FoxOs cooperatively regulate diverse pathways governing neural stem cell homeostasis

Mitochondria in Early Forebrain Development: From Neurulation to Mid-Corticogenesis

Function of the mature central nervous system (CNS) requires a substantial proportion of the body’s energy consumption. During development, the CNS anlage must maintain its structure and perform stage-specific functions as it proceeds through discrete developmental stages. While key extrinsic signals and internal transcriptional controls over these processes are well appreciated, metabolic and mitochondrial states are also critical to appropriate forebrain development. Specifically, metabolic state, mitochondrial function, and mitochondrial dynamics/localization play critical roles in neurulation and CNS progenitor specification, progenitor proliferation and survival, neurogenesis, neural migration, and neurite outgrowth and synaptogenesis. With the goal of integrating neurodevelopmental biologists and mitochondrial specialists, this review synthesizes data from disparate models and processes to compile and highlight key roles of mitochondria in the early development of the CNS with specific focus on forebrain development and corticogenesis.

The role of forkhead box class O1 during implant osseointegration

FOXO1, a member of the forkhead family of transcription factors, plays a vital role in the osteogenic lineage commitment of mesenchymal stem cells, and affects multiple cellular functions of osteogenic cells. However, prior studies have focused on mesenchymal stem cells but not on differentiated osteoblasts. In addition, studies about the role of FOXO1 during osseointegration are lacking. In this present study, we constructed osteoblast conditional FOXO1 knock-out mice and lentivirus-mediated FoxO1 overexpression to investigate maxillary titanium implant osseointegration. After 4 wk post implant placement, micro-computed tomography, histomorphometric analyses, and RT-qPCR assays were performed. Results showed that compared with the control group, overexpression of FOXO1 significantly enhanced bone formation around implant and bone-implant contact ratio, while loss of FOXO1 impaired peri-implant osteogenesis and osseointegration. Moreover, overexpression of FoxO1 enhanced expression of osteogenesis-related genes, such as Runx2, Alp1, Col1a1, and Bglap. Whereas, knock-out of Foxo1 reduced the expression of osteogenesis-related genes. Taken together, our results suggested that FOXO1 in osteoblasts could enhance osteogenesis-related gene expression to improve osseointegration.

Aging-associated stem/progenitor cell dysfunction in the salivary glands of mice

Although stem cell aging leads to a decline in tissue homeostasis and regenerative capacity, it remains unclear whether salivary gland stem cell function changes during this process. However, the salivary glands are gradually replaced by connective tissue during aging. Here, we show a decline in the stem cell ability of CD133-positive stem/progenitor cells in the salivary glands of aged mice. The CD133-positive cells were isolated from young, adult, and aged mice. The number of CD133-positive cells was significantly decreased in aged mice. They also showed a lower sphere formation capacity compared to young and adult mice. RNA sequencing revealed that CD133-positive cells in aged mice exhibited lower gene expression of several aging-related genes, including FoxO3a, than those in young and adult mice. Salivary gland cells infected with a recombinant lentivirus encoding the FoxO3a gene showed a reduction in oxidative stress induced by hydrogen peroxide compared with those infected with a control virus. Thus, FoxO3a may inhibit stem cell aging via oxidative stress.

FOXO3 regulates a common genomic program in aging and glioblastoma stem cells

Background

Glioblastoma (GBM) is an aggressive, age-associated malignant glioma that contains populations of cancer stem cells. These glioma stem cells (GSCs) evade therapeutic interventions and repopulate tumors due to their existence in a slowly cycling quiescent state. Although aging is well known to increase cancer initiation, the extent to which the mechanisms supporting GSC tumorigenicity are related to physiological aging remains unknown.

Aims

Here, we investigate the transcriptional mechanisms by which Forkhead Box O3 (FOXO3), a transcriptional regulator that promotes healthy aging, affects GSC function and the extent to which FOXO3 transcriptional networks are dysregulated in aging and GBM.

Methods and results

We performed transcriptome analysis of clinical GBM tumors and observed that high FOXO3 activity is associated with gene expression signatures of stem cell quiescence, reduced oxidative metabolism, and improved patient outcomes. Consistent with these findings, we show that elevated FOXO3 activity significantly reduces the proliferation of GBM-derived GSCs. Using RNA-seq, we find that functional ablation of FOXO3 in GSCs rewires the transcriptional circuitry associated with metabolism, epigenetic stability, quiescence, and differentiation. Since FOXO3 has been implicated in healthy aging, we then investigated the extent to which it regulates common transcriptional programs in aging neural stem cells (NSCs) and GSCs. We uncover a shared transcriptional program and, most strikingly, find that FOXO3-regulated pathways are associated with altered mitochondrial functions in both aging and GBM.

Conclusions

This work identifies a FOXO-associated transcriptional program that correlates between GSCs and aging NSCs and is enriched for metabolic and stemness pathways connected with GBM and aging.

FoxO1 Regulates Neuropeptide Y and Pro-opiomelanocortin in the Hypothalamus of Rat Offspring Small for Gestational Age

Adulthood obesity, diabetes, and metabolic diseases are associated with small for gestational age (SGA) newborns. This association could be related to abnormal appetite signaling pathways in the hypothalamus. This study investigated the appetite regulation by the hypothalamus of SGA newborns by establishing an SGA rat model and culturing SGA neural progenitor cells (NPCs) in vitro. Models of SGA were established by maternal food restriction embryonic day 10 (E10). At E18, postpartum day 1 (P1), and P5, hypothalamic neural precursor cells (NPCs) of offspring were cultured in vitro. Immunofluorescence, Western blot (WB), and qRT-PCR were used to assess NPY, POMC, and FoxO1 expression levels. The effects on mRNA expression of the FoxO1-specific inhibitor AS1842856 were examined. The results indicated that compared with controls, NPY was higher, and POMC was lower at embryonic day 18 (E18), postpartum day 1 (P1), and P5. The proliferation and migration of NPCs in the third ventricle of SGA hypothalami were lower than in controls. After treatment with the FoxO1 inhibitor AS1842856, the differences in the mRNA expression of NPY and POMC between the two groups disappeared. NPY and POMC mRNA levels in the SGA group treated with AS1842856 were not significantly different compared with the control group without AS1842856 treatment. In conclusion, SGA pups showed an increase in appetite-promoting NPY and a decrease in appetite-reducing POMC, probably contributing to adulthood weight gain, obesity, and endocrine disorders.

Role of FoxO transcription factors in aging and age-related metabolic and neurodegenerative diseases

Aging happens to all of us as we live. Thanks to the improved living standard and discovery of life-saving medicines, our life expectancy has increased substantially across the world in the past century. However, the rise in lifespan leads to unprecedented increases in both the number and the percentage of individuals 65 years and older, accompanied by the increased incidences of age-related diseases such as type 2 diabetes mellitus and Alzheimer’s disease. FoxO transcription factors are evolutionarily conserved molecules that play critical roles in diverse biological processes, in particular aging and metabolism. Their dysfunction is often found in the pathogenesis of many age-related diseases. Here, we summarize the signaling pathways and cellular functions of FoxO proteins. We also review the complex role of FoxO in aging and age-related diseases, with focus on type 2 diabetes and Alzheimer’s disease and discuss the possibility of FoxO as a molecular link between aging and disease risks.

Changing and stable chromatin accessibility supports transcriptional overhaul during neural stem cell activation and is altered with age

Neural stem cells (NSCs) in the adult and aged brain are largely quiescent, and require transcriptional reprogramming to re-enter the cell cycle. However, the mechanisms underlying these changes and how they are altered with age remain undefined. Here, we identify the chromatin accessibility differences between primary neural stem/progenitor cells in quiescent and activated states. These distinct cellular states exhibit shared and unique chromatin profiles, both associated with gene regulation. Accessible chromatin states specific to activation or quiescence are active enhancers bound by key pro-neurogenic and quiescence factors. In contrast, shared sites are enriched for core promoter elements associated with translation and metabolism. Unexpectedly, through integrated analysis, we find that many sites that become accessible during NSC activation are linked to gene repression and associated with pro-quiescence factors, revealing a novel mechanism that may preserve quiescence re-entry. Furthermore, we report that in aged NSCs, chromatin regions associated with metabolic and transcriptional functions bound by key pro-quiescence transcription factors lose accessibility, suggesting a novel mechanism of age-associated NSC dysfunction. Together, our findings reveal how accessible chromatin states regulate the transcriptional switch between NSC quiescence and activation, and how this switch is affected with age.

Wnt/β-catenin signalling is dispensable for adult neural stem cell homeostasis and activation

Adult mouse hippocampal neural stem cells (NSCs) generate new neurons that integrate into existing hippocampal networks and modulate mood and memory. These NSCs are largely quiescent and are stimulated by niche signals to activate and produce neurons. Wnt/β-catenin signalling acts at different steps along the hippocampal neurogenic lineage, but whether it has a direct role in the regulation of NSCs remains unclear. Here, we used Wnt/β-catenin reporters and transcriptomic data from in vivo and in vitro models to show that adult NSCs respond to Wnt/β-catenin signalling. Wnt/β-catenin stimulation instructed the neuronal differentiation of proliferating NSCs and promoted the activation or differentiation of quiescent NSCs in a dose-dependent manner. However, deletion of β-catenin in NSCs did not affect either their activation or maintenance of their stem cell characteristics. Together, these results indicate that, although NSCs do respond to Wnt/β-catenin stimulation in a dose-dependent and state-specific manner, Wnt/β-catenin signalling is not cell-autonomously required to maintain NSC homeostasis, which reconciles some of the contradictions in the literature as to the role of Wnt/β-catenin signalling in adult hippocampal NSCs.

Summary: Wnt/β-catenin signalling stimulation promotes the exit from quiescence and differentiation of adult hippocampal neural stem cells but is dispensable for homeostatic neurogenesis in the dentate gyrus of young mice.

Differential Marker Expression between Keratinocyte Stem Cells and Their Progeny Generated from a Single Colony

The stemness in keratinocyte stem cells (KSCs) is determined by their gene expression patterns. KSCs are crucial in maintaining epidermal homeostasis and wound repair and are widely used candidates for therapeutic applications. Although several studies have reported their positive identifiers, unique biomarkers for KSCs remain elusive. Here, we aim to identify potential candidate stem cell markers. Human epidermal keratinocytes (HEKs) from neonatal foreskin tissues were isolated and cultured. Single-cell clonal analysis identified and characterized three types of cells: KSCs (holoclones), transient amplifying cells (TACs; meroclones), and differentiated cells (DSCs; paraclones). The clonogenic potential of KSCs demonstrated the highest proliferation potential of KSCs, followed by TACs and DSCs, respectively. Whole-transcriptome analysis using microarray technology unraveled the molecular signatures of these cells. These results were validated by quantitative real-time polymerase chain reaction and flow cytometry analysis. A total of 301 signature upregulated and 149 downregulated differentially expressed genes (DEGs) were identified in the KSCs, compared to TACs and DSCs. Furthermore, DEG analyses revealed new sets of genes related to cell proliferation, cell adhesion, surface makers, and regulatory factors. In conclusion, this study provides a useful source of information for the identification of potential SC-specific candidate markers.

Autophagy in major human diseases

Autophagy is a core molecular pathway for the preservation of cellular and organismal homeostasis. Pharmacological and genetic interventions impairing autophagy responses promote or aggravate disease in a plethora of experimental models. Consistently, mutations in autophagy-related processes cause severe human pathologies. Here, we review and discuss preclinical data linking autophagy dysfunction to the pathogenesis of major human disorders including cancer as well as cardiovascular, neurodegenerative, metabolic, pulmonary, renal, infectious, musculoskeletal, and ocular disorders.

D-cysteine is an endogenous regulator of neural progenitor cell dynamics in the mammalian brain

d-amino acids are increasingly recognized as important signaling molecules in the mammalian central nervous system. However, the d-stereoisomer of the amino acid with the fastest spontaneous racemization ratein vitro in vitro, cysteine, has not been examined in mammals. Using chiral high-performance liquid chromatography and a stereospecific luciferase assay, we identify endogenous d-cysteine in the mammalian brain. We identify serine racemase (SR), which generates the N-methyl-d-aspartate (NMDA) glutamate receptor coagonist d-serine, as a candidate biosynthetic enzyme for d-cysteine. d-cysteine is enriched more than 20-fold in the embryonic mouse brain compared with the adult brain. d-cysteine reduces the proliferation of cultured mouse embryonic neural progenitor cells (NPCs) by ∼50%, effects not shared with d-serine or l-cysteine. The antiproliferative effect of d-cysteine is mediated by the transcription factors FoxO1 and FoxO3a. The selective influence of d-cysteine on NPC proliferation is reflected in overgrowth and aberrant lamination of the cerebral cortex in neonatal SR knockout mice. Finally, we perform an unbiased screen for d-cysteine-binding proteins in NPCs by immunoprecipitation with a d-cysteine-specific antibody followed by mass spectrometry. This approach identifies myristoylated alanine-rich C-kinase substrate (MARCKS) as a putative d-cysteine-binding protein. Together, these results establish endogenous mammalian d-cysteine and implicate it as a physiologic regulator of NPC homeostasis in the developing brain.

FoxO3 deficiency in cortical astrocytes leads to impaired lipid metabolism and aggravated amyloid pathology

The rise of life expectancy of the human population is accompanied by the drastic increases of age‐associated diseases, in particular Alzheimer's disease (AD), and underscores the need to understand how aging influences AD development. The Forkhead box O transcription factor 3 (FoxO3) is known to mediate aging and longevity downstream of insulin/insulin‐like growth factor signaling across species. However, its function in the adult brain under physiological and pathological conditions is less understood. Here, we report a region and cell‐type‐specific regulation of FoxO3 in the central nervous system (CNS). We found that FoxO3 protein levels were reduced in the cortex, but not hippocampus, of aged mice. FoxO3 was responsive to insulin/AKT signaling in astrocytes, but not neurons. Using CNS Foxo3‐deficient mice, we reveal that loss of FoxO3 led to cortical astrogliosis and altered lipid metabolism. This is associated with impaired metabolic homoeostasis and β‐amyloid (Aβ) uptake in primary astrocyte cultures. These phenotypes can be reversed by expressing a constitutively active FOXO3 but not a FOXO3 mutant lacking the transactivation domain. Loss of FoxO3 in 5xFAD mice led to exacerbated Aβ pathology and synapse loss and altered local response of astrocytes and microglia in the vicinity of Aβ plaques. Astrocyte‐specific overexpression of FOXO3 displayed opposite effects, suggesting that FoxO3 functions cell autonomously to mediate astrocyte activity and also interacts with microglia to address Aβ pathology. Our studies support a protective role of astroglial FoxO3 against brain aging and AD.

Minor Allele Frequencies and Molecular Pathways Differences for SNPs Associated with Amyotrophic Lateral Sclerosis in Subjects Participating in the UKBB and 1000 Genomes Project

Amyotrophic lateral sclerosis (ALS) is a complex disease with a late onset and is characterized by the progressive loss of muscular and respiratory functions. Although recent studies have partially elucidated ALS's mechanisms, many questions remain such as what the most important molecular pathways involved in ALS are and why there is such a large difference in ALS onset among different populations. In this study, we addressed this issue with a bioinformatics approach, using the United Kingdom Biobank (UKBB) and the European 1000 Genomes Project (1KG) in order to analyze the most ALS-representative single nucleotide polymorphisms (SNPs) that differ for minor allele frequency (MAF) between the United Kingdom population and some European populations including Finnish in Finland, Iberian population in Spain, and Tuscans in Italy. We found 84 SNPs associated with 46 genes that are involved in different pathways including: "Ca²⁺ activated K⁺ channels", "cGMP effects", "Nitric oxide stimulates guanylate cyclase", "Proton/oligopeptide cotransporters", and "Signaling by MAPK mutants". In addition, we revealed that 83% of the 84 SNPs can alter transcription factor-motives binding sites of 224 genes implicated in "Regulation of beta-cell development", "Transcription-al regulation by RUNX3", "Transcriptional regulation of pluripotent stem cells", and "FOXO-mediated transcription of cell death genes". In conclusion, the genes and pathways analyzed could explain the cause of the difference of ALS onset.

MiR-421 Binds to PINK1 and Enhances Neural Stem Cell Self-Renewal via HDAC3-Dependent FOXO3 Activation

Dysfunctions of neural stem cells (NSCs) often lead to a variety of neurological diseases. Thus, therapies based on NSCs have gained increasing attention recently. It has been documented that microRNA (miR)-421 represses the autophagy and apoptosis of mouse hippocampal neurons and confers a role in the repair of ischemic brain injury (IBI). Herein, we aimed to illustrate the effects of miR-421 on NSC self-renewal. The downstream factors of miR-421 were predicted initially, followed by gain- and loss-of-function assays to examine their effects on NSC self-renewal. Immunoprecipitation and dual luciferase assays were conducted to validate the interaction among miR-421, PTEN-induced putative kinase 1 (PINK1), HDAC3, and forkhead box O3 (FOXO3). A mouse model with IBI was developed to substantiate the impact of the miR-421/PINK1/HDAC3/FOXO3 axis on NSC self-renewal. The expression of miR-421 was downregulated during differentiation of human embryonic NSCs, and miR-421 overexpression accelerated NSC self-renewal. Besides, miR-421 targeted PINK1 and restricted its expression in NSCs and further suppressed HDAC3 phosphorylation and enhanced FOXO3 acetylation. In conclusion, our data elucidated that miR-421 overexpression may facilitate NSC self-renewal through the PINK1/HDAC3/FOXO3 axis, which may provide potential therapeutic targets for the development of novel therapies for IBI.

Epigenetic plasticity and redox regulation of neural stem cell state and fate

The neural stem cells (NSCs) are essential for normal brain development and homeostasis. The cell state (i.e. quiescent versus activated) and fate (i.e. the cell lineage of choice upon differentiation) of NSCs are tightly controlled by various redox and epigenetic regulatory mechanisms. There is an increasing appreciation that redox and epigenetic regulations are intimately linked, but how this redox-epigenetics crosstalk affects NSC activity remains poorly understood. Another unresolved topic is whether the NSCs actually contribute to brain ageing and neurodegenerative diseases. In this review, we aim to 1) distill concepts that underlie redox and epigenetic regulation of NSC state and fate; 2) provide examples of the redox-epigenetics crosstalk in NSC biology; and 3) highlight potential redox- and epigenetic-based therapeutic opportunities to rescue NSC dysfunctions in ageing and neurodegenerative diseases.

From Transcriptome to Behavior: Intranasal Injection of Late Passage Human Olfactory Stem Cells Displays Potential in a Rat Model of Parkinson's Disease

Parkinson's disease (PD) is one of the most common neurodegenerative disorders, which is caused by the loss of dopaminergic (DAergic) neurons. Thus, cell replacement therapy (CRT) might be regarded as an alternative therapy to effectively treat motor functional defects in PD patients. Human olfactory ectomesenchymal stem cells (OE-MSCs) are a novel type of mesenchymal stem cells (MSCs) with a strong tendency to differentiate into DAergic neurons. However, there are various barriers to successful CRT including the proliferation capacity of stem cells at higher passage numbers as well as the route of stem cell delivery. In this regard, we aimed to explore the efficacy of late passage OE-MSC administration through the intranasal (IN) route in PD rat models. Herein, the proliferation capacity of OE-MSCs was compared at early and late passage numbers; then, the results were validated via RNA sequencing analysis. Subsequently, the efficacy of IN injection of late passage OE-MSC in PD models was evaluated. The results manifested the absence of noticeable differences in proliferation capacity and signaling pathways in OE-MSCs at early and late passage numbers. Moreover, it was found that the IN administration of OE-MSCs with a high passage number substantially increased the levels of DAergic markers and improved the motor function in rat models of PD. Overall, our findings suggested that OE-MSCs with a high passage number are a promising CRT candidate due to their fundamental potential to provide a large number of cells with an enormous proliferation capacity. Moreover, they exhibit the high efficiency of IN administration as a noninvasive route of late-passage OE-MSC delivery for CRT, particularly for PD.

Elucidating the Possible Role of FoxO in Depression

Forkhead box-O (FoxO) transcriptional factors perform essential functions in several physiological and biological processes. Recent studies have shown that FoxO is implicated in the pathophysiology of depression. Changes in the upstream mediators of FoxOs including brain-derived neurotrophic factor (BDNF) and protein kinase B have been associated with depressive disorder and the antidepressant agents are known to alter the phosphorylation of FoxOs. Moreover, FoxOs might be regulated by serotonin or noradrenaline signaling and the hypothalamic-pituitary-adrenal (HPA)-axis,both of them are associated with the development of the depressive disorder. FoxO also regulates neural morphology, synaptogenesis, and neurogenesis in the hippocampus, which accounts for the pathogenesis of the depressive disorder. The current article underlined the potential functions of FoxOs in the etiology of depressive disorder and formulate few essential proposals for further investigation. The review also proposes that FoxO and its signal pathway might establish possible therapeutic mediators for the management of depressive disorder.

Oxidative stress sensing and response in neural stem cell fate

Neural stem/progenitor cells (NSPCs) contribute to the physiological cellular turnover of the adult brain and make up its regenerative potential. It is thus essential to understand how different factors influence their proliferation and differentiation to gain better insight into potential therapeutic targets in neurodegenerative diseases and traumatic brain injuries. Recent evidences indicate the roles of redox stress sensing and coping mechanisms in mediating the balance between NSPC self-renewal and differentiation. Such mechanisms involve direct cysteine modification, signaling and metabolic reprogramming, epigenetic alterations and transcription changes leading to adaptive responses like autophagy. Here, we discuss emerging findings on the involvement of redox sensors and effectors and their mechanisms in influencing changes in cellular redox potential and NSPC fate.

MHC class I H2-Kb negatively regulates neural progenitor cell proliferation by inhibiting FGFR signaling

Proteins of the major histocompatibility complex class I (MHC I), predominantly known for antigen presentation in the immune system, have recently been shown to be necessary for developmental neural refinement and adult synaptic plasticity. However, their roles in nonneuronal cell populations in the brain remain largely unexplored. Here, we identify classical MHC I molecule H2-Kb as a negative regulator of proliferation in neural stem and progenitor cells (NSPCs). Using genetic knockout mouse models and in vivo viral-mediated RNA interference (RNAi) and overexpression, we delineate a role for H2-Kb in negatively regulating NSPC proliferation and adult hippocampal neurogenesis. Transcriptomic analysis of H2-Kb knockout NSPCs, in combination with in vitro RNAi, overexpression, and pharmacological approaches, further revealed that H2-Kb inhibits cell proliferation by dampening signaling pathways downstream of fibroblast growth factor receptor 1 (Fgfr1). These findings identify H2-Kb as a critical regulator of cell proliferation through the modulation of growth factor signaling.

Foxo1 selectively regulates static mechanical pain by interacting with Nav1.7

ABSTRACT

Mechanical allodynia is a debilitating condition for millions of patients with chronic pain. Mechanical allodynia can manifest in distinct forms, including brush-evoked dynamic and filament-evoked static allodynia. In the nervous system, the forkhead protein Foxo1 plays a critical role in neuronal structures and functions. However, the role of Foxo1 in the somatosensory signal remains unclear. Here, we found that Foxo1 selectively regulated static mechanical pain. Foxo1 knockdown decreased sensitivity to static mechanical stimuli in normal rats and attenuated static mechanical allodynia in rat models for neuropathic, inflammatory, and chemotherapy pain. Conversely, Foxo1 overexpression selectively enhanced sensitivity to static mechanical stimuli and provoked static mechanical allodynia. Furthermore, Foxo1 interacted with voltage-gated sodium Nav1.7 channels and increased the Nav1.7 current density by accelerating activation rather than by changing the expression of Nav1.7 in dorsal root ganglia neurons. In addition, the serum level of Foxo1 was found to be increased in chronic pain patients and to be positively correlated with the severity of chronic pain. Altogether, our findings suggest that serum Foxo1 level could be used as a biological marker for prediction and diagnosis of chronic pain. Moreover, selective blockade of Foxo1/Nav1.7 interaction may offer a new therapeutic approach in patients with mechanical pain.

Mitochondria as Signaling Organelles Control Mammalian Stem Cell Fate

Recent evidence supports the notion that mitochondrial metabolism is necessary for the determination of stem cell fate. Historically, mitochondrial metabolism is linked to the production of ATP and tricarboxylic acid (TCA) cycle metabolites to support stem cell survival and growth, respectively. However, it is now clear that beyond these canonical roles, mitochondria as signaling organelles dictate stem cell fate and function. In this review, we focus on key conceptual ideas on how mitochondria control mammalian stem cell fate and function through reactive oxygen species (ROS) generation, TCA cycle metabolite production, NAD⁺/NADH ratio regulation, pyruvate metabolism, and mitochondrial dynamics.

Methamphetamine Enhances HIV-Induced Aberrant Proliferation of Neural Progenitor Cells via the FOXO3-Mediated Mechanism

Maintaining an intact pool of neural progenitor cells (NPCs) is crucial for generating new and functionally active neurons. Methamphetamine (METH) can exacerbate the HIV-induced deficit of adult neurogenesis; however, potential mechanisms of this influence are still poorly understood. In the present study, we present evidence that chronic exposure to METH combined with brain infection by EcoHIV results in enhanced proliferation of NPCs in the subventricular zone (SVZ) in mice. This effect was long-lasting as it was preserved ex vivo in NPCs isolated from the exposed mice over several passages in the absence of additional treatments. Increased proliferation in response to METH plus HIV was associated with dysregulation of cyclin B1 and cyclin D. Transcriptomic studies indicated that 27 out of the top 30 differentially expressed genes in response to METH plus EcoHIV were targets of the forkhead box O transcriptional factor (FOXO) and primarily FOXO3. Additional ex vivo studies and in vitro experiments using human NPCs exposed to METH and infected with HIV revealed upregulation of the CXCL12-CXCR4 axis, leading to activation of downstream pAkt and pErk, the pathways that can phosphorylate FOXO3 and force its exports from the nuclei into the cytoplasm. Indeed, nuclear expulsion of FOXO3 was demonstrated both in mice exposed to METH and infected with EcoHIV and in cell cultures of human NPCs. These results provide novel information that exposure to METH combined with HIV infection can induce aberrant proliferation of SVZ-derived NPCs and identifies CXCL12-CXCR4-Akt-1-mediated phosphorylation of FOXO3 as the mechanism responsible for this effect.

Regulation of Adult Mammalian Neural Stem Cells and Neurogenesis by Cell Extrinsic and Intrinsic Factors

Tissue-specific stem cells give rise to new functional cells to maintain tissue homeostasis and restore damaged tissue after injury. To ensure proper brain functions in the adult brain, neural stem cells (NSCs) continuously generate newborn neurons that integrate into pre-existing neuronal networks. Proliferation, as well as neurogenesis of NSCs, are exquisitely controlled by extrinsic and intrinsic factors, and their underlying mechanisms have been extensively studied with the goal of enhancing the neurogenic capacity of NSCs for regenerative medicine. However, neurogenesis of endogenous NSCs alone is insufficient to completely repair brains damaged by neurodegenerative diseases and/or injury because neurogenic areas are limited and few neurons are produced in the adult brain. An innovative approach towards replacing damaged neurons is to induce conversion of non-neuronal cells residing in injured sites into neurons by a process referred to as direct reprogramming. This review describes extrinsic and intrinsic factors controlling NSCs and neurogenesis in the adult brain and discusses prospects for their applications. It also describes direct neuronal reprogramming technology holding promise for future clinical applications.

Metabolic Regulation of Stem Cells and Differentiation: A Forkhead Box O Transcription Factor Perspective

Significance: Stem cell activation and differentiation occur along changes in cellular metabolism. Metabolic transitions translate into changes in redox balance, cell signaling, and epigenetics, thereby regulating these processes. Metabolic transitions are key regulators of cell fate and exemplify the moonlighting nature of many metabolic enzymes and their associated metabolites. Recent Advances: Forkhead box O transcription factors (FOXOs) are bona fide regulators of cellular homeostasis. FOXOs are multitasking proteins able to regulate cell cycle, cellular metabolism, and redox state. Recent and ongoing research poses FOXOs as key factors in stem cell maintenance and differentiation in several tissues. Critical Issues: The multitasking nature of FOXOs and their tissue-specific expression patterns hinders to disclose a possible conserved mechanism of regulation of stem cell maintenance and differentiation. Moreover, cellular metabolism, cell signaling, and epigenetics establish complex regulatory interactions, which challenge the establishment of the causal/temporal nature of metabolic changes and stem cell activation and differentiation. Future Directions: The development of single-cell technologies and in vitro models able to reproduce the dynamics of stem cell differentiation are actively contributing to define the role of metabolism in this process. This knowledge is key to understanding and designing therapies for those pathologies where the balance between proliferation and differentiation is lost. Importantly, metabolic interventions could be applied to optimize stem cell cultures meant for therapeutical applications, such as transplantations, to treat autoimmune and degenerative disorders. Antioxid. Redox Signal. 34, 1004-1024.

G-quadruplex regulation of neural gene expression

G-quadruplexes are four-stranded helical nucleic acid structures characterized by stacked tetrads of guanosine bases. These structures are widespread throughout mammalian genomic DNA and RNA transcriptomes, and prevalent across all tissues. The role of G-quadruplexes in cancer is well-established, but there has been a growing exploration of these structures in the development and homeostasis of normal tissue. In this review, we focus on the roles of G-quadruplexes in directing gene expression in the nervous system, including the regulation of gene transcription, mRNA processing, and trafficking, as well as protein translation. The role of G-quadruplexes and their molecular interactions in the pathology of neurological diseases is also examined. Outside of cancer, there has been only limited exploration of G-quadruplexes as potential intervention targets to treat disease or injury. We discuss studies that have used small-molecule ligands to manipulate G-quadruplex stability in order to treat disease or direct neural stem/progenitor cell proliferation and differentiation into therapeutically relevant cell types. Understanding the many roles that G-quadruplexes have in the nervous system not only provides critical insight into fundamental molecular mechanisms that control neurological function, but also provides opportunities to identify novel therapeutic targets to treat injury and disease.

Gene Regulation and Cellular Metabolism: An Essential Partnership

It is recognized that cell metabolism is tightly connected to other cellular processes such as regulation of gene expression. Metabolic pathways not only provide the precursor molecules necessary for gene expression, but they also provide ATP, the primary fuel driving gene expression. However, metabolic conditions are highly variable since nutrient uptake is not a uniform process. Thus, cells must continually calibrate gene expression to their changing metabolite and energy budgets. This review discusses recent advances in understanding the molecular and biophysical mechanisms that connect metabolism and gene regulation as cells navigate their growth, proliferation, and differentiation. Particular focus is given to these mechanisms in the context of organismal development.

Mitochondrial and Autophagic Regulation of Adult Neurogenesis in the Healthy and Diseased Brain

Adult neurogenesis is a highly regulated process during which new neurons are generated from neural stem cells in two discrete regions of the adult brain: the subventricular zone of the lateral ventricle and the subgranular zone of the dentate gyrus in the hippocampus. Defects of adult hippocampal neurogenesis have been linked to cognitive decline and dysfunction during natural aging and in neurodegenerative diseases, as well as psychological stress-induced mood disorders. Understanding the mechanisms and pathways that regulate adult neurogenesis is crucial to improving preventative measures and therapies for these conditions. Accumulating evidence shows that mitochondria directly regulate various steps and phases of adult neurogenesis. This review summarizes recent findings on how mitochondrial metabolism, dynamics, and reactive oxygen species control several aspects of adult neural stem cell function and their differentiation to newborn neurons. It also discusses the importance of autophagy for adult neurogenesis, and how mitochondrial and autophagic dysfunction may contribute to cognitive defects and stress-induced mood disorders by compromising adult neurogenesis. Finally, I suggest possible ways to target mitochondrial function as a strategy for stem cell-based interventions and treatments for cognitive and mood disorders.

FOXO3 Regulates Sevoflurane-Induced Neural Stem Cell Differentiation in Fetal Rats

With the increase in fetal surgeries, the effect of maternal anesthesia on progeny has attracted much attention. Our previous studies have demonstrated that 3.5% sevoflurane maternal exposure resulted in over-activated autophagy and cognitive impairment in the offspring. The autophagy activation resulted in increased apoptosis and decreased proliferation. However, the effects of sevoflurane on neural stem cell (NSC) differentiation is unclear. There is evidence that autophagy might participate in anesthesia-induced NSC differentiation. Firstly, we examined the effects of sevoflurane on NSC differentiation and explored possible mechanisms. Then, we investigated whether autophagy was related to differentiation. On gestational day 14 (G14), rats were exposed to 2% or 3.5% sevoflurane for 2 h, then markers of neurons and astrocytes, and the FOXO3 expression was measured in fetal brains 48 h later. The differentiation of NSCs was detected after autophagy inhibition by 3-MA. Changes in NSC differentiation, autophagy level, and FOXO3 were examined after administration of lithium chloride. After 3.5% sevoflurane exposure, the expressions of β-Tubulin III, NeuN, SYP, GFAP and FOXO3 increased. Autophagy inhibition alleviates improper NSC differentiation. Lithium chloride attenuated FOXO3 and autophagy activation, ameliorated NSC differentiation and the decline of Nestin expression. Our results demonstrated that maternal exposure to 3.5% sevoflurane for 2 h during the mid-trimester induced NSC differentiation in the fetal brain through the activation of FOXO3. Autophagy inhibitor or lithium chloride reversed the improper differentiation of NSCs.

Single-cell analyses reveal YAP/TAZ as regulators of stemness and cell plasticity in Glioblastoma

Glioblastoma (GBM) is a devastating human malignancy. GBM stem-like cells (GSCs) drive tumor initiation and progression. Yet, the molecular determinants defining GSCs in their native state in patients remain poorly understood. Here we used single cell datasets and identified GSCs at the apex of the differentiation hierarchy of GBM. By reconstructing the GSCs' regulatory network, we identified the YAP/TAZ coactivators as master regulators of this cell state, irrespectively of GBM subtypes. YAP/TAZ are required to install GSC properties in primary cells downstream of multiple oncogenic lesions, and required for tumor initiation and maintenance in vivo in different mouse and human GBM models. YAP/TAZ act as main roadblock of GSC differentiation and their inhibition irreversibly lock differentiated GBM cells into a non-tumorigenic state, preventing plasticity and regeneration of GSC-like cells. Thus, GSC identity is linked to a key molecular hub integrating genetics and microenvironmental inputs within the multifaceted biology of GBM.

Cellular stress signaling activates type-I IFN response through FOXO3-regulated lamin posttranslational modification

Neural stem/progenitor cells (NSPCs) persist over the lifespan while encountering constant challenges from age or injury related brain environmental changes like elevated oxidative stress. But how oxidative stress regulates NSPC and its neurogenic differentiation is less clear. Here we report that acutely elevated cellular oxidative stress in NSPCs modulates neurogenic differentiation through induction of Forkhead box protein O3 (FOXO3)-mediated cGAS/STING and type I interferon (IFN-I) responses. We show that oxidative stress activates FOXO3 and its transcriptional target glycine-N-methyltransferase (GNMT) whose upregulation triggers depletion of s-adenosylmethionine (SAM), a key co-substrate involved in methyl group transfer reactions. Mechanistically, we demonstrate that reduced intracellular SAM availability disrupts carboxymethylation and maturation of nuclear lamin, which induce cytosolic release of chromatin fragments and subsequent activation of the cGAS/STING-IFN-I cascade to suppress neurogenic differentiation. Together, our findings suggest the FOXO3-GNMT/SAM-lamin-cGAS/STING-IFN-I signaling cascade as a critical stress response program that regulates long-term regenerative potential.

Neural stem and progenitor cells (NSPCs) encounter constant stresses during aging, such as elevated oxidative stress. Here the authors show that oxidative stress induced reduction in NSPC neural differentiation is mediated by a FOXO3-GNMT/SAM-lamin-cGAS/STING-IFN-I signalling cascade initiated by FOXO3 oxidation.

FOXO Regulates Neuromuscular Junction Homeostasis During Drosophila Aging

The transcription factor foxo is a known regulator of lifespan extension and tissue homeostasis. It has been linked to the maintenance of neuronal processes across many species and has been shown to promote youthful characteristics by regulating cytoskeletal flexibility and synaptic plasticity at the neuromuscular junction (NMJ). However, the role of foxo in aging neuromuscular junction function has yet to be determined. We profiled adult Drosophila foxo- null mutant abdominal ventral longitudinal muscles and found that young mutants exhibited morphological profiles similar to those of aged wild-type flies, such as larger bouton areas and shorter terminal branches. We also observed changes to the axonal cytoskeleton and an accumulation of late endosomes in foxo null mutants and motor neuron-specific foxo knockdown flies, similar to those of aged wild-types. Motor neuron-specific overexpression of foxo can delay age-dependent changes to NMJ morphology, suggesting foxo is responsible for maintaining NMJ integrity during aging. Through genetic screening, we identify several downstream factors mediated through foxo-regulated NMJ homeostasis, including genes involved in the MAPK pathway. Interestingly, the phosphorylation of p38 was increased in the motor neuron-specific foxo knockdown flies, suggesting foxo acts as a suppressor of p38/MAPK activation. Our work reveals that foxo is a key regulator for NMJ homeostasis, and it may maintain NMJ integrity by repressing MAPK signaling.

An NRF2 Perspective on Stem Cells and Ageing

Redox and metabolic mechanisms lie at the heart of stem cell survival and regenerative activity. NRF2 is a major transcriptional controller of cellular redox and metabolic homeostasis, which has also been implicated in ageing and lifespan regulation. However, NRF2's role in stem cells and their functioning with age is only just emerging. Here, focusing mainly on neural stem cells, which are core to adult brain plasticity and function, we review recent findings that identify NRF2 as a fundamental player in stem cell biology and ageing. We also discuss NRF2-based molecular programs that may govern stem cell state and function with age, and implications of this for age-related pathologies.

Pax3 inhibits Neuro-2a cells proliferation and neurite outgrowth

Pax3 and Pax7 are closely related transcription factors that are widely expressed in the developing nervous system and somites. During the normal development in the central nervous system (CNS), Pax3 and Pax7 are mainly expressed in the dorsal part of the neural tube. Further analysis revealed that Pax3 and Pax7 shared redundant functions in the spinal cord development. However, it is still unknown whether Pax3 and Pax7 play a role in neuronal differentiation. In this study, Pax3 and Pax7 genes were overexpressed in Neuro‐2a, the mouse neuroblastoma cell line. CCK‐8 and EdU assay results showed that overexpression of Pax3 inhibited cell viability and proliferation of Neuro‐2a cells, whereas the overexpression of Pax7 had no significant difference on their cell viability and proliferation. Overexpression of Pax3 not only increased the percentage of cells in the S phase and G0/G1 phase, but also decreased that in the G2 phase. Moreover, the total neurite lengths of Neuro‐2a cells were significantly shorter in Pax3 overexpressed group than those in negative control group and showed no significant difference between Pax7 overexpressed group and negative control group. These results suggested that Pax3 not only inhibited the cell viability and proliferation but also affected the cell cycle and the neurite outgrowth of Neuro‐2a cells. RNA sequencing analysis showed up‐regulated genes in Pax3 overexpressed group were involved in cell cycle machinery, which may reveal the potential mechanism of Neuro‐2a cells proliferation.

p53 upregulated mediator of apoptosis (Puma) deficiency increases survival of adult neural stem cells generated physiologically in the hippocampus, but does not protect stem cells generated in surplus after an excitotoxic lesion

OBJECTIVES

Neurogenesis occurs in the mammalian brain throughout adulthood and increases in response to metabolic, toxic or traumatic insults. To remove potentially superfluous or unwanted neural stem cells/neuronal progenitors, their rate of proliferation and differentiation is fine-tuned against their rate of apoptosis. Apoptosis requires the transcriptional and posttranslational activation of Bcl-2-homolgy domain 3 (BH3)-only proteins. Previously, we demonstrated that the BH3-only protein p53-upregulated mediator of apoptosis (Puma) controls the physiological rate of apoptosis of neural precursor cells in the adult mouse hippocampus. Puma's role in controlling a lesion-induced increase in neural stem cells is currently not known.

METHODS

We employed a model of local, N-methyl-D-asparte (NMDA)-induced excitotoxic injury to the CA1 hippocampal subfield and immunofluorescence labelling to produce increased neural stem cell proliferation/ neurogenesis in the dentate gyrus at two survival times following the excitotoxic lesion.

RESULTS

Deletion of puma failed to rescue any NMDA-induced increase in adult born cells as assessed by BrdU or Doublecortin labelling in the long-term. No difference in the proportion of BrdU/NeuN-positive cells comparing the different genotypes and treatments suggested that the phenotypic fate of the cells was preserved regardless of the genotype and the treatment.

CONCLUSIONS

While neurogenesis is up-regulated in puma-deficient animals following NMDA-induced excitotoxicity to the hippocampal CA1 subfield, puma deficiency could not protect this surplus of newly generated cells from apoptotic cell death.

Mitochondria Define Intestinal Stem Cell Differentiation Downstream of a FOXO/Notch Axis

Differential WNT and Notch signaling regulates differentiation of Lgr5⁺ crypt-based columnar cells (CBCs) into intestinal cell lineages. Recently we showed that mitochondrial activity supports CBCs, while adjacent Paneth cells (PCs) show reduced mitochondrial activity. This implies that CBC differentiation into PCs involves a metabolic transition toward downregulation of mitochondrial dependency. Here we show that Forkhead box O (FoxO) transcription factors and Notch signaling interact in determining CBC fate. In agreement with the organoid data, Foxo1/3/4 deletion in mouse intestine induces secretory cell differentiation. Importantly, we show that FOXO and Notch signaling converge on regulation of mitochondrial fission, which in turn provokes stem cell differentiation into goblet cells and PCs. Finally, scRNA-seq-based reconstruction of CBC differentiation trajectories supports the role of FOXO, Notch, and mitochondria in secretory differentiation. Together, this points at a new signaling-metabolic axis in CBC differentiation and highlights the importance of mitochondria in determining stem cell fate.

Lysosomes and signaling pathways for maintenance of quiescence in adult neural stem cells

Quiescence is a cellular strategy for maintaining somatic stem cells in a specific niche in a low metabolic state without senescence for a long period of time. During development, neural stem cells (NSCs) actively proliferate and self-renew, and their progeny differentiate into both neurons and glial cells to form mature brain tissues. On the other hand, most NSCs in the adult brain are quiescent and arrested in G0/G1 phase of the cell cycle. Quiescence is essential in order to avoid the precocious exhaustion of NSCs, ensuring a sustainable source of available stem cells in the brain throughout the lifespan. After receiving activation signals, quiescent NSCs reenter the cell cycle and generate new neurons. This switching between quiescence and proliferation is tightly regulated by diverse signaling pathways. Recent studies suggest significant involvement of cellular proteostasis (homeostasis of the proteome) in the quiescent state of NSCs. Proteostasis is the result of integrated regulation of protein synthesis, folding, and degradation. In this review, we discuss regulation of quiescence by multiple signaling pathways, especially bone morphogenetic protein and Notch signaling, and focus on the functional involvement of the lysosome, an organelle governing cellular degradation, in quiescence of adult NSCs.

Autophagy in Neuronal Development and Plasticity

Autophagy is a highly conserved intracellular clearance pathway in which cytoplasmic contents are trafficked to the lysosome for degradation. Within neurons, it helps to remove damaged organelles and misfolded or aggregated proteins and has therefore been the subject of intense research in relation to neurodegenerative disease. However, far less is understood about the role of autophagy in other aspects of neuronal physiology. Here we review the literature on the role of autophagy in maintaining neuronal stem cells and in neuronal plasticity in adult life and we discuss how these contribute to structural and functional deficits observed in a range of human disorders.

Mechanisms of enhanced quiescence in neural stem cell aging

The maintenance of neural stem cell function is vital to ensure neurogenesis throughout adulthood. During aging, there is a significant reduction in adult neurogenesis that correlates with a decline in cognitive function. Although recent studies have revealed novel extrinsic and intrinsic mechanisms that regulate the adult neural stem cell (NSC) pool and lineage progression, the precise molecular mechanisms that drive dysregulation of adult neurogenesis in the context of aging are only beginning to emerge. Recent studies have shed light on mechanisms that regulate the earliest step of adult neurogenesis, the activation of quiescent NSCs. Interestingly, the ability of NSCs to enter the cell cycle in the aged brain significantly declines suggesting a deepend state of quiescence. Given the likely contribution of adult neurogenesis to supporting cognitive function in humans, enhancing neurogenesis may be a strategy to combat age-related cognitive decline. This review highlights the mechanisms that regulate the NSC pool throughout adulthood and discusses how dysregulation of these processes may contribute to the decline in neurogenesis and cognitive function throughout aging.

Stem Cells of the Aging Brain

The adult central nervous system (CNS) contains resident stem cells within specific niches that maintain a self-renewal and proliferative capacity to generate new neurons, astrocytes, and oligodendrocytes throughout adulthood. Physiological aging is associated with a progressive loss of function and a decline in the self-renewal and regenerative capacities of CNS stem cells. Also, the biggest risk factor for neurodegenerative diseases is age, and current in vivo and in vitro models of neurodegenerative diseases rarely consider this. Therefore, combining both aging research and appropriate interrogation of animal disease models towards the understanding of the disease and age-related stem cell failure is imperative to the discovery of new therapies. This review article will highlight the main intrinsic and extrinsic regulators of neural stem cell (NSC) aging and discuss how these factors impact normal homeostatic functions within the adult brain. We will consider established in vivo animal and in vitro human disease model systems, and then discuss the current and future trajectories of novel senotherapeutics that target aging NSCs to ameliorate brain disease.

Amyloid precursor protein intracellular domain-dependent regulation of FOXO3a inhibits adult hippocampal neurogenesis

The amyloid precursor protein (APP) intracellular domain (AICD) is a metabolic by-product of APP produced through sequential proteolytic cleavage by α-, β-, and γ-secretases. The interaction between AICD and Fe65 has been reported to impair adult neurogenesis in vivo. However, the exact role of AICD in mediating neural stem cell fate remains unclear. To identify the role of AICD in neuronal proliferation and differentiation, as well as to clarify the molecular mechanisms underlying the role of AICD in neurogenesis, we first generated a mouse model expressing the Rosa26-based AICD transgene. AICD overexpression did not alter the spatiotemporal expression pattern of full-length APP or accumulation of its metabolites. In addition, AICD decreased the newly generated neural progenitor cell (NPC) pool, inhibited the proliferation and differentiation efficiency of NPCs, and increased cell death both in vitro and in vivo. Given that abnormal neurogenesis is often associated with depression-like behavior in adult mice, we conducted a forced swim test and tail suspension test with AICD mice and found a depression-like behavioral phenotype in AICD transgenic mice. Moreover, AICD stimulated FOXO3a transcriptional activation, which in turn negatively regulated AICD. In addition, functional loss of FOXO3a in NPCs derived from the hippocampal dentate gyrus of adult AICD transgenic mice rescued neurogenesis defects. AICD also increased the mRNA expression of FOXO3a target genes related to neurogenesis and cell death. These results suggest that FOXO3a is the functional target of AICD in neurogenesis regulation. Our study reveals the role of AICD in mediating neural stem cell fate to maintain homeostasis during brain development via interaction with FOXO3a.

Aging and Rejuvenation of Neural Stem Cells and Their Niches

Aging has a profound and devastating effect on the brain. Old age is accompanied by declining cognitive function and enhanced risk of brain diseases, including cancer and neurodegenerative disorders. A key question is whether cells with regenerative potential contribute to brain health and even brain "rejuvenation." This review discusses mechanisms that regulate neural stem cells (NSCs) during aging, focusing on the effect of metabolism, genetic regulation, and the surrounding niche. We also explore emerging rejuvenating strategies for old NSCs. Finally, we consider how new technologies may help harness NSCs' potential to restore healthy brain function during physiological and pathological aging.

Aberrant ASPM expression mediated by transcriptional regulation of FoxM1 promotes the progression of gliomas

Gliomas are the most common form of malignant tumour in the central nervous system. However, the molecular mechanism of the tumorigenesis and progression of gliomas remains unclear. In this study, we used the GEO database to identify genes differentially expressed in gliomas and predict the prognosis of glioma. We observed that ASPM mRNA was increased obviously in glioma tissue, and higher ASPM mRNA expression predicted worse disease prognosis. ASPM was highly expressed in glioma cell lines U87‐MG and U251, and knockdown of ASPM expression in these cells significantly repressed the proliferation, migration and invasion ability and induced G0/G1 phase arrest. In addition, down‐regulation of ASPM suppressed the growth of glioma in nude mice. Five potential binding sites for transcription factor FoxM1 were predicted in the ASPM promoter. FoxM1 overexpression significantly increased the expression of ASPM and promoted the proliferation and migration of glioma cells, which was abolished by ASPM ablation. ChIP and dual‐luciferase reporter analysis confirmed that FoxM1 bound to the ASPM promoter at −236 to ‐230 bp and −1354 to ‐1348 bp and activated the transcription of ASPM directly. Collectively, our results demonstrated for the first time that aberrant ASPM expression mediated by transcriptional regulation of FoxM1 promotes the malignant properties of glioma cells.

Conserved and Divergent Features of Adult Neurogenesis in Zebrafish

Adult neurogenesis, i.e., the generation of neurons from neural stem cells (NSCs) in the adult brain, contributes to brain plasticity in all vertebrates. It varies, however, greatly in extent, location and physiological characteristics between species. During the last decade, the teleost zebrafish (D. rerio) was increasingly used to study the molecular and cellular properties of adult NSCs, in particular as a prominent NSC population was discovered at the ventricular surface of the dorsal telencephalon (pallium), in territories homologous to the adult neurogenic niches of rodents. This model, for its specific features (large NSC population, amenability to intravital imaging, high regenerative capacity) allowed rapid progress in the characterization of basic adult NSC features. We review here these findings, with specific comparisons with the situation in rodents. We specifically discuss the cellular nature of NSCs (astroglial or neuroepithelial cells), their heterogeneities and their neurogenic lineages, and the mechanisms controlling NSC quiescence and fate choices, which all impact the neurogenic output. We further discuss the regulation of NSC activity in response to physiological triggers and non-physiological conditions such as regenerative contexts.

Low FoxO expression in Drosophila somatosensory neurons protects dendrite growth under nutrient restriction

During prolonged nutrient restriction, developing animals redistribute vital nutrients to favor brain growth at the expense of other organs. In Drosophila, such brain sparing relies on a glia-derived growth factor to sustain proliferation of neural stem cells. However, whether other aspects of neural development are also spared under nutrient restriction is unknown. Here we show that dynamically growing somatosensory neurons in the Drosophila peripheral nervous system exhibit organ sparing at the level of arbor growth: Under nutrient stress, sensory dendrites preferentially grow as compared to neighboring non-neural tissues, resulting in dendrite overgrowth. These neurons express lower levels of the stress sensor FoxO than neighboring epidermal cells, and hence exhibit no marked induction of autophagy and a milder suppression of Tor signaling under nutrient stress. Preferential dendrite growth allows for heightened animal responses to sensory stimuli, indicative of a potential survival advantage under environmental challenges.

Quadrella incana (Capparaceae) Leaf Extract Enhances Proliferation and Maintenance of Neural Stem/Progenitor Cells through Upregulating Glycolytic Flux and Redox Potential

Neural stem/progenitor cells (NSPCs) are self-renewing, multipotent cells located in the embryonic and adult central nervous system (CNS). Extensive preclinical and clinical studies have shed light on the potential of stem cell replacement therapy for various neurodegenerative diseases. The key prerequisite for the success of these clinical applications is the procurement of a sufficient number of high-quality NSPCs. In this study, we explored the biological activity of Quadrella incana leaf in NSPC homeostasis. We showed that the leaf extract of Quadrella incana upregulated NSPC marker and proliferative potential. On the other hand, Quadrella incana leaf suppressed spontaneous unintended NSPC differentiation. Mechanistically, Quadrella incana leaf contributed to the maintenance of NSPCs by upregulating glycolytic flux and redox potential.

Metabolic Regulation and Related Molecular Mechanisms in Various Stem Cell Functions

Recent studies on the mechanisms that link metabolic changes with stem cell fate have deepened our understanding of how specific metabolic pathways can regulate various stem cell functions during the development of an organism. Although it was originally thought to be merely a consequence of the specific cell state, metabolism is currently known to play a critical role in regulating the self-renewal capacity, differentiation potential, and quiescence of stem cells. Many studies in recent years have revealed that metabolic pathways regulate various stem cell behaviors (e.g., selfrenewal, migration, and differentiation) by modulating energy production through glycolysis or oxidative phosphorylation and by regulating the generation of metabolites, which can modulate multiple signaling pathways. Therefore, a more comprehensive understanding of stem cell metabolism could allow us to establish optimal culture conditions and differentiation methods that would increase stem cell expansion and function for cell-based therapies. However, little is known about how metabolic pathways regulate various stem cell functions. In this context, we review the current advances in metabolic research that have revealed functional roles for mitochondrial oxidative phosphorylation, anaerobic glycolysis, and oxidative stress during the self-renewal, differentiation and aging of various adult stem cell types. These approaches could provide novel strategies for the development of metabolic or pharmacological therapies to promote the regenerative potential of stem cells and subsequently promote their therapeutic utility.

Waking up quiescent neural stem cells: Molecular mechanisms and implications in neurodevelopmental disorders

Neural stem cells (NSCs) are crucial for development, regeneration, and repair of the nervous system. Most NSCs in mammalian adult brains are quiescent, but in response to extrinsic stimuli, they can exit from quiescence and become reactivated to give rise to new neurons. The delicate balance between NSC quiescence and activation is important for adult neurogenesis and NSC maintenance. However, how NSCs transit between quiescence and activation remains largely elusive. Here, we discuss our current understanding of the molecular mechanisms underlying the reactivation of quiescent NSCs. We review recent advances on signaling pathways originated from the NSC niche and their crosstalk in regulating NSC reactivation. We also highlight new intrinsic paradigms that control NSC reactivation in Drosophila and mammalian systems. We also discuss emerging evidence on modeling human neurodevelopmental disorders using NSCs.

Evaluation of ASPM and TEF Gene Expressions as Potential Biomarkers for Bladder Cancer

Bladder cancer is one of the most predominant tumors of the genitourinary tract. In addition to pathological findings, the molecular modifications that might affect tumorigenesis and tumor outcome should be considered when treating bladder cancer. Accordingly, we aimed to investigate the expression levels of both the ASPM and TEF genes in bladder cancer tissues and their value in disease prognosis. The expression levels of the ASPM and TEF genes were analyzed by quantitative real-time PCR (qRT-PCR) in 90 bladder cancer tissue specimens and 90 specimens of normal urinary bladder tissue taken away from the tumor site. The upregulation of ASPM expression and the downregulation of TEF expression were observed in bladder cancer tissues compared to adjacent normal tissues, and these levels were correlated with high-grade tumors, advanced stage disease and the presence of metastasis. Both genes had the ability to predict metastatic association with sensitivity (84.62%) and specificity (68.42%; *P < 0.001) for the ASPM gene and for the TEF gene with sensitivity (80.77%) and specificity (78.95%; *P < 0.001). Additionally, Kaplan-Meier survival analysis indicated that elevated ASPM expression levels and reduced TEF expression levels significantly correlated with decreased overall survival and progression-free survival. The current analysis concludes that ASPM and TEF expressions might be used as potential biomarkers in bladder cancer patients.

Interaction Between Neurogenic Stimuli and the Gene Network Controlling the Activation of Stem Cells of the Adult Neurogenic Niches, in Physiological and Pathological Conditions

In the adult mammalian brain new neurons are continuously generated throughout life in two niches, the dentate gyrus of the hippocampus and the subventricular zone. This process, called adult neurogenesis, starts from stem cells, which are activated and enter the cell cycle. The proliferative capability of stem cells progressively decreases during aging. The population of stem cells is generally quiescent, and it is not clear whether the potential for stem cells to expand is limited, or whether they can expand and then return to quiescence, remaining available for further activation. Certain conditions may deregulate stem cells quiescence and self-renewal. In fact we discuss the possibility of activation of stem cells by neurogenic stimuli as a function of the intensity of the stimulus (i.e., whether this is physiological or pathological), and of the deregulation of the system (i.e., whether the model is aged or carrying genetic mutations in the gene network controlling quiescence). It appears that when the system is aged and/or carrying mutations of quiescence-maintaining genes, preservation of the quiescent state of stem cells is more critical and stem cells can be activated by a neurogenic stimulus which is ineffective in normal conditions. Moreover, when a neurogenic stimulus is in itself a cause of brain damage (e.g., kainic acid treatment) the activation of stem cells occurs bypassing any inhibitory control. Plausibly, with strong neurogenic stimuli, such as kainic acid injected into the dentate gyrus, the self-renewal capacity of stem cells may undergo rapid exhaustion. However, the self-renewal capability of stem cells persists when normal stimuli are elicited in the presence of a mutation of one of the quiescence-maintaining genes, such as p16Ink4a, p21Cip1 or Btg1. In this case, stem cells become promptly activated by a neurogenic stimulus even during aging. This indicates that stem cells retain a high proliferative capability and plasticity, and suggests that stem cells are protected against the response to stimulus and are resilient to exhaustion. It will be interesting to assess at which functional degree of deregulation of the quiescence-maintaining system, stem cells will remain responsive to repeated neurogenic stimuli without undergoing exhaustion of their pool.

Lifestyle mediates the role of nutrient-sensing pathways in cognitive aging: cellular and epidemiological evidence

Aging induces cellular and molecular changes including modification of stem cell pools. In particular, alterations in aging neural stem cells (NSCs) are linked to age-related cognitive decline which can be modulated by lifestyle. Nutrient-sensing pathways provide a molecular basis for the link between lifestyle and cognitive decline. Adopting a back-translation strategy using stem cell biology to inform epidemiological analyses, here we show associations between cellular readouts of NSC maintenance and expression levels of nutrient-sensing genes following NSC exposure to aging human serum as well as morphological and gene expression alterations following repeated passaging. Epidemiological analyses on the identified genes showed associations between polymorphisms in SIRT1 and ABTB1 and cognitive performance as well as interactions between SIRT1 genotype and physical activity and between GRB10 genotype and adherence to a Mediterranean diet. Our study contributes to the understanding of neural stem cell molecular mechanisms underlying human cognitive aging and hints at lifestyle modifiable factors.