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

Icariside II alleviates lipopolysaccharide-induced acute lung injury by inhibiting lung epithelial inflammatory and immune responses mediated by neutrophil extracellular traps

AIMS

Acute lung injury (ALI) is a life-threatening lung disease characterized by inflammatory cell infiltration and lung epithelial injury. Icariside II (ICS II), one of the main active ingredients of Herba Epimedii, exhibits anti-inflammatory and immunomodulatory effects. However, the effect and mechanism of ICS II in ALI remain unclear. The purpose of the current study was to investigate the pharmacological effect and underlying mechanism of ICS II in ALI.

MAIN METHODS

Models of neutrophil-like cells, human peripheral blood neutrophils, and lipopolysaccharide (LPS)-induced ALI mouse model were utilized. RT-qPCR and Western blotting determined the gene and protein expression levels. Protein distribution and quantification were analyzed by immunofluorescence.

KEY FINDINGS

ICS II significantly reduced lung histopathological damage, edema, and inflammatory cell infiltration, and it reduced pro-inflammatory cytokines in ALI. There is an excessive activation of neutrophils leading to a significant production of NETs in ALI mice, a process mitigated by the administration of ICS II. In vivo and in vitro studies found that ICS II could decrease NET formation by targeting neutrophil C-X-C chemokine receptor type 4 (CXCR4). Further data showed that ICS II reduces the overproduction of dsDNA, a NETs-related component, thereby suppressing cGAS/STING/NF-κB signalling pathway activation and inflammatory mediators release in lung epithelial cells.

SIGNIFICANCE

This study suggested that ICS II may alleviate LPS-induced ALI by modulating the inflammatory response, indicating its potential as a therapeutic agent for ALI treatment.

Astilbin inhibited neutrophil extracellular traps in gouty arthritis through suppression of purinergic P2Y6 receptor

BACKGROUND

Gouty arthritis (GA), a common inflammatory condition triggered by monosodium urate crystal accumulation, often necessitates safer treatment alternatives due to the limitations of current therapies. Astilbin, a flavonoid from Smilax glabra Roxb, has demonstrated potential in traditional Chinese medicine for its anti-inflammatory properties. However, the anti-GA effect and its underlying mechanism have not been fully elucidated.

PURPOSE

This study aimed to investigate the therapeutic potential of astilbin in GA, focusing on its effects on neutrophil extracellular traps (NETs), as well as the potential molecular target of GA both in vitro and in vivo.

STUDY DESIGN

Firstly, astilbin inhibited the citrullinated histone H3 (Cit h3) protein levels and reduced the NETs formation in neutrophils stimulated by monosodium urate (MSU). Secondly, we wondered the effect of astilbin on migration of neutrophils and dimethyl-sulfoxide (DMSO)-differentiated HL-60 (dHL-60) cells under the stimulation of MSU. Then, the effect of astilbin on suppressing NETs through purinergic P2Y6 receptor (P2Y6R) and Interlukin-8 (IL-8)/ CXC chemokine receptor 2 (CXCR2) pathway was investigated. Also, the relationship between P2Y6R and IL-8/CXCR2 was explored in dHL-60 cells under stimulation of MSU. Finally, we testified the effect of astilbin on reducing NETs in GA through suppressing P2Y6R and then down-regulating IL-8/CXCR2 pathway.

METHODS

MSU was used to induce NETs in neutrophils and dHL-60 cells. Real-time formation of NETs and migration of neutrophils were monitored by cell living imaging with or without MSU. Then, the effect of astilbin on NETs formation, P2Y6R and IL-8/CXCR2 pathway were detected by immunofluorescence (IF) and western blotting. P2Y6R knockdown dHL-60 cells were established by small interfering RNA to investigate the association between P2Y6R and IL-8/CXCR2 pathway. Also, plasmid of P2Y6R was used to overexpress P2Y6R in dHL-60 cells, which was employed to explore the role of P2Y6R in astilbin inhibiting NETs. Within the conditions of knockdown and overexpression of P2Y6R, migration and NETs formation were assessed by transmigration assay and IF staining, respectively. In vivo, MSU-induced GA mice model was established to assess the effect of astilbin on inflammation by haematoxylin-eosin and ELISA. Additionally, the effects of astilbin on neutrophils infiltration, NETs, P2Y6R and IL-8/CXCR2 pathway were analyzed by IF, ELISA, immunohistochemistry (IHC) and western blotting.

RESULTS

Under MSU stimulation, astilbin significantly suppressed the level of Cit h3 and NETs formation including the fluorescent expressions of Cit h3, neutrophils elastase, myeloperoxidase, and intra/extracellular DNA. Also, results showed that MSU caused NETs release in neutrophils as well as a trend towards recruitment of dHL-60 cells to MSU. Astilbin could markedly decrease expressions of P2Y6R and IL-8/CXCR2 pathway which were upregulated by MSU. By silencing P2Y6R, the expression of IL-8/CXCR2 pathway and migration of dHL-60 cells were inhibited, leading to the suppression of NETs. These findings indicated the upstream role of P2Y6R in the IL-8/CXCR2 pathway. Moreover, overexpression of P2Y6R was evidently inhibited by astilbin, causing a downregulation in IL-8/CXCR2 pathway, migration of dHL-60 cells and NETs formation. These results emphasized that astilbin inhibited the IL-8/CXCR2 pathway primarily through P2Y6R. In vivo, astilbin administration led to marked reductions in ankle swelling, inflammatory infiltration as well as neutrophils infiltration. Expressions of P2Y6R and IL-8/CXCR2 pathway were evidently decreased by astilbin and P2Y6R inhibitor MRS2578 either alone or in combination. Also, astilbin and MRS2578 showed notable effect on reducing MSU-induced NETs formation and IL-8/CXCR2 pathway whether used alone or in combination, parallelly demonstrating that astilbin decreased NETs formation mainly through P2Y6R.

CONCLUSION

This study revealed that astilbin suppressed NETs formation via downregulating P2Y6R and subsequently the IL-8/CXCR2 pathway, which evidently mitigated GA induced by MSU. It also highlighted the potential of astilbin as a promising natural therapeutic for GA.

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.

Intracellular Accumulation and Secretion of YKL-40 (CHI3L1) in the Course of DMSO-Induced HL-60 Cell Differentiation

YKL-40 (CHI3L1) is a matrix glycoprotein stored in human neutrophil-specific granules and released upon activation. While it is implicated in inflammation, cancer progression, and cell differentiation, its exact physiological role remains unclear. This study investigated the intracellular expression and secretion of YKL-40 by untreated and DMSO-treated HL-60 cells in association with surface expression of CD11b and CD66b throughout the differentiation process (up to 120 h). Secreted YKL-40 protein and mRNA levels of YKL-40, CD66b, and CD11b were measured by ELISA and quantitative RT-PCR, respectively. The intracellular YKL-40 and surface CD11b and CD66b expression were assessed by flow cytometry. A significant increase in CD11b expression confirmed DMSO-induced differentiation of HL-60 cells. Upon DMSO stimulation, YKL-40 mRNA expression increased in a time-dependent manner, unlike CD66b. The lack of CD66b (a granulocyte maturation and activation marker) on the surface of HL-60 cells might suggest that DMSO treatment did not induce full maturation or activation. The intracellular YKL-40 protein expression was increasing up to 96 h of DMSO treatment and then declined. YKL-40 secretion into the culture medium was detectable only at later time points (96 and 120 h), which was correlated with a decreased proliferation of DMSO-treated HL-60 cells. These findings suggest sequential changes in YKL-40 production and secretion during DMSO-induced differentiation of HL-60 cells and might contribute to a better understanding of YKL-40's involvement in both physiological processes and disease development, including multiple sclerosis.

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.

Neutrophil-like cells derived from the HL-60 cell-line as a genetically-tractable model for neutrophil degranulation

Research on neutrophil biology has been limited by the short life span and limited genetic manipulability of these cells, driving the need for representative and efficient model cell lines. The promyelocytic cell line HL-60 and its subline PLB-985 can be differentiated into neutrophil-like cells (NLCs) and have been used to study neutrophil functions including chemotaxis, phagocytosis, endocytosis, and degranulation. Compared to neutrophils derived from hematopoietic stem cells, NLCs serve as a cost-effective neutrophil model. NLCs derived from both HL-60 and PLB-985 cells have been shown to perform degranulation, an important neutrophil function. However, no study has directly compared the two lines as models for degranulation including their release of different types of mobilizable organelles. Furthermore, Nutridoma, a commercially available supplement, has recently been shown to improve the chemotaxis, phagocytosis, and oxidative burst abilities of NLCs derived from promyelocytic cells, however it is unknown whether this reagent also improves the degranulation ability of NLCs. Here, we show that NLCs derived from both HL-60 and PLB-985 cells are capable of degranulating, with each showing markers for the release of multiple types of secretory organelles, including primary granules. We also show that differentiating HL-60 cells using Nutridoma does not enhance their degranulation activity over NLCs differentiated using Dimethyl Sulfoxide (DMSO) plus Granulocyte-colony stimulating factor (G-CSF). Finally, we show that promyelocytic cells can be genetically engineered and differentiated using these methods, to yield NLCs with a defect in degranulation. Our results indicate that both cell lines serve as effective models for investigating the mechanisms of neutrophil degranulation, which can advance our understanding of the roles of neutrophils in inflammation and immunity.

IDH1/MDH1 deacetylation promotes acute liver failure by regulating NETosis

BACKGROUND

Acute liver failure (ALF) is a life-threatening disease, but its pathogenesis is not fully understood. NETosis is a novel mode of cell death. Although the formation of neutrophil extracellular traps (NETs) has been found in various liver diseases, the specific mechanism by which NETosis regulates the development of ALF is unclear. In this article, we explore the role and mechanism of NETosis in the pathogenesis of ALF.

METHODS

Clinically, we evaluated NETs-related markers in the liver and peripheral neutrophils of patients with ALF. In in vitro experiments, HL-60 cells were first induced to differentiate into neutrophil-like cells (dHL-60 cells) with dimethyl sulfoxide (DMSO). NETs were formed by inducing dHL-60 cells with PMA. In in vivo experiments, the ALF model in mice was established with LPS/D-gal, and the release of NETs was detected by immunofluorescence staining and western blotting. Finally, the acetylation levels of IDH1 and MDH1 were detected in dHL-60 cells and liver samples by immunoprecipitation.

RESULTS

Clinically, increased release of NETs in liver tissue was observed in patients with ALF, and NETs formation was detected in neutrophils from patients with liver failure. In dHL-60 cells, mutations at IDH1-K93 and MDH1-K118 deacetylate IDH1 and MDH1, which promotes the formation of NETs. In a mouse model of ALF, deacetylation of IDH1 and MDH1 resulted in NETosis and promoted the progression of acute liver failure.

CONCLUSIONS

Deacetylation of IDH1 and MDH1 reduces their activity and promotes the formation of NETs. This change aggravates the progression of acute liver failure.

Culture and Maintenance of Immune Cells to Model Innate Immune Status at the Feto-maternal Interface

The inflammatory process leading to human labor is mostly facilitated by immune cells, which can be studied by isolating and characterizing primary immune cells from the feto-maternal interface. However, difficulty and inconsistency in sampling approaches of immune cells and short lifespan in vitro prevent their usage in mechanistic studies to understand the maternal-fetal immunobiology. To address these limitations, existing cell line models can be differentiated into immune-like cells for use in reproductive biology experiments. In this chapter, we discussed cell culture methods of maintaining and differentiating HL-60, THP-1, and NK-92 cells to obtain neutrophil-like, macrophage-like, and decidual natural killer-like cells, respectively, which can then be used together with intrauterine cells to elucidate and investigate immune mechanisms that contribute to parturition.

Human neutrophil-like cells demonstrate antimicrobial responses to the chronic cyst form of Toxoplasma gondii

The protozoan parasite Toxoplasma gondii infects approximately 2.5 billion people worldwide. Infection induces a rapid dissemination of parasites throughout the body followed by the formation of lifelong cysts within neurons of the host brain. Both stages require a dynamic immune response comprised of both innate and adaptive cells. Neutrophils are a primary responding cell to acute infection and have been observed in the brain during murine chronic infection. Previous studies investigating human neutrophils found that invasion by Toxoplasma tachyzoites inhibits apoptosis of neutrophils, prolonging their survival under inflammatory conditions. Here, we demonstrate the differentiation of two distinct subsets following exposure of human neutrophil-like-cells (HNLC) to Toxoplasma cysts. In vitro stimulation and imaging studies show cyst-specific induction of cytokines and cyst clearance by HNLCs. Further testing demonstrates that aged HNLCs perform less phagocytosis of cysts compared to non-aged HNLCs. In conclusion, this study identifies a novel response of HNLCs to Toxoplasma cysts and may indicate a role for neutrophils in the clearance of cysts during human infection with Toxoplasma.

Single-cell detection of DMSO promoted HL-60 differentiation toward granulocyte based on DC-iDEP for medicine screening

The most common form of leukemia in adults is acute leukemia. Drug differentiation control is an extremely critical treatment for acute leukemia. Unfortunately, current techniques detecting differentiation control experience long time and complex steps of verification hindering the pace of medicine discovery: flow cytometry and RT-PCR are highly accurate and efficient at a cost of inconvenient fluorescent labeling or a high risk of contamination; conventional staining leads to cell death unavailable for further pharmacological tests. There is a great interest in developing simple, fast, and non-invasive techniques to screen medicine. DC-iDEP is an emerging label-free identification technique taking advantage of the whole cell native biophysical property for sorting cell populations. Here, HL-60 cell line has been used as a model to study the differentiation process toward granulocytes and medicine efficacy. The results showed that DEP succeeded in detecting the DMSO promoted HL-60 differentiation degree by the weighted average characterization factor. This factor is related to the single cell biophysical property, which accumulates to generate differences in each population with distinct constitutions. Furthermore, cichoric acid was investigated to be capable of promoting DMSO-induced differentiation efficiently. Using the change induced by cichoric acid, the HL-60 medicine screening application has been first attempted based on DEP. A rapid, label-free medicine screening method has been established to monitor HL-60 differentiation toward granulocyte and has great potential for medicine screening.

Evaluation of the innate immune response of caprine neutrophils against Mycobacterium avium subspecies paratuberculosis in vitro

Neutrophils constitute an essential component of the innate immune response, readily killing most bacteria through phagocytosis, degranulation, and the release of neutrophil extracellular traps (NETs) among other mechanisms. These cells play an unclear role in mycobacterial infections such as Mycobacterium avium subspecies paratuberculosis (Map), the etiological agent of paratuberculosis, and its response is particularly understudied in ruminants. Herein, a wide set of techniques were adapted, or newly developed, to study the in vitro response of caprine neutrophils after Map infection. Immunofluorescence was used to demonstrate, simultaneously, chemotaxis, phagocytosis, degranulation, and NETs. The quantification of neutrophil phagocytic activity against Map at a 1:10 multiplicity of infection (MOI), through flow cytometry, showed values that varied from 4.54 to 5.63% of phagocyting neutrophils. By immunofluorescence, a 73.3 ± 14.5% of the fields showed NETs, and the mean release of DNA, attributable to NETosis, calculated through a fluorometric method, was 16.2 ± 3.5%. In addition, the RNA expression of TGF-β, TNF and IL-1β cytokines, measured through reverse transcription qPCR, was significantly higher in the two latter. Overall, neutrophil response was proportional to the number of bacteria. This work confirms that the simultaneous study of several neutrophil mechanisms, and the combination of different methodologies, are essential to reach a comprehensive understanding of neutrophil response against pathogens, demonstrates that, in vitro, caprine neutrophils display a strong innate response against Map, using their entire repertoire of effector functions, and sets the basis for further in vitro and in vivo studies on the role of neutrophils in paratuberculosis.

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.

Comprehensive Discovery of the Accessible Primary Amino Group-Containing Segments from Cell Surface Proteins by Fine-Tuning a High-Throughput Biotinylation Method

Cell surface proteins, including transmembrane and other surface-anchored proteins, play a key role in several critical cellular processes and have a strong diagnostic value. The development of quick and robust experimental methods remains vital for the accurate and comprehensive characterization of the cell surface subproteome of individual cells. Here we present a high-throughput technique which relies on the biotinylation of the accessible primary amino groups in the extracellular segments of the proteins, using HL60 as a model cell line. Several steps of the method have been thoroughly optimized to capture labeled surface proteins selectively and in larger quantities. These include the following: improving the efficiency of the cell surface biotinylation; reducing the endogen protease activity; applying an optimal amount of affinity column and elution steps for labeled peptide enrichment; and examining the effect of various solid-phase extraction methods, different HPLC gradients, and various tandem mass spectrometry settings. Using the optimized workflow, we identified at least 1700 surface-associated individual labeled peptides (~6000-7000 redundant peptides) from the model cell surface in a single nanoHPLC-MS/MS run. The presented method can provide a comprehensive and specific list of the cell surface available protein segments that could be potential targets in various bioinformatics and molecular biology research.

Sourcing cells for in vitro models of human vascular barriers of inflammation

The vascular system plays a critical role in the progression and resolution of inflammation. The contributions of the vascular endothelium to these processes, however, vary with tissue and disease state. Recently, tissue chip models have emerged as promising tools to understand human disease and for the development of personalized medicine approaches. Inclusion of a vascular component within these platforms is critical for properly evaluating most diseases, but many models to date use "generic" endothelial cells, which can preclude the identification of biomedically meaningful pathways and mechanisms. As the knowledge of vascular heterogeneity and immune cell trafficking throughout the body advances, tissue chip models should also advance to incorporate tissue-specific cells where possible. Here, we discuss the known heterogeneity of leukocyte trafficking in vascular beds of some commonly modeled tissues. We comment on the availability of different tissue-specific cell sources for endothelial cells and pericytes, with a focus on stem cell sources for the full realization of personalized medicine. We discuss sources available for the immune cells needed to model inflammatory processes and the findings of tissue chip models that have used the cells to studying transmigration.

Low NETosis Induced in Anaplasma phagocytophilum-Infected Cells

Anaplasma phagocytophilum are obligatory intracellular bacteria that preferentially replicate inside leukocytes by utilizing biological compounds and processes of these primary host defensive cells. In this study, bioinformatics analysis was conducted to further characterize A. phagocytophilum–host interactions using the neutrophil-like model of human Caucasian promyelocytic leukemia HL60 cells. We detected a hierarchy of molecules involved in A. phagocytophilum-HL60 interactions with overrepresentation in infected human cells of proteins involved in the reactive oxygen species (ROS) pathway and cell surface monocyte markers. As A. phagocytophilum phagocytosis by neutrophils is inhibited, the results suggested a possible explanation for our bioinformatics data: radical oxygen compounds could induce the killing of bacteria activating NETosis, a unique form of defense mechanism resulting in cell death that is characterized by the release of decondensed chromatin and granular contents to the extracellular space, forming neutrophil extracellular traps (NETs) to eliminate invading microorganisms. Thus, we confirmed the existence of a low NETosis induced in A. phagocytophilum-infected cells by immunofluorescence (IF) experiments. These results provide new insights into the complex mechanisms that govern immune response during A. phagocytophilum host interactions.

Autophagy-driven neutrophil extracellular traps: The dawn of sepsis

Sepsis is a systemic inflammatory syndrome caused by infection disorders. The core mechanism of sepsis is immune dysfunction. Neutrophils are the most abundant circulating white blood cells, which play a crucial role in mediating the innate immune response. Previous studies have shown that an effective way to treat sepsis is through the regulation of neutrophil functions. Autophagy, a highly conserved degradation process, is responsible for removing denatured proteins or damaged organelles within cells and protecting cells from external stimuli. It is a key homeostasis process that promotes neutrophil function and differentiation. Autophagy has been shown to be closely associated with inflammation and immunity. Neutrophils, the first line of innate immunity, migrate to inflammatory sites upon their activation. Neutrophil-mediated autophagy may participate in the clinical course of sepsis. In this review, we summarized and analyzed the latest research findings on the changes in neutrophil external traps during sepsis, the regulatory role of autophagy in neutrophil, and the potential application of autophagy-driven NETs in sepsis, so as to guide clinical treatment of sepsis.

Elastase-Activated Antimicrobial Peptide for a Safer Pulmonary Treatment of Cystic Fibrosis Infections

As bioactive small proteins with antimicrobial and immunomodulatory activities that are naturally produced by all living organisms, antimicrobial peptides (AMPs) have a marked potential as next-generation antibiotics. However, their development as antibacterial agents is limited by low stability and cytotoxicity. D-BMAP18, a membrane-permeabilizing antimicrobial peptide composed of D-amino acids, has shown good antibacterial and anti-inflammatory activities but also a non-negligible cytotoxicity against eukaryotic cell lines. In this study, a prodrug has been developed that extends the peptide with a negatively charged, inactivating sequence containing the cleavage site for neutrophil elastase (NE). The ultimate goal was to allow the activation of D-BMAP18 by endogenous elastase only at the site of infection/inflammation, enabling a slow and targeted release of the pharmacologically active peptide. In vitro activation of Pro-D-BMAP18 was confirmed using purified NE. Its antimicrobial and cytotoxic activities were tested in the presence and absence of elastase and compared to those of the parental form. The prodrug had minimal activity in the absence of elastase, while its proteolysis product retained an appreciable antimicrobial activity but lower cytotoxicity. Moreover, Pro-D-BMAP18 was found to be correctly converted to D-BMAP18 in the presence of CF sputum as a model of the lung environment and showed good antimicrobial activity under these conditions.

The FcγRIII Engagement Augments PMA-Stimulated Neutrophil Extracellular Traps (NETs) Formation by Granulocytes Partially via Cross-Talk between Syk-ERK-NF-κB and PKC-ROS Signaling Pathways

Polymorphonuclear neutrophils (PMNs) are the most abundant white blood cell in the circulation capable of neutrophil extracellular traps (NETs) formation after stimulation. Both NADPH oxidase-dependent and -independent pathways are involved in NET formation. The IgG is the most abundant immunoglobulin in human serum. However, the impact of the circulating IgG on NET formation is totally unexplored. In this study, the all-trans retinoic acid (ATRA)-induced mature granulocytes (dHL-60) were pre-treated with monomeric human IgG, papain-digested Fab fragment, crystallizable IgG Fc portion, rituximab (a human IgG1), or IgG2. The NET formation of the dHL-60 in the presence/absence of phorbol 12-myristate 13-acetate (PMA) stimulation was then measured by the fluorescent area after SYTOX green nucleic acid stain. The intracellular reactive oxygen species (ROS) generation was measured by flow cytometry. Total and phosphorylated Syk, SHP-1, and ERK were detected by immunoblot. We found that human monomeric IgG and its subclasses IgG1 and IgG2 per se induced negligible NET formation of dHL-60, but the FcγRIII engagement by these IgG subclasses and Fc portion augment PMA-stimulated dHL-60 NET formation in a dose-dependent manner. Furthermore, we found that increased Syk and ERK phosphorylation, intracellular ROS generation, and pro-inflammatory cytokines, IL-8 and TNF-α, production could be induced after FcγRIII engagement. Blocking FcγRIII engagement by a specific antibody diminished the augmented NET formation. In conclusion, we discovered that cross-talk between FcγRIII engagement-induced Syk-ERK and PMA-induced PKC signaling pathways augment NET formation of dHL-60 via increased ROS generation and pro-inflammatory cytokines, IL-8 and TNF-α, production.