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Journal of Neurochemistry Aug 2021There is growing evidence that excessive microglial phagocytosis of neurons and synapses contributes to multiple brain pathologies. RNA-seq and genome-wide association... (Review)
Review
There is growing evidence that excessive microglial phagocytosis of neurons and synapses contributes to multiple brain pathologies. RNA-seq and genome-wide association (GWAS) studies have linked multiple phagocytic genes to neurodegenerative diseases, and knock-out of phagocytic genes has been found to protect against neurodegeneration in animal models, suggesting that excessive microglial phagocytosis contributes to neurodegeneration. Here, we review recent evidence that microglial phagocytosis of live neurons and synapses causes neurodegeneration in animal models of Alzheimer's disease and other tauopathies, Parkinson's disease, frontotemporal dementias, multiple sclerosis, retinal degeneration and neurodegeneration induced by ischaemia, infection or ageing. We also review factors regulating microglial phagocytosis of neurons, including: nucleotides, frackalkine, phosphatidylserine, calreticulin, UDP, CD47, sialylation, complement, galectin-3, Apolipoprotein E, phagocytic receptors, Siglec receptors, cytokines, microglial epigenetics and expression profile. Some of these factors may be potential treatment targets to prevent neurodegeneration mediated by excessive microglial phagocytosis of live neurons and synapses.
Topics: Animals; Brain; Humans; Microglia; Neurodegenerative Diseases; Neurons; Phagocytosis; Signal Transduction
PubMed: 33608912
DOI: 10.1111/jnc.15327 -
Journal of Visualized Experiments : JoVE Feb 2021Microglia are the mononuclear phagocytes in the central nervous system (CNS), which play key roles in maintaining homeostasis and regulating the inflammatory process in...
Microglia are the mononuclear phagocytes in the central nervous system (CNS), which play key roles in maintaining homeostasis and regulating the inflammatory process in the CNS. To study the microglial biology in vitro, primary microglia show great advantages compared to immortalized microglial cell lines. However, microglia isolation from the postnatal mouse brain is relatively less efficient and time-consuming. In this protocol, we provide a quick and easy-to-follow method to isolate primary microglia from the neonatal mouse brain. The overall steps of this protocol include brain dissection, primary brain cell culture, and microglia isolation. Using this approach, researchers can obtain primary microglia with high purity. In addition, the harvested primary microglia were able to respond to the lipopolysaccharides challenge, indicating they retained their immune function. Collectively, we developed a simplified approach to efficiently isolate primary microglia with high purity, which facilitates a wide range of microglial biology investigations in vitro.
Topics: Animals; Animals, Newborn; Brain; Cell Separation; Cells, Cultured; Dissection; Lipopolysaccharides; Mice, Inbred C57BL; Microglia; Mice
PubMed: 33720125
DOI: 10.3791/62237 -
Single cell RNA sequencing of human microglia uncovers a subset associated with Alzheimer's disease.Nature Communications Nov 2020The extent of microglial heterogeneity in humans remains a central yet poorly explored question in light of the development of therapies targeting this cell type. Here,...
The extent of microglial heterogeneity in humans remains a central yet poorly explored question in light of the development of therapies targeting this cell type. Here, we investigate the population structure of live microglia purified from human cerebral cortex samples obtained at autopsy and during neurosurgical procedures. Using single cell RNA sequencing, we find that some subsets are enriched for disease-related genes and RNA signatures. We confirm the presence of four of these microglial subpopulations histologically and illustrate the utility of our data by characterizing further microglial cluster 7, enriched for genes depleted in the cortex of individuals with Alzheimer's disease (AD). Histologically, these cluster 7 microglia are reduced in frequency in AD tissue, and we validate this observation in an independent set of single nucleus data. Thus, our live human microglia identify a range of subtypes, and we prioritize one of these as being altered in AD.
Topics: Alzheimer Disease; Cerebral Cortex; Female; Humans; Male; Microglia; Myeloid Cells; Sequence Analysis, RNA
PubMed: 33257666
DOI: 10.1038/s41467-020-19737-2 -
Cell Reports Aug 2020Microglia are important immune cells in the central nervous system (CNS). Dysfunctions of gene-deficient microglia contribute to the development and progression of...
Microglia are important immune cells in the central nervous system (CNS). Dysfunctions of gene-deficient microglia contribute to the development and progression of multiple CNS diseases. Microglia replacement by nonself cells has been proposed to treat microglia-associated disorders. However, some attempts have failed due to low replacement efficiency, such as with the traditional bone marrow transplantation approach. In this study, we develop three efficient strategies for microglia replacement: microglia replacement by bone marrow transplantation (mrBMT), microglia replacement by peripheral blood (mrPB), and microglia replacement by microglia transplantation (mrMT). mrBMT and mrPB allow microglia-like cells to efficiently replace resident microglia in the whole CNS. On the other hand, mrMT achieves microglia replacement in brain regions of interest. In summary, the present study offers effective tactics for microglia replacement with diverse application scenarios, which potentially opens up a window on treating microglia-associated CNS disorders.
Topics: Animals; Central Nervous System; Humans; Mice; Microglia
PubMed: 32783928
DOI: 10.1016/j.celrep.2020.108041 -
Journal of Visualized Experiments : JoVE Oct 2019This is a protocol for the dual visualization of microglia and infiltrating macrophages in mouse brain tissue. TMEM119 (which labels microglia selectively), when...
This is a protocol for the dual visualization of microglia and infiltrating macrophages in mouse brain tissue. TMEM119 (which labels microglia selectively), when combined with IBA1 (which provides an exceptional visualization of their morphology), allows investigation of changes in density, distribution, and morphology. Quantifying these parameters is important in providing insights into the roles exerted by microglia, the resident macrophages of the brain. Under normal physiological conditions, microglia are regularly distributed in a mosaic-like pattern and present a small soma with ramified processes. Nevertheless, as a response to environmental factors (i.e., trauma, infection, disease, or injury), microglial density, distribution, and morphology are altered in various manners, depending on the insult. Additionally, the described double-staining method allows visualization of infiltrating macrophages in the brain based on their expression of IBA1 and without colocalization with TMEM119. This approach thus allows discrimination between microglia and infiltrating macrophages, which is required to provide functional insights into their distinct involvement in brain homeostasis across various contexts of health and disease. This protocol integrates the latest findings in neuroimmunology that pertain to the identification of selective markers. It also serves as a useful tool for both experienced neuroimmunologists and researchers seeking to integrate neuroimmunology into projects.
Topics: Animals; Brain; Fluorescent Antibody Technique; Homeostasis; Macrophages; Mice; Microglia; Myeloid Cells; Staining and Labeling
PubMed: 31710033
DOI: 10.3791/60510 -
Nature Aug 2022Microglia are specialized macrophages in the brain parenchyma that exist in multiple transcriptional states and reside within a wide range of neuronal environments....
Microglia are specialized macrophages in the brain parenchyma that exist in multiple transcriptional states and reside within a wide range of neuronal environments. However, how and where these states are generated remains poorly understood. Here, using the mouse somatosensory cortex, we demonstrate that microglia density and molecular state acquisition are determined by the local composition of pyramidal neuron classes. Using single-cell and spatial transcriptomic profiling, we unveil the molecular signatures and spatial distributions of diverse microglia populations and show that certain states are enriched in specific cortical layers, whereas others are broadly distributed throughout the cortex. Notably, conversion of deep-layer pyramidal neurons to an alternate class identity reconfigures the distribution of local, layer-enriched homeostatic microglia to match the new neuronal niche. Leveraging the transcriptional diversity of pyramidal neurons in the neocortex, we construct a ligand-receptor atlas describing interactions between individual pyramidal neuron subtypes and microglia states, revealing rules of neuron-microglia communication. Our findings uncover a fundamental role for neuronal diversity in instructing the acquisition of microglia states as a potential mechanism for fine-tuning neuroimmune interactions within the cortical local circuitry.
Topics: Animals; Cell Count; Mice; Microglia; Neocortex; Pyramidal Cells; Single-Cell Analysis; Somatosensory Cortex; Transcriptome
PubMed: 35948630
DOI: 10.1038/s41586-022-05056-7 -
Nature Dec 2023Ageing is a critical factor in spinal-cord-associated disorders, yet the ageing-specific mechanisms underlying this relationship remain poorly understood. Here, to...
Ageing is a critical factor in spinal-cord-associated disorders, yet the ageing-specific mechanisms underlying this relationship remain poorly understood. Here, to address this knowledge gap, we combined single-nucleus RNA-sequencing analysis with behavioural and neurophysiological analysis in non-human primates (NHPs). We identified motor neuron senescence and neuroinflammation with microglial hyperactivation as intertwined hallmarks of spinal cord ageing. As an underlying mechanism, we identified a neurotoxic microglial state demarcated by elevated expression of CHIT1 (a secreted mammalian chitinase) specific to the aged spinal cords in NHP and human biopsies. In the aged spinal cord, CHIT1-positive microglia preferentially localize around motor neurons, and they have the ability to trigger senescence, partly by activating SMAD signalling. We further validated the driving role of secreted CHIT1 on MN senescence using multimodal experiments both in vivo, using the NHP spinal cord as a model, and in vitro, using a sophisticated system modelling the human motor-neuron-microenvironment interplay. Moreover, we demonstrated that ascorbic acid, a geroprotective compound, counteracted the pro-senescent effect of CHIT1 and mitigated motor neuron senescence in aged monkeys. Our findings provide the single-cell resolution cellular and molecular landscape of the aged primate spinal cord and identify a new biomarker and intervention target for spinal cord degeneration.
Topics: Animals; Humans; Biomarkers; Cellular Senescence; Chitinases; Microglia; Motor Neurons; Neuroinflammatory Diseases; Primates; Reproducibility of Results; Single-Cell Gene Expression Analysis; Spinal Cord
PubMed: 37907096
DOI: 10.1038/s41586-023-06783-1 -
The Journal of Prevention of... 2023Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive cognitive decline, amyloid-β (Aβ) plaques and the formation of neurofibrillary... (Review)
Review
Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive cognitive decline, amyloid-β (Aβ) plaques and the formation of neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau. Increasing evidence has demonstrated that the damage of cell plays an important role in AD. Cell death is a critical phenomenon for physiological functions, which promotes AD pathogenesis. Programmed cell death, including necroptosis, pyroptosis, autophagy, and ferroptosis, have been discovered that have unique biological functions and pathophysiological characteristics. Here, we review the available evidence detailing the mechanisms of programmed microglial death, including pyroptosis, autophagy, and ferroptosis. We also highlight the role of programmed death of microglia during the process of AD and focus on the connection between the disease and cell death.
Topics: Humans; Alzheimer Disease; Microglia; Pyroptosis; Ferroptosis; Autophagy
PubMed: 36641613
DOI: 10.14283/jpad.2023.3 -
Journal of Cerebral Blood Flow and... Dec 2020The blood-brain barrier (BBB) is a critical regulator of CNS homeostasis. It possesses physical and biochemical characteristics (i.e. tight junction protein complexes,... (Review)
Review
The blood-brain barrier (BBB) is a critical regulator of CNS homeostasis. It possesses physical and biochemical characteristics (i.e. tight junction protein complexes, transporters) that are necessary for the BBB to perform this physiological role. Microvascular endothelial cells require support from astrocytes, pericytes, microglia, neurons, and constituents of the extracellular matrix. This intricate relationship implies the existence of a neurovascular unit (NVU). NVU cellular components can be activated in disease and contribute to dynamic remodeling of the BBB. This is especially true of microglia, the resident immune cells of the brain, which polarize into distinct proinflammatory (M1) or anti-inflammatory (M2) phenotypes. Current data indicate that M1 pro-inflammatory microglia contribute to BBB dysfunction and vascular "leak", while M2 anti-inflammatory microglia play a protective role at the BBB. Understanding biological mechanisms involved in microglia activation provides a unique opportunity to develop novel treatment approaches for neurological diseases. In this review, we highlight characteristics of M1 proinflammatory and M2 anti-inflammatory microglia and describe how these distinct phenotypes modulate BBB physiology. Additionally, we outline the role of other NVU cell types in regulating microglial activation and highlight how microglia can be targeted for treatment of disease with a focus on ischemic stroke and Alzheimer's disease.
Topics: Blood-Brain Barrier; Humans; Microglia; Oxidative Stress
PubMed: 32928017
DOI: 10.1177/0271678X20951995 -
Nature Protocols Feb 2021Microglia are critically involved in complex neurological disorders with a strong genetic component, such as Alzheimer's disease, Parkinson's disease and frontotemporal...
Microglia are critically involved in complex neurological disorders with a strong genetic component, such as Alzheimer's disease, Parkinson's disease and frontotemporal dementia. Although mouse microglia can recapitulate aspects of human microglia physiology, they do not fully capture the human genetic aspects of disease and do not reproduce all human cell states. Primary cultures of human microglia or microglia derived from human induced pluripotent stem cells (PSCs) are difficult to maintain in brain-relevant cell states in vitro. Here we describe MIGRATE (microglia in vitro generation refined for advanced transplantation experiments, which provides a combined in vitro differentiation and in vivo xenotransplantation protocol to study human microglia in the context of the mouse brain. This article details an accurate, step-by-step workflow that includes in vitro microglia differentiation from human PSCs, transplantation into the mouse brain and quantitative analysis of engraftment. Compared to current differentiation and xenotransplantation protocols, we present an optimized, faster and more efficient approach that yields up to 80% chimerism. To quantitatively assess engraftment efficiency by flow cytometry, access to specialized flow cytometry is required. Alternatively, the percentage of chimerism can be estimated by standard immunohistochemical analysis. The MIGRATE protocol takes ~40 d to complete, from culturing PSCs to engraftment efficiency assessment.
Topics: Animals; Brain; Cell Differentiation; Disease Models, Animal; Female; Humans; Induced Pluripotent Stem Cells; Mesenchymal Stem Cell Transplantation; Mice; Microglia; Pluripotent Stem Cells; Pregnancy
PubMed: 33424025
DOI: 10.1038/s41596-020-00447-4