Early Fate Defines Microglia and Non-parenchymal Brain Macrophage Development

DDR2 alleviates retinal vaso-obliteration and pathological neovascularization by modulating microglia M1/M2 phenotypic polarization in a mouse model of proliferative retinopathy

Retinopathy of prematurity (ROP), a leading cause of blindness in premature infants, is characterized by retinal vaso-obliteration during hyperoxia and pathological neovascularization (NV) in relative hypoxia phase. Current treatments, which focus on the late stages of pathological neovascularization, are associated with numerous side effects. Studies demonstrated that discoidin domain receptor 2 (DDR2), a collagen-binding receptor tyrosine kinase, inhibits the experimental choroidal neovascularization and participates in tumor angiogenesis. However, the role of DDR2 in ROP and underlying mechanisms is unclear. In this study, we initially found that DDR2 expressed during mouse physiological retinal vascular development and significantly decreased in vaso-obliteration phase followed by increase during pathological neovascularization phase in mouse oxygen-induced retinopathy (OIR) model. Early upregulation of DDR2 before hyperoxia attenuates oxygen-induced vaso-obliteration, reduces pathological neovascularization, and promotes retinal vascular maturation. Additionally, DDR2 upregulation increased the number of microglia around retinal blood vessels and induced anti-inflammatory M2 polarization. Furthermore, the STAT6/TGF-β signaling pathway suppressed during hyperoxia was activated after DDR2 upregulation. In conclusion, DDR2 attenuated vaso-obliteration and inhibited pathological neovascularization by switching the microglia polarization from M1 to M2 phenotype via the STAT6/TGF-β signaling pathway in OIR. This suggests that DDR2 could be a novel target for the early treatment of ROP.

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.

Transcription factors that define the epigenome structures and transcriptomes in microglia

Microglia, the resident macrophages of the brain, play critical roles in maintaining brain health. Recent genome-wide analyses, including ATAC-seq, ChIP-seq/CUT&RUN, and single-cell RNA-seq, have identified key transcription factors that define the transcriptome programs of microglia. Four transcription factors-PU.1, IRF8, SALL1, and SMAD4-form enhancer complexes and act as lineage-determining factors, shaping microglial identity. These factors co-bind with other lineage-determining transcription factors, directing one towards designated regions that program microglia while inhibiting the other from binding to DNA. Other transcription factors, such as BATF3 and MAFB, contribute to transcriptional cascades in microglia. TGF-β is a crucial cytokine driving these transcription factors to bind DNA and maintain homeostatic microglia. These findings provide insights into the physiological aspects of microglia and their roles in neuroinflammatory and neurodegenerative diseases. TEASER ABSTRACT: eTOC blurb: In this article, we compiled more than 100 transcription factors expressed in microglia. Our analysis illustrates that some transcription factors are under a distinct hierarchical rank and are sequentially activated to achieve microglia specific transcriptome programs. This article offers a new scope on the mechanistic foundation underlying microglia's complex activity.

Chronic Stress Modulates Microglial Activation Dynamics, Shaping Priming Responses to Subsequent Stress

(1) Background: The high recurrence rate and individual differences in stress susceptibility contribute to the diverse symptoms of depression, making full recovery and relapse prevention challenging. Emerging evidence suggests that fluctuations in microglial activity are closely linked to depression progression under chronic stress exposure. Changes in the brain microenvironment can elicit microglial priming, enhancing their sensitivity to external stimuli. However, few studies have longitudinally examined how microglial characteristics evolve throughout depression progression. (2) Methods: In this study, we investigated microglial morphological changes and their responses to acute stress at different stages of depression using the chronic unpredictable mild stress (CUMS) paradigm in mice. (3) Results: Our findings reveal that in the dentate gyrus, microglial activation indices, including cell number and morphology, exhibit distinct dynamic patterns depending on CUMS exposure duration. Notably, after 2 and 4 weeks of CUMS exposure followed by acute stress re-exposure, microglia display opposing response patterns. In contrast, after 6 weeks of CUMS exposure, primed microglia exhibit dysfunction, failing to respond to acute stress. Notably, depressive behaviors are not prominent after 2 weeks of CUMS exposure but become more pronounced after 4 and 6 weeks of exposure. Additionally, regardless of CUMS duration, body weight demonstrates an intrinsic capacity to normalize after stress cessation. (4) Conclusions: These findings suggest that microglial priming responses are state-dependent, either enhancing or suppressing secondary stimulus responses, or exceeding physiological limits, thereby preventing further activation. This study provides novel insights into the role of microglial priming in stress vulnerability and its contribution to depression progression.

Border-associated macrophages as gatekeepers of brain homeostasis and immunity

The brain's border tissues serve as essential hubs for neuroimmune regulation and the trafficking of biomaterials to and from the brain. These complex tissues-including the meninges, perivascular spaces, choroid plexus, and circumventricular organs-balance the brain's need for immune privilege with immune surveillance and blood-brain communication. Macrophages are integral components of these tissues, taking up key strategic positions within the brain's circulatory system. These border-associated macrophages, or "BAMs," are therefore emerging as pivotal for brain homeostasis and disease. BAMs perform trophic functions that help to support border homeostasis but also act as immune sentinels essential for border defense. In this review, we integrate recent findings on BAM origins, cell states, and functions, aiming to provide global insights and perspectives on the complex relationship between these macrophages and their border niche.

IL-10 sensing by lung interstitial macrophages prevents bacterial dysbiosis-driven pulmonary inflammation and maintains immune homeostasis

Crosstalk between the immune system and the microbiome is critical for maintaining immune homeostasis. Here, we examined this communication and the impact of immune-suppressive IL-10 signaling on pulmonary homeostasis. We found that IL-10 sensing by interstitial macrophages (IMs) is required to prevent spontaneous lung inflammation. Loss of IL-10 signaling in IMs initiated an inflammatory cascade through the activation of classical monocytes and CD4+ T cell subsets, leading to chronic lung inflammation with age. Analyses of antibiotic-treated and germ-free mice established that lung inflammation in the animals lacking IL-10 signaling was triggered by commensal bacteria. 16S rRNA sequencing revealed Delftia acidovorans and Rhodococcus erythropolis as potential drivers of lung inflammation. Intranasal administration of these bacteria or transplantation of human fecal microbiota elicited lung inflammation in gnotobiotic Il10-deficient mice. These findings highlight that IL-10 sensing by IMs contributes to pulmonary homeostasis by preventing lung inflammation caused by commensal dysbiosis.

Interleukin-34-dependent perivascular macrophages promote vascular function in the brain

The development of most macrophages depends on the colony-stimulating factor 1 (CSF-1) receptor, which has two ligands: CSF-1 and interleukin-34 (IL-34). While IL-34 is required for the homeostasis of microglia, the parenchymal macrophages in the central nervous system (CNS), it is unclear whether brain border-associated macrophages (BAMs) also depend on this cytokine. Here, we demonstrated that the embryonic development of murine BAMs in the choroid plexus, leptomeninges, and perivascular spaces required CSF-1, while IL-34 was critical for their maintenance in adulthood. In the brain, Il34 was expressed by mural cells and perivascular fibroblasts, and its transgenic deletion in these cells interrupted BAM maintenance. Il34 deficiency coincided with transcriptional changes in vascular cells, leading to increased flow velocity and vasomotion in pial and penetrating arterioles. Similarly, Mrc1CreCsf1rfl/fl mice lacking CD206+ perivascular BAMs exhibited increased hemodynamics in arterial networks. These findings reveal a crosstalk between vascular cells and CNS macrophages regulating cerebrovascular function.

Monocytes can efficiently replace all brain macrophages and fetal liver monocytes can generate bona fide SALL1+ microglia

Microglia and border-associated macrophages (BAMs) are critical for brain health, and their dysfunction is associated to disease. Replacing brain macrophages holds substantial therapeutic promise but remains challenging. Here, we demonstrate that monocytes can efficiently replace all brain macrophages. Monocytes readily replaced embryonal BAMs upon their depletion and engrafted as monocyte-derived microglia (Mo-Microglia) upon more sustained niche availability. Mo-Microglia expanded comparably to their embryonic counterparts and showed similar longevity. However, monocytes were unable to replicate the distinct identity of embryonically derived BAMs and microglia. Using xenotransplantation, we found that human monocytes exhibited similar behavior, enabling identification of putative Mo-Microglia in Alzheimer's disease individuals. In mice and humans, monocyte ontogeny shaped their identity as brain macrophages. Importantly, mouse fetal liver monocytes exhibited a distinct epigenetic landscape and could develop a bona fide microglial identity. Our results illuminate brain macrophage development and highlight monocytes as an abundant progenitor source for brain macrophage replacement therapies.

Rodent monocyte-derived macrophages do not express CD163: Comparative analysis using macrophages from living boreoeutherians

BACKGROUND

CD163 is a scavenger receptor predominantly expressed on the surfaces of macrophages in various mammalian species and is a marker of anti-inflammatory (M2-like) macrophages. High density of CD163-positive tumor-associated macrophages (TAMs) is associated with worse prognosis in various patient tumors. Interestingly, studies on mice have shown that CD163-positive TAMs only infiltrate the margins of tumor tissues, not the center. Based on these observations, we hypothesized that circulating monocyte-derived macrophages (MDMs), which are the origin of most TAMs, do not express CD163 in mice.

RESULTS

We examined CD163 expression in MDMs, differentiated from healthy animals in vitro, and in normal, pathogenic, and tumorigenic macrophages infiltrating various tumors and organs across multiple species including primates, rodents, cetartiodactylans, and carnivores. We found that MDMs, including TAMs, do not express CD163 in mice. Our findings also suggest that murine CD163-positive macrophages likely originate from a specific subset of resident macrophages, namely fetal liver monocytes/macrophages, as indicated by fetal analysis. Furthermore, we revealed that the CD163-negative expression pattern in MDMs is a trait shared by the rodent clade.

CONCLUSIONS

Rodent MDMs do not express CD163, a phenotype not shared with MDMs of other mammals. Our findings caution against the extrapolation of rodent experimental results to other animal models.

Dynamic regulation and targeted interventions of macrophages in ischemia-reperfusion injury

BACKGROUND

Ischemia-Reperfusion Injury (IRI) is a complex pathophysiological process characterized by oxidative stress and inflammatory responses during tissue reperfusion, leading to severe organ dysfunction. Macrophages, as key immune cells, play a pivotal role in the pathogenesis of IRI, exhibiting dynamic functions that influence both tissue damage and repair. Despite extensive research, the precise mechanisms underlying macrophage-mediated IRI remain incompletely understood, necessitating a comprehensive review to explore their multifaceted roles and potential therapeutic targets.

AIM OF REVIEW

This review aims to elucidate the diverse roles of macrophages in IRI, focusing on their involvement in programmed cell death mechanisms, communication with other immune cells, and regulatory effects on key organs affected by IRI. The review also explores potential therapeutic strategies targeting macrophages to mitigate IRI-induced injury. Key Scientific Concepts of Review: This article reviews the multifaceted roles of macrophages in IRI and explores various modes of macrophage programmed cell death induced by IRI, including gasdermin D-mediated pyroptosis, lipid peroxidation-associated ferroptosis, PARP-1-mediated PAR-dependent cell death, PANoptosis regulated by the PANoptosome, and the formation of macrophage extracellular traps (METs) induced by both reactive oxygen species-dependent and -independent pathways. Additionally, it discusses intercellular communication between macrophages and other immune cells in IRI, focusing on the bidirectional regulatory effects between macrophages and neutrophils, as well as their synergistic role in resolving inflammation. Moreover, the regulatory mechanisms of macrophages in IRI affecting key organs, such as the brain, lung, heart, kidneys and liver, have been systematically summarized. Finally, innovative therapeutic strategies targeting macrophages, including precise approaches such as regulating cell polarization, inhibiting excessive METs formation, and utilizing nano-drug delivery systems, are thoroughly analyzed. This review provides a significant theoretical foundation for clinical translational research on IRI.

Macrophage is crucial for tongue development by regulating myogenesis and vascularization

BACKGROUND

Abnormal tongue development is a craniofacial deformity that affects dental-maxillofacial esthetics and function. Recent evidence has identified macrophages as multi-functional immune cells crucial for heart and brain development. However, it is still unknown whether macrophages affect tongue development. Therefore, this study aims to assess the distribution, phenotype, and roles of macrophages in the developing tongue.

METHODS

In this study, immunohistochemical (IHC) and multiplex immunofluorescence (mIF) staining were conducted on C57BL/6 mice at embryonic day (E) 13.5, E14.5, E16.5, and E18.5 to analyze the distribution and phenotype of macrophages. Hematoxylin-Eosin (HE), IHC, IF, and mIF staining were also performed on embryonic CX3 CR1-CreERT2; Rosa-DTA conditional macrophage-depleted mice to investigate the effects on fetal tongue development and elucidate mechanisms from myogenesis, vascularization, and cell apoptosis. Statistical significance between the two groups was determined using unpaired two-tailed Student's t-tests. For comparisons involving three or more groups, one-way analysis of variance (ANOVA) followed by Tukey's multiple comparison tests was utilized. A significance level of P < 0.05 was set for statistical significance.

RESULTS

Macrophages were present in the developing tongue from E13.5 to E18.5, with a majority being of the M2 phenotype. Depletion of macrophages resulted in abnormal tongue morphology, decreased tongue height, width, and size, as well as reduced and disorganized muscle fibers. Depletion of macrophages also increased apoptosis. Vascular morphogenesis was impacted, with reductions in the luminal and vascular wall cross-sectional areas of the lingual artery. Vascular endothelial cells were reduced and disorganized with decreased expression of VEGFA and TGF-β1. Moreover, macrophages were located near vascular endothelial cells and secreted pro-angiogenic factors, suggesting their involvement in promoting vascularization.

CONCLUSIONS

Our findings indicate that macrophages play crucial roles in fetal tongue development by affecting myogenesis, cell apoptosis, and vascular growth.

Aging and neurodegeneration: when systemic dysregulations affect brain macrophage heterogeneity

Microglia, the major population of brain resident macrophages, differentiate from yolk sac progenitors in the embryo and play multiple nonimmune roles in brain organization throughout development and life. Various microglia subtypes have been described by transcriptomic and proteomic signatures, involved metabolic pathways, morphology, intracellular complexity, time of residency, and ontogeny, both in development and in disease settings. Such macrophage heterogeneity increases with aging or neurodegeneration. Monocytes' infiltration and differentiation into monocyte-derived macrophages (MDMs) in the brain contribute to this diversity. Microbiota's role in brain diseases has been recently highlighted, revealing how microbial signals, such as metabolites, influence microglia and MDMs. In this brief review, we describe how these signals can influence microglia through their sensome and shape MDMs from their development in the bone marrow to their differentiation in the brain. Monocytes could then be a crucial player in the constitution of a dysbiotic gut-brain axis in neurodegenerative diseases and aging.

Perivascular macrophages in the central nervous system: insights into their roles in health and disease

Perivascular macrophages (PVMs) are a specialized subset of macrophages situated near blood vessels in the brain. Their strategic positioning around these vessels enables them to perform key functions in immune surveillance and response to inflammation and injury. These cells are crucial for modulating the immune response within the brain, contributing to normal central nervous system (CNS) processes. In pathological conditions, the role of PVMs becomes more complex. Depending on the specific disease or injury, they may contribute to inflammation, blood-brain barrier (BBB) dysfunction, and the clearance of abnormal materials. PVMs are implicated in degenerative diseases, cerebrovascular impairment, and microhemorrhages associated with amyloid-β immunotherapy. Despite their important roles in the CNS, research on PVMs remains limited, and the mechanisms underlying their involvement in both physiological and pathological processes within the brain are not yet fully elucidated. Therefore, this review will focus on the current advancements in PVM research, including their origin, classification, roles in neuroinflammation and neuroprotection, and their potential roles as therapeutic targets for neurodegenerative diseases.

Microglial colonization routes and their impacts on cellular diversity

Microglia are the resident immune cells of the central nervous system. Unlike other glial cells-such as astrocytes and oligodendrocytes-which originate from neural stem cells alongside neurons, microglia derive from erythromyeloid progenitors that emerge in the yolk sac during early embryonic development. Once they reach the brain, microglia expand their population through proliferation during development. A growing body of research has revealed that microglia play diverse roles throughout life, both in physiological and pathological contexts. With recent advancements in single-cell transcriptomics, it has become increasingly evident that microglia exhibit substantial heterogeneity in their gene expression patterns. While various functions and subtypes of microglia are being uncovered, the mechanisms underlying their diversity remain largely unknown. Two key hypotheses may explain how microglial diversity arises. One possibility is that their diversity is influenced by the different colonization routes they take before settling in the brain. Alternatively, microglia may acquire distinct properties in response to their local environment. This review explores both possibilities, with a particular focus on the first hypothesis, drawing on recent findings that highlight the multiple routes microglia utilize to colonize the brain. It discusses how these processes contribute to the establishment of microglial diversity during brain development.

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 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.

Edaravone Alleviates BV-2 Microglia-Mediated Neuroinflammation Through the PI3K/AKT/ NF-κB Pathway

Ischemic stroke (IS) poses a significant threat to human health. Research has demonstrated that microglia (MG)-mediated neuroinflammatory responses play a crucial role in the pathogenesis of IS. Consequently, inhibiting MG activation and reducing the inflammatory response may be key strategies for the clinical treatment of stroke and neurodegenerative diseases. Edaravone (EDA), a potent anti-inflammatory and antioxidant, is currently used in the clinical treatment of IS; however, its anti-inflammatory mechanisms remain inadequately understood. To address this, network pharmacology (NP) analysis is employed to identify the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling pathway as a potential mediator of the inflammatory response triggered by activated microglia following EDA treatment. In vitro oxygen-glucose deprivation (OGD) is used to induce BV-2 MG activation, and an in vivo middle cerebral artery occlusion (MCAO) mouse model is established. Western blot and immunofluorescence staining are used to detect changes in the phosphorylation levels of pathway-related proteins and the expression of inflammatory factors. Additionally, the PI3K pathway inhibitor LY294002 and a PI3K overexpression plasmid are introduced to further analyze the expression changes of these markers. The results suggest that EDA may alleviate the inflammatory response mediated by activated MG through the PI3K/Akt signaling pathway.

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.

The Integrated Transcriptome Bioinformatics Analysis of Energy Metabolism-Related Profiles for Dorsal Root Ganglion of Neuropathic Pain

Neuropathic pain (NP) is a debilitating disease and is associated with energy metabolism alterations. This study aimed to identify energy metabolism-related differentially expressed genes (EMRDEGs) in NP, construct a diagnostic model, and analyze immune cell infiltration and single-cell gene expression characteristics of NP. GSE89224, GSE123919, and GSE134003 were downloaded from the Gene Expression Omnibus. Differentially expressed genes (DEGs) analysis and an intersection with highly energy metabolism-related modules in weighted gene co-expression network analysis (WGCNA) was performed in GSE89224. Least absolute shrinkage and selection operator (LASSO), random forest, and logistic regression were used for model genes selection. NP samples were divided into high- and low-risk groups and different disease subtypes based on risk score of LASSO algorithm and consensus clustering analysis, respectively. Immune cell composition was estimated in different risk groups and NP subtypes. Datasets 134,003 were performed for identification of single-cell DEGs and functional enrichment. Cell-cell communications and pseudo-time analysis to reveal the expression profile of NP. A total of 38 EMRDEGs were obtained and are majorly enriched in metabolism about glioma and inflammation. LASSO, random forest, and logistic regression identified 6 model genes, which were Itpr1, Gng8, Socs3, Fscn1, Cckbr, and Camk1. The nomogram, based on six model genes, had a good predictive ability, concordance, and diagnostic value. The comparisons between different risk groups and NP subtypes identified important pathways and different immune cells component. The immune infiltration results majorly associated with inflammation and energy metabolism. Single-cell analysis revealed cell-cell communications and cells differentiation characteristics of NP. In conclusion, our results not only elucidate the involvement of energy metabolism in NP but also provides a robust diagnostic tool with six model genes. These findings might give insight into the pathogenesis of NP and provide effective therapeutic regimens for the treatment of NP.

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.

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.

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.

Glial Contribution to the Pathogenesis of Post-Operative Delirium Revealed by Multi-omic Analysis of Brain Tissue from Neurosurgery Patients

Post-operative delirium (POD) is a common complication after surgery especially in elderly patients, characterized by acute disturbances in consciousness and cognition, which negatively impacts long-term outcomes. Effective treatments remain elusive due to the unclear pathophysiology of POD. To address the knowledge gap, we investigated DNA methylation profiles and gene expression changes in brain cells from POD and non-POD patients who underwent brain resection surgery for medication refractory epilepsy. DNA methylation analysis revealed alteration in epigenetic status of immune and inflammation-related genes. Single-nucleus RNA sequencing (snRNAseq) identified POD-specific glial cell alterations, particularly in microglia, where neuroinflammation was strongly enhanced, consistent with epigenetic findings. Astrocytes exhibited changes in synapse-related functions and migration. Furthermore, downstream analysis indicated similarities between POD-associated glial cell states and pathologies such as encephalitis and dementia. Overall, this study-the first multi-omics analysis of brain tissue from POD patients-provides direct evidence of glial cell contributions to POD pathogenesis, and highlights potential therapeutic targets.

Tissue macrophages: origin, heterogenity, biological functions, diseases and therapeutic targets

Macrophages are immune cells belonging to the mononuclear phagocyte system. They play crucial roles in immune defense, surveillance, and homeostasis. This review systematically discusses the types of hematopoietic progenitors that give rise to macrophages, including primitive hematopoietic progenitors, erythro-myeloid progenitors, and hematopoietic stem cells. These progenitors have distinct genetic backgrounds and developmental processes. Accordingly, macrophages exhibit complex and diverse functions in the body, including phagocytosis and clearance of cellular debris, antigen presentation, and immune response, regulation of inflammation and cytokine production, tissue remodeling and repair, and multi-level regulatory signaling pathways/crosstalk involved in homeostasis and physiology. Besides, tumor-associated macrophages are a key component of the TME, exhibiting both anti-tumor and pro-tumor properties. Furthermore, the functional status of macrophages is closely linked to the development of various diseases, including cancer, autoimmune disorders, cardiovascular disease, neurodegenerative diseases, metabolic conditions, and trauma. Targeting macrophages has emerged as a promising therapeutic strategy in these contexts. Clinical trials of macrophage-based targeted drugs, macrophage-based immunotherapies, and nanoparticle-based therapy were comprehensively summarized. Potential challenges and future directions in targeting macrophages have also been discussed. Overall, our review highlights the significance of this versatile immune cell in human health and disease, which is expected to inform future research and clinical practice.

The contribution of the monocyte-macrophage lineage to immunotherapy outcomes

ABSTRACT

Macrophages execute core functions in maintaining tissue homeostasis, in which their extensive plasticity permits a spectrum of functions from tissue remodeling to immune defense. However, perturbations to tissue-resident macrophages during disease, and the subsequent emergence of monocyte-derived macrophages, can hinder tissue recovery and promote further damage through inflammatory and fibrotic programs. Gaining a fundamental understanding of the critical pathways defining pathogenic macrophage populations enables the development of targeted therapeutic approaches to improve disease outcomes. In the setting of chronic graft-versus-host disease (cGVHD), which remains the major complication of allogeneic hematopoietic stem cell transplantation, colony-stimulating factor 1 (CSF1)-dependent donor-derived macrophages have been identified as key pathogenic mediators of fibrotic skin and lung disease. Antibody blockade of the CSF1 receptor (CSF1R) to induce macrophage depletion showed remarkable capacity to prevent fibrosis in preclinical models and has subsequently demonstrated impressive efficacy for improving cGVHD in ongoing clinical trials. Similarly, macrophage depletion approaches are currently under investigation for their potential to augment responses to immune checkpoint inhibition. Moreover, both monocyte and tissue-resident macrophage populations have recently been implicated as mediators of the numerous toxicities associated with chimeric antigen receptor T-cell therapy, further highlighting potential avenues of macrophage-based interventions to improve clinical outcomes. Herein, we examine the current literature on basic macrophage biology and contextualize this in the setting of cellular and immunotherapy. Additionally, we highlight mechanisms by which macrophages can be targeted, largely by interfering with the CSF1/CSF1R signaling axis, for therapeutic benefit in the context of both cellular and immunotherapy.

How the gut microbiota impacts neurodegenerative diseases by modulating CNS immune cells

Alzheimer's disease (AD) is the most common neurodegenerative disease worldwide. Amyloid-β (Aβ) accumulation and neurofibrillary tangles are two key histological features resulting in progressive and irreversible neuronal loss and cognitive decline. The macrophages of the central nervous system (CNS) belong to the innate immune system and comprise parenchymal microglia and CNS-associated macrophages (CAMs) at the CNS interfaces (leptomeninges, perivascular space and choroid plexus). Microglia and CAMs have received attention as they may play a key role in disease onset and progression e. g., by clearing amyloid beta (Aβ) through phagocytosis. Genome-wide association studies (GWAS) have revealed that human microglia and CAMs express numerous risk genes for AD, further highlighting their potentially critical role in AD pathogenesis. Microglia and CAMs are tightly controlled by environmental factors, such as the host microbiota. Notably, it was further reported that the composition of the gut microbiota differed between AD patients and healthy individuals. Hence, emerging studies have analyzed the impact of gut bacteria in different preclinical mouse models for AD as well as in clinical studies, potentially enabling promising new therapeutic options.

Maternal immune activation followed by peripubertal stress combinedly produce reactive microglia and confine cerebellar cognition

The functional alteration of microglia arises in brains exposed to external stress during early development. Pathophysiological findings of neurodevelopmental disorders such as schizophrenia and autism spectrum disorder suggest cerebellar functional deficits. However, the link between stress-induced microglia reactivity and cerebellar dysfunction is missing. Here, we investigate the developmental immune environment in translational mouse models that combine two risk factors: maternal infection and repeated social defeat stress (2HIT). We find the synergy of inflammatory stress insults, leading to microglial increase specifically in the cerebellum of both sexes. Microglial turnover correlates with the Purkinje neuron loss in 2HIT mice. Highly multiplexed imaging-mass-cytometry identifies a cell transition to TREM2(+) stress-associated microglia in the cerebellum. Single-cell-proteomic clustering reveals IL-6- and TGFβ-signaling association with microglial cell transitions. Reduced excitability of remaining Purkinje cells, cerebellum-involved brain-wide functional dysconnectivity, and behavioral abnormalities indicate cerebellar cognitive dysfunctions in 2HIT animals, which are ameliorated by both systemic and cerebellum-specific microglia replacement.

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.

Propagation of neuronal micronuclei regulates microglial characteristics

Microglia-resident immune cells in the central nervous system-undergo morphological and functional changes in response to signals from the local environment and mature into various homeostatic states. However, niche signals underlying microglial differentiation and maturation remain unknown. Here, we show that neuronal micronuclei (MN) transfer to microglia, which is followed by changing microglial characteristics during the postnatal period. Neurons passing through a dense region of the developing neocortex give rise to MN and release them into the extracellular space, before being incorporated into microglia and inducing morphological changes. Two-photon imaging analyses have revealed that microglia incorporating MN tend to slowly retract their processes. Loss of the cGAS gene alleviates effects on micronucleus-dependent morphological changes. Neuronal MN-harboring microglia also exhibit unique transcriptome signatures. These results demonstrate that neuronal MN serve as niche signals that transform microglia, and provide a potential mechanism for regulation of microglial characteristics in the early postnatal neocortex.

Integrative Genomics Approach Identifies Glial Transcriptomic Dysregulation and Risk in the Cortex of Individuals With Alcohol Use Disorder

BACKGROUND

Alcohol use disorder (AUD) is a prevalent neuropsychiatric disorder that is a major global health concern, affecting millions of people worldwide. Previous studies of AUD used underpowered single-cell analysis or bulk homogenates of postmortem brain tissue, which obscure gene expression changes in specific cell types. Therefore, we sought to conduct the largest-to-date single-nucleus RNA sequencing (snRNA-seq) postmortem brain study in AUD to elucidate transcriptomic pathology with cell type-specific resolution.

METHODS

Here, we performed snRNA-seq and high-dimensional network analysis of 73 postmortem samples from individuals with AUD (n = 36, nnuclei = 248,873) and neurotypical control individuals (n = 37, nnuclei = 210,573) in the dorsolateral prefrontal cortex from both male and female donors. Additionally, we performed analysis for cell type-specific enrichment of aggregate genetic risk for AUD as well as integration of the AUD proteome for secondary validation.

RESULTS

We identified 32 distinct cell clusters and found widespread cell type-specific transcriptomic changes across the cortex in AUD, particularly affecting glial populations. We found the greatest dysregulation in novel microglial and astrocytic subtypes that accounted for the majority of differential gene expression and coexpression modules linked to AUD. Differential gene expression was secondarily validated by integration of a publicly available AUD proteome. Finally, analysis for aggregate genetic risk for AUD identified subtypes of glia as potential key players not only affected by but also causally linked to the progression of AUD.

CONCLUSIONS

These results highlight the importance of cell type-specific molecular changes in AUD and offer opportunities to identify novel targets for treatment on the single-nucleus level.

Early precursor-derived pituitary gland tissue-resident macrophages play a pivotal role in modulating hormonal balance

The pituitary gland is the central endocrine regulatory organ producing and releasing hormones that coordinate major body functions. The physical location of the pituitary gland at the base of the brain, though outside the protective blood-brain barrier, leads to an unexplored special immune environment. Using single-cell transcriptomics, fate mapping, and imaging, we characterize pituitary-resident macrophages (pitMØs), revealing their heterogeneity and spatial specialization. Microglia-like macrophages (ml-MACs) are enriched in the posterior pituitary, while other pitMØs in the anterior pituitary exhibit close interactions with hormone-secreting cells. Importantly, all pitMØs originate from early yolk sac progenitors and maintain themselves through self-renewal, independent of bone marrow-derived monocytes. Macrophage depletion experiments unveil the role of macrophages in regulating intrapituitary hormonal balance through extracellular ATP-mediated intercellular signaling. Altogether, these findings provide information on pituitary gland macrophages and advance our understanding of immune-endocrine system crosstalk.

Intermittent Fasting Improves Social Interaction and Decreases Inflammatory Markers in Cortex and Hippocampus

Autism spectrum disorder (ASD) is a psychiatric condition characterized by reduced social interaction, anxiety, and stereotypic behaviors related to neuroinflammation and microglia activation. We demonstrated that maternal exposure to Western diet (cafeteria diet or CAF) induced microglia activation, systemic proinflammatory profile, and ASD-like behavior in the offspring. Here, we aimed to identify the effect of alternate day fasting (ADF) as a non-pharmacologic strategy to modulate neuroinflammation and ASD-like behavior in the offspring prenatally exposed to CAF diet. We found that ADF increased plasma beta-hydroxybutyrate (BHB) levels in the offspring exposed to control and CAF diets but not in the cortex (Cx) and hippocampus (Hpp). We observed that ADF increased the CD45 + cells in Cx of both groups; In control individuals, ADF promoted accumulation of CD206 + microglia cells in choroid plexus (CP) and increased in CD45 + macrophages cells and lymphocytes in the Cx. Gestational exposure to CAF diet promoted defective sociability in the offspring; ADF improved social interaction and increased microglia CD206 + in the Hpp and microglia complexity in the dentate gyrus. Additionally, ADF led to attenuation of the ER stress markers (Bip/ATF6/p-JNK) in the Cx and Hpp. Finally, biological modeling showed that fasting promotes higher microglia complexity in Cx, which is related to improvement in social interaction, whereas in dentate gyrus sociability is correlated with less microglia complexity. These data suggest a contribution of intermittent fasting as a physiological stimulus capable of modulating microglia phenotype and complexity in the brain, and social interaction in male mice.

Immune conversations at the border: meningeal immunity in health and disease

The brain and spinal cord, collectively known as the central nervous system, are encapsulated by an overlapping series of membranes known as the meninges. Once considered primarily a physical barrier for central nervous system protection, the bordering meninges are now recognized as highly immunologically active. The meninges host diverse resident immune cells and serve as a critical interface with peripheral immunity, playing multifaceted roles in maintaining central nervous system homeostasis, responding to pathogenic threats, and neurological disorders. This review summarizes recent advancements in our understanding of meningeal immunity including its structural composition, physiological functions, and role in health and disease.

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.

Microglia modulate the cerebrovascular reactivity through ectonucleotidase CD39

Microglia and the border-associated macrophages contribute to the modulation of cerebral blood flow, but the mechanisms have remained uncertain. Here, we show that microglia regulate the cerebral blood flow baseline and the responses to whisker stimulation or intra-cisternal magna injection of adenosine triphosphate, but not intra-cisternal magna injection of adenosine in mice model. Notably, microglia repopulation corrects these cerebral blood flow anomalies. The microglial-dependent regulation of cerebral blood flow requires the adenosine triphosphate-sensing P2RY12 receptor and ectonucleotidase CD39 that initiates the dephosphorylation of extracellular adenosine triphosphate into adenosine in both male and female mice. Pharmacological inhibition or CX3CR1-CreER-mediated deletion of CD39 mimics the cerebral blood flow anomalies in microglia-deficient mice and reduces the upsurges of extracellular adenosine following whisker stimulation. Together, these results suggest that the microglial CD39-initiated breakdown of extracellular adenosine triphosphate co-transmitter is an important step in neurovascular coupling and the regulation of cerebrovascular reactivity.

Waste clearance shapes aging brain health

Brain health is intimately connected to fluid flow dynamics that cleanse the brain of potentially harmful waste material. This system is regulated by vascular dynamics, the maintenance of perivascular spaces, neural activity during sleep, and lymphatic drainage in the meningeal layers. However, aging can impinge on each of these layers of regulation, leading to impaired brain cleansing and the emergence of various age-associated neurological disorders, including Alzheimer's and Parkinson's diseases. Understanding the intricacies of fluid flow regulation in the brain and how this becomes altered with age could reveal new targets and therapeutic strategies to tackle age-associated neurological decline.

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.

Brain macrophages in vascular health and dysfunction

Diverse macrophage populations inhabit the rodent and human central nervous system (CNS), including microglia in the parenchyma and border-associated macrophages (BAMs) in the meninges, choroid plexus, and perivascular spaces. These innate immune phagocytes are essential in brain development and maintaining homeostasis, but they also play diverse roles in neurological diseases. In this review, we highlight the emerging roles of CNS macrophages in regulating vascular function in health and disease. We discuss that, in addition to microglia, BAMs, including perivascular macrophages, play roles in supporting vascular integrity and maintaining blood flow. We highlight recent advancements in understanding how these macrophages are implicated in protecting against vascular dysfunction and modulating the progression of cerebrovascular diseases, as seen in vessel-associated neurodegeneration.

Influenza A virus during pregnancy disrupts maternal intestinal immunity and fetal cortical development in a dose- and time-dependent manner

Epidemiological studies link exposure to viral infection during pregnancy, including influenza A virus (IAV) infection, with increased incidence of neurodevelopmental disorders (NDDs) in offspring. Models of maternal immune activation (MIA) using viral mimetics demonstrate that activation of maternal intestinal T helper 17 (TH17) cells, which produce effector cytokine interleukin (IL)-17, leads to aberrant fetal brain development, such as neocortical malformations. Fetal microglia and border-associated macrophages (BAMs) also serve as potential cellular mediators of MIA-induced cortical abnormalities. However, neither the inflammation-induced TH17 cell pathway nor fetal brain-resident macrophages have been thoroughly examined in models of live viral infection during pregnancy. Here, we inoculated pregnant mice with two infectious doses of IAV and evaluated peak innate and adaptive immune responses in the dam and fetus. While respiratory IAV infection led to dose-dependent maternal colonic shortening and microbial dysregulation, there was no elevation in intestinal TH17 cells nor IL-17. Systemically, IAV resulted in consistent dose- and time-dependent increases in IL-6 and IFN-γ. Fetal cortical abnormalities and global changes in fetal brain transcripts were observable in the high-but not the moderate-dose IAV group. Profiling of fetal microglia and BAMs revealed dose- and time-dependent differences in the numbers of meningeal but not choroid plexus BAMs, while microglial numbers and proliferative capacity of Iba1+ cells remained constant. Fetal brain-resident macrophages increased phagocytic CD68 expression, also in a dose- and time-dependent fashion. Taken together, our findings indicate that certain features of MIA are conserved between mimetic and live virus models, while others are not. Overall, we provide consistent evidence of an infection severity threshold for downstream maternal inflammation and fetal cortical abnormalities, which recapitulates a key feature of the epidemiological data and further underscores the importance of using live pathogens in NDD modeling to better evaluate the complete immune response and to improve translation to the clinic.

Neuroglial responses to bacterial, viral, and fungal neuroinfections

Evidence regarding the host's response to peripheral pathogens in humans abound, whereas studies on the pathogenesis of central nervous system-penetrating infections are relatively scarce. However, given the spate of epidemic and pandemic neuroinfections in the 21st century, the field has experienced a renewed interest lately. This chapter discusses a timely and exciting topic on the roles of glial cells, mainly microglia and astrocytes, in neuroinvasive infections. This chapter considered fungal, viral, and bacterial neuroinfections, X-raying their neuroinvasiveness, neurotropism, and neurovirulence before focusing on specific examples notable for each category, including Escherichia coli, Cryptococcus neoformans, and SARS-CoV-2. These infections are renowned worldwide for a high case-fatality rate, leaving many survivors with life-long morbidity and others with a bleak future neurologic prognosis. Importantly, the chapter discusses possible ways microglia and astrocytes are culpable in these infections and provides approaches by which they can be manipulated for therapeutic purposes, identifying viable research gaps in the process. Additionally, it offers a synopsis of ongoing works considering microglial selective targeting to attenuate the pathology, morbidity, and mortality associated with these neuroinfections. Considering that microglia and astrocytes are first responders in the central nervous system, targeting these glial cells could be the game changer in managing existing and emerging neuroinvasive infections.

Animal-based approaches to understanding neuroglia physiology in vitro and in vivo

This chapter describes the pivotal role of animal models for unraveling the physiology of neuroglial cells in the central nervous system (CNS). The two rodent species Mus musculus (mice) and Rattus norvegicus (rats) have been indispensable in scientific research due to their remarkable resemblance to humans anatomically, physiologically, and genetically. Their ease of maintenance, short gestation times, and rapid development make them ideal candidates for studying the physiology of astrocytes, oligodendrocyte-lineage cells, and microglia. Moreover, their genetic similarity to humans facilitates the investigation of molecular mechanisms governing neural physiology. Mice are largely the predominant model of neuroglial research, owing to advanced genetic manipulation techniques, whereas rats remain invaluable for applications requiring larger CNS structures for surgical manipulations. Next to rodents, other animal models, namely, Danio rerio (zebrafish) and Drosophila melanogaster (fruit fly), will be discussed to emphasize their critical role in advancing our understanding of glial physiology. Each animal model provides distinct advantages and disadvantages. By combining the strengths of each of them, researchers can gain comprehensive insights into glial function across species, ultimately promoting the understanding of glial physiology in the human CNS and driving the development of novel therapeutic interventions for CNS disorders.

Extrasinusoidal macrophages are a distinct subset of immunologically active dural macrophages

Although macrophages in the meningeal compartments of the central nervous system (CNS) have been comprehensively characterized under steady state, studying their contribution to physiological and pathological processes has been hindered by the lack of specific targeting tools in vivo. Recent findings have shown that the dural sinus and its adjacent lymphatic vessels act as a neuroimmune interface. However, the cellular and functional heterogeneity of extrasinusoidal dural macrophages outside this immune hub is not fully understood. Therefore, we comprehensively characterized these cells using single-cell transcriptomics, fate mapping, confocal imaging, clonal analysis, and transgenic mouse lines. Extrasinusoidal dural macrophages were distinct from leptomeningeal and CNS parenchymal macrophages in terms of their origin, expansion kinetics, and transcriptional profiles. During autoimmune neuroinflammation, extrasinusoidal dural macrophages performed efferocytosis of apoptotic granulocytes. Our results highlight a previously unappreciated myeloid cell diversity and provide insights into the brain's innate immune system.

Dura immunity configures leptomeningeal metastasis immunosuppression for cerebrospinal fluid barrier invasion

The cerebrospinal fluid (CSF) border accommodates diverse immune cells that permit peripheral cell immunosurveillance. However, the intricate interactions between CSF immune cells and infiltrating cancer cells remain poorly understood. Here we use fate mapping, longitudinal time-lapse imaging and multiomics technologies to investigate the precise origin, cellular crosstalk and molecular landscape of macrophages that contribute to leptomeningeal metastasis (LM) progression. Mechanically, we find that dura-derived LM-associated macrophages (dLAMs) migrate into the CSF in a matrix metalloproteinase 14 (MMP14)-dependent manner. Furthermore, we identify that dLAMs critically require the presence of secreted phosphoprotein 1 (SPP1) in cancer cells for their recruitment, fostering an immunosuppressed microenvironment characterized by T cell exhaustion and inactivation. Conversely, inhibition of the SPP1-MMP14 axis can impede macrophages from bypassing the border barrier, prevent cancer cell growth and improve survival in LM mouse models. Our findings reveal an unexpectedly private source of innate immunity within the meningeal space, shed light on CSF barrier dysfunction dynamics and supply potential targets of clinical immunotherapy.

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

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

CD36-mediated ROS/PI3K/AKT signaling pathway exacerbates cognitive impairment in APP/PS1 mice after noise exposure

There is an association between noise exposure and cognitive impairment, and noise may have a more severe impact on patients with Alzheimer's disease (AD) and mild cognitive impairment; however, the mechanisms need further investigation. This study used the classic AD animal model APP/PS1 mice to simulate the AD population, and C57BL/6J mice to simulate the normal population. We compared their cognitive abilities after noise exposure, analyzed changes in Cluster of Differentiation (CD) between the two types of mice using transcriptomics, identified the differential CD molecule: CD36 in APP/PS1 after noise exposure, and used its pharmacological inhibitor to intervene to explore the mechanism by which CD36 affects APP/PS1 cognitive abilities. Our study shows that noise exposure has a more severe impact on the cognitive abilities of APP/PS1 mice, and that the expression trends of differentiation cluster molecules differ significantly between C57BL/6J and APP/PS1 mice. Transcriptomic analysis showed that the expression of CD36 in the hippocampus of APP/PS1 mice increased by 2.45-fold after noise exposure (p < 0.001). Meanwhile, Western Blot results from the hippocampus and entorhinal cortex indicated that CD36 protein levels increased by approximately 1.5-fold (p < 0.001) and 1.3-fold (p < 0.05) respectively, after noise exposure in APP/PS1 mice. The changes in CD36 expression elevated oxidative stress levels in the hippocampus and entorhinal cortex, leading to a decrease in PI3K/AKT phosphorylation, which in turn increased M1-type microglia and A1-type astrocytes while reducing the numbers of M2-type microglia and A2-type astrocytes. This increased neuroinflammation in the hippocampus and entorhinal cortex, causing synaptic and neuronal damage in APP/PS1 mice, ultimately exacerbating cognitive impairment. These findings may provide new insights into the relationship between noise exposure and cognitive impairment, especially given the different expression trends of CD molecules in the two types of mice, which warrants further research.

The role of macrophage migratory behavior in development, homeostasis and tumor invasion

Tumor-associated macrophages (TAMs) recapitulate the developmental and homeostatic behaviors of tissue resident macrophages (TRMs) to promote tumor growth, invasion and metastasis. TRMs arise in the embryo and colonize developing tissues, initially to guide tissue morphogenesis and then to form complex networks in adult tissues to constantly search for threats to homeostasis. The macrophage growth factor, colony-stimulating factor-1 (CSF-1), which is essential for TRM survival and differentiation, is also responsible for the development of the unique motility machinery of mature macrophages that underpins their ramified morphologies, migratory capacity and ability to degrade matrix. Two CSF-1-activated kinases, hematopoietic cell kinase and the p110δ catalytic isoform of phosphatidylinositol 3-kinase, regulate this machinery and selective inhibitors of these proteins completely block macrophage invasion. Considering tumors co-opt the invasive capacity of TAMs to promote their own invasion, these proteins are attractive targets for drug development to inhibit tumor progression to invasion and metastasis.

Developmental programming of tissue-resident macrophages

Macrophages are integral components of the innate immune system that colonize organs early in development and persist into adulthood through self-renewal. Their fate, whether they are replaced by monocytes or retain their embryonic origin, depends on tissue type and integrity. Macrophages are influenced by their environment, a phenomenon referred to as developmental programming. This influence extends beyond the local tissue microenvironment and includes soluble factors that can reach the macrophage niche. These factors include metabolites, antibodies, growth factors, and cytokines, which may originate from maternal diet, lifestyle, infections, or other developmental triggers and perturbations. These influences can alter macrophage transcriptional, epigenetic, and metabolic profiles, affecting cell-cell communication and tissue integrity. In addition to their crucial role in tissue immunity, macrophages play vital roles in tissue development and homeostasis. Consequently, developmental programming of these long-lived cells can modulate tissue physiology and pathology throughout life. In this review, we discuss the ontogeny of macrophages, the necessity of developmental programming by the niche for macrophage identity and function, and how developmental perturbations can affect the programming of macrophages and their subtissular niches, thereby influencing disease onset and progression in adulthood. Understanding these effects can inform targeted interventions or preventive strategies against diseases. Finally, understanding the consequences of developmental programming will shed light on how maternal health and disease may impact the well-being of future generations.

Border-Associated Macrophages: From Embryogenesis to Immune Regulation

Border-associated macrophages (BAMs) play a pivotal role in maintaining brain homeostasis and responding to pathological conditions. Understanding their origins, characteristics, and roles in both healthy and diseased brains is crucial for advancing our knowledge of neuroinflammatory and neurodegenerative diseases. This review addresses the ontogeny, replenishment, microenvironmental regulation, and transcriptomic heterogeneity of BAMs, highlighting recent advancements in lineage tracing and fate-mapping studies. Furthermore, we examine the roles of BAMs in maintaining brain homeostasis, immune surveillance, and responses to injury and neurodegenerative diseases. Further research is crucial to clarify the dynamic interplay between BAMs and the brain's microenvironment in health and disease. This effort will not only resolve existing controversies but also reveal new therapeutic targets for neuroinflammatory and neurodegenerative disorders, pushing the boundaries of neuroscience.