RESUMEN
Although adult subependymal zone (SEZ) neural stem cells mostly generate GABAergic interneurons, a small progenitor population expresses the proneural gene Neurog2 and produces glutamatergic neurons. Here, we determined whether Neurog2 could respecify SEZ neural stem cells and their progeny toward a glutamatergic fate. Retrovirus-mediated expression of Neurog2 induced the glutamatergic lineage markers TBR2 and TBR1 in cultured SEZ progenitors, which differentiated into functional glutamatergic neurons. Likewise, Neurog2-transduced SEZ progenitors acquired glutamatergic neuron hallmarks in vivo. Intriguingly, they failed to migrate toward the olfactory bulb and instead differentiated within the SEZ or the adjacent striatum, where they received connections from local neurons, as indicated by rabies virus-mediated monosynaptic tracing. In contrast, lentivirus-mediated expression of Neurog2 failed to reprogram early SEZ neurons, which maintained GABAergic identity and migrated to the olfactory bulb. Our data show that NEUROG2 can program SEZ progenitors toward a glutamatergic identity but fails to reprogram their neuronal progeny.
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Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico , Células-Madre Neurales , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/genética , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/metabolismo , Neuronas/metabolismo , Células-Madre Neurales/metabolismo , Diferenciación Celular , Bulbo Olfatorio/metabolismo , Neurogénesis/fisiologíaRESUMEN
In this issue of Cell Stem Cell, Bershteyn et al.1 developed a human interneuron cell therapy that reduced spontaneous seizure activity in a mouse model of mesial temporal lobe epilepsy (MTLE). The data presented here support an ongoing phase 1/2 clinical trial for the treatment of pharmaco-resistant epilepsy in patients.
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Epilepsia del Lóbulo Temporal , Animales , Humanos , Ratones , Epilepsia del Lóbulo Temporal/tratamiento farmacológico , Hipocampo , Ensayos Clínicos Fase I como Asunto , Ensayos Clínicos Fase II como AsuntoRESUMEN
In vivo direct neuronal reprogramming relies on the implementation of an exogenous transcriptional program allowing to achieve conversion of a particular neuronal or glial cell type towards a new identity. The transcription factor (TF) Fezf2 is known for its role in neuronal subtype specification of deep-layer (DL) subcortical projection neurons. High ectopic Fezf2 expression in mice can convert both upper-layer (UL) and striatal projection neurons into a corticofugal fate, even if at low efficiency. In this study, we show that Fezf2 synergizes with the nuclear co-adaptor Lmo4 to further enhance reprogramming of UL cortical pyramidal neurons into DL corticofugal neurons, at both embryonic and early postnatal stages. Reprogrammed neurons express DL molecular markers and project toward subcerebral targets, including thalamus, cerebral peduncle (CP), and spinal cord (SC). We also show that co-expression of Fezf2 with the reprogramming factors Neurog2 and Bcl2 in early postnatal mouse glia promotes glia-to-neuron conversion with partial hallmarks of DL neurons and with Lmo4 promoting further morphological complexity. These data support a novel role for Lmo4 in synergizing with Fezf2 during direct lineage conversion in vivo.
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Proteínas de Unión al ADN , Neuronas , Animales , Ratones , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/metabolismo , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Proteínas del Tejido Nervioso/genética , Proteínas del Tejido Nervioso/metabolismo , Neuroglía/metabolismo , Neuronas/fisiología , Células Piramidales/metabolismo , Factores de Transcripción/genética , Factores de Transcripción/metabolismoRESUMEN
[This corrects the article DOI: 10.3389/fnins.2022.919462.].
RESUMEN
Most adult hippocampal neural stem cells (NSCs) remain quiescent, with only a minor portion undergoing active proliferation and neurogenesis. The molecular mechanisms that trigger the transition from quiescence to activation are still poorly understood. Here, we found the activity of the transcriptional co-activator Yap1 to be enriched in active NSCs. Genetic deletion of Yap1 led to a significant reduction in the relative proportion of active NSCs, supporting a physiological role of Yap1 in regulating the transition from quiescence to activation. Overexpression of wild-type Yap1 in adult NSCs did not induce NSC activation, suggesting tight upstream control mechanisms, but overexpression of a gain-of-function mutant (Yap1-5SA) elicited cell cycle entry in NSCs and hilar astrocytes. Consistent with a role of Yap1 in NSC activation, single cell RNA sequencing revealed a partial induction of an activated NSC gene expression program. Furthermore, Yap1-5SA expression also induced expression of Taz and other key components of the Yap/Taz regulon that were previously identified in glioblastoma stem cell-like cells. Consequently, dysregulated Yap1 activity led to repression of hippocampal neurogenesis, aberrant cell differentiation, and partial acquisition of a glioblastoma stem cell-like signature.
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Glioblastoma , Células-Madre Neurales , Adulto , Humanos , Glioblastoma/metabolismo , Diferenciación Celular/fisiología , Hipocampo/metabolismo , Neurogénesis/genética , Factores de Transcripción/genética , Factores de Transcripción/metabolismo , Proteínas Adaptadoras Transductoras de Señales/genética , Proteínas Adaptadoras Transductoras de Señales/metabolismo , Células-Madre Neurales/metabolismoRESUMEN
The proneural transcription factor Achaete-scute complex-like 1 (Ascl1) is a major regulator of neural fate decisions, implicated both in neurogenesis and oligodendrogliogenesis. Focusing on its neurogenic activity, Ascl1 has been widely used to reprogram non-neuronal cells into induced neurons. In vitro, Ascl1 induces efficient reprogramming of proliferative astroglia from the early postnatal cerebral cortex into interneuron-like cells. Here, we examined whether Ascl1 can similarly induce neuronal reprogramming of glia undergoing proliferation in the postnatal mouse cerebral cortex in vivo. Toward this goal, we targeted cortical glia during the peak of proliferative expansion (i.e., postnatal day 5) by injecting a retrovirus encoding for Ascl1 into the mouse cerebral cortex. In contrast to the efficient reprogramming observed in vitro, in vivo Ascl1-transduced glial cells were converted into doublecortin-immunoreactive neurons only with very low efficiency. However, we noted a drastic shift in the relative number of retrovirus-transduced Sox10-positive oligodendrocyte progenitor cells (OPCs) as compared to glial fibrillary acidic protein (GFAP)-positive astrocytes. Genetic fate mapping demonstrated that this increase in OPCs was not due to Ascl1-mediated astrocyte-to-OPC fate conversion. Rather, EdU incorporation experiments revealed that Ascl1 caused a selective increase in proliferative activity of OPCs, but not astrocytes. Our data indicate that rather than inducing neuronal reprogramming of glia in the early postnatal cortex, Ascl1 is a selective enhancer of OPC proliferation.
RESUMEN
Earlier work has implicated the neurotransmitter GABA in controlling forebrain progenitor proliferation. In this issue of Neuron, Everlien et al. (2022) demonstrate that diazepam binding inhibitor acts to keep the neurogenesis-promoting effect of GABA at bay.
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Inhibidor de la Unión a Diazepam , Neurogénesis , Diazepam/metabolismo , Diazepam/farmacología , Inhibidor de la Unión a Diazepam/metabolismo , Neurogénesis/fisiología , Neuronas/metabolismo , Receptores de GABA-A/metabolismo , Ácido gamma-Aminobutírico/metabolismoRESUMEN
The neurotrophin brain-derived neurotrophic factor (BDNF) stimulates adult neurogenesis, but also influences structural plasticity and function of serotonergic neurons. Both, BDNF/TrkB signaling and the serotonergic system modulate behavioral responses to stress and can lead to pathological states when dysregulated. The two systems have been shown to mediate the therapeutic effect of antidepressant drugs and to regulate hippocampal neurogenesis. To elucidate the interplay of both systems at cellular and behavioral levels, we generated a transgenic mouse line that overexpresses BDNF in serotonergic neurons in an inducible manner. Besides displaying enhanced hippocampus-dependent contextual learning, transgenic mice were less affected by chronic social defeat stress (CSDS) compared to wild-type animals. In parallel, we observed enhanced serotonergic axonal sprouting in the dentate gyrus and increased neural stem/progenitor cell proliferation, which was uniformly distributed along the dorsoventral axis of the hippocampus. In the forced swim test, BDNF-overexpressing mice behaved similarly as wild-type mice treated with the antidepressant fluoxetine. Our data suggest that BDNF released from serotonergic projections exerts this effect partly by enhancing adult neurogenesis. Furthermore, independently of the genotype, enhanced neurogenesis positively correlated with the social interaction time after the CSDS, a measure for stress resilience.
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Factor Neurotrófico Derivado del Encéfalo , Neuronas Serotoninérgicas , Animales , Antidepresivos , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Fluoxetina/metabolismo , Fluoxetina/farmacología , Hipocampo/metabolismo , Ratones , Ratones Transgénicos , Neurogénesis/fisiología , Neuronas Serotoninérgicas/metabolismoRESUMEN
New findings cast doubt on whether suppressing the RNA-binding protein PTBP1 can force astrocytes to become dopaminergic neurons.
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Astrocitos , Control de Acceso , Astrocitos/metabolismo , Células Cultivadas , Neuronas Dopaminérgicas/metabolismoRESUMEN
Cellular identity is established through complex layers of genetic regulation, forged over a developmental lifetime. An expanding molecular toolbox is allowing us to manipulate these gene regulatory networks in specific cell types in vivo. In principle, if we found the right molecular tricks, we could rewrite cell identity and harness the rich repertoire of possible cellular functions and attributes. Recent work suggests that this rewriting of cell identity is not only possible, but that newly induced cells can mitigate disease phenotypes in animal models of major human diseases. So, is the sky the limit, or do we need to keep our feet on the ground? This Spotlight synthesises key concepts emerging from recent efforts to reprogramme cellular identity in vivo. We provide our perspectives on recent controversies in the field of glia-to-neuron reprogramming and identify important gaps in our understanding that present barriers to progress.
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Reprogramación Celular , Animales , Linaje de la Célula , Proliferación Celular , Dependovirus/genética , Vectores Genéticos/genética , Vectores Genéticos/metabolismo , Neuroglía/citología , Neuroglía/metabolismo , Neuronas/citología , Neuronas/metabolismo , Medicina RegenerativaRESUMEN
In this issue of Cell, Wang et al. come to the unsettling conclusion that adeno-associated viruses, despite being engineered for glia-specific expression, can become widely active in endogenous neurons, misleading researchers in their quest for efficient conversion of glia into neurons for brain repair.
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Neuroglía , Neuronas , Encéfalo , DependovirusRESUMEN
Reprogramming brain-resident glial cells into clinically relevant induced neurons (iNs) is an emerging strategy toward replacing lost neurons and restoring lost brain functions. A fundamental question is now whether iNs can promote functional recovery in pathological contexts. We addressed this question in the context of therapy-resistant mesial temporal lobe epilepsy (MTLE), which is associated with hippocampal seizures and degeneration of hippocampal GABAergic interneurons. Using a MTLE mouse model, we show that retrovirus-driven expression of Ascl1 and Dlx2 in reactive hippocampal glia in situ, or in cortical astroglia grafted in the epileptic hippocampus, causes efficient reprogramming into iNs exhibiting hallmarks of interneurons. These induced interneurons functionally integrate into epileptic networks and establish GABAergic synapses onto dentate granule cells. MTLE mice with GABAergic iNs show a significant reduction in both the number and cumulative duration of spontaneous recurrent hippocampal seizures. Thus glia-to-neuron reprogramming is a potential disease-modifying strategy to reduce seizures in therapy-resistant epilepsy.
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Epilepsia del Lóbulo Temporal , Animales , Neuronas GABAérgicas , Hipocampo , Interneuronas , Ratones , Neuroglía , ConvulsionesRESUMEN
Spontaneous neuronal replacement is almost absent in the postnatal mammalian nervous system. However, several studies have shown that both early postnatal and adult astroglia can be reprogrammed in vitro or in vivo by forced expression of proneural transcription factors, such as Neurogenin-2 or Achaete-scute homolog 1 (Ascl1), to acquire a neuronal fate. The reprogramming process stably induces properties such as distinctly neuronal morphology, expression of neuron-specific proteins, and the gain of mature neuronal functional features. Direct conversion of astroglia into neurons thus possesses potential as a basis for cell-based strategies against neurological diseases. In this chapter, we describe a well-established protocol used for direct reprogramming of postnatal cortical astrocytes into functional neurons in vitro and discuss available tools and approaches to dissect molecular and cell biological mechanisms underlying the reprogramming process.
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Astrocitos/citología , Astrocitos/metabolismo , Reprogramación Celular , Neuronas/citología , Neuronas/metabolismo , Animales , Diferenciación Celular/genética , Separación Celular/métodos , Células Cultivadas , Reprogramación Celular/genética , Ratones , Neocórtex/citología , Neuroglía/citología , Neuroglía/metabolismo , Cultivo Primario de Células , Factores de Transcripción/genética , Factores de Transcripción/metabolismoRESUMEN
Astrocytes have essential functions in brain homeostasis that are established late in differentiation, but the mechanisms underlying the functional maturation of astrocytes are not well understood. Here we identify extensive transcriptional changes that occur during murine astrocyte maturation in vivo that are accompanied by chromatin remodelling at enhancer elements. Investigating astrocyte maturation in a cell culture model revealed that in vitro-differentiated astrocytes lack expression of many mature astrocyte-specific genes, including genes for the transcription factors Rorb, Dbx2, Lhx2 and Fezf2. Forced expression of these factors in vitro induces distinct sets of mature astrocyte-specific transcripts. Culturing astrocytes in a three-dimensional matrix containing FGF2 induces expression of Rorb, Dbx2 and Lhx2 and improves astrocyte maturity based on transcriptional and chromatin profiles. Therefore, extrinsic signals orchestrate the expression of multiple intrinsic regulators, which in turn induce in a modular manner the transcriptional and chromatin changes underlying astrocyte maturation.
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Astrocitos/citología , Astrocitos/fisiología , Cromatina/genética , Factores de Transcripción/genética , Animales , Técnicas de Cultivo de Célula/métodos , Diferenciación Celular , Corteza Cerebral/citología , Cromatina/metabolismo , Secuenciación de Inmunoprecipitación de Cromatina , Epigénesis Genética , Expresión Génica , Masculino , Ratones Endogámicos C57BL , Análisis de la Célula Individual , Factores de Transcripción/metabolismoRESUMEN
Neural cell diversity is essential to endow distinct brain regions with specific functions. During development, progenitors within these regions are characterized by specific gene expression programs, contributing to the generation of diversity in postmitotic neurons and astrocytes. While the region-specific molecular diversity of neurons and astrocytes is increasingly understood, whether these cells share region-specific programs remains unknown. Here, we show that in the neocortex and thalamus, neurons and astrocytes express shared region-specific transcriptional and epigenetic signatures. These signatures not only distinguish cells across these two brain regions but are also detected across substructures within regions, such as distinct thalamic nuclei, where clonal analysis reveals the existence of common nucleus-specific progenitors for neurons and astrocytes. Consistent with their shared molecular signature, regional specificity is maintained following astrocyte-to-neuron reprogramming. A detailed understanding of these regional-specific signatures may thus inform strategies for future cell-based brain repair.
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Astrocitos , Neocórtex , Astrocitos/metabolismo , Epigenómica , Neuronas/fisiología , TálamoRESUMEN
Excitation-inhibition (E-I) imbalance is considered a hallmark of various neurodevelopmental disorders, including schizophrenia and autism. How genetic risk factors disrupt coordinated glutamatergic and GABAergic synapse formation to cause an E-I imbalance is not well understood. Here, we show that knockdown of Disrupted-in-schizophrenia 1 (DISC1), a risk gene for major mental disorders, leads to E-I imbalance in mature dentate granule neurons. We found that excessive GABAergic inputs from parvalbumin-, but not somatostatin-, expressing interneurons enhance the formation of both glutamatergic and GABAergic synapses in immature mutant neurons. Following the switch in GABAergic signaling polarity from depolarizing to hyperpolarizing during neuronal maturation, heightened inhibition from excessive parvalbumin+ GABAergic inputs causes loss of excitatory glutamatergic synapses in mature mutant neurons, resulting in an E-I imbalance. Our findings provide insights into the developmental role of depolarizing GABA in establishing E-I balance and how it can be influenced by genetic risk factors for mental disorders.
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Predisposición Genética a la Enfermedad , Trastornos Mentales/genética , Neuronas/fisiología , Sinapsis/fisiología , Ácido gamma-Aminobutírico/fisiología , Animales , Polaridad Celular , Femenino , Neuronas GABAérgicas/fisiología , Técnicas de Silenciamiento del Gen , Masculino , Ratones Endogámicos C57BL , Proteínas del Tejido Nervioso/fisiología , Inhibición Neural , Neurogénesis/genética , Neurogénesis/fisiología , Factores de Riesgo , Sinapsis/genética , Potenciales SinápticosRESUMEN
The function of somatic stem cells declines with age. Understanding the molecular underpinnings of this decline is key to counteract age-related disease. Here, we report a dramatic drop in the neural stem cells (NSCs) number in the aging murine brain. We find that this smaller stem cell reservoir is protected from full depletion by an increase in quiescence that makes old NSCs more resistant to regenerate the injured brain. Once activated, however, young and old NSCs show similar proliferation and differentiation capacity. Single-cell transcriptomics of NSCs indicate that aging changes NSCs minimally. In the aging brain, niche-derived inflammatory signals and the Wnt antagonist sFRP5 induce quiescence. Indeed, intervention to neutralize them increases activation of old NSCs during homeostasis and following injury. Our study identifies quiescence as a key feature of old NSCs imposed by the niche and uncovers ways to activate NSCs to repair the aging brain.
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Encéfalo/fisiología , Factores de Edad , Animales , Encéfalo/citología , Diferenciación Celular/fisiología , División Celular/fisiología , Proliferación Celular/fisiología , Senescencia Celular/fisiología , Homeostasis , Masculino , Ratones , Ratones Endogámicos C57BL , Regeneración Nerviosa , Células-Madre Neurales/citología , Células-Madre Neurales/fisiología , Neurogénesis , Nicho de Células MadreRESUMEN
Adult neurogenesis is involved in cognitive performance but studies that manipulated this process to improve brain function are scarce. Here, we characterized a genetic mouse model in which neural stem cells (NSC) of the subventricular zone (SVZ) were temporarily expanded by conditional expression of the cell cycle regulators Cdk4/cyclinD1, thus increasing neurogenesis. We found that supernumerary neurons matured and integrated in the olfactory bulb similarly to physiologically generated newborn neurons displaying a correct expression of molecular markers, morphology and electrophysiological activity. Olfactory performance upon increased neurogenesis was unchanged when mice were tested on relatively easy tasks using distinct odor stimuli. In contrast, intriguingly, increasing neurogenesis improved the discrimination ability of mice when challenged with a difficult task using mixtures of highly similar odorants. Together, our study provides a mammalian model to control the expansion of somatic stem cells that can in principle be applied to any tissue for basic research and models of therapy. By applying this to NSC of the SVZ, we highlighted the importance of adult neurogenesis to specifically improve performance in a challenging olfactory task.
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Aprendizaje Discriminativo , Células-Madre Neurales/fisiología , Neurogénesis/fisiología , Odorantes/análisis , Bulbo Olfatorio/fisiología , Animales , Ciclina D1/fisiología , Quinasa 4 Dependiente de la Ciclina/fisiología , Modelos Animales de Enfermedad , Masculino , Ratones , Ratones Transgénicos , Células-Madre Neurales/citología , Células-Madre Neurales/efectos de los fármacos , Neurogénesis/efectos de los fármacos , Bulbo Olfatorio/citología , Bulbo Olfatorio/efectos de los fármacosRESUMEN
Spastic paraplegia gene 11(SPG11)-linked hereditary spastic paraplegia is a complex monogenic neurodegenerative disease that in addition to spastic paraplegia is characterized by childhood onset cognitive impairment, thin corpus callosum and enlarged ventricles. We have previously shown impaired proliferation of SPG11 neural progenitor cells (NPCs). For the delineation of potential defect in SPG11 brain development we employ 2D culture systems and 3D human brain organoids derived from SPG11 patients' iPSC and controls. We reveal that an increased rate of asymmetric divisions of NPCs leads to proliferation defect, causing premature neurogenesis. Correspondingly, SPG11 organoids appeared smaller than controls and had larger ventricles as well as thinner germinal wall. Premature neurogenesis and organoid size were rescued by GSK3 inhibititors including the Food and Drug Administration-approved tideglusib. These findings shed light on the neurodevelopmental mechanisms underlying disease pathology.