NET formation is a default epigenetic program controlled by PAD4 in apoptotic neutrophils

Single-cell atlas of human gingiva unveils a NETs-related neutrophil subpopulation regulating periodontal immunity

INTRODUCTION

Exaggerated neutrophil recruitment and activation are the major features of pathological alterations in periodontitis, in which neutrophil extracellular traps (NETs) are considered to be responsible for inflammatory periodontal lesions. Despite the critical role of NETs in the development and progression of periodontitis, their specific functions and mechanisms remain unclear.

OBJECTIVES

To demonstrate the important functions and specific mechanisms of NETs involved in periodontal immunopathology.

METHODS

We performed single-cell RNA sequencing on gingival tissues from both healthy individuals and patients diagnosed with periodontitis. High-dimensional weighted gene co-expression network analysis and pseudotime analysis were then applied to characterize the heterogeneity of neutrophils. Animal models of periodontitis were treated with NETs inhibitors to investigate the effects of NETs in severe periodontitis. Additionally, we established a periodontitis prediction model based on NETs-related genes using six types of machine learning methods. Cell-cell communication analysis was used to identify ligand-receptor pairs among the major cell groups within the immune microenvironment.

RESULTS

We constructed a single-cell atlas of the periodontal microenvironment and obtained nine major cell populations. We further identified a NETs-related subgroup (NrNeu) in neutrophils. An in vivo inhibition experiment confirmed the involvement of NETs in gingival inflammatory infiltration and alveolar bone absorption in severe periodontitis. We further screened three key NETs-related genes (PTGS2, MME and SLC2A3) and verified that they have the potential to predict periodontitis. Moreover, our findings revealed that gingival fibroblasts had the most interactions with NrNeu and that they might facilitate the production of NETs through the MIF-CD74/CXCR4 axis in periodontitis.

CONCLUSION

This study highlights the pathogenic role of NETs in periodontal immunity and elucidates the specific regulatory relationship by which gingival fibroblasts activate NETs, which provides new insights into the clinical diagnosis and treatment of periodontitis.

Programmable hierarchical hydrogel dressing for sequential release of growth factor and DNase to accelerate diabetic wound healing

Dysregulation of growth factor expression causes impaired healing of diabetic foot ulcer (DFU). Platelet-derived growth factor (PDGF)-containing gel has been clinically applied for topical treatment of DFU. Recruitment of neutrophils stimulated by PDGF favors the wound healing of DFU. However, overactivation of neutrophils induced by hyperglycemia causes massive generation and long-term persistence of neutrophil extracellular traps (NETs), ultimately leading to unexpected skin damage and delayed wound repair. Here, we engineer a hierarchically-assembled hydrogel to achieve local release of the growth factor, PDGF-BB and the NET scavenger, deoxyribonuclease (DNase) I with distinct kinetics for enhanced healing of DFU. The hydrogel is constructed by crosslinking of anti-bacterial quaternized chitosan and hypochlorite-degradable nanogel via a copper-free click reaction, in which PDGF-BB is loaded in the hydrogel matrix while DNase I is encapsulated in the inner nanogel. Programmable release of combinatorial therapeutics is implemented by the hydrogel in response to the wound microenvironment. We show that the hierarchical hydrogel co-loaded with PDGF-BB and DNase I promotes neutrophil recruitment, increases endothelial cell migration, degrades excess NETs, and prevents wound infection for accelerating the wound closure in the diabetic mouse wound models.

Targeting neutrophil extracellular traps in cancer progression and metastasis

Neutrophils serve as pivotal effectors and regulators of the intricate immune system. Their contributions are indispensable, encompassing the obliteration of pathogens and a significant role in both cancer initiation and progression. Conversely, malignancies profoundly affect neutrophil activity, maturation, and lifespans. Cancer cells manipulate their biology to enhance or suppress the key functions of neutrophils. This manipulation is one of the most remarkable defensive mechanisms used by neutrophils, including the formation of neutrophil extracellular traps (NETs). NETs are filamentous structures comprising DNA, histones, and proteins derived from cytotoxic granules. In this review, we discuss the bidirectional interplay in which cancer elicits NET formation, and NETs concurrently facilitate cancer progression. Here, we discuss how vascular dysfunction and thrombosis induced by neutrophils and NETs contribute to an elevated risk of mortality from cardiovascular complications in patients with cancer. Ultimately, we propose a series of therapeutic strategies that hold promise for effectively targeting NETs in clinical settings.

Targeting the HDAC6/Hint2/MICU1 axis to ameliorate acute liver failure via inhibiting NETosis

AIMS

Acute liver failure (ALF) is marked by extensive inflammation and immune dysregulation, which are closely associated with neutrophil infiltration and NETosis. However, the specific mechanisms that drive NETosis in ALF remain poorly understood.

MATERIALS AND METHODS

We employed flow cytometry, western blot, qRT-PCR, and cf-DNA assay to investigate the link between NETosis and ALF. The role of HDAC6-mediated deacetylation of histidine triad nucleotide-binding protein 2 (Hint2) was assessed, along with the effects of lentiviral vector-based overexpression and knockdown of Hint2 on mitochondrial function and NETosis. Additionally, CO-IP, IF, protein docking analysis, mCa2+ uptake assay, and mtROS measurement were used to explore the interaction between Hint2 and mitochondrial calcium uniporter complex (MCUc). Finally, experimental neutrophil depletion in mice was conducted to confirm the protective effect of NETosis inhibition in ALF.

KEY FINDINGS

Our study demonstrated that Hint2 undergoes HDAC6-mediated deacetylation, disrupting mitochondrial dynamics and triggering NETosis during ALF. Furthermore, MICU1 bridges Hint2 and NETosis by regulating mCa2+ homeostasis and mtROS production. Activation of Hint2, either through the HDAC6 inhibitor ACY1215 or via overexpression, increased the level of MICU1 to suppress the opening of the MCUc and the associated mtROS release, thereby inhibiting NETosis. Conversely, Hint2 knockdown induced NETosis by surging mCa2+ overload and mtROS production, while the MCUc inhibitor RU265 mitigates NETosis by blocking mCa2+ influx.

SIGNIFICANCE

Our findings recognized the HDAC6/Hint2/MICU1 axis as a novel pathway in neutrophils, the inhibition of which intercepts mCa2+ overload and mtROS accumulation, thereby reducing NETosis and facilitating liver recovery during ALF.

Glycyrrhizic acid reduces neutrophil extracellular trap formation to ameliorate colitis-associated colorectal cancer by inhibiting peptidylarginine deiminase 4

ETHNOPHARMACOLOGICAL RELEVANCE

In traditional Chinese medicine, the radices of Glycyrrhiza uralensis Fisch., known as liquorice, have been used for relieving cough, alleviating pain and harmonizing the actions of all medicinals in a formula. Glycyrrhizic acid (GA), a natural compound derived from licorice, exhibits notable anti-inflammatory properties.

AIM

Neutrophil extracellular trap (NET) generated by peptidylarginine deiminase 4 (PAD4) has been implicated in the progression of colitis to colitis-associated colorectal cancer (CAC). This study aims to investigate whether GA can ameliorate CAC through the inhibition of PAD4 activity and reduction of NET formation.

METHODS

We investigated the correlation between PAD4 expression levels and immune cell infiltration in colorectal cancer utilizing the TIMER database, while also assessing PAD4 levels and activity in human CAC biopsy samples. To evaluate the therapeutic potential of licorice acid on CAC in vivo, we employed the AOM/DSS model and confirmed its inhibitory effects on NET formation in vitro. Furthermore, we explored whether licorice acid can restore immune cell cytotoxicity by diminishing NET formation through fluorescence transfection of CT26 cell lines and subsequent sorting of CD8+ T cells. Additionally, we elucidated the detrimental role of PAD4 in CAC progression using PAD4-/- mice.

RESULTS

We observed that GA ameliorated colonic inflammation, reduced tumorigenicity, and decreased NET formation, as evidenced by decreased levels of PAD4, citH3, MPO and MMP-9. In vitro experiments demonstrated that GA effectively bound to PAD4 and inhibited its enzyme activity. Furthermore, GA prevented epithelial cell destruction while enhancing CD8+ T-cell-mediated tumor killing through the suppression of NET formation in a coculture system.

CONCLUSIONS

We demonstrate that GA inhibits CAC occurrence by suppressing PAD4 activity and reducing NET formation.

Myriscagayanone C, a new compound from the fruit of myristica cagayanensis, inhibits fMLP-induced respiratory bursts by specifically preventing Akt translocation in human neutrophils

Neutrophils that are overactivated can cause inflammatory diseases. Neutrophils possess various surface receptors, including G-protein-coupled chemoattractant receptors, which assist in recognizing pathogen attacks and the inflammatory environment. Therefore, targeting G-protein-coupled chemoattractant receptors and their downstream molecules is important for preventing abnormal neutrophil activation. This study examines the effects and underlying mechanism of myriscagayanone C, a new compound obtained from the fruit of myristica cagayanensis, on neutrophil respiratory burst induced by fMLP. The immunoblotting assay was conducted to assess the mechanisms by which myriscagayanone C inhibits fMLP-induced respiratory burst by disrupting the translocation of Akt to the cellular membrane. Briefly, myriscagayanone C suppressed the production of superoxide anions induced by fMLP on human neutrophils in a concentration-dependent manner (IC50: 4.73 ± 0.68 μM). Myriscagayanone C blocked fMLP-induced Akt translocation to the cell membrane, inhibiting AktT308 and AktS473 phosphorylation by PDK1Y373/376 and mTORS2481, respectively. Myriscagayanone C inhibited fMLP-induced p47phox phosphorylation and translocation. Myriscagayanone C did not inhibit the activity of PI3K, the amount of phosphatidylinositol (3, 4, 5)-trisphosphate, or the translocation of phosphorylated-PDK1Y373/376 and -mTORS2481 to the membrane. Myriscagayanone C did not inhibit fMLP-induced PKC, Src, ERK1/2, p38 phosphorylation, and intracellular calcium mobilization. Myriscagayanone C did not inhibit the chemotaxis and CD11b expression induced by fMLP. Myriscagayanone C did not inhibit PMA-induced superoxide anion production and neutrophil extracellular trap formation. According to this data, myriscagayanone C inhibits fMLP-induced neutrophil superoxide anion production by interrupting the translocation of Akt to the plasma membrane, which affects the NADPH oxidase activity by preventing p47phox phosphorylation and translocation.

Preliminary evidence of immune infiltration and neutrophil degranulation in peripheral blood of non-obese OSA patients related to cognitive decline

Obstructive sleep apnea (OSA) patients have varying degrees of cognitive impairment, but the specific pathogenic mechanism is still unclear. Meanwhile, poor compliance with continuous positive airway pressure (CPAP) in OSA prompts better solutions. This study aimed to identify differentially expressed genes between the non-obese OSA patients and healthy controls, and to explore potential biomarkers associated with cognitive impairment. Cohorts of healthy control (n = 20) and non-obese, treatment-naïve OSA patients (n = 20) were recruited. We collected their peripheral blood mononuclear cells and neutrophils, and their cognitive performances were evaluated by the Montreal Cognitive Assessment (MoCA). The differentially expressed genes were identified by bioinformatic analysis and confirmed by PCR. Imbalanced immune cell proportions were assessed by Cibersort. Biomarkers related to enriched cellular pathways were measured by ELISA. OSA patients showed a significant decline in overall cognitive function and were associated with higher daytime sleepiness scores. Multiple signaling pathways were enriched in the non-obese OSA cohort, including upregulation of neutrophil-degranulation. Increased monocyte proportion and decreased NK cell proportion were figured out. The relevant genes, including upregulated defensin alpha 4 (DEFA4), haptoglobin (HP), survivin (BIRC5), and suppressed interferon gamma (IFNG) expression were detected. The relative expression of DEFA4 was significantly correlated with the MoCA score and sleep parameters. Biomarkers such as myeloperoxidase (MPO), H2O2, and lipocalin-2, as representatives of neutrophils' activation, elevated significantly in the OSA group. The data demonstrated a positive correlation between MPO and oxygen desaturation index (ODI) and a negative correlation between MPO and lowest oxygen saturation (LSaO2). The level of Lipocalin-2 was positively correlated with apnea-hypopnea index (AHI) and ODI and negatively correlated with LSaO2 and MoCA score. We also observed a negative correlation between H2O2 and mean oxygen saturation (MSaO2). Degranulation of neutrophils was activated in non-obese OSA patients without other complications. The process is related to OSA severity and cognitive impairment, implying its role in pathogenesis.

Adaptations of neutrophils in cancer

There is a renewed interest in neutrophil biology, largely instigated by their prominence in cancer. From an immunologist's perspective, a conceptual breakthrough is the realization that prototypical inflammatory, cytotoxic leukocytes can be tamed to promote the survival and growth of other cells. This has sparked interest in defining the biological principles and molecular mechanisms driving the adaptation of neutrophils to cancer. Yet, many questions remain: is this adaptation mediated by reprogramming mature neutrophils inside the tumoral mass, or rather by rewiring granulopoiesis in the bone marrow? Why, in some instances, are neutrophils beneficial and in others detrimental to cancer? How many different functional programs can be induced in neutrophils by tumors, and is this dependent on the type of tumor? This review summarizes what we know about these questions and discusses therapeutic strategies based on our incipient knowledge of how neutrophils adapt to cancer.

Neutrophil PPIF exacerbates lung ischemia-reperfusion injury after lung transplantation by promoting calcium overload-induced neutrophil extracellular traps formation

Lung ischemia-reperfusion (I/R) injury is the main risk factor for primary graft dysfunction and patient death after lung transplantation (LTx). It is widely accepted that the main pathological mechanism of lung I/R injury are calcium overload, oxygen free radical explosion and neutrophil-mediated damage, which leading to the lack of effective treatment options. The aim of this study was to further explore the mechanisms of lung I/R injury after LTx and to provide potential therapeutic strategies. Our bioinformatics analysis revealed that the neutrophil extracellular traps (NETs) formation was closely involved in lung I/R injury after LTx, which was accompanied by up-regulation of peptidylprolyl isomerase F (PPIF) and peptidyl arginine deiminase 4 (PADI4). We further established an orthotopic LTx mouse model to simulate lung I/R injury in vivo, and found that PPIF and PADI4 inhibitors effectively reduced neutrophil infiltration, NETs formation, inflammatory response, and lung I/R injury. In the neutrophil model induced by HL-60 cell line in vitro, we found that PPIF inhibitor cyclosporin A (Cys A) better alleviated calcium overload induced inflammatory response, reactive oxygen species content and NETs formation. Further study demonstrated that interfering with neutrophil PPIF protected mitochondrial function by alleviating store-operated calcium entry (SOCE) during calcium overload and played the above positive role. On this basis, we found that the reduction of calcium content in neutrophils was accompanied by the inhibition of calcineurin (CN) and nuclear factor of activated T cells (NFAT). In conclusion, our findings suggested that neutrophil PPIF could serve as a novel biomarker and potential therapeutic target of lung I/R injury after LTx, which provided new clues for its treatment by inhibiting calcium overload-induced NETs formation.

Turning Neutrophil Cell Death Deadly in the Context of Hypertensive Vascular Disease

Hypertensive vascular disease (HVD) is a major health burden globally and is a comorbidity commonly associated with other metabolic diseases. Many factors are associated with HVD including obesity, diabetes, smoking, chronic kidney disease, and sterile inflammation. Increasing evidence points to neutrophils as an important component of the chronic inflammatory response in HVD. Neutrophils are abundant in the circulation and can respond rapidly upon stimulation to deploy an armament of antimicrobial effector functions. One of the outcomes of neutrophil activation is the generation of neutrophil extracellular traps (NETs), a regulated extrusion of chromatin and proteases. Although neutrophils and NETs are well described as components of the innate immune response to infection, recent evidence implicates them in HVD. Endothelial cell activation can trigger neutrophil adhesion, activation, and production of NETs promoting vascular dysfunction, vessel remodelling, and loss of resistance. The regulated release of NETs can be controlled by the pore-forming activities of distinct cell death pathways. The best characterized pathways in this context are apoptosis, pyroptosis, and necroptosis. In this review, we discuss how inflammatory cell death signalling and NET formation contribute to hypertensive disease. We also examine novel therapeutic approaches to limit NET production and their future potential as therapeutic drugs for cardiovascular disorders.

Mitochondrial calcium uniporter complex: Unveiling the interplay between its regulators and calcium homeostasis

The mitochondrial calcium uniporter complex (MCUc), serving as the specific channel for calcium influx into the mitochondrial matrix, is integral to calcium homeostasis and cellular integrity. Given its importance, ongoing research spans various disease models to understand the properties of the MCUc in pathophysiological contexts, but reported a different conclusion. Therefore, this review delves into the profound connection between MCUc-mediated calcium transients and cellular signaling pathways, mitochondrial dynamics, metabolism, and cell death. Additionally, we shed light on the recent advancements concerning the structural intricacies and auxiliary components of the MCUc in both resting and activated states. Furthermore, emphasis is placed on novel extrinsic and intrinsic regulators of the MCUc and their therapeutic implications across a spectrum of diseases. Meanwhile, we employed molecular docking simulations and identified candidate traditional Chinese medicine components with potential binding sites to the MCUc, potentially offering insights for further research on MCUc modulation.

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.

Nets in fibrosis: Bridging innate immunity and tissue remodeling

Fibrosis, a complex pathological process characterized by excessive deposition of extracellular matrix components, leads to tissue scarring and dysfunction. Emerging evidence suggests that neutrophil extracellular traps (NETs), composed of DNA, histones, and antimicrobial proteins, significantly contribute to fibrotic diseases pathogenesis. This review summarizes the process of NETs production, molecular mechanisms, and related diseases, and outlines the cellular and molecular mechanisms associated with fibrosis. Subsequently, this review comprehensively summarizes the current understanding of the intricate interplay between NETs and fibrosis across various organs, including the lung, liver, kidney, skin, and heart. The mechanisms by which NETs contribute to fibrogenesis, including their ability to promote inflammation, induce epithelial-mesenchymal transition (EMT), activate fibroblasts, deposit extracellular matrix (ECM) components, and trigger TLR4 signaling were explored. This review aimed to provide insights into the complex relationship between NETs and fibrosis via a comprehensive analysis of existing reports, offering novel perspectives for future research and therapeutic interventions.

Intraluminal release of citrullinated histone 3 from various cellular origins coincides with microvascular thrombosis in burn wounds

Loss of perfusion in the burn wound might cause wound deepening and impaired healing. We previously showed persistent microvascular thrombosis coinciding with intraluminal neutrophils extracellular traps in human burned skin. This study investigates the presence of intraluminal citrullinated histone 3 (H3cit) from different cellular origins (neutrophils, monocytes, and lymphocytes) in relation to microvascular thrombosis of burn wounds. Eschar was obtained from burn patients (n = 18) 6-40 days postburn with a mean total burned body surface area of 23%. Microvascular presence of tissue factor (TF), factor XII (FXII) and thrombi was assessed by immunohistochemistry. Intramicrovascular cell death was analyzed via immunofluorescent microscopy, combining antibodies for neutrophils (MPO), monocytes (CD14), and lymphocytes (CD45) with endothelial cell markers CD31 and H3cit. Significantly increased microvascular expression of TF, FXII, and thrombi (CD31+) was found in all eschar samples compared with control uninjured skin. Release of H3cit from different cellular origins was observed in the lumen of the dermal microvasculature in the eschar tissue 7-40 days postburn, with release from neutrophilic origin being 2.7 times more abundant. Intraluminal presence of extracellular H3cit colocalizing with either MPO, CD14, or CD45 is correlated to increased microvascular thrombosis in eschar of burn patients.

Neutrophils only die twice

After apoptotic cell death begins neutrophils initiate NETosis, a second cell death program.