Structural insights into blood coagulation factor VIII: Procoagulant complexes, membrane binding, and antibody inhibition

Serum KNG and FVIII may serve as potential biomarkers for depression

BACKGROUND

The global burden of major depressive disorder (MDD) is rising, with current diagnostic methods hindered by significant subjectivity and low inter-rater reliability. Several studies have implied underlying link between coagulation-related proteins, such as kininogen (KNG) and coagulation factor VIII (FVIII), and depressive symptoms, offering new insights into the exploration of depression biomarkers. This study aims to elucidate the roles of KNG and FVIII in depression, potentially providing a foundational basis for biomarker research in this field.

METHODS

A three-part experiment was conducted: (1) we measured serum levels of KNG and FVIII in the chronic unpredictable mild stress (CUMS) model; (2) KNG adeno-associated-virus overexpression (KNG-AAV-OE) model was constructed to further investigate the roles of KNG and FVIII. Meanwhile, quantity PCR, western blotting and immunofluorescence staining detected the KNG-FVIII pathway. (3) Peripheral blood samples were gathered from healthy control (HC, N = 21), as well as first-episode drug-naive patients with MDD (FEDN-MDD, N = 21), to further confirm the association between KNG, FVIII and depression.

RESULTS

Firstly, serum KNG and FVIII levels were significantly elevated in the CUMS model. Then, the rats exhibited pronounced depressive-like behaviors in the KNG-AAV-OE model, with corresponding increases in serum KNG and FVIII. Lastly, clinical data showed increased KNG and FVIII levels in FEDN-MDD compared to HC. Furthermore, KNG and FVIII levels exhibited a strong positive correlation with the scores of the 24-item Hamilton Depression Scale and the 14-item Hamilton Anxiety Scale.

CONCLUSION

To sum up, this study highlights critical roles of serum KNG and FVIII in depression and the KNG-AAV-OE may lead the augment of FVIII in serum. Consequently, our research may offer new evidence and foundation for depression biomarkers research in the future.

A mini review on the regulation of coagulation homeostasis through interfering with vitamin K-dependent coagulation/anticoagulation factors

Coagulation disorders, such as excessive bleeding or thrombosis, present significant health challenges. Vitamin K-dependent proteins (VKDPs), including coagulation and anticoagulation factors, are essential for maintaining the coagulation homeostasis due to their key roles in the coagulation cascade. Therefore, VKDPs have become significant targets for regulating coagulation homeostasis, and various strategies have been developed, primarily including small molecule drugs and nanomaterials. This review presents the summary of these strategies, focusing on the mechanisms, effectiveness and limitations. It first discusses the pivotal role of VKDPs in the coagulation cascade, followed by an in-depth analysis of how small molecule drugs and nanomaterials to regulate hemostasis through interfering with VKDPs. Furthermore, this review addresses the challenges faced in the current approaches and potential future research directions. We hope this review will contribute to advancing the development of novel methods for modulating coagulation homeostasis through VKDP interference.

Binding Promiscuity of Therapeutic Factor VIII

The binding promiscuity of proteins defines their ability to indiscriminately bind multiple unrelated molecules. Binding promiscuity is implicated, at least in part, in the off-target reactivity, nonspecific biodistribution, immunogenicity, and/or short half-life of potentially efficacious protein drugs, thus affecting their clinical use. In this review, we discuss the current evidence for the binding promiscuity of factor VIII (FVIII), a protein used for the treatment of hemophilia A, which displays poor pharmacokinetics, and elevated immunogenicity. We summarize the different canonical and noncanonical interactions that FVIII may establish in the circulation and that could be responsible for its therapeutic liabilities. We also provide information suggesting that the FVIII light chain, and especially its C1 and C2 domains, could play an important role in the binding promiscuity. We believe that the knowledge accumulated over years of FVIII usage could be exploited for the development of strategies to predict protein binding promiscuity and therefore anticipate drug efficacy and toxicity. This would open a mutational space to reduce the binding promiscuity of emerging protein drugs while conserving their therapeutic potency.

Clinical, Laboratory, Molecular, and Reproductive Aspects of Combined Deficiency of Factors V and VIII

Congenital combined deficiency of factor V (FV) and factor VIII (FVIII; F5F8D, OMIM 227300) is a rare hereditary coagulopathy and accounts for approximately 3% of cases of rare coagulation disorders. The prevalence of this disease in the general population is estimated to be 1:1,000,000 and is significantly higher in regions where consanguineous marriages are permitted, such as the Mideast and South Asia. The disease has an autosomal recessive mode of inheritance and therefore occurs with an equal incidence among males and females. Heterozygous mutation carriers usually do not have clinical manifestations. The molecular basis of this disease differs from that of stand-alone congenital deficiencies of FVIII and FV. F5F8D is caused by mutations in either LMAN1 or MCFD2, which encode components of a cargo receptor complex for endoplasmic reticulum to Golgi transport of FV and FVIII, leading to defects in an intracellular transport pathway shared by these two coagulation factors. Congenital combined deficiency of FV and FVIII is characterized by decreased activities of both FV and FVIII in plasma, usually to 5 to 30% of normal. Clinical manifestations in most cases are represented by mild or moderate hemorrhagic syndrome. The simultaneous decreases of two coagulation factors present complications in the diagnosis and management of the disease. In female patients, the disease requires a special approach for family planning, pregnancy management, and parturition. This review summarizes recent progress in clinical, laboratory, and molecular understanding of this disorder.

Atomistic Mechanism of Lipid Membrane Binding for Blood Coagulation Factor VIII with Molecular Dynamics Simulations on a Microsecond Time Scale

During the blood coagulation cascade, coagulation factor VIII (FVIII) is activated by thrombin to form activated factor VIII (FVIIIa). FVIIIa associates with platelet surfaces at the site of vascular damage to form an intrinsic tenase complex with activated factor IX. A working model for FVIII membrane binding involves the association of positively charged FVIII residues with negatively charged lipid headgroups and the burial of hydrophobic residues into the membrane interior. Currently, the atomic details of the FVIII lipid binding interactions and membrane orientation are lacking. This study reports residue-specific FVIII C domain interactions with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dioleoyl-sn-glycero-3-phospho-l-serine (DOPS) in atomistic detail. Contact maps between residues in the C domains with different lipid moieties support prior structural data describing how the C domains associate with membranes through electrostatic and hydrophobic interactions. Solvent-accessible surface area analysis quantified the extent to which residues in the C1 and C2 domains bury into the membrane. Calculations of the potential energy between the C domains and DOPC and DOPS revealed an FVIII membrane-binding orientation that agrees with previous experimental data. This study expands our knowledge of the structural basis of FVIII membrane association, which may be critical for the development of next-generation FVIII replacement constructs with improved activity.

Biophysical characterization of blood coagulation factor VIII binding to lipid nanodiscs that mimic activated platelet surfaces

BACKGROUND

Following proteolytic activation, activated blood coagulation factor (F)VIII (FVIIIa) binds to activated platelet membranes, forming the intrinsic tenase complex with activated FIX (FIXa). Previous studies have identified the C1 and C2 domains as the membrane binding domains of FVIII through conserved arginine residues. A membrane binding model for the FVIII C domains proposes that surface-exposed hydrophobic and positively charged residues at each C domain interact with the membrane, yet a comprehensive thermodynamic and structural description of this interaction is lacking.

OBJECTIVES

To determine residues of interaction, thermodynamics, and membrane binding preference for FVIII membrane association.

METHODS

The binding of FVIII constructs to lipid nanodiscs was characterized by nuclear magnetic resonance, isothermal titration calorimetry, bio-layer interferometry, and X-ray crystallography.

RESULTS

The thermodynamics of FVIII membrane binding indicated that the C1 domain associates through an enthalpically driven process while the C2 domain is entropically driven. Alanine mutations to surface-exposed hydrophobic residues in the C2 domain revealed differential effects on membrane binding, highlighting important determinants at the residue level. The structure of a C2 double mutant, L2251A/L2252A, demonstrated that its decreased affinity is likely due to decreasing the surface area hydrophobicity. Nuclear magnetic resonance studies with the C2 domain identified residues of interaction with soluble O-phospho-L-serine as well as lipid nanodiscs. Lastly, increasing phosphatidylethanolamine and decreasing phosphatidylserine content decreased overall FVIII affinity for membrane surfaces.

CONCLUSION

This study provides further insight into the molecular basis for how FVIII interacts with platelets to form the intrinsic tenase complex.

Flow Cytometry Evaluation of Blood-Cell-Bound Surface FVIII in Hemophilia A and Thrombosis

Hemophilia A (HA) is associated with FVIII coagulation insufficiency or inactivity leading to excessive bleeding. Elevated FVIII, on the contrary, is associated with thrombophilia, thrombosis, myocardial infarctions, and stroke. Active FVIII (aFVIII) uses its C2 domain to bind to blood cells' membranes, consequently carrying out its coagulative function. We developed a reliable flow cytometry (FC) method for FVIII detection that can be utilized for assessing surface-bound FVIII on leukocytes in different coagulation/clinical states; we analyzed 49 pediatric subjects, encompassing patients with HA, other coagulopathies, venous thrombosis, and normal coagulation. Interestingly, the total leukocyte surface FVIII showed a declining trend across thrombosis, normal, and hypo-coagulation states. As expected, the leukocytes of HA patients displayed significantly lower levels of cellular-surface FVIII in comparison to patients with thrombosis. However, no significant correlation was observed between circulating levels of FVIII in plasma and the levels of FVIII bound to leukocytes, indicating that the differences in FVIII surface binding are not directly proportional to the availability of FVIII in the circulation and suggesting a specific binding mechanism governing the interaction between FVIII and leukocytes. Intriguingly, when analyzing the distinct blood subpopulations, we observed that surface FVIII levels were significantly elevated in classical monocytes of thrombosis patients compared to HA patients, healthy controls, and patients with other coagulopathies. Our study highlights the reliability of our FC platform in assessing FVIII abundance on leukocytes' membranes across coagulation states. Monocytes, particularly in cases of thrombosis, exhibit active binding of FVIII on their surface, suggesting a potential role in the pathophysiology of thrombosis that requires further investigation.

Binding of coagulation factor IXa to procoagulant platelets revisited: Low affinity and interactions with other factors

Binding of activated factor IX (fIXa) to the phosphatidylserine-expressing procoagulant platelets is a critical step in blood coagulation, which is necessary for the membrane-dependent intrinsic tenase complex assembly and factor X activation. However, the nature and parameters of the fIXa binding sites on the procoagulant platelet surface remain unclear. We used flow cytometry to elucidate the quantitative details of the fluorescently labeled fIXa binding to gel-filtered activated platelets. FIXa bound to the procoagulant platelet subpopulation only, with the parameters (maximal number of binding sites at 58900 ± 3400, Kd at 1000 ± 170 nM) similar to binding observed with phospholipid vesicles. No specific high-affinity binding sites for fIXa were detected, and binding proceeded similarly for different methods of procoagulant platelet production (thrombin, thrombin receptor activation peptide, collagen-related peptide, their combinations, or calcium ionophore A23187). Factor VIII, known to form a high affinity complex with fIXa, enhanced fIXa binding to platelets. In contrast, only competition effects were observed for factor X, which binds fIXa with much lower affinity. Unexpectedly, fIXa itself, fIX, and prothrombin also dose-dependently enhance fIXa binding at concentrations below 1000 nM, suggesting the formation of membrane-bound fIXa dimers and fIXa-prothrombin complexes on platelets. These findings provide a novel perspective on the fIXa binding site on procoagulant platelets, which does not have any major differences from pure phospholipid-based model membranes, exhibits inherently low affinity (3-5 orders of magnitude below the physiologically relevant fIXa concentration) but is significantly enhanced by its cofactor VIII, and regulated by previously unknown membrane interactions.

Kinetics and regulation of coagulation factor X activation by intrinsic tenase on phospholipid membranes

BACKGROUND

Factor X activation by the phospholipid-bound intrinsic tenase complex is a critical membrane-dependent reaction of blood coagulation. Its regulation mechanisms are unclear, and a number of questions regarding diffusional limitation, pathways of assembly and substrate delivery remain open.

METHODS

We develop and analyze here a detailed mechanism-driven computer model of intrinsic tenase on phospholipid surfaces. Three-dimensional reaction-diffusion-advection and stochastic simulations were used where appropriate.

RESULTS

Dynamics of the system was predominantly non-stationary under physiological conditions. In order to describe experimental data, we had to assume both membrane-dependent and solution-dependent delivery of the substrate. The former pathway dominated at low cofactor concentration, while the latter became important at low phospholipid concentration. Factor VIIIa-factor X complex formation was the major pathway of the complex assembly, and the model predicted high affinity for their lipid-dependent interaction. Although the model predicted formation of the diffusion-limited layer of substrate for some conditions, the effects of this limitation on the fXa production were small. Flow accelerated fXa production in a flow reactor model by bringing in fIXa and fVIIIa rather than fX.

CONCLUSIONS

This analysis suggests a concept of intrinsic tenase that is non-stationary, employs several pathways of substrate delivery depending on the conditions, and is not particularly limited by diffusion of the substrate.

Humanization and functional characterization of enhanced coagulation factor IX variants identified through ancestral sequence reconstruction

BACKGROUND

Laboratory resurrection of ancient coagulation factor (F) IX variants generated through ancestral sequence reconstruction led to the discovery of a FIX variant, designated An96, which possesses enhanced specific activity independent of and additive to that provided by human p.Arg384Lys, referred to as FIX-Padua.

OBJECTIVES

The goal of the current study was to identify the amino acid substitution(s) responsible for the enhanced activity of An96 and create a humanized An96 FIX transgene for gene therapy application.

METHODS

Reductionist screening approaches, including domain swapping and scanning residue substitution, were used and guided by one-stage FIX activity assays. In vitro characterization of top candidates included recombinant high-purity preparation, specific activity determination, and enzyme kinetic analysis. Final candidates were packaged into adeno-associated viral (AAV) vectors and delivered to hemophilia B mice.

RESULTS

Five of 42 total amino acid substitutions in An96 appear sufficient to retain the enhanced activity of An96 in an otherwise human FIX variant. Additional substitution of the Padua variant further increased the specific activity 5-fold. This candidate, designated ET9, demonstrated 51-fold greater specific activity than hFIX. AAV2/8-ET9 treated hemophilia B mice produced plasma FIX activities equivalent to those observed previously for AAV2/8-An96-Padua, which were 10-fold higher than AAV2/8-hFIX-Padua.

CONCLUSION

Starting from computationally inferred ancient FIX sequences, novel amino acid substitutions conferring activity enhancement were identified and translated into an AAV-FIX gene therapy cassette demonstrating high potency. This ancestral sequence reconstruction discovery and sequence mapping refinement approach represents a promising platform for broader protein drug and gene therapy candidate optimization.

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.

Cellular stress and coagulation factor production: when more is not necessarily better

Remarkably, it has been 40 years since the isolation of the 2 genes involved in hemophilia A (HA) and hemophilia B (HB), encoding clotting factor (F) VIII (FVIII) and FIX, respectively. Over the years, these advances led to the development of purified recombinant protein factors that are free of contaminating viruses from human pooled plasma for hemophilia treatments, reducing the morbidity and mortality previously associated with human plasma-derived clotting factors. These discoveries also paved the way for modified factors that have increased plasma half-lives. Importantly, more recent advances have led to the development and Food and Drug Administration approval of a hepatocyte-targeted, adeno-associated viral vector-mediated gene transfer approach for HA and HB. However, major concerns regarding the durability and safety of HA gene therapy remain to be resolved. Compared with FIX, FVIII is a much larger protein that is prone to misfolding and aggregation in the endoplasmic reticulum and is poorly secreted by the mammalian cells. Due to the constraint of the packaging capacity of adeno-associated viral vector, B-domain deleted FVIII rather than the full-length protein is used for HA gene therapy. Like full-length FVIII, B-domain deleted FVIII misfolds and is inefficiently secreted. Its expression in hepatocytes activates the cellular unfolded protein response, which is deleterious for hepatocyte function and survival and has the potential to drive hepatocellular carcinoma. This review is focused on our current understanding of factors limiting FVIII secretion and the potential pathophysiological consequences upon expression in hepatocytes.

A graph-based machine learning framework identifies critical properties of FVIII that lead to hemophilia A

Introduction: Blood coagulation is an essential process to cease bleeding in humans and other species. This mechanism is characterized by a molecular cascade of more than a dozen components activated after an injury to a blood vessel. In this process, the coagulation factor VIII (FVIII) is a master regulator, enhancing the activity of other components by thousands of times. In this sense, it is unsurprising that even single amino acid substitutions result in hemophilia A (HA)-a disease marked by uncontrolled bleeding and that leaves patients at permanent risk of hemorrhagic complications. Methods: Despite recent advances in the diagnosis and treatment of HA, the precise role of each residue of the FVIII protein remains unclear. In this study, we developed a graph-based machine learning framework that explores in detail the network formed by the residues of the FVIII protein, where each residue is a node, and two nodes are connected if they are in close proximity on the FVIII 3D structure. Results: Using this system, we identified the properties that lead to severe and mild forms of the disease. Finally, in an effort to advance the development of novel recombinant therapeutic FVIII proteins, we adapted our framework to predict the activity and expression of more than 300 in vitro alanine mutations, once more observing a close agreement between the in silico and the in vitro results. Discussion: Together, the results derived from this study demonstrate how graph-based classifiers can leverage the diagnostic and treatment of a rare disease.

Efanesoctocog Alfa: First Approval

Efanesoctocog alfa (ALTUVIIIO^TM; [antihemophilic factor (recombinant), Fc-VWF-XTEN fusion protein-ehtl]), a von Willebrand factor (VWF) independent, recombinant DNA-derived Factor VIII (FVIII) concentrate, has been developed by Bioverativ Therapeutics, Inc (a Sanofi company) and Swedish Orphan Biovitrum AB (Sobi). Efanesoctocog alfa was approved in February 2023 in the USA for use in adults and children with hemophilia A (congenital FVIII deficiency) for: routine prophylaxis to reduce the frequency of bleeding episodes; on-demand treatment and control of bleeding episodes; perioperative management of bleeding. This article summarizes the milestones in the development of efanesoctocog alfa leading to this first approval for hemophilia A.

Complementary Sets of Autoantibodies Induced by SARS-CoV-2, Adenovirus and Bacterial Antigens Cross-React with Human Blood Protein Antigens in COVID-19 Coagulopathies

COVID-19 patients often develop coagulopathies including microclotting, thrombotic strokes or thrombocytopenia. Autoantibodies are present against blood-related proteins including cardiolipin (CL), serum albumin (SA), platelet factor 4 (PF4), beta 2 glycoprotein 1 (β2GPI), phosphodiesterases (PDE), and coagulation factors such as Factor II, IX, X and von Willebrand factor (vWF). Different combinations of autoantibodies associate with different coagulopathies. Previous research revealed similarities between proteins with blood clotting functions and SARS-CoV-2 proteins, adenovirus, and bacterial proteins associated with moderate-to-severe COVID-19 infections. This study investigated whether polyclonal antibodies (mainly goat and rabbit) against these viruses and bacteria recognize human blood-related proteins. Antibodies against SARS-CoV-2 and adenovirus recognized vWF, PDE and PF4 and SARS-CoV-2 antibodies also recognized additional antigens. Most bacterial antibodies tested (group A streptococci [GAS], staphylococci, Escherichia coli [E. coli], Klebsiella pneumoniae, Clostridia, and Mycobacterium tuberculosis) cross-reacted with CL and PF4. while GAS antibodies also bound to F2, Factor VIII, Factor IX, and vWF, and E. coli antibodies to PDE. All cross-reactive interactions involved antibody-antigen binding constants smaller than 100 nM. Since most COVID-19 coagulopathy patients display autoantibodies against vWF, PDE and PF4 along with CL, combinations of viral and bacterial infections appear to be necessary to initiate their autoimmune coagulopathies.