Triggering Receptor Expressed On Myeloid Cells-1 Inhibition Research Articles

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

BackgroundTraumatic 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. MethodsBrain 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. ResultsWe 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. ConclusionsThese findings suggest that TREM-1 can be a potential clinical therapeutic target for alleviating neuroinflammation after TBI.

Abstract 6530: TREM1 inhibition: A novel approach to suppress tumor growth and enhance immune checkpoint therapy

Abstract In the context of cancer, inflammation is a multifaceted contributor to tumorigenesis. The Triggering Receptor Expressed on Myeloid Cells 1 (TREM1) is recognized for its role in amplifying inflammatory responses, yet its specific pro-tumorigenic mechanisms have remained elusive. This study employs Trem1-deficient mice and a novel inhibitor, VJDT, to explore the therapeutic potential of targeting TREM1 in cancer. Both genetic silencing and pharmacological inhibiton of Trem1 led to remarkable reductions in tumor growth in mouse models of melanoma (B16F10) and fibrosarcoma (MCA205). In-depth analysis using single-cell RNA sequencing unveiled that TREM1 deficiency resulted in a decrease in the frequency and suppressive capabilities of myeloid-derived suppressor cells (MDSCs) within the tumor microenvironment, concomitant with an increase in cytotoxic CD8+ T cells and enhanced T cell activation. Furthermore, TREM1 inhibition not only curtailed tumor growth but also potentiated the effectiveness of anti-PD-1 therapy, primarily by mitigating MDSC frequency and reversing T cell exhaustion. Notably, in melanoma xenografts from patient samples, pharmacological TREM1 inhibition via VJDT treatment significantly downregulated critical oncogenic pathways linked to cell proliferation, migration, and survival. This research underscores the pivotal role of TREM1, expressed both within cancer cells and the tumor microenvironment, in driving cancer progression. Consequently, targeting TREM1 for therapeutic intervention holds promise for reshaping the immunosuppressive tumor milieu and augmenting the success of immune checkpoint therapy. Citation Format: Ashwin Ajith, Kenza Moamouni, Daniel D Horuzsko, Anatolij Horuzsko. TREM1 inhibition: A novel approach to suppress tumor growth and enhance immune checkpoint therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6530.

HIV-1 Tat Upregulates TREM1 Expression in Human Microglia.

Because microglia are a reservoir for HIV and are resistant to the cytopathic effects of HIV infection, they are a roadblock for any HIV cure strategy. We have previously identified that triggering receptor expressed on myeloid cells 1 (TREM1) plays a key role in human macrophage resistance to HIV-mediated cytopathogenesis. In this article, we show that HIV-infected human microglia express increased levels of TREM1 and are resistant to HIV-induced apoptosis. Moreover, upon genetic inhibition of TREM1, HIV-infected microglia undergo cell death in the absence of increased viral or proinflammatory cytokine expression or the targeting of uninfected cells. We also show that the expression of TREM1 is mediated by HIV Tat through a TLR4, TICAM1, PG-endoperoxide synthase 2, PGE synthase, and PGE2-dependent manner. These findings highlight the potential of TREM1 as a therapeutic target to eradicate HIV-infected microglia without inducing a proinflammatory response.

Nangibotide for precision immunomodulation in septic shock and COVID-19

Nangibotide for precision immunomodulation in septic shock and COVID-19

Inhibition of TREM-1 ameliorates Lipopolysaccharide-induced depressive-like behaviors by alleviating neuroinflammation in the PFC via PI3K/Akt signaling pathway

Neuroinflammation is closely related to depression and is a key pathophysiological process of depression. Triggering receptor expressed on myeloid cells 1 (TREM-1) has been proven to exert proinflammatory effects in various diseases. However, the role of TREM-1 in depression has not been elucidated. Thus, we hypothesized that TREM-1 inhibition might have protective effects in depression. Here, lipopolysaccharide (LPS) was used to induce depressive-like behaviors in mice, LP17 was treated to inhibit TREM-1, and LY294002 was administrated to inhibit phosphatidylinositol 3-kinase (PI3K) which is one of the downstream of TREM-1. Physical and neurobehavioral tests, Western blot analysis, and immunofluorescence staining were performed in this study. We found that LPS caused significant depressive-like behaviors in mice, including body weight decline, anodynia (sucrose preference decrease), lack of locomotor activity, and desperation in tail suspension test (TST) and forced swimming test (FST). Next, we revealed that TREM-1 was expressed on microglia, neurons, and astrocytes in the prefrontal cortex (PFC) after LPS administration. TREM-1 inhibition by LP17 suppressed the expression of TREM-1 in the PFC. In addition, LP17 could alleviate neuroinflammation and microglial activation in the PFC. Meanwhile, LP17 could prevent damage of LPS to neuronal primary cilia and neuronal activity. Finally, we revealed that PI3K/Akt might exert crucial role in the protective effects of TREM-1 inhibition to depressive-like behaviors induced by LPS. Taken together, TREM-1 inhibition by LP17 could alleviate depressive-like behaviors induced by LPS by mitigating neuroinflammation in the PFC via PI3K/Akt signaling pathway. Finally, we demonstrated that TREM-1 might be a promising therapeutic target for treatment of depression.

Role of triggering receptor expressed on myeloid cells-1 in the mechanotransduction signaling pathways that link low shear stress with inflammation

This study sought to investigate the role of triggering receptor expressed on myeloid cells-1 (TREM-1) in the mechanotransduction signaling pathways that link low shear stress with inflammation. Human coronary artery endothelial cells, human coronary artery smooth muscle cells, and THP-1 monocytes were co-cultured and exposed to varying endothelial shear stress (ESS) conditions: low (5 ± 3 dynes/cm2), medium (10 ± 3 dynes/cm2), and high (15 ± 3 dynes/cm2). We showed that low ESS increased the expression of TREM-1 by the cultured cells leading to increased production of inflammatory mediators and matrix-degrading enzymes, whereas high ESS did not have a significant effect in the expression of TREM-1 and inflammatory mediators. Furthermore, TREM-1 transcriptional inhibition with siRNA in endothelial cells, smooth muscle cells, and monocytes exposed to low ESS, led to a significant reduction in the production of vascular inflammatory mediators and matrix-degrading enzymes. Additionally, we identified the transcription factors that appear to upregulate the TREM-1 gene expression in response to low ESS. To the best of our knowledge, this is the first study to investigate the pathophysiologic association and molecular pathways that link low ESS, TREM-1, and inflammation using a sophisticated in-vitro model of atherosclerosis. Future studies on animals and humans are warranted to investigate the potential of TREM-1 inhibitors as adjunctive anti-atherosclerotic therapies.

Extracellular CIRP induces acute kidney injury via endothelial TREM-1.

Introduction: Acute kidney injury is associated with elevated serum levels of extracellular cold-inducible RNA-binding protein (eCIRP), a damage-associated molecular pattern released during ischemia/reperfusion injury, hemorrhagic shock, and sepsis. It is unknown if circulating eCIRP and eCIRP-induced activation of receptor triggering receptor expressed on myeloid cells-1 (TREM-1), expressed on endothelial cells, play an important role in the pathogenesis of AKI. Methods: Male B6 wild-type (WT) and TREM-1−/− mice were subjected to intravenous injection of recombinant murine (rm) CIRP. Serum, urine, and renal tissue were collected 6 h later for analysis. Additionally, primary human renal glomerular endothelial cells (HRGEC) were stimulated in vitro with rmCIRP after pretreatment with M3, a novel inhibitory peptide of TREM-1, or vehicle. Supernatants and cells were collected 20 h after stimulation. Results: After injection with rmCIRP, WT mice had a significant increase in serum levels of BUN, creatinine, and NGAL compared to control. Additionally, NGAL was significantly increased in the urine of rmCIRP-injected mice, suggesting that circulating eCIRP can directly induce AKI. The levels of TREM-1 mRNA in the kidneys, as well as soluble (s) TREM-1 released into the serum and urine, were significantly increased in rmCIRP-injected mice. TREM-1−/− mice injected with rmCIRP had attenuated AKI, indicated by significantly decreased serum BUN, creatinine, and NGAL, and renal mRNA expression of NGAL and KIM-1 compared to WT mice. TREM-1−/− mice also had attenuated endothelial activation, with decreased mRNA and protein expression of ICAM-1 in renal tissue. HRGEC stimulated with rmCIRP in vitro had significant increases in cytokine production and sTREM-1 release, which was attenuated in cells treated with M3. Conclusion: Activation of renal TREM-1 with circulating eCIRP is sufficient to cause AKI. Elevated levels of eCIRP may be critical for the development of AKI under conditions such as ischemia/reperfusion injury, hemorrhagic shock, and sepsis. Mice deficient in the TREM-1 receptor have attenuated AKI and reduced endothelial cell activation after injection of rmCIRP. TREM-1 inhibition with M3 attenuates HRGEC activation after eCIRP stimulation. Targeting eCIRP activation of TREM-1 may provide a novel and effective treatment for AKI.

Design of the lentivirus-driven sustained LR12 delivery system for TREM-1 inhibition for palliating atherosclerosis.

Triggering Receptor Expressed on Myeloid cells-1 (TREM-1) has been a potential target in the management of pathophysiology and clinical sequelae of atherosclerosis. LR12 peptide effectively blocks ligand-TREM-1 interaction; however, the short half-life of LR12 is a major hurdle in its translational application in atherosclerosis management warranting new methods for sustained bioavailability in clinical applications. The present study reports a novel method of packing the coding sequence of LR12 in a lentiviral system to ensure a sustained expression and bioavailability for effective TREM-1 inhibition. Lentivirus vector systems (LV-LR12 and LV-SP) for the expression of LR12 peptide and SP (scrambled peptide) were successfully designed, constructed, and tested in vitro in smooth muscle cells (SMCs). Viral amounts obtained were 703.6 ± 145.12 and 609.3 ± 145.93ng/ml p24 for LV-LR12 and LV-SP, respectively which correspond to ~ 107IFU/ml for both vectors. Dot blot assay revealed significantly increased expression of LR12-FLAG and SP-FLAG in 125μg total protein which was doubled in 250μg protein with respect to un-transduced SMCs suggesting the sustained release of LR12/SP as confirmed by ELISA. Cellular expression of LR12-FLAG and SP-FLAG displayed 8.44-fold and 7.55-fold increase, respectively compared to the control SMCs. The findings demonstrated a promising strategy for packing the LR12 coding sequence in lentiviral vector for TREM-1 inhibition for the management of atherosclerosis and other inflammatory diseases.

Inhibition of the Interaction of TREM-1 and eCIRP Attenuates Inflammation and Improves Survival in Hepatic Ischemia/Reperfusion.

Triggering receptor expressed on myeloid cells-1 (TREM-1) has important implications in sepsis and inflammation and is a novel receptor for extracellular cold-inducible RNA-binding protein (eCIRP). We hypothesize that the inhibition of TREM-1 via its interaction with eCIRP by novel peptide inhibitor M3 or knockout gene will attenuate the inflammation and injury associated with severe hepatic ischemia/reperfusion (I/R). Wild-type (WT) C57BL/6 and TREM-1-/- mice underwent 60 min of 70% hepatic ischemia, with 24 h of reperfusion. Additionally, WT mice underwent hepatic I/R and were treated with M3 (10 mg/kg body weight) or vehicle (normal saline) at the start of reperfusion. Blood and ischemic liver tissues were collected, and analysis was performed using enzymatic assays, enzyme-linked immunosorbent assay, reverse-transcription quantitative polymerase chain reaction, and pathohistology techniques. For survival surgery, mice additionally underwent resection of non-ischemic lobes of the liver and survival was monitored for 10 days. There was an increase in serum levels of tissue markers including aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase as well as cytokine levels (IL-6) and histological scoring of hematoxylin and eosin sections in WT I/R mice. These markers decreased substantially in TREM-1-/- mice. Additionally, neutrophil infiltration markers and markers of local inflammation (myeloperoxidase, macrophage inflammatory protein-2, cyclooxygenase-2) were attenuated in TREM-1-/- mice. Similarly, we show a significant decrease in injury and inflammation markers with M3 treatment. Additionally, we demonstrate decreased apoptosis with TREM-1 inhibition. Finally, M3 treatment improved the survival rate from 42% to 75% after hepatic I/R. TREM-1 is an important eCIRP receptor in the inflammatory response of hepatic I/R, and deficiency of TREM-1 via knockout gene or peptide inhibition attenuated liver injury and inflammation, and improved survival. Inhibition of the TREM-1 and eCIRP interaction in hepatic I/R may have important therapeutic potential.

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

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. 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-1cells 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. 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-1cells. Inhibition of TREM-1 significantly attenuated LPS-induced effects and suppressed migration and invasion. 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.

TREM1 Regulates Neuroinflammatory Injury by Modulate Proinflammatory Subtype Transition of Microglia and Formation of Neutrophil Extracellular Traps via Interaction With SYK in Experimental Subarachnoid Hemorrhage.

Neuroinflammation is a key process in the pathogenesis of subarachnoid hemorrhage (SAH) and contributes to poor outcome in patients. The purpose of this study is to explore the effect of triggering receptor expressed on myeloid cells 1 (TREM1) in the SAH, as well as its potential mechanism. In our study, plasma levels of soluble TREM1 was increased significantly after SAH and correlated to SAH severity and serum C-reactiveprotein. TREM1 inhibitory peptide LP17 alleviated the neurological deficits, attenuated brain water content, and reduced neuronal damage after SAH. Meanwhile, TREM1 inhibitory peptide decreased neuroinflammation (evidenced by the decreased levels of markers including IL-6, IL-1β, TNF-α) by attenuating proinflammatory subtype transition of microglia (evidenced by the decreased levels of markers including CD68, CD16, CD86) and decreasing the formation of neutrophil extracellular traps (evidenced by the decreased levels of markers including CitH3, MPO, and NE). Further mechanistic study identified that TREM1 can activate downstream proinflammatory pathways through interacting with spleen tyrosine kinase (SYK). In conclusion, inhibition of TREM1 alleviates neuroinflammation by attenuating proinflammatory subtype transition of microglia and decreasing the formation of neutrophil extracellular traps through interacting with SYK after SAH. TREM1 may be a a promising therapeutic target for SAH.

TREM-1 aggravates chronic obstructive pulmonary disease development via activation NLRP3 inflammasome-mediated pyroptosis.

Chronic obstructive pulmonary disease (COPD) is a major cause of death globally. Inflammation plays a crucial role in COPD development. Pyroptosis, an inflammatory form of cell death, may involve in the pathogenesis of COPD. This study aims to explore the role and action mechanism of triggering receptor expressed on myeloid cells 1 (TREM-1) in COPD. Here, cigarette smoke stimulation was used to establish COPD model in mice. Cigarette smoke extract combined with lipopolysaccharide was used to stimulate RAW264.7 cells for COPD model in vitro. QRT-PCR and Western blot were performed to detect the expression of mRNA and proteins, respectively, in the lung tissues and cells. Concentration of cytokines was measured using ELISA. H&E staining was used to analyze the pathological changes in lung tissues. The number of infiltrated macrophage was examined using immunofluorescence. LP17 was used to silence the expression of TREM-1. The results showed that TREM-1 was highly expressed in COPD. In vivo, inhibition of TREM-1 effectively improved the injury in lung tissues of COPD mouse, and reduced the infiltration of macrophages. Moreover, inhibition of TREM-1 in vivo and in vitro notably suppressed the activation of NLRP3 inflammasome and pyroptosis. Rescue experiment demonstrated that TREM-1 activated pyroptosis via regulating NLRP3 inflammasome. Overall, our results proved that TREM-1 promoted the lung injury and inflammation in COPD mouse through activation of NLRP3 inflammasome-mediated pyroptosis. Our data indicated a novel mechanism of TREM-1 in COPD development, and maybe provide a novel therapeutic target for COPD treatment.

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-1β 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-1β 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.

Tacrolimus Impairs Kupffer Cell Capacity to Control Bacteremia: Why Transplant Recipients Are Susceptible to Infection.

Kupffer cells (KCs) are the resident intravascular phagocyte population of the liver and critical to the capture and killing of bacteria. Calcineurin/nuclear factor of activated T cells (NFAT) inhibitors (CNIs) such as tacrolimus are used to prevent rejection in solid organ transplant recipients. Although their effect on lymphocytes has been studied extensively, there are limited experimental data about if and how CNIs shape innate immunity, and whether this contributes to the higher rates of infection observed in patients taking CNIs. Here, we investigated the impact of tacrolimus treatment on innate immunity and, more specifically, on the capability of Kupffer cells (KCs) to fight infections. Retrospective analysis of data of >2,700 liver transplant recipients showed that taking calcineurin inhibitors such as tacrolimus significantly increased the likelihood of Staphylococcus aureus infection. Using a mouse model of acute methicillin-resistant S. aureus (MRSA) bacteremia, most bacteria were sequestered in the liver and we found that bacteria were more likely to disseminate and kill the host in tacrolimus-treated mice. Using imaging, we unveiled the mechanism underlying this observation: the reduced capability of KCs to capture, phagocytose, and destroy bacteria in tacrolimus-treated animals. Furthermore, in a gene expression analysis of infected KCs, the triggering receptor expressed on myeloid cells 1 (TREM1) pathway was the one with the most significant down-regulation after tacrolimus treatment. TREM1 inhibition likewise inhibited KC bacteria capture. TREM1 levels on neutrophils as well as the overall neutrophil response after infection were unaffected by tacrolimus treatment. Our results indicate that tacrolimus treatment has a significant impact directly on KCs and on TREM1, thereby compromising their capacity to fend off infections.

Role of TREM-1 in the development of early brain injury after subarachnoid hemorrhage

Triggering receptor expressed on myeloid cells-1 (TREM-1) was found to be induced in the context of subarachnoid hemorrhage (SAH) before. This study further investigates its role in the development of SAH-induced early brain injury (EBI). Firstly, rats were randomly divided into Sham and SAH groups for analysis of temporal patterns and cellular localization of TREM-1. Secondly, TREM-1 intervention was administrated to produce Sham, vehicle, antagonist and agonist groups, for analyzing TREM-1, Toll-like receptor 4 (TLR4), myeloid differentiation factor 88 (MyD88) and NF-κB expressions at 24 h post-modeling, and EBI assessment at 24 h and 72 h. Thirdly, TLR4 inhibitor (TAK-242) was exploited to produce Sham, Sham+TAK-242, SAH, and SAH + TAK-242 groups to analyze the effects of TLR4 inhibition on TREM-1 induction and EBI evaluation at 72 h. Fourthly, the relationship of soluble TREM-1 (sTREM-1) levels in cerebrospinal fluid of SAH patients with Hunt-Hess grades were explored. The results showed that TREM-1 increased in the brain after experimental SAH (eSAH) early at 6 h and peaked at 48 h, which was found to be located in microglia and endothelial cells. TREM-1 inhibition attenuated EBI associated with TLR4/MyD88/NF-κB suppression, while enhancement had the opposite effects. Contrarily, TLR4 inhibition prevented TREM-1 induction and ameliorated EBI. In addition, sTREM-1 levels in SAH patients positively correlated with Hunt-Hess grades. Overall, the present study provides new evidence that TREM-1 increases dynamically in the brain after eSAH and it is located in microglia and endothelial cells, which may aggravate EBI by interacting with TLR4 pathway. And sTREM-1 in patients might act as a monitoring biomarker of EBI, providing new insights for future studies.

TREM-1 Exacerbates Neuroinflammatory Injury via NLRP3 Inflammasome-Mediated Pyroptosis in Experimental Subarachnoid Hemorrhage.

Neuroinflammation contributes to the pathogenesis of early brain injury induced by subarachnoid hemorrhage (SAH). Previous reports have demonstrated that triggering receptor expressed on myeloid cells 1 (TREM-1) regulates inflammatory response caused by ischemic stroke or myocardial infarction. However, whether TREM-1 could modulate neuroinflammation after SAH remains largely unknown. Here, using a mouse model of SAH, we found that the expression of TREM-1 was mainly located in microglia cells and increased to peak at 24h following SAH. Then, TREM-1 antagonist or mimic was intranasally administrated to investigate its effect on SAH. TREM-1 inhibition with LP17 improved neurological deficits, mitigated brain water content, and preserved brain-blood barrier integrity 24h after SAH, whereas recombinant TREM-1, a mimic of TREM-1, deteriorated these outcomes. In addition, LP17 administration restored long-term sensorimotor coordination and cognitive deficits. Pharmacological blockade of TREM-1 reduced TUNEL-positive and FJC-positive neurons, and CD68-stained microglia in ipsilateral cerebral cortex. Neutrophil invasion was inhibited as protein level of myeloperoxidase (MPO), and MPO-positive cells were both decreased. Moreover, we found that LP17 treatment ameliorated microglial pyroptosis by diminishing levels of N-terminal fragment of GSDMD (GSDMD-N) and IL-1β production. Mechanistically, both in vivo and in vitro, we depicted that TREM-1 can trigger microglial pyroptosis via activating NLRP3 inflammasome. In conclusion, our results revealed the critical role of TREM-1 in neuroinflammation following SAH, suggesting that TREM-1 inhibition might be a potential therapeutic approach for SAH.

Triggering Receptor Expressed on Myeloid Cells-1 Inhibitor Targeted to Endothelium Decreases Cell Activation.

TREM-1 (Triggering Receptor Expressed on Myeloid cells-1) is an immunoreceptor expressed on neutrophils, monocytes/macrophages, and endothelial cells. It amplifies the inflammatory response driven by Toll-Like Receptors (TLR) engagement. The pharmacological inhibition of TREM-1 confers protection in several pre-clinical models of acute inflammation. In this study, we aimed to investigate the role of TREM-1 in endothelial cells using a sneaking ligand construct (SLC) inhibiting TREM-1 in the endothelium. The SLC was made of 3 modules: an E-selectin targeting domain, a Pseudomonas aeruginosa exotoxin a translocation domain, and a 7 aa peptide (LSKSLVF) that contains the interaction site between TREM-1 and its adaptor protein DAP-12. SLC peptide was effectively picked up by endothelial cells following LPS stimulation. It decreased LPS induced TREM-1 up-regulation and cell activation, neutrophils extravasation, and improved median survival time during experimental peritonitis in mice. We reported that a targeted endothelial TREM-1 inhibition is able to dampen cell activation and to confer protection during septic shock in mice. The use of such cell-specific, ligand- independent TREM-1 inhibitors deserve further investigations during acute or chronic inflammatory disorders.

Peripheral TREM1 responses to brain and intestinal immunogens amplify stroke severity.

Stroke is a multiphasic process in which initial cerebral ischemia is followed by secondary injury from immune responses to ischemic brain components. Here we demonstrate that peripheral CD11b+CD45+ myeloid cells magnify stroke injury via activation of triggering receptor expressed on myeloid cells 1 (TREM1), an amplifier of proinflammatory innate immune responses. TREM1 was induced within hours after stroke peripherally in CD11b+CD45+ cells trafficking to ischemic brain. TREM1 inhibition genetically or pharmacologically improved outcome via protective antioxidant and anti-inflammatory mechanisms. Positron electron tomography imaging using radiolabeled antibody recognizing TREM1 revealed elevated TREM1 expression in spleen and, unexpectedly, in intestine. In the lamina propria, noradrenergic-dependent increases in gut permeability induced TREM1 on inflammatory Ly6C+MHCII+ macrophages, further increasing epithelial permeability and facilitating bacterial translocation across the gut barrier. Thus, following stroke, peripheral TREM1 induction amplifies proinflammatory responses to both brain-derived and intestinal-derived immunogenic components. Critically, targeting this specific innate immune pathway reduces cerebral injury.

Pseudomonas aeruginosa accentuates inflammatory responses under HIV infection through TREM‐1 activation

ObjectiveHuman immunodeficiency virus (HIV) threatens human health worldwide. Anti‐retroviral therapy (ART) extends survival but does not eliminate HIV from its cellular reservoirs. Patients accepting ART show altered immunity and immune activation, and continue to present increased risk of bacteria associated pneumonia, which is a major cause of morbidity and mortality. As an important opportunistic human pathogen, Pseudomonas aeruginosa causes a wide variety of severe nosocomial infections. Triggering receptor expressed on myeloid cells‐1 (TREM‐1) is an amplifier of inflammation, and has been recognized as a critical immunomodulator in inflammatory diseases of both infectious and non‐infectious etiologies. However, molecular mechanisms underlying the functional role of TREM‐1 in lung infections of HIV patients remains to be defined.MethodsWild type C57 BL/6J and HIV transgenic mice were treated with P. aeruginosa strain PAO1 through intranasal administration, mouse lung injury status was observed through Hematoxylin and Eosin (H&E) staining. Total RNA of lung tissues was isolated, real‐time RT‐PCR and western immunoblots were performed to quantify gene and protein expression. THP‐1 derived macrophages and human monocyte‐derived macrophages were treated with recombinant HIV viral proteins Tat and gp120, expression of miR‐155 and SOCS1 were quantified, and oxidative phosphorylation (OXPHOS) was measured through mitostress assay. Co‐culture model was used to analyze intracellular communications between macrophage and lung epithelial cells, and exosomes secreted by macrophages were isolated and cocultured with recipient cells, then expression of key tight junction proteins involved in epithelial barrier function were analyzed.ResultsCompared to wild type control, PAO1 accentuates acute neutrophilic inflammation in HIV transgenic mice with increase in neutrophil influx, expression levels of TREM‐1 and proinflammatory cytokines, particularly IL‐1β, TNF‐α and IL‐6. TREM‐1 silencing in macrophages exposed to HIV‐related proteins Tat or gp120, resulted in significant attenuation of miR‐155 expression with increased SOCS1 expression, and reduced mitochondrial reactive oxygen species (mtROS) and elevated oxygen consumption rate (OCR). Furthermore, TREM‐1 silencing in Tat‐treated macrophages reversed the disruption of tight junction barrier integrity in co‐cultured lung epithelial cells through modulation of macrophage‐derived exosome shuttling.ConclusionTREM‐1 escalates neutrophilic lung inflammation in HIV transgenic mice treated with PAO1, results in mitochondrial dysfunction of macrophages and disrupts tight junction barrier integrity of epithelia cells in lung microenvironment. These data suggest that TREM‐1 inhibition might be an important immunomodulatory therapeutic strategy for HIV‐infected patients with lung infections.Support or Funding InformationThis work is supported by VA Merit Review 2I01BX001786‐06A1 (Ruxana T Sadikot) and R01 HL125042(David M Guidot).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Inhibition of TREM-1 attenuates early brain injury after subarachnoid hemorrhage via downregulation of p38MAPK/MMP-9 and preservation of ZO-1

Early brain injury (EBI) mainly leads to the poor outcome of subarachnoid hemorrhage (SAH), with which inflammation is closely associated. It was reported that triggering receptor expressed on myeloid cells-1 (TREM-1), a critical inflammatory amplifier, increased in cerebrospinal fluid of SAH patients in our recent research. This study was conducted to examine the effects of TREM-1 inhibition on EBI after experimental SAH (eSAH). The endovascular perforation model of SAH was produced and 120 rats were randomly divided into four groups as sham, SAH + vehicle and SAH + LP17 (1.0 mg/kg and 3.5 mg/kg). The LP17, a selective inhibitor of TREM-1, or vehicle was administered by an intraperitoneal injection 1 h post-modeling. Western blot analysis for TREM-1, p38 mitogen-activated protein kinase (p38MAPK), matrix metalloproteinase-9 (MMP-9) and zonula occludens-1 (ZO-1) was conducted at 24 h post-modeling. EBI was assessed in terms of mortality, neuroscore, brain edema, blood–brain barrier (BBB) disruption in 24 and 72 h. The results showed that TREM-1 was induced in brain after eSAH. Both high dose (3.5 mg/kg) and low dose (1.0 mg/kg) of Lp17 significantly inhibited the induction of TREM-1, but only high dose of LP17 improved neuroscore, brain edema, and BBB disruption which are associated with downregulation of p38MAPK/MMP-9 and subsequent preservation of ZO-1. Overall, the current study provides new evidence that TREM-1 may participate in the pathogenesis of SAH-induced EBI via promoting p38MAPK/MMP-9 activation and ZO-1 degradation, while TREM-1 inhibition attenuated the EBI severity obviously, providing a novel approach for the treatment of EBI.