Role of fibronectin assembly in platelet thrombus formation

Platelet-targeted gene therapy induces immune tolerance in hemophilia and beyond

Blood platelets have unique storage and delivery capabilities. Platelets play fundamental roles in hemostasis, inflammatory reactions, and immune responses. Beyond their functions, platelets have been used as a target for gene therapy. Platelet-targeted gene therapy aims to deliver a sustained expression of neo-protein in vivo by genetically modifying the target cells, resulting in a cure for the disease. Even though there has been substantial progress in the field of gene therapy, the potential development of immune responses to transgene products or vectors remains a significant concern. Of note, multiple preclinical studies using platelet-specific lentiviral gene delivery to hematopoietic stem cells in hemophilia have demonstrated promising results with therapeutic levels of neo-protein that rescue the hemorrhagic bleeding phenotype and induce antigen-specific immune tolerance. Further studies using ovalbumin as a surrogate protein for platelet gene therapy have shown robust antigen-specific immune tolerance induced via peripheral clonal deletions of antigen-specific CD4- and CD8-T effector cells and induction of antigen-specific regulatory T (Treg) cells. This review discusses platelet-targeted gene therapy, focusing on immune tolerance induction.

Comprehensive multiparameter evaluation of platelet function using a highly sensitive membrane capacitance sensor

An accurate and comprehensive assessment of platelet function is essential for managing patients who receive antiplatelet therapies or require platelet transfusion either for treating active bleeding or for prophylaxis. Platelets contribute to clotting by undergoing a series of highly regulated functional responses including adhesion, spreading, granular secretion, aggregation, and cytoskeletal contraction. However, current platelet function assays evaluate only partial aspects of this intricate process and often under non-physiological testing conditions. Herein, we describe the development of a new approach to measure multiple key platelet function-related parameters, in a more physiologically relevant ex vivo semi-rigid microenvironment using a membrane capacitance sensor (MCS). MCS response to clotting provided three sensing parameters with sensitivities towards platelet counts, stimulation strengths, and activation pathways. Live confocal fluorescent imaging of stimulated platelets on MCS suggests that the presented system can readily and accurately convert the dynamics of cytoskeletal reorganization into analyzable electrical signals. Together, this new completely electrical sensing platform can be a promising diagnostic venue to recognize the impairment of primary hemostatic functions, evaluate the efficacy of therapeutic interventions, and gain further insights into the mechanisms of platelets in hemostasis and thrombosis.

Two-Molecule Force Spectroscopy on Proteins

Many elastomeric proteins, which play important roles in a wide range of biological processes, exist as parallel/antiparallelly arranged dimers or multimers to perform their mechanobiological functions. For example, in striated muscle sarcomeres, the giant muscle protein titin exists as hexameric bundles to mediate the passive elasticity of muscles. However, it has not been possible to directly probe the mechanical properties of such parallelly arranged elastomeric proteins. And it remains unknown if the knowledge obtained from single-molecule force spectroscopy studies can be directly extrapolated to such parallelly/antiparallelly arranged systems. Here, we report the development of atomic force microscopy (AFM)-based two-molecule force spectroscopy to directly probe the mechanical properties of two elastomeric proteins that are arranged in parallel. We developed a twin-molecule approach to allow two parallelly arranged elastomeric proteins to be picked up and stretched simultaneously in an AFM experiment. Our results clearly revealed the mechanical features of such parallelly arranged elastomeric proteins during force-extension measurements and allowed for the determination of mechanical unfolding forces of proteins in such an experimental setting. Our study provides a general and robust experimental strategy to closely mimic the physiological condition of such parallel elastomeric protein multimers.

Monocyte Recruitment for Vascular Tissue Regeneration

A strategy to recruit monocytes (MCs) from blood to regenerate vascular tissue from unseeded (cell-free) tissue engineered vascular grafts is presented. When immobilized on the surface of vascular grafts, the fusion protein, H2R5 can capture blood-derived MC under static or flow conditions in a shear stress dependent manner. The bound MC turns into macrophages (Mϕ) expressing both M1 and M2 phenotype specific genes. When H2R5 functionalized acellular-tissue engineered vessels (A-TEVs) are implanted into the mouse aorta, they remain patent and form a continuous endothelium expressing both endothelial cell (EC) and MC specific proteins. Underneath the EC layer, multiple cells layers are formed coexpressing both smooth muscle cell (SMC) and MC specific markers. Lineage tracing analysis using a novel CX3CR1-confetti mouse model demonstrates that fluorescently labeled MC populates the graft lumen by two and four weeks postimplantation, providing direct evidence in support of MC/Mϕ recruitment to the graft lumen. Given their abundance in the blood, circulating MCs may be a great source of cells that contribute directly to the endothelialization and vascular wall formation of acellular vascular grafts under the right chemical and biomechanical cues.

Adhesion of Bartonella henselae to Fibronectin Is Mediated via Repetitive Motifs Present in the Stalk of Bartonella Adhesin A

Adhesion to host cells is the first and most crucial step in infections with pathogenic Gram-negative bacteria and is often mediated by trimeric autotransporter adhesins (TAAs). Bartonella henselae targets the extracellular matrix glycoprotein fibronectin (Fn) via the Bartonella adhesin A (BadA) attaching the bacteria to the host cell. The TAA BadA is characterized by a highly repetitive passenger domain consisting of 30 neck/stalk domains with various degrees of similarity. To elucidate the motif sequences mediating Fn binding, we generated 10 modified BadA constructs and verified their expression via Western blotting, confocal laser scanning, and electron microscopy. We analyzed their ability to bind human plasma Fn using quantitative whole-cell enzyme-linked immunosorbent assays (ELISAs) and fluorescence microscopy. Polyclonal antibodies targeting a 15-mer amino acid motif sequence proved to reduce Fn binding. We suggest that BadA adheres to Fn in a cumulative effort with quick saturation primarily via unpaired β-strands appearing in motifs repeatedly present throughout the neck/stalk region. In addition, we demonstrated that the length of truncated BadA constructs correlates with the immunoreactivity of human patient sera. The identification of BadA-Fn binding regions will support the development of new "antiadhesive" compounds inhibiting the initial adherence of B. henselae and other TAA-expressing pathogens to host cells. IMPORTANCE Trimeric autotransporter adhesins (TAAs) are important virulence factors and are widely present in various pathogenic Gram-negative bacteria. TAA-expressing bacteria cause a wide spectrum of human diseases, such as cat scratch disease (Bartonella henselae), enterocolitis (Yersinia enterocolitica), meningitis (Neisseria meningitis), and bloodstream infections (multidrug-resistant Acinetobacter baumannii). TAA-targeted antiadhesive strategies (against, e.g., Bartonella adhesin A [BadA], Yersinia adhesin A [YadA], Neisseria adhesin A [NadA], and Acinetobacter trimeric autotransporter [Ata]) might represent a universal strategy to counteract such bacterial infections. BadA is one of the best characterized TAAs, and because of its high number of (sub)domains, it serves as an attractive adhesin to study the domain-function relationship of TAAs in the infection process. The identification of common binding motifs between TAAs (here, BadA) and their major binding partner (here, fibronectin) provides a basis toward the design of novel "antiadhesive" compounds preventing the initial adherence of Gram-negative bacteria in infections.

Dysregulated Hemostasis and Immunothrombosis in Cerebral Cavernous Malformations

Cerebral cavernous malformation (CCM) is a neurovascular disease that affects 0.5% of the general population. For a long time, CCM research focused on genetic mutations, endothelial junctions and proliferation, but recently, transcriptome and proteome studies have revealed that the hemostatic system and neuroinflammation play a crucial role in the development and severity of cavernomas, with some of these publications coming from our group. The aim of this review is to give an overview of the latest molecular insights into the interaction between CCM-deficient endothelial cells with blood components and the neurovascular unit. Specifically, we underscore how endothelial dysfunction can result in dysregulated hemostasis, bleeding, hypoxia and neurological symptoms. We conducted a thorough review of the literature and found a field that is increasingly poised to regard CCM as a hemostatic disease, which may have implications for therapy.

Platelet-Neutrophil Interaction and Thromboinflammation in Diabetes: Considerations for Novel Therapeutic Approaches

Thromboinflammation has become a topic of key interest in cardiovascular disease and the prevention of diabetes complications because of the interplay between thrombosis and inflammation in diabetes. Specifically, the significant risk of vascular thrombotic disease in diabetes highlights the need for new and better therapeutic targets to help manage and prevent vascular thrombo-occlusive disease in this condition. Similarly, the prominent role of inflammation in diabetes has sparked interest in anti-inflammatory agents to better prevent and control vascular disease. Investigations on the effects of anticoagulation and antiplatelet interventions in patients with diabetes and cardiovascular disease show a potential role for these agents in decreasing morbidity and mortality. Neutrophils and platelets are key players in inflammation and wound-healing response, respectively. The interaction between neutrophils and platelets is thought to be an important driver of thromboinflammation. Therefore, this review describes the mechanisms involved in platelet-neutrophil interactions that contribute to the development or exacerbation of thromboinflammation in the context of diabetes and its associated comorbidities. The effects observed by the antithrombotic/antidiabetic treatments and physical activity/dietary interventions on attenuating thromboinflammation are discussed. These data suggest that mechanisms involved in platelet-neutrophil interaction, platelet activation/aggregation, and the recruitment of neutrophils have a promising potential to become therapeutic targets to decrease thromboinflammation in patients with diabetes.

Surface functionalization of anticoagulation and anti-nonspecific adsorption with recombinant hirudin modification

Surface functionalization to improve the blood compatibility is pivotal for the application of biomaterials. In this article, the surface of silicon was first functionalized with chemical groups, such as amino, quinone and phenol groups by the self-polymerization of dopamine, which were used to immobilize anticoagulant drugs hirudin. The detailed analysis and discussion about the grafting groups, morphology, wettability, the dynamic adsorption of proteins, the cytological property and the blood compatibility on the surfaces were carried on by the technology of contact angle, X-ray photoelectron spectroscopy, quartz crystal microbalance, endothelial cells culture and anticoagulant blood test in vivo. The surface with hirudin modification exhibited hydrophilic property and significantly inhibited the nonspecific adsorption of albumin, while it was more approachable to fibronectin. In vitro study displayed that the surface loaded with hirudin could promote the proliferation of endothelial cells. The evaluation of anticoagulant showed good anti-adhesion effect on platelets and the hemolysis rate decreased significantly to less than 0.4%. Activated partial thromboplastin time (APTT) of the silicon wafer loaded with hirudin can exceed 38 s, and the APTT prolongs as the hirudin concentration rises. This study suggested that such simple but effective surface functionalization technique, combining excellent anticoagulant activity together with reendothelialization potential due to the preferable fibronectin adsorption, provide great practical significance to the application of cardiovascular materials.

A novel mouse model of type 2N VWD was developed by CRISPR/Cas9 gene editing and recapitulates human type 2N VWD

A novel type 2N VWD mouse model was established in which VWF is incapable of binding FVIII but is otherwise fully functional.

VWF^2N/2N mice exhibited a severe bleeding phenotype after tail tip amputation but not in lateral tail vein or ventral artery injury models.

Type 2N von Willebrand disease is caused by mutations in the factor VIII (FVIII) binding site of von Willebrand factor (VWF), resulting in dysfunctional VWF with defective binding capacity for FVIII. We developed a novel type 2N mouse model using CRISPR/Cas9 technology. In homozygous VWF^2N/2N mice, plasma VWF levels were normal (1167 ± 257 mU/mL), but the VWF was completely incapable of binding FVIII, resulting in 53 ± 23 mU/mL of plasma FVIII levels that were similar to those in VWF-deficient (VWF^−/−) mice. When wild-type human or mouse VWF was infused into VWF^2N/2N mice, endogenous plasma FVIII was restored, peaking at 4 to 6 hours post-infusion, demonstrating that FVIII expressed in VWF^2N mice is viable but short-lived unprotected in plasma due to dysfunctional 2N VWF. The whole blood clotting time and thrombin generation were impaired in VWF^2N/2N but not in VWF^−/− mice. Bleeding time and blood loss in VWF^2N/2N mice were similar to wild-type mice in the lateral tail vein or ventral artery injury model. However, VWF^2N/2N mice, but not VWF^−/− mice, lost a significant amount of blood during the primary bleeding phase after a tail tip amputation injury model, indicating that alternative pathways can at least partially restore hemostasis when VWF is absent. In summary, we have developed a novel mouse model by gene editing with both the pathophysiology and clinical phenotype found in severe type 2N patients. This unique model can be used to investigate the biological properties of VWF/FVIII association in hemostasis and beyond.

Potential Use of Serum Proteomics for Monitoring COVID-19 Progression to Complement RT-PCR Detection

RT-PCR is the primary method to diagnose COVID-19 and is also used to monitor the disease course. This approach, however, suffers from false negatives due to RNA instability and poses a high risk to medical practitioners. Here, we investigated the potential of using serum proteomics to predict viral nucleic acid positivity during COVID-19. We analyzed the proteome of 275 inactivated serum samples from 54 out of 144 COVID-19 patients and shortlisted 42 regulated proteins in the severe group and 12 in the non-severe group. Using these regulated proteins and several key clinical indexes, including days after symptoms onset, platelet counts, and magnesium, we developed two machine learning models to predict nucleic acid positivity, with an AUC of 0.94 in severe cases and 0.89 in non-severe cases, respectively. Our data suggest the potential of using a serum protein-based machine learning model to monitor COVID-19 progression, thus complementing swab RT-PCR tests. More efforts are required to promote this approach into clinical practice since mass spectrometry-based protein measurement is not currently widely accessible in clinic.

Platelet PD-L1 reflects collective intratumoral PD-L1 expression and predicts immunotherapy response in non-small cell lung cancer

Immune-checkpoint inhibitors (ICI) have transformed oncological therapy. Up to 20% of all non-small cell lung cancers (NSCLCs) show durable responses upon treatment with ICI, however, robust markers to predict therapy response are missing. Here we show that blood platelets interact with lung cancer cells and that PD-L1 protein is transferred from tumor cells to platelets in a fibronectin 1, integrin α5β1 and GPIbα-dependent manner. Platelets from NSCLC patients are found to express PD-L1 and platelet PD-L1 possess the ability to inhibit CD4 and CD8 T-cells. An algorithm is developed to calculate the activation independent adjusted PD-L1 payload of platelets (pPD-L1^Adj.), which is found to be superior in predicting the response towards ICI as compared to standard histological PD-L1 quantification on tumor biopsies. Our data suggest that platelet PD-L1 reflects the collective tumor PD-L1 expression, plays important roles in tumor immune evasion and overcomes limitations of histological quantification of often heterogeneous intratumoral PD-L1 expression.

Fibronectin Molecular Status in Plasma of Women with Endometriosis and Fertility Disorders

The diagnosis of endometriosis and fertility disorders is difficult; therefore, it is necessary to look for reliable biomarkers. Analysis of the molecular status of fibronectin as a key player in repair and wound healing processes, as well as in coagulation and fibrinolysis pathways, is justified. ELISA and SDS-agarose immunoblotting were applied to determine the fibronectin concentration and presence and occurrence of soluble FN-fibrin complexes in the blood plasma of women with endometriosis (n = 38), fertility disorders (n = 28) and the healthy group (n = 25). The concentration of fibronectin in the blood plasma of women with endometriosis (292.61 ± 96.17 mg/L) and fertility disorders (287.53 ± 122.68 mg/L) was significantly higher than in the normal group (226.55 ± 91.98 mg/L). The presence of FN-fibrin complexes of 750, 1000, 1300, 1600 and 1900 kDa in the plasma of women with endometriosis and fertility disorders was shown. The presence of FN-fibrin complexes with a molecular mass of more than 1300 kDa in women with endometriosis and infertility and the complete absence of these complexes in healthy women may indicate an increased and chronic activation of coagulation mechanisms in these patients. The presence of complexes of high molecular mass may be one of the biomarkers of fertility disorders in women.

Protein adsorption/desorption dynamics on Ca-enriched titanium surfaces: biological implications

Calcium ions are used in the development of biomaterials for the promotion of coagulation, bone regeneration, and implant osseointegration. Upon implantation, the time-dependent release of calcium ions from titanium implant surfaces modifies the physicochemical characteristics at the implant-tissue interface and thus, the biological responses. The aim of this study is to examine how the dynamics of protein adsorption on these surfaces change over time. Titanium discs with and without Ca were incubated with human serum for 2 min, 180 min, and 960 min. The layer of proteins attached to the surface was characterised using nLC-MS/MS. The adsorption kinetics was different between materials, revealing an increased adsorption of proteins associated with coagulation and immune responses prior to Ca release. Implant-blood contact experiments confirmed the strong coagulatory effect for Ca surfaces. We employed primary human alveolar osteoblasts and THP-1 monocytes to study the osteogenic and inflammatory responses. In agreement with the proteomic results, Ca-enriched surfaces showed a significant initial inflammation that disappeared once the calcium was released. The distinct protein adsorption/desorption dynamics found in this work demonstrated to be useful to explain the differential biological responses between the titanium and Ca-ion modified implant surfaces.

Pro-Con Debate: Fibrinogen Concentrate or Cryoprecipitate for Treatment of Acquired Hypofibrinogenemia in Cardiac Surgical Patients

Cryoprecipitate has been the gold standard for treating acquired hypofibrinogenemia in cardiac surgery for nearly 50 years. More recently, fibrinogen concentrate has been used off-label in the United States and is the standard in European countries and Canada to treat the acquired hypofibrinogenemia during cardiac surgery. Fibrinogen concentrate has multiple potential advantages including rapid reconstitution, greater dose predictability, viral inactivation during processing, and reduced transfusion-related adverse events. However, because fibrinogen concentrate lacks the other components contained in the cryoprecipitate, it may not be the "ideal" product for replacing fibrinogen in all cardiac surgical patients, particularly those with longer cardiopulmonary bypass duration. In this Pro-Con commentary article, we discuss the advantages and disadvantages of using fibrinogen concentrate and cryoprecipitate to treat acquired hypofibrinogenemia in cardiac surgical patients.

Updated Understanding of Platelets in Thrombosis and Hemostasis: The Roles of Integrin PSI Domains and their Potential as Therapeutic Targets

Platelets are small blood cells known primarily for their ability to adhere and aggregate at injured vessels to arrest bleeding. However, when triggered under pathological conditions, the same adaptive mechanism of platelet adhesion and aggregation may cause thrombosis, a primary cause of heart attack and stroke. Over recent decades, research has made considerable progress in uncovering the intricate and dynamic interactions that regulate these processes. Integrins are heterodimeric cell surface receptors expressed on all metazoan cells that facilitate cell adhesion, movement, and signaling, to drive biological and pathological processes such as thrombosis and hemostasis. Recently, our group discovered that the plexin-semaphorin-integrin (PSI) domains of the integrin β subunits exert endogenous thiol isomerase activity derived from their two highly conserved CXXC active site motifs. Given the importance of redox reactions in integrin activation and its location in the knee region, this PSI domain activity may be critically involved in facilitating the interconversions between integrin conformations. Our monoclonal antibodies against the β3 PSI domain inhibited its thiol isomerase activity and proportionally attenuated fibrinogen binding and platelet aggregation. Notably, these antibodies inhibited thrombosis without significantly impairing hemostasis or causing platelet clearance. In this review, we will update mechanisms of thrombosis and hemostasis, including platelet versatilities and immune-mediated thrombocytopenia, discuss critical contributions of the newly discovered PSI domain thiol isomerase activity, and its potential as a novel target for anti-thrombotic therapies and beyond.

Extracellular matrix and its therapeutic potential for cancer treatment

The extracellular matrix (ECM) is one of the major components of tumors that plays multiple crucial roles, including mechanical support, modulation of the microenvironment, and a source of signaling molecules. The quantity and cross-linking status of ECM components are major factors determining tissue stiffness. During tumorigenesis, the interplay between cancer cells and the tumor microenvironment (TME) often results in the stiffness of the ECM, leading to aberrant mechanotransduction and further malignant transformation. Therefore, a comprehensive understanding of ECM dysregulation in the TME would contribute to the discovery of promising therapeutic targets for cancer treatment. Herein, we summarized the knowledge concerning the following: (1) major ECM constituents and their functions in both normal and malignant conditions; (2) the interplay between cancer cells and the ECM in the TME; (3) key receptors for mechanotransduction and their alteration during carcinogenesis; and (4) the current therapeutic strategies targeting aberrant ECM for cancer treatment.

Successful Infliximab Treatment is Associated With Reversal of Clotting Abnormalities in Inflammatory Bowel Disease Patients

BACKGROUND AND GOALS

Active inflammatory bowel diseases (IBD) represent an independent risk factor for venous thromboembolism. The authors investigated the hemostatic profile of IBD patients before and after induction treatment with infliximab, vedolizumab, and methylprednisolone.

STUDY

This prospective study included 62 patients with active IBD starting infliximab, vedolizumab, and/or methylprednisolone, and 22 healthy controls (HC). Plasma was collected before (w0) and after induction therapy (w14). Using a clot lysis assay, amplitude (marker for clot intensity), time to peak (Tmax; marker for clot formation rate), area under the curve (AUC; global marker for coagulation/fibrinolysis), and 50% clot lysis time (50%CLT; marker for fibrinolytic capacity) were determined. Plasminogen activator inhibitor-1 (PAI-1) and fibronectin were measured by ELISA. Clinical remission was evaluated at w14.

RESULTS

At baseline, AUC, amplitude, and 50%CLT were significantly higher in IBD patients as compared with HC. In 34 remitters, AUC [165 (103-229)% vs. 97 (78-147)%, P=0.001], amplitude [119 (99-163)% vs. 95 (82-117)%, P=0.002], and 50%CLT [122 (94-146)% vs. 100 (87-129)%, P=0.001] decreased significantly and even normalized to the HC level. Vedolizumab trough concentration correlated inversely to fibronectin concentration (r, -0.732; P=0.002). The increase in Tmax for infliximab-treated remitters was significantly different from the decrease in Tmax for vedolizumab-treated remitters (P=0.028). The 50%CLT increased (P=0.038) when remitters were concomitantly treated with methylprednisolone.

CONCLUSIONS

Control of inflammation using infliximab most strongly reduced those parameters that are associated with a higher risk of venous thromboembolism.

What Makes Wounds Chronic

Chronic wounds present a unique therapeutic challenge to heal. Chronic wounds are colonized with bacteria and the presence of a biofilm that further inhibits the normal wound healing processes, and are locked into a very damaging proinflammatory response. The treatment of chronic wounds requires a coordinated approach, including debridement of devitalized tissue, minimizing bacteria and biofilm, control of inflammation, and the use of specialized dressings to address the specific aspects of the particular nonhealing ulcer.

Contribution of exome sequencing to the identification of genes involved in the response to clopidogrel in cardiovascular patients

BACKGROUND

On-clopidogrel platelet reactivity (PR) is associated with the risk of thrombotic or bleeding event in selected populations of high-risk patients. PR is a highly heritable phenotype and a few variants of cytochrome genes, essentially CYP2C19, are associated with PR but only explain 5% to 12% of the variability.

OBJECTIVE

The aim of this study is to delineate genetic determinants of on-clopidogrel PR using high-throughput sequencing.

METHODS

We performed a whole exome sequencing of 96 low- and matched high-PR patients in a discovery cohort. Exomes from genes with variants significantly associated with PR were sequenced in 96 low- and matched high-PR patients from an independent replication cohort.

RESULTS

We identified 585 variants in 417 genes with an adjusted P value < .05. In the replication cohort, all top variants including CYP2C8, CYP2C18, and CYP2C19 from the discovery population were found again. An original network analysis identified several candidate genes of potential interest such as a regulator of PI3K, a key actor in the downstream signaling pathway of the P2Y12 receptor.

CONCLUSION

This study emphasizes the role of CYP-related genes as major regulators of clopidogrel response, including the poorly investigated CYP2C8 and CYP2C18.

Interaction with the host: the role of fibronectin and extracellular matrix proteins in the adhesion of Gram-negative bacteria

The capacity of pathogenic microorganisms to adhere to host cells and avoid clearance by the host immune system is the initial and most decisive step leading to infections. Bacteria have developed different strategies to attach to diverse host surface structures. One important strategy is the adhesion to extracellular matrix (ECM) proteins (e.g., collagen, fibronectin, laminin) that are highly abundant in connective tissue and basement membranes. Gram-negative bacteria express variable outer membrane proteins (adhesins) to attach to the host and to initiate the process of infection. Understanding the underlying molecular mechanisms of bacterial adhesion is a prerequisite for targeting this interaction by “anti-ligands” to prevent colonization or infection of the host. Future development of such “anti-ligands” (specifically interfering with bacteria-host matrix interactions) might result in the development of a new class of anti-infective drugs for the therapy of infections caused by multidrug-resistant Gram-negative bacteria. This review summarizes our current knowledge about the manifold interactions of adhesins expressed by Gram-negative bacteria with ECM proteins and the use of this information for the generation of novel therapeutic antivirulence strategies.

The impact of GPIbα on platelet-targeted FVIII gene therapy in hemophilia A mice with pre-existing anti-FVIII immunity

Essentials Platelet-specific FVIII gene therapy is effective in hemophilia A mice even with inhibitors. The impact of platelet adherence via VWF/GPIbα binding on platelet gene therapy was investigated. GPIbα does not significantly affect platelet gene therapy of hemophilia A with inhibitors. Platelet gene therapy induces immune tolerance in hemophilia A mice with pre-existing immunity. SUMMARY: Background We have previously demonstrated that von Willebrand factor (VWF) is essential in platelet-specific FVIII (2bF8) gene therapy of hemophilia A (HA) with inhibitory antibodies (inhibitors). At the site of injury, platelet adherence is initiated by VWF binding to the platelet GPIb complex. Objective To investigate the impact of GPIbα on platelet gene therapy of HA with inhibitors. Methods Platelet-FVIII expression was introduced by 2bF8 lentivirus (2bF8LV) transduction of hematopoietic stem cells (HSCs) from GPIbαnull (Ibnull ) mice or rhF8-primed FVIIInull (F8null ) mice followed by transplantation into lethally irradiated rhF8-primed F8null recipients. Animals were analyzed by flow cytometry, FVIII assays and the tail bleeding test. Results After transplantation, 99% of platelets were derived from donors. The macrothrombocytopenia phenotype was maintained in F8null mice that received 2bF8LV-transduced Ibnull HSCs (2bF8-Ibnull /F8null ). The platelet-FVIII expression level in 2bF8-Ibnull /F8null recipients was similar to that obtained from F8null mice that received 2bF8LV-transduced F8null HSCs (2bF8-F8null /F8null ). The tail bleeding test showed that the remaining hemoglobin level in the 2bF8-Ibnull /F8null group was significantly higher than in the F8null control group, but there was no significant difference between the 2bF8-Ibnull /F8null and 2bF8-F8null /F8null groups. The half-life of inhibitor disappearance time was comparable between the 2bF8-Ibnull /F8null and 2bF8-F8null /F8null groups. The rhF8 re-challenge did not elicit a memory immune response once inhibitor titers dropped to undetectable levels after 2bF8 gene therapy. Conclusion GPIbα does not significantly impact platelet gene therapy of HA with inhibitors. 2bF8 gene therapy restores hemostasis and promotes immune tolerance in HA mice with pre-existing immunity.

The Molecular Dance of Fibronectin: Conformational Flexibility Leads to Functional Versatility

Fibronectin, a large multimodular protein and one of the major fibrillar components of the extracellular matrix, has been the subject of study for many decades and plays critical roles in embryonic development and tissue homeostasis. Moreover, fibronectin has been implicated in the pathology of many diseases, including cancer, and abnormal depositions of fibronectin have been identified in a number of amyloid and nonamyloid lesions. The ability of fibronectin to carry all these diverse functionalities depends on interactions with a large number of molecules, including adhesive and signaling cell surface receptors, other components of the extracellular matrix, and growth factors and cytokines. The regulation and integration of such large number of interactions depends on the modular architecture of fibronectin, which allows a large number of conformations, exposing or destroying different binding sites. In this Review, we summarize the current knowledge regarding the conformational flexibility of fibronectin, with an emphasis on how it regulates the ability of fibronectin to interact with various signaling molecules and cell-surface receptors and to form supramolecular assemblies and fibrillar structures.

Evaluation of Cellular Fibronectin Plasma Levels as a Useful Staging Tool in Different Stages of Transitional Cell Carcinoma of the Bladder and Renal Cell Carcinoma

Reliable markers for both renal cell carcinoma (RCC) and transitional cell carcinoma of the bladder (TCC) are lacking.

During tumor progression and invasion components of extracellular matrix (ECM) are degraded and parts of these different components are detectable in plasma. Cellular fibronectin (cFN) represents a well characterized ECM protein. In contrast to fibronectin in plasma produced by hepatocytes (FN) cFN has a total extra domain sequence and occurs in much smaller amounts in the circulation. The aim of our study was to evaluate cFN as a marker and to determine its possible role in clinical staging of TCC and RCC.

Blood samples were collected from 30 patients before they underwent transurethral resection of the bladder because of newly diagnosed TCC. Additionally samples were collected from 69 patients with RCC before therapy. Sixty patients with non-malignant urological disorders were recruited as control group. Determination of cFN in plasma was performed by using a highly sensitive time-resolved fluorescence immunoassay (TRFIA).

The control group had median cFN plasma levels of 437 ng/ml. Patients suffering from TCC or RCC showed significantly higher cFN levels. In patients with muscle invasive TCC significant higher cFN levels (p < 0.05) could be demonstrated compared to non-muscle invasive TCC. Similar results were found in RCC with significant elevated cFN levels in metastatic RCC (p < 0.005) compared to localized stage of disease. No differences were found concerning tumor grading in both malignancies.

In the face of significant elevated cFN levels in TCC and RCC our data underline the important role of cFN. For future investigations the elevated cFN levels in locally progressed and metastastic disease, indicating a clinically useful tool for preoperative staging and postoperative monitoring, are of high interest.

Platelets as crucial partners for tumor metastasis: from mechanistic aspects to pharmacological targeting

Platelets are anucleated cells that circulate in the blood as sentinels of tissue integrity. In fact, they are rich in a plethora of proteins and other factors stored in different granules which they selectively release upon stimulation. Moreover, platelets synthesize a vast number of lipids and release various types of vesicles, including exosomes which are rich in genetic material. Platelets possess a central function to interact with other cell types, including inflammatory cells and cancer cells. Recent findings have enlightened the capacity of platelets to induce changes in the phenotype of cancer cells which acquire invasiveness thus enhancing their metastatic potential. Thus, it has been hypothesized that targeting the platelet may represent a novel strategy to prevent the development and progression of cancer. This is supported by the efficacy of the antiplatelet agent low-dose aspirin. Studies are ongoing to verify whether other antiplatelet agents share the anticancer effectiveness of aspirin.

Interplay between elevated cellular fibronectin and plasma fibrin clot properties in type 2 diabetes

Type 2 diabetes is associated with faster formation of poorly lysable, denser fibrin clots and elevated cellular fibronectin (cFn), a marker of vascular injury. We investigated whether cFn affects clot properties in type 2 diabetes. In 200 consecutive patients with type 2 diabetes and 100 control subjects matched for age and sex, we determined plasma cFn along with clot formation and degradation using turbidimetric and permeability assays. Diabetic patients had elevated cFn (median, 3.99 [interquartile range, 2.87-4.81] µg/ml]), increased clot density (MaxAbsC) and prolonged lysis time (LysT) compared with those without type 2 diabetes (all p<0.01). Diabetic patients with documented cardiovascular disease (CVD, n=127, 63.5 %) had increased cFn (4.53 [3.68-4.95] µg/ml), decreased clot permeability (Ks) and increased MaxAbsC compared with those without CVD (all p<0.001). Diabetic patients with cFn in the top quartile (>4.81 µg/ml) were two times more likely to have CVD compared with those in the lowest quartile (odds ratio 1.80, 95 % confidence interval 1.41-2.46, p<0.001). No differences in cFn were observed in relation to microvascular complications. After adjustment for potential confounders, cFn accounted for 10.2 % of variance in Ks, 18.2 % of variance in clot density and 10.2 % of variance in AUC in diabetic patients. This study shows that elevated cFn is associated with unfavourably modified clot properties in type 2 diabetes, especially with concomitant CVD, which indicates novel links between vascular injury and prothrombotic alterations in diabetes. Coagulation, cellular fibronectin, type 2 diabetes, cardiovascular disease.

Comprehensive Gene expression meta-analysis and integrated bioinformatic approaches reveal shared signatures between thrombosis and myeloproliferative disorders

Thrombosis is a leading cause of morbidity and mortality in patients with myeloproliferative disorders (MPDs), particularly polycythemia vera (PV) and essential thrombocythemia (ET). Despite the attempts to establish a link between them, the shared biological mechanisms are yet to be characterized. An integrated gene expression meta-analysis of five independent publicly available microarray data of the three diseases was conducted to identify shared gene expression signatures and overlapping biological processes. Using INMEX bioinformatic tool, based on combined Effect Size (ES) approaches, we identified a total of 1,157 differentially expressed genes (DEGs) (697 overexpressed and 460 underexpressed genes) shared between the three diseases. EnrichR tool's rich library was used for comprehensive functional enrichment and pathway analysis which revealed "mRNA Splicing" and "SUMO E3 ligases SUMOylate target proteins" among the most enriched terms. Network based meta-analysis identified MYC and FN1 to be the most highly ranked hub genes. Our results reveal that the alterations in biomarkers of the coagulation cascade like F2R, PROS1, SELPLG and ITGB2 were common between the three diseases. Interestingly, the study has generated a novel database of candidate genetic markers, pathways and transcription factors shared between thrombosis and MPDs, which might aid in the development of prognostic therapeutic biomarkers.

Fibronectin maintains the balance between hemostasis and thrombosis

Fibronectin is a dimeric protein widely distributed in solid tissues and blood. This major extracellular matrix protein is indispensable for embryogenesis and plays crucial roles in many physiological and pathological processes. Fibronectin pre-mRNA undergoes alternative splicing to generate over 20 splicing variants, which are categorized as either plasma fibronectin (pFn) or cellular fibronectin (cFn). All fibronectin variants contain integrin binding motifs, as well as N-terminus collagen and fibrin binding motifs. With motifs that can be recognized by platelet integrins and coagulation factors, fibronectin, especially pFn, has long been suspected to be involved in hemostasis and thrombosis, but the exact function of fibronectin in these processes is controversial. The advances made using intravital microscopy models and fibronectin deficient and mutant mice have greatly facilitated the direct investigation of fibronectin function in vivo. Recent studies revealed that pFn is a vital hemostatic factor that is especially crucial for hemostasis in both genetic and anticoagulant-induced deficiencies of fibrin formation. pFn may also be an important self-limiting regulator to prevent hemorrhage as well as excessive thrombus formation and vessel occlusion. In addition to pFn, cFn is found to be prothrombotic and may contribute to thrombotic complications in various diseases. Further investigations of the role of pFn and cFn in thrombotic and hemorrhagic diseases may provide insights into development of novel therapeutic strategies (e.g., pFn transfusion) for the maintenance of the fine balance between hemostasis and thrombosis.

Dynamic structure of plasma fibronectin

Fibronectin is a large vertebrate glycoprotein that is found in soluble and insoluble forms and involved in diverse processes. Protomeric fibronectin is a dimer of subunits, each of which comprises 29-31 modules - 12 type I, two type II and 15-17 type III. Plasma fibronectin is secreted by hepatocytes and circulates in a compact conformation before it binds to cell surfaces, converts to an extended conformation and is assembled into fibronectin fibrils. Here we review biophysical and structural studies that have shed light on how plasma fibronectin transitions from the compact to the extended conformation. The three types of modules each have a well-organized secondary and tertiary structure as defined by NMR and crystallography and have been likened to "beads on a string". There are flexible sequences in the N-terminal tail, between the fifth and sixth type I modules, between the first two and last two of the type III modules, and at the C-terminus. Several specific module-module interactions have been identified that likely maintain the compact quaternary structure of circulating fibronectin. The quaternary structure is perturbed in response to binding events, including binding of fibronectin to the surface of vertebrate cells for fibril assembly and to bacterial adhesins.

A multiple-phenotype imputation method for genetic studies

Genetic association studies have yielded a wealth of biological discoveries. However, these studies have mostly analyzed one trait and one SNP at a time, thus failing to capture the underlying complexity of the data sets. Joint genotype-phenotype analyses of complex, high-dimensional data sets represent an important way to move beyond simple genome-wide association studies (GWAS) with great potential. The move to high-dimensional phenotypes will raise many new statistical problems. Here we address the central issue of missing phenotypes in studies with any level of relatedness between samples. We propose a multiple-phenotype mixed model and use a computationally efficient variational Bayesian algorithm to fit the model. On a variety of simulated and real data sets from a range of organisms and trait types, we show that our method outperforms existing state-of-the-art methods from the statistics and machine learning literature and can boost signals of association.

The N-terminal domain of the thermo-regulated surface protein PrpA of Enterococcus faecium binds to fibrinogen, fibronectin and platelets

Enterococcus faecium is a commensal of the mammalian gastrointestinal tract, but is also found in non-enteric environments where it can grow between 10 °C and 45 °C. E. faecium has recently emerged as a multi-drug resistant nosocomial pathogen. We hypothesized that genes involved in the colonization and infection of mammals exhibit temperature-regulated expression control and we therefore performed a transcriptome analysis of the clinical isolate E. faecium E1162, during mid-exponential growth at 25 °C and 37 °C. One of the genes that exhibited differential expression between 25 °C and 37 °C, was predicted to encode a peptidoglycan-anchored surface protein. The N-terminal domain of this protein is unique to E. faecium and closely related enterococci, while the C-terminal domain is homologous to the Streptococcus agalactiae surface protein BibA. This region of the protein contains proline-rich repeats, leading us to name the protein PrpA for proline-rich protein A. We found that PrpA is a surface-exposed protein which is most abundant during exponential growth at 37 °C in E. faecium E1162. The heterologously expressed and purified N-terminal domain of PrpA was able to bind to the extracellular matrix proteins fibrinogen and fibronectin. In addition, the N-terminal domain of PrpA interacted with both non-activated and activated platelets.

Influenza Virus Infection Induces Platelet-Endothelial Adhesion Which Contributes to Lung Injury

Lung injury after influenza infection is characterized by increased permeability of the lung microvasculature, culminating in acute respiratory failure. Platelets interact with activated endothelial cells and have been implicated in the pathogenesis of some forms of acute lung injury. Autopsy studies have revealed pulmonary microthrombi after influenza infection, and epidemiological studies suggest that influenza vaccination is protective against pulmonary thromboembolism; however, the effect of influenza infection on platelet-endothelial interactions is unclear. We demonstrate that endothelial infection with both laboratory and clinical strains of influenza virus increased the adhesion of human platelets to primary human lung microvascular endothelial cells. Platelets adhered to infected cells as well as to neighboring cells, suggesting a paracrine effect. Influenza infection caused the upregulation of von Willebrand factor and ICAM-1, but blocking these receptors did not prevent platelet-endothelial adhesion. Instead, platelet adhesion was inhibited by both RGDS peptide and a blocking antibody to platelet integrin α5β1, implicating endothelial fibronectin. Concordantly, lung histology from infected mice revealed viral dose-dependent colocalization of viral nucleoprotein and the endothelial marker PECAM-1, while platelet adhesion and fibronectin deposition also were observed in the lungs of influenza-infected mice. Inhibition of platelets using acetylsalicylic acid significantly improved survival, a finding confirmed using a second antiplatelet agent. Thus, influenza infection induces platelet-lung endothelial adhesion via fibronectin, contributing to mortality from acute lung injury. The inhibition of platelets may constitute a practical adjunctive strategy to the treatment of severe infections with influenza.IMPORTANCE There is growing appreciation of the involvement of the lung endothelium in the pathogenesis of severe infections with influenza virus. We have recently shown that the virus can infect human lung endothelial cells, but the functional consequences of this infection are unknown (S. M. Armstrong, C. Wang, J. Tigdi, X. Si, C. Dumpit, S. Charles, A. Gamage, T. J. Moraes, and W. L. Lee, PLoS One 7:e47323, 2012, http://dx.doi.org/10.1371/journal.pone.0047323). Here, we show that this infection causes platelets to adhere to the lung endothelium. Importantly, blocking platelets using two distinct antiplatelet drugs improved survival in a mouse model of severe influenza infection. Thus, platelet inhibition may constitute a novel therapeutic strategy to improve the host response to severe infections with influenza.

Hemolysis exacerbates hyperfibrinolysis, whereas platelolysis shuts down fibrinolysis: evolving concepts of the spectrum of fibrinolysis in response to severe injury

INTRODUCTION

We have recently identified a spectrum of fibrinolysis in response to injury, in which there is increased mortality in patients who have either excessive fibrinolysis (hyperfibrinolysis [HF]) or impaired fibrinolysis (shutdown). The regulation of the fibrinolytic system after trauma remains poorly understood. Our group's previous proteomic and metabolomic work identified elevated red blood cell (RBC) degradation products in trauma patients manifesting HF. We therefore hypothesized that hemolysis was contributory to the pathogenesis of HF. Given the central role of platelets in the cell-based model of coagulation, we further investigated the potential role of platelet lysis in mediation of the fibrinolytic system.

METHODS

Red blood cells from healthy donors were frozen in liquid nitrogen and vortexed to create mechanical membrane disruption. Platelets were prepared in a similar fashion. Assays were performed with citrated whole blood mixed ex vivo with either RBC or platelet lysates. Tissue plasminogen activator (tPA) was then added to promote fibrinolysis, mimicking the tPA release from ischemic endothelium during hemorrhagic shock. The degree of fibrinolysis was evaluated with thromboelastography. To identify the mediators of the fibrinolysis system present in RBC and platelet lysates, these lysates were passed over immobilized tPA and plasminogen affinity columns to capture protein-binding partners from RBC or platelet lysates.

RESULTS

The addition of 75 ng/mL of tPA to whole blood increased fibrinolysis from median 30-min lysis of 1.4% (interquartile range [IQR], 0.9%-2.0%) to 8.9% (IQR, 6.5%-11.5%). Red blood cell lysate with tPA increased fibrinolysis to 20.1% (IQR, 12.5%-33.7%), which was nearly three times as much lysis as tPA alone (P < 0.001). Conversely, the addition of platelet lysate decreased tPA-mediated fibrinolysis to 0.35% (IQR, 0.2%-0.8%; P < 0.001). Affinity chromatography coupled with tandem mass spectrometry identified a number of proteins not previously associated with regulation of fibrinolysis and trauma.

CONCLUSION

Red blood cell lysate is a potent enhancer of fibrinolysis, whereas platelet lysate inhibits fibrinolysis. Intracellular proteins from circulating blood cells contain proteins that interact with the two key proteins of tPA-mediated fibrinolysis. Understanding the effect of tissue injury and shock on the lysis of circulating cells may provide insight to comprehending the spectrum of fibrinolysis in response to trauma.

Treponema pallidum subsp. pallidum TP0136 protein is heterogeneous among isolates and binds cellular and plasma fibronectin via its NH2-terminal end

Adherence-mediated colonization plays an important role in pathogenesis of microbial infections, particularly those caused by extracellular pathogens responsible for systemic diseases, such as Treponema pallidum subsp. pallidum (T. pallidum), the agent of syphilis. Among T. pallidum adhesins, TP0136 is known to bind fibronectin (Fn), an important constituent of the host extracellular matrix. To deepen our understanding of the TP0136-Fn interaction dynamics, we used two naturally-occurring sequence variants of the TP0136 protein to investigate which region of the protein is responsible for Fn binding, and whether TP0136 would adhere to human cellular Fn in addition to plasma Fn and super Fn as previously reported. Fn binding assays were performed with recombinant proteins representing the two full-length TP0136 variants and their discrete regions. As a complementary approach, we tested inhibition of T. pallidum binding to Fn by recombinant full-length TP0136 proteins and fragments, as well as by anti-TP0136 immune sera. Our results show that TP0136 adheres more efficiently to cellular Fn than to plasma Fn, that the TP0136 NH2-terminal conserved region of the protein is primarily responsible for binding to plasma Fn but that binding sites for cellular Fn are also present in the protein’s central and COOH-terminal regions. Additionally, message quantification studies show that tp0136 is highly transcribed during experimental infection, and that its message level increases in parallel to the host immune pressure on the pathogen, which suggests a possible role for this protein in T. pallidum persistence. In a time where syphilis incidence is high, our data will help in the quest to identify suitable targets for development of a much needed vaccine against this important disease.

The study of Treponema pallidum subsp. pallidum (T. pallidum) proteins that mediate adhesion to host tissue components is pivotal to understand how the syphilis agent establishes infection and is able to invade virtually every organ system following dissemination from the site of entry. This study focuses on T. pallidum TP0136, a known plasma fibronectin (Fn) and super Fn binding protein that is heterogeneous in sequence among T. pallidum isolates. This study shows that TP0136 also mediates attachment to human cellular Fn, that TP0136 conserved NH₂-terminus is primarily responsible for binding to plasma Fn, but that cellular Fn binding sites appears to be scattered throughout the molecule. Message quantification experiments reveal that tp0136 transcription is high during experimental syphilis and increases at the time of bacterial immune clearance, suggesting a role for this antigen in counteracting the host defenses during infection, as reported for other Fn binding proteins in other pathogens. Our data deepen the current knowledge of the function of T. pallidum TP0136 and further support a role for this virulence factor in syphilis pathogenesis.

Cellular fibronectin containing extra domain A promotes arterial thrombosis in mice through platelet Toll-like receptor 4

Cellular fibronectin containing extra domain A (Fn-EDA+), which is produced in response to tissue injury in several disease states, has prothrombotic activity and is known to interact with Toll-like-receptor 4 (TLR4). The underlying mechanism and cell types involved in mediating the prothrombotic effect of Fn-EDA+ still remain unknown. Using intravital microscopy, we evaluated susceptibility to carotid artery thrombosis after FeCl3-induced injury in mice expressing Fn lacking EDA (Fn-EDA(-/-) mice) or Fn containing EDA (Fn-EDA(+/+) mice). Fn-EDA(-/-) mice exhibited prolonged times to first thrombus formation and complete occlusion and a significant decrease in the rate of thrombus growth (P < .05 vs Fn-EDA(+/+) mice). Genetic deletion of TLR4 reversed the accelerated thrombosis in Fn-EDA(+/+) mice (P < .05) but had no effect in Fn-EDA(-/-) mice. Bone marrow transplantation experiments revealed that TLR4 expressed on hematopoietic cells contributes to accelerated thrombosis in Fn-EDA(+/+) mice. In vitro studies showed that cellular Fn-EDA+ interacts with platelet TLR4 and promotes agonist-induced platelet aggregation. Finally, Fn-EDA(+/+) mice specifically lacking platelet TLR4 exhibited prolonged times to first thrombus formation and complete occlusion (P < .05 vs Fn-EDA(+/+) mice containing platelet TLR4). We conclude that platelet TLR4 contributes to the prothrombotic effect of cellular Fn-EDA+, suggesting another link between thrombosis and innate immunity.

Involvement of platelet-tumor cell interaction in immune evasion. Potential role of podocalyxin-like protein 1

Besides their essential role in hemostasis and thrombosis, platelets are involved in the onset of cancer metastasis by interacting with tumor cells. Platelets release secretory factors that promote tumor growth, angiogenesis, and metastasis. Furthermore, the formation of platelet-tumor cell aggregates in the bloodstream provides cancer cells with an immune escape mechanism by protecting circulating malignant cells from immune-mediated lysis by natural killer (NK) cells. Platelet-tumor cell interaction is accomplished by specific adhesion molecules, including integrins, selectins, and their ligands. Podocalyxin-like protein 1 (PCLP1) is a selectin-ligand protein in which overexpression has been associated with several aggressive cancers. PCLP1 expression enhances cell adherence to platelets in an integrin-dependent process and through the interaction with P-selectin expressed on activated platelets. However, the involvement of PCLP1-induced tumor-platelet interaction in tumor immune evasion still remains unexplored. The identification of selectin ligands involved in the interaction of platelets with tumor cells may provide help for the development of effective therapies to restrain cancer cell dissemination. This article summarizes the current knowledge on molecules that participate in platelet-tumor cell interaction as well as discusses the potential role of PCLP1 as a molecule implicated in tumor immune evasion.

Plasma fibronectin supports hemostasis and regulates thrombosis

Plasma fibronectin (pFn) has long been suspected to be involved in hemostasis; however, direct evidence has been lacking. Here, we demonstrated that pFn is vital to control bleeding in fibrinogen-deficient mice and in WT mice given anticoagulants. At the site of vessel injury, pFn was rapidly deposited and initiated hemostasis, even before platelet accumulation, which is considered the first wave of hemostasis. This pFn deposition was independent of fibrinogen, von Willebrand factor, β3 integrin, and platelets. Confocal and scanning electron microscopy revealed pFn integration into fibrin, which increased fibrin fiber diameter and enhanced the mechanical strength of clots, as determined by thromboelastography. Interestingly, pFn promoted platelet aggregation when linked with fibrin but inhibited this process when fibrin was absent. Therefore, pFn may gradually switch from supporting hemostasis to inhibiting thrombosis and vessel occlusion following the fibrin gradient that decreases farther from the injured endothelium. Our data indicate that pFn is a supportive factor in hemostasis, which is vital under both genetic and therapeutic conditions of coagulation deficiency. By interacting with fibrin and platelet β3 integrin, pFn plays a self-limiting regulatory role in thrombosis, suggesting pFn transfusion may be a potential therapy for bleeding disorders, particularly in association with anticoagulant therapy.

LC-MS/MS analysis and comparison of oxidative damages on peptides induced by pathogen reduction technologies for platelets

Pathogen reduction technologies (PRT) are photochemical processes that use a combination of photosensitizers and UV-light to inactivate pathogens in platelet concentrates (PCs), a blood-derived product used to prevent hemorrhage. However, different studies have questioned the impact of PRT on platelet function and transfusion efficacy, and several proteomic analyses revealed possible oxidative damages to proteins. The present work focused on the oxidative damages produced by the two main PRT on peptides. Model peptides containing residues prone to oxidation (tyrosine, histidine, tryptophane, and cysteine) were irradiated with a combination of amotosalen/UVA (Intercept process) or riboflavin/UVB (Mirasol-like process). Modifications were identified and quantified by liquid chromatography coupled to tandem mass spectrometry. Cysteine-containing peptides formed disulfide bridges (R-SS-R, -2 Da; favored following amotosalen/UVA), sulfenic and sulfonic acids (R-SOH, +16 Da, R-SO3H, +48 Da, favored following riboflavin/UVB) upon treatment and the other amino acids exhibited different oxidations revealed by mass shifts from +4 to +34 Da involving different mechanisms; no photoadducts were detected. These amino acids were not equally affected by the PRT and the combination riboflavin/UVB generated more oxidation than amotosalen/UVA. This work identifies the different types and sites of peptide oxidations under the photochemical treatments and demonstrates that the two PRT may behave differently. The potential impact on proteins and platelet functions may thus be PRT-dependent.

The multifunctional role of the pallilysin-associated Treponema pallidum protein, Tp0750, in promoting fibrinolysis and extracellular matrix component degradation

The mechanisms that facilitate dissemination of the highly invasive spirochaete, Treponema pallidum, are incompletely understood. Previous studies showed the treponemal metalloprotease pallilysin (Tp0751) possesses fibrin clot degradation capability, suggesting a role in treponemal dissemination. In the current study we report characterization of the functionally linked protein Tp0750. Structural modelling predicts Tp0750 contains a von Willebrand factor type A (vWFA) domain, a protein-protein interaction domain commonly observed in extracellular matrix (ECM)-binding proteins. We report Tp0750 is a serine protease that degrades the major clot components fibrinogen and fibronectin. We also demonstrate Tp0750 cleaves a matrix metalloprotease (MMP) peptide substrate that is targeted by several MMPs, enzymes central to ECM remodelling. Through proteomic analyses we show Tp0750 binds the endothelial fibrinolytic receptor, annexin A2, in a specific and dose-dependent manner. These results suggest Tp0750 constitutes a multifunctional protein that is able to (1) degrade infection-limiting clots by both inhibiting clot formation through degradation of host coagulation cascade proteins and promoting clot dissolution by complexing with host proteins involved in the fibrinolytic cascade and (2) facilitate ECM degradation via MMP-like proteolysis of host components. We propose that through these activities Tp0750 functions in concert with pallilysin to enable T. pallidum dissemination.

Contribution of distinct platelet integrins to binding, unfolding, and assembly of fibronectin

Fibronectin (FN) fibrillogenesis depends on the binding of FN to cellular receptors and subsequent unfolding of bound FN. Integrins αIIbβ3, αvβ3, and α5β1 are known to assemble FN fibrils on platelets. In our study, we examined the contribution of these integrins to FN binding, unfolding, and assembly on platelets in suspension and adherent platelets in the presence or absence of agonists. Phorbol 12-myristate 13-acetate (PMA), but not adenosine diphosphate (ADP), induced binding of FN to platelets in suspension. In contrast, adherent platelets were able to deposit FN on their surfaces in the absence of agonists. β3 integrins had a major impact on the interaction of FN on platelets. αvβ3 showed a similar contribution to the binding of FN as αIIbβ3 on PMA-stimulated platelets in suspension but had a lesser contribution to unfolding and deposition of FN on adherent platelets. α5β1 also participated in the interaction of FN with platelets by mediating the unfolding and assembly of FN, but to a lesser extent than β3 integrins. None of the distinct antibodies directed against one of the three integrins caused a complete inhibition of binding, unfolding, and assembly of FN by platelets. Thus, it is likely that αIIbβ3, αvβ3, and α5β1 or another still unknown receptor can be substituted.

Shear-related fibrillogenesis of fibronectin

Biomechanical forces can induce the transformation of fibronectin (Fn) from its compact structure to an extended fibrillar state. Adsorption of plasma proteins onto metallic surfaces may also influence their conformation. We used a cone-plate rheometer to investigate the effect of shear and stainless steel on conformational changes of Fn. In control experiments, cones grafted once or twice with polyethylene glycol were used. Plasma Fn was added at concentrations of 50 or 100 μg/ml to bovine serum albumin (BSA)- or Fn-coated plates and subsequently exposed to dynamic shear rates stepwise increasing from 50 to 5000 s-1 within 5 min and subsequently decreasing from 5000 to 50 s-1 within 5 min. The viscosity (mPa s) of Fn solutions was recorded over 10 min. Upon exposure to shear, the viscosity in the sample increased, suggesting conformational changes in Fn. Western blotting and densitometric analyses demonstrated that conformational changes of plasma Fn depended both on shear and protein concentration. However, there was no significant difference in fibril formation between BSA- or Fn-coated plates, suggesting that physical properties of stainless steel and biomechanical forces such as shear can affect the molecular structure of Fn. Our model may provide useful information of surface- and flow-induced alterations of plasma proteins.

Molecular composition and function of integrin-based collagen glues-introducing COLINBRIs

BACKGROUND

Despite detailed knowledge about the structure and signaling properties of individual collagen receptors, much remains to be learned about how these receptors participate in linking cells to fibrillar collagen matrices in tissues. In addition to collagen-binding integrins, a group of proteins with affinity both for fibrillar collagens and integrins link these two protein families together. We have introduced the name COLINBRI (COLlagen INtegrin BRIdging) for this set of molecules. Whereas collagens are the major building blocks in tissues and defects in these structural proteins have severe consequences for tissue integrity, the mild phenotypes of the integrin type of collagen receptors have raised questions about their importance in tissue biology and pathology.

SCOPE OF REVIEW

We will discuss the two types of cell linkages to fibrillar collagen (direct- versus indirect COLINBRI-mediated) and discuss how the parallel existence of direct and indirect linkages to collagens may ensure tissue integrity.

MAJOR CONCLUSIONS

The observed mild phenotypes of mice deficient in collagen-binding integrins and the relatively restricted availability of integrin-binding sequences in mature fibrillar collagen matrices support the existence of indirect collagen-binding mechanisms in parallel with direct collagen binding in vivo.

GENERAL SIGNIFICANCE

A continued focus on understanding the molecular details of cell adhesion mechanisms to collagens will be important and will benefit our understanding of diseases like tissue- and tumor fibrosis where collagen dynamics are disturbed. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

Expression of cellular fibronectin mRNA in adult periodontitis and peri-implantitis: a real-time polymerase chain reaction study

Cellular fibronectin (cFn) is a type of bioactive non-collagen glycoprotein regarded as the main substance used to maintain periodontal attachment. The content of cFn in some specific sites can reflect the progress of periodontitis or peri-implantitis. This study aims to evaluate the expression of cFn messenger RNA (mRNA) in tissues of adult periodontitis and peri-implantitis by real-time fluorescent quantitative polymerase chain reaction (PCR) and to determine its clinical significance. A total of 30 patients were divided into three groups of 10: healthy, adult periodontitis and peri-implantitis. Periodontal tissue biopsies (1 mm×1 mm×1 mm) from each patient were frozen in liquid nitrogen. Total RNA was extracted from these tissues, and the content, purity and integrity were detected. Specific primers were designed according to the sequence, and the mRNA expression levels of cellular fibronectin were detected by real-time PCR. The purity and integrity of the extracted total RNA were both high, and the specificity of amplified genes was very high with no other pollution. The mRNA expression of cFn in the adult periodontitis group (1.526±0.441) was lower than that in the healthy group (3.253±0.736). However, the mRNA expression of cFn in the peri-implantitis group (3.965±0.537) was significantly higher than that in the healthy group. The difference revealed that although both processes were destructive inflammatory reactions in the periodontium, the pathomechanisms were different and the variation started from the transcription level of the cFn gene.

Inactivation of a fibronectin-binding TonB-dependent protein increases adhesion properties of Bacteroides fragilis

Bacteroides fragilis is the Gram-negative strictly anaerobic bacterium most frequently isolated from clinical infections, including intra-abdominal abscess and bacteraemia. A number of factors can contribute to its virulence, including the expression of adhesins. Some of them are already characterized and can recognize and bind to extracellular matrix components, such as fibronectin. One of the molecules responsible for fibronectin-binding is an outer-membrane protein previously described by our group, which belongs to the TonB-dependent family. The aim of the present work was to characterize this protein. Initially, it was confirmed by fluorescence and electron microscopy that the fibronectin-binding molecules were located in the bacterial surface, but the distribution of these molecules on the surface was not uniform. To further evaluate the role of this protein, the gene bf1991, responsible for encoding this protein, was inactivated by a suicide vector and the mutant strains generated were used in several experiments to verify possible phenotypical alterations. In adherence assays with fibronectin immobilized on latex beads an increased adhesion was observed with the mutant strains compared with the wild-type strain. Western blot analysis in the mutant strain revealed the absence of the 120 kDa TonB-dependent outer-membrane protein and an alteration in the expression of an unknown 30 kDa protein. Killing assays using peritoneal macrophages were performed to evaluate the role of this protein as a virulence attribute and it was observed that the mutant strains were more efficiently internalized than the wild-type strains, with more internalization in the samples covered with fibronectin than in the samples not covered with it.

Alterations in molecular status of plasma fibronectin associated with aging of normal human individuals

OBJECTIVES

Senescence, progressive deterioration of many bodily functions might be associated with age-dependent alterations of plasma fibronectin (FN) molecular status (i.e., domain, glycotope, and molecular form expressions).

DESIGN AND METHODS

FN molecular status was analyzed in 127 plasma samples of healthy individuals in groups of newborns, and subjects aged 3-14, 15-39, 41-59, and 60-82 years by FN-ELISA, lectin-FN-ELISA, and immunoblotting using a set of domain-specific monoclonal antibodies, specific lectins, and monoclonal antibody to FN, respectively.

RESULTS

During the first four decades of human life the levels of cell-binding-, carboxyl-terminal-, collagen-, heparin-, and fibrin-domains of plasma FN gradually increased. In subjects aged up to 82 years the cell-binding and carboxyl-terminal FN domain concentrations did not change, while the heparin, fibrin, and collagen domains significantly increased. The relative reactivity of plasma FN with Maackia amurensis lectin, specific to α2,3-linked sialic acid, significantly decreased after birth, reaching a stable level in the subsequent life period, whereas with Sambucus nigra lectin, specific to α2,6-linked sialic acid, it significantly decreased in the 60-82 year old group. Moreover, the appearance of 280-kDa and 320-kDa FN bands, absent in young and mature healthy individuals, was found in the groups of 41-59 and 60-82 year olds.

CONCLUSIONS

The alterations of FN molecular status throughout growth, maturation and senescence might be associated not only with disturbances in the balance of FN production rate and degradation, but concomitantly with conformational rearrangements of FN and its engagement in age-related vascular remodeling processes.