Mice lacking factor VII develop normally but suffer fatal perinatal bleeding

Sepsis-Induced Coagulopathy: A Comprehensive Narrative Review of Pathophysiology, Clinical Presentation, Diagnosis, and Management Strategies

Physiological hemostasis is a balance between pro- and anticoagulant pathways, and in sepsis, this equilibrium is disturbed, resulting in systemic thrombin generation, impaired anticoagulant activity, and suppression of fibrinolysis, a condition termed sepsis-induced coagulopathy (SIC). SIC is a common complication, being present in 24% of patients with sepsis and 66% of patients with septic shock, and is often associated with poor clinical outcomes and high mortality. 1 , 2 Recent preclinical and clinical studies have generated new insights into the molecular pathogenesis of SIC. In this article, we analyze the complex pathophysiology of SIC with a focus on the role of procoagulant innate immune signaling in hemostatic activation--tissue factor production, thrombin generation, endotheliopathy, and impaired antithrombotic functions. We also review clinical presentations of SIC, the diagnostic scoring system and laboratory tests, the current standard of care, and clinical trials evaluating the efficacies of anticoagulant therapies.

An update on novel therapies for treating patients with arterial thrombosis

INTRODUCTION

Antithrombotic therapy field is undergoing rapid and significant changes during the past decade. In addition to new therapeutic strategies with existing targets, investigators are exploring the potential use of new targets to address unmet needs to treat patients with arterial diseases.

AREAS COVERED

We aim to provide an update on and a comprehensive review of the antithrombic agents that are being explored in patients with arterial diseases. We discuss latest developments with respect to upstream antiplatelet agents, and collagen and thrombin pathway inhibitors. We searched PubMed databases for English language articles using keywords: antiplatelet agents, thrombin pathway inhibitors, collagen receptors, arterial disease.

EXPERT OPINION

Despite implementation of potent P2Y12 inhibitors, there are numerous unmet needs in the treatment of arterial diseases including ceiling effect of currently available antiplatelet agents along with and an elevated risk of bleeding. The latter observations encouraged investigators to explore new targets that can attenuate the generation of platelet-fibrin clot formation and subsequent ischemic event occurrences with minimal effect on bleeding. These targets include collagen receptors on platelets and thrombin generation including FXa, FXIa, and FXIIa. In addition, investigators are studying novel antiplatelet agents/strategies to facilitate upstream therapy in high-risk patients.

Tumor-expressed factor VII is associated with survival and regulates tumor progression in breast cancer

Cancer enhances the risk of venous thromboembolism, but a hypercoagulant microenvironment also promotes cancer progression. Although anticoagulants have been suggested as a potential anticancer treatment, clinical studies on the effect of such modalities on cancer progression have not yet been successful for unknown reasons. In normal physiology, complex formation between the subendothelial-expressed tissue factor (TF) and the blood-borne liver-derived factor VII (FVII) results in induction of the extrinsic coagulation cascade and intracellular signaling via protease-activated receptors (PARs). In cancer, TF is overexpressed and linked to poor prognosis. Here, we report that increased levels of FVII are also observed in breast cancer specimens and are associated with tumor progression and metastasis to the liver. In breast cancer cell lines, tumor-expressed FVII drives changes reminiscent of epithelial-to-mesenchymal transition (EMT), tumor cell invasion, and expression of the prometastatic genes, SNAI2 and SOX9. In vivo, tumor-expressed FVII enhanced tumor growth and liver metastasis. Surprisingly, liver-derived FVII appeared to inhibit metastasis. Finally, tumor-expressed FVII-induced prometastatic gene expression independent of TF but required a functional endothelial protein C receptor, whereas recombinant activated FVII acting via the canonical TF:PAR2 pathway inhibited prometastatic gene expression. Here, we propose that tumor-expressed FVII and liver-derived FVII have opposing effects on EMT and metastasis.

Translation termination codons in protein synthesis and disease

Fidelity of protein synthesis, a process shaped by several mechanisms involving specialized ribosome regions and external factors, ensures the precise reading of sense as well as stop codons (UGA, UAG, UAA), which are usually localized at the 3' of mRNA and drive the release of the polypeptide chain. However, either natural (NTCs) or premature (PTCs) termination codons, the latter arising from nucleotide changes, can undergo a recoding process named ribosome or translational readthrough, which insert specific amino acids (NTCs) or subset(s) depending on the stop codon type (PTCs). This process is particularly relevant for nonsense mutations, a relatively frequent cause of genetic disorders, which impair gene expression at different levels by potentially leading to mRNA degradation and/or synthesis of truncated proteins. As a matter of fact, many efforts have been made to develop efficient and safe readthrough-inducing compounds, which have been challenged in several models of human disease to provide with a therapy. In this view, the dissection of the molecular determinants shaping the outcome of readthrough, namely nucleotide and protein contexts as well as their interplay and impact on protein structure/function, is crucial to identify responsive nonsense mutations resulting in functional full-length proteins. The interpretation of experimental and mechanistic findings is also important to define a possibly clear picture of potential readthrough-favorable features useful to achieve rescue profiles compatible with therapeutic thresholds typical of each targeted disorder, which is of primary importance for the potential translatability of readthrough into a personalized and mutation-specific, and thus patient-oriented, therapeutic strategy.

Rare Coagulation Factor Deficiencies (Factors VII, X, V, and II)

Although rare clotting factor deficiencies primarily referred to as rare bleeding disorders (RBD), including factors II, V, VII, and X, make up ∼5% of all inherited bleeding disorders worldwide, each of these clotting factors play a critical role in the coagulation cascade. Incomplete bleeding evaluation or misinterpretation of laboratory studies can result in delayed diagnoses that ultimately affect patient outcomes. Bleeding manifestations can range from mild to severe, but the most common are mucocutaneous bleeding. The ideal treatment in RBD is dedicated single-factor concentrates that can be used for acute bleeding events, surgical management, and prophylaxis.

Novel factor VII gene mutations in six families with hereditary coagulation factor VII deficiency

Introduction

Hereditary human coagulation factor VII (FVII) deficiency is an inherited autosomal recessive hemorrhagic disease involving mutations in the F7 gene. The sites and types of F7 mutations may influence the coagulation activities of plasma FVII (FVII: C) and severity of hemorrhage symptoms. However, the specific mutations that impact FVII activity are not completely known.

Methods

We tested the coagulation functions and plasma activities of FVII in seven patients recruited from six families with hereditary FVII deficiency and sequenced the F7 gene of the patients and their families. Then, we analyzed the genetic information from the six families and predicted the structures of the mutated proteins.

Results

In this study, we detected 11 F7 mutations, including four novel mutations, in which the mutations p.Phe84Ser and p.Gly156Cys encoded the Gla and EGF domains of FVII, respectively, while the mutation p.Ser339Leu encoded the recognition site of the enzymatic protein and maintained the conformation of the catalytic domain structure. Meanwhile, the mutation in the 5′ untranslated region (UTR) was closely associated with the mRNA regulatory sequence.

Conclusion

We have identified novel genetic mutations and performed pedigree analysis that shed light on the pathogenesis of hereditary human coagulation FVII deficiency and may contribute to the development of treatments for this disease.

In this study, we performed coagulation index tests and gene sequencing on 7 hereditary FVII deficiency patients and their family members to explain the pathogenesis of the disease based on the analysis of their genetic information. Also, we compared the structures of newly discovered mutant proteins with the wild type and predicted their pathogenicity. To sum up, this study expands our insight on the pathogenesis of hereditary human coagulation FVII deficiency.

Pleiotropic actions of factor Xa inhibition in cardiovascular prevention: mechanistic insights and implications for anti-thrombotic treatment

Atherosclerosis is a chronic inflammatory disease in which atherothrombotic complications lead to cardiovascular morbidity and mortality. At advanced stages, myocardial infarction, ischaemic stroke, and peripheral artery disease, including major adverse limb events, are caused either by acute occlusive atherothrombosis or by thromboembolism. Endothelial dysfunction, vascular smooth muscle cell activation, and vascular inflammation are essential in the development of acute cardiovascular events. Effects of the coagulation system on vascular biology extend beyond thrombosis. Under physiological conditions, coagulation proteases in blood are pivotal in maintaining haemostasis and vascular integrity. Under pathological conditions, including atherosclerosis, the same coagulation proteases (including factor Xa, factor VIIa, and thrombin) become drivers of atherothrombosis, working in concert with platelets and vessel wall components. While initially atherothrombosis was attributed primarily to platelets, recent advances indicate the critical role of fibrin clot and plasma coagulation factors. Mechanisms of atherothrombosis and hypercoagulability vary depending on plaque erosion or plaque rupture. In addition to contributing to thrombus formation, factor Xa and thrombin can affect endothelial dysfunction, oxidative stress, vascular smooth muscle cell function as well as immune cell activation and vascular inflammation. By these mechanisms, they promote atherosclerosis and contribute to plaque instability. In this review, we first discuss the postulated vasoprotective mechanisms of protease-activated receptor signalling induced by coagulation enzymes under physiological conditions. Next, we discuss preclinical studies linking coagulation with endothelial cell dysfunction, thromboinflammation, and atherogenesis. Understanding these mechanisms is pivotal for the introduction of novel strategies in cardiovascular prevention and therapy. We therefore translate these findings to clinical studies of direct oral anticoagulant drugs and discuss the potential relevance of dual pathway inhibition for atherothrombosis prevention and vascular protection.

Differential roles of factors IX and XI in murine placenta and hemostasis under conditions of low tissue factor

The intrinsic tenase complex (FIXa-FVIIIa) of the intrinsic coagulation pathway and, to a lesser extent, thrombin-mediated activation of FXI, are necessary to amplify tissue factor (TF)-FVIIa-initiated thrombin generation. In this study, we determined the contribution of murine FIX and FXI to TF-dependent thrombin generation in vitro. We further investigated TF-dependent FIX activation in mice and the contribution of this pathway to hemostasis. Thrombin generation was decreased in FIX- but not in FXI-deficient mouse plasma. Furthermore, injection of TF increased levels of FIXa-antithrombin complexes in both wild-type and FXI-/- mice. Genetic studies were used to determine the effect of complete deficiencies of either FIX or FXI on the survival of mice expressing low levels of TF. Low-TF;FIX-/y male mice were born at the expected frequency, but none survived to wean. In contrast, low-TF;FXI-/- mice were generated at the expected frequency at wean and had a 6-month survival equivalent to that of low-TF mice. Surprisingly, a deficiency of FXI, but not FIX, exacerbated the size of blood pools in low-TF placentas and led to acute hemorrhage and death of some pregnant dams. Our data indicate that FIX, but not FXI, is essential for survival of low-TF mice after birth. This finding suggests that TF-FVIIa-mediated activation of FIX plays a critical role in murine hemostasis. In contrast, FXI deficiency, but not FIX deficiency, exacerbated blood pooling in low-TF placentas, indicating a tissue-specific requirement for FXI in the murine placenta under conditions of low TF.

Macrophage protease-activated receptor 2 regulates fetal liver erythropoiesis in mice

Deficiencies in many coagulation factors and protease-activated receptors (PARs) affect embryonic development. We describe a defect in definitive erythropoiesis in PAR2-deficient mice. Embryonic PAR2 deficiency increases embryonic death associated with variably severe anemia in comparison with PAR2-expressing embryos. PAR2-deficient fetal livers display reduced macrophage densities, erythroblastic island areas, and messenger RNA expression levels of markers for erythropoiesis and macrophages. Coagulation factor synthesis in the liver coincides with expanding fetal liver hematopoiesis during midgestation, and embryonic factor VII (FVII) deficiency impairs liver macrophage development. Cleavage-insensitive PAR2-mutant mice recapitulate the hematopoiesis defect of PAR2-deficient embryos, and macrophage-expressed PAR2 directly supports erythroblastic island function and the differentiation of red blood cells in the fetal liver. Conditional deletion of PAR2 in macrophages impairs erythropoiesis, as well as increases inflammatory stress, as evidenced by upregulation of interferon-regulated hepcidin antimicrobial peptide. In contrast, postnatal macrophage PAR2 deficiency does not have any effect on steady-state Kupffer cells, bone marrow macrophage numbers, or erythropoiesis, but erythropoiesis in macrophages from PAR2-deficient mice is impaired following hemolysis. These data identify a novel function for macrophage PAR2 signaling in adapting to rapid increases in blood demand during gestational development and postnatal erythropoiesis under stress conditions.

Novel mutation in coagulation factor VII (Carmel mutation): Identification and characterization

BACKGROUND

Measurement of factor VII (FVII) activity does not enable prediction of bleeding tendency in individuals with inherited FVII deficiency.

OBJECTIVE

To characterize the molecular and functional features of FVII in a family with FVII deficiency and correlate them with the bleeding tendency.

PATIENTS/METHODS

We studied 7 family members with very low FVII activity using prothrombin time (PT), activated factor VII (FVIIa), FVII activity level, and thrombin generation. The factor 7 gene was sequenced and the mutation was analyzed by prediction software.

RESULTS

The proband has very low FVII activity (0%-4%), with PT ranging between 5% to 18% depending on the tissue factor (TF) origin. Direct sequencing demonstrated a single homozygous nucleotide substitution G > A in exon 6, predicting a novel missense mutation Cys164Tyr. Three members of the family were found to be heterozygous carriers of this mutation. One of them was a compound heterozygote, carrying both the Cys164Tyr and Ala244Val mutation (linked to Arg353Gln polymorphism). Her FVII activity and antigen levels were 3%-7% and 8%, respectively. The other heterozygous carriers demonstrated FVII activity of 41%-54%, FVII antigen of 46%-66%, and FVIIa activity of 30%. FVIIa was undetectable in the homozygous and compound heterozygous subjects. Thrombin generation was normal in the presence of calcium, but no response to TF addition was observed in the homozygous proband, and a reduced response was observed in the compound heterozygous subject.

CONCLUSION

The patient homozygous for the "Carmel" mutation has mild clinical manifestations despite very low FVII activity, which correlates with thrombin generation results.

Molecular Characterization of Two Homozygous Factor VII Variants Associated with Intracranial Bleeding

Clinical parameters have been extensively studied in factor (F) VII deficiency, but the knowledge of molecular mechanisms of this disease is scarce. We report on three probands with intracranial bleeds at an early age, one of which had concomitant high titer of FVII inhibitor. The aim of the present study was to identify the causative mutations and to elucidate the underlying molecular mechanisms. All nine F7 exons were sequenced in the probands and the closest family members. A homozygous deletion in exon 1, leading to a frame shift and generation of a premature stop codon (p.C10Pfs*16), was found in proband 1. Probands 2 and 3 (siblings) were homozygous for a missense mutation in exon 8, resulting in a glycine (G) to arginine (R) substitution at amino acid 240 (p.G240R). All probands had severely reduced FVII activity (FVII:C < 1 IU/dL). Treatment consisted of recombinant FVIIa and/or plasma concentrate, and proband 1 developed a FVII inhibitor shortly after initiation of treatment. The FVII variants were overexpressed in mammalian cell lines. No FVII protein was produced in cells expressing the p.C10Pfs*16 variant, and the inhibitor development in proband 1 was likely linked to the complete absence of circulating FVII. Structural analysis suggested that the G to R substitution in FVII found in probands 2 and 3 would destabilize the protein structure, and cell studies demonstrated a defective intracellular transport and increased endoplasmic reticulum stress. The molecular mechanism underlying the p.G240R variant could be reduced secretion caused by protein destabilization and misfolding.

Molecular Insights into Determinants of Translational Readthrough and Implications for Nonsense Suppression Approaches

The fidelity of protein synthesis, a process shaped by several mechanisms involving specialized ribosome regions and external factors, ensures the precise reading of sense and stop codons. However, premature termination codons (PTCs) arising from mutations may, at low frequency, be misrecognized and result in PTC suppression, named ribosome readthrough, with production of full-length proteins through the insertion of a subset of amino acids. Since some drugs have been identified as readthrough inducers, this fidelity drawback has been explored as a therapeutic approach in several models of human diseases caused by nonsense mutations. Here, we focus on the mechanisms driving translation in normal and aberrant conditions, the potential fates of mRNA in the presence of a PTC, as well as on the results obtained in the research of efficient readthrough-inducing compounds. In particular, we describe the molecular determinants shaping the outcome of readthrough, namely the nucleotide and protein context, with the latter being pivotal to produce functional full-length proteins. Through the interpretation of experimental and mechanistic findings, mainly obtained in lysosomal and coagulation disorders, we also propose a scenario of potential readthrough-favorable features to achieve relevant rescue profiles, representing the main issue for the potential translatability of readthrough as a therapeutic strategy.

Antiviral anticoagulation

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel envelope virus that causes coronavirus disease 2019 (COVID-19). Hallmarks of COVID-19 are a puzzling form of thrombophilia that has elevated D-dimer but only modest effects on other parameters of coagulopathy. This is combined with severe inflammation, often leading to acute respiratory distress and possible lethality. Coagulopathy and inflammation are interconnected by the transmembrane receptor, tissue factor (TF), which initiates blood clotting as a cofactor for factor VIIa (FVIIa)-mediated factor Xa (FXa) generation. TF also functions from within the nascent TF/FVIIa/FXa complex to trigger profound changes via protease-activated receptors (PARs) in many cell types, including SARS-CoV-2-trophic cells. Therefore, aberrant expression of TF may be the underlying basis of COVID-19 symptoms. Evidence suggests a correlation between infection with many virus types and development of clotting-related symptoms, ranging from heart disease to bleeding, depending on the virus. Since numerous cell types express TF and can act as sites for virus replication, a model envelope virus, herpes simplex virus type 1 (HSV1), has been used to investigate the uptake of TF into the envelope. Indeed, HSV1 and other viruses harbor surface TF antigen, which retains clotting and PAR signaling function. Strikingly, envelope TF is essential for HSV1 infection in mice, and the FXa-directed oral anticoagulant apixaban had remarkable antiviral efficacy. SARS-CoV-2 replicates in TF-bearing epithelial and endothelial cells and may stimulate and integrate host cell TF, like HSV1 and other known coagulopathic viruses. Combined with this possibility, the features of COVID-19 suggest that it is a TFopathy, and the TF/FVIIa/FXa complex is a feasible therapeutic target.

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.

Contact activation-induced complex formation between complement factor H and coagulation factor XIIa

BACKGROUND

The complement and coagulation systems share an evolutionary origin with many components showing structural homology. Certain components, including complement factor H (FH) and coagulation factor XII (FXII), have separately been shown to have auxiliary activities across the two systems.

OBJECTIVES

The interaction between FXII and FH was investigated.

METHODS

Using enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance (SPR) complex formation between different FXII forms and FH was investigated. The presence of α-FXIIa:FH complexes upon contact activation in plasma was evaluated by ELISA and immunoprecipitation.

RESULTS

We identified and characterized a direct interaction between the components and demonstrated that among different forms of FXII, only the activated α-FXIIa formed complexes with FH, with an apparent binding strength Kd of 34 ± 9 nmol/L. The complex formation involved the kringle domain of the heavy chain of FXII. C1-inhibitor induced inhibition of α-FXIIa did not alter the binding of α-FXIIa toward FH. We further demonstrated the presence of α-FXIIa:FH complexes in normal human plasma upon contact activation, indicating formation of α-FXIIa:FH complexes as a consequence of α-FXIIa generation. Complex formation between α-FXIIa and FH was also assessed in hereditary angioedema (HAE) patients with C1-inhibitor deficiency as well as rheumatoid arthritis (RA) patients with high levels of anti-cyclic citrullinated peptide (anti-CCP) upon contact activation. We observed elevated levels of α-FXIIa:FH complexes in HAE patients, and equal levels of complexes in RA patients and healthy individuals upon contact activation.

CONCLUSION

A direct interaction between α-FXIIa and FH is demonstrated. Our findings represent a new crosstalk between these systems, potentially important in the onset and pathology of inflammatory vascular diseases.

Evaluation of the Antihemostatic and Antithrombotic Effects of Lowering Coagulation Factor VII Levels in a Non-human Primate

Introduction

Tissue factor (TF) and factor (F) VII, components of the extrinsic pathway of blood coagulation, are essential for hemostatic plug formation in response to injury; less clear are their roles in propagating thrombosis, as observational data in humans with congenital FVII deficiency suggests persistent thrombotic and bleeding risk even at significantly decreased FVII levels. We aimed to define the contribution of FVII to thrombus formation and hemostasis using a non-human primate model.

Methods

We treated baboons with a FVII antisense oligonucleotide (ASO) and measured platelet and fibrin deposition inside and distal to collagen- or TF-coated vascular grafts. We assessed hemostasis by measuring bleeding time (BT) and prothrombin time (PT). Enoxaparin and vehicle treatments served as controls.

Results

FVII-ASO treatment reduced FVII levels by 95% and significantly increased both the PT and BT. Lowering FVII levels did not decrease platelet deposition in collagen- or TF-coated grafts, in thrombi distal to the grafts, or fibrin content of either collagen- and TF-coated grafts. Lowering FVII levels were associated with a modest 25% reduction in platelet deposition at 60 min in the distal thrombus tail of TF-coated grafts only.

Conclusions

FVII inhibition by way of ASO is feasible yet significantly impairs hemostasis while only exhibiting antithrombotic effects when thrombosis is initiated by vessel wall surface-associated TF exposure.

Congenital factor VII deficiency in Iraqi children (Single Centre Experience)

Background and Objective

Factor VII (FVII) deficiency is probably one of the most common of the rare autosomal recessive coagulation disorders, with an estimated prevalence of l: 500000. All age groups can be affected with FVII deficiency. This study aimed to describe the demographic parameters, symptomatology, hemostatic values and the outcome of FVII deficiency.

Methods

This is a retrospective descriptive study of patients with congenital FVII deficiency over a period of seven years from (August 2008 to August 2015). The data were collected by reviewing the files for each patient diagnosed with FVII deficiency. Surgical interventions, complications and follow up visits were recorded.

Results

Twenty-four patients were included in this study, 17 females and seven males, below one year was the most common age at presentation. More than half of patients (58.3%) were diagnosed within six months of symptoms onset. The majority of patients had severe phenotype. The most common symptom was epitaxis (41.7%). Five out of 10 patients with FVII level < 1% have either mild to moderate phenotype of the disease without complications; while six out of 14 patients with FVII > 1% had at least one episode of severe bleeding. Three patients had hepatitis C; all were treated by blood products before the introduction of recombinant FVII in Iraq. The outcome of most patients (75%) was normal without complications at time of study.

Conclusion

Clinical manifestations of FVII deficiency are variable and they are not necessarily correlated to the FVII level.

Molecular Mechanisms and Determinants of Innovative Correction Approaches in Coagulation Factor Deficiencies

Molecular strategies tailored to promote/correct the expression and/or processing of defective coagulation factors would represent innovative therapeutic approaches beyond standard substitutive therapy. Here, we focus on the molecular mechanisms and determinants underlying innovative approaches acting at DNA, mRNA and protein levels in inherited coagulation factor deficiencies, and in particular on: (i) gene editing approaches, which have permitted intervention at the DNA level through the specific recognition, cleavage, repair/correction or activation of target sequences, even in mutated gene contexts; (ii) the rescue of altered pre-mRNA processing through the engineering of key spliceosome components able to promote correct exon recognition and, in turn, the synthesis and secretion of functional factors, as well as the effects on the splicing of missense changes affecting exonic splicing elements; this section includes antisense oligonucleotide- or siRNA-mediated approaches to down-regulate target genes; (iii) the rescue of protein synthesis/function through the induction of ribosome readthrough targeting nonsense variants or the correction of folding defects caused by amino acid substitutions. Overall, these approaches have shown the ability to rescue the expression and/or function of potentially therapeutic levels of coagulation factors in different disease models, thus supporting further studies in the future aimed at evaluating the clinical translatability of these new strategies.

Nonhemostatic Activities of Factor Xa: Are There Pleiotropic Effects of Anti-FXa Direct Oral Anticoagulants?

Factor Xa (FXa) is the key serine protease of the coagulation cascade as it is the point of convergence of the intrinsic and extrinsic pathways, leading to the formation of thrombin. Factor Xa is an established target of anticoagulation therapy, due to its central role in coagulation. Over the past years, several direct oral anticoagulants (DOACs) targeting FXa have been developed. Rivaroxaban, apixaban, and edoxaban are used in clinical practice for prevention and treatment of thrombotic diseases. Increasing evidence suggests that FXa exerts nonhemostatic cellular effects that are mediated mainly through protease-activated receptors-1 and -2 and are involved in pathophysiological conditions, such as atherosclerosis, inflammation, and fibrosis. Direct inhibition of FXa by DOACs could be beneficial in these conditions. This is a narrative review that focuses on the cellular effects of FXa in various cell types and conditions, as well as on the possible pleiotropic effects of FXa-targeting DOACs.

Missense changes in the catalytic domain of coagulation factor X account for minimal function preventing a perinatal lethal condition

INTRODUCTION

Inherited deficiencies in the coagulation pathway provide diversified models to investigate the molecular bases of perinatal lethality associated with null-like variants. Differently from X-linked haemophilias, homozygous/doubly heterozygous null variants in the rare autosomally inherited deficiency of factor X (FX) might be incompatible with perinatal survival.

AIM

To provide experimental evidence about the null/close-to-null FX function.

METHODS

The residual secreted (ELISA) and functional (thrombin generation assays) protein levels associated with the novel nonsense (c.1382G>A; p.Trp461Ter) and missense (c.752T>C; p.Leu251Pro) variants, found in the proposita with life-threatening symptoms at birth, were characterized through recombinant (r)FX expression.

RESULTS

The rFX-461Ter showed very low secretion and undetectable function. Expression and function of the predicted readthrough-deriving missense variants (rFX-461Tyr, rFX-461Gln) were also severely impaired. These unfavourable features, due to nucleotide and protein sequence constraints, precluded functional readthrough over the 461 stop codon. Differently, the poorly secreted rFX-251Pro variant displayed residual function that was characterized by anti-TFPI aptamer-based amplification or selective inhibition of activated FX function by fondaparinux in plasma and found to be reduced by approximately three orders of magnitude. Similarly to the rFX-251Pro, a group of catalytic domain missense variants cause poorly secreted molecules with modest function in FX-deficient patients with life-threatening symptoms.

CONCLUSIONS

Our data, contributing to the knowledge of the very severe FX deficiency forms, support life-saving requirement of trace FX function, clearly exemplified by the dysfunctional but not completely inactive rFX-251Pro variant that, albeit with severely reduced function, is compatible with a residual activity ensuring minimal haemostasis and permitting perinatal survival.

Meta-Analysis of Factor V, Factor VII, Factor XII, and Factor XIII-A Gene Polymorphisms and Ischemic Stroke

Numerous studies examined the association between factors FV, FVII, FXII, and FXIII-A gene polymorphisms and ischemic stroke, but conclusive evidence is yet to be obtained. Thus, this meta-analysis aimed to investigate the novel association of FV rs1800595, FVII rs5742910, FXII rs1801020, and FXIII-A rs5982 and rs3024477 polymorphisms with ischemic stroke risk. A systematic review was performed on articles retrieved before June 2018. Relevant data were extracted from eligible studies and meta-analyzed using RevMan version 5.3. The strength of association between studied polymorphisms and ischemic stroke risk was calculated as odds ratios and 95% confidence intervals, by applying both fixed- and random-effect models. A total of 25 studies involving 6100 ischemic stroke patients and 9249 healthy controls were incorporated in the final meta-analysis model. Specifically, rs1800595, rs5742910, rs1801020, rs5982, and rs3024477 consisted of 673, 3668, 922, 433, and 404 cases, as well as 995, 4331, 1285, 1321, and 1317 controls, respectively. The pooled analysis indicated that there was no significant association of FV rs1800595, FVII rs5742910, FXII rs1801020, FXIII-A rs5982, and FXIII-A rs3024477 polymorphisms with ischemic stroke risk, under any genetic models (dominant, recessive, over-dominant, and allelic). The present meta-analysis concluded that FV rs1800595, FVII rs5742910, FXII rs1801020, and FXIII-A rs5982 and rs3024477 polymorphisms are not associated with ischemic stroke risk.

Virus envelope tissue factor promotes infection in mice

Essentials The coagulation initiator, tissue factor (TF), is on the herpes simplex virus 1 (HSV1) surface. HSV1 surface TF was examined in mice as an antiviral target since it enhances infection in vitro. HSV1 surface TF facilitated infection of all organs evaluated and anticoagulants were antiviral. Protease activated receptor 2 inhibited infection in vivo and its pre-activation was antiviral. SUMMARY: Background Tissue factor (TF) is the essential cell surface initiator of coagulation, and mediates cell signaling through protease-activated receptor (PAR) 2. Having a diverse cellular distribution, TF is involved in many biological pathways and pathologies. Our earlier work identified host cell-derived TF on the envelope covering several viruses, and showed its involvement in enhanced cell infection in vitro. Objective In the current study, we evaluated the in vivo effects of virus surface TF on infection and on the related modulator of infection PAR2. Methods With the use of herpes simplex virus type 1 (HSV1) as a model enveloped virus, purified HSV1 was generated with or without envelope TF through propagation in a TF-inducible cell line. Infection was studied after intravenous inoculation of BALB/c, C57BL/6J or C57BL/6J PAR2 knockout mice with 5 × 105 plaque-forming units of HSV1, mimicking viremia. Three days after inoculation, organs were processed, and virus was quantified with plaque-forming assays and quantitative real-time PCR. Results Infection of brain, lung, heart, spinal cord and liver by HSV1 required viral TF. Demonstrating promise as a therapeutic target, virus-specific anti-TF mAbs or small-molecule inhibitors of coagulation inhibited infection. PAR2 modulates HSV1 in vivo as demonstrated with PAR2 knockout mice and PAR2 agonist peptide. Conclusion TF is a constituent of many permissive host cell types. Therefore, the results presented here may explain why many viruses are correlated with hemostatic abnormalities, and indicate that TF is a novel pan-specific envelope antiviral target.

Tissue Factor: An Essential Mediator of Hemostasis and Trigger of Thrombosis

Tissue factor (TF) is the high-affinity receptor and cofactor for factor (F)VII/VIIa. The TF-FVIIa complex is the primary initiator of blood coagulation and plays an essential role in hemostasis. TF is expressed on perivascular cells and epithelial cells at organ and body surfaces where it forms a hemostatic barrier. TF also provides additional hemostatic protection to vital organs, such as the brain, lung, and heart. Under pathological conditions, TF can trigger both arterial and venous thrombosis. For instance, atherosclerotic plaques contain high levels of TF on macrophage foam cells and microvesicles that drives thrombus formation after plaque rupture. In sepsis, inducible TF expression on monocytes leads to disseminated intravascular coagulation. In cancer patients, tumors release TF-positive microvesicles into the circulation that may contribute to venous thrombosis. TF also has nonhemostatic roles. For instance, TF-dependent activation of the coagulation cascade generates coagulation proteases, such as FVIIa, FXa, and thrombin, which induce signaling in a variety of cells by cleavage of protease-activated receptors. This review will focus on the roles of TF in protective hemostasis and pathological thrombosis.

Structural Basis for Activity and Specificity of an Anticoagulant Anti-FXIa Monoclonal Antibody and a Reversal Agent

Coagulation factor XIa is a candidate target for anticoagulants that better separate antithrombotic efficacy from bleeding risk. We report a co-crystal structure of the FXIa protease domain with DEF, a human monoclonal antibody that blocks FXIa function and prevents thrombosis in animal models without detectable increased bleeding. The light chain of DEF occludes the FXIa S1 subsite and active site, while the heavy chain provides electrostatic interactions with the surface of FXIa. The structure accounts for the specificity of DEF for FXIa over its zymogen and related proteases, its active-site-dependent binding, and its ability to inhibit substrate cleavage. The inactive FXIa protease domain used to obtain the DEF-FXIa crystal structure reversed anticoagulant activity of DEF in plasma and in vivo and the activity of a small-molecule FXIa active-site inhibitor in vitro. DEF and this reversal agent for FXIa active-site inhibitors may help support clinical development of FXIa-targeting anticoagulants.

Factor XIa-specific IgG and a reversal agent to probe factor XI function in thrombosis and hemostasis

Thrombosis is a major cause of morbidity and mortality. Current antithrombotic drugs are not ideal in that they must balance prevention of thrombosis against bleeding risk. Inhibition of coagulation factor XI (FXI) may offer an improvement over existing antithrombotic strategies by preventing some forms of thrombosis with lower bleeding risk. To permit exploration of this hypothesis in humans, we generated and characterized a series of human immunoglobulin Gs (IgGs) that blocked FXIa active-site function but did not bind FXI zymogen or other coagulation proteases. The most potent of these IgGs, C24 and DEF, inhibited clotting in whole human blood and prevented FeCl3-induced carotid artery occlusion in FXI-deficient mice reconstituted with human FXI and in thread-induced venous thrombosis in rabbits at clinically relevant doses. At doses substantially higher than those required for inhibition of intravascular thrombus formation in these models, DEF did not increase cuticle bleeding in rabbits or cause spontaneous bleeding in macaques over a 2-week study. Anticipating the desirability of a reversal agent, we also generated a human IgG that rapidly reversed DEF activity ex vivo in human plasma and in vivo in rabbits. Thus, an active site-directed FXIa-specific antibody can block thrombosis in animal models and, together with the reversal agent, may facilitate exploration of the roles of FXIa in human disease.

Coagulation factor VII variants resistant to inhibitory antibodies

Replacement therapy is currently used to prevent and treat bleeding episodes in coagulation factor deficiencies. However, structural differences between the endogenous and therapeutic proteins might increase the risk for immune complications. This study was aimed at identifying factor (F)VII variants resistant to inhibitory antibodies developed after treatment with recombinant activated factor VII (rFVIIa) in a FVII-deficient patient homozygous for the p.A354V-p.P464Hfs mutation, which predicts trace levels of an elongated FVII variant in plasma. We performed fluorescent bead-based binding, ELISA-based competition as well as fluorogenic functional (activated FX and thrombin generation) assays in plasma and with recombinant proteins. We found that antibodies displayed higher affinity for the active than for the zymogen FVII (half-maximal binding at 0.54 ± 0.04 and 0.78 ± 0.07 BU/ml, respectively), and inhibited the coagulation initiation phase with a second-order kinetics. Isotypic analysis showed a polyclonal response with a large predominance of IgG1. We hypothesised that structural differences in the carboxyl-terminus between the inherited FVII and the therapeutic molecules contributed to the immune response. Intriguingly, a naturally-occurring, poorly secreted and 5-residue truncated FVII (FVII-462X) escaped inhibition. Among a series of truncated rFVII molecules, we identified a well-secreted and catalytically competent variant (rFVII-464X) with reduced binding to antibodies (half-maximal binding at 0.198 ± 0.003 BU/ml) as compared to the rFVII-wt (0.032 ± 0.002 BU/ml), which led to a 40-time reduced inhibition in activated FX generation assays. Taken together our results provide a paradigmatic example of mutation-related inhibitory antibodies, strongly support the FVII carboxyl-terminus as their main target and identify inhibitor-resistant FVII variants.

Coagulation factor VIIa-mediated protease-activated receptor 2 activation leads to β-catenin accumulation via the AKT/GSK3β pathway and contributes to breast cancer progression

Cell migration and invasion are very characteristic features of cancer cells that promote metastasis, which is one of the most common causes of mortality among cancer patients. Emerging evidence has shown that coagulation factors can directly mediate cancer-associated complications either by enhancing thrombus formation or by initiating various signaling events leading to metastatic cancer progression. It is well established that, apart from its distinct role in blood coagulation, coagulation factor FVIIa enhances aggressive behaviors of breast cancer cells, but the underlying signaling mechanisms still remain elusive. To this end, we investigated FVIIa's role in the migration and invasiveness of the breast cancer cell line MDA-MB-231. Consistent with previous observations, we observed that FVIIa increased the migratory and invasive potential of these cells. We also provide molecular evidence that protease-activated receptor 2 activation followed by PI3K-AKT activation and GSK3β inactivation is involved in these processes and that β-catenin, a well known tumor-regulatory protein, contributes to this signaling pathway. The pivotal role of β-catenin was further indicated by the up-regulation of its downstream targets cyclin D1, c-Myc, COX-2, MMP-7, MMP-14, and Claudin-1. β-Catenin knockdown almost completely attenuated the FVIIa-induced enhancement of breast cancer migration and invasion. These findings provide a new perspective to counteract the invasive behavior of breast cancer, indicating that blocking PI3K-AKT pathway-dependent β-catenin accumulation may represent a potential therapeutic approach to control breast cancer.

Differential functional readthrough over homozygous nonsense mutations contributes to the bleeding phenotype in coagulation factor VII deficiency

Essentials Potentially null homozygous Factor(F)7 nonsense mutations are associated to variable bleeding symptoms. Readthrough of p.Ser112X (life-threatening) and p.Cys132X (moderate) stop codons was investigated. Readthrough-mediated insertion of wild-type or tolerated residues produce functional proteins. Functional readthrough over homozygous F7 nonsense mutations contributes to the bleeding phenotype.

SUMMARY

Background Whereas the rare homozygous nonsense mutations causing factor (F)VII deficiency may predict null conditions that are almost completely incompatible with life, they are associated with appreciable differences in hemorrhagic symptoms. The misrecognition of premature stop codons (readthrough) may account for variable levels of functional full-length proteins. Objectives To experimentally evaluate the basal and drug-induced levels of FVII resulting from the homozygous p.Cys132X and p.Ser112X nonsense mutations that are associated with moderate (132X) or life-threatening (112X) symptoms, and that are predicted to undergo readthrough with (132X) or without (112X) production of wild-type FVII. Methods We transiently expressed recombinant FVII (rFVII) nonsense and missense variants in human embryonic kidney 293 cells, and evaluated secreted FVII protein and functional levels by ELISA, activated FX generation, and coagulation assays. Results The levels of functional FVII produced by p.Cys132X and p.Ser112X mutants (rFVII-132X, 1.1% ± 0.2% of wild-type rFVII; rFVII-112X, 0.5% ± 0.1% of wild-type rFVII) were compatible with the occurrence of spontaneous readthrough, which was magnified by the addition of G418 - up to 12% of the wild-type value for the rFVII-132X nonsense variant. The predicted missense variants arising from readthrough abolished (rFVII-132Trp/Arg) or reduced (rFVII-112Trp/Cys/Arg, 22-45% of wild-type levels) secretion and function. These data suggest that the appreciable rescue of p.Cys132X function was driven by reinsertion of the wild-type residue, whereas the minimal p.Ser112X function was explained by missense changes permitting FVII secretion and function. Conclusions The extent of functional readthrough might explain differences in the bleeding phenotype of patients homozygous for F7 nonsense mutations, and prevent null conditions even for the most readthrough-unfavorable mutations.

Protective and detrimental effects of neuroectodermal cell-derived tissue factor in mouse models of stroke

Within the CNS, a dysregulated hemostatic response contributes to both hemorrhagic and ischemic strokes. Tissue factor (TF), the primary initiator of the extrinsic coagulation cascade, plays an essential role in hemostasis and also contributes to thrombosis. Using both genetic and pharmacologic approaches, we characterized the contribution of neuroectodermal (NE) cell TF to the pathophysiology of stroke. We used mice with various levels of TF expression and found that astrocyte TF activity reduced to ~5% of WT levels was still sufficient to maintain hemostasis after hemorrhagic stroke but was also low enough to attenuate inflammation, reduce damage to the blood-brain barrier, and improve outcomes following ischemic stroke. Pharmacologic inhibition of TF during the reperfusion phase of ischemic stroke attenuated neuronal damage, improved behavioral deficit, and prevented mortality of mice. Our data demonstrate that NE cell TF limits bleeding complications associated with the transition from ischemic to hemorrhagic stroke and also contributes to the reperfusion injury after ischemic stroke. The high level of TF expression in the CNS is likely the result of selective pressure to limit intracerebral hemorrhage (ICH) after traumatic brain injury but, in the modern era, poses the additional risk of increased ischemia-reperfusion injury after ischemic stroke.

Efficient generation of FVII gene knockout mice using CRISPR/Cas9 nuclease and truncated guided RNAs

We investigated the effects of 5'-end truncated CRISPR RNA-guided Cas9 nuclease (tru-RGN, 17/18 nucleotides) on genome editing capability in NIH/3T3 cells, and its efficiencies on generating Factor VII (FVII) gene-knockout (KO) mice. In cultured cells, RGNs on-target editing activity had been varied when gRNAs was truncated, higher at Site Two (tF7-2 vs. F7-2, 49.5 vs. 30.1%) while lower in other two sites (Site One, tF7-1 vs.F7-1, 12.1 vs. 23.6%; Site Three, tF7-3 vs.F7-3, 7.7 vs 10.9%) (P < 0.05). Out of 15 predicated off-target sites, tru-RGNs showed significantly decreased frequencies at 5 sites. By microinjecting tru-RGN RNAs into zygotes, FVII KO mice were generated with higher efficiency at Site Two (80.1 vs. 35.8%) and Site One (55.0 vs 3.7%) (P < 0.05), but not at Site three (39.4 vs 27.8%) (P > 0.05) when compared with standard RGN controls. Knockout FVII mice demonstrated a delayed prothrombin time and decreased plasma FVII expression. Our study first demonstrates that truncated gRNAs to 18 complementary nucleotides and Cas9 nucleases, can effectively generate FVII gene KO mice with a significantly higher efficiency in a site-dependent manner. In addition, the off-target frequency was much lower in KO mice than in cell lines via RGN expression vector-mediated genome editing.

Arterial thrombosis is accelerated in mice deficient in histidine-rich glycoprotein

Factor (F) XII, a key component of the contact system, triggers clotting via the intrinsic pathway, and is implicated in propagating thrombosis. Although nucleic acids are potent activators, it is unclear how the contact system is regulated to prevent uncontrolled clotting. Previously, we showed that histidine-rich glycoprotein (HRG) binds FXIIa and attenuates its capacity to trigger coagulation. To investigate the role of HRG as a regulator of the intrinsic pathway, we compared RNA- and DNA-induced thrombin generation in plasma from HRG-deficient and wild-type mice. Thrombin generation was enhanced in plasma from HRG-deficient mice, and accelerated clotting was restored to normal with HRG reconstitution. Although blood loss after tail tip amputation was similar in HRG-deficient and wild-type mice, carotid artery occlusion after FeCl3 injury was accelerated in HRG-deficient mice, and HRG administration abrogated this effect. To confirm that HRG modulates the contact system, we used DNase, RNase, and antisense oligonucleotides to characterize the FeCl3 model. Whereas DNase or FVII knockdown had no effect, carotid occlusion was abrogated with RNase or FXII knockdown, confirming that FeCl3-induced thrombosis is triggered by RNA in a FXII-dependent fashion. Therefore, in a nucleic acid-driven model, HRG inhibits thrombosis by modulating the intrinsic pathway of coagulation.

Sex differences in stroke: the contribution of coagulation

Stroke is now the leading cause of adult disability in the United States. Women are disproportionately affected by stroke. Women increasingly outnumber men in the elderly population, the period of highest risk for stroke. However, there is also a growing recognition that fundamental sex differences are present that contribute to differential ischemic sensitivity. In addition, gonadal hormone exposure can impact coagulation and fibrinolysis, key factors in the initiation of thrombosis. In this review we will discuss sex differences in stroke, with a focus on platelets, vascular reactivity and coagulation.

Genetic variants of the vitamin K dependent coagulation system and intraventricular hemorrhage in preterm infants

Background

Pathogenesis of intraventricular hemorrhage (IVH) in premature infants is multifactorial. Little is known about the impact of genetic variants in the vitamin K-dependent coagulation system on the development of IVH.

Methods

Polymorphisms in the genes encoding vitamin K epoxide reductase complex 1 (VKORC1 -1639G>A) and coagulation factor 7 (F7 -323Ins10) were examined prospectively in 90 preterm infants <32 weeks gestational age with respect to coagulation profile and IVH risk.

Results

F7-323Ins10 was associated with lower factor VII levels, but not with individual IVH risk. In VKORC1-wildtype infants, logistic regression analysis revealed a higher IVH risk compared to carriers of the -1639A allele. Levels of the vitamin K-dependent coagulation parameters assessed in the first hour after birth did not differ between VKORC1-wildtype infants and those carrying -1639A alleles.

Conclusions

Our data support the assumption that genetic variants in the vitamin K-dependent coagulation system influence the coagulation profile and the IVH risk in preterm infants. Further studies focussing on short-term changes in vitamin K-kinetics and the coagulation profile during the first days of life are required to further understand a possible link between development of IVH and genetic variants affecting the vitamin K-metabolism.

Tissue factor-fVIIa inhibition: update on an unfinished quest for a novel oral antithrombotic

The tissue factor-coagulation factor VIIa complex (TF-fVIIa) is a well-validated biological target and has been the focus of extensive research directed toward the discovery of novel oral antithrombotics. This review briefly summarizes the key antithrombotic target validation data and provides an update on recent advances in small molecule TF-fVIIa inhibitors.

Liver-specific γ-glutamyl carboxylase-deficient mice display bleeding diathesis and short life span

Vitamin K is a fat-soluble vitamin that plays important roles in blood coagulation and bone metabolism. One of its functions is as a co-factor for γ-glutamyl carboxylase (Ggcx). Conventional knockout of Ggcx causes death shortly after birth in homozygous mice. We created Ggcx-floxed mice by inserting loxP sequences at the sites flanking exon 6 of Ggcx. By mating these mice with albumin-Cre mice, we generated Ggcx-deficient mice specifically in hepatocytes (Ggcx^{Δliver/Δliver} mice). In contrast to conventional Ggcx knockout mice, Ggcx^{Δliver/Δliver} mice had very low activity of Ggcx in the liver and survived several weeks after birth. Furthermore, compared with heterozygous mice (Ggcx^+/Δliver), Ggcx^{Δliver/Δliver} mice had shorter life spans. Ggcx^{Δliver/Δliver} mice displayed bleeding diathesis, which was accompanied by decreased activity of coagulation factors II and IX. Ggcx-floxed mice can prove useful in examining Ggcx functions in vivo.

An engineered U1 small nuclear RNA rescues splicing defective coagulation F7 gene expression in mice

BACKGROUND

The ability of the spliceosomal small nuclear RNA U1 (U1snRNA) to rescue pre-mRNA splicing impaired by mutations makes it an attractive therapeutic molecule. Coagulation factor deficiencies due to splicing mutations are relatively frequent and could therefore benefit from this strategy. However, the effects of U1snRNAs in vivo remain unknown.

OBJECTIVES

To assess the rescue of the F7 c.859+5G>A splicing mutation (FVII+5A), causing severe human factor VII (hFVII) deficiency, by the modified U1snRNA+5a (U1+5a) in a murine model.

METHODS

Mice expressing the human F7 c.859+5G>A mutant were generated following liver-directed expression by plasmid or recombinant adeno-associated viral (AAV) vector administration. The rescue of the splice-site defective pre-mRNA by U1+5a was monitored in liver and plasma through hFVII-specific assays.

RESULTS

Injection of plasmids encoding the U1+5a rescued plasma hFVII levels, which increased from undetectable to ~8.5% of those obtained with the wild-type hFVII plasmid control. To assess long-term effects, mice were injected with low and high doses of two AAV vectors encoding the FVII+5A splice site mutant as template to be corrected by U1+5a. This strategy resulted in hFVII plasma levels of 3.9 ± 0.8 or 23.3 ± 5.1 ng mL⁻¹ in a dose-dependent manner, corresponding in patients to circulating FVII levels of ~1-4.5% of normal. Moreover, in both experimental models, we also detected correctly spliced hFVII transcripts and hFVII-positive cells in liver cells.

CONCLUSIONS

Here we provide the first in vivo proof of-principle of the rescue of the expression of a splicing-defective F7 mutant by U1snRNAs, thus highlighting their therapeutic potential in coagulation disorders.

Role of Factor XII in hemostasis and thrombosis: clinical implications

The plasma coagulation system reacts quickly to limit blood loss from injury sites but also contributes to vascular thrombosis. In current models of hemostatic balance, normal coagulation and thrombosis represent two sides of the same coin, however, recent data from gene-deleted murine models have challenged this dogma. Deficiency of coagulation Factor XII (Hageman factor), a serine protease that initiates the intrinsic pathway of coagulation, severely impairs arterial thrombus formation but is not associated with excessive bleeding. These findings suggest that fibrin-generating mechanisms that operate during pathologic thrombus formation involve pathways distinct from those that are active during normal hemostasis. As Factor XII selectively contributes to thrombus formation in occlusive disease, but not to normal hemostasis, inhibition of this protease may offer a novel treatment strategy for prevention of arterial thrombosis with minimal or no risk of bleeding.

PPARγ activation rescues mitochondrial function from inhibition of complex I and loss of PINK1

Parkinson's disease has long been associated with impaired mitochondrial complex I activity, while several gene defects associated with familial Parkinson's involve defects in mitochondrial function or 'quality control' pathways, causing an imbalance between mitochondrial biogenesis and removal of dysfunctional mitochondria by autophagy. Amongst these are mutations of the gene for PTEN-induced kinase 1 (PINK1) in which mitochondrial function is abnormal. Peroxisome proliferator-activated receptor gamma (PPARγ), a nuclear receptor and ligand-dependent transcription factor, regulates pathways of inflammation, lipid and carbohydrate metabolism, antioxidant defences and mitochondrial biogenesis. We have found that inhibition of complex I in human differentiated SHSY-5Y cells by the complex I inhibitor rotenone irreversibly decrease mitochondrial mass, membrane potential and oxygen consumption, while increasing free radical generation and autophagy. Similar changes are seen in PINK1 knockdown cells, in which potential, oxygen consumption and mitochondrial mass are all decreased. In both models, all these changes were reversed by pre-treatment of the cells with the PPARγ agonist, rosiglitazone, which increased mitochondrial biogenesis, increased oxygen consumption and suppressed free radical generation and autophagy. Thus, rosiglitazone is neuroprotective in two different models of mitochondrial dysfunction associated with Parkinson's disease through a direct impact on mitochondrial function.

Hemostasis and alterations of the central nervous system

Modulation of coagulation has been successfully applied to ischemic disorders of the central nervous system (CNS). Some components of the coagulation system have been identified in the CNS, yet with limited exception their functions have not been clearly defined. Little is known about how events within the cerebral tissues affect hemostasis. Nonetheless, the interaction between cerebral cells and vascular hemostasis and the possibility that endogenous coagulation factors can participate in functions within the neurovascular unit provide intriguing possibilities for deeper insight into CNS functions and the potential for treatment of CNS injuries. Here, we consider the expression of coagulation factors in the CNS, the coagulopathy associated with focal cerebral ischemia (and its relationship to hemorrhagic transformation), the use of recombinant tissue plasminogen activator (rt-PA) in ischemic stroke and its study in animal models, the impact of rt-PA on neuron and CNS structure and function, and matrix protease generation and matrix degradation and hemostasis. Interwoven among these topics is evidence for interactions of coagulation factors with and within the CNS. How activation of hemostasis occurs in the cerebral tissues and how the brain responds are difficult questions that offer many research possibilities.

Genetic sequence analysis of inherited bleeding diseases

The genes encoding the coagulation factor proteins were among the first human genes to be characterized over 25 years ago. Since then, significant progress has been made in the translational application of this information for the 2 commonest severe inherited bleeding disorders, hemophilia A and B. For these X-linked disorders, genetic characterization of the disease-causing mutations is now incorporated into the standard of care and genetic information is used for risk stratification of treatment complications. With electronic databases detailing >2100 unique mutations for hemophilia A and >1100 mutations for hemophilia B, these diseases are among the most extensively characterized inherited diseases in humans. Experience with the genetics of the rare bleeding disorders is, as expected, less well advanced. However, here again, electronic mutation databases have been developed and provide excellent guidance for the application of genetic analysis as a confirmatory approach to diagnosis. Most recently, progress has also been made in identifying the mutant loci in a variety of inherited platelet disorders, and these findings are beginning to be applied to the genetic diagnosis of these conditions. Investigation of patients with bleeding phenotypes without a diagnosis, using genome-wide strategies, may identify novel genes not previously recognized as playing a role in hemostasis.

Newly diagnosed congenital factor VII deficiency and utilization of recombinant activated factor VII (NovoSeven(®))

This case report presents a newly diagnosed congenital factor VII deficiency treated with recombinant activated factor VII (rFVIIa). Congenital factor VII deficiency is a rare autosomal-recessive bleeding disorder that occurs in fewer than 1/500,000 persons. Its presentation can vary from epistaxis to hemarthroses and severe central nervous system bleeding, and correlates poorly with factor VII levels. Our patient had not had a significant hemostatic challenge prior to his presentation and therefore never had any symptomatology suggestive of this disease. He was treated with rFVIIa, and was able to undergo repair of his fractures without bleeding.

Recent advances in fetal gene therapy

Over the first decade of this new millennium gene therapy has demonstrated clear clinical benefits in several diseases for which conventional medicine offers no treatment. Clinical trials of gene therapy for single gene disorders have recruited predominantly young patients since older subjects may have suffered irrevocablepathological changes or may not be available because the disease is lethal relatively early in life. The concept of fetal gene therapy is an extension of this principle in that diseases in which irreversible changes occur at or beforebirth can be prevented by gene supplementation or repair in the fetus or associated maternal tissues. This article ccnsiders the enthusiasm and skepticism held for fetal gene therapy and its potential for clinical application. It coversa spectrum of candidate diseases for fetal gene therapy including Pompe disease, Gaucher disease, thalassemia, congenital protein C deficiency and cystic fibrosis. It outlines successful and not-so-successful examples of fetal gene therapy in animal models. Finally the application and potential of fetal gene transfer as a fundamental research tool for developmental biology and generation of somatic transgenic animals is surveyed.

Upregulation of the coagulation factor VII gene during glucose deprivation is mediated by activating transcription factor 4

Background

Constitutive production of blood coagulation proteins by hepatocytes is necessary for hemostasis. Stressful conditions trigger adaptive cellular responses and delay processing of most proteins, potentially affecting plasma levels of proteins secreted exclusively by hepatocytes. We examined the effect of glucose deprivation on expression of coagulation proteins by the human hepatoma cell line, HepG2.

Methodology/Principal Findings

Expression of coagulation factor VII, which is required for initiation of blood coagulation, was elevated by glucose deprivation, while expression of other coagulation proteins decreased. Realtime PCR and ELISA demonstrated that the relative percentage expression +/− SD of steady-state F7 mRNA and secreted factor VII antigen were significantly increased (from 100+/−15% to 188+/−27% and 100+/−8.8% to 176.3+/−17.3% respectively, p<0.001) at 24 hr of treatment. The integrated stress response was induced, as indicated by upregulation of transcription factor ATF4 and of additional stress-responsive genes. Small interfering RNAs directed against ATF4 potently reduced basal F7 expression, and prevented F7 upregulation by glucose deprivation. The response of the endogenous F7 gene was replicated in reporter gene assays, which further indicated that ATF4 effects were mediated via interaction with an amino acid response element in the F7 promoter.

Conclusions/Significance

Our data indicated that glucose deprivation enhanced F7 expression in a mechanism reliant on prior ATF4 upregulation primarily due to increased transcription from the ATF4 gene. Of five coagulation protein genes examined, only F7 was upregulated, suggesting that its functions may be important in a systemic response to glucose deprivation stress.

Activation of a cryptic splice site in a potentially lethal coagulation defect accounts for a functional protein variant

Changes at the invariable donor splice site + 1 guanine, relatively frequent in human genetic disease, are predicted to abrogate correct splicing, and thus are classified as null mutations. However, their ability to direct residual expression, which might have pathophysiological implications in several diseases, has been poorly investigated. As a model to address this issue, we studied the IVS6 + 1G > T mutation found in patients with severe deficiency of the protease triggering coagulation, factor VII (FVII), whose absence is considered lethal. In expression studies, the IVS6 + 1G > T induced exon 6 skipping and frame-shift, and prevented synthesis of correct FVII transcripts detectable by radioactive/fluorescent labelling or real-time RT-PCR. Intriguingly, the mutation induced the activation of a cryptic donor splice site in exon 6 and production of an in-frame 30 bp deleted transcript (8 ± 2%). Expression of this cDNA variant, lacking 10 residues in the activation domain, resulted in secretion of trace amounts (0.2 ± 0.04%) of protein with appreciable specific activity (48 ± 16% of wt-FVII). Altogether these data indicate that the IVS6 + 1G > T mutation is compatible with the synthesis of functional FVII molecules (~ 0.01% of normal, 1 pM), which could trigger coagulation. The low but detectable thrombin generation (352 ± 55 nM) measured in plasma from an IVS6 + 1G > T homozygote was consistent with a minimal initiation of the enzymatic cascade. In conclusion, we provide experimental clues for traces of FVII expression, which might have reverted an otherwise perinatally lethal genetic condition.