Heterogeneity in the distribution and morphology of microglia in the normal adult mouse brain

A novel selective NLRP3 inhibitor shows disease-modifying potential in animal models of Parkinson's disease

Pathological activation of the Nod-like receptor family pyrin domain containing protein 3 (NLRP3) inflammasome signaling underlies many autoimmune and neuroinflammatory conditions. Here we report that, a rationally designed, novel, orally active, selective NLRP3 inflammasome inhibitor, Usnoflast (ZYIL1), showed potent inhibition of ATP, Nigericin and monosodium urate-mediated interleukin (IL)-1β release in THP-1 cells and human PBMC. In isolated microglia cells, the IC50 of ZYIL1 mediated inhibition of IL-1β was 43 nM. ZYIL1 displayed good pharmacokinetic profile in mice, rats and primates after oral administration and the concentrations found in the brain and cerebrospinal fluid (CSF) were markedly higher than the IC50 values. In an in vivo model of neuroinflammation, ZYIL1 demonstrated robust suppression of NLRP3 inflammasome activation and IL-1β upon oral administration. This translated into efficacy in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 6-Hydroxydopamine (6-OHDA)-induced Parkinson's disease (PD) models in mice. In MPTP and/or 6-OHDA models, treatment with ZYIL1 ameliorated motor deficits, degeneration of nigrostriatal dopaminergic neurons and abnormal accumulation of α-synuclein. There were positive changes in the genes related to walking, locomotor activity, neurogenesis, neuroblast proliferation and neuronal differentiation in the PD brain indicating improvement in neural health which translated into improved mobility. These findings clearly indicate that selective NLRP3 inhibitor ZYIL1, ameliorates neuroinflammation and appears to have the potential for disease modification and progression associated with PD.

Optineurin regulates motor and learning behaviors by affecting dopaminergic neuron survival in mice

Optineurin (OPTN) is an autophagy receptor that participates in the degradation of damaged mitochondria, protein aggregates, and invading pathogens. OPTN is closely related to various types of neurodegenerative diseases. However, the role of OPTN in the central nervous system is unclear. Here, we found that OPTN dysregulation in the compact part of substantia nigra (SNc) led to motor and learning deficits in animal models. Knockdown of OPTN increased total and phosphorylated α-synuclein levels which induced microglial activation and dopaminergic neuronal loss in the SNc. Overexpression of OPTN can't reverse the motor and learning phenotypes. Mechanistic analysis revealed that upregulation of OPTN increased α-synuclein phosphorylation independent of its autophagy receptor activity, which further resulted in microglial activation and dopaminergic neuronal loss similar to OPTN downregulation. Our study uncovers the crucial role of OPTN in maintaining dopaminergic neuron survival and motor and learning functions which are disrupted in PD patients.

The role of microglia in neurological diseases with involvement of extracellular vesicles

As a subset of mononuclear phagocytes in the central nervous system, microglia play a crucial role in immune defense and homeostasis maintenance. Microglia can regulate their states in response to specific signals of health and pathology. Microglia-mediated neuroinflammation is a pathological hallmark of neurodegenerative diseases, neurological damage and neurological tumors, underscoring its key immunoregulatory role in these conditions. Intriguingly, a substantial body of research has indicated that extracellular vesicles can mediate intercellular communication by transporting cargoes from parental cells, a property that is also reflected in microenvironmental signaling networks involving microglia. Based on the microglial characteristics, we briefly outline the biological features of extracellular vesicles and focus on summarizing the integrative role played by microglia in the maintenance of nervous system homeostasis and progression of different neurological diseases. Extracellular vesicles may engage in the homeostasis maintenance and pathological process as a medium of intercellular communication. Here, we aim to provide new insights for further exploration of neurological disease pathogenesis, which may provide theoretical foundations for cell-free therapies.

Microglia Signatures: A Cause or Consequence of Microglia-Related Brain Disorders?

Microglia signatures refer to distinct gene expression profiles or patterns of gene activity that are characteristic of microglia. Advances in gene expression profiling techniques, such as single-cell RNA sequencing, have allowed us to study microglia at a more detailed level and identify unique gene expression patterns that are associated, but not always, with different functional states of these cells. Microglial signatures depend on the developmental stage, brain region, and specific pathological conditions. By studying these signatures, it has been possible to gain insights into the underlying mechanisms of microglial activation and begin to develop targeted therapies to modulate microglia-mediated immune responses in the CNS. Historically, the first two signatures coincide with M1 pro-inflammatory and M2 anti-inflammatory phenotypes. The first one includes upregulation of genes such as CD86, TNF-α, IL-1β, and iNOS, while the second one may involve genes like CD206, Arg1, Chil3, and TGF-β. However, it has long been known that many and more specific phenotypes exist between M1 and M2, likely with corresponding signatures. Here, we discuss specific microglial signatures and their association, if any, with neurodegenerative pathologies and other brain disorders.

Increased Parenchymal Macrophages are associated with decreased Tyrosine Hydroxylase mRNA levels in the Substantia Nigra of people with Schizophrenia and Bipolar Disorder

Increased activation of inflammatory macrophages and altered expression of dopamine markers are found in the midbrains of people with schizophrenia (SZ). The relationship of midbrain macrophages to dopamine neurons has not been explored, nor is it known if changes in midbrain macrophages are also present in bipolar disorder (BD) or major depressive disorder (MDD). Herein, we determined whether there were differences in CD163+ cell density in the Substantia Nigra (SN), and cerebral peduncles (CP) of SZ, BD, and MDD compared to controls (CTRL). We also analyzed whether CD163 protein and dopamine-synthesizing enzyme tyrosine hydroxylase (TH) mRNA levels differed among diagnostic groups and if they correlated with the density of macrophages. Overall, perivascular CD163+ cell density was higher in the gray matter (SN) than in the white matter (CP). Compared to CTRL, we found increased density of parenchymal CD163+ cells in the SN of the three psychiatric groups and increased CD163 protein levels in SZ. CD163 protein was positively correlated with density of perivascular CD163+ cells. TH mRNA was reduced in SZ and BD and negatively correlated with parenchymal CD163+ cell density. We provide the first quantitative and molecular evidence of an increase in the density of parenchymal macrophages in the midbrain of major mental illnesses and show that the presence of these macrophages may negatively impact dopaminergic neurons.

Microglia signaling in health and disease - Implications in sex-specific brain development and plasticity

Microglia, the intrinsic neuroimmune cells residing in the central nervous system (CNS), exert a pivotal influence on brain development, homeostasis, and functionality, encompassing critical roles during both aging and pathological states. Recent advancements in comprehending brain plasticity and functions have spotlighted conspicuous variances between male and female brains, notably in neurogenesis, neuronal myelination, axon fasciculation, and synaptogenesis. Nevertheless, the precise impact of microglia on sex-specific brain cell plasticity, sculpting diverse neural network architectures and circuits, remains largely unexplored. This article seeks to unravel the present understanding of microglial involvement in brain development, plasticity, and function, with a specific emphasis on microglial signaling in brain sex polymorphism. Commencing with an overview of microglia in the CNS and their associated signaling cascades, we subsequently probe recent revelations regarding molecular signaling by microglia in sex-dependent brain developmental plasticity, functions, and diseases. Notably, C-X3-C motif chemokine receptor 1 (CX3CR1), triggering receptors expressed on myeloid cells 2 (TREM2), calcium (Ca2+), and apolipoprotein E (APOE) emerge as molecular candidates significantly contributing to sex-dependent brain development and plasticity. In conclusion, we address burgeoning inquiries surrounding microglia's pivotal role in the functional diversity of developing and aging brains, contemplating their potential implications for gender-tailored therapeutic strategies in neurodegenerative diseases.

Inflammaging and Brain Aging

Progress made by the medical community in increasing lifespans comes with the costs of increasing the incidence and prevalence of age-related diseases, neurodegenerative ones included. Aging is associated with a series of morphological changes at the tissue and cellular levels in the brain, as well as impairments in signaling pathways and gene transcription, which lead to synaptic dysfunction and cognitive decline. Although we are not able to pinpoint the exact differences between healthy aging and neurodegeneration, research increasingly highlights the involvement of neuroinflammation and chronic systemic inflammation (inflammaging) in the development of age-associated impairments via a series of pathogenic cascades, triggered by dysfunctions of the circadian clock, gut dysbiosis, immunosenescence, or impaired cholinergic signaling. In addition, gender differences in the susceptibility and course of neurodegeneration that appear to be mediated by glial cells emphasize the need for future research in this area and an individualized therapeutic approach. Although rejuvenation research is still in its very early infancy, accumulated knowledge on the various signaling pathways involved in promoting cellular senescence opens the perspective of interfering with these pathways and preventing or delaying senescence.

HIV-TAT dysregulates microglial lipid metabolism through SREBP2/miR-124 axis: Implication of lipid droplet accumulation microglia in NeuroHIV

Chronic HIV infection can dysregulate lipid/cholesterol metabolism in the peripheral system, contributing to the higher incidences of diabetes and atherosclerosis in HIV (+) individuals. Recently, accumulating evidence indicate that HIV proteins can also dysregulate lipid/cholesterol metabolism in the brain and such dysregulation could be linked with the pathogenesis of HIV-associated neurological disorders (HAND)/NeuroHIV. To further characterize the association between lipid/cholesterol metabolism and HAND, we employed HIV-inducible transactivator of transcription (iTAT) and control mice to compare their brain lipid profiles. Our results reveal that HIV-iTAT mice possess dysregulated lipid profiles and have increased numbers of lipid droplets (LDs) accumulation microglia (LDAM) in the brains. HIV protein TAT can upregulate LDs formation through enhancing the lipid/cholesterol synthesis in vitro. Mechanistically, HIV-TAT increases the expression of sterol regulatory element-binding protein 2 (SREBP2) through microRNA-124 downregulation. Cholesterol synthesis inhibition can block HIV-TAT-mediated NLRP3 inflammasome activation and microglial activation in vitro as well as mitigate aging-related behavioral impairment and memory deficiency in HIV-iTAT mice. Taken together, our results indicate an inherent role of lipid metabolism and LDAM in the pathogenesis of NeuroHIV (immunometabolism). These findings suggest that LDAM reversal through modulating lipid/cholesterol metabolism could be a novel therapeutic target for ameliorating NeuroHIV symptoms in chronic HIV (+) individuals.

FANS Unfixed: Isolation and Proteomic Analysis of Mouse Cell Type-Specific Brain Nuclei

Epigenetic-mediated gene regulation orchestrates brain cell-type gene expression programs, and epigenetic dysregulation is a major driver of aging and disease-associated changes. Proteins that mediate gene regulation are mostly localized to the nucleus; however, nuclear-localized proteins are often underrepresented in gene expression studies and have been understudied in the context of the brain. To address this challenge, we have optimized an approach for nuclei isolation that is compatible with proteomic analysis. This was coupled to a mass spectrometry protocol for detecting proteins in low-concentration samples. We have generated nuclear proteomes for neurons, microglia, and oligodendrocytes from the mouse brain cortex and identified cell-type nuclear proteins associated with chromatin structure and organization, chromatin modifiers such as transcription factors, and RNA-binding proteins, among others. Our nuclear proteomics platform paves the way for assessing brain cell type changes in the nuclear proteome across health and disease, such as neurodevelopmental, aging, neurodegenerative, and neuroinflammatory conditions. Data are available via ProteomeXchange with the identifier PXD053515.

p53 lysine-lactylated modification contributes to lipopolysaccharide-induced proinflammatory activation in BV2 cell under hypoxic conditions

p53 has diversity functions in regulation of transcription, cell proliferation, cancer metastasis, etc. Recent studies have shown that p53 and nuclear factor-κB (NF-κB) co-regulate proinflammatory responses in macrophages. However, the role of p53 lysine lactylation (p53Kla) in mediating proinflammatory phenotypes in microglia under hypoxic conditions remains unclear. In the current study, we investigated the proinflammatory activation exacerbated by hypoxia and the levels of p53Kla in microglial cells. BV2 cells, an immortalized mouse microglia cell line, were divided into control, lipopolysaccharide (LPS)-induced, hypoxia (Hy), and LPS-Hy groups. The protein expression levels of p53 and p53Kla and the activation of microglia were compared among the four groups. Sodium oxamate and mutant p53 plasmids were transfected into BV2 cells to detect the effect of p53Kla on microglial proinflammatory activation. LPS-Hy stimulation significantly upregulated p53Kla levels in both the nucleus and the cytoplasm of BV2 cells. In contrast, the p53 protein levels were downregulated. LPS-Hy stimulation upregulated phosphorylated p65 protein levels in nuclear and activated the NF-κB pathway in BV2 cells, resulting in increased expression of pro-inflammatory cytokines (iNOS, IL6, IL1β, TNFα), enhanced cell viability, and concomitantly, increased cytotoxicity. In conclusion, p53 lysine-lactylated modification contributes to LPS-induced proinflammatory activation in BV2 cells under hypoxia through NF-κB pathway and inhibition of lactate production may alleviate neuroinflammatory injury.

Glial modulation of synapse development and plasticity: oligodendrocyte precursor cells as a new player in the synaptic quintet

Synaptic communication is an important process in the central nervous system that allows for the rapid and spatially specified transfer of signals. Neurons receive various synaptic inputs and generate action potentials required for information transfer, and these inputs can be excitatory or inhibitory, which collectively determines the output. Non-neuronal cells (glial cells) have been identified as crucial participants in influencing neuronal activity and synaptic transmission, with astrocytes forming tripartite synapses and microglia pruning synapses. While it has been known that oligodendrocyte precursor cells (OPCs) receive neuronal inputs, whether they also influence neuronal activity and synaptic transmission has remained unknown for two decades. Recent findings indicate that OPCs, too, modulate neuronal synapses. In this review, we discuss the roles of different glial cell types at synapses, including the recently discovered involvement of OPCs in synaptic transmission and synapse refinement, and discuss overlapping roles played by multiple glial cell types.

Mononuclear Phagocytes, Cellular Immunity, and Nobel Prizes: A Historic Perspective

The mononuclear phagocyte system includes monocytes, macrophages, some dendritic cells, and multinuclear giant cells. These cell populations display marked heterogeneity depending on their differentiation from embryonic and bone marrow hematopoietic progenitors, tissue location, and activation. They contribute to tissue homeostasis by interacting with local and systemic immune and non-immune cells through trophic, clearance, and cytocidal functions. During evolution, they contributed to the innate host defense before effector mechanisms of specific adaptive immunity emerged. Mouse macrophages appear at mid-gestation and are distributed throughout the embryo to facilitate organogenesis and clear cells undergoing programmed cell death. Yolk sac, AGM, and fetal liver-derived tissue-resident macrophages persist throughout postnatal and adult life, supplemented by bone marrow-derived blood monocytes, as required after injury and infection. Nobel awards to Elie Metchnikoff and Paul Ehrlich in 1908 drew attention to cellular phagocytic and humoral immunity, respectively. In 2011, prizes were awarded to Jules Hoffmann and Bruce Beutler for contributions to innate immunity and to Ralph Steinman for the discovery of dendritic cells and their role in antigen presentation to T lymphocytes. We trace milestones in the history of mononuclear phagocyte research from the perspective of Nobel awards bearing directly and indirectly on their role in cellular immunity.

Brain-Engrafted Monocyte-derived Macrophages from Blood and Skull-Bone Marrow Exhibit Distinct Identities from Microglia

Microglia are thought to originate exclusively from primitive macrophage progenitors in the yolk sac (YS) and to persist throughout life without much contribution from definitive hematopoiesis. Here, using lineage tracing, pharmacological manipulation, and RNA-sequencing, we elucidated the presence and characteristics of monocyte-derived macrophages (MDMs) in the brain parenchyma at baseline and during microglia repopulation, and defined the core transcriptional signatures of brain-engrafted MDMs. Lineage tracing mouse models revealed that MDMs transiently express CD206 during brain engraftment as CD206 + microglia precursors in the YS. We found that brain-engrafted MDMs exhibit transcriptional and epigenetic characteristics akin to meningeal macrophages, likely due to environmental imprinting within the meningeal space. Utilizing parabiosis and skull transplantation, we demonstrated that monocytes from both peripheral blood and skull bone marrow can repopulate microglia-depleted brains. Our results reveal the heterogeneous origins and cellular dynamics of brain parenchymal macrophages at baseline and in models of microglia depletion.

Aged-Related Changes in Microglia and Neurodegenerative Diseases: Exploring the Connection

Microglial cells exhibit properties akin to macrophages, thereby enabling them to support and protect the central nervous system environment. Aging induces alterations in microglial polarization, resulting in a shift toward a neurotoxic phenotype characterized by increased expression of pro-inflammatory markers. Dysregulation of microglial cells' regulatory pathways and interactions with neurons contribute to chronic activation and neurodegeneration. A better understanding of the involvement of microglia in neurodegenerative diseases such as Alzheimer's and Parkinson's is a critical topic for studying the role of inflammatory responses in disease progression. Furthermore, the metabolic changes in aged microglia, including the downregulation of oxidative phosphorylation, are discussed in this review. Understanding these mechanisms is crucial for developing better preventive and therapeutic strategies.

Contribution of microglia to the epileptiform activity that results from neonatal hypoxia

Microglia are described as the immune cells of the brain, their immune properties have been extensively studied since first described, however, their neural functions have only been explored over the last decade. Microglia have an important role in maintaining homeostasis in the central nervous system by surveying their surroundings to detect pathogens or damage cells. While these are the classical functions described for microglia, more recently their neural functions have been defined; they are critical to the maturation of neurons during embryonic and postnatal development, phagocytic microglia remove excess synapses during development, a process called synaptic pruning, which is important to overall neural maturation. Furthermore, microglia can respond to neuronal activity and, together with astrocytes, can regulate neural activity, contributing to the equilibrium between excitation and inhibition through a feedback loop. Hypoxia at birth is a serious neurological condition that disrupts normal brain function resulting in seizures and epilepsy later in life. Evidence has shown that microglia may contribute to this hyperexcitability after neonatal hypoxia. This review will summarize the existing data on the role of microglia in the pathogenesis of neonatal hypoxia and the plausible mechanisms that contribute to the development of hyperexcitability after hypoxia in neonates. This article is part of the Special Issue on "Microglia".

Exploring the Significance of Microglial Phenotypes and Morphological Diversity in Neuroinflammation and Neurodegenerative Diseases: From Mechanisms to Potential Therapeutic Targets

Studying various microglial phenotypes and their functions in neurodegenerative diseases is crucial due to the intricate nature of their phenomics and their vital immunological role. Microglia undergo substantial phenomic changes, encompassing morphological, transcriptional, and functional aspects, resulting in distinct cell types with diverse structures, functions, properties, and implications. The traditional classification of microglia as ramified, M1 (proinflammatory), or M2 (anti-inflammatory) phenotypes is overly simplistic, failing to capture the wide range of recently identified microglial phenotypes in various brain regions affected by neurodegenerative diseases. Altered and activated microglial phenotypes deviating from the typical ramified structure are significant features of many neurodegenerative conditions. Understanding the precise role of each microglial phenotype is intricate and sometimes contradictory. This review specifically focuses on elucidating recent modifications in microglial phenotypes within neurodegenerative diseases. Recognizing the heterogeneity of microglial phenotypes in diseased states can unveil novel therapeutic strategies for targeting microglia in neurodegenerative diseases. Moreover, the exploration of the use of healthy isolated microglia to mitigate disease progression has provided an innovative perspective. In conclusion, this review discusses the dynamic landscape of mysterious microglial phenotypes, emphasizing the need for a nuanced understanding to pave the way for innovative therapeutic strategies for neurodegenerative diseases.

Drp1 and neuroinflammation: Deciphering the interplay between mitochondrial dynamics imbalance and inflammation in neurodegenerative diseases

Neuroinflammation and mitochondrial dysfunction are closely intertwined with the pathophysiology of neurological disorders. Recent studies have elucidated profound alterations in mitochondrial dynamics across a spectrum of neurological disorders. Dynamin-related protein 1 (DRP1) emerges as a pivotal regulator of mitochondrial fission, with its dysregulation disrupting mitochondrial homeostasis and fueling neuroinflammation, thereby exacerbating disease severity. In addition to its role in mitochondrial dynamics, DRP1 plays a crucial role in modulating inflammation-related pathways. This review synthesizes important functions of DRP1 in the central nervous system (CNS) and the impact of epigenetic modification on the progression of neurodegenerative diseases. The intricate interplay between neuroinflammation and DRP1 in microglia and astrocytes, central contributors to neuroinflammation, is expounded upon. Furthermore, the use of DRP1 inhibitors to influence the activation of microglia and astrocytes, as well as their involvement in processes such as mitophagy, mitochondrial oxidative stress, and calcium ion transport in CNS-mediated neuroinflammation, is scrutinized. The modulation of microglia to astrocyte crosstalk by DRP1 and its role in inflammatory neurodegeneration is also highlighted. Overall, targeting DRP1 presents a promising avenue for ameliorating neuroinflammation and enhancing the therapeutic management of neurological disorders.

Role of microglia in diabetic neuropathic pain

Approximately one-third of the patients with diabetes worldwide suffer from neuropathic pain, mainly categorized by spontaneous and stimulus-induced pain. Microglia are a class of immune effector cells residing in the central nervous system and play a pivotal role in diabetic neuropathic pain (DNP). Microglia specifically respond to hyperglycemia along with inflammatory cytokines and adenosine triphosphate produced during hyperglycemic damage to nerve fibers. Because of the presence of multiple receptors on the microglial surface, microglia are dynamically and highly responsive to their immediate environment. Following peripheral sensitization caused by hyperglycemia, microglia are affected by the cascade of inflammatory factors and other substances and respond accordingly, resulting in a change in their functional state for DNP pathogenesis. Inhibition of receptors such as P2X reporters, reducing cytokine expression levels in the microglial reactivity mechanisms, and inhibiting their intracellular signaling pathways can effectively alleviate DNP. A variety of drugs attenuate DNP by inhibiting the aforementioned processes induced by microglial reactivity. In this review, we summarize the pathological mechanisms by which microglia promote and maintain DNP, the drugs and therapeutic techniques available, and the latest advances in this field.

Blood-brain barrier alterations and their impact on Parkinson's disease pathogenesis and therapy

There is increasing evidence for blood-brain barrier (BBB) alterations in Parkinson's disease (PD), the second most common neurodegenerative disorder with rapidly rising prevalence. Altered tight junction and transporter protein levels, accumulation of α-synuclein and increase in inflammatory processes lead to extravasation of blood molecules and vessel degeneration. This could result in a self-perpetuating pathophysiology of inflammation and BBB alteration, which contribute to neurodegeneration. Toxin exposure or α-synuclein over-expression in animal models has been shown to initiate similar pathologies, providing a platform to study underlying mechanisms and therapeutic interventions. Here we provide a comprehensive review of the current knowledge on BBB alterations in PD patients and how rodent models that replicate some of these changes can be used to study disease mechanisms. Specific challenges in assessing the BBB in patients and in healthy controls are discussed. Finally, a potential role of BBB alterations in disease pathogenesis and possible implications for therapy are explored. The interference of BBB alterations with current and novel therapeutic strategies requires more attention. Brain region-specific BBB alterations could also open up novel opportunities to target specifically vulnerable neuronal subpopulations.

The Role of the Thalamus in Nociception: Important but Forgotten

Pain is a complex response to noxious stimuli. Upon detection of the nociceptive stimulus by first-order neurons or nociceptors, an action potential ascends to the spinal dorsal horn, a crucial site for synapsing with second-order neurons. These second-order neurons carry the nociceptive stimulus to supraspinal regions, notably the thalamus. Although extensive research has focused on spinal-level nociceptive mechanisms (e.g., neurotransmitters, receptors, and glial cells), the thalamus is still poorly elucidated. The role of the thalamus in relaying sensory and motor responses to the cortex is well known. However, a comprehensive understanding of the mechanisms in the synapse between the second-order and third-order neurons that transmit this impulse to the somatosensory cortex, where the response is processed and interpreted as pain, is still lacking. Thus, this review investigated the thalamus's role in transmitting nociceptive impulses. Current evidence indicates the involvement of the neurotransmitters glutamate and serotonin, along with NMDA, P2X4, TLR4, FGR, and NLRP3 receptors, as well as signaling pathways including ERK, P38, NF-κB, cytokines, and glial cells at nociceptive synapses within the thalamus.

The influence of ferroptosis on the in vitro OGD/R model in rat microglia

OBJECTIVE

We aimed to explore the influence of ferroptosis on an oxygen-glucose deprivation/reoxygenation (OGD/R) model in primary rat microglia.

METHODS

Primary microglia were extracted from rats and cultured in vitro. The cells were subjected to a hypoxic environment for 6 h in a glucose-free medium, and then re-oxygenated for 24 h in DMEM/F12. Rat microglia were pretreated with the ferroptosis activator erastin and the ferroptosis inhibitor ferrostatin 1 for 24 h, followed by detection of cell cycle progression and apoptosis by flow cytometry. Intracellular total iron levels were measured. In addition, the relative levels of reactive oxygen species (ROS), malondialdehyde (MDA), and superoxide dismutase (SOD) were determined using enzyme-linked immunosorbent assay. The protein levels of 15-lox2, GPX4, SLC7A11, ACSL4, and TFR1 were examined by western blotting.

RESULTS

Compared with rat microglia subjected to OGD/R, pretreatment with erastin did not influence cell apoptosis but significantly enhanced total iron levels, MDA, and ROS levels, whereas it reduced SOD levels. Moreover, it upregulated ACSL4, TFR1, and 15-lox2 and downregulated GPX4 and SLC7A11. Pretreatment with ferrostatin 1 significantly inhibited cell apoptosis and cell cycle arrest in the G0/G1 phase. It significantly reduced total iron levels, MDA, and ROS levels and enhanced SOD levels, which also downregulated ACSL4, TFR1, and 15-lox2, and upregulated GPX4 and SLC7A11.

CONCLUSION

Our study showed that inhibition of ferroptosis is favorable against potential OGD/R-induced damage in rat microglia.

Glial cells in the mammalian olfactory bulb

The mammalian olfactory bulb (OB), an essential part of the olfactory system, plays a critical role in odor detection and neural processing. Historically, research has predominantly focused on the neuronal components of the OB, often overlooking the vital contributions of glial cells. Recent advancements, however, underscore the significant roles that glial cells play within this intricate neural structure. This review discus the diverse functions and dynamics of glial cells in the mammalian OB, mainly focused on astrocytes, microglia, oligodendrocytes, olfactory ensheathing cells, and radial glia cells. Each type of glial contributes uniquely to the OB's functionality, influencing everything from synaptic modulation and neuronal survival to immune defense and axonal guidance. The review features their roles in maintaining neural health, their involvement in neurodegenerative diseases, and their potential in therapeutic applications for neuroregeneration. By providing a comprehensive overview of glial cell types, their mechanisms, and interactions within the OB, this article aims to enhance our understanding of the olfactory system's complexity and the pivotal roles glial cells play in both health and disease.

Development of a High-Throughput Pipeline to Characterize Microglia Morphological States at a Single-Cell Resolution

As rapid responders to their environments, microglia engage in functions that are mirrored by their cellular morphology. Microglia are classically thought to exhibit a ramified morphology under homeostatic conditions which switches to an ameboid form during inflammatory conditions. However, microglia display a wide spectrum of morphologies outside of this dichotomy, including rod-like, ramified, ameboid, and hypertrophic states, which have been observed across brain regions, neurodevelopmental timepoints, and various pathological contexts. We applied dimensionality reduction and clustering to consider contributions of multiple morphology measures together to define a spectrum of microglial morphological states in a mouse dataset that we used to demonstrate the utility of our toolset. Using ImageJ, we first developed a semiautomated approach to characterize 27 morphology features from hundreds to thousands of individual microglial cells in a brain region-specific manner. Within this pool of features, we defined distinct sets of highly correlated features that describe different aspects of morphology, including branch length, branching complexity, territory span, and circularity. When considered together, these sets of features drove different morphological clusters. Our tools captured morphological states similarly and robustly when applied to independent datasets and using different immunofluorescent markers for microglia. We have compiled our morphology analysis pipeline into an accessible, easy-to-use, and fully open-source ImageJ macro and R package that the neuroscience community can expand upon and directly apply to their own analyses. Outcomes from this work will supply the field with new tools to systematically evaluate the heterogeneity of microglia morphological states across various experimental models and research questions.

Transgenic Targeting of Fcrls Creates a Highly Efficient Constitutively Active Microglia Cre Line with Differentiated Specificity

Microglia carry out important functions as the resident macrophages of the brain. To study their role in health and disease, the research community needs tools to genetically modify them with maximum completeness in a manner that distinguishes them from closely related cell types, such as monocytes. While currently available tamoxifen-inducible CreERT2 lines can achieve the differentiation from other cells, the field needs improved and publicly available constitutively active Cre lines, especially ones with favorable efficiency and specificity profiles for studies where high recombination efficiency is imperative and where tamoxifen administration is contraindicated. Here, we leverage the microglia-specific Fcrls gene to generate mice expressing Cre. Using genomic methods, we show correct positioning of the transgene and intact microglia homeostasis in Fcrls-2A-Cre mice. Crossing Fcrls-2A-Cre mice to four different reporters, we demonstrate highly efficient recombination in microglia across differentially sensitive loxP alleles in different genomic contexts, indicating robust applicability of the line. Further, we show that microglia recombine a loxP reporter during early embryonic development, supporting the use of the line for developmental studies. Finally, using immunofluorescence and flow cytometry, we reveal that most border-associated macrophages are also targeted whereas only few liver and spleen macrophages and virtually no white blood cell subsets exhibit Cre activity, distinguishing this line from another publicly available Cre line, Cx3cr1-CreM Fcrls-2A-Cre mice are immediately available (JAX #036591) and serve as a valuable addition to the community's microglia toolbox by providing highly efficient constitutive Cre activity with excellent specificity, particularly for studies where tamoxifen administration is undesirable.

Intrinsic organization of the corpus callosum

The corpus callosum-the largest commissural fiber system connecting the two cerebral hemispheres-is considered essential for bilateral sensory integration and higher cognitive functions. Most studies exploring the corpus callosum have examined either the anatomical, physiological, and neurochemical organization of callosal projections or the functional and/or behavioral aspects of the callosal connections after complete/partial callosotomy or callosal lesion. There are no works that address the intrinsic organization of the corpus callosum. We review the existing information on the activities that take place in the commissure in three sections: I) the topographical and neurochemical organization of the intracallosal fibers, II) the role of glia in the corpus callosum, and III) the role of the intracallosal neurons.

Contrasting Disease Progression, Microglia Reactivity, Tolerance, and Resistance to Toxoplasma gondii Infection in Two Mouse Strains

Our study investigated the innate immune response to Toxoplasma gondii infection by assessing microglial phenotypic changes and sickness behavior as inflammatory response markers post-ocular tachyzoite instillation. Disease progression in Swiss albino mice was compared with the previously documented outcomes in BALB/c mice using an identical ocular route and parasite burden (2 × 105 tachyzoites), with saline as the control. Contrary to expectations, the Swiss albino mice displayed rapid, lethal disease progression, marked by pronounced sickness behaviors and mortality within 11-12 days post-infection, while the survivors exhibited no apparent signs of infection. Comparative analysis revealed the T. gondii-infected BALB/c mice exhibited reduced avoidance of feline odors, while the infected Swiss albino mice showed enhanced avoidance responses. There was an important increase in microglial cells in the dentate gyrus molecular layer of the infected Swiss albino mice compared to the BALB/c mice and their respective controls. Hierarchical cluster and discriminant analyses identified three microglial morphological clusters, differentially affected by T. gondii infection across strains. The BALB/c mice exhibited increased microglial branching and complexity, while the Swiss albino mice showed reduced shrunken microglial arbors, diminishing their morphological complexity. These findings highlight strain-specific differences in disease progression and inflammatory regulation, indicating lineage-specific mechanisms in inflammatory responses, tolerance, and resistance. Understanding these elements is critical in devising control measures for toxoplasmosis.

Adult microglial TGFβ1 is required for microglia homeostasis via an autocrine mechanism to maintain cognitive function in mice

While TGF-β signaling is essential for microglial function, the cellular source of TGF-β1 ligand and its spatial regulation remains unclear in the adult CNS. Our data supports that microglia but not astrocytes or neurons are the primary producers of TGF-β1 ligands needed for microglial homeostasis. Microglia-Tgfb1 KO leads to the activation of microglia featuring a dyshomeostatic transcriptome that resembles disease-associated, injury-associated, and aged microglia, suggesting microglial self-produced TGF-β1 ligands are important in the adult CNS. Astrocytes in MG-Tgfb1 inducible (i)KO mice show a transcriptome profile that is closely aligned with an LPS-associated astrocyte profile. Additionally, using sparse mosaic single-cell microglia KO of TGF-β1 ligand we established an autocrine mechanism for signaling. Here we show that MG-Tgfb1 iKO mice present cognitive deficits, supporting that precise spatial regulation of TGF-β1 ligand derived from microglia is required for the maintenance of brain homeostasis and normal cognitive function in the adult brain.

Mis-localization of endogenous TDP-43 leads to ALS-like early-stage metabolic dysfunction and progressive motor deficits

BACKGROUND

The key pathological signature of ALS/ FTLD is the mis-localization of endogenous TDP-43 from the nucleus to the cytoplasm. However, TDP-43 gain of function in the cytoplasm is still poorly understood since TDP-43 animal models recapitulating mis-localization of endogenous TDP-43 from the nucleus to the cytoplasm are missing.

METHODS

CRISPR/Cas9 technology was used to generate a zebrafish line (called CytoTDP), that mis-locates endogenous TDP-43 from the nucleus to the cytoplasm. Phenotypic characterization of motor neurons and the neuromuscular junction was performed by immunostaining, microglia were immunohistochemically localized by whole-mount tissue clearing and muscle ultrastructure was analyzed by scanning electron microscopy. Behavior was investigated by video tracking and quantitative analysis of swimming parameters. RNA sequencing was used to identify mis-regulated pathways with validation by molecular analysis.

RESULTS

CytoTDP fish have early larval phenotypes resembling clinical features of ALS such as progressive motor defects, neurodegeneration and muscle atrophy. Taking advantage of zebrafish's embryonic development that solely relys on yolk usage until 5 days post fertilization, we demonstrated that microglia proliferation and activation in the hypothalamus is independent from food intake. By comparing CytoTDP to a previously generated TDP-43 knockout line, transcriptomic analyses revealed that mis-localization of endogenous TDP-43, rather than TDP-43 nuclear loss of function, leads to early onset metabolic dysfunction.

CONCLUSIONS

The new TDP-43 model mimics the ALS/FTLD hallmark of progressive motor dysfunction. Our results suggest that functional deficits of the hypothalamus, the metabolic regulatory center, might be the primary cause of weight loss in ALS patients. Cytoplasmic gain of function of endogenous TDP-43 leads to metabolic dysfunction in vivo that are reminiscent of early ALS clinical non-motor metabolic alterations. Thus, the CytoTDP zebrafish model offers a unique opportunity to identify mis-regulated targets for therapeutic intervention early in disease progression.

Quantitative susceptibility mapping in the brain reflects spatial expression of genes involved in iron homeostasis and myelination

Quantitative susceptibility mapping (QSM) is an MRI modality used to non-invasively measure iron content in the brain. Iron exhibits a specific anatomically varying pattern of accumulation in the brain across individuals. The highest regions of accumulation are the deep grey nuclei, where iron is stored in paramagnetic molecule ferritin. This form of iron is considered to be what largely contributes to the signal measured by QSM in the deep grey nuclei. It is also known that QSM is affected by diamagnetic myelin contents. Here, we investigate spatial gene expression of iron and myelin related genes, as measured by the Allen Human Brain Atlas, in relation to QSM images of age-matched subjects. We performed multiple linear regressions between gene expression and the average QSM signal within 34 distinct deep grey nuclei regions. Our results show a positive correlation (p < .05, corrected) between expression of ferritin and the QSM signal in deep grey nuclei regions. We repeated the analysis for other genes that encode proteins thought to be involved in the transport and storage of iron in the brain, as well as myelination. In addition to ferritin, our findings demonstrate a positive correlation (p < .05, corrected) between the expression of ferroportin, transferrin, divalent metal transporter 1, several gene markers of myelinating oligodendrocytes, and the QSM signal in deep grey nuclei regions. Our results suggest that the QSM signal reflects both the storage and active transport of iron in the deep grey nuclei regions of the brain.

Role of microglia in stress-induced alcohol intake in female and male mice

Rates of alcohol use disorder (AUD) have escalated in recent years, with a particular increase among women. Women are more susceptible to stress-induced alcohol drinking, and preclinical data suggest that stress can increase alcohol intake in female rodents; however, a comprehensive understanding of sex-specific neurobiological substrates underlying this phenomenon is still emerging. Microglia, the resident macrophages of the brain, are essential for reshaping neuronal processes, and microglial activity contributes to overall neuronal plasticity. We investigated microglial dynamics and morphology in limbic brain structures of male and female mice following exposure to stress, alcohol or both challenges. In a modified paradigm of intermittent binge drinking (repeated "drinking in the dark"), we determined that female, but not male, mice increased their alcohol consumption after exposure to a physical stressor and re-exposure trials in the stress-paired context. Ethanol (EtOH) drinking and stress altered a number of microglial parameters, including overall number, in subregions of the amygdala and hippocampus, with effects that were somewhat more pronounced in female mice. We used the CSF1R antagonist PLX3397 to deplete microglia in female mice to determine whether microglia contribute to stress-induced escalation of EtOH intake. We observed that microglial depletion attenuated stress-induced alcohol intake with no effect in the unstressed group. These findings suggest that microglial activity can contribute to alcohol intake under stressful conditions, and highlight the importance of evaluating sex-specific mechanisms that could result in tailored interventions for AUD in women.

An overview on microglial origin, distribution, and phenotype in Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease that is responsible for about one-third of dementia cases worldwide. It is believed that AD is initiated with the deposition of Ab plaques in the brain. Genetic studies have shown that a high number of AD risk genes are expressed by microglia, the resident macrophages of brain. Common mode of action by microglia cells is neuroinflammation and phagocytosis. Moreover, it has been discovered that inflammatory marker levels are increased in AD patients. Recent studies advocate that neuroinflammation plays a major role in AD progression. Microglia have different activation profiles depending on the region of brain and stimuli. In different activation, profile microglia can generate either pro-inflammatory or anti-inflammatory responses. Microglia defend brain cells from pathogens and respond to injuries; also, microglia can lead to neuronal death along the way. In this review, we will bring the different roles played by microglia and microglia-related genes in the progression of AD.

The dichotomous activities of microglia: A potential driver for phenotypic heterogeneity in Alzheimer's disease

Alzheimer's disease (AD) is a leading cause of dementia, characterized by two defining neuropathological hallmarks: amyloid plaques composed of Aβ aggregates and neurofibrillary pathology. Recent research suggests that microglia have both beneficial and detrimental effects in the development of AD. A new theory proposes that microglia play a beneficial role in the early stages of the disease but become harmful in later stages. Further investigations are needed to gain a comprehensive understanding of this shift in microglia's function. This transition is likely influenced by specific conditions, including spatial, temporal, and transcriptional factors, which ultimately lead to the deterioration of microglial functionality. Additionally, recent studies have also highlighted the potential influence of microglia diversity on the various manifestations of AD. By deciphering the multiple states of microglia and the phenotypic heterogeneity in AD, significant progress can be made towards personalized medicine and better treatment outcomes for individuals affected by AD.

Neuronal deletion of Gtf2i results in developmental microglial alterations in a mouse model related to Williams syndrome

Williams syndrome (WS) is a genetic neurodevelopmental disorder caused by a heterozygous microdeletion, characterized by hypersociability and unique neurocognitive abnormalities. Of the deleted genes, GTF2I has been linked to hypersociability in WS. We have recently shown that Gtf2i deletion from forebrain excitatory neurons, referred to as Gtf2i conditional knockout (cKO) mice leads to multi-faceted myelination deficits associated with the social behaviors affected in WS. These deficits were potentially mediated also by microglia, as they present a close relationship with oligodendrocytes. To study the impact of altered myelination, we characterized these mice in terms of microglia over the course of development. In postnatal day 30 (P30) Gtf2i cKO mice, cortical microglia displayed a more ramified state, as compared with wild type (controls). However, postnatal day 4 (P4) microglia exhibited high proliferation rates and an elevated activation state, demonstrating altered properties related to activation and inflammation in Gtf2i cKO mice compared with control. Intriguingly, P4 Gtf2i cKO-derived microglial cells exhibited significantly elevated myelin phagocytosis in vitro compared to control mice. Lastly, systemic injection of clemastine to P4 Gtf2i cKO and control mice until P30, led to a significant interaction between genotypes and treatments on the expression levels of the phagocytic marker CD68, and a significant reduction of the macrophage/microglial marker Iba1 transcript levels in the cortex of the Gtf2i cKO treated mice. Our data thus implicate microglia as important players in WS, and that early postnatal manipulation of microglia might be beneficial in treating inflammatory and myelin-related pathologies.

The molecular determinants of microglial developmental dynamics

Microglia constitute the largest population of parenchymal macrophages in the brain and are considered a unique subset of central nervous system glial cells owing to their extra-embryonic origins in the yolk sac. During development, microglial progenitors readily proliferate and eventually colonize the entire brain. In this Review, we highlight the origins of microglial progenitors and their entry routes into the brain and discuss the various molecular and non-molecular determinants of their fate, which may inform their specific functions. Specifically, we explore recently identified mechanisms that regulate microglial colonization of the brain, including the availability of space, and describe how the expansion of highly proliferative microglial progenitors facilitates the occupation of the microglial niche. Finally, we shed light on the factors involved in establishing microglial identity in the brain.

The contribution of the meningeal immune interface to neuroinflammation in traumatic brain injury

Traumatic brain injury (TBI) is a major cause of disability and mortality worldwide, particularly among the elderly, yet our mechanistic understanding of what renders the post-traumatic brain vulnerable to poor outcomes, and susceptible to neurological disease, is incomplete. It is well established that dysregulated and sustained immune responses elicit negative consequences after TBI; however, our understanding of the neuroimmune interface that facilitates crosstalk between central and peripheral immune reservoirs is in its infancy. The meninges serve as the interface between the brain and the immune system, facilitating important bi-directional roles in both healthy and disease settings. It has been previously shown that disruption of this system exacerbates neuroinflammation in age-related neurodegenerative disorders such as Alzheimer's disease; however, we have an incomplete understanding of how the meningeal compartment influences immune responses after TBI. In this manuscript, we will offer a detailed overview of the holistic nature of neuroinflammatory responses in TBI, including hallmark features observed across clinical and animal models. We will highlight the structure and function of the meningeal lymphatic system, including its role in immuno-surveillance and immune responses within the meninges and the brain. We will provide a comprehensive update on our current knowledge of meningeal-derived responses across the spectrum of TBI, and identify new avenues for neuroimmune modulation within the neurotrauma field.

Additive aluminum as a cause of induced immunoexcitoxicity resulting in neurodevelopmental and neurodegenerative disorders: A biochemical, pathophysiological, and pharmacological analysis

Much has been learned about the neurotoxicity of aluminum over the past several decades in terms of its ability to disrupt cellular function, result in slow accumulation, and the difficulty of its removal from cells. Newer evidence suggests a central pathophysiological mechanism may be responsible for much of the toxicity of aluminum and aluminofluoride compounds on the brain and spinal cord. This mechanism involves activation of the brain's innate immune system, primarily the microglia, astrocytes, and macrophages, with a release of neurotoxic concentrations of excitotoxins and proinflammatory cytokines, chemokines, and immune mediators. Many studies suggest that excitotoxicity plays a significant role in the neurotoxic action of several metals, including aluminum. Recently, researchers have found that while most of the chronic pathology involved in the observed neurodegenerative effects of these metals are secondary to prolonged inflammation, it is the enhancement of excitotoxicity by the immune mediators that are responsible for most of the metal's toxicity. This enhancement occurs through a crosstalk between cytokines and glutamate-related mechanisms. The author coined the name immunoexcitotoxicity to describe this process. This paper reviews the evidence linking immunoexcitotoxicity to aluminum's neurotoxic effects and that a slow accumulation of aluminum may be the cause of neurodevelopmental defects as well as neurodegeneration in the adult.

Microglia in Ischemic Stroke: Pathogenesis Insights and Therapeutic Challenges

Ischemic stroke is the most common type of stroke, which is the main cause of death and disability on a global scale. As the primary immune cells in the brain that are crucial for preserving homeostasis of the central nervous system microenvironment, microglia have been found to exhibit dual or even multiple effects at different stages of ischemic stroke. The anti-inflammatory polarization of microglia and release of neurotrophic factors may provide benefits by promoting neurological recovery at the lesion in the early phase after ischemic stroke. However, the pro-inflammatory polarization of microglia and secretion of inflammatory factors in the later phase of injury may exacerbate the ischemic lesion, suggesting the therapeutic potential of modulating the balance of microglial polarization to predispose them to anti-inflammatory transformation in ischemic stroke. Microglia-mediated signaling crosstalk with other cells may also be key to improving functional outcomes following ischemic stroke. Thus, this review provides an overview of microglial functions and responses under physiological and ischemic stroke conditions, including microglial activation, polarization, and interactions with other cells. We focus on approaches that promote anti-inflammatory polarization of microglia, inhibit microglial activation, and enhance beneficial cell-to-cell interactions. These targets may hold promise for the creation of innovative therapeutic strategies.

Stress, pain, anxiety, and depression in endometriosis-Targeting glial activation and inflammation

Endometriosis (EM) is a gynecological inflammatory disease often accompanied by stress, chronic pelvic pain (CPP), anxiety, and depression, leading to a diminished quality of life. This review aims to discuss the relationship between systemic and local inflammatory responses in the central nervous system (CNS), focusing on glial dysfunctions (astrocytes and microglia) as in critical brain regions involved in emotion, cognition, pain processing, anxiety, and depression. The review presents that EM is connected to increased levels of pro-inflammatory cytokines in the circulation. Additionally, chronic stress and CPP as stressors may contribute to the dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, depleting the production of inflammatory mediators in the circulatory system and the brain. The systemic cytokines cause blood-brain barrier (BBB) breakdown, activate microglia in the brain, and lead to neuroinflammation. Furthermore, CPP may induce neuronal morphological alterations in critical regions through central sensitization and the activation of glial cells. The activation of glial cells, particularly the polarization of microglia, leads to the activation of the NLRP3 inflammasome and the overproduction of inflammatory cytokines. These inflammatory cytokines interact with the signaling pathways involved in neural plasticity. Additionally, persistent inflammatory conditions in the brain lead to neuronal death, which is correlated with a reduced volume of key brain regions such as the hippocampus. This review highlights the involvement of glial cells in the pathogenesis of the mental comorbidities of EM (i.e., pain, anxiety, and depression) and to discuss potential therapeutic approaches for targeting the inflammation and activation of microglia in key brain regions.

Glycometabolic Reprogramming of Microglia in Neurodegenerative Diseases: Insights from Neuroinflammation

Neurodegenerative diseases (ND) are conditions defined by progressive deterioration of the structure and function of the nervous system. Some major examples include Alzheimer's disease (AD), Parkinson's disease (PD), and Amyotrophic lateral sclerosis (ALS). These diseases lead to various dysfunctions, like impaired cognition, memory, and movement. Chronic neuroinflammation may underlie numerous neurodegenerative disorders. Microglia, an important immunocell in the brain, plays a vital role in defending against neuroinflammation. When exposed to different stimuli, microglia are activated and assume different phenotypes, participating in immune regulation of the nervous system and maintaining tissue homeostasis. The immunological activity of activated microglia is affected by glucose metabolic alterations. However, in the context of chronic neuroinflammation, specific alterations of microglial glucose metabolism and their mechanisms of action remain unclear. Thus, in this paper, we review the glycometabolic reprogramming of microglia in ND. The key molecular targets and main metabolic pathways are the focus of this research. Additionally, this study explores the mechanisms underlying microglial glucose metabolism reprogramming in ND and offers an analysis of the most recent therapeutic advancements. The ultimate aim is to provide insights into the development of potential treatments for ND.

CD22 blockade aggravates EAE and its role in microglia polarization

AIMS

Multiple sclerosis (MS) is a neuroinflammatory demyelinating disease. Microglia are reportedly involved in the pathogenesis of MS. However, the key molecules that control the inflammatory activity of microglia in MS have not been identified.

METHODS

Experimental autoimmune encephalomyelitis (EAE) mice were randomized into CD22 blockade and control groups. The expression levels of microglial CD22 were measured by flow cytometry, qRT-PCR, and immunofluorescence. The effects of CD22 blockade were examined via in vitro and in vivo studies.

RESULTS

We detected increased expression of microglial CD22 in EAE mice. In addition, an in vitro study revealed that lipopolysaccharide upregulated the expression of CD22 in microglia and that CD22 blockade modulated microglial polarization. Moreover, an in vivo study demonstrated that CD22 blockade aggravated EAE in mice and promoted microglial M1 polarization.

CONCLUSION

Collectively, our study indicates that CD22 may be protective against EAE and may play a critical role in the maintenance of immune homeostasis in EAE mice.

Sex matters: The MouseX DW-ALLEN Atlas for mice diffusion-weighted MR imaging

Overcoming sex bias in preclinical research requires not only including animals of both sexes in the experiments, but also developing proper tools to handle such data. Recent work revealed sensitivity of diffusion-weighted MRI to glia morphological changes in response to inflammatory stimuli, opening up exciting possibilities to characterize inflammation in a variety of preclinical models of pathologies, the great majority of them available in mice. However, there are limited resources dedicated to mouse imaging, like those required for the data processing and analysis. To fill this gap, we build a mouse MRI template of both structural and diffusion contrasts, with anatomical annotation according to the Allen Mouse Brain Atlas, the most detailed public resource for mouse brain investigation. To achieve a standardized resource, we use a large cohort of animals in vivo, and include animals of both sexes. To prove the utility of this resource to integrate imaging and molecular data, we demonstrate significant association between the mean diffusivity from MRI and gene expression-based glia density. To demonstrate the need of equitable sex representation, we compared across sexes the warp fields needed to match a male-based template, and our template built with both sexes. Then, we use both templates for analysing mice imaging data obtained in animals of different ages, demonstrating that using a male-based template creates spurious significant sex effects, not present otherwise. All in all, our MouseX DW-ALLEN Atlas will be a widely useful resource getting us one step closer to equitable healthcare.

Unraveling the enigma: housekeeping gene Ugt1a7c as a universal biomarker for microglia

Background

Microglia, brain resident macrophages, play multiple roles in maintaining homeostasis, including immunity, surveillance, and protecting the central nervous system through their distinct activation processes. Identifying all types of microglia-driven populations is crucial due to the presence of various phenotypes that differ based on developmental stages or activation states. During embryonic development, the E8.5 yolk sac contains erythromyeloid progenitors that go through different growth phases, eventually resulting in the formation of microglia. In addition, microglia are present in neurological diseases as a diverse population. So far, no individual biomarker for microglia has been discovered that can accurately identify and monitor their development and attributes.

Summary

Here, we highlight the newly defined biomarker of mouse microglia, UGT1A7C, which exhibits superior stability in expression during microglia development and activation compared to other known microglia biomarkers. The UGT1A7C sensing chemical probe labels all microglia in the 3xTG AD mouse model. The expression of Ugt1a7c is stable during development, with only a 4-fold variation, while other microglia biomarkers, such as Csf1r and Cx3cr1, exhibit at least a 10-fold difference. The UGT1A7C expression remains constant throughout its lifespan. In addition, the expression and activity of UGT1A7C are the same in response to different types of inflammatory activators' treatment in vitro.

Conclusion

We propose employing UGT1A7C as the representative biomarker for microglia, irrespective of their developmental state, age, or activation status. Using UGT1A7C can reduce the requirement for using multiple biomarkers, enhance the precision of microglia analysis, and even be utilized as a standard for gene/protein expression.

Disease and brain region specific immune response profiles in neurodegenerative diseases with pure and mixed protein pathologies

The disease-specific accumulation of pathological proteins has long been the major focus of research in neurodegenerative diseases (ND), including Alzheimer's disease (AD) and related dementias (RD), but the recent identification of a multitude of genetic risk factors for ND in immune-associated genes highlights the importance of immune processes in disease pathogenesis and progression. Studies in animal models have characterized the local immune response to disease-specific proteins in AD and ADRD, but due to the complexity of disease processes and the co-existence of multiple protein pathologies in human donor brains, the precise role of immune processes in ND is far from understood. To better characterize the interplay between different extracellular and intracellular protein pathologies and the brain's intrinsic immune system in ND, we set out to comprehensively profile the local immune response in postmortem brain samples of individuals with "pure" beta-Amyloid and tau pathology (AD), "pure" α-Synuclein pathology in Lewy body diseases (LBD), as well as cases with Alzheimer's disease neuropathological changes (ADNC) and Lewy body pathology (MIX). Combining immunohistochemical profiling of microglia and digital image analysis, along with deep immunophenotyping using gene expression profiling on the NanoString nCounter® platform and digital spatial profiling on the NanoString GeoMx® platform we identified a robust immune activation signature in AD brain samples. This signature is maintained in persons with mixed pathologies, irrespective of co-existence of AD pathology and Lewy body (LB) pathology, while LBD brain samples with "pure" LB pathology exhibit an attenuated and distinct immune signature. Our studies highlight disease- and brain region-specific immune response profiles to intracellular and extracellular protein pathologies and further underscore the complexity of neuroimmune interactions in ND.

Magnesium-lithium thin films for neurological applications-An in vitro investigation of glial cytocompatibility and neuroinflammatory response

Lithium (Li), a widely used drug for bipolar disorder management, is associated with many side effects due to systemic exposure. The localized delivery of lithium through implants could be an approach to overcome this challenge, for which biodegradable magnesium (Mg)-based materials are a promising choice. In this study, we focus on Mg-Li thin film alloys as potential Li-releasing implants. Therefore, we investigated the in vitro short-term corrosion behavior and cytocompatibility of two alloys, Mg-1.6wt%Li and Mg-9.5wt%Li. As glial cells are the key players of foreign body responses to implants, we used human glial cell lines for cytocompatibility studies, and a murine brain slice model for a more holistic view at the neuroinflammatory response. We found that Mg-1.6wt%Li corrodes approximately six times slower than Mg-9.5wt%Li. Microscopic analysis showed that the material surface (Mg-1.6wt%Li) is suitable for cell adhesion. The cytocompatibility test with Mg-1.6wt%Li and Mg-9.5wt%Li alloy extracts revealed that both cell types proliferated well up to 10 mM Mg concentration, irrespective of the Li concentration. In the murine brain slice model, Mg-1.6wt%Li and Mg-9.5wt%Li alloy extracts did not provoke a significant upregulation of glial inflammatory/ reactivity markers (IL-1β, IL-6, FN1, TNC) after 24 h of exposure. Furthermore, the gene expression of IL-1β (up to 3-fold) and IL-6 (up to 16-fold) were significantly downregulated after 96 h, and IL-6 downregulation showed a Li concentration dependency. Together, these results indicate the acute cytocompatibility of two Mg-Li thin film alloys and provide basis for future studies to explore promising applications of the material. STATEMENT OF SIGNIFICANCE: We propose the idea of lithium delivery to the brain via biodegradable implants to reduce systemic side effects of lithium for bipolar disorder therapy and other neurological applications. This is the first in vitro study investigating Mg-xLi thin film degradation under physiological conditions and its influence on cellular responses such as proliferation, viability, morphology and inflammation. Utilizing human brain-derived cell lines, we showed that the material surface of such a thin film alloy is suitable for normal cell attachment. Using murine brain slices, which comprise a multicellular network, we demonstrated that the material extracts did not elicit a pro-inflammatory response. These results substantiate that degradable Mg-Li materials are biocompatible and support the further investigation of their potential as neurological implants.

Border-associated macrophages in the central nervous system

Tissue-resident macrophages play an important role in the local maintenance of homeostasis and immune surveillance. In the central nervous system (CNS), brain macrophages are anatomically divided into parenchymal microglia and non-parenchymal border-associated macrophages (BAMs). Among these immune cell populations, microglia have been well-studied for their roles during development as well as in health and disease. BAMs, mostly located in the choroid plexus, meningeal and perivascular spaces, are now gaining increased attention due to advancements in multi-omics technologies and genetic methodologies. Research on BAMs over the past decade has focused on their ontogeny, immunophenotypes, involvement in various CNS diseases, and potential as therapeutic targets. Unlike microglia, BAMs display mixed origins and distinct self-renewal capacity. BAMs are believed to regulate neuroimmune responses associated with brain barriers and contribute to immune-mediated neuropathology. Notably, BAMs have been observed to function in diverse cerebral pathologies, including Alzheimer's disease, Parkinson's disease, multiple sclerosis, ischemic stroke, and gliomas. The elucidation of the heterogeneity and diverse functions of BAMs during homeostasis and neuroinflammation is mesmerizing, since it may shed light on the precision medicine that emphasizes deep insights into programming cues in the unique brain immune microenvironment. In this review, we delve into the latest findings on BAMs, covering aspects like their origins, self-renewal capacity, adaptability, and implications in different brain disorders.

Investigation of Antibody Pharmacokinetics in the Brain Following Intra-CNS Administration and Development of PBPK Model to Characterize the Data

Despite the promising potential of direct central nervous system (CNS) antibody administration to enhance brain exposure, there remains a significant gap in understanding the disposition of antibodies following different intra-CNS injection routes. To bridge this knowledge gap, this study quantitatively investigated the brain pharmacokinetics (PK) of antibodies following intra-CNS administration. The microdialysis samples from the striatum (ST), cerebrospinal fluid (CSF) samples through cisterna magna (CM) puncture, plasma, and brain homogenate samples were collected to characterize the pharmacokinetics (PK) profiles of a non-targeting antibody, trastuzumab, following intracerebroventricular (ICV), intracisternal (ICM), and intrastriatal (IST) administration. For a comprehensive analysis, these intra-CNS injection datasets were juxtaposed against our previously acquired intravenous (IV) injection data obtained under analogous experimental conditions. Our findings highlighted that direct CSF injections, either through ICV or ICM, resulted in ~ 5-6-fold higher interstitial fluid (ISF) drug exposure than IV administration. Additionally, the low bioavailability observed following IST administration indicates the existence of a local degradation process for antibody elimination in the brain ISF along with the ISF bulk flow. The study further refined a physiologically based pharmacokinetic (PBPK) model based on new observations by adding the perivascular compartments, oscillated CSF flow, and the nonspecific uptake and degradation of antibodies by brain parenchymal cells. The updated model can well characterize the antibody PK following systemic and intra-CNS administration. Thus, our research offers quantitative insight into antibody brain disposition pathways and paves the way for determining optimal dosing and administration strategies for antibodies targeting CNS disorders.

Role of pyroptosis in the pathogenesis of various neurological diseases

Pyroptosis, an inflammatory programmed cell death process, has recently garnered significant attention due to its pivotal role in various neurological diseases. This review delves into the intricate molecular signaling pathways governing pyroptosis, encompassing both caspase-1 dependent and caspase-1 independent routes, while emphasizing the critical role played by the inflammasome machinery in initiating cell death. Notably, we explore the Nucleotide-binding domain leucine-rich repeat (NLR) containing protein family, the Absent in melanoma 2-like receptor family, and the Pyrin receptor family as essential activators of pyroptosis. Additionally, we comprehensively examine the Gasdermin family, renowned for their role as executioner proteins in pyroptosis. Central to our review is the interplay between pyroptosis and various central nervous system (CNS) cell types, including astrocytes, microglia, neurons, and the blood-brain barrier (BBB). Pyroptosis emerges as a significant factor in the pathophysiology of each cell type, highlighting its far-reaching impact on neurological diseases. This review also thoroughly addresses the involvement of pyroptosis in specific neurological conditions, such as HIV infection, drug abuse-mediated pathologies, Alzheimer's disease, and Parkinson's disease. These discussions illuminate the intricate connections between pyroptosis, chronic inflammation, and cell death in the development of these disorders. We also conducted a comparative analysis, contrasting pyroptosis with other cell death mechanisms, thereby shedding light on their unique aspects. This approach helps clarify the distinct contributions of pyroptosis to neuroinflammatory processes. In conclusion, this review offers a comprehensive exploration of the role of pyroptosis in various neurological diseases, emphasizing its multifaceted molecular mechanisms within various CNS cell types. By elucidating the link between pyroptosis and chronic inflammation in the context of neurodegenerative disorders and infections, it provides valuable insights into potential therapeutic targets for mitigating these conditions.

Differential effects of sleep deprivation on behavior and microglia in a brain-region-specific manner in young and aged male mice

Microglia, resident immune cells in the central nervous system, constantly monitor the state of the surrounding brain activity. The animal model induced by sleep deprivation (SD) is widely used to study the pathophysiological mechanisms of insomnia and bipolar disorder. However, it remains unclear whether SD affects behaviors in young and aged male mice and microglia in various brain regions. In this study, we confirmed brain region-specific changes in microglial density and morphology in the accumbens nucleus (Acb), amygdala (AMY), cerebellum (Cb), corpus callosum (cc), caudate putamen, hippocampus (HIP), hypothalamus (HYP), medial prefrontal cortex (mPFC), and thalamus (TH) of young mice. In addition, the density of microglia in old mice was higher than that in young mice. Compared with young mice, old mice showed a markedly increased microglial size, decreased total length of microglial processes, and decreased maximum length. Importantly, we found that 48-h SD decreased microglial density and morphology in old mice, whereas SD increased microglial density and morphology in most observed brain regions in young mice. SD-induced hyperactivity was observed only in young mice but not in old mice. Moreover, microglial density (HIP, AMY, mPFC, CPu) was significantly positively correlated with behaviors in SD- and vehicle-treated young mice. Contrarily, negative correlations were shown between the microglial density (cc, Cb, TH, HYP, Acb, AMY) and behaviors in vehicle-treated young and old mice. These results suggest that SD dysregulates the homeostatic state of microglia in a region- and age-dependent manner. Microglia may be involved in regulating age-related behavioral responses to SD.

The role of microglia heterogeneity in synaptic plasticity and brain disorders: Will sequencing shed light on the discovery of new therapeutic targets?

Microglia play a crucial role in interacting with neuronal synapses and modulating synaptic plasticity. This function is particularly significant during postnatal development, as microglia are responsible for removing excessive synapses to prevent neurodevelopmental deficits. Dysregulation of microglial synaptic function has been well-documented in various pathological conditions, notably Alzheimer's disease and multiple sclerosis. The recent application of RNA sequencing has provided a powerful and unbiased means to decipher spatial and temporal microglial heterogeneity. By identifying microglia with varying gene expression profiles, researchers have defined multiple subgroups of microglia associated with specific pathological states, including disease-associated microglia, interferon-responsive microglia, proliferating microglia, and inflamed microglia in multiple sclerosis, among others. However, the functional roles of these distinct subgroups remain inadequately characterized. This review aims to refine our current understanding of the potential roles of heterogeneous microglia in regulating synaptic plasticity and their implications for various brain disorders, drawing from recent sequencing research and functional studies. This knowledge may aid in the identification of pathogenetic biomarkers and potential factors contributing to pathogenesis, shedding new light on the discovery of novel drug targets. The field of sequencing-based data mining is evolving toward a multi-omics approach. With advances in viral tools for precise microglial regulation and the development of brain organoid models, we are poised to elucidate the functional roles of microglial subgroups detected through sequencing analysis, ultimately identifying valuable therapeutic targets.

Microglial reactivity in brainstem chemosensory nuclei in response to hypercapnia

Microglia, the resident immune cells of the CNS, surveil, detect, and respond to various extracellular signals. Depending on the nature of these signals, an integrative microglial response can be triggered, resulting in a phenotypic transformation. Here, we evaluate whether hypercapnia modifies microglia phenotype in brainstem respiratory-related nuclei. Adult C57BL/6 inbred mice were exposed to 10% CO2 enriched air (hypercapnia), or pure air (control), for 10 or 30 min and immediately processed for immunohistochemistry to detect the ubiquitous microglia marker, ionized calcium binding adaptor molecule 1 (Iba1). Hypercapnia for thirty, but not 10 min reduced the Iba1 labeling percent coverage in the ventral respiratory column (VRC), raphe nucleus (RN), and nucleus tractus solitarius (NTS) and the number of primary branches in VRC. The morphological changes persisted, at least, for 60 min breathing air after the hypercapnic challenge. No significant changes were observed in Iba1+ cells in the spinal trigeminal nucleus (Sp5) and the hippocampus. In CF-1 outbred mice, 10% CO2 followed by 60 min of breathing air, resulted in the reduction of Iba1 labeling percent coverage and the number and length of primary branches in VRC, RN, and NTS. No morphological change was observed in Iba1+ cells in Sp5 and hippocampus. Double immunofluorescence revealed that prolonged hypercapnia increased the expression of CD86, an inflammatory marker for reactive state microglia, in Iba1+ cells in VRC, RN, and NTS, but not in Sp5 and hippocampus in CF-1 mice. By contrast, the expression of CD206, a marker of regulatory state microglia, persisted unmodified. In brainstem, but not in hippocampal microglia cultures, hypercapnia increased the level of IL1β, but not that of TGFβ measured by ELISA. Our results show that microglia from respiratory-related chemosensory nuclei, are reactive to prolonged hypercapnia acquiring an inflammatory-like phenotype.