Single-Cell Analysis of Regional Differences in Adult V-SVZ Neural Stem Cell Lineages

Enhanced hippocampal neurogenesis mediated by PGC-1α-activated OXPHOS after neonatal low-dose Propofol exposure

Background

Developing brain is highly plastic and can be easily affected. Growing pediatric usage of anesthetics during painless procedures has raised concerns about the effect of low-dose anesthetics on neurodevelopment. It is urgent to ascertain the neuronal effect of low-dose Propofol, a widely used anesthetic in pediatrics, on developing brains.

Methods

The behavioral tests after neonatal exposure to low-dose/high-dose Propofol in mice were conducted to clarify the cognitive effect. The nascent cells undergoing proliferation and differentiation stage in the hippocampus and cultured neural stem cells (NSCs) were further identified. In addition, single-nuclei RNA sequencing (snRNA-seq), NSCs bulk RNA-seq, and metabolism trials were performed for pathway investigation. Furthermore, small interfering RNA and stereotactic adenovirus injection were, respectively, used in NSCs and hippocampal to confirm the underlying mechanism.

Results

Behavioral tests in mice showed enhanced spatial cognitive ability after being exposed to low-dose Propofol. Activated neurogenesis was observed both in hippocampal and cultured NSCs. Moreover, transcriptome analysis of snRNA-seq, bulk RNA-seq, and metabolism trials revealed a significantly enhanced oxidative phosphorylation (OXPHOS) level in NSCs. Furthermore, PGC-1α, a master regulator in mitochondria metabolism, was found upregulated after Propofol exposure both in vivo and in vitro. Importantly, downregulation of PGC-1α remarkably prevented the effects of low-dose Propofol in activating OXPHOS and neurogenesis.

Conclusions

Taken together, this study demonstrates a novel alteration of mitochondrial function in hippocampal neurogenesis after low-dose Propofol exposure, suggesting the safety, even potentially beneficial effect, of low-dose Propofol in pediatric use.

A brain precursor atlas reveals the acquisition of developmental-like states in adult cerebral tumours

Human cerebral cancers are known to contain cell types resembling the varying stages of neural development. However, the basis of this association remains unclear. Here, we map the development of mouse cerebrum across the developmental time-course, from embryonic day 12.5 to postnatal day 365, performing single-cell transcriptomics on >100,000 cells. By comparing this reference atlas to single-cell data from >100 glial tumours of the adult and paediatric human cerebrum, we find that tumour cells have an expression signature that overlaps with temporally restricted, embryonic radial glial precursors (RGPs) and their immediate sublineages. Further, we demonstrate that prenatal transformation of RGPs in a genetic mouse model gives rise to adult cerebral tumours that show an embryonic/juvenile RGP identity. Together, these findings implicate the acquisition of embryonic-like states in the genesis of adult glioma, providing insight into the origins of human glioma, and identifying specific developmental cell types for therapeutic targeting.

Transcriptome dynamics of hippocampal neurogenesis in macaques across the lifespan and aged humans

Whether adult hippocampal neurogenesis (AHN) persists in adult and aged humans continues to be extensively debated. A major question is whether the markers identified in rodents are reliable enough to reveal new neurons and the neurogenic trajectory in primates. Here, to provide a better understanding of AHN in primates and to reveal more novel markers for distinct cell types, droplet-based single-nucleus RNA sequencing (snRNA-seq) is used to investigate the cellular heterogeneity and molecular characteristics of the hippocampi in macaques across the lifespan and in aged humans. All of the major cell types in the hippocampus and their expression profiles were identified. The dynamics of the neurogenic lineage was revealed and the diversity of astrocytes and microglia was delineated. In the neurogenic lineage, the regulatory continuum from adult neural stem cells (NSCs) to immature and mature granule cells was investigated. A group of primate-specific markers were identified. We validated ETNPPL as a primate-specific NSC marker and verified STMN1 and STMN2 as immature neuron markers in primates. Furthermore, we illustrate a cluster of active astrocytes and microglia exhibiting proinflammatory responses in aged samples. The interaction analysis and the comparative investigation on published datasets and ours imply that astrocytes provide signals inducing the proliferation, quiescence and inflammation of adult NSCs at different stages and that the proinflammatory status of astrocytes probably contributes to the decrease and variability of AHN in adults and elderly individuals.

Activation of STAT3 through combined SRC and EGFR signaling drives resistance to a mitotic kinesin inhibitor in glioblastoma

Inhibitors of the mitotic kinesin Kif11 are anti-mitotics that, unlike vinca alkaloids or taxanes, do not disrupt microtubules and are not neurotoxic. However, development of resistance has limited their clinical utility. While resistance to Kif11 inhibitors in other cell types is due to mechanisms that prevent these drugs from disrupting mitosis, we find that in glioblastoma (GBM), resistance to the Kif11 inhibitor ispinesib works instead through suppression of apoptosis driven by activation of STAT3. This form of resistance requires dual phosphorylation of STAT3 residues Y705 and S727, mediated by SRC and epidermal growth factor receptor (EGFR), respectively. Simultaneously inhibiting SRC and EGFR reverses this resistance, and combined targeting of these two kinases in vivo with clinically available inhibitors is synergistic and significantly prolongs survival in ispinesib-treated GBM-bearing mice. We thus identify a translationally actionable approach to overcoming Kif11 inhibitor resistance that may work to block STAT3-driven resistance against other anti-cancer therapies as well.

Ubiquitin-Specific Protease 22 Promotes Neural Stem Cells Stemness Maintenance and Adult Hippocampal Neurogenesis, Contributing to Cognitive Recovery Following Traumatic Brain Injury

Ubiquitin-specific protease 22 (USP22), a potential marker of cancer stem cells, significantly influences stem cell fate choices. However, its functions in neural stem cells (NSCs) and adult neurogenesis, especially following traumatic brain injury (TBI), remain only partially understood. Here, we found that aberrant USP22 expression could affect NSC proliferation and stemness maintenance, as assessed by the generation of neurospheres, cell counting kit-8 (CCK-8) and immunofluorescence staining in vitro. Moreover, USP22 depletion promotes the differentiation of NSCs, both in vitro and in vivo. In contrast, USP22 overexpression inhibits NSC differentiation into neurons. Interestingly, our data showed that USP22 promotes the proliferation but inhibits the differentiation of NSCs in the dentate gyrus (DG)of the hippocampus soon after TBI. The Morris water maze (MWM) test was adopted to evaluate neurological function, which confirmed that USP22 could improve the learning and memory capacity that was already compromised following TBI. Overall, this study uncovers a potentially novel regulatory role of USP22 in the proliferation and differentiation ability of NSCs, contributing to the hippocampus-dependent cognitive function of TBI mice and may be a novel target for future therapeutic approaches.

Isolation and comparison of neural stem cells from the adult rat brain and spinal cord canonical neurogenic niches

Here, we present a unified protocol for the extraction, culture, and basic characterization of rat neural stem cells (NSCs) from all three canonical neurogenic niches in the brain and spinal cord. We describe tissue dissection and dissociation, cell culture, followed by EdU labeling and characterization of NSCs. By yielding considerable numbers of viable cells per animal, this protocol enables the establishment of substantial, long-term cell banks, thus offering cost and labor efficiency while significantly reducing the numbers of animals used.

•

Extraction, culture, and characterization of adult neurogenic niche neural stem cells

•

Comparison of neural stem cells from the different neurogenic niches

•

High yield of viable neural stem cells obtainable per animal

Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.

Single-Cell and Single-Nucleus RNAseq Analysis of Adult Neurogenesis

The complexity of adult neurogenesis is becoming increasingly apparent as we learn more about cellular heterogeneity and diversity of the neurogenic lineages and stem cell niches within the adult brain. This complexity has been unraveled in part due to single-cell and single-nucleus RNA sequencing (sc-RNAseq and sn-RNAseq) studies that have focused on adult neurogenesis. This review summarizes 33 published studies in the field of adult neurogenesis that have used sc- or sn-RNAseq methods to answer questions about the three main regions that host adult neural stem cells (NSCs): the subventricular zone (SVZ), the dentate gyrus (DG) of the hippocampus, and the hypothalamus. The review explores the similarities and differences in methodology between these studies and provides an overview of how these studies have advanced the field and expanded possibilities for the future.

scMAGIC: accurately annotating single cells using two rounds of reference-based classification

Here, we introduce scMAGIC (Single Cell annotation using MArker Genes Identification and two rounds of reference-based Classification [RBC]), a novel method that uses well-annotated single-cell RNA sequencing (scRNA-seq) data as the reference to assist in the classification of query scRNA-seq data. A key innovation in scMAGIC is the introduction of a second-round RBC in which those query cells whose cell identities are confidently validated in the first round are used as a new reference to again classify query cells, therefore eliminating the batch effects between the reference and the query data. scMAGIC significantly outperforms 13 competing RBC methods with their optimal parameter settings across 86 benchmark tests, especially when the cell types in the query dataset are not completely covered by the reference dataset and when there exist significant batch effects between the reference and the query datasets. Moreover, when no reference dataset is available, scMAGIC can annotate query cells with reasonably high accuracy by using an atlas dataset as the reference.

Single-nucleus RNA sequencing identified cells with ependymal cell-like features enriched in neonatal mice after spinal cord injury

The adult mammalian central nervous system has limited regenerative ability, and spinal cord injury (SCI) often causes lifelong motor disability. While regeneration is limited in adults, injured spinal cord tissue can be regenerated and neural function can be almost completely restored in neonates. However, difference of cellular composition in lesion has not been well characterized. To gain insight into the age-dependent cellular reaction after SCI, we performed single-nucleus RNA sequencing, analyzing 4,076 nuclei from sham and injured spinal cords from adult and neonatal mice. Clustering analysis identified 18 cell populations. We identified previously undescribed cells with ependymal cell-like gene expression profile, the number of which was increased in neonates after SCI. Histological analysis revealed that these cells line the central canal under physiological conditions in both adults and neonates. We confirmed that they were enriched in the lesion only in neonates. We further showed that these cells were positive for the cellular markers of ependymal cells, astrocytes and radial glial cells. This study provides a deeper understanding of neonate-specific cellular responses after SCI, which may determine regenerative capacity.

Loss of neurodevelopmental-associated miR-592 impairs neurogenesis and causes social interaction deficits

microRNA-592 (miR-592) has been linked to neurogenesis, but the influence of miR-592 knockout in vivo remains unknown. Here, we report that miR-592 knockout represses IPC-to-mature neuron transition, impairs motor coordination and reduces social interaction. Combining the RNA-seq and tandem mass tagging-based quantitative proteomics analysis (TMT protein quantification) and luciferase reporter assays, we identified MeCP2 as the direct targetgene of miR-592 in the mouse cortex. In Tg(MECP2) mice, lipofection of miR-592 efficiently reduced MECP2 expression in the brains of Tg(MECP2) mice at E14.5. Furthermore, treatment with miR-592 partially ameliorated the autism-like phenotypes observed in adult Tg(MECP2) mice. The findings demonstrate that miR-592 might play a novel role in treating the neurodevelopmental-associated disorder.

Impaired neurogenesis alters brain biomechanics in a neuroprogenitor-based genetic subtype of congenital hydrocephalus

Hydrocephalus, characterized by cerebral ventricular dilatation, is routinely attributed to primary defects in cerebrospinal fluid (CSF) homeostasis. This fosters CSF shunting as the leading reason for brain surgery in children despite considerable disease heterogeneity. In this study, by integrating human brain transcriptomics with whole-exome sequencing of 483 patients with congenital hydrocephalus (CH), we found convergence of CH risk genes in embryonic neuroepithelial stem cells. Of all CH risk genes, TRIM71/lin-41 harbors the most de novo mutations and is most specifically expressed in neuroepithelial cells. Mice harboring neuroepithelial cell-specific Trim71 deletion or CH-specific Trim71 mutation exhibit prenatal hydrocephalus. CH mutations disrupt TRIM71 binding to its RNA targets, causing premature neuroepithelial cell differentiation and reduced neurogenesis. Cortical hypoplasia leads to a hypercompliant cortex and secondary ventricular enlargement without primary defects in CSF circulation. These data highlight the importance of precisely regulated neuroepithelial cell fate for normal brain-CSF biomechanics and support a clinically relevant neuroprogenitor-based paradigm of CH.

Could a Different View of Quiescence Help Us Understand How Neurogenesis Is Regulated?

The majority of adult neural stem cells (aNSCs) are in a distinct metabolic state of reversible cell cycle exit also known as quiescence. The rate of aNSC activation determines the number of new neurons generated and directly influences the long-term maintenance of neurogenesis. Despite its relevance, it is still unclear how aNSC quiescence is regulated. Many factors contribute to this, like aNSC heterogeneity, the lack of reliable quiescence markers, the complexity of the neurogenic niches or the intricacy of the transcriptional and post-transcriptional mechanisms involved. In this perspective article I discuss possible solutions to these problems. But, first and foremost, I believe we require a model that goes beyond a simple transition toward activation. Instead, we must acknowledge the full complexity of aNSC states, which include not only activation but also differentiation and survival as behavioural outcomes. I propose a model where aNSCs dynamically transition through a cloud of highly interlinked cellular states driven by intrinsic and extrinsic cues. I also show how a new perspective enables us to integrate current results into a coherent framework leading to the formulation of new testable hypothesis. This model, like all others, is still far from perfect and will be reshaped by future findings. I believe that having a more complete view of aNSC transitions and embracing their complexity will bring us closer to understand how aNSC activity and neurogenesis are controlled throughout life.

Dissection of artifactual and confounding glial signatures by single-cell sequencing of mouse and human brain

A key aspect of nearly all single-cell sequencing experiments is dissociation of intact tissues into single-cell suspensions. While many protocols have been optimized for optimal cell yield, they have often overlooked the effects that dissociation can have on ex vivo gene expression. Here, we demonstrate that use of enzymatic dissociation on brain tissue induces an aberrant ex vivo gene expression signature, most prominently in microglia, which is prevalent in published literature and can substantially confound downstream analyses. To address this issue, we present a rigorously validated protocol that preserves both in vivo transcriptional profiles and cell-type diversity and yield across tissue types and species. We also identify a similar signature in postmortem human brain single-nucleus RNA-sequencing datasets, and show that this signature is induced in freshly isolated human tissue by exposure to elevated temperatures ex vivo. Together, our results provide a methodological solution for preventing artifactual gene expression changes during fresh tissue digestion and a reference for future deeper analysis of the potential confounding states present in postmortem human samples.

Olig2 defines a subset of neural stem cells that produce specific olfactory bulb interneuron subtypes in the subventricular zone of adult mice

Distinct neural stem cells (NSCs) reside in different regions of the subventricular zone (SVZ) and generate multiple olfactory bulb (OB) interneuron subtypes in the adult brain. However, the molecular mechanisms underlying such NSC heterogeneity remain largely unknown. Here, we show that the basic helix-loop-helix transcription factor Olig2 defines a subset of NSCs in the early postnatal and adult SVZ. Olig2-expressing NSCs exist broadly but are most enriched in the ventral SVZ along the dorsoventral axis complementary to dorsally enriched Gsx2-expressing NSCs. Comparisons of Olig2-expressing NSCs from early embryonic to adult stages using single cell transcriptomics reveal stepwise developmental changes in their cell cycle and metabolic properties. Genetic studies further show that cross-repression contributes to the mutually exclusive expression of Olig2 and Gsx2 in NSCs/progenitors during embryogenesis, but that their expression is regulated independently from each other in adult NSCs. Finally, lineage-tracing and conditional inactivation studies demonstrate that Olig2 plays an important role in the specification of OB interneuron subtypes. Altogether, our study demonstrates that Olig2 defines a unique subset of adult NSCs enriched in the ventral aspect of the adult SVZ.

Single-cell profiling of human subventricular zone progenitors identifies SFRP1 as a target to re-activate progenitors

Following the decline of neurogenesis at birth, progenitors of the subventricular zone (SVZ) remain mostly in a quiescent state in the adult human brain. The mechanisms that regulate this quiescent state are still unclear. Here, we isolate CD271⁺ progenitors from the aged human SVZ for single-cell RNA sequencing analysis. Our transcriptome data reveal the identity of progenitors of the aged human SVZ as late oligodendrocyte progenitor cells. We identify the Wnt pathway antagonist SFRP1 as a possible signal that promotes quiescence of progenitors from the aged human SVZ. Administration of WAY-316606, a small molecule that inhibits SFRP1 function, stimulates activation of neural stem cells both in vitro and in vivo under homeostatic conditions. Our data unravel a possible mechanism through which progenitors of the adult human SVZ are maintained in a quiescent state and a potential target for stimulating progenitors to re-activate.

The decline in neurogenesis following birth is accompanied with a quiescent state characteristic of neural progenitors of the adult brain. Here, the authors identify the Wnt pathway antagonist SFRP1 as a potential signal that promotes quiescence and show that its inhibition stimulates stem cell activation.

Singular Adult Neural Stem Cells Do Not Exist

Adult neural stem cells (aNSCs) are the source for the continuous production of new neurons throughout life. This so-called adult neurogenesis has been extensively studied; the intermediate cellular stages are well documented. Recent discoveries have raised new controversies in the field, such as the notion that progenitor cells hold similar self-renewal potential as stem cells, or whether different types of aNSCs exist. Here, we discuss evidence for heterogeneity of aNSCs, including short-term and long-term self-renewing aNSCs, regional and temporal differences in aNSC function, and single cell transcriptomics. Reviewing various genetic mouse models used for targeting aNSCs and lineage tracing, we consider potential lineage relationships between Ascl1-, Gli1-, and Nestin-targeted aNSCs. We present a multidimensional model of adult neurogenesis that incorporates recent findings and conclude that stemness is a phenotype, a state of properties that can change with time, rather than a cell property, which is static and immutable. We argue that singular aNSCs do not exist.

Suppression of adult cytogenesis in the rat brain leads to sex-differentiated disruption of the HPA axis activity

OBJECTIVES

The action of stress hormones, mainly glucocorticoids, starts and coordinates the systemic response to stressful events. The HPA axis activity is predicated on information processing and modulation by upstream centres, such as the hippocampus where adult-born neurons (hABN) have been reported to be an important component in the processing and integration of new information. Still, it remains unclear whether and how hABN regulates HPA axis activity and CORT production, particularly when considering sex differences.

MATERIALS AND METHODS

Using both sexes of a transgenic rat model of cytogenesis ablation (GFAP-Tk rat model), we examined the endocrinological and behavioural effects of disrupting the generation of new astrocytes and neurons within the hippocampal dentate gyrus (DG).

RESULTS

Our results show that GFAP-Tk male rats present a heightened acute stress response. In contrast, GFAP-Tk female rats have increased corticosterone secretion at nadir, a heightened, yet delayed, response to an acute stress stimulus, accompanied by neuronal hypertrophy in the basal lateral amygdala and increased expression of the glucocorticoid receptors in the ventral DG.

CONCLUSIONS

Our results reveal that hABN regulation of the HPA axis response is sex-differentiated.

Robust Transcriptional Profiling and Identification of Differentially Expressed Genes With Low Input RNA Sequencing of Adult Hippocampal Neural Stem and Progenitor Populations

Multipotent neural stem cells (NSCs) are found in several isolated niches of the adult mammalian brain where they have unique potential to assist in tissue repair. Modern transcriptomics offer high-throughput methods for identifying disease or injury associated gene expression signatures in endogenous adult NSCs, but they require adaptation to accommodate the rarity of NSCs. Bulk RNA sequencing (RNAseq) of NSCs requires pooling several mice, which impedes application to labor-intensive injury models. Alternatively, single cell RNAseq can profile hundreds to thousands of cells from a single mouse and is increasingly used to study NSCs. The consequences of the low RNA input from a single NSC on downstream identification of differentially expressed genes (DEGs) remains insufficiently explored. Here, to clarify the role that low RNA input plays in NSC DEG identification, we directly compared DEGs in an oxidative stress model of cultured NSCs by bulk and single cell sequencing. While both methods yielded DEGs that were replicable, single cell sequencing using the 10X Chromium platform yielded DEGs derived from genes with higher relative transcript counts compared to non-DEGs and exhibited smaller fold changes than DEGs identified by bulk RNAseq. The loss of high fold-change DEGs in the single cell platform presents an important limitation for identifying disease-relevant genes. To facilitate identification of such genes, we determined an RNA-input threshold that enables transcriptional profiling of NSCs comparable to standard bulk sequencing and used it to establish a workflow for in vivo profiling of endogenous NSCs. We then applied this workflow to identify DEGs after lateral fluid percussion injury, a labor-intensive animal model of traumatic brain injury. Our work joins an emerging body of evidence suggesting that single cell RNA sequencing may underestimate the diversity of pathologic DEGs. However, our data also suggest that population level transcriptomic analysis can be adapted to capture more of these DEGs with similar efficacy and diversity as standard bulk sequencing. Together, our data and workflow will be useful for investigators interested in understanding and manipulating adult hippocampal NSC responses to various stimuli.

Developmental thyroid disruption permanently affects the neuroglial output in the murine subventricular zone

Neural stem cells (NSCs) in the adult brain are a source of neural cells for brain injury repair. We investigated whether their capacity to generate new neurons and glia is determined by thyroid hormone (TH) during development because serum levels peak during postnatal reorganization of the main NSC niche, the subventricular zone (SVZ). Re-analysis of mouse transcriptome data revealed increased expression of TH transporters and deiodinases in postnatal SVZ NSCs, promoting local TH action, concomitant with a burst in neurogenesis. Inducing developmental hypothyroidism reduced NSC proliferation, disrupted expression of genes implicated in NSC determination and TH signaling, and altered the neuron/glia output in newborns. Three-month-old adult mice recovering from developmental hypothyroidism had fewer olfactory interneurons and underperformed on short-memory odor tests, dependent on SVZ neurogenesis. Our data provide readouts permitting comparison with adverse long-term events following thyroid disruptor exposure and ideas regarding the etiology of prevalent neurodegenerative diseases in industrialized countries.

•

Thyroid hormone peak associates with a neurogenic wave in the postnatal murine SVZ

•

Single-cell RNA-seq data show increased TH action in SVZ progenitors at that stage

•

Developmental hypothyroidism disrupts neuroglial commitment and associated genes

•

Transient developmental TH depletion impairs adult neurogliogenesis and olfaction

Astrocyte and Oligodendrocyte Responses From the Subventricular Zone After Injury

Under normal conditions, neural stem cells (NSCs or B cells) in the adult subventricular zone (SVZ) give rise to amplifying neural progenitor cells (NPCs or C cells), which can produce neuroblasts (or A cells) that migrate to the olfactory bulb and differentiate into new neurons. However, following brain injury, these cells migrate toward the injury site where they differentiate into astrocytes and oligodendrocytes. In this review, we will focus on recent findings that chronicle how astrocytes and oligodendrocytes derived from SVZ-NSCs respond to different types of injury. We will also discuss molecular regulators of SVZ-NSC proliferation and their differentiation into astrocytes and oligodendrocytes. Overall, the goal of this review is to highlight how SVZ-NSCs respond to injury and to summarize the regulatory mechanisms that oversee their glial response. These molecular and cellular processes will provide critical insights needed to develop strategies to promote brain repair following injury using SVZ-NSCs.

GLI3 Is Required for OLIG2+ Progeny Production in Adult Dorsal Neural Stem Cells

The ventricular-subventricular zone (V-SVZ) is a postnatal germinal niche. It holds a large population of neural stem cells (NSCs) that generate neurons and oligodendrocytes for the olfactory bulb and (primarily) the corpus callosum, respectively. These NSCs are heterogeneous and generate different types of neurons depending on their location. Positional identity among NSCs is thought to be controlled in part by intrinsic pathways. However, extrinsic cell signaling through the secreted ligand Sonic hedgehog (Shh) is essential for neurogenesis in both the dorsal and ventral V-SVZ. Here we used a genetic approach to investigate the role of the transcription factors GLI2 and GLI3 in the proliferation and cell fate of dorsal and ventral V-SVZ NSCs. We find that while GLI3 is expressed in stem cell cultures from both dorsal and ventral V-SVZ, the repressor form of GLI3 is more abundant in dorsal V-SVZ. Despite this high dorsal expression and the requirement for other Shh pathway members, GLI3 loss affects the generation of ventrally-, but not dorsally-derived olfactory interneurons in vivo and does not affect trilineage differentiation in vitro. However, loss of GLI3 in the adult dorsal V-SVZ in vivo results in decreased numbers of OLIG2-expressing progeny, indicating a role in gliogenesis.

Identifying gene expression profiles associated with neurogenesis and inflammation in the human subependymal zone from development through aging

The generation of new neurons within the mammalian forebrain continues throughout life within two main neurogenic niches, the subgranular zone (SGZ) of the hippocampal dentate gyrus, and the subependymal zone (SEZ) lining the lateral ventricles. Though the SEZ is the largest neurogenic niche in the adult human forebrain, our understanding of the mechanisms regulating neurogenesis from development through aging within this region remains limited. This is especially pertinent given that neurogenesis declines dramatically over the postnatal lifespan. Here, we performed transcriptomic profiling on the SEZ from human post-mortem tissue from eight different life-stages ranging from neonates (average age ~ 2 months old) to aged adults (average age ~ 86 years old). We identified transcripts with concomitant profiles across these decades of life and focused on three of the most distinct profiles, namely (1) genes whose expression declined sharply after birth, (2) genes whose expression increased steadily with age, and (3) genes whose expression increased sharply in old age in the SEZ. Critically, these profiles identified neuroinflammation as becoming more prevalent with advancing age within the SEZ and occurring with time courses, one gradual (starting in mid-life) and one sharper (starting in old age).

Neural Stem Cells in Adult Mammals are not Astrocytes

At the turn of the 21st century studies of the cells that resided in the adult mammalian subventricular zone (SVZ) characterized the neural stem cells (NSCs) as a subtype of astrocyte. Over the ensuing years, numerous studies have further characterized the properties of these NSCs and compared them to parenchymal astrocytes. Here we have evaluated the evidence collected to date to establish whether classifying the NSCs as astrocytes is appropriate and useful. We also performed a meta-analysis with 4 previously published datasets that used cell sorting and unbiased single-cell RNAseq to highlight the distinct gene expression profiles of adult murine NSCs and niche astrocytes. On the basis of our understanding of the properties and functions of astrocytes versus the properties and functions of NSCs, and from our comparative transcriptomic analyses we conclude that classifying the adult mammalian NSC as an astrocyte is potentially misleading. From our vantage point, it is more appropriate to refer to the cells in the adult mammalian SVZ that retain the capacity to produce new neurons and macroglia as NSCs without attaching the term "astrocyte-like."

Isolation and Culture of Neural Stem/Progenitor Cells from the Postnatal Periventricular Region

Due to the complexity of the neural stem cell (NSC) niche organization, the lack of specific NSC markers, and the difficulty of long-term tracking these cells and their progeny in vivo, the functional properties of the endogenous NSCs remain largely unexplored. These limitations have led to the development of methodologies to efficiently isolate, expand, and differentiate NSCs ex vivo. We describe here the peculiarities of the neurosphere assay (NSA) as a methodology that allows to efficiently isolate, expand, and differentiate somatic NSCs derived from the postnatal and adult forebrain periventricular region while preserving proliferation, self-renewal, and multipotency, the main attributes that provide their functional identification.

Stress Signal ULBP4, an NKG2D Ligand, Is Upregulated in Multiple Sclerosis and Shapes CD8+ T-Cell Behaviors

BACKGROUND AND OBJECTIVES

We posit the involvement of the natural killer group 2D (NKG2D) pathway in multiple sclerosis (MS) pathology via the presence of specific NKG2D ligands (NKG2DLs). We aim to evaluate the expression of NKG2DLs in the CNS and CSF of patients with MS and to identify cellular stressors inducing the expression of UL16-binding protein 4 (ULBP4), the only detectable NKG2DL. Finally, we evaluate the impact of ULBP4 on functions such as cytokine production and motility by CD8⁺ T lymphocytes, a subset largely expressing NKG2D, the cognate receptor.

METHODS

Human postmortem brain samples and CSF from patients with MS and controls were used to evaluate NKG2DL expression. In vitro assays using primary cultures of human astrocytes and neurons were performed to identify stressors inducing ULBP4 expression. Human CD8⁺ T lymphocytes from MS donors and age/sex-matched healthy controls were isolated to evaluate the functional impact of soluble ULBP4.

RESULTS

We detected mRNA coding for the 8 identified human NKG2DLs in brain samples from patients with MS and controls, but only ULBP4 protein expression was detectable by Western blot. ULBP4 levels were greater in patients with MS, particularly in active and chronic active lesions and normal-appearing white matter, compared with normal-appearing gray matter from MS donors and white and gray matter from controls. Soluble ULBP4 was also detected in CSF of patients with MS and controls, but a smaller shed/soluble form of 25 kDa was significantly elevated in CSF from female patients with MS compared with controls and male patients with MS. Our data indicate that soluble ULBP4 affects various functions of CD8⁺ T lymphocytes. First, it enhanced the production of the proinflammatory cytokines GM-CSF and interferon-γ (IFNγ). Second, it increased CD8⁺ T lymphocyte motility and favored a kinapse-like behavior when cultured in the presence of human astrocytes. CD8⁺ T lymphocytes from patients with MS were especially altered by the presence of soluble ULBP4 compared with healthy controls.

DISCUSSION

Our study provides new evidence for the involvement of NKG2D and its ligand ULBP4 in MS pathology. Our results point to ULBP4 as a viable target to specifically block 1 component of the NKG2D pathway without altering immune surveillance involving other NKG2DL.

The cortical hem lacks stem cell potential despite expressing SOX9 and HOPX

The adult dentate gyrus (DG) of rodents hosts a neural stem cell (NSC) niche capable of generating new neurons throughout life. The embryonic origin and molecular mechanisms underlying formation of DG NSCs are still being investigated. We performed a bulk transcriptomic analysis on mouse developing archicortex conditionally deleted for Sox9, a SoxE transcription factor controlling both gliogenesis and NSC formation, and identified Hopx, a recently identified marker of both prospective adult DG NSCs and astrocytic progenitors, as being downregulated. We confirm SOX9 is required for HOPX expression in the embryonic archicortex. In particular, we found that both NSC markers are highly expressed in the cortical hem (CH), while only weakly in the adjacent dentate neuroepithelium (DNE), suggesting a potential CH embryonic origin for DG NSCs. However, we demonstrate both in vitro and in vivo that the embryonic CH, as well as its adult derivatives, lacks stem cell potential. Instead, deletion of Sox9 in the DNE affects both HOPX expression and NSC formation in the adult DG. We conclude that HOPX expression in the CH is involved in astrocytic differentiation downstream of SOX9, which we previously showed regulates DG development by inducing formation of a CH-derived astrocytic scaffold. Altogether, these results suggest that both proteins work in a dose-dependent manner to drive either astrocytic differentiation in CH or NSC formation in DNE.

Lipid droplet availability affects neural stem/progenitor cell metabolism and proliferation

Neural stem/progenitor cells (NSPCs) generate new neurons throughout adulthood. However, the underlying regulatory processes are still not fully understood. Lipid metabolism plays an important role in regulating NSPC activity: build-up of lipids is crucial for NSPC proliferation, whereas break-down of lipids has been shown to regulate NSPC quiescence. Despite their central role for cellular lipid metabolism, the role of lipid droplets (LDs), the lipid storing organelles, in NSPCs remains underexplored. Here we show that LDs are highly abundant in adult mouse NSPCs, and that LD accumulation is significantly altered upon fate changes such as quiescence and differentiation. NSPC proliferation is influenced by the number of LDs, inhibition of LD build-up, breakdown or usage, and the asymmetric inheritance of LDs during mitosis. Furthermore, high LD-containing NSPCs have increased metabolic activity and capacity, but do not suffer from increased oxidative damage. Together, these data indicate an instructive role for LDs in driving NSPC behaviour.

Adult Neural Stem Cell Migration Is Impaired in a Mouse Model of Alzheimer's Disease

Neurogenesis in the adult brain takes place in two neurogenic niches: the ventricular-subventricular zone (V-SVZ) and the subgranular zone. After differentiation, neural precursor cells (neuroblasts) have to move to an adequate position, a process known as neuronal migration. Some studies show that in Alzheimer’s disease, the adult neurogenesis is impaired. Our main aim was to investigate some proteins involved both in the physiopathology of Alzheimer’s disease and in the neuronal migration process using the APP/PS1 Alzheimer’s mouse model. Progenitor migrating cells are accumulated in the V-SVZ of the APP/PS1 mice. Furthermore, we find an increase of Cdh1 levels and a decrease of Cdk5/p35 and cyclin B1, indicating that these cells have an alteration of the cell cycle, which triggers a senescence state. We find less cells in the rostral migratory stream and less mature neurons in the olfactory bulbs from APP/PS1 mice, leading to an impaired odour discriminatory ability compared with WT mice. Alzheimer’s disease mice present a deficit in cell migration from V-SVZ due to a senescent phenotype. Therefore, these results can contribute to a new approach of Alzheimer’s based on senolytic compounds or pro-neurogenic factors.

Injury-induced ASCL1 expression orchestrates a transitory cell state required for repair of the neonatal cerebellum

To understand repair processes, it is critical to identify the molecular foundations underlying progenitor diversity and plasticity. Upon injury to the neonatal cerebellum, a normally gliogenic nestin-expressing progenitor (NEP) in the Bergmann glia layer (BgL) undergoes adaptive reprograming to restore granule cell production. However, the cellular states and genes regulating the NEP fate switch are unknown. Using single-cell RNA sequencing and fate mapping, we defined molecular subtypes of NEPs and their lineages under homeostasis and repair. NEPs contain two major subtypes: Hopx+ astrogliogenic and Ascl1+ neurogenic NEPs that are further subdivided based on their location, lineage, and differentiation status. Upon injury, an Ascl1+ transitory cellular state arises from Hopx+ BgL-NEPs. Furthermore, mutational analysis revealed that induction of Ascl1 is required for adaptive reprogramming by orchestrating a glial-to-neural switch in vivo following injury. Thus, we provide molecular and cellular insights into context-dependent progenitor plasticity and repair mechanisms in the brain.

Recent advances in tissue stem cells

Stem cells are undifferentiated cells capable of self-renewal and differentiation, giving rise to specialized functional cells. Stem cells are of pivotal importance for organ and tissue development, homeostasis, and injury and disease repair. Tissue-specific stem cells are a rare population residing in specific tissues and present powerful potential for regeneration when required. They are usually named based on the resident tissue, such as hematopoietic stem cells and germline stem cells. This review discusses the recent advances in stem cells of various tissues, including neural stem cells, muscle stem cells, liver progenitors, pancreatic islet stem/progenitor cells, intestinal stem cells, and prostate stem cells, and the future perspectives for tissue stem cell research.

Protein kinase Cι and SRC signaling define reciprocally related subgroups of glioblastoma with distinct therapeutic vulnerabilities

We report that atypical protein kinase Cι (PKCι) is an oncogenic driver of glioblastoma (GBM). Deletion or inhibition of PKCι significantly impairs tumor growth and prolongs survival in murine GBM models. GBM cells expressing elevated PKCι signaling are sensitive to PKCι inhibitors, whereas those expressing low PKCι signaling exhibit active SRC signaling and sensitivity to SRC inhibitors. Resistance to the PKCι inhibitor auranofin is associated with activated SRC signaling and response to a SRC inhibitor, whereas resistance to a SRC inhibitor is associated with activated PKCι signaling and sensitivity to auranofin. Interestingly, PKCι- and SRC-dependent cells often co-exist in individual GBM tumors, and treatment of GBM-bearing mice with combined auranofin and SRC inhibitor prolongs survival beyond either drug alone. Thus, we identify PKCι and SRC signaling as distinct therapeutic vulnerabilities that are directly translatable into an improved treatment for GBM.

Novel Galectin-3 Roles in Neurogenesis, Inflammation and Neurological Diseases

Galectin-3 (Gal-3) is an evolutionarily conserved and multifunctional protein that drives inflammation in disease. Gal-3's role in the central nervous system has been less studied than in the immune system. However, recent studies show it exacerbates Alzheimer's disease and is upregulated in a large variety of brain injuries, while loss of Gal-3 function can diminish symptoms of neurodegenerative diseases such as Alzheimer's. Several novel molecular pathways for Gal-3 were recently uncovered. It is a natural ligand for TREM2 (triggering receptor expressed on myeloid cells), TLR4 (Toll-like receptor 4), and IR (insulin receptor). Gal-3 regulates a number of pathways including stimulation of bone morphogenetic protein (BMP) signaling and modulating Wnt signalling in a context-dependent manner. Gal-3 typically acts in pathology but is now known to affect subventricular zone (SVZ) neurogenesis and gliogenesis in the healthy brain. Despite its myriad interactors, Gal-3 has surprisingly specific and important functions in regulating SVZ neurogenesis in disease. Gal-1, a similar lectin often co-expressed with Gal-3, also has profound effects on brain pathology and adult neurogenesis. Remarkably, Gal-3's carbohydrate recognition domain bears structural similarity to the SARS-CoV-2 virus spike protein necessary for cell entry. Gal-3 can be targeted pharmacologically and is a valid target for several diseases involving brain inflammation. The wealth of molecular pathways now known further suggest its modulation could be therapeutically useful.

Immunohistochemical evidence for adult human neurogenesis in health and disease

Postnatal and adult neurogenesis in the subventricular zone and subgranular zone of animals such as rodents and non-human primates has been observed with many different technical approaches. Since most techniques used in animals cannot be used in humans, the majority of human neurogenesis studies rely on postmortem immunohistochemistry. This technique is difficult in human tissue, due to poor and variable preservation of antigens and samples. Nevertheless, a survey of the literature reveals that most published studies provide evidence for childhood and adult neurogenesis in the human brain stem cell niches. There are some conflicting results even when assessing the same markers and when using the same antibodies. Focusing on immunohistochemical studies on post-mortem human sections, we discuss the relative robustness of the literature on adult neurogenesis. We also discuss the response of the subventricular and subgranular zones to human disease, showing that the two niches can respond differently and that the stage of disease impacts neurogenesis levels. Thus, we highlight strong evidence for adult human neurogenesis, discuss other work that did not find it, describe obstacles in analysis, and offer other approaches to evaluate the neurogenic potential of the subventricular and subgranular zones of Homo sapiens. This article is categorized under: Neurological Diseases > Stem Cells and Development Reproductive System Diseases > Stem Cells and Development.

Adult Neurogenesis: A Story Ranging from Controversial New Neurogenic Areas and Human Adult Neurogenesis to Molecular Regulation

The generation of new neurons in the adult brain is a currently accepted phenomenon. Over the past few decades, the subventricular zone and the hippocampal dentate gyrus have been described as the two main neurogenic niches. Neurogenic niches generate new neurons through an asymmetric division process involving several developmental steps. This process occurs throughout life in several species, including humans. These new neurons possess unique properties that contribute to the local circuitry. Despite several efforts, no other neurogenic zones have been observed in many years; the lack of observation is probably due to technical issues. However, in recent years, more brain niches have been described, once again breaking the current paradigms. Currently, a debate in the scientific community about new neurogenic areas of the brain, namely, human adult neurogenesis, is ongoing. Thus, several open questions regarding new neurogenic niches, as well as this phenomenon in adult humans, their functional relevance, and their mechanisms, remain to be answered. In this review, we discuss the literature and provide a compressive overview of the known neurogenic zones, traditional zones, and newly described zones. Additionally, we will review the regulatory roles of some molecular mechanisms, such as miRNAs, neurotrophic factors, and neurotrophins. We also join the debate on human adult neurogenesis, and we will identify similarities and differences in the literature and summarize the knowledge regarding these interesting topics.

Neuroinflammatory astrocyte subtypes in the mouse brain

Astrocytes undergo an inflammatory transition after infections, acute injuries and chronic neurodegenerative diseases. How this transition is affected by time and sex, its heterogeneity at the single-cell level and how sub-states are spatially distributed in the brain remains unclear. In this study, we investigated transcriptome changes of mouse cortical astrocytes after an acute inflammatory stimulus using the bacterial cell wall endotoxin lipopolysaccharide. We identified fast transcriptomic changes in astrocytes occurring within hours that drastically change over time. By sequencing ~80,000 astrocytes at single-cell resolution, we show that inflammation causes a widespread response with subtypes of astrocytes undergoing distinct inflammatory transitions with defined transcriptomic profiles. We also attribute key sub-states of inflammation-induced reactive astrocytes to specific brain regions using spatial transcriptomics and in situ hybridization. Together, our datasets provide a powerful resource for profiling astrocyte heterogeneity and will be useful for understanding the biological importance of regionally constrained reactive astrocyte sub-states.

Diversity of Adult Neural Stem and Progenitor Cells in Physiology and Disease

Adult neural stem and progenitor cells (NSPCs) contribute to learning, memory, maintenance of homeostasis, energy metabolism and many other essential processes. They are highly heterogeneous populations that require input from a regionally distinct microenvironment including a mix of neurons, oligodendrocytes, astrocytes, ependymal cells, NG2+ glia, vasculature, cerebrospinal fluid (CSF), and others. The diversity of NSPCs is present in all three major parts of the CNS, i.e., the brain, spinal cord, and retina. Intrinsic and extrinsic signals, e.g., neurotrophic and growth factors, master transcription factors, and mechanical properties of the extracellular matrix (ECM), collectively regulate activities and characteristics of NSPCs: quiescence/survival, proliferation, migration, differentiation, and integration. This review discusses the heterogeneous NSPC populations in the normal physiology and highlights their potentials and roles in injured/diseased states for regenerative medicine.

Fractalkine signaling regulates oligodendroglial cell genesis from SVZ precursor cells

Neural and oligodendrocyte precursor cells (NPCs and OPCs) in the subventricular zone (SVZ) of the brain contribute to oligodendrogenesis throughout life, in part due to direct regulation by chemokines. The role of the chemokine fractalkine is well established in microglia; however, the effect of fractalkine on SVZ precursor cells is unknown. We show that murine SVZ NPCs and OPCs express the fractalkine receptor (CX3CR1) and bind fractalkine. Exogenous fractalkine directly enhances OPC and oligodendrocyte genesis from SVZ NPCs in vitro. Infusion of fractalkine into the lateral ventricle of adult NPC lineage-tracing mice leads to increased newborn OPC and oligodendrocyte formation in vivo. We also show that OPCs secrete fractalkine and that inhibition of endogenous fractalkine signaling reduces oligodendrocyte formation in vitro. Finally, we show that fractalkine signaling regulates oligodendrogenesis in cerebellar slices ex vivo. In summary, we demonstrate a novel role for fractalkine signaling in regulating oligodendrocyte genesis from postnatal CNS precursor cells.

hiPSC Modeling of Lineage-Specific Smooth Muscle Cell Defects Caused by TGFBR1A230T Variant, and its Therapeutic Implications for Loeys-Dietz Syndrome

Background: Loeys-Dietz Syndrome (LDS) is an inherited disorder predisposing individuals to thoracic aortic aneurysm and dissection (TAAD). Currently, there are no medical treatments except surgical resection. Although the genetic basis of LDS is well-understood, molecular mechanisms underlying the disease remain elusive impeding the development of a therapeutic strategy. In addition, aortic smooth muscle cells (SMC) have heterogenous embryonic origins depending on their spatial location, and lineage-specific effects of pathogenic variants on SMC function, likely causing regionally constrained LDS manifestations, have been unexplored. Methods: We identified an LDS family with a dominant pathogenic variant in TGFBR1 gene (TGFBR1^A230T) causing aortic root aneurysm and dissection. To accurately model the molecular defects caused by this mutation, we used human-induced pluripotent stem cells (hiPSC) from subject with normal aorta to generate hiPSC carrying TGFBR1^A230T, and corrected the mutation in patient-derived hiPSC using CRISPR-Cas9 gene editing. Following their lineage-specific SMC differentiation through cardiovascular progenitor cell (CPC) and neural crest stem cell (NCSC) lineages, we employed conventional molecular techniques and single-cell RNA-sequencing (scRNA-seq) to characterize the molecular defects. The resulting data led to subsequent molecular and functional rescue experiments employing Activin A and rapamycin. Results: Our results indicate the TGFBR1^A230T mutation impairs contractile transcript and protein levels, and function in CPC-SMC, but not in NCSC-SMC. ScRNA-seq results implicate defective differentiation even in TGFBR1^A230T/+ CPC-SMC including disruption of SMC contraction, and extracellular matrix formation. Comparison of patient-derived and mutation-corrected cells supported the contractile phenotype observed in the mutant CPC-SMC. TGFBR1^A230T selectively disrupted SMAD3 and AKT activation in CPC-SMC, and led to increased cell proliferation. Consistently, scRNA-seq revealed molecular similarities between a loss-of-function SMAD3 mutation (SMAD3^c.652delA/+) and TGFBR1^A230T/+. Lastly, combination treatment with Activin A and rapamycin during or after SMC differentiation significantly improved the mutant CPC-SMC contractile gene expression, and function; and rescued the mechanical properties of mutant CPC-SMC tissue constructs. Conclusions: This study reveals that a pathogenic TGFBR1 variant causes lineage-specific SMC defects informing the etiology of LDS-associated aortic root aneurysm. As a potential pharmacological strategy, our results highlight a combination treatment with Activin A and rapamycin that can rescue the SMC defects caused by the variant.

Histological Studies of the Ventricular-Subventricular Zone as Neural Stem Cell and Glioma Stem Cell Niche

The neural stem cell niche of the ventricular-subventricular zone supports the persistence of stem and progenitor cells in the mature brain. This niche has many notable cytoarchitectural features that affect the activity of stem cells and may also support the survival and growth of invading tumor cells. Histochemical studies of the niche have revealed many proteins that, in combination, can help to reveal stem-like cells in the normal or cancer context, although many caveats persist in the quest to consistently identify these cells in the human brain. Here, we explore the complex relationship between the persistent proliferative capacity of the neural stem cell niche and the malignant proliferation of brain tumors, with a special focus on histochemical identification of stem cells and stem-like tumor cells and an eye toward the potential application of high-dimensional imaging approaches to the field.

Single-cell analysis of the ventricular-subventricular zone reveals signatures of dorsal & ventral adult neurogenesis

The ventricular-subventricular zone (V-SVZ), on the walls of the lateral ventricles, harbors the largest neurogenic niche in the adult mouse brain. Previous work has shown that neural stem/progenitor cells (NSPCs) in different locations within the V-SVZ produce different subtypes of new neurons for the olfactory bulb. The molecular signatures that underlie this regional heterogeneity remain largely unknown. Here, we present a single-cell RNA-sequencing dataset of the adult mouse V-SVZ revealing two populations of NSPCs that reside in largely non-overlapping domains in either the dorsal or ventral V-SVZ. These regional differences in gene expression were further validated using a single-nucleus RNA-sequencing reference dataset of regionally microdissected domains of the V-SVZ and by immunocytochemistry and RNAscope localization. We also identify two subpopulations of young neurons that have gene expression profiles consistent with a dorsal or ventral origin. Interestingly, a subset of genes are dynamically expressed, but maintained, in the ventral or dorsal lineages. The study provides novel markers and territories to understand the region-specific regulation of adult neurogenesis.

Nerve cells, or neurons, are the central building blocks of brain circuits. Their damage, death or loss of function leads to cognitive decline. Neural stem/progenitor cells (NSPCs) first appear during embryo development, generating most of the neurons found in the nervous system. However, the adult brain retains a small subpopulation of NSPCs, which in some species are an important source of new neurons throughout life.

In the adult mouse brain the largest population of NSPCs, known as B cells, is found in an area called the ventricular-subventricular zone (V-SVZ). These V-SVZ B cells have properties of specialized support cells known as astrocytes, but they can also divide and generate intermediate ‘progenitor cells’ called C cells. These, in turn, divide to generate large numbers of young ‘A cells’ neurons that undertake a long and complex migration from V-SVZ to the olfactory bulb, the first relay in the central nervous system for the processing of smells.

Depending on their location in the V-SVZ, B cells can generate different kinds of neurons, leading to at least ten subtypes of neurons. Why this is the case is still poorly understood.

To examine this question, Cebrián-Silla, Nascimento, Redmond, Mansky et al. determined which genes were expressed in B, C and A cells from different parts of the V-SVZ. While cells within each of these populations had different expression patterns, those that originated in the same V-SVZ locations shared a set of genes, many of which associated with regional specification in the developing brain. Some, however, were intriguingly linked to hormonal regulation.

Salient differences between B cells depended on whether the cells originated closer to the top (‘dorsal’ position) or to the bottom of the brain (‘ventral’ position). This information was used to stain slices of mouse brains for the RNA and proteins produced by these genes in different regions. These experiments revealed dorsal and ventral territories containing B cells with distinct ‘gene expression’.

This study highlights the heterogeneity of NSPCs, revealing key molecular differences among B cells in dorsal and ventral areas of the V-SVZ and reinforcing the concept that the location of NSPCs determines the types of neuron they generate. Furthermore, the birth of specific types of neurons from B cells that are so strictly localized highlights the importance of neuronal migration to ensure that young neurons with specific properties reach their appropriate destination in the olfactory bulb.

The work by Cebrián-Silla, Nascimento, Redmond, Mansky et al. has identified sets of genes that are differentially expressed in dorsal and ventral regions which may contribute to regional regulation. Furthering the understanding of how adult NSPCs differ according to their location will help determine how various neuron types emerge in the adult brain.

Glioblastoma Proximity to the Lateral Ventricle Alters Neurogenic Cell Populations of the Subventricular Zone

Despite current strategies combining surgery, radiation, and chemotherapy, glioblastoma (GBM) is the most common and aggressive malignant primary brain tumor in adults. Tumor location plays a key role in the prognosis of patients, with GBM tumors located in close proximity to the lateral ventricles (LVs) resulting in worse survival expectancy and higher incidence of distal recurrence. Though the reason for worse prognosis in these patients remains unknown, it may be due to proximity to the subventricular zone (SVZ) neurogenic niche contained within the lateral wall of the LVs. We present a novel rodent model to analyze the bidirectional signaling between GBM tumors and cells contained within the SVZ. Patient-derived GBM cells expressing GFP and luciferase were engrafted at locations proximal, intermediate, and distal to the LVs in immunosuppressed mice. Mice were either sacrificed after 4 weeks for immunohistochemical analysis of the tumor and SVZ or maintained for survival analysis. Analysis of the GFP+ tumor bulk revealed that GBM tumors proximal to the LV show increased levels of proliferation and tumor growth than LV-distal counterparts and is accompanied by decreased median survival. Conversely, numbers of innate proliferative cells, neural stem cells (NSCs), migratory cells and progenitors contained within the SVZ are decreased as a result of GBM proximity to the LV. These results indicate that our rodent model is able to accurately recapitulate several of the clinical aspects of LV-associated GBM, including increased tumor growth and decreased median survival. Additionally, we have found the neurogenic and cell division process of the SVZ in these adult mice is negatively influenced according to the presence and proximity of the tumor mass. This model will be invaluable for further investigation into the bidirectional signaling between GBM and the neurogenic cell populations of the SVZ.

From seed to flower: blossoming of microglia in development and brain repair

Physiological functions require coordination of processes between diverse organs, tissues, and cells. This integrative view of science has reemerged complementary to the reductionist philosophy of studying individual cell types. An integrative approach has proven particularly powerful within the field of neuroscience where, intermingled among the most numerous neural cell types of the brain, are immune cells called microglia. Microglia act as a line of defense in the CNS by phagocytizing harmful pathogens and cellular debris and by releasing a variety of factors that mediate immune responses. However, microglia are also appreciated as critical mediators of neurophysiology making them a desired target to rectify neuropathological states. The goal of this review is to discuss microglia ontogenesis, referred to as microgliogenesis, a term that encompasses the events that drive the production, differentiation, migration, and maturation of microglia and opportunities to target microglia for brain repair.

Creation and validation of 3D-printed head molds for stereotaxic injections of neonatal mouse brains

BACKGROUND

An increasing number of rodent model systems use injection of DNA or viral constructs in the neonatal brain. However, approaches for reliable positioning and stereotaxic injection at this developmental stage are limited, typically relying on handheld positioning or molds that must be re-aligned for use in a given laboratory.

NEW METHOD

A complete protocol and open-source software pipeline for generating 3D-printed head molds derived from a CT scan of a neonatal mouse head cast, together with a universal adapter that can be placed on a standard stereotaxic stage.

RESULTS

A series of test injections with adenovirus encoding red fluorescent protein, or Fluorogold, were conducted using original clay molds and newly generated 3D printed molds. Several metrics were used to compare spread and localization of targeted injections.

COMPARISON WITH EXISTING METHODS

The new method of head mold generation gave comparable results to the field standard, but also allowed the rapid generation of additional copies of each head mold with standardized positioning of the head each time.

CONCLUSIONS

This 3D printing pipeline can be used to efficiently develop a series of head molds with standardized injection coordinates across multiple laboratories. More broadly, this pipeline can easily be adapted to other perinatal ages or species.

Release of stem cells from quiescence reveals gliogenic domains in the adult mouse brain

Quiescent neural stem cells (NSCs) in the adult mouse ventricular-subventricular zone (V-SVZ) undergo activation to generate neurons and some glia. Here we show that platelet-derived growth factor receptor beta (PDGFRβ) is expressed by adult V-SVZ NSCs that generate olfactory bulb interneurons and glia. Selective deletion of PDGFRβ in adult V-SVZ NSCs leads to their release from quiescence, uncovering gliogenic domains for different glial cell types. These domains are also recruited upon injury. We identify an intraventricular oligodendrocyte progenitor derived from NSCs inside the brain ventricles that contacts supraependymal axons. Together, our findings reveal that the adult V-SVZ contains spatial domains for gliogenesis, in addition to those for neurogenesis. These gliogenic NSC domains tend to be quiescent under homeostasis and may contribute to brain plasticity.

ACSA-2 and GLAST classify subpopulations of multipotent and glial-restricted cerebellar precursors

The formation of the cerebellum is highly coordinated to obtain its characteristic morphology and all cerebellar cell types. During mouse postnatal development, cerebellar progenitors with astroglial‐like characteristics generate mainly astrocytes and oligodendrocytes. However, a subset of astroglial‐like progenitors found in the prospective white matter (PWM) produces astroglia and interneurons. Characterizing these cerebellar astroglia‐like progenitors and distinguishing their developmental fates is still elusive. Here, we reveal that astrocyte cell surface antigen‐2 (ACSA‐2), lately identified as ATPase, Na+/K+ transporting, beta 2 polypeptide, is expressed by glial precursors throughout postnatal cerebellar development. In contrast to common astrocyte markers, ACSA‐2 appears on PWM cells but is absent on Bergmann glia (BG) precursors. In the adult cerebellum, ACSA‐2 is broadly expressed extending to velate astrocytes in the granular layer, white matter astrocytes, and to a lesser extent to BG. Cell transplantation and transcriptomic analysis revealed that marker staining discriminates two postnatal progenitor pools. One subset is defined by the co‐expression of ACSA‐2 and GLAST and the expression of markers typical of parenchymal astrocytes. These are PWM precursors that are exclusively gliogenic. They produce predominantly white matter and granular layer astrocytes. Another subset is constituted by GLAST positive/ACSA‐2 negative precursors that express neurogenic and BG‐like progenitor genes. This population displays multipotency and gives rise to interneurons besides all glial types, including BG. In conclusion, this work reports about ACSA‐2, a marker that in combination with GLAST enables for the discrimination and isolation of multipotent and glia‐committed progenitors, which generate different types of cerebellar astrocytes.

Single-Cell Profiling Shows Murine Forebrain Neural Stem Cells Reacquire a Developmental State when Activated for Adult Neurogenesis

The transitions from developing to adult quiescent and activated neural stem cells (NSCs) are not well understood. Here, we use single-cell transcriptional profiling and lineage tracing to characterize these transitions in the murine forebrain. We show that the two forebrain NSC parental populations, embryonic cortex and ganglionic eminence radial precursors (RPs), are highly similar even though they make glutamatergic versus gabaergic neurons. Both RP populations progress linearly to transition from a highly active embryonic to a dormant adult stem cell state that still shares many similarities with embryonic RPs. When adult NSCs of either embryonic origin become reactivated to make gabaergic neurons, they acquire a developing ganglionic eminence RP-like identity. Thus, transitions from embryonic RPs to adult NSCs and back to neuronal progenitors do not involve fundamental changes in cell identity, but rather reflect conversions between activated and dormant NSC states that may be determined by the niche environment.

Deep learning-based predictive identification of neural stem cell differentiation

The differentiation of neural stem cells (NSCs) into neurons is proposed to be critical in devising potential cell-based therapeutic strategies for central nervous system (CNS) diseases, however, the determination and prediction of differentiation is complex and not yet clearly established, especially at the early stage. We hypothesize that deep learning could extract minutiae from large-scale datasets, and present a deep neural network model for predictable reliable identification of NSCs fate. Remarkably, using only bright field images without artificial labelling, our model is surprisingly effective at identifying the differentiated cell types, even as early as 1 day of culture. Moreover, our approach showcases superior precision and robustness in designed independent test scenarios involving various inducers, including neurotrophins, hormones, small molecule compounds and even nanoparticles, suggesting excellent generalizability and applicability. We anticipate that our accurate and robust deep learning-based platform for NSCs differentiation identification will accelerate the progress of NSCs applications.

The differentiation of neural stem cells (NSCs) into neurons is a critical part in devising potential cell-based therapeutic strategies for central nervous system diseases but NSCs fate determination and prediction is problematic. Here, the authors present a deep neural network model for predictable reliable identification of NSCs fate.

A cellular and spatial map of the choroid plexus across brain ventricles and ages

The choroid plexus (ChP) in each brain ventricle produces cerebrospinal fluid (CSF) and forms the blood-CSF barrier. Here, we construct a single-cell and spatial atlas of each ChP in the developing, adult, and aged mouse brain. We delineate diverse cell types, subtypes, cell states, and expression programs in epithelial and mesenchymal cells across ages and ventricles. In the developing ChP, we predict a common progenitor pool for epithelial and neuronal cells, validated by lineage tracing. Epithelial and fibroblast cells show regionalized expression by ventricle, starting at embryonic stages and persisting with age, with a dramatic transcriptional shift with maturation, and a smaller shift in each aged cell type. With aging, epithelial cells upregulate host-defense programs, and resident macrophages upregulate interleukin-1β (IL-1β) signaling genes. Our atlas reveals cellular diversity, architecture and signaling across ventricles during development, maturation, and aging of the ChP-brain barrier.

Single-Cell Profiling and SCOPE-Seq Reveal Lineage Dynamics of Adult Ventricular-Subventricular Zone Neurogenesis and NOTUM as a Key Regulator

In the adult ventricular-subventricular zone (V-SVZ), neural stem cells (NSCs) generate new olfactory bulb (OB) neurons and glia throughout life. To map adult neuronal lineage progression, we profiled >56,000 V-SVZ and OB cells by single-cell RNA sequencing (scRNA-seq). Our analyses reveal the molecular diversity of OB neurons, including fate-mapped neurons, lineage progression dynamics, and an NSC intermediate enriched for Notum, which encodes a secreted WNT antagonist. SCOPE-seq technology, which links live-cell imaging with scRNA-seq, uncovers cell-size transitions during NSC differentiation and preferential NOTUM binding to proliferating neuronal precursors. Consistently, application of NOTUM protein in slice cultures and pharmacological inhibition of NOTUM in slice cultures and in vivo demonstrated that NOTUM negatively regulates V-SVZ proliferation. Timely, context-dependent neurogenesis demands adaptive signaling among neighboring progenitors. Our findings highlight a critical regulatory state during NSC activation marked by NOTUM, which attenuates WNT-stimulated proliferation in NSC progeny.

Cell-type and fetal-sex-specific targets of prenatal alcohol exposure in developing mouse cerebral cortex

Prenatal alcohol exposure (PAE) results in cerebral cortical dysgenesis. Single-cell RNA sequencing was performed on murine fetal cerebral cortical cells from six timed pregnancies, to decipher persistent cell- and sex-specific effects of an episode of PAE during early neurogenesis. We found, in an analysis of 38 distinct neural subpopulations across 8 lineage subtypes, that PAE altered neural maturation and cell cycle and disrupted gene co-expression networks. Whereas most differentially regulated genes were inhibited, particularly in females, PAE also induced sex-independent neural expression of fetal hemoglobin, a presumptive epigenetic stress adaptation. PAE inhibited Bcl11a, Htt, Ctnnb1, and other upstream regulators of differentially expressed genes and inhibited several autism-linked genes, suggesting that neurodevelopmental disorders share underlying mechanisms. PAE females exhibited neural loss of X-inactivation, with correlated activation of autosomal genes and evidence for spliceosome dysfunction. Thus, episodic PAE persistently alters the developing neural transcriptome, contributing to sex- and cell-type-specific teratology.

•

The neurogenic murine fetal cortex contains about 33 distinct cell subtypes

•

Prenatal Alcohol Exposure (PAE) resulted in sex-specific alterations in developmental trajectory and cell cycle

•

PAE females exhibited neural loss of X-inactivation and spliceosomal dysfunction

•

PAE induced sex-independent neural expression of fetal hemoglobin gene transcripts