PAD4 is essential for antibacterial innate immunity mediated by neutrophil extracellular traps

Peptidyl arginine deiminase-4 inhibitor ameliorates pulmonary fibrosis through positive regulation of developmental endothelial locus-1

Recurring lung injury, chronic inflammation, aberrant tissue repair and impaired tissue remodelling contribute to the pathogenesis of pulmonary fibrosis (PF). Neutrophil extracellular traps (NETs) are released by activated neutrophils to trap, immobilise and kill invading pathogen and is facilitated by peptidyl arginine deiminase-4 (PAD-4). Dysregulated NETs release and abnormal PAD-4 activation plays a crucial role in activating pro-fibrotic events in PF. Developmental endothelial locus-1 (Del-1), expressed by the endothelial cells of lungs and brain acts as an endogenous inhibitor of inflammation and fibrosis. We have hypothesised that PAD-4 inhibitor exerts anti-inflammatory and anti-fibrotic effects in mice model of PF. We have also hypothesised by PAD-4 regulated the transcription of Del-1 through co-repression and its inhibition potentiates anti-fibrotic effects of Del-1. In our study, the PAD-4 inhibitor chloro-amidine (CLA) demonstrated anti-NETotic and anti-inflammatory effects in vitro in differentiated HL-60 cells. In a bleomycin-induced PF mice model, CLA administration in two doses (3 mg/kg, I.P and 10 mg/kg, I.P) improved lung function, normalized bronchoalveolar lavage fluid parameters, and attenuated fibrotic events, including markers of extracellular matrix and epithelial-mesenchymal transition. Histological analyses confirmed the restoration of lung architecture and collagen deposition with CLA treatment. ELISA, IHC, IF, RT-PCR, and immunoblot analysis supported the anti-NETotic effects of CLA. Furthermore, BLM-induced PF reduced Del-1 and p53 expression, which was normalized by CLA treatment. These findings suggest that inhibition of PAD-4 results in amelioration of PF in animal model and may involve modulation of Del-1 and p53 pathways, warranting further investigation.

Neutrophils' dual role in cancer: from tumor progression to immunotherapeutic potential

The tumor microenvironment (TME) is intricately associated with cancer progression, characterized by dynamic interactions among various cellular and molecular components that significantly impact the carcinogenic process. Notably, neutrophils play a crucial dual role in regulating this complex environment. These cells oscillate between promoting and inhibiting tumor activity, responding to a multitude of cytokines, chemokines, and tumor-derived factors. This response modulates immune reactions and affects the proliferation, metastasis, and angiogenesis of cancer cells. A significant aspect of their influence is their interaction with the endoplasmic reticulum (ER) stress responses in cancer cells, markedly altering tumor immunodynamics by modulating the phenotypic plasticity and functionality of neutrophils. Furthermore, neutrophil extracellular traps (NETs) exert a pivotal influence in the progression of malignancies by enhancing inflammation, metastasis, immune suppression, and thrombosis, thereby exacerbating the disease. In the realm of immunotherapy, checkpoint inhibitors targeting PD-L1/PD-1 and CTLA-4 among others have underscored the significant role of neutrophils in enhancing therapeutic responses. Recent research has highlighted the potential of using neutrophils for targeted drug delivery through nanoparticle systems, which precisely control drug release and significantly enhance antitumor efficacy. This review thoroughly examines the diverse functions of neutrophils in cancer treatment, emphasizing their potential in regulating immune therapy responses and as drug delivery carriers, offering innovative perspectives and profound implications for the development of targeted diagnostic and therapeutic strategies in oncology.

Low-Dose Ionizing γ-Radiation Elicits the Extrusion of Neutrophil Extracellular Traps

PURPOSE

Patients with cancer frequently undergo radiotherapy in their clinical management with unintended irradiation of blood vessels and copiously irrigated organs in which polymorphonuclear leukocytes circulate. Following the observation that such low doses of ionizing radiation are able to induce neutrophils to extrude neutrophil extracellular traps (NET), we have investigated the mechanisms, consequences, and occurrence of such phenomena in patients undergoing radiotherapy.

EXPERIMENTAL DESIGN

NETosis was analyzed in cultures of neutrophils isolated from healthy donors, patients with cancer, and cancer-bearing mice under confocal microscopy. Cocultures of radiation-induced NETs, immune effector lymphocytes, and tumor cells were used to study the effects of irradiation-induced NETs on immune cytotoxicity. Radiation-induced NETs were intravenously injected to mice for assessing their effects on metastasis. Circulating NETs in irradiated patients with cancer were measured using ELISA methods for detecting MPO-DNA complexes and citrullinated histone 3.

RESULTS

Irradiation of neutrophils with very low γ-radiation doses (0.5-1 Gy) elicits NET formation in a manner dependent on oxidative stress, NADPH oxidase activity, and autocrine IL8. Radiation-induced NETs interfere with NK cell and T-cell cytotoxicity. As a consequence, preinjection of irradiation-induced NETs increases the number of successful metastases in mouse tumor models. Increases in circulating NETs were readily detected in two prospective series of patients following the first fraction of their radiotherapy courses.

CONCLUSIONS

NETosis is induced by low-dose ionizing irradiation in a neutrophil-intrinsic fashion, and radiation-induced NETs are able to interfere with immune-mediated cytotoxicity. Radiation-induced NETs foster metastasis in mouse models and can be detected in the circulation of patients undergoing conventional radiotherapy treatments. See related commentary by Mowery and Luke, p. 3965.

Identification of neutrophil extracellular trap-related biomarkers in non-alcoholic fatty liver disease through machine learning and single-cell analysis

Non-alcoholic Fatty Liver Disease (NAFLD), noted for its widespread prevalence among adults, has become the leading chronic liver condition globally. Simultaneously, the annual disease burden, particularly liver cirrhosis caused by NAFLD, has increased significantly. Neutrophil Extracellular Traps (NETs) play a crucial role in the progression of this disease and are key to the pathogenesis of NAFLD. However, research into the specific roles of NETs-related genes in NAFLD is still a field requiring thorough investigation. Utilizing techniques like AddModuleScore, ssGSEA, and WGCNA, our team conducted gene screening to identify the genes linked to NETs in both single-cell and bulk transcriptomics. Using algorithms including Random Forest, Support Vector Machine, Least Absolute Shrinkage, and Selection Operator, we identified ZFP36L2 and PHLDA1 as key hub genes. The pivotal role of these genes in NAFLD diagnosis was confirmed using the training dataset GSE164760. This study identified 116 genes linked to NETs across single-cell and bulk transcriptomic analyses. These genes demonstrated enrichment in immune and metabolic pathways. Additionally, two NETs-related hub genes, PHLDA1 and ZFP36L2, were selected through machine learning for integration into a prognostic model. These hub genes play roles in inflammatory and metabolic processes. scRNA-seq results showed variations in cellular communication among cells with different expression patterns of these key genes. In conclusion, this study explored the molecular characteristics of NETs-associated genes in NAFLD. It identified two potential biomarkers and analyzed their roles in the hepatic microenvironment. These discoveries could aid in NAFLD diagnosis and management, with the ultimate goal of enhancing patient outcomes.

Calpain-1 weakens the nuclear envelope and promotes the release of neutrophil extracellular traps

The inducers of neutrophil extracellular trap (NET) formation are heterogeneous and consequently, there is no specific pathway or signature molecule indispensable for NET formation. But certain events such as histone modification, chromatin decondensation, nuclear envelope breakdown, and NET release are ubiquitous. During NET formation, neutrophils drastically rearrange their cytoplasmic, granular and nuclear content. Yet, the exact mechanism for decoding each step during NET formation still remains elusive. Here, we investigated the mechanism of nuclear envelope breakdown during NET formation. Immunofluorescence microscopic evaluation revealed a gradual disintegration of outer nuclear membrane protein nesprin-1 and alterations in nuclear morphology during NET formation. MALDI-TOF analysis of NETs that had been generated by various inducers detected the accumulation of nesprin-1 fragments. This suggests that nesprin-1 degradation occurs before NET release. In the presence of a calpain-1, inhibitor nesprin-1 degradation was decreased in calcium driven NET formation. Microscopic evaluation confirmed that the disintegration of the lamin B receptor (LBR) and the collapse of the actin cytoskeleton occurs in early and later phases of NET release, respectively. We conclude that the calpain-1 degrades nesprin-1, orchestrates the weakening of the nuclear membrane, contributes to LBR disintegration, and promoting DNA release and finally, NETs formation.

Lupus-prone NZM2328 mice exhibit enhanced UV-induced myeloid cell recruitment and activation in a type I interferon dependent manner

Though the exact causes of systemic lupus erythematosus (SLE) remain unknown, exposure to ultraviolet (UV) light is one of the few well-known triggers of cutaneous inflammation in SLE. However, the precise cell types which contribute to the early cutaneous inflammatory response in lupus, and the ways that UV dosing and interferons modulate these findings, have not been thoroughly dissected. Here, we explore these questions using the NZM2328 spontaneous murine model of lupus. In addition, we use iNZM mice, which share the NZM2328 background but harbor a whole-body knockout of the type I interferon (IFN) receptor, and wild-type BALB/c mice. 10-13-week-old female mice of each strain were treated with acute (300 mJ/cm2 x1), chronic (100 mJ/cm2 daily x5 days), or no UVB, and skin was harvested and processed for bulk RNA sequencing and flow cytometry. We identify that inflammatory pathways and gene signatures related to myeloid cells - namely neutrophils and monocyte-derived dendritic cells - are a shared feature of the acute and chronic UVB response in NZM skin greater than iNZM and wild-type skin. We also verify recruitment and activation of these cells by flow cytometry in both acutely and chronically irradiated NZM and WT mice and demonstrate that these processes are dependent on type I IFN signaling. Taken together, these data indicate a skewed IFN-driven inflammatory response to both acute and chronic UVB exposure in lupus-prone skin dominated by myeloid cells, suggesting both the importance of type I IFNs and myeloid cells as therapeutic targets for photosensitive patients and highlighting the risks of even moderate UV exposure in this patient population.

Citrullination modulation stabilizes HIF-1α to promote tumour progression

Citrullination plays an essential role in various physiological or pathological processes, however, whether citrullination is involved in regulating tumour progression and the potential therapeutic significance have not been well explored. Here, we find that peptidyl arginine deiminase 4 (PADI4) directly interacts with and citrullinates hypoxia-inducible factor 1α (HIF-1α) at R698, promoting HIF-1α stabilization. Mechanistically, PADI4-mediated HIF-1αR698 citrullination blocks von Hippel-Lindau (VHL) binding, thereby antagonizing HIF-1α ubiquitination and subsequent proteasome degradation. We also show that citrullinated HIF-1αR698, HIF-1α and PADI4 are highly expressed in hepatocellular carcinoma (HCC) tumour tissues, suggesting a potential correlation between PADI4-mediated HIF-1αR698 citrullination and cancer development. Furthermore, we identify that dihydroergotamine mesylate (DHE) acts as an antagonist of PADI4, which ultimately suppresses tumour progression. Collectively, our results reveal citrullination as a posttranslational modification related to HIF-1α stability, and suggest that targeting PADI4-mediated HIF-1α citrullination is a promising therapeutic strategy for cancers with aberrant HIF-1α expression.

The role of NETosis in heart failure

The hallmark of heart failure (HF) is structural myocardial remodeling including cardiomyocyte hypertrophy, fibrosis, cardiomyocyte cell death, and a low-grade aseptic inflammation. The initiation and maintenance of persistent chronic low-grade inflammation in HF are not fully understood. Oxidative stress-mediated neutrophil extracellular traps (NETs) are the main immune defense mechanism against external bacterial infections. Furthermore, NETs play important roles in noninfectious diseases. In the settings of myocardial infarction, myocarditis, or cardiomyopathies, neutrophils infiltrate the cardiac tissue and undergo NETosis that further aggravate the inflammation. A number of stimuli may cause NETosis that is a form of programmed cell death of neutrophils that is different from apoptosis of these cells. Whether NETosis is directly involved in the pathogenesis and development of HF is still unclear. In this review, we analyzed the mechanisms and markers of NETosis, especially placing the accent on the activation of the neutrophil-specific myeloperoxidase (MPO), elastase (NE), and peptidylarginine deiminase 4 (PAD4). These conclusions are supported by the recent genetic and pharmacological studies which demonstrated that MPO, NE, and PAD4 inhibitors are effective at least in the settings of post-myocardial infarction adverse remodeling, cardiac valve diseases, cardiomyopathies, and decompensated left ventricular hypertrophy whose deterioration can lead to HF. This is essential for understanding NETosis as a contributor to pathophysiology of HF and developments of new therapies of HF.

Cathepsin C inhibition reduces neutrophil serine protease activity and improves activated neutrophil-mediated disorders

Cathepsin C (CatC) is an enzyme which regulates the maturation of neutrophil serine proteases (NSPs) essential for neutrophil activation. Activated neutrophils are key players in the innate immune system, and are also implicated in the etiology of various inflammatory diseases. This study aims to demonstrate a therapeutic potential for CatC inhibitors against disorders in which activated neutrophil-derived neutrophil extracellular traps (NETs) play a significant role. We demonstrate that a CatC inhibitor, MOD06051, dose-dependently suppresses the cellular activity of NSPs, including neutrophil elastase (NE), in vitro. Neutrophils derived from MOD06051-administered rats exhibit significantly lower NE activity and NET-forming ability than controls. Furthermore, MOD06051 dose-dependently ameliorates vasculitis and significantly decreases NETs when administered to a rat model of myeloperoxidase (MPO)-antineutrophil cytoplasmic antibody-associated vasculitis (AAV). These findings suggest that CatC inhibition is a promising strategy to reduce neutrophil activation and improve activated neutrophil-mediated diseases such as MPO-AAV.

Post-translational modifications in sepsis-induced organ dysfunction: mechanisms and implications

As a grave and highly lethal clinical challenge, sepsis, along with its consequent multiorgan dysfunction, affects millions of people worldwide. Sepsis is a complex syndrome caused by a dysregulated host response to infection, leading to fatal organ dysfunction. An increasing body of evidence suggests that the pathogenesis of sepsis is both intricate and rapid and involves various cellular responses and signal transductions mediated by post-translational modifications (PTMs). Hence, a comprehensive understanding of the mechanisms and functions of PTMs within regulatory networks is imperative for understanding the pathological processes, diagnosis, progression, and treatment of sepsis. In this review, we provide an exhaustive and comprehensive summary of the relationship between PTMs and sepsis-induced organ dysfunction. Furthermore, we explored the potential applications of PTMs in the treatment of sepsis, offering a forward-looking perspective on the understanding of infectious diseases.

TRIM8 as a predictor for prognosis in childhood acute lymphoblastic leukemia based on a signature of neutrophil extracellular traps

Background

Neutrophil extracellular traps (NETs) can be attributed to the metastasis, occurrence, and immune evasion of cancer cells. We investigated the prognostic value of NET-related genes in childhood acute lymphoblastic leukemia (cALL) patients.

Methods

Differential gene expression analysis was conducted on samples collected from public databases. Grouping them based on the expression level of NET-related genes, we assessed the correlation between immune cell types and the risk score for having a poor prognosis of cALL, with an evaluation of the sensitivity of drugs used in cALL. We further divided the groups, integrating survival data. Subsequently, methods including multivariable Cox algorithms, least absolute shrinkage and selection operator (LASSO), and univariable were utilized to create a risk model predicting prognosis. Experiments in cell lines and animals were performed to explore the functions of TRIM8, a gene selected by the model. To validate the role of TRIM8 in leukemia development, lentivirus-mediated overexpression or knockdown of TRIM8 was employed in mice with T-ALL and B-ALL.

Results

Kaplan-Meier (KM) analysis underscored the importance of differentially expressed genes identified in the groups divided by genes participated in NETs, with enrichment analysis showing the mechanism. Correlation analysis revealed significant associations with B cells, NK cells, mast cells, T cells, plasma cells, dendritic cells, and monocytes. The IC50 values of drugs such as all-trans-retinoic acid (ATRA), axitinib, doxorubicin, methotrexate, sorafenib, and vinblastine were increased, while dasatinib exhibited a lower IC50. A total of 13 NET-related genes were selected in constructing the risk model. In the training, testing, and merged cohorts, KM analysis demonstrated significantly improved survival for low-risk cALL patients compared to high-risk cALL patients (p < 0.001). The area under the curve (AUC) indicated strong predictive performance. Experiments in Jurkat and SUP-B15 revealed that TRIM8 knockdown decreased the proliferation of leukemia cell lines. Further experiments demonstrated a more favorable prognosis in mice with TRIM8-knockdown leukemia cells. Results of cell lines and animals showed better outcomes in prognosis when TRIM8 was knocked down.

Conclusion

We identified a novelty in a prognostic model that could aid in the development of personalized treatments for cALL patients. Furthermore, it revealed that the expression of TRIM8 is a contributing factor to the proliferation of leukemia cells and worsens the prognosis of cALL.

NETs: Important players in cancer progression and therapeutic resistance

Neutrophil extracellular traps (NETs) are web-like structures composed of cytoplasmic contents, DNA chromatin and various granular proteins released by neutrophils in response to viruses, bacteria, immune complexes and cytokines. Studies have shown that NETs can promote the occurrence, development and metastasis of tumors. In this paper, the mechanism underlying the formation and degradation of NETs and the malignant biological behaviors of NETs, such as the promotion of tumor cell proliferation, epithelial mesenchymal transition, extracellular matrix remodeling, angiogenesis, immune evasion and tumor-related thrombosis, are described in detail. NETs are being increasingly studied as therapeutic targets for tumors. We have summarized strategies for targeting NETs or interfering with NET-cancer cell interactions and explored the potential application value of NETs as biomarkers in cancer diagnosis and treatment, as well as the relationship between NETs and therapeutic resistance.

The pivotal role of neutrophil extracellular traps in cardiovascular diseases: Mechanisms and therapeutic implications

Cardiovascular diseases (CVDs) continue to pose a significant burden on global health, prominently contributing to morbidity and mortality rates worldwide. Recent years have witnessed an increasing recognition of the intricate involvement of neutrophil extracellular traps (NETs) in the pathology of diverse cardiovascular conditions. This review provides a comprehensive analysis of the multifaceted functions of NETs in cardiovascular diseases, shedding light on the impact on atherosclerosis, myocardial infarction, heart failure, myocarditis, atrial fibrillation, aortic stenosis, and the potential therapeutic avenues targeting NETs.

Zinc Supplementation Reduces the Formation of Neutrophil Extracellular Traps by Decreasing the Expression of Peptidyl Arginine Deiminase 4

SCOPE

Neutrophils play a decisive role during the immediate defense against infections. However, as observed during rheumatoid arthritis, activated neutrophils can also cause tissue damage. Previous studies indicate that zinc supplementation may alter certain neutrophil functions. However, precise underlying mechanisms and possible effects of zinc deficiency remain incompletely understood. The objective of this study is to investigate the effects of changes in zinc status on formation of neutrophil extracellular traps (NETs) and other fundamental neutrophil functions.

METHODS AND RESULTS

Interleukin (IL)-17 and tumor necrosis factor (TNF)-α are used to simulate the inflammatory environment observed in autoimmune diseases. The study analyzes the impact of the zinc status on NETs release, using a fluorescence plate reader, and on the expression of peptidylarginine deiminase 4 (PAD4), S100A8/A9, and certain cytokines by PCR and western blot. These results show that zinc supplementation significantly reduces NETs formation and downregulates PAD4 protein expression. Zinc supplementation results in increased protein expression of interleukin-1 receptor antagonist (IL-1RA) and IL-8 in stimulated cells.

CONCLUSION

The results suggest that changes in extracellular zinc availability may influence the functions of neutrophils. Therefore, maintaining an appropriate zinc level is advisable for preserving innate immunity and to prevent hyper-activation of neutrophils.

Sodium Acetate Enhances Neutrophil Extracellular Trap Formation via Histone Acetylation Pathway in Neutrophil-like HL-60 Cells

Neutrophil extracellular trap formation has been identified as a new cell death mediator, termed NETosis, which is distinct from apoptosis and necrosis. NETs capture foreign substances, such as bacteria, by releasing DNA into the extracellular environment, and have been associated with inflammatory diseases and altered immune responses. Short-chain fatty acids, such as acetate, are produced by the gut microbiota and reportedly enhance innate immune responses; however, the underlying molecular mechanisms remain unclear. Here, we investigated the effects of sodium acetate, which has the highest SCFA concentration in the blood and gastrointestinal tract, on NETosis by focusing on the mechanisms associated with histone acetylation in neutrophil-like HL-60 cells. Sodium acetate enhanced NETosis, as shown by fluorescence staining with SYTOX green, and the effect was directly proportional to the treatment duration (16-24 h). Moreover, the addition of sodium acetate significantly enhanced the acetylation of Ace-H3, H3K9ace, and H3K14ace. Sodium acetate-induced histone acetylation rapidly decreased upon stimulation with the calcium ionophore A23187, whereas histone citrullination markedly increased. These results demonstrate that sodium acetate induces NETosis via histone acetylation in neutrophil-like HL-60 cells, providing new insights into the therapeutic effects based on the innate immunity-enhancing effect of dietary fiber.

The emerging role of neutrophil extracellular traps in ulcerative colitis

Ulcerative colitis (UC) is characterized by chronic non-recessive inflammation of the intestinal mucosa involving both innate and adaptive immune responses. Currently, new targeted therapies are urgently needed for UC, and neutrophil extracellular traps (NETs) are new therapeutic options. NETs are DNA-based networks released from neutrophils into the extracellular space after stimulation, in which a variety of granule proteins, proteolytic enzymes, antibacterial peptides, histones, and other network structures are embedded. With the deepening of the studies on NETs, their regulatory role in the development of autoimmune and autoinflammatory diseases has received extensive attention in recent years. Increasing evidence indicates that excess NETs exacerbate the inflammatory response in UC, disrupting the structure and function of the intestinal mucosal barrier and increasing the risk of thrombosis. Although NETs are usually assigned a deleterious role in promoting the pathological process of UC, they also appear to have a protective role in some models. Despite such progress, comprehensive reviews describing the therapeutic promise of NETs in UC remain limited. In this review, we discuss the latest evidence for the formation and degradation of NETs, focusing on their double-edged role in UC. Finally, the potential implications of NETs as therapeutic targets for UC will be discussed. This review aims to provide novel insights into the pathogenesis and therapeutic options for UC.

Neutrophil extracellular traps: Potential targets for the treatment of rheumatoid arthritis with traditional Chinese medicine and natural products

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease. Abnormal formation of neutrophil extracellular traps (NETs) at the synovial membrane leads to the release of many inflammatory cytokines, including IL-1β, IL-6, and TNF-α. Elastase, histone H3, and myeloperoxidase, which are carried by NETs, damage the soft tissues of the joints and aggravate the progression of RA. The balance of NET formation coordinates the pro-inflammatory and anti-inflammatory effects and plays a key role in the development of RA. Therefore, when NETs are used as effector targets, highly targeted drugs with fewer side effects can be developed to treat RA without damaging the host immune system. Currently, an increasing number of studies have shown that traditional Chinese medicines and natural products can regulate the formation of NETs through multiple pathways to counteract RA, which shows great potential for the treatment of RA and has a promising future for clinical application. In this article, we review the latest biological progress in understanding NET formation, the mechanism of NETs in RA, and the potential targets or pathways related to the modulation of NET formation by Chinese medicines and natural products. This review provides a relevant basis for the use of Chinese medicines and natural products as natural adjuvants in the treatment of RA.

Cardiovascular Risk in Philadelphia-Negative Myeloproliferative Neoplasms: Mechanisms and Implications-A Narrative Review

Myeloproliferative neoplasms (MPNs), encompassing disorders like polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF), are characterized by clonal hematopoiesis without the Philadelphia chromosome. The JAK2 V617F mutation is prevalent in PV, ET, and PMF, while mutations in MPL and CALR also play significant roles. These conditions predispose patients to thrombotic events, with PMF exhibiting the lowest survival among MPNs. Chronic inflammation, driven by cytokine release from aberrant leukocytes and platelets, amplifies cardiovascular risk through various mechanisms, including atherosclerosis and vascular remodeling. Additionally, MPN-related complications like pulmonary hypertension and cardiac fibrosis contribute to cardiovascular morbidity and mortality. This review consolidates recent research on MPNs' cardiovascular implications, emphasizing thrombotic risk, chronic inflammation, and vascular stiffness. Understanding these associations is crucial for developing targeted therapies and improving outcomes in MPN patients.

Neutrophil extracellular traps in cancer

Neutrophil extracellular traps (NETs), which consist of chromatin DNA studded with granule proteins, are released by neutrophils in response to both infectious and sterile inflammation. Beyond the canonical role in defense against pathogens, the extrusion of NETs also contributes to the initiation, metastasis, and therapeutic response of malignant diseases. Recently, NETs have been implicated in the development and therapeutic responses of various types of tumors. Although extensive work regarding inflammation in tumors has been reported, a comprehensive summary of how these web-like extracellular structures initiate and propagate tumor progression under the specific microenvironment is lacking. In this review, we demonstrate the initiators and related signaling pathways that trigger NETs formation in cancers. Additionally, this review will outline the current molecular mechanisms and regulatory networks of NETs during dormant cancer cells awakening, circulating tumor cells (CTCs) extravasation, and metastatic recurrence of cancer. This is followed by a perspective on the current and potential clinical potential of NETs as therapeutic targets in the treatment of both local and metastatic disease, including the improvement of the efficacy of existing therapies.

NETosis of psoriasis: a critical step in amplifying the inflammatory response

NETosis, a regulated form of neutrophil death, is crucial for host defense against pathogens. However, the release of neutrophil extracellular traps (NETs) during NETosis can have detrimental effects on surrounding tissues and contribute to the pro-inflammatory response, in addition to their role in controlling microbes. Although it is well-established that the IL-23-Th17 axis plays a key role in the pathogenesis of psoriasis, emerging evidence suggests that psoriasis, as an autoinflammatory disease, is also associated with NETosis. The purpose of this review is to provide a comprehensive understanding of the mechanisms underlying NETosis in psoriasis. It will cover topics such as the formation of NETs, immune cells involved in NETosis, and potential biomarkers as prognostic/predicting factors in psoriasis. By analyzing the intricate relationship between NETosis and psoriasis, this review also aims to identify novel possibilities targeting NETosis for the treatment of psoriasis.

Neutrophil extracellular traps mediate neuro-immunothrombosis

Neutrophil extracellular traps are primarily composed of DNA and histones and are released by neutrophils to promote inflammation and thrombosis when stimulated by various inflammatory reactions. Neutrophil extracellular trap formation occurs through lytic and non-lytic pathways that can be further classified by formation mechanisms. Histones, von Willebrand factor, fibrin, and many other factors participate in the interplay between inflammation and thrombosis. Neuro-immunothrombosis summarizes the intricate interplay between inflammation and thrombosis during neural development and the pathogenesis of neurological diseases, providing cutting-edge insights into post-neurotrauma thrombotic events. The blood-brain barrier defends the brain and spinal cord against external assaults, and neutrophil extracellular trap involvement in blood-brain barrier disruption and immunothrombosis contributes substantially to secondary injuries in neurological diseases. Further research is needed to understand how neutrophil extracellular traps promote blood-brain barrier disruption and immunothrombosis, but recent studies have demonstrated that neutrophil extracellular traps play a crucial role in immunothrombosis, and identified modulators of neuro-immunothrombosis. However, these neurological diseases occur in blood vessels, and the mechanisms are unclear by which neutrophil extracellular traps penetrate the blood-brain barrier to participate in immunothrombosis in traumatic brain injury. This review discusses the role of neutrophil extracellular traps in neuro-immunothrombosis and explores potential therapeutic interventions to modulate neutrophil extracellular traps that may reduce immunothrombosis and improve traumatic brain injury outcomes.

Tumor necrosis factor regulates leukocyte recruitment but not bacterial persistence during Staphylococcus aureus craniotomy infection

BACKGROUND

Craniotomy is a common neurosurgery used to treat intracranial pathologies. Nearly 5% of the 14 million craniotomies performed worldwide each year become infected, most often with Staphylococcus aureus (S. aureus), which forms a biofilm on the surface of the resected bone segment to establish a chronic infection that is recalcitrant to antibiotics and immune-mediated clearance. Tumor necrosis factor (TNF), a prototypical proinflammatory cytokine, has been implicated in generating protective immunity to various infections. Although TNF is elevated during S. aureus craniotomy infection, its functional importance in regulating disease pathogenesis has not been explored.

METHODS

A mouse model of S. aureus craniotomy infection was used to investigate the functional importance of TNF signaling using TNF, TNFR1, and TNFR2 knockout (KO) mice by quantifying bacterial burden, immune infiltrates, inflammatory mediators, and transcriptional changes by RNA-seq. Complementary experiments examined neutrophil extracellular trap formation, leukocyte apoptosis, phagocytosis, and bactericidal activity.

RESULTS

TNF transiently regulated neutrophil and granulocytic myeloid-derived suppressor cell recruitment to the brain, subcutaneous galea, and bone flap as evident by significant reductions in both cell types between days 7 to 14 post-infection coinciding with significant decreases in several chemokines, which recovered to wild type levels by day 28. Despite these defects, bacterial burdens were similar in TNF KO and WT mice. RNA-seq revealed enhanced lymphotoxin-α (Lta) expression in TNF KO granulocytes. Since both TNF and LTα signal through TNFR1 and TNFR2, KO mice for each receptor were examined to assess potential redundancy; however, neither strain had any impact on S. aureus burden. In vitro studies revealed that TNF loss selectively altered macrophage responses to S. aureus since TNF KO macrophages displayed significant reductions in phagocytosis, apoptosis, IL-6 production, and bactericidal activity in response to live S. aureus, whereas granulocytes were not affected.

CONCLUSION

These findings implicate TNF in modulating granulocyte recruitment during acute craniotomy infection via secondary effects on chemokine production and identify macrophages as a key cellular target of TNF action. However, the lack of changes in bacterial burden in TNF KO animals suggests the involvement of additional signals that dictate S. aureus pathogenesis during craniotomy infection.

Targeting NETosis: nature's alarm system in cancer progression

Neutrophils are recognized active participants in inflammatory responses and are intricately linked to cancer progression. In response to inflammatory stimuli, neutrophils become activated, releasing neutrophils extracellular traps (NETs) for the capture and eradication of pathogens, a phenomenon termed NETosis. With a deeper understanding of NETs, there is growing evidence supporting their role in cancer progression and their involvement in conferring resistance to various cancer therapies, especially concerning tumor reactions to chemotherapy, radiation therapy (RT), and immunotherapy. This review summarizes the roles of NETs in the tumor microenvironment (TME) and their mechanisms of neutrophil involvement in the host defense. Additionally, it elucidates the mechanisms through which NETs promote tumor progression and their role in cancer treatment resistance, highlighting their potential as promising therapeutic targets in cancer treatment and their clinical applicability.

PI3Kγ promotes neutrophil extracellular trap formation by noncanonical pyroptosis in abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is one of the most life-threatening cardiovascular diseases; however, effective drug treatments are still lacking. The formation of neutrophil extracellular traps (NETs) has been shown to be a crucial trigger of AAA, and identifying upstream regulatory targets is thus key to discovering therapeutic agents for AAA. We revealed that phosphoinositide-3-kinase γ (PI3Kγ) acted as an upstream regulatory molecule and that PI3Kγ inhibition reduced NET formation and aortic wall inflammation, thereby markedly ameliorating AAA. However, the mechanism of NET formation regulated by PI3Kγ remains unclear. In this study, we showed that PI3Kγ deficiency inactivated the noncanonical pyroptosis pathway, which suppressed downstream NET formation. In addition, PI3Kγ regulation of noncanonical pyroptosis was dependent on cyclic AMP/protein kinase A signaling. These results clarify the molecular mechanism and crosstalk between PI3Kγ and NETosis in the development of AAA, potentially facilitating the discovery of therapeutic options for AAA.

Identification of organs of origin of macrophages that produce presepsin via neutrophil extracellular trap phagocytosis

Presepsin (P-SEP) is a specific biomarker for sepsis. Monocytes produce P-SEP by phagocytosing neutrophil extracellular traps (NETs). Herein, we investigated whether M1 macrophages (M1 MΦs) are the primary producers of P-SEP after NET phagocytosis. We co-cultured M1 MΦs and NETs from healthy participants, measured P-SEP levels in the culture medium supernatant, and detected P-SEP using western blotting. When NETs were co-cultured with M1 MΦs, the P-SEP level of the culture supernatant was high. Notably, we demonstrated, for the first time, the intracellular kinetics of P-SEP production by M1 MΦs via NET phagocytosis: M1 MΦs produced P-SEP intracellularly 15 min after NET phagocytosis and then released it extracellularly. In a sepsis mouse model, the blood NET ratio and P-SEP levels, detected using ELISA, were significantly increased (p < 0.0001). Intracellular P-SEP analysis via flow cytometry demonstrated that lung, liver, and kidney MΦs produced large amounts of P-SEP. Therefore, we identified these organs as the origin of M1 MΦs that produce P-SEP during sepsis. Our data indicate that the P-SEP level reflects the trend of NETs, suggesting that monitoring P-SEP can be used to both assess NET-induced organ damage in the lungs, liver, and kidneys during sepsis and determine treatment efficacy.

Berbamine ameliorates DSS-induced colitis by inhibiting peptidyl-arginine deiminase 4-dependent neutrophil extracellular traps formation

Ulcerative colitis (UC) is a chronic inflammatory bowel disease with immune dysregulation affecting colon inflammatory response. Recent studies have highlighted that neutrophil extracellular traps (NETs) play an important role in the pathogenesis of UC. Berbamine (BBM), one of the bioactive ingredients extracted from Chinese herbal medicine Berberis vulgaris L, has attracted intensive attentions due to its significant anti-inflammatory activity and a marketing drug for treating leukemia in China. However, the exact role and potential molecular mechanism of BBM against UC remains elusive. In the present study, our results showed that BBM could markedly improve the pathological phenotype and the colon inflammation in mice with dextran sulfate sodium (DSS)-induced colitis. Then, comprehensive approaches combining network pharmacology and molecular docking analyses were employed to predict the therapeutic potential of BBM in treating UC by peptidyl-arginine deiminase 4 (PAD4), a crucial molecule involved in NETs formation. The molecular docking results showed BBM had a high affinity for PAD4 with a binding energy of -9.3 kcal/mol Moreover, PAD4 expression and NETs productions, including citrullination of histone H3 (Cit-H3), neutrophil elastase (NE), myeloperoxidase (MPO) in both neutrophils and colonic tissue were reduced after BBM administration. However, in the mice with DSS-induced colitis pretreated with GSK484, a PAD4-specific inhibitor, BBM could not further reduce disease related indexes, expression of PAD4 and NETs productions. Above all, the identification of PAD4 as a potential target for BBM to inhibit NETs formation in colitis provides novel insights into the development of BBM-derived drugs for the clinical management of UC.

The role of anti-citrullinated protein antibody in pathogenesis of RA

Rheumatoid arthritis (RA) is a common autoimmune rheumatic disease that causes chronic synovitis, bone erosion, and joint destruction. The autoantigens in RA include a wide array of posttranslational modified proteins, such as citrullinated proteins catalyzed by peptidyl arginine deiminase4a. Pathogenic anti-citrullinated protein antibodies (ACPAs) directed against a variety of citrullinated epitopes are abundant both in plasma and synovial fluid of RA patients. ACPAs play an important role in the onset and progression of RA. Intensive and extensive studies are being conducted to unveil the mechanisms of RA pathogenesis and evaluate the efficacy of some investigative drugs. In this review, we focus on the formation and pathogenic function of ACPAs.

NETscape or NEThance: tailoring anti-cancer therapy

Neutrophils, major regulators of innate immunity, have recently emerged as key components of the tumor microenvironment. The role of neutrophils in cancer has been linked to their ability to form neutrophil extracellular traps (NETs), structures composed of decondensed DNA decorated with enzymes that are released into the extracellular space. Here, we discuss the pivotal roles of NETs in influencing responses to anticancer therapies such as chemotherapy, radiotherapy, immunotherapy, and targeted therapy. Highlighting recent insights, we delve into the dual nature of NETs in the context of anticancer treatments, examining their potential to either counteract or enhance treatment outcomes. Strategic targeting of NETs may be a promising avenue for crafting combination therapies to counteract resistance or enhance anticancer treatments' efficacy.

Intraperitoneal activation of myeloid cells clears ascites and reveals IL27-dependent regression of metastatic ovarian cancer

Patients with metastatic ovarian cancer (OvCa) have a 5-year survival rate of less than 30% due to persisting dissemination of chemoresistant cells in the peritoneal fluid and the immunosuppressive microenvironment in the peritoneal cavity. Here, we report that intraperitoneal administration of β-glucan and IFNγ (BI) induced robust tumor regression in clinically relevant models of metastatic OvCa. BI induced tumor regression by controlling fluid tumor burden and activating localized antitumor immunity. β-glucan alone cleared ascites and eliminated fluid tumor cells by inducing intraperitoneal clotting in the fluid and Dectin-1-Syk-dependent NETosis in the omentum. In omentum tumors, BI expanded a novel subset of immunostimulatory IL27+ macrophages and neutralizing IL27 impaired BI efficacy in vivo. Moreover, BI directly induced IL27 secretion in macrophages where single agent treatment did not. Finally, BI extended mouse survival in a chemoresistant model and significantly improved chemotherapy response in a chemo-sensitive model. In summary, we propose a new therapeutic strategy for the treatment of metastatic OvCa.

An update on periodontal inflammation and bone loss

Periodontal disease is a chronic inflammatory condition that affects the supporting structures of the teeth, including the periodontal ligament and alveolar bone. Periodontal disease is due to an immune response that stimulates gingivitis and periodontitis, and its systemic consequences. This immune response is triggered by bacteria and may be modulated by environmental conditions such as smoking or systemic disease. Recent advances in single cell RNA-seq (scRNA-seq) and in vivo animal studies have provided new insight into the immune response triggered by bacteria that causes periodontitis and gingivitis. Dysbiosis, which constitutes a change in the bacterial composition of the microbiome, is a key factor in the initiation and progression of periodontitis. The host immune response to dysbiosis involves the activation of various cell types, including keratinocytes, stromal cells, neutrophils, monocytes/macrophages, dendritic cells and several lymphocyte subsets, which release pro-inflammatory cytokines and chemokines. Periodontal disease has been implicated in contributing to the pathogenesis of several systemic conditions, including diabetes, rheumatoid arthritis, cardiovascular disease and Alzheimer's disease. Understanding the complex interplay between the oral microbiome and the host immune response is critical for the development of new therapeutic strategies for the prevention and treatment of periodontitis and its systemic consequences.

Classical monocyte ontogeny dictates their functions and fates as tissue macrophages

Classical monocytes (CMs) are ephemeral myeloid immune cells that circulate in the blood. Emerging evidence suggests that CMs can have distinct ontogeny and originate from either granulocyte-monocyte- or monocyte-dendritic-cell progenitors (GMPs or MDPs). Here, we report surface markers that allowed segregation of murine GMP- and MDP-derived CMs, i.e., GMP-Mo and MDP-Mo, as well as their functional characterization, including fate definition following adoptive cell transfer. GMP-Mo and MDP-Mo yielded an equal increase in homeostatic CM progeny, such as blood-resident non-classical monocytes and gut macrophages; however, these cells differentially seeded various other selected tissues, including the dura mater and lung. Specifically, GMP-Mo and MDP-Mo differentiated into distinct interstitial lung macrophages, linking CM dichotomy to previously reported pulmonary macrophage heterogeneity. Collectively, we provide evidence for the existence of two functionally distinct CM subsets in the mouse that differentially contribute to peripheral tissue macrophage populations in homeostasis and following challenge.

A quantitative and site-specific atlas of the citrullinome reveals widespread existence of citrullination and insights into PADI4 substrates

Despite the importance of citrullination in physiology and disease, global identification of citrullinated proteins, and the precise targeted sites, has remained challenging. Here we employed quantitative-mass-spectrometry-based proteomics to generate a comprehensive atlas of citrullination sites within the HL60 leukemia cell line following differentiation into neutrophil-like cells. We identified 14,056 citrullination sites within 4,008 proteins and quantified their regulation upon inhibition of the citrullinating enzyme PADI4. With this resource, we provide quantitative and site-specific information on thousands of PADI4 substrates, including signature histone marks and transcriptional regulators. Additionally, using peptide microarrays, we demonstrate the potential clinical relevance of certain identified sites, through distinct reactivities of antibodies contained in synovial fluid from anti-CCP-positive and anti-CCP-negative people with rheumatoid arthritis. Collectively, we describe the human citrullinome at a systems-wide level, provide a resource for understanding citrullination at the mechanistic level and link the identified targeted sites to rheumatoid arthritis.

Neutrophil-derived PAD4 induces citrullination of CKMT1 exacerbates mucosal inflammation in inflammatory bowel disease

Peptidyl arginine deiminase 4 (PAD4) plays a pivotal role in infection and inflammatory diseases by facilitating the formation of neutrophil extracellular traps (NETs). However, the substrates of PAD4 and its exact role in inflammatory bowel disease (IBD) remain unclear. In this study, we employed single-cell RNA sequencing (scRNA-seq) and substrate citrullination mapping to decipher the role of PAD4 in intestinal inflammation associated with IBD. Our results demonstrated that PAD4 deficiency alleviated colonic inflammation and restored intestinal barrier function in a dextran sulfate sodium (DSS)-induced colitis mouse model. scRNA-seq analysis revealed significant alterations in intestinal cell populations, with reduced neutrophil numbers and changes in epithelial subsets upon PAD4 deletion. Gene expression analysis highlighted pathways related to inflammation and epithelial cell function. Furthermore, we found that neutrophil-derived extracellular vesicles (EVs) carrying PAD4 were secreted into intestinal epithelial cells (IECs). Within IECs, PAD4 citrullinates mitochondrial creatine kinase 1 (CKMT1) at the R242 site, leading to reduced CKMT1 protein stability via the autophagy pathway. This action compromises mitochondrial homeostasis, impairs intestinal barrier integrity, and induces IECs apoptosis. IEC-specific depletion of CKMT1 exacerbated intestinal inflammation and apoptosis in mice with colitis. Clinical analysis of IBD patients revealed elevated levels of PAD4, increased CKMT1 citrullination, and decreased CKMT1 expression. In summary, our findings highlight the crucial role of PAD4 in IBD, where it modulates IECs plasticity via CKMT1 citrullination, suggesting that PAD4 may be a potential therapeutic target for IBD.

NETosis in tumour microenvironment of liver: From primary to metastatic hepatic carcinoma

BACKGROUND

Hepatocellular carcinoma is a common and highly lethal tumour. The tumour microenvironment (TME) plays an important role in the progression and metastasis of hepatocellular carcinoma (HCC). A cell death mechanism, termed NETosis, has been found to play an important role in the TME of HCC.

SUMMARY

This review article focuses on the role of NETosis in the TME of HCC, a novel form of cell death in which neutrophils capture and kill microorganisms by releasing a type of DNA meshwork fibres called "NETs". This process is associated with neutrophil activation, local inflammation and cytokines. The study suggests that NETs play a multifaceted role in the development and metastasis of HCC. The article also discusses the role of NETs in tumour proliferation and metastasis, epithelial-mesenchymal transition (EMT), and surgical stress. In addition, the article discusses the interaction of NETosis with other immune cells in the TME and related therapeutic strategies. A deeper understanding of NETosis can help us better understand the complexity of the immune system and provide a new therapeutic basis for the treatment and prevention of HCC.

KEY INFORMATION

In conclusion, NETosis is important in the TME of liver. NETs have been shown to contribute to the progression and metastasis of liver cancer. The interaction between NETosis and immune cells in the TME, as well as related therapies, are important areas of research.

Involvement of peptidylarginine deiminase 4 in eosinophil extracellular trap formation and contribution to citrullinated histone signal in thrombi

BACKGROUND

Extracellular traps formed by neutrophils (NETs) and eosinophils (EETs) have been described in coronary thrombi, contributing to thrombus stability. A key mechanism during NET formation is histone modification by the enzyme PAD4. Citrullinated histones, the product of PAD4 activity, are often attributed to neutrophils. Eosinophils also express high levels of PAD4.

OBJECTIVES

We aimed to explore the contribution of PAD4 to EET formation.

METHODS

We performed immunohistological analyses on thrombi, including a large, intact, and eosinophil-containing thrombus retrieved from the right coronary artery using an aspiration catheter and stroke thrombi from thrombectomy retrieval. We studied eosinophils for their capability to form PAD4-dependent EETs in response to strong ET-inducing agonists as well as activated platelets and bacteria.

RESULTS

Histopathology and immunofluorescence microscopy identified a coronary thrombus rich in platelets and neutrophils, with distinct areas containing von Willebrand factor and citrullinated histone H3 (H3Cit). Eosinophils were also identified in leukocyte-rich areas. The majority of the H3Cit+ signal colocalized with myeloperoxidase, but some colocalized with eosinophil peroxidase, indicating EETs. Eosinophils isolated from healthy volunteers produced H3Cit+ EETs, indicating an involvement of PAD4 activity. The selective PAD4 inhibitor GSK484 blocked this process, supporting PAD4 dependence of H3Cit+ EET release. Citrullinated histones were also present in EETs produced in response to live Staphylococci. However, limited evidence for EETs was found in mouse models of venous thrombosis or infective endocarditis.

CONCLUSION

As in NETosis, PAD4 can catalyze the formation of EETs. Inhibition of PAD4 decreases EET formation, supporting the future utility of PAD4 inhibitors as possible antithrombotic agents.

Characterization of extracellular trap production and release by equine neutrophils in response to different stimuli

This study explores Neutrophil Extracellular Trap (NET) formation in equine neutrophils, which is crucial for eliminating infections and is implicated in various equine inflammatory diseases. We investigated the molecular pathways involved in NET release by equine neutrophils in response to stimuli. We use PMA, A23187, LPS, PAF, OZ, and cytokines, observing NET release in response to PMA, PAF, and A23187. In contrast, LPS, OZ, and the cytokines tested did not induce DNA release or did not consistently induce citrullination of histone 4. Peptidyl-arginine deiminase inhibition completely halted NET release, while NADPH oxidase and mitochondrial reactive oxygen species only played a role in PMA-induced NETs. Neutrophil elastase inhibition modestly affected PAF-induced NET liberation but not in PMA or A23187-induced NET, while myeloperoxidase did not contribute to NET release. We expect to provide a foundation for future investigations into the role of NETs in equine health and disease and the search for potential therapeutic targets.

Pancreatectomy Induces Cancer-Promoting Neutrophil Extracellular Traps

BACKGROUND

Neutrophil extracellular traps (NETs) occur when neutrophil chromatin is decondensed and extruded into the extracellular space in a web-like structure. Originally described as an anti-microbial function, this process has been implicated in the pathogenesis of pancreatic disease. In addition, NETs are upregulated during physiologic wound-healing and coagulation. This study evaluated how the inflammatory response to pancreatic surgery influences NET formation.

METHODS

For this study, 126 patients undergoing pancreatectomy gave consent before participation. Plasma was collected at several time points (preoperatively and through the postoperative outpatient visit). Plasma levels of NET markers, including cell-free DNA (cfDNA), citrullinated histone H3 (CitH3), interleukin (IL)-8, IL-6, and granulocyte colony-stimulating factor (G-CSF) were measured using enzyme-linked immunosorbent assay (ELISA). Patient clinical data were retrospectively collected from a prospectively maintained database.

RESULTS

After pancreatic resection, NET markers (cfDNA and CitH3) were elevated, peaking on postoperative days 3 and 4. This increase in NETs was due to an inherent change in neutrophil biology. Postoperatively, NET-inducing cytokines (IL-8, IL-6, and G-CSF) were increased, peaking early in the postoperative course. The patients undergoing the robotic approach had a reduction in NETs during the postoperative period compared with those who underwent the open approach. The patients who experienced a pancreatic leak had an increase in NET markers during the postoperative period.

CONCLUSIONS

Pancreatectomy induces cancer-promoting NET formation. The minimally invasive robotic approach may induce fewer NETs, although the current analysis was limited by selection bias. Pancreatic leak resulted in increased NETs. Further study into the potential for NET inhibition during the perioperative period is warranted.

Neutrophil extracellular trap formation and its implications in nonsteroidal anti-inflammatory drug-induced small intestinal injury

BACKGROUND AND AIM

Nonsteroidal anti-inflammatory drugs (NSAIDs) damage the small intestine via neutrophil infiltration driven by the mucosal invasion of enterobacteria. The antimicrobial function of neutrophils is partially dependent on neutrophil extracellular traps (NETs). Excessive NET formation has been associated with several inflammatory diseases. Here, we aimed to investigate the role of NETs in NSAID-induced small intestinal damage using human samples and an experimental mouse model.

METHODS

Human small intestine specimens were obtained from NSAID users during double-balloon enteroscopy. Wild-type, protein arginine deiminase 4 (PAD4) knockout, and antibiotic-treated mice were administered indomethacin to induce small intestinal injury. The expression of NET-associated proteins, including PAD4, citrullinated histone H3 (CitH3), cell-free DNA, and myeloperoxidase (MPO), was evaluated.

RESULTS

The double-positive stained area with CitH3 and MPO, which is specific for neutrophil-derived extracellular traps, was significantly high in the injured small intestinal mucosa of NSAID users. In a mouse model, small intestinal damage developed at 6 h after indomethacin administration, accompanied by increased mRNA levels of interleukin-1β and keratinocyte chemoattractant and elevated NET-associated protein levels of PAD4, CitH3, and MPO in small intestine and serum levels of cell-free DNA. Both genetic deletion and pharmacological inhibition of PAD4 attenuated this damage by reducing the mRNA expression of inflammatory cytokines and NET-associated proteins. Furthermore, mice pretreated with antibiotics showed resistance to indomethacin-induced small intestinal damage, with less NET formation.

CONCLUSION

These results suggest that NETs aggravate NSAID-induced small intestinal injury. Therefore, NET inhibition could be a potential treatment for NSAID-induced small intestinal injury.

Chromatin as alarmins in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a severe gastrointestinal disease primarily affecting premature neonates, marked by poorly understood pro-inflammatory signaling cascades. Recent advancements have shed light on a subset of endogenous molecular patterns, termed chromatin-associated molecular patterns (CAMPs), which belong to the broader category of damage-associated molecular patterns (DAMPs). CAMPs play a crucial role in recognizing pattern recognition receptors and orchestrating inflammatory responses. This review focuses into the realm of CAMPs, highlighting key players such as extracellular cold-inducible RNA-binding protein (eCIRP), high mobility group box 1 (HMGB1), cell-free DNA, neutrophil extracellular traps (NETs), histones, and extracellular RNA. These intrinsic molecules, often perceived as foreign, have the potential to trigger immune signaling pathways, thus contributing to NEC pathogenesis. In this review, we unravel the current understanding of the involvement of CAMPs in both preclinical and clinical NEC scenarios. We also focus on elucidating the downstream signaling pathways activated by these molecular patterns, providing insights into the mechanisms that drive inflammation in NEC. Moreover, we scrutinize the landscape of targeted therapeutic approaches, aiming to mitigate the impact of tissue damage in NEC. This in-depth exploration offers a comprehensive overview of the role of CAMPs in NEC, bridging the gap between preclinical and clinical insights.

Differential requirement of Formyl Peptide Receptor 1 in macrophages and neutrophils in the host defense against Mycobacterium tuberculosis Infection

Formyl peptide receptors (FPR), part of the G-protein coupled receptor superfamily, are pivotal in directing phagocyte migration towards chemotactic signals from bacteria and host tissues. Although their roles in acute bacterial infections are well-documented, their involvement in immunity against tuberculosis (TB) remains unexplored. This study investigates the functions of Fpr1 and Fpr2 in defense against Mycobacterium tuberculosis (Mtb), the causative agent of TB. Elevated levels of Fpr1 and Fpr2 were found in the lungs of mice, rabbits and peripheral blood of humans infected with Mtb, suggesting a crucial role in the immune response. The effects of Fpr1 and Fpr2 deletion on bacterial load, lung damage, and cellular inflammation were assessed using a TB model of hypervirulent strain of Mtb from the W-Beijing lineage. While Fpr2 deletion showed no impact on disease outcome, Fpr1-deficient mice demonstrated improved bacterial control, especially by macrophages. Bone marrow-derived macrophages from these Fpr1 -/- mice exhibited an enhanced ability to contain bacterial growth over time. Contrarily, treating genetically susceptible mice with Fpr1-specific inhibitors caused impaired early bacterial control, corresponding with increased bacterial persistence in necrotic neutrophils. Furthermore, ex vivo assays revealed that Fpr1 -/- neutrophils were unable to restrain Mtb growth, indicating a differential function of Fpr1 among myeloid cells. These findings highlight the distinct and complex roles of Fpr1 in myeloid cell-mediated immunity against Mtb infection, underscoring the need for further research into these mechanisms for a better understanding of TB immunity.

A multi-platform analysis of human gingival crevicular fluid reveals ferroptosis as a relevant regulated cell death mechanism during the clinical progression of periodontitis

Ferroptosis is implicated in the pathogenesis of numerous chronic-inflammatory diseases, yet its association with progressive periodontitis remains unexplored. To investigate the involvement and significance of ferroptosis in periodontitis progression, we assessed sixteen periodontitis-diagnosed patients. Disease progression was clinically monitored over twelve weeks via weekly clinical evaluations and gingival crevicular fluid (GCF) collection was performed for further analyses. Clinical metrics, proteomic data, in silico methods, and bioinformatics tools were combined to identify protein profiles linked to periodontitis progression and to explore their potential connection with ferroptosis. Subsequent western blot analyses validated key findings. Finally, a single-cell RNA sequencing (scRNA-seq) dataset (GSE164241) for gingival tissues was analyzed to elucidate cellular dynamics during periodontitis progression. Periodontitis progression was identified as occurring at a faster rate than traditionally thought. GCF samples from progressing and non-progressing periodontal sites showed quantitative and qualitatively distinct proteomic profiles. In addition, specific biological processes and molecular functions during progressive periodontitis were revealed and a set of hub proteins, including SNCA, CA1, HBB, SLC4A1, and ANK1 was strongly associated with the clinical progression status of periodontitis. Moreover, we found specific proteins - drivers or suppressors - associated with ferroptosis (SNCA, FTH1, HSPB1, CD44, and GCLC), revealing the co-occurrence of this specific type of regulated cell death during the clinical progression of periodontitis. Additionally, the integration of quantitative proteomic data with scRNA-seq analysis suggested the susceptibility of fibroblasts to ferroptosis. Our analyses reveal proteins and processes linked to ferroptosis for the first time in periodontal patients, which offer new insights into the molecular mechanisms of progressive periodontal disease. These findings may lead to novel diagnostic and therapeutic strategies.

Neutrophil Virucidal Activity Against SARS-CoV-2 Is Mediated by Neutrophil Extracellular Traps

BACKGROUND

Inflammation in the lungs and other vital organs in COVID-19 is characterized by the presence of neutrophils and a high concentration of neutrophil extracellular traps (NETs), which seems to mediate host tissue damage. However, it is not known whether NETs could have virucidal activity against SARS-CoV-2.

METHODS

We investigated whether NETs could prevent SARS-CoV-2 replication in neutrophils and epithelial cells and what the consequence of NETs degradation would be in K18-humanized ACE2 transgenic mice infected with SARS-CoV-2.

RESULTS

Here, by immunofluorescence microscopy, we observed that viral particles colocalize with NETs in neutrophils isolated from patients with COVID-19 or healthy individuals and infected in vitro. The inhibition of NETs production increased virus replication in neutrophils. In parallel, we observed that NETs inhibited virus abilities to infect and replicate in epithelial cells after 24 hours of infection. Degradation of NETs with DNase I prevented their virucidal effect in vitro. Using K18-humanized ACE2 transgenic mice, we observed a higher viral load in animals treated with DNase I. However, the virucidal effect of NETs was not dependent on neutrophil elastase or myeloperoxidase activity.

CONCLUSIONS

Our results provide evidence of the role of NETosis as a mechanism of SARS-CoV-2 viral capture and inhibition.

DNA of Neutrophil Extracellular Traps Binds TMCO6 to Impair CD8+ T-cell Immunity in Hepatocellular Carcinoma

Neutrophil extracellular traps (NET), formed by the extracellular release of decondensed chromatin and granules, have been shown to promote tumor progression and metastasis. Tumor-associated neutrophils in hepatocellular carcinoma (HCC) are prone to NET formation, highlighting the need for a more comprehensive understanding of the mechanisms of action of NETs in liver cancer. Here, we showed that DNA of NETs (NET-DNA) binds transmembrane and coiled-coil domains 6 (TMCO6) on CD8+ T cells to impair antitumor immunity and thereby promote HCC progression. TGFβ1 induced NET formation, which recruited CD8+ T cells. Binding to NET-DNA inhibited CD8+ T cells function while increasing apoptosis and TGFβ1 secretion, forming a positive feedback loop to further stimulate NET formation and immunosuppression. Mechanistically, the N-terminus of TMCO6 interacted with NET-DNA and suppressed T-cell receptor signaling and NFκB p65 nuclear translocation. Blocking NET formation by inhibiting PAD4 induced potent antitumor effects in wild-type mice but not TMCO6-/- mice. In clinical samples, CD8+ T cells expressing TMCO6 had an exhausted phenotype. TGFβ1 signaling inhibition or TMCO6 deficiency combined with anti-PD-1 abolished NET-driven HCC progression in vivo. Collectively, this study unveils the role of NET-DNA in impairing CD8+ T-cell immunity by binding TMCO6 and identifies targeting this axis as an immunotherapeutic strategy for blocking HCC progression.

SIGNIFICANCE

TMCO6 is a receptor for DNA of NETs that mediates CD8+ T-cell dysfunction in HCC, indicating that the NET-TMCO6 axis is a promising target for overcoming immunosuppression in liver cancer.

Neutrophils in glioma microenvironment: from immune function to immunotherapy

Glioma is a malignant tumor of the central nervous system (CNS). Currently, effective treatment options for gliomas are still lacking. Neutrophils, as an important member of the tumor microenvironment (TME), are widely distributed in circulation. Recently, the discovery of cranial-meningeal channels and intracranial lymphatic vessels has provided new insights into the origins of neutrophils in the CNS. Neutrophils in the brain may originate more from the skull and adjacent vertebral bone marrow. They cross the blood-brain barrier (BBB) under the action of chemokines and enter the brain parenchyma, subsequently migrating to the glioma TME and undergoing phenotypic changes upon contact with tumor cells. Under glycolytic metabolism model, neutrophils show complex and dual functions in different stages of cancer progression, including participation in the malignant progression, immune suppression, and anti-tumor effects of gliomas. Additionally, neutrophils in the TME interact with other immune cells, playing a crucial role in cancer immunotherapy. Targeting neutrophils may be a novel generation of immunotherapy and improve the efficacy of cancer treatments. This article reviews the molecular mechanisms of neutrophils infiltrating the central nervous system from the external environment, detailing the origin, functions, classifications, and targeted therapies of neutrophils in the context of glioma.

Neutrophil ALDH2 is a new therapeutic target for the effective treatment of sepsis-induced ARDS

Acetaldehyde dehydrogenase 2 (ALDH2) mutations are commonly found in a subgroup of the Asian population. However, the role of ALDH2 in septic acute respiratory distress syndrome (ARDS) remains unknown. Here, we showed that human subjects carrying the ALDH2rs671 mutation were highly susceptible to developing septic ARDS. Intriguingly, ALDH2rs671-ARDS patients showed higher levels of blood cell-free DNA (cfDNA) and myeloperoxidase (MPO)-DNA than ALDH2WT-ARDS patients. To investigate the mechanisms underlying ALDH2 deficiency in the development of septic ARDS, we utilized Aldh2 gene knockout mice and Aldh2rs671 gene knock-in mice. In clinically relevant mouse sepsis models, Aldh2-/- mice and Aldh2rs671 mice exhibited pulmonary and circulating NETosis, a specific process that releases neutrophil extracellular traps (NETs) from neutrophils. Furthermore, we discovered that NETosis strongly promoted endothelial destruction, accelerated vascular leakage, and exacerbated septic ARDS. At the molecular level, ALDH2 increased K48-linked polyubiquitination and degradation of peptidylarginine deiminase 4 (PAD4) to inhibit NETosis, which was achieved by promoting PAD4 binding to the E3 ubiquitin ligase CHIP. Pharmacological administration of the ALDH2-specific activator Alda-1 substantially alleviated septic ARDS by inhibiting NETosis. Together, our data reveal a novel ALDH2-based protective mechanism against septic ARDS, and the activation of ALDH2 may be an effective treatment strategy for sepsis.

Unraveling the intriguing interplay: Exploring the role of lncRNAs in caspase-independent cell death

Cell death plays a crucial role in various physiological and pathological processes. Until recently, programmed cell death was mainly attributed to caspase-dependent apoptosis. However, emerging evidence suggests that caspase-independent cell death (CICD) mechanisms also contribute significantly to cellular demise. We and others have reported and functionally characterized numerous long noncoding RNAs (lncRNAs) that modulate caspase-dependent apoptotic pathways potentially in a pathway-dependent manner. However, the interplay between lncRNAs and CICD pathways has not been comprehensively documented. One major reason for this is that most CICD pathways have been recently discovered with some being partially characterized at the molecular level. In this review, we discuss the emerging evidence that implicates specific lncRNAs in the regulation and execution of CICD. We summarize the diverse mechanisms through which lncRNAs modulate different forms of CICD, including ferroptosis, necroptosis, cuproptosis, and others. Furthermore, we highlight the intricate regulatory networks involving lncRNAs, protein-coding genes, and signaling pathways that orchestrate CICD in health and disease. Understanding the molecular mechanisms and functional implications of lncRNAs in CICD may unravel novel therapeutic targets and diagnostic tools for various diseases, paving the way for innovative strategies in disease management and personalized medicine. This article is categorized under: RNA in Disease and Development > RNA in Disease.

Platelet factor 4 promotes deep venous thrombosis by regulating the formation of neutrophil extracellular traps

The presence of neutrophil extracellular traps (NETs) in thrombotic diseases has been extensively studied. The exact mechanism of NET formation in deep venous thrombosis (DVT) has not been largely studied. This study is aimed to explore the role of NETs and their interaction with platelet factor 4 (PF4) in DVT. In plasma samples from 51 healthy volunteers and 52 DVT patients, NET markers and PF4 were measured using enzyme-linked immunosorbent assays (ELISA). NET generation in blood samples from healthy subjects and DVT patients was analyzed by confocal microscopy and flow cytometry. The plasma levels of NETs were significantly elevated in DVT patients, and neutrophils from patients showed a stronger ability to generate NETs after treatment. PF4 was upregulated in plasma samples from DVT patients and mediated NET formation. NETs enhanced procoagulant (PCA) via tissue factor and activating platelets to induce procoagulant activity. In addition, we established an inferior vena cava ligation (IVC) model to examine the role of NETs in thrombogenicity in DVT. In conclusion, NET formation was mediated by PF4 and enhance the procoagulant activity in DVT.

Neutrophil extracellular trap induction through peptidylarginine deiminase 4 activity is involved in 2,4,6-trinitrobenzenesulfonic acid-induced colitis

Neutrophil extracellular traps (NETs) are induced in the innate immune response against infectious agents and are also implicated in the pathogenesis of various cancers and autoimmune diseases. Peptidylarginine deiminase 4 (PAD4), an enzyme that converts arginine to citrulline, is also involved in NET formation. In this study, we investigated the pathogenic effect of PAD4 on NETs in inflammatory bowel disease using a trinitrobenzene sulfonic acid (TNBS)-induced murine colitis model. PAD4-deficient (PAD4KO) mice were generated by CRISPR-Cas9-mediated genomic editing. NETs were triggered in peritoneal neutrophils obtained from wild-type mice by A23187 (a calcium ionophore), but these responses were completely abolished in the PAD4KO mice. Experimental colitis was induced in wild-type and PAD4KO mice via an intrarectal injection of TNBS. TNBS injection resulted in body weight loss, extensive colonic erosion, and ulceration in wildtype mice. However, these responses were significantly attenuated following the administration of Cl-amidine (an inhibitor of pan-PADs) and DNase I (an inhibitor of NET formation), in combination with PAD4KO in mice. TNBS-induced increases in myeloperoxidase activity, inflammatory cytokine expression, and NET formation in the colon were significantly reduced following the administration of Cl-amidine, DNase I injection, and PAD4KO. These findings suggest that NET formation contributes to the pathogenesis of TNBS-induced colitis via PAD4. Thus, PAD4 is a promising target for the treatment of inflammatory bowel disease.

The Role of Neutrophils in Multiple Sclerosis and Ischemic Stroke

Inflammation plays an important role in numerous central nervous system (CNS) disorders. Its role is ambiguous-it can induce detrimental effects, as well as repair and recovery. In response to injury or infection, resident CNS cells secrete numerous factors that alter blood-brain barrier (BBB) function and recruit immune cells into the brain, like neutrophils. Their role in the pathophysiology of CNS diseases, like multiple sclerosis (MS) and stroke, is highly recognized. Neutrophils alter BBB permeability and attract other immune cells into the CNS. Previously, neutrophils were considered a homogenous population. Nowadays, it is known that various subtypes of these cells exist, which reveal proinflammatory or immunosuppressive functions. The primary goal of this review was to discuss the current knowledge regarding the important role of neutrophils in MS and stroke development and progression. As the pathogenesis of these two disorders is completely different, it gives the opportunity to get insight into diverse mechanisms of neutrophil involvement in brain pathology. Our understanding of the role of neutrophils in CNS diseases is still evolving as new aspects of their activity are being unraveled. Neutrophil plasticity adds another level to their functional complexity and their importance for CNS pathophysiology.

The Bifunctional Effects of Lactoferrin (LFcinB11) in Inhibiting Neural Cell Adhesive Molecule (NCAM) Polysialylation and the Release of Neutrophil Extracellular Traps (NETs)

The expression of polysialic acid (polySia) on the neuronal cell adhesion molecule (NCAM) is called NCAM-polysialylation, which is strongly related to the migration and invasion of tumor cells and aggressive clinical status. Thus, it is important to select a proper drug to block tumor cell migration during clinical treatment. In this study, we proposed that lactoferrin (LFcinB11) may be a better candidate for inhibiting NCAM polysialylation when compared with CMP and low-molecular-weight heparin (LMWH), which were determined based on our NMR studies. Furthermore, neutrophil extracellular traps (NETs) represent the most dramatic stage in the cell death process, and the release of NETs is related to the pathogenesis of autoimmune and inflammatory disorders, with proposed involvement in glomerulonephritis, chronic lung disease, sepsis, and vascular disorders. In this study, the molecular mechanisms involved in the inhibition of NET release using LFcinB11 as an inhibitor were also determined. Based on these results, LFcinB11 is proposed as being a bifunctional inhibitor for inhibiting both NCAM polysialylation and the release of NETs.