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Astrogliosis is a condition shared by acute and chronic neurological diseases and includes morphological, proteomic, and functional rearrangements of astroglia. In Alzheimer's disease (AD), reactive astrocytes frame amyloid deposits and exhibit structural changes associated with the overexpression of specific proteins, mostly belonging to intermediate filaments. At a functional level, amyloid beta triggers dysfunctional calcium signaling in astrocytes, which contributes to the maintenance of chronic neuroinflammation. Therefore, the identification of intracellular players that participate in astrocyte calcium signaling can help unveil the mechanisms underlying astrocyte reactivity and loss of function in AD. We have recently identified the calcium-binding protein centrin-2 (CETN2) as a novel astrocyte marker in the human brain and, in order to determine whether astrocytic CETN2 expression and distribution could be affected by neurodegenerative conditions, we examined its pattern in control and sporadic AD patients. By immunoblot, immunohistochemistry, and targeted-mass spectrometry, we report a positive correlation between entorhinal CETN2 immunoreactivity and neurocognitive impairment, along with the abundance of amyloid depositions and neurofibrillary tangles, thus highlighting a linear relationship between CETN2 expression and AD progression. CETN2-positive astrocytes were dispersed in the entorhinal cortex with a clustered pattern and colocalized with reactive glia markers STAT3, NFATc3, and YKL-40, indicating a human-specific role in AD-induced astrogliosis. Collectively, our data provide the first evidence that CETN2 is part of the astrocytic calcium toolkit undergoing rearrangements in AD and adds CETN2 to the list of proteins that could play a role in disease evolution.
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During brain maturation, astrocytes establish complex morphologies unveiling intense structural plasticity. Connexin 30 (Cx30), a gap-junction channel-forming protein expressed postnatally, dynamically regulates during development astrocyte morphological properties by controlling ramification and extension of fine processes. However, the underlying mechanisms remain unexplored. Here, we found in vitro that Cx30 interacts with the actin cytoskeleton in astrocytes and inhibits its structural reorganization and dynamics during cell migration. This translates into an alteration of local physical surface properties, as assessed by correlative imaging using stimulated emission depletion (STED) super resolution imaging and atomic force microscopy (AFM). Specifically, Cx30 impaired astrocyte cell surface topology and cortical stiffness in motile astrocytes. As Cx30 alters actin organization, dynamics, and membrane physical properties, we assessed whether it controls astrocyte migration. We found that Cx30 reduced persistence and directionality of migrating astrocytes. Altogether, these data reveal Cx30 as a brake for astrocyte structural and mechanical plasticity.
Assuntos
Citoesqueleto de Actina , Astrócitos , Movimento Celular , Conexina 30 , Astrócitos/metabolismo , Animais , Movimento Celular/fisiologia , Citoesqueleto de Actina/metabolismo , Conexina 30/metabolismo , Células Cultivadas , Camundongos , Microscopia de Força Atômica/métodos , Camundongos Endogâmicos C57BLRESUMO
The 18 kDa translocator protein (TSPO) is a classical marker of neuroinflammation targeted for in vivo molecular imaging. Microglial cells were originally thought to be the only source of TSPO overexpression but astrocytes, neurons and endothelial cells can also up-regulate TSPO depending on the pathological context. This study aims to determine the cellular origin of TSPO overexpression in a simplified model of neuroinflammation and to identify the molecular pathways involved. This is essential to better interpret TSPO molecular imaging in preclinical and clinical settings. We used lentiviral vectors (LV) to overexpress the ciliary neurotrophic factor (CNTF) in the right striatum of 2-month-old Sprague Dawley rats. A LV encoding for ß-Galactosidase (LV-LacZ) was used as control. One month later, TSPO expression was measured by single-photon emission computed tomography (SPECT) imaging using [125I]CLINDE. The fluorescence-activated cell sorting to radioligand-treated tissue (FACS-RTT) method was used to quantify TSPO levels in acutely sorted astrocytes, microglia, neurons and endothelial cells. A second cohort was injected with LV-CNTF and a LV encoding suppressor of cytokine signaling 3 (SOCS3), to inhibit the JAK-STAT3 pathway specifically in astrocytes. GFAP and TSPO expressions were quantified by immunofluorescence. We measured a significant increase in TSPO signal in response to CNTF by SPECT imaging. Using FACS-RTT, we observed TSPO overexpression in reactive astrocytes (+ 153 ± 62%) but also in microglia (+ 2088 ± 500%) and neurons (+ 369 ± 117%), accompanied by an increase in TSPO binding sites per cell in those three cell populations. Endothelial cells did not contribute to TSPO signal increase. Importantly, LV-SOCS3 reduced CNTF-induced astrocyte reactivity and decreased global TSPO immunoreactivity (-71% ± 30%), suggesting that TSPO overexpression is primarily mediated by reactive astrocytes. Overall, this study reveals that CNTF induces TSPO in multiple cell types in the rat striatum, through the JAK2-STAT3 pathway in astrocytes, identifying this cell type as the primary mediator of CNTF effects neuroinflammatory processes. Our results highlight the difficulty to interpret TSPO imaging in term of cellular origin without addition cellular analysis by FACS-RTT or quantitative immunostainings. Consequently, TSPO should only be used as a global marker of neuroinflammation.
Assuntos
Astrócitos , Fator Neurotrófico Ciliar , Animais , Ratos , Astrócitos/metabolismo , Proteínas de Transporte/metabolismo , Fator Neurotrófico Ciliar/metabolismo , Fator Neurotrófico Ciliar/farmacologia , Células Endoteliais/metabolismo , Doenças Neuroinflamatórias , Ratos Sprague-DawleyRESUMO
Astrocytes are thought to play a crucial role in brain iron homeostasis. How they accomplish this regulation in vivo is unclear. In a recent transcriptomic analysis, we showed that polysomal Ftl1 and Fth1 mRNAs, encoding the ferritin light (Ftl) and heavy (Fth) chains that assemble into ferritin, a critical complex for iron storage and reduction, are enriched in perisynaptic astrocytic processes as compared to astrocytic soma. These data suggested that ferritin translation plays a specific role at the perisynaptic astrocytic interface and is tighly regulated by local translation. Here, we used our recently described AstroDot 3D in situ methodology to study the density and localization of ferritin mRNAs in astrocytes in the hippocampus in three different contexts in which local or systemic iron overload has been documented: aging, the hepcidin knock-out mouse model of hemochromatosis and the APP/PS1dE9 mouse model of Alzheimer's disease (AD). Our results showed that in wild type mice, Fth1 mRNA density was higher than Ftl1 and that both mRNAs were mostly distributed in astrocyte fine processes. Aging and absence of hepcidin caused an increased Fth1/Ftl1 ratio in astrocytes and in the case of aging, led to a redistribution of Fth1 mRNAs in astrocytic fine processes. In contrast, in AD mice, we observed a lower Fth1/Ftl1 ratio. Fth1 mRNAs became more somatic and Ftl1 mRNAs redistributed in large processes of astrocytes proximal to Amyloid beta (Aß) deposits. Hence, we propose that regulation of ferritin mRNA density and distribution in astrocytes contribute to iron homeostasis in physiology and pathophysiology.
Assuntos
Doença de Alzheimer , Ferritinas , Camundongos , Animais , Ferritinas/genética , Ferritinas/metabolismo , Hepcidinas , Astrócitos/metabolismo , Peptídeos beta-Amiloides , RNA Mensageiro , Ferro/metabolismo , Doença de Alzheimer/patologia , Camundongos Knockout , Hipocampo/metabolismoRESUMO
Huntington's disease is a fatal neurodegenerative disease characterized by striatal neurodegeneration, aggregation of mutant Huntingtin and the presence of reactive astrocytes. Astrocytes are important partners for neurons and engage in a specific reactive response in Huntington's disease that involves morphological, molecular and functional changes. How reactive astrocytes contribute to Huntington's disease is still an open question, especially because their reactive state is poorly reproduced in experimental mouse models. Here, we show that the JAK2-STAT3 pathway, a central cascade controlling astrocyte reactive response, is activated in the putamen of Huntington's disease patients. Selective activation of this cascade in astrocytes through viral gene transfer reduces the number and size of mutant Huntingtin aggregates in neurons and improves neuronal defects in two complementary mouse models of Huntington's disease. It also reduces striatal atrophy and increases glutamate levels, two central clinical outcomes measured by non-invasive magnetic resonance imaging. Moreover, astrocyte-specific transcriptomic analysis shows that activation of the JAK2-STAT3 pathway in astrocytes coordinates a transcriptional program that increases their intrinsic proteolytic capacity, through the lysosomal and ubiquitin-proteasome degradation systems. This pathway also enhances their production and exosomal release of the co-chaperone DNAJB1, which contributes to mutant Huntingtin clearance in neurons. Together, our results show that the JAK2-STAT3 pathway controls a beneficial proteostasis response in reactive astrocytes in Huntington's disease, which involves bi-directional signalling with neurons to reduce mutant Huntingtin aggregation, eventually improving disease outcomes.
Assuntos
Doença de Huntington , Doenças Neurodegenerativas , Animais , Camundongos , Doença de Huntington/genética , Astrócitos/metabolismo , Proteostase , Doenças Neurodegenerativas/patologia , Neurônios/metabolismo , Proteína Huntingtina/genética , Proteína Huntingtina/metabolismoRESUMO
Astrocytes are essential partners of neurons in the central nervous system. In response to many brain diseases, astrocytes change at the morphological, molecular and functional levels: they become reactive. These multiple changes are likely to have significant impacts on neurons, which are dependent on several astrocyte functions. Astrocyte reactivity is context-specific. It is therefore essential to determine the changes occurring in reactive astrocytes in each pathological situation, through dedicated and selective approaches. This will promote the development of innovative therapies that target the cellular partners of neurons, as well as the identification of specific disease biomarkers.
Title: Astrocytes réactifs et maladies cérébrales - Biomarqueurs et cibles thérapeutiques. Abstract: Les astrocytes sont des partenaires essentiels des neurones dans le système nerveux central. En réponse à de nombreuses maladies qui touchent le cerveau, les astrocytes subissent des modifications morphologiques, moléculaires et fonctionnelles : ils deviennent réactifs. Ces changements multiples sont susceptibles d'avoir un impact important sur les neurones, qui dépendent de nombreuses fonctions remplies par les astrocytes. La réponse de réactivité astrocytaire dépend du contexte pathologique. Il est donc indispensable de définir précisément les changements qui se produisent dans les astrocytes réactifs dans chaque situation pathologique, par des approches adaptées et sélectives. Cela permettra le développement de thérapies innovantes ciblant ces cellules partenaires des neurones, ainsi que l'identification de biomarqueurs spécifiques de certaines maladies cérébrales.
Assuntos
Astrócitos , Encefalopatias , Astrócitos/fisiologia , Biomarcadores , Encéfalo/patologia , Encefalopatias/terapia , Sistema Nervoso Central , Humanos , Neurônios/fisiologiaRESUMO
The phenotypic transformation of astrocytes in Alzheimer's disease (AD) is still not well understood. Recent analyses based on single-nucleus RNA sequencing of postmortem Alzheimer's disease (AD) samples are limited by the low number of sequenced astrocytes, small cohort sizes, and low number of differentially expressed genes detected. To optimize the detection of astrocytic genes, we employed a novel strategy consisting of the localization of pre-determined astrocyte and neuronal gene clusters in publicly available whole-brain transcriptomes. Specifically, we used cortical transcriptomes from 766 individuals, including cognitively normal subjects (Controls), and people diagnosed with mild cognitive impairment (MCI) or dementia due to AD. Samples came from three independent cohorts organized by the Mount Sinai Hospital, the Mayo Clinic, and the Religious Order Study/Memory and Aging Project (ROSMAP). Astrocyte- and neuron-specific gene clusters were generated from human brain cell-type specific RNAseq data using hierarchical clustering and cell-type enrichment scoring. Genes from each cluster were manually annotated according to cell-type specific functional Categories. Gene Set Variation Analysis (GSVA) and Principal Component Analysis (PCA) were used to establish changes in these functional categories among clinical cohorts. We highlight three novel findings of the study. First, individuals with the same clinical diagnosis were molecularly heterogeneous. Particularly in the Mayo Clinic and ROSMAP cohorts, over 50% of Controls presented down-regulation of genes encoding synaptic proteins typical of AD, whereas 30% of patients diagnosed with dementia due to AD presented Control-like transcriptomic profiles. Second, down-regulation of neuronal genes related to synaptic proteins coincided, in astrocytes, with up-regulation of genes related to perisynaptic astrocytic processes (PAP) and down-regulation of genes encoding endolysosomal and mitochondrial proteins. Third, down-regulation of astrocytic mitochondrial genes inversely correlated with the disease stages defined by Braak and CERAD scoring. Finally, we interpreted these changes as maladaptive or adaptive from the point of view of astrocyte biology in a model of the phenotypical transformation of astrocytes in AD. The main prediction is that early malfunction of the astrocytic endolysosomal system, associated with progressive mitochondrial dysfunction, contribute to Alzheimer's disease. If this prediction is correct, therapies preventing organelle dysfunction in astrocytes may be beneficial in preclinical and clinical AD.
Assuntos
Doença de Alzheimer , Disfunção Cognitiva , Doença de Alzheimer/metabolismo , Astrócitos/metabolismo , Disfunção Cognitiva/complicações , Perfilação da Expressão Gênica , Humanos , Organelas/metabolismo , TranscriptomaRESUMO
We are at a time of considerable growth in the use and development of transcriptomics studies and subsequent in silico analysis. RNA sequencing is one of the most widely used approaches, now integrated in many studies. The processing of these data may typically require a noteworthy number of steps, statistical knowledge, and coding skills which is not accessible to all scientists. Despite the undeniable development of software applications over the years to address this concern, it is still possible to improve. Here we present DEVEA, an R shiny application tool developed to perform differential expression analysis, data visualization and enrichment pathway analysis mainly from transcriptomics data, but also from simpler gene lists with or without statistical values. Its intuitive and easy-to-manipulate interface facilitates gene expression exploration through numerous interactive figures and tables, statistical comparisons of expression profile levels between groups and further meta-analysis such as enrichment analysis, without bioinformatics expertise. DEVEA performs a thorough analysis from multiple and flexible input data representing distinct analysis stages. From them, it produces dynamic graphs and tables, to explore the expression levels and statistical differential expression analysis results. Moreover, it generates a comprehensive pathway analysis to extend biological insights. Finally, a complete and customizable HTML report can be extracted for further result exploration outside the application. DEVEA is accessible at https://shiny.imib.es/devea/ and the source code is available on our GitHub repository https://github.com/MiriamRiquelmeP/DEVEA.
Assuntos
Visualização de Dados , Transcriptoma , Software , Perfilação da Expressão Gênica/métodos , Biologia Computacional/métodosRESUMO
Neurodegenerative diseases (NDs) are characterized by primary symptoms, such as cognitive or motor deficits. In addition, the presence of neuropsychiatric symptoms (NPS) in patients with ND is being increasingly acknowledged as an important disease feature. Yet, their neurobiological basis remains unclear and mostly centered on neurons while overlooking astrocytes, which are crucial regulators of neuronal function underlying complex behaviors. In this opinion article, we briefly review evidence for NPS in ND and discuss their experimental assessment in preclinical models. We then present recent studies showing that astrocyte-specific dysfunctions can lead to NPS. Because many astrocyte alterations are also observed in ND, we suggest that they might underlie ND-associated NPS. We argue that there is a need for dedicated preclinical studies assessing astrocyte-based therapeutic strategies targeting NPS in the context of ND.
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Transtornos Mentais , Doenças Neurodegenerativas , Astrócitos , Humanos , NeurôniosRESUMO
Deposits of different abnormal forms of tau in neurons and astrocytes represent key anatomo-pathological features of tauopathies. Although tau protein is highly enriched in neurons and poorly expressed by astrocytes, the origin of astrocytic tau is still elusive. Here, we used innovative gene transfer tools to model tauopathies in adult mouse brains and to investigate the origin of astrocytic tau. We showed in our adeno-associated virus (AAV)-based models and in Thy-Tau22 transgenic mice that astrocytic tau pathology can emerge secondarily to neuronal pathology. By designing an in vivo reporter system, we further demonstrated bidirectional exchanges of tau species between neurons and astrocytes. We then determined the consequences of tau accumulation in astrocytes on their survival in models displaying various status of tau aggregation. Using stereological counting of astrocytes, we report that, as for neurons, soluble tau species are highly toxic to some subpopulations of astrocytes in the hippocampus, whereas the accumulation of tau aggregates does not affect their survival. Thus, astrocytes are not mere bystanders of neuronal pathology. Our results strongly suggest that tau pathology in astrocytes may significantly contribute to clinical symptoms.
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Astrócitos/patologia , Hipocampo/patologia , Tauopatias/patologia , Proteínas tau/toxicidade , Animais , Humanos , Masculino , Camundongos , Neurônios/patologia , Agregados Proteicos , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Isoformas de Proteínas/toxicidade , Tauopatias/metabolismo , Proteínas tau/genética , Proteínas tau/metabolismoRESUMO
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.
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Envelhecimento/patologia , Astrócitos/patologia , Encéfalo/patologia , Medula Espinal/patologia , Animais , Encefalopatias/patologia , Lesões Encefálicas/patologia , Humanos , Traumatismos da Medula Espinal/patologiaRESUMO
Brain water and some critically important energy metabolites, such as lactate or glucose, are present in both intracellular and extracellular spaces (ICS/ECS) at significant levels. This ubiquitous nature makes diffusion MRI/MRS data sometimes difficult to interpret and model. While it is possible to glean information on the diffusion properties in ICS by measuring the diffusion of purely intracellular endogenous metabolites (such as NAA), the absence of endogenous markers specific to ECS hampers similar analyses in this compartment. In past experiments, exogenous probes have therefore been injected into the brain to assess their apparent diffusion coefficient (ADC) and thus estimate tortuosity in ECS. Here, we use a similar approach in mice by injecting sucrose, a well-known ECS marker, in either the lateral ventricles or directly in the prefrontal cortex. For the first time, we propose a thorough characterization of ECS diffusion properties encompassing (1) short-range restriction by looking at signal attenuation at high b values, (2) tortuosity and long-range restriction by measuring ADC time-dependence at long diffusion times and (3) microscopic anisotropy by performing double diffusion encoding (DDE) measurements. Overall, sucrose diffusion behavior is strikingly different from that of intracellular metabolites. Acquisitions at high b values not only reveal faster sucrose diffusion but also some sensitivity to restriction, suggesting that the diffusion in ECS is not fully Gaussian at high b. The time evolution of the ADC at long diffusion times shows that the tortuosity regime is not reached yet in the case of sucrose, while DDE experiments suggest that it is not trapped in elongated structures. No major difference in sucrose diffusion properties is reported between the two investigated routes of injection and brain regions. These original experimental insights should be useful to better interpret and model the diffusion signal of molecules that are distributed between ICS and ECS compartments.
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Encéfalo/metabolismo , Espectroscopia de Ressonância Magnética/métodos , Sacarose/farmacocinética , Animais , Difusão , Imagem de Difusão por Ressonância Magnética , Camundongos , Camundongos Endogâmicos C57BLRESUMO
Brain function relies on complex interactions between neurons and different types of glial cells, such as astrocytes, microglia and oligodendrocytes. The relatively young field of "gliobiology" is thriving. Thanks to various technical innovations, it is now possible to address challenging biological questions on glial cells and unravel their multiple roles in brain function and dysfunction.
TITLE: De nouvelles techniques pour dévoiler le rôle des cellules gliales du cerveau. ABSTRACT: L'exécution des fonctions cérébrales requiert des interactions optimales entre les neurones et les différents types de cellules gliales (astrocytes, microglies et oligodendrocytes). Le domaine de la gliobiologie, qui s'intéresse aux cellules gliales, est en pleine expansion. Les innovations techniques permettent désormais d'aborder des questions biologiques complexes quant aux rôles de ces cellules dans le fonctionnement physiologique et pathologique du cerveau. Dans cette synthèse, nous décrivons comment certaines de ces avancées techniques nous ont permis d'en apprendre davantage sur les origines et les rôles fonctionnels des cellules gliales. Nous illustrons également comment ces techniques et les découvertes qui en ont découlé, peuvent être transposées en clinique et pourraient, dans un futur proche, offrir des nouvelles perspectives thérapeutiques.
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Encéfalo/citologia , Glicômica/tendências , Neuroglia/fisiologia , Animais , Encéfalo/fisiologia , Química Encefálica , Glicômica/métodos , Humanos , Invenções , Metabolômica/métodos , Metabolômica/tendênciasRESUMO
Astrocytes are thought to play a pivotal role in coupling neural activity and cerebral blood flow. However, it has been shown that astrocytes undergo morphologic changes in response to brain metastasis, switching to a reactive phenotype, which has the potential to significantly compromise cerebrovascular function and contribute to the neurological sequelae associated with brain metastasis. Given that STAT3 is a key regulator of astrocyte reactivity, we aimed here to determine the impact of STAT3-mediated astrocyte reactivity on neurovascular function in brain metastasis. Rat models of brain metastasis and ciliary neurotrophic factor were used to induce astrocyte reactivity. Multimodal imaging, electrophysiology, and IHC were performed to determine the relationship between reactive astrocytes and changes in the cerebrovascular response to electrical and physiological stimuli. Subsequently, the STAT3 pathway in astrocytes was inhibited with WP1066 to determine the role of STAT3-mediated astrocyte reactivity, specifically, in brain metastasis. Astrocyte reactivity associated with brain metastases impaired cerebrovascular responses to stimuli at both the cellular and functional level and disrupted astrocyte-endothelial interactions in both animal models and human brain metastasis samples. Inhibition of STAT3-mediated astrocyte reactivity in rats with brain metastases restored cerebrovascular function, as shown by in vivo imaging, and limited cerebrovascular changes associated with tumor growth. Together these findings suggest that inhibiting STAT3-mediated astrocyte reactivity may confer significant improvements in neurological outcome for patients with brain metastases and could potentially be tested in other brain tumors. SIGNIFICANCE: These findings demonstrate that selectively targeting STAT3-mediated astrocyte reactivity ameliorates the cerebrovascular dysfunction associated with brain metastasis, providing a potential therapeutic avenue for improved patient outcome.
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Astrócitos/patologia , Neoplasias Encefálicas/patologia , Fator de Transcrição STAT3/metabolismo , Animais , Astrócitos/metabolismo , Neoplasias Encefálicas/irrigação sanguínea , Neoplasias Encefálicas/diagnóstico por imagem , Linhagem Celular Tumoral , Circulação Cerebrovascular , Fator Neurotrófico Ciliar/genética , Fator Neurotrófico Ciliar/metabolismo , Feminino , Humanos , Imagem de Contraste de Manchas a Laser , Espectroscopia de Ressonância Magnética , Imagem Multimodal , Neoplasias Experimentais/diagnóstico por imagem , Neoplasias Experimentais/patologia , Piridinas/farmacologia , Ratos , Ratos Endogâmicos , Tirfostinas/farmacologiaRESUMO
In Alzheimer disease (AD), astrocytes undergo complex changes and become reactive. The consequences of this reaction are still unclear. To evaluate the net impact of reactive astrocytes in AD, we developed viral vectors targeting astrocytes that either activate or inhibit the Janus kinase-signal transducer and activator of transcription 3 (JAK2-STAT3) pathway, a central cascade controlling astrocyte reaction. We aimed to evaluate whether reactive astrocytes contribute to tau as well as amyloid pathologies in the hippocampus of 3xTg-AD mice, an AD model that develops tau hyper-phosphorylation and amyloid deposition. JAK2-STAT3 pathway-mediated modulation of reactive astrocytes in 25% of the hippocampus of 3xTg-AD mice did not significantly influence tau phosphorylation or amyloid processing and deposition at early, advanced, and terminal disease stage. Interestingly, inhibition of the JAK2-STAT3 pathway in hippocampal astrocytes did not improve spatial memory in the Y maze but it did reduce anxiety in the elevated plus maze. Our unique approach to specifically manipulate reactive astrocytes in situ show they may impact behavioral outcomes without influencing tau or amyloid pathology.
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Doença de Alzheimer/genética , Doença de Alzheimer/metabolismo , Astrócitos/metabolismo , Doença de Alzheimer/patologia , Proteínas Amiloidogênicas/metabolismo , Animais , Astrócitos/patologia , Modelos Animais de Doenças , Hipocampo/citologia , Hipocampo/metabolismo , Hipocampo/patologia , Janus Quinase 2/metabolismo , Camundongos Transgênicos , Fosforilação , Fator de Transcrição STAT3/metabolismo , Transdução de Sinais/genética , Proteínas tau/metabolismoRESUMO
Development, physiological functions, and pathologies of the brain depend on tight interactions between neurons and different types of glial cells, such as astrocytes, microglia, oligodendrocytes, and oligodendrocyte precursor cells. Assessing the relative contribution of different glial cell types is required for the full understanding of brain function and dysfunction. Over the recent years, several technological breakthroughs were achieved, allowing "glio-scientists" to address new challenging biological questions. These technical developments make it possible to study the roles of specific cell types with medium or high-content workflows and perform fine analysis of their mutual interactions in a preserved environment. This review illustrates the potency of several cutting-edge experimental approaches (advanced cell cultures, induced pluripotent stem cell (iPSC)-derived human glial cells, viral vectors, in situ glia imaging, opto- and chemogenetic approaches, and high-content molecular analysis) to unravel the role of glial cells in specific brain functions or diseases. It also illustrates the translation of some techniques to the clinics, to monitor glial cells in patients, through specific brain imaging methods. The advantages, pitfalls, and future developments are discussed for each technique, and selected examples are provided to illustrate how specific "gliobiological" questions can now be tackled.
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Astrócitos , Neuroglia , Humanos , Microglia , Neurônios , OligodendrogliaRESUMO
Astrocytes are key cellular partners for neurons in the central nervous system. Astrocytes react to virtually all types of pathological alterations in brain homeostasis by significant morphological and molecular changes. This response was classically viewed as stereotypical and is called astrogliosis or astrocyte reactivity. It was long considered as a nonspecific, secondary reaction to pathological conditions, offering no clues on disease-causing mechanisms and with little therapeutic value. However, many studies over the last 30 years have underlined the crucial and active roles played by astrocytes in physiology, ranging from metabolic support, synapse maturation, and pruning to fine regulation of synaptic transmission. This prompted researchers to explore how these new astrocyte functions were changed in disease, and they reported alterations in many of them (sometimes beneficial, mostly deleterious). More recently, cell-specific transcriptomics revealed that astrocytes undergo massive changes in gene expression when they become reactive. This observation further stressed that reactive astrocytes may be very different from normal, nonreactive astrocytes and could influence disease outcomes. To make the picture even more complex, both normal and reactive astrocytes were shown to be molecularly and functionally heterogeneous. Very little is known about the specific roles that each subtype of reactive astrocytes may play in different disease contexts. In this review, we have interrogated researchers in the field to identify and discuss points of consensus and controversies about reactive astrocytes, starting with their very name. We then present the emerging knowledge on these cells and future challenges in this field.
Assuntos
Astrócitos/metabolismo , Encéfalo/metabolismo , Doenças do Sistema Nervoso Central/metabolismo , Animais , Astrócitos/patologia , Encéfalo/patologia , Doenças do Sistema Nervoso Central/patologia , Gliose/metabolismo , Gliose/patologia , HumanosRESUMO
Reactive astrocytes exhibit hypertrophic morphology and altered metabolism. Deciphering astrocytic status would be of great importance to understand their role and dysregulation in pathologies, but most analytical methods remain highly invasive or destructive. The diffusion of brain metabolites, as non-invasively measured using diffusion-weighted magnetic resonance spectroscopy (DW-MRS) in vivo, depends on the structure of their micro-environment. Here we perform advanced DW-MRS in a mouse model of reactive astrocytes to determine how cellular compartments confining metabolite diffusion are changing. This reveals myo-inositol as a specific intra-astrocytic marker whose diffusion closely reflects astrocytic morphology, enabling non-invasive detection of astrocyte hypertrophy (subsequently confirmed by confocal microscopy ex vivo). Furthermore, we measure massive variations of lactate diffusion properties, suggesting that intracellular lactate is predominantly astrocytic under control conditions, but predominantly neuronal in case of astrocyte reactivity. This indicates massive remodeling of lactate metabolism, as lactate compartmentation is tightly linked to the astrocyte-to-neuron lactate shuttle mechanism.
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Astrócitos/metabolismo , Encéfalo/metabolismo , Inositol/análise , Espectroscopia de Ressonância Magnética/métodos , Animais , Biomarcadores/análise , Biomarcadores/metabolismo , Imagem de Difusão por Ressonância Magnética , Inositol/metabolismo , Ácido Láctico/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos C57BLRESUMO
Astrocyte reactivity and neuroinflammation are hallmarks of CNS pathological conditions such as Alzheimer's disease. However, the specific role of reactive astrocytes is still debated. This controversy may stem from the fact that most strategies used to modulate astrocyte reactivity and explore its contribution to disease outcomes have only limited specificity. Moreover, reactive astrocytes are now emerging as heterogeneous cells and all types of astrocyte reactivity may not be controlled efficiently by such strategies.Here, we used cell type-specific approaches in vivo and identified the JAK2-STAT3 pathway, as necessary and sufficient for the induction and maintenance of astrocyte reactivity. Modulation of this cascade by viral gene transfer in mouse astrocytes efficiently controlled several morphological and molecular features of reactivity. Inhibition of this pathway in mouse models of Alzheimer's disease improved three key pathological hallmarks by reducing amyloid deposition, improving spatial learning and restoring synaptic deficits.In conclusion, the JAK2-STAT3 cascade operates as a master regulator of astrocyte reactivity in vivo. Its inhibition offers new therapeutic opportunities for Alzheimer's disease.
Assuntos
Doença de Alzheimer/patologia , Doença de Alzheimer/fisiopatologia , Astrócitos/patologia , Secretases da Proteína Precursora do Amiloide/metabolismo , Peptídeos beta-Amiloides/metabolismo , Precursor de Proteína beta-Amiloide/genética , Precursor de Proteína beta-Amiloide/metabolismo , Animais , Apolipoproteínas E/metabolismo , Ácido Aspártico Endopeptidases/metabolismo , Astrócitos/metabolismo , Modelos Animais de Doenças , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Potenciais Pós-Sinápticos Excitadores/genética , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Proteína Glial Fibrilar Ácida/metabolismo , Hipocampo/citologia , Janus Quinase 2/genética , Janus Quinase 2/metabolismo , Masculino , Aprendizagem em Labirinto/efeitos dos fármacos , Camundongos , Camundongos Transgênicos , Mutação/genética , Presenilina-1/genética , Presenilina-1/metabolismo , Fator de Transcrição STAT1/metabolismo , Proteína 3 Supressora da Sinalização de Citocinas/genética , Proteína 3 Supressora da Sinalização de Citocinas/metabolismoRESUMO
Astrocytes play multiple important roles in brain physiology. In pathological conditions, they become reactive, which is characterized by morphological changes and upregulation of intermediate filament proteins. Besides these descriptive hallmarks, astrocyte reactivity involves significant transcriptional and functional changes that are far from being fully understood. Most importantly, astrocyte reactivity seems to encompass multiple states, each having a specific influence on surrounding cells and disease progression. These diverse functional states of reactivity must be regulated by subtle signaling networks. Many signaling cascades have been associated with astrocyte reactivity, but among them, the JAK-STAT3 pathway is emerging as a central regulator. In this review, we aim (i) to show that the JAK-STAT3 pathway plays a key role in the control of astrocyte reactivity, (ii) to illustrate that STAT3 is a pleiotropic molecule operating multiple functions in reactive astrocytes, and (iii) to suggest that each specific functional state of reactivity is governed by complex molecular interactions within astrocytes, which converge on STAT3. More research is needed to precisely identify the signaling networks controlling the diverse states of astrocyte reactivity. Only then, we will be able to precisely delineate the therapeutic potential of reactive astrocytes in each neurological disease context.