Triggering Receptor Expressed On Myeloid Cells 2 Expression Research Articles

Regulatory mechanism of TRIM21 in sepsis-induced acute lung injury by promoting IRF1 ubiquitination.

Sepsis-induced acute lung injury (ALI) is characterized by inflammatory damage to pulmonary endothelial and epithelial cells. The aim of this study is to probe the significance and mechanism of tripartite motif-containing protein 21 (TRIM21) in sepsis-induced ALI. The sepsis-induced ALI mouse model was established by cecum ligation and puncture. The mice were infected with lentivirus and treated with proteasome inhibitor MG132. The lung respiratory damage, levels of interleukin-6 (IL-6), tumour necrosis factor α (TNF-α), IL-10 and pathological changes were observed. The expression levels of TRIM21, interferon regulatory factors 1 (IRF1) and triggering receptor expressed on myeloid cells 2 (TREM2) were measured and their interactions were analysed. The ubiquitination level of IRF1 was detected. TRIM21 and TREM2 were downregulated and IRF1 was upregulated in sepsis-induced ALI mice. TRIM21 overexpression eased inflammation and lung injury. TRIM21 promoted IRF1 degradation via ubiquitination modification. IRF1 bonded to the TREM2 promoter to inhibit its transcription. Overexpression of IRF1 or silencing TREM2 reversed the improvement of TRIM21 overexpression on lung injury in mice. In conclusion, TRIM21 reduced IRF1 expression by ubiquitination to improve TREM2 expression and ameliorate sepsis-induced ALI.

Upregulation of TREM2 expression in M2 macrophages promotes Brucella abortus chronic infection.

Brucella abortus (B.abortus) is a zoonotic bacterial pathogen that causes chronic host infections. The eradication of brucellosis using antibiotic therapy is often incomplete or slow. In a mouse model, the predominance of alternatively activated macrophages (also known as M2) plays an essential role in sustaining chronic infection. The underlying functional mechanism by which M2 sustains chronic infection remains unclear. Here, we show that B. abortus can enter M2 via triggering receptor expressed on myeloid cells 2 (TREM2) and promotes the upregulation of TREM2 expression of M2 in a type IV secretion system (T4SS)-dependent manner. Increased TREM2 enhances B. abortus growth within M2 by suppressing intracellular ROS production, preventing M2 pyroptosis via suppression of mitochondrial ROS (mROS), and promoting M2 proliferation by increasing β-catenin expression. In line with these results, downregulation of TREM2 expression suppressed B. abortus intracellular growth and M2 proliferation and induced M2 pyroptosis. In our mouse model, upregulation of TREM2 expression sustained the accumulation of M2 and B. abortus chronic infection, whereas downregulation of TREM2 expression restricted M2 proliferation and chronic infection. Collectively, our results suggest that targeting TREM2 may be a potential adjunct to antibiotic therapy for the prevention of chronic Brucella infection.

Lipidomics Analysis of Human HMC3 Microglial Cells in an In Vitro Model of Metabolic Syndrome.

Metabolic endotoxemia (ME) is associated with bacterial lipopolysaccharide (LPS, endotoxin) and increased levels of saturated fatty acids (SFAs) in the bloodstream, causing systemic inflammation. ME usually accompanies obesity and a diet rich in fats, especially SFAs. Numerous studies confirm the effect of ME-related endotoxin on microglial activation. Our study aimed to assess lipid metabolism and immune response in microglia pre-stimulated with TNFα (Tumor Necrosis Factor α) and then with endotoxin and palmitic acid (PA). Using ELISA, we determined cytokines IL-1β, IL-10, IL-13 (interleukin-1β, -10, -13, and TGFβ (Transforming Growth Factor β) in the culture medium from microglial cells stimulated for 24 h with TNFα and then treated with LPS (10 ng/mL) and PA (200 µM) for 24 h. HMC3 (Human Microglial Cells clone 3) cells produced negligible amounts of IL-1β, IL-10, and IL-13 after stimulation but secreted moderate levels of TGFβ. Changes in lipid metabolism accompanied changes in TREM2 (Triggering Receptor Expressed on Myeloid Cells 2) expression. HMC3 stimulation with endotoxin increased TREM2 expression, while PA treatment decreased it. Endotoxin increased ceramide levels, while PA increased triglyceride levels. These results indicated that pre-stimulation of microglia with TNFα significantly affects its interactions with LPS and PA and modulates lipid metabolism, which may lead to microglial activation silencing and neurodegeneration.

Cannabis Use and Cannabidiol Modulate HIV-Induced Alterations in TREM2 Expression: Implications for Age-Related Neuropathogenesis.

Triggering receptor expressed on myeloid cells 2 (TREM2) is involved in neuroinflammation and HIV-associated neurocognitive impairment (NCI). People with HIV (PWH) using cannabis exhibit lower inflammation and neurological disorders. We hypothesized that TREM2 dysfunction mediates HIV neuropathogenesis and can be reversed by cannabinoids. EcoHIV-infected wildtype (WT) and TREM2R47H mutant mice were used to study HIV's impact on TREM2 and behavior. TREM2 and related gene expressions were examined in monocyte-derived macrophages (MDMs) from PWH (n = 42) and people without HIV (PWoH; n = 19) with varying cannabis use via RNA sequencing and qPCR. Differences in membrane-bound and soluble TREM2 (sTREM2) were evaluated using immunocytochemistry (ICC) and ELISA. EcoHIV increased immature and C-terminal fragment forms of TREM2 in WT mice but not in TREM2R47H mice, with increased IBA1 protein in TREM2R47H hippocampi, correlating with worse memory test performance. TREM2 mRNA levels increased with age in PWoH but not in PWH. Cannabidiol (CBD) treatment increased TREM2 mRNA alone and with IL1β. RNA-seq showed the upregulation of TREM2-related transcripts in cannabis-using PWH compared to naïve controls. IL1β increased sTREM2 and reduced membrane-bound TREM2, effects partially reversed by CBD. These findings suggest HIV affects TREM2 expression modulated by cannabis and CBD, offering insights for therapeutic strategies.

TREM2 alleviates long-term cognitive dysfunction after subarachnoid hemorrhage in mice by attenuating hippocampal neuroinflammation via PI3K/Akt signaling pathway

Subarachnoid hemorrhage (SAH) often leads to long-term cognitive deficits in patients, particularly due to injury to brain regions such as the hippocampus. This study aims to investigate the role of the triggering receptor expressed on myeloid cells 2 (TREM2) in mitigating hippocampal injury and associated cognitive impairments following SAH. To explore the protective effects of TREM2, we utilized the TREM2 agonist COG1410 to upregulate TREM2 expression and employed TREM2 knockout (KO) mice to verify the necessity of TREM2 for this protective role. The study further examined the involvement of the PI3K/Akt signaling pathway in TREM2-mediated neuroprotection. Our findings indicate that the upregulation of TREM2 significantly alleviated long-term cognitive deficits and promoted the recovery of hippocampal neural activity post-SAH. The neuroprotective effects were linked to reduced microglial activation and decreased secretion of inflammatory factors within the hippocampus. In contrast, TREM2 KO mice did not exhibit these protective effects. Furthermore, inhibition of the PI3K/Akt pathway also diminished these protective effects of TREM2 upregulation and worsened cognitive outcomes. In conclusion, TREM2 upregulation mitigates long-term cognitive dysfunction following SAH by attenuating hippocampal neuroinflammation via the PI3K/Akt signaling pathway. These findings suggest that TREM2 could be a potential therapeutic target for improving cognitive outcomes after SAH.

Galectin-3 induces pathogenic immunosuppressive macrophages through interaction with TREM2 in lung cancer

BackgroundHigh infiltration of tumor-associated macrophages (TAMs) is associated with tumor promotion and immunosuppression. The triggering receptor expressed on myeloid cells 2 (TREM2) is emerged as a key immunosuppressive regulator for TAMs, however, how TREM2-expressing TAMs are recruited and what ligands TREM2 interacts with to mediate immunosuppression is unknown.MethodsFlow cytometry and single-cell RNA sequencing were used to analyze TREM2 expression. Mechanistically, mass spectrometry and immunoprecipitation were employed to identify proteins binding to TREM2. Phagocytosis and co-culture experiments were used to explore the in vitro functions of galectin3-TREM2 pair. Establishment of TREM2f/f-Lyz2-cre mice to validate the role of TREM2 signaling pathway in lung carcinogenesis. GB1107 were further supplemented to validate the therapeutic effect of Galectin3 based on TREM2 signaling regulation.ResultsThis study identified that abundant TREM2+ macrophages were recruited at the intra-tumor site through the CCL2-CCR2 chemotactic axis. Galectin-3 impaired TREM2-mediated phagocytosis and promoted the conversion of TREM2+ macrophages to immunosuppressive TAMs with attenuated antigen presentation and co-stimulatory functions both in vitro both in vivo, and galectin-3 is a potential ligand for TREM2. Genetic and pharmacological blockade of TREM2 and galectin-3 significantly inhibited lung cancer progression in subcutaneous and orthotopic cancer models by remodeling the tumor immune microenvironment.ConclusionOur findings revealed a previously unknown association between galectin-3 and TREM2 in TAMs of lung cancer, and suggested simultaneous inhibition of galectin3 and TREM2 as potent therapeutic approach for lung cancer therapy.Graphical

Raphanus sativus Linne Protects Human Nucleus Pulposus Cells against H2O2-Induced Damage by Inhibiting TREM2.

Intervertebral disc degeneration (IDD) progresses owing to damage and depletion of nucleus pulposus (NP) cells. Cytoprotection mitigates oxidative stress, nutrient deprivation, and mechanical stress, which lead to cell damage and necrosis. We aimed to examine the protective effect of Raphanus sativus Linne (RSL), common radish, against oxidative stress by H2O2 in human NP cells and whether the RSL extracts can inhibit triggering receptor expressed on myeloid cells 2 (TREM2), an inducer of apoptosis and degeneration in NP cells. We administered hydrogen peroxide (H2O2) to cultured human NP cells treated with RSL extracts. We used immunoblotting and quantitative PCR to investigate expression of the apoptosis-associated proteins in cultured cells. RSL significantly enhanced cell survival by suppressing the activation of cleaved caspase-3 and Bax. In contrast, RSL extract increased Bcl2 concentration to downregulate apoptosis. Additionally, RSL treatment notably enhanced the mRNA levels of ACAN and Col2a1 while significantly reducing those of ADAMTS-4, ADAMTS-5, MMP3, and MMP13, key genes involved in NP degeneration. While H2O2 elevated TREM2 expression, causing disc degeneration, RSL downregulated TREM2 expression. Thus, our findings imply that RSL supports human NP cells under oxidative stress and regulates the pathways underlying disc degeneration, particularly TREM2, and that RSL extracts may potentially prevent IDD.

CD33 Ameliorates Surgery-Induced Spatial Learning and Memory Impairments Through TREM2.

Neuroinflammation is implicated in the onset of postoperative cognitive dysfunction (POCD), with CD33 and triggering receptor expressed on myeloid cells 2 (TREM2) playing crucial roles in immune response modulation and neuroinflammatory processes. A total of 96 aged male C57/BL6 mice (9-12 months) were randomly assigned to one of four groups, each receiving an siRNA injection into the lateral ventricle. Subsequently, the mice underwent partial hepatectomy under general anesthesia. To assess cognitive function, the Morris water maze tests were conducted both pre- and post-surgery. Following behavioral assessments, hippocampal tissues were swiftly harvested. The regulation of CD33 and TREM2 expression was achieved through siRNA in the BV2 microglia cell line. Expression levels of CD33 and TREM2 were evaluated both in vitro and in vivo using quantitative RT-PCR and western blot analyses. This study explored the impact of CD33 and TREM2 on POCD in aged mice and revealed that surgery and anesthesia increased CD33 expression, leading to spatial learning and memory impairments. Inhibiting CD33 expression via siRNA administration ameliorated cognitive deficits and mitigated the neuroinflammatory response triggered by surgery. Additionally, CD33 inhibition reversed the surgery-induced decrease in synaptic-related proteins, highlighting its role in preserving synaptic integrity. Moreover, our experiments suggest that CD33 may influence neuroinflammation and cognitive function through mechanisms involving TREM2. This is evidenced by the suppression of pro-inflammatory cytokines following CD33 knockdown in microglia and the reversal of these effects when both CD33 and TREM2 are concurrently knocked down. These findings imply that CD33 might promote neuroinflammation by inhibiting TREM2. This study highlights the potential of targeting CD33 as a promising therapeutic strategy for preventing and treating POCD. It provides valuable insights into the intricate mechanisms underlying cognitive dysfunction following surgical procedures.

Triggering Receptor Expressed on Myeloid Cells 2 Alleviated Sevoflurane-Induced Developmental Neurotoxicity via Microglial Pruning of Dendritic Spines in the CA1 Region of the Hippocampus.

Sevoflurane induces developmental neurotoxicity in mice; however, the underlying mechanisms remain unclear. Triggering receptor expressed on myeloid cells 2 (TREM2) is essential for microglia-mediated synaptic refinement during the early stages of brain development. We explored the effects of TREM2 on dendritic spine pruning during sevoflurane-induced developmental neurotoxicity in mice. Mice were anaesthetized with sevoflurane on postnatal days 6, 8, and 10. Behavioral performance was assessed using the open field test and Morris water maze test. Genetic knockdown of TREM2 and overexpression of TREM2 by stereotaxic injection were used for mechanistic experiments. Western blotting, immunofluorescence, electron microscopy, three-dimensional reconstruction, Golgi staining, and whole-cell patch-clamp recordings were performed. Sevoflurane exposures upregulated the protein expression of TREM2, increased microglia-mediated pruning of dendritic spines, and reduced synaptic multiplicity and excitability of CA1 neurons. TREM2 genetic knockdown significantly decreased dendritic spine pruning, and partially aggravated neuronal morphological abnormalities and cognitive impairments in sevoflurane-treated mice. In contrast, TREM2 overexpression enhanced microglia-mediated pruning of dendritic spines and rescued neuronal morphological abnormalities and cognitive dysfunction. TREM2 exerts a protective role against neurocognitive impairments in mice after neonatal exposures to sevoflurane by enhancing microglia-mediated pruning of dendritic spines in CA1 neurons. This provides a potential therapeutic target in the prevention of sevoflurane-induced developmental neurotoxicity.

Astrocyte-TREM2 alleviates brain injury by regulating reactive astrocyte states following ischemic stroke.

Triggering receptor expressed on myeloid cells 2 (TREM2) has been shown to confer strong neuroprotective effects in acute ischemic stroke (AIS). However, as the vast majority of research findings to date are based on its functions in microglia, the precise role of TREM2 in astrocytes after AIS is unknown. Here, both loss- and gain-of-function experiments were employed to investigate how astrocytic TREM2 influences the pathogenesis of AIS in vivo and in vitro. Our results demonstrated that cerebral ischemia triggered induction of TREM2 expression on reactive astrocytes following AIS. In addition, astrocyte-specific TREM2 knockout mice exhibited much greater brain injury than TREM2 flox/flox controls following AIS, as evidenced by increased cerebral infarct volume, neuronal apoptosis and neurological deficit, which was associated with an increased expression of pro-inflammatory molecule complement component 3 (C3) on reactive astrocytes and activation of microglia/macrophages but decreased expression of S100 calcium binding protein A10 (S100A10) and arginase1 (Arg1) on reactive astrocytes. Mechanistic analyses revealed that astrocytic TREM2 alleviated brain injury by inhibiting detrimental actions of reactive astrocytes but promoting their neuro- and glioprotective actions via the kruppel-like transcription factor-4-nuclear factor-κB axis. Together, this study provides novel evidence for a critical protective role of astrocyte-derived TREM2 in AIS and highlights a potential therapeutic target for the treatment of AIS.

Systematic analysis of TREM2 and its carcinogenesis in pancreatic cancer.

Triggering receptor expressed on myeloid cells 2 (TREM2), a transmembrane immunoglobulin-superfamily receptor, is expressed primarily on cells such as macrophages and dendritic cells. TREM2 has been shown to be associated with diseases such as neurodegeneration, fatty liver, obesity, and atherosclerosis. Currently, it has become one of the hotspots in oncology research. However, the role of TREM2 in pan-cancer, especially pancreatic cancer, remains unclear. We used the Tumor-immune System Interactions Database (TISIDB) to explore TREM2 expression differences, Tumor Immune Single-cell Hub 2 (TISCH2) to explore TREM2 expression distribution, Tumor IMmune Estimation Resource 2.0 (TIMER 2.0) to explore immune infiltration, cBio Cancer Genomics Portal (cBioPortal) to explore genetic variation, Genomics of Drug Sensitivity in Cancer (GDSC) to explore drug resistance, and Kaplan-Meier plotter database to explore the relationship between TREM2 and prognosis in pancreatic cancer. In addition, we used The Cancer Genome Atlas-pancreatic adenocarcinoma (TCGA-PAAD) and normal pancreas samples from the Genotype-Tissue Expression (GTEx) databases to explore the relationship between TREM2 and lymph node metastasis. We verified the protein level of TREM2 in pancreatic cancer by Human Protein Atlas (HPA) and western blotting and detected the colocalization of TREM2 with malignant cell markers by multiplex immunohistochemistry (mIHC). Finally, we identified the tumor-promoting role of TREM2 in pancreatic cancer via in vitro experiments, such as cell cycle assays, colony formation assays, and transwell migration and invasion assays. Our results showed that TREM2 was differentially expressed in various tumors according to different molecular and immune subtypes of pan-cancer. It was found that TREM2 was mainly expressed in monocytes/macrophages. In addition, our study showed that TREM2 expression was closely associated with macrophages in the tumor microenvironment (TME) of pan-cancer. TREM2 was shown to be related to anti-inflammatory and immunosuppressive effects in most cancers. Furthermore, we found that amplification was the main somatic mutation of TREM2 in pan-cancer. Further correlational analysis revealed a significant negative association of TREM2 expression with sensitivity to AZD8186, which is a selective inhibitor of PI3K, but not gemcitabine and paclitaxel. Finally, through the knockdown and overexpression of TREM2, our findings verified that TREM2 on cancer cells promoted the progression of PAAD. In conclusion, our comprehensive analysis identified that TREM2 expression level was correlated with the TME and the immunosuppressive effects. In particular, our study indicated that TREM2 was involved in the progression of pancreatic cancer.

Distinct roles of TREM2 in central nervous system cancers and peripheral cancers

Glioblastomas (GBM) are incurable central nervous system (CNS) cancers characterized by substantial myeloid cell infiltration. Whether myeloid cell-directed therapeutic targets identified in peripheral non-CNS cancers are applicable to GBM requires further study. Here, we identify that the critical immunosuppressive target in peripheral cancers, triggering receptor expressed on myeloid cells-2 (TREM2), is immunoprotective in GBM. Genetic or pharmacological TREM2 deficiency promotes GBM progression invivo. Single-cell and spatial sequencing reveals downregulated TREM2 in GBM-infiltrated myeloid cells. TREM2 negatively correlates with immunosuppressive myeloid and Tcell exhaustion signatures in GBM. We further demonstrate that during GBM progression, CNS-enriched sphingolipids bind TREM2 on myeloid cells and elicit antitumor responses. Clinically, high TREM2 expression in myeloid cells correlates with better survival in GBM. Adeno-associated virus-mediated TREM2 overexpression impedes GBM progression and synergizes with anti-PD-1 therapy. Our results reveal distinct functions of TREM2 in CNS cancers and support organ-specific myeloid cell remodeling in cancer immunotherapy.

TREM2 protects against inflammation by regulating the release of mito-DAMPs from hepatocytes during liver fibrosis

BackgroundLiver fibrosis typically develops as a result of chronic liver injury, which involves inflammatory and regenerative processes. The triggering receptor expressed on myeloid cells 2 (TREM2), predominantly expressing in hepatic non-parenchymal cells, plays a crucial role in regulating the function of macrophages. However, its mechanism in liver fibrosis remains poorly defined. MethodsExperimental liver fibrosis models in wild type and TREM2−/− mice, and in vitro studies with AML-12 cells and Raw264.7 cells were conducted. The expression of TREM2 and related molecular mechanism were evaluated by using samples from patients with liver fibrosis. ResultsWe demonstrated that TREM2 was upregulated in murine model with liver fibrosis. Mice lacking TREM2 exhibited reduced phagocytosis activity in macrophages following carbon tetrachloride (CCl4) intoxication. As a result, there was an increased accumulation of necrotic apoptotic hepatocytes. Additionally, TREM2 knockout aggravated the release of mitochondrial damage-associated molecular patterns (mito-DAMPs) from dead hepatocytes during CCl4 exposure, and further promoted the occurrence of macrophage-mediated M1 polarization. Then, TREM2−/− mice showed more serious fibrosis pathological changes. In vitro, the necrotic apoptosis inhibitor GSK872 effectively alleviated the release of mito-DAMPs in AML-12 cells after CCl4 intoxication, which confirmed that mito-DAMPs originated from dead liver cells. Moreover, direct stimulation of Raw264.7 cells by mito-DAMPs from liver tissue can induce intracellular inflammatory response. More importantly, TREM2 was elevated and inflammatory factors were markedly accumulated surrounding dead cells in the livers of human patients with liver fibrosis. ConclusionOur study highlights that TREM2 serves as a negative regulator of liver fibrosis, suggesting its potential as a novel therapeutic target.

SHIP inhibition mediates select TREM2-induced microglial functions

Microglia play a pivotal role in the pathology of Alzheimer's Disease (AD), with the Triggering Receptor Expressed on Myeloid cells 2 (TREM2) central to their neuroprotective functions. The R47H variant of TREM2 has emerged as a significant genetic risk factor for AD, leading to a loss-of-function phenotype in mouse AD models. This study elucidates the roles of TREM2 in human microglia-like HMC3 cells and the regulation of these functions by SH2-containing inositol-5′-phosphatase 1 (SHIP1). Using stable cell lines expressing wild-type TREM2, the R47H variant, and TREM2-deficient lines, we found that functional TREM2 is essential for the phagocytosis of Aβ, lysosomal capacity, and mitochondrial activity. Notably, the R47H variant displayed increased phagocytic activity towards apoptotic neurons. Introducing SHIP1, known to modulate TREM2 signaling in other cells, revealed its role as a negative regulator of these TREM2-mediated functions. Moreover, pharmacological inhibition of both SHIP1 and its isoform SHIP2 amplified Aβ phagocytosis and lysosomal capacity, independently of TREM2 or SHIP1 expression, suggesting a potential regulatory role for SHIP2 in these functions. The absence of TREM2, combined with the presence of both SHIP isoforms, suppressed mitochondrial activity. However, pan-SHIP1/2 inhibition enhanced mitochondrial function in these cells. In summary, our findings offer a deeper understanding of the relationship between TREM2 variants and SHIP1 in microglial functions, and emphasize the therapeutic potential of targeting the TREM2 and SHIP1 pathways in microglia for neurodegenerative diseases.

Effect of Huanglian Jiedu Decoction on TREM2/Akt/GSK3β pathway in cerebral cortex of APP/PS1 transgenic mice

The Chinese medical mechanism of Huanglian Jieduo Decoction on treating Alzheimer's disease(AD) characterized by "toxin damaging brain collateral" is still unclear. This study aims to explore the mechanism of Huanglian Jieduo Decoction on regulating triggering receptor expressed on myeloid cells 2(TREM2)/protein kinase B(Akt)/glycogen synthase kinase 3β(GSK3β) pathway to improve the cognitive deficit in APP/PS1 transgenic mice. APP/PS1 mice of approximately nine months old were randomly divided into the model group, the low, medium, and high(2.5, 5, and 10 g·kg~(-1)) groups of Huanglian Jiedu Decoction, and 0.75 mg·kg~(-1) donepezil hydrochloride group, and the C57BL/6J mice with the same age were taken as the normal group. After one month of continuous oral administration, a Morris water maze was performed to detect the learning and memory ability of mice. Hematoxylin-eosin(HE) staining was applied to observe the morphology of neuronal cells in the cortical area of mice. Immunofluorescence was used to detect the protein expressions of β-amyloid(Aβ_(1-42)), CD86, and arginase 1(Arg1). The mRNA levels of interleukin(IL)-1β, IL-6, and IL-10 in the cortex of mice were detected by real-time fluorescence quantitative polymerase chain reaction(RT-qPCR). The protein expressions of TREM2, phosphoinositide-3 kinase(PI3K), Akt, GSK3β, and beta-catenin(β-catenin) in mouse cortex were determined by Western blot. The results indicated that the escape latency of the model group was significantly prolonged, and the residence time in the target quadrant and the number of crossing the platform were significantly reduced compared with the normal group. Mice in the model group had a significantly lower number of neurons in the cortex and showed nuclear pyknosis and a significant increase in the expressions of Aβ_(1-42) and CD86. The mRNA levels of IL-1β and IL-6 in tissue were significantly increased, IL-10 were increased, while Arg1 were significantly decreased. The expression of TREM2, p-PI3K(Y607), p-Akt(T308), p-GSK3β(Ser9), and β-catenin in the cortex were significantly down-regulated. Compared with the model group, the escape latency of the mice in the administration group was significantly shortened, and the number of crossing the platform and the residence time in the target quadrant were significantly increased. Furthermore, the number of neurons in the cortex of mice was increased, and nuclear pyknosis was improved. Aβ_(1-42) deposition was decreased significantly. The mRNA levels of IL-1β, IL-6 and CD86 were significantly decreased, while IL-10 and Arg1 levels were significantly increased. The expression of TREM2, p-PI3K(Y607), p-Akt(T308), p-GSK3β(Ser9), and β-catenin protein in the cortex of each administration group was significantly up-regulated compared with the model group. In conclusion, Huanglian Jiedu Decoction reduced the expression of Aβ_(1-42) and neuroinflammation to a neuro-protective effect, thereby improving the learning and memory ability in APP/PS1 mice, which may be related to the TREM2/Akt/GSK3β signaling pathway.

Abstract 3923: Targeting immunosuppressive TREM2+tumor associated macrophages in prostate cancer

Abstract With over 250,000 new cases annually, prostate cancer (PCa) is amongst the most diagnosed cancers in the United States. Despite a near-perfect 5-year survival rate in patients with localized disease with androgen deprivation therapy (ADT), about 10-20% of patients on ADT eventually develop castration-resistant prostate cancer (CRPC). Immunotherapies are typically ineffective in treating these treatment-resistant patients due to the abundance of immunosuppressive tumor-associated macrophages (TAMs) and lack of infiltrating lymphocytes. We propose to target these immunosuppressive macrophages through the triggering receptor expressed on myeloid cells 2 (TREM2), which has been identified as a major mediator of suppressive macrophage function but has not been studied in the context of PCa and CRPC. For this study, we analyzed publicly available RNA-seq datasets to query for TREM2 expression amongst patients with a range of prostate cancer disease states and cell types, measured tumor growth kinetics in two subcutaneous models of prostate cancer, and compared tumor immune infiltrates by flow cytometry. Our analysis of the TCGA prostate adenocarcinoma (PRAD) and the Stand Up to Cancer/Prostate Cancer Foundation (SU2C/PCF) datasets implicate TREM2 expression with prostate cancer progression, by Gleason score and progression-free status, and with worse overall survival of patients with metastatic CRPC (mCRPC). Manual curation and analysis of 10 single-cell RNA-seq datasets with a total of 84 patients, encompassing primary PCa, CRPC, and mCRPC indicate that TREM2 is highly and specifically expressed on TAMs in prostate cancer, with macrophages from patient-matched tumor samples expressing higher TREM2 compared to normal adjacent tissue. B6CaP tumors, with a luminal cytokeratin profile, high AR expression, and high Myc expression, show slower tumor growth in Trem2−/− mice compared to tumors in Trem2wt mice. On the other hand, RM1 tumors show no difference in growth kinetics on Trem2−/− mice. A major difference between the B6CaP and RM1 tumor microenvironments is the level of macrophage infiltration, where only 2-5% of immune cells in RM1 tumors are macrophages, compared to the 40-50% in B6CaP tumors. RM1 cells co-implanted with Trem2−/− macrophages show slower tumor growth, compared to tumor cells co-implanted with Trem2wt macrophages, confirming the role of Trem2-expressing macrophages in mediating tumor growth. Consistent with previous reports of suppressive Trem2 signaling, we also observed higher levels of inflammatory cytokine production in ex vivo stimulated Trem2−/− TAMs. By targeting TREM2 in prostate cancer, we find that TAMs are less suppressive, more inflammatory, and permit cytotoxic lymphocyte infiltration to enhance anti-tumor responses by synergizing with chemo and immune checkpoint therapy. Citation Format: Alex J. Lee, Kenneth Adusei, Monali Praharaj, Fan Shen, Xiaoxu Wang, Kaavya Bhatia, Thomas Nirschl, Jelani C. Zarif. Targeting immunosuppressive TREM2+tumor associated macrophages in prostate cancer [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 3923.

Triggering receptor expressed on myeloid cells 2 (TREM2) regulates phagocytosis in glioblastoma.

Glioblastomas (GBMs) are central nervous system tumors that resist standard-of-care interventions and even immune checkpoint blockade. Myeloid cells in the tumor microenvironment can contribute to GBM progression; therefore, emerging immunotherapeutic approaches include reprogramming these cells to achieve desirable antitumor activity. Triggering receptor expressed on myeloid cells 2 (TREM2) is a myeloid signaling regulator that has been implicated in a variety of cancers and neurological diseases with contrasting functions, but its role in GBM immunopathology and progression is still under investigation. Our reverse translational investigations leveraged single-cell RNA sequencing and cytometry of human gliomas to characterize TREM2 expression across myeloid subpopulations. Using 2 distinct murine glioma models, we examined the role of Trem2 on tumor progression and immune modulation of myeloid cells. Furthermore, we designed a method of tracking phagocytosis of glioma cells in vivo and employed in vitro assays to mechanistically understand the influence of TREM2 signaling on tumor uptake. We discovered that TREM2 expression does not correlate with immunosuppressive pathways, but rather showed strong a positive association with the canonical phagocytosis markers lysozyme (LYZ) and macrophage scavenger receptor (CD163) in gliomas. While Trem2 deficiency was found to be dispensable for gliomagenesis, Trem2+ myeloid cells display enhanced tumor uptake compared to Trem2- cells. Mechanistically, we demonstrate that TREM2 mediates phagocytosis via Syk signaling. These results indicate that TREM2 is not associated with immunosuppression in gliomas. Instead, TREM2 is an important regulator of phagocytosis that may be exploited as a potential therapeutic strategy for brain tumors.

Different Splice Isoforms of Peripheral Triggering Receptor Expressed on Myeloid Cells 2 mRNA Expressions are Associated With Cognitive Decline in Mild Dementia Due to Alzheimer's Disease and Reflect Central Neuroinflammation.

Triggering receptor expressed on myeloid cells 2 (TREM2) is upregulated in activated microglia and may be related to cognitive decline in patients with Alzheimer's disease (AD). There is conflicting evidence regarding the association of peripheral TREM2 mRNA expression/soluble TREM2 (the extracellular domain of TREM2) with cognitive function/neuroinflammation in patients with AD. Herein, we studied the TREM2 and TREM2alt mRNA expression and their association with the cognitive performance in subjects with mild dementia due to AD and healthy controls. In a subgroup of patients with AD, magnetic resonance spectroscopy was used to measure the myo-inositol level in the posterior cingulate cortex, a surrogate marker for neuroinflammation. The results showed that increased TREM2 and TREM2alt mRNA expression is associated with AD pathogenesis at the mild dementia stage, thereby serving as a potential biomarker for early symptomatic stage of AD. TREM2 may exert protective effects on both cognition and central neuroinflammation.

PET imaging of microglia in Alzheimer's disease using copper-64 labeled TREM2 antibodies.

Triggering receptor expressed on myeloid cells 2 (TREM2) plays an essential role in microglia activation and is being investigated as a potential therapeutic target for modulation of microglia in several neurological diseases. In this study, we present the development and preclinical evaluation of 64Cu-labeled antibody-based PET radiotracers as tools for non-invasive assessment of TREM2 expression. Furthermore, we tested the potential of an antibody transport vehicle (ATV) that binds human transferrin receptor to facilitate transcytosis of TREM2 antibody-based radiotracers to the CNS and improve target engagement. Methods: A TREM2 antibody with an engineered transport vehicle (ATV:4D9) and without (4D9) were covalently modified with pNCS-benzyl-NODAGA and labeled with copper-64. Potency, stability, and specificity were assessed in vitro followed by in vivo PET imaging at the early 2 h, intermediate 20 h, and late imaging time points 40 h post-injection using a human transferrin receptor (hTfR) expressing model for amyloidogenesis (5xFAD;TfRmu/hu) or wild-type mice (WT;TfRmu/hu), and hTfR negative controls. Organs of interest were isolated to determine biodistribution by ex vivo autoradiography. Cell sorting after in vivo tracer injection was used to demonstrate cellular specificity for microglia and to validate TREM2 PET results in an independent mouse model for amyloidogenesis (AppSAA;TfRmu/hu). For translation to human imaging, a human TREM2 antibody (14D3) was radiolabeled and used for in vitro autoradiography on human brain sections. Results: The 64Cu-labeled antibodies were obtained in high radiochemical purity (RCP), radiochemical yield (RCY), and specific activity. Antibody modification did not impact TREM2 binding. ATV:4D9 binding proved to be specific, and the tracer stability was maintained over 48 h. The uptake of [64Cu]Cu-NODAGA-ATV:4D9 in the brains of hTfR expressing mice was up to 4.6-fold higher than [64Cu]Cu-NODAGA-4D9 in mice without hTfR. TREM2 PET revealed elevated uptake in the cortex of 5xFAD mice compared to wild-type, which was validated by autoradiography. PET-to-biodistribution correlation revealed that elevated radiotracer uptake in brains of 5xFAD;TfRmu/hu mice was driven by microglia-rich cortical and hippocampal brain regions. Radiolabeled ATV:4D9 was selectively enriched in microglia and cellular uptake explained PET signal enhancement in AppSAA;TfRmu/hu mice. Human autoradiography showed elevated TREM2 tracer binding in the cortex of patients with Alzheimer's disease. Conclusion: [64Cu]Cu-NODAGA-ATV:4D9 has potential for non-invasive assessment of TREM2 as a surrogate marker for microglia activation in vivo. ATV engineering for hTfR binding and transcytosis overcomes the blood-brain barrier restriction for antibody-based PET radiotracers. TREM2 PET might be a versatile tool for many applications beyond Alzheimer's disease, such as glioma and chronic inflammatory diseases.

TREM2 promotes macrophage polarization from M1 to M2 and suppresses osteoarthritis through the NF-κB/CXCL3 axis.

Objective: Osteoarthritis (OA) is the most prominent chronic arthritic disease, affecting over 3 billion people globally. Synovial macrophages, as immune cells, play an essential role in cartilage damage in OA. Therefore, regulating macrophages is crucial for controlling the pathological changes in OA. Triggering receptor expressed on myeloid cells 2 (TREM2), as expressed on immune cell surfaces, such as macrophages and dendritic cells, has suppressed inflammation and regulated M2 macrophage polarization but demonstrated an unknown role in synovial macrophage polarization in OA. This study aimed to investigate TREM2 expression downregulation in OA mice macrophages. Furthermore, the expression trend of TREM2 was associated with polarization-related molecule expression in macrophages of OA mice. Results: We used TREM2 knockout (TREM2-KO) mice to observe that TREM2 deficiency significantly exacerbated the joint inflammation response in OA mice, thereby accelerating disease progression. Separating macrophages and chondrocytes from TREM2-KO mice and co-cultivating them significantly increased chondrocyte apoptosis and inhibited chondrocyte proliferation. Further, TREM2 deficiency also significantly enhanced phosphatidylinositol 3-kinase(PI3K)/AKT signaling pathway activation, increasing nuclear factor kappa light chain enhancer of activated B cells (NF-κB) signaling and C-X-C Motif Chemokine Ligand 3 (CXCL3) expression. Furthermore, NF-κB signaling pathway inhibition significantly suppressed arthritis inflammation in OA mice, thereby effectively alleviating TREM2 deficiency-related adverse effects on chondrocytes. Notably, knocking down CXCL3 of TREM2-KO mice macrophages significantly inhibits inflammatory response and promotes chondrocyte proliferation. Intravenous recombinant TREM2 protein (soluble TREM2, sTREM2) injection markedly promotes macrophage polarization from M1 to M2 and improves the joint tissue pathology and inflammatory response of OA. Conclusion: Our study reveals that TREM2 promotes macrophage polarization from M1 to M2 during OA by NF-κB/CXCL3 axis regulation, thereby improving the pathological state of OA.