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

TREM-1 mediates interaction between substantia nigra microglia and peripheral neutrophils

JOURNAL/nrgr/04.03/01300535-202406000-00043/inline-graphic1/v/2023-10-30T152229Z/r/image-tiff

Microglia-mediated neuroinflammation is considered a pathological feature of Parkinson’s disease. Triggering receptor expressed on myeloid cell-1 (TREM-1) can amplify the inherent immune response, and crucially, regulate inflammation. In this study, we found marked elevation of serum soluble TREM-1 in patients with Parkinson’s disease that positively correlated with Parkinson’s disease severity and dyskinesia. In a mouse model of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinson’s disease, we found that microglial TREM-1 expression also increased in the substantia nigra. Further, TREM-1 knockout alleviated dyskinesia in a mouse model of Parkinson’s disease and reduced dopaminergic neuronal injury. Meanwhile, TREM-1 knockout attenuated the neuroinflammatory response, dopaminergic neuronal injury, and neutrophil migration. Next, we established an in vitro 1-methyl-4-phenyl-pyridine-induced BV2 microglia model of Parkinson’s disease and treated the cells with the TREM-1 inhibitory peptide LP17. We found that LP17 treatment reduced apoptosis of dopaminergic neurons and neutrophil migration. Moreover, inhibition of neutrophil TREM-1 activation diminished dopaminergic neuronal apoptosis induced by lipopolysaccharide. TREM-1 can activate the downstream CARD9/NF-κB proinflammatory pathway via interaction with SYK. These findings suggest that TREM-1 may play a key role in mediating the damage to dopaminergic neurons in Parkinson’s disease by regulating the interaction between microglia and peripheral neutrophils.

Gut-Brain Axis: Focus on Sex Differences in Neuroinflammation

In recent years, there has been a growing interest in the concept of the "gut-brain axis". In addition to well-studied diseases associated with an imbalance in gut microbiota, such as cancer, chronic inflammation, and cardiovascular diseases, research is now exploring the potential role of gut microbial dysbiosis in the onset and development of brain-related diseases. When the function of the intestinal barrier is altered by dysbiosis, the aberrant immune system response interacts with the nervous system, leading to a state of "neuroinflammation". The gut microbiota-brain axis is mediated by inflammatory and immunological mechanisms, neurotransmitters, and neuroendocrine pathways. This narrative review aims to illustrate the molecular basis of neuroinflammation and elaborate on the concept of the gut-brain axis by virtue of analyzing the various metabolites produced by the gut microbiome and how they might impact the nervous system. Additionally, the current review will highlight how sex influences these molecular mechanisms. In fact, sex hormones impact the brain-gut microbiota axis at different levels, such as the central nervous system, the enteric nervous one, and enteroendocrine cells. A deeper understanding of the gut-brain axis in human health and disease is crucial to guide diagnoses, treatments, and preventive interventions.

Salvianolic acid C attenuates cerebral ischemic injury through inhibiting neuroinflammation via the TLR4-TREM1-NF-κB pathway

BACKGROUND

Stroke is a leading cause of mortality and disability with ischemic stroke being the most common type of stroke. Salvianolic acid C (SalC), a polyphenolic compound found in Salviae Miltiorrhizae Radix et Rhizoma, has demonstrated therapeutic potential in the recovery phase of ischemic stroke. However, its pharmacological effects and underlying mechanisms during the early stages of ischemic stroke remain unclear. This study aimed to examine the potential mechanism of action of SalC during the early phase of ischemic stroke using network pharmacology strategies and RNA sequencing analysis.

METHODS

SalC effects on infarct volume, neurological deficits, and histopathological changes were assessed in a mouse model of transient middle cerebral artery occlusion (tMCAO). By integrating RNA sequencing data with a cerebral vascular disease (CVD)-related gene database, a cerebral ischemic disease (CID) network containing dysregulated genes from the tMCAO model was constructed. Network analysis algorithms were applied to evaluate the key nodes within the CID network. In vivo and in vitro validation of crucial targets within the identified pathways was conducted.

RESULTS

SalC treatment significantly reduced infarct volume, improved neurological deficits, and reversed pathological changes in the tMCAO mouse model. The integration of RNA sequencing data revealed an 80% gene reversion rate induced by SalC within the CID network. Among the reverted genes, 53.1% exhibited reversion rates exceeding 50%, emphasizing the comprehensive rebalancing effect of SalC within the CID network. Neuroinflammatory-related pathways regulated by SalC, including the toll-like-receptor 4 (TLR4)- triggering receptor expressed on myeloid cells 1 (TREM1)-nuclear factor kappa B (NF-κB) pathway, were identified. Further in vivo and in vitro experiments confirmed that TLR4-TREM1-NF-κB pathway was down-regulated by SalC in microglia, which was essential for its anti-inflammatory effect on ischemic stroke.

CONCLUSIONS

SalC attenuated cerebral ischemic injury by inhibiting neuroinflammation mediated by microglia, primarily through the TLR4-TREM1-NF-κB pathway. These findings provide valuable insights into the potential therapeutic benefits of SalC in ischemic stroke.

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.

TRPV1 modulated NLRP3 inflammasome activation via calcium in experimental subarachnoid hemorrhage

Neuroinflammation plays a key role in early brain injury (EBI) of subarachnoid hemorrhage (SAH), and NLRP3 inflammasome plays an important role in the development of neuroinflammation after SAH, but the mechanism of NLRP3 inflammasome activation after SAH is still unclear. TRPV1 is a non-selective calcium channel that is involved in the pathology of neuroinflammation, but its role in SAH has not been revealed. Our study showed that TRPV1 was significantly upregulated after SAH and was predominantly expressed in microglia/macrophages. Antagonism of TRPV1 was effective in ameliorating neurological impairment, brain edema, neuronal damage, and reducing the inflammatory response (evidenced by reducing the number of CD16/32 positive microglia/macrophages, inhibiting the expression of CD16, CD32, CD86, IL-1b, TNF-a and blocking NLRP3 inflammasome activation). However, this effect can be abolished by NLRP3 inflammasome antagonist MCC950. In vitro experiment confirmed that TRPV1 activated NLRP3 inflammasome by increasing intracellular calcium levels. In conclusion, TRPV1 mediates EBI after SAH via calcium/NLRP3, and TRPV1 is a potential therapeutic target after SAH.

The orchestrating role of deteriorating neurons and TREM-1 in crosstalk with SYK in Alzheimer's disease progression and neuroinflammation

Alzheimer's disease (AD) is a progressive type of neurodegenerative disease characterized by successive loss of the conventional structure and functions of neurons. In addition to dead neurons type detected within AD brain tissues, there are a predominantly varying number of deteriorating neurons (DTNs). As the number of deteriorating neurons increases, they exaggerate the release of inflammatory factors and oxidative stress that trigger the cascade of neuroinflammation. Triggering receptor expressed on myeloid cells 1 (TREM-1) which is a transmembrane immune receptor type regularly expressed by phagocytic cells, may act as a stimulating factor for neuroinflammation. Once TREM-1 is activated, it directly activates spleen tyrosine kinase (SYK) downstream signaling cascades, which can be considered an initiating phase for AD pathology and AD progression. Sequentially, SYK activates the pro-inflammatory microglia M1 phenotype which executes several inflammatory actions, leading to neurotoxicity. These released neurotoxins promote neuronal cell death, synaptic dysfunctions, and memory impairments. Thus, the current review outlines the direct etiological and pathologic features of Alzheimer's disease linked with deteriorating neurons, TREM-1, and SYK.

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.

High Expression of Triggering Receptor Expressed on Myeloid Cells 1 Predicts Poor Prognosis in Glioblastoma

Background

Glioblastoma (GBM) is a highly malignant tumor with poor prognosis, and new treatment strategies are urgently needed. Currently, the role of triggering receptor expressed on myeloid cells 1 (TREM-1) in tumors has been studied, but the role of TREM-1 in GBM remains unclear.

Methods

Immunohistochemical staining for TREM-1 was performed in 91 patients diagnosed with GBM. Clinicopathological characteristics and survival times were recorded. TREM-1 expression and its effect on prognosis were analyzed using online Gene Expression Profiling Interactive Analysis (GEPIA), The Cancer Genome Atlas (TCGA), and Chinese Glioma Genome Atlas (CGGA) databases. The expression profile of TCGA-GBM cohort was used to perform functional enrichment analysis. The CIBERSORT method and Tumor Immune Estimation Resource (TIMER) database were used to estimate the tumor-infiltrating immune cells (TIICs). The ESTIMATE algorithm was used to estimate the immune-stromal scores. Finally, the relationships of TREM-1 with TIICs, immune-stromal score, and immune checkpoint genes (ICGs) were analyzed.

Results

The expression of TREM-1 was upregulated in GBM, and high TREM-1 expression predicted a poor prognosis. TREM-1, surgical resection, postoperative radiotherapy, and temozolomide (TMZ) chemotherapy were associated with the survival time of patients with GBM, but only surgical resection and TREM-1 expression were independent prognostic factors. GBM with high TREM-1 expression exhibited increased neutrophil and macrophage infiltration. TREM-1 was positively associated with the immune-stromal score and multiple ICGs, and most of which were involved in immunosuppressive responses.

Conclusion

The present study revealed that high expression of TREM-1 in GBM is an independent poor prognosis factor and that TREM-1 is associated with the immunosuppressive microenvironment. Thus, blocking TREM-1 may be a strategy for enhancing the GBM immune response.

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.

Alantolactone reduced neuron injury via activating PI3K/Akt signaling pathway after subarachnoid hemorrhage in rats

Subarachnoid hemorrhage (SAH) is a common disease with high morbidity and mortality, which can cause pathological, physiological, and biological reactions. SAH causes a series of responses such as neuronal and cerebral cortex damage, which in turn leads to inflammation and apoptosis. Traditional Chinese medicine has a strong anti-inflammatory effect, such as Alantolactone (ATL). However, studies on ATL therapy for SAH have not been reported. We observed the neurological scores, brain water content, Evans blue (EB) extravasation, neuroinflammation, and apoptosis via performing an enzyme-linked immunosorbent assay (ELISA), western blotting, immunofluorescence staining, and other methods after SAH. In this study, we found that ATL treatment attenuated the neurologic deficits, inhibited neuronal apoptosis and inflammatory reaction, promoted polarization of microglia toward the M2 phenotype, and activated the PI3K/Akt signaling pathway. ATL can reduce the neurons and cerebral cortex damage of SAH rats through activating PI3K/Akt signaling pathway.