Microglial M1/M2 polarization and metabolic states

High-dose dexamethasone regulates microglial polarization via the GR/JAK1/STAT3 signaling pathway after traumatic brain injury

JOURNAL/nrgr/04.03/01300535-202509000-00023/figure1/v/2024-11-05T132919Z/r/image-tiff Although microglial polarization and neuroinflammation are crucial cellular responses after traumatic brain injury, the fundamental regulatory and functional mechanisms remain insufficiently understood. As potent anti-inflammatory agents, the use of glucocorticoids in traumatic brain injury is still controversial, and their regulatory effects on microglial polarization are not yet known. In the present study, we sought to determine whether exacerbation of traumatic brain injury caused by high-dose dexamethasone is related to its regulatory effects on microglial polarization and its mechanisms of action. In vitro cultured BV2 cells and primary microglia and a controlled cortical impact mouse model were used to investigate the effects of dexamethasone on microglial polarization. Lipopolysaccharide, dexamethasone, RU486 (a glucocorticoid receptor antagonist), and ruxolitinib (a Janus kinase 1 antagonist) were administered. RNA-sequencing data obtained from a C57BL/6 mouse model of traumatic brain injury were used to identify potential targets of dexamethasone. The Morris water maze, quantitative reverse transcription-polymerase chain reaction, western blotting, immunofluorescence and confocal microscopy analysis, and TUNEL, Nissl, and Golgi staining were performed to investigate our hypothesis. High-throughput sequencing results showed that arginase 1, a marker of M2 microglia, was significantly downregulated in the dexamethasone group compared with the traumatic brain injury group at 3 days post-traumatic brain injury. Thus dexamethasone inhibited M1 and M2 microglia, with a more pronounced inhibitory effect on M2 microglia in vitro and in vivo . Glucocorticoid receptor plays an indispensable role in microglial polarization after dexamethasone treatment following traumatic brain injury. Additionally, glucocorticoid receptor activation increased the number of apoptotic cells and neuronal death, and also decreased the density of dendritic spines. A possible downstream receptor signaling mechanism is the GR/JAK1/STAT3 pathway. Overactivation of glucocorticoid receptor by high-dose dexamethasone reduced the expression of M2 microglia, which plays an anti-inflammatory role. In contrast, inhibiting the activation of glucocorticoid receptor reduced the number of apoptotic glia and neurons and decreased the loss of dendritic spines after traumatic brain injury. Dexamethasone may exert its neurotoxic effects by inhibiting M2 microglia through the GR/JAK1/STAT3 signaling pathway.

Metabolic reprogramming: a new option for the treatment of spinal cord injury

Spinal cord injuries impose a notably economic burden on society, mainly because of the severe after-effects they cause. Despite the ongoing development of various therapies for spinal cord injuries, their effectiveness remains unsatisfactory. However, a deeper understanding of metabolism has opened up a new therapeutic opportunity in the form of metabolic reprogramming. In this review, we explore the metabolic changes that occur during spinal cord injuries, their consequences, and the therapeutic tools available for metabolic reprogramming. Normal spinal cord metabolism is characterized by independent cellular metabolism and intercellular metabolic coupling. However, spinal cord injury results in metabolic disorders that include disturbances in glucose metabolism, lipid metabolism, and mitochondrial dysfunction. These metabolic disturbances lead to corresponding pathological changes, including the failure of axonal regeneration, the accumulation of scarring, and the activation of microglia. To rescue spinal cord injury at the metabolic level, potential metabolic reprogramming approaches have emerged, including replenishing metabolic substrates, reconstituting metabolic couplings, and targeting mitochondrial therapies to alter cell fate. The available evidence suggests that metabolic reprogramming holds great promise as a next-generation approach for the treatment of spinal cord injury. To further advance the metabolic treatment of the spinal cord injury, future efforts should focus on a deeper understanding of neurometabolism, the development of more advanced metabolomics technologies, and the design of highly effective metabolic interventions.

Inhibiting SHP2 reduces glycolysis, promotes microglial M1 polarization, and alleviates secondary inflammation following spinal cord injury in a mouse model

JOURNAL/nrgr/04.03/01300535-202503000-00030/figure1/v/2024-06-17T092413Z/r/image-tiff Reducing the secondary inflammatory response, which is partly mediated by microglia, is a key focus in the treatment of spinal cord injury. Src homology 2-containing protein tyrosine phosphatase 2 (SHP2), encoded by PTPN11, is widely expressed in the human body and plays a role in inflammation through various mechanisms. Therefore, SHP2 is considered a potential target for the treatment of inflammation-related diseases. However, its role in secondary inflammation after spinal cord injury remains unclear. In this study, SHP2 was found to be abundantly expressed in microglia at the site of spinal cord injury. Inhibition of SHP2 expression using siRNA and SHP2 inhibitors attenuated the microglial inflammatory response in an in vitro lipopolysaccharide-induced model of inflammation. Notably, after treatment with SHP2 inhibitors, mice with spinal cord injury exhibited significantly improved hind limb locomotor function and reduced residual urine volume in the bladder. Subsequent in vitro experiments showed that, in microglia stimulated with lipopolysaccharide, inhibiting SHP2 expression promoted M2 polarization and inhibited M1 polarization. Finally, a co-culture experiment was conducted to assess the effect of microglia treated with SHP2 inhibitors on neuronal cells. The results demonstrated that inflammatory factors produced by microglia promoted neuronal apoptosis, while inhibiting SHP2 expression mitigated these effects. Collectively, our findings suggest that SHP2 enhances secondary inflammation and neuronal damage subsequent to spinal cord injury by modulating microglial phenotype. Therefore, inhibiting SHP2 alleviates the inflammatory response in mice with spinal cord injury and promotes functional recovery postinjury.

Interaction of microglia with the microenvironment in spinal cord injury

This article discusses the peculiarities of microglia behaviour and their interaction with other cells of the central nervous system (CNS) during neural tissue injury with a focus on spinal cord injury (SCI). Taking into account the plasticity of microglia, the influence of the microenvironment should be taken into account to establish the mechanisms determining the polarization pathways of these cells. Determination of the system of microglia interactions with other CNS cells during injury will reveal the patterns of post-traumatic microglia responses, in particular, determining both pro-inflammatory and anti-inflammatory responses. This review compiles information on changes in microglia activation, migration and phagocytosis, as well as their reciprocal effects on other CNS cells, such as neurons, astrocytes and oligodendrocytes, in the background of SCI. The information contained in this article may be of interest not only to scientists studying traumatic injuries of the central nervous system, but also to specialists in the field of studying and treating neurodegenerative diseases, since the mechanisms occurring in the injured spinal cord may also be characteristic of pathological events in degenerative processes.

Transcriptome analysis unveils PLSCR1 associated with microglial polarization in neuropathic pain

Neuropathic pain (NP) continues to be a significant problem that lacks effective treatment. Our study sought to explore a new promising gene target for the treatment of NP. Differential and enrichment analyses were performed on 24,197 genes and 12,088 genes from the NP microglial microarray and sequencing dataset. Candidate differentially expressed genes (DEGs), functions, and signaling pathways that are closely related to NP were identified by analyzing the bioinformatic results. For in vivo experiments, mice were divided into the sham and NP groups. The expressions of DEGs were validated to screen out the NP hub genes. For in vitro experiments, the hub genes in resting M0-BV2 and polarized M1-BV2 microglia were examined by immunofluorescence, flow cytometry, and qRT-PCR. DEGs in the NP microarray and sequencing data shared five candidate genes, CD244, MEGF9, PCGF2, PLSCR1, and NECAB2. The results of the in vivo experiment showed that the NP model group exhibited higher expression of PLSCR1 and MEGF9 compared to the sham group. The enrichment results of the DEGs revealed the biological processes of "response to lipopolysaccharide". PLSCR1 was highly expressed in the lipopolysaccharide-induced M1-BV2 microglia. PLSCR1 is a potential gene associated with microglial polarization in NP. These findings provide a new view on understanding the pathogenesis mechanism of NP.

Glial Biologist's Guide to Mass Spectrometry-Based Lipidomics: A Tutorial From Sample Preparation to Data Analysis

Neurological diseases are associated with disruptions in the brain lipidome that are becoming central to disease pathogenesis. Traditionally perceived as static structural support in membranes, lipids are now known to be actively involved in cellular signaling, energy metabolism, and other cellular activities involving membrane curvature, fluidity, fusion or fission. Glia are critical in the development, health, and function of the brain, and glial regulation plays a major role in disease. The major pathways of glial dysregulation related to function are associated with downstream products of metabolism including lipids. Taking advantage of significant innovations and technical advancements in instrumentation, lipidomics has emerged as a popular omics discipline, serving as the prevailing approach to comprehensively define metabolic alterations associated with organismal development, damage or disease. A key technological platform for lipidomics studies is mass spectrometry (MS), as it affords large-scale profiling of complex biological samples. However, as MS-based techniques are often refined and advanced, the relative comfort level among biologists with this instrumentation has not followed suit. In this review, we aim to highlight the importance of the study of glial lipids and to provide a concise record of best practices and steps for MS-based lipidomics. Specifically, we outline procedures for glia lipidomics workflows ranging from sample collection and extraction to mass spectrometric analysis to data interpretation. To ensure these approaches are more accessible, this tutorial aims to familiarize glia biologists with sample handling and analysis techniques for MS-based lipidomics, and to guide non-experts toward generating high quality lipidomics data.

Highly BBB-permeable nanomedicine reverses neuroapoptosis and neuroinflammation to treat Alzheimer's disease

The prevalence of Alzheimer's disease (AD) is increasing globally due to population aging. However, effective clinical treatment strategies for AD still remain elusive. The mechanisms underlying AD onset and the interplay between its pathological factors have so far been unclear. Evidence indicates that AD progression is ultimately driven by neuronal loss, which in turn is caused by neuroapoptosis and neuroinflammation. Therefore, the inhibition of neuroapoptosis and neuroinflammation could be a useful anti-AD strategy. Nonetheless, the delivery of active drug agents into the brain parenchyma is hindered by the blood-brain barrier (BBB). To address this challenge, we fabricated a black phosphorus nanosheet (BP)-based methylene blue (MB) delivery system (BP-MB) for AD therapy. After confirming the successful preparation of BP-MB, we proved that its BBB-crossing ability was enhanced under near-infrared light irradiation. In vitro pharmacodynamics analysis revealed that BP and MB could synergistically scavenge excessive reactive oxygen species (ROS) in okadaic acid (OA)-treated PC12 cells and lipopolysaccharide (LPS)-treated BV2 cells, thus efficiently reversing neuroapoptosis and neuroinflammation. To study in vivo pharmacodynamics, we established a mouse model of AD mice, and behavioral tests confirmed that BP-MB treatment could successfully improve cognitive function in these animals. Notably, the results of pathological evaluation were consistent with those of the in vitro assays. The findings demonstrated that BP-MB could scavenge excessive ROS and inhibit Tau hyperphosphorylation, thereby alleviating downstream neuroapoptosis and regulating the polarization of microglia from the pro-inflammatory M1 phenotype to the anti-inflammatory M2 phenotype. Overall, this study highlights the therapeutic potential of a smart nanomedicine with the capability of reversing neuroapoptosis and neuroinflammation for AD treatment.

ARL11 knockdown alleviates spinal cord injury by inhibiting neuroinflammation and M1 activation of microglia in mice

Spinal cord injury (SCI) is a severe central nervous system injury and microglia are major participants in neuroinflammation after injury. ADP-ribosylation factor-like GTPase 11 (ARL11) is a GTP-binding protein. Whether ARL11 is involved in the SCI progression is unknown. In the impactor-induced moderate SCI mouse model, ARL11 protein and mRNA expression were significantly increased in the injury site. LPS (100 ng/mL) and IFN-γ (20 ng/mL) were incubated with BV2 cells (immortalized mouse microglial cell line) to drive them into an M1-like phenotype. ARL11 up-regulation was also observed in activated microglia in SCI mice and LPS and IFN-γ treated BV2 cells. Basso Mouse Scale scores and inclined plate test revealed that ARL11 deletion promoted motor function recovery in SCI mice. Pathological examination showed ARL11 knockdown reduced spinal cord tissue damage, increased neuron numbers, and inhibited neuronal apoptosis in SCI mice. ARL11 knockdown notably inhibited IL-1β and IL-6 production in vivo and in vitro. Furthermore, ARL11 deletion significantly inhibited iNOS protein and mRNA expression in vivo and in vitro, and COX-2 expression in vivo. Mechanism studies revealed that ARL11 silencing decreased phosphorylated ERK1/2 protein expression. Additionally, ELF1 knockdown significantly inhibited ARL11 protein and mRNA expression in vitro. ELF1 acted as a transcription activator in regulating ARL11 expression by binding to the promoter. In conclusion, ARL11 knockdown protects neurons by inhibiting M1 microglia-induced neuroinflammation, thereby promoting motor functional recovery in SCI mice. This may occur in part under the regulation of ELF1. Our study provides a new molecular target for SCI treatment.

Evaluating the Evidence for Neuroprotective and Axonal Regenerative Activities of Different Inflammatory Cell Types After Optic Nerve Injury

The optic nerve contains retinal ganglion cell (RGC) axons and functions to transmit visual stimuli to the brain. Injury to the optic nerve from ischemia, trauma, or disease leads to retrograde axonal degeneration and subsequent RGC dysfunction and death, causing irreversible vision loss. Inflammatory responses to neurological damage and axonal injuries in the central nervous system (CNS) are typically harmful to neurons and prevent recovery. However, recent evidence indicates that certain inflammatory cell types and signaling pathways are protective after optic nerve injury and promote RGC survival and axonal regeneration. The objective of this review is to examine the evidence for diverse effects of inflammatory cell types on the retina and optic nerve after injury. Additionally, we highlight promising avenues for further research.

Thioredoxin-interacting protein (TXNIP) inhibition promotes retinal ganglion cell survival and facilitates M1-like microglial transformation via the PI3K/Akt pathway in glaucoma

BACKGROUND

Glaucoma is a group of heterogeneous neurodegenerative diseases with abnormal energy metabolism and imbalanced neuroinflammation in the retina. Thioredoxin-interacting protein (TXNIP) is involved in glucose and lipid metabolism, and associated with oxidative stress and inflammation, however, not known whether to be involved in glaucoma neuropathy and its underlying mechanisms.

METHODS

To establish the chronic ocular hypertension (COH) mice model. Western blot, RT-PCR, immunofluorescence and F-VEP were used to detect neuroinflammation level, glial activation and RGCs survival in retina of wild type, TXNIP knockout and MCC950 treatment COH mice. Microglia high-pressure cultured model was constructed. Western blot, RT-PCR and immunofluorescence were used to investigate the proinflammatory cytokines secretion, glucose uptake and phenotype transformation in wild type, TXNIP knockout and overexpressed microglia combined with IL-17A treatment. Finally, we explored the possible underlying mechanisms using relevant pathway inhibitor interventions.

RESULTS

In this study, for the first time we reported that TXNIP expression was remarkably increased in experimental glaucomatous retina of chronic ocular hypertension (COH) mice, and it was mainly expressed in the ganglion cells layer (GCL). In addition, we found that ablation of TXNIP promoted retinal ganglion cells (RGCs) survival and alleviated visual function impairment in experimental glaucoma. Then, we explored the spatiotemporal consistency between glial activation and retinal inflammation levels in COH mice respectively with TXNIP-deficiency and under treatment of a thermo-containing protein domain 3 (NLRP3) inhibitor MCC950, and the results indicated that TXNIP probably mediated neuroinflammation in glaucomatous retina by activating microglia. Furthermore, upregulation of TXNIP was found in pressure-stimulated microglia, whereas silencing TXNIP facilitated microglial polarization trending towards M1 type and reduced glucose transporter-1 (Glut-1) expression on microglia under high pressure in vitro. Moreover, IL-17A was found to play a role in acting synergistically with TXNIP upon the regulation of microglia polarity transformation. Finally, knockout of TXNIP was revealed to promote PI3K phosphorylation, whereas inhibition of PI3K by LY294002 effectively suppressed Glut-1 expression, glucose uptake, and M1-like transformation tendency in microglia obtained from TXNIP-deficiency mice under high pressure stimulation.

CONCLUSIONS

TXNIP is significantly involved in the inflammation-related neuropathy of experimental glaucoma and probably facilitates M1-like microglial transformation via PI3K/Akt pathway.

The role of the neurovascular unit in vascular cognitive impairment: Current evidence and future perspectives

Vascular cognitive impairment (VCI) is a progressive cognitive impairment caused by cerebrovascular disease or vascular risk factors. It is the second most common type of cognitive impairment after Alzheimer's disease. The pathogenesis of VCI is complex, and neurovascular unit destruction is one of its important mechanisms. The neurovascular unit (NVU) is responsible for combining blood flow with brain activity and includes endothelial cells, pericytes, astrocytes and many regulatory nerve terminals. The concept of an NVU emphasizes that interactions between different types of cells are essential for maintaining brain homeostasis. A stable NVU is the basis of normal brain function. Therefore, understanding the structure and function of the neurovascular unit and its role in VCI development is crucial for gaining insights into its pathogenesis. This article reviews the structure and function of the neurovascular unit and its contribution to VCI, providing valuable information for early diagnosis and prevention.

Wilms' tumor 1-associated protein aggravates ischemic stroke by promoting M1 polarization of microglia by enhancing PTGS2 mRNA stability in an m6A-dependent manner

Mounting evidence indicates the involvement of N6-methyladenosine (m6A) alterations in diverse neurological disorders and the activation of microglia. However, the role of m6A methyltransferase Wilms' tumor 1-associated protein (WTAP) in regulating microglial polarization during ischemic stroke (IS) remains unknown. We performed bioinformatics analysis to identify m6A-related differentially expressed genes in IS and validated these genes in a mouse middle cerebral artery occlusion model and a BV2 cell oxygen-glucose deprivation/reperfusion model. We found that microglial m6A modification was increased, and that WTAP was the most significantly differentially expressed m6A regulator during IS. High expression of WTAP is closely correlated with microglia-mediated neuroinflammation in IS. Mechanistically, WTAP promoted m6A modification, which promoted prostaglandin endoperoxide synthase-2 (PTGS2) by enhancing its mRNA stability. WTAP promoted M1 microglial polarization by elevating PTGS2 expression via m6A modification of PTGS2 mRNA in the oxygen-glucose deprivation/reperfusion model. In conclusion, WTAP is a crucial posttranscriptional regulator that contributes to post-IS neuroinflammation. WTAP knockdown confers cerebral protection by shifting the microglial phenotype from M1 to M2, primarily by reducing PTGS2 mRNA stability in an m6A-dependent manner.

Regulation of nerve cells and therapeutic potential in central nervous system injury using microglia-derived exosomes

The intercellular communication within the central nervous system (CNS) is of great importance for in maintaining brain function, homeostasis, and CNS regulation. When the equilibrium of CNS is disrupted or injured, microglia are immediately activated and respond to CNS injury. Microglia-derived exosomes are capable of participating in intercellular communication within the CNS by transporting various bioactive substances, including nucleic acids, proteins, lipids, amino acids, and metabolites. Nevertheless, microglia activation is a double-edged sword. Activated microglia can coordinate the neural repair process and, conversely, can amplify tissue injury and impede CNS repair. This work reviewed the roles of exosomes derived from microglia stimulated by different environments (mainly lipopolysaccharide, interleukin-4, and other specific preconditioning) in CNS injury and their possible therapeutic potentials. This work focuses on the regulation of exosomes derived from microglia stimulated by different environments on nerve cells. Meanwhile, we summarized the molecular mechanisms by which the relevant exosomes exert regulatory effects. Exosomes, derived from microglia stimulated by different environments, regulate other nerve cells during the repair of CNS injury, having beneficial or detrimental effects on CNS repair. A comprehensive understanding of the molecular mechanisms underlying their role can provide a robust foundation for the clinical treatment of CNS injury.

Minocycline inhibits microglial activation in the CA1 hippocampal region and prevents long-term cognitive sequel after experimental cerebral malaria

Cerebral malaria is the worst complication of malaria infection, has a high mortality rate, and may cause different neurodysfunctions, including cognitive decline. Neuroinflammation is an important cause of cognitive damage in neurodegenerative diseases, and microglial cells can be activated in a disease-associated profile leading to tissue damage and neuronal death. Here, we demonstrated that treatment with minocycline reduced blood-brain barrier breakdown and modulated ICAM1 mRNA expression; reduced proinflammatory cytokines, such as TNF-α, IL-1β, IFN-γ, and IL-6; and prevented long-term cognitive decline in contextual and aversive memory tasks. Taken together, our data suggest that microglial cells are activated during experimental cerebral malaria, leading to neuroinflammatory events that end up in cognitive damage. In addition, pharmacological modulation of microglial activation, by drugs such as minocycline may be an important therapeutic strategy in the prevention of long-term memory impairment.

Formononetin inhibits neuroinflammation in BV2 microglia induced by glucose and oxygen deprivation reperfusion through TLR4/NF-κB signaling pathway

Ischemic stroke, caused by diminished or interrupted cerebral blood flow, triggers the activation of microglial cells and subsequent inflammatory responses. Formononetin (FMN) has been observed to inhibit BV2 microglial cell activation and alleviate ensuing neuroinflammatory reactions. Despite extensive research, the precise underlying mechanism remains unclear. To investigate the neuroinflammatory response following FMN-mediated inhibition of BV2 microglial activation, we employed an in vitro oxygen-glucose deprivation/reperfusion (OGD/R) model. BV2 microglial cells were categorized into four groups: control, FMN, OGD/R, and OGD/R+FMN. Cell viability was assessed using the CCK-8 assay, while flow cytometry assessed M1 and M2 cell populations within BV2 cells. Immunofluorescence was utilized to detect the expression levels of apoptosis-inducing factor (AIF), p53, Toll-like receptor 4 (TLR4), and NF-κB p65. Western blotting (WB) was conducted to quantify p65/p-p65, IκB-α/p-IκB-α, and TLR4 protein levels in each group. Additionally, ELISA was employed to measure IL-1β and TNF-α levels in cell supernatants from each group. The results revealed a significant increase in the proportion of iNOS/CD206-positive M1/M2 cells in the OGD/R group compared to the control group (p < 0.05). There was also a notable increase in nuclear translocation of NF-κB p65 and elevated expression of inflammatory factors IL-1β and TNF-α in cell supernatants. Moreover, levels of p-p65, p-IκB-α, and TLR4 proteins were significantly elevated in the OGD/R group (p < 0.05). However, the addition of FMN reversed these effects. Specifically, FMN administration notably attenuated cell death and inflammation in BV2 microglia induced by OGD/R through modulation of the TLR4/NF-κB signaling pathway.These findings suggest that FMN may serve as a potential therapeutic agent against neuroinflammation associated with ischemic stroke by targeting microglial activation pathways.

NAD+ supplement relieved chronic sleep restriction (CSR)-induced microglial proinflammation in vivo and in vitro

Sleep insufficiency is a significant health problem worldwide and can induce multiple neurodevelopmental disorders in the central nervous system (CNS). Sleep deprivation (SD), especially chronic SD, leads to cognition and memory loss and worsens neurodegenerative disease liability. Microglia are the main inflammation-dominant glia and play a crucial role in SD-induced neurological impairments. Nicotinamide adenine dinucleotide (NAD+) is a redox reaction coenzyme that exerts anti-inflammatory and mitochondria-protective effects in microglia. Whether NAD+ mitigated SD-induced neurological disorders by regulating microglial functions is still unknown. In the current study, we designed an in vivo and in vitro model to evaluate the neuroprotective effect of NAD+ on chronic sleep restriction (CSR) and further investigate the underlying mechanisms. Behavioral tests and immunofluorescence staining were applied to investigate the cognition impairments and microglial activation. Biochemical experiments were tested to analyze the oxidative status and possible mechanism. In vitro data were used to verify the in vivo data. Our results displayed that NAD+ supplement mitigated CSR-induced cognitive decline and microglial activation response by suppressing the expression of pro-inflammatory cytokines in vivo. NAD+ administration also decreased oxidative stress and mitochondrial impairments in microglia. In vitro results showed that NAD+ treatment inhibited ROS production and prompted M1 conversion to M2 phenotype. cGAS-STING/NF-κB pathways were significantly activated but down-regulated by NAD+ administration. H151, a STING antagonist, was applied to validate that NAD+ treatment alleviates neuroinflammation partially by regulating cGAS-STING pathways in microglia. Our findings suggest that NAD+ supplement is a promising therapy for sleep disorders-induced neurological problems, and cGAS-STING pathway may act as a critical regulator in microglial proinflammation.

ATP5J regulates microglial activation via mitochondrial dysfunction, exacerbating neuroinflammation in intracerebral hemorrhage

Microglial-mediated neuroinflammation is crucial in the pathophysiological mechanisms of secondary brain injury (SBI) following intracerebral hemorrhage (ICH). Mitochondria are central regulators of inflammation, influencing key pathways such as alternative splicing, and play a critical role in cell differentiation and function. Mitochondrial ATP synthase coupling factor 6 (ATP5J) participates in various pathological processes, such as cell proliferation, migration, and inflammation. However, the role of ATP5J in microglial activation and neuroinflammation post-ICH is poorly understood. This study aimed to investigate the effects of ATP5J on microglial activation and subsequent neuroinflammation in ICH and to elucidate the underlying mechanisms. We observed that ATP5J was upregulated in microglia after ICH. AAV9-mediated ATP5J overexpression worsened neurobehavioral deficits, disrupted the blood-brain barrier, and increased brain water content in ICH mice. Conversely, ATP5J knockdown ameliorated these effects. ATP5J overexpression also intensified microglial activation, neuronal apoptosis, and inflammatory responses in surrounding tissues post-ICH. ATP5J impaired microglial dynamics and reduced the proliferation and migration of microglia to injury sites. We used oxyhemoglobin (OxyHb) to stimulate BV2 cells and model ICH in vitro. Further in vitro studies showed that ATP5J overexpression enhanced OxyHb-induced microglial functional transformation. Mechanistically, ATP5J silencing reversed dynamin-related protein 1 (Drp1) and mitochondrial fission 1 protein (Fis1) upregulation in microglia post-OxyHb induction; reduced mitochondrial overdivision, excessive mitochondrial permeability transition pore opening, and reactive oxygen species production; restored normal mitochondrial ridge morphology; and partially restored mitochondrial respiratory electron transport chain activity. ATP5J silencing further alleviated OxyHb-induced mitochondrial dysfunction by regulating mitochondrial metabolism. Our results indicate that ATP5J is a key factor in regulating microglial functional transformation post-ICH by modulating mitochondrial dysfunction and metabolism, thereby positively regulate neuroinflammation. By inhibiting ATP5J, SBI following ICH could be prevented. Therefore, ATP5J could be a candidate for molecular and therapeutic target exploration to alleviate neuroinflammation post-ICH.

Role of PI3Kγ in the polarization, migration, and phagocytosis of microglia

Phosphoinositide 3-kinase γ (PI3Kγ) is a signaling protein that is constitutively expressed in immune competent cells and plays a crucial role in cell proliferation, apoptosis, migration, deformation, and immunology. Several studies have shown that high expression of PI3Kγ can inhibit the occurrence of inflammation in microglia while also regulating the polarization of microglia to inhibit inflammation and enhance microglial migration and phagocytosis. It is well known that the regulation of microglial polarization, migration, and phagocytosis is key to the treatment of most neurodegenerative diseases. Therefore, in this article, we review the important regulatory role of PI3Kγ in microglia to provide a basis for the treatment of neurodegenerative diseases.

Glial polarization in neurological diseases: Molecular mechanisms and therapeutic opportunities

Glial cell polarization plays a pivotal role in various neurological disorders. In response to distinct stimuli, glial cells undergo polarization to either mitigate neurotoxicity or facilitate neural repair following injury, underscoring the importance of glial phenotypic polarization in modulating central nervous system function. This review presents an overview of glial cell polarization, focusing on astrocytes and microglia. It explores the involvement of glial polarization in neurological diseases such as Alzheimer's disease, Parkinson's disease, stroke, epilepsy, traumatic brain injury, amyotrophic lateral sclerosis, multiple sclerosis and meningoencephalitis. Specifically, it emphasizes the role of glial cell polarization in disease pathogenesis through mechanisms including neuroinflammation, neurodegeneration, calcium signaling dysregulation, synaptic dysfunction and immune response. Additionally, it summarizes various therapeutic strategies including pharmacological treatments, dietary supplements and cell-based therapies, aimed at modulating glial cell polarization to ameliorate brain dysfunction. Future research focused on the spatio-temporal manipulation of glial polarization holds promise for advancing precision diagnosis and treatment of neurological diseases.

The Role of Hypothalamic Microglia in the Onset of Insulin Resistance and Type 2 Diabetes: A Neuro-Immune Perspective

Historically, microglial activation has been associated with diseases of a neurodegenerative and neuroinflammatory nature. Some, like Alzheimer's disease, Parkinson's disease, and multiple system atrophy, have been explored extensively, while others pertaining to metabolism not so much. However, emerging evidence points to hypothalamic inflammation mediated by microglia as a driver of metabolic dysregulations, particularly insulin resistance and type 2 diabetes mellitus. Here, we explore this connection further and examine pathways that underlie this relationship, including the IKKβ/NF-κβ, IRS-1/PI3K/Akt, mTOR-S6 Kinase, JAK/STAT, and PPAR-γ signaling pathways. We also investigate the role of non-coding RNAs, namely microRNAs and long non-coding RNAs, in insulin resistance related to neuroinflammation and their diagnostic and therapeutic potential. Finally, we explore therapeutics further, searching for both pharmacological and non-pharmacological interventions that can help mitigate microglial activation.

Hidden role of microglia during neurodegenerative disorders and neurocritical care: A mitochondrial perspective

The incidence of aging-related neurodegenerative disorders and neurocritical care diseases is increasing worldwide. Microglia, the main inflammatory cells in the brain, could be potential viable therapeutic targets for treating neurological diseases. Interestingly, mitochondrial functions, including energy metabolism, mitophagy and transfer, fission and fusion, and mitochondrial DNA expression, also change in activated microglia. Notably, mitochondria play an active and important role in the pathophysiology of neurodegenerative disorders and neurocritical care diseases. This review briefly summarizes the current knowledge on mitochondrial dysfunction in microglia in neurodegenerative disorders and neurocritical care diseases and comprehensively discusses the prospects of the application of neurological injury prevention and treatment targets by mitochondria.

Mitochondrial transplantation in brain disorders: Achievements, methods, and challenges

Mitochondrial transplantation is a new treatment strategy aimed at repairing cellular damage by introducing healthy mitochondria into injured cells. The approach shows promise in protecting brain function in various neurological disorders such as traumatic brain injury/ischemia, neurodegenerative diseases, cognitive disorders, and cancer. These conditions are often characterized by mitochondrial dysfunction, leading to impaired energy production and neuronal death. The review highlights promising preclinical studies where mitochondrial transplantation has been shown to restore mitochondrial function, reduce inflammation, and improve cognitive and motor functions in several animal models. It also addresses significant challenges that must be overcome before this therapy can be clinically applied. Current efforts to overcome these challenges, including advancements in isolation techniques, cryopreservation methods, finding an appropriate mitochondria source, and potential delivery routes, are discussed. Considering the rising incidence of neurological disorders and the limited effectiveness of current treatments, this review offers a comprehensive overview of the current state of mitochondrial transplantation research and critically assesses the remaining obstacles. It provides valuable insights that could steer future studies and potentially lead to more effective treatments for various brain disorders.

MorphoGlia, an interactive method to identify and map microglia morphologies, demonstrates differences in hippocampal subregions of an Alzheimer's disease mouse model

Microglia are dynamic central nervous system cells crucial for maintaining homeostasis and responding to neuroinflammation, as evidenced by their varied morphologies. Existing morphology analysis often fails to detect subtle variations within the full spectrum of microglial morphologies due to their reliance on predefined categories. Here, we present MorphoGlia, an interactive, user-friendly pipeline that objectively characterizes microglial morphologies. MorphoGlia employs a machine learning ensemble to select relevant morphological features of microglia cells, perform dimensionality reduction, cluster these features, and subsequently map the clustered cells back onto the tissue, providing a spatial context for the identified microglial morphologies. We applied this pipeline to compare the responses between saline solution (SS) and scopolamine (SCOP) groups in a SCOP-induced mouse model of Alzheimer's disease, with a specific focus on the hippocampal subregions CA1 and Hilus. Next, we assessed microglial morphologies across four groups: SS-CA1, SCOP-CA1, SS-Hilus, and SCOP-Hilus. The results demonstrated that MorphoGlia effectively differentiated between SS and SCOP-treated groups, identifying distinct clusters of microglial morphologies commonly associated with pro-inflammatory states in the SCOP groups. Additionally, MorphoGlia enabled spatial mapping of these clusters, identifying the most affected hippocampal layers. This study highlights MorphoGlia's capability to provide unbiased analysis and clustering of microglial morphological states, making it a valuable tool for exploring microglial heterogeneity and its implications for central nervous system pathologies.

An overview on the impact of viral pathogens on Alzheimer's disease

Alzheimer's disease (AD) is the most common type of dementia which affects over than 60 million cases worldwide with higher incidence in low and middle-income countries by 2030. Based on the multifactorial nature of AD different risk factors are linked to the condition considering the brain's β-amyloid plaques (Aβ) and neurofibrillary tangles (NFTs) as its primary hallmarks. Lately, viral photogenes specially after recent SARS-CoV-2 pandemic has gained a lot of attention in promoting the neurodegenerative disorder such as AD based on their capacity to increase the permeability of the blood-brain barrier, dysregulation of immune responses, and the impact on Aβ processing and phosphorylation of tau proteins. Therefore, in this review, we summarized the important association of viral pathogens and their mechanism by which they contribute with AD formation and development. AN OVERVIEW OF THE ROLES OF VIRAL PATHOGENS IN AD: According to this figure, viruses can infect neurons directly by modulating the BBB, transferring from endothelial cells to glial cells and then to neurons, increasing the Aβ deposition, and affecting the tau protein phosphorylation or indirectly through the virus's entrance and pathogenicity that can be accelerated by genetic and epigenetic factors, as well as chronic neuroinflammation caused by activated microglia and astrocytes.

Prenatal amoxicillin exposure induces depressive-like behavior in offspring via gut microbiota and myristic acid-mediated modulation of the STING pathway

Amoxicillin is a widely used antibiotic globally, and its pervasive environmental presence poses significant risks to human health and ecosystems. Notably, prenatal amoxicillin exposure (PAmE) may have long-term neurodevelopmental toxicity for offspring. In this study, we investigated the lasting effects of PAmE on depressive-like behaviors in offspring rats, emphasizing the biological mechanisms mediated by changes in gut microbiota and its metabolite, myristic acid. Our results showed that PAmE significantly disrupted the gut microbiota composition in offspring, particularly through the reduction of Lachnospiraceae, leading to decreased levels of myristic acid. This disruption hindered the N-myristoylation of ADP-ribosylation factor 1 (ARF1), impaired the normal degradation of the stimulator of interferon genes protein, inhibited autophagic processes, and promoted M1 polarization of microglia, ultimately leading to depressive-like behaviors in the offspring. Remarkably, supplementation with Lachnospira or myristic acid effectively reversed the PAmE-induced neurodevelopmental and behavioral abnormalities, alleviating depressive-like symptoms. This study reveals how PAmE affects offspring neurodevelopment and behavior through gut microbiota and myristic acid, highlighting the crucial role of the gut-brain axis in the modulation of depressive symptoms. Supplementing Lachnospira or myristic acid could represent a novel strategy to mitigate PAmE-induced fetal-originated depression, providing new biological evidence and potential therapeutic avenues.

MSCs-derived ECM functionalized hydrogel regulates macrophage reprogramming for osteoarthritis treatment by improving mitochondrial function and energy metabolism

Osteoarthritis (OA) is a degenerative disease that affects the entire joint, with synovial inflammation being a major pathological feature. Macrophages, as the most abundant immune cells in the synovium, have an M1/M2 imbalance that is closely related to the occurrence and development of OA. Mesenchymal stem cells (MSCs) have been shown to effectively suppress inflammation in the treatment of OA, but they still pose issues such as immune rejection and tumorigenicity. The extracellular matrix (ECM), as a major mediator of MSCs' immunoregulatory effects, offers a cell-free therapy to circumvent these risks. In this study, we developed an ECM-functionalized hydrogel by combining MSC-derived ECM with gelatin methacryloyl (GelMA). To enhance the immunomodulatory potential of MSCs, we pre-stimulated MSCs with the inflammatory factor interleukin-6 (IL-6) present in OA. In vitro results showed that the ECM-functionalized hydrogel promoted M2 macrophage polarization and inhibited the expression of various inflammatory genes, strongly indicating the hydrogel's powerful immunoregulatory capabilities. In an in vivo rat OA model, the ECM-functionalized hydrogel significantly reduced synovial inflammation and cartilage matrix degradation, alleviating the progression of OA. Furthermore, we utilized proteomics and transcriptomics analysis to reveal that the hydrogel accomplished macrophage metabolic reprogramming by regulating mitochondrial function and energy metabolism, thereby reducing inflammation. These findings suggest that the ECM-functionalized hydrogel is a promising biomaterial-based strategy for treating OA by targeting key pathological mechanisms.

Wogonin mitigates microglia-mediated synaptic over-pruning and cognitive impairment following epilepsy

BACKGROUND

Epilepsy, a neurological disorder characterized by recurrent abnormal neuronal discharges, leading to brain dysfunction and imposing significant psychological and economic burdens on patients. Microglia, the resident immune cells within the central nervous system (CNS), play a crucial role in maintaining CNS homeostasis. However, activated microglia can excessively prune synapses, exacerbating neuronal damage and cognitive dysfunction following epilepsy. Wogonin, a flavonoid from Scutellaria Baicalensis, has known neuroprotective effects via anti-inflammatory and antioxidative mechanisms, but its impact on microglial activation and synaptic pruning in neurons post-epilepsy remains unclear.

METHODS

Synaptic density was assessed using presynaptic marker Synaptophysin and postsynaptic marker Psd-95, and microglial phagocytosis was evaluated with fluorescent microspheres. Pilocarpine-induced mouse model of status epilepticus was used to evaluate synaptic density changes of mouse hippocampus following an intraperitoneal injection of wogonin (50 and 100 mg/kg). Memory and cognitive function in mice were subsequently evaluated using the Y-maze, object recognition, and Morris water maze tests. Single-cell sequencing was employed to investigate the underlying causes of microglial state alterations, followed by experimental validation.

RESULTS

Microglia were transitioned to an activated state post-epilepsy, exhibiting significantly enhanced phagocytic capacity. Correspondingly, levels of synaptophysin and Psd-95 were markedly reduced in neurons. Treatment with wogonin (100 mg/kg) significantly increased neuronal synaptic density and improved learning and memory deficits in epileptic mice. Further investigation revealed that wogonin inhibits the release of pro-inflammatory cytokines and synaptic phagocytosis of microglia by activating the AKT/FoxO1 pathway.

CONCLUSIONS

Wogonin could alleviate excessive synaptic pruning of epileptic neurons by microglia and improve cognitive dysfunction of epileptic mice via the AKT/FoxO1 pathway.

Role of microglia polarization induced by glucose metabolism disorder in the cognitive impairment of mice from PM2.5 exposure

Studies have found that PM2.5 can damage the brain, accelerate cognitive impairment, and increase the risk of developing a variety of neurodegenerative diseases. However, the potential molecular mechanisms by which PM2.5 causes learning and memory problems are yet to be explored. In this study, we evaluated the neurotoxic effects in mice after 12 weeks of PM2.5 exposure, and found that this exposure resulted in learning and memory disorders, pathological brain damage, and M1 phenotype polarization on microglia, especially in the hippocampus. The severity of this damage increased with increasing PM2.5 concentration. Proteomic analysis, as well as validation results, suggested that PM2.5 exposure led to abnormal glucose metabolism in the mouse brain, which is mainly characterized by significant expression of hexokinase, phosphofructokinase, and lactate dehydrogenase. We therefore administered the glycolysis inhibitor 2-deoxy-d-glucose (2-DG) to the mice exposed to PM2.5, and showed that inhibition of glycolysis by 2-DG significantly alleviated PM2.5-induced hippocampal microglia M1 phenotype polarization, and reduced the release of inflammatory factors, improved synaptic structure and related protein expression, which alleviated the cognitive impairment induced by PM2.5 exposure. In summary, our study found that abnormal glucose metabolism-mediated inflammatory polarization of microglia played a role in learning and memory disorders in mice exposed to PM2.5. This study provides new insights into the neurotoxicity caused by PM2.5 exposure, and provides some theoretical references for the prevention and control of cognitive impairment induced by PM2.5 exposure.

Progress of Astrocyte-Neuron Crosstalk in Central Nervous System Diseases

Neurons are the primary cells responsible for information processing in the central nervous system (CNS). However, they are vulnerable to damage and insult in a variety of neurological disorders. As the most abundant glial cells in the brain, astrocytes provide crucial support to neurons and participate in synapse formation, synaptic transmission, neurotransmitter recycling, regulation of metabolic processes, and the maintenance of the blood-brain barrier integrity. Though astrocytes play a significant role in the manifestation of injury and disease, they do not work in isolation. Cellular interactions between astrocytes and neurons are essential for maintaining the homeostasis of the CNS under both physiological and pathological conditions. In this review, we explore the diverse interactions between astrocytes and neurons under physiological conditions, including the exchange of neurotrophic factors, gliotransmitters, and energy substrates, and different CNS diseases such as Alzheimer's disease, Parkinson's disease, stroke, traumatic brain injury, and multiple sclerosis. This review sheds light on the contribution of astrocyte-neuron crosstalk to the progression of neurological diseases to provide potential therapeutic targets for the treatment of neurological diseases.

Berberine modulates microglial polarization by activating TYROBP in Alzheimer's disease

BACKGROUND

Characterized by β-amyloid (Aβ) plaques, neurofibrillary tangles, and aberrant neuroinflammation in the brain, Alzheimer's disease (AD) is the most common neurodegenerative disease. Microglial polarization is a subtle mechanism which maintains immunological homeostasis and has emerged as a putative therapeutic to combat AD. Berberine (BBR) is a natural alkaloid compound with multiple pharmacological effects, and has shown considerable therapeutic potential against inflammatory disorders. However, BBR functions and underlying mechanisms in neuroinflammation remain unclear.

PURPOSE

To examine BBR pharmacological effects and mechanisms in neuroinflammation with a view to treating AD.

METHODS

BBR effects on cognitive performance in 5 × FAD mice were assessed using open field, Y-maze, and Morris Water Maze (MWM) tests. Neuroinflammation-related markers and Aβ pathology were examined in brain sections from mice. Transcriptomic analyses of hippocampus tissues were also conducted. Microglial BV2 cells were also used to verify potential BBR mechanisms in neuroinflammation and microglial polarization.

RESULTS

BBR improved cognitive performance, reduced amyloid pathology, and alleviated aberrant neuroinflammation in an AD mouse model. BBR induced microglial polarization to an M2-like phenotype, which was manifested by lowered and elevated proinflammatory and anti-inflammatory cytokine production, respectively, improved microglial uptake and Aβ clearance. Mechanistically, BBR directly interacted with TYROBP and promoted its activation by stabilizing TYROBP oligomerization. TYROBP knockdown aggravated M1-like polarization and pro-inflammatory gene expression in microglial cells in the presence of lipopolysaccharide (LPS)+Aβ, while blocked microglial M2-like polarization benefited from BBR administration.

CONCLUSIONS

BBR modulated neuroinflammation by regulating microglial polarization via TYROBP activation. Our study provided new insight into BBR pharmacological actions in regulating microglial homeostasis and combating AD.

Pulmonary Flora-Derived Lipopolysaccharide Mediates Lung-Brain Axis through Activating Microglia Involved in Polystyrene Microplastic-Induced Cognitive Dysfunction

Microplastics (MPs) have been detected in the atmospheric and the human respiratory system, indicating that the respiratory tract is a significant exposure route for MPs. However, the effect of inhaled MPs on cognitive function has not been adequately studied. Here, a C57BL/6 J mouse model of inhalation exposure to polystyrene MPs (PS-MPs, 5 µm, 60 d) is established by intratracheal instillation. Interestingly, in vivo fluorescence imaging and transmission electron microscopy reveal that PS-MPs do not accumulate in the brain. However, behavioral experiments shows that cognitive function of mice is impaired, accompanied by histopathological damage of lung and brain tissue. Transcriptomic studies in hippocampal and lung tissue have demonstrated key neuroplasticity factors as well as cognitive deficits linked to lung injury, respectively. Mechanistically, the lung-brain axis plays a central role in PS-MPs-induced neurological damage, as demonstrated by pulmonary flora transplantation, lipopolysaccharide (LPS) intervention, and cell co-culture experiments. Together, inhalation of PS-MPs reduces cognitive function by altering the composition of pulmonary flora to produce more LPS and promoting M1 polarization of microglia, which provides new insights into the mechanism of nerve damage caused by inhaled MPs and also sheds new light on the prevention of neurotoxicity of environmental pollutants.

Regulation of TREM2 on BV2 inflammation through PI3K/AKT/mTOR pathway

This work sought to determine how lipopolysaccharide (LPS)-induced pro-inflammatory factor production in BV2 microglia was influenced by myeloid cell 2 (TREM2) expressions. LPS (0.1, 1, and 10 µg/mL) induced inflammation in BV2 cells, MTT and QPCR were used to detect the occurrence of inflammation; TREM2 activation and inhibition vectors were used to activate and inhibit TREM2; Cell Proliferation was detected using CCK-8 and cell cloning experiments. LY294002 was used to inhibit the activity of PI3K/AKT signal pathway; Western blot and ELISA were used to detect cell polarization and signal pathway changes. CCK-8 and cell clone experiments found that the activation of TERM2 can promote the proliferation of BV2 cells; and the activation of TERM2 can promote the expression of IL6, IL1β, TNFα and the expression of M2 cell phenotype molecules Arg-1 and CD206. The effect of adding LY294002 signaling pathway by TERM2 activation was inhibited, indicating that TERM2 can affect the occurrence of inflammation by regulating the activity of PI3K/AKT signaling pathway. Finally, Western blotting and ELISA showed that activation of TERM2 can promote the expression of Arg-1 and CD206 in BV2 cells, and promote the transformation of BV2 cells to M2 polarization. TERM2 can affect the inflammatory response in microglia through the PI3K/AKT signaling pathway, suggesting that TERM2 may be a target for the treatment of inflammatory response in glial cells. This study provides a treatment plan for alleviating the impact of inflammation on central nervous system.

Virus-induced brain pathology and the neuroinflammation-inflammation continuum: the neurochemists view

Fascinatingly, an abundance of recent studies has subscribed to the importance of cytotoxic immune mechanisms that appear to increase the risk/trigger for many progressive neurodegenerative disorders, including Parkinson's disease (PD), Alzheimer's disease (AD), amyotrophic lateral sclerosis, and multiple sclerosis. Events associated with the neuroinflammatory cascades, such as ageing, immunologic dysfunction, and eventually disruption of the blood-brain barrier and the "cytokine storm", appear to be orchestrated mainly through the activation of microglial cells and communication with the neurons. The inflammatory processes prompt cellular protein dyshomeostasis. Parkinson's and Alzheimer's disease share a common feature marked by characteristic pathological hallmarks of abnormal neuronal protein accumulation. These Lewy bodies contain misfolded α-synuclein aggregates in PD or in the case of AD, they are Aβ deposits and tau-containing neurofibrillary tangles. Subsequently, these abnormal protein aggregates further elicit neurotoxic processes and events which contribute to the onset of neurodegeneration and to its progression including aggravation of neuroinflammation. However, there is a caveat for exclusively linking neuroinflammation with neurodegeneration, since it's highly unlikely that immune dysregulation is the only factor that contributes to the manifestation of many of these neurodegenerative disorders. It is unquestionably a complex interaction with other factors such as genetics, age, and environment. This endorses the "multiple hit hypothesis". Consequently, if the host has a genetic susceptibility coupled to an age-related weakened immune system, this makes them more susceptible to the virus/bacteria-related infection. This may trigger the onset of chronic cytotoxic neuroinflammatory processes leading to protein dyshomeostasis and accumulation, and finally, these events lead to neuronal destruction. Here, we differentiate "neuroinflammation" and "inflammation" with regard to the involvement of the blood-brain barrier, which seems to be intact in the case of neuroinflammation but defect in the case of inflammation. There is a neuroinflammation-inflammation continuum with regard to virus-induced brain affection. Therefore, we propose a staging of this process, which might be further developed by adding blood- and CSF parameters, their stage-dependent composition and stage-dependent severeness grade. If so, this might be suitable to optimise therapeutic strategies to fight brain neuroinflammation in its beginning and avoid inflammation at all.

Irisin Attenuates Neuroinflammation Targeting the NLRP3 Inflammasome

Neuroinflammation is defined as an immune response involving various cell types, particularly microglia, which monitor the neuroimmune axis. Microglia activate in two distinct ways: M1, which is pro-inflammatory and capable of inducing phagocytosis and releasing pro-inflammatory factors, and M2, which has anti-inflammatory properties. Inflammasomes are large protein complexes that form in response to internal danger signals, activating caspase-1 and leading to the release of pro-inflammatory cytokines such as interleukin 1β. Irisin, a peptide primarily released by muscles during exercise, was examined for its effects on BV2 microglial cells in vitro. Even at low concentrations, irisin was observed to influence the NLRP3 inflammasome, showing potential as a neuroprotective and anti-inflammatory agent after stimulation with lipopolysaccharides (LPSs). Irisin helped maintain microglia in their typical physiological state and reduced their migratory capacity. Irisin also increased Arg-1 protein expression, a marker of M2 polarization, while downregulating NLRP3, Pycard, caspase-1, IL-1β, and CD14. The results of this study indicate that irisin may serve as a crucial mediator of neuroprotection, thus representing an innovative tool for the prevention of neurodegenerative diseases.

DOCK2 deficiency alleviates neuroinflammation and affords neuroprotection after spinal cord injury

Neuroinflammation-caused secondary injury is a key event after spinal cord injury (SCI). Dedicator of cytokinesis 2 (DOCK2) belonging to DOCK-A subfamily has a vital role in microglia polarization and neuroinflammation via mediating Rac activation. However, the role of DOCK2 in SCI is unclear. In the present study, SCI model in mice was established by an impactor at thoracic T10 level. DOCK2 expression was significantly increased in the spinal cord after SCI. After knocking down DOCK2 using a lentivirus-mediated method, SCI mice exhibited improved motor function recovery, as revealed by increased Basso Mouse Scale (BMS) score, angle of incline, and relatively coordinated footprint, and decreased damaged area in the spinal cord. DOCK2 deficiency reduced neuronal apoptosis in the spinal cord after injury. Besides, deficiency of DOCK2 suppressed neuroinflammation after SCI, demonstrated by the reduction in pro-inflammatory mediators including IFN-γ, IL-1β and IL-6 and the increase in IL-4, IL-10 and IL-13, anti-inflammatory factors. The CD86, iNOS and COX-2 were down-regulated in the spinal cord, whereas CD206, Arg-1 and TGF-β were up-regulated by DOCK2 deficiency. Rac activation was prevented by DOCK2 deficiency following SCI. In vitro experiments were conducted for further verification. Treatment of BV-2 microglia with lentivirus-mediated DOCK2 inhibited IFN-γ/LPS-induced pro-inflammatory microglia polarization but increased IL-4-induced anti-inflammatory microglia, through inhibiting Rac activation. In brief, our data reveal that DOCK2 deficiency improves functional recovery in mice after SCI, which is related to Rac activation.

Phosphoproteomic analysis reveals CDK5-Mediated phosphorylation of MTDH inhibits protein synthesis in microglia

CDK5 plays a crucial role in maintaining normal central nervous system (CNS) development and synaptic function, while microglia are the primary immune cells present in the CNS and play vital physiological roles in CNS development, immune surveillance, and regulation of synaptic plasticity. Despite this, our understanding of both the substrate proteins and functional mechanisms of CDK5 in microglia remains limited. To address this, we utilized CRISPR-Cas9 knockout of Cdk5 in BV2 cells and conducted quantitative phosphoproteomics analysis to systematically screen potential CDK5 substrates in microglia. Our findings identified 335 phosphorylation sites on 234 proteins as potential CDK5 substrates in microglia based on the reported sequence motif. Through in vitro kinase assay and intracellular inhibition and knockout of CDK5 experiments, we confirmed that ER proteins MTDH (protein LYRIC) and Calnexin are novel substrate proteins of CDK5. Moreover, we demonstrated for the first time a critical mechanism for regulating protein synthesis in microglia, that the phosphorylation of S565 site on MTDH, a key protein mediating cell growth, by CDK5 inhibits protein synthesis. Our data provide valuable insights for the discovery of new substrate proteins of CDK5 and the in-depth investigation of the function and mechanism of CDK5 in microglia.

N-acetylaspartate mitigates pro-inflammatory responses in microglial cells by intersecting lipid metabolism and acetylation processes

BACKGROUND

Microglia play a crucial role in brain development and repair by facilitating processes such as synaptic pruning and debris clearance. They can be activated in response to various stimuli, leading to either pro-inflammatory or anti-inflammatory responses associated with specific metabolic alterations. The imbalances between microglia activation states contribute to chronic neuroinflammation, a hallmark of neurodegenerative diseases. N-acetylaspartate (NAA) is a brain metabolite predominantly produced by neurons and is crucial for central nervous system health. Alterations in NAA metabolism are observed in disorders such as Multiple Sclerosis and Canavan disease. While NAA's role in oligodendrocytes and astrocytes has been investigated, its impact on microglial function remains less understood.

METHODS

The murine BV2 microglial cell line and primary microglia were used as experimental models. Cells were treated with exogenous NAA and stimulated with LPS/IFN-γ to reproduce the pro-inflammatory phenomenon. HPLC and immunofluorescence analysis were used to study lipid metabolism following NAA treatment. Automated fluorescence microscopy was used to analyze phagocytic activity. The effects on the pro-inflammatory response were evaluated by analysis of protein/mRNA expression and ChIP assay of typical inflammatory markers.

RESULTS

NAA treatment promotes an increase in both lipid synthesis and degradation, and enhances the phagocytic activity of BV2 cells, thus fostering surveillant microglia characteristics. Importantly, NAA decreases the pro-inflammatory state induced by LPS/IFN-γ via the activation of histone deacetylases (HDACs). These findings were validated in primary microglial cells, highlighting the impact on cellular metabolism and inflammatory responses.

CONCLUSIONS

The study highlighted the role of NAA in reinforcing the oxidative metabolism of surveillant microglial cells and, most importantly, in buffering the inflammatory processes characterizing reactive microglia. These results suggest that the decreased levels of NAA observed in neurodegenerative disorders can contribute to chronic neuroinflammation.

Should We Consider Neurodegeneration by Itself or in a Triangulation with Neuroinflammation and Demyelination? The Example of Multiple Sclerosis and Beyond

Neurodegeneration is preeminent in many neurological diseases, and still a major burden we fail to manage in patient's care. Its pathogenesis is complicated, intricate, and far from being completely understood. Taking multiple sclerosis as an example, we propose that neurodegeneration is neither a cause nor a consequence by itself. Mitochondrial dysfunction, leading to energy deficiency and ion imbalance, plays a key role in neurodegeneration, and is partly caused by the oxidative stress generated by microglia and astrocytes. Nodal and paranodal disruption, with or without myelin alteration, is further involved. Myelin loss exposes the axons directly to the inflammatory and oxidative environment. Moreover, oligodendrocytes provide a singular metabolic and trophic support to axons, but do not emerge unscathed from the pathological events, by primary myelin defects and cell apoptosis or secondary to neuroinflammation or axonal damage. Hereby, trophic failure might be an overlooked contributor to neurodegeneration. Thus, a complex interplay between neuroinflammation, demyelination, and neurodegeneration, wherein each is primarily and secondarily involved, might offer a more comprehensive understanding of the pathogenesis and help establishing novel therapeutic strategies for many neurological diseases and beyond.

BHLHE40 regulates microglia polarization after spinal cord injury via the NF-κB pathway

Spinal cord injury (SCI) is a devastating disease characterized by neuroinflammation and irreversible neuronal loss. The basic helix-loop-helix family member e40 (Bhlhe40) is a stress-responsive transcription factor involved in the pathological process of inflammation. However, Bhlhe40 expression and its role in SCI are largely unknown. SCI rat models were established with an aneurysm clip and then the rats were injected with lentiviral Bhlhe40 shRNA to knock down Bhlhe40 expression. In vitro, BV2 microglia cells were stimulated with LPS and IFN-γ to promote M1 microglia polarization. The results showed that Bhlhe40 expression was significantly elevated in the injured spinal cord tissue. Bhlhe40 deficiency reduced neuroinflammation and neuronal loss, and then promoted the recovery of neurological function. Additionally, Bhlhe40 knockdown alleviated neuronal apoptosis by regulating microglia polarization. In our study, Bhlhe40 knockdown inhibited M1 microglia polarization and the secretion of pro-inflammatory factors (TNF-α, IL-1β, and IL-6). Meanwhile, the NF-κB pathway was inhibited after the Bhlhe40 knockdown in SCI rats. To further explore the functional role of Bhlhe40, we performed in vitro experiments. Bhlhe40 knockdown decreased M1 microglia polarization by inhibiting the NF-κB pathway. In conclusion, our study indicates that Bhlhe40 knockdown can alleviate the progression of SCI and its underlying mechanism in regulating macrophage polarization through the NF-κB pathway.

The Role of Inflammatory Cascade and Reactive Astrogliosis in Glial Scar Formation Post-spinal Cord Injury

Reactive astrogliosis and inflammation are pathologic hallmarks of spinal cord injury. After injury, dysfunction of glial cells (astrocytes) results in glial scar formation, which limits neuronal regeneration. The blood-spinal cord barrier maintains the structural and functional integrity of the spinal cord and does not allow blood vessel components to leak into the spinal cord microenvironment. After the injury, disruption in the spinal cord barrier causes an imbalance of the immunological microenvironment. This triggers the process of neuroinflammation, facilitated by the actions of microglia, neutrophils, glial cells, and cytokines production. Recent work has revealed two phenotypes of astrocytes, A1 and A2, where A2 has a protective type, and A1 releases neurotoxins, further promoting glial scar formation. Here, we first describe the current understanding of the spinal cord microenvironment, both pre-, and post-injury, and the role of different glial cells in the context of spinal cord injury, which forms the essential update on the cellular and molecular events following injury. We aim to explore in-depth signaling pathways and molecular mediators that trigger astrocyte activation and glial scar formation. This review will discuss the activated signaling pathways in astrocytes and other glial cells and their collaborative role in the development of gliosis through inflammatory responses.

Dual-phase SilMA hydrogel: a dynamic scaffold for sequential drug release and enhanced spinal cord repair via neural differentiation and immunomodulation

Introduction

Spinal cord injury (SCI) is a severe central nervous system disorder that results in significant sensory, motor, and autonomic dysfunctions. Current surgical techniques and high-dose hormone therapies have not achieved satisfactory clinical outcomes, highlighting the need for innovative therapeutic strategies.

Methods

In this study, we developed a Dual-Phase Silk Fibroin Methacryloyl (SilMA) hydrogel scaffold (DPSH) that incorporates PLGA microspheres encapsulating neurotrophin-3 (NT-3) and angiotensin (1-7) (Ang-(1-7)). The DPSH is designed for temporally controlled release of therapeutic agents to reduce inflammation during the acute phase of SCI and to promote neuronal differentiation and axonal regeneration in later stages.

Results

Comprehensive characterization of the DPSH revealed a highly porous architecture, suitable mechanical properties for spinal cord tissue, and stability unaffected by the incorporation of microspheres and drugs. In vitro studies demonstrated that Ang-(1-7) significantly induced M2 microglia polarization by 1.8-fold (p < 0.0001), effectively reducing inflammation. Additionally, NT-3 enhanced neural stem cell differentiation into neurons by 3.6-fold (p < 0.0001). In vivo experiments showed that the DPSH group exhibited significantly higher Basso Mouse Scale (BMS) scores (p < 0.0001), enhanced motor function, reduced astrocyte scarring by 54% (p < 0.05), and improved neuronal survival and regeneration.

Discussion

These findings underscore the therapeutic potential of the DPSH scaffold for SCI repair, presenting a novel strategy to enhance neural recovery through a combination of immunomodulation and neuroprotection.

Quercetin alleviates neonatal hypoxic-ischaemic brain injury by rebalancing microglial M1/M2 polarization through silent information regulator 1/ high mobility group box-1 signalling

Neonatal hypoxic-ischaemic encephalopathy (HIE) remains one of the major causes of neonatal death and long-term neurological disability. Due to its complex pathogenesis, there are still many challenges in its treatment. In our previous studies, we found that quercetin can alleviate neurological dysfunction after hypoxic-ischaemic brain injury (HIBI) in neonatal mice. As demonstrated through in vitro experiments, quercetin can inhibit the activation of the TLR4/MyD88/NF-κB signalling pathway and the inflammatory response in the microglial cell line BV2 after oxygen-glucose deprivation. However, the in-depth mechanism still needs to be further elucidated. In the present study, 7 day-old neonatal ICR mice or BV2 cells were treated with quercetin with or without the SIRT1 inhibitor EX527 via neurobehavioural, histopathological and molecular methods. In vivo experiments have shown that quercetin can significantly improve the performance of HI mice in behavioural tests, such as the Morris water maze, rotarod test and pole climbing test, and reduce HI insult-induced structural brain damage, cell apoptosis and hippocampal neuron loss. Quercetin also inhibited the immunofluorescence intensity of the microglial M1 marker CD16 + 32 and significantly downregulated the expression of the M1-related proteins iNOS, IL-1β and TNF-α. Moreover, quercetin increased the immunofluorescence intensity of the microglial M2 marker CD206 and significantly increased the expression of the M2-related proteins Arg-1 and IL-10. In addition, quercetin limits the nucleocytoplasmic translocation and release of microglial HMGB1 and further suppresses the activation of the downstream TLR4/MyD88/NF-κB signalling pathway. The above effects of quercetin are partially weakened by pretreatment with EX527. Similar results were found in in vitro experiments, and the mechanism further revealed that the rebalancing effect of quercetin on microglial polarization is achieved through the SIRT1-mediated reduction in HMGB1 acetylation levels. This study provides new and complementary insights into the neuroprotective effects of quercetin and a new direction for the treatment of neonatal HIE.

A novel role of peroxiredoxin 2 in diabetic kidney disease progression by activating the classically activated macrophages

Diabetic kidney disease (DKD) is the main cause of deaths due to diabetes mellitus (DM). Due to the complexity of its onset, it is difficult to achieve accurate prevention and treatment. The classically activated macrophage (M1) polarization is a crucial proinflammatory mechanism of DKD, while the interaction and cascade effects of oxidative stress and inflammatory response remain to be elucidated. A urine proteomic analysis of patients with DM indicated that peroxiredoxin 2 (PRDX2) had the higher abundance in DKD. We recently found that PRDX of parasitic protozoa Entamoeba histolytica, which was similar to human PRDX2 in amino acid sequence and spatial structure, could activate the inflammatory response of macrophages through toll-like receptor 4 (TLR4). Hence, our study was designed to explore the role of PRDX2 in chronic inflammation during DKD. Combined with in vivo and in vitro experiments, results showed that the PRDX2 was positively correlated with DKD progression and upregulated by high glucose or recombinant tumor necrosis factor-α in renal tubular epithelial cells; Besides, recombinant PRDX2 could promote M1 polarization of macrophages, and enhance the migration as well as phagocytic ability of macrophages through TLR4. In summary, our study has explored the novel role of PRDX2 in DKD to provide a basis for further research on the diagnosis and treatment of DKD.

Lactate reprograms glioblastoma immunity through CBX3-regulated histone lactylation

Glioblastoma (GBM), an aggressive brain malignancy with a cellular hierarchy dominated by GBM stem cells (GSCs), evades antitumor immunity through mechanisms that remain incompletely understood. Like most cancers, GBMs undergo metabolic reprogramming toward glycolysis to generate lactate. Here, we show that lactate production by patient-derived GSCs and microglia/macrophages induces tumor cell epigenetic reprogramming through histone lactylation, an activating modification that leads to immunosuppressive transcriptional programs and suppression of phagocytosis via transcriptional upregulation of CD47, a "don't eat me" signal, in GBM cells. Leveraging these findings, pharmacologic targeting of lactate production augments efficacy of anti-CD47 therapy. Mechanistically, lactylated histone interacts with the heterochromatin component chromobox protein homolog 3 (CBX3). Although CBX3 does not possess direct lactyltransferase activity, CBX3 binds histone acetyltransferase (HAT) EP300 to induce increased EP300 substrate specificity toward lactyl-CoA and a transcriptional shift toward an immunosuppressive cytokine profile. Targeting CBX3 inhibits tumor growth by both tumor cell-intrinsic mechanisms and increased tumor cell phagocytosis. Collectively, these results suggest that lactate mediates metabolism-induced epigenetic reprogramming in GBM that contributes to CD47-dependent immune evasion, which can be leveraged to augment efficacy of immuno-oncology therapies.

Autophagy-dependent ferroptosis may play a critical role in early stages of diabetic retinopathy

Diabetic retinopathy (DR), as one of the most common and significant microvascular complications of diabetes mellitus (DM), continues to elude effective targeted treatment for vision loss despite ongoing enrichment of the understanding of its pathogenic mechanisms from perspectives such as inflammation and oxidative stress. Recent studies have indicated that characteristic neuroglial degeneration induced by DM occurs before the onset of apparent microvascular lesions. In order to comprehensively grasp the early-stage pathological changes of DR, the retinal neurovascular unit (NVU) will become a crucial focal point for future research into the occurrence and progression of DR. Based on existing evidence, ferroptosis, a form of cell death regulated by processes like ferritinophagy and chaperone-mediated autophagy, mediates apoptosis in retinal NVU components, including pericytes and ganglion cells. Autophagy-dependent ferroptosis-related factors, including BECN1 and FABP4, may serve as both biomarkers for DR occurrence and development and potentially crucial targets for future effective DR treatments. The aforementioned findings present novel perspectives for comprehending the mechanisms underlying the early-stage pathological alterations in DR and open up innovative avenues for investigating supplementary therapeutic strategies.

Erianin alleviates cerebral ischemia-reperfusion injury by inhibiting microglial cell polarization and inflammation via the PI3K/AKT and NF-κB pathways

Cerebral ischemia-reperfusion injury (CI/RI) is a leading cause of disability and mortality worldwide, with limited therapeutic options available. Erianin, a natural compound derived from traditional Chinese medicine, has been reported to possess anti-inflammatory and neuroprotective properties. This study aimed to investigate the therapeutic potential of Erianin in CI/RI and elucidate its underlying mechanisms. Network pharmacology analysis predicted that Erianin could target the PI3K/AKT pathway, which are closely associated with CI/RI. In vivo experiments using a rat model of CI/RI demonstrated that Erianin treatment significantly alleviated neurological deficits, reduced infarct volume, and attenuated neuronal damage. Mechanistically, Erianin inhibited microglial cell polarization towards the pro-inflammatory M1 phenotype, as evidenced by the modulation of specific markers. Furthermore, Erianin suppressed the expression of pro-inflammatory cytokines and mediators, such as TNF-α, IL-6, and COX-2, while enhancing the production of anti-inflammatory factors, including Arg1, CD206, IL-4 and IL-10. In vitro studies using oxygen-glucose deprivation/reoxygenation (OGD/R)-stimulated microglial cells corroborated the anti-inflammatory and anti-apoptotic effects of Erianin. Notably, Erianin inhibited the NF-κB signaling pathway by inhibiting p65 phosphorylation and preventing the nuclear translocation of the p65 subunit. Collectively, these findings suggest that Erianin represents a promising therapeutic candidate for CI/RI by targeting microglial cell polarization and inflammation.

Visualize the time dynamics and research trends of macrophage associated periodontitis research from 2004 to 2023: Bibliometrix analysis

BACKGROUND

Macrophages play an important role in the symptoms and structural progression of periodontitis, and are receiving increasing attention. In recent years, research has shown significant progress in macrophage associated periodontitis. However, there is still lack of comprehensive and methodical bibliometric analysis in this domain. Therefore, this research aims to describe the state of the research and current research hotspots of macrophage associated periodontitis from the perspective of bibliometrics.

METHODS

This study collected and screened a total of 1424 articles on macrophage associated periodontitis retrieved between 2004 and 2023 from Web of Science Core Collection database. Use Citespace (6.1. R6), Bibliometrix-R (4.1.3), VOSviewer (1.6.19), and Graphpad Prism8 software to analyze and plot countries/regions, institutions, journals, authors, literature, and keywords to explore the research hotspots and development trends of macrophage associated periodontitis.

RESULT

After analysis, the amount of macrophage associated periodontitis publications has been rising consistently over time, with China having the most publications (29.32%). 3 countries accounted for 65.57% of the total publications: the United States, China, and Japan, occupying a dominant position in this research field. China publications have the fastest growth rate and played a driving role. The most productive institution is the Sichuan University in China. Journal of Periodontal Research is highly popular in the field of macrophage associated periodontitis, with the highest number of publications. Grenier, Daniel is the most prolific author. Inflammation and Bone Loss in Periodontal Disease are the most cited literature. "Biological pathogenic factors," "immune regulation," "mechanism research," "susceptibility factor research," "pathological processes and molecular correlation," "pathological characteristics," "inflammatory response" are the main keyword groups in this field.

CONCLUSION

This study systematically analyzes and describes the development process, direction, and hotspots of macrophage associated periodontitis using bibliometric methods, providing a reference for future researchers who continue to study macrophage associated periodontitis.

Acute hyperglycemia exacerbates neuroinflammation and cognitive impairment in sepsis-associated encephalopathy by mediating the ChREBP/HIF-1α pathway

OBJECTIVES

Delirium is a prominent symptom of sepsis-associated encephalopathy (SAE) and is highly prevalent in septic patients hospitalized in the intensive care unit, being closely connected with raised mortality rates. Acute hyperglycemia (AH) has been recognized as a separate risk factor for delirium and a worse prognosis in critically sick patients. Nevertheless, the exact contribution of AH to the advancement of SAE is still unknown.

METHODS

This research retrospectively evaluated the connection between blood glucose levels (BGLs) and the incidence of delirium and death rates in septic patients in the ICU of a tertiary comprehensive hospital. In addition, a septic rat model was induced through cecal ligation and puncture (CLP), after which continuous glucose infusion was promptly initiated via a central venous catheter post-surgery to evaluate the potential implications of AH on SAE. Next, septic rats were assigned to four groups based on target BGLs: high glucose group (HG, ≥ 300 mg/dL), moderate glucose group (MG, 200-300 mg/dL), normal glucose group (NG, < 200 mg/dL), and a high glucose insulin-treated group (HI, 200-300 mg/dL) receiving recombinant human insulin treatment (0.1 IU/kg/min). The sham group (SG) received an equivalent volume of saline infusion and denoted the NG group. The effects of AH on neuroinflammation and cognitive function in septic rats were evaluated using behavioral tests, histopathological examination, TUNEL staining, ELISA, and Western blot. The effects of glucose levels on microglial activation and glucose metabolism following lipopolysaccharide (LPS, 1 μg/mL) exposure were assessed using CCK8 assay, qRT-PCR, Western blot, and ELISA.

RESULTS

Our findings revealed that AH during sepsis was a separate risk factor for delirium and assisted in predicting delirium occurrence. AH raised the levels of systemic and central inflammatory cytokines in septic rats, promoting neuronal apoptosis, blood-brain barrier disruption, and cognitive impairment. In addition, both in vivo and in vitro, an elevated glucose challenge increased the ChREBP, HIF-1α, glycolytic enzymes, and inflammatory cytokines expressions in microglia after exposure to CLP or LPS.

CONCLUSIONS

These results collectively suggest that hyperglycemia can exacerbate neuroinflammation and delirium by enhancing microglial glycolysis under septic conditions, potentially mediated by upregulation of the ChREBP/HIF-1α signaling pathway.

Up-regulated succinylation modifications induce a senescence phenotype in microglia by altering mitochondrial energy metabolism

The aging of the central nervous system(CNS) is a primary contributor to neurodegenerative diseases in older individuals and significantly impacts their quality of life. Neuroinflammation, characterized by activation of microglia(MG) and release of cytokines, is closely associated with the onset of these neurodegenerative diseases. The activated status of MG is modulated by specifically programmed metabolic changes under various conditions. Succinylation, a novel post-translational modification(PTM) mainly involved in regulating mitochondrial energy metabolism pathways, remains unknown in its role in MG activation and aging. In the present study, we found that succinylation levels were significantly increased both during aging and upon lipopolysaccharide-induced(LPS-induced) MG activation undergoing metabolic reprogramming. Up-regulated succinylation induced by sirtuin 5 knockdown(Sirt5 KD) in microglial cell line BV2 resulted in significant up-regulation of aging-related genes, accompanied by impaired mitochondrial adaptability and a shift towards glycolysis as a major metabolic pathway. Furthermore, after LPS treatment, Sirt5 KD BV2 cells exhibited increased generation of reactive oxygen species(ROS), accumulation of lipid droplets, and elevated levels of lipid peroxidation. By employing immunoprecipitation, introducing point mutation to critical succinylation sites, and conducting enzyme activity assays for succinate dehydrogenase(SDH) and trifunctional enzyme subunit alpha(ECHA), we demonstrated that succinylation plays a regulatory role in modulating the activities of these mitochondrial enzymes. Finally, down-regulation the succinylation levels achieved through administration of succinyl phosphonate(SP) led to amelioration of MG senescence in vitro and neuroinflammation in vivo. To our knowledge, our data provide preliminary evidence indicating that up-regulated succinylation modifications elicit a senescence phenotype in MG through alterations in energy metabolism. Moreover, these findings suggest that manipulation of succinylation levels may offer valuable insights into the treatment of aging-related neuroinflammation.

Microglia Sing the Prelude of Neuroinflammation-Associated Depression

Major depressive disorder (MDD) is a psychiatric condition characterized by sadness and anhedonia and is closely linked to chronic low-grade neuroinflammation, which is primarily induced by microglia. Nonetheless, the mechanisms by which microglia elicit depressive symptoms remain uncertain. This review focuses on the mechanism linking microglia and depression encompassing the breakdown of the blood-brain barrier, the hypothalamic-pituitary-adrenal axis, the gut-brain axis, the vagus and sympathetic nervous systems, and the susceptibility influenced by epigenetic modifications on microglia. These pathways may lead to the alterations of microglia in cytokine levels, as well as increased oxidative stress. Simultaneously, many antidepressant treatments can alter the immune phenotype of microglia, while anti-inflammatory treatments can also have antidepressant effects. This framework linking microglia, neuroinflammation, and depression could serve as a reference for targeting microglia to treat depression.