Reversal of TREM-1 ectodomain shedding and improved bacterial clearance by intranasal metalloproteinase inhibitors

Effect of blockage of Trem1 on the M1 polarization of macrophages in the regulation dental pulp inflammation

Dental pulp inflammation is a common and significant factor related to poor dental prognosis. Current treatment strategies primarily concentrate on managing the inflammatory response, with specific targets for intervention still under investigation. Triggering receptors expressed on myeloid cells (TREMs) are a group of receptor molecules extensively present on myeloid cell surfaces, crucial in the regulation of inflammatory process. Our analysis of transcriptomic sequencing data from clinical pulp samples of dataset GSE77459 and animal models revealed up-regulation of Trem1 during pulpitis. Administration of the Trem1-blocking peptide LP17 led to lower (more than 1-fold) levels of several pro-inflammatory factors and inhibition of M1 macrophage polarization both in vivo and in vitro. This study of the expression patterns and functions of Trem1 in the development of dental pulp inflammation provides novel insights into the therapeutic strategies for clinical pulpitis.

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.

sTREM-1 as promising prognostic biomarker for acute-on-chronic liver failure and mortality in patients with acute decompensation of cirrhosis

BACKGROUND

Acute decompensation (AD) of cirrhosis is associated with high short-term mortality, mainly due to the development of acute-on-chronic liver failure (ACLF). Thus, there is a need for biomarkers for early and accurate identification of AD patients with high risk of development of ACLF and mortality. Soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) is released from activated innate immune cells and correlated with various inflammatory processes.

AIM

To explore the prognostic value of sTREM-1 in patients with AD of cirrhosis.

METHODS

A multicenter prospective cohort of 442 patients with cirrhosis hospitalized for AD was divided into a study cohort (n = 309) and validation cohort (n = 133). Demographic and clinical data were collected, and serum sTREM-1 was measured at admission. All enrolled patients were followed-up for at least 1 year.

RESULTS

In patients with AD and cirrhosis, serum sTREM-1 was an independent prognosis predictor for 1-year survival and correlated with liver, coagulation, cerebral and kidney failure. A new prognostic model of AD (P-AD) incorporating sTREM-1, blood urea nitrogen (BUN), total bilirubin (TBil), international normalized ratio (INR) and hepatic encephalopathy grades was established and performed better than the model for end-stage liver disease (MELD), MELD-sodium (MELD-Na), chronic liver failure-consortium (CLIF-C) ACLF and CLIF-C AD scores. Additionally, sTREM-1 was increased in ACLF and predicted the development of ACLF during first 28-d follow-up. The ACLF risk score incorporating serum sTREM-1, BUN, INR, TBil and aspartate aminotransferase levels was established and significantly superior to MELD, MELD-Na, CLIF-C ACLF, CLIF-C AD and P-AD in predicting risk of ACLF development.

CONCLUSION

Serum sTREM-1 is a promising prognostic biomarker for ACLF development and mortality in patients with AD of cirrhosis.

The Interaction of HMGB1 with the Proinflammatory TREM-1 Receptor Generates Cytotoxic Lymphocytes Active against HLA-Negative Tumor Cells

High mobility group protein (HMGB1) is secreted by myeloid cells and cells of damaged tissues during inflammation, causing inflammatory reactions through various receptors, including TLRS and RAGE. TREM-1 is considered to be one of the potential HMGB1 receptors. In this work, we have shown that the HMGB1 protein is able to bind to the TREM-1 receptor at high affinity both in solution and on the cell surface. This binding causes lymphocytes to release cytokines IL-2, IL-1b, IL-6, TNF and Ifny into the medium, which leads to the appearance of cytotoxic lymphocytes in PBMC capable of lysing HLA-negative tumor cells. Expanding the spectra of proinflammatory receptor ligands and understanding the mechanisms of their action is essential for the creation of new immunotherapy pathways.

Association of salivary TREM-1 and PGLYRP1 inflammatory markers with non-communicable diseases

AIM

Triggering receptor expressed on myeloid cells 1 (TREM-1) and peptidoglycan recognition protein 1 (PGLYRP1) are elevated in biofluids in the presence of various inflammatory conditions. This cross-sectional study aimed to evaluate the effect of age, sex, smoking and different oral and systemic non-communicable diseases on the levels of TREM-1 and PGLYRP1 in saliva.

MATERIALS AND METHODS

In total, 445 individuals (mean age 48.7 ± 16.9 years, female:male 51%:49%) were included. All provided self-reported information on smoking and systemic diseases and whole stimulated saliva. Periodontal and cariological parameters were recorded. Salivary levels of TREM-1, PGLYRP1 and total protein were measured using commercially available assays.

RESULTS

Salivary TREM-1 levels were significantly higher in stages III-IV periodontitis compared to other periodontal diagnoses (p < .05). Smoking, bleeding on probing (BOP), percentage of pockets ≥4 mm and the number of manifest caries were associated with TREM-1 (p < .05), while sex, BOP, number of manifest caries and muscle and joint diseases were associated with PGLYRP1 (p < .05).

CONCLUSIONS

Salivary TREM-1 is associated with periodontitis and caries, while PGLYRP1 is associated with gingival inflammation and caries. Additionally, TREM-1 levels are modified by smoking, while PGLYRP1 is modified by sex and muscle and joint diseases. TREM-1 and PGLYRP1 in saliva could serve as potential biomarkers for detecting and monitoring non-communicable diseases.

Systemic immune profiling of Omicron-infected subjects inoculated with different doses of inactivated virus vaccine

SARS-CoV-2 primary strain-based vaccination exerts a protective effect against Omicron variants-initiated infection, symptom occurrence, and disease severity in a booster-dependent manner. Yet, the underlying mechanisms remain unclear. During the 2022 Omicron outbreak in Shanghai, we enrolled 122 infected adults and 50 uninfected controls who had been unvaccinated or vaccinated with two or three doses of COVID-19 inactive vaccines and performed integrative analysis of 41-plex CyTOF, RNA-seq, and Olink on their peripheral blood samples. The frequencies of HLA-DRhi classical monocytes, non-classical monocytes, and Th1-like Tem tended to increase, whereas the frequency of Treg was reduced by booster vaccine, and they influenced symptom occurrence in a vaccine dose-dependent manner. Intercorrelation and mechanistic analysis suggested that the booster vaccination induced monocytic training, which would prime monocytic activation and maturation rather than differentiating into myeloid-derived suppressive cells upon Omicron infections. Overall, our study provides insights into how booster vaccination elaborates protective immunity across SARS-CoV-2 variants.

Soluble triggering receptor expressed on myeloid cell-1 reflects the cross-sectional activity of microscopic polyangiitis and granulomatosis with polyangiitis

Objectives

We investigated whether soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) reflects cross-sectional activity of microscopic polyangiitis (MPA) and granulomatosis with polyangiitis (GPA).

Methods

Forty-seven MPA and 32 GPA patients with well-documented clinical records and stored sera were enrolled. sTREM-1 levels were evaluated using Magnetic Luminex® assay, and disease activity was assessed using Birmingham vasculitis activity score (BVAS). Patients were divided into two groups according to the upper and lower halves of BVAS. Receiver operator characteristic (ROC) curve analysis was used to identify cut-off for determining upper half of BVAS. Linear and binary logistic regression was performed to evaluate the association between sTREM-1 and disease activity and status.

Results

The median age of patients was 67.0 years, and 58.2 % were women. The median BVAS and sTREM-1 were 12.0 and 467.1 pg/mL. sTREM-1 was significantly correlated with BVAS along with five-factor score, Short-Form 36-Item Health Surveys, and C-reactive protein. In multivariable linear regression analysis, erythrocyte sedimentation rate (standardised β 0.241), and sTREM-1 (standardised β 0.288) were correlated with BVAS. ROC analysis revealed that the cut-off of sTREM-1 for the upper half of BVAS was 474.1 pg/mL. MPA and GPA patients with sTREM-1 ≥474.1 pg/mL exhibited a significantly higher risk for the upper half of BVAS than those without (relative risk 5.932). Multivariable logistic regression analysis demonstrated sTREM-1 ≥474.1 pg/mL (odds ratio 5.662) was associated with the upper half of BVAS.

Conclusion

sTREM-1 reflects the activity of MPA and GPA, suggesting its role as a potential biomarker for assessing disease severity.

Correlation analysis of lung mucosa-colonizing bacteria with clinical features reveals metastasis-associated bacterial community structure in non-small cell lung cancer patients

BACKGROUND

Microbes colonizing lower airways can regulate the host immune profile and consequently participate in lung disease. Increasing evidence indicate that individual microbes promote lung cancer progression and are involved in metastasis incidence. To date, however, no study has revealed the community structure of lung bacteria in metastatic non-small cell lung cancer (NSCLC) patients.

METHODS

We prospectively enrolled 50 healthy subjects and 57 NSCLC patients. All healthy subjects and NSCLC patients underwent bronchoscope procedures for brush specimen collection. The 16 S ribosomal RNA gene was sequenced to characterize the community structure of lung mucosa-colonizing bacteria. The peripheral blood of NSCLC patients was also measured for leukocytes and cancer markers.

RESULTS

The lung bacteria of healthy subjects and NSCLC patients were divided into four communities. All community 2 members showed increased abundance in NSCLC patients compared with healthy subjects, and most community 2 members showed increased abundance in the metastatic NSCLC patients compared with the non-metastatic group. These bacteria were significantly and positively correlated with eosinophils, neutrophils and monocytes in the metastatic NSCLC group. In addition, the correlation between lung bacteria and cancer markers differed between the metastatic and non-metastatic NSCLC patients. Furthermore, bronchoalveolar lavage fluid from lung adenocarcinoma patients directly promoted NSCLC cell migration.

CONCLUSIONS

The community structure of lung mucosa-colonizing bacteria was relatively stable, but changed from the healthy population to NSCLC patients, especially the metastatic group. This distinct community structure and specific correlation with immune cells and cancer markers could help to distinguish NSCLC patients with or without metastasis.

Multiparametric Profiling of Neutrophil Function via a High-Throughput Flow Cytometry-Based Assay

Neutrophils are a vital component of the innate immune system and play an essential function in the recognition and clearance of bacterial and fungal pathogens. There is great interest in understanding mechanisms of neutrophil dysfunction in the setting of disease and deciphering potential side effects of immunomodulatory drugs on neutrophil function. We developed a high throughput flow cytometry-based assay for detecting changes to four canonical neutrophil functions following biological or chemical triggers. Our assay detects neutrophil phagocytosis, reactive oxygen species (ROS) generation, ectodomain shedding, and secondary granule release in a single reaction mixture. By selecting fluorescent markers with minimal spectral overlap, we merge four detection assays into one microtiter plate-based assay. We demonstrate the response to the fungal pathogen, Candida albicans and validate the assay's dynamic range using the inflammatory cytokines G-CSF, GM-CSF, TNFα, and IFNγ. All four cytokines increased ectodomain shedding and phagocytosis to a similar degree while GM-CSF and TNFα were more active in degranulation when compared to IFNγ and G-CSF. We further demonstrated the impact of small molecule inhibitors such as kinase inhibition downstream of Dectin-1, a critical lectin receptor responsible for fungal cell wall recognition. Bruton's tyrosine kinase (Btk), Spleen tyrosine kinase (Syk), and Src kinase inhibition suppressed all four measured neutrophil functions but all functions were restored with lipopolysaccharide co-stimulation. This new assay allows for multiple comparisons of effector functions and permits identification of distinct subpopulations of neutrophils with a spectrum of activity. Our assay also offers the potential for studying the intended and off-target effects of immunomodulatory drugs on neutrophil responses.

The role of triggering receptor expressed on myeloid cells-1 (TREM-1) in central nervous system diseases

Triggering receptor expressed on myeloid cells-1 (TREM-1) is a member of the immunoglobulin superfamily and is mainly expressed on the surface of myeloid cells such as monocytes, macrophages, and neutrophils. It plays an important role in the triggering and amplification of inflammatory responses, and it is involved in the development of various infectious and non-infectious diseases, autoimmune diseases, and cancers. In recent years, TREM-1 has also been found to participate in the pathological processes of several central nervous system (CNS) diseases. Targeting TREM-1 may be a promising strategy for treating these diseases. This paper aims to characterize TREM-1 in terms of its structure, signaling pathway, expression, regulation, ligands and pathophysiological role in CNS diseases.

TREM-1 is required for enhanced OpZ-induced superoxide generation following priming

Inflammatory agents, microbial products, or stromal factors pre-activate or prime neutrophils to respond to activating stimuli in a rapid and aggressive manner. Primed neutrophils exhibit enhanced chemotaxis, phagocytosis, and respiratory burst when stimulated by secondary activating stimuli. We previously reported that Triggering Receptor Expressed on Myeloid cells-1 (TREM-1) mediates neutrophil effector functions such as increased superoxide generation, transepithelial migration, and chemotaxis. However, it is unclear whether TREM-1 is required for the process of priming itself or for primed responses to subsequent stimulation. To investigate this, we utilized in vitro and in vivo differentiated neutrophils that were primed with TNF-α and then stimulated with the particulate agonist, opsonized zymosan (OpZ). Bone marrow progenitors isolated from WT and Trem-1-/- mice were transduced with estrogen regulated Homeobox8 (ER-Hoxb8) fusion transcription factor and differentiated in vitro into neutrophils following estrogen depletion. The resulting neutrophils expressed high levels of TREM-1 and resembled mature in vivo differentiated neutrophils. The effects of priming on phagocytosis and oxidative burst were determined. Phagocytosis did not require TREM-1 and was not altered by priming. In contrast, priming significantly enhanced OpZ-induced oxygen consumption and superoxide production in WT but not Trem-1-/- neutrophils indicating that TREM-1 is required for primed oxidative burst. TREM-1-dependent effects were not mediated during the process of priming itself as priming enhanced degranulation, ICAM-1 shedding, and IL-1ß release to the same extent in WT and Trem-1-/- neutrophils. Thus, TREM-1 plays a critical role in primed phagocytic respiratory burst and mediates its effects following priming.

N-Terminal Peptide of PGLYRP1/Tag7 Is a Novel Ligand for TREM-1 Receptor

An investigation of innate immunity receptors sheds light on the mechanisms of inflammation and associated immune reactions. One of the key immune regulators is the TREM-1 receptor, which is involved in both inflammation and antitumor immune response. In this article, we have obtained a new ligand for the TREM-1 receptor. The peptide, named N3, is a part of the innate immune protein PGLYRP1/Tag7. It is responsible for activating the TREM-1 signaling pathway. Here, we have demonstrated that the N3 peptide acts like other TREM-1 receptor ligands: its binding results in a mild inflammation response and appearance of cytotoxic lymphocytes. We have shown that cytotoxic populations of lymphocytes in N3 peptide-treated PBMCs are similar to those treated with Tag7 or Hsp70. We also determined the part of the N3 peptide responsible for binding to TREM-1. The resulting peptide (N9) consists of nine amino acids and can be considered as a potential peptide that blocks TREM-1 signaling.

Nano-chemically Modified Tetracycline-3 (nCMT-3) Attenuates Acute Lung Injury via Blocking sTREM-1 Release and NLRP3 Inflammasome Activation

BACKGROUND

Intratracheal (IT) lipopolysaccharide (LPS) causes severe acute lung injury (ALI) and systemic inflammation. CMT-3 has pleiotropic anti-inflammatory effects including matrix metalloproteinase (MMP) inhibition, attenuation of neutrophil (PMN) activation, and elastase release. CMT-3's poor water solubility limits its bioavailability when administered orally for treating ALI. We developed a nano-formulation of CMT-3 (nCMT-3) to test the hypothesis that the pleiotropic anti-inflammatory activities of IT nCMT-3 can attenuate LPS-induced ALI.

METHODS

C57BL/6 mice were treated with aerosolized IT nCMT-3 or saline, then had IT LPS or saline administered 2 h later. Tissues were harvested at 24 h. The effects of LPS and nCMT-3 on ALI were assessed by lung histology, MMP level/activity (zymography), NLRP3 protein, and activated caspase-1 levels. Blood and bronchoalveolar lavage fluid (BALF) cell counts, PMN elastase, and soluble triggering receptor expressed on myelocytes-1 (sTREM-1) levels, TNF-α, IL-1β, IL-6, IL-18, and BALF protein levels were also measured.

RESULTS

LPS-induced ALI was characterized by histologic lung injury (PMN infiltration, alveolar thickening, edema, and consolidation) elevated proMMP-2, -9 levels and activity, increased NLRP-3 protein and activated caspase-1 levels in lung tissue. LPS-induced increases in plasma and BALF levels of sTREM-1, TNF-α, IL-1β, IL-6, IL-18, PMN elastase and BALF protein levels demonstrate significant lung/systemic inflammation and capillary leak. nCMT-3 significantly ameliorated all of these LPS-induced inflammatory markers to control levels, and decreased the incidence of ALI.

CONCLUSIONS

Pre-treatment with nCMT3 significantly attenuates LPS-induced lung injury/inflammation by multiple mechanisms including: MMP activation, PMN elastase, sTREM-1 release, and NLRP3 inflammasome/caspase-1 activation.

sTREM-1 promotes the phagocytic function of microglia to induce hippocampus damage via the PI3K-AKT signaling pathway

Soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) is a soluble form of TREM-1 released during inflammation. Elevated sTREM-1 levels have been found in neuropsychiatric systemic lupus erythematosus (NPSLE) patients; yet, the exact mechanisms remain unclear. This study investigated the role of sTREM-1 in brain damage and its underlying mechanism. The sTREM-1 recombinant protein (2.5 μg/3 μL) was injected into the lateral ventricle of C57BL/6 female mice. After intracerebroventricular (ICV) injection, the damage in hippocampal neurons increased, and the loss of neuronal synapses and activation of microglia increased compared to the control mice (treated with saline). In vitro. after sTREM-1 stimulation, the apoptosis of BV2 cells decreased, the polarization of BV2 cells shifted to the M1 phenotype, the phagocytic function of BV2 cells significantly improved, while the PI3K-AKT signal pathway was activated in vivo and in vitro. PI3K-AKT pathway inhibitor LY294002 reversed the excessive activation and phagocytosis of microglia caused by sTREM-1 in vivo and in vitro, which in turn improved the hippocampus damage. These results indicated that sTREM-1 activated the microglial by the PI3K-AKT signal pathway, and promoted its excessive phagocytosis of the neuronal synapse, thus inducing hippocampal damage. sTREM-1 might be a potential target for inducing brain lesions.

Matrix Metalloproteinases on Severe COVID-19 Lung Disease Pathogenesis: Cooperative Actions of MMP-8/MMP-2 Axis on Immune Response through HLA-G Shedding and Oxidative Stress

Patients with COVID-19 predominantly have a respiratory tract infection and acute lung failure is the most severe complication. While the molecular basis of SARS-CoV-2 immunopathology is still unknown, it is well established that lung infection is associated with hyper-inflammation and tissue damage. Matrix metalloproteinases (MMPs) contribute to tissue destruction in many pathological situations, and the activity of MMPs in the lung leads to the release of bioactive mediators with inflammatory properties. We sought to characterize a scenario in which MMPs could influence the lung pathogenesis of COVID-19. Although we observed high diversity of MMPs in lung tissue from COVID-19 patients by proteomics, we specified the expression and enzyme activity of MMP-2 in tracheal-aspirate fluid (TAF) samples from intubated COVID-19 and non-COVID-19 patients. Moreover, the expression of MMP-8 was positively correlated with MMP-2 levels and possible shedding of the immunosuppression mediator sHLA-G and sTREM-1. Together, overexpression of the MMP-2/MMP-8 axis, in addition to neutrophil infiltration and products, such as reactive oxygen species (ROS), increased lipid peroxidation that could promote intensive destruction of lung tissue in severe COVID-19. Thus, the inhibition of MMPs can be a novel target and promising treatment strategy in severe COVID-19.

Peri-Implant Surgical Treatment Downregulates the Expression of sTREM-1 and MMP-8 in Patients with Peri-Implantitis: A Prospective Study

sTREM-1 and its ligand PGLYRP1 play an essential role in the inflammatory process around teeth and implants. In this study, we aimed to evaluate the impact of peri-implant treatment on the salivary levels of the sTREM-1/PGLYRP-1/MMP-8 axis after 3 months. A total of 42 participants (with a mean age of 61 years old ± 7.3) were enrolled in this longitudinal study, 24 having peri-implant mucositis (MU) and 18 having peri-implantitis (PI). Clinical peri-implant parameters, such as probing pocket depth (PPD), % of plaque, and bleeding on probing (BOP), and the whole unstimulated saliva samples were evaluated at baseline and 3 months after treatment. The MU group received nonsurgical peri-implant treatment, while the PI group received open-flap procedures. The levels of sTREM-1, PGLYRP-1, MMP-8, and TIMP-1 were analyzed using enzyme-linked immunosorbent assays. BOP, plaque levels, and PPD significantly reduced after treatment in both groups. A significant decrease in the salivary levels of sTREM-1, MMP-8, and TIMP-1 in the PI group and PGLYRP1 and TIMP-1 in the MU group were observed. Salivary levels of sTREM-1 were significantly reduced in patients with PI but not with MU. Additionally, peri-implant treatment had a significantly higher impact on MMP-8 reduction in patients with PI than in those with MU.

sTREM-1 Predicts Disease Severity and Mortality in COVID-19 Patients: Involvement of Peripheral Blood Leukocytes and MMP-8 Activity

Uncontrolled inflammatory responses play a critical role in coronavirus disease (COVID-19). In this context, because the triggering-receptor expressed on myeloid cells-1 (TREM-1) is considered an intrinsic amplifier of inflammatory signals, this study investigated the role of soluble TREM-1 (sTREM-1) as a biomarker of the severity and mortality of COVID-19. Based on their clinical scores, we enrolled COVID-19 positive patients (n = 237) classified into mild, moderate, severe, and critical groups. Clinical data and patient characteristics were obtained from medical records, and their plasma inflammatory mediator profiles were evaluated with immunoassays. Plasma levels of sTREM-1 were significantly higher among patients with severe disease compared to all other groups. Additionally, levels of sTREM-1 showed a significant positive correlation with other inflammatory parameters, such as IL-6, IL-10, IL-8, and neutrophil counts, and a significant negative correlation was observed with lymphocyte counts. Most interestingly, sTREM-1 was found to be a strong predictive biomarker of the severity of COVID-19 and was related to the worst outcome and death. Systemic levels of sTREM-1 were significantly correlated with the expression of matrix metalloproteinases (MMP)-8, which can release TREM-1 from the surface of peripheral blood cells. Our findings indicated that quantification of sTREM-1 could be used as a predictive tool for disease outcome, thus improving the timing of clinical and pharmacological interventions in patients with COVID-19.

TREM-1 amplifies trophoblastic inflammation via activating NF-κB pathway during preeclampsia

INTRODUCTION

Excessive activation of maternal systemic inflammation is one of the underlying causes of pathology during the disease course of preeclampsia (PE). The triggering receptor expressed on myeloid cells-1 (TREM-1) participates in the development and persistence of inflammation. We hypothesized that dysregulated TREM-1 may be involved in the pathogenesis of PE by promoting the secretion of trophoblastic pro-inflammatory cytokines that augment inflammation.

METHODS

The localization of TREM-1 in placenta and the extravillous trophoblast cell line (TEV-1) was determined by immunohistochemical staining. The expression level of TREM-1 and pro-inflammatory cytokines in placentas were compared between normal pregnancies and PE. We used lipopolysaccharide (LPS) to simulate trophoblastic inflammation. TEV-1 cells were transfected with TREM-1 plasmid and si-TREM-1 respectively, and then were incubated with LPS. The expression levels of pro-inflammatory cytokines and key molecules featured in nuclear transcription factor-kappaB (NF-κB) pathway were detected. Transwell assays were used to detect the effects of TREM-1 on cell migration and invasion.

RESULTS

TREM-1 was localized on both villous trophoblasts (VTs) and extravillous trophoblasts (EVTs). TREM-1 and pro-inflammatory cytokines were up-regulated in preeclamptic placenta. Overexpression of TREM-1 promoted the activation of NF-κB pathway and the release of pro-inflammatory factors induced by LPS, and enhanced migration and invasion of TEV-1 cells. Inhibition of TREM-1 significantly attenuated LPS-induced effects and suppressed migration and invasion.

DISCUSSION

This study suggested that TREM-1 was up-regulated in PE, and may promote the production of downstream inflammatory factors by activating NF-κB pathway in trophoblastic cells, thus exerting pro-inflammatory effects in the pathogenesis of PE.

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.

Influenza sequelae: from immune modulation to persistent alveolitis

Acute influenza virus infections are a global public health concern accounting for millions of illnesses worldwide ranging from mild to severe with, at time, severe complications. Once an individual is infected, the immune system is triggered in response to the pathogen. This immune response can be beneficial ultimately leading to the clearance of the viral infection and establishment of immune memory mechanisms. However, it can be detrimental by increasing susceptibility to secondary bacterial infections and resulting in permanent changes to the lung architecture, in the form of fibrotic sequelae. Here, we review influenza associated bacterial super-infection, the formation of T-cell memory, and persistent lung injury resulting from influenza infection.

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.

Regulation of Salivary Peptidoglycan Recognition Protein 1 in Adolescents

INTRODUCTION

Peptidoglycan recognition protein 1 (PGLYRP1), a member of peptidoglycan recognition proteins, is known to be involved in the proinflammatory response toward bacterial infections. Recently, PGLYRP1 was identified as a ligand for triggering receptor expressed on myeloid cells 1 (TREM-1). Although PGLYRP1 is involved in immune and inflammatory responses, its levels in initial stages of periodontal disease in adolescents are currently unknown.

OBJECTIVES

We aimed to investigate salivary levels of PGLYRP1 and its correlation with TREM-1, polymorphonuclear leukocyte elastase (PMN elastase), and an active matrix metalloproteinase 8 (aMMP-8) in adolescents.

METHODS

Whole saliva samples (n = 537) were collected from 15- to 16-y-old adolescents at Kotka Health Center, Finland, prior to periodontal examination, including measurement of periodontal pocket depth (PPD), visible plaque index (VPI), and bleeding on probing (BOP). Adolescents, clustered as periodontally healthy, gingivitis, or subclinical periodontitis, were tested for salivary levels of TREM-1, PGLYRP1, and PMN elastase by enzyme-linked immunosorbent assay and aMMP-8 by a time-resolved immunofluorometric assay (IFMA).

RESULTS

Salivary levels of PGLYRP1 and aMMP-8 were significantly higher in adolescents with subclinical periodontitis and gingivitis compared to individuals with healthy periodontium. TREM-1 and PMN elastase levels were higher in adolescents with subclinical periodontitis compared to healthy individuals but did not reach significance. PGLYRP1 correlated positively with BOP, PPD, VPI, aMMP-8, and TREM-1.

CONCLUSIONS

Elevated PGLYRP1 levels in adolescents with gingivitis and subclinical periodontitis and its positive correlation with TREM-1 and aMMP-8 may indicate an association of PGLYRP1 with initial stages of periodontal disease. Sex and poor oral hygiene but not smoking are also associated with higher levels of PGLYRP1. However, PGLYRP1 has a lower discriminating capacity and is therefore a less reliable marker alone in the diagnosis of initial stages of periodontal disease in adolescents.

KNOWLEDGE TRANSFER STATEMENT

PGLYRP1, a member of peptidoglycan recognition proteins, is a ligand for TREM-1. Elevated PGLYRP1 levels in adolescents with gingivitis and subclinical periodontitis and its positive correlation with TREM-1 and aMMP-8 may indicate an association of PGLYRP1 with initial stages of periodontal disease. However, it has a lower discriminating capacity and is therefore a less reliable marker alone in the diagnosis of periodontal disease in adolescents.

The modulation of the TREM-1/PGLYRP1/MMP-8 axis in peri-implant diseases

OBJECTIVES

The aim of this study is to investigate the expression of sTREM-1 and its ligand PGLYRP1, as well as the expression of MMP-8 and its inhibitor TIMP-1, in peri-implant diseases. As a secondary aim, we analyzed the influence of the concomitant existence of periodontitis in the expression of these biomarkers.

MATERIALS AND METHODS

This study included 77 patients (29 males and 48 females; mean age 55.0 ± 11.5), 18 having gingivitis, 16 having periodontitis, 20 having mucositis, and 23 having peri-implantitis. Patients were clinically examined, and unstimulated whole saliva was collected. sTREM-1, PGLYRP1, MMP-8, TIMP-1, and MMP-8/TIMP1 ratio were determined by ELISA.

RESULTS

The periodontitis group presented higher probing depth (PD) mean, and higher clinical attachment loss, compared with the other groups. The peri-implantitis group presented higher PD mean in implants compared to the mucositis group. Patients with PD ≥ 6 mm showed significantly higher levels of PGLYRP1, MMP-8, and MMP-8/TIMP-1 ratio than patients with PD < 6 mm. When all four markers were assessed, there were no significant differences between mucositis and peri-implantitis groups. Concomitant periodontitis resulted in higher significant levels of MMP-8 in patients with peri-implant disease.

CONCLUSION

We did not observe significant differences in the levels of the sTREM-1/PGLYRP1/MMP-8 axis between patients with periodontal and peri-implant diseases, suggesting that these markers are also involved in the inflammatory process around implants. Besides, the presence of periodontitis may affect the levels of MMP-8 in patients with peri-implant disease.

CLINICAL RELEVANCE

The sTREM-1/PGLYRP1/MMP-8 axis could be useful as potent markers in periodontal and peri-implant diseases.

Therapeutic Effect of Modulating TREM-1 via Anti-inflammation and Autophagy in Parkinson's Disease

Parkinson’s disease (PD) is one of the most common age-related neurodegenerative diseases, and neuroinflammation has been identified as one of its key pathological characteristics. Triggering receptors expressed on myeloid cells-1 (TREM-1) amplify the inflammatory response and play a role in sepsis and cancer. Recent studies have demonstrated that the attenuation of TREM-1 activity produces cytoprotective and anti-inflammatory effects in macrophages. However, no study has examined the role of TREM-1 in neurodegeneration. We showed that LP17, a synthetic peptide blocker of TREM-1, significantly inhibited the lipopolysaccharide (LPS)-induced upregulation of proinflammatory cascades of inducible nitric oxide synthase (iNOS), cyclooxygenase-2, and nuclear factor-kappa B. Moreover, LP17 enhanced the LPS-induced upregulation of autophagy-related proteins such as light chain-3 and histone deacetylase-6. We also knocked down TREM-1 expression in a BV2 cell model to further confirm the role of TREM-1. LP17 inhibited 6-hydroxydopamine-induced locomotor deficit and iNOS messenger RNA expression in zebrafish. We also observed therapeutic effects of LP17 administration in 6-hydroxydopamine-induced PD syndrome using a rat model. These data suggest that the attenuation of TREM-1 could ameliorate neuroinflammatory responses in PD and that this neuroprotective effect might occur via the activation of autophagy and anti-inflammatory pathways.

Prognostic Value of MMP-9 -1562 C/T Gene Polymorphism in Patients With Sepsis

Introduction:

Matrix metalloproteinase-9 (MMP-9) plays an important role in the pathophysiology of sepsis. A single-nucleotide polymorphism (SNP) at position -1562 (C/T) in the MMP-9 gene has been associated with differential MMP-9 expression, being higher when the -1562 T allele is present. We evaluated the association of the SNP MMP9 -1562 C/T with severity and mortality in patients with sepsis to establish whether the prognosis of the disease is affected.

Materials and Methods:

A case-control study exploratory was carried out in a cohort of infected patients. 540 individuals were selected in total, 270 patients with sepsis and 270 controls (infected but non-septic), classified according to the 2016 consensus (Sepsis-3). The presence of the single-nucleotide polymorphism (SNP; allele T and/or allele C) was determined through analyses of restriction fragment length polymorphism and plasma levels of MMP-9 were determined through enzyme-linked immunosorbent assay immunoassay.

Results:

SNP MMP-9 -1562 has two known alleles (T and C), with predominance of the C over the T allele; in the group of patients with sepsis, T allele was found in 7.2% of cases, while C allele in the rest (92.8%); in comparison, in the group of infected but non-septic patients, frequencies were 9.4% for T allele and 90.6% for the C allele (P = .33). Also, the presence of the polymorphic T allele was not related to the levels of MMP-9 in patients with sepsis in comparison with infected but non-septic patients 780 (397-1375) ng/mL vs 646 (172-1249) ng/mL (P = .64). There was also no association between the SNP and sepsis mortality (P = .78).

Conclusions:

We concluded that there was no association between the SNP MMP9 -1562 C/T and sepsis or between the SNP MMP9 -1562 C/T and sepsis mortality in the Northeastern Colombian septic patient cohort. Further research is needed to clarify the correlation among sepsis, genetic factors with allele T and MMP-9 plasma concentration.

An immunohistochemical study of the diagnostic value of TREM-1 as marker for fatal sepsis cases

Triggering receptor expressed on myeloid cells-1 (TREM-1) is produced and up-regulated by exposure of myeloid cells to lipopolysaccharides or other components of either bacterial or fungal origin, which causes it to be strongly expressed on phagocytes that accumulate in inflamed areas. Because TREM-1 participates in septic shock and in amplifying the inflammatory response to bacterial and fungal infections, we believe it could be an immunohistochemical marker for postmortem diagnosis of sepsis. We tested the anti-TREM-1 antibody in 28 cases of death by septic shock and divided them into two groups. The diagnosis was made according to the criteria of the Surviving Sepsis Campaign. In all cases, blood cultures were positive. The first group was comprised subjects that presented high ante-mortem serum procalcitonin and the soluble form of TREM-1 (s-TREM-1) values. The second group comprised subjects in which s-TREM-1 was not measured ante-mortem. We used samples of brain, heart, lung, liver and kidney for each case to test the anti-TREM-1 antibody. A semiquantitative evaluation of the immunohistochemical findings was made. In lung samples, we found immunostaining in the cells of the monocyte line in 24 of 28 cases, which suggests that TREM-1 is produced principally by cells of the monocyte line. In liver tissue, we found low TREM-staining in the hepatocyte cytoplasm, duct epithelium, the portal-biliary space and blood vessel. In kidney tissue samples, we found the TREM-1 antibody immunostaining in glomeruli and renal tubules. We also found TREM-1 staining in the lumen of blood vessels. Immunohistochemical staining using the anti-TREM-1 antibody can be useful for postmortem diagnosis of sepsis.

Low TREM1 expression in whole blood predicts anti-TNF response in inflammatory bowel disease

BACKGROUND

With the changed therapeutic armamentarium for Crohn's disease (CD) and ulcerative colitis (UC), biomarkers predicting treatment response are urgently needed. We studied whole blood and mucosal expression of genes previously reported to predict outcome to anti-TNF therapy, and investigated if the signature was specific for anti-TNF agents.

METHODS

We prospectively included 54 active IBD patients (24CD, 30UC) initiating anti-TNF therapy, as well as 22 CD patients initiating ustekinumab and 51 patients initiating vedolizumab (25CD, 26UC). Whole blood expression of OSM, TREM1, TNF and TNFR2 was measured prior to start of therapy using qPCR, and mucosal gene expression in inflamed biopsies using RNA-sequencing. Response was defined as endoscopic remission (SES-CD ≤ 2 at week 24 for CD and Mayo endoscopic sub-score ≤ 1 at week 10 for UC).

FINDINGS

Baseline whole blood TREM1 was downregulated in future anti-TNF responders, both in UC (FC = 0.53, p = .001) and CD (FC = 0.66, p = .007), as well as in the complete cohort (FC = 0.67, p < .001). Receiver operator characteristic statistics showed an area under the curve (AUC) of 0.78 (p = .001). A similar accuracy could be achieved with mucosal TREM1 (AUC 0.77, p = .003), which outperformed the accuracy of serum TREM1 (AUC 0.58, p = .31). Although differentially expressed in tissue, OSM, TNF and TNFR2 were not differentially expressed in whole blood. The TREM1 predictive signal was anti-TNF specific, as no changes were seen in ustekinumab and vedolizumab treated patients.

INTERPRETATION

We identified low TREM-1 as a specific biomarker for anti-TNF induced endoscopic remission. These results can aid in the selection of therapy in biologic-naïve patients.

TREM-1; Is It a Pivotal Target for Cardiovascular Diseases?

Cardiovascular diseases (CVDs) are as menacing as ever and still continue to kill adults worldwide, notwithstanding tremendous efforts to decrease their consequent mortality and morbidity. Lately, a growing body of research indicated that inflammation plays a pivotal role in the pathogenesis and complications of CVDs. A receptor of the immunoglobulin superfamily, triggering receptors expressed on myeloid cells-1 (TREM-1) was shown to induce and amplify the inflammation in both acute and chronic disease’ pathogenesis and progression, which hence makes it one of the most important complication factors of CVDs. Thus, studies endeavored to investigate the role played by TREM-1 in CVDs with respect to their etiologies, complications, and possible therapeutics. We examined here, for the first time, the most relevant studies regarding TREM-1 involvement in CVDs. We critically analyzed and summarized our findings and made some suggestions for furtherance of the investigations with the aim to utilize TREM-1 and its pathways for diagnostic, management, and prognosis of CVDs. Overall, TREM-1 was found to be involved in the pathogenesis of acute and chronic cardiovascular conditions, such as acute myocardial infarction (AMI) and atherosclerosis. Although most therapeutic approaches are yet to be elucidated, our present research outcome displays a promising future to utilizing the TREM-1 pathway as a potential target for understanding and managing CVDs.

Toll-like receptor 4 plays an important role to enhance bacterial clearance from the nose in synergy with triggering receptor expressed on myeloid cells (TREM)-1 expression on polymorphonuclear neutrophils

OBJECTIVE

Acute rhinosinusitis (ARS) is among the most common infectious diseases. Neutrophils play a major role in innate host defenses against pathogenic microorganisms such as fungi and bacteria. Recently, in neutrophils, ligation of the triggering receptor expressed on myeloid cells (TREM)-1 was found to activate the full spectrum of neutrophil effector mechanisms, including the release of inflammatory mediators, degranulation, phagocytosis, and oxidative burst in synergy with Toll-like receptors (TLRs). In this study, we investigated the effect of TREM-1 on the functions of neutrophils in relation to TLR4 in a nasal and nasopharyngeal inflammation mouse model via nontypeable Haemophilus influenzae (NTHi) intranasal inoculation.

METHODS

We used C3H/HeJ (TLR4-deficient) mice, which arose spontaneously and have non-functional TLR4 protein, and normal wild-type (WT) C3H/HeN mice. Mice were inoculated intranasally with NTHi (10⁷ cfu/mouse) to investigate the effects of TLR4 on the function of Neutrophils. We examined the kinetics of bacterial clearance and inflammatory cell infiltration in nasal washes at 6, 12, 24, and 72 h after inoculation. The expression of TREM-1 on neutrophils, and TREM-1 mRNA expression in neutrophils in the nasal washes were examined by flow cytometric analysis and RT-PCR.

RESULTS

Bacterial counts of NTHi from nasal washes were significantly lower in WT mice than in TLR4-mutant mice after inoculation. The numbers of inflammatory cells in nasal washes were significantly higher in WT mice at 6 h, 12 h, and 24 h after inoculation than in TLR4-deficient mice. The expression of TREM-1 protein on neutrophils and the mRNA levels were greater in WT mice than in TLR4-mutant mice. The concentrations of soluble TREM-1 in WT nasal washes were also significantly higher than in those of TLR4-deficient mice.

CONCLUSION

TREM-1 may play an important role together with TLR4 in the nasopharyngeal clearance of NTHi by neutrophils. Further studies will need to clarify the innate immune responses of neutrophils via TLR4 to prevent NTHi infection.

Soluble TREM-1 as a predictive factor of neonatal sepsis: a meta-analysis

BACKGROUND

The efficacy of soluble triggering receptor expressed on myeloid cell-1 (TREM-1) in detecting sepsis in adults has already been proven. To date, however, consensus in the field of neonatal sepsis is lacking. The purpose of the present systematic review is to accumulate current evidence in this field.

SEARCH STRATEGY

We systematically searched Medline (1966-2017), Scopus (2004-2017), Clinicaltrials.gov (2008-2017), EMBASE (1980-2017), Cochrane Central Register of Controlled Trials CENTRAL (1999-2017) and Google Scholar (2004-2017) along with reference lists from included studies.

MAIN RESULTS

Eight studies were finally included in the present analysis, with a total number of 667 neonates. The estimated sensitivity for the summary point was 0.95 [95% CI (0.81-0.99)] and the specificity was 0.87 [95% CI (0.56-0.97)]. The diagnostic odds ratio was calculated at 132.49 [95% CI (6.85-2560.70)]. Fagan's nomogram demonstrated that the post-test probability increased to 71% and decreased to 2%, when the pre-test probability was set at 25%. However, significant discrepancy was observed in terms of the used cut-offs; therefore, the sensitivity and specificity presented in our meta-analysis should be reviewed with caution, as they may present an overestimation of the actual predictive efficacy of this protein.

CONCLUSION

Current evidence suggests that sTREM-1 may become a useful biomarker for the prediction of neonatal sepsis. However, the small number of studies and the variation of the threshold values limit its implementation in clinical practice. Future large-scale studies are needed to determine the optimal cut-off value that may discriminate normal levels from those suggestive of the presence of neonatal sepsis.