RESUMO
Microglia sense the changes in their environment. How microglia actively translate these changes into suitable cues to adapt brain physiology is unknown. We reveal an activity-dependent regulation of cortical inhibitory synapses by microglia, driven by purinergic signaling acting on P2RX7 and mediated by microglia-derived TNFα. We demonstrate that sleep induces microglia-dependent synaptic enrichment of GABAARs in a manner dependent on microglial TNFα and P2RX7. We further show that microglia-specific depletion of TNFα alters slow waves during NREM sleep and blunt memory consolidation in sleep-dependent learning tasks. Together, our results reveal that microglia orchestrate sleep-intrinsic plasticity of synaptic GABAARs, sculpt sleep slow waves, and support memory consolidation.
Assuntos
Microglia , Receptores de GABA-A , Sono de Ondas Lentas , Sinapses , Fator de Necrose Tumoral alfa , Animais , Masculino , Camundongos , Consolidação da Memória , Camundongos Endogâmicos C57BL , Microglia/metabolismo , Plasticidade Neuronal/fisiologia , Receptores de GABA-A/metabolismo , Receptores Purinérgicos P2X7/metabolismo , Receptores Purinérgicos P2X7/genética , Transdução de Sinais , Sono/fisiologia , Sinapses/metabolismo , Fator de Necrose Tumoral alfa/metabolismoRESUMO
Sleep intensity is adjusted by the length of previous awake time, and under tight homeostatic control by protein phosphorylation. Here, we establish microglia as a new cellular component of the sleep homeostasis circuit. Using quantitative phosphoproteomics of the mouse frontal cortex, we demonstrate that microglia-specific deletion of TNFα perturbs thousands of phosphorylation sites during the sleep period. Substrates of microglial TNFα comprise sleep-related kinases such as MAPKs and MARKs, and numerous synaptic proteins, including a subset whose phosphorylation status encodes sleep need and determines sleep duration. As a result, microglial TNFα loss attenuates the build-up of sleep need, as measured by electroencephalogram slow-wave activity and prevents immediate compensation for loss of sleep. Our data suggest that microglia control sleep homeostasis by releasing TNFα which acts on neuronal circuitry through dynamic control of phosphorylation.
Assuntos
Microglia , Fator de Necrose Tumoral alfa , Camundongos , Animais , Microglia/metabolismo , Fosforilação , Fator de Necrose Tumoral alfa/metabolismo , Sono/fisiologia , Homeostase/fisiologiaRESUMO
Microglial research has advanced considerably in recent decades yet has been constrained by a rolling series of dichotomies such as "resting versus activated" and "M1 versus M2." This dualistic classification of good or bad microglia is inconsistent with the wide repertoire of microglial states and functions in development, plasticity, aging, and diseases that were elucidated in recent years. New designations continuously arising in an attempt to describe the different microglial states, notably defined using transcriptomics and proteomics, may easily lead to a misleading, although unintentional, coupling of categories and functions. To address these issues, we assembled a group of multidisciplinary experts to discuss our current understanding of microglial states as a dynamic concept and the importance of addressing microglial function. Here, we provide a conceptual framework and recommendations on the use of microglial nomenclature for researchers, reviewers, and editors, which will serve as the foundations for a future white paper.
Assuntos
MicrogliaRESUMO
Mononuclear phagocytes are key regulators of both tissue damage and repair in neuroinflammatory conditions such as multiple sclerosis. To examine divergent phagocyte phenotypes in the inflamed CNS, we introduce an in vivo imaging approach that allows us to temporally and spatially resolve the evolution of phagocyte polarization in a murine model of multiple sclerosis. We show that the initial proinflammatory polarization of phagocytes is established after spinal cord entry and critically depends on the compartment they enter. Guided by signals from the CNS environment, individual phagocytes then switch their phenotype as lesions move from expansion to resolution. Our study thus provides a real-time analysis of the temporospatial determinants and regulatory principles of phagocyte specification in the inflamed CNS.
Assuntos
Leucócitos Mononucleares/patologia , Esclerose Múltipla/patologia , Fagócitos/patologia , Animais , Astrócitos/patologia , Astrócitos/ultraestrutura , Células da Medula Óssea/patologia , Células da Medula Óssea/ultraestrutura , Polaridade Celular , Sistemas Computacionais , Encefalomielite Autoimune Experimental/patologia , Humanos , Inflamação/patologia , Leucócitos Mononucleares/ultraestrutura , Camundongos , Camundongos Endogâmicos C57BL , Neuroglia/patologia , Neuroglia/ultraestrutura , Fagócitos/ultraestrutura , Fagocitose , Fenótipo , Análise de Sequência de RNA , Medula Espinal/patologia , Medula Espinal/ultraestruturaRESUMO
Microglia control excitatory synapses, but their role in inhibitory neurotransmission has been less well characterized. Herein, we show that microglia control the strength of glycinergic but not GABAergic synapses via modulation of the diffusion dynamics and synaptic trapping of glycine (GlyR) but not GABAA receptors. We further demonstrate that microglia regulate the activity-dependent plasticity of glycinergic synapses by tuning the GlyR diffusion trap. This microglia-synapse cross talk requires production of prostaglandin E2 by microglia, leading to the activation of neuronal EP2 receptors and cyclic adenosine monophosphate-dependent protein kinase. Thus, we now provide a link between microglial activation and synaptic dysfunctions, which are common early features of many brain diseases.
Assuntos
Dinoprostona/metabolismo , Sinapses Elétricas/metabolismo , Glicina/metabolismo , Microglia/metabolismo , Inibição Neural , Medula Espinal/metabolismo , Transmissão Sináptica , Ácido gama-Aminobutírico/metabolismo , Animais , Proteínas de Transporte/genética , Proteínas de Transporte/metabolismo , Células Cultivadas , Proteínas Quinases Dependentes de AMP Cíclico/metabolismo , Difusão , Feminino , Masculino , Potenciais da Membrana , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Transporte Proteico , Receptores de GABA-A/metabolismo , Receptores de Glicina/metabolismo , Receptores de Prostaglandina E Subtipo EP2/metabolismo , Membranas Sinápticas/metabolismo , Fatores de Tempo , Técnicas de Cultura de TecidosRESUMO
Inflammation triggers the differentiation of Ly6Chi monocytes into microbicidal macrophages or monocyte-derived dendritic cells (moDCs). Yet, it is unclear whether environmental inflammatory cues control the polarization of monocytes toward each of these fates or whether specialized monocyte progenitor subsets exist before inflammation. Here, we have shown that naive monocytes are phenotypically heterogeneous and contain an NR4A1- and Flt3L-independent, CCR2-dependent, Flt3+CD11c-MHCII+PU.1hi subset. This subset acted as a precursor for FcγRIII+PD-L2+CD209a+, GM-CSF-dependent moDCs but was distal from the DC lineage, as shown by fate-mapping experiments using Zbtb46. By contrast, Flt3-CD11c-MHCII-PU.1lo monocytes differentiated into FcγRIII+PD-L2-CD209a-iNOS+ macrophages upon microbial stimulation. Importantly, Sfpi1 haploinsufficiency genetically distinguished the precursor activities of monocytes toward moDCs or microbicidal macrophages. Indeed, Sfpi1+/- mice had reduced Flt3+CD11c-MHCII+ monocytes and GM-CSF-dependent FcγRIII+PD-L2+CD209a+ moDCs but generated iNOS+ macrophages more efficiently. Therefore, intercellular disparities of PU.1 expression within naive monocytes segregate progenitor activity for inflammatory iNOS+ macrophages or moDCs.
Assuntos
Diferenciação Celular/imunologia , Células Dendríticas/imunologia , Macrófagos/imunologia , Monócitos/imunologia , Transferência Adotiva , Animais , Antígenos Ly/imunologia , Separação Celular , Células Dendríticas/citologia , Citometria de Fluxo , Macrófagos/citologia , Camundongos , Monócitos/citologia , Óxido Nítrico Sintase Tipo II/imunologia , Análise de Sequência com Séries de Oligonucleotídeos , Reação em Cadeia da PolimeraseRESUMO
The functional similarity between root and gut microbiota, both contributing to the nutrition and protection of the host, is often overlooked. A central mechanism for efficient protection against pathogens is defense priming, the preconditioning of immunity induced by microbial colonization after germination or birth. Microbiota have been recruited several times in evolution as developmental signals for immunity maturation. Because there is no evidence that microbial signals are more relevant than endogenous ones, we propose a neutral scenario for the evolution of this dependency: any hypothetic endogenous signal can be lost because microbial colonization, reliably occurring at germination or birth, can substitute for it, and without either positive selection or the acquisition of new functions. Dependency of development on symbiotic signals can thus evolve by contingent irreversibility.
Assuntos
Trato Gastrointestinal/microbiologia , Imunidade , Microbiota/imunologia , Microbiota/fisiologia , Raízes de Plantas/microbiologia , Simbiose , AnimaisRESUMO
Dysfunction of microglia, the tissue macrophages of the brain, has been associated with the etiology of several neuropsychiatric disorders. Consistently, microglia have been shown to regulate neurogenesis and synaptic maturation at perinatal and postnatal stages. However, microglia invade the brain during mid-embryogenesis and thus could play an earlier prenatal role. Here, we show that embryonic microglia, which display a transiently uneven distribution, regulate the wiring of forebrain circuits. Using multiple mouse models, including cell-depletion approaches and cx3cr1(-/-), CR3(-/-), and DAP12(-/-) mutants, we find that perturbing microglial activity affects the outgrowth of dopaminergic axons in the forebrain and the laminar positioning of subsets of neocortical interneurons. Since defects in both dopamine innervation and cortical networks have been linked to neuropsychiatric diseases, our study provides insights into how microglial dysfunction can impact forebrain connectivity and reveals roles for immune cells during normal assembly of brain circuits.
Assuntos
Microglia/metabolismo , Neurogênese , Prosencéfalo/citologia , Receptor de Fator Estimulador de Colônias de Macrófagos/metabolismo , Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Animais , Neurônios Dopaminérgicos/citologia , Neurônios Dopaminérgicos/metabolismo , Interneurônios/citologia , Interneurônios/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Prosencéfalo/embriologia , Prosencéfalo/fisiologia , Receptor de Fator Estimulador de Colônias de Macrófagos/genética , Receptores de Interleucina-8A/genética , Receptores de Interleucina-8A/metabolismoRESUMO
Microglia colonise the brain parenchyma at early stages of development and accumulate in specific regions where they participate in cell death, angiogenesis, neurogenesis and synapse elimination. A recurring feature of embryonic microglial is their association with developing axon tracts, which, together with in vitro data, supports the idea of a physiological role for microglia in neurite development. Yet the demonstration of this role of microglia is lacking. Here, we have studied the consequences of microglial dysfunction on the formation of the corpus callosum, the largest commissure of the mammalian brain, which shows consistent microglial accumulation during development. We studied two models of microglial dysfunction: the loss-of-function of DAP12, a key microglial-specific signalling molecule, and a model of maternal inflammation by peritoneal injection of lipopolysaccharide at embryonic day (E)15.5. We also took advantage of the Pu.1(-/-) mouse line, which is devoid of microglia. We performed transcriptional profiling of maternally inflamed and Dap12-mutant microglia at E17.5. The two treatments principally down-regulated genes involved in nervous system development and function, particularly in neurite formation. We then analysed the developmental consequences of these microglial dysfunctions on the formation of the corpus callosum. We show that all three models of altered microglial activity resulted in the defasciculation of dorsal callosal axons. Our study demonstrates that microglia display a neurite-development-promoting function and are genuine actors of corpus callosum development. It further shows that microglial activation impinges on this function, thereby revealing that prenatal inflammation impairs neuronal development through a loss of trophic support.
Assuntos
Axônios/fisiologia , Corpo Caloso/crescimento & desenvolvimento , Corpo Caloso/fisiopatologia , Microglia/fisiologia , Complicações Infecciosas na Gravidez/fisiopatologia , Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Animais , Receptor 1 de Quimiocina CX3C , Feminino , Perfilação da Expressão Gênica , Imuno-Histoquímica , Inflamação/fisiopatologia , Lipopolissacarídeos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Camundongos Transgênicos , Neuritos/fisiologia , Gravidez , Proteínas Proto-Oncogênicas/genética , Proteínas Proto-Oncogênicas/metabolismo , Receptores de Quimiocinas/genética , Receptores de Quimiocinas/metabolismo , Transativadores/genética , Transativadores/metabolismoRESUMO
Nitric oxide (NO) is a diffusible second messenger with a great variety of functions in the brain. NO is produced by three isoforms of NO synthase (NOS), NOS1, NOS2, and NOS3. Although broad agreement exists regarding the expression of NOS1 and NOS3 in neurons and endothelial cells, the pattern of NOS2 expression is still controversial and remains elusive. We have now generated a novel transgenic mouse that expresses the fluorescent reporter tdTomato and the CRE recombinase under the control of the Nos2 gene regulatory regions. Such tool allows the reliable tracking of NOS2 expression in tissue and further unravels episodes of transient NOS2 expression. Using this transgenic mouse, we show that in the healthy brain, NOS2 is only transiently expressed in neurons scattered in the piriform and entorhinal cortex, the amygdaloid nuclei, the medial part of the thalamus, the hypothalamus, the dentate gyrus, and the cerebellum. NOS2 expression was rarely detected in microglia. We further show that inflammation, induced by intracerebral injection of LPS and IFNγ, triggers transient expression of NOS2 in microglia but not in neurons. This novel transgenic tool has thus allowed us to clarify the NOS2 expression pattern and its differential profile in neurons and microglia in healthy and inflammatory conditions.
Assuntos
Encéfalo/enzimologia , Regulação Enzimológica da Expressão Gênica , Microglia/enzimologia , Óxido Nítrico Sintase Tipo II/biossíntese , Animais , Encéfalo/patologia , Células Cultivadas , Inflamação/enzimologia , Inflamação/patologia , Camundongos , Camundongos Transgênicos , Microglia/patologiaRESUMO
BACKGROUND: Parkinson's disease (PD) is a neurodegenerative disorder characterized by a loss of dopaminergic neurons (DN) in the substantia nigra (SN). Several lines of evidence suggest that apoptotic cell death of DN is driven in part by non-cell autonomous mechanisms orchestrated by microglial cell-mediated inflammatory processes. Although the mechanisms and molecular network underlying this deleterious cross-talk between DN and microglial cells remain largely unknown, previous work indicates that, upon DN injury, activation of the ß2 integrin subunit CD11b is required for microglia-mediated DN cell death. Interestingly, during brain development, the CD11b integrin is also involved in microglial induction of neuronal apoptosis and has been shown to act in concert with the DAP12 immunoreceptor. Whether such a developmental CD11b/DAP12 pathway could be reactivated in a pathological context such as PD and play a role in microglia-induced DN cell death is a tantalizing hypothesis that we wished to test in this study. METHODS: To test the possibility that DAP12 could be involved in microglia-associated DN injury, we used both in vitro and in vivo toxin-based experimental models of PD recapitulating microglial-mediated non-cell autonomous mechanisms of DN cell death. In vitro, enriched mesencephalic neuronal/microglial co-cultures were exposed to the dopaminergic neurotoxin 1-methyl-4-phenylpyridinium (MPP+) whereas in vivo, mice were administrated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) according to acute or subchronic mode. Mice deficient for DAP12 or CD11b were used to determine the pathological function of the CD11b/DAP12 pathway in our disease models. RESULTS: Our results show that DAP12 and CD11b partially contribute to microglia-induced DN cell death in vitro. Yet, in vivo, mice deficient for either of these factors develop similar neuropathological alterations as their wild-type counterparts in two different MPTP mouse models of PD. CONCLUSION: Overall, our data suggest that DAP12 and CD11b contribute to microglial-induced DN cell death in vitro but not in vivo in the MPTP mouse model of PD. Therefore, the CD11b/DAP12 pathway may not be considered as a promising therapeutic target for PD.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/fisiologia , Antígeno CD11b/metabolismo , Modelos Animais de Doenças , Neurônios Dopaminérgicos/metabolismo , Microglia/metabolismo , Transtornos Parkinsonianos/metabolismo , Proteínas Adaptadoras de Transdução de Sinal/deficiência , Animais , Morte Celular/fisiologia , Células Cultivadas , Técnicas de Cocultura , Neurônios Dopaminérgicos/patologia , Técnicas de Introdução de Genes , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Microglia/patologia , Transtornos Parkinsonianos/patologiaRESUMO
Primary cultures are an important in vitro tool to study cellular processes and interactions. These cultures are complex systems, composed of many cell types, including neurons, astrocytes, oligodendrocytes, microglia, NG2 cells, and endothelial cells. For some studies it is necessary to be able to study a pure culture of one cell type, or eliminate a particular cell type, to better understand its function. There exist cell culture protocols for making pure astrocyte or microglia cultures. Here we present two protocols to produce cultures depleted for microglia: in the first case, from a mixed astrocyte-microglia culture and, in the second, for eliminating microglia from neuronal cultures.
Assuntos
Astrócitos/citologia , Microglia/citologia , Animais , Células Cultivadas , Humanos , Neurônios/citologiaRESUMO
Fine-tuning of neuronal activity was thought to be a neuron-autonomous mechanism until the discovery that astrocytes are active players of synaptic transmission. The involvement of astrocytes has changed our understanding of the roles of non-neuronal cells and shed new light on the regulation of neuronal activity. Microglial cells are the macrophages of the brain and they have been mostly investigated as immune cells. However, recent data discussed in this review support the notion that, similarly to astrocytes, microglia are involved in the regulation of neuronal activity. For instance, in most, if not all, brain pathologies a strong temporal correlation has long been known to exist between the pathological activation of microglia and dysfunction of neuronal activity. Recent studies have convincingly shown that alteration of microglial function is responsible for pathological neuronal activity. This causal relationship has also been demonstrated in mice bearing loss-of-function mutations in genes specifically expressed by microglia. In addition to these long-term regulations of neuronal activity, recent data show that microglia can also rapidly regulate neuronal activity, thereby acting as partners of neurotransmission.
RESUMO
Fine control of neuronal activity is crucial to rapidly adjust to subtle changes of the environment. This fine tuning was thought to be purely neuronal until the discovery that astrocytes are active players of synaptic transmission. In the adult hippocampus, microglia are the other major glial cell type. Microglia are highly dynamic and closely associated with neurons and astrocytes. They react rapidly to modifications of their environment and are able to release molecules known to control neuronal function and synaptic transmission. Therefore, microglia display functional features of synaptic partners, but their involvement in the regulation of synaptic transmission has not yet been addressed. We have used a combination of pharmacological approaches with electrophysiological analysis on acute hippocampal slices and ATP assays in purified cell cultures to show that activation of microglia induces a rapid increase of spontaneous excitatory postsynaptic currents. We found that this modulation is mediated by binding of ATP to P2Y1R located on astrocytes and is independent of TNFα or NOS2. Our data indicate that, on activation, microglia cells rapidly release small amounts of ATP, and astrocytes, in turn, amplified this release. Finally, P2Y1 stimulation of astrocytes increased excitatory postsynaptic current frequency through a metabotropic glutamate receptor 5-dependent mechanism. These results indicate that microglia are genuine regulators of neurotransmission and place microglia as upstream partners of astrocytes. Because pathological activation of microglia and alteration of neurotransmission are two early symptoms of most brain diseases, our work also provides a basis for understanding synaptic dysfunction in neuronal diseases.
Assuntos
Astrócitos/fisiologia , Potenciais Pós-Sinápticos Excitadores/fisiologia , Hipocampo/fisiologia , Microglia/fisiologia , Trifosfato de Adenosina/metabolismo , Análise de Variância , Animais , Astrócitos/metabolismo , Astrócitos/ultraestrutura , Western Blotting , Primers do DNA/genética , Eletrofisiologia , Imunofluorescência , Imuno-Histoquímica , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Microglia/metabolismo , Microglia/ultraestrutura , Microscopia Confocal , Microscopia Eletrônica , Reação em Cadeia da Polimerase em Tempo Real , Receptor de Glutamato Metabotrópico 5 , Receptores de Glutamato Metabotrópico/metabolismo , Receptores Purinérgicos P2Y1/metabolismoRESUMO
Microglia were recently shown to play unexpected roles in normal brain development and adult physiology. This has begun to dramatically change our view of these resident "immune" cells. Here, we briefly review topics covered in our 2011 Society for Neuroscience minisymposium "The Role of Microglia in the Healthy Brain." This summary is not meant to be a comprehensive review of microglia physiology, but rather to share new results and stimulate further research into the cellular and molecular mechanisms by which microglia influence postnatal development, adult neuronal plasticity, and circuit function.
Assuntos
Encéfalo/citologia , Microglia/fisiologia , Animais , Encéfalo/crescimento & desenvolvimento , Humanos , Rede Nervosa/fisiologia , Fagocitose/fisiologiaRESUMO
In all the species examined thus far, the behavior of microglia during development appears to be highly stereotyped. This reproducibility supports the notion that these cells have a physiological role in development. Microglia are macrophages that migrate from the yolk sac and colonize the central nervous system early during development. The first invading yolk-sac macrophages are highly proliferative and their role has not yet been addressed. At later developmental stages, microglia can be found throughout the brain and tend to preferentially reside at specific locations that are often associated with known developmental processes. Thus, it appears that microglia concentrate in areas of cell death, in proximity of developing blood vessels, in the marginal layer, which contains developing axon fascicles, and in close association with radial glial cells. This review describes the main features of brain colonization by microglia and discusses the possible physiological roles of these cells during development.
Assuntos
Sistema Nervoso Central/citologia , Sistema Nervoso Central/embriologia , Microglia/citologia , Microglia/fisiologia , Animais , Comunicação Celular/fisiologia , Sistema Nervoso Central/fisiologia , Humanos , Neurônios/citologia , Neurônios/fisiologia , Saco Vitelino/citologia , Saco Vitelino/fisiologiaRESUMO
Neurons and astrocytes are generated sequentially from radial glia. Once neurogenesis is completed, radial glia starts to differentiate into immature astrocytes. Astrocytes then maturate and change their morphology and electrophysiological properties. Neurotrophic cytokines or bone morphogenetic proteins have been identified as inducers of the developmental switch from neurogenesis to astrogenesis. However, the factors and mechanisms regulating the late differentiation of radial glia and the subsequent astrocyte maturation are poorly described. We used two independent approaches to examine the role of nitric oxide (NO) in the process of astrogenesis and maturation of astrocytes. First using a pharmacological approach, we depleted NO from developing hippocampus by intraventricular injection of a specific scavenger. Then by a genetic approach, we analyzed a nitric oxide synthase-2 (NOS2) knockout mouse. In both models, we found that differentiation of RC2-positive radial glia into late GFAP-positive radial glia was impaired. The cell-fate analysis after incorporation of BrdU demonstrated that astrogenesis was not altered upon NOS2 deficiency. Maturation of astrocytes was assessed by electrophysiological recordings at P7 and functional analysis. In wild type, 20% of astrocytes were immature as shown by their non-linear I/V relationship and high membrane resistance, whereas in NOS2-/- hippocampus, 51% of the astrocytes displayed an immature profile. The reduced branching of astrocytes upon NOS2 deficiency and their low content in connexin-43 further confirmed their immature profile. Our results highlight a novel developmental role of NO and NOS2 in the differentiation of radial glia and the maturation of astrocytes.
Assuntos
Astrócitos/fisiologia , Hipocampo/citologia , Óxido Nítrico Sintase Tipo II/metabolismo , Óxido Nítrico/metabolismo , Animais , Astrócitos/citologia , Diferenciação Celular/fisiologia , Células Cultivadas , Proteína Glial Fibrilar Ácida/genética , Proteína Glial Fibrilar Ácida/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Óxido Nítrico Sintase Tipo II/genética , Técnicas de Patch-ClampRESUMO
A growing number of long nuclear-retained non-coding RNAs (ncRNAs) have recently been described. However, few functions have been elucidated for these ncRNAs. Here, we have characterized the function of one such ncRNA, identified as metastasis-associated lung adenocarcinoma transcript 1 (Malat1). Malat1 RNA is expressed in numerous tissues and is highly abundant in neurons. It is enriched in nuclear speckles only when RNA polymerase II-dependent transcription is active. Knock-down studies revealed that Malat1 modulates the recruitment of SR family pre-mRNA-splicing factors to the transcription site of a transgene array. DNA microarray analysis in Malat1-depleted neuroblastoma cells indicates that Malat1 controls the expression of genes involved not only in nuclear processes, but also in synapse function. In cultured hippocampal neurons, knock-down of Malat1 decreases synaptic density, whereas its over-expression results in a cell-autonomous increase in synaptic density. Our results suggest that Malat1 regulates synapse formation by modulating the expression of genes involved in synapse formation and/or maintenance.
Assuntos
Biomarcadores/metabolismo , Núcleo Celular/genética , Regulação da Expressão Gênica/fisiologia , Neurogênese/fisiologia , RNA Nuclear/fisiologia , Sinapses/genética , Fatores de Transcrição/genética , Animais , Northern Blotting , Neoplasias Ósseas/genética , Neoplasias Ósseas/metabolismo , Neoplasias Ósseas/patologia , Núcleo Celular/metabolismo , Células Cultivadas , Perfilação da Expressão Gênica , Hipocampo/citologia , Hipocampo/metabolismo , Humanos , Camundongos , Neuroblastoma/genética , Neuroblastoma/metabolismo , Neuroblastoma/patologia , Neurônios/citologia , Neurônios/metabolismo , Análise de Sequência com Séries de Oligonucleotídeos , Osteossarcoma/genética , Osteossarcoma/metabolismo , Osteossarcoma/patologia , Precursores de RNA/genética , Splicing de RNA/genética , RNA Mensageiro/genética , Proteínas Repressoras , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Transativadores , Fatores de Transcrição/metabolismoRESUMO
In several brain regions, microglia actively promote neuronal apoptosis during development. However, molecular actors leading microglia to trigger death remain mostly unknown. Here, we show that, in the developing hippocampus, apoptotic neurons are contacted by microglia expressing both the integrin CD11b and the immunoreceptor DAP12. We demonstrate that developmental apoptosis decreases in mice deficient for CD11b or DAP12. In addition, function-blocking antibodies directed against CD11b decrease neuronal death when injected into wild-type neonates, but have no effect when injected into DAP12-deficient littermates. This demonstrates that DAP12 and CD11b act in converging pathways to induce neuronal death. Finally, we show that DAP12 and CD11b control the production of microglial superoxide ions, which kill the neurons. Thus, our data show that the process of developmental neuronal death triggered by microglia is similar to the elimination of pathogenic cells by the innate immune cells.