Soluble TREM2 induces inflammatory responses and enhances microglial survival

Identification of cytochrome P450 2E1 as a novel target in neuroinflammation and development of its inhibitor Q11 as a treatment strategy

Neuroinflammation is implicated in nearly all pathological processes of central nervous system (CNS) diseases. However, no medications specifically targeting neuroinflammation are clinically available, and conventional anti-inflammatory drugs exhibit limited efficacy. Here, we identified cytochrome P450 2E1 (CYP2E1) as a novel therapeutic target in neuroinflammation. Elevated CYP2E1 levels were observed in hippocampal tissues of mouse and rat neuroinflammation models, as well as in LPS-stimulated primary microglia. Genetic ablation of Cyp2e1 improved spatial learning and memory in neuroinflammatory rats and reduced pro-inflammatory cytokine levels in Cyp2e1-deficient microglia. Furthermore, Q11 (1-(4-methyl-5-thiazolyl) ethanone), a novel CYP2E1 inhibitor developed and synthesized in our laboratory, effectively ameliorated Alzheimer's disease-related spatial learning and memory functions and depression-related anxiety-like behaviors in mice/rats. Mechanistically, Q11 attenuated microglial activation, neuronal damage, oxidative stress, and neuroinflammation by suppressing the PI3K/Akt, STAT1/3, and NF-κB signaling pathways. These findings establish CYP2E1 as a druggable target for neuroinflammation and propose Q11 as a promising candidate for treating neuroinflammation-related diseases.

The potential mechanism and clinical application value of remote ischemic conditioning in stroke

Some studies have confirmed the neuroprotective effect of remote ischemic conditioning against stroke. Although numerous animal researches have shown that the neuroprotective effect of remote ischemic conditioning may be related to neuroinflammation, cellular immunity, apoptosis, and autophagy, the exact underlying molecular mechanisms are unclear. This review summarizes the current status of different types of remote ischemic conditioning methods in animal and clinical studies and analyzes their commonalities and differences in neuroprotective mechanisms and signaling pathways. Remote ischemic conditioning has emerged as a potential therapeutic approach for improving stroke-induced brain injury owing to its simplicity, non-invasiveness, safety, and patient tolerability. Different forms of remote ischemic conditioning exhibit distinct intervention patterns, timing, and application range. Mechanistically, remote ischemic conditioning can exert neuroprotective effects by activating the Notch1/phosphatidylinositol 3-kinase/Akt signaling pathway, improving cerebral perfusion, suppressing neuroinflammation, inhibiting cell apoptosis, activating autophagy, and promoting neural regeneration. While remote ischemic conditioning has shown potential in improving stroke outcomes, its full clinical translation has not yet been achieved.

Antibody-induced TREM2 ectodomain shedding inhibits TREM2 signaling in macrophage

Antibody-based therapy targeting triggering receptor expressed on myeloid cells 2 (TREM2) is a promising tumor immunotherapy strategy that blocks the TREM2 signaling pathway. How to develop inhibitory antibodies with better performance is the current challenge. Here, we aimed to explore how TREM2's stalk region (136-172 aa) protects the ectodomain from shedding and develop antibodies to promote TREM2 shedding and inhibit signal activation. Molecular dynamics simulations indicated a self-folding conformation in the stalk region of TREM2. The TREM2 risk variant (H157Y) reduces the stability of this conformation by affecting hydrogen bond formation. Histidine 154 (H154) also participated in maintaining the stability of the self-folding conformation and preventing shedding of TREM2. The screened antibody test-2 could target stalk region of TREM2, induce the shedding of TREM2 and regulate the expression of inflammatory factors in THP1 cells. These results suggest that antibodies targeting the stalk region of TREM2 have the potential to serve as inhibitory antibodies.

Soluble TREM2 ameliorates pathological phenotypes in ischemic stroke models via modulating neuronal and microglial functions

Although the neuroprotective effects of triggering receptor expressed on myeloid cell 2 (TREM2) upregulation after ischemic stroke has been demonstrated, the level change and effect of soluble TREM2 (sTREM2) derived from proteolytic cleavage of the TREM2 extracellular domain in ischemic stroke remain unknown. In our study, the level and function of sTREM2 were detected in neuron-microglia co-cultures subjected to oxygen glucose deprivation (OGD) and in the ischemic striatum of C57BL/6 J mice in a transient middle cerebral artery occlusion (tMCAO) model. sTREM2's effect on neuronal nitric oxide synthase (nNOS)-postsynaptic density protein-95 (PSD-95) interaction was determined by co-immunoprecipitation. The microglial-activated morphology in the striatum was identified by immunohistochemistry. Quantitative real-time polymerase chain reactionwas used to detect the transcriptional levels of TREM2, shorter variant TREM2, insulin-like growth factor 1, interleukin (IL)-4, and IL-13. Levels of sTREM2, generated through the cleavage of full-length TREM2 at the His157-Ser158 peptide bond, declined after OGD and tMCAO. sTREM2 reduced neuronal death after OGD and alleviated brain infarction and neurological deficits after tMCAO by disrupting the nNOS-PSD-95 interaction, promoting microglial activation, and increasing the expression of some cytokines associated with microglial polarization towards an anti-inflammatory phenotype. To the best of our knowledge, this is the first study to suggest that sTREM2 protects against transient cerebral ischemia.

TREM2 as a regulator of obesity-induced cardiac remodeling: mechanisms and therapeutic insights

Obesity and type 2 diabetes mellitus (T2DM) are global health challenges that significantly increase the risk of cardiovascular diseases (CVD). Advances in immunometabolism have identified triggering receptor expressed on myeloid cells 2 (TREM2) as a key regulator of macrophage function, lipid metabolism, and inflammation resolution. Although extensively studied in neurodegenerative diseases, TREM2's role in metabolic disorders and cardiovascular health is an emerging area of research. This review explores TREM2's molecular structure and functions, emphasizing its contributions to immunometabolic regulation in obesity and T2DM. Evidence from preclinical models demonstrates that TREM2 modulates macrophage-driven inflammatory responses, lipid clearance, plaque stability, fibrosis, and myocardial remodeling. Translational findings suggest that TREM2 expression correlates with cardiometabolic outcomes, underscoring its potential as a therapeutic target. Key knowledge gaps include TREM2's temporal dynamics during disease progression, sex-specific effects, and interactions with recruited or resident macrophage activation in obesity and T2DM. Integrating mechanistic and translational insights is critical to harness TREM2's immunoregulatory potential for improving CVD outcomes in metabolic disorders.

The late-onset Alzheimer's disease risk factor RHBDF2 is a modifier of microglial TREM2 proteolysis

The cell surface receptor TREM2 is a key genetic risk factor and drug target in Alzheimer's disease (AD). In the brain, TREM2 is expressed in microglia, where it undergoes proteolytic cleavage, linked to AD risk, but the responsible protease in microglia is still unknown. Another microglial-expressed AD risk factor is catalytically inactive rhomboid 2 (iRhom2, RHBDF2), which binds to and acts as a non-catalytic subunit of the metalloprotease ADAM17. A potential role in TREM2 proteolysis is not yet known. Using microglial-like BV2 cells, bone marrow-derived macrophages, and primary murine microglia, we identify iRhom2 as a modifier of ADAM17-mediated TREM2 shedding. Loss of iRhom2 increased TREM2 in cell lysates and at the cell surface and enhanced TREM2 signaling and microglial phagocytosis of the amyloid β-peptide (Aβ). This study establishes ADAM17 as a physiological TREM2 protease in microglia and suggests iRhom2 as a potential drug target for modulating TREM2 proteolysis in AD.

Brain-wide microglia replacement using a nonconditioning strategy ameliorates pathology in mouse models of neurological disorders

Growing genetic and pathological evidence has identified microglial dysfunction as a key contributor to the pathogenesis and progression of various neurological disorders, positioning microglia replacement as a promising therapeutic strategy. Traditional bone marrow transplantation (BMT) methods for replenishing brain microglia have limitations, including low efficiency and the potential for brain injury because of preconditioning regimens, such as irradiation or chemotherapy. Moreover, BM-derived cells that migrate to the brain do not recapitulate the phenotypic and functional properties of resident microglia. Here, we present a microglia transplantation strategy devoid of any conditioning, termed "tricyclic microglial depletion for transplantation" (TCMDT). This approach leverages three cycles of microglial depletion using the colony stimulating factor 1 receptor (CSF1R) inhibitor PLX3397, creating an optimal window for efficient engraftment of exogenous microglia. Transplantation of primary cultured microglia by TCMDT successfully restored the identity and functions of endogenous microglia. To evaluate the therapeutic potential of TCMDT, we applied this strategy to two distinct mouse models of neurologic disorder. In a Sandhoff disease model, a neurodegenerative lysosomal storage disorder caused by hexosaminidase subunit beta (Hexb) deficiency, TCMDT effectively replaced deficient microglia, attenuating neurodegeneration and improving motor performance. Similarly, in an Alzheimer's disease (AD)-related amyloid mouse model carrying the triggering receptor expressed on myeloid cells 2 (Trem2) R47H mutation, our transplantation strategy rescued microglial dysfunction and mitigated AD-related pathology. Overall, our study introduces TCMDT as a practical, efficient, and safe approach for microglia replacement, suggesting therapeutic potential for treating neurological disorders associated with microglial dysfunction.

TREM2 and sTREM2 in Alzheimer's disease: from mechanisms to therapies

Triggering receptor expressed on myeloid cells 2 (TREM2) is an innate immune receptor predominantly expressed by microglia in the brain. Recent studies have established TREM2 as a central immune signaling hub in neurodegeneration, where it triggers immune responses upon sensing pathological development and tissue damages. TREM2 binds diverse ligands and activates downstream pathways that regulate microglial phagocytosis, inflammatory responses, and metabolic reprogramming. Interestingly, TREM2 exists both in its membrane-bound form and as a soluble variant (sTREM2), that latter is generated through proteolytic shedding or alternative splicing and can be detected in cerebrospinal fluid and plasma. Emerging clinical and preclinical evidence underscores the potential of TREM2 and sTREM2 as diagnostic biomarkers and therapeutic targets in Alzheimer's disease (AD). This review provides a comprehensive overview of the molecular functions, regulatory mechanisms, and pathological implications of TREM2 and sTREM2 in AD. Furthermore, we explore their potential roles in diagnostics and therapeutics while suggesting key research directions for advancing TREM2/sTREM2-based strategies in combating AD.

IL-34/TREM2 modulates microglia-mediated inflammation and provides neuroprotection in a mouse model of sporadic Alzheimer's disease

BackgroundAs a recently identified cytokine, interleukin-34 (IL-34) is predominantly produced by neurons and functions as a modulator for glial functions. Emerging evidence indicates that IL-34 exerted neuroprotective effects in Alzheimer's disease (AD), but the underlying mechanism remained elusive.ObjectiveTo uncover the mechanisms by which IL-34 provides neuroprotection in AD.MethodsUsing senescence-accelerated mouse prone substrain 8 (SAMP8) mice, a well-established model for sporadic AD, we investigated the dynamic changes in brain IL-34 concentrations during AD progression. Afterwards, SAMP8 mice received a 4-week continuous intracerebroventricular infusion of IL-34. Morris water maze test was employed to assess the spatial cognitive functions. Neuronal and synaptic markers, oxidative stress makers, pro-inflammatory cytokines and glial activation markers in the brains of SAMP8 mice were measured. Finally, amyloid-β (Aβ)42-stimulated primary microglia, lentivirus-mediated gene knockdown strategy and co-immunoprecipitation assay were utilized to uncover the possible mechanisms by which IL-34 exerted neuroprotection in AD.ResultsIn SAMP8 mice, we revealed that brain IL-34 concentrations gradually decreased during AD progression. A 4-week continuous intracerebroventricular infusion of IL-34 rescued spatial cognitive impairments, ameliorated neuronal and synaptic damage, and suppressed oxidative stress and microglia-mediated inflammation in the brains of SAMP8 mice. Using Aβ42-stimulated primary microglia, we demonstrated for the first time that IL-34 suppressed microglial NLRP3 inflammasome activation and pro-inflammatory cytokines release by interacting with triggering receptor expressed on myeloid cells 2 (TREM2), a key regulator of microglial functions.ConclusionsThese findings uncover the mechanisms by which IL-34 provides neuroprotection in AD, indicating that IL-34/TREM2 signaling may represent a novel therapeutic strategy for this devastating disease.

Soluble TREM2 reflects liver fibrosis status and predicts postoperative liver dysfunction after liver surgery

Background & Aims

Triggering receptor expressed on myeloid cells 2 (TREM2)-expressing macrophages and systemic levels of soluble TREM2 (sTREM2) appear critical in the development of chronic liver disease (CLD) and seem relevant in its detection. The aim of this study was to examine sTREM2 as a marker for early CLD and its potential to predict posthepatectomy liver failure (PHLF) in patients undergoing partial hepatectomy.

Methods

sTREM2 was assessed in the plasma of 108 patients undergoing liver resection. Blood was drawn prior to surgery (preop) and on the first and fifth postoperative day.

Results

Preop sTREM2 levels were similar across different indications for resection (p = 0.091). Higher preop sTREM2 levels were associated with advanced hepatic fibrosis (p = 0.030) and PHLF (p = 0.007). Fibrosis-4 index (FIB-4) (p = 0.619) and model for end-stage liver disease (MELD) (p = 0.590) did not show a difference between patients grouped by their CLD. Comparing the AUC from receiver-operating characteristic analysis, sTREM2 (AUC = 0.708) outperformed FIB-4 (AUC = 0.529), MELD (AUC = 0.587), Child-Pugh grading (AUC = 0.570) and LiMAx (liver maximum capacity test) (AUC = 0.516) in predicting PHLF. Similarly, in uni- and multivariate analysis, only sTREM2 proved predictive for PHLF (p = 0.023). High-risk (p = 0.003) and low-risk (p = 0.011) cut-offs for systemic sTREM2 levels could identify patients at risk for adverse outcomes after surgery. Finally, high sTREM2 was associated with decreased overall survival after liver surgery (p <0.001).

Conclusions

Circulating sTREM2 shows sensitivity for early-stage, asymptomatic liver disease, irrespective of the underlying indication for liver surgery. Assessment of CLD via sTREM2 monitoring could improve early detection of CLD and improve outcomes after liver surgery.

Impact and implications

Soluble TREM2 (sTREM2) has previously been shown to correlate with the degree of chronic liver disease. We found that even in patients undergoing liver resection, who generally do not suffer from end-stage liver disease, sTREM2 reflects liver fibrosis status and predicts postoperative development of liver dysfunction. This is especially relevant for liver surgeons and patients, as postoperative liver dysfunction is the main reason for postoperative mortality. Our findings are also important for hepatologists, as early detection of liver fibrosis and cirrhosis is paramount for overall patient survival and we can show that even in a cohort with a median model for end-stage liver disease score of 6, sTREM2 is able to distinguish patients based on their liver fibrosis status.

Decoding microglial immunometabolism: a new frontier in Alzheimer's disease research

Alzheimer's disease (AD) involves a dynamic interaction between neuroinflammation and metabolic dysregulation, where microglia play a central role. These immune cells undergo metabolic reprogramming in response to AD-related pathology, with key genes such as TREM2, APOE, and HIF-1α orchestrating these processes. Microglial metabolism adapts to environmental stimuli, shifting between oxidative phosphorylation and glycolysis. Hexokinase-2 facilitates glycolytic flux, while AMPK acts as an energy sensor, coordinating lipid and glucose metabolism. TREM2 and APOE regulate microglial lipid homeostasis, influencing Aβ clearance and immune responses. LPL and ABCA7, both associated with AD risk, modulate lipid processing and cholesterol transport, linking lipid metabolism to neurodegeneration. PPARG further supports lipid metabolism by regulating microglial inflammatory responses. Amino acid metabolism also contributes to microglial function. Indoleamine 2,3-dioxygenase controls the kynurenine pathway, producing neurotoxic metabolites linked to AD pathology. Additionally, glucose-6-phosphate dehydrogenase regulates the pentose phosphate pathway, maintaining redox balance and immune activation. Dysregulated glucose and lipid metabolism, influenced by genetic variants such as APOE4, impair microglial responses and exacerbate AD progression. Recent findings highlight the interplay between metabolic regulators like REV-ERBα, which modulates lipid metabolism and inflammation, and Syk, which influences immune responses and Aβ clearance. These insights offer promising therapeutic targets, including strategies aimed at HIF-1α modulation, which could restore microglial function depending on disease stage. By integrating metabolic, immune, and genetic factors, this review underscores the importance of microglial immunometabolism in AD. Targeting key metabolic pathways could provide novel therapeutic strategies for mitigating neuroinflammation and restoring microglial function, ultimately paving the way for innovative treatments in neurodegenerative diseases.

Tetrahydroxy Stilbene Glycoside Reduces Abeta Deposition by Modulating Microglia Activation and via TREM2/PI3K/AKT Pathway in APP/PS1 Mice

Tetrahydroxy stilbene glycoside (TSG), which is the primary active substance of Chinese herbal medicine called Polygonum multiflorum, has been acknowledged to alleviate Alzheimer's disease (AD)-induced learning disorder in the transgene mice. Because the microglia activation is really important during the AD progression, herein, we determined the effects of TSG on AD neuropathology, microglia polarization and its underlying mechanism. We used APP/PS1 mice along with immunohistochemistry and immunofluorescence techniques to evaluate the function of TSG as 60, 120 and 180 mg/kg on Aβ deposition, neuronal loss and microglia polarization induced by AD. Additionally, we assessed the effects of TSG on TREM2 signalling using both molecular docking and Western blot analysis. TSG was found to promote neuronal survival and decrease Aβ deposition in APP/PS1 mice. Moreover, TSG reduced microglia M1 polarization and modulated the TREM2/PI3K/AKT signalling pathways. TSG could reduce neuronal impairment by mediating the microglia polarization by TREM2/PI3K/AKT signalling pathway in APP/PS1 mice and is a latent pharmacological research direction for the therapy in the patients with AD.

The various roles of TREM2 in cardiovascular disease

Triggering receptor expressed on myeloid cells-2 (TREM2) is a transmembrane immune receptor that is expressed mainly on macrophages. As a pathology-induced immune signaling hub, TREM2 senses tissue damage and activates immune remodeling in response. Previous studies have predominantly focused on the TREM2 signaling pathway in Alzheimer's disease, metabolic syndrome, and cancer. Recent research has indicated that TREM2 signaling is also activated in various cardiovascular diseases. In this review, we summarize the current understanding and the unanswered questions regarding the role of TREM2 signaling in mediating the metabolism and function of macrophages in atherosclerosis and various models of heart failure. In the context of atherosclerosis, TREM2 signaling promotes foam cell formation and is crucial for maintaining macrophage survival and plaque stability through efferocytosis and cholesterol efflux. Recent studies on myocardial infarction, sepsis-induced cardiomyopathy, and hypertensive heart failure also implicated the protective role of TREM2 signaling in cardiac macrophages through efferocytosis and paracrine functions. Additionally, we discuss the clinical significance of elevated soluble TREM2 (sTREM2) in cardiovascular disease and propose potential therapies targeting TREM2. The overall aim of this review is to highlight the various roles of TREM2 in cardiovascular diseases and to provide a framework for therapeutic strategies targeting TREM2.

Licochalcone A prevents cognitive decline in a lipopolysaccharide-induced neuroinflammation mice model

Inflammation plays a key role in the development of neurodegenerative disorders that are currently incurable. Licochalcone A (LCA) has been described as an emerging anti-inflammatory drug with multiple therapeutical properties that could potentially prevent neurodegeneration. However, its neuroprotective mechanism remains unclear. Here, we investigated if LCA prevents cognitive decline induced by Lipopolysaccharide (LPS) and elucidated its potential benefits. For that, 8-week-old C57BL6/J male mice were intraperitonially (i.p.) treated with saline solution or LCA (15 mg/kg/day, 3 times per week) for two weeks. The last day, a single i.p injection of LPS (1 mg/kg) or saline solution was administered 24 h before sacrifice. The results revealed a significant reduction in mRNA expression in genes involved in oxidative stress (Sod1, Cat, Pkm, Pdha1, Ndyfv1, Uqcrb1, Cycs and Cox4i1), metabolism (Slc2a1, Slc2a2, Prkaa1 and Gsk3b) and synapsis (Bdnf, Nrxn3 and Nlgn2) in LPS group compared to saline. These findings were linked to memory impairment and depressive-like behavior observed in this group. Interestingly, LCA protected against LPS alterations through its anti-inflammatory effect, reducing gliosis and regulating M1/M2 markers. Moreover, LCA-treated animals showed a significant improvement of antioxidant mechanisms, such as citrate synthase activity and SOD2. Additionally, LCA demonstrated protection against metabolic disturbances, downregulating GLUT4 and P-AKT, and enhanced the expression of synaptic-related proteins (P-CREB, BDNF, PSD95, DBN1 and NLG3), leading all together to dendritic spine preservation. In conclusion, our results demonstrate that LCA treatment prevents LPS-induced cognitive decline by reducing inflammation, enhancing the antioxidant response, protecting against metabolic disruptions and improving synapsis related mechanisms.

Retrotrans-genomics identifies aberrant THE1B endogenous retrovirus fusion transcripts in the pathogenesis of sarcoidosis

Transposon-like human element 1B (THE1B) originates from ancient retroviral sequences integrated into the primate genome approximately 50 million years ago, now accounting for at least 27,233 copies in the human genome, suggesting their extensive influence on human genomic architecture. Here we report identification of 19 THE1B fusion transcripts through short- and long-read RNA-seq analysis, 15 of which are previously unmapped, showing elevated expression in 16 individuals with sarcoid myopathy (SM), as compared to 400 controls with various other muscle diseases. Analysis of publicly available RNA-seq data indicated a correlation between the reduced expression of eight THE1B fusion transcripts and clinical improvement in individuals with cutaneous sarcoidosis receiving tofacitinib treatment. Single-cell or single-nucleus RNA-seq analyses of sarcoidosis not only confirmed these transcripts but also revealed a novel read-through transcript, SIRPB1-SIRPD, and TREM2.1, predominantly in granuloma-associated macrophages. The expression profiles of THE1B fusion transcripts in tuberculosis (TB) significantly differed from SM in single-cell RNA-seq data, suggesting that the differences between TB's caseous granulomas and sarcoidosis's non-caseous granulomas might be linked to disparate expression patterns of THE1B fusion transcripts. Our retrotrans-genomics approach has not only identified the genomic landscape of sarcoidosis but also provided new insights into its etiology.

HEBE: A novel chimeric chronokine for ameliorating memory deficits in Alzheimer's disease

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder characterized by amyloid-β and Tau protein depositions, with treatments focusing on single proteins have shown limited success due to the complexity of pathways involved. This study explored the potential of chronokines -proteins that modulate aging-related processes- as an alternative therapeutic approach. Specifically, we focused on a novel pleiotropic chimeric protein named HEBE, combining s-KL, sTREM2 and TIMP2, guided by bioinformatic analyses to ensure the preservation of each protein's conformation, crucial for their functions. In vitro studies confirmed HEBE's stability and enzymatic activities, even suggesting it has different activities compared to the individual chronokines. In vivo experiments on APP/Tau mice revealed improved learning and memory functions with HEBE treatment, along with decreased levels of phosphorylated Tau and minor effects on amyloid-β levels. These findings suggest that HEBE is as a promising therapeutic candidate for ameliorating memory deficits and reducing pTau in an AD mouse model.

Alzheimer's disease: insights into pathology, molecular mechanisms, and therapy

Alzheimer's disease (AD), the leading cause of dementia, is characterized by the accumulation of amyloid plaques and neurofibrillary tangles in the brain. This condition casts a significant shadow on global health due to its complex and multifactorial nature. In addition to genetic predispositions, the development of AD is influenced by a myriad of risk factors, including aging, systemic inflammation, chronic health conditions, lifestyle, and environmental exposures. Recent advancements in understanding the complex pathophysiology of AD are paving the way for enhanced diagnostic techniques, improved risk assessment, and potentially effective prevention strategies. These discoveries are crucial in the quest to unravel the complexities of AD, offering a beacon of hope for improved management and treatment options for the millions affected by this debilitating disease.

Neuraminidase 1 regulates neuropathogenesis by governing the cellular state of microglia via modulation of Trem2 sialylation

Neuraminidase 1 (NEU1) cleaves terminal sialic acids from sialoglycoproteins in endolysosomes and at the plasma membrane. As such, NEU1 regulates immune cells, primarily those of the monocytic lineage. Here, we examine how Neu1 influences microglia by modulating the sialylation of full-length Trem2 (Trem2-FL), a multifunctional receptor that regulates microglial survival, phagocytosis, and cytokine production. When Neu1 is deficient/downregulated, Trem2-FL remains sialylated, accumulates intracellularly, and is excessively cleaved into a C-terminal fragment (Trem2-CTF) and an extracellular soluble domain (sTrem2), enhancing their signaling capacities. Sialylated Trem2-FL (Sia-Trem2-FL) does not hinder Trem2-FL-DAP12-Syk complex assembly but impairs signal transduction through Syk, ultimately abolishing Trem2-dependent phagocytosis. Concurrently, Trem2-CTF-DAP12 complexes dampen NF-κB signaling, while sTrem2 propagates Akt-dependent cell survival and NFAT1-mediated production of TNF-α and CCL3. Because NEU1 and Trem2 are implicated in neurodegenerative/neuroinflammatory diseases, including Alzheimer disease and sialidosis, modulating NEU1 activity represents a therapeutic approach to broadly regulate microglia-mediated neuroinflammation.

Quantitative assessments of white matter hyperintensities and plasma biomarkers can predict cognitive impairment and cerebral microbleeds in cerebral small vessel disease patients

The objective of this study is to examine the efficacy of magnetic resonance imaging (MRI) features and peripheral blood biomarkers in assessing cognitive function in patients with cerebral small vessel disease (CSVD). A total of 58 CSVD patients were recruited. Six features of white matter hyperintensities (WMHs) were derived from MRI scans. Additionally, five neurodegenerative biomarkers (Aβ40, Aβ42, t-tau, p-tau181, NfL) and 13 serum inflammatory cytokines (VILIP-1, CCL2, IL-6, IL-18, TNF-α, CX3CL, sTREM-1/2, VEGF, s-RAGE, BNDF, TGF-β1, β-NGF) were quantified. Cognitive assessments were conducted using standardized neuropsychological scales. Spearman analysis revealed that the volumetric characteristics (absolute area, upper area, bottom area, absolute area percentage, upper percentage, and bottom percentage) of WMHs were negatively correlated with performance on all cognitive scale measures except the verbal fluency test (VFT) (r < -0.3, p > 0.05), while they were positively correlated with plasma neurofilament light (NFL) levels (r > 0.4, p < 0.05). Additionally, serum tumor necrosis factor-α (TNF-α) and soluble receptor for advanced glycation end-products (s-RAGE) showed significant correlations with scales of speech function. An integrated model incorporating WMHs features, neurodegenerative biomarkers, and neuroinflammatory markers was developed, demonstrating high predictive accuracy for cognitive impairment with an area under the curve (AUC) of 0.95 (accuracy 0.88, sensitivity 0.87, specificity 0.89). Another integrated model that includes features of WMHs and inflammatory cytokines for predicting cerebral microbleeds (CMBs) achieved an AUC of 0.95 (accuracy 0.88, sensitivity 0.82, specificity 0.92). Our findings suggest that these markers have the potential to be used for the early detection of cognitive decline and CMBs in patients with CSVD.

CD206+ Trem2+ macrophage accumulation in the murine knee joint after injury is associated with protection against post-traumatic osteoarthritis in MRL/MpJ mice

Post-traumatic osteoarthritis (PTOA) is a painful joint disease characterized by the degradation of bone, cartilage, and other connective tissues in the joint. PTOA is initiated by trauma to joint-stabilizing tissues, such as the anterior cruciate ligament, medial meniscus, or by intra-articular fractures. In humans, ~50% of joint injuries progress to PTOA, while the rest spontaneously resolve. To better understand molecular programs contributing to PTOA development or resolution, we examined injury-induced fluctuations in immune cell populations and transcriptional shifts by single-cell RNA sequencing of synovial joints in PTOA-susceptible C57BL/6J (B6) and PTOA-resistant MRL/MpJ (MRL) mice. We identified significant differences in monocyte and macrophage subpopulations between MRL and B6 joints. A potent myeloid-driven anti-inflammatory response was observed in MRL injured joints that significantly contrasted the pro-inflammatory signaling seen in B6 joints. Multiple CD206+ macrophage populations classically described as M2 were found enriched in MRL injured joints. These CD206+ macrophages also robustly expressed Trem2, a receptor involved in inflammation and myeloid cell activation. These data suggest that the PTOA resistant MRL mouse strain displays an enhanced capacity of clearing debris and apoptotic cells induced by inflammation after injury due to an increase in activated M2 macrophages within the synovial tissue and joint space.

TREM2 bridges microglia and extracellular microenvironment: Mechanistic landscape and therapeutical prospects on Alzheimer's disease

Neuroinflammation is closely related to the pathogenesis of Alzheimer's disease (AD). One of its prominent cellular components, microglia, is a potent coordinator of neuroinflammation in interplay with the characteristic AD pathological alterations including Aβ, tau, and neuronal defects, which constitute the AD-unique extracellular microenvironment. Mounting evidence implicates Triggering Receptors Expressed on Myeloid Cells 2 (TREM2) in the center of microglial activation, a vital event in the pathogenesis of AD. TREM2 is a pivotal microglial receptor that interacts with specific elements present in the AD microenvironment and induces microglial intracellular signallings contributing to phagocytosis, migration, cytokine production, metabolism, and survival, which shapes the microglial activation profile. It follows that TREM2 builds up a bridge between microglia and the extracellular microenvironment. This review illustrates how TREM2 modulates microglia to affect AD pathogenesis. Mainly presented facets in the review are i. the development of AD-specific microglial phenotypes (disease-associated microglia, DAM), ii. microglial interactions with major AD pathologies, and iii. the underlying intracellular signallings of microglial activation. Also, outstanding controversies regarding the nature of neuroinflammation are discussed. Through our illustration, we attempt to establish a TREM2-centered network of AD pathogenesis, in the hope as well to provide insights into the potential therapeutic strategies based on the underlying mechanisms.

CNS muscarinic receptors and muscarinic receptor agonists in Alzheimer disease treatment

This review explores the main aspects that form the basis of the cholinergic-oriented treatment of Alzheimer disease. Muscarinic acetylcholine receptor subtypes in the brain and periphery are discussed. It includes a new and updated overview of the involvement of muscarinic receptors in Alzheimer disease and the recent development of new and highly selective M1 muscarinic receptor agonists with disease-modifying potential. Activation of the M1 muscarinic receptor is a rational therapeutic strategy for the treatment of schizophrenia and Alzheimer disease, as this receptor plays a pivotal role in modulating cognitive deficits and the pathology of the disease. Such activation can be achieved through M1 allosteric and bitopic muscarinic agonists, M1 positive allosteric modulators (M1 PAMs), and direct-acting M1 muscarinic orthosteric agonists. The efficacy of M1 PAMs depends on acetylcholine, which declines in Alzheimer disease as postsynaptic neurons lose cholinergic input from the basal forebrain. On the other hand, the activity of M1 muscarinic orthosteric agonists is independent of the functional or anatomic integrity of presynaptic cholinergic terminals, and likely retain efficacy as the disease progresses, even after presynaptic degeneration of cholinergic fibers. Based on the acceptance criteria for a preferred M1 muscarinic agonist for the treatment of AD, aiming for efficacy, specificity, and safety in clinical use, few M1 muscarinic agonists fulfill these requirements, such as orthosteric M1 agonists-cevimeline (aka AF102B), the first FDA-approved M1 agonist, and NSC001 (aka AF267B). The pros and cons of various muscarinic agonists developed are critically discussed in comparison to these drugs. The review proposes new alternatives to cholinergic therapy, particularly selective M1 muscarinic drugs, that should be designed to amplify its clinical effect and supplement the disease-modifying effect of new treatments to slow down or arrest disease progression.

Longitudinal associations between cerebrospinal fluid glial activation markers, depression, and dopamine transporter availability in patients with Parkinson's disease

BACKGROUND

Depression and decreased dopamine transporter (DAT) availability are prevalent in Parkinson's disease (PD), yet early predictive biomarkers are lacking. This study investigates the longitudinal associations between cerebrospinal fluid (CSF) neuroglial activation markers, sTREM2 and YKL-40, and depression, as well as DAT availability, in PD patients.

METHODS

We analyzed data from 172 PD subjects and 80 matched healthy controls from a large longitudinal study. A generalized linear mixed-effects model assessed the longitudinal associations of CSF sTREM2 and YKL-40 with depression and DAT availability. Causal mediation analysis determined if DAT decline mediated the effects of sTREM2 and YKL-40 on depression.

RESULTS

Cross-sectional analysis revealed a negative correlation between CSF sTREM2 and baseline depression scores in PD patients. CSF YKL-40 negatively correlated with baseline left caudate nucleus, left anterior putamen, and right anterior putamen specific binding ratios (SBR). Longitudinally, higher baseline CSF sTREM2 predicted faster depression progression (β = 0.828, p < 0.001) and a rapid decline in right putamen SBR (β = 0.072, p = 0.016). Similarly, higher baseline CSF YKL-40 predicted faster depression progression (β = 0.586, p = 0.004) and a decline in left anterior putamen SBR (β = 0.058, p = 0.035). Causal mediation analysis indicated that baseline CSF sTREM2 accelerated depression progression via its effect on right putamen and right anterior putamen SBR (Indirect effect = 0.103, p = 0.020; Indirect effect = 0.129, p = 0.016).

CONCLUSION

CSF sTREM2 and YKL-40 are effective predictors for depression and DAT decline in PD, suggesting that neuroglial activation-induced dopaminergic neuron apoptosis significantly contributes to depression onset in PD.

The double-edged role and therapeutic potential of TREM2 in atherosclerosis

Atherosclerosis is a chronic lipid-driven inflammatory disease characterized by infiltration of large numbers of macrophages. The progression of the disease is closely related to the status of macrophages in atherosclerotic plaques. Recent advances in plaque analysis have revealed a subpopulation of macrophages that express high levels of triggering receptor expressed on myeloid cells 2 (TREM2). Although TREM2 is known to play a critical role in inflammation, lipid metabolism, and tissue repair, its role in atherosclerosis is still not fully understood. Recent studies have shown that TREM2 promotes macrophage cholesterol uptake and efflux, enhances efferocytosis function, regulates inflammation and metabolism, and promotes cell survival, all of which are significant functions in atherosclerosis. In early plaques TREM2 promotes lipid uptake and increases lesion size. In advanced plaques TREM2 promotes macrophage survival and increases plaque stability. The dualistic nature of TREM2 in atherosclerosis, where it can exert both protective effect and a side effect of increased lesion size, presents a complex but crucial area of study. Understanding these dual roles could help in the development of new therapeutic strategies to modulate TREM2 activity and utilize its atheroprotective function while mitigating its deleterious effects. In this review, we discuss the roles and mechanisms of TREM2 during different stages of atherosclerotic plaques, as well as the potential applications of TREM2 in the diagnosis and treatment of atherosclerosis.

Unveiling the impact of TREM-2+ Macrophages in metabolic disorders

The Triggering Receptor Expressed on Myeloid cells 2 (TREM-2) has been widely known by its anti-inflammatory activity. It can be activated in response to microbes and tissue damage, leading to phagocytosis, autophagy, cell polarization and migration, counter inflammation, and tissue repair. So far, the receptor has been largely explored in neurodegenerative disorders, however, a growing number of studies have been investigating its contribution in different pathological conditions, including metabolic diseases, in which (resident) macrophages play a crucial role. In this regard, TREM-2 + macrophages have been implicated in the onset and development of obesity, atherosclerosis, and fibrotic liver disease. These macrophages can be detected in the brain, white adipose tissue, liver, and vascular endothelium. In this review we discuss how different murine models have been demonstrating the ability of such cells to contribute to tissue and body homeostasis by phagocytosing cellular debris and lipid structures, besides contributing to lipid homeostasis in metabolic diseases. Therefore, understanding the role of TREM-2 in metabolic disorders is crucial to expand our current knowledge concerning their immunopathology as well as to foster the development of more targeted therapies to treat such conditions.

Tissue-Resident Macrophages in Cancer: Friend or Foe?

INTRODUCTION

Macrophages are essential in maintaining homeostasis, combating infections, and influencing the process of various diseases, including cancer. Macrophages originate from diverse lineages: Notably, tissue-resident macrophages (TRMs) differ from hematopoietic stem cells and circulating monocyte-derived macrophages based on genetics, development, and function. Therefore, understanding the recruited and TRM populations is crucial for investigating disease processes.

METHODS

By searching literature databses, we summarized recent relevant studies. Research has shown that tumor-associated macrophages (TAMs) of distinct origins accumulate in tumor microenvironment (TME), with TRM-derived TAMs closely resembling gene signatures of normal TRMs.

RESULTS

Recent studies have revealed that TRMs play a crucial role in cancer progression. However, organ-specific effects complicate TRM investigations. Nonetheless, the precise involvement of TRMs in tumors is unclear. This review explores the multifaceted roles of TRMs in cancer, presenting insights into their origins, proliferation, the latest research methodologies, their impact across various tumor sites, their potential and strategies as therapeutic targets, interactions with other cells within the TME, and the internal heterogeneity of TRMs.

CONCLUSIONS

We believe that a comprehensive understanding of the multifaceted roles of TRMs will pave the way for targeted TRM therapies in the treatment of cancer.

CSF GPNMB in Parkinson's disease: A potential association with age and microglial activation

BACKGROUND

Recent evidence suggests a link between glycoprotein non-metastatic melanoma protein B (GPNMB) and Parkinson's disease (PD) pathogenesis. Although elevated plasma GPNMB levels associated with disease severity have been reported in PD, cerebrospinal fluid (CSF) alterations remain elusive.

OBJECTIVE

To explore CSF GPNMB alterations and its clinical significance in PD.

METHODS

This study enrolled 118 sporadic PD patients and 40 controls. We examined the potential associations between CSF GPNMB levels and the clinical characteristics or biomarkers of neurodegenerative pathogenesis.

RESULTS

PD patients had higher CSF GPNMB levels than controls (p = 0.0159). In the PD group, CSF GPNMB levels correlated with age (age at examination: rs = 0.2511, p = 0.0061; age at onset: rs = 0.2800, p = 0.0021) and the severity of motor and cognitive dysfunction (MDS-UPDRS III score: rs = 0.1998, p = 0.0347; Mini-Mental State Examination score: rs = -0.1922, p = 0.0370). After correcting for multiple comparisons, the correlation with age at onset remained significant. CSF GPNMB levels were also positively correlated with CSF soluble triggering receptor expressed on myeloid cells 2 (sTREM2) levels in both the PD (rs = 0.3582, p < 0.0001) and control (rs = 0.4743, p = 0.0023) groups. Furthermore, multiple regression analysis revealed CSF sTREM2 level as the strongest determinant of CSF GPNMB levels in the PD group (t-value = 3.49, p = 0.0007).

CONCLUSIONS

Elevated CSF GPNMB levels, linked with age and microglial activation, may be a valuable marker for understanding the interplay between aging, neuroinflammation, and PD pathology.

Farnesylthiosalicylic Acid Through Inhibition of Galectin-3 Improves Neuroinflammation in Alzheimer Disease via Multiple Pathways

AIMS

Many factors affect the neuroinflammatory response in patients with Alzheimer disease (AD). Galectin-3 (Gal-3) is closely related to microglial activation in the nervous system and can promote the aggregation of cancer cells in tumors. This study aimed to investigate the mechanism by which farnesylthiosalicylic acid (FTS) affects neuroinflammation in Aβ1-42 mice through Gal-3.

METHODS

We used the Morris water maze, reverse transcription-polymerase chain reaction (RT-PCR), Western blotting, enzyme-linked immunosorbent assay (ELISA), and immunofluorescence to conduct our study.

RESULTS

FTS reduced the levels of proinflammatory factors and microglial activation in Aβ1-42 mice. FTS inhibited total and membrane expression levels of Gal-3 in Aβ1-42 mice, and the anti-inflammatory effect of FTS was reversed by Gal-3-adeno-associated viral (AAV). FTS reduced the expression levels of toll-like receptors (TLRs), effects that were reversed by Gal-3-AAV. Moreover, FTS ameliorated Aβ oligomerization and accumulation in Aβ1-42 mice, effects that were also reversed by Gal-3-AAV. FTS, through the inhibition of the Gal-3-c-Jun N-terminal kinase (JNK) pathway, reduced PS1 expression; in addition, inhibition of Gal-3 increased the Aβ-degrading enzymes in Aβ1-42 mice. FTS-induced improvements in cognition in Aβ1-42 mice were reversed by Gal-3-AAV.

CONCLUSION

FTS may through inhibiting Gal-3 reduce the expression of TLR4 and CD14 and alleviate Aβ pathology, downregulating Aβ-stimulated TLR2, TLR4, and CD14 expression, and thus alleviate neuroinflammation in Aβ1-42 mice.

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.

Exploring the Significance of Microglial Phenotypes and Morphological Diversity in Neuroinflammation and Neurodegenerative Diseases: From Mechanisms to Potential Therapeutic Targets

Studying various microglial phenotypes and their functions in neurodegenerative diseases is crucial due to the intricate nature of their phenomics and their vital immunological role. Microglia undergo substantial phenomic changes, encompassing morphological, transcriptional, and functional aspects, resulting in distinct cell types with diverse structures, functions, properties, and implications. The traditional classification of microglia as ramified, M1 (proinflammatory), or M2 (anti-inflammatory) phenotypes is overly simplistic, failing to capture the wide range of recently identified microglial phenotypes in various brain regions affected by neurodegenerative diseases. Altered and activated microglial phenotypes deviating from the typical ramified structure are significant features of many neurodegenerative conditions. Understanding the precise role of each microglial phenotype is intricate and sometimes contradictory. This review specifically focuses on elucidating recent modifications in microglial phenotypes within neurodegenerative diseases. Recognizing the heterogeneity of microglial phenotypes in diseased states can unveil novel therapeutic strategies for targeting microglia in neurodegenerative diseases. Moreover, the exploration of the use of healthy isolated microglia to mitigate disease progression has provided an innovative perspective. In conclusion, this review discusses the dynamic landscape of mysterious microglial phenotypes, emphasizing the need for a nuanced understanding to pave the way for innovative therapeutic strategies for neurodegenerative diseases.

Neutral or Detrimental Effects of TREM2 Agonist Antibodies in Preclinical Models of Alzheimer's Disease and Multiple Sclerosis

Human genetics and preclinical studies have identified key contributions of TREM2 to several neurodegenerative conditions, inspiring efforts to modulate TREM2 therapeutically. Here, we characterize the activities of three TREM2 agonist antibodies in multiple mixed-sex mouse models of Alzheimer's disease (AD) pathology and remyelination. Receptor activation and downstream signaling are explored in vitro, and active dose ranges are determined in vivo based on pharmacodynamic responses from microglia. For mice bearing amyloid-β (Aβ) pathology (PS2APP) or combined Aβ and tau pathology (TauPS2APP), chronic TREM2 agonist antibody treatment had limited impact on microglia engagement with pathology, overall pathology burden, or downstream neuronal damage. For mice with demyelinating injuries triggered acutely with lysolecithin, TREM2 agonist antibodies unexpectedly disrupted injury resolution. Likewise, TREM2 agonist antibodies limited myelin recovery for mice experiencing chronic demyelination from cuprizone. We highlight the contributions of dose timing and frequency across models. These results introduce important considerations for future TREM2-targeting approaches.

Bibliometric Analysis of TREM2 (2001-2022): Trends, Hotspots and Prospects in Human Disease

Background: Triggering receptor expressed in myeloid cells 2 (TREM2), a transmembrane receptor, has garnered extensive research attention due to its pivotal role in the diagnosis and treatment of various diseases. Despite the abundance of studies on its function, there is a gap in comprehensive analysis and summarization of the current state of this research field. Methods: Articles and reviews related to TREM2 were retrieved from the Web of Science Core Collection (WOSCC) on October 1, 2023. A bibliometric analysis of TREM2 was conducted using CiteSpace, VOSviewer and Bibliometrix (R package). Results: A total of 1,502 articles, spanning from 2001 to 2022, met the search criteria. The number of publications and citations has increased steadily over the years. The United States and China are the most active countries in TREM2 research, with the University of Washington as the leading research institution. The most influential journal in the field is Neurology of Aging. The predominant research areas include molecular, biology and immunology. Alzheimer's disease, microglia, variants, and inflammation are significant keywords. Emerging directions such as metabolism and tumor microenvironment have recently gained attention in numerous studies. Conclusion: The current study utilizes bibliometric analysis software and visual graphics to intuitively highlight TREM2-related hotspots, trends, and prospects in human disease. Such insights are valuable for scholars seeking a deeper understanding of TREM2-related research progress, enabling a focused approach to its application in human disease.

Associations of TRAF2 (rs867186), TAB2 (rs237025), IKBKB (rs13278372) Polymorphisms and TRAF2, TAB2, IKBKB Protein Levels with Clinical and Morphological Features of Pituitary Adenomas

AIM

The aim of this study was to determine associations of TRAF2 (rs867186), TAB2 (rs237025), IKBKB (rs13278372) gene polymorphisms and TRAF2, TAB2, IKBKB protein levels with clinical and morphological features of pituitary adenomas (PAs).

METHODS

This case-control study included 459 individuals divided into two groups: a control group (n = 320) and a group of individuals with PAs (n = 139). DNA from peripheral blood leukocytes was isolated using salt precipitation and column method. Real-time PCR was used for TRAF2 (rs867186), TAB2 (rs237025), and IKBKB (rs13278372) SNP genotyping, and TRAF2, TAB2, IKBKB protein concentration measurements were performed by immunoenzymatic analysis tests using a commercial ELISA kit according to the manufacturer's recommendations. The labeling index Ki-67 was determined by immunohistochemical analysis using a monoclonal antibody (clone SP6; Spring Bioscience Corporation). Statistical data analysis was performed using the programs "IMB SPSS Statistics 29.0".

RESULTS

We found significant differences in TRAF2 (rs867186) genotypes (AA, AG, GG) between groups: 79.1%, 17.3%, 3.6% vs. 55.3%, 20.9%, 23.8% (p < 0.001). The G allele was less frequent in the PA group than in controls (12.2% vs. 34.2%, p < 0.001). The AG and GG genotypes reduced PA occurrence by 1.74-fold and 9.43-fold, respectively, compared to AA (p < 0.001). In the dominant model, GG and AG genotypes reduced PA odds by 3.07-fold, while in the recessive model, the GG genotype reduced PA odds by 8.33-fold (p < 0.001). Each G allele decreased PA odds by 2.49-fold in the additive model (p < 0.001). Microadenomas had significant genotype differences compared to controls: 81.3%, 18.8%, 0.0% vs. 55.3%, 20.9%, 23.8% (p < 0.001), with the G allele being less frequent (9.4% vs. 34.2%, p < 0.001). In macroadenomas, genotype differences were 78%, 16.5%, 5.5% vs. 55.3%, 20.9%, 23.8% (p < 0.001), and the G allele was less common (13.7% vs. 34.2%, p < 0.001). The dominant model showed that GG and AG genotypes reduced microadenoma odds by 3.5-fold (p = 0.001), and each G allele reduced microadenoma odds by 3.1-fold (p < 0.001). For macroadenomas, the GG genotype reduced odds by 6.1-fold in the codominant model (p < 0.001) and by 2.9-fold in GG and AG genotypes combined compared to AA (p < 0.001). The recessive model indicated the GG genotype reduced macroadenoma odds by 5.3-fold (p < 0.001), and each G allele reduced odds by 2.2-fold in the additive model (p < 0.001).

CONCLUSIONS

The TRAF2 (rs867186) G allele and GG genotype are significantly associated with reduced odds of pituitary adenomas, including both microadenomas and macroadenomas, compared to the AA genotype. These findings suggest a protective role of the G allele against the occurrence of these tumors.

Targeting tau in Alzheimer's disease: from mechanisms to clinical therapy

ABSTRACT

Alzheimer's disease is the most prevalent neurodegenerative disease affecting older adults. Primary features of Alzheimer's disease include extracellular aggregation of amyloid-β plaques and the accumulation of neurofibrillary tangles, formed by tau protein, in the cells. While there are amyloid-β-targeting therapies for the treatment of Alzheimer's disease, these therapies are costly and exhibit potential negative side effects. Mounting evidence suggests significant involvement of tau protein in Alzheimer's disease-related neurodegeneration. As an important microtubule-associated protein, tau plays an important role in maintaining the stability of neuronal microtubules and promoting axonal growth. In fact, clinical studies have shown that abnormal phosphorylation of tau protein occurs before accumulation of amyloid-β in the brain. Various therapeutic strategies targeting tau protein have begun to emerge, and are considered possible methods to prevent and treat Alzheimer's disease. Specifically, abnormalities in post-translational modifications of the tau protein, including aberrant phosphorylation, ubiquitination, small ubiquitin-like modifier (SUMO)ylation, acetylation, and truncation, contribute to its microtubule dissociation, misfolding, and subcellular missorting. This causes mitochondrial damage, synaptic impairments, gliosis, and neuroinflammation, eventually leading to neurodegeneration and cognitive deficits. This review summarizes the recent findings on the underlying mechanisms of tau protein in the onset and progression of Alzheimer's disease and discusses tau-targeted treatment of Alzheimer's disease.

Association between sTREM2, an immune biomarker of microglial activation, and frontal lobe function in community-dwelling older adults: a cross-sectional study

Objective: Identifying the peripheral biomarkers related to the prevention or modification of unhealthy mental conditions in older adults is extremely beneficial. This study aimed to evaluate the serum levels of soluble triggering receptor expressed on myeloid cells 2 (sTREM2), a soluble form of an innate immune receptor expressed on microglia, in older adults living in a rural community, and their association with cognitive function. Materials and Methods: This survey was conducted between November 2016 and September 2017 in Kurokawa-cho, Imari, Saga Prefecture, Japan, among people aged ≥65 years. Blood samples were collected from the participants for serum sTREM2 level analysis using a peptide enzyme immunoassay. The participants underwent cognitive function assessments, including the Mini-Mental State Examination, Clinical Dementia Rating, and Frontal Assessment Battery. Therefore, we examined the association between serum sTREM2 levels and cognitive function. Results: Of the 95 participants, 25 were men and 70 were women with a mean age 78.24 ± 3.85 years and 77.96 ± 5.52 years, respectively. Serum sTREM2 levels were negatively associated with Frontal Assessment Battery scores, even after adjusting for age, sex, years of education, and serum high-sensitivity C-reactive protein levels. Conclusion: Serum sTREM2 levels may be associated with frontal lobe function in adults aged ≥65 years.

Current understanding on TREM-2 molecular biology and physiopathological functions

Triggering receptor expressed on myeloid cells 2 (TREM-2), a glycosylated receptor belonging to the immunoglobin superfamily and especially expressed in the myeloid cell lineage, is frequently explained as a reminiscent receptor for both adaptive and innate immunity regulation. TREM-2 is also acknowledged to influence NK cell differentiation via the PI3K and PLCγ signaling pathways, as well as the partial activation or direct inhibition of T cells. Additionally, TREM-2 overexpression is substantially linked to cell-specific functions, such as enhanced phagocytosis, reduced toll-like receptor (TLR)-mediated inflammatory cytokine production, increased transcription of anti-inflammatory cytokines, and reshaped T cell function. Whereas TREM-2-deficient cells exhibit diminished phagocytic function and enhanced proinflammatory cytokines production, proceeding to inflammatory injuries and an immunosuppressive environment for disease progression. Despite the growing literature supporting TREM-2+ cells in various diseases, such as neurodegenerative disorders and cancer, substantial facets of TREM-2-mediated signaling remain inadequately understood relevant to pathophysiology conditions. In this direction, herein, we have summarized the current knowledge on TREM-2 biology and cell-specific TREM-2 expression, particularly in the modulation of pivotal TREM-2-dependent functions under physiopathological conditions. Furthermore, molecular regulation and generic biological relevance of TREM-2 are also discussed, which might provide an alternative approach for preventing or reducing TREM-2-associated deformities. At last, we discussed the TREM-2 function in supporting an immunosuppressive cancer environment and as a potential drug target for cancer immunotherapy. Hence, summarized knowledge of TREM-2 might provide a window to overcome challenges in clinically effective therapies for TREM-2-induced diseases in humans.

Advances in the Understanding of the Correlation Between Neuroinflammation and Microglia in Alzheimer's Disease

Alzheimer's disease (AD) is a fatal neurodegenerative disease with a subtle and progressive onset and is the most common type of dementia. However, its etiology and pathogenesis have not yet been fully elucidated. The common pathological manifestations of AD include extraneuronal β-amyloid deposition (Aβ), intraneuronal tau protein phosphorylation leading to the formation of 'neurofibrillary tangles' (NFTs), neuroinflammation, progressive loss of brain neurons/synapses, and glucose metabolism disorders. Current treatment approaches for AD primarily focus on the 'Aβ cascade hypothesis and abnormal aggregation of hyperphosphorylation of tau proteins', but have shown limited efficacy. Therefore, there is an ongoing need to identify more effective treatment targets for AD. The central nervous system (CNS) inflammatory response plays a key role in the occurrence and development of AD. Neuroinflammation is an immune response activated by glial cells in the CNS that usually occurs in response to stimuli such as nerve injury, infection and toxins or in response to autoimmunity. Neuroinflammation ranks as the third most prominent pathological feature in AD, following Aβ and NFTs. In recent years, the focus on the role of neuroinflammation and microglia in AD has increased due to the advancements in genome-wide association studies (GWAS) and sequencing technology. Furthermore, research has validated the pivotal role of microglia-mediated neuroinflammation in the progression of AD. Therefore, this article reviews the latest research progress on the role of neuroinflammation triggered by microglia in AD in recent years, aiming to provide a new theoretical basis for further exploring the role of neuroinflammation in the process of AD occurrence and development.

Decoding sTREM2: its impact on Alzheimer's disease - a comprehensive review of mechanisms and implications

Soluble Triggering Receptor Expressed on Myeloid Cells 2 (sTREM2) plays a crucial role in the pathogenesis of Alzheimer's disease (AD). This review comprehensively examines sTREM2's involvement in AD, focusing on its regulatory functions in microglial responses, neuroinflammation, and interactions with key pathological processes. We discuss the dynamic changes in sTREM2 levels in cerebrospinal fluid and plasma throughout AD progression, highlighting its potential as a therapeutic target. Furthermore, we explore the impact of genetic variants on sTREM2 expression and its interplay with other AD risk genes. The evidence presented in this review suggests that modulating sTREM2 activity could influence AD trajectory, making it a promising avenue for future research and drug development. By providing a holistic understanding of sTREM2's multifaceted role in AD, this review aims to guide future studies and inspire novel therapeutic strategies.

George-Hyslop P, Fox NC, Suzuki K, Okhravi HR, Chhatwal J, Levin J, Jucker M, Sims JR, Holdridge KC, Proctor NK, Yaari R, Andersen SW, Mancini M, Llibre-Guerra J, Bateman RJ, McDade E. Downstream Biomarker Effects of Gantenerumab or Solanezumab in Dominantly Inherited Alzheimer Disease: The DIAN-TU-001 Randomized Clinical Trial

Importance

Effects of antiamyloid agents, targeting either fibrillar or soluble monomeric amyloid peptides, on downstream biomarkers in cerebrospinal fluid (CSF) and plasma are largely unknown in dominantly inherited Alzheimer disease (DIAD).

Objective

To investigate longitudinal biomarker changes of synaptic dysfunction, neuroinflammation, and neurodegeneration in individuals with DIAD who are receiving antiamyloid treatment.

Design, Setting, and Participants

From 2012 to 2019, the Dominantly Inherited Alzheimer Network Trial Unit (DIAN-TU-001) study, a double-blind, placebo-controlled, randomized clinical trial, investigated gantenerumab and solanezumab in DIAD. Carriers of gene variants were assigned 3:1 to either drug or placebo. The present analysis was conducted from April to June 2023. DIAN-TU-001 spans 25 study sites in 7 countries. Biofluids and neuroimaging from carriers of DIAD gene variants in the gantenerumab, solanezumab, and placebo groups were analyzed.

Interventions

In 2016, initial dosing of gantenerumab, 225 mg (subcutaneously every 4 weeks) was increased every 8 weeks up to 1200 mg. In 2017, initial dosing of solanezumab, 400 mg (intravenously every 4 weeks) was increased up to 1600 mg every 4 weeks.

Main Outcomes and Measures

Longitudinal changes in CSF levels of neurogranin, soluble triggering receptor expressed on myeloid cells 2 (sTREM2), chitinase 3-like 1 protein (YKL-40), glial fibrillary acidic protein (GFAP), neurofilament light protein (NfL), and plasma levels of GFAP and NfL.

Results

Of 236 eligible participants screened, 43 were excluded. A total of 142 participants (mean [SD] age, 44 [10] years; 72 female [51%]) were included in the study (gantenerumab, 52 [37%]; solanezumab, 50 [35%]; placebo, 40 [28%]). Relative to placebo, gantenerumab significantly reduced CSF neurogranin level at year 4 (mean [SD] β = -242.43 [48.04] pg/mL; P < .001); reduced plasma GFAP level at year 1 (mean [SD] β = -0.02 [0.01] ng/mL; P = .02), year 2 (mean [SD] β = -0.03 [0.01] ng/mL; P = .002), and year 4 (mean [SD] β = -0.06 [0.02] ng/mL; P < .001); and increased CSF sTREM2 level at year 2 (mean [SD] β = 1.12 [0.43] ng/mL; P = .01) and year 4 (mean [SD] β = 1.06 [0.52] ng/mL; P = .04). Solanezumab significantly increased CSF NfL (log) at year 4 (mean [SD] β = 0.14 [0.06]; P = .02). Correlation analysis for rates of change found stronger correlations between CSF markers and fluid markers with Pittsburgh compound B positron emission tomography for solanezumab and placebo.

Conclusions and Relevance

This randomized clinical trial supports the importance of fibrillar amyloid reduction in multiple AD-related processes of neuroinflammation and neurodegeneration in CSF and plasma in DIAD. Additional studies of antiaggregated amyloid therapies in sporadic AD and DIAD are needed to determine the utility of nonamyloid biomarkers in determining disease modification.

Trial Registration

ClinicalTrials.gov Identifier: NCT04623242.

Cognitively healthy centenarians are genetically protected against Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) prevalence increases with age, yet a small fraction of the population reaches ages > 100 years without cognitive decline. We studied the genetic factors associated with such resilience against AD.

METHODS

Genome-wide association studies identified 86 single nucleotide polymorphisms (SNPs) associated with AD risk. We estimated SNP frequency in 2281 AD cases, 3165 age-matched controls, and 346 cognitively healthy centenarians. We calculated a polygenic risk score (PRS) for each individual and investigated the functional properties of SNPs enriched/depleted in centenarians.

RESULTS

Cognitively healthy centenarians were enriched with the protective alleles of the SNPs associated with AD risk. The protective effect concentrated on the alleles in/near ANKH, GRN, TMEM106B, SORT1, PLCG2, RIN3, and APOE genes. This translated to >5-fold lower PRS in centenarians compared to AD cases (P = 7.69 × 10-71), and 2-fold lower compared to age-matched controls (P = 5.83 × 10-17).

DISCUSSION

Maintaining cognitive health until extreme ages requires complex genetic protection against AD, which concentrates on the genes associated with the endolysosomal and immune systems.

HIGHLIGHTS

Cognitively healthy cent enarians are enriched with the protective alleles of genetic variants associated with Alzheimer's disease (AD). The protective effect is concentrated on variants involved in the immune and endolysosomal systems. Combining variants into a polygenic risk score (PRS) translated to > 5-fold lower PRS in centenarians compared to AD cases, and ≈ 2-fold lower compared to middle-aged healthy controls.

Neuraminidase 1 regulates the cellular state of microglia by modulating the sialylation of Trem2

Neuraminidase 1 (Neu1) cleaves terminal sialic acids from sialoglycoproteins in endolysosomes and at the plasma membrane. As such, Neu1 regulates immune cells, primarily those of the monocytic lineage. Here we examined how Neu1 influences microglia by modulating the sialylation of full-length Trem2 (Trem2-FL), a multifunctional receptor that regulates microglial survival, phagocytosis, and cytokine production. When Neu1 was deficient/downregulated, Trem2-FL remained sialylated, accumulated intracellularly, and was excessively cleaved into a C-terminal fragment (Trem2-CTF) and an extracellular soluble domain (sTrem2), enhancing their signaling capacities. Sialylated Trem2-FL (Sia-Trem2-FL) did not hinder Trem2-FL-DAP12-Syk complex assembly but impaired signal transduction through Syk, ultimately abolishing Trem2-dependent phagocytosis. Concurrently, Trem2-CTF-DAP12 complexes dampened NFκB signaling, while sTrem2 propagated Akt-dependent cell survival and NFAT1-mediated production of TNFα and CCL3. Because Neu1 and Trem2 are implicated in neurodegenerative/neuroinflammatory diseases, including Alzheimer disease (AD) and sialidosis, modulating Neu1 activity represents a therapeutic approach to broadly regulate microglia-mediated neuroinflammation.

Cell autonomous microglia defects in a stem cell model of frontotemporal dementia

Neuronal dysfunction has been extensively studied as a central feature of neurodegenerative tauopathies. However, across neurodegenerative diseases, there is strong evidence for active involvement of immune cells like microglia in driving disease pathophysiology. Here, we demonstrate that tau mRNA and protein are expressed in microglia in human brains and in human induced pluripotent stem cell (iPSC)-derived microglia like cells (iMGLs). Using iMGLs harboring the MAPT IVS10+16 mutation and isogenic controls, we demonstrate that a tau mutation is sufficient to alter microglial transcriptional states. We discovered that MAPT IVS10+16 microglia exhibit cytoskeletal abnormalities, stalled phagocytosis, disrupted TREM2/TYROBP networks, and altered metabolism. Additionally, we found that secretory factors from MAPT IVS10+16 iMGLs impact neuronal health, reducing synaptic density in neurons. Key features observed in vitro were recapitulated in human brain tissue and cerebrospinal fluid from MAPT mutations carriers. Together, our findings that MAPT IVS10+16 drives cell-intrinsic dysfunction in microglia that impacts neuronal health has major implications for development of therapeutic strategies.

FoxG1 as a Potential Therapeutic Target for Alzheimer's Disease: Modulating NLRP3 Inflammasome via AMPK/mTOR Autophagy Pathway

An increasing body of research suggests that promoting microglial autophagy hinders the neuroinflammation initiated though the NLRP3 inflammasome activation in Alzheimer's disease (AD). The function of FoxG1, a crucial transcription factor involved in cell survival by regulating mitochondrial function, remains unknown during the AD process and neuroinflammation occurs. In the present study, we firstly found that Aβ peptides induced AD-like neuroinflammation upregulation and downregulated the level of autophagy. Following low-dose Aβ25-35 stimulation, FoxG1 expression and autophagy exhibited a gradual increase. Nevertheless, with high-concentration Aβ25-35 treatment, progressive decrease in FoxG1 expression and autophagy levels as the concentration of Aβ25-35 escalated. In addition, FoxG1 has a positive effect on cell viability and autophagy in the nervous system. In parallel with the Aβ25-35 stimulation, we employed siRNA to decrease the expression of FoxG1 in N2A cells. A substantial reduction in autophagy level (Beclin1, LC3II, SQSTM1/P62) and a notable growth in inflammatory response (NLRP3, TNF-α, and IL-6) were observed. In addition, we found FoxG1 overexpression owned the effect on the activation of AMPK/mTOR autophagy pathway and siRNA-FoxG1 successfully abolished this effect. Lastly, FoxG1 suppressed the NLRP3 inflammasome and enhanced the cognitive function in AD-like mouse model induced by Aβ25-35. Confirmed by cellular and animal experiments, FoxG1 suppressed NLRP3-mediated neuroinflammation, which was strongly linked to autophagy regulated by AMPK/mTOR. Taken together, FoxG1 may be a critical node in the pathologic progression of AD and has the potential to serve as therapeutic target.

Pectin: Health-promoting properties as a natural galectin-3 inhibitor

Galectin-3 has a variety of important pathophysiological significance in the human body. Much evidence shows that the abnormal expression of galectin-3 is related to the formation and development of many diseases. Pectin is mostly obtained from processed citrus fruits and apples and is a known natural inhibitor of galactin-3. A large number of peels produced each year are discarded, and it is necessary to recycle some of the economically valuable active compounds in these by-products to reduce resource waste and environmental pollution. By binding with galectin-3, pectin can directly reduce the expression level of galectin-3 on the one hand, and regulate the expression level of cytokines by regulating certain signaling pathways on the other hand, to achieve the effect of treating diseases. This paper begins by presenting an overview of the basic structure of pectin, subsequently followed by a description of the structure of galectin-3 and its detrimental impact on human health when expressed abnormally. The health effects of pectin as a galectin-3 inhibitor were then summarized from the perspectives of anticancer, anti-inflammatory, ameliorating fibrotic diseases, and anti-diabetes. Finally, the challenges and prospects of future research on pectin are presented, which provide important references for expanding the application of pectin in the pharmaceutical industry or developing functional dietary supplements.

Triggering Receptor Expressed on Myeloid Cells 2 Deficiency Exacerbates Methamphetamine-Induced Activation of Microglia and Neuroinflammation

Methamphetamine (METH) is a highly addictive psychostimulant and one of the most widely abused drugs worldwide. The continuous use of METH eventually leads to neurotoxicity and drug addiction. Studies have shown that neurotoxicity is strongly associated with METH-induced neuroinflammation, and microglia are the key drivers of neuroinflammation. Triggering receptor expressed on myeloid cells 2 (TREM2) is reported to play a key role in activation of microglia and neuroinflammation. Yet, the molecular mechanisms by which METH causes neuroinflammation and neurotoxicity remain elusive. In the current study, we investigated the role of TREM2 in neuroinflammation induced by METH in BV2 cells and the wild-type (WT) C57BL/6J mice, CX3CR1GFP/+ transgenic mice, and TREM2 knockout (KO) mice. Postmortem samples from the frontal cortex of humans with a history of METH use were also analyzed to determine the levels of TREM2, TLR4, IBA1, and IL-1β. The expression levels of TREM2, TLR4, IBA1, IL-1β, iNOS, and Arg-1 were then assessed in the BV2 cells and frontal cortex of mice and human METH users. Results revealed that the expression levels of TREM2, TLR4, IBA1, and IL-1β were significantly elevated in METH-using individuals and BV2 cells. Microglia were clearly activated in the frontal cortex of WT C57BL/6 mice and CX3CR1GFP/+ transgenic mice, and the protein levels of IBA1, TREM2, TLR4, and IL-1β were elevated in the METH-induced mouse models. Moreover, TREM2-KO mice showed further increased microglial activation, neuroinflammation, and excitotoxicity induced by METH. Thus, these findings suggest that TREM2 may be a target for regulating METH-induced neuroinflammation.

Established and emerging techniques for the study of microglia: visualization, depletion, and fate mapping

The central nervous system (CNS) is an essential hub for neuronal communication. As a major component of the CNS, glial cells are vital in the maintenance and regulation of neuronal network dynamics. Research on microglia, the resident innate immune cells of the CNS, has advanced considerably in recent years, and our understanding of their diverse functions continues to grow. Microglia play critical roles in the formation and regulation of neuronal synapses, myelination, responses to injury, neurogenesis, inflammation, and many other physiological processes. In parallel with advances in microglial biology, cutting-edge techniques for the characterization of microglial properties have emerged with increasing depth and precision. Labeling tools and reporter models are important for the study of microglial morphology, ultrastructure, and dynamics, but also for microglial isolation, which is required to glean key phenotypic information through single-cell transcriptomics and other emerging approaches. Strategies for selective microglial depletion and modulation can provide novel insights into microglia-targeted treatment strategies in models of neuropsychiatric and neurodegenerative conditions, cancer, and autoimmunity. Finally, fate mapping has emerged as an important tool to answer fundamental questions about microglial biology, including their origin, migration, and proliferation throughout the lifetime of an organism. This review aims to provide a comprehensive discussion of these established and emerging techniques, with applications to the study of microglia in development, homeostasis, and CNS pathologies.

sTREM2 in the prognostic evaluation of acute lung injury after cardiac surgery in infants

BACKGROUND

Previous studies have shown that TREM2 plays a protective role in acute lung injury (ALI). This prospective study aimed to investigate the role of sTREM2 as a forecasting factor for ALI in infants after pediatric cardiac surgery undergoing cardiopulmonary bypass (CPB).

METHODS

Seventy-five consecutive patients younger than 1 year who underwent cardiac surgery were enrolled in this study. Sixty-one fulfilled the inclusion criteria and had been divided into ALI and non-ALI groups. Children's demographic characteristics and clinical data were collected. Perioperative sTREM2 levels were analyzed at five timepoints.

RESULTS

In this study, children in the ALI group were younger, lighter, with higher RACHS-1 scores and underwent significantly longer CPB time. Post-CPB ALI had an impact on clinical outcomes, which contributed to a longer duration of mechanical ventilation, ICU and hospital stay than non-ALI group. Significant differences were manifested off-CPB, 1 h/6 h after CPB, and day 1 after surgery between the two groups. Binary logistic models revealed that off-CPB sTREM2 was significantly associated with the incidence of post-CPB ALI after adjustment. ROC analysis showed that the AUC of off-CPB sTREM2 level was 0.791, and the optimal cutoff value was 788.6 pg/ml.

CONCLUSIONS

The off-CPB sTREM2 level was an independent prognostic factor for post-CPB ALI in infants.

IMPACT

Plasma sTREM2 works together with downstream TREM2 to regulate inflammation response by binding the receptor to other cells. Previous studies have shown that TREM2 plays a protective role in ischemia-reperfusion and has anti-inflammatory effects on acute lung injury (ALI). This study analyzed the risk factors of post-cardiopulmonary bypass (CPB) ALI. We found that weight and off-CPB sTREM2 level were independent prognostic factors for post-CPB ALI. Plasma sTREM2 may serve as an early biomarker in the prognostic evaluation of acute lung injury after cardiac surgery in infants.

Defining and targeting macrophage heterogeneity in the mammary gland and breast cancer

INTRODUCTION

Macrophages are innate immune cells that are associated with extensive phenotypic and functional plasticity and contribute to normal development, tissue homeostasis, and diseases such as cancer. In this review, we discuss the heterogeneity of tissue resident macrophages in the normal mammary gland and tumor-associated macrophages in breast cancer. Tissue resident macrophages are required for mammary gland development, where they have been implicated in promoting extracellular matrix remodeling, apoptotic clearance, and cellular crosstalk. In the context of cancer, tumor-associated macrophages are key drivers of growth and metastasis via their ability to promote matrix remodeling, angiogenesis, lymphangiogenesis, and immunosuppression.

METHOD

We identified and summarized studies in Pubmed that describe the phenotypic and functional heterogeneity of macrophages and the implications of targeting individual subsets, specifically in the context of mammary gland development and breast cancer. We also identified and summarized recent studies using single-cell RNA sequencing to identify and describe macrophage subsets in human breast cancer samples.

RESULTS

Advances in single-cell RNA sequencing technologies have yielded nuances in macrophage heterogeneity, with numerous macrophage subsets identified in both the normal mammary gland and breast cancer tissue. Macrophage subsets contribute to mammary gland development and breast cancer progression in differing ways, and emerging studies highlight a role for spatial localization in modulating their phenotype and function.

CONCLUSION

Understanding macrophage heterogeneity and the unique functions of each subset in both normal mammary gland development and breast cancer progression may lead to more promising targets for the treatment of breast cancer.

Preclinical translational platform of neuroinflammatory disease biology relevant to neurodegenerative disease

Neuroinflammation is a key driver of neurodegenerative disease, however the tools available to model this disease biology at the systems level are lacking. We describe a translational drug discovery platform based on organotypic culture of murine cortical brain slices that recapitulate disease-relevant neuroinflammatory biology. After an acute injury response, the brain slices assume a chronic neuroinflammatory state marked by transcriptomic profiles indicative of activation of microglia and astrocytes and loss of neuronal function. Microglia are necessary for manifestation of this neuroinflammation, as depletion of microglia prior to isolation of the brain slices prevents both activation of astrocytes and robust loss of synaptic function genes. The transcriptomic pattern of neuroinflammation in the mouse platform is present in published datasets derived from patients with amyotrophic lateral sclerosis, Huntington's disease, and frontotemporal dementia. Pharmacological utility of the platform was validated by demonstrating reversal of microglial activation and the overall transcriptomic signature with transforming growth factor-β. Additional anti-inflammatory targets were screened and inhibitors of glucocorticoid receptors, COX-2, dihydrofolate reductase, and NLRP3 inflammasome all failed to reverse the neuroinflammatory signature. Bioinformatics analysis of the neuroinflammatory signature identified protein tyrosine phosphatase non-receptor type 11 (PTPN11/SHP2) as a potential target. Three structurally distinct inhibitors of PTPN11 (RMC-4550, TN0155, IACS-13909) reversed the neuroinflammatory disease signature. Collectively, these results highlight the utility of this novel neuroinflammatory platform for facilitating identification and validation of targets for neuroinflammatory neurodegenerative disease drug discovery.

sTREM2 Differentially Affects Cytokine Expression in Myeloid-Derived Cell Models via MAPK-JNK Signaling Pathway

TREM2 is a critical innate immune receptor primarily expressed on myeloid-derived cells, such as microglia and macrophages. Mutations in TREM2 are linked to several neurodegenerative diseases including Alzheimer's disease (AD). TREM2 can be cleaved from the cell membrane and released as soluble TREM2 (sTREM2). sTREM2 levels are shown to peak prior to AD, with its levels fluctuating throughout disease progression. However, the mechanism by which sTREM2 may affect innate immune responses is largely uncharacterized. In this study, we investigated whether sTREM2 can induce inflammatory response in myeloid-derived THP-1 monocytes and macrophages and characterized the signaling mechanisms involved. Our results show that sTREM2 was capable of stimulating the expression of several inflammatory cytokines in THP-1 cells throughout the time course of 2 h to 8 h but inducing anti-inflammatory cytokine expression at later time points. A TREM2 antibody was capable of inhibiting the expression of some cytokines induced by sTREM2 but enhancing others. The complex of sTREM2/TREM2 antibody was shown to enhance IL-1β expression, which was partially blocked by an NLRP3 specific inhibitor, indicating that the complex activated the NRLP3 inflammasome pathway. sTREM2 was also shown to have differential effects on cytokine expression in M0, M1, and M2 macrophages differentiated from THP-1 cells. sTREM2 has a more stimulating effect on cytokine expression in M0 macrophages, less of an effect on M2 macrophages, and some inhibitory effects on cytokine expression in M1 macrophages at early time points. Analyses of several signaling pathways revealed that sTREM2-induced expression of cytokines occurs mainly through MAPK-JNK signaling. Our work reveals differential effects of sTREM2 on cytokine expression profiles of THP-1 cells and macrophages and demonstrates that the MAPK-JNK signaling pathway is mainly responsible for sTREM2-induced cytokine expression.