Prospective identification and purification of quiescent adult neural stem cells from their in vivo niche

Injury primes mutation-bearing astrocytes for dedifferentiation in later life

Despite their latent neurogenic potential, most normal parenchymal astrocytes fail to dedifferentiate to neural stem cells in response to injury. In contrast, aberrant lineage plasticity is a hallmark of gliomas, and this suggests that tumor suppressors may constrain astrocyte dedifferentiation. Here, we show that p53, one of the most commonly inactivated tumor suppressors in glioma, is a gatekeeper of astrocyte fate. In the context of stab-wound injury, p53 loss destabilized the identity of astrocytes, priming them to dedifferentiate in later life. This resulted from persistent and age-exacerbated neuroinflammation at the injury site and EGFR activation in periwound astrocytes. Mechanistically, dedifferentiation was driven by the synergistic upregulation of mTOR signaling downstream of p53 loss and EGFR, which reinstates stemness programs via increased translation of neurodevelopmental transcription factors. Thus, our findings suggest that first-hit mutations remove the barriers to injury-induced dedifferentiation by sensitizing somatic cells to inflammatory signals, with implications for tumorigenesis.

Dopey2 and Pcdh7 orchestrate the development of embryonic neural stem cells/ progenitors in zebrafish

DOPEY2 has been shown to be associated with Down syndrome and PCDH7 might be involved in Rett syndrome and MECP2 duplication syndrome. The mechanism how both proteins play roles in these syndromes are largely unknown. Here, we show that Dopey2 and Pcdh7 balance the proliferation and differentiation of neural stem cells and progenitors during embryonic neurogenesis to generate proper size and architecture of zebrafish brains. Dopey2 and Pcdh7 mutually restricted expression of each other in zebrafish embryos. Dopey2 was responsible for the proliferation of neural stem cells/progenitors, whereas Pcdh7 was responsible for the differentiation of neural stem cells/progenitors. Both proteins were shown to orchestrate the proper development and arrangement of neural cells in zebrafish embryonic brains. The results provide an insight into mechanisms to understand how the embryonic brain is constituted and how developmental defects occur in the brains of patients with Down syndrome, Rett syndrome, or MECP2 duplication syndrome.

The atypical CDK activator RingoA/Spy1 regulates exit from quiescence in neural stem cells

In the adult mammalian brain, most neural stem cells (NSCs) are held in a reversible state of quiescence, which is essential to avoid NSC exhaustion and determine the appropriate neurogenesis rate. NSCs of the mouse adult subependymal niche provide neurons for olfactory circuits and can be found at different depths of quiescence, but very little is known on how their quiescence-to-activation transition is controlled. Here, we identify the atypical cyclin-dependent kinase (CDK) activator RingoA as a regulator of this process. We show that the expression of RingoA increases the levels of CDK activity and facilitates cell cycle entry of a subset of NSCs that divide slowly. Accordingly, RingoA-deficient mice exhibit reduced olfactory neurogenesis with an accumulation of quiescent NSCs. Our results indicate that RingoA plays an important role in setting the threshold of CDK activity required for adult NSCs to exit quiescence and may represent a dormancy regulator in adult mammalian tissues.

Genomic Interplay between Neoneurogenesis and Neoangiogenesis in Carcinogenesis: Therapeutic Interventions

Angiogenesis, the generation of new blood vessels, is one of the hallmarks of cancer. The growing tumor requires nutrients and oxygen. Recent evidence has shown that tumors release signals to attract new nerve fibers and stimulate the growth of new nerve fibers. Neurogenesis, neural extension, and axonogenesis assist in the migration of cancer cells. Cancer cells can use both blood vessels and nerve fibers as routes for cells to move along. In this way, neurogenesis and angiogenesis both contribute to cancer metastasis. As a result, tumor-induced neurogenesis joins angiogenesis and immunosuppression as aberrant processes that are exacerbated within the tumor microenvironment. The relationship between these processes contributes to cancer development and progression. The interplay between these systems is brought about by cytokines, neurotransmitters, and neuromodulators, which activate signaling pathways that are common to angiogenesis and the nervous tissue. These include the AKT signaling pathways, the MAPK pathway, and the Ras signaling pathway. These processes also both require the remodeling of tissues. The interplay of these processes in cancer provides the opportunity to develop novel therapies that can be used to target these processes.

Olig1/2-Expressing Intermediate Lineage Progenitors Are Predisposed to PTEN/p53-Loss-Induced Gliomagenesis and Harbor Specific Therapeutic Vulnerabilities

Malignant gliomas such as glioblastoma are highly heterogeneous with distinct cells of origin and varied genetic alterations. It remains elusive whether the specific states of neural cell lineages are differentially susceptible to distinct genetic alterations during malignant transformation. Here, an analysis of The Cancer Genome Atlas databases revealed that comutations of PTEN and TP53 are most significantly enriched in human high-grade gliomas. Therefore, we selectively ablated Pten and Trp53 in different progenitors to determine which cell lineage states are susceptible to malignant transformation. Mice with PTEN/p53 ablation mediated by multilineage-expressing human GFAP (hGFAP) promoter-driven Cre developed glioma but with incomplete penetrance and long latency. Unexpectedly, ablation of Pten and Trp53 in Nestin+ neural stem cells (NSC) or Pdgfra+/NG2+ committed oligodendrocyte precursor cells (OPC), two major cells of origin in glioma, did not induce glioma formation in mice. Strikingly, mice lacking Pten and Trp53 in Olig1+/Olig2+ intermediate precursors (pri-OPC) prior to the committed OPCs developed high-grade gliomas with 100% penetrance and short latency. The resulting tumors exhibited distinct tumor phenotypes and drug sensitivities from NSC- or OPC-derived glioma subtypes. Integrated transcriptomic and epigenomic analyses revealed that PTEN/p53-loss induced activation of oncogenic pathways, including HIPPO-YAP and PI3K signaling, to promote malignant transformation. Targeting the core regulatory circuitries YAP and PI3K signaling effectively inhibited tumor cell growth. Thus, our multicell state in vivo mutagenesis analyses suggests that transit-amplifying states of Olig1/2 intermediate lineage precursors are predisposed to PTEN/p53-loss-induced transformation and gliomagenesis, pointing to subtype-specific treatment strategies for gliomas with distinct genetic alterations.

SIGNIFICANCE

Multiple progenitor-state mutagenesis reveal that Olig1/2-expressing intermediate precursors are highly susceptible to PTEN/p53-loss-mediated transformation and impart differential drug sensitivity, indicating tumor-initiating cell states and genetic drivers dictate glioma phenotypes and drug responses. See related commentary by Zamler and Hu, p. 807.

Ganglioside GD3 regulates neural stem cell quiescence and controls postnatal neurogenesis

The postnatal neural stem cell (NSC) pool hosts quiescent and activated radial glia-like NSCs contributing to neurogenesis throughout adulthood. However, the underlying regulatory mechanism during the transition from quiescent NSCs to activated NSCs in the postnatal NSC niche is not fully understood. Lipid metabolism and lipid composition play important roles in regulating NSC fate determination. Biological lipid membranes define the individual cellular shape and help maintain cellular organization and are highly heterogenous in structure and there exist diverse microdomains (also known as lipid rafts), which are enriched with sugar molecules, such as glycosphingolipids. An often overlooked but key aspect is that the functional activities of proteins and genes are highly dependent upon their molecular environments. We previously reported that ganglioside GD3 is the predominant species in NSCs and that the reduced postnatal NSC pools are observed in global GD3-synthase knockout (GD3S-KO) mouse brains. The specific roles of GD3 in determining the stage and cell-lineage determination of NSCs remain unclear, since global GD3S-KO mice cannot distinguish if GD3 regulates postnatal neurogenesis or developmental impacts. Here we show that inducible GD3 deletion in postnatal radial glia-like NSCs promotes the NSC activation, resulting in the loss of the long-term maintenance of the adult NSC pools. The reduced neurogenesis in the subventricular zone (SVZ) and the dentate gyrus (DG) of GD3S-conditional-knockout mice led to impaired olfactory and memory functions. Thus, our results provide convincing evidence that postnatal GD3 maintains the quiescent state of radial glia-like NSCs in the adult NSC niche.

Brain washing and neural health: role of age, sleep, and the cerebrospinal fluid melatonin rhythm

The brain lacks a classic lymphatic drainage system. How it is cleansed of damaged proteins, cellular debris, and molecular by-products has remained a mystery for decades. Recent discoveries have identified a hybrid system that includes cerebrospinal fluid (CSF)-filled perivascular spaces and classic lymph vessels in the dural covering of the brain and spinal cord that functionally cooperate to remove toxic and non-functional trash from the brain. These two components functioning together are referred to as the glymphatic system. We propose that the high levels of melatonin secreted by the pineal gland directly into the CSF play a role in flushing pathological molecules such as amyloid-β peptide (Aβ) from the brain via this network. Melatonin is a sleep-promoting agent, with waste clearance from the CNS being highest especially during slow wave sleep. Melatonin is also a potent and versatile antioxidant that prevents neural accumulation of oxidatively-damaged molecules which contribute to neurological decline. Due to its feedback actions on the suprachiasmatic nucleus, CSF melatonin rhythm functions to maintain optimal circadian rhythmicity, which is also critical for preserving neurocognitive health. Melatonin levels drop dramatically in the frail aged, potentially contributing to neurological failure and dementia. Melatonin supplementation in animal models of Alzheimer's disease (AD) defers Aβ accumulation, enhances its clearance from the CNS, and prolongs animal survival. In AD patients, preliminary data show that melatonin use reduces neurobehavioral signs such as sundowning. Finally, melatonin controls the mitotic activity of neural stem cells in the subventricular zone, suggesting its involvement in neuronal renewal.

Promoting Endogenous Neurogenesis as a Treatment for Alzheimer's Disease

Alzheimer's disease (AD) is the most universal neurodegenerative disorder characterized by memory loss and cognitive impairment. AD is biologically defined by production and aggregation of misfolded protein including extracellular amyloid β (Aβ) peptide and intracellular microtubule-associated protein tau tangles in neurons, leading to irreversible neuronal loss. At present, regulation of endogenous neurogenesis to supplement lost neurons has been proposed as a promising strategy for treatment of AD. However, the exact underlying mechanisms of impaired neurogenesis in AD have not been fully explained and effective treatments targeting neurogenesis for AD are limited. In this review, we mainly focus on the latest research of impaired neurogenesis in AD. Then we discuss the factors affecting stages of neurogenesis and the interplay between neural stem cells (NSCs) and neurogenic niche under AD pathological conditions. This review aims to explore potential therapeutic strategies that promote endogenous neurogenesis for AD treatments.

Calcium signaling as an integrator and decoder of niche factors to control somatic stem cell quiescence and activation

Somatic stem cells (SSCs) play a major role in tissue homeostasis and respond to a panoply of micro-environmental cues by adjusting their quiescence and activation profiles. How these cells integrate and decode multiple niche signals remains elusive. In recent years, Ca²⁺ signaling has emerged as one of the key intracellular pathways that allow stem cells to dynamically adjust their fate and either to remain quiescent for future needs or to become activated to generate new progeny. Interestingly, not only distinct Ca²⁺ signatures are associated with the quiescence and activation states of stem cells, but also various extracellular cues impinge on Ca²⁺ pathways to dynamically regulate the responses of stem cells to different niche signals. This Viewpoint article deals with how Ca²⁺ signaling may be used to decode and integrate different niche factors and how Ca²⁺ fluctuations of distinct amplitudes, frequencies, and overall intracellular levels may trigger the differential gene transcription program. Knowledge about mechanisms that allow SSCs to translate the complexity of extracellular niche signaling into intrinsic states of cell quiescence and activation is crucial for understanding life-long tissue homeostasis and regeneration.

Prx1 cell subpopulations identified in various tissues with diverse quiescence and activation ability following fracture and BMP2 stimulation

The expression of Prx1 has been used as a marker to define the skeletal stem cells (SSCs) populations found within the bone marrow and periosteum that contribute to bone regeneration. However, Prx1 expressing SSCs (Prx1-SSCs) are not restricted to the bone compartments, but are also located within the muscle and able to contribute to ectopic bone formation. Little is known however, about the mechanism(s) regulating Prx1-SSCs that reside in muscle and how they participate in bone regeneration. This study compared both the intrinsic and extrinsic factors of the periosteum and muscle derived Prx1-SSCs and analyzed their regulatory mechanisms of activation, proliferation, and skeletal differentiation. There was considerable transcriptomic heterogeneity in the Prx1-SSCs found in muscle or the periosteum however in vitro cells from both tissues showed tri-lineage (adipose, cartilage and bone) differentiation. At homeostasis, periosteal-derived Prx1 cells were proliferative and low levels of BMP2 were able to promote their differentiation, while the muscle-derived Prx1 cells were quiescent and refractory to comparable levels of BMP2 that promoted periosteal cell differentiation. The transplantation of Prx1-SCC from muscle and periosteum into either the same site from which they were isolated, or their reciprocal sites showed that periosteal cell transplanted onto the surface of bone tissues differentiated into bone and cartilage cells but was incapable of similar differentiation when transplanted into muscle. Prx1-SSCs from the muscle showed no ability to differentiate at either site of transplantation. Both fracture and ten times the BMP2 dose was needed to promote muscle-derived cells to rapidly enter the cell cycle as well as undergo skeletal cell differentiation. This study elucidates the diversity of the Prx1-SSC population showing that cells within different tissue sites are intrinsically different. While muscle tissue must have factors that promote Prx1-SSC to remain quiescent, either bone injury or high levels of BMP2 can activate these cells to both proliferate and undergo skeletal cell differentiation. Finally, these studies raise the possibility that muscle SSCs are potential target for skeletal repair and bone diseases.

Post-transcriptional control of a stemness signature by RNA-binding protein MEX3A regulates murine adult neurogenesis

Neural stem cells (NSCs) in the adult murine subependymal zone balance their self-renewal capacity and glial identity with the potential to generate neurons during the lifetime. Adult NSCs exhibit lineage priming via pro-neurogenic fate determinants. However, the protein levels of the neural fate determinants are not sufficient to drive direct differentiation of adult NSCs, which raises the question of how cells along the neurogenic lineage avoid different conflicting fate choices, such as self-renewal and differentiation. Here, we identify RNA-binding protein MEX3A as a post-transcriptional regulator of a set of stemness associated transcripts at critical transitions in the subependymal neurogenic lineage. MEX3A regulates a quiescence-related RNA signature in activated NSCs that is needed for their return to quiescence, playing a role in the long-term maintenance of the NSC pool. Furthermore, it is required for the repression of the same program at the onset of neuronal differentiation. Our data indicate that MEX3A is a pivotal regulator of adult murine neurogenesis acting as a translational remodeller.

Developmental and functional relationships between hypothalamic tanycytes and embryonic radial glia

The hypothalamus is a key regulator of several homeostatic processes, such as circadian rhythms, energy balance, thirst, and thermoregulation. Recently, the hypothalamic third ventricle has emerged as a site of postnatal neurogenesis and gliogenesis. This hypothalamic neural stem potential resides in a heterogeneous population of cells known as tanycytes, which, not unlike radial glia, line the floor and ventrolateral walls of the third ventricle and extend a long process into the hypothalamic parenchyma. Here, we will review historical and recent data regarding tanycyte biology across the lifespan, focusing on the developmental emergence of these diverse cells from embryonic radial glia and their eventual role contributing to a fascinating, but relatively poorly characterized, adult neural stem cell niche.

Culture Protocol and Transcriptomic Analysis of Murine SVZ NPCs and OPCs

The mammalian adult brain contains two neural stem and precursor (NPC) niches: the subventricular zone [SVZ] lining the lateral ventricles and the subgranular zone [SGZ] in the hippocampus. From these, SVZ NPCs represent the largest NPC pool. While SGZ NPCs typically only produce neurons and astrocytes, SVZ NPCs produce neurons, astrocytes and oligodendrocytes throughout life. Of particular importance is the generation and replacement of oligodendrocytes, the only myelinating cells of the central nervous system (CNS). SVZ NPCs contribute to myelination by regenerating the parenchymal oligodendrocyte precursor cell (OPC) pool and by differentiating into oligodendrocytes in the developing and demyelinated brain. The neurosphere assay has been widely adopted by the scientific community to facilitate the study of NPCs in vitro. Here, we present a streamlined protocol for culturing postnatal and adult SVZ NPCs and OPCs from primary neurosphere cells. We characterize the purity and differentiation potential as well as provide RNA-sequencing profiles of postnatal SVZ NPCs, postnatal SVZ OPCs and adult SVZ NPCs. We show that primary neurospheres cells generated from postnatal and adult SVZ differentiate into neurons, astrocytes and oligodendrocytes concurrently and at comparable levels. SVZ OPCs are generated by subjecting primary neurosphere cells to OPC growth factors fibroblast growth factor (FGF) and platelet-derived growth factor-AA (PDGF-AA). We further show SVZ OPCs can differentiate into oligodendrocytes in the absence and presence of thyroid hormone T3. Transcriptomic analysis confirmed the identities of each cell population and revealed novel immune and signalling pathways expressed in an age and cell type specific manner.

Adult neurogenesis in the telencephalon of the lizard Podarcis liolepis

In adult lizards, new neurons are generated from neural stem cells in the ventricular zone of the lateral ventricles. These new neurons migrate and integrate into the main telencephalic subdivisions. In this work we have studied adult neurogenesis in the lizard Podarcis liolepis (formerly Podarcis hispanica) by administering [³H]-thymidine and bromodeoxyuridine as proliferation markers and euthanizing the animals at different survival times to determine the identity of progenitor cells and to study their lineage derivatives. After short survival times, only type B cells are labeled, suggesting that they are neural stem cells. Three days after administration, some type A cells are labeled, corresponding to recently formed neuroblasts. Type A cells migrate to their final destinations, where they differentiate into mature neurons and integrate into functional circuits. Our results after long survival periods suggest that, in addition to actively dividing type B cells, there is also a type B subpopulation with low proliferative activity. We also found that new neurons incorporated into the olfactory bulb are generated both in situ, in the walls of the anterior extension of the lateral ventricle of the olfactory bulbs, but also at more caudal levels, most likely in anterior levels of the sulcus ventralis/terminalis. These cells follow a tangential migration toward the olfactory bulbs where they integrate. We hypothesized that at least part of the newly generated neurons would undergo a specialization process over time. In support of this prediction, we found two neuronal populations in the cellular layer of the medial cortex, which we named type I and II neurons. At intermediate survival times (1 month) only type II neurons were labeled with [³H]-thymidine, while at longer survival times (3, 6, or 12 months) both type I and type II neurons were labeled. This study sheds light on the ultrastructural characteristics of the ventricular zone of P. liolepis as a neurogenic niche, and adds to our knowledge of the processes whereby newly generated neurons in the adult brain migrate and integrate into their final destinations.

Learning cell identity in immunology, neuroscience, and cancer

Suspension and imaging cytometry techniques that simultaneously measure hundreds of cellular features are powering a new era of cell biology and transforming our understanding of human tissues and tumors. However, a central challenge remains in learning the identities of unexpected or novel cell types. Cell identification rubrics that could assist trainees, whether human or machine, are not always rigorously defined, vary greatly by field, and differentially rely on cell intrinsic measurements, cell extrinsic tissue measurements, or external contextual information such as clinical outcomes. This challenge is especially acute in the context of tumors, where cells aberrantly express developmental programs that are normally time, location, or cell-type restricted. Well-established fields have contrasting practices for cell identity that have emerged from convention and convenience as much as design. For example, early immunology focused on identifying minimal sets of protein features that mark individual, functionally distinct cells. In neuroscience, features including morphology, development, and anatomical location were typical starting points for defining cell types. Both immunology and neuroscience now aim to link standardized measurements of protein or RNA to informative cell functions such as electrophysiology, connectivity, lineage potential, phospho-protein signaling, cell suppression, and tumor cell killing ability. The expansion of automated, machine-driven methods for learning cell identity has further created an urgent need for a harmonized framework for distinguishing cell identity across fields and technology platforms. Here, we compare practices in the fields of immunology and neuroscience, highlight concepts from each that might work well in the other, and propose ways to implement these ideas to study neural and immune cell interactions in brain tumors and associated model systems.

EGFL7 loss correlates with increased VEGF-D expression, upregulating hippocampal adult neurogenesis and improving spatial learning and memory

Neural stem cells reside in the subgranular zone, a specialized neurogenic niche of the hippocampus. Throughout adulthood, these cells give rise to neurons in the dentate gyrus, playing an important role in learning and memory. Given that these core cognitive processes are disrupted in numerous disease states, understanding the underlying mechanisms of neural stem cell proliferation in the subgranular zone is of direct practical interest. Here, we report that mature neurons, neural stem cells and neural precursor cells each secrete the neurovascular protein epidermal growth factor-like protein 7 (EGFL7) to shape this hippocampal niche. We further demonstrate that EGFL7 knock-out in a Nestin-CreERT2-based mouse model produces a pronounced upregulation of neurogenesis within the subgranular zone. RNA sequencing identified that the increased expression of the cytokine VEGF-D correlates significantly with the ablation of EGFL7. We substantiate this finding with intraventricular infusion of VEGF-D upregulating neurogenesis in vivo and further show that VEGF-D knock-out produces a downregulation of neurogenesis. Finally, behavioral studies in EGFL7 knock-out mice demonstrate greater maintenance of spatial memory and improved memory consolidation in the hippocampus by modulation of pattern separation. Taken together, our findings demonstrate that both EGFL7 and VEGF-D affect neurogenesis in the adult hippocampus, with the ablation of EGFL7 upregulating neurogenesis, increasing spatial learning and memory, and correlating with increased VEGF-D expression.

Cell-type-specific aging clocks to quantify aging and rejuvenation in neurogenic regions of the brain

The diversity of cell types is a challenge for quantifying aging and its reversal. Here we develop 'aging clocks' based on single-cell transcriptomics to characterize cell-type-specific aging and rejuvenation. We generated single-cell transcriptomes from the subventricular zone neurogenic region of 28 mice, tiling ages from young to old. We trained single-cell-based regression models to predict chronological age and biological age (neural stem cell proliferation capacity). These aging clocks are generalizable to independent cohorts of mice, other regions of the brains, and other species. To determine if these aging clocks could quantify transcriptomic rejuvenation, we generated single-cell transcriptomic datasets of neurogenic regions for two interventions-heterochronic parabiosis and exercise. Aging clocks revealed that heterochronic parabiosis and exercise reverse transcriptomic aging in neurogenic regions, but in different ways. This study represents the first development of high-resolution aging clocks from single-cell transcriptomic data and demonstrates their application to quantify transcriptomic rejuvenation.

Dormant SOX9-Positive Cells Facilitate MYC-Driven Recurrence of Medulloblastoma

Relapse is the leading cause of death in patients with medulloblastoma, the most common malignant pediatric brain tumor. A better understanding of the mechanisms underlying recurrence could lead to more effective therapies for targeting tumor relapses. Here, we observed that SOX9, a transcription factor and stem cell/glial fate marker, is limited to rare, quiescent cells in high-risk medulloblastoma with MYC amplification. In paired primary-recurrent patient samples, SOX9-positive cells accumulated in medulloblastoma relapses. SOX9 expression anti-correlated with MYC expression in murine and human medulloblastoma cells. However, SOX9-positive cells were plastic and could give rise to a MYC high state. To follow relapse at the single-cell level, an inducible dual Tet model of medulloblastoma was developed, in which MYC expression was redirected in vivo from treatment-sensitive bulk cells to dormant SOX9-positive cells using doxycycline treatment. SOX9 was essential for relapse initiation and depended on suppression of MYC activity to promote therapy resistance, epithelial-mesenchymal transition, and immune escape. p53 and DNA repair pathways were downregulated in recurrent tumors, whereas MGMT was upregulated. Recurrent tumor cells were found to be sensitive to treatment with an MGMT inhibitor and doxorubicin. These findings suggest that recurrence-specific targeting coupled with DNA repair inhibition comprises a potential therapeutic strategy in patients affected by medulloblastoma relapse.

SIGNIFICANCE

SOX9 facilitates therapy escape and recurrence in medulloblastoma via temporal inhibition of MYC/MYCN genes, revealing a strategy to specifically target SOX9-positive cells to prevent tumor relapse.

miR-17∼92 exerts stage-specific effects in adult V-SVZ neural stem cell lineages

Neural stem cells (NSCs) in the adult ventricular-subventricular zone (V-SVZ) generate neurons and glia throughout life. MicroRNAs are important post-transcriptional regulators frequently acting in a context-dependent manner. Here, microRNA profiling defines cohorts of miRNAs in quiescent and activated NSCs, with miR-17∼92 highly upregulated in activated NSCs and transit amplifying cells (TACs) versus quiescent NSCs. Conditional miR-17∼92 deletion in the adult V-SVZ results in stage-specific effects. In NSCs, it reduces proliferation in vitro and in vivo, whereas in TACs, it selectively shifts neurogenic OLIG2^- DLX2⁺ toward oligodendrogenic OLIG2⁺ DLX2^- TACs, due to de-repression of an oligodendrogenic program, leading to increased oligodendrogenesis in vivo. This differential regulation of TAC subpopulations highlights the importance of TAC heterogeneity. Finally, in the NSC lineage for intraventricular oligodendrocyte progenitors, miR-17∼92 deletion decreases proliferation and maturation. Together, these findings reveal multiple stage-specific functions of the miR-17∼92 cluster within different adult V-SVZ lineages.

Chitinase-like protein 3: A novel niche factor for mouse neural stem cells

The concept of a perivascular niche has been proposed for neural stem cells (NSCs). This study examined endothelial colony-forming cell (ECFC)-secreted proteins as potential niche factors for NSCs. Intraventricle infusion with ECFC-secreted proteins increased the number of NSCs. ECFC-secreted proteins were more effective in promoting NSC self-renewal than marrow stromal cell (MSC)-secreted proteins. Differential proteomics analysis of MSC-secreted and ECFC-secreted proteins was performed, which revealed chitinase-like protein 3 (CHIL3; also called ECF-L or Ym1) as a candidate niche factor for NSCs. Experiments with recombinant CHIL3, small interfering RNA, and neutralizing antibodies demonstrated that CHIL3 stimulated NSC self-renewal with neurogenic propensity. CHIL3 was endogenously expressed in the neurogenic niche of the brain and retina as well as in the injured brain and retina. Transcriptome and phosphoproteome analyses revealed that CHIL3 activated various genes and proteins associated with NSC maintenance or neurogenesis. Thus, CHIL3 is a novel niche factor for NSCs.

Single-cell multiomics identifies clinically relevant mesenchymal stem-like cells and key regulators for MPNST malignancy

Malignant peripheral nerve sheath tumor (MPNST), a highly aggressive Schwann cell (SC)-derived soft tissue sarcoma, arises from benign neurofibroma (NF); however, the identity, heterogeneity and origins of tumor populations remain elusive. Nestin+ cells have been implicated as tumor stem cells in MPNST; unexpectedly, single-cell profiling of human NF and MPNST and their animal models reveal a broad range of nestin-expressing SC lineage cells and dynamic acquisition of discrete cancer states during malignant transformation. We uncover a nestin-negative mesenchymal neural crest-like subpopulation as a previously unknown malignant stem-like state common to murine and human MPNSTs, which correlates with clinical severity. Integrative multiomics profiling further identifies unique regulatory networks and druggable targets against the malignant subpopulations in MPNST. Targeting key epithelial-mesenchymal transition and stemness regulators including ZEB1 and ALDH1A1 impedes MPNST growth. Together, our studies reveal the underlying principles of tumor cell-state evolution and their regulatory circuitries during NF-to-MPNST transformation, highlighting a hitherto unrecognized mesenchymal stem-like subpopulation in MPNST disease progression.

High-resolution transcriptomics informs glial pathology in human temporal lobe epilepsy

The pathophysiology of epilepsy underlies a complex network dysfunction between neurons and glia, the molecular cell type-specific contributions of which remain poorly defined in the human disease. In this study, we validated a method that simultaneously isolates neuronal (NEUN +), astrocyte (PAX6 + NEUN-), and oligodendroglial progenitor (OPC) (OLIG2 + NEUN-) enriched nuclei populations from non-diseased, fresh-frozen human neocortex and then applied it to characterize the distinct transcriptomes of such populations isolated from electrode-mapped temporal lobe epilepsy (TLE) surgical samples. Nuclear RNA-seq confirmed cell type specificity and informed both common and distinct pathways associated with TLE in astrocytes, OPCs, and neurons. Compared to postmortem control, the transcriptome of epilepsy astrocytes showed downregulation of mature astrocyte functions and upregulation of development-related genes. To gain further insight into glial heterogeneity in TLE, we performed single cell transcriptomics (scRNA-seq) on four additional human TLE samples. Analysis of the integrated TLE dataset uncovered a prominent subpopulation of glia that express a hybrid signature of both reactive astrocyte and OPC markers, including many cells with a mixed GFAP + OLIG2 + phenotype. A further integrated analysis of this TLE scRNA-seq dataset and a previously published normal human temporal lobe scRNA-seq dataset confirmed the unique presence of hybrid glia only in TLE. Pseudotime analysis revealed cell transition trajectories stemming from this hybrid population towards both OPCs and reactive astrocytes. Immunofluorescence studies in human TLE samples confirmed the rare presence of GFAP + OLIG2 + glia, including some cells with proliferative activity, and functional analysis of cells isolated directly from these samples disclosed abnormal neurosphere formation in vitro. Overall, cell type-specific isolation of glia from surgical epilepsy samples combined with transcriptomic analyses uncovered abnormal glial subpopulations with de-differentiated phenotype, motivating further studies into the dysfunctional role of reactive glia in temporal lobe epilepsy.

Roles of Chromatin Remodelling and Molecular Heterogeneity in Therapy Resistance in Glioblastoma

Cancer stem cells (CSCs) represent a therapy-resistant reservoir in glioblastoma (GBM). It is now becoming clear that epigenetic and chromatin remodelling programs link the stemlike behaviour of CSCs to their treatment resistance. New evidence indicates that the epigenome of GBM cells is shaped by intrinsic and extrinsic factors, including their genetic makeup, their interactions and communication with other neoplastic and non-neoplastic cells, including immune cells, and their metabolic niche. In this review, we explore how all these factors contribute to epigenomic heterogeneity in a tumour and the selection of therapy-resistant cells. Lastly, we discuss current and emerging experimental platforms aimed at precisely understanding the epigenetic mechanisms of therapy resistance that ultimately lead to tumour relapse. Given the growing arsenal of drugs that target epigenetic enzymes, our review addresses promising preclinical and clinical applications of epidrugs to treat GBM, and possible mechanisms of resistance that need to be overcome.

Copper Modulates Adult Neurogenesis in Brain Subventricular Zone

The subventricular zone (SVZ) in lateral ventricles is the largest neurogenic region in adult brain containing high amounts of copper (Cu). This study aims to define the role of Cu in adult neurogenesis by chelating labile Cu ions using a well-established Cu chelator D-Penicillamine (D-Pen). A neurosphere model derived from adult mouse SVZ tissues was established and characterized for its functionality with regards to neural stem/progenitor cells (NSPCs). Applying D-Pen in cultured neurospheres significantly reduced intracellular Cu levels and reversed the Cu-induced suppression of NSPC’s differentiation and migration. An in vivo intracerebroventricular (ICV) infusion model was subsequently established to infuse D-Pen directly into the lateral ventricle. Metal analyses revealed a selective reduction of Cu in SVZ by 13.1% (p = 0.19) and 21.4% (p < 0.05) following D-Pen infusions at low (0.075 μg/h) and high (0.75 μg/h) doses for 28 days, respectively, compared to saline-infused controls. Immunohistochemical studies revealed that the 7-day, low-dose D-Pen infusion significantly increased Ki67(+)/Nestin(+) cell counts in SVZ by 28% (p < 0.05). Quantification of BrdU(+)/doublecortin (DCX)(+) newborn neuroblasts in the rostral migration stream (RMS) and olfactory bulb (OB) further revealed that the short-term, low-dose D-Pen infusion, as compared with saline-infused controls, resulted in more newborn neuroblasts in OB, while the high-dose D-Pen infusion showed fewer newborn neuroblasts in OB but with more arrested in the RMS. Long-term (28-day) infusion revealed similar outcomes. The qPCR data from neurosphere experiments revealed altered expressions of mRNAs encoding key proteins known to regulate SVZ adult neurogenesis, including, but not limited to, Shh, Dlx2, and Slit1, in response to the changed Cu level in neurospheres. Further immunohistochemical data indicated that Cu chelation also altered the expression of high-affinity copper uptake protein 1 (CTR1) and metallothionein-3 (MT3) in the SVZ as well as CTR1 in the choroid plexus, a tissue regulating brain Cu homeostasis. Taken together, this study provides first-hand evidence that a high Cu level in SVZ appears likely to maintain the stability of adult neurogenesis in this neurogenic zone.

Expression of Transcription Factor ZBTB20 in the Adult Primate Neurogenic Niche under Physiological Conditions or after Ischemia

The Zbtb20 gene encodes for a transcription factor that plays an important role in mammalian cortical development. Recently, its expression was reported in the adult mouse subventricular zone (SVZ), a major neurogenic niche containing neural stem cells throughout life. Here, we analyzed its expression in the adult primate anterior SVZ (SVZa) and rostral migratory stream (RMS) using macaque monkeys (Macaca fuscata). We report that the majority of Ki67+ cells, 71.4% in the SVZa and 85.7% in the RMS, co-label for ZBTB20. Nearly all neuroblasts, identified by their Doublecortin expression, were positive for ZBTB20 in both regions. Nearly all GFAP+ neural stem cells/astrocytes were also positive for ZBTB20. Analysis of images derived from a public database of gene expression in control/ischemic monkey SVZa, showed evidence for ZBTB20 upregulation in postischemic monkey SVZa. Furthermore, the co-localization of ZBTB20 with Doublecortin and Ki67 was increased in the postischemic SVZa. Our results suggest that ZBTB20 expression is evolutionarily conserved in the mammalian neurogenic niche and is reactive to ischemia. This opens the possibility for further functional studies on the role of this transcription factor in neurogenesis in primates.

A slow-cycling/quiescent cells subpopulation is involved in glioma invasiveness

Pediatric and adult high-grade gliomas are the most common primary malignant brain tumors, with poor prognosis due to recurrence and tumor infiltration after therapy. Quiescent cells have been implicated in tumor recurrence and treatment resistance, but their direct visualization and targeting remain challenging, precluding their mechanistic study. Here, we identify a population of malignant cells expressing Prominin-1 in a non-proliferating state in pediatric high-grade glioma patients. Using a genetic tool to visualize and ablate quiescent cells in mouse brain cancer and human cancer organoids, we reveal their localization at both the core and the edge of the tumors, and we demonstrate that quiescent cells are involved in infiltration of brain cancer cells. Finally, we find that Harmine, a DYRK1A/B inhibitor, partially decreases the number of quiescent and infiltrating cancer cells. Our data point to a subpopulation of quiescent cells as partially responsible of tumor invasiveness, one of the major causes of brain cancer morbidity.

Quiescent cancer stem cells have been particularly associated to chemoresistance. Here, the authors show that a slowcycling subpopulation in high-grade glioma patients can invade the brain to promote tumourigenesis.

Utility of Exosomes in Ischemic and Hemorrhagic Stroke Diagnosis and Treatment

Stroke is the leading cause of death and neurological disorders worldwide. However, diagnostic techniques and treatments for stroke patients are still limited for certain types of stroke. Intensive research has been conducted so far to find suitable diagnostic techniques and treatments, but so far there has been no success. In recent years, various studies have drawn much attention to the clinical value of utilizing the mechanism of exosomes, low toxicity, biodegradability, and the ability to cross the blood–brain barrier. Recent studies have been reported on the use of biomarkers and protective and recovery effects of exosomes derived from stem cells or various cells in the diagnostic stage after stroke. This review focuses on publications describing changes in diagnostic biomarkers of exosomes following various strokes and processes for various potential applications as therapeutics.

Endogenous Neural Stem Cell Mediated Oligodendrogenesis in the Adult Mammalian Brain

Oligodendrogenesis is essential for replacing worn-out oligodendrocytes, promoting myelin plasticity, and for myelin repair following a demyelinating injury in the adult mammalian brain. Neural stem cells are an important source of oligodendrocytes in the adult brain; however, there are considerable differences in oligodendrogenesis from neural stem cells residing in different areas of the adult brain. Amongst the distinct niches containing neural stem cells, the subventricular zone lining the lateral ventricles and the subgranular zone in the dentate gyrus of the hippocampus are considered the principle areas of adult neurogenesis. In addition to these areas, radial glia-like cells, which are the precursors of neural stem cells, are found in the lining of the third ventricle, where they are called tanycytes, and in the cerebellum, where they are called Bergmann glia. In this review, we will describe the contribution and regulation of each of these niches in adult oligodendrogenesis.

Interferon-γ resistance and immune evasion in glioma develop via Notch-regulated co-evolution of malignant and immune cells

Immune surveillance is critical to prevent tumorigenesis. Gliomas evade immune attack, but the underlying mechanisms remain poorly understood. We show that glioma cells can sustain growth independent of immune system constraint by reducing Notch signaling. Loss of Notch activity in a mouse model of glioma impairs MHC-I and cytokine expression and curtails the recruitment of anti-tumor immune cell populations in favor of immunosuppressive tumor-associated microglia/macrophages (TAMs). Depletion of T cells simulates Notch inhibition and facilitates tumor initiation. Furthermore, Notch-depleted glioma cells acquire resistance to interferon-γ and TAMs re-educating therapy. Decreased interferon response and cytokine expression by human and mouse glioma cells correlate with low Notch activity. These effects are paralleled by upregulation of oncogenes and downregulation of quiescence genes. Hence, suppression of Notch signaling enables gliomas to evade immune surveillance and increases aggressiveness. Our findings provide insights into how brain tumor cells shape their microenvironment to evade immune niche control.

Hippocampal Mitochondrial Transplantation Alleviates Age-Associated Cognitive Decline via Enhancing Wnt Signaling and Neurogenesis

Gradual cognition decline and mitochondrial dysfunction are two notable changes closely associated with aging. Enhancing mitochondrial function has been assumed to be antiaging. However, most current mitochondria-promoting agents usually target 1-2 aspects of mitochondrial function. In the present study, we transplanted mitochondria isolated from young mice into the hippocampus of aged mice, which presumably boost mitochondrial function more thoroughly, examined the effects on cognition, and explored the possible underlying mechanism. Our data showed that exogenous mitochondria were efficiently internalized by nestin-positive neural progenitors in the hippocampus. Mitochondrial transplantation quickly increased ATP levels, enhanced the activity of mitochondrial complexes I, II, and IV, and decreased Tom20 expression in the hippocampus. In regard of cognitive function, mitochondria-treated mice displayed a remarkable improvement of novel object recognition and spatial memory. Utilizing the Wnt signaling reporting mouse line, TOPGAL mice, we detected activated canonical Wnt signaling in the neural progenitors of the mitochondria-treated hippocampus. Further, BrdU labeling showed that exogenous mitochondria significantly stimulated neural progenitor neurogenesis and proliferation. Taken together, our data demonstrated that exogenous mitochondria from young mice might be a novel way of rejuvenating the function of hippocampal neural progenitors to exert antiaging effects.

RBP-J deficiency promoted the proliferation and differentiation of CD133-positive cells in vitro and in vivo studies

Although Notch signaling pathway could control the proliferation and differentiation of neural stem cells (NSCs), it is largely unknown about the effect of Notch signaling pathway on the neurogenesis of CD133-positive cells. By using the primary cultured ependymal cells and the transgenic mouse, we found that CD133 immunoreactivity was exclusively localized in the ependymal layer of ventricles, moreover, most CD133-positive cells were co-labeled with Nestin. In addition, recombination signal binding protein J (RBP-J), a key nuclear effector of Notch signaling pathway, was highly active in CD133-positive cells. CD133-positive cells can differentiate into the immature and mature neurons, in particular, the number of CD133-positive cells differentiating into the immature and mature neurons was significantly increased following the deficiency or interference of RBP-J in vivo or in vitro. By using real-time qPCR and western blot, we found that RBP-J and Hes1 were down-regulated while Notch1 was up-regulated in the expression levels of mRNAs and proteins following the deficiency or interference of RBP-J. These results demonstrated RBP-J deficiency promoted the proliferation and differentiation of CD133-positive cells. Therefore, we speculated that RBP-J could maintain CD133-positive cells in the characteristics of NSCs possibly by regulating Notch1/RBP-J/Hes1 pathway. It will provide a novel molecular insight into the function of RBP-J, as well as facilitate a future investigation of CD133-positive cells with respect to their potential application in neurodegenerative disorder.

Dormant state of quiescent neural stem cells links Shank3 mutation to autism development

Autism spectrum disorders (ASDs) are common neurodevelopmental disorders characterized by deficits in social interactions and communication, restricted interests, and repetitive behaviors. Despite extensive study, the molecular targets that control ASD development remain largely unclear. Here, we report that the dormancy of quiescent neural stem cells (qNSCs) is a therapeutic target for controlling the development of ASD phenotypes driven by Shank3 deficiency. Using single-cell RNA sequencing (scRNA-seq) and transposase accessible chromatin profiling (ATAC-seq), we find that abnormal epigenetic features including H3K4me3 accumulation due to up-regulation of Kmt2a levels lead to increased dormancy of qNSCs in the absence of Shank3. This result in decreased active neurogenesis in the Shank3 deficient mouse brain. Remarkably, pharmacological and molecular inhibition of qNSC dormancy restored adult neurogenesis and ameliorated the social deficits observed in Shank3-deficient mice. Moreover, we confirmed restored human qNSC activity rescues abnormal neurogenesis and autism-like phenotypes in SHANK3-targeted human NSCs. Taken together, our results offer a novel strategy to control qNSC activity as a potential therapeutic target for the development of autism.

Radial Glia and Neuronal-like Ependymal Cells Are Present within the Spinal Cord of the Trunk (Body) in the Leopard Gecko (Eublepharis macularius)

As is the case for many lizards, leopard geckos (Eublepharis macularius) can self-detach a portion of their tail to escape predation, and then regenerate a replacement complete with a spinal cord. Previous research has shown that endogenous populations of neural stem/progenitor cells (NSPCs) reside within the spinal cord of the original tail. In response to tail loss, these NSPCs are activated and contribute to regeneration. Here, we investigate whether similar populations of NSPCs are found within the spinal cord of the trunk (body). Using a long-duration 5-bromo-2′-deoxyuridine pulse-chase experiment, we determined that a population of cells within the ependymal layer are label-retaining following a 20-week chase. Tail loss does not significantly alter rates of ependymal cell proliferation within the trunk spinal cord. Ependymal cells of the trunk spinal cord express SOX2 and represent at least two distinct cell populations: radial glial-like (glial fibrillary acidic protein- and Vimentin-expressing) cells; and neuronal-like (HuCD-expressing) cells. Taken together, these data demonstrate that NSPCs of the trunk spinal cord closely resemble those of the tail and support the use of the tail spinal cord as a less invasive proxy for body spinal cord injury investigations.

Single Cell/Nucleus Transcriptomics Comparison in Zebrafish and Humans Reveals Common and Distinct Molecular Responses to Alzheimer’s Disease

Neurogenesis is significantly reduced in Alzheimer’s disease (AD) and is a potential therapeutic target. Contrary to humans, a zebrafish can regenerate its diseased brain, and thus is ideal for studying neurogenesis. To compare the AD-related molecular pathways between humans and zebrafish, we compared single cell or nuclear transcriptomic data from a zebrafish amyloid toxicity model and its controls (N = 12) with the datasets of two human adult brains (N = 10 and N = 48 (Microglia)), and one fetal brain (N = 10). Approximately 95.4% of the human and zebrafish cells co-clustered. Within each cell type, we identified differentially expressed genes (DEGs), enriched KEGG pathways, and gene ontology terms. We studied synergistic and non-synergistic DEGs to point at either common or uniquely altered mechanisms across species. Using the top DEGs, a high concordance in gene expression changes between species was observed in neuronal clusters. On the other hand, the molecular pathways affected by AD in zebrafish astroglia differed from humans in favor of the neurogenic pathways. The integration of zebrafish and human transcriptomes shows that the zebrafish can be used as a tool to study the cellular response to amyloid proteinopathies. Uniquely altered pathways in zebrafish could highlight the specific mechanisms underlying neurogenesis, which are absent in humans, and could serve as potential candidates for therapeutic developments.

The extracellular matrix molecule tenascin-C modulates cell cycle progression and motility of adult neural stem/progenitor cells from the subependymal zone

Adult neurogenesis has been described in two canonical regions of the adult central nervous system (CNS) of rodents, the subgranular zone (SGZ) of the hippocampus and the subependymal zone (SEZ) of the lateral ventricles. The stem cell niche of the SEZ provides a privileged environment composed of a specialized extracellular matrix (ECM) that comprises the glycoproteins tenascin-C (Tnc) and laminin-1 (LN1). In the present study, we investigated the function of these ECM glycoproteins in the adult stem cell niche. Adult neural stem/progenitor cells (aNSPCs) of the SEZ were prepared from wild type (Tnc^+/+) and Tnc knockout (Tnc^−/−) mice and analyzed using molecular and cell biological approaches. A delayed maturation of aNSPCs in Tnc^−/− tissue was reflected by a reduced capacity to form neurospheres in response to epidermal growth factor (EGF). To examine a potential influence of the ECM on cell proliferation, aNSPCs of both genotypes were studied by cell tracking using digital video microscopy. aNSPCs were cultivated on three different substrates, namely, poly-d-lysine (PDL) and PDL replenished with either LN1 or Tnc for up to 6 days in vitro. On each of the three substrates aNSPCs displayed lineage trees that could be investigated with regard to cell cycle length. The latter appeared reduced in Tnc^−/− aNSPCs on PDL and LN1 substrates, less so on Tnc that seemed to compensate the absence of the ECM compound to some extent. Close inspection of the lineage trees revealed a subpopulation of late dividing aNSPCs_late that engaged into cycling after a notable delay. aNSPCs_late exhibited a clearly different morphology, with a larger cell body and conspicuous processes. aNSPCs_late reiterated the reduction in cell cycle length on all substrates tested, which was not rescued on Tnc substrates. When the migratory activity of aNSPC-derived progeny was determined, Tnc^−/− neuroblasts displayed significantly longer migration tracks. This was traced to an increased rate of migration episodes compared to the wild-type cells that rested for longer time periods. We conclude that Tnc intervenes in the proliferation of aNSPCs and modulates the motility of neuroblasts in the niche of the SEZ.

Assessing the Role of Ependymal and Vascular Cells as Sources of Extracellular Cues Regulating the Mouse Ventricular-Subventricular Zone Neurogenic Niche

Neurogenesis persists in selected regions of the adult mouse brain; among them, the ventricular-subventricular zone (V-SVZ) of the lateral ventricles represents a major experimental paradigm due to its conspicuous neurogenic output. Postnatal V-SVZ neurogenesis is maintained by a resident population of neural stem cells (NSCs). Although V-SVZ NSCs are largely quiescent, they can be activated to enter the cell cycle, self-renew and generate progeny that gives rise to olfactory bulb interneurons. These adult-born neurons integrate into existing circuits to modify cognitive functions in response to external stimuli, but cells shed by V-SVZ NSCs can also reach injured brain regions, suggesting a latent regenerative potential. The V-SVZ is endowed with a specialized microenvironment, which is essential to maintain the proliferative and neurogenic potential of NSCs, and to preserve the NSC pool from exhaustion by finely tuning their quiescent and active states. Intercellular communication is paramount to the stem cell niche properties of the V-SVZ, and several extracellular signals acting in the niche milieu have been identified. An important part of these signals comes from non-neural cell types, such as local vascular cells, ependymal and glial cells. Understanding the crosstalk between NSCs and other niche components may aid therapeutic approaches for neuropathological conditions, since neurodevelopmental disorders, age-related cognitive decline and neurodegenerative diseases have been associated with dysfunctional neurogenic niches. Here, we review recent advances in the study of the complex interactions between V-SVZ NSCs and their cellular niche. We focus on the extracellular cues produced by ependymal and vascular cells that regulate NSC behavior in the mouse postnatal V-SVZ, and discuss the potential implication of these molecular signals in pathological conditions.

The Subventricular Zone in Glioblastoma: Genesis, Maintenance, and Modeling

Glioblastoma (GBM) is a malignant tumor with a median survival rate of 15-16 months with standard care; however, cases of successful treatment offer hope that an enhanced understanding of the pathology will improve the prognosis. The cell of origin in GBM remains controversial. Recent evidence has implicated stem cells as cells of origin in many cancers. Neural stem/precursor cells (NSCs) are being evaluated as potential initiators of GBM tumorigenesis. The NSCs in the subventricular zone (SVZ) have demonstrated similar molecular profiles and share several distinctive characteristics to proliferative glioblastoma stem cells (GSCs) in GBM. Genomic and proteomic studies comparing the SVZ and GBM support the hypothesis that the tumor cells and SVZ cells are related. Animal models corroborate this connection, demonstrating migratory patterns from the SVZ to the tumor. Along with laboratory and animal research, clinical studies have demonstrated improved progression-free survival in patients with GBM after radiation to the ipsilateral SVZ. Additionally, key genetic mutations in GBM for the most part carry regulatory roles in the SVZ as well. An exciting avenue towards SVZ modeling and determining its role in gliomagenesis in the human context is human brain organoids. Here we comprehensively discuss and review the role of the SVZ in GBM genesis, maintenance, and modeling.

Response of murine neural stem/progenitor cells to gamma-neutron radiation

PURPOSE

In recent years, a growing number of studies have focused on the mechanisms of action of densely ionizing radiation. This is associated with the development of radiation therapy of tumors using accelerated ions. The use of densely ionizing radiation appears to be the most promising method, optimal for treating patients with severe radioresistant forms, such as widespread head and neck tumors, recurrent and metastatic tumors, and some forms of brain tumors. The goal of our study was to investigate the effects of gamma-neutron radiation on mouse neural stem/progenitor cells (NSCs/NPCs).

METHODS

NSCs/NPCs were isolated from neonatal mouse brains. Cells were irradiated in a collimated beam of neutrons and gamma rays of the IR-8 nuclear reactor. At 5 and 7 days after irradiation, cells and neurospheres were counted to assess survival. The number of DNA double-strand breaks and their repair efficiency were determined by immunocytochemical γH2AX staining followed by counting the number of γH2AX foci using a fluorescent microscope.

RESULTS

We observed a dose-dependent decrease in the survival of NSCs/NPCs after irradiation at doses above 100 mGy and stimulation of the proliferation of these cells at doses of 25 and 50 mGy. In terms of a decrease in cell survival, the effect of gamma-neutron irradiation significantly exceeded the effect of gamma irradiation: the maximum value of the relative biological efficiency for gamma-neutron irradiation comprised 9.7. Gamma-neutron irradiation led to the formation of double-strand DNA breaks detected by the formation of foci of histone γH2AX in the cell nuclei. The γH2AX foci formed after gamma-neutron irradiation of NSCs/NPCs at doses of 100-500 mGy were characterized by a larger size in comparison with foci induced by gamma irradiation and gamma-neutron irradiation at a dose of 50 mGy. The repair of double-strand DNA breaks induced by γ,n-irradiation was slow; the repair rate depended on the radiation dose.

CONCLUSIONS

The data obtained indicate high sensitivity of proliferating NSCs/NPCs to gamma-neutron radiation. High RBE of gamma-neutron radiation requires special measures to protect the neurogenic regions of the brain when using this type of radiation in radiation therapy.

Oleic acid is an endogenous ligand of TLX/NR2E1 that triggers hippocampal neurogenesis

SignificanceAdult hippocampal neurogenesis underpins learning, memory, and mood but diminishes with age and certain illnesses. The orphan nuclear receptor TLX/NR2E1 regulates neural stem and progenitor cell self-renewal and proliferation, but its orphan status has hindered its utilization as a therapeutic target to modulate adult neurogenesis. Here, we deorphanize TLX and report that oleic acid is an endogenous, metabolic ligand of TLX. These findings open avenues for future therapeutic modulation of TLX to counteract cognitive and mental decline in aging and diseases associated with decreased neurogenesis.

Deciphering heterogeneous populations of migrating cells based on the computational assessment of their dynamic properties

Neuronal migration is a highly dynamic process, and multiple cell movement metrics can be extracted from time-lapse imaging datasets. However, these parameters alone are often insufficient to evaluate the heterogeneity of neuroblast populations. We developed an analytical pipeline based on reducing the dimensions of the dataset by principal component analysis (PCA) and determining sub-populations using k-means, supported by the elbow criterion method and validated by a decision tree algorithm. We showed that neuroblasts derived from the same adult neural stem cell (NSC) lineage as well as across different lineages are heterogeneous and can be sub-divided into different clusters based on their dynamic properties. Interestingly, we also observed overlapping clusters for neuroblasts derived from different NSC lineages. We further showed that genetic perturbations or environmental stimuli affect the migratory properties of neuroblasts in a sub-cluster-specific manner. Our data thus provide a framework for assessing the heterogeneity of migrating neuroblasts.

•

Pipeline to study the heterogeneity of migrating cells based on their dynamic properties

•

Neuroblasts derived from the same neural stem cell (NSC) lineage are heterogeneous

•

Neuroblasts derived from different NSC lineages have overlapping and distinct clusters

•

These clusters are differently affected by genetic factors or environmental stimuli

Short-read and long-read full-length transcriptome of mouse neural stem cells across neurodevelopmental stages

During brain development, neural stem cells (NSCs) undergo multiple fate-switches to generate various neuronal subtypes and glial cells, exhibiting distinct transcriptomic profiles at different stages. However, full-length transcriptomic datasets of NSCs across different neurodevelopmental stages under similar experimental settings are lacking, which is essential for uncovering stage-specific transcriptional and post-transcriptional mechanisms underlying the fate commitment of NSCs. Here, we report the full-length transcriptome of mouse NSCs at five different stages during embryonic and postnatal development. We used fluorescent-activated cell sorting (FACS) to isolate CD133+Blbp+ NSCs from C57BL/6 transgenic mice that express enhanced green fluorescent protein (EGFP) under the control of a Blbp promoter. By integrating short- and long-read full-length RNA-seq, we created a transcriptomic dataset of gene and isoform expression profiles in NSCs at embryonic days 15.5, 17.5, and postnatal days 1.5, 8, and 60. This dataset provides a detailed characterization of full-length transcripts in NSCs at distinct developmental stages, which could be used as a resource for the neuroscience community to study NSC fate determination, neural development, and disease.

Regulating Endogenous Neural Stem Cell Activation to Promote Spinal Cord Injury Repair

Spinal cord injury (SCI) affects millions of individuals worldwide. Currently, there is no cure, and treatment options to promote neural recovery are limited. An innovative approach to improve outcomes following SCI involves the recruitment of endogenous populations of neural stem cells (NSCs). NSCs can be isolated from the neuroaxis of the central nervous system (CNS), with brain and spinal cord populations sharing common characteristics (as well as regionally distinct phenotypes). Within the spinal cord, a number of NSC sub-populations have been identified which display unique protein expression profiles and proliferation kinetics. Collectively, the potential for NSCs to impact regenerative medicine strategies hinges on their cardinal properties, including self-renewal and multipotency (the ability to generate de novo neurons, astrocytes, and oligodendrocytes). Accordingly, endogenous NSCs could be harnessed to replace lost cells and promote structural repair following SCI. While studies exploring the efficacy of this approach continue to suggest its potential, many questions remain including those related to heterogeneity within the NSC pool, the interaction of NSCs with their environment, and the identification of factors that can enhance their response. We discuss the current state of knowledge regarding populations of endogenous spinal cord NSCs, their niche, and the factors that regulate their behavior. In an attempt to move towards the goal of enhancing neural repair, we highlight approaches that promote NSC activation following injury including the modulation of the microenvironment and parenchymal cells, pharmaceuticals, and applied electrical stimulation.

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.

4D imaging analysis of the aging mouse neural stem cell niche reveals a dramatic loss of progenitor cell dynamism regulated by the RHO-ROCK pathway

In the adult ventricular-subventricular zone (V-SVZ), neural stem cells (NSCs) give rise to transit-amplifying progenitor (TAP) cells. These progenitors reside in different subniche locations, implying that cell movement must accompany lineage progression, but the dynamic behaviors of adult NSCs and TAPs remain largely unexplored. Here, we performed live time-lapse imaging with computer-based image analysis of young and aged 3D V-SVZ wholemounts from transgenic mice with fluorescently distinguished NSCs and TAP cells. Young V-SVZ progenitors are highly dynamic, with regular process outgrowth and retraction and cell migration. However, these activities dramatically declined with age. An examination of single-cell RNA sequencing (RNA-seq) data revealed age-associated changes in the Rho-Rock pathway that are important for cell motility. Applying a small molecule to inhibit ROCK transformed young into old V-SVZ progenitor cell dynamic behaviors. Hence RHO-ROCK signaling is critical for normal adult NSC and TAP movement and interactions, which are compromised with age, concomitant with the loss of regenerative ability.

Expression of Doublecortin, Glial Fibrillar Acidic Protein, and Vimentin in the Intact Subpallium and after Traumatic Injury to the Pallium in Juvenile Salmon, Oncorhynchus masou

Fetalization associated with a delay in development and the preservation of the features of the embryonic structure of the brain dominates the ontogeny of salmonids. The aim of the present study was to comparatively analyze the distribution of the glial-type aNSC markers such as vimentin and glial fibrillar acidic protein (GFAP) and the migratory neuronal precursors such as doublecortin in the telencephalon subpallium of juvenile masu salmon, Oncorhynchus masou, in normal conditions and at 1 week after an injury to the dorsal pallium. Immunohistochemical labeling of vimentin, GFAP, and doublecortin in the pallium of intact juvenile masu salmon revealed single cells with similar morphologies corresponding to a persistent pool of neuronal and/or glial progenitors. The study of the posttraumatic process showed the presence of intensely GFAP-labeled cells of the neuroepithelial type that form reactive neurogenic zones in all areas of the subpallial zone of juvenile masu salmon. A comparative analysis of the distribution of radial glia in the dorsal, ventral, and lateral zones of the subpallium showed a maximum concentration of cells in the dorsal part of subpallium (VD) and a minimum concentration in the lateral part of subpallium VL. An essential feature of posttraumatic immunolabeling in the masu salmon subpallium is the GFAP distribution patterns that are granular intracellular in the apical periventricular zone (PVZ) and fibrillar extracellular in the subventricular (SVZ) and parenchymal zones (PZ). In contrast to those in intact animals, most of the GFAP+ granules and constitutive neurogenic niches in injured fish were localized in the basal part of the PVZ. With the traumatic injury to the subpallium, the number of Vim+ cells in the lateral and ventral regions significantly increased. At 1 week post-injury, the total immunolabeling of vimentin cells in the PVZ was replaced by the granular pattern of Vim immunodistribution spreading from the PVZ to the SVZ and deeper parenchymal layers of the brain in all areas of the subpallium. A significant increase in the number of DC+ cells was observed also in all areas of the subpallium. The number of cells increased both in the PVZ and in the SVZ, as well as in the deeper PZ. Thus, at 1 week after the injury to the dorsal pallium, the number of DC, Vim, and GFAP expressing cells of the neuroepithelial type in the subpallium of juvenile masu salmon increased, and additionally GFAP+ radial glia appeared in VD, which was absent from intact animals.