Distinct signaling cascades of TREM-1, TLR and NLR in neutrophils and monocytic cells

TREM1: Activation, signaling, cancer and therapy

Triggering receptor expressed on myeloid cells 1 (TREM1) is a cell surface receptor expressed on neutrophils, monocytes and some tissue macrophages, where it functions as an immunoregulator that controls myeloid cell responses. The activation of TREM1 is suggested to be an upregulation-based, ligands-induced and structural multimerization-mediated process, in which damage- and pathogen-associated molecular patterns play important roles. Activated TREM1 initiates an array of downstream signaling pathways that ultimately result in the production of pro-inflammatory cytokines and chemokines, whereby it functions as an amplifier of inflammation and is implicated in the pathogenesis of many inflammation-associated diseases. Over the past decade, there has been growing evidence for the involvement of TREM1 overactivation in tumor stroma inflammation and cancer progression. Indeed, it was shown that TREM1 promotes tumor progression, immunosuppression, and resistance to therapy by activating tumor-infiltrating myeloid cells. TREM1-deficiency or blockade provide protection against tumors and reverse the resistance to anti-PD-1/PD-L1 therapy and arginine-deprivation therapy in preclinical models. Here, we first review the structure, activation modes and signaling pathways of TREM1 and emphasize the role of soluble TREM1 as a biomarker of infection and cancer. We then focus on the role of TREM1 in cancer and systematically summarize its expression patterns, upregulation mechanisms and functions in tumor development and progression. Lastly, we discuss the therapeutic prospects of TREM1 inhibition, via effective pharmacological inhibitors, in treating cancer and other diseases.

Effect of ethanol exposure on innate immune response in sepsis

Alcohol use disorder, reported by 1 in 8 critically ill patients, is a risk factor for death in sepsis patients. Sepsis, the leading cause of death, kills over 270,000 patients in the United States alone and remains without targeted therapy. Immune response in sepsis transitions from an early hyperinflammation to persistent inflammation and immunosuppression and multiple organ dysfunction during late sepsis. Innate immunity is the first line of defense against pathogen invasion. Ethanol exposure is known to impair innate and adaptive immune response and bacterial clearance in sepsis patients. Specifically, ethanol exposure is known to modulate every aspect of innate immune response with and without sepsis. Multiple molecular mechanisms are implicated in causing dysregulated immune response in ethanol exposure with sepsis, but targeted treatments have remained elusive. In this article, we outline the effects of ethanol exposure on various innate immune cell types in general and during sepsis.

Role of triggering receptor expressed on myeloid cells-1 in kidney diseases: A biomarker and potential therapeutic target

ABSTRACT

Triggering receptor expressed on myeloid cells-1 (TREM-1) is a member of the immunoglobulin superfamily. As an amplifier of the inflammatory response, TREM-1 is mainly involved in the production of inflammatory mediators and the regulation of cell survival. TREM-1 has been studied in infectious diseases and more recently in non-infectious disorders. More and more studies have shown that TREM-1 plays an important pathogenic role in kidney diseases. There is evidence that TREM-1 can not only be used as a biomarker for diagnosis of disease but also as a potential therapeutic target to guide the development of novel therapeutic agents for kidney disease. This review summarized molecular biology of TREM-1 and its signaling pathways as well as immune response in the progress of acute kidney injury, renal fibrosis, diabetic nephropathy, immune nephropathy, and renal cell carcinoma.

Evaluation of the efficacy and safety of TREM-1 inhibition with nangibotide in patients with COVID-19 receiving respiratory support: the ESSENTIAL randomised, double-blind trial

Background

Activation of the TREM-1 pathway is associated with outcome in life threatening COVID-19. Data suggest that modulation of this pathway with nangibotide, a TREM-1 modulator may improve survival in TREM-1 activated patients (identified using the biomarker sTREM-1).

Methods

Phase 2 double-blind randomized controlled trial assessing efficacy, safety, and optimum treatment population of nangibotide (1.0 mg/kg/h) compared to placebo. Patients aged 18–75 years were eligible within 7 days of SARS-CoV-2 documentation and within 48 h of the onset of invasive or non-invasive respiratory support because of COVID-19-related ARDS. Patients were included from September 2020 to April 2022, with a pause in recruitment between January and August 2021. Primary outcome was the improvement in clinical status defined by a seven-point ordinal scale in the overall population with a planned sensitivity analysis in the subgroup of patients with a sTREM-1 level above the median value at baseline (high sTREM-1 group). Secondary endpoints included safety and all-cause 28-day and day 60 mortality. The study was registered in EudraCT (2020-001504-42) and ClinicalTrials.gov (NCT04429334).

Findings

The study was stopped after 220 patients had been recruited. Of them, 219 were included in the mITT analysis. Nangibotide therapy was associated with an improved clinical status at day 28. Fifty-two (52.0%) of patients had improved in the placebo group compared to 77 (64.7%) of the nangibotide treated population, an odds ratio (95% CI) for improvement of 1.79 (1.02–3.14), p = 0.043. In the high sTREM-1 population, 18 (32.7%) of placebo patients had improved by day 28 compared to 26 (48.1%) of treated patients, an odds ratio (95% CI) of 2.17 (0.96–4.90), p = 0.063 was observed. In the overall population, 28 (28.0%) of placebo treated patients were not alive at the day 28 visit compared to 19 (16.0%) of nangibotide treated patients, an absolute improvement (95% CI) in all-cause mortality at day 28, adjusted for baseline clinical status of 12.1% (1.18–23.05). In the high sTREM-1 population (n = 109), 23 (41.8%) of patients in the placebo group and 12 (22.2%) of patients in the nangibotide group were not alive at day 28, an adjusted absolute reduction in mortality of 19.9% (2.78–36.98). The rate of treatment emergent adverse events was similar in both placebo and nangibotide treated patients.

Interpretation

Whilst the study was stopped early due to low recruitment rate, the ESSENTIAL study demonstrated that TREM-1 modulation with nangibotide is safe in COVID-19, and results in a consistent pattern of improved clinical status and mortality compared to placebo. The relationship between sTREM-1 and both risk of death and treatment response merits further evaluation of nangibotide using precision medicine approaches in life threatening viral pneumonitis.

Funding

The study was sponsored by Inotrem SA.

Knockdown of triggering receptor expressed on myeloid cells 1 (TREM1) inhibits endoplasmic reticulum stress and reduces extracellular matrix degradation and the apoptosis of human nucleus pulposus cells

According to the linear model of microarray data analysis, triggering receptor expressed on myeloid cells 1 (TREM1) has been shown to have a significantly different expression profile between intervertebral disc degeneration (IDD) samples and associated control samples. The purpose of the present study was to explore the probable role and underlying mechanism of TREM1 in IDD. To accomplish this, an in vitro model of IDD was established by using IL-1β to stimulate human nucleus pulposus cells (NPCs). After the level of TREM1 had been determined, its functions in terms of the viability of the NPCs, extracellular matrix (ECM) degradation, inflammation, apoptosis and endoplasmic reticulum stress (ERS) were assessed. The downstream target of TREM1 was predicted to be Toll-like receptor-4 (TLR-4) and its roles were then studied, incorporating experiments featuring an ERS agonist. IL-1β was found to elevate the level of TREM1 in NPCs. TREM1 knockdown reversed the observed effects of IL-1β on cell viability, ECM degradation, inflammation, apoptosis of NPCs, ERS and TLR4/NF-κB signaling. Subsequently, the TLR4 and ERS agonists were found to reverse the effect of TREM1 knockdown on NPCs, indicating that the TLR4/NF-κB signaling pathway and ERS were responsible for mediating the regulation of TREM1. In conclusion, the present study showed that TREM1 knockdown blocked the TLR4/NF-κB signaling pathway, inhibited ERS and reduced the levels of ECM degradation and apoptosis of NPCs induced by IL-1β.

Soluble TREM-1, as a new ligand for the membrane receptor Robo2, promotes hepatic stellate cells activation and liver fibrosis

Triggering receptor expressed on myeloid cells‐1 (TREM‐1) exists in two forms: a transmembrane form and a soluble form (sTREM‐1). The levels of sTREM‐1 are elevated in supernatants of activated HSCs. However, the role of sTREM‐1 in HSC activation and liver fibrosis remains undefined. Previous studies have primarily focused on the transmembrane form of TREM‐1; we innovatively observed the function of sTREM‐1 as a ligand in liver fibrosis and screened its receptor. Here, recombinant sTREM‐1 was used as a stimulator which induced HSC activation and further aggravated liver fibrosis. Then, screening for sTREM‐1 interacting membrane receptors was performed using pull‐down assay followed by mass spectrometry, and the membrane receptor roundabout guidance receptor 2 (Robo2) was identified as a candidate receptor for sTREM‐1. The interaction between sTREM‐1 and Robo2 was verified by pull‐down and immunofluorescence. The role of Robo2 on sTREM‐1‐induced HSC activation and its downstream signal pathways was assessed by knockdown of Robo2 in LX‐2 cells. Furthermore, HSC‐specific knockdown of Robo2 was achieved in a mouse model of liver fibrosis by using a recombinant adeno‐associated virus (AAV) vector to confirm the role of the receptor, and we proved that Robo2 knockdown inhibited the activation of HSC and liver fibrosis, which also led to the inactivation of Smad2/3 and PI3K/Akt pathways in sTREM‐1‐induced HSC activation and liver fibrosis. In conclusion, sTREM‐1 acts as a new ligand of Robo2; the binding of sTREM‐1 to Robo2 initiates the activation of the downstream Smad2/3 and PI3K/Akt signalling pathways, thereby promoting HSC activation and liver fibrosis.

Increased sTREM-1 plasma concentrations are associated with poor clinical outcomes in patients with COVID-19

Patients with sepsis display increased concentrations of sTREM-1 (soluble Triggering Receptor Expressed on Myeloid cells 1), and a phase II clinical trial focusing on TREM-1 modulation is ongoing. We investigated whether sTREM-1 circulating concentrations are associated with the outcome of patients with coronavirus disease 2019 (COVID-19) to assess the role of this pathway in COVID-19. This observational study was performed in two independent cohorts of patients with COVID-19. Plasma concentrations of sTREM-1 were assessed after ICU admission (pilot cohort) or after COVID-19 diagnosis (validation cohort). Routine laboratory and clinical parameters were collected from electronic patient files. Results showed sTREM-1 plasma concentrations were significantly elevated in patients with COVID-19 (161 [129-196] pg/ml) compared to healthy controls (104 [75-124] pg/ml; P<0.001). Patients with severe COVID-19 needing ICU admission displayed even higher sTREM-1 concentrations compared to less severely ill COVID-19 patients receiving clinical ward-based care (235 [176-319] pg/ml and 195 [139-283] pg/ml, respectively, P = 0.017). In addition, higher sTREM-1 plasma concentrations were observed in patients who did not survive the infection (326 [207-445] pg/ml) compared to survivors (199 [142-278] pg/ml, P<0.001). Survival analyses indicated that patients with higher sTREM-1 concentrations are at higher risk for death (hazard ratio = 3.3, 95%CI: 1.4-7.8). In conclusion, plasma sTREM-1 concentrations are elevated in patients with COVID-19, relate to disease severity, and discriminate between survivors and non-survivors. This suggests that the TREM-1 pathway is involved in the inflammatory reaction and the disease course of COVID-19, and therefore may be considered as a therapeutic target in severely ill patients with COVID-19.

TREM-1 isoforms in bacterial infections: to immune modulation and beyond

The triggering receptor expressed on myeloid cells 1 (TREM-1) is an innate immunity receptor associated with the amplification of inflammation in sterile and non-sterile inflammatory disorders. Since its first description, the two isoforms of the receptor, membrane and soluble (mTREM-1 and sTREM-1, respectively) have been largely explored in the immunopathogenesis of several bacterial diseases and sepsis. The role of the receptor in these scenarios seems to be at least partly dependent on the source/type of bacteria, host and context. As uncontrolled inflammation is a result of several bacterial infections, the inhibition of the receptor has been considered as a promising approach to treat such conditions. Further, sTREM-1 has been explored as a biomarker for diagnosis and/or prognosis of several bacterial diseases. Therefore, this review aims to provide an updated insight into how the receptor influences and is influenced by bacterial infections, highlighting the advances regarding the use/manipulation of TREM-1 isoforms in biomedical research and clinical practice.

Potentiation of NETs release is novel characteristic of TREM-1 activation and the pharmacological inhibition of TREM-1 could prevent from the deleterious consequences of NETs release in sepsis

During sepsis, neutrophil activation induces endothelial cell (EC) dysfunction partly through neutrophil extracellular trap (NET) release. The triggering receptor expressed on myeloid cell-1 (TREM-1) is an orphan immune receptor that amplifies the inflammatory response mediated by Toll-like receptor-4 (TLR4) engagement. Although the key role of TLR4 signaling in NETosis is known, the role of TREM-1 in this process has not yet been investigated. Here, we report that TREM-1 potentiates NET release by human and murine neutrophils and is a component of the NET structure. In contrast, pharmacologic inhibition or genetic ablation of TREM-1 decreased NETosis in vitro and during experimental septic shock in vivo. Moreover, isolated NETs were able to activate ECs and impair vascular reactivity, and these deleterious effects were dampened by TREM-1 inhibition. TREM-1 may, therefore, constitute a new therapeutic target to prevent NETosis and associated endothelial dysfunction.

Androgen receptor signalling in macrophages promotes TREM-1-mediated prostate cancer cell line migration and invasion

The androgen receptor (AR) is the master regulator of prostate cancer (PCa) development, and inhibition of AR signalling is the most effective PCa treatment. AR is expressed in PCa cells and also in the PCa-associated stroma, including infiltrating macrophages. Macrophages have a decisive function in PCa initiation and progression, but the role of AR in macrophages remains largely unexplored. Here, we show that AR signalling in the macrophage-like THP-1 cell line supports PCa cell line migration and invasion in culture via increased Triggering Receptor Expressed on Myeloid cells-1 (TREM-1) signalling and expression of its downstream cytokines. Moreover, AR signalling in THP-1 and monocyte-derived macrophages upregulates IL-10 and markers of tissue residency. In conclusion, our data suggest that AR signalling in macrophages may support PCa invasiveness, and blocking this process may constitute one mechanism of anti-androgen therapy.

Anti-androgen therapy inhibits prostate cancer (PC) progression, and is thought to act directly on cancer cells. Here the authors show that androgen receptor is expressed on normal and PC-associated macrophages, and its stimulation alters macrophage secretome to promote migration of cultured PC cell lines.

Triggering receptor expressed on myeloid cells-1 (TREM-1) as a therapeutic target in infectious and noninfectious disease: a critical review

The triggering receptor expressed on myeloid cells-1 (TREM-1) is an innate immune receptor found in the surface of several immune and non-immune cells. Since its first description in 2000, this molecule and its soluble form (sTREM-1) have been implicated in many diseases with infectious and noninfectious origins. As an amplifier of inflammation, the membrane-associated TREM-1 (mTREM-1) isoform induces the production of pro-inflammatory mediators, thus contributing to the pathogenesis of diseases such as sepsis, arthritis, colitis and infections. In this context, many studies have used molecules capable of inhibiting TREM-1 activity as anti-inflammatory drugs. In this regard, a few peptides have been showing promising results in the amelioration of detrimental immune responses. Some commercially available drugs, including corticosteroids and antibiotics, with known anti-inflammatory effects, have also shown activity in TREM-1 signaling. Therefore, considering the potential of this receptor as a therapeutic target, the present review encompasses the main compounds explored so far in TREM-1 modulation, highlighting and critically discussing its effects and major drawbacks of such approaches.

The role of the triggering receptor expressed on myeloid cells-1 (TREM-1) in non-bacterial infections

The triggering receptor expressed on myeloid cells 1 (TREM-1) is a receptor of the innate immune system, expressed mostly by myeloid cells and primarily associated with pro- inflammatory responses. Although the exact nature of its ligands has not yet been fully elucidated, many microorganisms or danger signals have been proposed as inducers of its activation or the secretion of sTREM-1, the soluble form with putative anti-inflammatory effects. In the course of the 20 years since its first description, several studies have investigated the involvement of TREM-1 in bacterial infections. However, the number of studies describing the role of TREM-1 in fungal, viral and parasite-associated infections has only increased in the last few years, showing a diverse contribution of the receptor in these scenarios, with beneficial or detrimental activities depending on the context. Therefore, this review aims to discuss how TREM-1 may influence viral, fungal and parasitic infection outcomes, highlighting its potential as a therapeutic target and biomarker for diagnosis and prognosis of non-bacterial infectious diseases.

Porphyromonas gingivalis and adverse pregnancy outcomes: a review on its intricate pathogenic mechanisms

Porphyromonas gingivalis (P. gingivalis), a Gram-negative facultative anaerobe of the oral cavity, is associated with the onset of various adverse pregnancy outcomes. P. gingivalis is linked with the development of preeclampsia, preterm labour, spontaneous abortion, gestational diabetes, foetal growth restriction, and misconception. The unique virulence factors, surface adhesions, enzymes of P. gingivalis can directly injure and alter the morphology, microbiome the foetal and maternal tissues. P. gingivalis can even exaggerate the production of cytokines, free radicals and acute-phase proteins in the uterine compartment that increases the risk of myometrial contraction and onset of preterm labour. Although evidence confirms the presence of P. gingivalis in the amniotic fluid and placenta of women with poor pregnancy outcomes, the intricate molecular mechanisms by which P. gingivalis initiates various antenatal and postnatal maternal and foetal complications are not well explained in the literature. Therefore, the present review aims to comprehensively summarise and highlight the recent and unique molecular pathogenic mechanisms of P. gingivalis associated with adverse pregnancy outcomes.

An update on possible pathogenic mechanisms of periodontal pathogens on renal dysfunction

Periodontitis is a potential source of permanent systemic inflammation that initiates renal dysfunction and contributes to the development of chronic kidney diseases (CKDs). Although numerous studies have confirmed the bidirectional role of periodontal infection and renal inflammation, no literature has yet highlighted the sophisticated pathogenic mechanisms by which periodontal pathogens, particularly Porphynomonas Gingivalis, induce renal dysfunction and contributed in the development of CKDs. The present review aims to critically analyze and highlight the novel pathogenesis of periodontitis induced CKDs.

The characteristics and pivotal roles of triggering receptor expressed on myeloid cells-1 in autoimmune diseases

Triggering receptor expressed on myeloid cells-1 (TREM-1) engagement can directly trigger inflammation or amplify an inflammatory response by synergizing with TLRs or NLRs. Autoimmune diseases are a family of chronic systemic inflammatory disorders. The pivotal role of TREM-1 in inflammation makes it important to explore its immunological effects in autoimmune diseases. In this review, we summarize the structural and functional characteristics of TREM-1. Particularly, we discuss recent findings on TREM-1 pathway regulation in various autoimmune diseases, including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), inflammatory bowel disease (IBD), type 1 diabetes (T1D), and psoriasis. This receptor may potentially be manipulated to alter the inflammatory response to chronic inflammation and possible therapies are explored in this review.

The role of β2 integrin associated heparin-binding protein release in ARDS

AIMS

PMNs (polymorphonuclear neutrophil) play important roles in early stage of inflammation induced ARDS (Acute Respiratory Distress Syndrome). Both HBP (Heparin-Binding Protein) released from active PMNs and β2 integrins on the surface of PMNs are involved in vascular leakage. The role and relationship of HBP and β2 integrins on ARDS still requires study.

MATERIALS AND METHODS

We established ARDS model using C57BL/6 mice with cecal ligation and puncture and eliminating HBP and β2 integrin with respective antibodies. The mice were also challenged with HBP endotracheal instillation. Histopathology score, lung wet/dry ratio, bronchoalveolar lavage fluid protein, plasma HBP and β2 integrin on PMNs from all groups were measured. β2 integrin and HBP were analyzed after incubated PMNs with streptococcal and pretreat with anti-CD18, anti-HBP, 1-phosphatidylinositol 3-kinase (PI3K) inhibitor and p38 mitogen-activated protein kinase (MAPK) inhibitor.

KEY FINDINGS

All lung injury indicatrix accompanied with HBP and β2 integrin elevated in CLP group, and HBP and β2 integrin were in correlation with each other and both were in correlation with the severity of lung injury. Endotracheal instillation HBP induced lung injury in CLP mice. Inhibiting both HBP and integrin ameliorated lung injury. HBP release was suppressed by inhibiting integrin and PI3K pathway, while integrin level did not decrease after eliminating HBP.

SIGNIFICANCE

Both HBP and β2 integrin play important roles in ARDS. HBP released from PMNs is β2 integrin-PI3K signaling pathway dependent process revealing potential novel therapeutic targets for ARDS treatment.

TREM-1 multimerization is essential for its activation on monocytes and neutrophils

The triggering receptor expressed on myeloid cells-1 (TREM-1) is a receptor expressed on innate immune cells. By promoting the amplification of inflammatory signals that are initially triggered by Toll-like receptors (TLRs), TREM-1 has been characterized as a major player in the pathophysiology of acute and chronic inflammatory diseases, such as septic shock, myocardial infarction, atherosclerosis, and inflammatory bowel diseases. However, the molecular events leading to the activation of TREM-1 in innate immune cells remain unknown. Here, we show that TREM-1 is activated by multimerization and that the levels of intracellular Ca²⁺ release, reactive oxygen species, and cytokine production correlate with the degree of TREM-1 aggregation. TREM-1 activation on primary human monocytes by LPS required a two-step process consisting of upregulation followed by clustering of TREM-1 at the cell surface, in contrast to primary human neutrophils, where LPS induced a rapid cell membrane reorganization of TREM-1, which confirmed that TREM-1 is regulated differently in primary human neutrophils and monocytes. In addition, we show that the ectodomain of TREM-1 is able to homooligomerize in a concentration-dependent manner, which suggests that the clustering of TREM-1 on the membrane promotes its oligomerization. We further show that the adapter protein DAP12 stabilizes TREM-1 surface expression and multimerization. TREM-1 multimerization at the cell surface is also mediated by its endogenous ligand, a conclusion supported by the ability of the TREM-1 inhibitor LR12 to limit TREM-1 multimerization. These results provide evidence for ligand-induced, receptor-mediated dimerization of TREM-1. Collectively, our findings uncover the mechanisms necessary for TREM-1 activation in monocytes and neutrophils.

TREM-1 Inhibition Restores Impaired Autophagy Activity and Reduces Colitis in Mice

BACKGROUND AND AIMS

Triggering receptor expressed on myeloid cells-1 [TREM-1] is known to amplify inflammation in several diseases. Autophagy and endoplasmic reticulum [ER] stress, which activate the unfolded protein response [UPR], are closely linked and defects in these pathways contribute to the pathogenesis of inflammatory bowel disease [IBD]. Both autophagy and UPR are deeply involved in host-microbiota interactions for the clearance of intracellular pathogens, thus contributing to dysbiosis. We investigated whether inhibition of TREM-1 would prevent aberrant inflammation by modulating autophagy and ER stress and preventing dysbiosis.

METHODS

An experimental mouse model of colitis was established by dextran sulphate sodium treatment. TREM-1 was inhibited, either pharmacologically by LR12 peptide or genetically with Trem-1 knock-out [KO] mice. Colon tissues and faecal pellets of control and colitic mice were used. Levels of macroautophagy, chaperone-mediated autophagy [CMA], and UPR proteins were evaluated by western blotting. The composition of the intestinal microbiota was assessed by MiSeq sequencing in both LR12-treated and KO animals.

RESULTS

We confirmed that inhibition of TREM-1 attenuates the severity of colitis clinically, endoscopically and histologically. We observed an increase in macroautophagy [ATG1/ULK-1, ATG13, ATG5, ATG16L1, and MAP1LC3-I/II] and in CMA [HSPA8 and HSP90AA1], whereas there was a decrease in the UPR [PERK, IRE-1α, and ATF-6α] protein expression levels in TREM-1 inhibited colitic mice. TREM-1 inhibition prevented dysbiosis.

CONCLUSIONS

TREM-1 may represent a novel drug target for the treatment of IBD, by modulating autophagy activity and ER stress.

TREM-1 and its potential ligands in non-infectious diseases: from biology to clinical perspectives

Triggering receptor expressed on myeloid cells-1 (TREM-1) is expressed on the majority of innate immune cells and to a lesser extent on parenchymal cells. Upon activation, TREM-1 can directly amplify an inflammatory response. Although it was initially demonstrated that TREM-1 was predominantly associated with infectious diseases, recent evidences shed new light into its role in sterile inflammatory diseases. Indeed, TREM-1 receptor and its signaling pathways contribute to the pathology of several non-infectious acute and chronic inflammatory diseases, including atherosclerosis, ischemia reperfusion-induced tissue injury, colitis, fibrosis and cancer. This review, aims to give an extensive overview of TREM-1 in non-infectious diseases, with the focus on the therapeutic potential of TREM-1 intervention strategies herein. In addition, we provide the reader with a functional enrichment analysis of TREM-1 signaling pathway and potential TREM-1 ligands in these diseases, obtained via in silico approach. We discuss pre-clinical studies which show that TREM-1 inhibition, via synthetic soluble TREM-1 protein mimickers, is effective in treating (preventing) specific inflammatory disorders, without significant effects on antibacterial response. Further research aimed at identifying specific TREM-1 ligands, in different inflammatory disorders, is required to further unravel the role of this receptor, and explore new avenues to modulate its function.

Methylome and transcriptome profiling in Myasthenia Gravis monozygotic twins

OBJECTIVE

To identify novel genetic and epigenetic factors associated with Myasthenia gravis (MG) using an identical twins experimental study design.

METHODS

The transcriptome and methylome of peripheral monocytes were compared between monozygotic (MZ) twins discordant and concordant for MG, as well as with MG singletons and healthy controls, all females. Sets of differentially expressed genes and differentially methylated CpGs were validated using RT-PCR for expression and target bisulfite sequencing for methylation on additional samples.

RESULTS

>100 differentially expressed genes and ∼1800 differentially methylated CpGs were detected in peripheral monocytes between MG patients and controls. Several transcripts associated with immune homeostasis and inflammation resolution were reduced in MG patients. Only a relatively few genes differed between the discordant healthy and MG co-twins, and both their expression and methylation profiles demonstrated very high similarity.

INTERPRETATION

This is the first study to characterize the DNA methylation profile in MG, and the expression profile of immune cells in MZ twins with MG. Results suggest that numerous small changes in gene expression or methylation might together contribute to disease. Impaired monocyte function in MG and decreased expression of genes associated with inflammation resolution could contribute to the chronicity of the disease. Findings may serve as potential new predictive biomarkers for disease and disease activity, as well as potential future targets for therapy development. The high similarity between the healthy and the MG discordant twins, suggests that a molecular signature might precede a clinical phenotype, and that genetic predisposition may have a stronger contribution to disease than previously assumed.

Activation of the TREM-1 pathway in human monocytes by periodontal pathogens and oral commensal bacteria

Periodontitis is a highly prevalent disease caused in part by an aberrant host response to the oral multi-species biofilm. A balance between the oral bacteria and host immunity is essential for oral health. Imbalances in the oral microbiome lead to an uncontrolled host inflammatory response and subsequent periodontal disease (i.e. gingivitis and periodontitis). TREM-1 is a signaling receptor present on myeloid cells capable of acting synergistically with other pattern recognition receptors leading to amplification of inflammatory responses. The aim of this study was to investigate the activation of the TREM-1 pathway in the human monocyte-like cell line THP-1 exposed to both oral pathogens and commensals. The relative expression of the genes encoding TREM-1 and its adapter protein DAP12 were determined by quantitative real-time polymerase chain reaction. The surface expression of TREM-1 was determined by flow cytometry. Soluble TREM-1 and cytokines were measured by enzyme-linked immunosorbent assay. The results demonstrate that both commensal and pathogenic oral bacteria activate the TREM-1 pathway, resulting in a proinflammatory TREM-1 activity-dependent increase in proinflammatory cytokine production.

Association of decreased serum sTREM-1 level with the severity of coronary artery disease: Inhibitory effect of sTREM-1 on TNF-α- and oxLDL-induced inflammatory reactions in endothelial cells

Soluble triggering receptor expressed on myeloid cells 1 (sTREM-1) is closely involved in autoimmune diseases and inflammatory reactions. We aimed to investigate whether serum sTREM-1 is related to coronary artery disease (CAD) and to evaluate the biological effects of sTREM-1 in cell experiments.This cross-sectional study included 263 consecutive patients with angiographically documented CAD, who were admitted for diagnosis and interventional treatment of CAD (CAD group), with 162 participants without CAD serving as controls (control group). Serum levels of sTREM-1 and high sensitivity C reactive protein (hsCRP) were determined in all participants. In cell experiments, the influence of sTREM-1 on tumor necrosis factor-α (TNF-α)- or oxidized low-density lipoprotein (oxLDL)-induced inflammatory reactions was evaluated in human umbilical vein endothelial cells (HUVECs).Serum level of sTREM-1 was significantly lower in CAD patients than in controls (P < 0.001). sTREM-1 values were related to the number of diseased coronary arteries (Spearman r = -0.413, P < 0.001) and the severity represented by Gensini score (Pearson r = -0.336, P < 0.001). Multivariable logistic regression analysis revealed that decreased sTREM-1 were independent determinants of CAD (OR = 0.428, P < 0.001). In cell experiments, recombinant sTREM-1 protein concentration-dependently inhibited the expression of IL-1β, IL-6, TNF-α, VCAM-1, and ICAM-1 induced by TNF-α or oxLDL in HUVECs.This study demonstrates that decreased serum sTREM-1 level is significantly associated with the presence and severity of CAD. sTREM-1 restrains inflammatory reaction in endothelial cells, suggesting that it might be a potential vascular protective factor.

TGF-β1 Upregulates the Expression of Triggering Receptor Expressed on Myeloid Cells 1 in Murine Lungs

Triggering receptor expressed on myeloid cells 1 (TREM-1) increases the expression of TGF-β family genes, which are known as profibrogenic cytokines in the pathogenesis of pulmonary fibrosis. In this study, we determined whether TGF-β1 regulated the expression of TREM-1 in a mouse model of pulmonary fibrosis. The expression of TGF-β1 and TREM-1 was increased on day 7, 14, and 21 after single intratracheal injection of bleomycin (BLM). And there was positive correlation between the expression of TGF-β1 and TREM-1. TGF-β1 increased expression of TREM-1 mRNA and protein in a time- and dose-dependent manner in mouse macrophages. The expression of the activator protein 1 (AP-1) was increased in lung tissues from mouse after BLM injection and in mouse macrophages after TGF-β1 treatment, respectively. TGF-β1 significantly increased the relative activity of luciferase in the cells transfected with plasmid contenting wild type-promoter of TREM-1. But TGF-β1 had no effect on the activity of luciferase in the cells transfected with a mutant-TREM1 plasmid carrying mutations in the AP-1 promoter binding site. In conclusion, we found the expression of TREM-1 was increased in lung tissues from mice with pulmonary fibrosis. TGF-β1 increased the expression of TREM-1 in mouse macrophages partly via the transcription factor AP-1.

Social networking of human neutrophils within the immune system

It is now widely recognized that neutrophils are highly versatile and sophisticated cells that display de novo synthetic capacity and may greatly extend their lifespan. In addition, concepts such as "neutrophil heterogeneity" and "neutrophil plasticity" have started to emerge, implying that, under pathological conditions, neutrophils may differentiate into discrete subsets defined by distinct phenotypic and functional profiles. A number of studies have shown that neutrophils act as effectors in both innate and adaptive immunoregulatory networks. In fact, once recruited into inflamed tissues, neutrophils engage into complex bidirectional interactions with macrophages, natural killer, dendritic and mesenchymal stem cells, B and T lymphocytes, or platelets. As a result of this cross-talk, mediated either by contact-dependent mechanisms or cell-derived soluble factors, neutrophils and target cells reciprocally modulate their survival and activation status. Altogether, these novel aspects of neutrophil biology have shed new light not only on the potential complex roles that neutrophils play during inflammation and immune responses, but also in the pathogenesis of several inflammatory disorders including infection, autoimmunity, and cancer.