RESUMEN
The wiring of the nervous system requires that axons navigate to the correct targets and maintain their correct positions during developmental growth. In this issue, Shao et al. (2013) now reveal a crucial new role for glia in preserving correct synaptic connectivity during developmental growth.
Asunto(s)
Proteínas de Caenorhabditis elegans/metabolismo , Caenorhabditis elegans/crecimiento & desarrollo , Caenorhabditis elegans/metabolismo , Neuroglía/metabolismo , Receptores de Factores de Crecimiento de Fibroblastos/metabolismo , Proteínas Cotransportadoras de Sodio-Fosfato de Tipo I/metabolismo , Sinapsis , AnimalesRESUMEN
Reactive astrocytes are strongly induced by central nervous system (CNS) injury and disease, but their role is poorly understood. Here we show that a subtype of reactive astrocytes, which we termed A1, is induced by classically activated neuroinflammatory microglia. We show that activated microglia induce A1 astrocytes by secreting Il-1α, TNF and C1q, and that these cytokines together are necessary and sufficient to induce A1 astrocytes. A1 astrocytes lose the ability to promote neuronal survival, outgrowth, synaptogenesis and phagocytosis, and induce the death of neurons and oligodendrocytes. Death of axotomized CNS neurons in vivo is prevented when the formation of A1 astrocytes is blocked. Finally, we show that A1 astrocytes are abundant in various human neurodegenerative diseases including Alzheimer's, Huntington's and Parkinson's disease, amyotrophic lateral sclerosis and multiple sclerosis. Taken together these findings help to explain why CNS neurons die after axotomy, strongly suggest that A1 astrocytes contribute to the death of neurons and oligodendrocytes in neurodegenerative disorders, and provide opportunities for the development of new treatments for these diseases.
Asunto(s)
Astrocitos/clasificación , Astrocitos/patología , Muerte Celular , Sistema Nervioso Central/patología , Microglía/patología , Neuronas/patología , Animales , Astrocitos/metabolismo , Axotomía , Técnicas de Cultivo de Célula , Supervivencia Celular , Complemento C1q/metabolismo , Progresión de la Enfermedad , Humanos , Inflamación/patología , Interleucina-1alfa/metabolismo , Ratones , Ratones Endogámicos C57BL , Microglía/metabolismo , Enfermedades Neurodegenerativas/patología , Oligodendroglía/patología , Fagocitosis , Fenotipo , Ratas , Ratas Sprague-Dawley , Sinapsis/patología , Toxinas Biológicas/metabolismo , Factor de Necrosis Tumoral alfa/metabolismoRESUMEN
The decline of cognitive function occurs with aging, but the mechanisms responsible are unknown. Astrocytes instruct the formation, maturation, and elimination of synapses, and impairment of these functions has been implicated in many diseases. These findings raise the question of whether astrocyte dysfunction could contribute to cognitive decline in aging. We used the Bac-Trap method to perform RNA sequencing of astrocytes from different brain regions across the lifespan of the mouse. We found that astrocytes have region-specific transcriptional identities that change with age in a region-dependent manner. We validated our findings using fluorescence in situ hybridization and quantitative PCR. Detailed analysis of the differentially expressed genes in aging revealed that aged astrocytes take on a reactive phenotype of neuroinflammatory A1-like reactive astrocytes. Hippocampal and striatal astrocytes up-regulated a greater number of reactive astrocyte genes compared with cortical astrocytes. Moreover, aged brains formed many more A1 reactive astrocytes in response to the neuroinflammation inducer lipopolysaccharide. We found that the aging-induced up-regulation of reactive astrocyte genes was significantly reduced in mice lacking the microglial-secreted cytokines (IL-1α, TNF, and C1q) known to induce A1 reactive astrocyte formation, indicating that microglia promote astrocyte activation in aging. Since A1 reactive astrocytes lose the ability to carry out their normal functions, produce complement components, and release a toxic factor which kills neurons and oligodendrocytes, the aging-induced up-regulation of reactive genes by astrocytes could contribute to the cognitive decline in vulnerable brain regions in normal aging and contribute to the greater vulnerability of the aged brain to injury.
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Envejecimiento/metabolismo , Astrocitos/metabolismo , Envejecimiento/genética , Envejecimiento/psicología , Animales , Cognición , Femenino , Perfilación de la Expresión Génica , Hipocampo/citología , Hipocampo/metabolismo , Humanos , Interleucina-1alfa/genética , Interleucina-1alfa/metabolismo , Masculino , Ratones , Ratones Endogámicos C57BL , Microglía/metabolismo , Neuronas/metabolismo , ARN/genética , ARN/metabolismo , Factor de Necrosis Tumoral alfa/genética , Factor de Necrosis Tumoral alfa/metabolismoRESUMEN
To achieve its precise neural connectivity, the developing mammalian nervous system undergoes extensive activity-dependent synapse remodelling. Recently, microglial cells have been shown to be responsible for a portion of synaptic pruning, but the remaining mechanisms remain unknown. Here we report a new role for astrocytes in actively engulfing central nervous system synapses. This process helps to mediate synapse elimination, requires the MEGF10 and MERTK phagocytic pathways, and is strongly dependent on neuronal activity. Developing mice deficient in both astrocyte pathways fail to refine their retinogeniculate connections normally and retain excess functional synapses. Finally, we show that in the adult mouse brain, astrocytes continuously engulf both excitatory and inhibitory synapses. These studies reveal a novel role for astrocytes in mediating synapse elimination in the developing and adult brain, identify MEGF10 and MERTK as critical proteins in the synapse remodelling underlying neural circuit refinement, and have important implications for understanding learning and memory as well as neurological disease processes.
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Astrocitos/metabolismo , Proteínas de la Membrana/metabolismo , Vías Nerviosas/metabolismo , Fagocitosis , Proteínas Proto-Oncogénicas/metabolismo , Proteínas Tirosina Quinasas Receptoras/metabolismo , Sinapsis/metabolismo , Animales , Astrocitos/citología , Encéfalo/citología , Técnicas In Vitro , Núcleos Talámicos Laterales/citología , Núcleos Talámicos Laterales/metabolismo , Aprendizaje/fisiología , Proteínas de la Membrana/deficiencia , Proteínas de la Membrana/genética , Ratones , Ratones Transgénicos , Vías Nerviosas/citología , Proteínas Proto-Oncogénicas/deficiencia , Proteínas Proto-Oncogénicas/genética , Proteínas Tirosina Quinasas Receptoras/deficiencia , Proteínas Tirosina Quinasas Receptoras/genética , Retina/fisiología , Tirosina Quinasa c-MerRESUMEN
The human cerebral cortex develops through an elaborate succession of cellular events that, when disrupted, can lead to neuropsychiatric disease. The ability to reprogram somatic cells into pluripotent cells that can be differentiated in vitro provides a unique opportunity to study normal and abnormal corticogenesis. Here, we present a simple and reproducible 3D culture approach for generating a laminated cerebral cortex-like structure, named human cortical spheroids (hCSs), from pluripotent stem cells. hCSs contain neurons from both deep and superficial cortical layers and map transcriptionally to in vivo fetal development. These neurons are electrophysiologically mature, display spontaneous activity, are surrounded by nonreactive astrocytes and form functional synapses. Experiments in acute hCS slices demonstrate that cortical neurons participate in network activity and produce complex synaptic events. These 3D cultures should allow a detailed interrogation of human cortical development, function and disease, and may prove a versatile platform for generating other neuronal and glial subtypes in vitro.
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Astrocitos/fisiología , Corteza Cerebral/fisiología , Células Madre Pluripotentes/citología , Astrocitos/citología , Células Cultivadas , Corteza Cerebral/citología , Humanos , Esferoides Celulares , Sinapsis/fisiologíaRESUMEN
Astrocytes are now emerging as key participants in many aspects of brain development, function and disease. In particular, new evidence shows that astrocytes powerfully control the formation, maturation, function and elimination of synapses through various secreted and contact-mediated signals. Astrocytes are also increasingly being implicated in the pathophysiology of many psychiatric and neurological disorders that result from synaptic defects. A better understanding of how astrocytes regulate neural circuit development and function in the healthy and diseased brain might lead to the development of therapeutic agents to treat these diseases.
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Astrocitos/fisiología , Encéfalo/citología , Encéfalo/crecimiento & desarrollo , Red Nerviosa/crecimiento & desarrollo , Animales , Comunicación Celular/fisiología , Transducción de Señal/fisiología , Sinapsis/fisiologíaAsunto(s)
Astrocitos/fisiología , Animales , Encéfalo/fisiología , Expresión Génica , Humanos , RatonesRESUMEN
Adjusting the thickness and internodal length of the myelin sheath is a mechanism for tuning the conduction velocity of axons to match computational needs. Interactions between oligodendrocyte precursor cells (OPCs) and developing axons regulate the formation of myelin around axons. We now show, using organotypic cerebral cortex slices from mice expressing eGFP in Sox10-positive oligodendrocytes, that endogenously released GABA, acting on GABAA receptors, greatly reduces the number of oligodendrocyte lineage cells. The decrease in oligodendrocyte number correlates with a reduction in the amount of myelination but also an increase in internode length, a parameter previously thought to be set by the axon diameter or to be a property intrinsic to oligodendrocytes. Importantly, while TTX block of neuronal activity had no effect on oligodendrocyte lineage cell number when applied alone, it was able to completely abolish the effect of blocking GABAA receptors, suggesting that control of myelination by endogenous GABA may require a permissive factor to be released from axons. In contrast, block of AMPA/KA receptors had no effect on oligodendrocyte lineage cell number or myelination. These results imply that, during development, GABA can act as a local environmental cue to control myelination and thus influence the conduction velocity of action potentials within the CNS. GLIA 2017;65:309-321.
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Axones/fisiología , Corteza Cerebral/citología , Vaina de Mielina/metabolismo , Oligodendroglía/fisiología , Organogénesis/fisiología , Ácido gamma-Aminobutírico/metabolismo , Animales , Axones/efectos de los fármacos , Axones/ultraestructura , Diferenciación Celular/efectos de los fármacos , Diferenciación Celular/genética , Proliferación Celular/efectos de los fármacos , Proliferación Celular/genética , Corteza Cerebral/fisiología , Antagonistas de Aminoácidos Excitadores/farmacología , GABAérgicos/farmacología , Regulación de la Expresión Génica/efectos de los fármacos , Regulación de la Expresión Génica/genética , Ratones , Ratones Transgénicos , Vaina de Mielina/ultraestructura , Neuronas/citología , Neuronas/efectos de los fármacos , Oligodendroglía/efectos de los fármacos , Oligodendroglía/ultraestructura , Técnicas de Cultivo de Órganos , Organogénesis/efectos de los fármacos , Quinoxalinas/farmacología , Receptores de GABA/genética , Receptores de GABA/metabolismo , Factores de Transcripción SOXE/genética , Factores de Transcripción SOXE/metabolismo , Transmisión Sináptica/efectos de los fármacos , Transmisión Sináptica/genética , Tetrodotoxina/farmacología , Ácido gamma-Aminobutírico/farmacologíaRESUMEN
Oligodendrocyte progenitor cells (OPCs) in the postnatal mouse corpus callosum (CC) and motor cortex (Ctx) reportedly generate only oligodendrocytes (OLs), whereas those in the piriform cortex may also generate neurons. OPCs have also been subdivided based on their expression of voltage-gated ion channels, ability to respond to neuronal activity, and proliferative state. To determine whether OPCs in the piriform cortex have inherently different physiological properties from those in the CC and Ctx, we studied acute brain slices from postnatal transgenic mice in which GFP expression identifies OL lineage cells. We whole-cell patch clamped GFP-expressing (GFP(+)) cells within the CC, Ctx, and anterior piriform cortex (aPC) and used prelabeling with 5-ethynyl-2'-deoxyuridine (EdU) to assess cell proliferation. After recording, slices were immunolabeled and OPCs were defined by strong expression of NG2. NG2(+) OPCs in the white and gray matter proliferated and coexpressed PDGFRα and voltage-gated Na(+) channels (I(Na)). Approximately 70% of OPCs were capable of generating regenerative depolarizations. In addition to OLIG2(+) NG2(+) I(Na)(+) OPCs and OLIG2(+) NG2(neg) I(Na)(neg) OLs, we identified cells with low levels of NG2 limited to the soma or the base of some processes. These cells had a significantly reduced I(Na) and a reduced ability to incorporate EdU when compared with OPCs and probably correspond to early differentiating OLs. By combining EdU labeling and lineage tracing using Pdgfrα-CreER(T2) : R26R-YFP transgenic mice, we double labeled OPCs and traced their fate in the postnatal brain. These OPCs generated OLs but did not generate neurons in the aPC or elsewhere at any time that we examined.
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Diferenciación Celular/fisiología , Linaje de la Célula/fisiología , Cuerpo Calloso/citología , Corteza Motora/citología , Vías Olfatorias/citología , Oligodendroglía/fisiología , Células Madre/fisiología , Animales , Antígenos/metabolismo , Proliferación Celular , Cuerpo Calloso/metabolismo , Femenino , Masculino , Potenciales de la Membrana/fisiología , Ratones , Ratones Transgénicos , Corteza Motora/metabolismo , Vías Olfatorias/metabolismo , Oligodendroglía/metabolismo , Proteoglicanos/metabolismo , Receptor alfa de Factor de Crecimiento Derivado de Plaquetas/metabolismo , Canales de Sodio/metabolismo , Células Madre/metabolismoRESUMEN
In the developing spinal cord, most oligodendrocyte precursors (OLPs) arise from the ventral ventricular zone (VZ) under the influence of Sonic Hedgehog, but a minority are generated from the dorsal VZ in a Hedgehog-independent manner. In the developing forebrain too, OLPs arise from both the ventral and the dorsal VZ. It is not known whether dorsally and ventrally derived oligodendrocyte (OL) lineage cells have different properties. We generated a dual reporter mouse line to color code ventrally and dorsally derived OLPs (vOLPs and dOLPs) and their differentiated oligodendrocyte progeny (vOLs and dOLs) for functional studies. We found that â¼80% of OL lineage cells in the postnatal spinal cord and â¼20% in the corpus callosum are ventrally derived. In both spinal cord and corpus callosum, vOLPs and dOLPs had indistinguishable electrical properties, as did vOLs and dOLs. However, vOLPs and dOLPs had different migration and settling patterns. In the spinal cord, vOLPs appeared early and spread uniformly throughout the cord, whereas dOLPs arrived later and remained mainly in the dorsal and dorsolateral funiculi. During adulthood, corticospinal and rubrospinal tracts became myelinated mainly by dOLs, even though vOLs dominated these tracts during early postnatal life. Thus, dOLPs are electrically similar to vOLPs but appear to outcompete them for dorsal axons.
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Linaje de la Célula/fisiología , Cuerpo Calloso/fisiología , Vaina de Mielina/fisiología , Oligodendroglía/fisiología , Médula Espinal/fisiología , Animales , Electrofisiología , Inmunohistoquímica , Ratones , Ratones TransgénicosRESUMEN
Microglia are increasingly recognized for their major contributions during brain development and neurodegenerative disease. It is currently unknown whether these functions are carried out by subsets of microglia during different stages of development and adulthood or within specific brain regions. Here, we performed deep single-cell RNA sequencing (scRNA-seq) of microglia and related myeloid cells sorted from various regions of embryonic, early postnatal, and adult mouse brains. We found that the majority of adult microglia expressing homeostatic genes are remarkably similar in transcriptomes, regardless of brain region. By contrast, early postnatal microglia are more heterogeneous. We discovered a proliferative-region-associated microglia (PAM) subset, mainly found in developing white matter, that shares a characteristic gene signature with degenerative disease-associated microglia (DAM). Such PAM have amoeboid morphology, are metabolically active, and phagocytose newly formed oligodendrocytes. This scRNA-seq atlas will be a valuable resource for dissecting innate immune functions in health and disease.
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Encéfalo , Regulación del Desarrollo de la Expresión Génica/fisiología , Microglía/fisiología , Células Mieloides/fisiología , Análisis de Secuencia de ARN , Transcriptoma/fisiología , Algoritmos , Animales , Animales Recién Nacidos , Antígenos CD/metabolismo , Encéfalo/citología , Encéfalo/embriología , Encéfalo/crecimiento & desarrollo , Proliferación Celular/fisiología , Plexo Coroideo/citología , Análisis por Conglomerados , Simulación por Computador , Embrión de Mamíferos , Redes Reguladoras de Genes/fisiología , Secuenciación de Nucleótidos de Alto Rendimiento , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Oligodendroglía/fisiología , Fagocitosis/fisiologíaRESUMEN
The functional and molecular similarities and distinctions between human and murine astrocytes are poorly understood. Here, we report the development of an immunopanning method to acutely purify astrocytes from fetal, juvenile, and adult human brains and to maintain these cells in serum-free cultures. We found that human astrocytes have abilities similar to those of murine astrocytes in promoting neuronal survival, inducing functional synapse formation, and engulfing synaptosomes. In contrast to existing observations in mice, we found that mature human astrocytes respond robustly to glutamate. Next, we performed RNA sequencing of healthy human astrocytes along with astrocytes from epileptic and tumor foci and compared these to human neurons, oligodendrocytes, microglia, and endothelial cells (available at http://www.brainrnaseq.org). With these profiles, we identified novel human-specific astrocyte genes and discovered a transcriptome-wide transformation between astrocyte precursor cells and mature post-mitotic astrocytes. These data represent some of the first cell-type-specific molecular profiles of the healthy and diseased human brain.