Protein arginine deiminase 4 inactivates tissue factor pathway inhibitor-alpha by enzymatic modification of functional arginine residues

Impact of peptidylarginine deiminase 4 (PAD4) deficiency in a fecal-induced peritonitis model of sepsis

BACKGROUND

Peptidylarginine deiminase 4 (PAD4) citrullinates histones, enabling the release of neutrophil extracellular traps. While neutrophil extracellular traps capture and kill pathogens, they also drive immunothrombosis, potentially worsening sepsis outcomes. However, it remains unclear whether PAD4 deficiency is beneficial or harmful in sepsis.

OBJECTIVES

To evaluate the impact of PAD4 deficiency in a fecal-induced peritonitis sepsis model, with and without antibiotic treatment, and incorporating fluid resuscitation in both sexes.

METHODS

Wild-type and PAD4 knockout (PAD4-/-) C57Bl/6 mice received intraperitoneal injections of fecal slurry (0.6 mg/g). Mice received buprenorphine every 8 hours and antibiotics/fluids every 12 hours. Survival studies were also conducted without antibiotics at a reduced fecal dose (0.4 mg/g). Mice were culled at 8 hours or 48 hours after infection. Organs, blood, and peritoneal cavity fluid were collected. Plasma levels of interleukin (IL)-6, IL-10, cell-free DNA, and thrombin-antithrombin were quantified, as well as bacterial loads in blood and peritoneal cavity fluid. Organ histology/immunohistochemistry was performed.

RESULTS

Female PAD4-/- mice had worsened survival compared with female wild-type mice. Male mice exhibited worse survival than females in both strains. Antibiotics eliminated survival differences between strains and sexes. Septic PAD4-/- mice had reduced IL-10 in the early phase of sepsis, increased lung myeloperoxidase, and exacerbated lung injury compared with septic wild-type mice.

CONCLUSION

PAD4 deficiency in female mice worsened survival in the fecal-induced peritonitis sepsis model. In both strains, male mice exhibited worse survival compared with their female counterparts. PAD4 deficiency is associated with reduced IL-10, increased neutrophil infiltration, and exacerbated lung injury. Antibiotics eliminated survival differences between strains and sexes.

Neutrophil Extracellular Traps: At the Interface of Thrombosis and Comorbidities

Since their discovery in 2004, neutrophil extracellular traps (NETs) have been at the center of multidisciplinary attention. Although a key tool in neutrophil-mediated immunity, these filamentous, enzyme-enriched DNA-histone complexes can be detrimental to tissues and have been identified as an underlying factor in a range of pathological conditions. Building on more than 20 years of research into NETs, this review places thrombosis, the pathological formation of blood clots, in the spotlight. From this point of view, we discuss the structure and formation of NETs, as well as the interaction of their components with the hemostatic system, dissecting the pathways through which NETs exert their marked effect on formation and the dissolution of thrombi. We pay distinct attention to the latest developments in the research of a key player in NET formation, peptidyl-arginine-deiminase (PAD) enzymes: their types, sources, and potential cross-play with the hemostatic machinery. Besides these molecular details, we elaborate on the link between pathological thrombosis, NETs, and widespread conditions that represent a debilitating public health burden worldwide, such as sepsis and neoplasms. Finally, future implications on the treatment of thrombosis-related conditions will be discussed.

Trapped in the NETs: Multiple Roles of Platelets in the Vascular Complications Associated with Neutrophil Extracellular Traps

Neutrophil extracellular traps (NETs) have received significant attention in recent years for their role in both the immune response and the vascular damage associated with inflammation. Platelets have been described as critical components of NETs since the initial description of this physio-pathological response of neutrophils. Platelets have been shown to play a dual role as responders and also as stimulators of NETs. The direct interaction with DNA leads to the entrapment of platelets into NETs, a phenomenon that significantly contributes to the thrombotic complications of inflammation and neutrophil activation, while the direct and paracrine stimulation of neutrophils by platelets has been shown to initiate the process of NET formation. In this review, we provide a comprehensive description of our current understanding of the molecular mechanisms underlying the entrapping of platelets into NETs and, in parallel, the platelet-driven cellular responses promoting NET formation. We then illustrate established examples of the contribution of NETs to vascular pathologies, describe the important questions that remain to be answered regarding the contribution of platelets to NET formation and NET-dependent cardiovascular complication, and highlight the fundamental steps taken towards the application of our understanding of platelets' contribution to NETs for the development of novel cardiovascular therapies.

Citrullination of tissue factor pathway inhibitor alpha by peptidylarginine deiminase 4 impairs its natural anticoagulant activity toward factors Xa and VIIa/tissue factor and reduces binding to its cofactor protein S

BACKGROUND

Neutrophils are known to externalize their DNA and intracellular contents to neutralize invading pathogens. This process may enhance blood coagulation during inflammation. Tissue factor (TF) pathway inhibitor (TFPI) binds to extracellular DNA and may be citrullinated by peptidylarginine deiminase 4. Citrullination of TFPI reduces its anticoagulant activity toward factor (F)Xa but appears to retain its inhibition of TF-triggered thrombin generation, indicating differential regulation of TFPI functions by peptidylarginine deiminase 4.

OBJECTIVES

This work aimed to study the effects of citrullination of TFPI-alpha on the inhibition of FXa, FVIIa/TF, and the cofactor activity of protein S.

METHODS

The effect of TFPI citrullination on the inhibition of FXa and FVIIa/TF was measured by chromogenic assays using purified components and by calibrated automated thrombography. Interaction with protein S was assessed by surface plasmon resonance and solid-phase binding assays using immobilized protein S, recombinant TFPI, and synthetic TFPI domains.

RESULTS

Citrullination of TFPI abolished its ability to inhibit FXa- and FXIa-triggered thrombin generation. However, its impaired inhibition of TF-triggered thrombin generation was still enhanced by protein S. Chromogenic assays revealed that citrullinated TFPI was essentially inactive as an inhibitor of the FVIIa-TF complex in the absence of protein S but partially restored by protein S. Interaction studies revealed that binding of citrullinated TFPI to protein S was reduced approximately 4-fold.

CONCLUSION

Citrullinated TFPI shows impaired natural anticoagulant activity. While anti-FXa activity is essentially absent, its anti-TF/FVIIa activity can still be enhanced by protein S. This enhancement is incomplete; however, protein S binding to citrullinated TFPI is impaired.

Hemostatic imbalance induced by tamoxifen in estrogen receptor-positive breast cancer patients: An observational study

BACKGROUND

Estrogen receptor (ER)-positive (ER+) breast cancer accounts for approximately 75% of all breast cancers. Tamoxifen, a selective estrogen receptor modulator, is the standard adjuvant treatment. Although better tolerated than aromatase inhibitors, tamoxifen increases the risk of venous thromboembolism (VTE) 1.4-fold.

AIM

To assess the hemostatic imbalance induced by tamoxifen in adjuvant treatment of ER+ breast cancer.

METHOD

Twenty-five patients in remission from ER+ breast cancer under tamoxifen were included. One hundred and thirty one age- and BMI-matched healthy controls were included to establish reference ranges of thrombin generation assay (TGA) parameters. TGA was performed in the absence and presence of exogenous activated protein C (APC) to calculate the normalized APC sensitivity ratio (nAPCsr), a marker of APC resistance.

RESULTS

All TG parameters except the endogenous thrombin potential (ETP) (-APC) were significantly impacted by tamoxifen (p < 0.001). In absence of APC, regardless of TGA parameters, at least 50% of results were outside the reference ranges except for ETP, which was above the upper reference limit in only two individuals. The most impacted parameter was the Peak Height with 52% (-APC) and 80% (+APC) of results above the upper reference range limit, respectively. The nAPCsr was significantly higher in tamoxifen users (mean ± standard deviation = 3.18 ± 0.91) compared to the control group (2.19 ± 0.92, p < 0.0001).

CONCLUSION

This observational study showed that patients in remission from ER+ breast cancer taking tamoxifen had altered thrombin generation, as well as an acquired APC resistance. Moreover, this is the first study using the validated ETP-based APC resistance assay in tamoxifen-treated patients.

Fundamental considerations for designing endothelialized in vitro models of thrombosis

Endothelialized in vitro models for cardiovascular disease have contributed greatly to our current understanding of the complex molecular mechanisms underlying thrombosis. To further elucidate these mechanisms, it is important to consider which fundamental aspects to incorporate into an in vitro model. In this review, we will focus on the design of in vitro endothelialized models of thrombosis. Expanding our understanding of the relation and interplay between the different pathways involved will rely in part on complex models that incorporate endothelial cells, blood, the extracellular matrix, and flow. Importantly, the use of tissue-specific endothelial cells will help in understanding the heterogeneity in thrombotic responses between different vascular beds. The dynamic and complex responses of endothelial cells to different shear rates underlines the importance of incorporating appropriate shear in in vitro models. Alterations in vascular extracellular matrix composition, availability of bioactive molecules, and gradients in concentration and composition of these molecules can all regulate the function of both endothelial cells and perivascular cells. Factors modulating these elements in in vitro models should therefore be considered carefully depending on the research question at hand. As the complexity of in vitro models increases, so can the variability. A bottom-up approach to designing such models will remain an important tool for researchers studying thrombosis. As new techniques are continuously being developed and new pathways are brought to light, research question-dependent considerations will have to be made regarding what aspects of thrombosis to include in in vitro models.

Elevated levels of citrullinated fibrinogen in patients with cancer

Neutrophil released peptidyl arginine deiminase 4 (PAD4) converts arginine residues on plasma proteins into citrulline. Here, we developed an assay to quantify citrullinated fibrinogen. We employed a biotin-conjugated phenylglyoxal (biotin-phenylglyoxal (PG)) compound that selectively labels citrulline. Patient samples were derived from a multicenter prospective cohort study that aimed to identify cancer patients at high risk for venous thromboembolism (VTE). Our data show that cancer patients have higher (median 2-fold increased) citrullinated fibrinogen levels when compared to normal human plasma and a cohort of healthy donors. Our results show that citrullination of fibrinogen is a common posttranslational modification in patients with cancer.

Role and intervention of PAD4 in NETs in acute respiratory distress syndrome

BACKGROUND

Sepsis is life-threatening organ dysfunction caused by a dysregulated host response to infection. Acute respiratory distress syndrome (ARDS) is a common sepsis-associated injury that can increase postoperative mortality but the mechanism is still unclear.

MAIN TEXT

The role of neutrophils in the pathophysiology of sepsis was deeply challenged after the discovery of NETosis, a process resulting in neutrophil extracellular traps (NETs) release. NETs can support thrombin generation and the concept of immunothrombosis has emerged as a new innate response to infection. Immunothrombosis leads to thrombosis in microvessels and supports immune cells together with specific thrombus-related molecules. ARDS is a common sepsis-associated organ injury. Immunothrombosis participates in thrombosis in pulmonary capillaries. Intervention regarding immunothrombosis in ARDS is a key scientific problem. PAD4 is the key enzyme regulating the NET skeleton protein histone H3 to citrulline histone to form NETs in immune thrombosis. This review summarizes NETosis and immunohaemostasis, ARDS and therapeutic opportunities targeting PAD4 via PAD4 inhibitors and lncRNAs potentially, providing future therapies.

CONCLUSIONS

We identified and summarized the fundamental definition of ARDS and the concept of immune thrombosis and its composition. NETs activation has become particularly relevant in the formation of immune thrombosis. The taskforce highlighted the intervention targets of PAD4, including noncoding RNAs, potentially providing future therapeutic targets to confront the high postoperative mortality of ARDS.

The Role of NETosis and Complement Activation in COVID-19-Associated Coagulopathies

Inflammation-induced coagulopathy is a common complication associated with coronavirus disease 2019 (COVID-19). We aim to evaluate the association of NETosis and complement markers with each other as well as their association with thrombogenicity and disease severity in COVID-19. The study included hospitalized patients with an acute respiratory infection: patients with SARS-CoV2 infection (COVpos, n = 47) or either pneumonia or infection-triggered acute exacerbated COPD (COVneg, n = 36). Our results show that NETosis, coagulation, and platelets, as well as complement markers, were significantly increased in COVpos patients, especially in severely ill COVpos patients. NETosis marker MPO/DNA complexes correlated with coagulation, platelet, and complement markers only in COVpos. Severely ill COVpos patients showed an association between complement C3 and SOFA (R = 0.48; p ≤ 0.028), C5 and SOFA (R = 0.46; p ≤ 0.038), and C5b-9 and SOFA (R = 0.44; p ≤ 0.046). This study provides further evidence that NETosis and the complement system are key players in COVID-19 inflammation and clinical severity. Unlike previous studies that found NETosis and complement markers to be elevated in COVID-19 patients compared to healthy controls, our findings show that this characteristic distinguishes COVID-19 from other pulmonary infectious diseases. Based on our results, we propose that COVID-19 patients at high risk for immunothrombosis could be identified via elevated complement markers such as C5.

Endothelial-dependent S-Sulfhydration of tissue factor pathway inhibitor regulates blood coagulation

Tissue factor pathway inhibitor (TFPI) is an important regulator of coagulation and a link between inflammation and thrombosis. Here we investigated whether endothelial cell-driven oxidative post-translational modifications could have an impact on TFPI activity. We focused on S-sulfhydration, which is a hydrogen sulfide-dependent post-translational modification that, in endothelial cells, is regulated by the enzyme cystathionine γ-lyase (CSE). The study made use of human primary endothelial cells and blood from healthy individuals or subjects with atherosclerosis as well as from mice lacking endothelial CSE. TFPI was S-sulfhydrated in endothelial cells from healthy individuals and mice, while the loss of endothelial CSE expression/activity reduced its modification. Non-S-sulfhydrated TFPI was no longer able to interact with factor Xa, which facilitated the activation of tissue factor. Similarly, non-S-sulfhydratable TFPI mutants bound less protein S, while supplementation with hydrogen sulfide donors, preserved TFPI activity. Phenotypically, loss of TFPI S-sulfhydration increased clot retraction, suggesting that this post-translational modification is a new endothelial cell-dependent mechanism that contributes to the regulation of blood coagulation.