MAGT1 deficiency in XMEN disease is associated with severe platelet dysfunction and impaired platelet glycoprotein N-glycosylation

BACKGROUND

X-linked immunodeficiency with magnesium defect, Epstein-Barr virus infection, and neoplasia (XMEN) disease is a primary immunodeficiency due to loss-of-function mutations in the gene encoding for magnesium transporter 1 (MAGT1). Furthermore, as MAGT1 is involved in the N-glycosylation process, XMEN disease is classified as a congenital disorder of glycosylation. Although XMEN-associated immunodeficiency is well described, the mechanisms underlying platelet dysfunction and those responsible for life-threatening bleeding events have never been investigated.

OBJECTIVES

To assess platelet functions in patients with XMEN disease.

METHODS

Two unrelated young boys, including one before and after hematopoietic stem cell transplantation, were investigated for their platelet functions, glycoprotein expression, and serum and platelet-derived N-glycans.

RESULTS

Platelet analysis highlighted abnormal elongated cells and unusual barbell-shaped proplatelets. Platelet aggregation, integrin αIIbβ3 activation, calcium mobilization, and protein kinase C activity were impaired between both patients. Strikingly, platelet responses to protease-activated receptor 1 activating peptide were absent at both low and high concentrations. These defects were also associated with decreased molecular weights of glycoprotein Ibα, glycoprotein VI, and integrin αIIb due to partial impairment of N-glycosylation. All these defects were corrected after hematopoietic stem cell transplantation.

CONCLUSION

Our results highlight prominent platelet dysfunction related to MAGT1 deficiency and defective N-glycosylation in several platelet proteins that could explain the hemorrhages reported in patients with XMEN disease.

Shear Forces Induced Platelet Clearance Is a New Mechanism of Thrombocytopenia

BACKGROUND

Thrombocytopenia has been consistently described in patients with extracorporeal membrane oxygenation (ECMO) and associated with poor outcome. However, the prevalence and underlying mechanisms remain largely unknown, and a device-related role of ECMO in thrombocytopenia has been hypothesized. This study aims to investigate the mechanisms underlying thrombocytopenia in ECMO patients.

METHODS

In a prospective cohort of 107 ECMO patients, we investigated platelet count, functions, and glycoprotein shedding. In an ex vivo mock circulatory ECMO loop, we assessed platelet responses and VWF (von Willebrand factor)-GP Ibα (glycoprotein Ibα) interactions at low- and high-flow rates, in the presence or absence of red blood cells. The clearance of human platelets subjected or not to ex vivo perfusion was studied using an in vivo transfusion model in NOD/SCID (nonobese diabetic/severe combined Immunodeficient) mice.

RESULTS

In ECMO patients, we observed a time-dependent decrease in platelet count starting 1 hour after device onset, with a mean drop of 7%, 35%, and 41% at 1, 24, and 48 hours post-ECMO initiation (P=0.00013, P<0.0001, and P<0.0001, respectively), regardless of the type of ECMO. This drop in platelet count was associated with a decrease in platelet GP Ibα expression (before: 47.8±9.1 versus 24 hours post-ECMO: 42.3±8.9 mean fluorescence intensity; P=0.002) and an increase in soluble GP Ibα plasma levels (before: 5.6±3.3 versus 24 hours post-ECMO: 10.8±4.1 µg/mL; P<0.0001). GP Ibα shedding was also observed ex vivo and was unaffected by (1) red blood cells, (2) the coagulation potential, (3) an antibody blocking VWF-GP Ibα interaction, (4) an antibody limiting VWF degradation, and (5) supraphysiological VWF plasma concentrations. In contrast, GP Ibα shedding was dependent on rheological conditions, with a 2.8-fold increase at high- versus low-flow rates. Platelets perfused at high-flow rates before being transfused to immunodeficient mice were eliminated faster in vivo with an accelerated clearance of GP Ibα-negative versus GP Ibα-positive platelets.

CONCLUSIONS

ECMO-associated shear forces induce GP Ibα shedding and thrombocytopenia due to faster clearance of GP Ibα-negative platelets. Inhibiting GP Ibα shedding could represent an approach to reduce thrombocytopenia during ECMO.

DOCK11 deficiency in patients with X-linked actinopathy and autoimmunity

Dedicator of cytokinesis (DOCK) proteins play a central role in actin cytoskeleton regulation. This is highlighted by the DOCK2 and DOCK8 deficiencies leading to actinopathies and immune deficiencies. DOCK8 and DOCK11 activate CDC42, a Rho-guanosine triphosphate hydrolases involved in actin cytoskeleton dynamics, among many cellular functions. The role of DOCK11 in human immune disease has been long suspected but, to the best of our knowledge, has never been described to date. We studied 8 male patients, from 7 unrelated families, with hemizygous DOCK11 missense variants leading to reduced DOCK11 expression. The patients were presenting with early-onset autoimmunity, including cytopenia, systemic lupus erythematosus, skin, and digestive manifestations. Patients' platelets exhibited abnormal ultrastructural morphology and spreading as well as impaired CDC42 activity. In vitro activated T cells and B-lymphoblastoid cell lines from patients exhibited aberrant protrusions and abnormal migration speed in confined channels concomitant with altered actin polymerization during migration. Knock down of DOCK11 recapitulated these abnormal cellular phenotypes in monocytes-derived dendritic cells and primary activated T cells from healthy controls. Lastly, in line with the patients' autoimmune manifestations, we also observed abnormal regulatory T-cell (Treg) phenotype with profoundly reduced FOXP3 and IKZF2 expression. Moreover, we found reduced T-cell proliferation and impaired STAT5B phosphorylation upon interleukin-2 stimulation of the patients' lymphocytes. In conclusion, DOCK11 deficiency is a new X-linked immune-related actinopathy leading to impaired CDC42 activity and STAT5 activation, and is associated with abnormal actin cytoskeleton remodeling as well as Treg phenotype, culminating in immune dysregulation and severe early-onset autoimmunity.

Multicolor flow cytometry in clinical samples for platelet signaling assessment

Background

Availability of multichannel cytometers and specific commercial antibodies makes flow cytometry a new option to simultaneously assess multiple intracellular platelet signaling pathways for clinical purposes, in small volume of blood or low platelet count.

Objectives

To describe a multicolor flow cytometry with fluorescent barcoding technique for screening signaling pathways downstream membrane receptors of major platelet agonists (adenosine diphosphate, thrombin, thromboxane, and collagen).

Methods

By comparison with immunoblotting, we first selected the target phosphoproteins, AKT, P38MAPK, LIMK, and SPL76; the times of stimulation; and phosphoflow barcoding conditions. We then performed a clinical study on whole blood of patients without evidence of blood platelet disorder on standard biological screening, consulting for trivial or occasionally provoked bleeds without familial antecedent (bleeding of unknown origin, n = 23) or type-1 von Willebrand disease (n = 9). In addition, we included a small group of patients with definite platelet disorders (Glanzmann thrombasthenia, δ-storage pool deficiency, and immune glycoprotein VI-related disease with granule secretion defect).

Results

The range, kinetics, and distribution of fluorescence intensity were established for each agonist-target protein combination. Principal component analysis indicates a correlation in response to a target phosphoprotein (AKT and P38MAPK) to different agonists but no correlation in the response of different target phosphoproteins to the same agonist. The heterogeneity of individual responses in the whole population displayed was analyzed using clustering algorithm. Patients with platelet storage pool deficiency were positioned as lowest responders on the heatmap.

Conclusion

In complement of functional tests, this study introduces a new approach for rapid platelet signaling profiling in clinical practice.

APOLD1 loss causes endothelial dysfunction involving cell junctions, cytoskeletal architecture, and Weibel-Palade bodies, while disrupting hemostasis

Vascular homeostasis is impaired in various diseases thereby contributing to the progression of their underlying pathologies. The endothelial immediate early gene Apolipoprotein L domain-containing 1 (APOLD1) helps to regulate endothelial function. However, its precise role in endothelial cell biology remains unclear. We have localized APOLD1 to endothelial cell contacts and to Weibel-Palade bodies (WPB) where it associates with von Willebrand factor (VWF) tubules. Silencing of APOLD1 in primary human endothelial cells disrupted the cell junction-cytoskeletal interface, thereby altering endothelial permeability accompanied by spontaneous release of WPB contents. This resulted in an increased presence of WPB cargoes, notably VWF and angiopoietin-2 in the extracellular medium. Autophagy flux, previously recognized as an essential mechanism for the regulated release of WPB, was impaired in the absence of APOLD1. In addition, we report APOLD1 as a candidate gene for a novel inherited bleeding disorder across three generations of a large family in which an atypical bleeding diathesis was associated with episodic impaired microcirculation. A dominant heterozygous nonsense APOLD1:p.R49* variant segregated to affected family members. Compromised vascular integrity resulting from an excess of plasma angiopoietin-2, and locally impaired availability of VWF may explain the unusual clinical profile of APOLD1:p.R49* patients. In summary, our findings identify APOLD1 as an important regulator of vascular homeostasis and raise the need to consider testing of endothelial cell function in patients with inherited bleeding disorders without apparent platelet or coagulation defects.

Platelet function studies in myeloproliferative neoplasms patients with Calreticulin or JAK2 V617F mutation

Background

JAK2 ^V617F and Calreticulin (CALR) mutations are the most frequent molecular causes of Phi-negative myeloproliferative neoplasms (MPN). Patients with CALR mutations are at lower risk of thrombosis than patients with JAK2 ^V617F. We hypothesized that CALR-mutated blood platelets would have platelet function defects that might explain why these patients are at lower risk of thrombosis.

Objectives

Our main objective was to explore and compare platelet function depending on the MPN molecular marker.

Methods

We analyzed platelet function in 16 patients with MPN with CALR mutations and 17 patients with JAK2 ^V617F mutation and compared them with healthy controls. None of these patients was taking antiplatelet therapy. We performed an extensive analysis of platelet function and measured plasmatic soluble P-selectin and CD40L levels.

Results

We observed significant defects in platelet aggregation, surface glycoprotein expression, fibrinogen binding, and granule content in platelets from patients with MPN compared with that in controls. Moreover, soluble CD40L and P-selectin levels were elevated in patients with MPN compared with that in controls, suggesting an in vivo platelet preactivation. Comparison of platelet function between patients with CALR and JAK2 ^V617F MPN revealed only minor differences in platelets from patients with CALR. However, these results need to be interpreted within the context of absence of an inflammatory environment that could impact platelet function during MPN.

Conclusions

These results do not support the hypothesis that calreticulin-mutated platelets have platelet function defects that could explain the lower thrombotic risk of patients with CALR.

Recombinant porcine factor VIII corrects thrombin generation in vitro in plasma from patients with congenital hemophilia A and inhibitors

Background

Neutralizing factor VIII (FVIII) antibodies are a major complication in hemophilia A. Antihemophilic factor VIII (recombinant), porcine sequence (rpFVIII; susoctocog alfa; Baxalta US Inc., a Takeda company) has low cross‐reactivity to anti‐human FVIII antibodies and can provide functional FVIII activity in the presence of FVIII inhibitors.

Objectives

Evaluate in vitro thrombin generation and clot formation responses to rpFVIII in blood from patients with congenital hemophilia A.

Methods

In this multicenter study, blood was obtained for in vitro analyses that included human and porcine FVIII inhibitors, low <5 Bethesda units (BU)/ml or high ≥5 BU/ml titer (Nijmegen‐modified Bethesda assay); thrombin generation assay (TGA), clot viscoelasticity (thromboelastography), fibrin clot structure analysis (scanning electron microscopy), and epitope mapping.

Results

Blood samples were from 20 patients with congenital hemophilia A (FVIII activity <1%, mean [range] inhibitor titers: anti‐human FVIII, 14 [1–427] BU/ml [n = 13 high, n = 6 low, n = 1 data unavailable]); anti‐porcine FVIII, 12 (0–886) BU/ml (n = 11 high, n = 8 low, n = 1 data unavailable). Porcine inhibitor titer and TGA response measured by endogenous thrombin potential showed an inverse correlation (2.7–10.8 U/ml rpFVIII Spearman correlation coefficient: −0.594 to −0.773; p < 0.01). Clot structures in low anti‐porcine inhibitor titer plasmas were similar to those in noninhibitor plasma.

Conclusions

Recombinant porcine factor VIII demonstrated a dose‐dependent correction of thrombin generation and clot formation in vitro, dependent on the anti‐porcine FVIII inhibitor titer. Procoagulant responses to rpFVIII occurred in plasma containing FVIII inhibitors.

Haemostatic effect of adding tranexamic acid to emicizumab prophylaxis in severe haemophilia A: A preclinical study

BACKGROUND

Patients with severe haemophilia have impaired haemostatic response, delayed clot formation and fibrin clots that are vulnerable to fibrinolysis. Emicizumab is a bispecific antibody that mimics activity of activated factor VIII (FVIII) and increases haemostatic capacity to the level of moderate-to-mild haemophilia, thereby used for prophylaxis. Regardless of the impressive clinical performance of emicizumab, breakthrough bleeds may still occur. We aimed to study, in FVIII knockout mice (FVIII-KO), whether haemostasis is improved with the addition of tranexamic acid (TxAc) to emicizumab.

METHODS

FVIII-KO mice received prophylaxis with emicizumab or emicizumab+TxAc before trauma. FVIII-KO mice were given emicizumab 1.5 mg/kg via IV injection. A second retro-orbital IV injection containing human FIX and FX (both 100U/kg) was given 24 h later and 5 min before the tail amputation or knee trauma. After trauma-induced knee joint bleeding, magnetic resonance imaging (MRI), and histological analysis were used to compare haemostatic efficacy of the two prophylactic strategies. Thrombin generation (TG) was measured and clots obtained with TG experiment were analysed by scanning electron microscopy.

RESULTS

In FVIII-KO mice, blood loss after tail clip was lower after prophylaxis with emicizumab+TxAc compared to emicizumab. MRI results and histological analysis of knee joints showed that the addition of TxAc significantly decreased joint bleeding. Fibrin fibre diameters of mice treated with emicizumab only was thicker than those who received combined prophylaxis with emicizumab+TxAc.

CONCLUSION

Our results suggest a potential benefit of TxAc when used in combination with emicizumab in prophylactic settings, especially in patients presenting breakthrough bleeds.

GATA1 pathogenic variants disrupt MYH10 silencing during megakaryopoiesis

BACKGROUND

GATA1 is an essential transcription factor for both polyploidization and megakaryocyte (MK) differentiation. The polyploidization defect observed in GATA1 variant carriers is not well understood.

OBJECTIVE

To extensively phenotype two pedigrees displaying different variants in the GATA1 gene and determine if GATA1 controls MYH10 expression levels, a key modulator of MK polyploidization.

METHOD

A total of 146 unrelated propositi with constitutional thrombocytopenia were screened on a multigene panel. We described the genotype-phenotype correlation in GATA1 variant carriers and investigated the effect of these novel variants on MYH10 transcription using luciferase constructs.

RESULTS

The clinical profile associated with the p.L268M variant localized in the C terminal zinc finger was unusual in that the patient displayed bleeding and severe platelet aggregation defects without early-onset thrombocytopenia. p.N206I localized in the N terminal zinc finger was associated, on the other hand, with severe thrombocytopenia (15G/L) in early life. High MYH10 levels were evidenced in platelets of GATA1 variant carriers. Analysis of MKs anti-GATA1 chromatin immunoprecipitation-sequencing data revealed two GATA1 binding sites, located in the 3' untranslated region and in intron 8 of the MYH10 gene. Luciferase reporter assays showed their respective role in the regulation of MYH10 gene expression. Both GATA1 variants significantly alter intron 8 driven MYH10 transcription.

CONCLUSION

The discovery of an association between MYH10 and GATA1 is a novel one. Overall, this study suggests that impaired MYH10 silencing via an intronic regulatory element is the most likely cause of GATA1-related polyploidization defect.

Platelet δ-Storage Pool Disease: An Update

Platelet dense-granules are small organelles specific to the platelet lineage that contain small molecules (calcium, adenyl nucleotides, serotonin) and are essential for the activation of blood platelets prior to their aggregation in the event of a vascular injury. Delta-storage pool diseases (δ-SPDs) are platelet pathologies leading to hemorrhagic syndromes of variable severity and related to a qualitative (content) or quantitative (numerical) deficiency in dense-granules. These pathologies appear in a syndromic or non-syndromic form. The syndromic forms (Chediak–Higashi disease, Hermansky–Pudlak syndromes), whose causative genes are known, associate immune deficiencies and/or oculocutaneous albinism with a platelet function disorder (PFD). The non-syndromic forms correspond to an isolated PFD, but the genes responsible for the pathology are not yet known. The diagnosis of these pathologies is complex and poorly standardized. It is based on orientation tests performed by light transmission aggregometry or flow cytometry, which are supplemented by complementary tests based on the quantification of platelet dense-granules by electron microscopy using the whole platelet mount technique and the direct determination of granule contents (ADP/ATP and serotonin). The objective of this review is to present the state of our knowledge concerning platelet dense-granules and the tools available for the diagnosis of different forms of δ-SPD.

BLOC1S5 pathogenic variants cause a new type of Hermansky-Pudlak syndrome

PURPOSE

Hermansky-Pudlak syndrome (HPS) is characterized by oculocutaneous albinism, excessive bleeding, and often additional symptoms. Variants in ten different genes have been involved in HPS. However, some patients lack variants in these genes. We aimed to identify new genes involved in nonsyndromic or syndromic forms of albinism.

METHODS

Two hundred thirty albinism patients lacking a molecular diagnosis of albinism were screened for pathogenic variants in candidate genes with known links to pigmentation or HPS pathophysiology.

RESULTS

We identified two unrelated patients with distinct homozygous variants of the BLOC1S5 gene. Patients had mild oculocutaneous albinism, moderate bleeding diathesis, platelet aggregation deficit, and a dramatically decreased number of platelet dense granules, all signs compatible with HPS. Functional tests performed on platelets of one patient displayed an absence of the obligate multisubunit complex BLOC-1, showing that the variant disrupts BLOC1S5 function and impairs BLOC-1 assembly. Expression of the patient-derived BLOC1S5 deletion in nonpigmented murine Bloc1s5^-/- melan-mu melanocytes failed to rescue pigmentation, the assembly of a functional BLOC-1 complex, and melanosome cargo trafficking, unlike the wild-type allele.

CONCLUSION

Mutation of BLOC1S5 is disease-causing, and we propose that BLOC1S5 is the gene for a new form of Hermansky-Pudlak syndrome, HPS-11.

A new case with Hermansky-Pudlak syndrome type 9, a rare cause of syndromic albinism with severe defect of platelets dense bodies

Hermansky-Pudlak syndrome (HPS) is a rare form of syndromic oculocutaneous albinism caused by disorders in lysosome-related organelles. Ten genes are associated with different forms of HPS. HPS type 9 (HPS-9) is caused by biallelic variants of BLOC1S6. To date, only three patients with HPS-9 have been reported. We described one patient presenting with ocular features of albinism. Genetic analysis revealed two compound heterozygous variants in the BLOC1S6 gene. Extended hematological studies confirmed the platelet storage pool disease with absence of dense granules and abnormal platelet aggregation. By reviewing the previous published cases we confirm the phenotype of HPS-9 patients. This patient is the only one described with dextrocardia and abnormal psychomotor development.

Hemostatic effect of tranexamic acid combined with factor VIII concentrate in prophylactic setting in severe hemophilia A: A preclinical study

BACKGROUND

Hemophilia is characterized by a compromised hemostatic response with delayed development of a clot and the formation of clots that are vulnerable to fibrinolysis. We proposed to study, in vitro and in factor VIII knockout mice (FVIII-KO), whether hemostasis is improved with the addition of tranexamic acid (TXA) to low FVIII plasma concentrations.

METHODS

In vitro, blood samples from adults with severe hemophilia-A, spiked to final concentrations of 0-3-10 and 30IU.dL-1 of FVIII, were studied with and without TXA 0.1 mg/mL using thromboelastography in the presence of tPA (ROTEM-tPA), thrombin generation (TG) assay, and scanning electron microscopy. FVIII-KO mice received prophylaxis before trauma, to obtain circulating plasma FVIII at 3 IU.dL-1 or FVIII 3IU.dL-1  + TXA 0.1 mg/mL. After trauma-induced knee joint bleeding, magnetic resonance imaging, histological analysis, and tail clip assay were used to compare hemostastic efficacy of the two prophylactic strategies.

RESULTS

A dose-dependent improvement of TG was observed with recombinant FVIII (rFVIII) alone (P = .024). As expected, no effect of TXA on TG capacity was observed. Fibrin fiber diameters were significantly decreased with TXA + rFVIII compared to rFVIII, suggesting a stronger fibrin network. Surprisingly, ROTEM-tPA was normalized with TXA alone. In FVIII-KO mice, blood loss after tail clip was lower after prophylaxis with rFVIII + TXA compared to rFVIII, with no statistical significance (P = .15). However, MRI results and histological analysis of knee joints showed that the addition of TXA significantly decreased joint bleeding (P = .022).

CONCLUSION

Our results suggest a potential benefit of TXA when used in combination with FVIII in prophylactic settings.

Recombinant Adeno-Associated Viral Vectors Expressing Human Coagulation FIX-E456H Variant in Hemophilia B Mice

Gene therapy using recombinant adeno-associated virus (AAV) has induced sustained long-term coagulation human factor IX (hFIX) levels in hemophilia B (HB) patients. However, asymptomatic transient liver toxicity was observed at high vector doses, highlighting the need to improve the potency of these vectors. We report the generation of an AAV transgene cassette containing the hyperfunctional hFIX-E456H variant showing improved binding to platelets, with a comparison to wild-type hFIX (hFIX-WT) and hFIX-R384L variant (Padua) transgenes, containing F9 truncated-intron 1 (I1). In vitro specific activity was increased by 3.2- and 4.2-fold with hFIX-E456H and hFIX-R384L variants compared with hFIX-WT, using chromogenic assay, and by 7-and 8.6-fold with hFIX-E456H and hFIX-R384L variants compared with hFIX-WT, using one-stage assay. The transgenes were packaged into single-stranded AAV2/8 vectors that were tail vein injected at 5 × 10⁹, 2 × 10¹⁰, and 5 × 10¹⁰ vg per mouse in HB mice. Plasma FIX activity level, assessed by chromogenic assay, was up to fourfold higher for hFIX-E456H compared with hFIX-WT and was not different compared with hFIX-R384L, among the three dose cohorts. Overall, the in vivo specific activity was increased by threefold for hFIX-E456H and 4.9-fold for hFIX-R384L compared with hFIX-WT. At the lower dose of 5 × 10⁹ vg, the blood loss was significantly lower for hFIX-E456H compared with hFIX-WT, but did not differ compared with hFIX-R384L. The results found for the hFIX-E456H variant indicate that it might be a suitable alternative for gene therapy of HB.

Increased levels of the megakaryocyte and platelet expressed cysteine proteases stefin A and cystatin A prevent thrombosis

Increased platelet activity occurs in type 2 diabetes mellitus (T2DM) and such platelet dysregulation likely originates from altered megakaryopoiesis. We initiated identification of dysregulated pathways in megakaryocytes in the setting of T2DM. We evaluated through transcriptomic analysis, differential gene expressions in megakaryocytes from leptin receptor-deficient mice (db/db), exhibiting features of human T2DM, and control mice (db/+). Functional gene analysis revealed an upregulation of transcripts related to calcium signaling, coagulation cascade and platelet receptors in diabetic mouse megakaryocytes. We also evidenced an upregulation (7- to 9.7-fold) of genes encoding stefin A (StfA), the human ortholog of Cystatin A (CSTA), inhibitor of cathepsin B, H and L. StfA/CSTA was present in megakaryocytes and platelets and its expression increased during obesity and diabetes in rats and humans. StfA/CSTA was primarily localized at platelet membranes and granules and was released upon agonist stimulation and clot formation through a metalloprotease-dependent mechanism. StfA/CSTA did not affect platelet aggregation, but reduced platelet accumulation on immobilized collagen from flowing whole blood (1200 s^-1). In-vivo, upon laser-induced vascular injury, platelet recruitment and thrombus formation were markedly reduced in StfA1-overexpressing mice without affecting bleeding time. The presence of CA-074Me, a cathepsin B specific inhibitor significantly reduced thrombus formation in-vitro and in-vivo in human and mouse, respectively. Our study identifies StfA/CSTA as a key contributor of platelet-dependent thrombus formation in both rodents and humans.

First description of an IgM monoclonal antibody causing αIIb β3 integrin activation and acquired Glanzmann thrombasthenia associated with macrothrombocytopenia

Essentials Acquired Glanzmann thrombasthenia (GT) is generally caused by anti-αIIb β3 autoantibodies. We report the case of a man with an acquired GT phenotype associated with macrothrombocytopenia. Perturbed platelet function were associated with an activating anti-αIIb β3 IgM autoantibody. This novel clinical entity raises interesting questions about the αIIb β3 integrin signaling. SUMMARY: Background Acquired Glanzmann thrombasthenia (GT) is a bleeding disorder generally caused by anti-αIIb β3 autoantibodies. Objectives We aimed to characterize the molecular mechanism leading to a progressive GT-like phenotype in a patient with chronic immune thrombocytopenia. Patient, Methods, and Results The patient suffered from repeated episodes of gastrointestinal bleeding; further studies indicated a moderate platelet aggregation defect. A few months later, platelet function showed abolished aggregation using all agonists, but normal agglutination with ristocetin. No platelet-bound antibodies were detected, but the presence of large amounts of an IgM type antibody detected together with αIIb β3 in the patient permeabilized platelets suggested that this IgM was an autoantibody causing the internalization of the complex. This was confirmed by the fact that the patient IgM bound to normal platelets but not to platelets from GT type I patients. Moreover, patient's plasma activated αIIb β3 on controls' platelets as evidenced by increased PAC-1 binding. We also demonstrated that the patient plasma triggered αIIb β3 outside-in signaling, as β3 Tyr773 and FAK were phosphorylated, and increased the rate of actin polymerization in resting platelets reflecting an impairment of cytoskeletal reorganization. Because different signs of dysmegakaryopoiesis were also observed in our patient, we evaluated the ability of its serum to impair proplatelets formation and showed that it significantly decreased the number of proplatelet-bearing megakaryocytes in controls' bone marrow stem cells culture compared with normal serum. Conclusions We present the case of a patient with a progressive and severely perturbed platelet function associated with the presence of an IgM activating autoantibody directed against αIIb β3 .

Kinesin-1 Is a New Actor Involved in Platelet Secretion and Thrombus Stability

OBJECTIVE

Platelet secretion is crucial for many physiological platelet responses. Even though several regulators of the fusion machinery for secretory granule exocytosis have been identified in platelets, the underlying mechanisms are not yet fully characterized.

APPROACH AND RESULTS

By studying a mouse model (cKO [conditional knockout]^Kif5b) lacking Kif5b (kinesin-1 heavy chain) in its megakaryocytes and platelets, we evidenced unstable hemostasis characterized by an increase of blood loss associated to a marked tendency to rebleed in a tail-clip assay and thrombus instability in an in vivo thrombosis model. This instability was confirmed in vitro in a whole-blood perfusion assay under blood flow conditions. Aggregations induced by thrombin and collagen were also impaired in cKO^Kif5b platelets. Furthermore, P-selectin exposure, PF4 (platelet factor 4) secretion, and ATP release after thrombin stimulation were impaired in cKO^Kif5b platelets, highlighting the role of kinesin-1 in α-granule and dense granule secretion. Importantly, exogenous ADP rescued normal thrombin induced-aggregation in cKO^Kif5b platelets, which indicates that impaired aggregation was because of defective release of ADP and dense granules. Last, we demonstrated that kinesin-1 interacts with the molecular machinery comprising the granule-associated Rab27 (Ras-related protein Rab-27) protein and the Slp4 (synaptotagmin-like protein 4/SYTL4) adaptor protein.

CONCLUSIONS

Our results indicate that a kinesin-1-dependent process plays a role for platelet function by acting into the mechanism underlying α-granule and dense granule secretion.

Mutations of the integrin αIIb/β3 intracytoplasmic salt bridge cause macrothrombocytopenia and enlarged platelet α-granules

Rare gain-of-function mutations within the ITGA2B or ITGB3 genes have been recognized to cause macrothrombocytopenia (MTP). Here we report three new families with autosomal dominant (AD) MTP, two harboring the same mutation of ITGA2B, αIIbR995W, and a third family with an ITGB3 mutation, β3D723H. In silico analysis shows how the two mutated amino acids directly modify the salt bridge linking the intra-cytoplasmic part of αIIb to β3 of the integrin αIIbβ3. For all affected patients, the bleeding syndrome and MTP was mild to moderate. Platelet aggregation tended to be reduced but not absent. Electron microscopy associated with a morphometric analysis revealed large round platelets; a feature being the presence of abnormal large α-granules with some giant forms showing signs of fusion. Analysis of the maturation and development of megakaryocytes reveal no defect in their early maturation but abnormal proplatelet formation was observed with increased size of the tips. Interestingly, this study revealed that in addition to the classical phenotype of patients with αIIbβ3 intracytoplasmic mutations there is an abnormal maturation of α-granules. It is now necessary to determine if this feature is a characteristic of all mutations disturbing the αIIb R995/β3 D723 salt bridge.

Comparison of current platelet functional tests for the assessment of aspirin and clopidogrel response

The two most widely used antiplatelet drugs in the world are aspirin and clopidogrel. However, some patients on aspirin and/or clopidogrel therapy do not respond appropriately to either aspirin or clopidogrel. This phenomenon is usually called “aspirin/clopidogrel resistance”. Several platelet function tests have been used in various studies for the assessment of aspirin and clopidogrel resistance in healthy individuals and patients admitted in cardiology departments. An accurate assessment of platelet response to aspirin/clopidogrel could benefit patients by proposing tailored-antiplatelet therapy based on test results. However, there is a clear lack of standardisation of such techniques and their analytical variability may induce misinterpretation. After a quick report of the mechanisms responsible for aspirin/clopidogrel resistance, we describe the pre-analytical aspects and the analytical performances of current platelet function tests (Light-transmission aggregometry, whole-blood aggregometry, VerifyNow®, Platelet Function Analyzer®, thromboelastography, VASP assay) that are used for the assessment of aspirin/clopidogrel resistance in clinical studies. Considering the different variables that have to be taken into account with each of the platelet function tests, a particular attention should be paid when interpreting results.

Gain-of-Function Mutation in Filamin A Potentiates Platelet Integrin αIIbβ3 Activation

OBJECTIVE

Dominant mutations of the X-linked filamin A (FLNA) gene are responsible for filaminopathies A, which are rare disorders including brain periventricular nodular heterotopia, congenital intestinal pseudo-obstruction, cardiac valves or skeleton malformations, and often macrothrombocytopenia.

APPROACH AND RESULTS

We studied a male patient with periventricular nodular heterotopia and congenital intestinal pseudo-obstruction, his unique X-linked FLNA allele carrying a stop codon mutation resulting in a 100-amino acid-long FLNa C-terminal extension (NP_001447.2: p.Ter2648SerextTer101). Platelet counts were normal, with few enlarged platelets. FLNa was detectable in all platelets but at 30% of control levels. Surprisingly, all platelet functions were significantly upregulated, including platelet aggregation and secretion, as induced by ADP, collagen, or von Willebrand factor in the presence of ristocetin, as well as thrombus formation in blood flow on a collagen or on a von Willebrand factor matrix. Most importantly, patient platelets stimulated with ADP exhibited a marked increase in α_IIbβ₃ integrin activation and a parallel increase in talin recruitment to β₃, contrasting with normal Rap1 activation. These results are consistent with the mutant FLNa affecting the last step of α_IIbβ₃ activation. Overexpression of mutant FLNa in the HEL megakaryocytic cell line correlated with an increase (compared with wild-type FLNa) in PMA-induced fibrinogen binding to and in talin and kindlin-3 recruitment by α_IIbβ₃.

CONCLUSIONS

Altogether, our results are consistent with a less binding of mutant FLNa to β₃ and the facilitated recruitment of talin by β₃ on platelet stimulation, explaining the increased α_IIbβ₃ activation and the ensuing gain-of-platelet functions.

Macrothrombocytopenia and dense granule deficiency associated with FLI1 variants: ultrastructural and pathogenic features

Congenital macrothrombocytopenia is a family of rare diseases, of which a significant fraction remains to be genetically characterized. To analyze cases of unexplained thrombocytopenia, 27 individuals from a patient cohort of the Bleeding and Thrombosis Exploration Center of the University Hospital of Marseille were recruited for a high-throughput gene sequencing study. This strategy led to the identification of two novel FLI1 variants (c.1010G>A and c.1033A>G) responsible for macrothrombocytopenia. The FLI1 variant carriers’ platelets exhibited a defect in aggregation induced by low-dose adenosine diphosphate (ADP), collagen and thrombin receptor-activating peptide (TRAP), a defect in adenosine triphosphate (ATP) secretion, a reduced mepacrine uptake and release and a reduced CD63 expression upon TRAP stimulation. Precise ultrastructural analysis of platelet content was performed using transmission electron microscopy and focused ion beam scanning electron microscopy. Remarkably, dense granules were nearly absent in the carriers’ platelets, presumably due to a biogenesis defect. Additionally, 25–29% of the platelets displayed giant α-granules, while a smaller proportion displayed vacuoles (7–9%) and autophagosome-like structures (0–3%). In vitro study of megakaryocytes derived from circulating CD34⁺ cells of the carriers revealed a maturation defect and reduced proplatelet formation potential. The study of the FLI1 variants revealed a significant reduction in protein nuclear accumulation and transcriptional activity properties. Intraplatelet flow cytometry efficiently detected the biomarker MYH10 in FLI1 variant carriers. Overall, this study provides new insights into the phenotype, pathophysiology and diagnosis of FLI1 variant-associated thrombocytopenia.

LIM kinase/cofilin dysregulation promotes macrothrombocytopenia in severe von Willebrand disease-type 2B

von Willebrand disease type 2B (VWD-type 2B) is characterized by gain-of-function mutations of von Willebrand factor (vWF) that enhance its binding to platelet glycoprotein Ibα and alter the protein's multimeric structure. Patients with VWD-type 2B display variable extents of bleeding associated with macrothrombocytopenia and sometimes with thrombopathy. Here, we addressed the molecular mechanism underlying the severe macrothrombocytopenia both in a knockin murine model for VWD-type 2B by introducing the p.V1316M mutation in the murine Vwf gene and in a patient bearing this mutation. We provide evidence of a profound defect in megakaryocyte (MK) function since: (a) the extent of proplatelet formation was drastically decreased in 2B MKs, with thick proplatelet extensions and large swellings; and (b) 2B MKs presented actin disorganization that was controlled by upregulation of the RhoA/LIM kinase (LIMK)/cofilin pathway. In vitro and in vivo inhibition of the LIMK/cofilin signaling pathway rescued actin turnover and restored normal proplatelet formation, platelet count, and platelet size. These data indicate, to our knowledge for the first time, that the severe macrothrombocytopenia in VWD-type 2B p.V1316M is due to an MK dysfunction that originates from a constitutive activation of the RhoA/LIMK/cofilin pathway and actin disorganization. This suggests a potentially new function of vWF during platelet formation that involves regulation of actin dynamics.

Platelet activation and aggregation promote lung inflammation and influenza virus pathogenesis

RATIONALE

The hallmark of severe influenza virus infection is excessive inflammation of the lungs. Platelets are activated during influenza, but their role in influenza virus pathogenesis and inflammatory responses is unknown.

OBJECTIVES

To determine the role of platelets during influenza A virus infections and propose new therapeutics against influenza.

METHODS

We used targeted gene deletion approaches and pharmacologic interventions to investigate the role of platelets during influenza virus infection in mice.

MEASUREMENTS AND MAIN RESULTS

Lungs of infected mice were massively infiltrated by aggregates of activated platelets. Platelet activation promoted influenza A virus pathogenesis. Activating protease-activated receptor 4, a platelet receptor for thrombin that is crucial for platelet activation, exacerbated influenza-induced acute lung injury and death. In contrast, deficiency in the major platelet receptor glycoprotein IIIa protected mice from death caused by influenza viruses, and treating the mice with a specific glycoprotein IIb/IIIa antagonist, eptifibatide, had the same effect. Interestingly, mice treated with other antiplatelet compounds (antagonists of protease-activated receptor 4, MRS 2179, and clopidogrel) were also protected from severe lung injury and lethal infections induced by several influenza strains.

CONCLUSIONS

The intricate relationship between hemostasis and inflammation has major consequences in influenza virus pathogenesis, and antiplatelet drugs might be explored to develop new antiinflammatory treatment against influenza virus infections.

MDA-9/syntenin is essential for factor VIIa-induced signaling, migration, and metastasis in melanoma cells

Melanoma differentiation associated gene-9 (MDA-9), also known as syntenin, is a novel gene that positively regulates cancer cell motility, invasion, and metastasis through distinct biochemical and signaling pathways, but how MDA-9/syntenin is regulated in response to signals with the extracellular environment and promotes tumor progression is unclear. We now demonstrate that MDA-9/syntenin is dramatically up-regulated by a combination of rFVIIa and factor F(X) in malignant melanoma. Induction of MDA-9/syntenin in melanoma was found to occur in a thrombin-independent signaling pathway and involves the PAR-1/c-Src/Rho GTPases Rac1 and Cdc42/c-Jun N-terminal kinase axis resulting in the activation of paxillin, NF-κB, and matrix metalloproteinase-2 (MMP-2). MDA-9/syntenin physically interacts with c-Src through its PDZ binding motif following stimulation of melanoma cells with rFVIIa and FX. We also document that induction of this signaling pathway is required for TF·FVIIa·Xa-induced cell migration, invasion, and metastasis by melanoma cells. The present finding uncovers a novel role of MDA-9/syntenin as an important TF·FVIIa·Xa/PAR-1-regulated gene that initiates a signaling circuit essential for cell motility and invasion of metastatic melanoma. In these contexts, targeting TF·FVIIa·Xa and its relevant downstream targets such as MDA-9/syntenin, may represent a novel therapeutic strategy to control the evolution of neoplastic cells.

Comparison of the capacities of two prothrombin complex concentrates to restore thrombin generation in plasma from orally anticoagulated patients: an in vitro study

BACKGROUND

Human prothrombin complex concentrates (PCCs) are used for prevention and treatment of bleeding episodes in patients under warfarin therapy. PCCs contain human factor (F) II, FVII, FIX, FX, protein C and protein S. The concentrations of these coagulation factors contained in PCCs are variable and do not reflect entirely the capacity of these drugs to correct hemostasis. Furthermore, commercially available PCCs do not have exactly the same composition, though they are all labelled and prescribed in units per kg of FIX (10-40 IU of FIX/kg). As the final product generated by PCCs is thrombin, a thrombin generation (TG) test could theoretically be used for monitoring the hemostatic correction.

METHODS

TG was measured in platelet free plasma in the presence of tissue factor 5 pm and phospholipids 4 microM with a final concentration of PCC of 0-0.1-0.2-0.3-0.4-0.5-0.75-1 IU ml(-1). The activity of vitamin K-dependent coagulation factors (i.e. FII, FVII, FIX, FX, protein C and protein S) were determined for each concentration of two different PCCs available on the French market.

RESULTS AND DISCUSSION

Our results showed that the addition of two different PCCs dose-dependently increased the TG capacity in patients with INR of 2-2.5-3-4 and >7 (n = 15 subjects) that reached the normal values. We also found a significant correlation between endogenous thrombin potential (ETP) and INR (Pearson test, P < 0.0001). The two PCCs improved the TG parameters differently with increasing concentrations. The difference in the correction of TG capacity observed between the two drugs could be explained by a variable increase in FX, FVII and protein C with similar doses. These results strongly suggest that TG assay could be used for monitoring the clinical efficacy of PCC and for optimizing the therapeutic regimen towards a more individualized therapy involving the type of the bleeding complications, the level of inhibition of the coagulation system and the molecule content of the PCC.

Thrombin-generating capacity in patients with von Willebrand's disease

BACKGROUND AND OBJECTIVES

on Willebrand's disease (VWD) is the most common hereditary bleeding disorder. Its severity can be classified on the basis of von Willebrand factor (VWF) and factor VIII (FVIII) plasma levels and according to the clinical relevance of bleeding episodes. However, patients with very low VWF activity may exhibit a mild bleeding tendency. The basis for this heterogeneous clinical expression of the deficit is still poorly understood. We investigated the relationship between thrombin generation and levels of factor VIII, VWF and clinical bleeding tendency.

DESIGN AND METHODS

Thrombin generation was measured in platelet-rich (PRP) and platelet-poor plasma (PPP) from 53 patients with VWD.

RESULTS

We observed a statistically significant higher risk of bleeding in patients with a low thrombin peak in PRP (OR=14.5; 95% CI=5-41.3). Similar results were found in PPP (OR=8.71; 95% CI=3.4-22.3). Two parameters of the thrombin generation curve, peak height and thrombin generation speed (slope), correlated significantly with VWF:RCo and FVIII levels both in PPP and in PRP. Regression analysis showed that thrombin generation was mainly dependent on plasma FVIII activity.

INTERPRETATION AND CONCLUSIONS

Our results suggest that the thrombin generation test, in combination with routine FVIII and VWF measurements, could be of interest in the assessment of the individual bleeding risk in patients with VWD.

Effect of standardization and normalization on imprecision of calibrated automated thrombography: an international multicentre study

Calibrated automated thrombography (CAT) enables continuous measurement of thrombin generation (TG). Initial clinical studies using the CAT method showed large variability of normal values, indicating the necessity for a standardized CAT protocol. This international study assessed the intra- and inter-assay imprecision of CAT as well as the inter-centre variability of results in five European centres using locally available reagents and conditions (study 1) and a standardized protocol in which results were normalized (study 2). Samples with and without corn trypsin inhibitor from six healthy volunteers, two haemophilia patients and one protein C deficient patient were assayed. Study 1 confirmed that the use of different sources and concentrations of tissue factor (TF) and different phospholipid (PL) mixtures produced large variability in results. The second study demonstrated that, using the same source and concentration of TF, PL and the same test procedure, this variability could be significantly reduced. Normalization of results improved the inter-centre variability. The benefit of contact factor inhibition prior to TG measurement was confirmed. These results demonstrated that standardization of CAT reduces the variability of results to acceptable limits. Standardization and normalization should be considered in future clinical studies which apply TG testing to clinical decision making.

Effect of Low Dose Antioxidant Vitamin and Trace Element Supplementation on the Urinary Concentrations of Thromboxane and Prostacyclin Metabolites

OBJECTIVE

This trial evaluated the effect of antioxidant supplementation on the urinary excretion of 11-dehydro TXB(2)/2,3 dinor 6 keto PGF(1alpha) ratio, a marker of the pathogenesis of thrombosis and arteriosclerosis.

METHODS

This study was a randomised, double-blind, placebo-controlled trial involving 186 presumably healthy volunteers. One hundred received a multi-antioxidant supplementation and 86 a placebo for two years. Blood zinc, selenium, beta-carotene, vitamin C and E and urinary excretion of 11-dehydro TXB(2) and 2,3 dinor 6 keto PGF(1alpha) were measured.

RESULTS

Baseline subject characteristics did not differ between the two groups. Blood zinc, selenium, and beta-carotene concentrations significantly increased between baseline and two years in the multi-antioxidant supplementation group supporting subject compliance (p < 0.05). At two years, the median urinary 11-dehydro TXB(2)/2,3 dinor 6 keto PGF(1alpha) ratio was significantly lower in the multi-antioxidant supplementation group (3.4 versus 2.78, p = 0.015). Serum selenium concentration was the only antioxidant studied that was significantly related to the urinary 11-dehydro TXB(2)/2,3 dinor 6 keto PGF(1alpha) ratio.

CONCLUSIONS

These results support the hypothesis that a low-dose multi-antioxidant supplementation may contributes to a reduction in platelet activation which is beneficial for cardiovascular function.

Basic aspects of bypassing agents

Bypassing agents consist of activated prothrombin complex concentrates (aPCC) and recombinant factor VIIa (rFVIIa). Their main utilization is for prevention and treatment of bleeding complications, which may occur in inhibitor-developing haemophiliacs, although new indications for rFVIIa (e.g. trauma-related and cerebral bleeds) are now under evaluation in clinical trials. The mechanisms of action for these agents are still not fully understood. The relative complexity of the composition of aPCC suggests the possibility of multiple modes of action for achieving haemostasis. Among those possibilities, the contributions of activated factor X and prothrombin have been demonstrated in recent years both in vitro and in animal models for the only aPCC which remains on the market. rFVIIa also exhibits a complex mode of action, improving coagulation through both tissue factor-dependent and -independent pathways. The various mechanisms that occur at the cellular surfaces, particularly on the outer leaflet of the platelet membrane, primarily contribute to Xase complex formation and thrombin generation. The ways in which these agents affect the complex kinetics of fibrin formation at the site of vascular damage need further clarification, although significant progress has been achieved in the last 10 years. In addition, the ex vivo monitoring that would reflect achievement of haemostasis in vivo is still not standardized, although several attempts using thromboelastography, thrombin generation and the kinetics of fibrin formation have been initiated.

The type 1 lysophosphatidic acid receptor is a target for therapy in bone metastases

Platelet-derived lysophosphatidic acid (LPA) supports the progression of breast and ovarian cancer metastasis to bone. The mechanisms through which LPA promotes bone metastasis formation are, however, unknown. Here we report that silencing of the type 1 LPA receptor (LPA(1)) in cancer cells blocks the production of tumor-derived cytokines that are potent activators of osteoclast-mediated bone destruction and significantly reduces the progression of osteolytic bone metastases. Moreover, functional blockade of LPA action on its cognate receptor LPA(1) using a pharmacological antagonist mimics the effects of silencing LPA(1) in tumor cells in vitro and substantially reduces bone metastasis progression in animals. Overall, these results suggest that inhibition of platelet-derived LPA action on LPA(1) expressed by tumor cells may be a promising therapeutic target for patients with bone metastases.

Platelet-derived lysophosphatidic acid supports the progression of osteolytic bone metastases in breast cancer

The role of lysophosphatidic acid (LPA) in cancer is poorly understood. Here we provide evidence for a role of LPA in the progression of breast cancer bone metastases. LPA receptors LPA(1), LPA(2), and LPA(3) were expressed in human primary breast tumors and a series of human breast cancer cell lines. The inducible overexpression of LPA(1) in MDA-BO2 breast cancer cells specifically sensitized these cells to the mitogenic action of LPA in vitro. In vivo, LPA(1) overexpression in MDA-BO2 cells enhanced the growth of subcutaneous tumor xenografts and promoted bone metastasis formation in mice by increasing both skeletal tumor growth and bone destruction. This suggested that endogenous LPA was produced in the tumor microenvironment. However, MDA-BO2 cells or transfectants did not produce LPA. Instead, they induced the release of LPA from activated platelets which, in turn, promoted tumor cell proliferation and the LPA(1)-dependent secretion of IL-6 and IL-8, 2 potent bone resorption stimulators. Moreover, platelet-derived LPA deprivation in mice, achieved by treatment with the platelet antagonist Integrilin, inhibited the progression of bone metastases caused by parental and LPA(1)-overexpressing MDA-BO2 cells and reduced the progression of osteolytic lesions in mice bearing CHO-beta3wt ovarian cancer cells. Overall, our data suggest that, at the bone metastatic site, tumor cells stimulate the production of LPA from activated platelets, which enhances both tumor growth and cytokine-mediated bone destruction.

Deletion of alanine 2201 in the FVIII C2 domain results in mild hemophilia A by impairing FVIII binding to VWF and phospholipids and destroys a major FVIII antigenic determinant involved in inhibitor development

The C2 domain of factor VIII (FVIII) mediates FVIII binding to von Willebrand factor (VWF) and phospholipids (PLs), thereby determining the stability and the activity of FVIII. A deletion of Ala2201 (Del2201) was identified in the FVIII C2 domain of 2 unrelated patients with mild hemophilia A (FVIII:C 11%-33%). This mutation prevents FVIII binding to a human monoclonal antibody recognizing the C2 domain and inhibiting FVIII binding to VWF and phospholipids. By comparison to healthy FVIII, Del2201 FVIII had a significantly reduced binding to VWF, which likely contributes to reduced FVIII levels in plasma. Del2201 FVIII interaction with phospholipids was evaluated in an FXa generation assay, using various concentrations of synthetic phospholipid vesicles mimicking an activated platelet surface. At the lowest phospholipid concentration allowing FXa generation, Del2201 FVIII activity was reduced 3-fold. This is the first report of a mutation altering FVIII binding to phospholipids and occurring in patients with hemophilia A.

Expression of coagulation factor IX in a haematopoietic cell line

We have developed a gene therapy project for haemophilia B which aims to express factor IX (FIX) in haematopoietic lineage. Haematopoietic stem cells and subsequent megakaryocyte-derived cells represent the target cells of this approach. Our speculation is that platelets can deliver the coagulation factor at the site of injury, and subsequently correct the haemostasis defect. In order to direct FIX expression in cells from the megakaryocytic lineage, we designed a FIX cassette where the FIX cDNA was placed under the control of the tissue-specific glycoprotein IIb (GPIIb) promoter. In stably transfected HEL cells, FIX production was higher when driven by the GPIIb promoter compared to the CMV promoter. Using a cassette containing both the GPIIb promoter and a truncated FIX intron 1, FIX synthesis was dramatically increased in HEL cells. Northern blot analysis demonstrated an increase in FIX mRNA amounts, which paralleled with an increase of FIX antigen in the culture supernatants. Using a one-stage clotting assay and an activation by FXIa and FVIIa/TF, the HEL-derived recombinant FIX was shown to be a biologically active protein. This recombinant protein exhibited a 60-kDa molecular mass and was more heterogeneous than plasma immunopurified FIX (Mononine). The molecular mass difference could be partly explained by a different glycosylation pattern. The GPIIb promoter appears therefore to be a very attractive sequence to specifically direct FIX production in the megakaryocytic compartment of hematopoietic cells. These data also demonstrate that hematopoietic cells may represent potential target cells in an approach to gene therapy of haemophilia B.

Intrahepatic mechanisms underlying the effect of metformin in decreasing basal glucose production in rats fed a high-fat diet

The aim of this study was to understand by which intrahepatic mechanism metformin (Met) may inhibit basal hepatic glucose production (HGP) in type 2 diabetes. We studied rats that were fed for 6 weeks a high-fat (HF) diet, supplemented (HF-Met) or not (HF) with Met (50 mg x kg(-1) x day(-1)). Basal HGP, assessed by 3-[(3)H]glucose tracer dilution, was lower by 20% in HF-Met rats compared with HF-rats: 41.6 +/- 0.7 vs. 52 +/- 1.5 micromol x kg(-1) x min(-1) (means +/- SE, n = 5; P < 0.01). Glucose-6 phosphatase (Glc6Pase) activity, assayed in a liver lobe freeze-clamped in situ, was lower by 25% in HF-Met rats compared with HF-rats (7.9 +/- 0.4 vs. 10.3 +/- 0.9 micromol x min(-1) x g(-1) wet liver; P < 0.05). Glucose-6 phosphate and glycogen contents, e.g., 42 +/- 5 nmol/g and 3.9 +/- 2.4 mg/g, respectively, in HF-rats were dramatically increased by three to five times in HF-Met rats, e.g., 118 +/- 12 nmol/g and 19.6 +/- 4.6 mg/g (P < 0.05 and P < 0.01, respectively). Glucose-6 phosphate dehydrogenase activity was increased in HF-Met compared with HF rats (1.51 +/- 0.1 vs. 1.06 +/- 0.08 micromol x min(-1) x g(-1); P < 0.01). Intrahepatic lactate concentration tended to be lower in the Met-group (-30%; NS), whereas plasma lactate concentration was higher in HF-Met rats (1.59 +/- 0.15 mmol/l) than in HF rats (1.06 +/- 0.06 mmol/l; P < 0.05). We concluded that Met decreases HGP in insulin-resistant HF-fed rats mainly by an inhibition of hepatic Glc6Pase activity, promoting glycogen sparing. Additional mechanisms might involve the diversion of glucose-6 phosphate into the pentose phosphate pathway and an inhibition of hepatic lactate uptake.

Description of 10 new mutations in platelet glycoprotein IIb (alphaIIb) and glycoprotein IIIa (beta3) genes

In this study we have used denaturing gradient gel electrophoresis (DGGE) for identifying sequence alterations in glycoprotein (GP) IIb and IIIa genes from 20 patients affected by Glanzmann's thrombasthenia. These patients were from 16 different families. Using computer modelling, we divided the promoters, coding sequences and flanking splicing regions, in 31 segments for the GPIIb gene and 19 domains for the GPIIIa gene. We were able to find a mutation potentially affecting GPIIb-IIIa expression or function in 16 patients out of 20. In six patients from three families, the gypsy mutation modifying the splice donor site of intron 15 of the GPIIb gene was detected. In the other patients, 10 novel mutations were characterised, which were located either in the GPIIb gene (nine cases) or in the GPIIIa gene (one case). The type of mutation was nonsense mutation (one case), missense mutation (five cases), small insertion of 1 bp (one case) and splicing modifications (three cases). Among these genetic events, three were directly responsible for Glanzmann's thrombasthenia, four were localised in regions known to be involved in GPIIb-IIIa complex expression and three mutations were potentially responsible for Glanzmann's thrombasthenia.

Inhibition of prostaglandin H synthase and activation of 12-lipoxygenase by 8,11,14,17-eicosatetraenoic acid in human endothelial cells and platelets

The effects of the marine fatty acid 20:4n-3, an isomer of arachidonic acid (20:4n-6), have been compared to that of 20:5n-3 on 20:4n-6 oxygenation in human platelets and endothelial cells. In platelets, 20:4n-3 added along with 20:4n-6 was as potent as 20:5n-3 in inhibiting prostaglandin H synthase (PGH synthase) activity. From 2.5- to 10 microM of 20:4n-6, the synthesis of thromboxane B2 and 12-hydroxy-5,8,10-heptadecatrienoic acid, reflecting the PGH/thromboxane synthase activity, was lowered by 5 and 10 microM of both fatty acids. In contrast, 20:4n-3, but not 20:5n-3, strongly stimulated the lipoxygenase activity at each concentration of 20:4n-6 used whatever the amount of 20:4n-3 added. The effects of both n-3 polyunsaturated fatty acids on endothelial cell PGH/prostacyclin synthases were compared after 2- and 24-hr incubation with the cells, leading to moderate (2 hr) and high (24 hr) concentrations of these fatty acids in membrane phospholipids. The incorporation of 20:4n-3 and 20:5n-3 occurred mostly in phosphatidylcholine and phosphatidylethanolamine and did not alter the 20:4n-6 level of phospholipid classes after 2-hr supplementation, whereas it was drastically decreased after 24 hr. The synthesis of prostacyclin obtained after cell stimulation by 0.1 U/mL thrombin was unaffected by the fatty acid modifications induced after 2-hr supplementation, whereas it was strongly depressed after 24 hr. It was concluded that 20:4n-3 is not an agonist for platelet activation, despite its close structural analogy with 20:4n-6, and is as potent as 20:5n-3 in inhibiting PGH synthase activities, showing that the double bond at C5 is not necessary for inhibition. In contrast, the oxygenation of 20:4n-6 by 12-lipoxygenase was stimulated by 20:4n-3 but not by 20:5n-3, which might be related to the efficient oxygenation of 20:4n-3 by this enzyme compared with 20:5n-3.

Ticlopidine increases nitric oxide generation in heart-transplant recipients: a possible novel property of ticlopidine

The objective of this study was to evaluate the effects of ticlopidine on the generation of eicosanoids and nitric oxide in heart-transplant recipients. In a randomized double-blind study, we studied the urinary excretion of the stable metabolites of thromboxane, prostacyclin, and nitric oxide before and after ticlopidine (250 mg/day). Platelet aggregation was significantly reduced in ticlopidine-treated patients [from 40.2 +/- 24.2% of maximal aggregation to 14.7 +/- 8.2% in response to adenosine diphosphate (ADP); p < 0.001] but not in the placebo group, confirming the efficacy of the drug with that dosage in these specific patients. The 24-h urinary excretion of prostacyclin metabolites was not modified by ticlopidine (1,865 +/- 833 ng/24 h at day 14 and 1,664 +/- 425 ng/24 h at day 0), whereas the excretion of thromboxane B2 tended to increase in the ticlopidine group (from 3,854 +/- 1,163 ng/24 h at day 0 to 5,014 +/- 2,914 ng/24 h at day 14), although not significantly. The excretion of nitric oxide metabolites (although not different from that of healthy nonimmunosuppressed subjects) was significantly (p < 0.005) increased in the ticlopidine group (from 3,082 +/- 1,683 micromol/24 h at day 0 to 4,133 +/- 2,262 micromol/24 h at day 14), but not in controls. Thus ticlopidine does not reduce prostacyclin but increases the systemic generation of nitric oxide, both substances having major antiplatelet and vasodilator properties. Further studies are warranted to examine whether ticlopidine could reduce the incidence of thromboembolic complications in these patients and whether this possible novel property of ticlopidine is restricted to immunosuppressed heart-transplant recipients.

Unsaturated fatty acids associated with glycogen may inhibit glucose-6 phosphatase in rat liver

This study was conducted to identify the nature of a glycogen-associated compound that had been shown to inhibit glucose-6 phosphatase in vitro. Glycogen was purified from the liver of fed rats by potassium hydroxyde digestion and ethanol precipitation. It inhibited glucose-6 phosphatase in microsomes isolated from rats deprived of food for 48 h. Two glycogen-associated fractions were purified by anion-exchange chromatography on DOWEX 1 (200-400 mesh). These fractions inhibited microsomal glucose-6-phosphatase activity in vitro (80 +/- 2 and 76 +/- 3% of control, respectively). After chromatography, glycogen was no longer inhibitory (101 +/- 3% of control). Because glycogen is associated with endoplasmic reticulum membranes in the liver, we tested the hypothesis that lipids could be involved in the inhibitory process. Lipids were extracted from glycogen by Folch's method and analyzed by thin-layer chromatography and gas chromatography. The glycogen-associated fractions did not contain complex lipids but contained unsaturated fatty acids, which had been shown previously to inhibit glucose-6-phosphatase in vitro. Because the concentration of unsaturated fatty acids in both fractions quantitatively accounted for the inhibition of glucose-6 phosphatase observed, and because noninhibitory chromatographed glycogen reconstituted with equivalent amounts of pure unsaturated fatty acids inhibited the enzyme as glycogen did, we conclude that unsaturated fatty acids likely constitute the glycogen-associated compound that inhibits glucose-6 phosphatase activity.

Delineation and quantitation of brain lesions by fuzzy clustering in positron emission tomography

In this study, we investigate the application of the fuzzy clustering to the anatomical localization and quantitation of brain lesions in Positron Emission Tomography (PET) images. The method is based on the Fuzzy C-Means (FCM) algorithm. The algorithm segments the PET image data points into a given number of clusters. Each cluster is an homogeneous region of the brain (e.g. tumor). A feature vector is assigned to a cluster which has the highest membership degree. Having the label affected by the FCM algorithm to a cluster, one may easily compute the corresponding spatial localization, area and perimeter. Studies concerning the evolution of a tumor after different treatments in two patients are presented.

Liver glucose-6 phosphatase activity is inhibited by refeeding in rats

This study was conducted to determine whether inhibition of hepatic glucose-6 phosphatase is involved in the mechanism of suppression of hepatic glucose production during the postprandial period. We studied the time course of changes in the enzyme activity by refeeding food-deprived rats with nonpurified diet. The Vmax of the enzyme, assayed in homogenates from livers freeze-clamped in situ in anesthetized 48-h unfed rats (12.3 +/- 0.15 U/g wet liver, mean +/- SEM, n = 6) was progressively decreased upon refeeding: 11.1 +/- 0.5, 8.5 +/- 0.4 and 7.9 +/- 0.5 U/g, in rats refed for 90, 180 (P < 0.01) and 360 min (P < 0.01), respectively. The Km of the enzyme was not affected by refeeding. No inhibition of the enzyme was observed in microsomes purified from these homogenates, suggesting a metabolite-induced inhibition mechanism. To assess the role of insulin in the inhibition, we assayed the glucose-6 phosphatase activity in similarly processed liver homogenates from food-deprived rats perfused with insulin at physiological and supraphysiological concentrations, whereas plasma glucose was maintained at the basal level by adapted glucose perfusion (euglycemic clamps). No inhibition of glucose-6 phosphatase was found under these conditions, suggesting that insulin cannot by itself account for the inhibition observed in the refeeding experiments. These data constitute the first demonstration of the inhibition of glucose-6 phosphatase activity during the postprandial period.

Oxidized low-density lipoprotein induces the expression of P-selectin (GMP140/PADGEM/CD62) on human endothelial cells

It is now well established that monocytes adhere to endothelial cells activated by oxidized low-density lipoproteins (LDL). However, the adhesive receptors on endothelial cells involved in binding monocytes, following an insult by oxidized LDL, remains to be elucidated. In this study we have looked at the effect of native or oxidized LDL on the expression of P-selectin. Native LDL (N-LDL) was oxidized by incubation with either endothelial cells (EC-LDL) or copper (Cu-LDL), or in culture medium as a control (C-LDL). Expression of P-selectin was assayed with an anti-P-selectin (CD62) monoclonal antibody (LYP20). Results show that EC-LDL and Cu-LDL, but not N-LDL or C-LDL, induce the expression of P-selectin by human umbilical-vein endothelial cells (HUVECs). Induction of P-selectin by low concentrations (20 micrograms/ml) of LDL is directly related to the state of oxidation of the LDL particles. In addition, high concentrations (100 micrograms/ml) of N-LDL also activate HUVECs by inducing P-selectin expression. This expression was sustained for a period of over 1 h on LDL-activated endothelial cells, in contrast with thrombin- or histamine-activated endothelial cells, whose P-selectin levels fall within 15-20 min after induction. E-selectin, in contrast with P-selectin, could not be induced by endothelial cells treated with low or high concentrations of oxidized LDL. Results in this study show that P-selectin expressed by oxidized-LDL-treated endothelial cells are involved in mediating the adhesion of a monocytic cell line (U937) or monocytes in peripheral-blood mononuclear cells. An anti-P-selectin monoclonal antibody (LYP20) inhibited the binding of U937 cells and monocytes. These results strongly suggest that P-selectin is involved in the early stages of atherogenesis.

The vitronectin receptor (alpha v beta 3) is implicated, in cooperation with P-selectin and platelet-activating factor, in the adhesion of monocytes to activated endothelial cells

In this study we have investigated the presence on endothelial cells of potential glycoprotein receptors, other than P-selectin, which are involved in the adhesion of monocytes at the early stages of activation. We report that the majority of cells binding to thrombin-activated endothelial cells from a peripheral blood mononuclear cell (PBMC) preparation are monocytes. The adhesion of PBMC to thrombin-activated, but not resting, endothelial cells was inhibited (66%) by a monoclonal antibody (mAb) directed against alpha v beta 3. Elutriated monocytes or a monocytic cell line (U937) were also inhibited by this antibody, its F(ab)'2 fragments and three other anti-(alpha v beta 3) mAbs. alpha v beta 3 isolated from endothelial-cell lysates significantly inhibited the adhesion of monocytes and U937 cells to endothelial cells. A peptide motif (RGDF) known to interact with alpha v beta 3 inhibited U937 cell adhesion to activated endothelial cells by 53%. Finally, an anti-(P-selectin) mAb (LYP20) or a platelet-activating factor (PAF)-receptor antagonist (WEB 2086) inhibited monocyte adhesion to activated endothelial cells. This study shows for the first time that alpha v beta 3 is implicated, in addition to P-selectin and PAF, in the adhesion of monocytes to activated endothelial cells.

Cloning of the cDNA encoding human platelet CD36: comparison to PCR amplified fragments of monocyte, endothelial and HEL cells

Glycoprotein CD36, also known as GPIIIb or GPIV, is a major platelet glycoprotein that bears the newly identified Naka alloantigen. The aim of this study was to clone platelet CD36 and investigate other forms of CD36-cDNA present in monocytes, endothelial and HEL cells. RNA from above mentioned cells were reverse transcribed (RT), using specific primers for CD36, and amplified by the polymerase chain reaction (PCR) technique. Sequencing the different amplified platelet derived cDNA fragments, spanning the whole coding and flanking regions, showed the near identity between platelet and CD36-placenta cDNA. Platelet CD36-cDNA cross-hybridized, in Southern blots, with RT-PCR amplified cDNA originating from monocytes, endothelial and HEL cells. However, monocytes showed a RT-PCR amplified cDNA fragment (561 bp) that was present in platelets and placenta but not on endothelial on HEL-cells. Northern blot analysis of platelet RNA hybridized with placenta CD36 indicated the presence of a major (1.95 kb) and a minor (0.95 kb) transcript. The 1.95 kb transcript was the only one observed on Northern blots of monocytes, endothelial and HEL cells. These results indicate that the structure of CD36 expressed in platelets is similar, with the exception of the 3' flanking region, to that of placenta. Differences in apparent molecular weight between CD36 and CD36-like glycoproteins may be due to post-translational modifications.