Expression of TREM-1 mRNA in acute pancreatitis

Blockade of TREM-1 prevents vitreoretinal neovascularization in mice with oxygen-induced retinopathy

In pathological retinal neovascularization (RNV) disorders, the retina is infiltrated by activated leukocytes and macrophages. Triggering receptor expressed on myeloid cells 1 (TREM-1), an inflammation amplifier, activates monocytes and macrophages and plays an important role in cancer, autoimmune and other inflammation-associated disorders. Hypoxia-inducible TREM-1 is involved in cancer angiogenesis but its role in RNV remains unclear. Here, to close this gap, we evaluated the role of TREM-1 in RNV using a mouse model of oxygen-induced retinopathy (OIR). We found that hypoxia induced overexpression of TREM-1 in the OIR retinas compared to that of the room air group. TREM-1 was observed specifically in areas of pathological RNV, largely colocalizing with macrophage colony-stimulating factor (M-CSF) and CD45- and Iba-1-positive cells. TREM-1 blockade using systemically administered first-in-class ligand-independent TREM-1 inhibitory peptides rationally designed using the signaling chain homooligomerization (SCHOOL) strategy significantly (up to 95%) reduced vitreoretinal neovascularization. The peptides were well-tolerated when formulated into lipopeptide complexes for peptide half-life extension and targeted delivery. TREM-1 inhibition substantially downregulated retinal protein levels of TREM-1 and M-CSF suggesting that TREM-1-dependent suppression of pathological angiogenesis involves M-CSF. Targeting TREM-1 using TREM-1-specific SCHOOL peptide inhibitors represents a novel strategy to treat retinal diseases that are accompanied by neovascularization including retinopathy of prematurity.

Postoperative inflammation and insulin resistance in relation to body composition, adiposity and carbohydrate treatment: A randomised controlled study

Background & aims

The aims of this study were to identify whether differences in distribution of adipose tissue and skeletal muscle in obese and non-obese individuals contribute to the magnitude of the postoperative inflammatory response and insulin resistance, with and without preoperative treatment with carbohydrate drinks.

Methods

Thirty-two adults (16 obese/16 non-obese) undergoing elective major open abdominal surgery participated in this 2 × 2 factorial, randomised, double-blind, placebo-controlled study. Participants received Nutricia preOp^® or placebo (800 ml on the night before surgery/400 ml 2–3 h preoperatively) after stratifying for obesity. Insulin sensitivity was measured using the hyperinsulinaemic-euglycaemic clamp preoperatively and on the 1st postoperative day. Vastus lateralis, omental and subcutaneous fat biopsies were taken pre- and postoperatively and analysed after RNA extraction. The primary endpoint was within subject differences in insulin sensitivity.

Results

Major abdominal surgery was associated with a 42% reduction in insulin sensitivity from mean(SD) M value of 37.3(11.8) μmol kg⁻¹ fat free mass (FFM) to 21.7(7.4) μmol kg⁻¹ FFM, but this was not influenced by obesity or preoperative carbohydrate treatment. Activation of the triggering receptor expressed on myeloid cells (TREM1) pathway was seen in response to surgery in omental fat samples. In postoperative muscle samples, gene expression differences indicated activation of the peroxisome proliferator-activated receptor (PPAR-α)/retinoid X-receptor (RXR-α) pathway in obese but not in non-obese participants. There were no significant changes in gene expression pathways associated with carbohydrate treatment.

Conclusion

The reduction in insulin sensitivity associated with major abdominal surgery was confirmed but there were no differences associated with preoperative carbohydrates or obesity.

Expression level of 12-amino acid triggering receptor on myeloid cells-like transcript 1 derived peptide alleviates lipopolysaccharide-induced acute lung injury in mice

Acute lung injury (ALI) is a critical illness with a high morbidity and mortality rate due to severe inflammation in the lungs. The effects and underlying mechanism of the triggering receptor expressed on myeloid cells‑1 (TREM‑1)‑like transcript‑1‑derived peptide (LR12) on ALI remain unclear. The aim of the present study was to determine whether LR12 attenuates lipopolysaccharide (LPS)‑induced ALI and elucidate the mechanism underlying it. Male C57BL/6 mice were randomly assigned to three groups as follows: Sham group, LPS + scramble group and LPS + LR12 group. Normal saline (NS) or LPS was administrated by intratracheal instillation, and NS, LR12 or LR12 scramble was administered intraperitoneally 30 min later. The treatment was repeated every 3 h three times. Mice were sacrificed 24 h later. Pulmonary pathological changes, the lung wet/dry weight ratio, the macrophage and neutrophil counts in bronchoalveolar lavage fluid and myeloperoxidase (MPO) activity in the lung tissues were observed. The inflammatory cytokines were evaluated by enzyme‑linked immunosorbent assay and lung neutrophil infiltration was detected by immunohistochemistry. Nuclear factor (NF)‑κB p65 and TREM‑1 were analyzed by western blotting, and the activation of NF‑κB was detected by electrophoretic mobility shift assay. LPS‑induced pathohistological injury, edema and neutrophil infiltration were significantly alleviated by TREM‑1 inhibitor, LR12. The proinflammatory cytokines [interleukin (IL)‑6, IL‑1β, tumor necrosis factor‑α] and chemokines (keratinocyte chemokine and monocyte chemoattractant protein‑1) were significantly reduced, whereas the anti‑inflammatory cytokines, IL‑10 were significantly increased by LR12. LR12 was identified to significantly decrease p65 expression levels in the nucleus and inhibit the activity of NF‑κB. Furthermore, LR12 alleviated LPS‑induced ALI by reducing the expression of TREM‑1, increasing the release of soluble TREM‑1 and inhibiting activation of the NF-κB signaling pathway.

Novel TREM-1 Inhibitors Attenuate Tumor Growth and Prolong Survival in Experimental Pancreatic Cancer

Pancreatic cancer (PC) is a highly lethal cancer with an urgent need to expand the limited treatment options for patients. Tumor-associated macrophages (TAMs) promote tumor aggressiveness and metastasis. High expression of triggering receptor expressed on myeloid cells 1 (TREM-1) on TAMs directly correlates with poor survival in patients with non-small cell lung cancer (NSCLC). We have previously hypothesized that blockade of TREM-1 could be a promising therapeutic strategy to treat cancer and shown that the novel, ligand-independent TREM-1 inhibitory peptides rationally designed using the signaling chain homooligomerization (SCHOOL) strategy suppress NSCLC growth in vivo. Here, we evaluated the therapeutic potential of these inhibitors in three human PC xenograft mouse models. Administration of SCHOOL peptides resulted in a strong antitumor effect achieving an optimal treatment/control (T/C) value of 19% depending on the xenograft and formulation used and persisting even after treatment was halted. The effect correlated significantly with increased survival and suppressed TAM infiltration. The peptides were well-tolerated when deployed either in free form or formulated into lipopeptide complexes for peptide half-life extension and targeted delivery. Finally, blockade of TREM-1 significantly reduced serum levels of interleukin (IL)-1α, IL-6, and macrophage colony-stimulating factor (M-CSF), but not vascular endothelial growth factor, suggesting M-CSF-dependent antitumor mechanisms. Collectively, these promising data suggest that SCHOOL TREM-1-specific peptide inhibitors have a cancer type independent, therapeutically beneficial antitumor activity and can be potentially used as a stand-alone therapy or as a component of combinational therapy for PC, NSCLC, and other solid tumors.

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.

sTREM-1 in patients with chronic kidney disease on hemodialysis

The triggering receptor expressed on myeloid cells-1 (TREM-1) is a member of the immunoglobulin superfamily. TREM-1 has been implicated as an amplifier of inflammation. Soluble TREM-1 (sTREM-1) was investigated in different clinical conditions, but not in hemodialysis (HD) patients. We aimed to investigate sTREM-1 as a marker of inflammation in HD patients. We investigated 40 CKD patients undergoing chronic HD treatment and 15 controls. Routine laboratory investigations in addition to CRP measured by immunoturbidimetry, TNF- α, and sTREM-1 measured by ELISA were assayed in post-hemodialysis patients' blood samples and in controls' blood samples. CRP, TNF-α, and sTREM-1 levels were significantly higher in HD patients than in controls (p < 0.001 for all). sTREM-1 was positively correlated with CRP and TNF-α (r = +0.50, p < 0.001 and r = +0.53, p < 0.001 respectively). It was negatively correlated with hemoglobin concentration (r = -0.69, p < 0.001). Hemoglobin concentration was the significant predictor of sTREM-1 level (p < 0.001). In conclusion, sTREM-1 level is significantly increased in HD patients as are other pro-inflammatory markers.

Tumor necrosis factor-α regulates triggering receptor expressed on myeloid cells-1-dependent matrix metalloproteinases in the carotid plaques of symptomatic patients with carotid stenosis

OBJECTIVE

To determine the relationship between increased triggering receptor expressed on myeloid cells (TREM)-1 and plaque stability in atherosclerotic carotid stenosis.

METHODS

The mRNA transcripts and protein for TREM-1, MMP-1, MMP-9, collagen type I (COL1A1) and collagen type III (COL3A1) were analyzed by qPCR and immunofluorescence in both tissues and VSMCs isolated from atherosclerotic carotid plaques of symptomatic and asymptomatic patients with carotid stenosis.

RESULTS

The TREM-1, MMP-1 and MMP-9 mRNA transcripts were significantly increased (TREM-1, p < 0.01; MMP-1, p < 0.01 and MMP-9, p < 0.001) while COL1A1 and COL3A1 mRNA transcripts were decreased (p < 0.001) in VSMCs isolated from carotid plaques of symptomatic (S) than asymptomatic (AS) patients. Stimulation of cells with TNF-α further increased the mRNA transcripts of TREM-1, MMPs, COL1A1 and COL3A1. Modulation of TREM-1 by treatment with TREM-1 decoy receptor rTREM-1/Fc, and either TREM-1 antibodies or TREM-1 siRNA attenuated the TNF-α-induced expression of MMP-1 and MMP-9 (p < 0.01) and COL1A1 and COL3A1 (p < 0.01) in S compared to AS VSMCs isolated from carotid plaques. Inhibition of NF-kB (BAY 11-7085), JNK (SP600125) and PI3K (LY294002) signaling pathways decreased the expression of TREM-1 (p < 0.01), MMP-1 (p < 0.001) and MMP-9 (p < 0.01) in TNF-α-treated VSMCs isolated from S carotid plaques compared to AS patients.

CONCLUSION

Increased expression of TREM-1 in S compared to AS patients involving MMP-1 and MMP-9 suggest a potential role of TREM-1 in plaque destabilization. Selective blockade of TREM-1 may contribute to the development of new therapies and promising targets for stabilizing vulnerable atherosclerotic plaques.

High Expression Levels of Trigger Receptor Expressed on Myeloid Cells-1 on Neutrophils Associated with Increased Severity of Acute Pancreatitis in Mice

Triggering receptor expressed on myeloid cells (TREM)-1 expression on neutrophils is associated with inflammation and infection. However, the dynamic changes of the TREM-1 expression on neutrophils have not been clarified in inflammatory acute pancreatitis (AP). The aim of this study was to longitudinally investigate the TREM-1 expression on peripheral blood and peritoneal neutrophils and its relationship with the levels of plasma cytokines and disease severity in a mouse model of AP following injection with varying doses of L-arginine to induce mild AP (MAP) or severe AP (SAP). The results indicated that induction of MAP or SAP was associated with moderate and severe pancreatic tissue damage and varying levels of serum and peritoneal fluid amylase as well as survival rates in mice. In comparison with that in the healthy controls, significantly increased percentages of peripheral blood and peritoneal fluid CD14-TREM-1(+) neutrophils and higher levels of TREM-1 mRNA transcripts in peripheral blood nuclear cells were detected in the MAP and SAP mice, particularly in the SAP mice. Higher levels of plasma tumor necrosis factor (TNF)-α and granulocyte-macrophage colony stimulating factor (GM-CSF), but lower levels of plasma interleukin (IL)-10, were detected in the MAP and SAP mice at varying time points post induction. The percentages of peripheral blood CD14-TREM-1(+) neutrophils were correlated positively with the levels of TNF-α, GM-CSF, and amylase as well as the pathogenic scores, but negatively with the levels of IL-10 in the AP mice. Therefore, TREM-1(+) neutrophils may participate in the pathogenesis of AP and serve as a biomarker for evaluating the severity of AP.

Inactivation of DAP12 in PMN inhibits TREM1-mediated activation in rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by dysregulated and chronic systemic inflammatory responses that affect the synovium, bone, and cartilage causing damage to extra-articular tissue. Innate immunity is the first line of defense against invading pathogens and assists in the initiation of adaptive immune responses. Polymorphonuclear cells (PMNs), which include neutrophils, are the largest population of white blood cells in peripheral blood and functionally produce their inflammatory effect through phagocytosis, cytokine production and natural killer-like cytotoxic activity. TREM1 (triggering receptor expressed by myeloid cells) is an inflammatory receptor in PMNs that signals through the use of the intracellular activating adaptor DAP12 to induce downstream signaling. After TREM crosslinking, DAP12's tyrosines in its ITAM motif get phosphorylated inducing the recruitment of Syk tyrosine kinases and eventual activation of PI3 kinases and ERK signaling pathways. While both TREM1 and DAP12 have been shown to be important activators of RA pathogenesis, their activity in PMNs or the importance of DAP12 as a possible therapeutic target have not been shown. Here we corroborate, using primary RA specimens, that isolated PMNs have an increased proportion of both TREM1 and DAP12 compared to normal healthy control isolated PMNs both at the protein and gene expression levels. This increased expression is highly functional with increased activation of ERK and MAPKs, secretion of IL-8 and RANTES and cytotoxicity of target cells. Importantly, based on our hypothesis of an imbalance of activating and inhibitory signaling in the pathogenesis of RA we demonstrate that inhibition of the DAP12 signaling pathway inactivates these important inflammatory cells.

Relationship between expression of triggering receptor-1 on myeloid cells in intestinal tissue and intestinal barrier dysfunction in severe acute pancreatitis

BACKGROUND

Triggering receptor expressed on myeloid cells-1 (TREM-1) in the intestine was upregulated and correlated with disease activity in inflammatory bowel diseases. Membrane-bound TREM-1 protein is increased in the pancreas, liver and kidneys of patients with severe acute pancreatitis (SAP), suggesting that TREM-1 may act as an important mediator of inflammation and subsequent extra-pancreatic organ injury. This study aimed to investigate the relationship between the expression of TREM-1 in intestinal tissue and intestinal barrier dysfunction in SAP.

METHODS

Sixty-four male Wistar rats were randomly divided into a sham operation group (SO group, n=32) and a SAP group (n=32). A SAP model was established by retrograde injection of 5% sodium deoxycholate into the bile-pancreatic duct. Specimens were taken from blood and intestinal tissue 2, 6, 12, and 48 hours after operation respectively. The levels of D-lactate, diamine oxidase (DAO) and endotoxin in serum were measured using an improved spectro-photometric method. The expression levels of TREM-1, interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) mRNA in terminal ileum were detected by real-time reverse transcription-polymerase chain reaction (RT-PCR). Specimens of the distal ileum were taken to determine pathological changes by a validated histology score.

RESULTS

The serum levels of D-lactate, DAO and endotoxin were significantly increased in each subgroup of SAP compared with the SO group (P<0.01, P<0.05). The expression levels of TREM-1, IL-1β and TNF-α mRNA in the terminal ileum in each subgroup of SAP were significantly higher than those in the SO group (P<0.01, P<0.05). The expression level of TREM-1mRNA was positively correlated with IL-1β and TNF-α mRNA (r=0.956, P=0.044; r=0.986, P=0.015), but the correlation was not found between IL-1β mRNA and TNF-α mRNA (P=0.133). Compared to the SO group, the pathological changes were aggravated significantly in the SAP group.

CONCLUSIONS

The expression level of TREM-1 in intestinal tissue of rats with SAP was elevated, leading to the release of inflammatory mediators and intestinal mucosal injury. This finding indicates that TREM-l might play an important role in the development of intestinal barrier dysfunction in rats with SAP.

A novel ligand-independent peptide inhibitor of TREM-1 suppresses tumor growth in human lung cancer xenografts and prolongs survival of mice with lipopolysaccharide-induced septic shock

Triggering receptor expressed on myeloid cells-1 (TREM-1) amplifies the inflammatory response and plays a role in cancer and sepsis. Inhibition of TREM-1 by short hairpin RNA (shRNA) in macrophages suppresses cancer cell invasion in vitro. In the clinical setting, high levels of TREM-1 expression on tumor-associated macrophages are associated with cancer recurrence and poor survival of patients with non-small cell lung cancer (NSCLC). TREM-1 upregulation on peritoneal neutrophils has been found in human sepsis patients and in mice with experimental lipopolysaccharide (LPS)-induced septic shock. However, the precise function of TREM-1 and the nature of its ligand are not yet known. In this study, we used the signaling chain homooligomerization (SCHOOL) model of immune signaling to design a novel, ligand-independent peptide-based TREM-1 inhibitor and demonstrated that this peptide specifically silences TREM-1 signaling in vitro and in vivo. Utilizing two human lung tumor xenograft nude mouse models (H292 and A549) and mice with LPS-induced sepsis, we show for the first time that blockade of TREM-1 function using non-toxic and non-immunogenic SCHOOL peptide inhibitors: 1) delays tumor growth in xenograft models of human NSCLC, 2) prolongs survival of mice with LPS-induced septic shock, and 3) substantially decreases cytokine production in vitro and in vivo. In addition, targeted delivery of SCHOOL peptides to macrophages utilizing lipoprotein-mimicking nanoparticles significantly increased peptide half-life and dosage efficacy. Together, the results suggest that ligand-independent modulation of TREM-1 function using small synthetic peptides might be a suitable treatment for sepsis and NSCLC and possibly other types of inflammation-associated disorders.

Correlation between soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) expression and endoscopic activity in inflammatory bowel diseases

BACKGROUND

Recently, a triggering receptor expressed on myeloid cells-1 was shown to be upregulated in the intestines of patients with inflammatory bowel diseases.

AIMS

To investigate the relationship between serum soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) level and endoscopic activity in patients with inflammatory bowel diseases.

METHODS

A total of 85 patients with ulcerative colitis and 34 patients with Crohn's disease were prospectively enrolled. Endoscopic disease activity was determined using the Mayo score and the Simplified Endoscopic Activity Score for Crohn's disease.

RESULTS

In ulcerative colitis, sTREM-1 level was correlated more strongly with the endoscopic activity (r=0.498) than the C-reactive protein level (r=0.386) or erythrocyte sedimentation rate (r=0.272), although not superior to the partial Mayo score (r=0.611). Moreover, only sTREM-1 was correlated significantly with the endoscopic activity irrespective of the disease extent. In Crohn's disease, the Simplified Endoscopic Activity Score for Crohn's disease was correlated with both the C-reactive protein level (r=0.585) and erythrocyte sedimentation rate (r=0.474), but not with sTREM-1 level (r=0.097).

CONCLUSIONS

In ulcerative colitis, sTREM-1 level was correlated most closely with the endoscopic disease activity among serum biomarkers, but was not superior to the clinical activity index. Our results suggest that sTREM-1 level may represent a complementary marker for the assessment of endoscopic activity in ulcerative colitis, but not in Crohn's disease.

[Blockade of Triggering receptor expressed on myeloid cells-1 as a new therapy of arthritis]

Triggering receptor expressed on myeloid cells (TREM)-1 belongs to an immunoglobulin super family and is expressed on neutrophils, mature monocytes and macrophages. The engagement of TREM-1 synergizes with several Toll Like Receptors (TLR) activation in amplifying the inflammatory response. TREM-1 blockade using a fusion protein containing murine TREM-1 extracellular domain and human immunoglobulin Fc portion was reported to prevent death in mouse models of microbial peritonitis and protect from organ damage during other inflammatory diseases. There are many reports suggesting the involvement of TREM-1 in the pathogenesis of rheumatoid arthritis. Blockade of TREM-1 could be a new therapeutic target in rheumatoid arthritis without impairing the host defense against microbes. In this report, we outline the role of TREM-1 and the trial of developing anti-rheumatic drugs by targeting its ligand.

Levels of plasma-soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) are correlated with disease activity in rheumatoid arthritis

OBJECTIVE

To determine whether levels of plasma-soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) are elevated in patients with rheumatoid arthritis (RA) and whether levels are correlated with disease activity and other variables.

METHODS

Our study included 71 patients with RA and 50 age- and sex-matched healthy controls. Clinical characteristics and laboratory measures, including erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and 28-joint Disease Activity Score (DAS28) were assessed. Plasma levels of sTREM-1 and tumor necrosis factor-α (TNF-α) were measured by ELISA.

RESULTS

Patients with RA had significantly higher plasma sTREM-1 levels than healthy controls (170.10 ± 84.71 pg/ml vs 97.41 ± 40.64 pg/ml; p < 0.001). In patients with RA, plasma sTREM-1 levels were found to be correlated with DAS28, ESR, CRP, white blood cell counts, neutrophil counts, and plasma TNF-α levels (r = 0.329, p = 0.005; r = 0.241, p = 0.043; r = 0.314, p < 0.001; r = 0.261, p = 0.028; r = 0.278, p = 0.019; and r = 0.313, p = 0.009, respectively). Plasma sTREM-1 levels in patients with active disease status (DAS28 > 3.2) were significantly higher than in those with low disease status (DAS28 ≤ 3.2; 208.89 ± 100.14 pg/ml vs 150.29 ± 68.70 pg/ml; p = 0.005).

CONCLUSION

Patients with RA had higher plasma sTREM-1 levels than healthy controls, and plasma sTREM-1 levels were correlated with disease activity measures, suggesting that plasma sTREM-1 could play a role in the inflammatory process associated with TNF-α, and that it may be a useful disease activity marker in RA.

TREM-1 Promotes Pancreatitis-Associated Intestinal Barrier Dysfunction

Severe acute pancreatitis (SAP) can cause intestinal barrier dysfunction (IBD), which significantly increases the disease severity and risk of mortality. We hypothesized that the innate immunity- and inflammatory-related protein-triggering receptor expressed on myeloid cells-1 (TREM-1) contributes to this complication of SAP. Thus, we investigated the effect of TREM-1 pathway modulation on a rat model of pancreatitis-associated IBD. In this study we sought to clarify the role of TREM-1 in the pathophysiology of intestinal barrier dysfunction in SAP. Specifically, we evaluated levels of serum TREM-1 and membrane-bound TREM-1 in the intestine and pancreas from an animal model of experimentally induced SAP. TREM-1 pathway blockade by LP17 treatment may suppress pancreatitis-associated IBD and ameliorate the damage to the intestinal mucosa barrier.

Soluble triggering receptor expressed on myeloid cells-1 as a new therapeutic molecule in rheumatoid arthritis

Triggering receptor expressed on myeloid cells-1 (TREM-1) is a recently identified cell surface receptor that is expressed mainly on monocytes and neutrophils, and plays an important role as an amplifier of inflammatory response in acute and chronic inflammatory conditions. Recent studies suggested that TREM-1 contributes to the pathogenesis of rheumatoid arthritis (RA) and therefore TREM-1 could be a new therapeutic target in RA. In addition to its membrane-bound form, a soluble form of TREM-1 (sTREM-1) exists that is liberated by the proteolytic cleavage of membrane-bound form. This soluble form works as decoy receptor to prevent the binding of its ligand to membrane-bound TREM-1 and to inhibit the effect of TREM-1 activation. Proteolytic cleavage of TNF receptor (TNFR) has been reported and soluble TNFR are capable of binding and neutralizing TNF, thus working as natural TNF antagonist. Currently, etanercept, a soluble TNF-receptor fusion protein has been widely used to treat RA. In this report, we suggest that sTREM-1 can be used as a new therapeutic molecule in RA.

Triggering receptor expressed on myeloid cell 1

Sepsis is a common cause of morbidity and mortality in intensive care units. There is no gold standard for diagnosing sepsis because clinical and laboratory signs are neither sensitive nor specific enough and microbiological studies often show negative results. The triggering receptor expressed on myeloid cell 1 (TREM-1) is a member of the immunoglobulin superfamily. Its expression is upregulated on phagocytic cells in the presence of bacteria or fungi. This article reports on the potential usefulness of the assessment of the soluble form of TREM-1 in biologic fluids in the diagnosis of infection.

Expression and function of triggering receptor expressed on myeloid cells-1 (TREM-1) on canine neutrophils

The dog is both a valued veterinary species and a widely used translational model for sepsis research. However, relatively little work has been performed evaluating potential biomarkers present during canine infection. Triggering receptor expressed on myeloid cells-1 (TREM-1) has shown promise as a biomarker for infection and pneumonia in humans. Here we describe, for the first time, the expression and function of the canine orthologue of TREM-1. Expression of TREM-1 on canine neutrophils is significantly up-regulated by stimulation with microbial agonists of TLR2/6, TLR1/2, and TLR4/MD2. Kinetics of TREM-1 protein up-regulation are rapid, with significant increases observed within 2 hr of neutrophil activation. Functionally, canine TREM-1 synergistically enhances LPS-induced production of IL-8, TNF-α and a canine orthologue of CXCL1. Collectively, these data suggest that TREM-1 expression in dogs, as it is in humans, is an amplifier of pro-inflammatory responses to microbial products. These results have direct application to veterinary diagnostics as well as the potential to enhance the utility of canine disease models in the assessment of potential therapeutics in the treatment of human sepsis.

Relationships between genetic polymorphisms of triggering receptor expressed on myeloid cells-1 and inflammatory bowel diseases in the Korean population

AIMS

Triggering receptor expressed on myeloid cells-1 (TREM-1) has been shown to play a crucial role in the propagation of inflammatory responses. Recent studies have reported that TREM-1 expression is up-regulated in patients with inflammatory bowel disease (IBD). Therefore, we investigated the associations between TREM-1 genetic polymorphisms and IBD development and its phenotypes in the Korean population.

MAIN METHODS

Three TREM-1 single nucleotide polymorphisms (SNPs, rs2234237, rs3789205, and rs9471535) were genotyped by Taqman technology on 202 Crohn's disease (CD), 265 ulcerative colitis (UC), 138 with intestinal Behcet's disease (BD), and 234 healthy controls and the relationships between these SNPs and IBD development and phenotypes were evaluated.

KEY FINDINGS

We found that TREM-1 SNPs are significantly associated with the development of intestinal Behcet's disease (rs9471535: odds ratio [OR]=1.637, P=0.025; rs3789205: OR=1.668, P=0.019; rs2234237: OR=1.691, P=0.016), and in particular with skin involvement (rs9471535: OR=2.723, P=0.009; rs3789205: OR=2.477, P=0.017; rs2234237: OR=2.278, P=0.030) and the risk of azathioprine use (rs9471535: OR=2.722, P=0.021; rs3789205: OR=2.493, P=0.032; rs2234237: OR=2.638, P=0.026). However, TREM-1 SNPs were not significantly associated with the development of Crohn's disease or ulcerative colitis.

SIGNIFICANCE

The results of our study suggest that TREM-1 SNPs may play a significant role in the development of intestinal Behcet's disease and may have modest effects on disease severity.

TNF-alpha promotes LPA1- and LPA3-mediated recruitment of leukocytes in vivo through CXCR2 ligand chemokines

Lysophosphatidic acid (LPA) is a bioactive lysophospholipid present in low concentrations in serum and biological fluids but in high concentrations at sites of inflammation. LPA evokes a variety of cellular responses via binding to and activation of its specific G protein-coupled receptors (GPCR), namely LPA(1-6). Even though LPA is a chemoattractant for inflammatory cells in vitro, such a role for LPA in vivo remains largely unexplored. In the present study, we used the murine air pouch model to study LPA-mediated leukocyte recruitment in vivo using selective LPA receptor agonist/antagonist and LPA(3)-deficient mice. We report that 1) LPA injection into the air pouch induced leukocyte recruitment and that both LPA(1) and LPA(3) were involved in this process; 2) LPA stimulated the release of the pro-inflammatory chemokines keratinocyte-derived chemokine (KC) and interferon-inducible protein-10 (IP-10) in the air pouch; 3) tumor necrosis factor-α (TNF-α) injected into the air pouch prior to LPA strongly potentiated LPA-mediated secretion of cytokines/chemokines, including KC, IL-6, and IP-10, which preceded the enhanced leukocyte influx; and 4) blocking CXCR2 significantly reduced leukocyte infiltration. We suggest that LPA, via LPA(1) and LPA(3) receptors, may play a significant role in inducing and/or sustaining the massive infiltration of leukocytes during inflammation.

Serum soluble triggering receptor expressed on myeloid cells-1 in acute respiratory distress syndrome: a prospective observational cohort study

Background/Purpose

Serum soluble triggering receptor expressed on myeloid cells-1 (sTREM-1), a detector of acute inflammatory response to microbial products and a good marker for diagnosing sepsis and pneumonia, has not yet been described as a predictor for infection or a prognostic factor in patients with acute respiratory distress syndrome (ARDS).

Methods

This prospective observational cohort study enrolled 63 ventilated adult patients with ARDS; 50 as septic and 13 as non-septic, and followed them for 28 days in intensive care units at a university hospital in Taiwan. Serial serum sTREM-1 levels and cytokines, such as interleukin (IL)-1, IL-8, and tumor necrosis factor-α, on days 1, 3, 5, 7 and 14 were measured by an enzyme-linked immunosorbent assay. The association between biomarkers and clinical infectious diagnosis/outcome in ARDS was explored.

Results

Serum sTREM-1 and cytokine levels could not differentiate septic from non-septic ARDS. Serum log sTREM-1 and inflammatory cytokine levels were correlated positively (r = 0.325 for IL-1β; r = 0.247 for IL-8; r = 0.480 for tumor necrosis factor-α). As prognostic factors, higher serum sTREM-1 level on day 1 and increasing levels over time, especially in the first 5 days, were independent predictors of mortality on day 28, using a multivariate Cox regression model. Serum sTREM-1 levels remained stable or even increased in the non-surviving patients, but decreased in the survivors.

Conclusion

Serum sTREM-1 level might not be a reliable marker for infection in ARDS patients. However, as an inflammatory marker, initial serum sTREM-1 level and its trend over time, especially in the first 5 days, could be predictive of short-term mortality. A progressive decline in serum sTREM-1 levels during follow-up indicates a favorable outcome, whereas persistently elevated sTREM-1 indicates a poor prognosis and should lead to a re-evaluation of therapy.

Triggering receptor expressed on myeloid cells-1 as a new therapeutic target during inflammatory diseases

The Triggering Receptor Expressed on Myeloid cells (TREM)-1 is a recently identified molecule involved in monocytic activation and inflammatory response. It belongs to a family related to Natural Killer cell-receptors and is expressed on neutrophils, mature monocytes and macrophages. The engagement of TREM-1 synergizes with several Toll Like Receptors (TLR) and/or NOD Like Receptors (NLR) activation in amplifying the inflammatory response mediated by microbial components or danger signals. The implication of TREM-1 during experimental models of acute or chronic inflammatory conditions, as well as during cancer, begins to understand. Furthermore, the modulation of the TREM-1 signaling pathway by the use of small synthetic peptides derived from its extracellular moiety confers interesting survival advantages during experimental murine septic shock and protects from organ damage during other inflammatory diseases. This review summarizes the recent advances on TREM-1 biology and highlights the promises of its therapeutic modulation.

Amniotic fluid sTREM-1 in normal pregnancy, spontaneous parturition at term and preterm, and intra-amniotic infection/inflammation

OBJECTIVE

Intra-amniotic infection/inflammation (IAI) is one of the most important mechanisms of disease in preterm birth. Triggering receptor expressed on myeloid cells (TREM)- 1 is a transmembrane glycoprotein expressed by neutrophils, macrophages and mature monocytes. TREM-1 is upregulated in biological fluids and tissues infected by Gram (+) and Gram (-) bacteria and fungi, amplifies the production of pro-inflammatory cytokines and chemokines, and its soluble form (sTREM-1) is released in the presence of infection. The aim of this study was to determine the effect of gestational age, parturition (term and preterm) and IAI in the amniotic fluid (AF) concentrations of sTREM-1.

STUDY DESIGN

This cross-sectional study included 434 patients in the following groups: (1) mid-trimester of pregnancy (14-18 weeks, n = 38); (2) normal pregnant women at term with (n = 39) and without (n = 39) labor; (3) patients with spontaneous preterm labor (PTL) and intact membranes classified into: (a) PTL who delivered at term (n = 99); (b) PTL who delivered preterm (<37 weeks gestation) without IAI (n = 80); and (c) PTL with IAI (n = 59); and (4) women with preterm prelabor rupture of membranes (PROM) with (n = 40) and without (n = 40) IAI. The AF concentration of sTREM-1 was determined by enzyme-linked immunoassay. Non-parametric statistics were used for analyses.

RESULTS

(1) sTREM-1 was detected in all the AF samples; (2) the median AF sTREM-1 concentration at term was higher than in the mid-trimester (4277.6 pg/ml vs. 1140.4 pg/ml; p < 0.001); (3) among patients with PTL, the median AF sTREM-1 concentration was higher in patients with IAI than in those without IAI (6154.4 pg/ml vs. 3282.8 pg/ml; p < 0.001) and those with PTL who delivered at term (6154.4 pg/ml vs. 2794 pg/ml; p < 0.001); (4) patients with preterm PROM with IAI had a higher median AF sTREM-1 concentration than those without IAI (7893.1 pg/ml vs. 3386.6 pg/ml; p < 0.001); (5) no differences were observed in the median AF sTREM-1 concentration between patients with spontaneous labor at term and those at term not in labor (4712.4 pg/ml vs. 4277.6 pg/ml; respectively p = 0.4); and 6) an AF sTREM-1 concentration >or=6416 pg/ml (derived from a ROC curve) had a sensitivity of 72% and a specificity of 89% for the diagnosis of intra-amniotic infection.

CONCLUSIONS

sTREM-1 is a physiologic constituent of the AF, and its concentration: (1) is significantly elevated in the presence of IAI; (2) increases with advancing gestation; and (3) does not change in the presence of spontaneous labor at term. We propose that sTREM-1 play a role in the innate immune response against intra-amniotic infection.

Role of triggering receptor expressed on myeloid cells-1 in experimental severe acute pancreatitis

BACKGROUND/PURPOSE

Triggering receptor expressed on myeloid cells-1 (TREM-1) is a regulator of immunity and an amplifier of inflammatory signaling. The aim was to clarify the role of TREM-1 in the pathophysiology of experimental severe acute pancreatitis (SAP).

METHODS

SAP was induced by retrograde injection of 3 and 20% sodium deoxycholate (DCA) into the biliopancreatic ducts in rats (DCA pancreatitis). Soluble TREM-1 levels in serum, ascitic fluid, pancreas, liver and kidney were determined with an established available enzyme-linked immunosorbent assay (ELISA) kit. To clarify the source of soluble TREM-1 in serum and ascitic fluid, peritoneal macrophage depletion was done. Moreover, the effect of blockade of TREM-1 pathway was examined using LP17 (a synthetic TREM-1 inhibitor).

RESULTS

Soluble TREM-1 levels in serum and ascitic fluid were higher in SAP. Membrane-bound TREM-1 protein was increased in pancreas, liver and kidney in SAP. Peritoneal macrophage depletion resulted in the reduction of soluble TREM-1 levels in serum and ascitic fluid. Pretreatment with LP17 improved the hepatic and renal dysfunction (serum aspartate aminotransferase and blood urea nitrogen levels) in SAP.

CONCLUSIONS

TREM-1 may act as an important mediator for inflammation and organ injury in SAP. TREM-1 may be a potential therapeutic target for the development of SAP and associated organ dysfunction.

TREM-1 expression is increased in the synovium of rheumatoid arthritis patients and induces the expression of pro-inflammatory cytokines

OBJECTIVES

To investigate the expression and function of triggering receptor expressed on myeloid cells-1 (TREM-1) in the synovium of human RA patients as well as the level of soluble TREM-1 in the plasma of RA patients.

METHODS

Twenty-four RA synovial samples were analysed by gene expression oligonucleotide microarrays. Expression levels of TREM-1 mRNA in murine CIA paws were determined by quantitative PCR (qPCR). TREM-1 protein expression was detected by immunohistochemistry in five RA synovial samples and two OA synovial samples. TREM-1-positive cells from five RA synovial tissues were analysed by FACS staining to determine the cell type. Activation of TREM-1 was tested in five RA synovial samples. Soluble TREM-1 was measured in serum from 32 RA patients.

RESULTS

The expression of TREM-1 mRNA was found to increase 6.5-fold in RA synovial samples, whereas it was increased 132-fold in CIA paws. Increased numbers of TREM-1-positive cells were seen in RA synovium sections and these cells co-expressed CD14. Using a TREM-1-activating cross-linking antibody in RA synovial cultures, multiple pro-inflammatory cytokines were induced. The average amount of soluble TREM-1 in plasma from RA patients was found to be higher than that in plasma from healthy volunteers.

CONCLUSIONS

These findings suggest that the presence of high levels of functionally active TREM-1 in RA synovium may contribute to the development or maintenance of RA, or both. Inhibiting TREM-1 activity may, therefore, have a therapeutic effect on RA. High levels of soluble TREM-1 in the plasma of RA patients compared with healthy volunteers may indicate disease activity.

Monocyte TREM-1 membrane expression in non-infectious inflammation

Sterile or non-infectious inflammation and severe infection are accompanied by very similar events. Damage (or danger)-associated molecular patterns and pathogen-associated molecular patterns trigger the release of inflammatory mediators and modulate the expression of cell surface receptors. The increased expression on monocytes and neutrophils of triggering receptor expressed on myeloid cells 1 is a hallmark of both infectious and non-infectious inflammation.

Triggering receptor expressed on myeloid cells-1 expression on monocytes is associated with inflammation but not with infection in acute pancreatitis

Introduction

Acute pancreatitis (AP) is usually a mild and self-limiting disease, but some patients develop a severe form that is associated with high mortality. In AP, local inflammation is followed first by the systemic inflammatory response syndrome and then by the compensatory anti-inflammatory response syndrome, which is defined by low human leukocyte antigen (HLA)-DR expression on monocytes, increased concentration of the anti-inflammatory cytokine IL-10, and decreased monocyte function. Our aim was to measure the expression of triggering receptor expressed on myeloid cells (TREM)-1 (a proposed marker of infection or inflammation) and HLA-DR on monocytes, and the serum concentrations of IL-6 (a proinflammatory cytokine) and IL-10 in patients with AP to determine whether these markers can identify patients at high risk of developing severe AP or infection.

Methods

Fifty healthy volunteers, 18 patients with mild AP, and 11 patients with severe AP were included in this study. Samples were taken at admission and one and three days later. TREM-1 and HLA-DR expression was evaluated by flow cytometry, and soluble TREM-1, IL-6 and IL-10 concentrations were measured by ELISA.

Results

TREM-1 expression was higher in patients with AP than in healthy volunteers, but there was no difference between patients with mild and severe AP. TREM-1 expression was not associated with mortality or with the presence of infection. Soluble TREM-1 concentration in serum was higher in non-survivors than in survivors. HLA-DR expression was lower and IL-6 concentration higher in patients with severe AP and in infected patients.

Conclusions

Increased TREM-1 expression was associated with the presence of inflammation but not infection in AP. In patients with AP, low HLA-DR expression and high IL-6 concentration could predict severity and infection in samples taken shortly after admission.

TREM and TREM-like receptors in inflammation and disease

Since the discovery of triggering receptor expressed on myeloid cells (TREM)-1 in 2000, evidence documenting the profound ability of the TREM and TREM-like receptors to regulate inflammation has rapidly accumulated. Monocytes, macrophages, myeloid dendritic cells, plasmacytoid dendritic cells, neutrophils, microglia, osteoclasts, and platelets all express at least one member of the TREM family, underscoring the importance of these proteins in the regulation of innate resistance. Recent work on the TREM family includes: characterization of a new receptor expressed on plasmacytoid dendritic cells; definition of a key role for TREM in inflammatory bowel disease and multiple sclerosis; an expanded list of diseases associated with the release of soluble forms of TREM proteins; and identification of the first well characterized TREM ligand: B7-H3, a ligand for TREM-like Transcript (TLT)-2. Moreover, analysis of TREM signaling has now identified key regulatory components and defined pathways that may be responsible for the complex functional interactions between the TREM and toll-like receptors. In addition, there is expanding evidence of a role for TREM in the regulation of integrin function via Plexin-A1. Together these new findings define the TREM and TREM-like receptors as pluripotent modifiers of disease through the integration of inflammatory signals with those associated with leukocyte adhesion.

Increased levels of soluble triggering receptor expressed on myeloid cells-1 in patients with acute pancreatitis

OBJECTIVE

To determine the contribution of triggering receptor expressed on myeloid cells (TREM)-1 in acute pancreatitis (AP).

DESIGN

Prospective study.

SETTING

General intensive care unit at Kobe University Hospital.

PATIENTS

Forty-eight patients with AP and seven patients as control.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We measured serum concentrations of soluble TREM-1 (sTREM-1) at the time of admission by enzyme-linked immunoadsorbent assay. Serum sTREM-1 levels increased significantly in AP (63 +/- 11 pg/mL) and correlated with Ranson score (R = .628, p < .001) and Acute Physiology and Chronic Health Evaluation II score (R = .504, p < .001). Serum TREM-1 levels were higher in patients with early organ dysfunction (which occurred within 7 days after onset) than those without early organ dysfunction (101 +/- 19 vs. 25 +/- 4 pg/mL, p < .001). Incidences of early organ dysfunction in patients whose serum sTREM-1 levels were < or = 40 and > 40 pg/mL were 17% and 83%, respectively (p < .001). The usefulness of serum sTREM-1 in detecting early organ dysfunction was superior to that of C-reactive protein, interleukin-6, interleukin-8, Ranson score, and Acute Physiology and Chronic Health Evaluation II score. Serum sTREM-1 levels decreased with resolution of early organ dysfunction.

CONCLUSIONS

Serum sTREM-1 levels were significantly increased and correlated with disease severity and early organ dysfunction in patients with AP. Serum sTREM-1 level may be a useful marker for early organ dysfunction in AP.

The increased expression of TREM-1 on monocytes is associated with infectious and noninfectious inflammatory processes

BACKGROUND

Inflammation is the response of an organism to tissue injury or infection. It is usually limited to the affected tissue, but sometimes the inflammatory mediators reach the bloodstream and act systemically. A compensatory anti-inflammatory response syndrome, in which expression of major histocompatibility complex class II (MHC-II) molecules are decreased, regulates the resulting systemic inflammatory response syndrome (SIRS). SIRS and compensatory anti-inflammatory response syndrome can lead to the development of sepsis. Triggering receptor expressed on myeloid cells (TREM)-1 has been proposed as a biomarker of the presence of sepsis. In this study, we investigated whether TREM-1 is increased only in septic patients, and not in patients with systemic inflammatory response but no infection. We also looked for a possible correlation between TREM-1 and MHC-II expression levels and the patients' progress.

MATERIALS AND METHODS

Fifty-eight surgical patients, 14 septic patients and 50 healthy volunteers, were included in this study. TREM-1 and MHC-II expression on blood monocytes was determined by flow cytometry.

RESULTS

TREM-1 expression was increased in all patients after surgery, and its expression was higher in patients with preexisting SIRS. No association was found with the presence of infection. In septic patients, the increase in TREM-1 expression was transitory. MHC-II expression was decreased in both surgical and septic patients, and this decrease was greater in patients with a worse outcome.

CONCLUSIONS

Increased TREM-1 expression on monocytes is associated with both infectious and noninfectious inflammatory processes, and the levels of MHC-II expression is better correlated with the patient outcome.

Expression of triggering receptor on myeloid cell 1 and histocompatibility complex molecules in sepsis and major abdominal surgery

AIM

To evaluate the surface expression of triggering receptor on myeloid cell 1 (TREM-1), class II major histocompatibility complex molecules (HLA-DR), and the expression of the splicing variant (svTREM-1) of TREM-1 in septic patients and those subjected to major abdominal surgery.

METHODS

Using flow cytometry, we examined the surface expression of TREM-1 and HLA-DR in peripheral blood monocytes from 11 septic patients, 7 elective gastrointestinal surgical patients, and 10 healthy volunteers. svTREM-1 levels were analyzed by RT-PCR.

RESULTS

Basal expression of TREM-1 and HLA-DR in healthy volunteers was 35.91+/-14.75 MFI and 75.8+/-18.3%, respectively. In septic patients, TREM-1 expression was 59.9+/-23.9 MFI and HLA-DR expression was 44.39+/-20.25%, with a significant difference between healthy and septic groups (P<0.05) for both molecules. In the surgical patients, TREM-1 and HLA-DR expressions were 56.8+/-20.85 MFI and 71+/-13.8% before surgery and 72.65+/-29.92 MFI and 72.82+/-22.55% after surgery. TREM-1 expression was significantly different (P = 0.0087) between the samples before and after surgery and svTREM-1 expression was 0.8590+/-0.1451 MF1, 0.8820+/-0.1460 MF1, and 2.210+/-0.7873 MF1 in the healthy, surgical (after surgery) and septic groups, respectively. There was a significant difference (P = 0.048) in svTREM-1 expression between the healthy and surgical groups and the septic group.

CONCLUSION

TREM-1 expression is increased during systemic inflammatory conditions such as sepsis and the postoperative phase. Simultaneous low expression of HLA-DR molecules correlates with the severity of illness and increases susceptibility to infection. Additionally, TREM-1 expression is distinctly different in surgical patients at different stages of the inflammatory response before and after surgery. Thus, surface TREM-1 appears to be an endogenous signal during the course of the inflammatory response. svTREM-1 expression is significantly increased during sepsis, appearing to be an indicator of severity of illness. Together, these data indicate that TREM-1 may play an important role in establishing and amplifying the systemic inflammatory response. TREM-1, HLA-DR, and svTREM-1 expression analysis can provide useful diagnostic and prognostic indicators during SIRS, CARS, and sepsis.

Intrapulmonary, adenovirus-mediated overexpression of KARAP/DAP12 enhances fungal clearance during invasive aspergillosis

Herein, we report that the intrapulmonary delivery of an adenovirus vector expressing KARAP/DAP12, an adaptor protein expressed in granulocytes and mononuclear cells, enhanced fungal clearance during experimental invasive pulmonary aspergillosis in neutropenic mice.