Platelets from Calreticulin mutated essential thrombocythemia patients are less reactive than JAK2 V617F mutated platelets.

Both JAK2V617F and calreticulin (CALR) mutated essential thrombocythemia (ET) patients have different clinical characteristics, with lower thrombosis risk in patients with CALR mutations. To elucidate the mechanism for this lower risk we studied platelet function in ET patients with either JAK2V617F or a CALR mutation. Platelet activation state was similar in ET and healthy controls at baseline using P-selectin and PAC1 flow cytometry analysis.

The reduced form of coagulation factor XI is associated with illness severity and coagulopathy in critically-ill septic patients.

Coagulation Factor XI (FXI) contributes to the pathobiology of sepsis-associated thrombosis and is a target for new therapeutics. Through cleavage of disulfide bonds, FXI becomes reduced (rFXI), accelerating intrinsic coagulation cascade activation. The role of rFXI in human sepsis has never been studied.

Low Concentrations of Recombinant Factor VIIa May Improve the Impaired Thrombin Generation of Glanzmann Thrombasthenia Patients.

Introduction:  Glanzmann thrombasthenia (GT) is a rare bleeding disorder. The disease is caused by the lack or dysfunction of platelet membrane glycoprotein IIb/IIIa (integrin αIIbβ3) which is essential for platelet aggregation. Bleeding episodes are usually managed by platelet transfusions.

Platelet factor XI: intracellular localization and mRNA splicing following platelet activation.

Background: The structure and function of platelet factor XI (FXI) protein and the presence of F11 mRNA in platelets are controversial. Although platelets are anucleated cells they contain spliceosome components and pre-mRNAs. Three platelet proteins have been demonstrated to be spliced upon platelet activation.

An allosteric disulfide bond is involved in enhanced activation of factor XI by protein disulfide isomerase.

Unlabelled: Essentials Reduction of three disulfide bonds in factor (F) XI enhances chromogenic substrate cleavage. We measured FXI activity upon reduction and identified a bond involved in the enhanced activity. Reduction of FXI augments FIX cleavage, probably by faster conversion of FXI to FXIa.

Thromboembolic events in patients with severe inherited fibrinogen deficiency.

Inherited afibrinogenemia and hypofibrinogenemia are rare bleeding disorders characterized by markedly reduced levels of fibrinogen in blood. Thrombotic complications in these disorders have been rarely described. We performed a multicenter retrospective study and reviewed the occurrence of thrombotic complications among patients with inherited fibrinogen deficiency.

The role of protein disulfide isomerase in the post-ligation phase of β3 integrin-dependent cell adhesion.

Introduction: Protein disulfide isomerase (PDI) catalyzes disulfide bond exchange. It is crucial for integrin-mediated platelet adhesion and aggregation and disulfide bond exchange is necessary for αIIbβ3 and αvβ3 activation. However, the role of disulfide bond exchange and PDI in the post-ligation phase of αIIbβ3 and αvβ3 mediated cell adhesion has yet to be determined.

Persistent neonatal thrombocytopenia can be caused by IgA antiplatelet antibodies in breast milk of immune thrombocytopenic mothers.

Immune thrombocytopenia (ITP) in pregnant women can cause neonatal thrombocytopenia by transport of antiplatelet autoantibodies across the placenta. Usually, an infant's platelet count normalizes within 2 months. We observed neonatal thrombocytopenia that persisted more than 4 months and disappeared following discontinuation of breastfeeding.

Abnormal cytoplasmic extensions associated with active αIIbβ3 are probably the cause for macrothrombocytopenia in Glanzmann thrombasthenia-like syndrome.

Mutations in the ITGA2B or ITGB3 genes that encode for the αIIbβ3 platelet integrin usually cause Glanzmann thrombasthenia, a severe autosomal recessive bleeding disorder characterized by absence of platelet aggregation, but normal platelet number and size. Several rare mutations cause a Glanzmann-like syndrome which manifests macrothrombocytopenia and usually displays autosomal dominant inheritance. The exact mechanism causing Glanzmann-like syndrome is unknown.

Natural and artificial mutations in αIIb integrin lead to a structural deformation of a calcium-binding site.

The platelet integrin αIIbβ3 is widely accepted as a structural and a functional model of the broad integrin protein family. The four calcium-binding sites in the αIIb subunit contribute to biogenesis and stability of the protein. Mansour et al.

Abnormal plasma clot structure and stability distinguish bleeding risk in patients with severe factor XI deficiency.

Background: Factor XI (FXI) deficiency is a rare autosomal recessive disorder. Many patients with even very low FXI levels (< 20 IU dL(-1) ) are asymptomatic or exhibit only mild bleeding, whereas others experience severe bleeding, usually following trauma. Neither FXI antigen nor activity predicts the risk of bleeding in FXI-deficient patients.

Disulfide bond exchanges in integrins αIIbβ3 and αvβ3 are required for activation and post-ligation signaling during clot retraction.

Background: Integrin αIIbβ3 mediates platelet adhesion, aggregation and fibrin clot retraction. These processes require activation of αIIbβ3 and post-ligation signaling. Disulfide bond exchanges are involved in αIIbβ3 and αvβ3 activation.

Type I mutation in the F11 gene is a third ancestral mutation which causes factor XI deficiency in Ashkenazi Jews.

Background: Factor XI (FXI) deficiency is one of the most frequent inherited disorders in Ashkenazi Jews (AJ). Two predominant founder mutations termed type II (p.Glu117Stop) and type III (p.

Treatment of inherited platelet disorders.

For patients affected by severe inherited platelet dysfunctions, e.g. Glanzmann thrombasthenia (GT) or Bernard-Soulier syndrome (BSS), platelet transfusion is frequently needed for controlling spontaneous bleeding, and is always needed when trauma occurs or surgery is performed.

Inherited platelet disorders.

Inherited diseases of the megakaryocyte lineage give rise to bleeding when platelets fail to fulfill their hemostatic function upon vessel injury. Platelet defects extend from the absence or malfunctioning of adhesion (GPIb-IX-V, Bernard-Soulier syndrome) or aggregation receptors (integrin αIIbβ3, Glanzmann thrombasthenia) to defects of primary receptors for soluble agonists, secretion from storage organelles, activation pathways and the generation of procoagulant activity. In disorders such as the Chediak-Higashi, Hermansky-Pudlak, Wiskott-Aldrich and Scott syndromes the molecular lesion extends to other cells.

Unique disulfide bonds in epidermal growth factor (EGF) domains of β3 affect structure and function of αIIbβ3 and αvβ3 integrins in different manner.

The β3 subunit of αIIbβ3 and αvβ3 integrins contains four epidermal growth factor (EGF)-like domains. Each domain harbors four disulfide bonds of which one is unique for integrins. We previously discerned a regulatory role of the EGF-4 Cys-560-Cys-583 unique bond for αIIbβ3 activation.

A mutation in the β3 cytoplasmic tail causes variant Glanzmann thrombasthenia by abrogating transition of αIIb β3 to an active state.

Background: The cytoplasmic tails of α(IIb) and β(3) regulate essential α(IIb) β(3) functions. We previously described a variant Glanzmann thrombasthenia mutation in the β(3) cytoplasmic tail, IVS14: -3C>G, which causes a frameshift with an extension of β(3) by 40 residues.

Objectives: The aim of this study was to characterize the mechanism by which the mutation abrogates transition of α(IIb) β(3) from a resting state to an active state.

Point mutations regarded as missense mutations cause splicing defects in the factor XI gene.

Background: Point mutations within exons are frequently defined as missense mutations. In the factor (F)XI gene, three point mutations, c.616C>T in exon 7, c.

Patients with severe factor XI deficiency have a reduced incidence of deep-vein thrombosis.

Factor XI (FXI) plays a dual role in haemostasis and thrombosis. It contributes to thrombin generation and promotes inhibition of fibrinolysis. Severe FXI deficiency was shown to confer protection against arterial and venous thrombosis in animal models without compromising haemostasis.

An αIIb mutation in patients with Glanzmann thrombasthenia located in the N-terminus of blade 1 of the β-propeller (Asn2Asp) disrupts a calcium binding site in blade 6.

Background: Studies of Glanzmann thrombasthenia (GT)-causing mutations has generated invaluable information on the formation and function of integrin αIIbβ(3).

Objective: To characterize the mutation in four siblings of an Israeli Arab family affected by GT, and to analyze the relationships between the mutant protein structure and its function using artificial mutations.

Methods And Results: Sequencing disclosed a new A97G transversion in the αIIb gene predicting Asn2Asp substitution at blade 1 of the β-propeller.

[Inherited bleeding disorders common in Jews].

Four inherited disorders of hemostasis have been identified in Jews with a relatively high frequency: Factor XI deficiency, factor VII deficiency, combined factor V and VIII deficiency and GLanzmann thrombasthenia. During the past decades, the bleeding manifestations of these disorders, the diagnosis, the molecular-genetic basis and therapy have been discerned. Furthermore, the prevalence of the respective mutant genes have been delineated in various Jewish Communities.

The association of factor V leiden and prothrombin gene mutation and placenta-mediated pregnancy complications: a systematic review and meta-analysis of prospective cohort studies.

Background: Factor V Leiden (FVL) and prothrombin gene mutation (PGM) are common inherited thrombophilias. Retrospective studies variably suggest a link between maternal FVL/PGM and placenta-mediated pregnancy complications including pregnancy loss, small for gestational age, pre-eclampsia and placental abruption. Prospective cohort studies provide a superior methodologic design but require larger sample sizes to detect important effects.

A unique interaction between alphaIIb and beta3 in the head region is essential for outside-in signaling-related functions of alphaIIbbeta3 integrin.

The main interface of the 2 subunits of platelet integrin alphaIIbbeta3 comprises the beta-propeller domain of alphaIIb and the betaA domain of beta3. In the center of the beta-propeller, several aromatic residues interact by cation-pi and hydrophobic bonds with Arg261 of betaA. In this study, we substituted alphaIIb-Trp110 or beta3-Arg261 by residues abundant in other alpha or beta subunits at corresponding locations and expressed them in baby hamster kidney cells along with normal beta3 or alphaIIb, respectively.

Variable effects of alpha v suppression on VEGFR-2 expression in endothelial cells of different vascular beds.

Integrins alphavbeta3 and alphavbeta5 have been long considered as proangiogenic receptors, yet genetic ablation studies demonstrated enhanced angiogenesis in mice lacking alphavbeta3 and alphavbeta5 integrins, which was attributed to increased expression of vascular endothelial growth factor receptor-2 (VEGFR-2). In this study, we determined the effect of alphavbeta3 and alphavbeta5 suppression in endothelial cells (EC) on vascular endothelial growth factor (VEGF) and VEGFR-2 expression. alphav was suppressed by shRNA in HUVEC (venous endothelial cells) and HMVEC (microvascular endothelial cells).