Early elevated levels of soluble triggering receptor expressed on myeloid cells-1 in subarachnoid hemorrhage patients

Propofol alleviates M1 polarization and neuroinflammation of microglia in a subarachnoid hemorrhage model in vitro, by targeting the miR-140-5p/TREM-1/NF-κB signaling axis

Subarachnoid hemorrhage (SAH) is a devastating stroke caused by ruptured intracranial aneurysms, leading to blood accumulation around the brain. Early brain injury (EBI) within 72 h post-SAH worsens prognosis, primarily due to intense neuroinflammation. Microglia, pivotal in central nervous system defense and repair, undergo M1 to M2 polarization post-SAH, with M1 exacerbating neuroinflammation. Propofol (PPF), an anesthetic with anti-inflammatory properties, shows promise in mitigating neuroinflammation in SAH by modulating microglial activation. It likely acts through microRNAs like miR-140-5p, which attenuates microglial activation and inflammation by targeting TREM-1 and the NF-κB pathway. Understanding these mechanisms could lead to new therapeutic approaches for SAH-related EBI. In this study, BV-2 cell was used to establish in vitro model of SAH, and the expression of miR-140-5p and TREM-1 was detected after modeling. Microglial activity, apoptosis, the inflammatory pathway and response, oxidative damage, and M1/M2 polarization of microglia were evaluated by drug administration or transfection according to experimental groups. Finally, the targeting relationship between miR-140-5p and TREM-1 was verified by dual luciferase reporter assays, and the effect of PPF on the miR-140-5p/TREM-1/NF-κB signaling cascade was evaluated by RT‒qPCR or Western blotting. PPF effectively mitigates apoptosis, neuroinflammation, oxidative damage, and M1 microglial polarization in SAH. In SAH cells, PPF upregulates miR-140-5p and downregulates TREM-1. Mechanistically, PPF boosts miR-140-5p expression, while TREM-1, a downstream target of miR-140-5p, inhibits NF-κB signaling by regulating TREM-1, promoting M1 to M2 microglial polarization. Reduced miR-140-5p or increased TREM-1 counters PPF's therapeutic impact on SAH cells. In conclusion, PPF plays a neuroprotective role in SAH by regulating the miR-140-5p/TREM-1/NF-κB signaling axis to inhibit neuroinflammation and M1 polarization of microglia.

Unveiling the significance of TREM1/2 in hemorrhagic stroke: structure, function, and therapeutic implications

Stroke has long been a major threat to human health worldwide. Hemorrhagic stroke, including intracerebral hemorrhage and subarachnoid hemorrhage, exhibits a high incidence rate and a high mortality and disability rate, imposing a substantial burden on both public health and the economy and society. In recent years, the triggering receptor expressed on myeloid cells (TREM) family has garnered extensive attention in various pathological conditions, including hemorrhagic stroke. This review comprehensively summarizes the structure and function of TREM1/2, as well as their roles and potential mechanisms in hemorrhagic stroke, with the aim of providing guidance for the development of targeted therapeutic strategies in the future.

HIV-1 Tat Upregulates TREM1 Expression in Human Microglia

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

Neuroinflammatory CSF biomarkers MIF, sTREM1, and sTREM2 show dynamic expression profiles in Alzheimer's disease

BACKGROUND

There is a need for novel fluid biomarkers tracking neuroinflammatory responses in Alzheimer's disease (AD). Our recent cerebrospinal fluid (CSF) proteomics study revealed that migration inhibitory factor (MIF) and soluble triggering receptor expressed on myeloid cells 1 (sTREM1) increased along the AD continuum. We aimed to assess the potential use of these proteins, in addition to sTREM2, as CSF biomarkers to monitor inflammatory processes in AD.

METHODS

We included cognitively unimpaired controls (n = 67, 63 ± 9 years, 24% females, all amyloid negative), patients with mild cognitive impairment (MCI; n = 92, 65 ± 7 years, 47% females, 65% amyloid positive), AD (n = 38, 67 ± 6 years, 8% females, all amyloid positive), and DLB (n = 50, 67 ± 6 years, 5% females, 54% amyloid positive). MIF, sTREM1, and sTREM2 levels were measured by validated immunoassays. Differences in protein levels between groups were tested with analysis of covariance (corrected for age and sex). Spearman correlation analysis was performed to evaluate the association between these neuroinflammatory markers with AD-CSF biomarkers (Aβ42, tTau, pTau) and mini-mental state examination (MMSE) scores.

RESULTS

MIF levels were increased in MCI (p < 0.01), AD (p < 0.05), and DLB (p > 0.05) compared to controls. Levels of sTREM1 were specifically increased in AD compared to controls (p < 0.01), MCI (p < 0.05), and DLB patients (p > 0.05), while sTREM2 levels were increased specifically in MCI compared to all other groups (all p < 0.001). Neuroinflammatory proteins were highly correlated with CSF pTau levels (MIF: all groups; sTREM1: MCI, AD and DLB; sTREM2: controls, MCI and DLB). Correlations with MMSE scores were observed in specific clinical groups (MIF in controls, sTREM1 in AD, and sTREM2 in DLB).

CONCLUSION

Inflammatory-related proteins show diverse expression profiles along different AD stages, with increased protein levels in the MCI stage (MIF and sTREM2) and AD stage (MIF and sTREM1). The associations of these inflammatory markers primarily with CSF pTau levels indicate an intertwined relationship between tau pathology and inflammation. These neuroinflammatory markers might be useful in clinical trials to capture dynamics in inflammatory responses or monitor drug-target engagement of inflammatory modulators.

The role of triggering receptor expressed on myeloid cells-1 (TREM-1) in central nervous system diseases

Triggering receptor expressed on myeloid cells-1 (TREM-1) is a member of the immunoglobulin superfamily and is mainly expressed on the surface of myeloid cells such as monocytes, macrophages, and neutrophils. It plays an important role in the triggering and amplification of inflammatory responses, and it is involved in the development of various infectious and non-infectious diseases, autoimmune diseases, and cancers. In recent years, TREM-1 has also been found to participate in the pathological processes of several central nervous system (CNS) diseases. Targeting TREM-1 may be a promising strategy for treating these diseases. This paper aims to characterize TREM-1 in terms of its structure, signaling pathway, expression, regulation, ligands and pathophysiological role in CNS diseases.

The associations between plasma soluble Trem1 and neurological diseases: a Mendelian randomization study

Background

Triggering receptor expressed on myeloid cell 1 (Trem1) is an important regulator of cellular inflammatory responses. Neuroinflammation is a common thread across various neurological diseases. Soluble Trem1 (sTrem1) in plasma is associated with the development of central nervous system disorders. However, the extent of any causative effects of plasma sTrem1 on the risk of these disorders is still unclear.

Method

Genetic variants for plasma sTrem1 levels were selected as instrumental variables. Summary-level statistics of neurological disorders, including Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), epilepsy, cerebrovascular diseases, and migraine were collected from genome-wide association studies (GWASs). Whether plasma sTrem1 was causally associated with neurological disorders was assessed using a two-sample Mendelian randomization (MR) analysis, with false discovery rate (FDR)-adjusted methods applied.

Results

We inferred suggestive association of higher plasma sTrem1 with the risk of AD (odds ratio [OR] per one standard deviation [SD] increase = 1.064, 95% CI 1.012–1.119, P = 0.014, P_FDR = 0.056). Moreover, there was significant association between plasma sTrem1 level and the risk of epilepsy (OR per one SD increase = 1.044, 95% CI 1.016–1.072, P = 0.002, P_FDR = 0.032), with a modest statistical power of 41%. Null associations were found for plasma sTrem1 with other neurological diseases and their subtypes.

Conclusions

Taken together, this study indicates suggestive association between plasma sTrem1 and AD. Moreover, higher plasma sTrem1 was associated with the increased risk of epilepsy. The findings support the hypothesis that sTrem1 may be a vital element on the causal pathway to AD and epilepsy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02582-z.

sTREM-1 promotes the phagocytic function of microglia to induce hippocampus damage via the PI3K-AKT signaling pathway

Soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) is a soluble form of TREM-1 released during inflammation. Elevated sTREM-1 levels have been found in neuropsychiatric systemic lupus erythematosus (NPSLE) patients; yet, the exact mechanisms remain unclear. This study investigated the role of sTREM-1 in brain damage and its underlying mechanism. The sTREM-1 recombinant protein (2.5 μg/3 μL) was injected into the lateral ventricle of C57BL/6 female mice. After intracerebroventricular (ICV) injection, the damage in hippocampal neurons increased, and the loss of neuronal synapses and activation of microglia increased compared to the control mice (treated with saline). In vitro. after sTREM-1 stimulation, the apoptosis of BV2 cells decreased, the polarization of BV2 cells shifted to the M1 phenotype, the phagocytic function of BV2 cells significantly improved, while the PI3K-AKT signal pathway was activated in vivo and in vitro. PI3K-AKT pathway inhibitor LY294002 reversed the excessive activation and phagocytosis of microglia caused by sTREM-1 in vivo and in vitro, which in turn improved the hippocampus damage. These results indicated that sTREM-1 activated the microglial by the PI3K-AKT signal pathway, and promoted its excessive phagocytosis of the neuronal synapse, thus inducing hippocampal damage. sTREM-1 might be a potential target for inducing brain lesions.

Soluble triggering receptor expressed on myeloid cells-1 as a serum biomarker of early neurologic deterioration and prognosis in acute supratentorial intracerebral hemorrhage

BACKGROUND

Triggering receptor expressed on myeloid cells-1 (TREM-1) participates in neuroinflammation. We intended to ascertain whether serum soluble TREM-1 (sTREM-1) could be utilized as a biomarker of inflammation, severity, early neurologic deterioration (END) and outcome after primary intracerebral hemorrhage (ICH).

METHODS

Serum sTREM-1 levels were gauged in 104 ICH patients and 104 healthy controls. END was diagnosed when the National Institutes of Health Stroke Scale (NIHSS) score increased ≥ 4 points or death between admission and 24 h after admission. Patients with a modified Rankin scale score of > 2 at 3 months were considered to have poor outcome.

RESULTS

As compared to controls, patients exhibited significantly elevated serum sTREM-1 levels (median: 309.0 vs 67.9 pg/ml). Serum sTREM-1 concentrations were intimately correlated with NIHSS score (r = 0.574), hematoma volume (r = 0.554), blood leukocyte count (r = 0.529) and serum C-reactive protein concentrations (r = 0.509). Serum sTREM-1 concentrations > 309.0 pg/ml independently predicted END and poor outcome with odds ratio values of 4.054 and 4.721 respectively. Serum sTREM-1 concentrations distinguished END and poor outcome with areas under receiver operating characteristic curve of 0.789 and 0.813 respectively.

CONCLUSION

Serum sTREM-1 may represent a promising inflammatory biomarker for assessment of severity and prediction of END and poor outcome after ICH.

Biomarkers in the prognostic evaluation of ischemic stroke: Is there benefit in the measurements of TREM-1 and TREM-2 in the acute phase?

BACKGROUND AND PURPOSE

Triggering receptors expressed on myeloid cells 1 and 2 (TREM-1 and TREM-2) are cell surface receptors important for modulation of microglia immune response. In this study, we evaluate serum levels of TREM-1 and TREM-2 as potential biomarkers in acute ischemic stroke (AIS).

MATERIAL AND METHODS

Prospective cohort study of 50 patients with AIS admitted at our hospital. Serum TREM-1 and TREM-2 was evaluated within 24 h of the acute event and on the third and fifth days after the stroke. Neurological stroke severity and global disability were determined with the National Institutes of Health Stroke Scale (NIHSS) and modified Rankin Scale (mRS) at the same three times and at the time of hospital discharge.

RESULTS

TREM-1 and TREM-2 levels were elevated in stroke. TREM-1, but not TREM-2, exhibited correlations with NIHSS and mRS within 24 h (NIHSS and TREM-1: r_S = 0.31, p = 0.029; mRS and TREM-1: r_S = 0.32, p = 0.023). The serum level of TREM-1 within 24 h correlated with the neurological outcomes at hospital discharge (NIHSS and TREM-1: p = 0.021; mRS and TREM-1: p = 0.049). The serum concentrations of TREM-1 protein within 24 h after stroke was significantly higher in patients with poor outcome (mRS > 2) at hospital discharge (p = 0.021). After Exact Logistic Regression, large segmental stroke (O.R. = 4.14; 95CI = 1.07-16.09; p = 0.040) and initial sTREM levels (O.R. = 1.02; 95CI 1.00-1.04; p = 0.045) remained independent prognostic factors for AIS poor outcome (mRS > 2).

CONCLUSION

In our study, TREM-1 and TREM-2 were significantly increased in AIS. Early elevation of TREM-1 correlated with stroke severity and it was an independent prognostic factor for stroke outcome.

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

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

Serum Levels of Soluble Triggering Receptor Expressed on Myeloid Cells-1 Associated with the Severity and Outcome of Acute Ischemic Stroke

Stroke is a neurological emergency, where the mechanism of the blood supply to the brain is impaired, resulting in brain cell ischemia and death. Neuroinflammation is a key component in the ischemic cascade that results in cell damage and death after cerebral ischemia. The triggering receptor expressed on myeloid cells-1 (TREM-1) modulates neuroinflammation after acute ischemic stroke. In the present study, 60 patients with acute ischemic stroke, who had been subjected to neurological examinations and National Institutes of Health Stroke Scale (NIHSS) and brain magnetic resonance imaging studies, were enrolled in the emergency room of Kaohsiung Chang Gung Memorial Hospital. Twenty-four healthy volunteers were recruited as controls. The serum levels of soluble TREM-1 (sTREM-1), human S100 calcium-binding protein B (S100B), and proinflammatory cytokines and chemokines, including tumor necrosis α (TNF-α), interleukin 1β, interleukin 6 (IL-6), interleukin 8, and interferon-γ were measured immediately after acute ischemic stroke. The serum levels of sTREM-1, TNFα, IL-6, and S100B were correlated with the stroke volume and NIHSS, after acute ischemic stroke. Additionally, the serum levels of sTREM-1 were significantly positively correlated with S100B. The functional outcomes were evaluated 6 months after ischemic stroke by the Barthel index, which was correlated with the age and levels of sTREM-1 and S100B. We suggest that acute ischemic stroke induces neuroinflammation by the activation of the TREM-1 signaling pathway and the downstream inflammatory machinery that modulates the inflammatory response and ischemic neuronal cell death. From a translational perspective, our results may allow for the development of a new therapeutic strategy for acute ischemic stroke by targeting the TREM-1 signaling pathway.

Soluble TREM1 concentrations are increased and positively correlated with total tau levels in the plasma of patients with Alzheimer's disease

BACKGROUND/AIMS

Recently, we showed that triggering receptor expressed on myeloid cells 1 (TREM1) was involved in the pathogenesis of Alzheimer's disease (AD) since it modulated microglial phagocytic functions and thus affected amyloid-β clearance in the brain. Interestingly, a soluble form of TREM1 (sTREM1) can be detected in the plasma of human. To date, whether sTREM1 concentrations were altered in the plasma under AD context remained unclear.

METHODS

In this study, we compared the plasma concentrations of sTREM1 between 110 AD patients and 128 age- and gender-matched controls. Meanwhile, the relationship of sTREM1 concentrations with total tau levels in the plasma of AD patients was also assessed.

RESULTS

We revealed that the concentrations of sTREM1 were significantly increased in AD patients. Meanwhile, the sTREM1 concentrations were gradually increased during disease progression. More importantly, we showed that the sTREM1 concentrations were positively correlated with the levels of total tau in the plasma of AD patients (r = 0.61, P < 0.001). The subsequent subgroup analysis indicated that this correlation was more pronounced in patients with severe dementia (Mini-Mental State Exam score < 10, r = 0.81, P < 0.01).

CONCLUSION

These findings indicate a potential association between sTREM1 and tau pathology, and further confirm an involvement of this immune receptor in AD pathogenesis.

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

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

D-dimer may predict poor outcomes in patients with aneurysmal subarachnoid hemorrhage: a retrospective study

Serum biomarkers may play a reliable role in predicting the outcomes of patients with aneurysmal subarachnoid hemorrhage. This study retrospectively analyzed the relationship between serum biomarkers on admission and outcomes in patients with aneurysmal subarachnoid hemorrhage. We recruited 146 patients with aneurysmal subarachnoid hemorrhage who were treated in Renmin Hospital of Wuhan University of China between 1 May 2014 and 30 March 2016. There were 57 males and 89 females included and average age of included patients was 57.03 years old. Serum samples were taken immediately on admission (within 48 hours after initial hemorrhage) and the levels of serum biomarkers were detected. Baseline information, complications, and outcomes at 6 months were recorded. Univariate and multivariate logistic regression analyses were used to explore the relationship between biomarkers and clinical outcomes. Receiver operating characteristic curves were obtained to investigate the possibility of the biomarkers predicting prognosis. Of the 146 patients, 102 patients achieved good outcomes and 44 patients had poor outcomes. Univariate and multivariate analyses showed that high World Federation of Neurosurgical Societies grade, high serum D-dimer levels, and high neurological complications were significantly associated with poor outcomes. Receiver operating characteristic curves verified that D-dimer levels were associated with poor outcomes. D-dimer levels strongly correlated with neurological complications. In conclusion, we suggest that D-dimer levels are a good independent prognostic factor for poor outcomes in patients with aneurysmal subarachnoid hemorrhage.