NETs detection and quantification in paraffin embedded samples using confocal microscopy

Neutrophil extracellular traps are increased after extracorporeal membrane oxygenation support initiation and present in thrombus: A preclinical study using sheep as an animal model

BACKGROUND

The balance between thrombosis and hemostasis is a difficult issue during extracorporeal membrane oxygenation (ECMO) support. The pathogenesis leading to thrombotic complications during ECMO support is not well understood. Neutrophil extracellular traps (NETs) were reported to participate in thrombosis and have a key role in inflammation. This study aimed to explore the role of NETs in thrombosis during ECMO support and investigate NETs as a predictive biomarker for thrombotic complications during ECMO assistance.

METHODS

Ten ovine models of ECMO support were established. Animals were then randomly divided into 2 groups (5 sheep/group): venoarterial (VA) ECMO group and venovenous (VV) ECMO group. The venous blood samples were collected at different time points. Markers of NETs were detected in plasma, neutrophils, and thrombi from the vessels and membrane. Moreover, circulating NETs levels in 8 adults treated in the intensive care unit (ICU) who received VA-ECMO and 8 healthy controls were detected; patient survival was also recorded.

RESULTS

In vivo study showed that neutrophils and NETs markers (dsDNA and citH3) levels were significantly elevated 6 h after ECMO compared to baseline. Isolated neutrophils from fresh blood at 6 h could release more NETs. dsDNA and citH3 levels were significantly higher in the VA mode than in the VV mode. NETs were found in thrombi from the vessel and membrane. Clinical data further revealed that dsDNA, citH3, and nucleosomes were higher in patients who received ECMO than in healthy controls.

CONCLUSIONS

These data suggest NETs might be associated with thrombus during ECMO support, especially in the VA mode. These findings provide new insight into preventing thrombotic complications by targeting NETs. Also, NETs may potentially become an early warning biomarker for thrombosis under ECMO assistance.

Prognostic implications of Neutrophil Extracellular Traps in coronary thrombi of patients with ST-elevation myocardial infarction

AIMS

The mechanisms of coronary thrombosis can influence prognosis after STEMI and allow for different treatment groups to be identified; an association between neutrophil extracellular traps (NETs) and unfavorable clinical outcomes has been suggested. Our aim was to determine the role played by NETs in coronary thrombosis and their influence on prognosis. The role of other histological features in prognosis and the association between NETs and bacteria in the coronary thrombi were also explored.

METHODS AND RESULTS

We studied 406 patients with STEMI in which coronary thrombi were consecutively obtained by aspiration during angioplasty between 2012 and 2018. Analysis of NETs in paraffin-embedded thrombi was based on the colocalization of specific NET components by means of confocal microscopy. Immunohistochemistry stains were used to identify plaque fragments. Fluorescence in situ hybridization was used to detect bacteria. NETs were detected in 51% of the thrombi [NET density, median (IQR): 25% (17-38%)]. The median follow-up was 47 months (95% CI 43-51); 105 (26%) patients experienced major adverse cardiac events (MACE). A significant association was found between the presence of NETs in coronary aspirates and the occurrence of MACE in the first 30 days after infarction (HR 2.82; 95% CI 1.26-6.35, p=.012), mainly due to cardiac deaths and stent thrombosis.

CONCLUSIONS

The presence of NETs in coronary thrombi was associated with a worse prognosis soon after STEMI. In some patients, NETs could be a treatment target and a feasible way to prevent reinfarction.

Assessment of Neutrophil Extracellular Traps in Coronary Thrombus of a Case Series of Patients With COVID-19 and Myocardial Infarction

Importance

Severe coronavirus disease 2019 (COVID-19) is characterized by the intense formation of neutrophil extracellular traps (NETs), leading to the occlusion of microvessels, as shown in pulmonary samples. The occurrence of ST-elevated myocardial infarction (STEMI) is a serious cardiac manifestation of COVID-19; the intrinsic mechanism of coronary thrombosis appears to still be unknown.

Objective

To determine the role of NETs in coronary thrombosis in patients with COVID-19.

Design, Setting, and Participants

This was a consecutive series of patients with COVID-19 at an academic tertiary hospital in Madrid, Spain, who underwent primary coronary interventions for STEMI in which coronary aspirates were obtained in the catheterization laboratory using a thrombus aspiration device. Patients with COVID-19 who experienced a STEMI between March 23 and April 11, 2020, from whom coronary thrombus samples were aspirated during primary coronary intervention, were included in the analysis. These patients were compared with a series conducted from July 2015 to December 2015 of patients with STEMI.

Main Outcomes and Measures

The presence and quantity of NETs in coronary aspirates from patients with STEMI and COVID-19. The method for the analysis of NETs in paraffin-embedded coronary thrombi was based on the use of confocal microscopy technology and image analysis for the colocalization of myeloperoxidase-DNA complexes and citrullinated histone H3. Immunohistochemical analysis of thrombi was also performed. Clinical and angiographic variables were prospectively collected.

Results

Five patients with COVID-19 were included (4 men [80%]; mean [SD] age, 62 [14] years); the comparison group included 50 patients (44 males [88%]; mean [SD] age, 58 [12] years). NETs were detected in the samples of all 5 patients with COVID-19, and the median density of NETs was 61% (95% CI, 43%-91%). In the historical series of patients with STEMI, NETs were found in 34 of 50 thrombi (68%), and the median NET density was 19% (95% CI, 13%-22%; P < .001). All thrombi from patients with COVID-19 were composed of fibrin and polymorphonuclear cells. None of them showed fragments of atherosclerotic plaque or iron deposits indicative of previous episodes of plaque rupture.

Conclusions and Relevance

In this small case series of patients with COVID-19 and myocardial infarction, NETs seem to play a major role in the pathogenesis of STEMI in COVID-19 disease. Our findings support the idea that targeting intravascular NETs might be a relevant goal of treatment and a feasible way to prevent coronary thrombosis in patients with severe COVID-19 disease.

Gold nanoparticles synergize with bacterial lipopolysaccharide to enhance class A scavenger receptor dependent particle uptake in neutrophils and augment neutrophil extracellular traps formation

Gold nanoparticles (AuNPs) are extensively utilized in biomedical fields. However, their potential interaction with host cells has not been comprehensively elucidated. In this study, we demonstrated a size-dependent effect of AuNPs to synergize with bacterial lipopolysaccharide (LPS) in promoting neutrophil extracellular traps (NETs) release in human peripheral neutrophils. Mechanistically, LPS was more efficient to contact with 10 nm AuNPs and promote their uptake in neutrophils compared to 40 and 100 nm AuNPs, leading to a synergistic upregulation of class A scavenger receptor (SRA) which mediated AuNPs uptake and triggered activation of extracellular regulated protein kinase (ERK) and p38. Blocking SRA or inhibiting ERK and p38 activation remarkably abrogated the effect of AuNPs and LPS to induce NETs formation. Further experiments demonstrated that AuNPs and LPS augmented the production of cytosolic reactive oxygen species (ROS) in p38 and ERK dependent manner, through upregulating and activating NADPH oxidase 2 (NOX2). Accordingly, scavenging of ROS or inhibiting the NOX2 dampened NETs release induced by combined AuNPs and LPS treatment. AuNPs and LPS also synergized to upregulate reactive oxygen species modulator 1 (ROMO1) via activating ERK, thereby increasing mitochondrial ROS generation and promoting the release of NETs. In summary, we provide new evidences about the synergy of AuNPs and LPS to augment cellular responses in neutrophils, which implicates the need to consider the amplifying effect by pathogenic stimuli when utilizing nanomaterials in infectious or inflammatory conditions.

An Imaging Flow Cytometry Method to Measure Citrullination of H4 Histone as a Read-out for Neutrophil Extracellular Traps Formation

The formation of neutrophil extracellular traps (NETs) is thought to play a critical role in infections and propagating sterile inflammation. Histone citrullination is an essential and early step in NETs formation, detectable prior to the formation of the hallmark extracellular DNA-scaffolded strands. In addition to the classical microscopy method, new technologies are being developed for studies of NETs and their detection, both for research and clinical purposes. Classical microscopy studies of NETs are subjective, low throughput and semi-quantitative, and limited in their ability to capture the early steps. We have developed this novel Imaging Flow Cytometry (IFC) method that specifically identifies and quantifies citrullination of histone H4 as a NETs marker and its relationship with other alterations at nuclear and cellular level. These include nuclear decondensation and super-condensation, multi-lobulated nuclei versus 1-lobe nuclei and cell membrane damage. NETs markers can be quantified following variable periods of treatment with NETs inducers, prior to the formation of the specific extracellular DNA-scaffolded strands. Because these high throughput image-based cell analysis features can be performed with statistical rigor, this protocol is suited for both experimental and clinical applications as well as clinical evaluations of NETosis as a biomarker.

Age dependent trans-cellular propagation of human tau aggregates in Drosophila disease models

Tauopathies is a class of neurodegenerative disorders which involves the transformation of physiological tau into pathogenic tau. One of the prime causes reported to drive this conversion is tau hyperphosphorylation and the subsequent propagation of pathogenic protein aggregates across the nervous system. Although past attempts have been made to deduce the details of tau propagation, yet not much is known about its mechanism. A better understanding of this aspect of disease pathology can prove to be beneficial for the development of diagnostic and therapeutic approaches. For the first time, we demonstrate that the human tau possesses an intrinsic property to spread trans-cellularly in the fly nervous system irrespective of the tau allele or the neuronal tissue type. Aggregate migration restricted by targeted down-regulation of a specific kinase, elucidates the role of hyper-phosphorylation in its movement. On the contrary to the previous models, our study delivers an easy and rapid in-vivo model for comprehensive examination of tau migration pathology. Henceforth, the developed model would not only be immensely helpful in uncovering the mechanistic in-depths of tau propagation pathology but also aid in modifier and/or drug screening for amelioration of tauopathies.

Lysophosphatidic acid promotes thrombus stability by inducing rapid formation of neutrophil extracellular traps: A new mechanism of thrombosis

BACKGROUND

Lysophosphatidic acid (LPA), a bioactive phospholipid released by activated platelets, can induce platelet shape changes and aggregation, which may play an important role in thrombosis. In contrast, the interaction of LPA with neutrophils in thrombosis has not been studied. Recently, neutrophil extracellular traps (NETs) have been shown to bind plasma proteins and activate platelets, which promotes thrombosis.

OBJECTIVES

To investigate whether LPA could activate neutrophils to release NETs, predisposing to thrombosis and promoting thrombus stability.

METHODS

Levels of neutrophils, NETs, and LPA were detected in 56 participants. Immunofluorescence of NETs and autotaxin, the LPA-producing ectoenzyme, were performed. Induction of NETs and signaling pathways were explored in vitro.

RESULTS

Patients with acute pulmonary embolism showed elevated levels of neutrophils, NETs (dsDNA, MPO-DNA, citrullinated histone H3, and nucleosomes), LPA18:1, and LPA20:4. NETs were present in human intrapulmonary thrombi and were surrounded by autotaxin. LPA18:1 induced rapid release of NETs from human neutrophils via a peptidylarginine deiminase 4-dependent pathway. LPA-induced NETs provided a scaffolding for plasma protein binding and generated a tissue plasminogen activator (tPA)-resistant blood clot. Addition of deoxyribonuclease I to tPA significantly accelerated the lysis of clots and human intrapulmonary thrombi. Furthermore, LPA-induced NETs could activate platelets to release LPA.

CONCLUSION

This is the first study to implicate LPA in regulating the stability of thrombi by inducing rapid release of NETs in vitro and ex vivo, which could be a new mechanism of thrombosis. These findings provide new insight into the prevention and therapy of venous thromboembolic disease by targeting the LPA-NET signaling pathway.

Production of neutrophil extracellular traps (NETs) in response to Scedosporium apiospermum in a murine model of pulmonary infection

Scedosporium apiospermum is an opportunistic emerging pathogen that can develop in both immunosuppressive and immunocompetent patients with pulmonary infections. Neutrophils are recognized as critical cells in the early response to a fungal infection through different mechanisms that eliminate or control the infection such as neutrophil extracellular traps (NETs). In this work, we investigate the presence of NETs in the lung tissue of immunocompetent mice infected with Scedosporium apiospermum. In the histopathological study the presence of filamentous basophilic material with hematoxylin-eosin and periodic acid Schiff stains suggestive of extracellular DNA was observed. We demonstrated the presence of NETs by immunofluorescence staining of extracellular DNA, myeloperoxidase, and elastase in lung tissue. Our results showed that on days 1 and 3 post-infection extracellular DNA, myeloperoxidase, and elastase correlate with areas of high concentration of cell infiltrates and fungal structures. The observation of fungal structures in the tissue decreased as did the presence of NETs by day 5 post-infection. We suggest that NETs release may play an important role in the early containment of Scedosporium apiospermum lung infection.

Effects of anti-PD-1 immunotherapy on tumor regression: insights from a patient-derived xenograft model

Immunotherapies, such as checkpoint blockade of programmed cell death protein-1 (PD-1), have resulted in unprecedented improvements in survival for patients with lung cancer. Nonetheless, not all patients benefit equally and many issues remain unresolved, including the mechanisms of action and the possible effector function of immune cells from non-lymphoid lineages. The purpose of this study was to investigate whether anti-PD-1 immunotherapy acts on malignant tumor cells through mechanisms beyond those related to T lymphocyte involvement. We used a murine patient-derived xenograft (PDX) model of early-stage non–small cell lung carcinoma (NSCLC) devoid of host lymphoid cells, and studied the tumor and immune non-lymphoid responses to immunotherapy with anti-PD-1 alone or in combination with standard chemotherapy (cisplatin). An antitumor effect was observed in animals that received anti-PD-1 treatment, alone or in combination with cisplatin, likely due to a mechanism independent of T lymphocytes. Indeed, anti-PD-1 treatment induced myeloid cell mobilization to the tumor concomitant with the production of exudates compatible with an acute inflammatory reaction mediated by murine polymorphonuclear leukocytes, specifically neutrophils. Thus, while keeping in mind that more research is needed to corroborate our findings, we report preliminary evidence for a previously undescribed immunotherapy mechanism in this model, suggesting a potential cytotoxic action of neutrophils as PD-1 inhibitor effector cells responsible for tumor regression by necrotic extension.

Machine Learning to Quantitate Neutrophil NETosis

We introduce machine learning (ML) to perform classification and quantitation of images of nuclei from human blood neutrophils. Here we assessed the use of convolutional neural networks (CNNs) using free, open source software to accurately quantitate neutrophil NETosis, a recently discovered process involved in multiple human diseases. CNNs achieved >94% in performance accuracy in differentiating NETotic from non-NETotic cells and vastly facilitated dose-response analysis and screening of the NETotic response in neutrophils from patients. Using only features learned from nuclear morphology, CNNs can distinguish between NETosis and necrosis and between distinct NETosis signaling pathways, making them a precise tool for NETosis detection. Furthermore, by using CNNs and tools to determine object dispersion, we uncovered differences in NETotic nuclei clustering between major NETosis pathways that is useful in understanding NETosis signaling events. Our study also shows that neutrophils from patients with sickle cell disease were unresponsive to one of two major NETosis pathways. Thus, we demonstrate the design, performance, and implementation of ML tools for rapid quantitative and qualitative cell analysis in basic science.

Computational Methodologies for the in vitro and in situ Quantification of Neutrophil Extracellular Traps

Neutrophil extracellular traps (NETs) are a neutrophil defensive mechanism where chromatin is expelled together with antimicrobial proteins in response to a number of stimuli. Even though beneficial in many cases, their dysfunction has been implicated in many diseases, such as rheumatoid arthritis and cancer. Accurate quantification of NETs is of utmost importance for correctly studying their role in various diseases, especially when considering them as therapeutic targets. Unfortunately, NET quantification has a number of limitations. However, recent developments in computational methodologies for quantifying NETs have vastly improved the ability to study NETs. Methods range from using ImageJ to user friendly applications and to more sophisticated machine-learning approaches. These various methods are reviewed and discussed in this review.