The EAHAD blood coagulation factor VII variant database.

Hereditary blood coagulation factor VII (FVII) deficiency is a rare autosomal recessive bleeding disorder resulting from variants in the gene encoding FVII (F7). Integration of genetic variation with functional consequences on protein function is essential for the interpretation of the pathogenicity of novel variants. Here, we describe the integration of previous locus-specific databases for F7 into a single curated database with enhanced features. The database provides access to in silico analyses that may be useful in the prediction of variant pathogenicity as well as cross-species sequence alignments, structural information, and functional and clinical severity described for each variant, where appropriate. The variant data is shared with the F7 Leiden Open Variation Database. The updated database now includes 221 unique variants, representing gene variants identified in 728 individuals. Single nucleotide variants are the most common type (88%) with missense representing 74% of these variants. A number of variants are found with relatively high minor allele frequencies that are not pathogenic but contribute significantly to the likely pathogenicity of coinherited variants due to their effect on FVII plasma levels. This comprehensive collection of curated information significantly aids the assessment of pathogenicity.

The European Association for Haemophilia and Allied Disorders (EAHAD) Coagulation Factor Variant Databases: Important resources for haemostasis clinicians and researchers.

INTRODUCTION: Advances in genomic sequencing have facilitated the sequencing of genes associated with disorders of haemostasis. The identification of variants within genes and access to curated data incorporating structural, functional, evolutionary as well as phenotypic data has become increasingly important in order to ascribe pathogenicity. AIM: The European Association for Haemophilia and Allied Disorders (EAHAD) Coagulation Factor Variant Database Project aims to provide a single port of entry to a web-accessible resource for variants in genes involved in clinical bleeding disorders. RESULTS: New databases have evolved from previously developed single gene variant coagulation database projects, incorporating new data, new analysis tools and a new common database architecture with new interfaces and filters. These new databases currently present information about the genotype, phenotype (laboratory and clinical) and structural and functional effects of variants described in the genes of factor (F) VII (F7), FVIII (F8), FIX (F9) and von Willebrand factor (VWF). CONCLUSION: The project has improved the quality and quantity of information available to the haemostasis research and clinical communities, thereby enabling accurate classification of disease severity in order to make assessments of likely pathogenicity.

A novel role for the Aurora B kinase in epigenetic marking of silent chromatin in differentiated postmitotic cells.

Combinatorial modifications of the core histones have the potential to fine-tune the epigenetic regulation of chromatin states. The Aurora B kinase is responsible for generating the double histone H3 modification tri-methylated K9/phosphorylated S10 (H3K9me3/S10ph), which has been implicated in chromosome condensation during mitosis. In this study, we have identified a novel role for Aurora B in epigenetic marking of silent chromatin during cell differentiation. We find that phosphorylation of H3 S10 by Aurora B generates high levels of the double H3K9me3/S10ph modification in differentiated postmitotic cells and also results in delocalisation of HP1beta away from heterochromatin in terminally differentiated plasma cells. Microarray analysis of the H3K9me3/S10ph modification shows a striking increase in the modification across repressed genes during differentiation of mesenchymal stem cells. Our results provide evidence that the Aurora B kinase has a role in marking silent chromatin independently of the cell cycle and suggest that targeting of Aurora B-mediated phosphorylation of H3 S10 to repressed genes could be a mechanism for epigenetic silencing of gene expression.

In silico prediction of FVIII epitopes recognised by natural autoantibodies in polyvalent immunoglobulin concentrates.

Inhibitory antibodies directed against blood coagulation factor VIII (FVIII) impair FVIII replacement therapy, constituting a serious complication in haemophilic and autoimmune patients. Identifying B-cell FVIII epitopes and mapping them on the molecule remain important challenges. Using a combination of different algorithms, more than 30 hypothetical linear epitopes were predicted on the FVIII molecule surface. We selected several major predicted sequences, spanning all FVIII domains, for specific antibody induction in rabbits. All peptides tested successfully induced production of specific anti-FVIII rabbit antibodies, supporting the relevance of our approach. To investigate the presence of FVIII-reactive antibodies in the healthy donor population, a pooled fraction rich in all IgG subclasses was purified on peptide-Sepharose columns. Substantial amounts of Ig, specific for each FVIII peptide, were purified with yields ranging from 8 to 223 ng/mg immunoglobulins. Our results confirm the diversity of FVIII epitopes recognised by natural human anti-FVIII autoantibodies. All IgG subclasses were found in the affinity-isolated anti-peptide material, with overrepresentation of IgG2 and IgG4. Evidence was also found for new FVIII epitopes. Five human anti-peptide preparations displayed FVIII-neutralising activity, ranging from 1.3 to 5.3 BU/mg. Although the presence of naturally occurring anti-FVIII antibodies in healthy donors has been previously described, our methodology has allowed, for the first time, a fine mapping of several inhibitory and non-inhibitory epitopes. Our observations support the hypothesis that FVIII inhibitors in haemophilia A and autoimmune disease may originate from the proliferation of natural FVIII-specific B-cell clones.

The spectrum of mutations and molecular pathogenesis of hemophilia A in 181 Portuguese patients.

Disease-causing alterations within the F8 gene were identified in 177 hemophilia A families of Portuguese origin. The spectrum of non-inversion F8 mutations in 101 families included 67 different alterations, namely: 36 missense, 8 nonsense and 4 splice site mutations, as well as 19 insertions/deletions. Thirty-four of these mutations are novel. Molecular modeling allowed prediction of the conformational changes introduced by selected amino acid substitutions and their correlation with the patients' phenotypes. The relatively frequent, population-specific, missense mutations together with de novo alterations can lead to significant differences in the spectrum of F8 mutations among different populations.

Generation of a polyclonal rabbit anti-mouse tissue factor antibody by nucleic acid immunisation.

Tissue factor (TF) the cellular receptor and cofactor for factor VII, initiates coagulation and has also been implicated in several coagulation-independent functions, including inflammation, angiogenesis and tumour metastasis. Investigations of TF expression in mouse models of these processes has been limited by the availability of antibodies that specifically recognise mouse TF. We have generated a rabbit polyclonal antibody to mTF by DNA immunisation. This has yielded an antiserum that recognises native mTF in immunohistochemical and flow cytometric analyses. Furthermore, the antiserum is inhibitory in coagulation assays. This antiserum will be a valuable investigative tool in the analysis of mTF expression.

Characterisation of blood coagulation factor XI T475I.

PCR-SSCP and DNA sequence analysis of a factor XI (FXI) deficient patient (FXI:C 39 U/dL; FXI:Ag 27 U/dL) identified a C to T transition in exon 12 of the FXI gene (F11 c.1521C>T) that predicts the substitution of Thr475 by Ile (FXI T475I) within the serine protease domain of FXI. This mutation destroys a consensus sequence for N-linked glycosylation, N473-Y-T475, known to be utilized in vivo. The FXIT475I variant was generated by site-directed mutagenesis, together with other variants that could help explain the phenotype, and recombinant FXI variants were expressed in Chinese hamster ovary cells. FXI:Ag expression was analysed by Western blot analysis, ELISA and immunocytochemical staining. Wild-type FXI:Ag was secreted at high levels, however the mutant (FXI T475I) was secreted very poorly. Substitution of Thr475 by Ala, Pro, Lys or Arg (all of which abolish the glycosylation consensus sequence) also severely reduced the level of secreted FXI:Ag suggesting that glycosylation at Asn473 is required for folding or secretion. Concordant with this hypothesis the conservative substitution of Thr475 by Ser (which preserves the glycosylation consensus sequence) had no effect on FXI secretion. Thr/Ser475 is highly conserved in serine protease domains but the glycosylation site (Asn473) is not. Surprisingly, substitution of Asn473 by Ala (which removes the N-linked glycosylation site) had no effect on the levels of FXI:Ag secreted. In conclusion, although the FXI-T475I mutation destroys an N-linked glycosylation consensus sequence, the cause of failure to secrete FXI is not the loss of a glycosylation site but rather a direct effect of the substitution of this highly conserved residue.

Hemophilia A mutations within the factor VIII A2-A3 subunit interface destabilize factor VIIIa and cause one-stage/two-stage activity discrepancy.

Thrombin-activated factor VIII (FVIIIa) is a heterotrimer with the A2 subunit in a weak ionic interaction with the A1 and A3-C1-C2 subunits. Dissociation of the A2 subunit correlates with inactivation of FVIIIa. A homology model (Blood 89:2413, 1997) of the triplicated A domains of factor VIII (FVIII) predicts a pseudo-threefold axis at the tightly packed hydrophobic core with several interdomain interactions. These lie at the interface of A1-A2, A2-A3 and A1-A3. We have previously demonstrated that hemophilia A mutations (R531H, A284E, S289L) within the predicted A1-A2 and A1-A3 interface disrupt potential intersubunit hydrogen bonds and have the molecular phenotype of increased rate of inactivation of FVIIIa due to increased rate of A2 subunit dissociation. Patients with these mutations exhibit a clinical phenotype where the FVIII activity by one-stage(1-st) assay is at least two-fold higher than by two-stage(2-st) assay. We have now also explored mutations within the predicted A2-A3 interface (N694I, R698W and R698L) that also have the phenotype of 1-st/2-st activity discrepancy. These mutations exhibit the same molecular mechanism of increased instability of FVIIIa as those mutations described along the A1-A2 and A1-A3 interfaces. This suggests that the entire tightly packed hydrophobic core within the predicted pseudo-threefold axis contributes to stabilization of FVIIIa.

Self-complementary adeno-associated virus vectors containing a novel liver-specific human factor IX expression cassette enable highly efficient transduction of murine and nonhuman primate liver.

Transduction with recombinant adeno-associated virus (AAV) vectors is limited by the need to convert its single-stranded (ss) genome to transcriptionally active double-stranded (ds) forms. For AAV-mediated hemophilia B (HB) gene therapy, we have overcome this obstacle by constructing a liver-restricted mini-human factor IX (hFIX) expression cassette that can be packaged as complementary dimers within individual AAV particles. Molecular analysis of murine liver transduced with these self-complementary (sc) vectors demonstrated rapid formation of active ds-linear genomes that persisted stably as concatamers or monomeric circles. This unique property resulted in a 20-fold improvement in hFIX expression in mice over comparable ssAAV vectors. Administration of only 1 x 10(10) scAAV particles led to expression of hFIX at supraphysiologic levels (8I U/mL) and correction of the bleeding diathesis in FIX knock-out mice. Of importance, therapeutic levels of hFIX (3%-30% of normal) were achieved in nonhuman primates using a significantly lower dose of scAAV than required with ssAAV. Furthermore, AAV5-pseudotyped scAAV vectors mediated successful transduction in macaques with pre-existing immunity to AAV8. Hence, this novel vector represents an important advance for hemophilia B gene therapy.

Multiple vitamin K-dependent coagulation zymogens promote adenovirus-mediated gene delivery to hepatocytes.

Upon local delivery, adenovirus (Ad) serotype 5 viruses use the coxsackie and Ad receptor (CAR) for cell binding and alpha(v) integrins for internalization. When administered systemically, however, their role in liver tropism is limited because CAR-permissive and mutated viruses show similar biodistribution, a finding recently attributed to blood coagulation factor (F) IX or complement protein C4BP binding to the adenovirus fiber and "bridging" to either low-density lipoprotein receptor-related protein or heparan sulfate proteoglycans. Here, we show that hepatocyte transduction in vitro can be enhanced by the vitamin K-dependent factors FX, protein C, and FVII in addition to FIX but not by prothrombin (FII), FXI, and FXII. This phenomenon was not dependent on proteolytic activation or cell signaling activity and for FX was mediated by direct virus-factor binding. Human FX substantially enhanced hepatocyte transduction by CAR-permissive and mutated viruses in an ex vivo liver perfusion model. In vivo, global down-regulation of vitamin K-dependent zymogens by warfarin significantly diminished liver uptake of CAR-deleted Ads; however, this phenomenon was fully rescued by acute infusion of human FX. Our results indicate a common and pivotal role for distinct vitamin K-dependent coagulation factors in mediating hepatocyte transduction by adenoviruses in vitro and in vivo.

Use of a non-depleting anti-CD4 antibody to modulate the immune response to coagulation factors VIII and IX.

The generation of antibodies to therapeutic factors VIII or IX is a major problem in the management of haemophilia and places potential limitations on the application of gene therapy. We have investigated the administration of a non-depleting anti-CD4 antibody for modulation of the immune response to human recombinant coagulation factors VIII and IX. In mice given these clotting factors, co-administration of anti-CD4 antibody significantly reduced the appearance of factor-specific antibodies. These data provide evidence that the neutralizing antibody response to exogenous coagulation factors may be controllable if non-depleting anti-CD4 antibody is co-administered at the time of initial replacement therapy.

3-Dimensional structure of membrane-bound coagulation factor VIII: modeling of the factor VIII heterodimer within a 3-dimensional density map derived by electron crystallography.

Despite recent studies, the organization of coagulation factor VIII (FVIII) on a phospholipid (PL) membrane is not known in detail. Thus, 2-dimensional (2D) crystals of human FVIII lacking the B domain were prepared for electron microscopy onto negatively charged PL monolayers. The 3-dimensional (3D) density map of the PL-bound FVIII protein was calculated at 1.5 nm. Existing atomic data and models for FVIII domains were fitted unambiguously within the 3D density map of the molecule. FVIII domains arrangement followed a compact spiral organization with the A3 domains in close association with the C1 and C2 domains near the PL surface. Viewed toward the membrane the A domains' heterotrimer is oriented side-on with the pseudo-3-fold axis almost parallel to the PL surface and A1 fully covering C1. The C2 domain is partially overlapped by the A2 domain of an adjacent molecule in the 2D crystal, favoring close packing. Viewed parallel to the membrane, C2 is slightly inclined to the PL surface covering an area of 12 nm(2). Four C2 loops are embedded within the lipid monolayer at about 0.7 to 1.0 nm depth. C1 forms almost a right angle with C2, its long axis nearly parallel to the membrane. The proposed structure for membrane-bound FVIII results from modeling of the FVIII domains within a 3D density map obtained from electron crystallography and accords with the main biochemical and structural information known to date. A model is proposed for FVIIIa and factor IXa assembly within the membrane-bound factor X-activating complex. (Blood. 2002;99:1215-1223)

Complete inhibition of acute humoral rejection using regulated expression of membrane-tethered anticoagulants on xenograft endothelium.

Xenotransplantation promises an unlimited supply of organs for clinical transplantation. However, an aggressive humoral immune response continues to limit the survival of pig organs after transplantation into primates. Because intravascular thrombosis and systemic coagulopathy are prominent features of acute humoral xenograft rejection, we hypothesized that expression of anticoagulants on xenogeneic vascular endothelium might inhibit the process. Hearts from novel transgenic mice, expressing membrane-tethered fusion proteins based on human tissue factor pathway inhibitor and hirudin, respectively, were transplanted into rats. In contrast to control non-transgenic mouse hearts, which were all rejected within 3 days, 100% of the organs from both strains of transgenic mice were completely resistant to humoral rejection and survived for more than 100 days when T-cell-mediated rejection was inhibited by administration of ciclosporin A. These results demonstrate the critical role of coagulation in the pathophysiology of acute humoral rejection and the potential for inhibiting rejection by targeting the expression of anticoagulants to graft endothelial cells. This genetic strategy could be applied in a clinically relevant species such as the pig.

Two novel mutations in severe factor VII deficiency.

We have characterized the molecular defect in two families with severe factor VII (FVII) deficiency. In family I, the proband was found to be homozygous for a novel 18 bp deletion in exon 8 (g.10896-10913del) resulting in the in-frame deletion of six amino acids in the serine protease domain. Molecular modelling suggests the deletion is likely to disrupt folding of the FVII molecule. The reduced FVII antigen (21 U/dl) and negligible activity (0.4 U/dl) in the patient's plasma indicated that the deletion affected both the secretion/stability and function of the mutant protein. In family II, the proband was found to be a compound heterozygote for a novel missense mutation (g.7884G>A; FVII G117R) in exon 5 encoding the EGF2 domain of FVII and a nonsense mutation (g.8960C>T; FVII R152X) in exon 6. Extensive sequence comparison in a wide evolutionary context suggested that the Gly117 residue is critical for structure of FVII. The grossly reduced FVII antigen (1.1 U/dl) and activity (0.4 U/dl) plasma values indicate the mutation primarily affected the folding/secretion or stability of the protein.

A Tyr346-->Cys substitution in the interdomain acidic region a1 of factor VIII in an individual with factor VIII:C assay discrepancy.

The interdomain acidic region a1 is a unique structural feature of coagulation factor VIII (FVIII) and may mediate the proteolytic activation of FVIII and the inactivation of FVIIIa. We report an individual with a Tyr346-->Cys substitution within region a1, who presented with a one-stage FVIII activity (FVIII:C) of 0.34 iu/ml (normal range 0.5-2.0) but normal two-stage FVIII:C and FVIII antigen values. In a factor Xa (FXa)-generation assay for FVIII in which the activation time with thrombin was varied, the variant plasma showed normal FVIII:C at both short and long activation times. However, at intermediate activation times the FXa generation of the variant plasma was less than that of normal pooled plasma. In a modified one-stage FVIII:C assay in which partially purified FVIII was activated with thrombin at low concentrations, the variant FVIII showed less activation than wild-type FVIII, although this defect corrected with increasing concentrations of thrombin. When partially purified variant FVIII was activated with a large molar excess of thrombin, the subsequent rate of decay of FVIII:C was greater for variant FVIII. The complex defects in activation and inactivation displayed by FVIII Tyr346-->Cys support the hypothesis that the a1 sequence is a key regulator of FVIII activity.

Permanent phenotypic correction of hemophilia B in immunocompetent mice by prenatal gene therapy.

Hemophilia B, also known as Christmas disease, arises from mutations in the factor IX (F9) gene. Its treatment in humans, by recombinant protein substitution, is expensive, thus limiting its application to intermittent treatment in bleeding episodes and prophylaxis during surgery; development of inhibitory antibodies is an associated hazard. This study demonstrates permanent therapeutic correction of his disease without development of immune reactions by introduction of an HIV-based lentiviral vector encoding the human factor IX protein into the fetal circulation of immunocompetent hemophiliac and normal outbred mice. Plasma factor IX antigen remained at around 9%, 13%, and 16% of normal in the 3 hemophilia B mice, respectively, until the last measurement at 14 months. Substantial improvement in blood coagulability as measured by coagulation assay was seen in all 3 mice and they rapidly stopped bleeding after venipuncture. No humoral or cellular immunity against the protein, elevation of serum liver enzymes, or vector spread to the germline or maternal circulation were detected.