Sensing adhesion forces between erythrocytes and γ' fibrinogen, modulating fibrin clot architecture and function

Aggregation and disaggregation of red blood cells: Depletion versus bridging

The aggregation of red blood cells (RBCs) is a complex phenomenon that strongly impacts blood flow and tissue perfusion. Despite extensive research for more than 50 years, physical mechanisms that govern RBC aggregation are still under debate. Two proposed mechanisms are based on bridging and depletion interactions between RBCs due to the presence of macromolecules in blood plasma. The bridging hypothesis assumes the formation of bonds between RBCs through adsorbing macromolecules, while the depletion mechanism results from the exclusion of macromolecules from the intercellular space, leading to effective attraction. Existing experimental studies generally cannot differentiate between these two aggregation mechanisms, although several recent investigations suggest concurrent involvement of the both mechanisms. We explore dynamic aggregation and disaggregation of two RBCs using three simulation models: a potential-based model mimicking depletion interactions, a bridging model with immobile bonds, and a new bridging model with mobile bonds that can slide along RBC membranes. Simulation results indicate that dynamic aggregation of RBCs primarily arises from depletion interactions, while disaggregation of RBCs involves both mechanisms. The bridging model with mobile bonds reproduces well the corresponding experimental data, offering insights into the interplay between bridging and depletion interactions and providing a framework for studying similar interactions between other biological cells.

The procoagulant signature of cancer cells drives fibrin network formation in tumor microenvironment and impacts its quality. Implications in cancer cell migration and the resistance to anticancer agents

INTRODUCTION

Cancer cells induce hypercoagulability in the tumoral microenvironment by expressing Tissue Factor (TF). We aimed to study the impact of the procoagulant signature of cancer cells on the quality and structure of fibrin network. We also studied the impact of fibrin clot shield (FCS) on the efficiency of anticancer agents and the migration of cancer cells.

MATERIALS AND METHODS

Pancreatic cancer cells BXPC3 and breast cancer cells MDA-MB231 and MCF7, were cultured in the presence of normal Platelet Poor Plasma (PPP), diluted 10 % in conditioning media. Their potential to induce thrombin generation and their fibrinolytic activity were assessed. The structure of fibrin network was analyzed with Scanning Electron Microscopy (SEM). Cancer cells' mobility with fibrin clot and their interactions with fibrin were observed. Cancer cells were treated with paclitaxel (PTX) or 4-hydroxy-tamoxifen (4OHTam) in the presence or absence of FCS.

RESULTS

Cancer cells, in presence of PPP, induced fibrin network formation. High TF-expressing cancer cells (BXPC3 and MDA-MB23 cells), led to dense fibrin network with fine fibers. Low TF expressing cells MCF7 led to thick fibers. Exogenous TF enhanced the density of fibrin network formed by MCF7 cells. Cancer cells through their inherent profibrinolytic potential migrated within the fiber scaffold. The BXPC3 and MCF7 cells moved in clusters whereas the MDA-MB231 cells moved individually within the fibrin network. FCS decreased the efficiency of PTX and 4OHTam on the viability of cancer cells.

CONCLUSIONS

The procoagulant signature of cancer cells is determinant for the quality and structure of fibrin network in the microenvironment. Original SEM images show the architecture of "bird's nest"-like fibrin network being in touch with the cell membranes and surrounding cancer cells. Fibrin network constructed by triggering thrombin generation by cancer cells, provides a scaffold for cell migration. Fibrin clot shields protect cancer cells against PTX and 4OHTam.

Synergism of red blood cells and tranexamic acid in the inhibition of fibrinolysis

BACKGROUND

Postpartum hemorrhage (PPH) is the leading cause of maternal death worldwide. The World Maternal Antifibrinolytic trial showed that antifibrinolytic tranexamic acid (TXA) reduces PPH deaths. Maternal anemia increases the risk of PPH. The World Maternal Antifibrinolytic-2 trial is now assessing whether TXA can prevent PPH in women with anemia. Low red blood cell (RBC) counts promote fibrinolysis by altering fibrin structure and plasminogen activation.

OBJECTIVES

We explored interactions between RBCs and TXA in inhibiting fibrinolysis.

METHODS

We used global fibrinolytic assays (ball sedimentation and viscoelasticity) to monitor the lysis of fibrin containing plasminogen and tissue-type plasminogen activator. We applied a fluorogenic kinetic assay to measure plasmin generation in fibrin clots and scanning electron microscopy to study fibrin structure.

RESULTS

According to parallel-line bioassay analysis of the fibrin lysis-time data, the antifibrinolytic potency of 4-128 μM TXA was increased in the presence of 10% to 40% (v/v) RBCs. Global fibrinolysis assays showed that the joint effect of RBCs and TXA was about 15% larger than the sum of their individual effects in the inhibition of fibrinolysis. In plasminogen activation, TXA added the same increment of inhibition to the effect of RBCs at any cell count in the fibrin clot. Regarding fibrin structure, TXA thickened fibrin fibers, which impaired plasminogen activation, whereas RBCs promoted fine fibers that were more resistant to plasmin.

CONCLUSIONS

The antifibrinolytic potency of TXA is enhanced in fibrin formed in the presence of RBCs through inhibition of plasminogen activation and fibrin lysis, which correlates with modifications of fibrin structures.

The role of fibrinogen in traumatic brain injury: from molecular pathological mechanisms to clinical management

Fibrinogen is the substrate of plasma coagulation. It plays an important role in the formation of reticular network, which is crucial to the strength and stability of blood clots. In addition to directly participating in coagulation, fibrinogen also participates in the destruction of blood-brain barrier and neuroinflammation. This article reviews the pathophysiological changes of fibrinogen after traumatic brain injury. Considerable efforts have been made to understand the mechanisms by which fibrinogen damages the central nervous system. Combined with the latest research hotspots, potentially promising treatment strategies at the molecular level were discussed. We believe that understanding the role of fibrinogen-mediated damage in nerve and blood-brain barrier function will enable timely intervention in patients with nerve damage, and guide the development of novel targeted therapeutics.

Fibrin clot properties in cardiovascular disease: from basic mechanisms to clinical practice

Fibrinogen conversion into insoluble fibrin and the formation of a stable clot is the final step of the coagulation cascade. Fibrin clot porosity and its susceptibility to plasmin-mediated lysis are the key fibrin measures, describing the properties of clots prepared ex vivo from citrated plasma. Cardiovascular disease (CVD), referring to coronary heart disease, heart failure, stroke, and hypertension, has been shown to be associated with the formation of dense fibrin networks that are relatively resistant to lysis. Denser fibrin mesh characterized acute patients at the onset of myocardial infarction or ischaemic stroke, while hypofibrinolysis has been identified as a persistent fibrin feature in patients following thrombotic events or in those with stable coronary artery disease. Traditional cardiovascular risk factors, such as smoking, diabetes mellitus, hyperlipidaemia, obesity, and hypertension, have also been linked with unfavourably altered fibrin clot properties, while some lifestyle modifications and pharmacological treatment, in particular statins and anticoagulants, may improve fibrin structure and function. Prospective studies have suggested that prothrombotic fibrin clot phenotype can predict cardiovascular events in short- and long-term follow-ups. Mutations and splice variants of the fibrinogen molecule that have been proved to be associated with thrombophilia or increased cardiovascular risk, along with fibrinogen post-translational modifications, prothrombotic state, inflammation, platelet activation, and neutrophil extracellular traps formation, contribute also to prothrombotic fibrin clot phenotype. Moreover, about 500 clot-bound proteins have been identified within plasma fibrin clots, including fibronectin, α2-antiplasmin, factor XIII, complement component C3, and histidine-rich glycoprotein. This review summarizes the current knowledge on the mechanisms underlying unfavourable fibrin clot properties and their implications in CVD and its thrombo-embolic manifestations.

A mathematical model of fibrinogen-mediated erythrocyte-erythrocyte adhesion

Erythrocytes are deformable cells that undergo progressive biophysical and biochemical changes affecting the normal blood flow. Fibrinogen, one of the most abundant plasma proteins, is a primary determinant for changes in haemorheological properties, and a major independent risk factor for cardiovascular diseases. In this study, the adhesion between human erythrocytes is measured by atomic force microscopy (AFM) and its effect observed by micropipette aspiration technique, in the absence and presence of fibrinogen. These experimental data are then used in the development of a mathematical model to examine the biomedical relevant interaction between two erythrocytes. Our designed mathematical model is able to explore the erythrocyte-erythrocyte adhesion forces and changes in erythrocyte morphology. AFM erythrocyte-erythrocyte adhesion data show that the work and detachment force necessary to overcome the adhesion between two erythrocytes increase in the presence of fibrinogen. The changes in erythrocyte morphology, the strong cell-cell adhesion and the slow separation of the two cells are successfully followed in the mathematical simulation. Erythrocyte-erythrocyte adhesion forces and energies are quantified and matched with experimental data. The changes observed on erythrocyte-erythrocyte interactions may give important insights about the pathophysiological relevance of fibrinogen and erythrocyte aggregation in hindering microcirculatory blood flow.

Aquaporin-3 and Aquaporin-5 Facilitate Migration and Cell-Cell Adhesion in Pancreatic Cancer by Modulating Cell Biomechanical Properties

BACKGROUND

Aquaporins are membrane channels responsible for the bidirectional transfer of water and small non-charged solutes across cell membranes. AQP3 and AQP5 are overexpressed in pancreatic ductal adenocarcinoma, playing key roles in cell migration, proliferation, and invasion. Here, we evaluated AQP3 and AQP5 involvement in cell biomechanical properties, cell-cell adhesion, and cell migration, following a loss-of-function strategy on BxPC-3 cells.

RESULTS

Silencing of AQP3 and AQP5 was functionally validated by reduced membrane permeability and had implications on cell migration, slowing wound recovery. Moreover, silenced AQP5 and AQP3/5 cells showed higher membrane fluidity. Biomechanical and morphological changes were assessed by atomic force microscopy (AFM), revealing AQP5 and AQP3/5 silenced cells with a lower stiffness than their control. Through cell-cell adhesion measurements, the work (energy) necessary to detach two cells was found to be lower for AQP-silenced cells than control, showing that these AQPs have implications on cell-cell adhesion.

CONCLUSION

These findings highlight AQP3 and AQP5 involvement in the biophysical properties of cell membranes, whole cell biomechanical properties, and cell-cell adhesion, thus having potential implication in the settings of tumor development.

Nanomechanics of Blood Clot and Thrombus Formation

Mechanical properties have been extensively studied in pure elastic or viscous materials; however, most biomaterials possess both physical properties in a viscoelastic component. How the biomechanics of a fibrin clot is related to its composition and the microenvironment where it is formed is not yet fully understood. This review gives an outline of the building mechanisms for blood clot mechanical properties and how they relate to clot function. The formation of a blood clot in health conditions or the formation of a dangerous thrombus go beyond the mere polymerization of fibrinogen into a fibrin network. The complex composition and localization of in vivo fibrin clots demonstrate the interplay between fibrin and/or fibrinogen and blood cells. Studying these protein–cell interactions and clot mechanical properties may represent new methods for the evaluation of cardiovascular diseases (the leading cause of death worldwide), creating new possibilities for clinical diagnosis, prognosis, and therapy.

Expected final online publication date for the Annual Review of Biophysics, Volume 51 is May 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Red blood cells: the forgotten player in hemostasis and thrombosis

New evidence has stirred up a long-standing but undeservedly forgotten interest in the role of erythrocytes, or red blood cells (RBCs), in blood clotting and its disorders. This review summarizes the most recent research that describes the involvement of RBCs in hemostasis and thrombosis. There are both quantitative and qualitative changes in RBCs that affect bleeding and thrombosis, as well as interactions of RBCs with cellular and molecular components of the hemostatic system. The changes in RBCs that affect hemostasis and thrombosis include RBC counts or hematocrit (modulating blood rheology through viscosity) and qualitative changes, such as deformability, aggregation, expression of adhesive proteins and phosphatidylserine, release of extracellular microvesicles, and hemolysis. The pathogenic mechanisms implicated in thrombotic and hemorrhagic risk include variable adherence of RBCs to the vessel wall, which depends on the functional state of RBCs and/or endothelium, modulation of platelet reactivity and platelet margination, alterations of fibrin structure and reduced susceptibility to fibrinolysis, modulation of nitric oxide availability, and the levels of von Willebrand factor and factor VIII in blood related to the ABO blood group system. RBCs are involved in platelet-driven contraction of clots and thrombi that results in formation of a tightly packed array of polyhedral erythrocytes, or polyhedrocytes, which comprises a nearly impermeable barrier that is important for hemostasis and wound healing. The revisited notion of the importance of RBCs is largely based on clinical and experimental associations between RBCs and thrombosis or bleeding, implying that RBCs are a prospective therapeutic target in hemostatic and thrombotic disorders.

Impact of γ'γ' fibrinogen interaction with red blood cells on fibrin clots

AIM

γ' fibrinogen has been associated with thrombosis. Here the interactions between γ'γ' or γAγA fibrinogen and red blood cells (RBCs), and their role on fibrin clot properties were studied.

MATERIALS & METHODS

Atomic Force microscopy (AFM)-based force spectroscopy, rheological, electron and confocal microscopy, and computational approaches were conducted for both fibrinogen variants.

RESULTS & CONCLUSION

AFM shows that the recombinant human (rh)γ'γ' fibrinogen increases the binding force and the frequency of the binding to RBCs compared with rhγAγA, promoting cell aggregation. Structural changes in rhγ'γ' fibrin clots, displaying a nonuniform fibrin network were shown by microscopy approaches. The presence of RBCs decreases the fibrinolysis rate and increases viscosity of rhγ'γ' fibrin clots. The full length of the γ' chain structure, revealed by computational analysis, occupies a much wider surface and is more flexible, allowing an increase of the binding between γ' fibers, and eventually with RBCs.

Influencing the adhesion properties and wettability of mucin protein films by variation of the environmental pH

Mucins, the main component of the mucus secretions of goblet and epithelial cells, are known for exhibiting a different behaviour in accordance with their surrounding environment (i.e. among others the environmental pH), which induces a drastic change in their measured mechanical properties. In this work, we have first employed Atomic Force Microscopy (AFM) in Force Spectroscopy mode to evaluate the adhesion of porcine mucin films at the nanoscale, and the changes caused in this particular factor by a pH variation between 7.0 and 4.0, both quite common values in biological conditions. Measurements also involved additional varying factors such as the indenting tip chemistry (hydrophobic vs hydrophilic), its residence time on the measured film (0, 1 and/or 2 seconds), and increasing pulling rates (ranging from 0.1 up to 10 µm/s). A second approach regarded the macroscale behaviour of the films, due to their potential applicability in the development of a new set of stimuli-responsive biomaterials. This was possible by means of complementary Wilhelmy plate method (to test the wetting properties) and cell proliferation studies on films previously exposed to the corresponding pH solution. According to our results, treatment with lowest pH (4.0) provides porcine mucin with a more hydrophilic character, showing a much stronger adhesion for analogous chemistries, as well as enhanced capability for cell attachment and proliferation, which opens new pathways for their future use and consideration as scaffold-forming material.

The 95RGD97 sequence on the Aα chain of fibrinogen is essential for binding to its erythrocyte receptor

Background

Erythrocyte aggregation, a cardiovascular risk factor, is increased by high plasma fibrinogen levels. Here, the effect of different fibrinogen mutations on binding to its human erythrocyte receptor was assessed in order to identify the interaction sites.

Methods

Three fibrinogen variants were tested, specifically mutated in their putative integrin recognition sites on the Aα chain (mutants D97E, D574E and D97E/D574E) and compared with wild-type fibrinogen.

Results

Atomic force microscopy-based force spectroscopy measurements showed a significant decrease both on the fibrinogen-erythrocyte binding force and on its frequency for fibrinogen with the D97E mutation, indicating that the corresponding arginine-glycine-aspartate sequence (residues 95-97) is involved in this interaction, and supporting that the fibrinogen receptor on erythrocytes has a β₃ subunit. Changes in the fibrin clot network structure obtained with the D97E mutant were observed by scanning electron microscopy.

Conclusion

These findings may lead to innovative perspectives on the development of new therapeutic approaches to overcome the risks of fibrinogen-driven erythrocyte hyperaggregation.