Functional diversity of astrocytes in neural circuit regulation
TL;DR: An overview of the regional heterogeneity of neuron–astrocyte interactions indicates novel ways in which they could regulate normal neurological function and shows how they might become dysregulated in disease.
Abstract: Emerging evidence suggests that astrocytes may be as diverse in their physiological and functional characteristics as neurons. Ben Haim and Rowitch describe astrocyte heterogeneity, consider the mechanisms by which such diversity may arise and discuss the consequences of its disruption in disease.
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TL;DR: RNA sequencing of half a million single cells was used to create a detailed census of cell types in the mouse nervous system and mapped cell types spatially and derived a hierarchical, data-driven taxonomy.
1,735 citations
Université Paris-Saclay1, Autonomous University of Barcelona2, University of Cambridge3, National Institute for Occupational Safety and Health4, University of Bonn5, German Center for Neurodegenerative Diseases6, Harvard University7, University of Lausanne8, National Research Council9, University of Padua10, Heidelberg University11, Salk Institute for Biological Studies12, University of Minnesota13, Pasteur Institute14, Tel Aviv University15, Johns Hopkins University16, University of Portsmouth17, Katholieke Universiteit Leuven18, PSL Research University19, Trinity College, Dublin20, Baylor College of Medicine21, University College London22, University of Edinburgh23, Oregon Health & Science University24, National Institutes of Health25, Columbia University26, University of Copenhagen27, University of Rochester28, Ludwig Maximilian University of Munich29, University of Málaga30, Tufts University31, University of Freiburg32, Utrecht University33, Nihon University34, Max Delbrück Center for Molecular Medicine35, University of California, Los Angeles36, University of Yamanashi37, New York University38, University of British Columbia39, King Abdullah University of Science and Technology40, University of Wisconsin-Madison41, University of California, San Francisco42, McGill University43, University of Kentucky44, Kyushu University45, University of Bordeaux46, University of Minho47, Polytechnic Institute of Cávado and Ave48, University of Alabama at Birmingham49, University of Gothenburg50, University of Poitiers51, Cajal Institute52, King's College London53, University of Strasbourg54, Virginia Tech55, University of Düsseldorf56, I.M. Sechenov First Moscow State Medical University57, Russian Academy of Sciences58, University of Seville59, Georgia Institute of Technology60, University of Texas Health Science Center at Houston61, University of California, San Diego62, Universidade Federal do Rio Grande do Sul63, University of Ljubljana64, Ikerbasque65, University of Manchester66
TL;DR: In this article, the authors point out the shortcomings of binary divisions of reactive astrocytes into good-vs-bad, neurotoxic vs-neuroprotective or A1-vs.A2.
Abstract: Reactive astrocytes are astrocytes undergoing morphological, molecular, and functional remodeling in response to injury, disease, or infection of the CNS. Although this remodeling was first described over a century ago, uncertainties and controversies remain regarding the contribution of reactive astrocytes to CNS diseases, repair, and aging. It is also unclear whether fixed categories of reactive astrocytes exist and, if so, how to identify them. We point out the shortcomings of binary divisions of reactive astrocytes into good-vs-bad, neurotoxic-vs-neuroprotective or A1-vs-A2. We advocate, instead, that research on reactive astrocytes include assessment of multiple molecular and functional parameters-preferably in vivo-plus multivariate statistics and determination of impact on pathological hallmarks in relevant models. These guidelines may spur the discovery of astrocyte-based biomarkers as well as astrocyte-targeting therapies that abrogate detrimental actions of reactive astrocytes, potentiate their neuro- and glioprotective actions, and restore or augment their homeostatic, modulatory, and defensive functions.
797 citations
TL;DR: RNA sequencing of half a million single cells is used to create a detailed census of cell types in the mouse nervous system and lays a solid foundation for understanding the molecular architecture of the mammalian nervous system, and enables genetic manipulation of specific cell types.
Abstract: The mammalian nervous system executes complex behaviors controlled by specialised, precisely positioned and interacting cell types. Here, we used RNA sequencing of half a million single cells to create a detailed census of cell types in the mouse nervous system. We mapped cell types spatially and derived a hierarchical, data-driven taxonomy. Neurons were the most diverse, and were grouped by developmental anatomical units, and by the expression of neurotransmitters and neuropeptides. Neuronal diversity was driven by genes encoding cell identity, synaptic connectivity, neurotransmission and membrane conductance. We discovered several distinct, regionally restricted, astrocytes types, which obeyed developmental boundaries and correlated with the spatial distribution of key glutamate and glycine neurotransmitters. In contrast, oligodendrocytes showed a loss of regional identity, followed by a secondary diversi cation. The resource presented here lays a solid foundation for understanding the molecular architecture of the mammalian nervous system, and enables genetic manipulation of specific cell types.
602 citations
Cites background from "Functional diversity of astrocytes ..."
...…of the cerebellum and olfactory bulb, the modern understanding of astrocyte diversity essentially stands as it stood in 1900: the main types of mature astrocytes are believed to be the Müller glia, the Bergmann glia, and the protoplasmic and fibrous astrocytes (Ben Haim and Rowitch, 2016)....
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TL;DR: It is reported that TGFα and VEGF-B produced by microglia regulate the pathogenic activities of astrocytes in the experimental autoimmune encephalomyelitis mouse model of multiple sclerosis, and this pathway may guide new therapies for multiple sclerosis and other neurological disorders.
Abstract: Microglia and astrocytes modulate inflammation and neurodegeneration in the central nervous system (CNS)1–3. Microglia modulate pro-inflammatory and neurotoxic activities in astrocytes, but the mechanisms involved are not completely understood4,5. Here we report that TGFα and VEGF-B produced by microglia regulate the pathogenic activities of astrocytes in the experimental autoimmune encephalomyelitis (EAE) mouse model of multiple sclerosis. Microglia-derived TGFα acts via the ErbB1 receptor in astrocytes to limit their pathogenic activities and EAE development. Conversely, microglial VEGF-B triggers FLT-1 signalling in astrocytes and worsens EAE. VEGF-B and TGFα also participate in the microglial control of human astrocytes. Furthermore, expression of TGFα and VEGF-B in CD14+ cells correlates with the multiple sclerosis lesion stage. Finally, metabolites of dietary tryptophan produced by the commensal flora control microglial activation and TGFα and VEGF-B production, modulating the transcriptional program of astrocytes and CNS inflammation through a mechanism mediated by the aryl hydrocarbon receptor. In summary, we identified positive and negative regulators that mediate the microglial control of astrocytes. Moreover, these findings define a pathway through which microbial metabolites limit pathogenic activities of microglia and astrocytes, and suppress CNS inflammation. This pathway may guide new therapies for multiple sclerosis and other neurological disorders.
601 citations
TL;DR: In this article, the authors used multiple integrated approaches, including RNA sequencing (RNA-seq), mass spectrometry, electrophysiology, immunohistochemistry, serial block-face-scanning electron microscopy, morphological reconstructions, pharmacogenetics, and diffusible dye, calcium, and glutamate imaging, to directly compare adult striatal and hippocampal astrocytes under identical conditions.
479 citations
Cites background from "Functional diversity of astrocytes ..."
...One hypothesis that has been recently advanced to explain this quandary is the possibility that astrocytes are not a homogeneous population of glue-like cells in different neural circuits (Ben Haim and Rowitch, 2017; Khakh and Sofroniew, 2015; Zhang and Barres, 2010)....
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...However, astrocyte diversity has beenwidely invoked recently to explain the plethora of physiological processes that astrocytes participate in (Ben Haim and Rowitch, 2017; Khakh and Sofro- Figure 8....
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References
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TL;DR: Astrocyte functions in healthy CNS, mechanisms and functions of reactive astrogliosis and glial scar formation, and ways in which reactive astrocytes may cause or contribute to specific CNS disorders and lesions are reviewed.
Abstract: Astrocytes are specialized glial cells that outnumber neurons by over fivefold. They contiguously tile the entire central nervous system (CNS) and exert many essential complex functions in the healthy CNS. Astrocytes respond to all forms of CNS insults through a process referred to as reactive astrogliosis, which has become a pathological hallmark of CNS structural lesions. Substantial progress has been made recently in determining functions and mechanisms of reactive astrogliosis and in identifying roles of astrocytes in CNS disorders and pathologies. A vast molecular arsenal at the disposal of reactive astrocytes is being defined. Transgenic mouse models are dissecting specific aspects of reactive astrocytosis and glial scar formation in vivo. Astrocyte involvement in specific clinicopathological entities is being defined. It is now clear that reactive astrogliosis is not a simple all-or-none phenomenon but is a finely gradated continuum of changes that occur in context-dependent manners regulated by specific signaling events. These changes range from reversible alterations in gene expression and cell hypertrophy with preservation of cellular domains and tissue structure, to long-lasting scar formation with rearrangement of tissue structure. Increasing evidence points towards the potential of reactive astrogliosis to play either primary or contributing roles in CNS disorders via loss of normal astrocyte functions or gain of abnormal effects. This article reviews (1) astrocyte functions in healthy CNS, (2) mechanisms and functions of reactive astrogliosis and glial scar formation, and (3) ways in which reactive astrocytes may cause or contribute to specific CNS disorders and lesions.
4,075 citations
TL;DR: Developments in the signaling mechanisms that regulate specific aspects of reactive astrogliosis are reviewed and the potential to identify novel therapeutic molecular targets for diverse neurological disorders is highlighted.
2,213 citations
TL;DR: The mechanisms that specify the identity of neural cells have been examined in many regions of the nervous system and reveal a high degree of conservation in the specification of cell fate by key signalling molecules.
Abstract: Neural circuits are assembled with remarkable precision during embryonic development, and the selectivity inherent in their formation helps to define the behavioural repertoire of the mature organism. In the vertebrate central nervous system, this developmental program begins with the differentiation of distinct classes of neurons from progenitor cells located at defined positions within the neural tube. The mechanisms that specify the identity of neural cells have been examined in many regions of the nervous system and reveal a high degree of conservation in the specification of cell fate by key signalling molecules.
2,060 citations
TL;DR: The findings provide transcriptome databases for two subtypes of reactive astrocytes that will be highly useful in generating new and testable hypotheses of their function, as well as for providing new markers to detect different types of reactiveAstrocyte reactive gliosis in human neurological diseases.
Abstract: Reactive astrogliosis is characterized by a profound change in astrocyte phenotype in response to all CNS injuries and diseases. To better understand the reactive astrocyte state, we used Affymetrix GeneChip arrays to profile gene expression in populations of reactive astrocytes isolated at various time points after induction using two mouse injury models, ischemic stroke and neuroinflammation. We find reactive gliosis consists of a rapid, but quickly attenuated, induction of gene expression after insult and identify induced Lcn2 and Serpina3n as strong markers of reactive astrocytes. Strikingly, reactive astrocyte phenotype strongly depended on the type of inducing injury. Although there is a core set of genes that is upregulated in reactive astrocytes from both injury models, at least 50% of the altered gene expression is specific to a given injury type. Reactive astrocytes in ischemia exhibited a molecular phenotype that suggests that they may be beneficial or protective, whereas reactive astrocytes induced by LPS exhibited a phenotype that suggests that they may be detrimental. These findings demonstrate that, despite well established commonalities, astrocyte reactive gliosis is a highly heterogeneous state in which astrocyte activities are altered to respond to the specific injury. This raises the question of how many subtypes of reactive astrocytes exist. Our findings provide transcriptome databases for two subtypes of reactive astrocytes that will be highly useful in generating new and testable hypotheses of their function, as well as for providing new markers to detect different types of reactive astrocytes in human neurological diseases.
1,730 citations
TL;DR: These findings reinforce the emerging view that astrocytes have an active regulatory role—rather than merely supportive roles traditionally assigned to them—in the mature central nervous system.
Abstract: During an investigation of the mechanisms through which the local environment controls the fate specification of adult neural stem cells, we discovered that adult astrocytes from hippocampus are capable of regulating neurogenesis by instructing the stem cells to adopt a neuronal fate. This role in fate specification was unexpected because, during development, neurons are generated before most of the astrocytes. Our findings, together with recent reports that astrocytes regulate synapse formation and synaptic transmission, reinforce the emerging view that astrocytes have an active regulatory role—rather than merely supportive roles traditionally assigned to them—in the mature central nervous system.
1,468 citations