A new look at blood coagulation factor V:

Importance of individual residues in hydrophobic patch PLVIVGL (1481-1487) in FV-Short for synergistic TFPIα cofactor activity with protein S, an alanine-scanning study: AlphaFold-mediated prediction of FV-Short/TFPIα/protein S trimolecular complex structure

BACKGROUND

In the splice variant factor (F)V-Short, 702 residues are deleted from the B domain, resulting in exposure of an acid region (AR2; 1493-1537) that binds TFPIα. FV-Short and protein S serve as synergistic TFPIα cofactors in inhibition of FXa. In the preAR2 region, a hydrophobic patch PLVIVGL (1481-1487) is crucial for synergistic TFPIα-cofactor activity and assembly of FV-Short, TFPIα, and protein S.

OBJECTIVES

To elucidate the importance of individual residues in the PLVIVGL patch for synergism between FV-Short and protein S as TFPIα cofactors.

METHODS

An alanine scanning of the hydrophobic patch was performed in which 7 FV-Short variants were created. The synergistic TFPIα-cofactor activity was analyzed by FXa inhibition and a microtiter-based assay tested binding between the proteins. AlphaFold 3 was used to predict protein-protein interactions between FV-Short, protein S, and TFPIα.

RESULTS

Five of the 7 variants (V1483A, I1484A, V1485A, G1486A, and L1487A) demonstrated decreased synergistic TFPIα cofactor activity; in particular, G1486A and L1487A were severely affected. Neither wild-type FV-Short nor any of the mutants bound protein S in the absence of TFPIα. In the presence of TFPIα, wild-type FV-Short, P1481A, L1482A, and V1485A bound protein S, whereas V1483A, I1484A, G1486A, and L1487A did not. AlphaFold predicted an interaction between the hydrophobic patch in FV-Short and a hydrophobic patch in protein S involving residues 268-276 and 422-426.

CONCLUSION

Individual residues (V1483, I1484, G1486, and L1487) in the hydrophobic patch are demonstrated to be important for the synergistic TFPIα-cofactor activity and for the assembly of a trimolecular FXa-inhibitory complex.

Clinical, Laboratory, and Molecular Aspects of Factor V Deficiency

Factor V (FV) is a glycoprotein that plays a pivotal role in hemostasis, being involved in coagulant and anticoagulant pathways. Congenital FV deficiency is a rare bleeding disorder with an incidence of 1 per million live births, considering the most severe homozygous form. FV deficiency is diagnosed using routine coagulation tests and FV activity assays. Several mutations, including missense, nonsense, and frameshift, have been detected in the F5 gene. Clinical symptoms are variable, ranging from mild ecchymoses and mucosal bleeding to life-threatening intracranial hemorrhage. The mainstay of treatment includes fresh-frozen plasma, preferentially virus-inactivated. In this narrative review, we provide an update of the main laboratory, molecular, clinical, and therapeutic features of inherited FV deficiency.

Factor V Serves as an Early Biomarker for Graft Loss After Liver Transplant: A Prospective Evaluation

BACKGROUND

Low post-operative day (POD) 1 Factor V has been retrospectively associated with graft loss after liver transplantation when stratified by a cutoff of 0.36 U/mL. We aimed to validate this prospectively.

METHODS

Patients transplanted at Toronto General Hospital were recruited (May 2018-March 2021). Factor V measurements were obtained on POD1-3, 5, and 7. Graft and patient survival at 3, 6, and 12 months were primary and secondary outcomes, respectively. We identified an optimal cutoff through receiver operating characteristic (ROC) analysis and the Youden index. Kaplan-Meier method and Log-rank tests were used to assess/compare survival.

RESULTS

One hundred and twenty-nine patients were included. One hundred and eight had Factor V >0.36 and 21 had ≤0.36 U/mL. This cutoff was predictive of 6- and 12-month graft survival and 12-month patient survival. With an optimal cutoff of 0.46 U/mL on POD1, 87 patients had Factor V >0.46 and 42 had ≤0.46 U/mL. Three-, 6-, and 12-month graft survival rates were 100%, 98.8%, and 98.8%, for patients with Factor V >0.46 U/mL, and 92.9%, 87.7%, and 87.7% for Factor V ≤0.46 U/mL. Similarly, 3-, 6-, and 12-month patient survival rates were 98.8%, 96.4%, and 95.0% for patients with Factor V >0.46 U/mL, and 92.9%, 88.0%, and 82.9% for Factor V ≤0.46 U/mL. Stratification below the novel cutoff was associated with decreased graft survival at months 3 (p = 0.012), 6 (p = 0.006), and 12 (p = 0.006), and decreased patient survival at 12 months (p = 0.022).

CONCLUSIONS

Factor V serves as an early biomarker for graft loss, with an optimal predictive cutoff of 0.46 U/mL in this prospective population. Validation of this new cutoff is necessary.

The Prothrombin-Prothrombinase Interaction

The hemostatic response to vascular injury entails a sequence of proteolytic events where several inactive zymogens of the trypsin family are converted to active proteases. The cascade starts with exposure of tissue factor from the damaged endothelium and culminates with conversion of prothrombin to thrombin in a reaction catalyzed by the prothrombinase complex composed of the enzyme factor Xa, cofactor Va, Ca2+, and phospholipids. This cofactor-dependent activation is paradigmatic of analogous reactions of the blood coagulation and complement cascades, which makes elucidation of its molecular mechanism of broad significance to the large class of trypsin-like zymogens to which prothrombin belongs. Because of its relevance as the most important reaction in the physiological response to vascular injury, as well as the main trigger of pathological thrombotic complications, the mechanism of prothrombin activation has been studied extensively. However, a molecular interpretation of this mechanism has become available only recently from important developments in structural biology. Here we review current knowledge on the prothrombin-prothrombinase interaction and outline future directions for the study of this key reaction of the coagulation cascade.

The role of proteolytic cleavage at Arg336 and Arg372 of the A1 domain in factor VIIa/tissue factor-catalyzed reactions of B domain-deleted factor VIII

BACKGROUND

We previously demonstrated that factor (F)VIII was rapidly activated through proteolytic cleavage at Arg372 and Arg740 by activated FVII (FVIIa)/tissue factor (TF) in very early coagulation phase, followed by inactivation by cleavage at Arg336. The influence of the absence of FVIII B domain in this series of FVIIa/TF-catalyzed reaction remains unclear, however.

AIM

To examine the FVIIa/TF-catalyzed reaction of B domain-deleted (BDD-)FVIII.

METHODS AND RESULTS

The FVIII activity (FVIII:C) of commercial full-length (FL-)FVIII and BDD-FVIII increased by ∼1.7-fold within 0.5 min after addition of FVIIa/TF (1 nM/0.1 nM).

FVIII

C decreased to initial levels with inactivation rate constant (k; ∼0.035) within 15 min of FL-FVIII activation, but decreased gradually to initial levels (k; ∼0.017) within 30 min of BDD-FVIII activation. SDS-PAGE analyses demonstrated that the FVIIa/TF-catalyzed cleavage of BDD-FVIII occurred at Arg336 within 0.5 min in parallel with elevation of FVIII:C, but cleavage at Arg372 was not evident. FVIIa/TF-catalyzed activation of both recombinant BDD-FVIII R336A and R372A mutants that were prepared, were similar to that of wild-type (WT) BDD-FVIII. However, FVIII:C returned to initial levels (k; ∼0.046) within 30 min of R336A mutant activation, but little reduction of FVIII:C was observed with R372A mutant (k; ∼0.0046). SDS-PAGE analysis indicated that FVIIa/TF-catalyzed cleavage of WT and R372A mutant was predominant at Arg336, whereas that of R336A mutant was observed at Arg372.

CONCLUSIONS

FVIIa/TF-catalyzed activation of BDD-FVIII was initiated by cleavage at Arg336, and the FVIII B domain appeared to control FVIIa/TF-catalyzed reactions by altering pattern of cleavage at Arg336 and Arg372.

Treatment of congenital coagulopathies, from biologic to biotechnological drugs: The relevance of gene editing (CRISPR/Cas)

Congenital coagulopathies have, throughout the history of medicine, been a focus of scientific study and of great interest as they constitute an alteration of one of the most important and conserved pathways of evolution. The first therapeutic strategies developed to address them were aimed at restoring the blood components lost during hemorrhage by administering whole blood or plasma. Later on, the use of cryoprecipitates was a significant breakthrough as it made it possible to decrease the volumes of blood infused. In the 1970' and 80', clotting factor concentrates became the treatment and, from the 1990's to the present day, recombinant factors -with increasingly longer half-lives- have taken over as the treatment of choice for certain coagulopathies in a seamless yet momentous transition from biological to biotechnological drugs. The beginning of this century, however, saw the emergence of new advanced (gene and cell) treatments, which are currently transforming the therapeutic landscape. The possibility to use cells and viruses as well as specific or bispecific antibodies as medicines is likely to spark a revolution in the world of pharmacology where therapies will be individualized and have long-term effects. Specifically, attention is nowadays focused on the development of gene editing strategies, chiefly those based on CRISPR/Cas technology. Rare coagulopathies such as hemophilia A and B, or even ultra-rare ones such as factor V deficiency, could be among those deriving the greatest benefit from these new developments.

Coagulation side effects of enzymatic debridement in burned patients

OBJECTIVES

Bromelain-based enzymatic debridement has emerged as a valuable option to the standard surgical intervention for debridement in burn injuries. Adverse effects on coagulation parameters after enzymatic debridement have been described. The purpose of this study was to compare the effect of enzymatic and surgical debridement on coagulation.

METHODS

Between 03/2017 and 02/2021 patients with burn injuries with a total body surface area (TBSA) ≥ 1% were included in the study. Patients were categorized into two groups: the surgically debrided group and the enzymatically debrided group. Coagulation parameters were assessed daily for the first seven days of hospitalization.

RESULTS

In total 132 patients with a mean TBSA of 17% were included in this study, of which 66 received enzymatic debridement and 66 received regular surgical-debridement. Patients receiving enzymatic debridement presented significantly higher factor-V concentration values over the first seven days after admission (p = <0.01). Regarding coagulation parameters, we found no difference in INR-, aPTT-, fibrinogen-, factor-XIII- and thrombocyte-concentrations over the first seven days (p = >0.05).

CONCLUSION

Enzymatic debridement in burned patients does not appear to increase the risk of coagulation abnormalities compared with the regular surgical approach.

Full-scale network analysis reveals properties of the FV protein structure organization

Blood coagulation is a vital process for humans and other species. Following an injury to a blood vessel, a cascade of molecular signals is transmitted, inhibiting and activating more than a dozen coagulation factors and resulting in the formation of a fibrin clot that ceases the bleeding. In this process, the Coagulation factor V (FV) is a master regulator, coordinating critical steps of this process. Mutations to this factor result in spontaneous bleeding episodes and prolonged hemorrhage after trauma or surgery. Although the role of FV is well characterized, it is unclear how single-point mutations affect its structure. In this study, to understand the effect of mutations, we created a detailed network map of this protein, where each node is a residue, and two residues are connected if they are in close proximity in the three-dimensional structure. Overall, we analyzed 63 point-mutations from patients and identified common patterns underlying FV deficient phenotypes. We used structural and evolutionary patterns as input to machine learning algorithms to anticipate the effects of mutations and anticipated FV-deficiency with fair accuracy. Together, our results demonstrate how clinical features, genetic data and in silico analysis are converging to enhance treatment and diagnosis of coagulation disorders.

Cryo-EM structures of coagulation factors

A State of the Art lecture titled "Cryo-EM structures of coagulation factors" was presented at the ISTH Congress in 2022. Cryogenic electron microscopy (cryo-EM) is a revolutionary technique capable of solving the structure of high molecular weight proteins and their complexes, unlike nuclear magnetic resonance (NMR), and under conditions not biased by crystal contacts, unlike X-ray crystallography. These features are particularly relevant to the analysis of coagulation factors that are too big for NMR and often recalcitrant to X-ray investigation. Using cryo-EM, we have solved the structures of coagulation factors V and Va, prothrombinase on nanodiscs, and the prothrombin-prothrombinase complex. These structures have advanced basic knowledge in the field of thrombosis and hemostasis, especially on the function of factor V and the molecular mechanism for prothrombin activation, and set the stage for exciting new lines of investigation. Finally, we summarize relevant new data on this topic presented during the 2022 ISTH Congress.

Possible effect of genetic background in thrombophilia genes on clinical severity of patients with coronavirus disease-2019: A prospective cohort study

Background and objective: Thrombotic and microangiopathic effects have been reported in Coronavirus Disease-2019 (COVID-19) patients. In the present study, we aimed to examine the relationship between hereditary thrombophilia factors and the clinical picture severity of COVID-19 patients. Methods: Ninety COVID-19 patients were included and grouped according to the severity to three groups: severe/critical (n=30), mild/moderate (n=30) and asymptomatic (n=30). Hereditary thrombophilia genetic markers [prothrombin (FII) G20210A, factor V Leiden (FVL) G1691A, factor XIII (FXIII) V34L, methylene tetrahydrofolate reductase (MTHFR) A1298C and C677T, and plasminogen activator inhibitor-1 (PAI-1) 4G & 5G] were genotyped for all patients. Results: Seventeen (18.9%) patients had the polymorphism 4G/4G PAI-1 and 48 (53.3%) had 4G/5G. In addition, the heterozygous GA FVL, MTHRF677CT, and MTHRF1298AC polymorphisms were detected in 11 (12.2%), 26 (28.9%), and 38 (42.2%) patients, respectively. The rate of severe/critical patients with PAI 4G/5G gene polymorphism was higher than the asymptomatic+moderate/mild patients, and the rate of severe/critically ill patients with PAI 4G/4G polymorphism was found to be lower than the asymptomatic+moderate/mild patients. No difference was evidenced between the distribution of deceased and survivors of the genotype groups. Conclusions: In the present study, we found that heterozygous 4G/5G PAI-1 polymorphism is associated with critical or severe COVID-19 picture, and that FVL, MTHFR, FXIII, and prothrombin polymorphisms were not directly related to COVID-19 severity.

Standardization of Coagulation Factor V Reference Intervals, Prothrombin Time, and Activated Partial Thromboplastin Time in Mice for Use in Factor V Deficiency Pathological Models

Factor V together with activated factor X forms the prothrombinase complex, which transforms prothrombin into thrombin. The Mus musculus species is characterized by very high levels of this factor and short clotting times, which hinders accurate measurements. For that reason, a detailed characterization of such parameters is indispensable. A method was designed as part of this study to provide an accurate determination and standardization of factor V levels, prothrombin time and activated partial thromboplastin time in Mus musculus. Those parameters were evaluated in a sample of 66 healthy animals using a semi-automated coagulometer and human diagnostic reagents in an attempt to determine the most appropriate time of day for the extractions. A mouse-based protocol was designed, capable of making corrections to the samples at dilutions of 1:100 for factor V and at of 1:3 for prothrombin time. The goal was to smoothen the calibration curves, which often present with steep slopes and narrow measurement ranges between one calibration point and another. It was found that the most stable period for blood sample extraction was that comprised between the first 6 h of light. No clinical differences were observed between the sexes and reference intervals were established for factor V (95.80% ± 18.14; 25.21 s ± 1.34), prothrombin time (104.31% ± 14.52; 16.85 s ± 1.32) and activated partial thromboplastin time (32.86 s ± 3.01). The results obtained are applicable to human or veterinary biomedical research, to transfusional medicine or to pathological models for diseases such as factor V deficiency.

An engineered activated factor V for the prevention and treatment of acute traumatic coagulopathy and bleeding in mice

^superFVa arrests severe bleeding and prevents the development of ATC after trauma.

^superFVa therapy restores functional hemostasis when initiated after onset of ATC caused by traumatic bleeding.

Acute traumatic coagulopathy (ATC) occurs in approximately 30% of patients with trauma and is associated with increased mortality. Excessive generation of activated protein C (APC) and hyperfibrinolysis are believed to be driving forces for ATC. Two mouse models were used to investigate whether an engineered activated FV variant (^superFVa) that is resistant to inactivation by APC and contains a stabilizing A2-A3 domain disulfide bond can reduce traumatic bleeding and normalize hemostasis parameters in ATC. First, ATC was induced by the combination of trauma and shock. ATC was characterized by activated partial thromboplastin time (APTT) prolongation and reductions of factor V (FV), factor VIII (FVIII), and fibrinogen but not factor II and factor X. Administration of ^superFVa normalized the APTT, returned FV and FVIII clotting activity levels to their normal range, and reduced APC and thrombin-antithrombin (TAT) levels, indicating improved hemostasis. Next, a liver laceration model was used where ATC develops as a consequence of severe bleeding. ^superFVa prophylaxis before liver laceration reduced bleeding and prevented APTT prolongation, depletion of FV and FVIII, and excessive generation of APC. Thus, prophylactic administration of ^superFVa prevented the development of ATC. ^superFVa intervention started after the development of ATC stabilized bleeding, reversed prolonged APTT, returned FV and FVIII levels to their normal range, and reduced TAT levels that were increased by ATC. In summary, ^superFVa prevented ATC and traumatic bleeding when administered prophylactically, and ^superFVa stabilized bleeding and reversed abnormal hemostasis parameters when administered while ATC was in progress. Thus, ^superFVa may be an attractive strategy to intercept ATC and mitigate traumatic bleeding.

High Mutational Heterogeneity, and New Mutations in the Human Coagulation Factor V Gene. Future Perspectives for Factor V Deficiency Using Recombinant and Advanced Therapies

Factor V is an essential clotting factor that plays a key role in the blood coagulation cascade on account of its procoagulant and anticoagulant activity. Eighty percent of circulating factor V is produced in the liver and the remaining 20% originates in the α-granules of platelets. In humans, the factor V gene is about 80 kb in size; it is located on chromosome 1q24.2, and its cDNA is 6914 bp in length. Furthermore, nearly 190 mutations have been reported in the gene. Factor V deficiency is an autosomal recessive coagulation disorder associated with mutations in the factor V gene. This hereditary coagulation disorder is clinically characterized by a heterogeneous spectrum of hemorrhagic manifestations ranging from mucosal or soft-tissue bleeds to potentially fatal hemorrhages. Current treatment of this condition consists in the administration of fresh frozen plasma and platelet concentrates. This article describes the cases of two patients with severe factor V deficiency, and of their parents. A high level of mutational heterogeneity of factor V gene was identified, nonsense mutations, frameshift mutations, missense changes, synonymous sequence variants and intronic changes. These findings prompted the identification of a new mutation in the human factor V gene, designated as Jaén-1, which is capable of altering the procoagulant function of factor V. In addition, an update is provided on the prospects for the treatment of factor V deficiency on the basis of yet-to-be-developed recombinant products or advanced gene and cell therapies that could potentially correct this hereditary disorder.

Cryo-EM structures of human coagulation factors V and Va

Coagulation factor V (fV) is the precursor of fVa, which, together with fXa, Ca2+, and phospholipids, defines the prothrombinase complex and activates prothrombin in the penultimate step of the coagulation cascade. We solved the cryogenic electron microscopy (cryo-EM) structures of human fV and fVa at atomic (3.3 Å) and near-atomic (4.4 Å) resolution, respectively. The structure of fV reveals the entire A1-A2-B-A3-C1-C2 assembly, but with a surprisingly disordered B domain. The C1 and C2 domains provide a platform for interaction with phospholipid membranes and support the A1 and A3 domains, with the A2 domain sitting on top of them. The B domain is highly dynamic and visible only for short segments connecting to the A2 and A3 domains. The A2 domain reveals all sites of proteolytic processing by thrombin and activated protein C, a partially buried epitope for binding fXa, and fully exposed epitopes for binding activated protein C and prothrombin. Removal of the B domain and activation to fVa exposes the sites of cleavage by activated protein C at R306 and R506 and produces increased disorder in the A1-A2-A3-C1-C2 assembly, especially in the C-terminal acidic portion of the A2 domain that is responsible for prothrombin binding. Ordering of this region and full exposure of the fXa epitope emerge as necessary steps in the assembly of the prothrombin-prothrombinase complex. These structures offer molecular context for the function of fV and fVa and pioneer the analysis of coagulation factors by cryo-EM.

Regulation of factor V and factor V-short by TFPIα: Relationship between B-domain proteolysis and binding

Coagulation factor V (FV) plays an anticoagulant role but serves as a procoagulant cofactor in the prothrombinase complex once activated to FVa. At the heart of these opposing effects is the proteolytic removal of its central B-domain, including conserved functional landmarks (basic region, BR; 963–1008 and acidic region 2, AR2; 1493–1537) that enforce the inactive FV procofactor state. Tissue factor pathway inhibitor α (TFPIα) has been associated with FV as well as FV-short, a physiologically relevant isoform with a shortened B-domain missing the BR. However, it is unclear which forms of FV are physiologic ligands for TFPIα. Here, we characterize the binding and regulation of FV and FV-short by TFPIα via its positively charged C-terminus (TFPIα-BR) and examine how bond cleavage in the B-domain influences these interactions. We show that FV-short is constitutively active and functions in prothrombinase like FVa. Unlike FVa, FV-short binds with high affinity (K_d ∼1 nM) to TFPIα-BR, which blocks procoagulant function unless FV-short is cleaved at Arg¹⁵⁴⁵, removing AR2. Importantly, we do not observe FV binding (μM detection limit) to TFPIα. However, cleavage at Arg⁷⁰⁹ and Arg¹⁰¹⁸ displaces the FV BR, exposing AR2 and allowing TFPIα to bind via its BR. We conclude that for full-length FV, the detachment of FV BR from AR2 is necessary and sufficient for TFPIα binding and regulation. Our findings pinpoint key forms of FV, including FV-short, that act as physiologic ligands for TFPIα and establish a mechanistic framework for assessing the functional connection between these proteins.

Aortic Valve Replacement in Severe Factor V Deficiency and Inhibitor: Diagnostic and Management Challenges

Factor V (FV) deficiency (F5D) is a rare hematological disorder with a variable spectrum of bleeding manifestations. Until now, no specific protocols for the management of these patients have been established. However, available literature suggests that perioperative infusion of fresh frozen plasma (FFP) may help maintain FV levels to prevent bleeding. We present the case of a 64-year-old man with previously undiagnosed severe FV deficiency and mild FV inhibitor, who underwent aortic valve replacement with no bleeding complications.

Serum Factor V Is a Continuous Biomarker of Graft Dysfunction and a Predictor of Graft Loss After Liver Transplantation

BACKGROUND

Factor V has never been compared to a validated early allograft dysfunction (EAD) definition. We aimed to assess factor V as a biomarker of EAD and a predictor of graft loss after liver transplantation (LT).

METHODS

We retrospectively assessed the serum factor V levels on postoperative day 1 after LT. Patients were divided according to their factor V levels into the ≤36.1 U/mL and > 36.1 U/mL groups. The primary outcome was graft loss within 1, 3, and 6 months. The secondary outcome was EAD, as defined by Olthoff et al. Predictors of outcomes were identified by multivariable logistic regression.

RESULTS

Two hundred twenty-seven patients were included in the study: 74 with factor V of 36.1 U/mL or less and 153 with factor V >36.1 U/mL. EAD was diagnosed in 41 (55.4%) of 74 patients with factor V of 36.1 U/mL or less and in 20/153 (13.1%) patients with factor V >36.1 U/mL (P < 0.001). According to the multivariable regression model, factor V was a continuous marker of EAD (odds ratio [OR], 0.96; 95% confidence interval [CI], 0.94-0.98 per U/mL). Among the study groups, the 1-, 3-, and 6-month graft survival rates were 82%, 74%, and 74%, respectively, for patients with factor V of 36.1 U/mL or less and 98%, 95%, and 95%, respectively, for patients with factor V >36.1 U/mL (P = 0.001). Factor V was a continuous predictor for 3- and 6-month graft losses (OR, 0.96; 95% CI, 0.94-0.99 and OR, 0.97; 95% CI, 0.94-0.99 per U/mL), whereas EAD was not significant when adjusted for factor V.

CONCLUSION

Factor V is an early marker for EAD and is a continuous predictor of short-term graft loss after LT.

Proteomic analysis of rat serum revealed the effects of chronic sleep deprivation on metabolic, cardiovascular and nervous system

Sleep is an essential and fundamental physiological process that plays crucial roles in the balance of psychological and physical health. Sleep disorder may lead to adverse health outcomes. The effects of sleep deprivation were extensively studied, but its mechanism is still not fully understood. The present study aimed to identify the alterations of serum proteins associated with chronic sleep deprivation, and to seek for potential biomarkers of sleep disorder mediated diseases. A label-free quantitative proteomics technology was used to survey the global changes of serum proteins between normal rats and chronic sleep deprivation rats. A total of 309 proteins were detected in the serum samples and among them, 117 proteins showed more than 1.8-folds abundance alterations between the two groups. Functional enrichment and network analyses of the differential proteins revealed a close relationship between chronic sleep deprivation and several biological processes including energy metabolism, cardiovascular function and nervous function. And four proteins including pyruvate kinase M1, clusterin, kininogen1 and profilin-1were identified as potential biomarkers for chronic sleep deprivation. The four candidates were validated via parallel reaction monitoring (PRM) based targeted proteomics. In addition, protein expression alteration of the four proteins was confirmed in myocardium and brain of rat model. In summary, the comprehensive proteomic study revealed the biological impacts of chronic sleep deprivation and discovered several potential biomarkers. This study provides further insight into the pathological and molecular mechanisms underlying sleep disorders at protein level.

Mechanisms Regulating Acquisition of Platelet-Derived Factor V/Va by Megakaryocytes

Factor Va serves as the nonenzymatic protein cofactor for the prothrombinase complex, which converts prothrombin to thrombin in the events leading to formation of a hemostatic plug. Several observations support the concept that platelet-derived factor V/Va is physically and functionally distinct and plays a more important role in thrombin generation at sites of vascular injury as compared to its plasma counterpart. Platelet-derived factor V/Va is generated following endocytosis of the plasma-derived molecule by the platelet precursor cells, megakaryocytes, via a two receptor system consisting of low density lipoprotein (LDL) receptor-related protein-1 (LRP-1) and an unidentified specific "binding site". More recently, it was suggested that a cell surface-expressed β-galactoside binding protein, galectin-8, was involved in factor V endocytosis. Endocytosed factor V is trafficked through the cell and retailored prior to its storage in α-granules. Given the essential role of platelet-derived factor Va in clot formation, understanding the cellular and molecular mechanisms that regulate how platelets acquire this molecule will be important for the treatment of excessive bleeding or clotting.

Factor V Deficiency in Korean Patients: Clinical and Laboratory Features, Treatment, and Outcome

Due to rarity of factor V (FV) deficiency, there have been only a few case reports in Korea. We retrospectively analysed the clinical-laboratory features of FV deficiency in 10 Korean patients. Between January 1987 and December 2013, 10 case reports published in a Korean journal or proceedings of Korea Society on Thrombosis and Hemostasis were reviewed. Severity is defined as mild (> 5% of factor activity), moderate (1%-5%), and severe (< 1%). The median age at diagnosis, six males and four females, was 26 years (range, 1 month-73 years). Six of 10 patients were classified as moderate, three as mild, and one as severe disease. Eight patients were diagnosed as inherited FV deficiency. The most frequent symptoms were mucosal tract bleedings (40%) such as epistaxis, and menorrhagia in female. Hemarthroses and postoperative bleeding occurred in one and four patients, respectively. Life-threatening bleeding episodes occurred in the peritoneal cavity (n = 2), central nerve system (n = 1), and retroperitoneal space (n = 1). No lethal haemorrhages happened to patients with mild disease. The majority of bleeding episodes were controlled with local measures and fresh-frozen plasma replacement. Two acquired FV deficient-patients showing life-threatening haemorrhages received the immunosuppressive therapy, but one of them died from postoperative bleeding complications. Despite the small sample size of this study due to rarity of the disease, we found that Korean patients with FV deficiency had similar clinical manifestations and treatment outcomes shown in previous studies.

Characterization of an apparently synonymous F5 mutation causing aberrant splicing and factor V deficiency

Coagulation factor V (FV) deficiency is a rare autosomal recessive bleeding disorder. We investigated a patient with severe FV deficiency (FV:C < 3%) and moderate bleeding symptoms. Thrombin generation experiments showed residual FV expression in the patient's plasma, which was quantified as 0.7 ± 0.3% by a sensitive prothrombinase-based assay. F5 gene sequencing identified a novel missense mutation in exon 4 (c.578G>C, p.Cys193Ser), predicting the abolition of a conserved disulphide bridge, and an apparently synonymous variant in exon 8 (c.1281C>G). The observation that half of the patient's F5 mRNA lacked the last 18 nucleotides of exon 8 prompted us to re-evaluate the c.1281C>G variant for its possible effects on splicing. Bioinformatics sequence analysis predicted that this transversion would activate a cryptic donor splice site and abolish an exonic splicing enhancer. Characterization in a F5 minigene model confirmed that the c.1281C>G variant was responsible for the patient's splicing defect, which could be partially corrected by a mutation-specific morpholino antisense oligonucleotide. The aberrantly spliced F5 mRNA, whose stability was similar to that of the normal mRNA, encoded a putative FV mutant lacking amino acids 427-432. Expression in COS-1 cells indicated that the mutant protein is poorly secreted and not functional. In conclusion, the c.1281C>G mutation, which was predicted to be translationally silent and hence neutral, causes FV deficiency by impairing pre-mRNA splicing. This finding underscores the importance of cDNA analysis for the correct assessment of exonic mutations.

Polyphosphate accelerates factor V activation by factor XIa

Factor Va enhances the rate of prothrombin activation by factor Xa by four to five orders of magnitude. Production of initiating levels of factor Va from its precursor, factor V, is a critical event early in haemostasis, as factor V exhibits negligible cofactor activity. While thrombin is the most potent physiological back-activator of factor V, the first prothrombinase complexes require a source of factor Va prior to thrombin generation. A recent study by Whelihan et al. (J Thromb Haemost 2010; 8:1532-1539) identified factor XIa as a candidate for the initial thrombin-independent activation of factor V, although this reaction was slow and required relatively high concentrations of factors V and XIa. Activated platelets secrete polyphosphate, which we previously showed to be potently procoagulant. We now report that polyphosphate greatly accelerates factor V activation by factor XIa, and that this is supported by polyphosphate polymers of the size secreted by activated human platelets. This finding provides additional evidence that factor XIa-mediated generation of factor Va may contribute to the initiation of haemostasis.