The influence of agents differentiating HL-60 cells toward granulocyte-like cells on their ability to release neutrophil extracellular traps

An In Vitro Cell Model of Intestinal Barrier Function Using a Low-Cost 3D-Printed Transwell Device and Paper-Based Cell Membrane

Current in vitro methods for intestinal barrier assessment predominantly utilize two-dimensional (2D) membrane inserts in standard culture plates, which are widely recognized for their inability to replicate the microenvironment critical to intestinal barrier functionality. Our study focuses on creating an alternative method for intestinal barrier function by integrating a 3D-printed transwell device with a paper-based membrane. Caco-2 cells were grown on a Matrigel-modified paper membrane, in which the tight junction formation was evaluated using TEER measurements. Neutrophil-like dHL-60 cells were employed for neutrophil extracellular trap (NET) formation experiments. Furthermore, intestinal barrier dysfunction was demonstrated using NET-isolated and Staurosporine interventions. Intestinal barrier characteristics were investigated through immunofluorescence staining of specific proteins and scanning electron microscopy (SEM). Our paper-based intestinal barrier exhibited an increased resistance in a time-dependent manner, consistent with immunofluorescence images of Zonulin Occludens-1 (ZO-1) expression. Interestingly, immunofluorescence analysis revealed changes in the morphology of the intestinal barrier and the formation of surface villi. These disruptions were found to alter the localization of tight junctions, impacting epithelial polarization and surface functionality. Moreover, we successfully demonstrated the permeability of a paper-based intestinal barrier using FITC-dextran assay. Hence, the 3D-printed transwell device integrated with a paper membrane insert presents a straightforward, cost-effective, and sustainable platform for an in vitro cell model to evaluate intestinal barrier function.

Lipocalin 2 inhibits the expressions of interleukin-8 and macrophage inflammatory protein-1α in human neutrophil-like cells

OBJECTIVES

Lipocalin 2 (LCN2) is a glycoprotein with multiple functions, including antimicrobial activity, inflammatory response modulation, and cell migration. LCN2 is expressed in some cells, such as epithelial cells and neutrophils, and its levels are increased in inflammatory diseases. This study investigated the presence of LCN2 receptor (24p3R) in cells around periodontal tissues and function of LCN2 in cells with a receptor to explore the role of LCN2 in periodontal diseases.

METHODS

The presence of 24p3R was examined in periodontal cells, including human gingival fibroblasts, periodontal ligament fibroblasts, human oral epithelial cells (HOECs), and neutrophil-like cells (HL-60), by Western blotting. Changes in periodontal disease-associated proteins in the presence of recombinant LCN2 (rLCN2) were examined using a protein array in differentiated HL-60 (dHL-60) cells. Interleukin-8 (IL-8) and macrophage inflammatory protein-1α (MIP-1α) mRNA expressions were analyzed by qRT-PCR, and IL-8 and MIP-1α levels in dHL-60 cells treated with rLCN2 or Porphyromonas gingivalis-lipopolysaccaharide (P.g-LPS) were determined by enzyme-linked immunosorbent assay.

RESULTS

We detected 24p3R in dHL-60 cells. IL-8 was highly expressed and MIP-1α was weakly expressed in dHL-60 cells using a protein array. rLCN2 significantly decreased IL-8 mRNA and protein levels and suppressed P.g-LPS-induced IL-8 production in dHL-60 cells. As dHL-60 cells were co-cultured with HOECs in which LCN2 was knocked down, IL-8 mRNA expression increased in dHL-60 cells. Furthermore, rLCN2 inhibited MIP-1α production in dHL-60 cells.

CONCLUSION

LCN2 suppresses inflammatory responses by regulating IL-8 and MIP-1α expression in periodontal diseases.

Characterization of the atypical antipsychotic drug aripiprazole cytotoxicity in the neutrophil model cell line HL-60

Atypical antipsychotics are widely used for the treatment of mental and behavioral disorders such as bipolar disorder, obsessive-compulsive disorder, and schizophrenia. However, these drugs can occasionally induce neutropenia or agranulocytosis, characterized by a significant reduction in circulating neutrophils, the primary white blood cells responsible for immune responses. This drug-induced neutropenia poses a considerable risk of life-threatening infections. However, the precise mechanism by which atypical antipsychotics induce neutropenia remains unclear. This study investigates the effects of four atypical antipsychotics, namely - aripiprazole, clozapine, olanzapine, and quetiapine - on the human neutrophil model cell line HL-60. These drugs, which modulate dopamine receptor signaling alongside other mechanisms, were analyzed for their effects. Among these, aripiprazole - but not the others - uniquely induced apoptosis in a dose-dependent manner, accompanied by an increased expression of pro-apoptotic genes - BAK, BCL10, and caspase-3. Moreover, our study elucidates that while differentiated HL-60 cells express D1-like and D2-like dopamine receptors, aripiprazole's cytotoxic effects appear to operate through dopamine-independent pathways and significantly reduce phosphorylated Src family kinase levels. Our results align with previous studies suggesting that aripiprazole exhibits cytotoxic properties in neutrophils. Nevertheless, further investigations are warranted to investigate the mechanisms underlying aripiprazole-induced apoptosis in neutrophils.

Neutrophils promote laser-induced choroidal neovascularization by increasing pro-inflammatory cytokines secretion and cell cycle arrest in retinal pigment epithelium

Inflammation is hypothesized to have essential functions in the development of wet age-related macular degeneration (AMD). Polymorphonuclear neutrophils (PMNs), recognized as major players in inflammation, are typically the first leukocytes to be recruited to an inflammatory site. Previous studies have identified neutrophil aggregates in the lesion site of the choroidal neovascularization model, and systemic depletion of neutrophils in adult mice is associated with reduced choroidal neovascularization (CNV) area, suggesting a pivotal role of PMNs in CNV pathogenesis. Here, we investigate the role of neutrophils in promoting CNV, a key feature of wet AMD. The malfunction and demise of retinal pigment epithelium cells are essential elements in CNV pathogenesis. Our hypothesis posits that neutrophils exacerbate CNV by influencing pro-inflammatory cytokines secreted by retinal pigment epithelium (RPE) cells. Using in vivo laser-induced CNV models with mice and in vitro experiments with the human ARPE-19 cell line, we demonstrated that co-culturing neutrophils with ARPE-19 cells induces an increase in pro-inflammatory cytokines and leads to S-phase cell cycle arrest, potentially through the induction of double-strand breaks (DSBs). Further exploration of this interaction revealed a potential pathway involving reactive oxygen species (ROS) and microRNA-23a, wherein PMNs induce DSBs by initiating the downregulation of LB1 via microRNA-23a. Additionally, we found that dHL-60 cell line could serve as a substitute for primary PMNs, highlighting its potential as a valuable tool in experimental models involving interactions with retinal cells. Our findings underscore the significant role of neutrophils in CNV pathogenesis, providing insights into potential therapeutic targets for wet AMD.

pH-Dependent migratory behaviors of neutrophil-like cells in a microfluidic device with controllability of dissolved gas concentrations

Inflammatory microenvironments often become acidic (pH < 7.4) due to tissue oxygen deprivation and lactate release in glycolysis by activated immune cells. Although neutrophils are known to accumulate in such microenvironments, the effects of pH on their migration are not fully understood. Here, we first investigated the pH control around cultured cells with a microfluidic device, which was equipped with two gas channels above three parallel media channels. By supplying gas mixtures with predefined carbon dioxide (CO2) concentrations to the gas channels, the gas exchange adjusted the dissolved CO2 and affected the chemical equilibrium of sodium hydrogen carbonate in the cell culture medium. A pH gradient from 8.3 to 6.8 was generated along the media channels when gas mixtures containing 1% and 50% CO2 were supplied to the left and right gas channels, respectively. Neutrophil-like differentiated human promyelocytic leukemia cells (HL-60) were then seeded to the fibronectin-coated media channels and their migratory behaviors were quantified while varying the pH. The cell migration became more active and faster under high pH than under low pH conditions. However, no directional migration along the pH gradient was detected during the three-hour observation. Thus, the microfluidic device is useful to elucidate pH-dependent cellular dynamics.

Environment-sensitive turn-on fluorescent probe enables live cell imaging of myeloperoxidase activity during NETosis

Myeloperoxidase (MPO) plays an important role in the immune response of human neutrophils and has been implicated in autoimmune conditions, cardiovascular disorders, and neurodegeneration. Current methods to detect MPO activity rely on the detection of HOCl using activatable probes or require challenging experimental procedures. Therefore, these tools provide limited information about the dynamics and localization of MPO in complex molecular processes such as NETosis in real time. In this study, we report a ''turn-on" activity-based probe that fluoresces exclusively upon binding to MPO, exhibits minimal background fluorescence in buffered aqueous media, and is blocked by MPO inhibitors. Our probe facilitates real-time imaging of direct MPO activity in human neutrophils and HL-60-derived granulocytes during NETosis under wash-free conditions. Furthermore, it allows for the discrimination between different triggers of NETosis in human neutrophils. These findings hold promise for advancing our understanding of the role of MPO in immune responses and inflammatory conditions.

Inhibition of neutrophil swarming by type I interferon promotes intracellular bacterial evasion

Listeria monocytogenes (LM) possesses the ability to breach multiple barriers and elicit intricate immune responses. However, there remains a lack of explicit understanding regarding how LM evades innate immune surveillance within the body. Here, we utilized liver intravital imaging to elucidate the dynamic process of LM during infection in the liver. We discovered that LM can rapidly escape from Kupffer cells (KCs) through listeriolysin O (LLO) and proliferate within hepatocytes. Upon LM exposure to the hepatic sinusoids, neutrophils rapidly aggregate at the site of infection. Subsequently, LM can induce type I interferon (IFN-I) production primarily in the spleen, which acts systemically on neutrophils to hamper their swarming by deactivating the ERK pathway, thus evading neutrophil-mediated eradication. Furthermore, our findings suggest that virus-induced IFN-I suppresses neutrophil swarming, and COVID-19 patients exhibit impaired neutrophil aggregation function. In conclusion, our findings provide compelling evidence demonstrating that intracellular bacteria represented by LM can hijack host defense mechanisms against viral infections to evade immune surveillance. Additionally, impaired neutrophil swarming caused by IFN-I is one of the significant factors contributing to the increased susceptibility to bacterial infections following viral infections.

Tumor-associated neutrophils upregulate Nectin2 expression, creating the immunosuppressive microenvironment in pancreatic ductal adenocarcinoma

BACKGROUND

Tumor-associated neutrophils (TANs) constitute an abundant component among tumor-infiltrating immune cells and have recently emerged as a critical player in pancreatic ductal adenocarcinoma (PDAC) progression. This study aimed to elucidate the pro-tumor mechanisms of TAN and identify a novel target for effective immunotherapy against PDAC.

METHODS

Microarray and cytokine array analyses were performed to identify the mechanisms underlying the function of TANs. Human and mouse TANs were obtained from differentiated HL-60 cells and orthotopically transplanted PDAC tumors, respectively. The interactions of TANs with cancer and cytotoxic T-cells were evaluated through in vitro co-culture and in vivo orthotopic or subcutaneous models. Single-cell transcriptomes from patients with PDAC were analyzed to validate the cellular findings.

RESULTS

Increased neutrophil infiltration in the tumor microenvironment was associated with poor survival in patients with PDAC. TANs secreted abundant amounts of chemokine ligand 5 (CCL5), subsequently enhancing cancer cell migration and invasion. TANs subpopulations negatively correlated with cytotoxic CD8+ T-cell infiltration in PDAC and promoted T-cell dysfunction. TANs upregulated the membranous expression of Nectin2, which contributed to CD8+ T-cell exhaustion. Blocking Nectin2 improved CD8+ T-cell function and suppressed tumor progression in the mouse model. Single-cell analysis of human PDAC revealed two immunosuppressive TANs phenotypes: Nectin2+ TANs and OLR1+ TANs. Endoplasmic reticulum stress regulated the protumor activities in TANs.

CONCLUSIONS

TANs enhance PDAC progression by secreting CCL5 and upregulating Nectin2. Targeting the immune checkpoint Nectin2 could represent a novel strategy to enhance immunotherapy efficacy in PDAC.

HL-60 cells as a valuable model to study LPS-induced neutrophil extracellular traps release

Neutrophil Extracellular Traps (NETs) present a paradoxical role in infectious diseases, contributing to both immunity and pathogenesis. The complex nature of this process necessitates further characterization to elucidate its clinical implications. However, studying NETs faces challenges with primary neutrophils due to their heterogeneity, short lifespan, and lack of adequate cryopreservation. Researchers often turn to alternative models, such as differentiated HL-60 cells (dHL-60). This study explored LPS-induced NETs formation in dHL-60 cells, revealing significant responses to LPS from Pseudomonas aeruginosa, although significantly lower than primary neutrophils. Moreover, Spleen Tyrosine Kinase (SYK) inhibition with R406, the active metabolite of the drug Fostamatinib, previously demonstrated to suppress NETs in primary neutrophils, effectively reduced NETs release in dHL-60 cells. dHL-60 cells, offering easier manipulation, consistent availability, and no donor variability in functional responses, possess characteristics suitable for high-throughput studies evaluating NETosis. Overall, dHL-60 cells may be a valuable in vitro model for deciphering the molecular mechanisms of NETosis in response to LPS, contributing to our available tools for understanding this complex immune process.

NADPH oxidase-dependent free radical generation and protein adduct formation in neutrophils

Neutrophils mediate the early innate immune response through extracellular traps comprising intracellular protein and DNA. These traps play a pivotal role in both immunity against invading pathogens and the development of immunopathological reactions through the production of reactive oxygen species (ROS). Proteins serve as the main target for ROS, resulting in the formation of protein adducts. Herein, we report that the superoxide anion radical (O2˙-) plays a vital role in neutrophil function through sequential events involving 5-lipoxygenase (5-LOX) and NADPH oxidase (NOX). More specifically, differences in NOX homologs expression were observed post-stimulation with PMA and LPS. Differentiation conditions and O2˙- generation were confirmed using flow cytometry. Immunoblotting analysis confirmed the time-dependent expression of NOX underlying its requirement and 5-LOX-mediated lipid peroxidation events in neutrophil function. Protein-malondialdehyde (MDA) adducts formed were detected using immunoblotting, and quercetin was evaluated for its ability to scavenge free radicals through electron paramagnetic resonance (EPR) spin-trapping spectroscopy and results were confirmed with blotting analysis. Free radical-mediated protein oxidation events influence neutrophil function and protein adducts formed serve as markers of neutrophil activation upon infection and inflammation. The study warrants further corroboration and the study of specific proteins involved in neutrophil activation and their role in inflammation.

Suppressive effect of resveratrol, catechin and their conformationally constrained analogs on neutrophil extracellular trap formation by HL-60-derived neutrophils

Neutrophil extracellular trap (NET) formation is a unique self-defense mechanism of neutrophils; however, it is also involved in many diseases, including atherosclerosis. Resveratrol and catechin are antioxidants with anti-atherosclerotic properties. Here, we examined the effects of resveratrol, catechin, and other related compounds on NET formation. HL-60-derived neutrophils were pretreated with resveratrol and other compounds before stimulation with phorbol-myristate acetate (PMA). DNA and myeloperoxidase released from neutrophils were determined. Resveratrol suppressed the DNA release from neutrophils in a dose-dependent manner. NET formation was enhanced by 1-palmitoyl-2-oxovaleroyl phosphatidylcholine (POVPC), a truncated form of oxidized phospholipid, and resveratrol suppressed NET formation induced by POVPC and PMA. Furthermore, we designed several analogs of resveratrol or catechin whose conformation was restricted by the inhibition of the free rotation of aromatic rings. The conformationally constrained analogs were more effective at inhibiting NET formation; however, their inhibitory function decreased when compound was a large, hydrophobic analog. The most potent compounds, planar catechin and resveratrol, suppressed myeloperoxidase release from activated neutrophils. In addition, these compounds suppressed DNA release from neutrophils stimulated with calcium ionophore. These results suggest that resveratrol, catechin and their analogs exert anti-NET effects, and that constraining the geometry of these compounds enhanced their inhibitory effects.

Activin A signaling stimulates neutrophil activation and macrophage migration in pancreatitis

Acute Pancreatitis (AP) is associated with high mortality and current treatment options are limited to supportive care. We found that blockade of activin A (activin) in mice improves outcomes in two murine models of AP. To test the hypothesis that activin is produced early in response to pancreatitis and is maintained throughout disease progression to stimulate immune cells, we first performed digital spatial profiling (DSP) of human chronic pancreatitis (CP) patient tissue. Then, transwell migration assays using RAW264.7 mouse macrophages and qPCR analysis of "neutrophil-like" HL-60 cells were used for functional correlation. Immunofluorescence and western blots on cerulein-induced pancreatitis samples from pancreatic acinar cell-specific Kras knock-in (Ptf1aCreER™; LSL-KrasG12D) and functional WT Ptf1aCreER™ mouse lines mimicking AP and CP to allow for in vivo confirmation. Our data suggest activin promotes neutrophil and macrophage activation both in situ and in vitro, while pancreatic activin production is increased as early as 1 h in response to pancreatitis and is maintained throughout CP in vivo. Taken together, activin is produced early in response to pancreatitis and is maintained throughout disease progression to promote neutrophil and macrophage activation.

Auto-amplification and spatial propagation of neutrophil extracellular traps

The release of cellular DNA as neutrophil extracellular traps (NETs) plays a pivotal role in the immune response to pathogens by physically entrapping and killing microbes. NET release occurs at a greater frequency within neutrophil clusters and swarms, indicating a potential for collective behavior. However, little is known about how dense clustering of cells influences the frequency of NET release. Using an image-based assay for NETosis in nanowells, we show that the frequency of NETosis increases with cell density. We then co-incubate NETotic neutrophils with naïve neutrophils and find that NETotic neutrophils can induce secondary NETosis in naïve neutrophils in a cell density-dependent manner. Further mechanistic studies show that secondary NETosis is caused by a combination of DNA and protein factors. Finally, we immobilize NETotic neutrophils in a plaque, and then place the plaque near naïve neutrophils to characterize the spatial propagation of secondary NETosis. We find that secondary NETosis from naïve neutrophils increases over time, but remains spatially restricted to the periphery of the plaque. Together, we show that NETosis is an auto-amplified process, but that the spatial propagation of NET release is strictly regulated.

Targeting Neutrophil Extracellular Traps in Gouty Arthritis: Insights into Pathogenesis and Therapeutic Potential

Gouty arthritis (GA) is an immune-mediated disorder characterized by severe inflammation due to the deposition of monosodium urate (MSU) crystals in the joints. The pathophysiological mechanisms of GA are not yet fully understood, and therefore, the identification of effective therapeutic targets is of paramount importance. Neutrophil extracellular traps (NETs), an intricate structure of DNA scaffold, encompassing myeloperoxidase, histones, and elastases - have gained significant attention as a prospective therapeutic target for gouty arthritis, due to their innate antimicrobial and immunomodulatory properties. Hence, exploring the therapeutic potential of NETs in gouty arthritis remains an enticing avenue for further investigation. During the process of gouty arthritis, the formation of NETs triggers the release of inflammatory cytokines, thereby contributing to the inflammatory response, while MSU crystals and cytokines are sequestered and degraded by the aggregation of NETs. Here, we provide a concise summary of the inflammatory processes underlying the initiation and resolution of gouty arthritis mediated by NETs. Furthermore, this review presents an overview of the current pharmacological approaches for treating gouty arthritis and summarizes the potential of natural and synthetic product-based inhibitors that target NET formation as novel therapeutic options, alongside elucidating the intrinsic challenges of these inhibitors in NETs research. Lastly, the limitations of HL-60 cell as a suitable substitute of neutrophils in NETs research are summarized and discussed. Series of recommendations are provided, strategically oriented towards guiding future investigations to effectively address these concerns. These findings will contribute to an enhanced comprehension of the interplay between NETs and GA, facilitating the proposition of innovative therapeutic strategies and novel approaches for the management of GA.

Dengue virus infection in mice induces bone marrow myeloid cell differentiation and generates Ly6Glow immature neutrophils with modulated functions

While neutrophil activation during dengue virus infection is known, the effect of dengue virus infection on neutrophil biogenesis has not been studied. We demonstrate that dengue virus serotype 2 induces the differentiation of mice progenitor cells ex vivo toward the CD11b+Ly6C+Ly6G+ granulocyte population. We further observed an expansion of CD11b+Ly6CintLy6Glow myeloid cells in the bone marrow of dengue virus serotype 2-infected AG129 mice with low CXCR2 expression, implying an immature population. Additionally, dengue virus serotype 2 alone could induce the differentiation of promyelocyte cell line HL-60 into neutrophil-like cells, as evidenced by increased expression of CD10, CD66b, CD16, CD11b, and CD62L, corroborating the preferential shift toward neutrophil differentiation by dengue virus serotype 2 in the mouse model of dengue infection. The functional analysis showed that dengue virus serotype 2-induced neutrophil-like cells exhibited reduced phagocytic activity and enhanced NETosis, as evidenced by the increased production of myeloperoxidase, citrullinated histones, extracellular DNA, and superoxide. These neutrophil-like cells lose their ability to proliferate irreversibly and undergo arrest in the G0 to G1 phase of the cell cycle. Further studies show that myeloperoxidase-mediated signaling operating through the reactive oxygen species axis may be involved in dengue virus serotype 2-induced proliferation and differentiation of bone marrow cells as ABAH, a myeloperoxidase inhibitor, limits cell proliferation in vitro and ex vivo, affects the cell cycle, and reduces reactive oxygen species production. Additionally, myeloperoxidase inhibitor reduced NETosis and vascular leakage in dengue virus serotype 2-infected AG129 mice. Our study thus provides evidence that dengue virus serotype 2 can accelerate the differentiation of bone marrow progenitor cells into neutrophils through myeloperoxidase and modulate their functions.

Hsa_circRNA_103124 upregulation in Crohn's disease promoted macrophage M1 polarization to maintain an inflammatory microenvironment via activation of the AKT2 and TLR4/NF-κB pathways

An accumulating body of research indicates that circular RNAs participate in the pathogenesis of Crohn's disease (CD). Hsa_circRNA_103124, which was upregulated in the peripheral blood mononuclear cells of patients with CD, was reported to inhibit autophagy in our previous studies. However, how hsa_circRNA_103124 participates in CD progression remains unclear. In this study, TLR4 was found to be upregulated in THP1 cells overexpressing hsa_circRNA_103124. Bioinformatic analysis indicated that overexpressed hsa_circRNA_103124 was associated with the PI3K/AKT signaling pathway and TLR4-associated innate immunity in inflammatory bowel disease. Therefore, we inferred a possible role for hsa_circRNA_103124 in macrophage polarization. Hsa_circRNA_103124, AKT2 and TLR4 were significantly upregulated in the PBMCs of patients with CD. Further analysis revealed a positive correlation between hsa_circRNA_103124 and AKT2 (r = 0.8029, p < 0.0001), TLR4 (r = 0.2529, p = 0.0089) and the Crohn's disease activity index (r = 0.4535, p < 0.0001) in patients with CD. Notably, hsa_circRNA_103124 promoted macrophage M1 polarization with increased expression of CD80 and CD86, while it inhibited macrophage M2 polarization with decreased expression of CD206 and CD163. Hsa_circRNA_103124 promoted an inflammatory microenvironment by activating the AKT2 and TLR4/NF-κB signaling pathways in M1 polarized THP1 cells. Nevertheless, hsa-miR-650 reversed the role of hsa_circRNA_103124 in M1 polarization. Hsa_circRNA_103124 promoted the formation of neutrophil extracellular traps and reduced the expression of ZO-1. In summary, the results of this study indicated that hsa_circRNA_103124 promoted macrophage M1 polarization to maintain an inflammatory microenvironment via activation of the TLR4/NF-κB pathway in a hsa-miR-650/AKT2 dependent manner. Hsa_circRNA_103124 could serve as a potential biomarker and a novel therapeutic target in CD progression.

Dual inhibition of EZH2 and G9A/GLP histone methyltransferases by HKMTI-1-005 promotes differentiation of acute myeloid leukemia cells

All-trans-retinoic acid (ATRA)-based differentiation therapy of acute promyelocytic leukemia (APL) represents one of the most clinically effective examples of precision medicine and the first example of targeted oncoprotein degradation. The success of ATRA in APL, however, remains to be translated to non-APL acute myeloid leukemia (AML). We previously showed that aberrant histone modifications, including histone H3 lysine 4 (H3K4) and lysine 27 (H3K27) methylation, were associated with this lack of response and that epigenetic therapy with small molecule inhibitors of the H3K4 demethylase LSD1/KDM1A could reprogram AML cells to respond to ATRA. Serving as the enzymatic component of Polycomb Repressive Complex 2, EZH2/KMT6A methyltransferase plays a critical role in normal hematopoiesis by affecting the balance between self-renewal and differentiation. The canonical function of EZH2 is methylation of H3K27, although important non-canonical roles have recently been described. EZH2 mutation or deregulated expression has been conclusively demonstrated in the pathogenesis of AML and response to treatment, thus making it an attractive therapeutic target. In this study, we therefore investigated whether inhibition of EZH2 might also improve the response of non-APL AML cells to ATRA-based therapy. We focused on GSK-343, a pyridone-containing S-adenosyl-L-methionine cofactor-competitive EZH2 inhibitor that is representative of its class, and HKMTI-1-005, a substrate-competitive dual inhibitor targeting EZH2 and the closely related G9A/GLP H3K9 methyltransferases. We found that treatment with HKMTI-1-005 phenocopied EZH2 knockdown and was more effective in inducing differentiation than GSK-343, despite the efficacy of GSK-343 in terms of abolishing H3K27 trimethylation. Furthermore, transcriptomic analysis revealed that in contrast to treatment with GSK-343, HKMTI-1-005 upregulated the expression of differentiation pathway genes with and without ATRA, while downregulating genes associated with a hematopoietic stem cell phenotype. These results pointed to a non-canonical role for EZH2, which was supported by the finding that EZH2 associates with the master regulator of myeloid differentiation, RARα, in an ATRA-dependent manner that was enhanced by HKMTI-1-005, possibly playing a role in co-regulator complex exchange during transcriptional activation. In summary, our results strongly suggest that addition of HKMTI-1-005 to ATRA is a new therapeutic approach against AML that warrants further investigation.

In vitro differentiation of myeloid suppressor cells (MDSC-like) from an immature myelomonocytic precursor THP-1

BACKGROUND

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population with a potent suppressor profile that regulates immune responses. These cells are one of the main components of the microenvironment of several diseases, including solid and hematologic tumors, autoimmunities, and chronic inflammation. However, their wide use in studies is limited due to they comprehend a rare population, which is difficult to isolate, expand, differentiate, and maintain in culture. Additionally, this population has a complex phenotypic and functional characterization.

OBJECTIVE

To develop a protocol for the in vitro production of MDSC-like population from the differentiation of the immature myeloid cell line THP-1.

METHODS

We stimulated THP-1 with G-CSF (100 ng/mL) and IL-4 (20 ng/mL) for seven days to differentiate into the MDSC-like profile. At the end of the protocol, we characterized these cells phenotypically and functionally by immunophenotyping, gene expression analysis, cytokine release dosage, lymphocyte proliferation, and NK-mediated killing essays.

RESULTS

We differentiate THP-1 cells in an MDSC-like population, named THP1-MDSC-like, which presented immunophenotyping and gene expression profiles compatible with that described in the literature. Furthermore, we verified that this phenotypic and functional differentiation did not deviate to a macrophage profile of M1 or M2. These THP1-MDSC-like cells secreted several immunoregulatory cytokines into the microenvironment, consistent with the suppressor profile related to MDSC. In addition, the supernatant of these cells decreased the proliferation of activated lymphocytes and impaired the apoptosis of leukemic cells induced by NK cells.

CONCLUSIONS

We developed an effective protocol for MDSC in vitro production from the differentiation of the immature myeloid cell line THP-1 induced by G-CSF and IL-4. Furthermore, we demonstrated that THP1-MDSC-like suppressor cells contribute to the immune escape of AML cells. Potentially, these THP1-MDSC-like cells can be applied on a large-scale platform, thus being able to impact the course of several studies and models such as cancer, immunodeficiencies, autoimmunity, and chronic inflammation.

Molecular and epigenetic alterations in normal and malignant myelopoiesis in human leukemia 60 (HL60) promyelocytic cell line model

In vitro cell line model systems are essential in supporting the research community due to their low cost, uniform culturing conditions, homogeneous biological resources, and easy experimental design to study the cause and effect of a gene or a molecule. Human leukemia 60 (HL60) is an in-vitro hematopoietic model system that has been used for decades to study normal myeloid differentiation and leukemia biology. Here, we show that IMDM supplemented with 20% FBS is an optimal culturing condition and induces effective myeloid differentiation compared with RPMI supplemented with 10% FBS when HL60 is induced with 1α,25-dihydroxyvitamin D3 (Vit D3) and all-trans retinoic acid (ATRA). The chromatin organization is compacted, and the repressive epigenetic mark H3K27me3 is enhanced upon HL60-mediated terminal differentiation. Differential gene expression analysis obtained from RNA sequencing in HL60 cells during myeloid differentiation showed the induction of pathways involved in epigenetic regulation, myeloid differentiation, and immune regulation. Using high-throughput transcriptomic data (GSE74246), we show the similarities (genes that did not satisfy |log2FC|>1 and FDR<0.05) and differences (FDR <0.05 and |log2FC|>1) between granulocyte-monocyte progenitor vs HL60 cells, Vit D3 induced monocytes (vMono) in HL60 cells vs primary monocytes (pMono), and HL60 cells vs leukemic blasts at the transcriptomic level. We found striking similarities in biological pathways between these comparisons, suggesting that the HL60 model system can be effectively used for studying myeloid differentiation and leukemic aberrations. The differences obtained could be attributed to the fact that the cellular programs of the leukemic cell line and primary cells are different. We validated several gene expression patterns for different comparisons with CD34⁺ cells derived from cord blood for myeloid differentiation and AML patients. In addition to the current knowledge, our study further reveals the significance of using HL60 cells as in vitro model system under optimal conditions to understand its potential as normal myeloid differentiation model as well as leukemic model at the molecular level.

A persistent neutrophil-associated immune signature characterizes post-COVID-19 pulmonary sequelae

Interstitial lung disease and associated fibrosis occur in a proportion of individuals who have recovered from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection through unknown mechanisms. We studied individuals with severe coronavirus disease 2019 (COVID-19) after recovery from acute illness. Individuals with evidence of interstitial lung changes at 3 to 6 months after recovery had an up-regulated neutrophil-associated immune signature including increased chemokines, proteases, and markers of neutrophil extracellular traps that were detectable in the blood. Similar pathways were enriched in the upper airway with a concomitant increase in antiviral type I interferon signaling. Interaction analysis of the peripheral phosphoproteome identified enriched kinases critical for neutrophil inflammatory pathways. Evaluation of these individuals at 12 months after recovery indicated that a subset of the individuals had not yet achieved full normalization of radiological and functional changes. These data provide insight into mechanisms driving development of pulmonary sequelae during and after COVID-19 and provide a rational basis for development of targeted approaches to prevent long-term complications.

Integrating network pharmacology and transcriptomic validation to investigate the efficacy and mechanism of Mufangji decoction preventing lung cancer

ETHNOPHARMACOLOGICAL RELEVANCE

Mufangji decoction (MFJD), a famous traditional Chinese medicine formula in Synopsis of Golden Chamber (Jingui yaolue), has been utilized to treat cough and asthma and release chest pain over 2000 years in China. Chinese old herbalist doctor use MFJD to treat lung cancer and cancerous pleural fluid, but the preventive effect of MFJD on lung cancer and the underlying mechanism are indefinite.

AIM OF THE STUDY

The goal of this study is to explore the efficacy and mechanism of Mufangji decoction preventing lung cancer referring to the traditional use.

MATERIALS AND METHODS

Tumor allograft experiment and host versus tumor experiment were used to observe the direct anti-tumor effect and indirect anti-tumor immune effect, the mouse lung carcinogenic model was used to evaluate the dose-response and the preventive effect of MFJD on lung cancer. The active ingredients of MFJD were obtained by UPLC-MS/MS. The potential targets of MFJD were screened by network pharmacology and transcriptomics. The therapeutic targets and pathways of MFJD on lung cancer were obtained by protein-protein interaction, molecular docking and David database. The predicted results were verified in vitro and in vivo.

RESULTS

MFJD could significantly prevent tumor growth in host versus tumor experiment but could not in tumor allograft experiment, indicating an anti-tumor immune effect against lung cancer. MFJD could reduce lung nodules with a dose-response in mouse lung carcinogenic model. Myeloperoxidase (MPO) was selected as the core target due to the highest degree value in Protein-Protein interaction network and had potently binding activity to sinomenine and dehydrocostus lactone in molecular docking. In vivo, MPO-expressed neutrophils are negatively correlated with lung cancer progression and MFJD could promote the neutrophil-related immune surveillance. In vitro, sinomenine and dehydrocostus lactone could promote neutrophil phagocytosis, MPO and ROS production in a dose dependent manner. The major compounds from MFJD were identified to regulate 36 targets for lung cancer prevention by UPLC-MS/MS, network pharmacology and transcriptomics. David database exhibited that MFJD plays an important role in immunoregulation by modulating 4 immune-related biological processes and 3 immune-related pathways.

CONCLUSIONS

MFJD prevents lung cancer by mainly promoting MPO expression to maintain neutrophil immune surveillance, its key compounds are sinomenine and dehydrocostus lactone.

HMGB1-Promoted Neutrophil Extracellular Traps Contribute to Cardiac Diastolic Dysfunction in Mice

Background Heart failure with preserved ejection fraction (HFpEF) remains an increasing public health problem with substantial morbidity and mortality but with few effective treatments. A novel inflammatory mechanism has been proposed, but the inflammatory signals promoting the development of HFpEF remain greatly unknown. Methods and Results Serum of patients with HFpEF was collected for measurement of circulating neutrophils and markers of neutrophil extracellular traps (NETs). To induce HFpEF phenotype, male C57BL/6 mice underwent uninephrectomy, received a continuous infusion of d-aldosterone for 4 weeks, and maintained on 1.0% sodium chloride drinking water. Heart tissues were harvested, immune cell types determined by flow cytometry, NETs formation by immunofluorescence, and western blotting. Differentiated neutrophils were cultured to investigate the effect of HMGB1 (high mobility group protein B1) and SGLT2 (sodium-glucose cotransporter-2) inhibitor on NETs formation in vitro. Circulating neutrophils and NETs markers are elevated in patients with HFpEF, as are cardiac neutrophils and NETs formation in HFpEF mice. NETs inhibition with deoxyribonuclease 1 in experimental HFpEF mice reduces heart macrophages infiltration and inflammation and ameliorates cardiac fibrosis and diastolic function. Damage-associated molecular pattern HMGB1 expression is elevated in cardiac tissue of HFpEF mice, and HMGB1 inhibition reduces heart neutrophil infiltration and NETs formation and ameliorates diastolic function. Lastly, SGLT2 inhibitor empagliflozin down-regulates heart HMGB1 expression, attenuates NETs formation and cardiac fibrosis, and improves diastolic function in HFpEF mice. Conclusions NETs contribute to the pathogenesis of HFpEF, which can be ameliorated by HMGB1 inhibition and SGLT2 inhibitors. Thus, HMGB1 and NETs may represent novel therapeutic targets for the treatment of HFpEF.

Procollagen C-Endopeptidase Enhancer 2 Secreted by Tonsil-Derived Mesenchymal Stem Cells Increases the Oxidative Burst of Promyelocytic HL-60 Cells

Simple Summary

Tonsil-derived mesenchymal stem cells (TMSCs) improved the reactive oxygen species (ROS) production in human promyelocytic leukaemia cells (HL-60) differentiated into neutrophil-like cells (dHL-60). TMSC-induced enhancement of ROS generation in dHL-60 cells was different depending on the TMSC donor. Comparison of RNA-sequencing data between high and low potentiating TMSC groups for ROS generation in dHL-60 cells showed elevated expressions of four genes: secreted frizzled-related protein 4, mesenteric estrogen-dependent adipogenesis, microfibrillar associated protein 5, and procollagen C-endopeptidase enhancer 2 (PCOLCE2). Real-time PCR and Western blotting confirmed high levels of PCOLCE2 in the high potentiating TMSC group for ROS generation in dHL-60 cells. In addition, knockdown of PCOLCE2 in TMSCs reduced the enhancing efficacy of TMSCs regarding ROS generation in dHL-60 cells. Finally, treatment of recombinant PCOLCE2 protein augmented ROS production in dHL-60 cells with concomitant increases of NADPH oxidase (NOX) 3, NOX4, NOX5, and dual oxidase 2. Taken together, this study showed that PCOLCE2 levels in TMSCs could be used to select TMSCs with the high potentiating ability for ROS generation in neutrophils, and both TMSCs and PCOLCE2 may have the potential to enhance a frontline defence by increasing the efficiency of ROS generation in neutrophils.

Abstract

Reactive oxygen species (ROS) generated by neutrophils provide a frontline defence against invading pathogens. We investigated the supportive effect of tonsil-derived mesenchymal stem cells (TMSCs) on ROS generation from neutrophils using promyelocytic HL-60 cells. Methods: Differentiated HL-60 (dHL-60) cells were cocultured with TMSCs isolated from 25 independent donors, and ROS generation in dHL-60 cells was measured using luminescence. RNA sequencing and real-time PCR were performed to identify the candidate genes of TMSCs involved in augmenting the oxidative burst of dHL-60 cells. Transcriptome analysis of TMSCs derived from 25 independent donors revealed high levels of procollagen C-endopeptidase enhancer 2 (PCOLCE2) in TMSCs, which were highly effective in potentiating ROS generation in dHL-60 cells. In addition, PCOLCE2 knockdown in TMSCs abrogated TMSC-induced enhancement of ROS production in dHL-60 cells, indicating that TMSCs increased the oxidative burst in dHL-60 cells via PCOLCE2. Furthermore, the direct addition of recombinant PCOLCE2 protein increased ROS production in dHL-60 cells. These results suggest that PCOLCE2 secreted by TMSCs may be used as a therapeutic candidate to enhance host defences by increasing neutrophil oxidative bursts. PCOLCE2 levels in TMSCs could be used as a marker to select TMSCs exhibiting high efficacy for enhancing neutrophil oxidative bursts.

Antithrombin protects against Plasmodium falciparum histidine-rich protein II-mediated inflammation and coagulation

Plasmodium falciparum (Pf)-derived histidine-rich protein II (HRPII) has been shown to inhibit heparin-dependent anticoagulant activity of antithrombin (AT) and induce inflammation in vitro and in vivo. In a recent study, we showed that HRPII interacts with the AT-binding vascular glycosaminoglycans (GAGs) to not only disrupt the barrier-permeability function of endothelial cells but also inhibit the anti-inflammatory signaling function of AT. Here we investigated the mechanisms of the pro-inflammatory function of HRPII and the protective activity of AT in cellular and animal models. We found that AT competitively inhibits the GAG-dependent HRPII-mediated activation of NF-κB and expression of intercellular cell adhesion molecule 1 (ICAM1) in endothelial cells. Furthermore, AT inhibits HRPII-mediated histone H3 citrullination and neutrophil extracellular trap (NET) formation in HL60 cells and freshly isolated human neutrophils. In vivo, HRPII induced Mac1 expression on blood neutrophils, MPO release in plasma, neutrophil infiltration and histone H3 citrullination in the lung tissues. HRPII also induced endothelial cell activation as measured by increased ICAM1 expression and elevated vascular permeability in the lungs. AT effectively inhibited HRPII-mediated neutrophil infiltration, NET formation and endothelial cell activation in vivo. AT also inhibited HRPII-meditated deposition of platelets and fibrin(ogen) in the lungs and circulating level of von Willebrand factor in the plasma. We conclude that AT exerts protective effects against pathogenic effects of Pf-derived HRPII in both cellular and animal models.

Neutrophil Extracellular Traps (NETs) and Hypercoagulability in Plasma Cell Dyscrasias-Is This Phenomenon Worthy of Exploration?

Plasma cell dyscrasias (PCDs) are neoplastic diseases derived from plasma cells. Patients suffering from PCDs are at high risk of hypercoagulability and thrombosis. These conditions are associated with disease-related factors, patient-related factors, or the use of immunomodulatory drugs. As PCDs belong to neoplastic diseases, some other factors related to the cancer-associated hypercoagulability state in the course of PCDs are also considered. One of the weakest issues studied in PCDs is the procoagulant activity of neutrophil extracellular traps (NETs). NETs are web-like structures released from neutrophils in response to different stimuli. These structures are made of deoxyribonucleic acid (DNA) and bactericidal proteins, such as histones, myeloperoxidase, neutrophil elastase, and over 300 other proteins, which are primarily stored in neutrophil granules. NETs immobilize, inactivate the pathogens, and expose them to specialized cells of immune response. Despite their pivotal role in innate immunity, they contribute to the development and exacerbation of autoimmune diseases, trigger inflammatory response, or even facilitate the formation of cancer metastases. NETs were also found to induce activity of coagulation and are considered one of the most important factors inducing thrombosis. Here, we summarize how PCDs influence the release of NETs, and hypothesize whether NETs contribute to hypercoagulability in PCDs patients.

NETs decorated with bioactive IL-33 infiltrate inflamed tissues and induce IFN-α production in patients with SLE

IL-33, a nuclear alarmin released during cell death, exerts context-specific effects on adaptive and innate immune cells, eliciting potent inflammatory responses. We screened blood, skin, and kidney tissues from patients with systemic lupus erythematosus (SLE), a systemic autoimmune disease driven by unabated type I IFN production, and found increased amounts of extracellular IL-33 complexed with neutrophil extracellular traps (NETs), correlating with severe, active disease. Using a combination of molecular, imaging, and proteomic approaches, we show that SLE neutrophils, activated by disease immunocomplexes, release IL-33–decorated NETs that stimulate robust IFN-α synthesis by plasmacytoid DCs in a manner dependent on the IL-33 receptor ST2L. IL33-silenced neutrophil-like cells cultured under lupus-inducing conditions generated NETs with diminished interferogenic effect. Importantly, NETs derived from patients with SLE are enriched in mature bioactive isoforms of IL-33 processed by the neutrophil proteases elastase and cathepsin G. Pharmacological inhibition of these proteases neutralized IL-33–dependent IFN-α production elicited by NETs. We believe these data demonstrate a novel role for cleaved IL-33 alarmin decorating NETs in human SLE, linking neutrophil activation, type I IFN production, and end-organ inflammation, with skin pathology mirroring that observed in the kidneys.

Iron excess affects release of neutrophil extracellular traps and reactive oxygen species but does not influence other functions of neutrophils

Neutrophils apply several antimicrobial strategies including degranulation, phagocytosis, the generation of reactive oxygen species (ROS) and the release of neutrophil extracellular traps (NETs) to fight pathogens. Iron is considered to be an invaluable constituent of host immune defense and plays a dual role in immunity. It is a well-known component of antimicrobial proteins and is a necessary microelement for pathogen survival. The aim of this study was to broaden the knowledge regarding the impact of iron on the function of neutrophils. Neutrophils from healthy blood donors and patients with mild iron-deficiency anemia and HL-60 cells differentiated toward granulocyte-like cells were incubated with Fe²⁺ , Fe³⁺ or holo-transferrin (holo-Tf). Moreover, we isolated murine neutrophils of HFE gene knockout (KO) mice and mice fed iron-deficient, iron-equivalent and high-iron diets. We analyzed the release of NETs, phagocytosis, degranulation of azurophilic granules, ROS release, bactericidal activity of granulocytes against Escherichia coli and neutrophil elastase (NE) activity. We show that holo-Tf inhibits the release of NETs stimulated by phorbol 12-myristate 13-acetate by inhibiting NE activity. Studies performed in mice models reveal that iron overload inhibits the release of NETs and ROS production in neutrophils isolated from HFE KO mice and mice fed a high-iron diet. No impact of a low-iron diet on neutrophil phagocytosis, ROS production or release of NETs was observed. Our study underscores the physiological significance of iron in neutrophil function, specifically in the release of NETs.

NAP1051, a Lipoxin A4 Biomimetic Analogue, Demonstrates Antitumor Activity Against the Tumor Microenvironment

Resolving tumor-associated inflammation in the tumor microenvironment (TME) may promote antitumor effects. Lipoxin A4 (LXA4) is a short-lived endogenous bioactive lipid with potent anti-inflammatory and pro-resolving properties. Here, a biomimetic of LXA4, NAP1051, was shown to have LXA4-like in vitro properties and antitumor activity in colorectal cancer xenograft models. NAP1051 inhibited neutrophil chemotaxis toward fMLP and dose-dependently promoted dTHP-1 efferocytosis which was equipotent to aspirin-triggered lipoxin A4 (ATLA). In dTHP-1 cells, NAP1051 induced strong phosphorylation on ERK1/2 and AKT similar to formyl peptide receptor 2 (FPR2/ALX) agonists. In two mouse xenograft colorectal cancer models, NAP1051 significantly inhibited tumor growth when given orally at 4.8 to 5 mg/kg/day. Flow cytometric analyses showed that NAP1051 reduced splenic and intratumoral neutrophil and myeloid-derived suppressor cell populations, which correlated to the antitumor effect. In addition, NAP1051 reduced NETosis in the TME while stimulating T-cell recruitment. Overall, these results show that NAP1051 possesses key lipoxin-like properties and has antitumor activity against colorectal cancer via modulation of neutrophils and NETosis in the TME.

Memantine Promotes Bactericidal Effect of Neutrophils Against Infection with Pseudomonas aeruginosa and Its Drug-Resistant Strain, by Improving Reactive Oxygen Species Generation

Pseudomonas aeruginosa is an opportunistic pathogen, which usually presents multiple antibiotic resistance. Host-directed therapy involves modulating the host defense system and the interplay between innate and adaptive immunity is a new strategy for designing anti-infection drugs. Memantine (MEM), a drug used to treat Alzheimer's disease, has a good inhibitory effect on neonatal mice with Escherichia coli-associated bacteremia and meningitis; however, the inhibitory effect and mechanisms of MEM against P. aeruginosa infection remain unclear. Here, we investigated whether MEM could inhibit P. aeruginosa infection and explored the potential mechanisms. MEM significantly promoted the bactericidal effect of neutrophils against P. aeruginosa and its drug-resistant strain. The combination index of MEM and amikacin (AMK) was <1. In vivo experiments showed that the bacteremia and inflammation severities in the MEM-treated group were less than those in the untreated group, and the bacterial load in the organs was significantly less than that in the control group. Combining MEM with the reactive oxygen species (ROS) inhibitor, N-acetyl-l-cysteine, weakened the anti-infective effect of MEM. MEM increased the expression of NADPH p67phox and promoted neutrophilic ROS production. Deleting the p67phox gene significantly weakened the effects of MEM on ROS generation and improving bactericidal effect of neutrophils. In conclusion, MEM promoted the bactericidal effect of neutrophils against P. aeruginosa and its drug-resistant strain, and had a synergistic antibacterial effect when combined with AMK. MEM may exert its anti-infective effects by promoting neutrophilic bactericidal activity via increasing the expression level of p67phox and further stimulating ROS generation.

Differentiation of HL-60 cells in serum-free hematopoietic cell media enhances the production of neutrophil extracellular traps

Neutrophil extracellular traps (NETs) are web-like structures made of chromatin and have been identified to have a role in the host's immune defense. Differentiated human promyelocytic leukemia HL-60 cells (dHL-60) have been used to study the mechanisms of NETs formation, as neutrophils have a short lifespan that limits their use. However, dHL-60 cells are inefficient at generating NETs and therefore are not ideal replacements for neutrophils in studying of NET formation. In the present study, the optimal cell culture conditions and differentiation time that result in the most effective release of NETs from dHL-60 cells upon stimulation were determined. HL-60 cells were cultured in serum (FBS) or serum-free (X-VIVO) medium and differentiated using all-trans retinoic acid (ATRA) or dimethyl sulfoxide (DMSO). dHL-60 cells were stimulated with phorbol 12-myristate 13-acetate (PMA) or Ca²⁺ ionophore (CI). Cell differentiation and apoptosis, as well as the formation of reactive oxygen species (ROS) and citrullinated histone H3 (citH3) were analyzed using flow cytometry. NETs were visualized using fluorescence microscopy and NET quantification was performed using PicoGreen. Induction of HL-60 cells for five days produced the best results in terms of differentiation markers and cell viability. Both ATRA- and DMSO-induced dHL-60 cells were able to release NETs upon PMA and CI stimulation; dHL-60 cells in serum-free medium produced more NETs than those in serum-containing medium. DMSO-dHL-60 (X-VIVO) cells were most efficient at producing NETs and ROS upon stimulation with PMA, while ATRA-dHL-60 (X-VIVO) cells were most efficient at producing NETs and citH3 upon stimulation with CI. It was concluded that DMSO-dHL-60 (X-VIVO) may be a model for the study of ROS-high NETosis and ATRA-dHL-60 (X-VIVO) may be suitable for ROS-low NETosis.

Studying Neutrophil Function in vitro: Cell Models and Environmental Factors

Neutrophils are the most abundant immune cell type in the blood and constitute the first line of defense against invading pathogens. Despite their important role in many diseases, they are challenging to study due to their short life span and the inability to cryopreserve or expand them in vitro. Thus, research into neutrophils has to rely on cells freshly isolated from peripheral blood of human donors, introducing donor-dependent variation in the experimental data. To counteract these problems, researchers tried to develop adequate cell models, such as cell lines. For those functional studies that cannot rely on cell models, a standardization of protocols regarding neutrophil purification and culturing could be a solution. In this review, we provide an overview of the most commonly used models for neutrophil function (HL-60, PLB-985, NB4, Kasumi-1 and induced pluripotent stem cells). In addition, we describe the effects of glucose concentration, pH, oxygen tension and temperature on neutrophil function.

Zinc Supplementation Modulates NETs Release and Neutrophils' Degranulation

Zinc plays an important physiological role in the entire body, especially in the immune system. It is one of the most abundant microelements in our organism and an essential component of enzymes and antibacterial proteins. Zinc levels were reported to be correlated with the intensity of innate immunity responses, especially those triggered by neutrophils. However, as the results are fragmentary, the phenomenon is still not fully understood and requires further research. In this study, we aimed to perform a comprehensive assessment and study the impact of zinc on several basic neutrophils’ functions in various experimental setups. Human and murine neutrophils were preincubated in vitro with zinc, and then phagocytosis, oxidative burst, degranulation and release of neutrophil extracellular traps (NETs) were analyzed. Moreover, a murine model of zinc deficiency and zinc supplementation was introduced in the study and the functions of isolated cells were thoroughly studied. We showed that zinc inhibits NETs release as well as degranulation in both human and murine neutrophils. Our study revealed that zinc decreases NETs release by inhibiting citrullination of histone H3. On the other hand, studies performed in zinc-deficient mice demonstrated that low zinc levels result in increased release of NETs and enhanced neutrophils degranulation. Overall, it was shown that zinc affects neutrophils’ functions in vivo and in vitro. Proper zinc level is necessary to maintain efficient functioning of the innate immune response.

Synthetic Siglec-9 Agonists Inhibit Neutrophil Activation Associated with COVID-19

Severe cases of coronavirus disease 2019 (COVID-19), caused by infection with SARS-Cov-2, are characterized by a hyperinflammatory immune response that leads to numerous complications. Production of proinflammatory neutrophil extracellular traps (NETs) has been suggested to be a key factor in inducing a hyperinflammatory signaling cascade, allegedly causing both pulmonary tissue damage and peripheral inflammation. Accordingly, therapeutic blockage of neutrophil activation and NETosis, the cell death pathway accompanying NET formation, could limit respiratory damage and death from severe COVID-19. Here, we demonstrate that synthetic glycopolymers that activate the neutrophil checkpoint receptor Siglec-9 suppress NETosis induced by agonists of viral toll-like receptors (TLRs) and plasma from patients with severe COVID-19. Thus, Siglec-9 agonism is a promising therapeutic strategy to curb neutrophilic hyperinflammation in COVID-19.
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Combined Effect of Naturally-Derived Biofilm Inhibitors and Differentiated HL-60 Cells in the Prevention of Staphylococcus aureus Biofilm Formation

Nosocomial diseases represent a huge health and economic burden. A significant portion is associated with the use of medical devices, with 80% of these infections being caused by a bacterial biofilm. The insertion of a foreign material usually elicits inflammation, which can result in hampered antimicrobial capacity of the host immunity due to the effort of immune cells being directed to degrade the material. The ineffective clearance by immune cells is a perfect opportunity for bacteria to attach and form a biofilm. In this study, we analyzed the antibiofilm capacity of three naturally derived biofilm inhibitors when combined with immune cells in order to assess their applicability in implantable titanium devices and low-density polyethylene (LDPE) endotracheal tubes. To this end, we used a system based on the coculture of HL-60 cells differentiated into polymorphonuclear leukocytes (PMNs) and Staphylococcus aureus (laboratory and clinical strains) on titanium, as well as LDPE surfaces. Out of the three inhibitors, the one coded DHA1 showed the highest potential to be incorporated into implantable devices, as it displayed a combined activity with the immune cells, preventing bacterial attachment on the titanium and LDPE. The other two inhibitors seemed to also be good candidates for incorporation into LDPE endotracheal tubes.

Neutrophils as a Novel Target of Modified Low-Density Lipoproteins and an Accelerator of Cardiovascular Diseases

Neutrophil extracellular traps (NETs) significantly contribute to various pathophysiological conditions, including cardiovascular diseases. NET formation in the vasculature exhibits inflammatory and thrombogenic activities on the endothelium. NETs are induced by various stimulants such as exogenous damage-associated molecular patterns (DAMPs). Oxidatively modified low-density lipoprotein (oxLDL) has been physiologically defined as a subpopulation of LDL that comprises various oxidative modifications in the protein components and oxidized lipids, which could act as DAMPs. oxLDL has been recognized as a crucial initiator and accelerator of atherosclerosis through foam cell formation by macrophages; however, recent studies have demonstrated that oxLDL stimulates neutrophils to induce NET formation and enhance NET-mediated inflammatory responses in vascular endothelial cells, thereby suggesting that oxLDL may be involved in cardiovascular diseases through neutrophil activation. As NETs comprise myeloperoxidase and proteases, they have the potential to mediate oxidative modification of LDL. This review summarizes recent updates on the analysis of NETs, their implications for cardiovascular diseases, and prospects for a possible link between NET formation and oxidative modification of lipoproteins.

Nitric oxide and peroxynitrite trigger and enhance release of neutrophil extracellular traps

Despite great interest, the mechanism of neutrophil extracellular traps (NETs) release is not fully understood and some aspects of this process, e.g. the role of reactive nitrogen species (RNS), still remain unclear. Therefore, our aim was to investigate the mechanisms underlying RNS-induced formation of NETs and contribution of RNS to NETs release triggered by various physiological and synthetic stimuli. The involvement of RNS in NETs formation was studied in primary human neutrophils and differentiated human promyelocytic leukemia cells (HL-60 cells). RNS (peroxynitrite and nitric oxide) efficiently induced NETs release and potentiated NETs-inducing properties of platelet activating factor and lipopolysaccharide. RNS-induced NETs formation was independent of autophagy and histone citrullination, but dependent on the activity of phosphoinositide 3-kinases (PI3K) and myeloperoxidase, as well as selective degradation of histones H2A and H2B by neutrophil elastase. Additionally, NADPH oxidase activity was required to release NETs upon stimulation with NO, as shown in NADPH-deficient neutrophils isolated from patients with chronic granulomatous disease. The role of RNS was further supported by increased RNS synthesis upon stimulation of NETs release with phorbol 12-myristate 13-acetate and calcium ionophore A23187. Scavenging or inhibition of RNS formation diminished NETs release triggered by these stimuli while scavenging of peroxynitrite inhibited NO-induced NETs formation. Our data suggest that RNS may act as mediators and inducers of NETs release. These processes are PI3K-dependent and ROS-dependent. Since inflammatory reactions are often accompanied by nitrosative stress and NETs formation, our studies shed a new light on possible mechanisms engaged in various immune-mediated conditions.

Resistance to differentiation affects ribo- and deoxyribonucleotide pools and sensitivity to pyrimidine metabolism antagonists in HL60 cells

HL60 myeloid leukemia cells are extensively used as a differentiation model. We investigated a variant of HL60 which is resistant to differentiation induction (HL60-R) by standard differentiation inducers such as retinoic acid and dimethylsulfoxide (DMSO). To find an explanation for this resistance, we examined nucleotide (NTP) and deoxynucleotide (dNTP) pools in HL60-R and its parent cell line, sensitive to differentiation, HL60-S. We also explored whether these differences led to a difference in sensitivity to various antimetabolites. Drug sensitivity was measured with the tetrazolium (MTT) assay, while nucleotides were measured with anion-exchange HPLC. HL60-R cells were between 2- and 5-fold resistant to the antimetabolites 5-fluorouracil, Brequinar, hydroxyurea and N-(phosphonacetyl)-L-aspartate (PALA), but more sensitive to aza-2'-deoxycytidine (DAC), cytarabine and thymidine (5- to 10-fold). The NTP pools in both HL60 variants showed a normal pattern with ATP being the highest (2530-2876 pmol/106 cells) and CTP being lowest. However, UTP pools were 2-fold higher in the HL60-S cells (p < .01), while CTP and GTP pools were 30% higher (p < .01) compared to HL60-R cells. For the dNTP pools, larger differences were observed, with dATP (50 pmol/106 cells) being highest in HL60-R cells, but dATP was 4-fold lower in HL60-S cells. In HL-60-R, the triple combination retinoic acid, DMSO and DAC increased all NTPs almost 2-fold in contrast to HL60-S. Uridine increased UTP (1.4-fold), CTP (2-fold) and dCTP (1.4.-fold) pools in both cell lines, but thymidine increased only dTTP pools (4- to 7-fold), with a depletion of dCTP. PALA decreased UTP and CTP in both cell lines, but increased ATP (only in HL60-R). Hydroxyurea decreased dNTP especially in HL60-S cells. In conclusion, the pronounced differences in NTP and dNTP pools between HL60-S and HL60-R possibly play a role in the induction of differentiation and drug sensitivity.

Overexpression of ATG5 Gene Makes Granulocyte-Like HL-60 Susceptible to Release Reactive Oxygen Species

Neutrophils represent the first line of defense against pathogens using various strategies, such as phagocytosis, production of reactive oxygen species (ROS) and neutrophil extracellular traps (NETs) formation. Recently, an autophagy-independent role of autophagy related (ATG) gene 5 in immune cells, including neutrophils, was emphasized. Our aim was to investigate the role of ATG5 protein in neutrophils' antimicrobial functions, proliferation and apoptosis. To this end, we used genetically modified human promyelocytic leukemia (HL-60) cells overexpressing ATG5, differentiated toward granulocyte-like cells with all-trans retinoic acid (ATRA) and dimethylformamide. The level of differentiation, phagocytosis, proliferation and apoptosis were determined by flow cytometry. ROS production and NETs release was assessed by fluorometry and fluorescent microscopy. ATG5 gene expression was evaluated by real-time PCR, whereas the protein level of ATG5 and LC3-II was determined by Western blot. We did not observe the induction of autophagy in differentiated HL-60 cells overexpressing ATG5. The increased expression of ATG5 affects the differentiation of HL-60 cells with ATRA, ROS production and phagocytosis. However, we did not detect changes in NETs release. Moreover, ATG5 protects differentiated HL-60 cells from apoptosis but does not cause changes in proliferation rate.

ERK is involved in the differentiation and function of dimethyl sulfoxide-induced HL-60 neutrophil-like cells, which mimic inflammatory neutrophils

Reports show that particulate matter (PM) is related to respiratory and cardiovascular diseases. We previously reported the biological effects of PM in vivo and the endocytosis of PM by primary neutrophils from mice. Cell lines can be used to elucidate the mechanism underlying immune responses in detail; however, information is limited regarding the functions of neutrophils after PM exposure. Here, we investigated the immune response of primary neutrophils and dimethyl sulfoxide (DMSO)- and all-trans retinoic acid (ATRA)-differentiated HL-60 (neutrophil-like) cells to PM. We showed that endocytosis by ATRA-HL cells was enhanced compared to that by DMSO-HL cells and that endocytosis in both cells was inhibited by dynamin inhibitors. A MEK inhibitor, but not p38 or JNK inhibitors, inhibited endocytosis. The MEK inhibitor also inhibited the differentiation of ATRA-HL cells to neutrophils. We identified that endocytosis of PM by neutrophils activated the MAPK ERK and p38 pathways. DMSO-HL and ATRA-HL cells both produced TNF-α and IL-8 after lipopolysaccharide (LPS) or PM treatment, whereas non-differentiated HL-60 cells did not. MCP-1 production was enhanced in DMSO-HL cells after LPS or PM treatment, whereas it was high in ATRA-HL cells. Reactive oxygen species (ROS) production was enhanced after PM treatment to DMSO-HL cells. Further, extracellular extracts promoted endocytosis. The MEK inhibitor also reduced the production of TNF-α, IL-8, and MCP-1. Taken together, ERK activation is key for both differentiation and endocytosis, and DMSO-HL cells at day 6 can serve as a model of inflammatory neutrophils, such as bronchus neutrophils, and a good tool to analyze the molecular events involved in immune responses to PM.

Advanced glycation end-products increase lipocalin 2 expression in human oral epithelial cells

BACKGROUND AND OBJECTIVES

Diabetes mellitus (DM), a risk factor of periodontal diseases, exacerbates the pathological condition of periodontitis. A major factor for DM complications is advanced glycation end-products (AGEs) that accumulate in periodontal tissues and cause inflammatory events. Lipocalin 2 (LCN2) is an antimicrobial peptide and inflammation-related factor, and LCN2 levels increase in DM. In this study, the effects of AGEs and lipopolysaccharide of Porphyromonas gingivalis (P g-LPS) on LCN2 expression in human oral epithelial cells (TR146 cells) and the role of secreted LCN2 in periodontitis with DM were investigated.

MATERIAL AND METHODS

TR146 cells were cultured with AGEs (AGE2) and control BSA and cell viability was estimated, or with P g-LPS. Conditioned medium and cell lysates were prepared from cultures of epithelial cells and used for Western blotting and ELISA to analyze LCN2, RAGE, IL-6, MAPK, and NF-κB. RNA was isolated from AGE-treated TR146 cells and differentiated HL-60 (D-HL-60) cells and used for quantitative real-time PCR to examine the expression of LCN2 and interleukin-6 (IL-6) mRNAs. RAGE- and LCN2-siRNAs (siRAGE, siLCN2) were transfected into epithelial cells, and AGE-induced LCN2 expression was investigated. D-HL-60 cells were co-cultured with TR146 cells that were transfected with siLCN2 and treated with AGEs, and IL-6 mRNA expression in D-HL-60 cells and cell migration was investigated.

RESULTS

AGEs increased the expression levels of LCN2 and IL-6 in oral epithelial cells. siRAGE and a neutralizing antibody for RAGE inhibited AGE-induced LCN2 expression. AGEs stimulated the phosphorylation of ERK, p38, and NF-κB in epithelial cells, and their inhibitors suppressed AGE-induced LCN2 expression. In contrast, P g-LPS did not show a significant increase in LCN2 level in TR146 cells that expressed Toll-like receptor 2. In co-culture experiments, AGE-induced LCN2 inhibited IL-6 mRNA expression in D-HL-60 cells, and LCN2 knockdown in epithelial cells suppressed HL-60 cell migration.

CONCLUSION

These results suggested that AGEs increase LCN2 expression via RAGE, MAPK, and NF-κB signaling pathways in oral epithelial cells, and secreted LCN2 may influence the pathological condition of periodontitis with DM.

Three Ingredients of Safflower Alleviate Acute Lung Injury and Inhibit NET Release Induced by Lipopolysaccharide

Xuebijing injection is a Chinese herb compound to treat sepsis in China, but it contains many different kinds of components, and each component may have different effects in treating sepsis. The present study was performed to investigate the effect of three ingredients of Xuebijing, safflor yellow A (SYA), hydroxysafflor yellow A (HSYA), and anhydrosafflor yellow B (AHSYB), in lipopolysaccharide- (LPS-) induced acute lung injury (ALI). LPS (10 mg/kg) was injected intratracheally to induce acute lung injury in mice, which were then treated with SYA, HSYA, and AHSYB. The blood, bronchoalveolar lavage fluid (BALF), and lung tissues were collected to detect degree of lung injury, level of inflammation, and neutrophil extracellular traps (NETs). In vitro experiments were performed using HL-60 cells stimulated with phorbol myristate acetate (PMA). Lung injury induced by LPS was alleviated by SYA, HSYA, and AHSYB as demonstrated by the histopathologic test. The three components inhibit LPS-induced elevation of the levels of inflammatory factors and wet-to-dry weight ratio as well as the amount of protein and cells in the BALF. They also induced a remarkably less overlay of myeloperoxidase (MPO) and histone in the immunofluorescence assay and reduced level of MPO-DNA complex in plasma. The in vitro assay showed a similar trend that the three components inhibited PMA-induced NET release in neutrophil-like HL-60 cells. Western blot demonstrated that phosphorylation of c-rapidly accelerated fibrosarcoma (c-Raf), mitogen-activated protein kinase ERK kinase (MEK), and extracellular signal-regulated kinase (ERK) in the lungs of LPS-challenged mice, and PMA-treated HL-60 cells were all significantly reduced by SYA, HSYA, and AHSYB. Therefore, our data demonstrated that three components of XBJ, including SYA, HSYA, and AHSYB, showed a protective effect against LPS-induced lung injury and NET release.

Convolutional Neural Networks-Based Image Analysis for the Detection and Quantification of Neutrophil Extracellular Traps

Over a decade ago, the formation of neutrophil extracellular traps (NETs) was described as a novel mechanism employed by neutrophils to tackle infections. Currently applied methods for NETs release quantification are often limited by the use of unspecific dyes and technical difficulties. Therefore, we aimed to develop a fully automatic image processing method for the detection and quantification of NETs based on live imaging with the use of DNA-staining dyes. For this purpose, we adopted a recently proposed Convolutional Neural Network (CNN) model called Mask R-CNN. The adopted model detected objects with quality comparable to manual counting—Over 90% of detected cells were classified in the same manner as in manual labelling. Furthermore, the inhibitory effect of GW 311616A (neutrophil elastase inhibitor) on NETs release, observed microscopically, was confirmed with the use of the CNN model but not by extracellular DNA release measurement. We have demonstrated that a modern CNN model outperforms a widely used quantification method based on the measurement of DNA release and can be a valuable tool to quantitate the formation process of NETs.

Autophagy-mediated regulation of neutrophils and clinical applications

Autophagy, an adaptive catabolic process, plays a cytoprotective role in enabling cellular homeostasis in the innate and adaptive immune systems. Neutrophils, the most abundant immune cells in circulation, are professional killers that orchestrate a series of events during acute inflammation. The recent literature indicates that autophagy has important roles in regulating neutrophil functions, including differentiation, degranulation, metabolism and neutrophil extracellular trap formation, that dictate neutrophil fate. It is also becoming increasingly clear that autophagy regulation is critical for neutrophils to exert their immunological activity. However, evidence regarding the systematic communication between neutrophils and autophagy is insufficient. Here, we provide an updated overview of the function of autophagy as a regulator of neutrophils and discuss its clinical relevance to provide novel insight into potentially relevant treatment strategies.

Monoclonal antibody 2C5 specifically targets neutrophil extracellular traps

Neutrophils can release DNA and granular cytoplasmic proteins that form smooth filaments of stacked nucleosomes (NS). These structures, called neutrophil extracellular traps (NETs), are involved in multiple pathological processes, and NET formation and removal are clinically significant. The monoclonal antibody 2C5 has strong specificity toward intact NS but not to individual NS components, indicating that 2C5 could potentially target NS in NETs. In this study, NETs were generated in vitro using neutrophils and HL-60 cells differentiated into granulocyte-like cells. The specificity of 2C5 toward NETs was evaluated by ELISA, which showed that it binds to NETs with the specificity similar to that for purified nucleohistone substrate. Immunofluorescence showed that 2C5 stains NETs in both static and perfused microfluidic cell cultures, even after NET compaction. Modification of liposomes with 2C5 dramatically enhanced liposome association with NETs. Our results suggest that 2C5 could be used to identify and visualize NETs and serve as a ligand for NET-targeted diagnostics and therapies.

Formation of neutrophil extracellular traps in mitochondrial DNA-deficient cells

Neutrophil extracellular trap (NET) formation plays an important role in inflammatory diseases. Although it is known that NET formation occurs via NADPH oxidase (NOX)-dependent and NOX-independent pathways, the detailed mechanism remains unknown. Therefore, in this study, we aimed to elucidate the role of mitochondria in NOX-dependent and NOX-independent NET formation. We generated mitochondrial DNA-deficient cells (ρ⁰ cells) by treating HL-60 cells with dideoxycytidine and differentiated them to neutrophil-like cells. These neutrophil-like ρ⁰ cells showed markedly reduced NOX-independent NET formation but not NOX-dependent NET formation. However, NET-associated intracellular histone citrullination was not inhibited in ρ⁰ cells. Furthermore, cells membrane disruption in NOX-dependent NET formation occurred in a Myeloperoxidase (MPO) and mixed lineage kinase domain like pseudokinase (MLKL)-dependent manner; however, cell membrane disruption in NOX-independent NET formation partially occurred in an MLKL-dependent manner. These results highlight the importance of mitochondria in NOX-independent NET formation.

The state of art of neutrophil extracellular traps in protozoan and helminthic infections

Neutrophil extracellular traps (NETs) are DNA fibers associated with histones, enzymes from neutrophil granules and anti-microbial peptides. NETs are released in a process denominated NETosis, which involves sequential steps that culminate with the DNA extrusion. NETosis has been described as a new mechanism of innate immunity related to defense against different pathogens. The initial studies of NETs were carried out with bacteria and fungi, but currently a large variety of microorganisms capable of inducing NETs have been described including protozoan and helminth parasites. Nevertheless, we have little knowledge about how NETosis process is carried out in response to the parasites, and about its implication in the resolution of this kind of disease. In the best case, the NETs entrap and kill parasites in vitro, but in others, immobilize the parasites without affecting their viability. Moreover, insufficient studies on the NETs in animal models of infections that would help to define their role, and the association of NETs with chronic inflammatory pathologies such as those occurring in several parasitic infections have left open the possibility of NETs contributing to pathology instead of protection. In this review, we focus on the reported mechanisms that lead to NET release by protozoan and helminth parasites and the evidence that support the role of NETosis in the resolution or pathogenesis of parasitic diseases.