RESUMEN
Myelin sheaths provide critical functional and trophic support for axons in white matter tracts of the brain. Oligodendrocyte precursor cells (OPCs) have extraordinary metabolic requirements during development as they differentiate to produce multiple myelin segments, implying that they must first secure adequate access to blood supply. However, mechanisms that coordinate myelination and angiogenesis are unclear. Here, we show that oxygen tension, mediated by OPC-encoded hypoxia-inducible factor (HIF) function, is an essential regulator of postnatal myelination. Constitutive HIF1/2α stabilization resulted in OPC maturation arrest through autocrine activation of canonical Wnt7a/7b. Surprisingly, such OPCs also show paracrine activity that induces excessive postnatal white matter angiogenesis in vivo and directly stimulates endothelial cell proliferation in vitro. Conversely, OPC-specific HIF1/2α loss of function leads to insufficient angiogenesis in corpus callosum and catastrophic axon loss. These findings indicate that OPC-intrinsic HIF signaling couples postnatal white matter angiogenesis, axon integrity, and the onset of myelination in mammalian forebrain.
Asunto(s)
Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/metabolismo , Subunidad alfa del Factor 1 Inducible por Hipoxia/metabolismo , Vaina de Mielina/metabolismo , Oligodendroglía/metabolismo , Animales , Diferenciación Celular , Cuerpo Calloso/metabolismo , Células Endoteliales/citología , Técnicas In Vitro , Ratones , Neovascularización Fisiológica , Células-Madre Neurales , Oxígeno/metabolismo , Comunicación Paracrina , Proteínas Proto-Oncogénicas/metabolismo , Proteína Supresora de Tumores del Síndrome de Von Hippel-Lindau/metabolismo , Proteínas Wnt/metabolismoRESUMEN
Astrocytes respond and contribute to neuroinflammation by adopting inflammatory reactive states. Although recent efforts have characterized the gene expression signatures associated with these reactive states, the cell biology underlying inflammatory reactive astrocyte phenotypes remains under-explored. Here, we used CRISPR-based screening in human iPSC-derived astrocytes to identify mTOR activation a driver of cytokine-induced endolysosomal system remodeling, manifesting as alkalinization of endolysosomal compartments, decreased autophagic flux, and increased exocytosis of certain endolysosomal cargos. Through endolysosomal proteomics, we identified and focused on one such cargo-IL-32, a disease-associated pro-inflammatory cytokine not present in rodents, whose secretion mechanism is not well understood. We found that IL-32 was partially secreted in extracellular vesicles likely to be exosomes. Furthermore, we found that IL-32 was involved in the polarization of inflammatory reactive astrocyte states and was upregulated in astrocytes in multiple sclerosis lesions. We believe that our results advance our understanding of cell biological pathways underlying inflammatory reactive astrocyte phenotypes and identify potential therapeutic targets.
Asunto(s)
Astrocitos , Exosomas , Interleucinas , Lisosomas , Serina-Treonina Quinasas TOR , Astrocitos/metabolismo , Humanos , Exosomas/metabolismo , Serina-Treonina Quinasas TOR/metabolismo , Lisosomas/metabolismo , Interleucinas/metabolismo , Endosomas/metabolismo , Células Madre Pluripotentes Inducidas/metabolismo , Células Cultivadas , Enfermedades Neuroinflamatorias/metabolismo , Enfermedades Neuroinflamatorias/patología , Inflamación/metabolismo , Inflamación/patologíaRESUMEN
It is now well-established that the macrophage and microglial response to CNS demyelination influences remyelination by removing myelin debris and secreting a variety of signaling molecules that influence the behaviour of oligodendrocyte progenitor cells (OPCs). Previous studies have shown that changes in microglia contribute to the age-related decline in the efficiency of remyelination. In this study, we show that microglia increase their expression of the proteoglycan NG2 with age, and that this is associated with an altered micro-niche generated by aged, but not young, microglia that can divert the differentiation OPCs from oligodendrocytes into astrocytes in vitro. We further show that these changes in ageing microglia are generated by exposure to high levels of TGFß. Thus, our findings suggest that the rising levels of circulating TGFß known to occur with ageing contribute to the age-related decline in remyelination by impairing the ability of microglia to promote oligodendrocyte differentiation from OPCs, and therefore could be a potential therapeutic target to promote remyelination.
Asunto(s)
Senescencia Celular/fisiología , Microglía/metabolismo , Células Precursoras de Oligodendrocitos/metabolismo , Oligodendroglía/metabolismo , Factor de Crecimiento Transformador beta/farmacología , Factores de Edad , Animales , Animales Recién Nacidos , Diferenciación Celular/fisiología , Células Cultivadas , Senescencia Celular/efectos de los fármacos , Sistema Nervioso Central/efectos de los fármacos , Sistema Nervioso Central/metabolismo , Relación Dosis-Respuesta a Droga , Microglía/efectos de los fármacos , Células Precursoras de Oligodendrocitos/efectos de los fármacos , Oligodendroglía/efectos de los fármacos , Ratas , Ratas Sprague-DawleyRESUMEN
The developmental process of myelination and the adult regenerative process of remyelination share the common objective of investing nerve axons with myelin sheaths. A central question in myelin biology is the extent to which the mechanisms of these two processes are conserved, a concept encapsulated in the recapitulation hypothesis of remyelination. This question also has relevance for translating myelin biology into a better understanding of and eventual treatments for human myelin disorders. Here we review the current evidence for the recapitulation hypothesis and discuss recent findings in the development and regeneration of myelin in the context of human neurological disease.
Asunto(s)
Enfermedades Desmielinizantes/patología , Enfermedades Desmielinizantes/fisiopatología , Vaina de Mielina/fisiología , Regeneración Nerviosa/fisiología , Animales , Tipificación del Cuerpo/fisiología , Humanos , Leucoencefalopatías/genética , Leucoencefalopatías/patología , Leucoencefalopatías/fisiopatología , Modelos Biológicos , Oligodendroglía/fisiología , Transducción de Señal/fisiología , Células Madre/fisiologíaRESUMEN
Hypoxia can injure brain white matter tracts, comprised of axons and myelinating oligodendrocytes, leading to cerebral palsy in neonates and delayed post-hypoxic leukoencephalopathy (DPHL) in adults. In these conditions, white matter injury can be followed by myelin regeneration, but myelination often fails and is a significant contributor to fixed demyelinated lesions, with ensuing permanent neurological injury. Non-myelinating oligodendrocyte precursor cells are often found in lesions in plentiful numbers, but fail to mature, suggesting oligodendrocyte precursor cell differentiation arrest as a critical contributor to failed myelination in hypoxia. We report a case of an adult patient who developed the rare condition DPHL and made a nearly complete recovery in the setting of treatment with clemastine, a widely available antihistamine that in preclinical models promotes oligodendrocyte precursor cell differentiation. This suggested possible therapeutic benefit in the more clinically prevalent hypoxic injury of newborns, and we demonstrate in murine neonatal hypoxic injury that clemastine dramatically promotes oligodendrocyte precursor cell differentiation, myelination, and improves functional recovery. We show that its effect in hypoxia is oligodendroglial specific via an effect on the M1 muscarinic receptor on oligodendrocyte precursor cells. We propose clemastine as a potential therapy for hypoxic brain injuries associated with white matter injury and oligodendrocyte precursor cell maturation arrest.
Asunto(s)
Clemastina/uso terapéutico , Enfermedades Desmielinizantes/tratamiento farmacológico , Enfermedades Desmielinizantes/etiología , Antagonistas de los Receptores Histamínicos H1/uso terapéutico , Hipoxia Encefálica/complicaciones , Recuperación de la Función/efectos de los fármacos , Potenciales de Acción/efectos de los fármacos , Animales , Animales Recién Nacidos , Diferenciación Celular/efectos de los fármacos , Células Cultivadas , Cerebelo/efectos de los fármacos , Cerebelo/metabolismo , Cerebelo/ultraestructura , Enfermedades Desmielinizantes/diagnóstico por imagen , Enfermedades Desmielinizantes/patología , Modelos Animales de Enfermedad , Regulación del Desarrollo de la Expresión Génica/efectos de los fármacos , Humanos , Hipoxia Encefálica/diagnóstico por imagen , Masculino , Ratones , Ratones Noqueados , Persona de Mediana Edad , Vaina de Mielina/efectos de los fármacos , Vaina de Mielina/ultraestructura , Células Precursoras de Oligodendrocitos/efectos de los fármacos , Nervio Óptico/fisiopatología , Oxígeno/farmacología , Receptor Muscarínico M1/genética , Receptor Muscarínico M1/metabolismoRESUMEN
The progressive loss of CNS myelin in patients with multiple sclerosis (MS) has been proposed to result from the combined effects of damage to oligodendrocytes and failure of remyelination. A common feature of demyelinated lesions is the presence of oligodendrocyte precursors (OLPs) blocked at a premyelinating stage. However, the mechanistic basis for inhibition of myelin repair is incompletely understood. To identify novel regulators of OLP differentiation, potentially dysregulated during repair, we performed a genome-wide screen of 1040 transcription factor-encoding genes expressed in remyelinating rodent lesions. We report that approximately 50 transcription factor-encoding genes show dynamic expression during repair and that expression of the Wnt pathway mediator Tcf4 (aka Tcf7l2) within OLPs is specific to lesioned-but not normal-adult white matter. We report that beta-catenin signaling is active during oligodendrocyte development and remyelination in vivo. Moreover, we observed similar regulation of Tcf4 in the developing human CNS and lesions of MS. Data mining revealed elevated levels of Wnt pathway mRNA transcripts and proteins within MS lesions, indicating activation of the pathway in this pathological context. We show that dysregulation of Wnt-beta-catenin signaling in OLPs results in profound delay of both developmental myelination and remyelination, based on (1) conditional activation of beta-catenin in the oligodendrocyte lineage in vivo and (2) findings from APC(Min) mice, which lack one functional copy of the endogenous Wnt pathway inhibitor APC. Together, our findings indicate that dysregulated Wnt-beta-catenin signaling inhibits myelination/remyelination in the mammalian CNS. Evidence of Wnt pathway activity in human MS lesions suggests that its dysregulation might contribute to inefficient myelin repair in human neurological disorders.
Asunto(s)
Sistema Nervioso Central/crecimiento & desarrollo , Sistema Nervioso Central/fisiopatología , Regulación del Desarrollo de la Expresión Génica , Esclerosis Múltiple/fisiopatología , Vaina de Mielina/metabolismo , Proteínas Wnt/metabolismo , Animales , Factores de Transcripción Básicos con Cremalleras de Leucinas y Motivos Hélice-Asa-Hélice , Proteínas de Unión al ADN/metabolismo , Perfilación de la Expresión Génica , Humanos , Ratones , Proteínas del Tejido Nervioso/metabolismo , Transducción de Señal , Factores de Transcripción TCF/metabolismo , Factor de Transcripción 4 , Factores de Transcripción/metabolismo , Proteínas Wnt/fisiología , beta Catenina/metabolismoRESUMEN
The Sox family of transcription factors have been widely studied in the context of oligodendrocyte development. However, comparatively little is known about the role of Sox2, especially during CNS remyelination. Here we show that the expression of Sox2 occurs in oligodendrocyte progenitor cells (OPCs) in rodent models during myelination and in activated adult OPCs responding to demyelination, and is also detected in multiple sclerosis lesions. In normal adult white matter of both mice and rats, it is neither expressed by adult OPCs nor by oligodendrocytes (although it is expressed by a subpopulation of adult astrocytes). Overexpression of Sox2 in rat OPCs in vitro maintains the cells in a proliferative state and inhibits differentiation, while Sox2 knockout results in decreased OPC proliferation and survival, suggesting that Sox2 contributes to the expansion of OPCs during the recruitment phase of remyelination. Loss of function in cultured mouse OPCs also results in an impaired ability to undergo normal differentiation in response to differentiation signals, suggesting that Sox2 expression in activated OPCs also primes these cells to eventually undergo differentiation. In vivo studies on remyelination following experimental toxin-induced demyelination in mice with inducible loss of Sox2 revealed impaired remyelination, which was largely due to a profound attenuation of OPC recruitment and likely also due to impaired differentiation. Our results reveal a key role of Sox2 expression in OPCs responding to demyelination, enabling them to effectively contribute to remyelination. SIGNIFICANCE STATEMENT: Understanding the mechanisms of CNS remyelination is central to developing effective means by which this process can be therapeutically enhanced in chronic demyelinating diseases such as multiple sclerosis. In this study, we describe the role of Sox2, a transcription factor widely implicated in stem cell biology, in CNS myelination and remyelination. We show how Sox2 is expressed in oligodendrocyte progenitor cells (OPCs) preparing to undergo differentiation, allowing them to undergo proliferation and priming them for subsequent differentiation. Although Sox2 is unlikely to be a direct therapeutic target, these data nevertheless provide more information on how OPC differentiation is controlled and therefore enriches our understanding of this important CNS regenerative process.
Asunto(s)
Enfermedades Desmielinizantes/patología , Oligodendroglía/metabolismo , Oligodendroglía/patología , Factores de Transcripción SOXB1/metabolismo , Células Madre/metabolismo , Células Madre/patología , Animales , Diferenciación Celular , Células Cultivadas , Enfermedades Desmielinizantes/metabolismo , Femenino , Ratones , Ratones Transgénicos , Regeneración Nerviosa/fisiología , Ratas , Ratas Sprague-DawleyRESUMEN
Precise temporal and spatial control of the neural stem/progenitor cells within the subventricular zone (SVZ) germinal matrix of the brain is important for normal development in the third trimester and the early postnatal period. The high metabolic demands of proliferating germinal matrix precursors, coupled with the flimsy structure of the germinal matrix cerebral vasculature, are thought to account for the high rates of haemorrhage in extremely- and very-low-birth-weight preterm infants. Germinal matrix haemorrhage can commonly extend to intraventricular haemorrhage (IVH). Because neural stem/progenitor cells are sensitive to microenvironmental cues from the ventricular, intermediate, and basal domains within the germinal matrix, haemorrhage has been postulated to impact neurological outcomes through aberration of normal neural stem/progenitor cell behaviour. We developed an animal model of neonatal germinal matrix haemorrhage using stereotactic injection of autologous blood into the mouse neonatal germinal matrix. Pathological analysis at 4 days postinjury showed high rates of intraventricular extension and ventricular dilatation but low rates of parenchymal disruption outside the germinal zone, recapitulating key features of human "Papile grade III" IVH. At 4 days postinjury we observed proliferation in the wall of the lateral ventricle with significantly increased numbers of transient amplifying cells within the SVZ and the corpus callosum. Analysis at 21 days postinjury revealed that cortical development was also affected, with increased neuronal and concomitant reduced oligodendroglial differentiation. At the molecular level, we showed downregulation of the expression of the transmembrane receptor Notch2 in CD133+ve cells of the SVZ, raising the possibility that the burst of precocious proliferation seen in our experimental mouse model and the skewed differentiation could be mediated by downregulation of the Notch pathway within the proximal/ventricular domain. These findings raise the possibility that Notch regulation plays a critical role in mediating the response of the neonatal SVZ to ischaemic and haemorrhagic insults.
Asunto(s)
Hemorragia Cerebral/complicaciones , Ventrículos Laterales/patología , Células-Madre Neurales/patología , Animales , Animales Recién Nacidos , División Celular/fisiología , Ratones , Ratones Endogámicos C57BL , Células-Madre Neurales/metabolismo , Receptor Notch2/metabolismoRESUMEN
Wnt signaling plays an essential role in developmental and regenerative myelination of the CNS, therefore it is critical to understand how the factors associated with the various regulatory layers of this complex pathway contribute to these processes. Recently, Apcdd1 was identified as a negative regulator of proximal Wnt signaling, however its role in oligodendrocyte (OL) differentiation and reymelination in the CNS remain undefined. Analysis of Apcdd1 expression revealed dynamic expression during OL development, where its expression is upregulated during differentiation. Functional studies using ex vivo and in vitro OL systems revealed that Apcdd1 promotes OL differentiation, suppresses Wnt signaling, and associates with ß-catenin. Application of these findings to white matter injury (WMI) models revealed that Apcdd1 similarly promotes OL differentiation after gliotoxic injury in vivo and acute hypoxia ex vivo. Examination of Apcdd1 expression in white matter lesions from neonatal WMI and adult multiple sclerosis revealed its expression in subsets of oligodendrocyte (OL) precursors. These studies describe, for the first time, the role of Apcdd1 in OLs after WMI and reveal that negative regulators of the proximal Wnt pathway can influence regenerative myelination, suggesting a new therapeutic strategy for modulating Wnt signaling and stimulating repair after WMI.
Asunto(s)
Diferenciación Celular/fisiología , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Proteínas de la Membrana/metabolismo , Oligodendroglía/fisiología , Enfermedad del Músculo Blanco/patología , Factores de Edad , Animales , Modelos Animales de Enfermedad , Regulación del Desarrollo de la Expresión Génica/efectos de los fármacos , Regulación del Desarrollo de la Expresión Génica/fisiología , Proteínas Fluorescentes Verdes/genética , Proteínas Fluorescentes Verdes/metabolismo , Humanos , Hipoxia/complicaciones , Técnicas In Vitro , Péptidos y Proteínas de Señalización Intracelular/genética , Lisofosfatidilcolinas/toxicidad , Proteínas de la Membrana/genética , Ratones , Técnicas de Cultivo de Órganos , Médula Espinal/patología , Células Madre/metabolismo , Células Madre/fisiología , Enfermedad del Músculo Blanco/inducido químicamente , Proteínas Wnt/metabolismo , Vía de Señalización Wnt/efectos de los fármacos , Vía de Señalización Wnt/fisiología , beta Catenina/metabolismoRESUMEN
A requisite component of nervous system development is the achievement of cellular recognition and spatial segregation through competition-based refinement mechanisms. Competition for available axon space by myelinating oligodendrocytes ensures that all relevant CNS axons are myelinated properly. To ascertain the nature of this competition, we generated a transgenic mouse with sparsely labeled oligodendrocytes and establish that individual oligodendrocytes occupying similar axon tracts can greatly vary the number and lengths of their myelin internodes. Here we show that intercellular interactions between competing oligodendroglia influence the number and length of myelin internodes, referred to as myelinogenic potential, and identify the amino-terminal region of Nogo-A, expressed by oligodendroglia, as necessary and sufficient to inhibit this process. Exuberant and expansive myelination/remyelination is detected in the absence of Nogo during development and after demyelination, suggesting that spatial segregation and myelin extent is limited by microenvironmental inhibition. We demonstrate a unique physiological role for Nogo-A in the precise myelination of the developing CNS. Maximizing the myelinogenic potential of oligodendrocytes may offer an effective strategy for repair in future therapies for demyelination.
Asunto(s)
Sistema Nervioso Central/patología , Enfermedades Desmielinizantes/fisiopatología , Proteínas de la Mielina/metabolismo , Vaina de Mielina/fisiología , Oligodendroglía/fisiología , Animales , Western Blotting , Sistema Nervioso Central/citología , Técnicas de Silenciamiento del Gen , Técnicas Histológicas , Ratones , Ratones Transgénicos , Microscopía Electrónica , Microesferas , Proteínas de la Mielina/genética , Proteínas Nogo , Oligodendroglía/metabolismo , Oligodendroglía/ultraestructura , Poliestirenos , ARN Interferente Pequeño/genética , UltracentrifugaciónRESUMEN
Developmental regulation of gliogenesis in the mammalian CNS is incompletely understood, in part due to a limited repertoire of lineage-specific genes. We used Aldh1l1-GFP as a marker for gliogenic radial glia and later-stage precursors of developing astrocytes and performed gene expression profiling of these cells. We then used this dataset to identify candidate transcription factors that may serve as glial markers or regulators of glial fate. Our analysis generated a database of developmental stage-related markers of Aldh1l1+ cells between murine embryonic day 13.5-18.5. Using these data we identify the bZIP transcription factor Nfe2l1 and demonstrate that it promotes glial fate under direct Sox9 regulatory control. Thus, this dataset represents a resource for identifying novel regulators of glial development.
Asunto(s)
Regulación del Desarrollo de la Expresión Génica/fisiología , Isoenzimas/metabolismo , Factor 1 Relacionado con NF-E2/metabolismo , Neuroglía/metabolismo , Retinal-Deshidrogenasa/metabolismo , Factor de Transcripción SOX9/metabolismo , Médula Espinal/citología , Factores de Edad , Familia de Aldehído Deshidrogenasa 1 , Animales , Diferenciación Celular , Células Cultivadas , Pollos , Biología Computacional , Electroporación , Embrión de Mamíferos , Citometría de Flujo , Perfilación de la Expresión Génica , Proteína Ácida Fibrilar de la Glía , Proteínas Fluorescentes Verdes/genética , Proteínas Fluorescentes Verdes/metabolismo , Isoenzimas/genética , Ratones , Ratones Transgénicos , Factor 1 Relacionado con NF-E2/genética , Proteínas del Tejido Nervioso/genética , Proteínas del Tejido Nervioso/metabolismo , Neuronas/clasificación , Neuronas/metabolismo , Análisis de Secuencia por Matrices de Oligonucleótidos , Retinal-Deshidrogenasa/genética , Factor de Transcripción SOX9/genética , Médula Espinal/embriología , Factores de Transcripción/genética , Factores de Transcripción/metabolismoRESUMEN
OBJECTIVE: Chronic demyelination can result in axonopathy and is associated with human neurological conditions such as multiple sclerosis (MS) in adults and cerebral palsy in infants. In these disorders, myelin regeneration is inhibited by impaired differentiation of oligodendrocyte progenitors into myelin-producing oligodendrocytes. However, regulatory factors relevant in human myelin disorders and in myelin regeneration remain poorly understood. Here we have investigated the role of the transcription factor nuclear factor IA (NFIA) in oligodendrocyte progenitor differentiation during developmental and regenerative myelination. METHODS: NFIA expression patterns in human neonatal hypoxic-ischemic encephalopathy (HIE) and MS as well as developmental expression in mice were evaluated. Functional studies during remyelination were performed using a lysolecithin model, coupled with lentiviral misexpression of NFIA. The role of NFIA during oligodendrocyte lineage development was characterized using chick and mouse models and in vitro culture of oligodendrocyte progenitors. Biochemical mechanism of NFIA function was evaluated using chromatin immunoprecipitation and reporter assays. RESULTS: NFIA is expressed in oligodendrocyte progenitors, but not differentiated oligodendrocytes during mouse embryonic development. Examination of NFIA expression in white matter lesions of human newborns with neonatal HIE, as well active MS lesions in adults, revealed that it is similarly expressed in oligodendrocyte progenitors and not oligodendrocytes. Functional studies indicate that NFIA is sufficient to suppress oligodendrocyte progenitor differentiation during adult remyelination and embryonic development through direct repression of myelin gene expression. INTERPRETATION: These studies suggest that NFIA participates in the control of oligodendrocyte progenitor differentiation and may contribute to the inhibition of remyelination in human myelin disorders.
Asunto(s)
Regulación del Desarrollo de la Expresión Génica/fisiología , Leucoencefalopatías/metabolismo , Leucoencefalopatías/patología , Factores de Transcripción NFI/metabolismo , Oligodendroglía/metabolismo , Proteína de la Poliposis Adenomatosa del Colon/metabolismo , Animales , Proteínas de Arabidopsis/metabolismo , Diferenciación Celular/efectos de los fármacos , Células Cultivadas , Corteza Cerebral/citología , Inmunoprecipitación de Cromatina , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Modelos Animales de Enfermedad , Electroporación , Embrión de Mamíferos , Regulación del Desarrollo de la Expresión Génica/genética , Proteínas de Homeodominio/metabolismo , Humanos , Hipoxia-Isquemia Encefálica/metabolismo , Lactante , Recién Nacido , Transferasas Intramoleculares/metabolismo , Leucoencefalopatías/inducido químicamente , Lisofosfatidilcolinas/toxicidad , Ratones , Ratones Transgénicos , Esclerosis Múltiple/metabolismo , Proteína Básica de Mielina/metabolismo , Factores de Transcripción NFI/genética , Oligodendroglía/efectos de los fármacos , Médula Espinal/patología , Células Madre/efectos de los fármacos , Células Madre/metabolismo , Factores de Tiempo , Factores de Transcripción/genética , Factores de Transcripción/metabolismoRESUMEN
Oligodendrocyte precursor cells (OPCs) undergo an extensive and coordinated migration in the developing CNS, using the pre-formed scaffold of developed blood vessels as their physical substrate for migration. While OPC association with vasculature is critical for dispersal, equally important for permitting differentiation and proper myelination of target axons is their appropriate and timely detachment, but regulation of this process remains unclear. Here we demonstrate a correlation between the developmental formation of astrocytic endfeet on vessels and the termination of OPC perivascular migration. Ex vivo and in vivo live imaging shows that astrocyte endfeet physically displace OPCs from vasculature, and genetic abrogation of endfoot formation hinders both OPC detachment from vessels and subsequent differentiation. Astrocyte-derived semaphorins 3a and 6a act to repel OPCs from blood vessels at the cessation of their perivascular migration and, in so doing, permit subsequent OPC differentiation by insulating them from a maturation inhibitory endothelial niche.
Asunto(s)
Células Precursoras de Oligodendrocitos , Astrocitos , Oligodendroglía/fisiología , Diferenciación Celular/fisiología , Movimiento Celular/fisiologíaRESUMEN
Remyelination after white matter injury (WMI) often fails in diseases such as multiple sclerosis because of improper recruitment and repopulation of oligodendrocyte precursor cells (OPCs) in lesions. How OPCs elicit specific intracellular programs in response to a chemically and mechanically diverse environment to properly regenerate myelin remains unclear. OPCs construct primary cilia, specialized signaling compartments that transduce Hedgehog (Hh) and G-protein-coupled receptor (GPCR) signals. We investigated the role of primary cilia in the OPC response to WMI. Removing cilia from OPCs genetically via deletion of Ift88 results in OPCs failing to repopulate WMI lesions because of reduced proliferation. Interestingly, loss of cilia does not affect Hh signaling in OPCs or their responsiveness to Hh signals but instead leads to dysfunctional cyclic AMP (cAMP)-dependent cAMP response element-binding protein (CREB)-mediated transcription. Because inhibition of CREB activity in OPCs reduces proliferation, we propose that a GPCR/cAMP/CREB signaling axis initiated at OPC cilia orchestrates OPC proliferation during development and in response to WMI.
Asunto(s)
Células Precursoras de Oligodendrocitos , Sustancia Blanca , Células Precursoras de Oligodendrocitos/metabolismo , Cilios/metabolismo , Sustancia Blanca/metabolismo , Proteínas Hedgehog/metabolismo , Oligodendroglía/metabolismo , Vaina de Mielina/metabolismo , Proteína de Unión a Elemento de Respuesta al AMP Cíclico/metabolismo , Proliferación Celular , Diferenciación Celular/fisiologíaRESUMEN
Astrocytes become reactive in response to insults to the central nervous system by adopting context-specific cellular signatures and outputs, but a systematic understanding of the underlying molecular mechanisms is lacking. In this study, we developed CRISPR interference screening in human induced pluripotent stem cell-derived astrocytes coupled to single-cell transcriptomics to systematically interrogate cytokine-induced inflammatory astrocyte reactivity. We found that autocrine-paracrine IL-6 and interferon signaling downstream of canonical NF-κB activation drove two distinct inflammatory reactive signatures, one promoted by STAT3 and the other inhibited by STAT3. These signatures overlapped with those observed in other experimental contexts, including mouse models, and their markers were upregulated in human brains in Alzheimer's disease and hypoxic-ischemic encephalopathy. Furthermore, we validated that markers of these signatures were regulated by STAT3 in vivo using a mouse model of neuroinflammation. These results and the platform that we established have the potential to guide the development of therapeutics to selectively modulate different aspects of inflammatory astrocyte reactivity.
Asunto(s)
Enfermedad de Alzheimer , Células Madre Pluripotentes Inducidas , Humanos , Astrocitos , Transducción de Señal , Citocinas , InflamaciónRESUMEN
OBJECTIVE: Repair of myelin injury in multiple sclerosis may fail, resulting in chronic demyelination, axonal loss, and disease progression. As cellular pathways regulated by phosphatase and tensin homologue deleted on chromosome 10 (PTEN; eg, phosphatidylinositol-3-kinase [PI-3K]) have been reported to enhance axon regeneration and oligodendrocyte maturation, we investigated potentially beneficial effects of Pten loss of function in the oligodendrocyte lineage on remyelination. METHODS: We characterized oligodendrocyte numbers and myelin sheath thickness in mice with conditional inactivation of Pten in oligodendrocytes, Olig2-cre, Pten(fl/fl) mice. Using a model of central nervous system demyelination, lysolecithin injection into the spinal cord white matter, we performed short- and long-term lesioning experiments and quantified oligodendrocyte maturation and myelin sheath thickness in remyelinating lesions. RESULTS: During development, we observed dramatic hypermyelination in the corpus callosum and spinal cord. Following white matter injury, however, there was no detectable improvement in remyelination. Moreover, we observed progressive myelin sheath abnormalities and massive axon degeneration in the fasciculus gracilis of mutant animals, as indicated by ultrastructure and expression of SMI-32, amyloid precursor protein, and caspase 6. INTERPRETATION: These studies indicate adverse effects of chronic Pten inactivation (and by extension, activation PI-3K signaling) on myelinating oligodendrocytes and their axonal targets. We conclude that PTEN function in oligodendrocytes is required to regulate myelin thickness and preserve axon integrity. In contrast, PTEN is dispensable during myelin repair, and its inactivation confers no detectable benefit.
Asunto(s)
Axones/enzimología , Vaina de Mielina/metabolismo , Oligodendroglía/enzimología , Fosfohidrolasa PTEN/fisiología , Factores de Edad , Animales , Axones/patología , Encéfalo/patología , Encéfalo/ultraestructura , Línea Celular Transformada , Enfermedades Desmielinizantes/enzimología , Enfermedades Desmielinizantes/patología , Enfermedades Desmielinizantes/fisiopatología , Modelos Animales de Enfermedad , Eliminación de Gen , Humanos , Lisofosfatidilcolinas , Ratones , Ratones Transgénicos , Vaina de Mielina/patología , Vaina de Mielina/ultraestructura , Fibras Nerviosas Mielínicas/patología , Fibras Nerviosas Mielínicas/fisiología , Fibras Nerviosas Mielínicas/ultraestructura , Oligodendroglía/patología , Oligodendroglía/fisiología , Oligodendroglía/ultraestructura , Fosfohidrolasa PTEN/antagonistas & inhibidores , Transducción de Señal/efectos de los fármacos , Transducción de Señal/fisiología , Médula Espinal/patología , Médula Espinal/ultraestructuraRESUMEN
Oligodendrocytes, the myelinating cells of the central nervous system (CNS), develop from oligodendrocyte progenitor cells (OPCs) that must first migrate extensively throughout the developing brain and spinal cord. Specified at particular times from discrete regions in the developing CNS, OPCs are one of the most migratory of cell types and disperse rapidly. A variety of factors act on OPCs to trigger intracellular changes that regulate their migration. We will discuss factors that act as long-range guidance cues, those that act to regulate cellular motility, and those that are critical in determining the final positioning of OPCs. In addition, recent evidence has identified the vasculature as the physical substrate used by OPCs for their migration. Several new findings relating to this oligodendroglial-vascular signaling axis reveal new insight on the relationship between OPCs and blood vessels in the developing and adult brain.
Asunto(s)
Células Precursoras de Oligodendrocitos , Diferenciación Celular/fisiología , Sistema Nervioso Central , Células Precursoras de Oligodendrocitos/metabolismo , Oligodendroglía/metabolismo , Médula EspinalRESUMEN
Oligodendrocyte (OL) maturation arrest in human white matter injury contributes significantly to the failure of endogenous remyelination in multiple sclerosis (MS) and newborn brain injuries such as hypoxic ischemic encephalopathy (HIE) that cause cerebral palsy. In this study, we identify an oligodendroglial-intrinsic factor that controls OL maturation specifically in the setting of injury. We find a requirement for the ring finger protein Rnf43 not in normal development but in neonatal hypoxic injury and remyelination in the adult mammalian CNS. Rnf43, but not the related Znrf3, is potently activated by Wnt signaling in OL progenitor cells (OPCs) and marks activated OPCs in human MS and HIE. Rnf43 is required in an injury-specific context, and it promotes OPC differentiation through negative regulation of Wnt signal strength in OPCs at the level of Fzd1 receptor presentation on the cell surface. Inhibition of Fzd1 using UM206 promotes remyelination following ex vivo and in vivo demyelinating injury.
Asunto(s)
Lesiones Encefálicas/genética , Lesiones Encefálicas/patología , Oligodendroglía/patología , Ubiquitina-Proteína Ligasas/genética , Animales , Lesiones Encefálicas/metabolismo , Enfermedades Desmielinizantes/genética , Receptores Frizzled/efectos de los fármacos , Receptores Frizzled/genética , Humanos , Ratones , Vaina de Mielina/efectos de los fármacos , Vaina de Mielina/fisiología , Oligodendroglía/efectos de los fármacos , Oligodendroglía/metabolismo , Remielinización/efectos de los fármacos , Remielinización/genética , Células Madre/metabolismo , Células Madre/patología , Sustancia Blanca/metabolismo , Sustancia Blanca/patología , Vía de Señalización WntRESUMEN
Fibrosis is a common pathological response to inflammation in many peripheral tissues and can prevent tissue regeneration and repair. Here, we identified persistent fibrotic scarring in the CNS following immune cell infiltration in the experimental autoimmune encephalomyelitis (EAE) mouse model of multiple sclerosis. Using lineage tracing and single-cell sequencing in EAE, we determined that the majority of the fibrotic scar is derived from proliferative CNS fibroblasts, not pericytes or infiltrating bone marrow-derived cells. Ablating proliferating fibrotic cells using cell-specific expression of herpes thymidine kinase led to an increase in oligodendrocyte lineage cells within the inflammatory lesions and a reduction in motor disability. We further identified that interferon-gamma pathway genes are enriched in CNS fibrotic cells, and the fibrotic cell-specific deletion of Ifngr1 resulted in reduced fibrotic scarring in EAE. These data delineate a framework for understanding the CNS fibrotic response.
Asunto(s)
Barrera Hematoencefálica/patología , Encefalomielitis Autoinmune Experimental/patología , Fibroblastos/patología , Fibrosis/patología , Infiltración Neutrófila , Médula Espinal/patología , Animales , Ratones , Oligodendroglía/patologíaRESUMEN
To determine the role of extracellular matrix molecules and their integrin ligands in CNS remyelination, we have examined in experimentally induced focal demyelinated lesions the expression of the two classes of integrins implicated in oligodendrocyte development and myelination: alpha6 laminin-binding integrins and alphaV integrins that bind a range of extracellular matrix proteins containing the -Arg-Gly-Asp- (RGD) recognition sequence. Only alphaV integrins were up-regulated during remyelination, being expressed on oligodendrocyte precursor cells during their recruitment into the lesion. Next, therefore, we examined the expression of extracellular matrix ligands for alphaV integrins and documented increased expression of tenascin-C, tenascin-R, fibronectin, and vitronectin. Taken together with our previous discovery of high levels of expression of another alphaV ligand, osteopontin, during remyelination in these lesions, our findings suggest that alphaV integrins make an important contribution to successful repair in the CNS.