Microglia development follows a stepwise program to regulate brain homeostasis

Gut microbiome depletion modulates cocaine-induced behavioral and transcriptional responses in female mice

Cocaine use disorder is a chronic relapsing condition with no FDA-approved biological treatments. The gut microbiome has emerged as a key modulator of neurobehavioral responses to drugs of abuse, yet its role in female animals has been under studied. Here, we investigated the effects of gut microbiome depletion on cocaine-induced behavioral and transcriptional responses in female mice. Adult female C57BL/6 J mice were treated with a non-absorbable oral antibiotic (Abx) cocktail for two weeks to deplete the gut microbiome, followed by behavioral assays assessing locomotor sensitization and conditioned place preference (CPP) to cocaine. Abx-treated females displayed reduced locomotor sensitization and a shifted CPP dose-response curve, characterized by attenuated preference at higher cocaine doses. Transcriptional analysis of the nucleus accumbens (NAc) revealed that microbiome depletion suppressed cocaine-induced expression of immediate early genes (c-Fos, FosB, Nr4a1, Egr4) and altered dopamine-related (Drd1) and microglial (Cx3cr1) markers. These findings contrast with prior studies in males, where microbiome depletion enhanced cocaine-induced behavioral plasticity. The observed effects suggest distinct gut-brain signaling as an important contributor to cocaine reinforcement and neuroadaptations in females. This study provides novel insights into microbiome regulation of addiction-relevant behaviors and highlights the necessity of sex-specific investigations in neuropsychiatric disorders. Further research is needed to elucidate the molecular pathways linking gut dysbiosis to substance use vulnerability in females.

Generation of an Inducible Destabilized-Domain Cre Mouse Line to Target Disease Associated Microglia

The function of microglia during progression of Alzheimer's disease (AD) can be investigated using mouse models that enable genetic manipulation of microglial subpopulations in a temporal manner. We developed mouse lines that express either Cre recombinase (Cre) for constitutive targeting, or destabilized-domain Cre recombinase (DD-Cre) for inducible targeting from the Cst7 locus (Cst7 DD-Cre) to specifically manipulate disease associated microglia (DAM) and crossed with Ai14 tdTomato cre-reporter line mice. Cst7Cre was found to target all brain resident myeloid cells, due to transient developmental expression of Cst7, but no expression was found in the inducible Cst7 DD-Cre mice. Further crossing of this line with 5xFAD mice combined with dietary administration of trimethoprim to induce DD-Cre activity produces long-term labeling in DAM without evidence of leakiness, with tdTomato-expression restricted to cells surrounding plaques. Using this model, we found that DAMs are a subset of plaque-associated microglia (PAMs) and their transition to DAM increases with age and disease stage. Spatial transcriptomic analysis revealed that tdTomato+ cells show higher expression of disease and inflammatory genes compared to other microglial populations, including non-labeled PAMs. These models allow either complete cre-loxP targeting of all brain myeloid cells (Cst7Cre), or inducible targeting of DAMs, without leakiness (Cst7 DD-Cre).

Multiple Sclerosis: A Story of the Interaction Between Gut Microbiome and Components of the Immune System

Multiple sclerosis (MS) is defined as an inflammatory disorder that chronically affects the central nervous system of young people mostly and is distributed globally. It is associated with degeneration and demyelination of the myelin sheath around the nerves, resulting in multiple neurological disability symptoms ranging from mild to severe cases that end with paralysis sometimes. MS is one of the rising diseases globally that is unfortunately associated with reduced quality of life and adding national economic burdens. The definite MS mechanism is not clearly defined; however, all the previous researches confirm the role of the immune system as the master contributor in the pathogenesis. Innate and adaptive immune cells are activated peripherally then attracted toward the central nervous system (CNS) due to the breakdown of the blood-brain barrier. Recently, the gut-brain axis was shown to depend on gut metabolites that are produced by different microorganisms in the colon. The difference in microbiota composition between individuals is responsible for diversity in secreted metabolites that affect immune responses locally in the gut or systemically when reach blood circulation to the brain. It may enhance or suppress immune responses in the central nervous system (CNS) (repeated short forms); consequently, it may exacerbate or ameliorate MS symptoms. Recent data showed that some metabolites can be used as adjuvant therapy in MS and other inflammatory diseases. This review sheds light on the nature of MS and the possible interaction between gut microbiota and immune system regulation through the gut-brain axis, hence contributing to MS pathogenesis.

Drivers and shapers of macrophages specification in the developing brain

The brain harbors two major macrophage populations: microglia reside within the brain parenchyma, while border-associated macrophages (BAMs) are situated at central nervous system (CNS) interfaces. BAMs can be further classified into distinct subsets based on their localization: perivascular macrophages surround blood vessels, meningeal macrophages reside in the leptomeninges, dura macrophages in the dura mater, and choroid plexus macrophages are confined to the choroid plexus. The environmental factors and molecular mechanisms driving the specification of these macrophage populations are still being elucidated. Deciphering the communication pathways between CNS macrophages and their tissue niches during development, homeostasis, and pathologic conditions offers significant potential for treating a wide range of brain disorders, from neurodevelopmental and neuroinflammatory diseases to neurovascular and neurodegenerative conditions. With this short review, we will address the current understanding and knowledge gaps in the field, as well as the future directions for the upcoming years.

Microbiota-induced inflammation mediates the impacts of a Western diet on hippocampal-dependent memory

Obesity is associated with impaired hippocampal-dependent memory, but the mechanisms driving this pathology are not fully understood. Western diets (WD) contribute to obesity, and previous reviews have described a role for WD in impaired hippocampal-dependent memory. However, there is need for a more detailed description of the pathways by which WD may impair memory. The short vs long-term effect of specific dietary components on brain structure and functions as well as the precise mechanism and molecular pathways involved are still not fully understood. This review focuses on the mechanisms and effects of gut microbiota-driven neuroinflammation. WD leads to changes and imbalance in bacterial taxa abundances that are deleterious to the host health (gut dysbiosis) and studies in rodent models show these changes are sufficient to impair hippocampal-dependent memory. Here, we discuss a variety of proposed mechanisms linking microbiota composition to hippocampal function, with a focus on neuroinflammation. Gut microbiota impacts gastrointestinal barrier function, leading to increased circulating proinflammatory bacterial products, increased blood-brain barrier permeability, and neuroinflammation.

Epimedii Folium and Curculiginis Rhizoma ameliorate age-related cognitive decline and neuroinflammation through modulation of the NLRP3 inflammasome

ETHNOPHARMACOLOGICAL RELEVANCE

Age-related cognitive decline and neuroinflammation are significant contributors to neurodegenerative diseases. In Traditional Chinese Medicine, aging is often associated with "kidney deficiency," a concept linked to impaired bone marrow production and brain function. Epimedii Folium and Curculiginis Rhizoma (XY), a classic herbal pair used to tonify the kidney, are traditionally employed to enhance vitality, bone health, and cognitive function. While previous studies suggest XY's efficacy in pathological models, its impact on natural aging process requires further investigation.

AIM OF THE STUDY

This study aimed to investigate the neuroprotective effects of XY against cognitive impairment and neuroinflammation in naturally aged mice and to explore the underlying mechanisms.

MATERIALS AND METHODS

Network pharmacology was used to identify potential targets and pathways, while molecular docking assessed the binding interactions between active compounds from XY and key target proteins. Naturally aged mice were orally treated with XY (2.34, 4.68 g/kg/day) for 26 days. Cognitive function was assessed using behavioral tests. Histological analysis, ELISA, real-time PCR, and Western blotting were employed to evaluate hippocampal neuronal damage, inflammatory markers, senescence-related proteins, and NLRP3 inflammasome components.

RESULTS

Network pharmacology identified key targets and pathways associated with aging and neuroinflammation. Molecular docking confirmed strong binding affinities between active components (e.g., Icariin, Epimedin B, Epimedin C) and relevant protein targets. In vivo, XY treatment significantly improved cognitive performance, ameliorated hippocampal neuronal damage, and suppressed microglial activation in aged mice. Furthermore, XY downregulated the expression of senescence markers (p53, p21, p16, CDK6), pro-inflammatory cytokines (IL-1β, TNF-α, IL-6, IFN-γ), factors associated with the senescence-associated secretory phenotype (SASP), and key components indicative of NLRP3 inflammasome activation (ASC, Caspase-1, IL-1β).

CONCLUSIONS

XY alleviates age-related cognitive decline and neuroinflammation in naturally aged mice. These beneficial effects are mediated, at least in part, by reducing inflammatory mediators, modulating microglial activation, attenuating cellular senescence pathways, and suppressing NLRP3 inflammasome activity. These findings highlight the therapeutic potential of XY for managing age-related cognitive impairment and associated neuroinflammation.

RiboTag-based RNA profiling uncovers oligodendroglial lineage-specific inflammation in autoimmune encephalomyelitis: implications for pathogenesis

Oligodendroglial lineage cells (OLCs) are essential for myelination, remyelination and neuronal metabolic support, but recent evidence suggests they also play active roles in neuroinflammation. This study aimed to identify the inflammatory translatome of OLCs during the onset of experimental autoimmune encephalomyelitis (EAE), a widely used model for Multiple Sclerosis (MS), using RiboTag-based RNA sequencing. We crossed RiboTag mice with Olig2-Cre mice to obtain strain-specific expression of HA-tagged ribosomal protein Rpl22 in OLCs, enabling the isolation of ribosome-associated mRNA from these cells for sequencing by using HA beads. Compared to controls, 1,556 genes were upregulated and 683 were downregulated in EAE OLCs. Gene enrichment revealed elevated immune-related pathways, including cytokine signaling, interferon responses and antigen presentation, whereas downregulated genes were associated with myelination and neuronal development. Notably, significant expression of cytokines/chemokines and their receptors was detected in OLCs. Further investigations focused on the role of IFNGR and IFNAR in EAE pathogenesis. IFN-γ signaling in OLCs exacerbated EAE pathogenesis by enhancing antigen processing, presentation, and chemokine production (e.g., Ccl2, Ccl7). In contrast, IFN-β signaling appeared less critical. These findings highlight the inflammatory role of OLCs in EAE, suggesting OLCs as a potential therapeutic target for mitigating neuroinflammation in MS and related disorders.

Microglia transcriptional states and their functional significance: Context drives diversity

In the brain, microglia are continuously exposed to a dynamic microenvironment throughout life, requiring them to adapt accordingly to specific developmental or disease-related demands. The advent of single-cell sequencing technologies has revealed the diversity of microglial transcriptional states. In this review, we explore the various contexts that drive transcriptional diversity in microglia and assess the extent to which non-homeostatic conditions induce context-specific signatures. We discuss our current understanding and knowledge gaps regarding the relationship between transcriptional states and microglial function, review the influence of complex microenvironments and prior experiences on microglial state induction, and highlight strategies to bridge the gap between mouse and human studies to advance microglia-targeting therapeutics.

Microglial and TREM2 dialogues in the developing brain

From the migration of precursor cells to the refinement of neural circuits, the immune system plays a critical role in the development of the central nervous system. As the brain resident macrophages, microglia are integral to these processes, influencing key developmental stages and contributing to circuit remodeling. Recent years have brought a wealth of new insights into how microglia regulate key stages of brain development, particularly through their continuous crosstalk with various brain cell types. In this review, we synthesize this growing body of literature on microglia and neurodevelopment, highlighting the involvement of the TREM2 receptor, known for its role in aging and neurodegeneration, which profoundly affects the state of microglia and guides target cells by shaping their transcriptional and functional fate. We examine microglial communication with four major cell types-neural precursors, neurons, astrocytes, and oligodendrocytes-also delving into the described mechanisms that underpin these interactions.

Gut-immune-brain interactions during neurodevelopment: from a brain-centric to a multisystem perspective

BACKGROUND

Neurodevelopmental disorders (NDDs) and epileptic syndromes are complex neurological conditions linked by shared abnormal neurobiological processes. Existing therapies mostly target symptoms, rather than addressing the underlying causes of the disease, leaving a burden of unmet clinical needs.

MAIN BODY

Emerging evidence suggests a significant role for the gut microbiota and associated immune responses in influencing brain development and function, changing the paradigm of a brain-centric origin of NDDs. This review discusses the pivotal interactions within the gut-immune-brain axis, highlighting how microbial dysbiosis and immune signaling contribute to neurological pathologies. We also explore the potential of microbial management and immunomodulation as novel therapeutic avenues, emphasizing the need for a shift towards addressing the root causes of these disorders rather than just their symptoms.

CONCLUSIONS

This integrated perspective offers new insights into the biological underpinnings of NDDs and epilepsy, proposing innovative biomarkers and therapeutic strategies.

Morphological diversity of microglia: Implications for learning, environmental adaptation, ageing, sex differences and neuropathology

Microglia are the brain resident macrophages that respond rapidly to any insult. These non-neuroectodermal cells are decorated with plenty of receptors allowing them to recognise and respond precisely to a multitude of stimuli. To do so, microglia undergo structural and functional changes aiming to actively keep the brain's homeostasis. However, some microglial responses, when sustained or exacerbated, can contribute to neuropathology and neurodegeneration. Many microglial molecular and cellular changes were identified that display a strong correlation with neuronal damage and neuroinflammation/disease status, as well as present key sex-related differences that modulate microglial outcomes. Nevertheless, the relationship between microglial structural and functional features is just beginning to be unravelled. Several reports show that microglia undergo soma and branch remodelling in response to environmental stimuli, ageing, neurodegenerative diseases, trauma, and systemic inflammation, suggesting a complex form and function link. Also, it is reasonable overall to suppose that microglia diminishing their process length and ramification also reduce their monitoring activity of synapses, which is critical for detecting any synaptic disturbance and performing synaptic remodelling. Elucidating the complex interactions between microglial morphological plasticity and its functional implications appears essential for the understanding of complex cognitive and behavioural processes in health and neuropathological conditions.

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

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

Type I interferon signalling and interferon-responsive microglia in health and disease

Recent evidence suggests that type I interferon (IFN-I) signalling extends beyond its canonical roles in antiviral defence and immunomodulation. Over the past decade, dysregulated IFN-I signalling has been linked to genetic disorders and neurodegenerative diseases, where it may contribute to neurological impairments. Microglia have emerged as key mediators of IFN-I responses in the central nervous system. A distinct transcriptional state responsive to interferons has recently been identified in microglia. The activation of the IFN-I pathway in these cells is now recognised as pivotal in both development and neurodegeneration. This review is divided into two main sections: the first examines the broader role of IFN-I signalling in the central nervous system, particularly its contribution to neurological dysfunction; the second focuses on the specific state of interferon-responsive microglia, exploring its mechanisms and relevance in neurodegenerative conditions. Finally, we discuss how these areas intersect and their implications for both healthy and diseased states.

IUPHAR Review: Microbiota-Gut-Brain Axis and its role in Neuropsychiatric Disorders

The human gut microbiome, composed of a vast array of microorganisms that have co-evolved with humans, is crucial for the development and function of brain systems. Research has consistently shown bidirectional communication between the gut and the brain through neuronal, endocrine, and immunological, and chemical pathways. Recent neuroscience studies have linked changes in the microbiome and microbial metabolites to various neuropsychiatric disorders such as autism, depression, anxiety, schizophrenia, eating disorders, and neurocognitive disorders. Novel metagenome-wide association studies have confirmed these microbiome variations in large samples and expanded our understanding of the interactions between human genes and the gut microbiome. The causal relationship between gut microbiota and neuropsychiatric disorders is being elucidated through the establishment of large cohort studies incorporating microbiome data and advanced statistical techniques. Ongoing animal and human studies focused on the microbiota-gut-brain axis are promising for developing new prevention and treatment strategies for neuropsychiatric conditions. The scope of these studies has broadened from microbiome-modulating therapies including prebiotics, probiotics, synbiotics and postbiotics to more extensive approaches such as fecal microbiota transplantation. Recent systematic reviews and meta-analyses have strengthened the evidence base for these innovative treatments. Despite extensive research over the past decade, many intriguing aspects still need to be elucidated regarding the role and therapeutic interventions of the microbiota-gut-brain axis in neuropsychiatric disorders.

Age-dependent glial heterogeneity and traumatic injury responses in a vertebrate brain structure

The progression of traumatic brain injury (TBI) pathology is significantly influenced by age and involves a complex interplay of glial cells. However, the influence of age on the glial dynamics and their TBI responses remains mostly unexplored. Here, we obtain a comprehensive single-cell transcriptome atlas of three major glial types under the physiological and TBI conditions across four post-embryonic life stages in the zebrafish midbrain optic tectum. We identify a library of glial subtypes and states with specific age-dependent patterns that respond distinctly to TBI. Combining the glial interactome analysis and CRISPR-Cas9-mediated gene disruption, we reveal the essential roles of dla-notch3 and cxcl12a-cxcr4b interactions in the early-larval-stage-specific unresponsiveness of radial astrocytes to TBI and the TBI-induced age-independent recruitment of microglia to injury sites, respectively. Overall, our findings provide the molecular and cellular framework of TBI-induced age-related glial dynamics in vertebrate brains.

Endothelial-driven TGFβ signaling supports lung interstitial macrophage development from monocytes

Lung interstitial macrophages (IMs) are monocyte-derived parenchymal macrophages whose tissue-supportive functions remain unclear. Despite progress in understanding lung IM diversity and transcriptional regulation, the signals driving their development from monocytes and their functional specification remain unknown. Here, we found that lung endothelial cell-derived Tgfβ1 triggered a core Tgfβ receptor-dependent IM signature in mouse bone marrow-derived monocytes. Myeloid-specific impairment of Tgfβ receptor signaling severely disrupted monocyte-to-IM development, leading to the accumulation of perivascular immature monocytes, reduced IM numbers, and a loss of IM-intrinsic identity, a phenomenon similarly observed in the absence of endothelial-specific Tgfβ1. Mice lacking the Tgfβ receptor in monocytes and IMs exhibited altered monocyte and IM niche occupancy and hallmarks of aging including impaired immunoregulation, hyperinflation, and fibrosis. Our work identifies a Tgfβ signaling-dependent endothelial-IM axis that shapes IM development and sustains lung integrity, providing foundations for IM-targeted interventions in aging and chronic inflammation.

Peripheral nervous system microglia-like cells regulate neuronal soma size throughout evolution

Microglia, essential in the central nervous system (CNS), were historically considered absent from the peripheral nervous system (PNS). Here, we show a PNS-resident macrophage population that shares transcriptomic and epigenetic profiles as well as an ontogenetic trajectory with CNS microglia. This population (termed PNS microglia-like cells) enwraps the neuronal soma inside the satellite glial cell envelope, preferentially associates with larger neurons during PNS development, and is required for neuronal functions by regulating soma enlargement and axon growth. A phylogenetic survey of 24 vertebrates revealed an early origin of PNS microglia-like cells, whose presence is correlated with neuronal soma size (and body size) rather than evolutionary distance. Consistent with their requirement for soma enlargement, PNS microglia-like cells are maintained in vertebrates with large peripheral neuronal soma but absent when neurons evolve to have smaller soma. Our study thus reveals a PNS counterpart of CNS microglia that regulates neuronal soma size during both evolution and ontogeny.

The Complementary Role of Morphology in Understanding Microglial Functional Heterogeneity

A search of the PubMed database for publications on microglia reveals an intriguing shift in scientific interest over time. Dividing microglia into categories such as "resting" and "activated" or M1 versus M2 is nowadays obsolete, with the current research focusing on unraveling microglial heterogeneity. The onset of transcriptomics, especially single-cell RNA sequencing (scRNA-seq), has profoundly reshaped our understanding of microglia heterogeneity. Conversely, microglia morphology analysis can offer important insights regarding their activation state or involvement in tissue responses. This review explores microglial heterogeneity under homeostatic conditions, developmental stages, and disease states, with a focus on integrating transcriptomic data with morphological analysis. Beyond the core gene expression profile, regional differences are observed with cerebellar microglia exhibiting a uniquely immune-vigilant profile. During development, microglia express homeostatic genes before birth, yet the bushy appearance is a characteristic that appears later on. In neurodegeneration, microglia alternate between proinflammatory and neuroprotective roles, influenced by regional factors and disease onset. Understanding these structural adaptations may help identify specific microglial subpopulations for targeted therapeutic strategies.

Inactivation of microglial LXRβ in early postnatal mice impairs microglia homeostasis and causes long-lasting cognitive dysfunction

Microglia, the largest population of brain immune cells, play an essential role in regulating neuroinflammation by removing foreign materials and debris and in cognition by pruning synapses. Since liver X receptor β (LXRβ) has been identified as a regulator of microglial homeostasis, this study examined whether its removal from microglia affects neuroinflammation and cognitive function. We used a cell-specific tamoxifen-inducible Cre-loxP-mediated recombination to remove LXRβ from microglia specifically. We now report that ablation of LXRβ in microglia in early postnatal life led to a reduction in microglial numbers, distinct morphological changes indicative of microglial activation, and enhanced synapse engulfment accompanied by cognitive deficits. Removal of LXRβ from microglia in adult mice caused no cognitive defects. RNAseq analysis of microglia revealed that loss of LXRβ led to reduced expression of SAll1, a master regulator of microglial homeostasis, while increasing expression of genes associated with microglial activation and CNS disease. This study demonstrates distinctly different functions of microglial LXRβ in developing and adult mice and points to long-term consequences of defective LXRβ signaling in microglia in early life.

The roles of immune factors in neurodevelopment

The development of the nervous system is a highly complex process orchestrated by a multitude of factors, including various immune elements. These immune components play a dual role, not only regulating the immune response but also actively influencing brain development under both physiological and pathological conditions. The brain's immune barrier includes microglia in the brain parenchyma, which act as resident macrophages, astrocytes that support neuronal function and contribute to the inflammatory response, as well as circulating immune cells that reside at the brain's borders, including the choroid plexus, meninges, and perivascular spaces. Cytokines-soluble signaling molecules released by immune cells-play a crucial role in mediating communication between immune cells and the developing nervous system. Cytokines regulate processes such as neurogenesis, synaptic pruning, and inflammation, helping to shape the neural environment. Dysregulation of these immune cells, astrocytes, or cytokine signaling can lead to alterations in neurodevelopment, potentially contributing to neurodevelopmental abnormalities. This article reviews the central role of microglia, astrocytes, cytokines, and other immune factors in neurodevelopment, and explores how neuroinflammation can lead to the onset of neurodevelopmental disorders, shedding new light on their pathogenesis.

Physiological roles of embryonic microglia and their perturbation by maternal inflammation

The interplay between the nervous and immune systems is well documented in the context of adult physiology and disease. Recent advances in understanding immune cell development have highlighted a significant interaction between neural lineage cells and microglia, the resident brain macrophages, during developmental stages. Throughout development, particularly from the embryonic to postnatal stages, diverse neural lineage cells are sequentially generated, undergo fate determination, migrate dynamically to their appropriate locations while maturing, and establish connections with their surroundings to form neural circuits. Previous studies have demonstrated that microglia contribute to this highly orchestrated process, ensuring the proper organization of brain structure. These findings underscore the need to further investigate how microglia behave and function within a broader framework of neurodevelopment. Importantly, recent epidemiological studies have suggested that maternal immune activation (MIA), triggered by various factors, such as viral or bacterial infections, environmental stressors, or other external influences, can affect neurogenesis and neural circuit formation, increasing the risk of neurodevelopmental disorders (NDDs) in offspring. Notably, many studies have revealed that fetal microglia undergo significant changes in response to MIA. Given their essential roles in neurogenesis and vascular development, inappropriate activation or disruption of microglial function may impair these critical processes, potentially leading to abnormal neurodevelopment. This review highlights recent advances in rodent models and human studies that have shed light on the behaviors and multifaceted roles of microglia during brain development, with a particular focus on the embryonic stage. Furthermore, drawing on insights from rodent MIA models, this review explores how MIA disrupts microglial function and how such disturbances may impair brain development, ultimately contributing to the onset of NDDs.

Microglia heterogeneity, modeling and cell-state annotation in development and neurodegeneration

Within the CNS, microglia execute various functions associated with brain development, maintenance of homeostasis and elimination of pathogens and protein aggregates. This wide range of activities is closely associated with a plethora of cellular states, which may reciprocally influence or be influenced by their functional dynamics. Advancements in single-cell RNA sequencing have enabled a nuanced exploration of the intricate diversity of microglia, both in health and disease. Here, we review our current understanding of microglial transcriptional heterogeneity. We provide an overview of mouse and human microglial diversity encompassing aspects of development, neurodegeneration, sex and CNS regions. We offer an insight into state-of-the-art technologies and model systems that are poised to improve our understanding of microglial cell states and functions. We also provide suggestions and a tool to annotate microglial cell states on the basis of gene expression.

Expanding the neuroimmune research toolkit with in vivo brain organoid technologies

Human pluripotent stem cell-derived microglia-like cells (MLCs) and brain organoid systems have revolutionized the study of neuroimmune interactions, providing new opportunities to model human-specific brain development and disease. Over the past decade, advances in protocol design have improved the fidelity, reproducibility and scalability of MLC and brain organoid generation. Co-culturing of MLCs and brain organoids have enabled direct investigations of human microglial interactions in vitro, although opportunities remain to improve microglial maturation and long-term survival. To address these limitations, innovative xenotransplantation approaches have introduced MLCs, organoids or neuroimmune organoids into the rodent brain, providing a vascularized environment that supports prolonged development and potential behavioral readouts. These expanding in vitro and in vivo toolkits offer complementary strategies to study neuroimmune interactions in health and disease. In this Perspective, we discuss the strengths, limitations and synergies of these models, highlighting important considerations for their future applications.

Single-Cell Analysis in Cerebrovascular Research: Primed for Breakthroughs and Clinical Impact

Data generated using single-cell RNA-sequencing has the potential to transform understanding of the cerebral circulation and advance clinical care. However, the high volume of data, sometimes generated and presented without proper pathophysiological context, can be difficult to interpret and integrate into current understanding of the cerebral circulation and its disorders. Furthermore, heterogeneity in the representation of brain regions and vascular segments makes it difficult to compare results across studies. There are currently no standards for tissue collection and processing that allow easy comparisons across studies and analytical platforms. There are no standards either for single-cell data analysis and presentation. This topical review introduces single-cell RNA-sequencing to physicians and scientists in the cerebrovascular field, with the goals of highlighting opportunities and challenges of applying this technology in the cerebrovascular field and discussing key concepts and knowledge gaps that can be addressed by single-cell RNA-sequencing.

Central Nervous System Macrophages in Health and Disease

The central nervous system (CNS) has a unique set of macrophages that seed the tissue early during embryonic development. Microglia reside in the parenchyma, and border-associated macrophages are present in border regions, including the meninges, perivascular spaces, and choroid plexus. CNS-resident macrophages support brain homeostasis during development and steady state. In the diseased brain, however, the immune landscape is altered, with phenotypic and transcriptional changes in resident macrophages and the invasion of blood-borne monocytes, which differentiate into monocyte-derived macrophages upon entering the CNS. In this review, we focus on the fate and function of the macrophage compartment in health, neurodegenerative conditions such as amyloidosis, and neuroinflammation as observed in multiple sclerosis and infection. We discuss our current understanding that monocyte-derived macrophages contribute to neuropathology whereas native macrophages play a neuroprotective role in disease.

A specific GPR56/ADGRG1 splicing isoform is associated with antidepressant response in major depressive disorder

Major Depressive Episode (MDE) is one of the most common psychiatric disorders. Often difficult to treat, this disease is one of the leading causes of suicide. A recent study showed an association between GPR56/ADGRG1 mRNA, MDE and response to antidepressant treatment in blood and in brain. Among GPR56 splicing variant, the S4 isoform has recently been associated with microglial synaptic pruning, while microglia are already known as a central player in MDE. Therefore, we hypothesized that S4 is the specific isoform associated to MDE and antidepressant response. To test our hypothesis, an in silico analysis was first performed to identify the different proteins and transcript isoforms of GPR56. This analysis allowed to design PCR and qPCR primers. GPR56 total, S4 and S3 were assessed by RT-qPCR in leukocytes from a cohort of 46 MDE patients including non-responders (NR, n = 31) and responders-remitters (R, n = 17) to antidepressant treatment. We replicated the result of one of our previous studies, which described an increase in total GPR56 mRNA in Rs. Additionally, we observed that this variation differs among mRNA splicing variants, with S4 exhibiting a similar pattern of variation while S3 shows no significant change. The differences observed withstood statistical correction for covariates of interest such as smoking, gender and suicidal ideation, demonstrating the robustness of the model. These findings confirm our hypothesis that certain mRNA splicing variants of GPR56 may play a more significant role in depression. This study highlighted a link between the GPR56-S4 and response to antidepressant treatment.

Life cycle exposure to differentially charged polystyrene nanoplastics leads to gender-specific particle accumulation and neurotoxicity in zebrafish (Danio rerio)

Nanoplastics (NPs) have been widely detected in freshwater environments and photodegradation, as well as physical and chemical breakdown, lead to different surface charges on the plastics. Although evidence in the literature highlights the importance of NPs surface charge to neurotoxicity, substantial gaps in mechanistic understanding remain. In the current study, zebrafish (Danio rerio) were exposed to differentially charged NPs (PS, PS-NH2, PS-COOH) at environmentally relevant concentration (10 μg/L). After full life cycle exposure, the potential neurotoxicity, brain damage, and the altered brain metabolism was investigated through light sheet microscopy 3-dimensional imaging, histopathology, Evans blue dye (EBD) extravasation, gene expression, and untargeted and targeted metabolomics of brain tissue in zebrafish. Exposure to PS, PS-NH2, PS-COOH caused adverse effects on the performance of neurobehaviors, blood-brain-barrier (BBB) permeability, amino acid metabolism, damage to the BBB and mitochondria, and overt inflammatory response. PS-NH2 (4.56-fold) and PS-COOH (3.59-fold) accumulated in the reticular formation (RF) of the male brain, while only PS-NH2 was detected in the RF (6.57-fold) and ventral hypothalamus (Hv) (3.08-fold) of female brains. Several important biological pathways were negatively impacted in a charge- and gender-specific fashion. This study provides novel insights into the underlying toxicity mechanisms of differentially charged NPs in a model aquatic species, as well as the associated environmental risks of this important group of emerging contaminants.

Acute TREM2 inhibition depletes MAFB-high microglia and hinders remyelination

We investigated the role of Triggering Receptor Expressed on Myeloid cells 2 (TREM2) in myelin regeneration in the brain. TREM2 is a receptor that activates microglia, which are crucial for clearing myelin debris and promoting remyelination. Previous studies in a mouse model of demyelination induced by the copper-chelating agent Cuprizone (CPZ) have shown that stimulation of TREM2 with a monoclonal antibody reduces demyelination, while deleting the Trem2 gene in mice impairs remyelination. Here, we blocked TREM2 function acutely with an antibody during both the demyelination and remyelination phases of the CPZ model and analyzed the impact of the antibody treatment on myelination and gene expression in single cells. We found that blocking TREM2 depleted a distinct population of microglia with high expression of the transcription factor MAFB during remyelination. The loss of these MAFB-high microglia was linked to impaired generation of myelinating oligodendrocytes. Importantly, we identified MAFB+ microglia in acute and acute-chronic brain lesions from individuals with multiple sclerosis (MS), but not in inactive lesions. We conclude that TREM2 is essential for maintaining a population of MAFB-high microglia that is associated with myelin repair. This finding has significant implications for understanding demyelinating diseases like MS and suggests that stimulating TREM2 could be a promising therapeutic approach for myelin repair.

The Meninges as CNS Interfaces and the Roles of Meningeal Macrophages

The brain, the most important component of the central nervous system (CNS), is protected by multiple intricate barriers that strictly regulate the entry of proteins and cells. Thus, the brain is often described as an organ with immune privilege. Within the brain parenchyma, microglia are thought to be the primary resident immune cells, with no other immune-related cells present under normal conditions. On the other hand, recent studies in the meningeal border regions have revealed the presence of meningeal-specific lymphatic vessels and channels that connect to the skull bone marrow. Importantly, resident macrophage populations specific to these boundary regions, known as CNS-associated macrophages (CAMs) or border-associated macrophages (BAMs), have been identified. In contrast to the brain parenchyma, the meninges contain many immune-related structures and cells, making them an important immune interface at the CNS border. CAMs serve a dual function, triggering immune responses under pathological conditions and supporting the maintenance of brain homeostasis. This review focuses on the immune architecture of the meninges and the roles of CAMs in humans and mice, summarizing and discussing recent advances in this field.

Mast cells proliferate in the peri-hippocampal space during early development and modulate local and peripheral immune cells

Brain development is a non-linear process of regionally specific epochs occurring during windows of sensitivity to endogenous and exogenous stimuli. We have identified an epoch in the neonatal rat brain defined by a transient population of peri-hippocampal mast cells (phMCs) that are abundant from birth through 2-weeks post-natal but absent thereafter. The phMCs are maintained by proliferation and harbor a unique transcriptome compared with mast cells residing in the skin, bone marrow, or other brain regions. Pharmacological activation of this population broadly increases blood-brain barrier permeability, recruits peripheral immune cells, and stunts local microglia proliferation. Examination of the post-mortem human brain demonstrated mast cells in the peri-hippocampal region of a newborn, but not an older infant, suggesting a similar developmental period exists in humans. Mast cells specifically, and early-life inflammation generally, have been linked to heightened risk for neurodevelopmental disorders, and these results demonstrate a plausible source of that risk.

Radial glia integrin avb8 regulates cell autonomous microglial TGFβ1 signaling that is necessary for microglial identity

Microglial diversity arises from the interplay between inherent genetic programs and external environmental signals. However, the mechanisms by which these processes develop and interact within the growing brain are not yet fully understood. Here, we show that radial glia-expressed integrin beta 8 (ITGB8) activates microglia-expressed TGFβ1 to drive microglial development. Domain-restricted deletion of Itgb8 in these progenitors results in regionally restricted and developmentally arrested microglia that persist into adulthood. In the absence of autocrine TGFβ1 signaling, microglia adopt a similar phenotype, leading to neuromotor symptoms almost identical to Itgb8 mutant mice. In contrast, microglia lacking the canonical TGFβ signal transducers Smad2 and Smad3 have a less polarized dysmature phenotype and correspondingly less severe neuromotor dysfunction. Our study describes the spatio-temporal regulation of TGFβ activation and signaling in the brain necessary to promote microglial development, and provides evidence for the adoption of microglial developmental signaling pathways in brain injury or disease.

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.

Maternal Obesity and Neurodevelopment of the Offspring

BACKGROUND

An increasing amount of evidence, derived from both human epidemiological studies and animal research, suggests that exposure to maternal obesity in utero is linked to adverse neurodevelopmental outcomes in the offspring. These can include attention deficit hyperactivity disorder, autism spectrum disorders, intellectual disability, and cerebral palsy.

METHODS

A thorough search in Medline/PubMed and Google Scholar databases was performed by two independent reviewers in order to investigate the link between the exposure to maternal obesity and neurodevelopmental outcomes in the offspring. A list of keywords, including maternal obesity, maternal overweight, maternal diet, neurodevelopment, and neuropsychiatric disorders, was used in the search algorithm.

RESULTS

The existing evidence regarding the potential mechanisms through which maternal obesity may impact offspring neurodevelopment and programming, such as inflammation, hormone dysregulation, alterations to the microbiome, and epigenetics, as well as evidence from animal studies, was summarized in this narrative review.

CONCLUSIONS

Maternal obesity seems to be overall associated with various neuropsychiatric and neurodevelopmental disorders. However, more robust data from future studies are needed to establish this association, which will take into account the role of potential confounders such as genetic factors and gene-environment interactions.

Monocyte-derived macrophages act as reinforcements when microglia fall short in Alzheimer's disease

The central nervous system (CNS) is endowed with its own resident innate immune cells, the microglia. They constitute approximately 10% of the total cells within the CNS parenchyma and act as 'sentinels', sensing and mitigating any deviation from homeostasis. Nevertheless, under severe acute or chronic neurological injury or disease, microglia are unable to contain the damage, and the reparative activity of monocyte-derived macrophages (MDMs) is required. The failure of the microglia under such conditions could be an outcome of their prolonged exposure to hostile stimuli, leading to their exhaustion or senescence. Here, we describe the conditions under which the microglia fall short, focusing mainly on the context of Alzheimer's disease, and shed light on the functions performed by MDMs. We discuss whether and how MDMs engage in cross-talk with the microglia, why their recruitment is often inadequate, and potential ways to augment their homing to the brain in a well-controlled manner.

Multiple Sclerosis: Glial Cell Diversity in Time and Space

Multiple sclerosis (MS) is the most prevalent human inflammatory disease of the central nervous system with demyelination and glial scar formation as pathological hallmarks. Glial cells are key drivers of lesion progression in MS with roles in both tissue damage and repair depending on the surrounding microenvironment and the functional state of the individual glial subtype. In this review, we describe recent developments in the context of glial cell diversity in MS summarizing key findings with respect to pathological and maladaptive functions related to disease-associated glial subtypes. A particular focus is on the spatial and temporal dynamics of glial cells including subtypes of microglia, oligodendrocytes, and astrocytes. We contextualize recent high-dimensional findings suggesting that glial cells dynamically change with respect to epigenomic, transcriptomic, and metabolic features across the inflamed rim and during the progression of MS lesions. In summary, detailed knowledge of spatially restricted glial subtype functions is critical for a better understanding of MS pathology and its pathogenesis as well as the development of novel MS therapies targeting specific glial cell types.

Exploiting the gut microbiome for brain tumour treatment

Increasing evidence suggests that the gut microbiome plays a key role in a host of pathological conditions, including cancer. Indeed, the bidirectional communication that occurs between the gut and the brain, known as the 'gut-brain axis,' has recently been implicated in brain tumour pathology. Here, we focus on current research that supports a gut microbiome-brain tumour link with emphasis on high-grade gliomas, the most aggressive of all brain tumours, and the impact on the glioma tumour microenvironment. We discuss the potential use of gut-brain axis signals to improve responses to current and future therapeutic approaches. We highlight that the success of novel treatment strategies may rely on patient-specific microbiome profiles, and these should be considered for personalised treatment approaches.

Prenatal Maternal Immune Activation with Lipopolysaccharide Accelerates the Developmental Acquisition of Neonatal Reflexes in Rat Offspring Without Affecting Maternal Care Behaviors

Maternal immune activation (MIA)-infection with an immunogen during pregnancy-is linked to an increased risk of neurodevelopmental disorders (NDDs) in offspring. Both MIA and NDDs are associated with developmental delays in offsprings' motor behavior. Therefore, the current study examined the effects of MIA on neonatal reflex development in male and female offspring. Sprague Dawley rats were administered lipopolysaccharide (LPS; 50 μg/mL/kg, i.p.) or saline on embryonic day (E)15 of gestation. The offspring were then tested daily from postnatal day (P)3-P21 to determine their neonatal reflex abilities. The maternal care behaviors of the dam were also quantified on P1-P5, P10, and P15. We found that, regardless of sex, the E15 LPS offspring were able to forelimb grasp, cliff avoid, and right with a correct posture at an earlier postnatal age than the E15 saline offspring did. The E15 LPS offspring also showed better performance of forelimb grasping, hindlimb grasping, righting with correct posture, and walking with correct posture than the E15 saline offspring did. There were no significant differences in maternal licking/grooming, arched-back nursing, non-arched-back nursing, or total nursing across the E15 groups. Overall, these findings suggest that MIA with LPS on E15 accelerates reflex development in offspring without affecting maternal care. This may be explained by the stress acceleration hypothesis, whereby early-life stress accelerates development to promote survival.

Indigenous gut microbes modulate neural cell state and neurodegenerative disease susceptibility

The native microbiome influences a plethora of host processes, including neurological function. However, its impacts on diverse brain cell types remains poorly understood. Here, we performed single nucleus RNA sequencing on hippocampi from wildtype, germ-free mice and reveal the microbiome-dependent transcriptional landscape across all major neural cell types. We found conserved impacts on key adaptive immune and neurodegenerative transcriptional pathways, underscoring the microbiome's contributions to disease-relevant processes. Mono-colonization with select indigenous microbes identified species-specific effects on the transcriptional state of brain myeloid cells. Colonization by Escherichia coli induced a distinct adaptive immune and neurogenerative disease-associated cell state, suggesting increased disease susceptibility. Indeed, E. coli exposure in the 5xFAD mouse model resulted in exacerbated cognitive decline and amyloid pathology, demonstrating its sufficiency to worsen Alzheimer's disease-relevant outcomes. Together, these results emphasize the broad, species-specific, microbiome-dependent consequences on neurological transcriptional state and highlight the capacity of specific microbes to modulate disease susceptibility.

Highlights

The microbiome impacts the transcriptional landscape of all major brain cell types.Discrete microbes specifically modulate resident myeloid cell status. Gut E. coli triggers dynamic transcriptional responses across neural cell types. Exposure to E. coli exacerbates behavioral and cellular pathologies in 5xFAD mice.

Activity-dependent regulation of microglia numbers by pyramidal cells during development shape cortical functions

Beyond their role as immune sentinels, microglia are actively involved in establishing and maintaining cortical circuits. Alteration in microglial numbers has been associated with abnormal behaviors akin to those observed in neurodevelopmental disorders. Consequently, establishing the appropriate microglial numbers during development is crucial for ensuring normal cortical function. Here, we uncovered a dynamic relationship between pyramidal cells and microglia that tunes microglial numbers and development through distinct phases of mouse postnatal development. Changes in pyramidal cell activity during development induce differential release of activity-dependent proteins such as Activin A, which, in turn, adjusts microglial numbers accordingly. Decoupling of this relationship not only changes microglial numbers but has a long-term consequence on their role as synaptic organizers, which ultimately affects cortical function. Our findings reveal that microglia adapt their numbers to changes in pyramidal cell activity during a critical time window in development, consequently adjusting their numbers and function to the demands of the developing local circuits.

Hormonal contraceptives in adolescence impact the neuroimmune environment of the medial prefrontal cortex and hippocampus in female rats

Adolescence is a period of protracted neurodevelopment, during which the prefrontal cortex (PFC) undergoes significant remodeling. Microglia are integral to neurodevelopment and are sensitive to gonadal hormones, which increase during adolescence. Microglia and gonadal hormones can interact to influence adolescent development of the PFC (or medial prefrontal cortex [mPFC] in rodents). In females, gonadal hormones can be perturbed by using hormonal contraceptives (HCs). We predicted that HC administration over adolescence could affect microglia, other immunocompetent cells, and the neuroimmune environment of the developing mPFC. We also assessed HC effects on neuroimmune measures in the hippocampus, as the hippocampus also matures throughout adolescence and is sensitive to ovarian hormones. Intact post-pubertal female Sprague-Dawley rats received daily subcutaneous injections of vehicle or 10 ug ethinyl estradiol + 20 ug levonorgestrel (HCs) throughout adolescence from postnatal day (PND) 35-56. On PND 57 or 58, brains were collected for immunohistochemistry and qPCR. In the mPFC, HC-treated rats showed less Iba1 (microglia) immunolabeling and fewer Iba1+ cells. HC treatment also altered microglia morphology and reduced the spacing between microglia in the mPFC. In the hippocampus, HC-treated rats had reduced Iba1 immunolabeling in the dorsal CA1 and reductions in microglial cell complexity in dorsal CA1, ventral CA1, and ventral CA3. There were no effects of HCs on GFAP (astrocyte) immunolabeling in the mPFC or on astrocytes in any hippocampal subregion analyzed, except an increase in astrocyte number in the dorsal dentate gyrus. mPFC expression of genes related to phagocytosis (Cd68, Trem2) and neuroimmune signaling (Cx3cr1, Cx3cl1) were reduced in rats treated with HCs, but no gene expression changes were seen in the hippocampus. These data provide the first evidence that HCs given during the critical developmental period of adolescence can affect microglia properties in limbic brain regions.

Timing matters: modeling the effects of gestational cannabis exposure on social behavior and microglia in the developing amygdala

Cannabis is the most frequently used illicit drug during pregnancy, with use steadily increasing in the United States as legalization and decriminalization expand to more states. Many pregnant individuals use cannabis to reduce adverse symptoms of pregnancy, considering it to be less harmful than other pharmaceuticals or alcohol. The primary psychoactive component of cannabis, delta-9-tetrahydrocannabinol (THC), acts on the endocannabinoid (eCB) system, yet whether it perturbs neural development of the fetus is poorly understood. Previously we have shown that androgen mediated eCB tone in the developing amygdala promotes microglial phagocytosis of newborn astrocytes which has enduring consequences on the neural circuits regulating sex differences in social behavior. Microglia are the resident immune cells of the brain and express both receptors of the eCB system, CB1R and CB2R, making them likely targets of modulation by THC. It is also plausible that exposure to THC at differing gestational timepoints can result in distinct outcomes, as is the case with alcohol exposure. To model human cannabis use during either late or early pregnancy, we exposed rodents to THC either directly during the early postnatal period via intraperitoneal (IP) injection or in utero during the prenatal period via dam IP injection respectively. Here we show that postnatal THC exposure results in sex specific changes in microglial phagocytosis during development as well as social behavior during the juvenile period. Interestingly prenatal exposure to THC resulted in inverse changes to phagocytosis and social behavior. These findings highlight the differential effects of THC exposure across gestation.

Photobiomodulation of gut microbiota with low-level laser therapy: a light for treating neuroinflammation

The gut microbiota is known to interact with various organs in the body, including the central nervous system, through the gut-brain axis. Intestinal dysbiosis can lead to increased peripheral inflammation and, consequently, affect the brain, resulting in neuroinflammation. Photobiomodulation (PBM) has demonstrated positive regulatory effects on the imbalance of certain body functions, including pain, inflammation, immunity, wound healing, and gut microbiota dysbiosis. Therefore, PBM at the intestinal level could help improve intestinal dysbiosis and reestablish cerebral homeostasis. In this context, this study aimed to conduct a narrative review of the literature on the effects of PBM at the intestinal level on intestinal dysbiosis and neuroinflammation. Overall, the findings highlight that PBM modulates the gut microbiota, suggesting it could serve as a therapy for neurological conditions affecting the gut-brain axis. Future research should focus on further elucidating the molecular mechanisms underlying this therapy.

The microglial response to inhibition of Colony-stimulating-factor-1 receptor by PLX3397 differs by sex in adult mice

Microglia, the resident macrophages of the brain, are derived from the yolk sac and colonize the brain before the blood-brain barrier forms. Once established, they expand locally and require Colony-stimulating-factor-1 receptor (CSF1R) signaling for their development and maintenance. CSF1R inhibitors have been used extensively to deplete microglia in the healthy and diseased brain. In this study, we demonstrated sex-dependent differences in the microglial response to the CSF1R inhibitor PLX3397. Male mice exhibited greater microglial depletion compared to females. Transcriptomic and flow cytometry analysis revealed sex-specific differences in the remaining microglia population, with female microglia upregulating autophagy and proteostasis pathways while male microglia increased mitobiogenesis. Furthermore, manipulating key microglial receptors by using different transgenic mouse lines resulted in changes in depletion efficacies that were also sex dependent. These findings suggest sex-dependent microglial survival mechanisms, which might contribute to the well-documented sex differences in various neurological disorders.

Intestinal Bacteroides drives glioma progression by regulating CD8+ T cell tumor infiltration

BACKGROUND

The intestinal microbiota regulates normal brain physiology and the pathogenesis of several neurological disorders. While prior studies suggested that this regulation operates through immune cells, the underlying mechanisms remain unclear. Leveraging two well characterized murine models of low-grade glioma (LGG) occurring in the setting of the neurofibromatosis type 1 (NF1) cancer predisposition syndrome, we sought to determine the impact of the gut microbiome on optic glioma progression.

METHODS

Nf1-mutant mice genetically engineered to develop optic pathway gliomas (Nf1OPG mice) by 3 months of age were reared under germ-free (GF) conditions, treated with specific cocktails of antibiotics, or given fecal matter transplants (FMTs). Intestinal microbial species were identified by 16S genotyping. Neutralizing TGFβ antibodies were delivered systemically, while in vitro experiments used isolated murine microglia and T cells. Single cell RNA sequencing analysis was performed using established methods.

RESULTS

Nf1 OPG mice raised in a GF environment or postnatally treated with vancomycin did not harbor optic gliomas or exhibit OPG-induced retinal nerve fiber layer thinning, which was reversed following conventionally raised mouse FMT or colonization with Bacteroides species. Moreover, this intestinal microbiota-regulated gliomagenesis was mediated by circulating TGFβ, such that systemic TGFβ neutralization reduced Nf1-OPG growth. TGFβ was shown to act on tumor-associated monocytes to induce Ccl3 expression and recruit CD8+ T cells necessary for glioma growth.

CONCLUSIONS

Taken together, these findings establish, for the first time, a mechanistic relationship between Bacteroides in the intestinal microbiome and NF1-LGG pathobiology, suggesting both future predictive risk assessment strategies and therapeutic opportunities.

Mechanisms and environmental factors shaping the ecosystem of brain macrophages

Brain macrophages encompass two major populations: microglia in the parenchyma and border-associated macrophages (BAMs) in the extra-parenchymal compartments. These cells play crucial roles in maintaining brain homeostasis and immune surveillance. Microglia and BAMs are phenotypically and epigenetically distinct and exhibit highly specialized functions tailored to their environmental niches. Intriguingly, recent studies have shown that both microglia and BAMs originate from the same myeloid progenitor during yolk sac hematopoiesis, but their developmental fates diverge within the brain. Several works have partially unveiled the mechanisms orchestrating the development of microglia and BAMs in both mice and humans; however, many questions remain unanswered. Defining the molecular underpinnings controlling the transcriptional and epigenetic programs of microglia and BAMs is one of the upcoming challenges for the field. In this review, we outline current knowledge on ontogeny, phenotypic diversity, and the factors shaping the ecosystem of brain macrophages. We discuss insights garnered from human studies, highlighting similarities and differences compared to mice. Lastly, we address current research gaps and potential future directions in the field. Understanding how brain macrophages communicate with their local environment and how the tissue instructs their developmental trajectories and functional features is essential to fully comprehend brain physiology in homeostasis and disease.

Neurological impact of HIV/AIDS and substance use alters brain function and structure

Human immunodeficiency virus (HIV) infection is the cause of acquired immunodeficiency syndrome (AIDS). Combination antiretroviral therapy (cART) has successfully controlled AIDS, but HIV-associated neurocognitive disorders (HANDs) remain prevalent among people with HIV. HIV infection is often associated with substance use, which promotes HIV transmission and viral replication and exacerbates HANDs even in the era of cART. Thus, the comorbid effects of substance use exacerbate the neuropathogenesis of HANDs. Unraveling the mechanism(s) of this comorbid exacerbation at the molecular, cell-type, and brain region levels may provide a better understanding of HAND persistence. This review aims to highlight the comorbid effects of HIV and substance use in specific brain regions and cell types involved in the persistence of HANDs. This review includes an overview of post-translational modifications, alterations in microglia-specific biomarkers, and possible mechanistic pathways that may link epigenomic modifications to functional protein alterations in microglia. The impairment of the microglial proteins that are involved in neural circuit function appears to contribute to the breakdown of cellular communication and neurodegeneration in HANDs. The epigenetic modification of N-terminal acetylation is currently understudied, which is discussed in brief to demonstrate the important role of this epigenetic modification in infected microglia within specific brain regions. The discussion also explores whether combined antiretroviral therapy is effective in preventing HIV infection or substance-use-mediated post-translational modifications and protein alterations in the persistence of neuropathogenesis in HANDs.

Common and distinct features of diverse macrophage populations in the central nervous system

Tissue-resident macrophages perform indispensable functions in the development, maintenance, and repair of tissues. Microglia are the primary resident immune cells in the central nervous system (CNS), functioning as intracerebral macrophages distributed throughout the brain parenchyma. In addition to microglia, there is another, less well-characterized type of macrophage known as CNS border-associated macrophages (CAMs), and the existence of these cells has been recognized for several decades. With recent advances in research technologies, an increasing number of studies have focused on CAMs, and our understanding of them has begun to improve. In this article, we review the cellular characteristics and functions of CAMs that have been elucidated thus far, with a particular focus on the similarities and differences between CAMs and microglia.

Orchestrating the neuroglial compartment: Ontogeny and developmental interaction of astrocytes, oligodendrocytes, and microglia

Neuroglial cells serve as the master regulators of the central nervous system, making it imperative for glial development to be tightly regulated both spatially and temporally to ensure optimal brain function. In this chapter, we will discuss the origin and development of the three major glia cells such as astrocytes, oligodendrocytes, and microglia in the central nervous system. While much of our understanding of neuroglia development stems from studies using animal models, we will also explore recent insights into human glial development and potential differences from rodent models. Finally, the extensive crosstalk between glia cells will be highlighted, discussing how interactions among astrocyte, oligodendrocyte, and microglial influence their respective developmental pathways.

Ontogenetic Neuroimmune Changes Following Prenatal Alcohol Exposure: Implications for Neurobehavioral Function

This chapter reviews the enduring effects of prenatal alcohol exposure (PAE) on neuroimmune function across the lifespan, including discussion of associated neurobehavioral alterations. Alcohol has potent teratogenic effects, with a large body of work linking PAE to perturbations in neuroimmune function. These PAE-related neuroimmune disturbances may have downstream effects on neurobehavioral function given the critical role of the neuroimmune system in central nervous system development. The neuroimmune system matures over time, playing distinct roles depending on the developmental processes occurring within that maturational stage. This chapter thus takes an ontogenetic approach to understanding how PAE induces unique neuroimmune changes across the lifespan, beginning with a review of changes in early life before moving into adolescence and ending in adulthood. The focus will be on work utilizing rodent models, which allow for more tightly controlled conditions than are possible in human research. The chapter concludes with a discussion of possible mechanisms underlying the developmental changes in neuroimmune function following PAE, with a specific focus on the role of the gut microbiota.

Neuroinflammatory Loop in Schizophrenia, Is There a Relationship with Symptoms or Cognition Decline?

Schizophrenia (SZ), a complex psychiatric disorder of neurodevelopment, is characterised by a range of symptoms, including hallucinations, delusions, social isolation and cognitive deterioration. One of the hypotheses that underlie SZ is related to inflammatory events which could be partly responsible for symptoms. However, it is unknown how inflammatory molecules can contribute to cognitive decline in SZ. This review summarises and exposes the possible contribution of the imbalance between pro-inflammatory and anti-inflammatory interleukins like IL-1beta, IL-4 and TNFalfa among others on cognitive impairment. We discuss how this inflammatory imbalance affects microglia and astrocytes inducing the disruption of the blood-brain barrier (BBB) in SZ, which could impact the prefrontal cortex or associative areas involved in executive functions such as planning and working tasks. We also highlight that inflammatory molecules generated by intestinal microbiota alterations, due to dysfunctional microbial colonisers or the use of some anti-psychotics, could impact the central nervous system. Finally, the question arises as to whether it is possible to modulate or correct the inflammatory imbalance that characterises SZ, and if an immunomodulatory strategy can be incorporated into conventional clinical treatments, either alone or in complement, to be applied in specific phases, such as prodromal or in the first-episode psychosis.