarly journals TLT-1 Regulates Thrombus Growth Under Non-Inflammatory Conditions

Blood ◽  
2021 ◽  
Vol 138 (Supplement 1) ◽  
pp. 1050-1050
Author(s):  
Angela Doerr ◽  
Denise Pedrosa ◽  
Maria Schander ◽  
Yotis A. Senis ◽  
Alexandra Mazharian ◽  
...  
Keyword(s):  
Platelet Activation ◽  
Type I Collagen ◽  
Platelet Rich Plasma ◽  
Thrombus Formation ◽  
Type I ◽  
Wild Type ◽  
Platelet Surface ◽  
Knock Out ◽  
Integrin Αiibβ3

Abstract Background Thrombus formation is a complex, dynamic and multistep process, based on two crucial steps: platelet adhesion and platelet aggregation that both involve the large multimeric plasma glycoprotein Von Willebrand Factor (VWF). VWF binding to the GPIb/X/V complex initiates platelet adhesion to the vessel wall at high shear stress and triggers platelet activation resulting in the generation of thrombin and activation of integrin αIIbβ3 on the platelet surface. This activation of αIIbβ3 in turn leads to outside-in signalling and promotes binding of αIIbβ3 to fibrinogen and VWF, mediating thrombus growth. Trigging receptor expressed on myeloid cells like transcript-1 (TLT-1) is a transmembrane receptor, which is targeted to α-granules of platelets and megakaryocytes. Thrombin-induced platelet activation rapidly presents TLT-1 on the platelet surface and releases a soluble form (sTLT-1) into the circulation. To date the only known ligand for TLT-1 is fibrinogen and TLT-1 has been implicated in the regulation of inflammation-associated thrombosis. Interestingly, a putative interaction of VWF with TLT-1 was indicated by a screen with known platelet receptors. Aim We aimed to evaluate the effect of TLT-1/VWF interaction on platelet aggregation and thrombus formation. Methods Recombinant TLT-1 and VWF were purified and the interaction between TLT-1 and VWF was analyzed by surface plasmon resonance. Static interaction was confirmed by an ELISA based binding assay. Flow assays assessed TLT-1 dependent thrombus formation in vitro. The effects of TLT-1 knockout on thrombus formation in vivo were examined via intravital microscopy of the flow restricted inferior vena cava (IVC) and imaging of platelet attachment and fibrin formation over 6 hours. Furthermore, thrombus formation and resolution was followed by high resolution ultrasound imaging after stenosis induction for 28 days. Integrin aIIbb3 activation was analysed by flow cytometry using the JonA antibody in murine platelet rich plasma. Results VWF bound to soluble TLT-1 with high affinity in a calcium dependent manner (K D = 1.9 nM). The binding site on VWF was mapped to the A3D4 domains and high molecular weight VWF multimers had the greatest affinity for TLT-1. Moreover, HEK293 cells transfected with TLT-1 bound to VWF and VWF strings formed specifically on TLT-1 expressing cells, confirming the interaction between the two proteins. VWF inhibited the binding of fibrinogen to TLT-1, suggesting that VWF is a preferred binding partner of TLT-1. Human platelets exhibited increased TLT-1 surface expression after TRAP-6 induced platelet activation and TLT-1 was detected throughout thrombi formed under flow. Furthermore, a TLT-1 blocking antibody inhibited the interaction of TLT-1 with VWF and reduced platelet capture to type I collagen under shear stress. Ex vivo perfusion of blood from TLT-1 knock out mice over type I collagen also resulted in reduced thrombus formation compared to blood from wild-type mice. TLT-1 knock-out platelets were activated by thrombin similar to wild-type controls, based on P-selectin expression in platelet rich plasma. However, activation of integrin αIIbβ3 determined by JonA staining was reduced in the absence of TLT-1. This phenotype of reduced integrin αIIbβ3 activation on P-selectin positive platelets was phenocopied by the thrombin platelet response in platelet rich plasma from VWF -/- mice, but not GPIbα-deficient mice, indicating that the TLT-1-VWF interaction on platelets directly influences integrin αIIbβ3 activation. Significantly, thrombus formation was markedly reduced in TLT-1 knockout mice in the IVC model in vivo in comparison to wild-type mice. Conclusions This study demonstrates that TLT-1 is a novel platelet ligand for VWF, and that TLT-1 may preferentially bind VWF over fibrinogen. We propose a TLT-1/VWF dependent integrin αIIbβ3 activation mechanism which plays a pivotal role in thrombus formation under non-inflammatory and potentially inflammatory conditions. Disclosures Ruf: ICONIC Therapeutics: Consultancy; MeruVasimmune: Current holder of individual stocks in a privately-held company; ARCA bioscience: Consultancy, Patents & Royalties.

Role of Caspase in a Subset of Human Platelet Activation Responses

Blood ◽  
1999 ◽  
Vol 93 (12) ◽  
pp. 4222-4231 ◽  
Author(s):  
Anna Shcherbina ◽  
Eileen Remold-O’Donnell
Keyword(s):  
Platelet Activation ◽  
Caspase 3 ◽  
Human Platelet ◽  
Thrombus Formation ◽  
Shape Change ◽  
Vascular Wall ◽  
Human Platelets ◽  
Granule Secretion ◽  
Platelets Function

Abstract Platelets function to protect the integrity of the vascular wall. A subset of platelet activation responses that are especially important for thrombus formation include exposure of phosphatidylserine and release of microparticles, which generate procoagulant surfaces. The resemblance of these platelet activation processes to events occurring in nucleated cells undergoing apoptosis suggests a possible role for caspases, which are major effector enzymes of nucleated cell apoptosis. We demonstrate here the presence of caspase-3 in human platelets and its activation by physiological platelet agonists. Using cell-permeable specific inhibitors, we demonstrate a role for a caspase-3–like protease in the agonist-induced (collagen plus thrombin or Ca2+ ionophore) platelet activation events of phosphatidylserine exposure, microparticle release, and cleavage of moesin, a cytoskeletal-membrane linker protein. The role of caspase-3 in platelet activation is restricted rather than global, because other activation responses,  granule secretion, shape change, and aggregation were unaffected by caspase-3 inhibitors. Experiments with two classes of protease inhibitors show that caspase-3 function is distinct from that of calpain, which is also involved in late platelet activation events. These findings show novel functions of caspase and provide new insights for understanding of platelet activation.

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