Roles of microglia in brain development, tissue maintenance and repair

Microbiota fasting-related changes ameliorate cognitive decline in obesity and boost ex vivo microglial function through the gut-brain axis

BACKGROUND

Obesity-related cognitive decline is linked to gut microbiota dysbiosis, with emerging evidence suggesting that dietary interventions may ameliorate cognitive impairment via gut-brain axis modulation. The role of microglial cells in this process remains underexplored.

OBJECTIVE

To investigate how diet-induced changes in gut microbiota influence cognitive function in individuals with obesity and their microglial activity, and to determine the impact of specific dietary interventions.

DESIGN

This study included 96 participants with obesity who were randomised into three dietary intervention groups: Mediterranean diet (Med), alternate-day fasting (ADF) and ketogenic diet (Keto). Cognitive performance and microbiota composition were assessed pre-intervention and post-intervention. The effects of microbiota-related changes on microglial function were further evaluated in mice models through faecal transplantation and in vitro model with microbiota exosome treatment.

RESULTS

Both the Keto and ADF groups demonstrated significant weight loss, but cognitive performance improved most notably in the ADF group, in association with reduced inflammation. Diet-related microbiota composition was correlated with the cognitive outcomes in the human study. Mice models confirmed that the cognitive benefits of ADF were microbiota-dependent and linked to enhanced microglial phagocytic capacity and reduced inflammation, accompanied by changes in microglia morphology.

CONCLUSION

Fasting-induced modifications in gut microbiota contribute to cognitive improvement in individuals with obesity, with microglial cells playing a crucial mediatory role. Among the interventions, ADF most effectively enhanced microglial function and cognitive performance, suggesting its potential as a therapeutic strategy for obesity-related cognitive decline. Further studies are required to fully elucidate the underlying mechanisms.

TRIAL REGISTRATION NUMBER

NCT04453150.

Microglial dynamics and emerging therapeutic strategies in CNS homeostasis and pathology

Microglia, the resident immune cells of the central nervous system (CNS), are highly dynamic and play critical roles in maintaining CNS homeostasis. Under normal conditions, microglia continuously monitor their environment, clear cellular debris, and regulate homeostasis. In response to disease or injury, however, they undergo rapid morphological and functional changes, often adopting an amoeboid shape that facilitates phagocytosis of abnormal cells, pathogens, and external antigens. Microglia also proliferate in areas of injury or pathology, contributing to immune responses and tissue remodeling. Recently, pharmacological approaches targeting microglial depletion and repopulation have gained attention as a means to reset or modulate microglial function. Techniques such as CSF1R inhibition enable transient depletion of microglia, followed by rapid repopulation, potentially restoring homeostatic functions and mitigating chronic inflammation. This review explores the current understanding of microglial dynamics and highlights emerging therapeutic applications of microglial depletion and repopulation within the CNS.

Comparative Analysis of HMC3 and C20 Microglial Cell Lines Reveals Differential Myeloid Characteristics and Responses to Immune Stimuli

Microglia are the primary resident immune cells of the central nervous system (CNS) that respond to injury and infections. Being critical to CNS homeostasis, microglia also have been shown to contribute to neurodegenerative diseases and brain cancer. Hence, microglia are regarded as a potential therapeutic target in CNS diseases, resulting in an increased demand for reliable in vitro models. Two human microglia cell lines (HMC3 and C20) are being used in multiple in vitro studies, however, the knowledge of their biological and immunological characteristics remains limited. Our aim was to identify and compare the biological changes in these immortalised immune cells under normal physiological and immunologically challenged conditions. Using high-resolution quantitative mass spectrometry, we have examined in-depth proteomic profiles of non-stimulated and LPS or IFN-γ challenged HMC3 and C20 cells. Our findings reveal that HMC3 cells responded to both treatments through upregulation of immune, metabolic, and antiviral pathways, while C20 cells showed a response associated with mitochondrial and immune activities. Additionally, the secretome analysis demonstrated that both cell lines release IL-6 in response to LPS, while IFN-γ treatment resulted in altered kynurenine pathway activity, highlighting distinct immune and metabolic adaptations.

Irisin restrains neuroinflammation in mouse experimental autoimmune encephalomyelitis via regulating microglia activation

Introduction

Multiple sclerosis is a chronic autoimmune demyelinating disorder predominantly affecting the white matter of the central nervous system, with experimental autoimmune encephalomyelitis (EAE) serving as its classical animal model. Irisin, a glycosylated protein derived from the proteolytic cleavage of fibronectin type III domain-containing protein 5, plays a significant role in metabolic regulation and inflammatory modulation within the organism.

Methods

In this study, we systematically investigated the therapeutic effects and underlying mechanism of Irisin on EAE and BV2 microglial cells through comprehensive methodologies including quantitative real-time polymerase chain reaction, immunofluorescence staining and western blot.

Results

Irisin exerts neuroprotective effects in EAE mice, significantly ameliorating both clinical and pathological manifestations of the disease. Mechanistically, Irisin attenuated inflammatory response and reduced the number of microglia through NF-κBp65 signaling pathway.

Conclusion

In conclusion, these results collectively suggest that Irisin alleviates EAE progression by suppressing microglia activation via the NF-κBp65 pathway, highlighting its potential as a promising therapeutic target for multiple sclerosis treatment.

A 3D human iPSC-derived multi-cell type neurosphere system to model cellular responses to chronic amyloidosis

BACKGROUND

Alzheimer's disease (AD) is characterized by progressive amyloid beta (Aβ) deposition in the brain, with eventual widespread neurodegeneration. While the cell-specific molecular signature of end-stage AD is reasonably well characterized through autopsy material, less is known about the molecular pathways in the human brain involved in the earliest exposure to Aβ. Human model systems that not only replicate the pathological features of AD but also the transcriptional landscape in neurons, astrocytes and microglia are crucial for understanding disease mechanisms and for identifying novel therapeutic targets.

METHODS

In this study, we used a human 3D iPSC-derived neurosphere model to explore how resident neurons, microglia and astrocytes and their interplay are modified by chronic amyloidosis induced over 3-5 weeks by supplementing media with synthetic Aβ1 - 42 oligomers. Neurospheres under chronic Aβ exposure were grown with or without microglia to investigate the functional roles of microglia. Neuronal activity and oxidative stress were monitored using genetically encoded indicators, including GCaMP6f and roGFP1, respectively. Single nuclei RNA sequencing (snRNA-seq) was performed to profile Aβ and microglia driven transcriptional changes in neurons and astrocytes, providing a comprehensive analysis of cellular responses.

RESULTS

Microglia efficiently phagocytosed Aβ inside neurospheres and significantly reduced neurotoxicity, mitigating amyloidosis-induced oxidative stress and neurodegeneration following different exposure times to Aβ. The neuroprotective effects conferred by the presence of microglia was associated with unique gene expression profiles in astrocytes and neurons, including several known AD-associated genes such as APOE. These findings reveal how microglia can directly alter the molecular landscape of AD.

CONCLUSIONS

Our human 3D neurosphere culture system with chronic Aβ exposure reveals how microglia may be essential for the cellular and transcriptional responses in AD pathogenesis. Microglia are not only neuroprotective in neurospheres but also act as key drivers of Aβ-dependent APOE expression suggesting critical roles for microglia in regulating APOE in the AD brain. This novel, well characterized, functional in vitro platform offers unique opportunities to study the roles and responses of microglia to Aβ modelling key aspects of human AD. This tool will help identify new therapeutic targets, accelerating the transition from discovery to clinical applications.

Strategic delivery of omega-3 fatty acids for modulating inflammatory neurodegenerative diseases

Objectives

Early-life inflammatory events like infections and injuries may predispose the brain to Alzheimer's disease (AD) by disrupting neurodevelopment and raising vulnerability. The association between early neuroinflammation and subsequent neurodegeneration leading to dementia remains unclear. We hypothesize that omega-3 (n-3) fatty acids (FA), especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), positively regulate neuro-immune cells, preserving their cell membrane structure and metabolic homeostasis. Our study examined whether strategic delivery of n-3 FA via injectable n-3 triglycerides (TG) can influence microglial lipid metabolism to prevent or delay AD progression.

Methods and results

We characterized n-3 treatment effects on modulating lipid and metabolic homeostasis in microglia during the critical window of brain development. Our preliminary studies on determining the effects of early n-3 treatment on brain cell homeostasis indicate that perinatal bolus n-3 TG injections suppressed activation of gliosis-associated markers in young mice predisposed to AD (5xFAD) and yielded sustained regulatory effects on the expression of inflammatory molecules, such as interleukin-6 (Il6) and tumor necrosis factor-alpha (Tnfα), in adult brains. A significant increase in high-frequency ultrasonic vocalizations (USV) was observed in P6 5xFAD mice that received perinatal n-3 compared to vehicle control, implicating enhanced active communication patterns. Improvement in behavior deficits was observed in n-3-treated adult AD mice. Perinatal n-3 TG treatment modified brain lipid composition in young offspring, increasing key membrane lipid species, such as phospholipids (PL) and lysophospholipids (lysoPL). Pro-inflammatory sphingolipids associated with neurodegeneration, including lactosylceramide, were significantly lower in mice treated with n-3 than those in saline-treated AD mice.

Conclusion

Our study establishes a proof of principle for targeting brain immune cell metabolism with injectable n-3 TG to mitigate neuroinflammation in AD pathogenesis, paving the way for future research into early treatments for related central nervous system (CNS) disorders.

Immunity and neuroinflammation in early stages of life and epilepsy

The immune system is crucial for the correct brain development, and recent findings also point toward central control of immune response. As the immune system is not fully developed at birth, the early years become an important window for infections and for the development of epilepsy. Both central and even peripheral inflammation may impact brain function, promoting opening of the blood-brain/blood and cerebrospinal barriers and allowing entry of immune cells and cytokines, which in turn may affect neuron function and connections. The resident brain immune cells, microglia, besides providing protection, also affect neurons, myelination, and astrocyte function. They may, via the complement system, remove synapses, both physiologically and pathologically. After seizures during development, activated microglia releases proinflammatory molecules, which are detrimental for neurons, and inhibition of microglial activation shows promising antiepileptogenic effects. In addition to cytokines, seizures and excessive excitability stimulate calpain 2 expression, which can promote neuron loss and contribute to amplification of inflammatory responses via stimulation of proinflammatory cytokines. In summary, the immature immune system during postnatal early life may be an important target for the development of long-desired antiepileptogenic drugs.

The roles and therapeutic potential of exosomal non-coding RNAs in microglia-mediated intercellular communication

Exosomes, which are small extracellular vesicles (sEVs), serve as versatile regulators of intercellular communication in the progression of various diseases, including neurological disorders. Among the diverse array of cargo they carry, non-coding RNAs (ncRNAs) play key regulatory roles in various pathophysiological processes. Exosomal ncRNAs derived from distinct cells modulate their reciprocal crosstalk locally or remotely, thereby mediating neurological diseases. Nevertheless, the emerging role of exosomal ncRNAsin microglia-mediated phenotypes remains largely unexplored. This review aims to summarise the biological functions of exosomal ncRNAs and the molecular mechanisms that underlie their impact on microglia-mediated intercellular communication, modulating neuroinflammation and synaptic functions within the landscape of neurological disorders. Furthermore, this review comprehensively described the potential applications of exosomal ncRNAs as diagnostic and prognostic biomarkers, as well as innovative therapeutic targets for the treatment of neurological diseases.

Phenotypic and Functional Alterations in Peripheral Blood Mononuclear Cell-Derived Microglia in a Primate Model of Chronic Alcohol Consumption

Alcohol-induced dysregulation of microglial activity is associated with neuroinflammation, cognitive decline, heightened risk for neurodegenerative diseases, alcohol dependence, and escalation of alcohol drinking. Given the challenge of longitudinally sampling primary microglia, we optimized an in vitro method to differentiate peripheral blood mononuclear cells (PBMC) from non-human primates (NHP) into microglia-like cells (induced-microglia; iMGL). The iMGLs displayed transcriptional profiles distinct from those of monocyte progenitors and closely resembling those of primary microglia. Notably, morphological features showed that differentiated iMGLs derived from NHPs with chronic alcohol consumption (CAC) possessed a more mature-like microglial morphology. Additionally, dysregulation in key inflammatory and regulatory markers alongside increased baseline phagocytic activity was observed in CAC-derived IMGLs in the resting state. Phenotypic and functional assessments following LPS stimulation indicated the presence of an immune-tolerant phenotype and enrichment of a CD86+ hyper-inflammatory subpopulation in iMGLs derived from ethanol-exposed animals. Collectively, these findings demonstrate that in vitro differentiation of PBMC offers a minimally invasive approach to studying the impact of CAC on microglial function revealing that CAC reshapes both functional and transcriptional profiles of microglia.

Neuroimmunometabolism: how metabolism orchestrates immune response in healthy and diseased brain

Neuroimmunometabolism describes how neuroimmune cells, such as microglia, adapt their intracellular metabolic pathways to alter their immune functions in the central nervous system (CNS). Emerging evidence indicates that neurons also orchestrate the microglia-mediated immune response through neuro-immune cross talk, perhaps through metabolic signaling. However, little is known about how the brain's metabolic microenvironment and microglial intracellular metabolism orchestrate the neuroimmune response in healthy and diseased brains. This review addresses the balance of immunometabolic substrates in healthy and diseased brains, their metabolism by brain-resident microglia, and the potential impact of metabolic dysregulation of these substrates on the neuroimmune response and pathophysiology of psychiatric disorders. This review also suggests metabolic reprogramming of microglia as a preventive strategy for the management of neuroinflammation-related brain disorders, including psychiatric diseases.

Exploratory analysis of a Novel RACK1 mutation and its potential role in epileptic seizures via Microglia activation

Seizures is a prevalent neurological disorder with a largely elusive pathogenesis. In this study, we identified the key gene RACK1 and its novel mutation RACK1-p.L206P as being associated with seizures through single-cell transcriptome sequencing (scRNA-seq) and whole exome sequencing (WES) techniques. Our findings reveal that the RACK1-p.L206P mutation significantly enhances proliferation, migration, phagocytic ability, and inflammatory activation in human microglia, which in turn affects neuronal excitability and synaptic function, culminating in typical seizure symptoms in the seizures. These effects were further validated in a mouse model using CRISPR/Cas9 gene editing technology. Mutant microglia exhibited increased activation and induced apoptosis in hippocampal neurons, leading to higher action potential frequency and excitatory synaptic marker expression. In vivo experiments demonstrated that RACK1-p.L206P mutant mice displayed classic seizure symptoms, with increased neuronal excitability and a tendency for action potential bursts during initial depolarization, along with more frequent spike discharges. Additionally, excitatory synapse density and size in the hippocampal CA1 region of mutant mice were significantly elevated, accompanied by increased expression of VGLUT1 and PSD95 within microglia. This study offers novel insights into the molecular mechanisms underlying seizures in the seizures and presents valuable clues for the development of future therapeutic strategies.

Rotating magnetic field improved cognitive and memory impairments in a sporadic ad model of mice by regulating microglial polarization

Neuroinflammation, triggered by aberrantly activated microglia, is widely recognized as a key contributor to the initiation and progression of Alzheimer's disease (AD). Microglial activation in the central nervous system (CNS) can be classified into two distinct phenotypes: the pro-inflammatory M1 phenotype and the anti-inflammatory M2 phenotype. In this study, we investigated the effects of a non-invasive rotating magnetic field (RMF) (0.2T, 4Hz) on cognitive and memory impairments in a sporadic AD model of female Kunming mice induced by AlCl3 and D-gal. Our findings revealed significant improvements in cognitive and memory impairments following RMF treatment. Furthermore, RMF treatment led to reduced amyloid-beta (Aβ) deposition, mitigated damage to hippocampal morphology, prevented synaptic and neuronal loss, and alleviated cell apoptosis in the hippocampus and cortex of AD mice. Notably, RMF treatment ameliorated neuroinflammation, facilitated the transition of microglial polarization from M1 to M2, and inhibited the NF-кB/MAPK pathway. Additionally, RMF treatment resulted in reduced aluminum deposition in the brains of AD mice. In cellular experiments, RMF promoted the M1-M2 polarization transition and enhanced amyloid phagocytosis in cultured BV2 cells while inhibiting the TLR4/NF-кB/MAPK pathway. Collectively, these results demonstrate that RMF improves memory and cognitive impairments in a sporadic AD model, potentially by promoting the M1 to M2 transition of microglial polarization through inhibition of the NF-кB/MAPK signaling pathway. These findings suggest the promising therapeutic applications of RMF in the clinical treatment of AD.

Neuroinflammation and the immune system in hypoxic ischaemic brain injury pathophysiology after cardiac arrest

Hypoxic ischaemic brain injury after resuscitation from cardiac arrest is associated with dismal clinical outcomes. To date, most clinical interventions have been geared towards the restoration of cerebral oxygen delivery after resuscitation; however, outcomes in clinical trials are disappointing. Therefore, alternative disease mechanism(s) are likely to be at play, of which the response of the innate immune system to sterile injured tissue in vivo after reperfusion has garnered significant interest. The innate immune system is composed of three pillars: (i) cytokines and signalling molecules; (ii) leucocyte migration and activation; and (iii) the complement cascade. In animal models of hypoxic ischaemic brain injury, pro-inflammatory cytokines are central to propagation of the response of the innate immune system to cerebral ischaemia-reperfusion. In particular, interleukin-1 beta and downstream signalling can result in direct neural injury that culminates in cell death, termed pyroptosis. Leucocyte chemotaxis and activation are central to the in vivo response to cerebral ischaemia-reperfusion. Both parenchymal microglial activation and possible infiltration of peripherally circulating monocytes might account for exacerbation of an immunopathological response in humans. Finally, activation of the complement cascade intersects with multiple aspects of the innate immune response by facilitating leucocyte activation, further cytokine release and endothelial activation. To date, large studies of immunomodulatory therapies have not been conducted; however, lessons learned from historical studies using therapeutic hypothermia in humans suggest that quelling an immunopathological response might be efficacious. Future work should delineate the precise pathways involved in vivo in humans to target specific signalling molecules.

Microglia-mediated neuroinflammation in traumatic brain injury: a review

Traumatic brain injury (TBI) is a leading cause of disability worldwide, characterized by a complex interplay of primary and secondary injury mechanisms. Microglia, the resident immune cells of the central nervous system, play a crucial role in the inflammatory response following TBI. To review the current understanding of microglia-mediated neuroinflammation in TBI, exploring its dual nature as a protective and detrimental process. A comprehensive literature review was conducted using databases such as PubMed, Scopus, and Google Scholar. Relevant studies investigating the role of microglia in TBI were included. In the early stages of TBI, microglia exhibit a protective response, releasing cytokines and chemokines to promote neuronal survival and tissue repair. However, prolonged or excessive microglial activation can lead to neurotoxicity and exacerbate secondary injury. Microglia-mediated neuroinflammation involves complex signaling pathways, including Toll-like receptors, purinergic receptors, and the complement system. Microglia-mediated neuroinflammation in TBI is a double-edged sword. While acute microglial activation can promote repair, chronic or excessive inflammation contributes to neuronal damage and functional deficits. Understanding the temporal and molecular dynamics of microglial responses is crucial for developing therapeutic strategies to modulate neuroinflammation and improve outcomes after TBI.

Microsporidia secretory effectors and their roles in pathogenesis

Microsporidia, a group of unicellular eukaryotic parasites, rely intensely on secretory effectors for successful invasion and proliferation within host cells. This review focuses on the identification, characterization, and functional roles of effectors, including secretory proteins and microRNAs. The adhesion proteins like the Ricin-B-lectin facilitate initial invasion, which binds to the host cell surface. Once inside, microsporidia deploy a range of effectors to modulate host immune responses, such as serpin proteins, and redirect host cell metabolism to meet the parasite's nutritional needs through hexokinase. Some effectors such as microRNAs, alter the host gene expression to create a more favorable intracellular parasitic environment. In conclusion, the secretory effectors of microsporidia play a pivotal role spanning from host cell invasion to intracellular establishment. In the future, more effectors secreted by microsporidia will be studied, which will not only help to elucidate the molecular mechanism of pathogenic manipulation of the host but also help to provide the potential targets for anti-parasitic treatments.

The arrangements of the microvasculature and surrounding glial cells are linked to blood-brain barrier formation in the cerebral cortex

The blood-brain barrier (BBB) blocks harmful substances from entering the brain and dictates the central nervous system (CNS)-specific pharmacokinetics. Recent studies have shown that perivascular astrocytes and microglia also control BBB functions, however, information about the formation of BBB glial architecture remains scarce. We investigated the time course of the formation of BBB glial architecture in the rat brain cerebral cortex using Evans blue (EB) and tissue fixable biotin (Sulfo-NHS Biotin). The extent of the leakage into the brain parenchyma showed that the BBB was not formed at postnatal Day 4 (P4). The BBB gradually strengthened and reached a plateau at P15. We then investigated the changes in the configurations of blood vessels, astrocytes, and microglia with age by 3D image reconstruction of the immunohistochemical data. The endfeet of astrocytes covered the blood vessels, and the coverage rate rapidly increased after birth and reached a plateau at P15. Interestingly, microglia were also in contact with the capillaries, and the coverage rate was highest at P15 and stabilized at P30. It was also clarified that the microglial morphology changed from the amoeboid type to the ramified type, while the areas of the respective contact sites became smaller during P4 and P15. These results suggest that the perivascular glial architecture formation of the rat BBB occurs from P4 to P15 because the paracellular transport and the arrangements of perivascular glial cells at P15 are totally the same as those of P30. In addition, the contact style of perivascular microglia dramatically changed during P4-P15.

H7N7 viral infection elicits pronounced, sex-specific neuroinflammatory responses in vitro

Influenza A virus (IAV) infection can increase the risk of neuroinflammation, and subsequent neurodegenerative diseases. Certain IAV strains, such as avian H7N7 subtype, possess neurotropic properties, enabling them to directly invade the brain parenchyma and infect neurons and glia cells. Host sex significantly influences the severity of IAV infections. Studies indicate that females of the reproductive age exhibit stronger innate and adaptive immune responses to IAVs compared to males. This heightened immune response correlates with increased morbidity and mortality, and potential neuronal damage in females. Understanding the sex-specific neurotropism of IAV and associated mechanisms leading to adverse neurological outcomes is essential. Our study reveals that primary hippocampal cultures from female mice show heightened interferon-β and pro-inflammatory chemokine secretion following neurotropic IAV infection. We observed sex-specific differences in microglia activation: both sexes showed a transition into a hyper-ramified state, but only male-derived microglia exhibited an increase in amoeboid-shaped cells. These disparities extended to alterations in neuronal morphology. Neurons derived from female mice displayed increased spine density within 24 h post-infection, while no significant change was observed in male cultures. This aligns with sex-specific differences in microglial synaptic pruning. Data suggest that amoeboid-shaped microglia preferentially target postsynaptic terminals, potentially reducing neuronal hyperexcitability. Conversely, hyper-ramified microglia may focus on presynaptic terminals, potentially limiting viral spread. In conclusion, our findings underscore the utility of primary hippocampal cultures, incorporating microglia, as an effective model to study sex-specific, virus-induced effects on brain-resident cells.

Deleterious effect of sustained neuroinflammation in pediatric traumatic brain injury

INTRODUCTION

Despite improved management of traumatic brain injury (TBI), it still leads to lifelong sequelae and disability, particularly in children. Chronic neuroinflammation (the so-called tertiary phase), in particular, microglia/macrophage and astrocyte reactivity, is among the main mechanisms suspected of playing a role in the generation of lesions associated with TBI. The role of acute neuroinflammation is now well understood, but its persistent effect and impact on the brain, particularly during development, are not. Here, we investigated the long-term effects of pediatric TBI on the brain in a mouse model.

METHODS

Pediatric TBI was induced in mice on postnatal day (P) 7 by weight-drop trauma. The time course of neuroinflammation and myelination was examined in the TBI mice. They were also assessed by magnetic resonance, functional ultrasound, and behavioral tests at P45.

RESULTS

TBI induced robust neuroinflammation, characterized by acute microglia/macrophage and astrocyte reactivity. The long-term consequences of pediatric TBI studied on P45 involved localized scarring astrogliosis, persistent microgliosis associated with a specific transcriptomic signature, and a long-lasting myelination defect consisting of the loss of myelinated axons, a decreased level of myelin binding protein, and severe thinning of the corpus callosum. These results were confirmed by reduced fractional anisotropy, measured by diffusion tensor imaging, and altered inter- and intra-hemispheric connectivity, measured by functional ultrasound imaging. In addition, adolescent mice with pediatric TBI showed persistent social interaction deficits and signs of anxiety and depressive behaviors.

CONCLUSIONS

We show that pediatric TBI induces tertiary neuroinflammatory processes associated with white matter lesions and altered behavior. These results support our model as a model for preclinical studies for tertiary lesions following TBI.

Short-chain fatty acids abrogate Japanese encephalitis virus-induced inflammation in microglial cells via miR-200a-3p/ZBTB20/IKβα axis

Japanese encephalitis virus (JEV), a member of the Flaviviridae family, is a leading cause of viral encephalitis in humans. Survivors of this infection often develop lifelong neurological sequelae. Short-chain fatty acids (SCFAs) produced in the gut are vital mediators of the gut-brain axis. We aimed to study microRNA-based mechanisms of SCFAs in an in vitro model of JEV infection. N9 microglial cells were pretreated with SCFA cocktail before JEV infection. Cytokine bead analysis, immunoblotting, and PCR were performed to analyze relevant inflammatory markers. microRNA sequencing was performed using Illumina Hiseq, and bioinformatics tools were used for differentially expressed (DE) miRNAs and weighted gene co-expression network analysis (WGCNA). microRNA mimic/inhibitor experiments and luciferase assay were performed to study miRNA-target interaction. A significant reduction in monocyte chemoattractant protein (MCP1) and tumor necrosis factor alpha (TNFα) along with reduced expression of phospho-nuclear factor kappa B (phospho-NF-κB) was observed in SCFA conditions. Significant attenuation of histone deacetylase activity and protein expression was recorded. miRNA sequencing revealed 160 DE miRNAs in SCFA + JEV-treated cells at 6 h post-infection. WGCNA revealed miR-200a-3p, a hub miRNA significantly upregulated in SCFA conditions. Transcription factor ZBTB20 was bioinformatically predicted and validated as a gene target for miR-200a-3p. Further miRNA mimic/inhibitor assay demonstrated that miR-200-3p regulated ZBTB20 along with Iκβα that possibly dampened NF-κB signal activation downstream.

IMPORTANCE

The gut-brain axis plays a pivotal role in the physiological state of an organism. Gut microbiota-derived metabolites are known to play a role in brain disorders including neuroviral infections. Short-chain fatty acids (SCFAs) appear to quench inflammatory markers in Japanese encephalitis virus-infected microglial cells in vitro. Mechanistically, we demonstrate the interaction between miR-200a-3p and ZBTB20 in regulating the canonical nuclear factor kappa B (NF-κB) signaling pathway via transcriptional regulation of Iκβα. Findings of this study pave the way to a better understanding of SCFA mechanisms that can be used to develop strategies against viral neuroinflammation.

Macrophages and HLA-Class II Alleles in Multiple Sclerosis: Insights in Therapeutic Dynamics

Antigen presentation is a crucial mechanism that drives the T cell-mediated immune response and the development of Multiple Sclerosis (MS). Genetic alterations within the highly variable Major Histocompatibility Complex Class II (MHC II) have been proven to result in significant changes in the molecular basis of antigen presentation and the clinical course of patients with both Adult-Onset MS (AOMS) and Pediatric-Onset MS (POMS). Among the numerous polymorphisms of the Human Leucocyte Antigens (HLA), within MHC II complex, HLA-DRB1*15:01 has been labeled, in Caucasian ethnic groups, as a high-risk allele for MS due to the ability of its structure to increase affinity to Myelin Basic Protein (MBP) epitopes. This characteristic, among others, in the context of the trimolecular complex or immunological synapsis, provides the foundation for autoimmunity triggered by environmental or endogenous factors. As with all professional antigen presenting cells, macrophages are characterized by the expression of MHC II and are often implicated in the formation of MS lesions. Increased presence of M1 macrophages in MS patients has been associated both with progression and onset of the disease, each involving separate but similar mechanisms. In this critical narrative review, we focus on macrophages, discussing how HLA genetic alterations can promote dysregulation of this population's homeostasis in the periphery and the Central Nervous System (CNS). We also explore the potential interconnection in observed pathological macrophage mechanisms and the function of the diverse structure of HLA alleles in neurodegenerative CNS, seen in MS, by comparing available clinical with molecular data through the prism of HLA-immunogenetics. Finally, we discuss available and experimental pharmacological approaches for MS targeting the trimolecular complex that are based on cell phenotype modulation and HLA genotype involvement and try to reveal fertile ground for the potential development of novel drugs.

Advances in gene therapy approaches targeting neuro-inflammation in neurodegenerative diseases

Over the last three decades, neurodegenerative diseases (NDs) have increased in frequency. About 15% of the world's population suffers from NDs in some capacity, which causes cognitive and physical impairment. Neurodegenerative diseases, including Amyotrophic Lateral Sclerosis, Parkinson's disease, Alzheimer's disease, and others represent a significant and growing global health challenge. Neuroinflammation is recognized to be related to all NDs, even though NDs are caused by a complex mix of genetic, environmental, and lifestyle factors. Numerous genes and pathways such as NFκB, p38 MAPK, Akt/mTOR, caspase, nitric oxide, and COX are involved in triggering brain immune cells like astrocytes and microglia to secrete inflammatory cytokines such as tumor necrosis factor-α, interleukin (IL)-1β, and IL-6. In AD, the binding of Aβ with CD36, TLR4, and TLR6 receptors results in activation of microglia which start to produce proinflammatory cytokines and chemokines. Consequently, the pro-inflammatory cytokines worsen and spread neuroinflammation, causing the deterioration of healthy neurons and the impairment of brain functions. Gene therapy has emerged as a promising therapeutic approach to modulate the inflammatory response in NDs, offering potential neuroprotective effects and disease-modifying benefits. This review article focuses on recent advances in gene therapy strategies targeting neuroinflammation pathways in NDs. We discussed the molecular pathways involved in neuroinflammation, highlighted key genes and proteins implicated in these processes, and reviewed the latest preclinical and clinical studies utilizing gene therapy to modulate neuroinflammatory responses. Additionally, this review addressed the prospects and challenges in translating gene therapy approaches into effective treatments for NDs.

Research on the signaling pathways related to the intervention of traditional Chinese medicine in Parkinson's disease:A literature review

ETHNOPHARMACOLOGICAL RELEVANCE

Parkinson's disease (PD) is the most common progressive neurodegenerative disorder affecting more than 10 million people worldwide and is characterized by the progressive loss of Daergic (DA) neurons in the substantia nigra pars compacta. It has been reported that signaling pathways play a crucial role in the pathogenesis of PD, while the active ingredients of traditional Chinese medicine (TCM) have been found to possess a protective effect against PD. TCM has demonstrated significant potential in mitigating oxidative stress (OS), neuroinflammation, and apoptosis of DA neurons via the regulation of signaling pathways associated with PD.

AIM OF THE REVIEW

This study discussed and analyzed the signaling pathways involved in the occurrence and development of PD and the mechanism of active ingredients of TCM regulating PD via signaling pathways, with the aim of providing a basis for the development and clinical application of therapeutic strategies for TCM in PD.

MATERIALS AND METHODS

With "Parkinson's disease", "Idiopathic Parkinson's Disease", "Lewy Body Parkinson's Disease", "Parkinson's Disease, Idiopathic", "Parkinson Disease, Idiopathic", "Parkinson's disorders", "Parkinsonism syndrome", "Traditional Chinese medicine", "Chinese herbal medicine", "active ingredients", "medicinal plants" as the main keywords, PubMed, Web of Science and other online search engines were used for literature retrieval.

RESULTS

PD exhibits a close association with various signaling pathways, including but not limited to MAPKs, NF-κB, PI3K/Akt, Nrf2/ARE, Wnt/β-catenin, TLR/TRIF, NLRP3, Notch. The therapeutic potential of TCM lies in its ability to regulate these signaling pathways. In addition, the active ingredients of TCM have shown significant effects in improving OS, neuroinflammation, and DA neuron apoptosis in PD.

CONCLUSION

The active ingredients of TCM have unique advantages in regulating PD-related signaling pathways. It is suggested to combine network pharmacology and bioinformatics to study the specific targets of TCM. This not only provides a new way for the prevention and treatment of PD with the active ingredients of TCM, but also provides a scientific basis for the selection and development of TCM preparations.

MicroRNAs in microglia: deciphering their role in neurodegenerative diseases

This review presents a comprehensive analysis of the role of microRNAs in microglia and their implications in the pathogenesis of neurodegenerative diseases. Microglia, as the resident immune cells of the central nervous system (CNS), are pivotal in maintaining neural homeostasis and responding to pathological changes. Recent studies have highlighted the significance of miRNAs, small non-coding RNA molecules, in regulating microglial functions. In neurodegenerative diseases, such as Alzheimer's Disease (AD), Parkinson's Disease (PD), Amyotrophic Lateral Sclerosis (ALS), and Multiple Sclerosis (MS), dysregulated miRNA expression in microglia contributes to disease progression through various mechanisms such regulation of gene expression, as modulation of cytokine response and phagocytosis. This review synthesizes current knowledge on how miRNAs influence microglial activation, cytokine production, and phagocytic activity. Specific miRNAs, such as miR-155, are explored for their roles in modulating microglial responses in the context of neuroinflammation and neurodegeneration. The study also discusses the impact of miRNA dysregulation on the transition of microglia from a neuroprotective to a neurotoxic phenotype, a critical aspect in the progression of neurodegenerative diseases.

Electroacupuncture reduces oxidative stress response and improves secondary injury of intracerebral hemorrhage in rats by activating the peroxisome proliferator-activated receptor-γ/nuclear factor erythroid2-related factor 2/γ-glutamylcysteine synthetase pathway

Intracerebral hemorrhage (ICH) is a severe stroke subtype. Secondary injury is a key factor leading to neurological deficits after ICH. Electroacupuncture (EA) can improve the neurological function after ICH, however, its internal mechanism is still unclear. The aim of this study is to investigate whether EA could ameliorate secondary injury after ICH through antioxidative stress and its potential regulatory mechanism. A rat model of ICH was established by injecting autologous blood into striatum. After the intervention of EA and EA combined with peroxisome proliferator-activated receptor-γ (PPARγ) blocker, Zea-longa scores, modified neurological severity scores and open field tests were used to evaluate the neurological function of the rats. Flow cytometry detected tissue reactive oxygen species (ROS) levels. Tissue tumor necrosis factor-α (TNF-α) levels were analyzed by enzyme-linked immunosorbent assays. The protein expressions of PPAR γ, nuclear factor erythroid2-related factor 2 (Nrf2) and γ-glutamylcysteine synthetase (γ-GCS) were detected by Western blot. Immunohistochemistry was used to observe the activation of microglia. The demyelination degree of axon myelin was observed by transmission electron microscope. Compared with the model group, EA intervention improved neurological function, decreased ROS and TNF-α levels, increased the protein expression of PPARγ, Nrf2 and γ-GCS, and reduced the activation of microglia, it also alleviated axonal myelin sheath damage. In addition, the neuroprotective effect of EA was partially attenuated by PPARγ blocker. EA ameliorated the neurological function of secondary injury after ICH in rats, possibly by activating the PPARγ/Nrf2/γ-GCS signaling pathway, reducing microglia activation, and inhibiting oxidative stress, thus alleviating the extent of axonal demyelination plays a role.

Nanomaterials as Microglia Modulators in the Treatment of Central Nervous System Disorders

Microglia play a pivotal role in the central nervous system (CNS) homeostasis, acting as housekeepers and defenders of the surrounding environment. These cells can elicit their functions by shifting into two main phenotypes: pro-inflammatory classical phenotype, M1, and anti-inflammatory alternative phenotype, M2. Despite their pivotal role in CNS homeostasis, microglia phenotypes can influence the development and progression of several CNS disorders such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, ischemic stroke, traumatic brain injuries, and even brain cancer. It is thus clear that the possibility of modulating microglia activation has gained attention as a therapeutic tool against many CNS pathologies. Nanomaterials are an unprecedented tool for manipulating microglia responses, in particular, to specifically target microglia and elicit an in situ immunomodulation activity. This review focuses the discussion on two main aspects: analyzing the possibility of using nanomaterials to stimulate a pro-inflammatory response of microglia against brain cancer and introducing nanostructures able to foster an anti-inflammatory response for treating neurodegenerative disorders. The final aim is to stimulate the analysis of the development of new microglia nano-immunomodulators, paving the way for innovative and effective therapeutic approaches for the treatment of CNS disorders.

Functional regulation of microglia by vitamin B12 alleviates ischemic stroke-induced neuroinflammation in mice

Ischemic stroke is the second leading cause of death and disability worldwide, and efforts to prevent stroke, mitigate secondary neurological damage, and promote neurological recovery remain paramount. Recent findings highlight the critical importance of microbiome-related metabolites, including vitamin B12 (VB12), in alleviating toxic stroke-associated neuroinflammation. Here, we showed that VB12 tonically programmed genes supporting microglial cell division and activation and critically controlled cellular fatty acid metabolism in homeostasis. Intriguingly, VB12 promoted mitochondrial transcriptional and metabolic activities and significantly restricted stroke-associated gene alterations in microglia. Furthermore, VB12 differentially altered the functions of microglial subsets during the acute phase of ischemic stroke, resulting in reduced brain damage and improved neurological function. Pharmacological depletion of microglia before ischemic stroke abolished VB12-mediated neurological improvement. Thus, our preclinical studies highlight the relevance of VB12 in the functional programming of microglia to alleviate neuroinflammation, minimize ischemic injury, and improve host neurological recovery after ischemic stroke.

4R-cembranoid suppresses glial cells inflammatory phenotypes and prevents hippocampal neuronal loss in LPS-treated mice

Chronic neuroinflammation has been implicated in neurodegenerative disease pathogenesis. A key feature of neuroinflammation is neuronal loss and glial activation, including microglia and astrocytes. 4R-cembranoid (4R) is a natural compound that inhibits hippocampal pro-inflammatory cytokines and increases memory function in mice. We used the lipopolysaccharide (LPS) injection model to study the effect of 4R on neuronal density and microglia and astrocyte activation. C57BL/6J wild-type mice were injected with LPS (5 mg/kg) and 2 h later received either 4R (6 mg/kg) or vehicle. Mice were sacrificed after 72 h for analysis of brain pathology. Confocal images of brain sections immunostained for microglial, astrocyte, and neuronal markers were used to quantify cellular hippocampal phenotypes and neurons. Hippocampal lysates were used to measure the expression levels of neuronal nuclear protein (NeuN), inducible nitrous oxide synthase (iNOS), arginase-1, thrombospondin-1 (THBS1), glial cell-derived neurotrophic factor (GDNF), and orosomucoid-2 (ORM2) by western blot. iNOS and arginase-1 are widely used protein markers of pro- and anti-inflammatory microglia, respectively. GDNF promotes neuronal survival, and ORM2 and THBS1 are astrocytic proteins that regulate synaptic plasticity and inhibit microglial activation. 4R administration significantly reduced neuronal loss and the number of pro-inflammatory microglia 72 h after LPS injection. It also decreased the expression of the pro-inflammatory protein iNOS while increasing arginase-1 expression, supporting its anti-inflammatory role. The protein expression of THBS1, GDNF, and ORM2 was increased by 4R. Our data show that 4R preserves the integrity of hippocampal neurons against LPS-induced neuroinflammation in mice.

A novel microglia-targeting strategy based on nanoparticle-mediated delivery of miR-26a-5p for long-lasting analgesia in chronic pain

Accumulating evidence supports the notion that microglia play versatile roles in different chronic pain conditions. However, therapeutic strategies of chronic pain by targeting microglia remain largely overlooked. This study seeks to develop a miRNA-loaded nano-delivery system by targeting microglia, which could provide a decent and long-lasting analgesia for chronic pain. Surface aminated mesoporous silica nanoparticles were adopted to load miR-26a-5p, a potent analgesic miRNA, by electrostatic adsorption, which can avoid miR-26a-5p is rapidly released and degraded. Then, targeting peptide MG1 was modified on the surface of aminated mesoporous silica particles for microglia targeting. In peripheral nerve injury induced neuropathic pain model, a satisfactory anti-allodynia effect with about 6 weeks pain-relief duration were achieved through targeting microglia strategy, which decreased microglia activation and inflammation by Wnt5a, a non-canonical Wnt pathway. In inflammatory pain and chemotherapy induced peripheral neuropathic pain, microglia targeting strategy also exhibited more efficient analgesia and longer pain-relief duration than others. Overall, we developed a microglia-targeting nano-delivery system, which facilitates precisely miR-26a-5p delivery to enhance analgesic effect and duration for several chronic pain conditions.

Sex biology in amyotrophic lateral sclerosis

Although sex differences in amyotrophic lateral sclerosis (ALS) have not been studied systematically, numerous clinical and preclinical studies have shown sex to be influential in disease prognosis. Moreover, with the development of advanced imaging tools, the difference between male and female brain in structure and function and their response to neurodegeneration are more definitive. As discussed in this review, ALS patients exhibit a sex bias pertaining to the features of the disease, and their clinical, pathological, (and pathophysiological) phenotypes. Several epidemiological studies have indicated that this sex disparity stems from various aetiologies, including sex-specific brain structure and neural functioning, genetic predisposition, age, gonadal hormones, susceptibility to traumatic brain injury (TBI)/head trauma and lifestyle factors.

Microglia heterogeneity in health and disease

Microglia, the resident immune cells of the central nervous system (CNS), have received significant attention due to their critical roles in maintaining brain homeostasis and mediating cerebral immune responses. Understanding the origin of microglia has been a subject of great interest, and emerging evidence suggests that microglia consist of multiple subpopulations with unique molecular and functional characteristics. These subpopulations of microglia may exhibit specialized roles in response to different environmental cues as in disease conditions. The newfound understanding of microglial heterogeneity has significant implications for elucidating their roles in both physiological and pathological conditions. In the context of disease, microglia have been studied rigorously as they play a very important role in neuroinflammation. Dysregulated microglial activation and function contribute to chronic inflammation. Further exploration of microglial heterogeneity and their interactions with other cell types in the CNS will undoubtedly pave the way to novel therapeutic strategies targeting microglia-mediated pathologies. In this review, we discuss the latest advances in the field of microglia research, focusing specifically on the origin and subpopulations of microglia, the populations of microglia types in the brains of patients with neurodegenerative diseases, and how microglia are regulated in the healthy CNS.

Non-invasive in vivo imaging of brain and retinal microglia in neurodegenerative diseases

Microglia play crucial roles in immune responses and contribute to fundamental biological processes within the central nervous system (CNS). In neurodegenerative diseases, microglia undergo functional changes and can have both protective and pathogenic roles. Microglia in the retina, as an extension of the CNS, have also been shown to be affected in many neurological diseases. While our understanding of how microglia contribute to pathological conditions is incomplete, non-invasive in vivo imaging of brain and retinal microglia in living subjects could provide valuable insights into their role in the neurodegenerative diseases and open new avenues for diagnostic biomarkers. This mini-review provides an overview of the current brain and retinal imaging tools for studying microglia in vivo. We focus on microglia targets, the advantages and limitations of in vivo microglia imaging approaches, and applications for evaluating the pathogenesis of neurological conditions, such as Alzheimer's disease and multiple sclerosis.

Isolation and Enrichment of Major Primary Neuroglial Cells from Neonatal Mouse Brain

The central nervous system (CNS) relies on the complex interaction of neuroglial cells to carry out vital physiological functions. To comprehensively understand the structural and functional interplay between these neuroglial cells, it is essential to establish an appropriate in vitro system that can be utilized for thorough investigation. Traditional protocols for establishing primary neuronal and mixed glial cultures from prenatal mice or neural stem cells require sacrificing pregnant mice and have the drawback of yielding only specific types of cells. Our current protocol overcomes these drawbacks by utilizing the brain from day-0 pups to isolate CNS resident neuroglial cells including astrocytes, microglia, oligodendrocytes [oligodendrocyte precursor cells (OPCs) and differentiated oligodendrocytes], and meningeal fibroblasts, as well as hippocampal neurons, avoiding sacrificing pregnant mice, which makes this procedure efficient and cost effective. Furthermore, through this protocol, we aim to provide step-by-step instructions for isolating and establishing different primary neuroglial cells and their characterization using cell-specific markers. This study presents an opportunity to isolate, culture, and establish all major CNS resident cells individually. These cells can be utilized in various cell-based and biochemical assays to comprehensively investigate the cell-specific roles and behaviors of brain resident cells in a reductionist approach. Key features • Efficient isolation of major neuroglial cells like meningeal fibroblasts, neurons, astrocytes, oligodendrocytes, and microglia from a single day-0 neonatal mouse pup's brain. • Circumvents the sacrifice of pregnant female mice. • Acts as a bridging experimental method between secondary cell lines and in vivo systems. • Isolated cells can be used for performing various cell-based and biochemical assays.

MIF contribution to progressive brain diseases

Progressive brain diseases create a huge social and economic burden on modern societies as a major cause of disability and death. Incidence of brain diseases has a significantly increasing trend and merits new therapeutic strategies. At the base of many progressive brain malfunctions is a process of unresolved, chronic inflammation. Macrophage migration inhibitory factor, MIF, is an inflammatory mediator that recently gained interest of neuro-researchers due to its varied effects on the CNS such as participation of nervous system development, neuroendocrine functions, and modulation of neuroinflammation. MIF appears to be a candidate as a new biomarker and target of novel therapeutics against numerous neurologic diseases ranging from cancer, autoimmune diseases, vascular diseases, neurodegenerative pathology to psychiatric disorders. In this review, we will focus on MIF's crucial role in neurological diseases such as multiple sclerosis (MS), Alzheimer's disease (AD) and glioblastoma (GBM).

Neuroinflammatory Responses Occur in Brain Lesions During Alzheimer's Disease: Postmortem Case Report

BACKGROUND

Alzheimer's disease (AD) is a progressive and irreversible neurodegenerative disorder. It is characterized by a gradual decrease in cognitive function and is considered a disorder in which the intensifying neuronal loss. The autopsy is considered the gold standard for the diagnosis of AD and non-AD dementia.

OBJECTIVE

Our study aims to clarify the involvement of neuroinflammation processes in brain lesions of AD.

METHODS

The defunct was admitted to the forensic medicine department of Issad Hassani Hospital (Algeria). In order to recover the brain, an autopsy was performed within 24 hours of death and then immediately fixed in formaldehyde to maintain structural brain integrity for histological and immunohistochemical analysis.

RESULTS

Our findings indicate the presence of tissue lesions in the specific brain regions: right middle frontal gyrus, right cingulate gyrus, right putamen and globus pallidus, right caudate nucleus, right hippocampus, inferior parietal lobule, left parahippocampal gyrus, and left hippocampus. Notably, there is a predominant occurrence of lesions: granulovacuolar degeneration, Hirano bodies, cotton-wool, and neuritic plaques. The causes of neurodegenerative processes are probably related to TNF-α, IL-1β, and TGF-β production and iNOS expression by the NF-κB activation pathway in the R-HP, inducing necroptosis.

CONCLUSIONS

The occurrence of neuroinflammatory responses is linked to tissue lesions in AD. The production of inflammatory cytokines is the basis of this process, which ultimately leads to the necroptosis, which is triggered by neuroinflammation amplification. The inhibition of neuroinflammation by targeting TNF-α/iNOS could stop tissue damage, this may be a promising therapeutic pathway.

The Impact of Juvenile Microglia Transcriptomics on the Adult Brain Regeneration after Cerebral Ischemia

Microglial cells play a pivotal role in the brain's health and operation through all stages of life and in the face of illness. The contributions of microglia during the developmental phase of the brain markedly contrast with their contributions in the brain of adults after injury. Enhancing our understanding of the pathological mechanisms that involve microglial activity in brains as they age and in cerebrovascular conditions is crucial for informing the creation of novel therapeutic approaches. In this work we provide results on microglia transcriptomics in the juvenile vs injured adult brain and its impact on adult brain regeneration after cerebral ischemia. During fetal brain development, microglia cells are involved in gliogenesis, angiogenesis, axonal outgrowth, synaptogenesis, neurogenesis and synaptic reorganization by engulfing neuronal extensions. Within the mature, intact brain, microglial cells exhibit reduced movement of their processes in response to minimal neuronal activity, while they continuously monitor their surroundings and clear away cellular debris. Following a stroke in the adult brain, inflammation, neurodegeneration, or disruptions in neural equilibrium trigger alterations in both the genetic blueprint and the structure and roles of microglia, a state often described as "activated" microglia. Such genetic shifts include a notable increase in the pathways related to phagosomes, lysosomes, and the presentation of antigens, coupled with a rise in the expression of genes linked to cell surface receptors. We conclude that a comparison of microglia transcriptomic activity during brain development and post-stroke adult brain might provide us with new clues about how neurodegeneration occurs in the adult brain. This information could very useful to develop drugs to slow down or limit the post-stroke pathology and improve clinical outcome.

The inflammatory response to birth requires MyD88 and is driven by both mother and offspring

Birth is an inflammatory event for the newborn, characterized by elevations in interleukin (IL)-6, IL-10, and tumor necrosis factor (TNF)-α peripherally and/or centrally, as well as changes in brain microglia. However, the mechanism(s) underlying these responses is unknown. Toll-like receptors (TLRs) play crucial roles in innate immunity and initiate inflammatory cascades upon recognition of endogenous or exogenous antigens. Most TLR signaling depends on the adaptor molecule myeloid differentiation primary response 88 (MyD88). We independently varied MyD88 gene status in mouse dams and their offspring to determine whether the inflammatory response to birth depends on MyD88 signaling and, if so, whether that signaling occurs in the offspring, the mother, or both. We find that the perinatal surges in plasma IL-6 and brain expression of TNF-α depend solely on MyD88 gene status of the offspring, whereas postnatal increases in plasma IL-10 and TNF-α depend on MyD88 in both the pup and dam. Interestingly, MyD88 genotype of the dam primarily drives differences in offspring brain microglial density and has robust effects on developmental neuronal cell death. Milk cytokines were evaluated as a possible source of postnatal maternal influence; although we found high levels of CXCL1/GROα and several other cytokines in ingested post-partum milk, their presence did not require MyD88. Thus, the inflammatory response previously described in the late-term fetus and newborn depends on MyD88 (and, by extension, TLRs), with signaling in both the dam and offspring contributing. Unexpectedly, naturally-occuring neuronal cell death in the newborn is modulated primarily by maternal MyD88 gene status.

The Standardized Extract of Centella asiatica and Its Fractions Exert Antioxidative and Anti-Neuroinflammatory Effects on Microglial Cells and Regulate the Nrf2/HO-1 Signaling Pathway

Background

Neuroinflammation and oxidative stress can aggravate the progression of Alzheimer's disease (AD). Centella asiatica has been traditionally consumed for memory and cognition. The triterpenes (asiaticoside, madecassoside, asiatic acid, madecassic acid) have been standardized in the ethanolic extract of Centella asiatica (SECA). The bioactivity of the triterpenes in different solvent polarities of SECA is still unknown.

Objective

In this study, the antioxidative and anti-neuroinflammatory effects of SECA and its fractions were explored on lipopolysaccharides (LPS)-induced microglial cells.

Methods

HPLC measured the four triterpenes in SECA and its fractions. SECA and its fractions were tested for cytotoxicity on microglial cells using MTT assay. NO, pro-inflammatory cytokines (TNF-α, IL-6, IL-1β), ROS, and MDA (lipid peroxidation) produced by LPS-induced microglial cells were measured by colorimetric assays and ELISA. Nrf2 and HO-1 protein expressions were measured using western blotting.

Results

The SECA and its fractions were non-toxic to BV2 microglial cells at tested concentrations. The levels of NO, TNF-α, IL-6, ROS, and lipid peroxidation in LPS-induced BV2 microglial cells were significantly reduced (p < 0.001) by SECA and its fractions. SECA and some of its fractions can activate the Nrf2/HO-1 signaling pathway by significantly enhancing (p < 0.05) the Nrf2 and HO-1 protein expressions.

Conclusions

This study suggests that the inhibitory activity of SECA and its fractions on pro-inflammatory and oxidative stress events may be the result of the activation of antioxidant defense systems. The potential of SECA and its fractions in reducing neuroinflammation and oxidative stress can be further studied as a potential therapeutic strategy for AD.

Aging spinal cord microglia become phenotypically heterogeneous and preferentially target motor neurons and their synapses

Microglia have been found to acquire unique region-dependent deleterious features with age and diseases that contribute to neuronal dysfunction and degeneration in the brain. However, it remains unknown whether microglia exhibit similar phenotypic heterogeneity in the spinal cord. Here, we performed a regional analysis of spinal cord microglia in 3-, 16-, 23-, and 30-month-old mice. Using light and electron microscopy, we discovered that spinal cord microglia acquire an increasingly activated phenotype during the course of aging regardless of regional location. However, aging causes microglia in the ventral but not dorsal horn to lose their spatial organization. Aged ventral horn microglia also aggregate around the somata of motor neurons and increase their contacts with motor synapses, which have been shown to be lost with age. These findings suggest that microglia may affect the ability of motor neurons to receive and relay motor commands during aging. To generate additional insights about aging spinal cord microglia, we performed RNA-sequencing on FACS-isolated microglia from 3-, 18-, 22-, and 29-month-old mice. We found that spinal cord microglia acquire a similar transcriptional identity as those in the brain during aging that includes altered expression of genes with roles in microglia-neuron interactions and inflammation. By 29 months of age, spinal cord microglia exhibit additional and unique transcriptional changes known and predicted to cause senescence and to alter lysosomal and ribosomal regulation. Altogether, this work provides the foundation to target microglia to ameliorate aged-related changes in the spinal cord, and particularly on the motor circuit.

New insight on microglia activation in neurodegenerative diseases and therapeutics

Microglia are immune cells within the central nervous system (CNS) closely linked to brain health and neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease. In response to changes in the surrounding environment, microglia activate and change their state and function. Several factors, example for circadian rhythm disruption and the development of neurodegenerative diseases, influence microglia activation. In this review, we explore microglia's function and the associated neural mechanisms. We elucidate that circadian rhythms are essential factors influencing microglia activation and function. Circadian rhythm disruption affects microglia activation and, consequently, neurodegenerative diseases. In addition, we found that abnormal microglia activation is a common feature of neurodegenerative diseases and an essential factor of disease development. Here we highlight the importance of microglia activation in neurodegenerative diseases. Targeting microglia for neurodegenerative disease treatment is a promising direction. We introduce the progress of methods targeting microglia for the treatment of neurodegenerative diseases and summarize the progress of drugs developed with microglia as targets, hoping to provide new ideas for treating neurodegenerative diseases.

The role of CD47 in non-neoplastic diseases

CD47 is a 50 kDa five-spanning membrane receptor that plays a crucial role in multiple cellular processes, including myeloid cell activation, neutrophils transmigration, vascular remodeling, leukocyte adhesion and trans-endothelial migration. Recent studies have revealed that CD47 is a highly expressed anti-phagocytic signal in several types of cancer, and therefore, blocking of CD47 has shown an effective therapeutic potential in cancer immunotherapy. In addition, CD47 has been found to be involved in a complex interplay with microglia and other types of cells, and increasing evidence indicates that CD47 can be targeted as part of immune modulatory strategies for non-neoplastic diseases as well. In this review, we focus on CD47 and its role in non-neoplastic diseases, including neurological disorders, atherosclerosis and autoimmune diseases. In addition, we discuss the major challenges and potential remedies associated with CD47-SIRPα-based immunotherapies.

To re-examine the intersection of microglial activation and neuroinflammation in neurodegenerative diseases from the perspective of pyroptosis

Neurodegenerative diseases (NDs), such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and motor neuron disease, are diseases characterized by neuronal damage and dysfunction. NDs are considered to be a multifactorial disease with diverse etiologies (immune, inflammatory, aging, genetic, etc.) and complex pathophysiological processes. Previous studies have found that neuroinflammation and typical microglial activation are important mechanisms of NDs, leading to neurological dysfunction and disease progression. Pyroptosis is a new mode involved in this process. As a form of programmed cell death, pyroptosis is characterized by the expansion of cells until the cell membrane bursts, resulting in the release of cell contents that activates a strong inflammatory response that promotes NDs by accelerating neuronal dysfunction and abnormal microglial activation. In this case, abnormally activated microglia release various pro-inflammatory factors, leading to the occurrence of neuroinflammation and exacerbating both microglial and neuronal pyroptosis, thus forming a vicious cycle. The recognition of the association between pyroptosis and microglia activation, as well as neuroinflammation, is of significant importance in understanding the pathogenesis of NDs and providing new targets and strategies for their prevention and treatment.

Signaling pathways in macrophages: molecular mechanisms and therapeutic targets

Macrophages play diverse roles in development, homeostasis, and immunity. Accordingly, the dysfunction of macrophages is involved in the occurrence and progression of various diseases, such as coronavirus disease 2019 and atherosclerosis. The protective or pathogenic effect that macrophages exert in different conditions largely depends on their functional plasticity, which is regulated via signal transduction such as Janus kinase-signal transducer and activator of transcription, Wnt and Notch pathways, stimulated by environmental cues. Over the past few decades, the molecular mechanisms of signaling pathways in macrophages have been gradually elucidated, providing more alternative therapeutic targets for diseases treatment. Here, we provide an overview of the basic physiology of macrophages and expound the regulatory pathways within them. We also address the crucial role macrophages play in the pathogenesis of diseases, including autoimmune, neurodegenerative, metabolic, infectious diseases, and cancer, with a focus on advances in macrophage-targeted strategies exploring modulation of components and regulators of signaling pathways. Last, we discuss the challenges and possible solutions of macrophage-targeted therapy in clinical applications. We hope that this comprehensive review will provide directions for further research on therapeutic strategies targeting macrophage signaling pathways, which are promising to improve the efficacy of disease treatment.

Human microglia maturation is underpinned by specific gene regulatory networks

Microglia phenotypes are highly regulated by the brain environment, but the transcriptional networks that specify the maturation of human microglia are poorly understood. Here, we characterized stage-specific transcriptomes and epigenetic landscapes of fetal and postnatal human microglia and acquired corresponding data in induced pluripotent stem cell (iPSC)-derived microglia, in cerebral organoids, and following engraftment into humanized mice. Parallel development of computational approaches that considered transcription factor (TF) co-occurrence and enhancer activity allowed prediction of shared and state-specific gene regulatory networks associated with fetal and postnatal microglia. Additionally, many features of the human fetal-to-postnatal transition were recapitulated in a time-dependent manner following the engraftment of iPSC cells into humanized mice. These data and accompanying computational approaches will facilitate further efforts to elucidate mechanisms by which human microglia acquire stage- and disease-specific phenotypes.

Phenomic Microglia Diversity as a Druggable Target in the Hippocampus in Neurodegenerative Diseases

Phenomics, the complexity of microglia phenotypes and their related functions compels the continuous study of microglia in disease animal models to find druggable targets for neurodegenerative disorders. Activation of microglia was long considered detrimental for neuron survival, but more recently it has become apparent that the real scenario of microglia morphofunctional diversity is far more complex. In this review, we discuss the recent literature on the alterations in microglia phenomics in the hippocampus of animal models of normal brain aging, acute neuroinflammation, ischemia, and neurodegenerative disorders, such as AD. Microglia undergo phenomic changes consisting of transcriptional, functional, and morphological changes that transform them into cells with different properties and functions. The classical subdivision of microglia into M1 and M2, two different, all-or-nothing states is too simplistic, and does not correspond to the variety of phenotypes recently discovered in the brain. We will discuss the phenomic modifications of microglia focusing not only on the differences in microglia reactivity in the diverse models of neurodegenerative disorders, but also among different areas of the brain. For instance, in contiguous and highly interconnected regions of the rat hippocampus, microglia show a differential, finely regulated, and region-specific reactivity, demonstrating that microglia responses are not uniform, but vary significantly from area to area in response to insults. It is of great interest to verify whether the differences in microglia reactivity may explain the differential susceptibility of different brain areas to insults, and particularly the higher sensitivity of CA1 pyramidal neurons to inflammatory stimuli. Understanding the spatiotemporal heterogeneity of microglia phenomics in health and disease is of paramount importance to find new druggable targets for the development of novel microglia-targeted therapies in different CNS disorders. This will allow interventions in three different ways: (i) by suppressing the pro-inflammatory properties of microglia to limit the deleterious effect of their activation; (ii) by modulating microglia phenotypic change to favor anti-inflammatory properties; (iii) by influencing microglia priming early in the disease process.

TREM2, microglial and ischemic stroke

Ischemic stroke (IS) is a leading cause of morbidity and mortality worldwide. Immunity and inflammation are key factors in the pathophysiology of IS. The inflammatory response is involved in all stages of stroke, and microglia are the predominant cells involved in the post-stroke inflammatory response. Resident microglia are the main immune cells of the brain and the first line of defense of the nervous system. After IS, activated microglia can be both advantageous and detrimental to surrounding tissue; they can be divided into the harmful M1 types or the neuro-protective M2 type. Currently, with the latest progress of transcriptomics analysis, different and more complex phenotypes of microglia activation have been described, such as disease-related microglia (DAM) associated with Alzheimer's disease (AD), white matter associated microglia (WAMs) in aging, and stroke-related microglia (SAM) etc. The triggering receptor expressed on myeloid cell 2 (TREM2) is an immune-related receptor on the surface of microglia. Its expression increases after IS, which is related to microglial inflammation and phagocytosis, however, its relationship with the microglia phenotype is not clear. This paper reviews the following: 1) the phenotypic changes of microglia in various pathological stages after IS and its relationship with inflammatory factors; 2) the relationship between the expression of the TREM2 receptor and inflammatory factors; 3) the relationship between phenotypic changes of microglia and its surface receptor TREM2; 4) the TREM2-related signalling pathway of microglia after IS and treatment for TREM2 receptor; and finally 5) To clarify the relationship among TREM2, inflammation, and microglia phenotype after IS, as well as the mechanism among them and the some possible treatment of IS targeting TREM2. Moreover, the relationship between the new phenotype of microglia such as SAM and TREM2 has also been systematically summarized, but there are no relevant research reports on the relationship between TREM2 and SAM after IS.

Microglial cGAS deletion protects against amyloid-β induced Alzheimer's disease pathogenesis

Innate immune activation plays a vital role in the development of Alzheimer's disease (AD) and related dementias (ADRD). Among which, the DNA sensing cyclic GMP-AMP synthase (cGAS)- STING pathway has been implicated in diverse aspects of AD progression. In the current study, we showed that the cGAS-STING signaling was up-regulated in AD and this elevation was mainly contributed by the microglial population other than non-microglial cell types in the brain. By establishing an inducible, microglia-specific cGAS knockout mouse model in 5xFAD background, we found that deleting microglial cGAS at the onset of amyloid-β (Aβ) pathology significantly limited plaque formation, and protected mice from Aβ-induced cognitive impairment. Mechanistically, we found cGAS was necessary for plaque-associated microglial enrichment potentially driven by IRF8, and was indispensable for the development of disease-associated microglia (DAM) phenotype. Meanwhile, the loss of microglial cGAS reduced the levels of dystrophic neurites which led to preserved synaptic integrity and neuronal function. Our study provides new insights in understanding the effects of innate immune in AD via a cell-type specific manner, and lays the foundation for potential targeted intervention of the microglial cGAS-STING pathway toward the improvement of AD.

Electroacupuncture relieves chronic pain by promoting microglia M2 polarization in lumbar disc herniation rats

Electroacupuncture has an effective analgesia on chronic pain caused by lumbar disc herniation (LDH) clinically, however, the underlying mechanism is unclear. In this study, we investigated whether electroacupuncture alleviated pain in LDH model rats by inducing spinal microglia M2 polarization. We established a noncompression LDH rat model by implanting autologous caudal nucleus pulposus into L5/L6 nerve root. Electroacupuncture (30 min/day) treatment on the ipsilateral side was started on the 8th postoperative day, once a day for consecutive 7 days. Paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) were tested for pain behavior. Western blotting was used to detect the protein expression in lumbar enlargement (L5/L6). Immunofluorescence was used to detect iNOS+/Iba-1+ and Arg-1+/Iba-1+ and CB2R+/Iba-1+ in lumbar enlargement (L5/L6). We show that PWT and PWL decreased in the LDH group while Iba-1, iNOS, and TNF-α expression increased significantly in lumbar spinal dorsal horn (SDH) after LDH surgery, and revealing that microglia were activated and polarized towards proinflammatory M1 phenotype. Electroacupuncture treatment significantly increased PWT and PWL while reducing Iba-1, iNOS, and TNF-α expression, interestingly, Arg-1 and IL-10 expression were significantly increased. Moreover, electroacupuncture treatment led to CB2 receptors on microglia upregulation, while NF-κB and p-NF-κB expression in lumbar SDH downregulation. Our study indicated that electroacupuncture may reduce nociceptive hyperalgesia by inhibiting microglia activation and microglia M1 polarization and promoting microglia M2 polarization in lumbar SDH of LDH rats, which may be caused by the activation of CB2 receptors on microglia and inhibition of NF-κB pathway in lumbar SDH.

Role of microglial metabolic reprogramming in Parkinson's disease

Parkinson's disease (PD) is a common age-related neurodegenerative disorder characterized by damage to nigrostriatal dopaminergic neurons. Key pathogenic mechanisms underlying PD include alpha-synuclein misfolding and aggregation, impaired protein clearance, mitochondrial dysfunction, oxidative stress, and neuroinflammation. However, to date, no study has confirmed the specific pathogenesis of PD. Similarly, current PD treatment methods still have shortcomings. Although some emerging therapies have proved effective for PD, the specific mechanism still needs further clarification. Metabolic reprogramming, a term first proposed by Warburg, is applied to the metabolic energy characteristics of tumor cells. Microglia have similar metabolic characteristics. Pro-inflammatory M1 type and anti-inflammatory M2 type are the two types of activated microglia, which exhibit different metabolic patterns in glucose, lipid, amino acid, and iron metabolism. Additionally, mitochondrial dysfunction may be involved in microglial metabolic reprogramming by activating various signaling mechanisms. Functional changes in microglia resulting from metabolic reprogramming can cause changes in the brain microenvironment, thus playing an important role in neuroinflammation or tissue repair. The involvement of microglial metabolic reprogramming in PD pathogenesis has been confirmed. Neuroinflammation and dopaminergic neuronal death can effectively be reduced by inhibiting certain metabolic pathways in M1 microglia or reverting M1 cells to the M2 phenotype. This review summarizes the relationship between microglial metabolic reprogramming and PD and provides strategies for PD treatment.

Neuroprotective potential of biochanin-A and review of the molecular mechanisms involved

Biochanin-A is a naturally occurring plant phytoestrogen, which mimics specific the agonistic activity of estrogens. Biochanin-A is known to possess numerous activities, including neuroprotective, anti-diabetic, hepatoprotective, anti-inflammatory, antioxidant, and antimicrobial activities, along with the anticancer activity. Neuroinflammation is thought to play a pivotal pathological role in neurodegenerative disease. Sustained neuroinflammatory processes lead to progressive neuronal damage in Parkinson's and Alzheimer's disease. Activation of PI3K/Akt cascade and inhibition of MAPK signaling cascade have been observed to be responsible for conferring protection against neuroinflammation in neurodegenerative diseases. An increased oxidative stress promotes neuronal apoptosis via potentiating the TLR-4/NF-κB and inhibiting PI3K/Akt signaling mediated increase in pro-apoptotic and decreases in antiapoptotic proteins. Various authors have explored biochanin-A's neuroprotective effect by using various cell lines and animal models. Biochanin-A has been reported to mediate its neuroprotective via reducing the level of oxidants, inflammatory mediators, MAPK, TLR-4, NF-κB, NADPH oxidase, AchE, COX-2 and iNOS. Whereas, it has been observed to increase the level of anti-oxidants, along with phosphorylation of PI3K and Akt proteins. The current review has been designed to provide insights into the neuroprotective effect of biochanin-A and possible signaling pathways leading to protection against neuroinflammation and apoptosis in the central nervous system. This review will be helpful in guiding future researchers to further explore biochanin A at a mechanistic level to obtain useful lead molecules.