Updated understanding of platelets in thrombosis and hemostasis: the roles of integrin PSI domains and their potential as therapeutic targets

2020 ◽  
Vol 20 ◽  
Author(s):  
Daniel Thomas MacKeigan ◽  
Tiffany Ni ◽  
Chuanbin Shen ◽  
Tyler William Stratton ◽  
Wenjing Ma ◽  
...  
Keyword(s):  
Redox Reactions ◽  
Platelet Adhesion ◽  
Adaptive Mechanism ◽  
Dynamic Interactions ◽  
Surface Receptors ◽  
Isomerase Activity ◽  
Pathological Conditions ◽  
Fibrinogen Binding ◽  
Immune Mediated ◽  
Novel Target

: Platelets are small blood cells known primarily for their ability to adhere and aggregate at injured vessels to arrest bleeding. However, when triggered under pathological conditions, the same adaptive mechanism of platelet adhesion and aggregation may cause thrombosis, a primary cause of heart attack and stroke. Over recent decades, research has made considerable progress in uncovering the intricate and dynamic interactions that regulate these processes. Integrins are heterodimeric cell surface receptors expressed on all metazoan cells that facilitate cell adhesion, movement, and signaling, to drive biological and pathological processes such as thrombosis and hemostasis. Recently, our group discovered that the plexinsemaphorin-integrin (PSI) domains of the integrin β subunits exert endogenous thiol isomerase activity derived from their two highly conserved CXXC active site motifs. Given the importance of redox reactions in integrin activation and its location in the knee region, this PSI domain activity may be critically involved in facilitating the interconversions between integrin conformations. Our monoclonal antibodies against the β3 PSI domain inhibited its thiol isomerase activity and proportionally attenuated fibrinogen binding and platelet aggregation. Notably, these antibodies inhibited thrombosis without significantly impairing hemostasis or causing platelet clearance. In this review, we will update mechanisms of thrombosis and hemostasis including platelet versatilities and immune-mediated thrombocytopenia, discuss critical contributions of the newly discovered PSI domain thiol isomerase activity, and its potential as a novel target for anti-thrombotic therapies and beyond.

Partial Inhibition of Platelet Aggregation and Fibrinogen Binding by a Murine Monoclonal Antibody to GPIIIa: Requirement for Antibody Bivalency

1994 ◽  
Vol 72 (06) ◽  
pp. 964-972 ◽  
Author(s):  
Jeffery L Kutok ◽  
Barry S Coller
Keyword(s):  
Monoclonal Antibody ◽  
Platelet Aggregation ◽  
Murine Monoclonal Antibody ◽  
Platelet Glycoprotein ◽  
Igg Antibody ◽  
Surface Receptors ◽  
Partial Inhibition ◽  
Fibrinogen Binding ◽  
Igg Binding ◽  
Agonist Concentration

SummaryWe produced a murine monoclonal antibody, 7H2, and localized its epitope to one or more small regions on platelet glycoprotein (GP) Ilia. 7H2-IgG and 7H2-F(ab’)2 completely inhibit platelet aggregation and fibrinogen binding at low agonist concentrations, but only partially inhibit aggregation and fibrinogen binding at high agonist concentrations; 7H2-Fab has no effect on aggregation or fibrinogen binding at any agonist concentration. 7H2-IgG binds to the entire platelet population as judged by flow cytometry. At near saturating concentrations, ∼40,000 7H2-IgG antibody molecules bind per platelet. In contrast, ∼80,000 7H2 Fab molecules bind per platelet, suggesting that 7H2-IgG binding is bivalent. 7H2 was unable to inhibit fibrinogen binding to purified, immobilized GPIIb/IIIa. These data indicate that the bivalent binding of 7H2 to GPIIIa is required for its partial inhibition of fibrinogen binding to platelets, perhaps through dimerization of GPIIb/IIIa surface receptors (or more complex GPIIb/IIIa redistribution triggered by 7H2 binding) resulting in limited accessibility of fibrinogen to its binding site(s).

scholarly journals The (Patho)Biology of SRC Kinase in Platelets and Megakaryocytes

Medicina ◽  
2020 ◽  
Vol 56 (12) ◽  
pp. 633
Author(s):  
Lore De Kock ◽  
Kathleen Freson
Keyword(s):  
Platelet Activation ◽  
Knockout Mice ◽  
Missense Variant ◽  
Surface Receptors ◽  
Src Signaling ◽  
Normal Platelet ◽  
Fibrinogen Binding ◽  
Cellular Environment ◽  
Proplatelet Formation

Proto-oncogene tyrosine-protein kinase SRC (SRC), as other members of the SRC family kinases (SFK), plays an important role in regulating signal transduction by different cell surface receptors after changes in the cellular environment. Here, we reviewed the role of SRC in platelets and megakaryocytes (MK). In platelets, inactive closed SRC is coupled to the β subunit of integrin αIIbβ3 while upon fibrinogen binding during platelet activation, αIIbβ3-mediated outside-in signaling is initiated by activation of SRC. Active open SRC now further stimulates many downstream effectors via tyrosine phosphorylation of enzymes, adaptors, and especially cytoskeletal components. Functional platelet studies using SRC knockout mice or broad spectrum SFK inhibitors pointed out that SRC mediates their spreading on fibrinogen. On the other hand, an activating pathological SRC missense variant E527K in humans that causes bleeding inhibits collagen-induced platelet activation while stimulating platelet spreading. The role of SRC in megakaryopoiesis is much less studied. SRC knockout mice have a normal platelet count though studies with SFK inhibitors point out that SRC could interfere with MK polyploidization and proplatelet formation but these inhibitors are not specific. Patients with the SRC E527K variant have thrombocytopenia due to hyperactive SRC that inhibits proplatelet formation after increased spreading of MK on fibrinogen and enhanced formation of podosomes. Studies in humans have contributed significantly to our understanding of SRC signaling in platelets and MK.

scholarly journals Neurofascin as a novel target for autoantibody-mediated axonal injury

2007 ◽  
Vol 204 (10) ◽  
pp. 2363-2372 ◽  
Author(s):  
Emily K. Mathey ◽  
Tobias Derfuss ◽  
Maria K. Storch ◽  
Kieran R. Williams ◽  
Kimberly Hales ◽  
...  
Keyword(s):  
Axonal Injury ◽  
Dependent Manner ◽  
Nodes Of Ranvier ◽  
Native Form ◽  
Neuronal Protein ◽  
Axonal Pathology ◽  
Immune Mediated ◽  
Novel Target

Axonal injury is considered the major cause of disability in patients with multiple sclerosis (MS), but the underlying effector mechanisms are poorly understood. Starting with a proteomics-based approach, we identified neurofascin-specific autoantibodies in patients with MS. These autoantibodies recognize the native form of the extracellular domains of both neurofascin 186 (NF186), a neuronal protein concentrated in myelinated fibers at nodes of Ranvier, and NF155, the oligodendrocyte-specific isoform of neurofascin. Our in vitro studies with hippocampal slice cultures indicate that neurofascin antibodies inhibit axonal conduction in a complement-dependent manner. To evaluate whether circulating antineurofascin antibodies mediate a pathogenic effect in vivo, we cotransferred these antibodies with myelin oligodendrocyte glycoprotein–specific encephalitogenic T cells to mimic the inflammatory pathology of MS and breach the blood–brain barrier. In this animal model, antibodies to neurofascin selectively targeted nodes of Ranvier, resulting in deposition of complement, axonal injury, and disease exacerbation. Collectively, these results identify a novel mechanism of immune-mediated axonal injury that can contribute to axonal pathology in MS.

scholarly journals Drug-induced thrombocytopenia: pathogenesis, evaluation, and management

Hematology ◽  
2009 ◽  
Vol 2009 (1) ◽  
pp. 153-158 ◽  
Author(s):  
James N. George ◽  
Richard H. Aster
Keyword(s):  
Single Dose ◽  
Causal Relation ◽  
Severe Thrombocytopenia ◽  
Antithrombotic Agents ◽  
Drug Induced ◽  
Level Of Evidence ◽  
Common Cause ◽  
Fibrinogen Binding ◽  
Immune Mediated ◽  
Drug Dependent

AbstractAlthough drugs are a common cause of acute immune-mediated thrombocytopenia in adults, the drug etiology is often initially unrecognized. Most cases of drug-induced thrombocytopenia (DITP) are caused by drug-dependent antibodies that are specific for the drug structure and bind tightly to platelets by their Fab regions but only in the presence of the drug. A comprehensive database of 1301 published reports describing 317 drugs, available at www.ouhsc.edu/platelets, provides information on the level of evidence for a causal relation to thrombocytopenia. Typically, DITP occurs 1 to 2 weeks after beginning a new drug or suddenly after a single dose when a drug has previously been taken intermittently. However, severe thrombocytopenia can occur immediately after the first administration of antithrombotic agents that block fibrinogen binding to platelet GP IIb-IIIa, such as abciximab, tirofiban, and eptifibatide. Recovery from DITP usually begins within 1 to 2 days of stopping the drug and is typically complete within a week. Drug-dependent antibodies can persist for many years; therefore, it is important that the drug etiology be confirmed and the drug be avoided thereafter.

Abstract 18698: Identification of a Novel Cardiac Progenitor Population Expressing Pw1/peg3 in the Murine Heart

Circulation ◽  
2014 ◽  
Vol 130 (suppl_2) ◽  
Author(s):  
Elisa Yaniz-Galende ◽  
Luigi Formicola ◽  
Nathalie Mougenot ◽  
Lise Legrand ◽  
Jiqiu Chen ◽  
...  
Keyword(s):  
Progenitor Cells ◽  
Fold Increase ◽  
Cardiac Regeneration ◽  
Cardiac Repair ◽  
Cardiac Progenitor Cells ◽  
Average Percentage ◽  
Pathological Conditions ◽  
Reporter Mice ◽  
Novel Target

The myocardium responds to injury by recruiting cardiac progenitor cells (CPCs) to the injured tissue to promote cardiac repair. Although different classes of CPCs have been identified, their contribution in physiological and pathological conditions remains unclear. PW1 gene has recently been proposed as a marker of resident adult stem and progenitor cell populations in several adult tissues. Our goal was to characterize and determine the role of PW1+ population in the heart. Here, we employ immunostaining and fluorescence-activated cell sorting (FACS) analysis in PW1-reporter mouse to perform qualitative and quantitative analyses of PW1+ population in the heart. We first found that PW1+ cells are mainly located in the epicardium and myocardial interstitium of normal hearts. The average percentage of PW1+ cells, as assessed by FACS, was 1.56±1.41%. A subset of PW1+ cells also co-express other CPC markers such as Sca-1 (52±22%) or PDGFR1α (43±14%). In contrast, a very small proportion of PW1+ cells co-express c-kit (6±5%). To investigate the contribution of PW1+ cells in pathological conditions, we then performed myocardial infarction (MI) by LAD ligation in PW1-reporter mice. We found that MI resulted in a 3-fold increase in the number of PW1+ cells in infarcted mice compared with sham-operated groups, at 1 week post-MI (1.16%±0.47% in sham versus 3.43%±0.82 in MI). This population preferentially localized in the injured myocardium and border area. PW1+ cells were isolated by FACS from the whole infarcted heart from PW1-reporter mice. In vitro differentiation assays reveal that purified PW1+ cells are multipotent and can spontaneously differentiate into smooth muscle cells, endothelial cells and cardiomyocyte-like cells. Taken together, our data identify a novel PW1+ cardiac progenitor population with the potential to undergo differentiation into multiple cardiac lineages, suggesting their involvement in cardiac repair in normal and pathological conditions. The discovery of a novel population of cardiac progenitor cells, augmented following MI and with cardiogenic potential, provides a novel target for therapeutic approaches aimed at improving cardiac regeneration.

scholarly journals Does the conformation of adsorbed fibrinogen dictate platelet interactions with artificial surfaces?

Blood ◽  
1986 ◽  
Vol 68 (2) ◽  
pp. 355-362 ◽  
Author(s):  
JN Lindon ◽  
G McManama ◽  
L Kushner ◽  
EW Merrill ◽  
EW Salzman
Keyword(s):  
Platelet Adhesion ◽  
Surface Coverage ◽  
Platelet Reactivity ◽  
Polymer Surfaces ◽  
Side Chain ◽  
Alkyl Side Chain ◽  
Fibrinogen Binding ◽  
Artificial Surfaces ◽  
Antibody Preparations ◽  
Fibrinogen Adsorption

Abstract Platelet activation by polymer surfaces is thought to require preliminary adsorption of fibrinogen and perhaps changes in fibrinogen conformation. We measured fibrinogen adsorption by a series of polymers by two methods, using either 125I-labeled fibrinogen or 125I-labeled antifibrinogen antibodies, and correlated the results with platelet reactivity (retention and secretion) in columns of beads coated with the polymers. For polyalkyl methacrylates with 1 to 4 carbon side chains, platelet reactivity varied directly with increasing length of the alkyl side chain and with the quantity of bound fibrinogen recognizable by antifibrinogen antibody but not with the total quantity of fibrinogen adsorbed. The same pattern of results was seen with five antibody preparations, including affinity-purified Fab fragments against the D or E domain of fibrinogen. Tests of platelet retention and fibrinogen binding to four polyalkyl acrylates and to three unrelated polymers (polystyrene, polymethyl methacrylate, and a polyether polyurethane) indicated that platelet retention correlated positively with both total fibrinogen binding and with the amount of antibody-recognizable fibrinogen bound. Drugs that block platelet aggregation, but not adhesion, did not alter the hierarchy of platelet retention to the polyalkyl methacrylates. These data suggest that, contrary to previous views, platelet adhesion to artificial surfaces increases with increasing surface coverage of adsorbed fibrinogen if the bound fibrinogen maintains a conformation such that its functional domains remain recognizable by antibody probes.

Genetic and Pharmacological Analyses of Syk Function in IIbβ3 Signaling in Platelets

Blood ◽  
1999 ◽  
Vol 93 (8) ◽  
pp. 2645-2652 ◽  
Author(s):  
Debbie A. Law ◽  
Lisa Nannizzi-Alaimo ◽  
Kathleen Ministri ◽  
Paul E. Hughes ◽  
Jane Forsyth ◽  
...  
Keyword(s):  
Tyrosine Kinase ◽  
Tyrosine Kinases ◽  
Platelet Adhesion ◽  
Kinase Inhibitor ◽  
Human Platelet ◽  
Human Platelets ◽  
Protein Tyrosine Kinases ◽  
Fibrinogen Binding ◽  
Multiple Protein ◽  
Inside Out

Agonists induce inside-out IIbβ3signaling resulting in fibrinogen binding and platelet aggregation. These in turn trigger outside-in signaling resulting in further platelet stimulation. Because the Syk tyrosine kinase is activated during both phases of integrin signaling, we evaluated its role in IIbβ3 function in murine platelets rendered null for Syk by gene targeting and in human platelets incubated with piceatannol, a tyrosine kinase inhibitor reportedly selective for Syk. Both Syk null murine platelets and piceatannol-treated human platelets exhibited a partial, but statistically significant defect in activation of IIbβ3 by adenine diphosphate (ADP) ± epinephrine as assessed by fibrinogen binding. Syk null platelets adhered normally to immobilized fibrinogen, and mice with these platelets exhibited normal tail bleeding times. In contrast, piceatannol treatment of human platelets completely inhibited platelet adhesion to immobilized fibrinogen. The discrepancy in extent of integrin dysfunction between murine and human platelet models may be due to lack of specificity of piceatannol, because this compound inhibited the activity of Src and FAK as well as Syk and also reduced tyrosine phosphorylation of multiple platelet proteins. These results provide genetic evidence that Syk plays a role in IIbβ3 signaling in platelets and pharmacological evidence that, although piceatannol also inhibits IIbβ3 signaling, it does so by inhibtion of multiple protein tyrosine kinases.

Cell-Based Therapeutic Strategies in Multiple Sclerosis

2014 ◽  
Vol 9 (1) ◽  
pp. 37
Author(s):  
Ian Rossman ◽  
Jeffrey A Cohen ◽  
◽  
Keyword(s):  
Multiple Sclerosis ◽  
Neurological Deficits ◽  
Perivascular Spaces ◽  
Cns Injury ◽  
Surface Receptors ◽  
Immune Mediated ◽  
Relapsing Remitting ◽  
Disease Stages ◽  
Ongoing Phase

Multiple sclerosis (MS) is an immune-mediated disease in which acute inflammatory demyelination leads to axonal injury and neurodegeneration, and is manifested clinically by relapsing–remitting neurological deficits superimposed on chronic accumulation of disability. MS treatments are largely immunomodulatory with little, if any, effect on neurodegeneration. Mesenchymal stem cells MSCs) are pluripotent cells derived from adult tissues with intrinsic anti-inflammatory and repair-promoting properties. They cross the blood–brain barrier and target perivascular spaces, which are the sites of inflammatory cell infiltration in MS.In vitro, MSCs can be purified and expanded, labelled for post-transplant tracking and be manipulated to express surface receptors or neurotrophic factors for central nervous system (CNS) targeting or neuroprotection, respectively. Animal models of MS, traumatic CNS injury and neurodegenerative diseases demonstrate clinical and pathological benefits following MSC transplantation. Potentially, MSCs can be used to treat MS patients at various disease stages, which is the current focus of ongoing phase I/II clinical trials at multiple centres.

scholarly journals Role of Leptin in the Activation of Immune Cells

2010 ◽  
Vol 2010 ◽  
pp. 1-8 ◽  
Author(s):  
Patricia Fernández-Riejos ◽  
Souad Najib ◽  
Jose Santos-Alvarez ◽  
Consuelo Martín-Romero ◽  
Antonio Pérez-Pérez ◽  
...  
Keyword(s):  
Immune Response ◽  
Immune Cells ◽  
Energy Homeostasis ◽  
Humoral Factors ◽  
Endocrine Organ ◽  
Pathological Conditions ◽  
Immune Mediated ◽  
Infection Susceptibility

Adipose tissue is an active endocrine organ that secretes various humoral factors (adipokines), and its shift to production of proinflammatory cytokines in obesity likely contributes to the low-level systemic inflammation that may be present in metabolic syndrome-associated chronic pathologies such as atherosclerosis. Leptin is one of the most important hormones secreted by adipocytes, with a variety of physiological roles related to the control of metabolism and energy homeostasis. One of these functions is the connection between nutritional status and immune competence. The adipocyte-derived hormone leptin has been shown to regulate the immune response, innate and adaptive response, both in normal and pathological conditions. The role of leptin in regulating immune response has been assessed in vitro as well as in clinical studies. It has been shown that conditions of reduced leptin production are associated with increased infection susceptibility. Conversely, immune-mediated disorders such as autoimmune diseases are associated with increased secretion of leptin and production of proinflammatory pathogenic cytokines. Thus, leptin is a mediator of the inflammatory response.

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