Thrombin cleaves and activates the protease-activated receptor 2 dependent on thrombomodulin co-receptor availability

Coagulation Protease-Driven Cancer Immune Evasion: Potential Targets for Cancer Immunotherapy

Blood coagulation and cancer are intrinsically connected, hypercoagulation-associated thrombotic complications are commonly observed in certain types of cancer, often leading to decreased survival in cancer patients. Apart from the common role in coagulation, coagulation proteases often trigger intracellular signaling in various cancers via the activation of a G protein-coupled receptor superfamily protease: protease-activated receptors (PARs). Although the role of PARs is well-established in the development and progression of certain types of cancer, their impact on cancer immune response is only just emerging. The present review highlights how coagulation protease-driven PAR signaling plays a key role in modulating innate and adaptive immune responses. This is followed by a detailed discussion on the contribution of coagulation protease-induced signaling in cancer immune evasion, thereby supporting the growth and development of certain tumors. A special section of the review demonstrates the role of coagulation proteases, thrombin, factor VIIa, and factor Xa in cancer immune evasion. Targeting coagulation protease-induced signaling might be a potential therapeutic strategy to boost the immune surveillance mechanism of a host fighting against cancer, thereby augmenting the clinical consequences of targeted immunotherapeutic regimens.

Anti-Inflammatory and Anticancer Effects of Anticoagulant Therapy in Patients with Malignancy

Optimizing the anticoagulation therapy is of pivotal importance in patients with a malignant tumor, as venous thromboembolism (VTE) has become the second-leading cause of death in this population. Cancer can highly increase the risk of thrombosis and bleeding. Consequently, the management of cancer-associated VTE is complex. In recent years, translational research has intensified, and several studies have highlighted the role of inflammatory cytokines in cancer growth and progression. Simultaneously, the pleiotropic effects of anticoagulants currently recommended for VTE have emerged. In this review, we describe the anti-inflammatory and anticancer effects of both direct oral anticoagulants (DOACs) and low-molecular-weight heparins (LWMHs).

An Emerging Role for Type I Interferons as Critical Regulators of Blood Coagulation

Type I interferons (IFNs) are central mediators of anti-viral and anti-bacterial host defence. Detection of microbes by innate immune cells via pattern recognition receptors (PRRs), including Toll-like receptors (TLRs) and cGAS-STING, induces the expression of type I IFN-stimulated genes. Primarily comprising the cytokines IFN-α and IFN-β, type I IFNs act via the type I IFN receptor in an autocrine or exocrine manner to orchestrate rapid and diverse innate immune responses. Growing evidence pinpoints type I IFN signalling as a fulcrum that not only induces blood coagulation as a core feature of the inflammatory response but is also activated by components of the coagulation cascade. In this review, we describe in detail recent studies identifying the type I IFN pathway as a modulator of vascular function and thrombosis. In addition, we profile discoveries showing that thrombin signalling via protease-activated receptors (PARs), which can synergize with TLRs, regulates the host response to infection via induction of type I IFN signalling. Thus, type I IFNs can have both protective (via maintenance of haemostasis) and pathological (facilitating thrombosis) effects on inflammation and coagulation signalling. These can manifest as an increased risk of thrombotic complications in infection and in type I interferonopathies such as systemic lupus erythematosus (SLE) and STING-associated vasculopathy with onset in infancy (SAVI). We also consider the effects on coagulation of recombinant type I IFN therapies in the clinic and discuss pharmacological regulation of type I IFN signalling as a potential mechanism by which aberrant coagulation and thrombosis may be treated therapeutically.

Delineation of the healthy rabbit heart by immunohistochemistry - A technical note

Heart failure poses a big health problem and may result from obesity, smoking, alcohol and/or growing age. Studying pathological heart tissue demands accurate histological and immunohistochemical stainings in animal models, including chromogenic and fluorescent approaches. Moreover, a reliable set of healthy heart stainings and labeling are required, in order to provide a reference for the pathological situation. Heart and brain tissue of a healthy rabbit were collected, and different histological key steps were compared, such as paraffin embedding after formalin fixation versus cryopreservation; an antigen retrieval (AR) step in processing paraffin sections versus the same procedure without AR; or a chromogenic with a fluorescent detection system, respectively. Using serial sections, we stained the same morphological structure with classic approaches (HE, Masson Goldner Trichrome (GT) and Elastica van Gieson (EL)) and with different markers, including collagen I, collagen III, fibronectin, α-SMA, protease-activated receptor-2 (PAR-2) which is an inflammation-related marker, and ki67 for proliferating cells. Differences between conditions were quantitatively assessed by measuring the color intensity. Generally, cryosections exhibited a more prominent signal intensity in immunohistochemically labeled sections than in paraffin sections, but the strong staining was slurry, which sometimes impeded proper identification of morphological structures, particularly at higher magnifications. In addition, the advantage of an AR step was observed when compared to the condition without AR, where signal intensities were significantly lower. Different stainings of the heart arteries and the myocardium revealed a clear distribution of extracellular matrix components, with prominent collagen III in the artery wall, but an absence of collagen III in the myocardium. Moreover, paraffin-embedded sections provided more distinct structures compared to cryosections after collagen III, ki67, fibronectin, and α-SMA labeling. As for the Purkinje cells that were depicted in the heart and the cerebellum (Purkinje neurons), we found GT staining most suitable to depict them in the heart, while HE as well as EL staining was ideal to depict Purkinje neurons in the cerebellum. In sum, we provide useful reference images with different stainings for researchers using the rabbit heart or brain model. Such images can help to decide which of the immunohistochemical protocols are valuable to reach a specific aim. Recommendations are given for the best visualization of the target structures and specific (immunohistochemical) staining.

Coagulation-independent effects of thrombin and Factor Xa: role of protease-activated receptors in pulmonary hypertension

AIMS

Pulmonary arterial hypertension (PAH) is a devastating disease with limited therapeutic options. Vascular remodelling of pulmonary arteries, characterized by increased proliferation and migration of pulmonary arterial smooth muscle cells (PASMCs), is a hallmark of PAH. Here, we aimed to systematically characterize coagulation-independent effects of key coagulation proteases thrombin and Factor Xa (FXa) and their designated receptors, protease-activated receptor (PAR)-1 and -2, on PASMCs in vitro and experimental PAH in vivo.

METHODS AND RESULTS

In human and murine PASMCs, both thrombin and FXa were identified as potent mitogens, and chemoattractants. FXa mediated its responses via PAR-1 and PAR-2, whereas thrombin signalled through PAR-1. Extracellular-signal regulated kinases 1/2, protein kinase B (AKT), and sphingosine kinase 1 were identified as downstream mediators of PAR-1 and PAR-2. Inhibition of FXa or thrombin blunted cellular responses in vitro, but unexpectedly failed to protect against hypoxia-induced PAH in vivo. However, pharmacological inhibition as well as genetic deficiency of both PAR-1 and PAR-2 significantly reduced vascular muscularization of small pulmonary arteries, diminished right ventricular systolic pressure, and right ventricular hypertrophy upon chronic hypoxia compared to wild-type controls.

CONCLUSION

Our findings indicate a coagulation-independent pathogenic potential of thrombin and FXa for pulmonary vascular remodelling via acting through PAR-1 and PAR-2, respectively. While inhibition of single coagulation proteases was ineffective in preventing experimental PAH, our results propose a crucial role for PAR-1 and PAR-2 in its pathobiology, thus identifying PARs but not their dedicated activators FXa and thrombin as suitable targets for the treatment of PAH.

Thrombin generation potential is increased in patients with autoimmune inflammatory myopathies

PURPOSE

Dermatomyositis and polymyositis (DM/PM) are rare autoimmune inflammatory myopathies, characterized by an increased risk of cardiovascular and thromboembolic events, likely related to the prothrombotic plasma properties. The aim of this study was to assess the in vitro thrombin generation profile as a biomarker of plasma procoagulant properties in DM/PM patients.

METHODS

In 58 clinically stable DM/PM patients and 67 controls matched for sex, age, body mass index, we measured plasma thrombin generation potential using the Calibrated Automated Thrombinography (CAT) and analyzed its relationship with clinical disease characteristics, including autoantibodies profile.

RESULTS

Patients with DM/PM had a 21% increase in endogenous thrombin potential (ETP), 36% higher peak thrombin concentration, and 11% faster thrombin generation, compared to controls (p ​< ​0.001, all, also after adjustment for potential confounders). Interestingly, although both diseases did not differ in thrombin generation potential, heterogenous variables predicted elevated ETPs in both of them. In DM, that was higher fibrinogen, C-reactive protein, and total cholesterol, whereas in PM, presence of arthritis and increased blood platelet count. Surprisingly, thrombin formation capacity remained in a robust inverse relationship with serum troponin (r ​= ​-0.67, p ​< ​0.001) in the patient group.

CONCLUSIONS

DM/PM patients are characterized by an increased thrombin generation potential, suggesting prothrombotic plasma properties in both diseases. However, more studies are needed to verify its rationale and role in DM/PM clinical course and unfavorable clinical outcomes.

Piezo1 activation attenuates thrombin-induced blebbing in breast cancer cells

Cancer cells exploit a variety of migration modes to leave primary tumors and establish metastases, including amoeboid cell migration, which is typically reliant on bleb formation. Here we demonstrate that thrombin induces dynamic blebbing in the MDA-MB-231 breast cancer cell line and confirm that protease-activated receptor 1 (PAR1) activation is sufficient to induce this effect. Cell confinement has been implicated as a driving force in bleb-based migration. Unexpectedly, we found that gentle contact compression, exerted using a custom built ‘cell press’ to mechanically stimulate cells, reduced thrombin-induced blebbing. Thrombin-induced blebbing was similarly attenuated using the small molecule Yoda1, an agonist of the mechanosensitive Ca²⁺ channel Piezo1, and this attenuation was impaired in Piezo1-depleted cells. Additionally, Piezo1 activation suppressed thrombin-induced phosphorylation of ezrin, radixin and moesin (ERM) proteins, which are implicated in the blebbing process. Our results provide mechanistic insights into Piezo1 activation as a suppressor of dynamic blebbing, specifically that which is induced by thrombin.

Summary: Thrombin and protease-activated receptor agonists induce dynamic blebbing in breast cancer cells, which can be attenuated by contact-mediated compression, and activation of the mechanosensitive ion channel Piezo1.

Staphylococcus aureus and Neutrophil Extracellular Traps: The Master Manipulator Meets Its Match in Immunothrombosis

Over the past 10 years, neutrophil extracellular traps (NETs) have become widely accepted as an integral player in immunothrombosis, due to their complex interplay with both pathogens and components of the coagulation system. While the release of NETs is an attempt by neutrophils to trap pathogens and constrain infections, NETs can have bystander effects on the host by inducing uncontrolled thrombosis, inflammation, and tissue damage. From an evolutionary perspective, pathogens have adapted to bypass the host innate immune response. Staphylococcus aureus (S. aureus), in particular, proficiently overcomes NET formation using several virulence factors. Here we review mechanisms of NET formation and how these are intertwined with platelet activation, the release of endothelial von Willebrand factor, and the activation of the coagulation system. We discuss the unique ability of S. aureus to modulate NET formation and alter released NETs, which helps S. aureus to escape from the host's defense mechanisms. We then discuss how platelets and the coagulation system could play a role in NET formation in S. aureus-induced infective endocarditis, and we explain how targeting these complex cellular interactions could reveal novel therapies to treat this disease and other immunothrombotic disorders.

Delineation of the healthy rabbit liver by immunohistochemistry - A technical note

Liver diseases pose a big global health problem and liver failure may result from viral infection, overnutrition or tumors. Studying pathologic liver tissue demands for accurate and specific histological stainings and immunohistochemical labellings, including chromogenic and fluorescent approaches. Moreover, a reliable set of healthy liver stainings and labellings are required, to provide a baseline or reference for the pathological situation. Here, we used the liver tissue of a healthy rabbit and compared different histological key steps, such as paraffin embedding after formalin fixation versus cryopreservation; or an antigen retrieval (AR) step in processing paraffin sections versus the same procedure without AR; or chromogenic with fluorescent detection system, respectively. Moreover, we provide images of serial sections, where we stained the same morphological structure with different markers, including collagen I, collagen III, fibronectin, α-SMA, elastin, protease-activated receptor-2 (PAR-2) which is an inflammation-related marker, ki67 for proliferating cells, and orcein (as negative control for pathological aberrations like Wilson disease). Differences between conditions were quantitatively assessed by measuring the colour intensity. Generally, we observed that cryosections exhibited a stronger signal intensity in immunohistochemically labelled sections than in paraffin sections; however, the strong staining got slurred, which sometimes hampered proper identification of morphological structures at higher magnifications. Moreover, there was a clear increase in signal intensity for paraffin sections when an AR step was performed compared to condition without AR. Results for mouse isotype staining as a negative control clearly supported those findings. Different stainings of the portal triad, the central vein and the bile ducts revealed a clear-cut distribution of extracellular matrix components, with prominent fibronectin and elastin around the lumen of the central vein as well as a patchy PAR-2 expression. As for the bile ducts, complete absence of α-SMA and PAR-2 was found at the margins, however, collagen I expression and elastin were positive and showed a strong signal. Like this, we provide useful and valuable reference images for researchers using the rabbit liver model. It may help to decide which of the immunohistochemical protocols are valuable to reach a certain aim and which protocols lead to the best visualization of the target structure.

The development of proteinase-activated receptor-2 modulators and the challenges involved

Protease-activated receptor-2 (PAR2) has been extensively studied since its discovery in the mid-1990. Despite the advances in understanding PAR2 pharmacology, it has taken almost 25 years for the first inhibitor to reach clinical trials, and so far, no PAR2 antagonist has been approved for human use. Research has employed classical approaches to develop a wide array of PAR2 agonists and antagonists, consisting of peptides, peptoids and antibodies to name a few, with a surge in patent applications over this period. Recent breakthroughs in PAR2 structure determination has provided a unique insight into proposed PAR2 ligand binding sites. Publication of the first crystal structures of PAR2 resolved in complex with two novel non-peptide small molecule antagonists (AZ8838 and AZ3451) revealed two distinct binding pockets, originally presumed to be allosteric sites, with a PAR2 antibody (Fab3949) used to block tethered ligand engagement with the peptide-binding domain of the receptor. Further studies have proposed orthosteric site occupancy for AZ8838 as a competitive antagonist. One company has taken the first PAR2 antibody (MEDI0618) into phase I clinical trial (NCT04198558). While this first-in-human trial is at the early stages of the assessment of safety, other research into the structural characterisation of PAR2 is still ongoing in an attempt to identify new ways to target receptor activity. This review will focus on the development of novel PAR2 modulators developed to date, with an emphasis placed upon the advances made in the pharmacological targeting of PAR2 activity as a strategy to limit chronic inflammatory disease.

A thrombin-PAR1/2 feedback loop amplifies thromboinflammatory endothelial responses to the viral RNA analogue poly(I:C)

Activation of blood coagulation and endothelial inflammation are hallmarks of respiratory infections with RNA viruses that contribute significantly to the morbidity and mortality of patients with severe disease. We investigated how signaling by coagulation proteases affects the quality and extent of the response to the TLR3-ligand poly(I:C) in human endothelial cells. Genome-wide RNA profiling documented additive and synergistic effects of thrombin and poly(I:C) on the expression level of many genes. The most significantly active genes exhibiting synergistic induction by costimulation with thrombin and poly(I:C) included the key mediators of 2 critical biological mechanisms known to promote endothelial thromboinflammatory functions: the initiation of blood coagulation by tissue factor and the control of leukocyte trafficking by the endothelial-leukocyte adhesion receptors E-selectin (gene symbol, SELE) and VCAM1, and the cytokines and chemokines CXCL8, IL-6, CXCL2, and CCL20. Mechanistic studies have indicated that synergistic costimulation with thrombin and poly(I:C) requires proteolytic activation of protease-activated receptor 1 (PAR1) by thrombin and transactivation of PAR2 by the PAR1-tethered ligand. Accordingly, a small-molecule PAR2 inhibitor suppressed poly(I:C)/thrombin-induced leukocyte-endothelial adhesion, cytokine production, and endothelial tissue factor expression. In summary, this study describes a positive feedback mechanism by which thrombin sustains and amplifies the prothrombotic and proinflammatory function of endothelial cells exposed to the viral RNA analogue, poly(I:C) via activation of PAR1/2.

PAR2 Activation on Human Kidney Tubular Epithelial Cells Induces Tissue Factor Synthesis, That Enhances Blood Clotting

Coagulation abnormalities and increased risk of atherothrombosis are common in patients with chronic kidney diseases (CKD). Mechanisms that alter renal hemostasis and lead to thrombotic events are not fully understood. Here we show that activation of protease activated receptor-2 (PAR2) on human kidney tubular epithelial cells (HTECs), induces tissue factor (TF) synthesis and secretion that enhances blood clotting. PAR-activating coagulation-associated protease (thrombin), as well as specific PAR2 activators (matriptase, trypsin, or synthetic agonist 2f-LIGRLO-NH2 (2F), induced TF synthesis and secretion that were potently inhibited by PAR2 antagonist, I-191. Thrombin-induced TF was also inhibited by a PAR1 antagonist, Vorapaxar. Peptide activators of PAR1, PAR3, and PAR4 failed to induce TF synthesis. Differential centrifugation of the 2F-conditoned medium sedimented the secreted TF, together with the exosome marker ALG-2 interacting protein X (ALIX), indicating that secreted TF was associated with extracellular vesicles. 2F-treated HTEC conditioned medium significantly enhanced blood clotting, which was prevented by pre-incubating this medium with an antibody for TF. In summary, activation of PAR2 on HTEC stimulates synthesis and secretion of TF that induces blood clotting, and this is attenuated by PAR2 antagonism. Thrombin-induced TF synthesis is at least partly mediated by PAR1 transactivation of PAR2. These findings reveal how underlying hemostatic imbalances might increase thrombosis risk and subsequent chronic fibrin deposition in the kidneys of patients with CKD and suggest PAR2 antagonism as a potential therapeutic strategy for intervening in CKD progression.

Mechanisms of Bone Remodeling Disorder in Hemophilia

Hemophilia is caused by a lack of antihemophilic factor(s), for example, factor VIII (FVIII; hemophilia A) and factor IX (FIX; hemophilia B). Low bone mass is widely reported in epidemiological studies of hemophilia, and patients with hemophilia are at an increased risk of fracture. The detailed etiology of bone homeostasis imbalance in hemophilia is unclear. Clinical and experimental studies show that FVIII and FIX are involved in bone remodeling. However, it is likely that antihemophilic factors affect bone biology through thrombin pathways rather than via their own intrinsic properties. In addition, among patients with hemophilia, there are pathophysiological processes in several systems that might contribute to bone loss. This review summarizes studies on the association between hemophilia and bone remodeling, and might shed light on the challenges facing the care and prevention of osteoporosis and fracture in patients with hemophilia.

Delineation of the healthy rabbit lung by immunohistochemistry - a technical note

Investigation and studies of pulmonary diseases and injuries require pre-clinical animal models. The rabbit lung model is widely used and allows for a diverse set of readouts. Among them, histology and immunohistochemistry are of invaluable merit because qualitative and quantitative information about tissue morphology and composition can be easily obtained. In this technical note, we performed several histological and immunohistochemical stainings in the rabbit healthy naïve lung tissue. Overnight formalin fixation with subsequent paraffin embedding was compared to cryopreservation with a subsequent 10-minute formalin fixation prior to staining. Antigen retrieval (AR) for paraffin embedded sections proved to enhance the corresponding signals compared to analogous staining without AR. Advantages and disadvantages of chromogenic versus immunofluorescence stainings were discussed. In addition, several morphological structures, such as the intrapulmonary bronchus with its mucosal folds, the pulmonary artery, the alveoli and the lymph nodes, were stained with various stainings at the same site in order to give a comprehensive picture of their composition. Besides Haematoxylin&Eosin and Elastica van Gieson staining, collagen I, collagen III, fibronectin, α-SMA, ki-67 and protease-activated receptor-2 (PAR-2) immunohistochemistry was performed. Collagen I, collagen III and fibronectin expression was positive at the outer rim of the pulmonary arteries, while the inner rim was collagen III positive. Moreover, the fibronectin staining in the intrapulmonary bronchus showed an opposite trend when compared to the collagen III staining. The alveoli exhibited PAR-2 expression, while PAR-2 was not expressed in lymph nodes of the healthy rabbit lung.