Extracellular Chromatin Research Articles

NETosis and the Immune System in COVID-19: Mechanisms and Potential Treatments.

NETosis is a form of neutrophil death leading to the release of extracellular chromatin and the assembling of proteins, including antiviral proteins, primed by an initial pathogenic stimulus. Under certain specific conditions, neutrophils can exhibit a double-edged activity. This event has been implicated in COVID-19 among other conditions. Neutrophil extracellular traps (NETs) are involved in the pathogenesis of COVID-19 by promoting a pro-inflammatory and a procoagulant state leading to multiorgan failure. This particular form of host defense promoted by neutrophils is closely related to the well-known cytokine storm observed in severe COVID-19 patients. These two elements therefore represent possible targets for treatment of severe SARS-CoV-2 infections.

Pioneer neutrophils release chromatin within in vivo swarms.

Neutrophils are rapidly recruited to inflammatory sites where their coordinated migration forms clusters, a process termed neutrophil swarming. The factors that modulate early stages of neutrophil swarming are not fully understood, requiring the development of new in vivo models. Using transgenic zebrafish larvae to study endogenous neutrophil migration in a tissue damage model, we demonstrate that neutrophil swarming is a conserved process in zebrafish immunity, sharing essential features with mammalian systems. We show that neutrophil swarms initially develop around an individual pioneer neutrophil. We observed the violent release of extracellular cytoplasmic and nuclear fragments by the pioneer and early swarming neutrophils. By combining in vitro and in vivo approaches to study essential components of neutrophil extracellular traps (NETs), we provide in-depth characterisation and high-resolution imaging of the composition and morphology of these release events. Using a photoconversion approach to track neutrophils within developing swarms, we identify that the fate of swarm-initiating pioneer neutrophils involves extracellular chromatin release and that the key NET components gasdermin, neutrophil elastase, and myeloperoxidase are required for the swarming process. Together our findings demonstrate that release of cellular components by pioneer neutrophils is an initial step in neutrophil swarming at sites of tissue injury.

Neutrophil Extracellular Traps in Colorectal Cancer Progression and Metastasis.

Neutrophils form sticky web-like structures known as neutrophil extracellular traps (NETs) as part of innate immune response. NETs are decondensed extracellular chromatin filaments comprising nuclear and cytoplasmic proteins. NETs have been implicated in many gastrointestinal diseases including colorectal cancer (CRC). However, the regulatory mechanisms of NET formation and potential pharmacological inhibitors in the context of CRC have not been thoroughly discussed. In this review, we intend to highlight roles of NETs in CRC progression and metastasis as well as the potential of targeting NETs during colon cancer therapy.

Neutrophil Extracellular Traps Affecting Cardiovascular Health in Infectious and Inflammatory Diseases

Neutrophil extracellular traps (NETs) are web-like structures of decondensed extracellular chromatin fibers and neutrophil granule proteins released by neutrophils. NETs participate in host immune defense by entrapping pathogens. They are pro-inflammatory in function, and they act as an initiator of vascular coagulopathies by providing a platform for the attachment of various coagulatory proteins. NETs are diverse in their ability to alter physiological and pathological processes including infection and inflammation. In this review, we will summarize recent findings on the role of NETs in bacterial/viral infections associated with vascular inflammation, thrombosis, atherosclerosis and autoimmune disorders. Understanding the complex role of NETs in bridging infection and chronic inflammation as well as discussing important questions related to their contribution to pathologies outlined above may pave the way for future research on therapeutic targeting of NETs applicable to specific infections and inflammatory disorders.

Culprit site extracellular DNA and microvascular obstruction in ST-elevation myocardial infarction.

Extracellular chromatin and deoxyribonuclease (DNase) have been identified as important players of thrombosis, inflammation, and homeostasis in a murine model. We previously demonstrated that activated neutrophils release neutrophil extracellular traps (NETs) at the culprit site in ST-elevation myocardial infarction (STEMI), which significantly contribute to extracellular chromatin burden, and are associated with larger infarcts. To understand the correlation between neutrophil activation, extracellular chromatin, and infarct size (IS), we investigated these parameters in a porcine myocardial infarction model, and at different time points and sites in a prospective STEMI trial with cardiac magnetic resonance (CMR) endpoints. In a prospective STEMI trial (NCT01777750), 101 STEMI patients were included and blood samples were obtained from first medical contact until 6 months after primary percutaneous coronary intervention (pPCI) including direct sampling from the culprit site. CMR was performed 4 ± 2 days and 6 months after pPCI. Neutrophil counts, markers of extracellular chromatin, and inflammation were measured. Double-stranded deoxyribonucleic acid (dsDNA), citrullinated histone 3, nucleosomes, myeloperoxidase, neutrophil elastase, and interleukin (IL)-6 were significantly increased, while DNase activity was significantly decreased at the culprit site in STEMI patients. High neutrophil counts and dsDNA levels at the culprit site correlated with high microvascular obstruction (MVO) and low ejection fraction (EF). High DNase activity at the culprit site correlated with low MVO and high EF. In correspondence, dsDNA correlated with IS in the porcine myocardial infarction model. In porcine infarcts, neutrophils and extracellular chromatin were detected in congested small arteries corresponding with MVO. Markers of neutrophil activation, extracellular chromatin, DNase activity and CMR measurements correlated with markers of systemic inflammation C-reactive protein and IL-6 in patients. NETs and extracellular chromatin are important determinants of MVO in STEMI. Rapid degradation of extracellular chromatin by DNases appears to be crucial for microvascular patency and outcome.

Recent progress in the mechanistic understanding of NET formation in neutrophils.

Neutrophils are the most abundant circulating white blood cells and one of the major cell types of the innate immune system. Neutrophil extracellular traps (NETs) are a result of the extracellular release of nuclear chromatin from the ruptured nuclear envelope and plasma membrane. The externalized chromatin is an ancient defense weapon for animals to entrap and kill microorganisms in the extracellular milieu, thus protecting animals ranging from lower invertebrates to higher vertebrates. Although the externalized chromatin has the advantage of acting as anti-infective to protect against infections, extracellular chromatin might be problematic in higher vertebrate animals as they have an adaptive immune system that can trigger further immune or autoimmune responses. NETs and their associated nuclear and/or cytoplasmic components may induce sterile inflammation, immune, and autoimmune responses, leading to various human diseases. Though important in human pathophysiology, the cellular and molecular mechanisms of NET formation (also called NETosis) are not well understood. Given that nuclear chromatin forms the backbone of NETs, the nucleus is the root of the nuclear DNA extracellular traps. Thus, nuclear chromatin decondensation, along with the rupture of nuclear envelope and plasma membrane, is required for nuclear chromatin extracellular release and NET formation. So far, most of the literature focuses on certain signaling pathways, which are involved in NET formation but without explanation of cellular events and morphological changes described above. Here, we have summarized emerging evidence and discuss new mechanistic understanding, with our perspectives, in NET formation in neutrophils.

Increased Concentrations of Circulating Soluble MHC Class I-Related Chain A (sMICA) and sMICB and Modulation of Plasma Membrane MICA Expression: Potential Mechanisms and Correlation With Natural Killer Cell Activity in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a severe autoimmune disease of unknown etiology. The major histocompatibility complex (MHC) class I-related chain A (MICA) and B (MICB) are stress-inducible cell surface molecules. MICA and MICB label malfunctioning cells for their recognition by cytotoxic lymphocytes such as natural killer (NK) cells. Alterations in this recognition have been found in SLE. MICA/MICB can be shed from the cell surface, subsequently acting either as a soluble decoy receptor (sMICA/sMICB) or in CD4+ T-cell expansion. Conversely, NK cells are frequently defective in SLE and lower NK cell numbers have been reported in patients with active SLE. However, these cells are also thought to exert regulatory functions and to prevent autoimmunity. We therefore investigated whether, and how, plasma membrane and soluble MICA/B are modulated in SLE and whether they influence NK cell activity, in order to better understand how MICA/B may participate in disease development. We report significantly elevated concentrations of circulating sMICA/B in SLE patients compared with healthy individuals or a control patient group. In SLE patients, sMICA concentrations were significantly higher in patients positive for anti-SSB and anti-RNP autoantibodies. In order to study the mechanism and the potential source of sMICA, we analyzed circulating sMICA concentration in Behcet patients before and after interferon (IFN)-α therapy: no modulation was observed, suggesting that IFN-α is not intrinsically crucial for sMICA release in vivo. We also show that monocytes and neutrophils stimulated in vitro with cytokines or extracellular chromatin up-regulate plasma membrane MICA expression, without releasing sMICA. Importantly, in peripheral blood mononuclear cells from healthy individuals stimulated in vitro by cell-free chromatin, NK cells up-regulate CD69 and CD107 in a monocyte-dependent manner and at least partly via MICA-NKG2D interaction, whereas NK cells were exhausted in SLE patients. In conclusion, sMICA concentrations are elevated in SLE patients, whereas plasma membrane MICA is up-regulated in response to some lupus stimuli and triggers NK cell activation. Those results suggest the requirement for a tight control in vivo and highlight the complex role of the MICA/sMICA system in SLE.

The vitals of NETs.

Neutrophils produce neutrophil extracellular traps (NETs) by expelling their extracellular chromatin embedded with citrullinated histone H3, myeloperoxidase, and other intracellular molecules. Since their discovery in 2004, numerous articles have demonstrated the mechanism of NET formation and their function in innate immunity and inflammation. NET components often play an antimicrobial role, but excessive NETs are deleterious and can cause inflammation and tissue damage. This review highlights recent advancements in the identification of novel pathways and mechanisms of NET formation. We also focus on the specific damaging impact of NETs in individual organs. We then discuss the progress and limitations of various NET detection assays. Collectively, these vital aspects of NETs significantly improve our understanding of the pathobiology of NETs and future diagnostics and therapeutic tools for examining and modulating NETs in inflammatory diseases.

Transcriptome and proteome mapping in the sheep atria reveal molecular featurets of atrial fibrillation progression.

AimsAtrial fibrillation (AF) is a progressive cardiac arrhythmia that increases the risk of hospitalization and adverse cardiovascular events. There is a clear demand for more inclusive and large-scale approaches to understand the molecular drivers responsible for AF, as well as the fundamental mechanisms governing the transition from paroxysmal to persistent and permanent forms. In this study, we aimed to create a molecular map of AF and find the distinct molecular programmes underlying cell type-specific atrial remodelling and AF progression.Methods and resultsWe used a sheep model of long-standing, tachypacing-induced AF, sampled right and left atrial tissue, and isolated cardiomyocytes (CMs) from control, intermediate (transition), and late time points during AF progression, and performed transcriptomic and proteome profiling. We have merged all these layers of information into a meaningful three-component space in which we explored the genes and proteins detected and their common patterns of expression. Our data-driven analysis points at extracellular matrix remodelling, inflammation, ion channel, myofibril structure, mitochondrial complexes, chromatin remodelling, and genes related to neural function, as well as critical regulators of cell proliferation as hallmarks of AF progression. Most important, we prove that these changes occur at early transitional stages of the disease, but not at later stages, and that the left atrium undergoes significantly more profound changes than the right atrium in its expression programme. The pattern of dynamic changes in gene and protein expression replicate the electrical and structural remodelling demonstrated previously in the sheep and in humans, and uncover novel mechanisms potentially relevant for disease treatment.ConclusionsTranscriptomic and proteomic analysis of AF progression in a large animal model shows that significant changes occur at early stages, and that among others involve previously undescribed increase in mitochondria, changes to the chromatin of atrial CMs, and genes related to neural function and cell proliferation.

Neutrophilic Extracellular Traps (NETs); A Subset of Smudge Cells Identifiable by Peripheral Smear Autoanalyzers in the Rising Era of Artificial Intelligence

Abstract Background Digitized microscopy such as CellaVision® technology has revolutionized the laboratory. Smudge cells, also called basket cells, are usually seen in lymphoproliferative disorders representing remnants from degenerated lymphocytes (DLs). CellaVision® classifies DLs and web-like remnants as smudge cells. The morphology of the web-like remnants is compatible with Neutrophil Extracellular Traps (NETs) where extracellular decondensed DNA chromatin network is formed as one of several neutrophilic reactions to stress. Currently, we lack clinical tests that reliably identify and quantify NETs. Aims To develop an in-vitro model for NETs formation in blood, create a library of their morphological changes at different maturation stages; correlate their presence to infections in absence of leukocytosis and develop an artificial intelligence platform (AI-Heme-1) for their detection. Methods A library was built to develop AI-Heme-1 where NETs were induced with classic triggers (phorbol-myristate-acetate, lipopolysaccharide and ionomycin) in EDTA whole blood from normal subjects. Smears were prepared at 30 minutes intervals for 24 hours to identify NETs by Immunofluorescence and immunohistochemistry. WBC differentials were performed by CellaVision® to capture different stages of NETs. AI-Heme-1 was modified from Python online convolutional neural network. For the clinical correlation, smears with >20% smudge cells were classified morphologically as NETs vs. DLs compared to a control group, < 5% smudge cells. We used morphologic characteristics, immunohistochemistry, immunofluorescence and flow cytometry to differentiate NETs from DLs. Medical chart review performed by blinded investigators, included patient demographics, CBC and presence of microbial infection occurring < 1 week of sample collection. Statistical analyses included two sided t-test and chi square. Results The classical triggers for Netosis showed consistent morphological changes following a canonical order: vacuolation, nuclear decondensation, degranulation and chromatin ejection. These cell remnants were positive for citrullinated histones, myeloperoxidase, leukocyte alkaline phosphatase and neutrophil elastase by immunofluorescence. On Wright Giemsa stain, web-like remnants resembling NETs stained for SytoxGreen. On flow cytometry, NETs were large with extracellular DNA and MPO. For the clinical study group of >20% smudge cells, 88 were morphologically designated as NETs, 8 as DL vs. 59 as control group. A random sampling from >20% smudge cells showed cases with NET subclassification stained strongly with myeloperoxidase, neutrophil elastase and SytoxGreen while DLs were negative. Comparing patients with >20% smudge and NET sub-classification to <5% smudge cells, the formers had higher incidence of bacterial and viral infections (p=0.009/0.005 and p=0.008/0.007). Conclusions Our study was able to identify NETs on peripheral smears performed by a routine Hematology Autoanalyzer using a reliable set of morphologic characteristics, immunohistochemical stains and flow cytometry. It supports data that associate NETs with infections in the absence of leukocytosis. AI-Heme-1 was able to identify NETs on blood smears. This approach can provide a rapid, early and accurate tool to screen patients with infections.

Neutrophil Extracellular Traps Increase Airway Mucus Viscoelasticity and Slow Mucus Particle Transit.

Mucus obstruction is a key feature of many inflammatory airway diseases. Neutrophil extracellular traps (NETs) are released upon neutrophil stimulation and consist of extracellular chromatin networks studded with cytotoxic proteins. When released in the airways, these NETs can become part of the airway mucus. We hypothesized that the extracellular DNA and/or oxidative stress (e.g., by the release of reactive oxygen species and myeloperoxidase during NETs formation in the airways) would increase mucus viscoelasticity. We collected human airway mucus from endotracheal tubes of healthy patients admitted for elective surgery and coincubated these samples with NETs from phorbol 12-myristate 13-acetate-stimulated neutrophils. Unstimulated neutrophils served as controls, and blocking experiments were performed with dornase alfa for extracellular DNA and the free radical scavenger dimethylthiourea for oxidation. Compared with controls, the coincubation of mucus with NETs resulted in 1) significantly increased mucus viscoelasticity (macrorheology) and 2) significantly decreased mesh pore size of the mucus and decreased movement of muco-inert nanoparticles through the mucus (microrheology), but 3) NETs did not cause visible changes in the microstructure of the mucus by scanning EM. Incubation with either dornase alfa or dimethylthiourea attenuated the observed changes in macrorheology and microrheology. This suggests that the release of NETs may contribute to airway mucus obstruction by increasing mucus viscoelasticity and that this effect is not solely due to the release of DNA but may in part be due to oxidative stress.

Cardiovascular Disease in Systemic Lupus Erythematosus: Recent Data on Epidemiology, Risk Factors and Prevention.

Systemic Lupus Erythematosus (SLE) is associated with increased risk for accelerated atherosclerosis and cardiovascular (CV) events including coronary heart disease, cerebrovascular and peripheral artery disease. CV events occur both early and late during the disease course, with younger patients being at much higher risk than age-matched counterparts. The risk cannot be fully accounted for by the increased prevalence of traditional atherosclerotic factors and may be due to pathophysiologic intermediates such as type I interferons and other inflammatory cytokines, oxidative stress, activated granulocytes and production of extracellular chromatin traps, antiphospholipid and other autoantibodies causing dysfunction of lipoproteins, altogether resulting in endothelial injury and pro-atherogenic dyslipidaemia. These mechanisms may be further aggravated by chronic intake of prednisone (even at doses <7.5 mg/day), whereas immunomodulatory drugs, especially hydroxychloroquine, may exert antiatherogenic properties. To date, there is a paucity of randomized studies regarding the effectiveness of preventative strategies and pharmacological interventions specifically in patients with SLE. Nevertheless, both the European League Against Rheumatism recommendations and extrapolated evidence from the general population emphasize that SLE patients should undergo regular monitoring for atherosclerotic risk factors and calculation of the 10-year CV risk. Risk stratification should include diseaserelated factors and accordingly, general (lifestyle modifications/smoking cessation, antihypertensive and statin treatment, low-dose aspirin in selected cases) and SLE-specific (control of disease activity, minimization of glucocorticoids, use of hydroxychloroquine) preventive measures be applied as appropriate. Further studies will be required regarding the use of non-invasive tools and biomarkers for CV assessment and of risk-lowering strategies tailored to SLE.

Autoantibodies to neutrophil extracellular traps represent a potential serological biomarker in rheumatoid arthritis

Neutrophil extracellular traps (NETs) are networks of extracellular chromatin decorated with antimicrobial proteins, formed by neutrophils to entrap pathogens. NETs have been implicated in the generation of autoimmune reactions. Here, we investigate the reactivity of rheumatoid arthritis (RA) serum antibodies with NETs and explore whether anti-NET antibodies (ANETA) have a potential as biomarker in RA. To quantify ANETA, we developed an ELISA with NETs isolated from stimulated human neutrophils and verified the results by immunofluorescence staining of NETs. ANETA were detected in 22%–69% of RA sera. No significant differences were observed in the reactivity of RA sera with NETs originating from RA patients and healthy control neutrophils, nor with NETs induced by phorbol 12-myristate 13-acetate or the calcium ionophore A23187. ANETA were detected already at baseline in newly diagnosed RA patients and both increased and decreased levels were observed in samples with a median follow-up of 7 years. By ANETA ELISA, we showed that ANETA are also present in sera of patients with systemic lupus erythematosus (36%), Sjögren's syndrome (76%) and scleroderma (61%). In addition to antibodies to NETs, also the presence of NETs or NET fragments in RA sera was determined using a sandwich ELISA. Elevated levels of NETs or NET fragments were detected in 32% of the sera. To assess the potency of ANETA as a biomarker in RA, we compared ANETA positivity with other clinical features. The presence of ANETA was significantly higher in rheumatoid factor (RF)-positive patients, but did not correlate with anti-citrullinated protein antibodies (ACPA), nor with the presence of NET fragments in serum. In addition, no correlation was observed with age, gender, onset of the disease, disease activity and inflammatory markers. These findings suggest that ANETA may be an independent biomarker in RA and possibly also in other autoimmune diseases.

Endogenous PAD4 in Breast Cancer Cells Mediates Cancer Extracellular Chromatin Network Formation and Promotes Lung Metastasis.

Peptidyl arginine deiminase 4 (PAD4/PADI4) is a posttranslational modification enzyme that converts protein arginine or mono-methylarginine to citrulline. The PAD4-mediated hypercitrullination reaction in neutrophils causes the release of nuclear chromatin to form a chromatin network termed neutrophil extracellular traps (NET). NETs were first described as antimicrobial fibers that bind and kill bacteria. However, it is not known whether PAD4 can mediate the release of chromatin DNA into the extracellular space of cancer cells. Here, we report that murine breast cancer 4T1 cells expressing high levels of PADI4 can release cancer extracellular chromatin networks (CECN) in vitro and in vivo. Deletion of Padi4 using CRISPR/Cas9 abolished CECN formation in 4T1 cells. Padi4 deletion from 4T1 cells also reduced the rate of tumor growth in an allograft model, and decreased lung metastasis by 4T1 breast cancers. DNase I treatment, which degrades extracellular DNA including CECNs, also reduced breast to lung metastasis of Padi4 wild-type 4T1 cells in allograft experiments in the Padi4-knockout mice. We further demonstrated that DNase I treatment in this mouse model did not alter circulating tumor cells but decreased metastasis through steps after intravasation. Taken together, our genetic studies show that PAD4 plays a cell autonomous role in cancer metastasis, thus revealing a novel strategy for preventing cancer metastasis by inhibiting cancer cell endogenous PAD4. IMPLICATIONS: This study shows that PADI4 can mediate the formation of CECNs in 4T1 cells, and that endogenous PADI4 plays an essential role in breast cancer lung metastasis. VISUAL OVERVIEW: http://mcr.aacrjournals.org/content/molcanres/18/5/735/F1.large.jpg.

Dolphin-derived NETosis results in rapid Toxoplasma gondii tachyzoite ensnarement and different phenotypes of NETs

Toxoplasma gondii is a cosmopolitan zoonotic parasite and nowadays considered as an emerging neozoan pathogen in the marine environment. Cetacean innate immune reactions against T. gondii stages have not yet been investigated. Thus, T. gondii tachyzoites were utilized to trigger neutrophil extracellular traps (NETs) in bottlenose dolphin (Tursiops truncatus) polymorphonuclear neutrophils (PMN). Scanning electron microscopy unveiled T. gondii tachyzoites as potent and rapid inducers of cetacean-derived NETosis. Co-localization of extracellular chromatin with global histones, granulocytic myeloperoxidase and neutrophil elastase confirmed classical characteristics of NETosis. Interestingly, different phenotypes of NETs were induced by tachyzoites resulting in spread, diffuse and aggregated NET formation and moreover, ‘anchored’ and ‘cell free’ NETosis was also detected.Current data indicate that cetacean-derived NETosis might represent an early, ancient and well-conserved host innate defense mechanism that not only acts against T. gondii but might also occur in response to other closely related emerging apicomplexan parasites affecting marine cetaceans.

Treatment with DNases rescues hidden neutrophil elastase from aggregated NETs.

The release of neutrophil extracellular traps (NETs) is one of the weapons neutrophils have in their armory. NETs consist of extracellular chromatin fibers decorated with a plethora of cytoplasmic and granular proteins, such as the antimicrobial serine protease neutrophil elastase (NE). Because the first description of NETs as beneficial to the host, reports on their double-faced role in health and disease have considerably increased recently. On one hand, NETs reportedly trap and kill bacteria and also participate in the resolution of the acute inflammation associated with infection and with tissue damage. On the other hand, numerous negative aspects of NETs contribute to the etiopathogenesis of autoimmune disorders. Employing soluble and solid fluorescent substrates, we demonstrate the interaction of NE with aggregated NETs (aggNETs), the limitation of its enzymatic activity and the containment of the enzyme from surrounding tissues. These events prevent the spread of inflammation and tissue damage. The detection of DNase1-dependent elevation of NE activity attests the continuous presence of patrolling neutrophils forming NETs and aggNETs even under conditions physiologic conditions.

Charcot-Leyden Crystals in Eosinophilic Inflammation: Active Cytolysis Leads to Crystal Formation.

Charcot-Leyden crystals (CLCs), slender bipyramidal hexagonal crystals, were first described by Jean-Martin Charcot in 1853, predating Paul Ehrlich's "discovery" of eosinophils by 26years. To date, CLCs are known as a classical hallmark of eosinophilic inflammation. CLC protein expresses palmitate cleaving lysophospholipase activity and is a member of the family of S-type lectins, galectin-10. We summarize current knowledge regarding the pathological observations of CLCs and their mechanism of generation focusing on eosinophil cell death. The presence of CLCs in vivo has been consistently associated with lytic eosinophils. Recent evidence revealed that cytolysis represents the occurrence of extracellular trap cell death (ETosis), an active non-apoptotic cell death process releasing filamentous chromatin structure. Galectin-10 is a predominant protein present within the cytoplasm of eosinophils but not stored in secretory granules. Activated eosinophils undergo ETosis and loss of galectin-10 cytoplasmic localization results in intracellular CLC formation. Free galectin-10 released following plasma membrane disintegration forms extracellular CLCs. Of interest, galectin-10-containing extracellular vesicles are also released during ETosis. Mice models indicated that CLCs could be a novel therapeutic target for Th2-type airway inflammation. The concept of ETosis, which represents a major fate of activated eosinophils, expands our current understanding by which cytoplasmic galectin-10 is crystalized/externalized. Besides CLCs and free galectin-10, cell-free granules, extracellular chromatin traps, extracellular vesicles, and other alarmins, all released through the process of ETosis, have novel implications in various eosinophilic disorders.

Extracellular Chromatin Triggers Release of Soluble CEACAM8 Upon Activation of Neutrophils.

Increased concentrations of extracellular chromatin are observed in cancer, sepsis, and inflammatory autoimmune diseases like systemic lupus erythematosus (SLE) or rheumatoid arthritis (RA). In SLE and RA, extracellular chromatin may behave as a danger-associated molecular pattern (DAMP). Polymorphonuclear neutrophils (PMN) are described as typical pro-inflammatory cells but possess also immunoregulatory properties. They are activated in SLE and RA but surprisingly remain moderately studied in these diseases, and especially the disease-associated stimuli triggering PMN activation are still not completely characterized. PMN express plasma membrane carcinoembryonic antigen-related cell adhesion molecule (CEACAM) 8 (CD66b) and secrete a soluble form of CEACAM8 after activation. Soluble CEACAM8 has in turn immunoregulatory functions. However, few natural stimuli inducing soluble CEACAM8 secretion by PMN have been identified. Here we demonstrate for the first time that extracellular chromatin triggers secretion of soluble CEACAM8 by primary human PMN. Priming of PMN was not required. Secretion was associated with activation of PMN. Similar induction of soluble CEACAM8 release was observed with purified mono-nucleosomes as well as long chromatin fragments and occurred in a time-dependent and concentration-dependent manner. Results indicate that chromatin induces both neo-synthesis of soluble CEACAM8 and release of soluble CEACAM8 through degranulation. In addition, we report the presence of soluble CEACAM8 at high concentration in the synovial fluid of RA patients. Thus, we describe here a novel mechanism by which a natural DAMP, with inflammatory properties in SLE and RA, induces soluble CEACAM8 secretion by activated PMN with potential immunoregulatory consequences on other immune cells, including PMN.

Chromatin outside the cell: the new paradigm in biology

Since the discovery of the structure of DNA by Watson and Crick in 1953, “DNA inside the nucleus” has been the dominant biological paradigm which has spawned the complex science of molecular biology and genomics. Although this reductionist approach has been a commercial success, produced an enormous quantity of information and given us intricate insights into cellular functioning, it has provided little understanding of human health and disease and to that extent has been largely unproductive. This is primarily because this DNA-centric molecular approach has entirely ignored physiology. We know now that there is a huge amount of DNA in the form of extra-cellular cell-free chromatin (cfCh) that exists in the extracellular compartment of the body, including in circulation, that is derived from the billions of cells that die in the body every day

Neutrophil Extracellular Traps Promote Hypercoagulability in ST-Elevated Myocardial Infarction Following Fibrinolytic Administration

Introduction:Fibrinolysis plays an important role in the treatment of ST-elevated myocardial infarction (STEMI) when percutaneous coronary intervention is not readily available. Early and successful myocardial reperfusion with thrombolytic therapy effectively reduces the infarct size and improves the clinical outcome. However, the process of restoring blood flow to the ischemic myocardium can induce injury and reduce the beneficial effects of myocardial reperfusion. Previous studies had shown that platelets, leukocytes and TF play important role in thrombotic complications after fibrinolysis in AMI. However, there are still 10-15% patients who have risk for re-occlusion after antiplatelet and anticoagulant therapies. Thus, we speculate that there may be other mechanisms involved in the hypercoagulability after STEMI fibrinolysis. Neutrophil extracellular traps (NETs) are double-edge swords that could ensnare and kill microbial pathogens but also contribute to thrombosis. However, the role of NETs during STEMI fibrinolysis-induced re-occlusion is largely unknown. Our aims were to determine the procoagulant role of NETs after successful thrombolysis, and to elucidate its interaction with endothelial cells (ECs).Methods:31 STEMI patients with successfully fibrinolysis and 12 healthy controls were enrolled. Patient blood samples were collected at 0 h, 2 h, 6 h, 12 h and 24 h after fibrinolysis. Cell-free DNA (cf-DNA) was quantified using the Quant-iT PicoGreen dsDNA Assay Kit. ELISA was used to detect MPO-DNA complexes and TAT (thrombin-antithrombin) complexes. Wright-Giemsa and immunofluorescence confocal microscope were used to analyze and quantify NETs formation in neutrophil cells. ECs were incubated in growth media containing 20% pooled serum obtained from healthy donors in the presence or absence of 20-fold concentrated neutrophil extracellular chromatin. The procoagulant activity (PCA) of neutrophils and ECs was measured by clotting time and purified coagulation complex assays. DNase I or anti-TF were included in the inhibition assays.Results: We found that cf-DNA, MPO-DNA and TAT are significantly reduced at 2 hours in STEMI patients with successful fibrinolysis. Their levels then increased and peaked at 6 hours (Figure 1A, B, E). Interestingly, the level of cf-DNA at 6 hours in STEMI thrombotic patients was positively correlated with TAT (r=0.959; p<0.01; Figure 1G). Wright-Giemsa and immunofluorescence staining showed that NETs were released by STEMI reperfusion neutrophils or by control neutrophils treated with plasma obtained from STEMI patients with fibrinolysis (Figure 1D,F), and the percentage of NETs-releasing PMNs was about 30% (Figure 1C). Isolated neutrophils from fibrinolytic patients in vitro demonstrated significantly shortened coagulation time and increased fibrin formation after 2 hours fibrinolysis, and peaked at 6 hours. DNase I but not anti-tissue factor antibody could inhibit these effects. Co-incubation assays revealed that NETs triggered PS exposure on ECs, converting them to a procoagulant phenotype. Confocal imaging of NETs-treated ECs illustrated that bound FVa and FXa colocalized within PS-enriched areas of ECs to form prothrombinase, and further supported fibrin formation. Moreover, patients with recurrent ischemia showed significantly higher NETs release and thrombin generation than non-recurrent ischemia.Conclusions: Our study reveals that the PCA of STEMI following fibrinolytic administration decrease after 2 hours, then increase and peak at 6 hours, which is at least partly due to the release of NETs induced by activated PMNs. Additionally, NETs partly contribute to ECs injury after myocardial reperfusion. DNase I can disconnect NETs and may therefore serve as a promising therapeutic target in STEMI reinfarction and recurrent ischemia. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.