Human autoinflammatory disease reveals ELF4 as a transcriptional regulator of inflammation.

Transcription factors specialized to limit the destructive potential of inflammatory immune cells remain ill-defined. We discovered loss-of-function variants in the X-linked ETS transcription factor gene ELF4 in multiple unrelated male patients with early onset mucosal autoinflammation and inflammatory bowel disease (IBD) characteristics, including fevers and ulcers that responded to interleukin-1 (IL-1), tumor necrosis factor or IL-12p40 blockade. Using cells from patients and newly generated mouse models, we uncovered ELF4-mutant macrophages having hyperinflammatory responses to a range of innate stimuli. In mouse macrophages, Elf4 both sustained the expression of anti-inflammatory genes, such as Il1rn, and limited the upregulation of inflammation amplifiers, including S100A8, Lcn2, Trem1 and neutrophil chemoattractants. Blockade of Trem1 reversed inflammation and intestine pathology after in vivo lipopolysaccharide challenge in mice carrying patient-derived variants in Elf4. Thus, ELF4 restrains inflammation and protects against mucosal disease, a discovery with broad translational relevance for human inflammatory disorders such as IBD.

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.

Anticytokine Agents: Targeting Interleukin Signaling Pathways for the Treatment of Atherothrombosis

The recognition that atherosclerosis is a complex chronic inflammatory disorder mediated through both adaptive and innate immunity has led to the hypothesis that anticytokine therapies targeting specific IL (interleukin) signaling pathways could serve as powerful adjuncts to lipid lowering in the prevention and treatment of cardiovascular disease. Cytokines involved in human atherosclerosis can be broadly classified as proinflammatory and proatherogenic (such as IL-1, IL-6, and TNF [tumor necrosis factor]) or as anti-inflammatory and antiatherogenic (such as IL-10 and IL-1rA). The recent CANTOS (Canakinumab Anti-Inflammatory Thrombosis Outcomes Study) has shown that specific targeting of IL-1ß can significantly reduce cardiovascular event rates without lipid or blood pressure lowering. In CANTOS, the magnitude of benefit of this cytokine-targeted approach to atherosclerosis treatment was associated to the magnitude of reduction of the central signaling cytokine IL-6 and the downstream clinical biomarker high-sensitivity CRP (C-reactive protein). By contrast, in the recent CIRT (Cardiovascular Inflammation Reduction Trial), low-dose methotrexate neither reduced IL-1ß, IL-6, or high-sensitivity CRP nor lowered cardiovascular event rates. Taken together, these 2 contemporary trials provide proof of principle that focused cytokine inhibition, not broad-spectrum anti-inflammatory therapy, is likely to be crucial for atheroprotection. This review provides an overview of cytokines in atherosclerosis, the potential benefits and risks associated with targeted anticytokine therapies, and a look to the future of clinical practices addressing residual inflammatory risk.

Protein PGLYRP1/Tag7 Peptides Decrease the Proinflammatory Response in Human Blood Cells and Mouse Model of Diffuse Alveolar Damage of Lung through Blockage of the TREM-1 and TNFR1 Receptors.

Infection caused by the severe acute respiratory syndrome coronavirus (SARS-CoV-2) in many cases is accompanied by the release of a large amount of proinflammatory cytokines in an event known as "cytokine storm", which is associated with severe coronavirus disease 2019 (COVID-19) cases and high mortality. The excessive production of proinflammatory cytokines is linked, inter alia, to the enhanced activity of receptors capable of recognizing the conservative regions of pathogens and cell debris, namely TLRs, TREM-1 and TNFR1. Here we report that peptides derived from innate immunity protein Tag7 inhibit activation of TREM-1 and TNFR1 receptors during acute inflammation. Peptides from the N-terminal fragment of Tag7 bind only to TREM-1, while peptides from the C-terminal fragment interact solely with TNFR1. Selected peptides are capable of inhibiting the production of proinflammatory cytokines both in peripheral blood mononuclear cells (PBMCs) from healthy donors and in vivo in the mouse model of acute lung injury (ALI) by diffuse alveolar damage (DAD). Treatment with peptides significantly decreases the infiltration of mononuclear cells to lungs in animals with DAD. Our findings suggest that Tag7-derived peptides might be beneficial in terms of the therapy or prevention of acute lung injury, e.g., for treating COVID-19 patients with severe pulmonary lesions.

TREM-1-targeting LP17 attenuates cerebral ischemia-induced neuronal injury by inhibiting oxidative stress and pyroptosis.

Stroke ranks as the second leading cause of disability and death globally. Trigger receptors expressed on myeloid cells (TREM) -1 are responsible for the activation of the innate immune response and also play a critical role in inflammation. In this study, we reported the contribution of TREM-1 after ischemic damage in a rat middle cerebral artery occlusion (MCAO) model. This study also demonstrated that TREM-1 expression was upregulated following cerebral infarction in rats. TREM-1 inhibition was determined using its selective inhibitor, LP17, which indicated a neuroprotective effect on cerebral infarction damage. The findings revealed that inhibition of TREM-1 by administering LP17 improved cerebral damage and decreased ischemic areas and brain water contents. Moreover, LP17 decreased MCAO-induced microglial activation and neurodegeneration, evidenced by a reduction in the expression of microglial Iba-1 and FJ-B positive cells, and reversed neuronal loss. Besides, the contribution of LP17 to ischemic neuronal damage may be associated with a decrease in the production of pro-inflammatory cytokines, and enhanced production of anti-inflammatory cytokine IL-10. Both in vivo and in vitro studies showed that inhibiting TREM-1 attenuated ROS accumulation, lipid per-oxidation (LPO) contents such as malondialdehyde (MDA) and enhanced the superoxide dismutase (SOD) activity after ischemia. Inhibiting TREM-1 alleviated inflammation and pyroptosis found in MCAO rats. This was achieved through the inhibition of the levels of NLRP3, caspase-1, ASC (an apoptosis-associated speck-like protein containing a CARD) and gasdermin D. These results confirmed that inhibiting TREM-1 protects against ischemia-induced neuronal damage and alleviates microglial mediated neuro-inflammation by reducing oxidative stress and pyroptosis. Therefore, blocking TREM-1 expression provides an effective intervention for improving ischemic stroke.

Pravastatin sodium attenuated TREM-1-mediated inflammation in human peripheral blood mononuclear cells.

Pravastatin sodium on triggering receptor expressed on myeloid cell-1 (TREM-1)-mediated inflammation in human peripheral blood mononuclear cells (PBMCs) has been poorly investigated. In this study, we isolated PBMCs from the peripheral blood samples of patients with chronic obstructive pulmonary disease, treated the cells with pravastatin sodium, and determined a concentration at which more than 90% cells could survive. Then we treated cells with 10 ng/ml of lipopolysaccharide, added with 10, 50, 100 µM of pravastatin sodium combined with or without LR-12, a known TREM-1 inhibitor. The expression of TREM-1 was determined by quantitative RT-PCR. The levels of TREM-1, IL-6, and TNF-α in cell culture supernatant were measured with ELISA. Simultaneously, NF-κB signaling pathway-related protein p-p65 and p-IκBα were detected by Western blot assay. Results demonstrated that pravastatin sodium significantly mitigated lipopolysaccharide-stimulated TREM-1 over-expression at mRNA and protein levels dose-dependently. Elevated IL-6 and TNF-α levels changed synchronously. LR-12 inhibited the TREM-1 over-expression and inflammatory factor production but did not show extra synergistic effect to pravastatin. Lipopolysaccharide induced phospho-p65 and -IκBα over-expression was weakened significantly when cells were treated with pravastatin sodium. In conclusion, pravastatin could inhibit TREM-1-medieted inflammation and NF-κB signaling pathway was involved.

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.

A first-in-man safety and pharmacokinetics study of nangibotide, a new modulator of innate immune response through TREM-1 receptor inhibition.

AIMS: The peptide nangibotide is the first clinical-stage agent targeting the immunoreceptor TREM-1 (triggering receptor expressed on myeloid cells-1) and is being investigated as a novel therapy for acute inflammatory disorders such as septic shock. This first-in-man, randomized, double-blind, ascending dose, placebo-controlled Phase I study evaluated the safety, tolerability and pharmacokinetics of nangibotide. METHODS: Twenty-seven healthy subjects (aged 18-45 years) were randomized into eight groups. Nangibotide was administered as a single continuous intravenous infusion. The first two groups received a single i.v. dose of 1 and 10 mg, respectively, over 15 min. Subsequent groups were randomized in a product : placebo ratio of 3:1 at doses ranging from 0.03 to 6 mg kg-1  h-1 over 7 h 45 min, preceded by a 15-minute loading dose of up to 5 mg kg-1 . RESULTS: Nangibotide was safe and well tolerated up to the highest dose tested. There were only few adverse events and they were mild in severity and considered unrelated to treatment. Nangibotide displayed dose-proportional PK properties, with a clearance of 6.6 l kg-1  h-1 for a subject of 70 kg and a 3 min effective half-life, which are compatible with extensive enzymatic metabolism in blood. Central and peripheral volumes of distribution were 16.7 l and 15.9 l respectively, indicating limited distribution of the drug mainly in blood and interstitial fluid. No circulating anti-drug antibodies were detectable up to 28 days after administration. CONCLUSIONS: The novel immunomodulator nangibotide displayed favourable safety and PK profiles at all doses, including expected pharmacologically active doses, and warrants further clinical development.

Rationally designed ligand-independent peptide inhibitors of TREM-1 ameliorate collagen-induced arthritis.

Triggering receptor expressed on myeloid cells 1 (TREM-1) is critically involved in the pathogenesis of rheumatoid arthritis (RA). In contrast to cytokine blockers, therapeutic blockade of TREM-1 can blunt excessive inflammation while preserving the capacity for microbial control. However, the nature of the TREM-1 ligand(s) and mechanisms of TREM-1 signalling are still not yet well understood, impeding the development of clinically relevant inhibitors of TREM-1. The aim of this study was to evaluate the anti-arthritic activity of a novel, ligand-independent TREM-1 inhibitory nonapeptide GF9 that was rationally designed using the signalling chain homo oligomerization (SCHOOL) model of cell signalling. Free GF9 and GF9 bound to macrophage-targeted nanoparticles that mimic human high-density lipoproteins (GF9-HDL) were used to treat collagen-induced arthritis (CIA). We also tested if 31-mer peptides with sequences from GF9 and helices 4 (GE31) and 6 (GA31) of the major HDL protein, apolipoprotein A-I, are able to perform three functions: assist in the self-assembly of GA/E31-HDL, target these particles to macrophages and block TREM-1 signalling. We showed that GF9, but not control peptide, ameliorated CIA and protected against bone and cartilage damage. The therapeutic effect of GF9 was accompanied by a reduction in the plasma levels of macrophage colony-stimulating factor and pro-inflammatory cytokines such as tumour necrosis factor-α, interleukin (IL)-1 and IL-6. Incorporation of GF9 alone or as a part of GE31 and GA31 peptides into HDL significantly increased its therapeutic efficacy. Collectively, our findings suggest that TREM-1 inhibitory SCHOOL sequences may be promising alternatives for the treatment of RA.

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.

Effect of Triggering Receptor Expressed on Myeloid Cells 1 (TREM-1) Blockade in Rats with Cecal Ligation and Puncture (CLP)-Induced Sepsis.

BACKGROUND Blocking of TREM-1 signaling improves survival of mice with sepsis induced by Pseudomonas aeruginosa. However, whether TREM-1 blockade has beneficial effects in polymicrobial sepsis is poorly understood. Here, we aimed to investigate the effect of modulation of the TREM-1 pathway in rats with polymicrobial sepsis induced by cecal ligation and puncture (CLP). MATERIAL AND METHODS Normal Sprague-Dawley (SD) rats with sepsis induced by CLP were allocated randomly to received scramble peptide or LP17 via the jugular vein. Serum level of sTREM-1, IL6, TNF-α, and IL-1ß were detected by ELISA assay. The mRNA and protein levels of JAK2 and STAT3 were detected by real-time PCR and Western blot analysis. RESULTS STREM-1 concentration was greatly and progressively increased in rats with CLP-induced sepsis, and the increase was attenuated by TREM-1 inhibitory peptide LP17. More than 60% survival was observed in rats at the experiment endpoint after LP17 treatment. TREM-1 blockade also attenuated the increased level of pro-inflammatory cytokines TNF-α, IL-6, and IL-1ß, and thus attenuated systematic and distant inflammatory responses. Furthermore, TREM-1 blockade significantly attenuated the increased levels of pJAK2 and pSTAT3. CONCLUSIONS TREM-1 blockade by the use of an inhibitory peptide LP17 could prolong survival of rats with polymicrobial sepsis and attenuate systematic inflammatory responses through the JAK2/STAT3 signaling pathway. Our results suggest that modulation of TREM-1 by a synthetic peptide might be a potential therapeutic option for polymicrobial sepsis.

Inhibition of TREM-1 alleviates neuroinflammation by modulating microglial polarization via SYK/p38MAPK signaling pathway after traumatic brain injury.

BACKGROUND: Traumatic brain injury (TBI), as a major public health problem, is characterized by high incidence rate, disability rate, and mortality rate. Neuroinflammation plays a crucial role in the pathogenesis of TBI. Triggering receptor expressed on myeloid cells-1 (TREM-1) is recognized as an amplifier of the inflammation in diseases of the central nervous system (CNS). However, the function of TREM-1 remains unclear post-TBI. This study aimed to investigate the function of TREM-1 in neuroinflammation induced by TBI. METHODS: Brain water content (BWC), modified neurological severity score (mNSS), and Morris Water Maze (MWM) were measured to evaluate the effect of TREM-1 inhibition on nervous system function and outcome after TBI. TREM-1 expression in vivo was evaluated by Western blotting. The cellular localization of TREM-1 in the damaged region was observed via immunofluorescence staining. We also conducted Western blotting to examine expression of SYK, p-SYK and other downstream proteins. RESULTS: We found that inhibition of TREM-1 reduced brain edema, decreased mNSS and improved neurobehavioral outcomes after TBI. It was further determined that TREM-1 was expressed on microglia and modulated subtype transition of microglia. Inhibition of TREM-1 alleviated neuroinflammation, which was associated with SYK/p38MAPK signaling pathway. CONCLUSIONS: These findings suggest that TREM-1 can be a potential clinical therapeutic target for alleviating neuroinflammation after TBI.

TREM-1 induces pyroptosis in cardiomyocytes by activating NLRP3 inflammasome through the SMC4/NEMO pathway.

Sepsis often causes cell death via pyroptosis and hence results in septic cardiomyopathy. Triggering receptors expressed in myeloid cells-1 (TREM-1) may initiate cellular cascade pathways and, in turn, induce cell death and vital organ dysfunction in sepsis, but the evidence is limited. We set to investigate the role of TREM-1 on nucleotide-binding oligomerization domain-like receptors with pyrin domain-3 (NLRP3) inflammasome activation and cardiomyocyte pyroptosis in sepsis models using cardiac cell line (HL-1) and mice. In this study, TREM-1 was found to be significantly increased in HL-1 cells challenged with lipopolysaccharide (LPS). Pyroptosis was also significantly increased in the HL-1 cells challenged with lipopolysaccharide and an NLRP3 inflammasome activator, nigericin. The close interaction between TREM-1 and structural maintenance of chromosome 4 (SMC4) was also identified. Furthermore, inhibition of TREM-1 or SMC4 prevented the upregulation of NLRP3 and decreased Gasdermin-D, IL-1ß and caspase-1 cleavage. In mice subjected to caecal ligation and puncture, the TREM-1 inhibitor LR12 decreased the expression of NLRP3 and attenuated cardiomyocyte pyroptosis, leading to improved cardiac function and prolonged survival of septic mice. Our work demonstrates that, under septic conditions, TREM-1 plays a critical role in cardiomyocyte pyroptosis. Targeting TREM-1 and its associated molecules may therefore lead to novel therapeutic treatments for septic cardiomyopathy.

A novel eCIRP/TREM-1 pathway inhibitor attenuates acute kidney injury.

BACKGROUND: Extracellular cold-inducible RNA-binding protein aggravates acute kidney injury after renal ischemia/reperfusion. Although extracellular cold-inducible RNA-binding protein activates triggering receptor expressed on myeloid cells-1, how this receptor and its antagonism with a novel peptide M3 affects acute kidney injury is poorly understood. We, therefore, hypothesize that inhibiting the extracellular cold-inducible RNA-binding protein/triggering receptor expressed on myeloid cells-1 pathway with M3 attenuates acute kidney injury. METHODS: Wild-type and triggering receptor expressed on myeloid cells-1-/- mice were subjected to bilateral 30-minute renal hilum clamping followed by reperfusion or sham. After 4 hours, wild-type mice received M3 (10 mg/kg BW) or normal saline intraperitoneally. After 24 hours, renal tissue and serum were collected for analysis. Additionally, wild-type mice were subjected to bilateral renal ischemia for 34 minutes and treated with M3 at 10 mg/kg BW or vehicle at the time of reperfusion. Survival was monitored for 10 days. RESULTS: After renal ischemia/reperfusion, triggering receptor expressed on myeloid cells-1 messenger ribonucleic acid expression increased by 9-fold in wild-type mice compared to sham mice. Wild-type mice also demonstrated significant increases in serum blood urea nitrogen, creatinine, and interleukin-6 and renal tissue levels of interleukin-6 and neutrophil gelatinase-associated lipocalin after renal ischemia/reperfusion compared to sham mice. Triggering receptor expressed on myeloid cells-1-/- mice demonstrated significant reductions in serum blood urea nitrogen, creatinine, and interleukin-6 compared to wild-type mice after renal ischemia/reperfusion. Levels of renal interleukin-6 and neutrophil gelatinase-associated lipocalin were also significantly decreased in the kidneys of triggering receptor expressed on myeloid cells-1-/- mice. Furthermore, treatment with M3 in wild-type mice significantly decreased serum and renal levels of interleukin-6 after renal ischemia/reperfusion. M3 treatment demonstrated significant reductions in renal messenger ribonucleic acid and protein levels of neutrophil gelatinase-associated lipocalin, serum blood urea nitrogen and creatinine, and histologic structural damage as well as apoptosis. Treatment with M3 also increased survival from 35% to 65% in mice with acute kidney injury. CONCLUSION: Triggering receptor expressed on myeloid cells-1 mediates the deleterious effects of extracellular cold-inducible RNA-binding protein in acute kidney injury after renal ischemia/reperfusion. The novel extracellular cold-inducible RNA-binding protein/triggering receptor expressed on myeloid cells-1 pathway antagonist, M3, attenuates acute kidney injury and has the potential to be developed as a therapeutic agent for acute kidney injury.

TREM1 Blockade Ameliorates Lipopolysaccharide-Induced Acute Intestinal Dysfunction through Inhibiting Intestinal Apoptosis and Inflammation Response.

OBJECTIVE: The lipopolysaccharide- (LPS-) induced acute intestinal dysfunction model has been widely applied in recent years. Here, our aim was to investigate the effect of triggering receptor expressed on myeloid cells-1 (TREM1) inhibitor in LPS-induced acute intestinal dysfunction. METHODS: Male rats were randomly assigned into normal (saline injection), model (LPS and saline injection), and LP17 (LPS and LP17 (a synthetic TREM1 inhibitor) injection) groups. The levels of intestinal TREM1 expression were evaluated by immunohistochemistry and western blot. Intestinal permeability and apoptosis were separately assessed by the lactulose/mannitol (L/M) ratio and TUNEL assay. The levels of soluble TREM1 (sTREM1), TNF-α, IL-6, and IL-1ß were measured in the plasma and intestinal tissues by ELISA. The expression levels of NF-κB, high-mobility group box 1 (HMGB1), and toll-like receptor 4 (TLR-4) were measured with RT-qPCR and western blot. After transfection with si-TREM1 in LPS-induced intestinal epithelium-6 (IEC-6) cells, p-p65 and p-IκBα levels were detected by western blot. RESULTS: LP17-mediated TREM1 inhibition alleviated the intestine tissue damage in rats with LPS-induced acute intestinal dysfunction. LP17 attenuated the LPS-induced increase in sTREM1, TNF-α, IL-6, and IL-1ß levels in the plasma and intestinal tissues. Furthermore, intestine permeability and epithelial cell apoptosis were ameliorated by LP17. LP17 attenuated the LPS-induced increase in the expression of TREM1, HMGB1, TLR-4, and NF-κB in the intestine tissues. In vitro, TREM1 knockdown inactivated the NF-κB signaling in LPS-induced IEC-6 cells. CONCLUSION: LP17 could ameliorate LPS-induced acute intestinal dysfunction, which was associated with inhibition of intestinal apoptosis and inflammation response.

Transcriptomic Profiling Reveals a Role for TREM-1 Activation in Enterovirus D68 Infection-Induced Proinflammatory Responses.

Increasing cases related to the pathogenicity of Enterovirus D68 (EV-D68) have made it a growing worldwide public health concern, especially due to increased severe respiratory illness and acute flaccid myelitis (AFM) in children. There are currently no vaccines or medicines to prevent or treat EV-D68 infections. Herein, we performed genome-wide transcriptional profiling of EV-D68-infected human rhabdomyosarcoma (RD) cells to investigate host-pathogen interplay. RNA sequencing and subsequent experiments revealed that EV-D68 infection induced a profound transcriptional dysregulation of host genes, causing significantly elevated inflammatory responses and altered antiviral immune responses. In particular, triggering receptor expressed on myeloid cells 1 (TREM-1) is involved in highly activated TREM-1 signaling processes, acting as an important mediator in EV-D68 infection, and it is related to upregulation of interleukin 8 (IL-8), IL-6, IL-12p70, IL-1ß, and tumor necrosis factor alpha (TNF-α). Further results demonstrated that NF-κB p65 was essential for EV-D68-induced TREM-1 upregulation. Moreover, inhibition of the TREM1 signaling pathway by the specific inhibitor LP17 dampened activation of the p38 mitogen-activated protein kinase (MAPK) signaling cascade, suggesting that TREM-1 mainly transmits activation signals to phosphorylate p38 MAPK. Interestingly, treatment with LP17 to inhibit TREM-1 inhibited viral replication and infection. These findings imply the pathogenic mechanisms of EV-D68 and provide critical insight into therapeutic intervention in enterovirus diseases.

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

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

Cigarette smoke extract-treated airway epithelial cells-derived exosomes promote M1 macrophage polarization in chronic obstructive pulmonary disease.

Chronic obstructive pulmonary disease (COPD) is a persistent respiratory disorder that is primarily caused by exposure to cigarette smoke (CS). Exosomes have emerged as crucial mediators of intercellular communication, but their role in CS-induced COPD is not fully understood. Here, we investigated whether exosomes derived from cigarette smoke extract (CSE)-treated mouse airway epithelial cells (MAECs) promote M1 macrophage polarization by upregulating triggering receptor expressed on myeloid cells-1 (TREM-1) expression during COPD pathogenesis. The exosomes isolated from PBS- or CSE-treated MAECs were named as ExoPBS or ExoCSE, respectively. Macrophages were transfected with si-TREM-1 to explore the role of TREM-1 in ExoCSE-induced M1 macrophage polarization. The lentivirus expressing shTREM-1 was injected into COPD model mice by intranasal instillation, which was carried out to explore the in vivo role of TREM-1 in ExoCSE-induced M1 macrophage polarization and CS-induced lung injury. We isolated ExoPBS and ExoCSE successfully, and found that ExoCSE promoted M1 macrophage polarization. Furthermore, we found that the promotion of ExoCSE to M1 macrophage polarization was partly reversed by TREM-1 knockdown. The results of animal experiments showed that ExoCSE administration aggravated CS-induced impairment in pulmonary function, lung injury and M1 macrophage polarization, which were partly rescued by TREM-1 silencing. Overall, ExoCSE promoted M1 macrophage polarization by upregulating TREM-1 expression, thereby aggravating the development of COPD.

Activation of TREM-1 induces endoplasmic reticulum stress through IRE-1α/XBP-1s pathway in murine macrophages.

Increasing evidence suggests that endoplasmic reticulum (ER) stress activates several pro-inflammatory signaling pathways in many diseases, including acute lung injury (ALI). We have reported that blocking triggering receptor expressed on myeloid cells 1 (TREM-1) protects against ALI by suppressing pulmonary inflammation in mice with ALI induced by lipopolysaccharides (LPS). However, the molecular mechanism underlying the TREM-1-induced pro-inflammatory microenvironment in macrophages remains unclearly. Herein, we aimed to determine whether TREM-1 regulates the inflammatory responses induced by LPS associated with ER stress activation. We found that the activation of TREM-1 by a monoclonal agonist antibody (anti-TREM-1) increased the mRNA and protein levels of IL-1ß, TNF-α, and IL-6 in primary macrophages. Treatment of the anti-TREM-1 antibody increased the expression of ER stress markers (ATF6, PERK, IRE-1α, and XBP-1s) in primary macrophages. While pretreatment with 4-PBA, an inhibitor of ER stress, significantly inhibited the expression of ER stress markers and pro-inflammatory cytokines and reduced LDH release. Furthermore, inhibiting the activity of the IRE-1α/XBP-1s pathway by STF-083010 significantly mitigated the increased levels of IL-1ß, TNF-α, and IL-6 in macrophages treated by the anti-TREM-1 antibody. XBP-1 silencing attenuated pro-inflammatory microenvironment evoked by activation of TREM-1. Besides, we found that blockade of TREM-1 with LR12 ameliorated ER stress induced by LPS in vitro and in vivo. In conclusion, we conclude that TREM-1 activation induces ER stress through the IRE-1α/XBP-1s pathway in macrophages, contributing to the pro-inflammatory microenvironment.

Salmonella effector SpvB aggravates dysregulation of systemic iron metabolism via modulating the hepcidin-ferroportin axis.

Iron withholding, an essential component of nutritional immunity, plays a fundamental role in host resistance to Salmonella infection. Our previous study showed that SpvB, an important pSLT-encoded cytotoxic effector, facilitated Salmonella pathogenesis within macrophages via perturbing cellular iron metabolism. However, the underlying mechanisms of SpvB in Salmonella-relevant disorders of systemic iron metabolism have not yet been identified. Here, we demonstrated that SpvB facilitated Salmonella to scavenge iron from the host by modulating the hepcidin-ferroportin axis, a key regulator of systemic iron metabolism. We observed that SpvB enhanced hepatic hepcidin synthesis in a STAT3-dependent manner, but not the BMP/SMAD pathway. This subsequently resulted in a reduction of the unique cellular iron exporter ferroportin, which facilitated hypoferremia and hepatic iron accumulation and ultimately countered the limitation of iron availability, thereby improving the chances of Salmonella survival and replication. Moreover, SpvB promoted the production of proinflammatory molecules associated with the infiltration of inflammatory cells via highly upregulating TREM-1 signaling. Our data supported a role of TREM-1 in SpvB-related dysregulation of host iron metabolism and suggested that targeting TREM-1 might provide a potential therapeutic strategy to prevent or alleviate Salmonella pathogenesis.