Sequence and structure relationships within von Willebrand factor

Proteomic analysis of the sponge Aggregation Factor implicates an ancient toolkit for allorecognition and adhesion in animals

The discovery that sponges (Porifera) can fully regenerate from aggregates of dissociated cells launched them as one of the earliest experimental models to study the evolution of cell adhesion and allorecognition in animals. This process depends on an extracellular glycoprotein complex called the Aggregation Factor (AF), which is composed of proteins thought to be unique to sponges. We used quantitative proteomics to identify additional AF components and interacting proteins in the classical model, Clathria prolifera, and compared them to proteins involved in cell interactions in Bilateria. Our results confirm MAFp3/p4 proteins as the primary components of the AF but implicate related proteins with calx-beta and wreath domains as additional components. Using AlphaFold, we unveiled close structural similarities of AF components to protein domains in other animals, previously masked by the mutational decay of sequence similarity. The wreath domain, believed to be unique to the AF, was predicted to contain a central beta-sandwich of the same organization as the vWFD domain (also found in extracellular, gel-forming glycoproteins in other animals). Additionally, many copurified proteins share a conserved C-terminus, containing divergent immunoglobulin (Ig) and Fn3 domains predicted to serve as an AF-interaction interface. One of these proteins, MAF-associated protein 1, resembles Ig superfamily cell adhesion molecules and we hypothesize that it may function to link the AF to the surface of cells. Our results highlight the existence of an ancient toolkit of conserved protein domains regulating cell-cell and cell-extracellular matrix protein interactions in all animals, and likely reflect a common origin of cell adhesion and allorecognition.

Endothelial colony-forming cells in the spotlight: insights into the pathophysiology of von Willebrand disease and rare bleeding disorders

Endothelial cells deliver a vital contribution to the maintenance of hemostasis by constituting an anatomical as well as functional barrier between the blood and the rest of the body. Apart from the physical barrier function, endothelial cells maintain the hemostatic equilibrium by their pro- and anticoagulant functions. An important part of their procoagulant contribution is the production of von Willebrand factor (VWF), which is a carrier protein for coagulation factor VIII and facilitates the formation of a platelet plug. Thus, VWF is indispensable for both primary and secondary hemostasis, which is exemplified by the bleeding disorder von Willebrand disease that results from qualitative or quantitative deficiencies in VWF. A cellular model that was found to accurately reflect the endothelium and its secretory organelles are endothelial colony-forming cells, which can be readily isolated from peripheral blood and constitute a robust ex vivo model to investigate the donor's endothelial cell function. This review summarizes some of the valuable insights on biology of VWF and pathogenic mechanisms of von Willebrand disease that have been made possible using studies with endothelial colony-forming cells derived from patients with bleeding disorders.

How unique structural adaptations support and coordinate the complex function of von Willebrand factor

ABSTRACT

von Willebrand factor (VWF) is a multimeric protein consisting of covalently linked monomers, which share an identical domain architecture. Although involved in processes such as inflammation, angiogenesis, and cancer metastasis, VWF is mostly known for its role in hemostasis, by acting as a chaperone protein for coagulation factor VIII (FVIII) and by contributing to the recruitment of platelets during thrombus formation. To serve its role in hemostasis, VWF needs to bind a variety of ligands, including FVIII, platelet-receptor glycoprotein Ib-α, VWF-cleaving protease ADAMTS13, subendothelial collagen, and integrin α-IIb/β-3. Importantly, interactions are differently regulated for each of these ligands. How are these binding events accomplished and coordinated? The basic structures of the domains that constitute the VWF protein are found in hundreds of other proteins of prokaryotic and eukaryotic organisms. However, the determination of the 3-dimensional structures of these domains within the VWF context and especially in complex with its ligands reveals that exclusive, VWF-specific structural adaptations have been incorporated in its domains. They provide an explanation of how VWF binds its ligands in a synchronized and timely fashion. In this review, we have focused on the domains that interact with the main ligands of VWF and discuss how elucidating the 3-dimensional structures of these domains has contributed to our understanding of how VWF function is controlled. We further detail how mutations in these domains that are associated with von Willebrand disease modulate the interaction between VWF and its ligands.

Unravelling the spectrum of von Willebrand factor variants in quantitative von Willebrand disease: results from a German cohort study

BACKGROUND

Von Willebrand disease (VWD), the most prevalent hereditary bleeding disorder, results from deficiency of von Willebrand factor (VWF).

OBJECTIVES

This large cohort study aims to offer a comprehensive exploration of mutation spectra and laboratory features in quantitative VWF deficiencies, shedding light on genetic underpinnings and genotype-phenotype associations.

METHODS

Our cohort consisted of 221 Caucasian index patients with quantitative VWD, along with 47 individuals whose plasma VWF levels fell within the lower normal boundaries (50-70 IU/dL). We conducted comprehensive VWF assays and genetic analyses, encompassing VWF gene sequencing, copy number variation investigations, and bioinformatic assessments.

RESULTS

Following International Society on Thrombosis and Haemostasis-Scientific and Standardization Committee VWF guidelines, 77 index patients were characterized as having type 1 VWD (VWF antigen [VWF:Ag] < 30 IU/dL), 111 as having type 1 VWD (VWF:Ag, 30-50 IU/dL), and 33 as having type 3 VWD. Mutation detection rates were 88%, 65%, and 92%, respectively. Notably, blood group O overrepresentation was evident in type 1 with VWF:Ag of 30 to 50 IU/dL, particularly among mutation-negative patients, suggesting a potential causal role of blood group O. A total of 223 VWF variants, comprising 147 distinct variations, were identified in quantitative VWD patients, of which 57 were novel variants (39%). Additionally, approximately 70% of individuals with VWF levels within the lower normal boundaries (50-70 IU/dL) displayed VWF variants.

CONCLUSION

Our data advance our understanding of the molecular mechanisms underlying quantitative VWD, offering valuable insights for future research and clinical management. Distinct mutation patterns were observed among subgroups, particularly the contrast between type 1 VWD (VWF:Ag < 30 IU/dL) and type 1 VWD (VWF:Ag, 30-50 IU/dL), an area with limited prior investigation.

Novel GPIb-independent platelet aggregation induced by botrocetin: implications for diagnosis and antithrombotic therapy

BACKGROUND

Snake venom botrocetin facilitates von Willebrand factor (VWF) binding to platelet GPIbα and has been widely used for the diagnosis of von Willebrand disease and GPIb-related disorders. Botrocetin is also commonly employed for the development/characterization of antithrombotics targeting the GPIb-VWF axis.

OBJECTIVES

To explore the alternative receptor(s)/mechanisms that participate in botrocetin-induced platelet aggregation.

METHODS

The effects of botrocetin on platelet aggregation were examined using platelets from wild-type, VWF- and fibrinogen-deficient, GPIbα-deficient, IL4Rα/GPIbα-transgenic, ITGA2B and ITGB3-deficient mice, and Bernard-Soulier syndrome and healthy human samples. Platelet-fibrinogen and platelet-VWF interaction were measured using flow cytometry. GPIbα-VWF binding was evaluated utilizing enzyme-linked immunosorbent assay. Botrocetin-αIIbβ3 and botrocetin-GPIbα interactions were measured using enzyme-linked immunosorbent assay and fluorescence anisotropy assays. Heparinized whole blood from healthy donors was examined for thrombus formation and growth in a perfusion chamber.

RESULTS

Botrocetin could induce aggregation of platelets from a Bernard-Soulier syndrome patient and GPIbα-deficient mice as well as platelets lacking the N-terminal extracellular domain of GPIbα. Botrocetin could interact with αIIbβ3 and facilitated αIIbβ3-VWF interaction independent of GPIb. Botrocetin competitively bound to the ligand-binding domain of activated rather than resting αIIbβ3. Although botrocetin-induced platelet aggregation requires VWF, strikingly, in the absence of VWF, botrocetin blocked fibrinogen and other ligand binding to αIIbβ3 and inhibited platelet aggregation and thrombus formation. Consistently, recombinant botrocetin defective in VWF binding inhibited αIIbβ3- and GPIb-mediated platelet aggregation, spreading, and thrombus formation.

CONCLUSION

Our study provides insights into avoiding the misdiagnosis of GPIb-related disorders and developing botrocetin mutants as potential new antithrombotics that may simultaneously target both αIIbβ3 and GPIbα.

Mechanosensory entities and functionality of endothelial cells

The endothelial cells of the blood circulation are exposed to hemodynamic forces, such as cyclic strain, hydrostatic forces, and shear stress caused by the blood fluid's frictional force. Endothelial cells perceive mechanical forces via mechanosensors and thus elicit physiological reactions such as alterations in vessel width. The mechanosensors considered comprise ion channels, structures linked to the plasma membrane, cytoskeletal spectrin scaffold, mechanoreceptors, and junctional proteins. This review focuses on endothelial mechanosensors and how they alter the vascular functions of endothelial cells. The current state of knowledge on the dysregulation of endothelial mechanosensitivity in disease is briefly presented. The interplay in mechanical perception between endothelial cells and vascular smooth muscle cells is briefly outlined. Finally, future research avenues are highlighted, which are necessary to overcome existing limitations.

Heyde Syndrome Unveiled: A Case Report with Current Literature Review and Molecular Insights

Heyde syndrome, marked by aortic stenosis, gastrointestinal bleeding from angiodysplasia, and acquired von Willebrand syndrome, is often underreported. Shear stress from a narrowed aortic valve degrades von Willebrand factor multimers, leading to angiodysplasia formation and von Willebrand factor deficiency. This case report aims to raise clinician awareness of Heyde syndrome, its complexity, and the need for a multidisciplinary approach. We present a 75-year-old man with aortic stenosis, gastrointestinal bleeding from angiodysplasia, and acquired von Willebrand syndrome type 2A. The patient was successfully treated with argon plasma coagulation and blood transfusions. He declined further treatment for aortic stenosis but was in good overall health with improved laboratory results during follow-up. Additionally, we provide a comprehensive review of the molecular mechanisms involved in the development of this syndrome, discuss current diagnostic and treatment approaches, and offer future perspectives for further research on this topic.

Von Willebrand factor and hematogenous cancer metastasis under flow

Hematogenous metastasis involves cancer cell migration to different locations from the primary tumor through the blood circulation. Von Willebrand factor (VWF) has been shown to play an important role in tumor cell adhesion to and extravasation from the endothelial cell lining of blood vessel walls during cancer metastasis. VWF may contribute to this process by interacting with tumor cells, endothelial cells, and platelets through various cell membrane receptors, such as platelet glycoprotein (GP)Ibα, P-selectin, ανβ3 and αIIbβ3 integrins, and glycocalyx. Blood flow can mechanically extend and activate VWF to bind platelets and associate intermolecularly with other VWF molecules in plasma or on the surface of endothelial cells, cancer cells, or platelets. This suggests a mechanoregulatory role of VWF in mediating the interactions between VWF and these cells to promote cancer cell adhesion to blood vessels. In this review, we will summarize the current knowledge of VWF function and the role of hydrodynamic forces in hematogenous cancer metastasis.

von Willebrand disease

von Willebrand disease (VWD) is the most common inherited bleeding disorder. The disorder is characterized by excessive mucocutaneous bleeding. The most common bleeding manifestations of this condition include nosebleeds, bruising, bleeding from minor wounds, menorrhagia or postpartum bleeding in women as well as bleeding after surgery. Other less frequent symptoms include gastrointestinal bleeding, haematomas or haemarthroses. VWD pathophysiology is complex and results from defects in von Willebrand factor (VWF) glycoprotein. Quantitative deficiencies are responsible for type 1 VWD with a partial decrease of VWF and type 3 with the complete absence of VWF. Qualitative abnormalities cause type 2 VWD, being further divided into types 2A, 2B, 2M and 2N. Although common, VWD is at risk of misdiagnosis, overdiagnosis and underdiagnosis owing to several factors, including complex diagnosis, variability of bleeding symptoms, presence of external variables (blood groups and other physiological modifiers such as exercise, thyroid hormones, oestrogens, and ageing), and lack of disease awareness among non-specialist health-care providers. Establishing the correct VWD diagnosis requires an array of specialized phenotypic assays and/or molecular genetic testing of the VWF gene. The management of bleeding includes increasing endogenous VWF levels with desmopressin or infusion of exogenous VWF concentrates (plasma-derived or recombinant). Fibrinolytic inhibitors, topical haemostatic agents and hormonal therapies are used as effective adjunctive measures.

Cryptic Extensibility in von Willebrand Factor Revealed by Molecular Nanodissection

Von Willebrand factor (VWF) is a multimer with a variable number of protomers, each of which is a head-to-head dimer of two multi-domain monomers. VWF responds to shear through the unfolding and extension of distinct domains, thereby mediating platelet adhesion and aggregation to the injured blood vessel wall. VWF's C1-6 segment uncoils and then the A2 domain unfolds and extends in a hierarchical and sequential manner. However, it is unclear whether there is any reservoir of further extensibility. Here, we explored the presence of cryptic extensibility in VWF by nanodissecting individual, pre-stretched multimers with atomic force microscopy (AFM). The AFM cantilever tip was pressed into the surface and moved in a direction perpendicular to the VWF axis. It was possible to pull out protein loops from VWF, which resulted in a mean contour length gain of 217 nm. In some cases, the loop became cleaved, and a gap was present along the contour. Frequently, small nodules appeared in the loops, indicating that parts of the nanodissected VWF segment remained folded. After analyzing the nodal structure, we conclude that the cryptic extensibility lies within the C1-6 and A1-3 regions. Cryptic extensibility may play a role in maintaining VWF's functionality in extreme shear conditions.

Variant mapping using mass spectrometry-based proteotyping as a diagnostic tool in von Willebrand disease

BACKGROUND

von Willebrand disease (VWD) is the most common inherited bleeding disorder, characterized by either partial or complete von Willebrand factor (VWF) deficiency or by the occurrence of VWF proteoforms of altered functionality. The gene encoding VWF is highly polymorphic, giving rise to a variety of proteoforms with varying plasma concentrations and clinical significance.

OBJECTIVES

To address this complexity, we translated genomic variation in VWF to corresponding VWF proteoforms circulating in blood.

METHODS

VWF was characterized in VWD patients (n = 64) participating in the Willebrand in the Netherlands study by conventional laboratory testing, DNA sequencing and complementary discovery, and targeted mass spectrometry-based plasma proteomic strategies.

RESULTS

Unbiased plasma profiling combined with immune enrichment of VWF verified VWF and its binding partner factor VIII as key determinants of VWD and revealed a remarkable heterogeneity in VWF amino acid sequence coverage among patients. Subsequent VWF proteotyping enabled identification of both polymorphisms (eg, p.Thr789Ala, p.Gln852Arg, and p.Thr1381Ala), as well as pathogenic variants (n = 16) along with their corresponding canonical sequences. Targeted proteomics using stable isotope-labeled peptides confirmed unbiased proteotyping for 5 selected variants and suggested differential proteoform quantities in plasma. The variant-to-wild-type peptide ratio was determined in 6 type 2B patients heterozygous for p.Arg1306Trp, confirming the relatively low proteoform concentration of the pathogenic variant. The elevated VWF propeptide/VWF ratio indicated increased clearance of specific VWF proteoforms.

CONCLUSION

This study highlights how VWF proteotyping from plasma could be the first step to bridge the gap between genotyping and functional testing in VWD.

The effect of ADAMTS13 on graft-versus-host disease

Allogeneic haematopoietic stem cell transplantation (allo-HSCT) can potentially cure malignant blood disorders and benign conditions such as haemoglobinopathies and immunologic diseases. However, allo-HSCT is associated with significant complications. The most common and debilitating among them is graft-versus-host disease (GVHD). In GVHD, donor-derived T cells mount an alloimmune response against the recipient. The alloimmune response involves several steps, including recognition of recipient antigens, activation and proliferation of T cells in secondary lymphoid organs, and homing into GVHD-targeted organs. Adhesion molecules on T cells and endothelial cells mediate homing of T cells into lymphoid and non-lymphoid tissues. In this study, we showed that Von Willebrand factor (VWF), an adhesion molecule secreted by activated endothelial cells, plays an important role in mouse models of GVHD. We investigated the effect of the VWF-cleaving protease ADAMTS13 on GVHD. We found that ADAMTS13 reduced the severity of GVHD after bone marrow transplantation from C57BL6 donor to BALB/C recipient mice. A recombinant VWF-A2 domain peptide also reduced GVHD in mice. We showed that ADAMTS13 and recombinant VWF-A2 reduced the binding of T cells to endothelial cells and VWF in vitro, and reduced the number of T cells in lymph nodes, Peyer's patches and GVHD-targeted organs in vivo. We identified LFA-1 (αLβ2) as the binding site of VWF on T cells. Our results showed that blocking T-cell homing by ADAMTS13 or VWF-A2 peptide reduced the severity of the GVHD after allo-HSCT, a potentially novel method for treating and preventing GVHD.

The MUC2 Gene Product: Polymerisation and Post-Secretory Organisation-Current Models

MUC2 mucin, the primary gel-forming component of intestinal mucus, is well researched and a model of polymerisation and post-secretory organisation has been published previously. Recently, several significant developments have been made which either introduce new ideas or challenge previous theories. New ideas include an overhaul of the MUC2 C-terminal globular structure which is proposed to harbour several previously unobserved domains, and include a site for an extra intermolecular disulphide bridge dimer between the cysteine 4379 of adjacent MUC2 C-termini. MUC2 polymers are also now thought to be secreted attached to the epithelial surface of goblet cells in the small intestine and removed following secretion via a metalloprotease meprin β-mediated cleavage of the von Willebrand D2 domain of the N-terminus. It remains unclear whether MUC2 forms intermolecular dimers, trimers, or both, at the N-termini during polymerisation, with several articles supporting either trimer or dimer formation. The presence of a firm inner mucus layer in the small intestine is similarly unclear. Considering this recent research, this review proposes an update to the previous model of MUC2 polymerisation and secretion, considers conflicting theories and data, and highlights the importance of this research to the understanding of MUC2 mucus layers in health and disease.

Clinical relevance of genetic variants in the von Willebrand factor according to in-silico methods

Clinical interpretation of genetic variants in the context of the patient's phenotype is a time-consuming and costly process. In-silico analysis using in-silico prediction tools, and molecular modeling have been developed to predict the influence of genetic variants on the quality and/or quantity of the resulting translated protein, and in this way, to alert clinicians of disease likelihood in the absence of previous evidence. Our objectives were to evaluate the success rate of the in-silico analysis in predicting the disease-causing variants as pathogenic and the single-nucleotide variants as neutral, and to establish the reliability of in-silico analysis for determining pathogenicity or neutrality of von Willebrand factor gene-associated genetic variants. Using in-silico analysis, we studied pathogenicity in 31 disease-causing variants, and neutrality in 61 single-nucleotide variants from patients previously diagnosed as type 2 von Willebrand disease. Disease-causing variants and non-synonymous single-nucleotide variants were explored by in-silico tools that analyze the amino acidic sequence. Intronic and synonymous single-nucleotide variants were analyzed by in-silico methods that evaluate the nucleotidic sequence. We found a consistent agreement between predictions achieved by in-silico prediction tools and molecular modeling, both for defining the pathogenicity of disease-causing variants and the neutrality of single-nucleotide variants. Based on our results, the in-silico analysis would help to define the pathogenicity or neutrality in novel genetic variants observed in patients with clinical and laboratory phenotypes suggestive of von Willebrand disease.

Destruxin A inhibits the hemocytin-mediated hemolymph immunity of host insects to facilitate Metarhizium infection

Insects have an effective innate immune system to protect themselves against fungal invasion. Metarhizium employs a toxin-based strategy using a nonribosomal peptide called destruxin A (DA) to counteract the host immune response. However, the mechanism by which DA inhibits insect immunity is still unclear. Here, we identified 48 DA-binding proteins in silkworm hemolymph, with the binding affinity (KD) ranging from 2 to 420 μM. Among these proteins, hemocytin, an important immune factor, was determined to be the strongest DA-binding protein. DA binds to hemocytin and regulates its conformation in a multisite manner. Furthermore, DA exerts a significant inhibitory effect on hemocytin-mediated hemocyte aggregation. By disrupting the interaction between hemocytin, actin A3, and gelsolin, DA prevents the transformation of granules into vesicles in hemocytes. These vesicles are responsible for storing, maturing, and exocytosing hemocytin. Therefore, hemocytin secretion is reduced, and the formation of structures that promote aggregation in outer hemocytes is inhibited.

Hemocytin, the special aggregation factor connecting insect hemolymph immunity, a potential target of insecticidal immunosuppresant

Insects possess an effective innate immunity that enables them to adapt to their intricate living environment and fend off various pathogens (or parasites). This innate immunity comprises both humoral and cellular immunity, which synergistically orchestrate immune responses. Hemocytin, a lectin with a distinctive structure, plays a crucial role in insect hemolymph immunity. Hemocytin is involved in the early immune response, facilitating processes such as coagulation, nodulation, and encapsulation in the hemolymph. It prevents hemolymph overflow and microbial pathogens invasion resulting from epidermal damage, and also aids in the recognition and elimination of invaders. However, the research on hemocytin is still limited. Our previous findings demonstrated that destruxin A effectively inhibits insect hemolymph immunity by interacting with hemocytin, suggesting that hemocytin could be a potential target for insecticides development. Therefore, it is crucial to gain a deeper understanding of hemocytin. This review integrates recent advancements in the study of the structure and function of insect hemocytin and also explores the potential of hemocytin as a target for insecticides. This review aims to enhance our comprehension of insect innate immunity and provide innovative ideas for the development of environmentally friendly pesticides.

Dynamic and functional linkage between von Willebrand factor and ADAMTS-13 with aging: an Atherosclerosis Risk in Community study

BACKGROUND

von Willebrand factor (VWF) is a multimeric glycoprotein critically involved in hemostasis, thrombosis, and inflammation. VWF function is regulated by its antigen levels, multimeric structures, and the state of enzymatic cleavage. Population studies in the past have focused almost exclusively on VWF antigen levels in cross-sectional study designs.

OBJECTIVE

To identify subjects in the Atherosclerosis Risk in Community study who had persistently low and high VWF antigen over 10 years and to quantify longitudinal changes in the biological activities and cleavage of VWF in these subjects.

METHODS

We measured VWF antigen, propeptide, adhesive activities, and cleavage by ADAMTS-13 quantified using a mass spectrometry method that detected the cleaved VWF peptide EQAPNLVY, as well as coagulation factor VIII activity.

RESULTS

We determined the mean subject-specific increase in VWF to be 22.0 International Units (IU)/dL over 10 years, with 95% between -0.3 and 59.7 IU/dL. This aging-related increase was also detected in VWF propeptide levels, ristocetin cofactor activity, and VWF binding to collagen. We identified 4.1% and 25.0% of subjects as having persistently low (<50 IU/dL) and high (>200 IU/dL) VWF antigen, respectively. Subjects with persistently low VWF had enhanced ristocetin cofactor activity, whereas those with persistently high VWF had elevated levels of ADAMTS-13, resulting in a comparable rate of VWF cleavage between the 2 groups.

CONCLUSIONS

These results provide new information about the effects of aging on VWF antigens and adhesive activity and identify a functional coordination between VWF and the rate of its cleavage by ADAMTS-13.

Mass Spectrometry Analysis of Shark Skin Proteins

The mucus layer covering the skin of fish has several roles, including protection against pathogens and mechanical damage in which proteins play a key role. While proteins in the skin mucus layer of various common bony fish species have been explored, the proteins of shark skin mucus remain unexplored. In this pilot study, we examine the protein composition of the skin mucus in spiny dogfish sharks and chain catsharks through mass spectrometry (NanoLC-MS/MS). Overall, we identified 206 and 72 proteins in spiny dogfish (Squalus acanthias) and chain catsharks (Scyliorhinus retifer), respectively. Categorization showed that the proteins belonged to diverse biological processes and that most proteins were cellular albeit a significant minority were secreted, indicative of mucosal immune roles. The secreted proteins are reviewed in detail with emphasis on their immune potentials. Moreover, STRING protein-protein association network analysis showed that proteins of closely related shark species were more similar as compared to a more distantly related shark and a bony fish, although there were also significant overlaps. This study contributes to the growing field of molecular shark studies and provides a foundation for further research into the functional roles and potential human biomedical implications of shark skin mucus proteins.

Population-based prevalence and mutational landscape of von Willebrand disease using large-scale genetic databases

Von Willebrand disease (VWD) is a common bleeding disorder caused by mutations in the von Willebrand factor gene (VWF). The true global prevalence of VWD has not been accurately established. We estimated the worldwide and within-population prevalence of inherited VWD by analyzing exome and genome data of 141,456 individuals gathered by the genome Aggregation Database (gnomAD). We also extended our data deepening by mining the main databases containing VWF variants i.e., the Leiden Open Variation Database (LOVD) and the Human Gene Mutation Database (HGMD) with the goal to explore the global mutational spectrum of VWD. A total of 4,313 VWF variants were identified in the gnomAD population, of which 505 were predicted to be pathogenic or already reported to be associated with VWD. Among the 282,912 alleles analyzed, 31,785 were affected by the aforementioned variants. The global prevalence of dominant VWD in 1000 individuals was established to be 74 for type 1, 3 for 2A, 3 for 2B and 6 for 2M. The global prevalences for recessive VWD forms (type 2N and type 3) were 0.31 and 0.7 in 1000 individuals, respectively. This comprehensive analysis provided a global mutational landscape of VWF by means of 927 already reported variants in the HGMD and LOVD datasets and 287 novel pathogenic variants identified in the gnomAD. Our results reveal that there is a considerably higher than expected prevalence of putative disease alleles and variants associated with VWD and suggest that a large number of VWD patients are undiagnosed.

Mucosa-Mimetic Materials for the Study of Intestinal Homeostasis and Disease

Mucus is a viscoelastic hydrogel that lines and protects the epithelial surfaces of the body that houses commensal microbiota and functions in host defense against pathogen invasion. As a first-line physical and biochemical barrier, intestinal mucus is involved in immune surveillance and spatial organization of the microbiome, while dysfunction of the gut mucus barrier is implicated in several diseases. Mucus can be collected from a variety of mammalian sources for study, however, established methods are challenging in terms of scale and efficiency, as well as with regard to rheological similarity to native human mucus. Therefore, there is a need for mucus-mimetic hydrogels that more accurately reflect the physical and chemical profile of the in vivo human epithelial environment to enable the investigation of the role of mucus in human disease and interactions with the intestinal microbiome. This review will evaluate the material properties of synthetic mucus mimics to date designed to address the above need, with a focus toward an improved understanding of the biochemical and immunological functions of these biopolymers related to utility for research and therapeutic applications.

Characterization of copy-number variants in a large cohort of patients with von Willebrand disease reveals a relationship between disrupted regions and disease type

Background

Genetic analysis for von Willebrand disease (VWD) commonly utilizes DNA sequencing to identify variants in the von Willebrand factor (VWF) gene; however, this technique cannot always detect copy-number variants (CNVs). Additional mapping of CNVs in patients with VWD is needed.

Objectives

This study aimed to characterize CNVs in a large sample of VWF mutation-negative VWD patients.

Methods

To determine the role of CNVs in VWD, a VWF high-resolution comparative genomic hybridization array was custom-designed to avoid multiple sequence variations, repeated sequences, and the VWF pseudogene. This was performed on 204 mutation-negative subjects for whom clinical variables were also available.

Results

Among the 204 patients, 7 unique CNVs were found, with a total of 24 CNVs (12%). Of the 7 unique CNVs, 1 was novel, 1 was found in a VWF database, and 5 were previously reported. All patients with type 1C VWD and a CNV had the same exon 33 and 34 in-frame deletion. Certain clinical variables were also significantly different between those with and without CNVs.

Conclusion

The in-frame deletion in patients with type 1C VWD exactly matches the D4N module of the D4 domain, a region where mutations and deletions are known to affect clearance. We observed significantly higher VWF-to-ristocetin cofactor levels in patients with type 1C VWD and a CNV than in patients without a CNV, suggesting a relationship between CNVs and the increased clearance observed in patients with type 1C VWD. Glycoprotein IbM activity was significantly lower in patients with type 1 VWD and a CNV than in patients without a CNV, suggesting that platelet binding is more affected by CNVs than single base pair mutations. This work elucidates some of the underlying genetic mechanisms of CNVs in these patients.

Shear-induced acquired von Willebrand syndrome: an accomplice of bleeding events in adults on extracorporeal membrane oxygenation support

Extracorporeal membrane oxygenation (ECMO) is an increasingly acceptable life-saving mechanical assistance system that provides cardiac and/or respiratory support for several reversible or treatable diseases. Despite important advances in technology and clinical management, bleeding remains a significant and common complication associated with increased morbidity and mortality. Some studies suggest that acquired von Willebrand syndrome (AVWS) is one of the etiologies of bleeding. It is caused by shear-induced deficiency of von Willebrand factor (VWF). VWF is an important glycoprotein for hemostasis that acts as a linker at sites of vascular injury for platelet adhesion and aggregation under high shear stress. AVWS can usually be diagnosed within 24 h after initiation of ECMO and is always reversible after explantation. Nonetheless, the main mechanism for the defect in the VWF multimers under ECMO support and the association between AVWS and bleeding complications remains unknown. In this review, we specifically discuss the loss of VWF caused by shear induction in the context of ECMO support as well as the current diagnostic and management strategies for AVWS.

Kidney cell culture Macaca fascicularis as a candidate for vaccine development and in vitro model

BACKGROUND

Cell culture is the proliferation of a cell population in vitro by isolating from the original tissue or growing from existing ones. One essential source is the monkey kidney cell cultures which have an essential role in biomedical study. This is due to the significant homology between the human and macaque genomes making these useful for cultivating human viruses, especially enteroviruses, and growing vaccines.

METHODS

This study developed cell cultures derived from the kidney of Macaca fascicularis (Mf) and validated its gene expression.

RESULTS

The primary cultures were successfully subcultured up to six passages, grew as monolayers, and exhibited epithelial-like morphology. The cultured cells remained heterogeneous in phenotype and they expressed CD155 and CD46 as viral receptors, cell morphology (CD24, endosialin, and vWF), proliferation, also apoptosis markers (Ki67 and p53).

CONCLUSIONS

These results indicated that the cell cultures can be used as in vitro model cells for vaccine development and bioactive compound.

The intestinal MUC2 mucin C-terminus is stabilized by an extra disulfide bond in comparison to von Willebrand factor and other gel-forming mucins

The MUC2 mucin polymer is the main building unit of the intestinal mucus layers separating intestinal microbiota from the host epithelium. The MUC2 mucin is a large glycoprotein with a C-terminal domain similar to the MUC5AC and MUC5B mucins and the von Willebrand factor (VWF). A structural model of the C-terminal part of MUC2, MUC2-C, was generated by combining Cryo-electron microscopy, AlphaFold prediction, information of its glycosylation, and small angle X-ray scattering information. The globular VWD4 assembly in the N-terminal of MUC2-C is followed by 3.5 linear VWC domains that form an extended flexible structure before the C-terminal cystine-knot. All gel-forming mucins and VWF form tail-tail disulfide-bonded dimers in their C-terminal cystine-knot domain, but interestingly the MUC2 mucin has an extra stabilizing disulfide bond on the N-terminal side of the VWD4 domain, likely essential for a stable intestinal mucus barrier.

Structural hierarchy of mechanical extensibility in human von Willebrand factor multimers

The von Willebrand factor (VWF) is a multimeric glycoprotein composed of 80- to 120-nm-long protomeric units and plays a fundamental role in mediating platelet function at high shear. The exact nature of the shear-induced structural transitions have remained elusive; uncovering them requires the high-resolution quantitative analysis of gradually extended VWF. Here, we stretched human blood-plasma-derived VWF with molecular combing and analyzed the axial structure of the elongated multimers with atomic force microscopy. Protomers extended through structural intermediates that could be grouped into seven distinct topographical classes. Protomer extension thus progresses through the uncoiling of the C_1-6 domain segment, rearrangements among the N-terminal VWF domains, and unfolding and elastic extension of the A₂ domain. The least and most extended protomer conformations were localized at the ends and the middle of the multimer, respectively, revealing an apparent necking phenomenon characteristic of plastic-material behavior. The structural hierarchy uncovered here is likely to provide a spatial control mechanism to the complex functions of VWF.

The investigation into the effect of the length of RGD peptides and temperature on the interaction with the αIIbβ3 integrin: a molecular dynamic study

The tripeptide Arg-Gly-Asp acid (RGD) is a protein sequence in the binding of proteins to cell surfaces, and is involved in various biological processes such as cell adhesion to the extracellular matrix, platelet activation, hemostasis, etc. The C2 domain of the Von Willebrand Factor (VWF), containing the RGD motif, plays an important role in the initial homeostasis process. It binds to the αIIbβ3 integrin and stimulates platelet aggregation. We have investigated, using the molecular Dynamic (MD) simulation method, the effect of the RGD-peptide length, and temperature variation, on the binding to the αIIbβ3 integrin receptor. We examined 10 different structural modes of the αIIbβ3 at three different temperatures; 237 K, 310 K and 318 K. Our findings show that the amino acids that form a binding pocket include Asp₂₂₄, Tyr₂₃₄, Ser₂₂₆, Tyr₁₉₀, Tyr₁₈₉, Trp₂₆₀, Trp₂₆₂, Asp_259, Lys₂₅₃, Arg₂₁₄, Asp₂₁₇, Ser₁₆₁ and Ala₂₁₈ and that the ligand-receptor interaction was increased at higher temperatures. It was also found that the increase in the number of ligands' amino acids and their types (% glycine) plays an important role in the stability, conformation, and ligand-receptor interaction.Communicated by Ramaswamy H. Sarma.

A Deeper Insight into the Tick Salivary Protein Families under the Light of Alphafold2 and Dali: Introducing the TickSialoFam 2.0 Database

Hard ticks feed for several days or weeks on their hosts and their saliva contains thousands of polypeptides belonging to dozens of families, as identified by salivary transcriptomes. Comparison of the coding sequences to protein databases helps to identify putative secreted proteins and their potential functions, directing and focusing future studies, usually done with recombinant proteins that are tested in different bioassays. However, many families of putative secreted peptides have a unique character, not providing significant matches to known sequences. The availability of the Alphafold2 program, which provides in silico predictions of the 3D polypeptide structure, coupled with the Dali program which uses the atomic coordinates of a structural model to search the Protein Data Bank (PDB) allows another layer of investigation to annotate and ascribe a functional role to proteins having so far being characterized as "unique". In this study, we analyzed the classification of tick salivary proteins under the light of the Alphafold2/Dali programs, detecting novel protein families and gaining new insights relating the structure and function of tick salivary proteins.

Von Willebrand factor in diagnostics and treatment of cardiovascular disease: Recent advances and prospects

Von Willebrand factor (VWF) is a large multimeric glycoprotein involved in hemostasis. It is essential for platelet adhesion to the subendothelium of the damaged endothelial layer at high shear rates. Such shear rates occur in small-diameter arteries, especially at stenotic sites. Moreover, VWF carries coagulation factor VIII and protects it from proteolysis in the bloodstream. Deficiency or dysfunction of VWF predisposes to bleeding. In contrast, an increase in the concentration of high molecular weight multimers (HMWM) of VWF is closely associated with arterial thrombotic events. Severe aortic stenosis (AS) or hypertrophic obstructive cardiomyopathy (HOCM) can deplete HMWM of VWF and lead to cryptogenic, gastrointestinal, subcutaneous, and mucosal bleeding. Considering that VWF facilitates primary hemostasis and a local inflammatory response at high shear rates, its dysfunction may contribute to the development of coronary artery disease (CAD) and its complications. However, current diagnostic methods do not allow for an in-depth analysis of this contribution. The development of novel diagnostic techniques, primarily microfluidic, is underway. Such methods can provide physiologically relevant assessments of VWF function at high shear rates; however, they have not been introduced into clinical practice. The development and use of agents targeting VWF interaction with the vessel wall and/or platelets may be reasonable in prevention of CAD and its complications, given the prominent role of VWF in arterial thrombosis.

Structure and dynamics of the von Willebrand Factor C6 domain

Von Willebrand disease (VWD) is a bleeding disorder with different levels of severity. VWD-associated mutations are located in the von Willebrand factor (VWF) gene, coding for the large multidomain plasma protein VWF with essential roles in hemostasis and thrombosis. On the one hand, a variety of mutations in the C-domains of VWF are associated with increased bleeding upon vascular injury. On the other hand, VWF gain-of-function (GOF) mutations in the C4 domain have recently been identified, which induce an increased risk of myocardial infarction. Mechanistic insights into how these mutations affect the molecular behavior of VWF are scarce and holistic approaches are challenging due to the multidomain and multimeric character of this large protein. Here, we determine the structure and dynamics of the C6 domain and the single nucleotide polymorphism (SNP) variant G2705R in C6 by combining nuclear magnetic resonance spectroscopy, molecular dynamics simulations and aggregometry. Our findings indicate that this mutation mostly destabilizes VWF by leading to a more pronounced hinging between both subdomains of C6. Hemostatic parameters of variant G2705R are close to normal under static conditions, but the missense mutation results in a gain-of-function under flow conditions, due to decreased VWF stem stability. Together with the fact that two C4 variants also exhibit GOF characteristics, our data underline the importance of the VWF stem region in VWF's hemostatic activity and the risk of mutation-associated prothrombotic properties in VWF C-domain variants due to altered stem dynamics.

What is the role of Von Willebrand factor in chronic hepatitis B virus infection to hepatocellular carcinoma: a review article

Von Willebrand factor (VWF) is a glycoprotein synthesized and secreted by vascular endothelial cells and megakaryocytes, found on plasma surface, endothelial cells, and α-granule of platelets. VWF can be interacted with collagen and platelet membrane glycoproteins GPIb and GPIb-IIa and play an important role in platelet adhesion and aggregation. Growing research evidence suggests that VWF also mediates the prevention or protesting of hepatocellular carcinoma (HCC) in chronic hepatitis B (CHB) patients from several clinical studies. While the mechanism of VWF in HCC protection or protest is still unclear, further study is required. This article aims to rationalize the role of VWF in the development of HCC, and the functional domain of VWF in cancer as well as cross-talking with platelets and miRNAs. This article also looks forward to the future development and challenges of VWF research.

Polyphosphate Activates von Willebrand Factor Interaction with Glycoprotein Ib in the Absence of Factor VIII In Vitro

Polyphosphate (polyP), a phosphate polymer released by activated platelets, may modulate various stages of hemostasis by binding to blood proteins. In this context, we previously reported that polyP binds to the von Willebrand factor (VWF). One of the most significant functions of VWF is to bind to and protect the blood circulating Factor VIII (FVIII). Therefore, here, we study the role of polyP in the VWF-FVIII complex in vitro and suggest its biological significance. Surface plasmon resonance and electrophoretic mobility assays indicated that polyP binds dynamically to VWF only in the absence of FVIII. Using the VWF Ristocetin Cofactor assay, the most accepted method for studying VWF in platelet adhesion, we found that polyP activates this role of VWF only at low levels of FVIII, such as in plasmas with chemically depleted FVIII and plasmas from severe hemophilia A patients. Moreover, we demonstrated that FVIII competes with polyP in the activation of VWF. Finally, polyP also increases the binding of VWF to platelets in samples from patients with type 2 and type 3 von Willebrand disease. We propose that polyP may be used in designing new therapies to activate VWF when FVIII cannot be used.

Regulation of VWF (Von Willebrand Factor) in Inflammatory Thrombosis

Increasing evidence indicates that inflammation promotes thrombosis via a VWF (von Willebrand factor)-mediated mechanism. VWF plays an essential role in maintaining the balance between blood coagulation and bleeding, and inflammation can lead to aberrant regulation. VWF is regulated on a transcriptional and (post-)translational level, and its secretion into the circulation captures platelets upon endothelial activation. The significant progress that has been made in understanding transcriptional and translational regulation of VWF is described in this review. First, we describe how VWF is regulated at the transcriptional and post-translational level with a specific focus on the influence of inflammatory and immune responses. Next, we describe how changes in regulation are linked with various cardiovascular diseases. Recent insights from clinical diseases provide evidence for direct molecular links between inflammation and thrombosis, including atherosclerosis, chronic thromboembolic pulmonary hypertension, and COVID-19. Finally, we will briefly describe clinical implications for antithrombotic treatment.

Analysis of von Willebrand Disease in the "Heart of Europe"

Background  von Willebrand disease (VWD) is a genetic bleeding disorder caused by defects of von Willebrand factor (VWF), quantitative (type 1 and 3) or qualitative (type 2). The laboratory phenotyping is heterogenic making diagnosis difficult.

Objectives  Complete laboratory analysis of VWD as an expansion of the previously reported cross-sectional family-based VWD study in the Czech Republic (BRNO-VWD) and Slovakia (BRA-VWD) under the name “Heart of Europe,” in order to improve the understanding of laboratory phenotype/genotype correlation.

Patients and Methods  In total, 227 suspected VWD patients were identified from historical records. Complete laboratory analysis was established using all available assays, including VWF multimers and genetic analysis.

Results  A total of 191 patients (from 119 families) were confirmed as having VWD. The majority was characterized as a type 1 VWD, followed by type 2. Multimeric patterns concordant with laboratory phenotypes were found in approximately 83% of all cases. A phenotype/genotype correlation was present in 84% (77% type 1, 99% type 2, and 61% type 3) of all patients. Another 45 candidate mutations (23 novel variations), not found in the initial study, could be identified (missense 75% and truncating 24%). An exon 1–3 gene deletion was identified in 14 patients where no mutation was found by direct DNA sequencing, increasing the linkage up to 92%, overall.

Conclusion  This study provides a cross-sectional overview of the VWD population in a part of Central Europe. It is an addition to the previously published BRNO-VWD study, and provides important data to the International Society of Thrombosis and Haemostasis/European Association for Haemophilia and Allied Disorders VWD mutation database with identification of novel causal mutations.

Prognostic value of von Willebrand factor and ADAMTS13 in patients with COVID-19: A systematic review and meta-analysis

BACKGROUND

Endotheliopathy and coagulopathy appear to be the main causes for critical illness and death in patients with coronavirus disease 2019 (COVID-19). The adhesive ligand von Willebrand factor (VWF) has been involved in immunothrombosis responding to endothelial injury. Here, we reviewed the current literature and performed meta-analyses on the relationship between both VWF and its cleaving protease ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13) with the prognosis of COVID-19.

METHODS

We searched MEDLINE, Cochrane Library, Web of Science, and EMBASE databases from inception to 4 March 2022 for studies analyzing the relationship between VWF-related variables and composite clinical outcomes of patients with COVID-19. The VWF-related variables analyzed included VWF antigen (VWF:Ag), VWF ristocetin cofactor (VWF:Rco), ADAMTS13 activity (ADAMTS13:Ac), the ratio of VWF:Ag to ADAMTS13:Ac, and coagulation factor VIII (FVIII). The unfavorable outcomes were defined as mortality, intensive care unit (ICU) admission, and severe disease course. We used random or fixed effects models to create summary estimates of risk. Risk of bias was assessed based on the principle of the Newcastle-Ottawa Scale.

RESULTS

A total of 3764 patients from 40 studies were included. The estimated pooled means indicated increased plasma levels of VWF:Ag, VWF:Rco, and VWF:Ag/ADAMTS13:Ac ratio, and decreased plasma levels of ADAMTS13:Ac in COVID-19 patients with unfavorable outcomes when compared to those with favorable outcomes (composite outcomes or subgroup analyses of non-survivor versus survivor, ICU versus non-ICU, and severe versus non-severe). In addition, FVIII were higher in COVID-19 patients with unfavorable outcomes. Subgroup analyses indicated that FVIII was higher in patients admitting to ICU, while there was no significant difference between non-survivors and survivors.

CONCLUSIONS

The imbalance of the VWF-ADAMTS13 axis (massive quantitative and qualitative increases of VWF with relative deficiency of ADAMTS13) is associated with poor prognosis of patients with COVID-19.

A conformational transition of the D'D3 domain primes von Willebrand factor for multimerization

Magnetic tweezers reveal a pH-dependent destabilization of the D3 interface priming VWF for multimerization by exposing Cys1099 and Cys1142.

The stability of the D3 interface is increased by FVIII, suggesting a binding site within the D3 submodules.

Von Willebrand factor (VWF) is a multimeric plasma glycoprotein that is critically involved in hemostasis. Biosynthesis of long VWF concatemers in the endoplasmic reticulum and the trans-Golgi is still not fully understood. We use the single-molecule force spectroscopy technique magnetic tweezers to analyze a previously hypothesized conformational change in the D′D3 domain crucial for VWF multimerization. We find that the interface formed by submodules C8-3, TIL3, and E3 wrapping around VWD3 can open and expose 2 buried cysteines, Cys1099 and Cys1142, that are vital for multimerization. By characterizing the conformational change at varying levels of force, we can quantify the kinetics of the transition and stability of the interface. We find a pronounced destabilization of the interface on lowering the pH from 7.4 to 6.2 and 5.5. This is consistent with initiation of the conformational change that enables VWF multimerization at the D′D3 domain by a decrease in pH in the trans-Golgi network and Weibel-Palade bodies. Furthermore, we find a stabilization of the interface in the presence of coagulation factor VIII, providing evidence for a previously hypothesized binding site in submodule C8-3. Our findings highlight the critical role of the D′D3 domain in VWF biosynthesis and function, and we anticipate our methodology to be applicable to study other, similar conformational changes in VWF and beyond.

Identification of Key Genes and Pathways in Genotoxic Stress Induced Endothelial Dysfunction: Results of Whole Transcriptome Sequencing

Atherosclerosis is a leading cause of cardiovascular morbidity and mortality worldwide. Endothelial disfunction underlying the atherogenesis can be triggered by genotoxic stress in endothelial cells. In the presented research whole transcriptome sequencing (RNA-seq) of human coronary artery (HCAEC) and internal thoracic artery (HITAEC) endothelial cells in vitro exposed to 500 ng/mL mitomycin C (treatment group) or 0.9% NaCl (control group) was performed. Resulting to bioinformatic analysis, 56 upregulated differentially expressed genes (DEGs) and 6 downregulated DEGs with absolute fold change ≥ 2 and FDR p-value < 0.05 were selected in HCAEC exposed to mitomycin C compared to the control group; in HITAEC only one upregulated DEG was found. According to Gene Ontology enrichment analysis, DEGs in HCAEC were classified into 25 functional groups of biological processes, while in HITAEC we found no statistically significant (FDR p-value < 0.05) groups. The four largest groups containing more than 50% DEGs (“signal transduction”, “response to stimulus”, “biological regulation”, and “regulation of biological process”) were identified. Finally, candidate DEGs and pathways underlying the genotoxic stress induced endothelial disfunction have been discovered that could improve our understanding of fundamental basis of atherogenesis and help to justification of genotoxic stress as a novel risk factor for atherosclerosis.

Posttranslational modifications of platelet adhesion receptors

Platelets play a key role in normal hemostasis, whereas pathological platelet adhesion is involved in various cardiovascular events. The underlying cause in cardiovascular events involves plaque rupture leading to subsequent platelet adhesion, activation, release, and eventual thrombosis. Traditional antithrombotic drugs often target the signal transduction process of platelet adhesion receptors by influencing the synthesis of some key molecules, and their effects are limited. Posttranslational modifications (PTMs) of platelet adhesion receptors increase the functional diversity of the receptors and affect platelet physiological and pathological processes. Antithrombotic drugs targeting PTMs of platelet adhesion receptors may represent a new therapeutic idea. In this review, various PTMs, including phosphorylation, glycosylation, ubiquitination, nitrosylation, methylation, lipidation, and proteolysis, of three platelet adhesion receptors, glycoprotein Ib-IX-V (GPIb-IX-V), glycoprotein VI (GPVI), and integrin α_IIbβ_3, are reviewed. It is important to comprehensively understand the PTMs process of platelet adhesion receptors.

The p.P1127S pathogenic variant lowers von Willebrand factor levels through higher affinity for the macrophagic scavenger receptor LRP1: Clinical phenotype and pathogenic mechanisms

BACKGROUND

The index case is a 21-year-old Italian woman with a mild hemorrhagic syndrome and von Willebrand factor antigen (VWF:Ag) = 34.3 U/dl, VWF recombinant glycoprotein Ib (VWF:GpIbR) = 32.8 U/dl, and factor VIII (FVIII) = 55.3 IU/dl.

AIMS

The aim of this study is to characterize from a genetic and biochemical standpoint this low VWF phenotype.

METHODS

Coagulation and biochemical methods were used to study the structural and functional pattern of VWF multimers in the index case's plasma. Recombinant wild-type and p.P1127S VWF variants were produced using human embryonic kidney (HEK)-293 cells. In addition, genetic screening was carried out to detect single nucleotide variants of some scavenger VWF/FVIII receptor genes such as CLEC4M, STAB2, and ASGR2.

RESULTS

Genetic investigation revealed that the index case inherited from her mother the heterozygous missense mutation c.3379C > T (VWF exon 25), causing the p.P1127S substitution in the VWF D'D3 domain. The index case was also homozygous for the scavenger receptor ASGR2 c.-95 CC-genotype. Desmopressin normalized the VWF level of the patient, although its clearance was faster (t1/2  = 6.7 h) than in normal subjects (t1/2  = 12 ± 0.7 h). FVIII-VWF interaction, A Disintegrin And Metalloprotease with ThromboSpondin type 1 motif-13 levels, ristocetin-induced-platelet-aggregation, and VWF multimeric pattern were normal. The p.P1127S variant was normally synthesized and secreted by HEK-293 cells, and molecular modeling predicts a conformational change showing higher affinity for the macrophagic scavenger receptor lipoprotein receptor-related protein 1 (LRP1), as also experimentally verified.

CONCLUSIONS

The p.P1127S variant may cause a low VWF phenotype, stemming from an increased VWF affinity for the scavenger receptor LRP1 and, consequently, an accelerated clearance of VWF.

The Vascular Endothelium and Coagulation: Homeostasis, Disease, and Treatment, with a Focus on the Von Willebrand Factor and Factors VIII and V

The vascular endothelium has several important functions, including hemostasis. The homeostasis of hemostasis is based on a fine balance between procoagulant and anticoagulant proteins and between fibrinolytic and antifibrinolytic ones. Coagulopathies are characterized by a mutation-induced alteration of the function of certain coagulation factors or by a disturbed balance between the mechanisms responsible for regulating coagulation. Homeostatic therapies consist in replacement and nonreplacement treatments or in the administration of antifibrinolytic agents. Rebalancing products reestablish hemostasis by inhibiting natural anticoagulant pathways. These agents include monoclonal antibodies, such as concizumab and marstacimab, which target the tissue factor pathway inhibitor; interfering RNA therapies, such as fitusiran, which targets antithrombin III; and protease inhibitors, such as serpinPC, which targets active protein C. In cases of thrombophilia (deficiency of protein C, protein S, or factor V Leiden), treatment may consist in direct oral anticoagulants, replacement therapy (plasma or recombinant ADAMTS13) in cases of a congenital deficiency of ADAMTS13, or immunomodulators (prednisone) if the thrombophilia is autoimmune. Monoclonal-antibody-based anti-vWF immunotherapy (caplacizumab) is used in the context of severe thrombophilia, regardless of the cause of the disorder. In cases of disseminated intravascular coagulation, the treatment of choice consists in administration of antifibrinolytics, all-trans-retinoic acid, and recombinant soluble human thrombomodulin.

Trypsin-like Inhibitor Domain (TIL)-Harboring Protein Is Essential for Aedes aegypti Reproduction

Cysteine-rich trypsin inhibitor-like domain (TIL)-harboring proteins are broadly distributed in nature but remain understudied in vector mosquitoes. Here we have explored the biology of a TIL domain-containing protein of the arbovirus vector Aedes aegypti, cysteine-rich venom protein 379 (CRVP379). CRVP379 was previously shown to be essential for dengue virus infection in Ae. aegypti mosquitoes. Gene expression analysis showed CRVP379 to be highly expressed in pupal stages, male testes, and female ovaries. CRVP379 expression is also increased in the ovaries at 48 h post-blood feeding. We used CRISPR-Cas9 genome editing to generate two mutant lines of CRVP379 with mutations inside or outside the TIL domain. Female mosquitoes from both mutant lines showed severe defects in their reproductive capability; mutant females also showed differences in their follicular cell morphology. However, the CRVP379 line with a mutation outside the TIL domain did not affect male reproductive performance, suggesting that some CRVP379 residues may have sexually dimorphic functions. In contrast to previous reports, we did not observe a noticeable difference in dengue virus infection between the wild-type and any of the mutant lines. The importance of CRVP379 in Ae. aegypti reproductive biology makes it an interesting candidate for the development of Ae. aegypti population control methods.

The soluble N-terminal autoinhibitory module of the A1 domain in von Willebrand factor partially suppresses its catch bond with glycoprotein Ibα in a sandwich complex

von Willebrand factor (VWF) senses and responds to the hemodynamic forces to interact with the circulatory system and platelets in hemostasis and thrombosis. The dark side of this mechanobiology is implicated in atherothrombosis, stroke, and, more recently, the COVID-19 thrombotic symptoms. The force-responsive element controlling VWF activation predominantly resides in the N terminal auto-inhibitory module (N-AIM) flanking its A1 domain. Nevertheless, the detailed mechano-chemistry of soluble VWF N-AIM is poorly understood at the sub-molecular level as it is assumed to be unstructured loops. Using the free molecular dynamics (MD) simulations, we first predicted a hairpin-like structure of the soluble A1 N-AIM derived polypeptide (Lp; sequences Q1238-E1260). Then we combined molecular docking and steered molecular dynamics (SMD) simulations to examine how Lp regulates the A1-GPIbα interaction under tensile forces. Our simulation results indicate that Lp suppresses the catch bond in a sandwich complex of A1-Lp-GPIbα yet contributes an additional catch-bond residue D1249. To experimentally benchmark the binding kinetics for A1-GPIbα in the absence or presence of Lp, we conducted the force spectroscopy-biomembrane force probe (BFP) assays. We found similar suppression on the A1-GPIbα catch bond with soluble Lp in presence. Clinically, as more and more therapeutic candidates targeting the A1-GPIbα axis have entered clinical trials to treat patients with TTP and acute coronary syndrome, our work represents an endeavor further towards an effective anti-thrombotic approach without severe bleeding side effects as most existing drugs suffer.

Colonization and Infection of Indwelling Medical Devices by Staphylococcus aureus with an Emphasis on Orthopedic Implants

The use of indwelling medical devices has constantly increased in recent years and has revolutionized the quality of life of patients affected by different diseases. However, despite the improvement of hygiene conditions in hospitals, implant-associated infections remain a common and serious complication in prosthetic surgery, mainly in the orthopedic field, where infection often leads to implant failure. Staphylococcus aureus is the most common cause of biomaterial-centered infection. Upon binding to the medical devices, these bacteria proliferate and develop dense communities encased in a protective matrix called biofilm. Biofilm formation has been proposed as occurring in several stages-(1) attachment; (2) proliferation; (3) dispersal-and involves a variety of host and staphylococcal proteinaceous and non-proteinaceous factors. Moreover, biofilm formation is strictly regulated by several control systems. Biofilms enable staphylococci to avoid antimicrobial activity and host immune response and are a source of persistent bacteremia as well as of localized tissue destruction. While considerable information is available on staphylococcal biofilm formation on medical implants and important results have been achieved on the treatment of biofilms, preclinical and clinical applications need to be further investigated. Thus, the purpose of this review is to gather current studies about the mechanism of infection of indwelling medical devices by S. aureus with a special focus on the biochemical factors involved in biofilm formation and regulation. We also provide a summary of the current therapeutic strategies to combat biomaterial-associated infections and highlight the need to further explore biofilm physiology and conduct research for innovative anti-biofilm approaches.

Novel cysteine substitution p.(Cys1084Tyr) causes variable expressivity of qualitative and quantitative VWF defects

von Willebrand factor (VWF) is an extremely cysteine-rich multimeric protein that is essential for maintaining normal hemostasis. The cysteine residues of VWF monomers form intra- and intermolecular disulfide bonds that regulate its structural conformation, multimer distribution, and ultimately its hemostatic activity. In this study, we investigated and characterized the molecular and pathogenic mechanisms through which a novel cysteine variant p.(Cys1084Tyr) causes an unusual, mixed phenotype form of von Willebrand disease (VWD). Phenotypic data including bleeding scores, laboratory values, VWF multimer distribution, and desmopressin response kinetics were investigated in 5 members (2 parents and 3 daughters) of a consanguineous family. VWF synthesis and secretion were also assessed in a heterologous expression system and in a transient transgenic mouse model. Heterozygosity for p.(Cys1084Tyr) was associated with variable expressivity of qualitative VWF defects. Heterozygous individuals had reduced VWF:GPIbM (<0.40 IU/mL) and VWF:CB (<0.35 IU/mL), as well as relative reductions in high-molecular-weight multimers, consistent with type 2A VWD. In addition to these qualitative defects, homozygous individuals also displayed reduced factor VIII (FVIII):C/VWF:Ag, leading to very low FVIII levels (0.03-0.1 IU/mL) and reduced VWF:Ag (<0.40 IU/mL) and VWF:GPIbM (<0.30 IU/mL). Accelerated VWF clearance and impaired VWF secretion contributed to the fully expressed homozygous phenotype with impaired secretion arising because of disordered disulfide connectivity.

Identification of von Willebrand factor D4 domain mutations in patients of Afro-Caribbean descent: In vitro characterization

Background

Von Willebrand disease was diagnosed in two Afro-Caribbean patients and sequencing of the VWF gene (VWF) revealed the presence of multiple variants located throughout the gene, including variants located in the D4 domain of VWF: p.(Pro2145Thrfs*5) in one patient and p.(Cys2216Phefs*9) in the other patient. Interestingly, D4 variants have not been studied often.

Objectives

Our goal was to characterize how the D4 variants p.(Pro2145Thrfs*5) and p.(Cys2216Phefs*9) influenced VWF biosynthesis/secretion and functions using in vitro assays.

Methods

Recombinant VWF (rVWF), mutant or wild-type, was produced via transient transfection of the human embryonic kidney cell line 293T. The use of different tags for the wild-type and the mutant allele allowed us to distinguish between the two forms when measuring VWF antigen in medium and cell lysates. Binding of rVWF to its ligands, collagen, factor VIII, ADAMTS13, and platelet receptors was also investigated.

Results

Homozygous expression of the p.(Cys2216Phefs*9)-rVWF mutation resulted in an almost complete intracellular retention of the protein. Heterozygous expression led to secretion of almost exclusively wild-type-rVWF, logically capable of normal interaction with the different ligands. In contrast, the p.(Pro2145Thrfs*5)-rVWF exhibited reduced binding to type III collagen and αIIbβ3 integrin compared to wild-type-rVWF.

Conclusions

We report two mutations of the D4 domains that induced combined qualitative and quantitative defects.

The differential expression of PilY1 proteins by the HsfBA phosphorelay allows twitching motility in the absence of exopolysaccharides

Type Four Pili (T4P) are extracellular appendages mediating several bacterial functions such as motility, biofilm formation and infection. The ability to adhere to substrates is essential for all these functions. In Myxococcus xanthus, during twitching motility, the binding of polar T4P to exopolysaccharides (EPS), induces pilus retraction and the forward cell movement. EPS are produced, secreted and weakly associated to the M. xanthus cell surface or deposited on the substrate. In this study, a genetic screen allowed us to identify two factors involved in EPS-independent T4P-dependent twitching motility: the PilY1.1 protein and the HsfBA phosphorelay. Transcriptomic analyses show that HsfBA differentially regulates the expression of PilY1 proteins and that the down-regulation of pilY1.1 together with the accumulation of its homologue pilY1.3, allows twitching motility in the absence of EPS. The genetic and bioinformatic dissection of the PilY1.1 domains shows that PilY1.1 might be a bi-functional protein with a role in priming T4P extension mediated by its conserved N-terminal domain and roles in EPS-dependent motility mediated by an N-terminal DUF4114 domain activated upon binding to Ca²⁺. We speculate that the differential transcriptional regulation of PilY1 homologs by HsfBA in response to unknown signals, might allow accessorizing T4P tips with different modules allowing twitching motility in the presence of alternative substrates and environmental conditions.

In the motile bacterium Myxococcus xanthus, T4P mediate twitching motility by binding to the sugar moiety of the extracellular matrix deposited on the neighboring cells or on the substrate. The binding of T4P to these sugars also termed exopolysaccharides (EPS) stimulates the pilus fiber retraction pulling the cell forwards. In this study, we performed a series of genetic analyses leading to the discovery that M. xanthus cells can move in the absence of EPS if two conditions are fulfilled: the pilY1.1 gene is down-regulated and the PilY1.3 protein is accumulated on pili. RNAseq, qRT-PCR and gel retardation assays show that the differential accumulation of PilY1 proteins is under the control of the HsfBA phosphorelay, which up-regulates the expression of pilY1.1 and down-regulates that of a homologue, pilY1.3. We also found that PilY1.1 has a domain at the N terminus probably requiring Ca²⁺ to be active in EPS-dependent motility, and a conserved domain at the C terminus essential for T4P assembly. Conversely, PilY1.3 contains a Von Willebrand factor A (VWA) domain and is potentially involved in the binding to proteins. We speculate that thanks to the HsfBA regulation, T4P can be equipped with different PilY1 homologues to allow twitching motility in the presence of different substrates.

Helical self-assembly of a mucin segment suggests an evolutionary origin for von Willebrand factor tubules

Extracellular proteins with mechanical functions often require specialized assembly processes to form covalent oligomers. Progress in tissue bioengineering and repair will benefit from an understanding of how to harness and manipulate these processes. Here, we show that a particular supramolecular assembly mode was pre-encoded in the ancient domain organization common to gel-forming mucins and von Willebrand factor, glycoproteins that are deceptively different due to their divergence for distinct mechanical tasks. This finding highlights symmetry principles and building blocks retooled in nature to construct polymers with wide-ranging properties. These building blocks and knowledge of their self-assembly can be used to design new polymeric structures.

The glycoprotein von Willebrand factor (VWF) contributes to hemostasis by stanching injuries in blood vessel walls. A distinctive feature of VWF is its assembly into long, helical tubules in endothelial cells prior to secretion. When VWF is released into the bloodstream, these tubules unfurl to release linear polymers that bind subendothelial collagen at wound sites, recruit platelets, and initiate the clotting cascade. VWF evolved from gel-forming mucins, the polymeric glycoproteins that coat and protect exposed epithelia. Despite the divergent function of VWF in blood vessel repair, sequence conservation and shared domain organization imply that VWF retained key aspects of the mucin bioassembly mechanism. Here, we show using cryo-electron microscopy that the ability to form tubules, a property hitherto thought to have arisen as a VWF adaptation to the vasculature, is a feature of the amino-terminal region of mucin. This segment of the human intestinal gel-forming mucin (MUC2) was found to self-assemble into tubules with a striking resemblance to those of VWF itself. To facilitate a comparison, we determined the residue-resolution structure of tubules formed by the homologous segment of VWF. The structures of the MUC2 and VWF tubules revealed the flexible joints and the intermolecular interactions required for tubule formation. Steric constraints in full-length MUC2 suggest that linear filaments, a previously observed supramolecular assembly form, are more likely than tubules to be the physiological mucin storage intermediate. Nevertheless, MUC2 tubules indicate a possible evolutionary origin for VWF tubules and elucidate design principles present in mucins and VWF.

Engineered Molecular Therapeutics Targeting Fibrin and the Coagulation System: a Biophysical Perspective

The coagulation cascade represents a sophisticated and highly choreographed series of molecular events taking place in the blood with important clinical implications. One key player in coagulation is fibrinogen, a highly abundant soluble blood protein that is processed by thrombin proteases at wound sites, triggering self-assembly of an insoluble protein hydrogel known as a fibrin clot. By forming the key protein component of blood clots, fibrin acts as a structural biomaterial with biophysical properties well suited to its role inhibiting fluid flow and maintaining hemostasis. Based on its clinical importance, fibrin is being investigated as a potentially valuable molecular target in the development of coagulation therapies. In this topical review, we summarize our current understanding of the coagulation cascade from a molecular, structural and biophysical perspective. We highlight single-molecule studies on proteins involved in blood coagulation and report on the current state of the art in directed evolution and molecular engineering of fibrin-targeted proteins and polymers for modulating coagulation. This biophysical overview will help acclimatize newcomers to the field and catalyze interdisciplinary work in biomolecular engineering toward the development of new therapies targeting fibrin and the coagulation system.

Thrombosis and Inflammation—A Dynamic Interplay and the Role of Glycosaminoglycans and Activated Protein C

Hemostasis, thrombosis, and inflammation are tightly interconnected processes which may give rise to thrombo-inflammation, involved in infectious and non-infectious acute and chronic diseases, including cardiovascular diseases (CVD). Traditionally, due to its hemostatic role, blood coagulation is isolated from the inflammation, and its critical contribution in the progressing CVD is underrated, until the full occlusion of a critical vessel occurs. Underlying vascular injury exposes extracellular matrix to deposit platelets and inflammatory cells. Platelets being key effector cells, bridge all the three key processes (hemostasis, thrombosis, and inflammation) associated with thrombo-inflammation. Under physiological conditions, platelets remain in an inert state despite the proximity to the endothelium and other cells which are decorated with glycosaminoglycan (GAG)-rich glycocalyx (GAGs). A pathological insult to the endothelium results in an imbalanced blood coagulation system hallmarked by increased thrombin generation due to losses of anticoagulant and cytoprotective mechanisms, i.e., the endothelial GAGs enhancing antithrombin, tissue factor pathway-inhibitor (TFPI) and thrombomodulin-protein C system. Moreover, the loss of GAGs promotes the release of mediators, such as von Willebrand factor (VWF), platelet factor 4 (PF4), and P-selectin, both locally on vascular surfaces and to circulation, further enhancing the adhesion of platelets to the affected sites. Platelet-neutrophil interaction and formation of neutrophil extracellular traps foster thrombo-inflammatory mechanisms exacerbating the cardiovascular disease course. Therefore, therapies which not only target the clotting mechanisms but simultaneously or independently convey potent cytoprotective effects hemming the inflammatory mechanisms are expected to provide clinical benefits. In this regard, we review the cytoprotective protease activated protein C (aPC) and its strong anti-inflammatory effects thereby preventing the ensuing thrombotic complications in CVD. Furthermore, restoring GAG-like vasculo-protection, such as providing heparin-proteoglycan mimetics to improve regulation of platelet and coagulation activity and to suppress of endothelial perturbance and leukocyte-derived pro-inflammatory cytokines, may provide a path to alleviate thrombo-inflammatory disorders in the future. The vascular tissue-modeled heparin proteoglycan mimic, antiplatelet and anticoagulant compound (APAC), dual antiplatelet and anticoagulant, is an injury-targeting and locally acting arterial antithrombotic which downplays collagen- and thrombin-induced and complement-induced activation and protects from organ injury.