Re-cycling paradigms: cell cycle regulation in adult hippocampal neurogenesis and implications for depression

StressMatic: A Novel Automated System to Induce Depressive- and Anxiety-like Phenotype in Rats

Major depressive disorder (MDD) is a multidimensional psychiatric disorder that is estimated to affect around 350 million people worldwide. Generating valid and effective animal models of depression is critical and has been challenging for neuroscience researchers. For preclinical studies, models based on stress exposure, such as unpredictable chronic mild stress (uCMS), are amongst the most reliable and used, despite presenting concerns related to the standardization of protocols and time consumption for operators. To overcome these issues, we developed an automated system to expose rodents to a standard uCMS protocol. Here, we compared manual (uCMS) and automated (auCMS) stress-exposure protocols. The data shows that the impact of the uCMS exposure by both methods was similar in terms of behavioral (cognition, mood, and anxiety) and physiological (cell proliferation and endocrine variations) measurements. Given the advantages of time and standardization, this automated method represents a step forward in this field of preclinical research.

Melatonin as a Harmonizing Factor of Circadian Rhythms, Neuronal Cell Cycle and Neurogenesis: Additional Arguments for Its Therapeutic Use in Alzheimer's Disease

The synthesis and release of melatonin in the brain harmonize various physiological functions. The apparent decline in melatonin levels with advanced aging is an aperture to the neurodegenerative processes. It has been indicated that down regulation of melatonin leads to alterations of circadian rhythm components, which further causes a desynchronization of several genes and results in an increased susceptibility to develop neurodegenerative diseases. Additionally, as circadian rhythms and memory are intertwined, such rhythmic disturbances influence memory formation and recall. Besides, cell cycle events exhibit a remarkable oscillatory system, which is downstream of the circadian phenomena. The linkage between the molecular machinery of the cell cycle and complex fundamental regulatory proteins emphasizes the conjectural regulatory role of cell cycle components in neurodegenerative disorders such as Alzheimer's disease. Among the mechanisms intervening long before the signs of the disease appear, the disturbances of the circadian cycle, as well as the alteration of the machinery of the cell cycle and impaired neurogenesis, must hold our interest. Therefore, in the present review, we propose to discuss the underlying mechanisms of action of melatonin in regulating the circadian rhythm, cell cycle components and adult neurogenesis in the context of AD pathogenesis with the view that it might further assist to identify new therapeutic targets.

Abnormal Development of Neural Stem Cell Niche in the Dentate Gyrus of Menkes Disease

Background and Objectives

Menkes disease (MNK) is a rare X-linked recessive disease, caused by mutations in the copper transporting ATP7A gene that is required for copper homeostasis. MNK patients experience various clinical symptoms including neurological defects that are closely related to the prognosis of MNK patients. Neural stem cells (NSCs) in the hippocampal dentate gyrus (DG) produce new neurons throughout life, and defects in DG neurogenesis are often correlated with cognitive and behavioral problems. However, neurodevelopmental defects in the DG during postnatal period in MNK have not been understood yet.

Methods and Results

Mottled-brindled (Mo^Br/y) mice (MNK mice) and littermate controls were used in this study. In vivo microCT imaging and immunohistochemistry results demonstrate that blood vasculatures in hippocampus are abnormally decreased in MNK mice. Furthermore, postnatal establishment of NSC population and their neurogenesis are severely compromised in the DG of MNK mice. In addition, in vitro analyses using hippocampal neurosphere culture followed by immunocytochemistry and immunoblotting suggest that neurogenesis from MNK NSCs is also significantly compromised, corresponding to defective neurogenic gene expression in MNK derived neurons.

Conclusions

Our study is the first reports demonstrating that improper expansion of the postnatal NSC population followed by significant reduction of neurogenesis may contribute to neurodevelopmental symptoms in MNK. In conclusion, our results provide new insight into early neurodevelopmental defects in MNK and emphasize the needs for early diagnosis and new therapeutic strategies in the postnatal central nerve system damage of MNK patients.

Beyond New Neurons in the Adult Hippocampus: Imipramine Acts as a Pro-Astrogliogenic Factor and Rescues Cognitive Impairments Induced by Stress Exposure

Depression is a prevalent, socially burdensome disease. Different studies have demonstrated the important role of astrocytes in the pathophysiology of depression as modulators of neurotransmission and neurovascular coupling. This is evidenced by astrocyte impairments observed in brains of depressed patients and the appearance of depressive-like behaviors upon astrocytic dysfunctions in animal models. However, little is known about the importance of de novo generated astrocytes in the mammalian brain and in particular its possible involvement in the precipitation of depression and in the therapeutic actions of current antidepressants (ADs). Therefore, we studied the modulation of astrocytes and adult astrogliogenesis in the hippocampal dentate gyrus (DG) of rats exposed to an unpredictable chronic mild stress (uCMS) protocol, untreated and treated for two weeks with antidepressants—fluoxetine and imipramine. Our results show that adult astrogliogenesis in the DG is modulated by stress and imipramine. This study reveals that distinct classes of ADs impact differently in the astrogliogenic process, showing different cellular mechanisms relevant to the recovery from behavioral deficits induced by chronic stress exposure. As such, in addition to those resident, the newborn astrocytes in the hippocampal DG might also be promising therapeutic targets for future therapies in the neuropsychiatric field.

Hippocampal BMP signaling as a common pathway for antidepressant action

The benefits of current treatments for depression are limited by low response rates, delayed therapeutic effects, and multiple side effects. Antidepressants affect a variety of neurotransmitter systems in different areas of the brain, and the mechanisms underlying their convergent effects on behavior have been unclear. Here we identify hippocampal bone morphogenetic protein (BMP) signaling as a common downstream pathway that mediates the behavioral effects of five different antidepressant classes (fluoxetine, bupropion, duloxetine, vilazodone, trazodone) and of electroconvulsive therapy. All of these therapies decrease BMP signaling and enhance neurogenesis in the hippocampus. Preventing the decrease in BMP signaling blocks the effect of antidepressant treatment on behavioral phenotypes. Further, inhibition of BMP signaling in hippocampal newborn neurons is sufficient to produce an antidepressant effect, while chemogenetic silencing of newborn neurons prevents the antidepressant effect. Thus, inhibition of hippocampal BMP signaling is both necessary and sufficient to mediate the effects of multiple classes of antidepressants.

Cell Cycle Regulation of Hippocampal Progenitor Cells in Experimental Models of Depression and after Treatment with Fluoxetine

Changes in adult hippocampal cell proliferation and genesis have been largely implicated in depression and antidepressant action, though surprisingly, the underlying cell cycle mechanisms are largely undisclosed. Using both an in vivo unpredictable chronic mild stress (uCMS) rat model of depression and in vitro rat hippocampal-derived neurosphere culture approaches, we aimed to unravel the cell cycle mechanisms regulating hippocampal cell proliferation and genesis in depression and after antidepressant treatment. We show that the hippocampal dentate gyrus (hDG) of uCMS animals have less proliferating cells and a decreased proportion of cells in the G2/M phase, suggesting a G1 phase arrest; this is accompanied by decreased levels of cyclin D1, E, and A expression. Chronic fluoxetine treatment reversed the G1 phase arrest and promoted an up-regulation of cyclin E. In vitro, dexamethasone (DEX) decreased cell proliferation, whereas the administration of serotonin (5-HT) reversed it. DEX also induced a G1-phase arrest and decreased cyclin D1 and D2 expression levels while increasing p27. Additionally, 5-HT treatment could partly reverse the G1-phase arrest and restored cyclin D1 expression. We suggest that the anti-proliferative actions of chronic stress in the hDG result from a glucocorticoid-mediated G1-phase arrest in the progenitor cells that is partly mediated by decreased cyclin D1 expression which may be overcome by antidepressant treatment.

Adult brain cytogenesis in the context of mood disorders: From neurogenesis to the emergent role of gliogenesis

Psychiatric disorders severely impact patients' lives. Motivational, cognitive and emotional deficits are the most common symptoms observed in these patients and no effective treatment is still available, either due to the adverse side effects or the low rate of efficacy of currently available drugs. Neurogenesis recovery has been one important focus in the treatment of psychiatric disorders, which undeniably contributes to the therapeutic action of antidepressants. However, glial plasticity is emerging as a new strategy to explore the deficits observed in mood disorders and the efficacy of therapeutic interventions. Thus, it is crucial to understand the mechanisms behind glio- and neurogenesis to better define treatments and preventive therapies, once adult cytogenesis is of pivotal importance to cognitive and emotional components of behavior, both in healthy and pathological contexts, including in psychiatric disorders. Here, we review the concepts and history of neuro- and gliogenesis, providing as well a reflection on the functional importance of cytogenesis in the context of disease.

Glial restricted precursor cells in central nervous system disorders: Current applications and future perspectives

The crosstalk between glial cells and neurons represents an exceptional feature for maintaining the normal function of the central nervous system (CNS). Increasing evidence has revealed the importance of glial progenitor cells in adult neurogenesis, reestablishment of cellular pools, neuroregeneration, and axonal (re)myelination. Several types of glial progenitors have been described, as well as their potentialities for recovering the CNS from certain traumas or pathologies. Among these precursors, glial-restricted precursor cells (GRPs) are considered the earliest glial progenitors and exhibit tripotency for both Type I/II astrocytes and oligodendrocytes. GRPs have been derived from embryos and embryonic stem cells in animal models and have maintained their capacity for self-renewal. Despite the relatively limited knowledge regarding the isolation, characterization, and function of these progenitors, GRPs are promising candidates for transplantation therapy and reestablishment/repair of CNS functions in neurodegenerative and neuropsychiatric disorders, as well as in traumatic injuries. Herein, we review the definition, isolation, characterization and potentialities of GRPs as cell-based therapies in different neurological conditions. We briefly discuss the implications of using GRPs in CNS regenerative medicine and their possible application in a clinical setting. MAIN POINTS: GRPs are progenitors present in the CNS with differentiation potential restricted to the glial lineage. These cells have been employed in the treatment of a myriad of neurodegenerative and traumatic pathologies, accompanied by promising results, herein reviewed.

Genetic origins of suicidality? A synopsis of genes in suicidal behaviours, with regard to evidence diversity, disorder specificity and neurodevelopmental brain transcriptomics

With regard to suicidal behavior (SB) genetics, many novel genes have been implicated over the years, in particular by a variety of hypothesis-free genomic methods (e.g. GWAS and exome sequencing). In addition, many novel SB gene findings appear enigmatic in their biological relevance and have weak statistical support, e.g. lack direct replications. Adding to this is the comorbidity between psychiatric disorders and SB. Here we provide a synopsis of SB genes, by prioritization of 106 (out of ~2500) genes based on their highest level of evidence diversity across mainly five genetic evidence types (candidate/GWAS SNP, CNV, linkage and whole exome sequencing), supplemented by three functional categories. This is a representative set of both old and new SB gene candidates, implicated by all kinds of evidence. Furthermore, we define a subset of 40 SB "specific" genes, which are not found among ~3900 genes implicated in other neuropsychiatric disorders, e.g. Autism spectrum disorders (ASD) or Schizophrenia. Biological research of suicidality contains a major developmental focus, e.g. with regard to the gene-environment interactions and epigenetic effects during childhood. Less is known about early (fetal) development and SB genes. Inspired by huge efforts to understand the role early (fetal) neurodevelopment in e.g. ASD by using brain transcriptomic data, we here also characterize the 106 SB genes. We find interesting spatiotemporal expression differences and similarities between SB specific and non-specific genes during brain neurodevelopment. These aspects are of interest to investigate further, to better understand and counteract the genetic origins suicidality.

Cyclins, Cyclin-Dependent Kinases, and Cyclin-Dependent Kinase Inhibitors in the Mouse Nervous System

Development and normal physiology of the nervous system require proliferation and differentiation of stem and progenitor cells in a strictly controlled manner. The number of cells generated depends on the type of cell division, the cell cycle length, and the fraction of cells that exit the cell cycle to become quiescent or differentiate. The underlying processes are tightly controlled and modulated by cyclin-dependent kinases (Cdks) and their interactions with cyclins and Cdk inhibitors (CKIs). Studies performed in the nervous system with mouse models lacking individual Cdks, cyclins, and CKIs, or combinations thereof, have shown that many of these molecules control proliferation rates in a cell-type specific and time-dependent manner. In this review, we will provide an update on the in vivo studies on cyclins, Cdks, and CKIs in neuronal and glial tissue. The goal is to highlight their impact on proliferation processes during the development of the peripheral and central nervous system, including and comparing normal and pathological conditions in the adult.

Pharmacological Stimulation of Nurr1 Promotes Cell Cycle Progression in Adult Hippocampal Neural Stem Cells

Nuclear receptor related-1 (Nurr1) protein performs a crucial role in hippocampal neural stem cell (hNSC) development as well as cognitive functions. We previously demonstrated that the pharmacological stimulation of Nurr1 by amodiaquine (AQ) promotes spatial memory by enhancing adult hippocampal neurogenesis. However, the role of Nurr1 in the cell cycle regulation of the adult hippocampus has not been investigated. This study aimed to examine changes in the cell cycle-related molecules involved in adult hippocampal neurogenesis induced by Nurr1 pharmacological stimulation. Fluorescence-activated cell sorting (FACS) analysis showed that AQ improved the progression of cell cycle from G0/G1 to S phase in a dose-dependent manner, and MEK1 or PI3K inhibitors attenuated this progression. In addition, AQ treatment increased the expression of cell proliferation markers MCM5 and PCNA, and transcription factor E2F1. Furthermore, pharmacological stimulation of Nurr1 by AQ increased the expression levels of positive cell cycle regulators such as cyclin A and cyclin-dependent kinases (CDK) 2. In contrast, levels of CDK inhibitors p27KIP1 and p57KIP2 were reduced upon treatment with AQ. Similar to the in vitro results, RT-qPCR analysis of AQ-administered mice brains revealed an increase in the levels of markers of cell cycle progression, PCNA, MCM5, and Cdc25a. Finally, AQ administration resulted in decreased p27KIP1 and increased CDK2 levels in the dentate gyrus of the mouse hippocampus, as quantified immunohistochemically. Our results demonstrate that the pharmacological stimulation of Nurr1 in adult hNSCs by AQ promotes the cell cycle by modulating cell cycle-related molecules.

The protective effects of Ghrelin/GHSR on hippocampal neurogenesis in CUMS mice

Ghrelin is an orexigenic hormone that also plays an important role in mood disorders. Our previous studies demonstrated that ghrelin administration could protect against depression-like behaviors of chronic unpredictable mild stress (CUMS) in rodents. However, the mechanism related to the effect of ghrelin on CUMS mice has yet to be revealed. This article shows that ghrelin (5 nmol/kg/day for 2 weeks, i.p.) decreased depression-like behaviors induced by CUMS and increased hippocampal integrity (neurogenesis and spine density) measured via Ki67, 5-bromo-2-deoxyuridine (BrdU), doublecortin (DCX) labeling and Golgi-cox staining, which were decreased under CUMS. The behavioral phenotypes of Growth hormone secretagogue receptor (Ghsr)-null and wild type (WT) mice were evaluated under no stress condition and after CUMS exposure to determine the effect of Ghsr knockout on the behavioral phenotypes and stress susceptibility of mice. Ghsr-null mice exhibited depression-like behaviors under no stress condition. CUMS induced similar depression- and anxiety-like behavioral manifestations in both Ghsr-null and WT mice. A similar pattern of behavioral changes was observed after hippocampal GHSR knockdown. Additionally, both Ghsr knockout as well as CUMS exhibited deleterious effects on neurogenesis and spine density in the dentate gyrus (DG). Besides, CCK8 assay and 5-Ethynyl-2'-deoxyuridine (EdU) incorporation assay showed that ghrelin has a proliferative effect on primary cultured hippocampal neural stem cells (NSCs) and this proliferation was blocked by D-Lys3-GHRP-6 (DLS, the antagonist of GHSR, 100 μM) pretreatment. Ghrelin-induced proliferation is associated with the inhibition of G1 arrest, and this inhibition was blocked by LY294002 (specific inhibitor of PI3K, 20 μM). Furthermore, the in vivo data displayed that LY294002 (50 nmol, i.c.v.) can significantly block the antidepressant-like action of exogenous ghrelin treatment. All these results suggest that ghrelin/GHSR signaling maintains the integrity of hippocampus and has an inherent neuroprotective effect whether facing stress or not.

Cell-Biological Requirements for the Generation of Dentate Gyrus Granule Neurons

The dentate gyrus (DG) receives highly processed information from the associative cortices functionally integrated in the trisynaptic hippocampal circuit, which contributes to the formation of new episodic memories and the spontaneous exploration of novel environments. Remarkably, the DG is the only brain region currently known to have high rates of neurogenesis in adults (Andersen et al., 1966, 1971). The DG is involved in several neurodegenerative disorders, including clinical dementia, schizophrenia, depression, bipolar disorder and temporal lobe epilepsy. The principal neurons of the DG are the granule cells. DG granule cells generated in culture would be an ideal model to investigate their normal development and the causes of the pathologies in which they are involved and as well as possible therapies. Essential to establish such in vitro models is the precise definition of the most important cell-biological requirements for the differentiation of DG granule cells. This requires a deeper understanding of the precise molecular and functional attributes of the DG granule cells in vivo as well as the DG cells derived in vitro. In this review we outline the neuroanatomical, molecular and cell-biological components of the granule cell differentiation pathway, including some growth- and transcription factors essential for their development. We summarize the functional characteristics of DG granule neurons, including the electrophysiological features of immature and mature granule cells and the axonal pathfinding characteristics of DG neurons. Additionally, we discuss landmark studies on the generation of dorsal telencephalic precursors from pluripotent stem cells (PSCs) as well as DG neuron differentiation in culture. Finally, we provide an outlook and comment critical aspects.

Establishment of a novel three-dimensional primary culture model for hippocampal neurogenesis

New neurons are generated in the adult hippocampus throughout life and contribute to the functions of learning and memory. Nevertheless, the mechanisms by which disrupted neurogenesis regulates central nervous system (CNS) disorders are not fully understood. Here, we established a novel 3D culture system of hippocampal neurogenesis using air liquid interface (ALI) culture and Matrigel culture from mouse hippocampus tissues. After isolated mouse hippocampus tissue fragments were seeded into ALI wells and cultured in stemness‐stimulated media containing Wnt, EGF, Noggin and R‐spondin for 7 days, small spheres gradually appeared in the tissues. To identify the cell components, immunohistochemical and immunofluorescence staining were performed. Expression of a mature neuronal cell marker, NeuN was observed in the tissues just after seeding. Expression of a neural stem cell marker, Nestin was observed in the tissues at day 7. To differentiate the Nestin‐positive cells, they were passaged into Matrigel. Expression of Nestin but not an immature neuronal cell marker, doublecortin (DCX) was observed in the isolated cells. After 7 days of Matrigel culture, they showed the neurite outgrowth. Expression of Nestin was decreased compared with the one just after passaging, while DCX expression was increased. Western blotting analysis also showed Nestin expression was decreased, while expression of DCX, a neuronal cell marker, Tuj1 and a granule cell marker, Prox‐1 was increased. Here, we establish the 3D culture of hippocampus tissues that might become a novel in vitro tool for monitoring the process of hippocampal neurogenesis. Our model might shed light into the mechanisms of pathogenesis of CNS disorders.

Peripheral blood microRNA and VEGFA mRNA changes following electroconvulsive therapy: implications for psychotic depression

OBJECTIVE

MicroRNAs are short, non-coding molecules that regulate gene expression. Here, we investigate the role of microRNAs in depression and electroconvulsive therapy (ECT).

METHODS

We performed three studies: a deep sequencing discovery-phase study of miRNA changes in whole blood following ECT (n = 16), followed by a validation study in a separate cohort of patients pre-/post-ECT (n = 37) and matched healthy controls (n = 34). Changes in an experimentally validated gene target (VEGFA) were then analysed in patients pre-/post-ECT (n = 97) and in matched healthy controls (n = 53).

RESULTS

In the discovery-phase study, we found no statistically significant differences in miRNA expression from baseline to end of treatment in the group as a whole, but post hoc analysis indicated a difference in patients with psychotic depression (n = 3). In a follow-up validation study, patients with psychotic depression (n = 7) had elevated baseline levels of miR-126-3p (t = 3.015, P = 0.006) and miR-106a-5p (t = 2.598, P = 0.025) compared to healthy controls. Following ECT, these differences disappeared. Baseline VEGFA levels were significantly higher in depressed patients compared to healthy controls (F(1,144) = 27.688, P = <0.001). Following ECT, there was a significant change in VEGFA levels in the psychotic group only (t = 2.915, P = 0.010).

CONCLUSION

Molecular differences (miRNA and VEGFA) may exist between psychotic and non-psychotic depression treated with ECT.

Translational Identification of Transcriptional Signatures of Major Depression and Antidepressant Response

Major depressive disorder (MDD) is a highly prevalent mental illness whose therapy management remains uncertain, with more than 20% of patients who do not achieve response to antidepressants. Therefore, identification of reliable biomarkers to predict response to treatment will greatly improve MDD patient medical care. Due to the inaccessibility and lack of brain tissues from living MDD patients to study depression, researches using animal models have been useful in improving sensitivity and specificity of identifying biomarkers. In the current study, we used the unpredictable chronic mild stress (UCMS) model and correlated stress-induced depressive-like behavior (n = 8 unstressed vs. 8 stressed mice) as well as the fluoxetine-induced recovery (n = 8 stressed and fluoxetine-treated mice vs. 8 unstressed and fluoxetine-treated mice) with transcriptional signatures obtained by genome-wide microarray profiling from whole blood, dentate gyrus (DG), and the anterior cingulate cortex (ACC). Hierarchical clustering and rank-rank hypergeometric overlap (RRHO) procedures allowed us to identify gene transcripts with variations that correlate with behavioral profiles. As a translational validation, some of those transcripts were assayed by RT-qPCR with blood samples from 10 severe major depressive episode (MDE) patients and 10 healthy controls over the course of 30 weeks and four visits. Repeated-measures ANOVAs revealed candidate trait biomarkers (ARHGEF1, CMAS, IGHMBP2, PABPN1 and TBC1D10C), whereas univariate linear regression analyses uncovered candidates state biomarkers (CENPO, FUS and NUBP1), as well as prediction biomarkers predictive of antidepressant response (CENPO, NUBP1). These data suggest that such a translational approach may offer new leads for clinically valid panels of biomarkers for MDD.

Quantitative assessment of fibroblast growth factor receptor 1 expression in neurons and glia

Background

Fibroblast growth factors (FGFs) and their receptors (FGFRs) have numerous functions in the developing and adult central nervous system (CNS). For example, the FGFR1 receptor is important for proliferation and fate specification of radial glial cells in the cortex and hippocampus, oligodendrocyte proliferation and regeneration, midline glia morphology and soma translocation, Bergmann glia morphology, and cerebellar morphogenesis. In addition, FGFR1 signaling in astrocytes is required for postnatal maturation of interneurons expressing parvalbumin (PV). FGFR1 is implicated in synapse formation in the hippocampus, and alterations in the expression of Fgfr1 and its ligand, Fgf2 accompany major depression. Understanding which cell types express Fgfr1 during development may elucidate its roles in normal development of the brain as well as illuminate possible causes of certain neuropsychiatric disorders.

Methods

Here, we used a BAC transgenic reporter line to trace Fgfr1 expression in the developing postnatal murine CNS. The specific transgenic line employed was created by the GENSAT project, tgFGFR1-EGFPGP338Gsat, and includes a gene encoding enhanced green fluorescent protein (EGFP) under the regulation of the Fgfr1 promoter, to trace Fgfr1 expression in the developing CNS. Unbiased stereological counts were performed for several cell types in the cortex and hippocampus.

Results

This model reveals that Fgfr1 is primarily expressed in glial cells, in both astrocytes and oligodendrocytes, along with some neurons. Dual labeling experiments indicate that the proportion of GFP+ (Fgfr1+) cells that are also GFAP+ increases from postnatal day 7 (P7) to 1 month, illuminating dynamic changes in Fgfr1 expression during postnatal development of the cortex. In postnatal neurogenic areas, GFP expression was also observed in SOX2, doublecortin (DCX), and brain lipid-binding protein (BLBP) expressing cells. Fgfr1 is also highly expressed in DCX positive cells of the dentate gyrus (DG), but not in the rostral migratory stream. Fgfr1 driven GFP was also observed in tanycytes and GFAP+ cells of the hypothalamus, as well as in Bergmann glia and astrocytes of the cerebellum.

Conclusions

The tgFGFR1-EGFPGP338Gsat mouse model expresses GFP that is congruent with known functions of FGFR1, including hippocampal development, glial cell development, and stem cell proliferation. Understanding which cell types express Fgfr1 may elucidate its role in neuropsychiatric disorders and brain development.

Fragile X related protein 1 (FXR1P) regulates proliferation of adult neural stem cells

Fragile X related protein 1 (FXR1P) is a member of the fragile X family of RNA-binding proteins, which includes FMRP and FXR2P. Both FMRP and FXR2P regulate neurogenesis, a process affected in a number of neurological and neuropsychiatric disorders, including fragile X syndrome. Although FXR1P has been implicated in various developmental processes and neuropsychiatric diseases, its role in neurodevelopment is not well understood. The goal of the present study was to elucidate the function of FXR1P in adult neurogenesis. We used an inducible mouse model that allows us to investigate how FXR1P deficiency in adult neural stem cells (aNSCs) affects proliferation and neuronal differentiation. Deletion of FXR1 in aNSCs resulted in fewer adult-born cells in the dentate gyrus (DG) overall, reducing populations across different stages of neurogenesis, including radial glia-like cells, intermediate progenitors, neuroblasts, immature neurons and neurons. We hypothesized that this reduction in new cell numbers resulted from impaired proliferation, which we confirmed both in vivo and in vitro. We discovered that FXR1P-deficient aNSCs have altered expression of a select number of cell-cycle genes, and we identified the mRNA of cyclin-dependent kinase inhibitor 1A (Cdkn1a, p21) as a direct target of FXR1P. Restoration of p21 mRNA to wild-type levels rescued the proliferation deficit in cells lacking FXR1P, demonstrating that p21 is a mediator of FXR1P in aNSCs. These results indicate that FXR1P plays an important role in regulating aNSC self-renewal and maintenance in the adult brain, which may have implications for a number of neurodevelopmental and psychiatric disorders.

Zika Virus Infects Neural Progenitors in the Adult Mouse Brain and Alters Proliferation

Zika virus (ZIKV)-related neuropathology is an important global health concern. Several studies have shown that ZIKV can infect neural stem cells in the developing brain, but infection in the adult brain has not been examined. Two areas in the adult mouse brain contain neural stem cells: the subventricular zone of the anterior forebrain and the subgranular zone of the hippocampus. Here, using 6-week-old mice triply deficient in interferon regulatory factor (IRF) as a model, we show that blood-borne ZIKV administration can lead to pronounced evidence of ZIKV infection in these adult neural stem cells, leading to cell death and reduced proliferation. Our data therefore suggest that adult as well as fetal neural stem cells are vulnerable to ZIKV neuropathology. Thus, although ZIKV is considered a transient infection in adult humans without marked long-term effects, there may in fact be consequences of exposure in the adult brain.

Ghrelin regulates cell cycle-related gene expression in cultured hippocampal neural stem cells

We have previously demonstrated that ghrelin stimulates the cellular proliferation of cultured adult rat hippocampal neural stem cells (NSCs). However, little is known about the molecular mechanisms by which ghrelin regulates cell cycle progression. The purpose of this study was to investigate the potential effects of ghrelin on cell cycle regulatory molecules in cultured hippocampal NSCs. Ghrelin treatment increased proliferation assessed by CCK-8 proliferation assay. The expression levels of proliferating cell nuclear antigen and cell division control 2, well-known cell-proliferating markers, were also increased by ghrelin. Fluorescence-activated cell sorting analysis revealed that ghrelin promoted progression of cell cycle from G0/G1 to S phase, whereas this progression was attenuated by the pretreatment with specific inhibitors of MEK/extracellular signal-regulated kinase 1/2, phosphoinositide 3-kinase/Akt, mammalian target of rapamycin, and janus kinase 2/signal transducer and activator of transcription 3. Ghrelin-induced proliferative effect was associated with increased expression of E2F1 transcription factor in the nucleus, as determined by Western blotting and immunofluorescence. We also found that ghrelin caused an increase in protein levels of positive regulators of cell cycle, such as cyclin A and cyclin-dependent kinase (CDK) 2. Moreover, p27(KIP1) and p57(KIP2) protein levels were reduced when cell were exposed to ghrelin, suggesting downregulation of CDK inhibitors may contribute to proliferative effect of ghrelin. Our data suggest that ghrelin targets both cell cycle positive and negative regulators to stimulate proliferation of cultured hippocampal NSCs.

Detection and Phenotypic Characterization of Adult Neurogenesis

Studies of adult neurogenesis have greatly expanded in the last decade, largely as a result of improved tools for detecting and quantifying neurogenesis. In this review, we summarize and critically evaluate detection methods for neurogenesis in mammalian and human brain tissue. Besides thymidine analog labeling, cell-cycle markers are discussed, as well as cell stage and lineage commitment markers. Use of these histological tools is critically evaluated in terms of their strengths and limitations, as well as possible artifacts. Finally, we discuss the method of radiocarbon dating for determining cell and tissue turnover in humans.

Mechanism of all-transretinoic acid increasing retinoblastoma sensitivity to vincristine

OBJECTIVE

To explore the mechanism of all-transretinoic acid (ATRA) increasing retinoblastoma (RB) sensitivity to vincristine, and the inhibiting effect of vincristine combined with ATRA treatment on the SO-RB50 cell proliferation.

METHODS

SO-RB50 cells were cultivated by routine culture method. Different concentrations of vincristine or ATRA were added into culture solution. After 48 h, cell counting kit-8 was used to detect the median inhibitory concentration (IC50) of vincristine combined with ATRT treatment to SO-RB50 cells. SO-RB50 cells were divided into drug combination group, vincristine group, ATRA group and control group. Different drugs were added into the culture solution respectively for cell culture based on the IC50 value. Cell counting kit-8 was used to detect the cell proliferation every 24-h cultivation. After continuous determination for 6 d, data was processed to draw the cell growth curve. After drug use for 72 h, flow cytometry was used to detect the proportion of different cell cycles of SO-RB50 cells in each group. After drug use for 48 h, annexin V/propidium iodide method was used to detect the SO-RB50 cell apoptosis in each group.

RESULTS

The IC50 value of vincristine treatment on the SO-RB50 cells was 0.11 μmol/L, and ATRT was 12.84 μmol/L. The cell growth curve in control group rose gradually along with the extended culture time, but after vincristine and ATRA treatment, the cell growth curve was smooth and steady. The cell increment was the least in drug combination group and its cell growth curve was the smoothest. There was significant difference in A450 48 h and 72 h after treatment (Fgrouping = 77.316, P < 0.001; Ftime = 86.985, P < 0.001). Compared with control group, A450 value in drug combination group, vincristine group, ATRA group was significant lower (P < 0.001). Compared with control group, the G2/M phase cell proportion in vincristine group was significantly increased, while the G0/G1 phase cell proportion was significantly decreased; the G0/G1 phase cell proportion in ATRA group was significantly increased, while the S phase cell proportion was significantly decreased (FG0/G1 = 85.878, Fs = 56.455, FG2/M = 85.878, P < 0.001). After 48 h, there was significant difference in SO-RB50 cell apoptosis rate among groups (F = 11.312, P < 0.05). The apoptosis rate in drug combination group was significantly higher than that of other groups (P < 0.001).

CONCLUSIONS

ATRA can increase the sensitivity of SO-RB50 cells to vincristine. Vincristine combined with ATRA treatment can significantly increase the inhibiting effect on SO-RB50 cells, which may be related with promoting cell apoptosis and involving in cell cycle control.

Influence of single and repeated cannabidiol administration on emotional behavior and markers of cell proliferation and neurogenesis in non-stressed mice

Therapeutic effects of antidepressants and atypical antipsychotics may arise partially from their ability to stimulate neurogenesis. Cannabidiol (CBD), a phytocannabinoid present in Cannabis sativa, presents anxiolytic- and antipsychotic-like effects in preclinical and clinical settings. Anxiolytic-like effects of repeated CBD were shown in chronically stressed animals and these effects were parallel with increased hippocampal neurogenesis. However, antidepressant-like effects of repeated CBD administration in non-stressed animals have been scarcely reported. Here we investigated the behavioral consequences of single or repeated CBD administration in non-stressed animals. We also determined the effects of CBD on cell proliferation and neurogenesis in the dentate gyrus (DG) and subventricular zone (SVZ). Single CBD 3mg/kg administration resulted in anxiolytic-like effect in mice submitted to the elevated plus maze (EPM). In the tail suspension test (TST), single or repeated CBD administration reduced immobility time, an effect that was comparable to those of imipramine (20 mg/kg). Moreover, repeated CBD administration at a lower dose (3 mg/kg) increased cell proliferation and neurogenesis, as seen by an increased number of Ki-67-, BrdU- and doublecortin (DCX)-positive cells in both in DG and SVZ. Despite its antidepressant-like effects in the TST, repeated CBD administration at a higher dose (30 mg/kg) decreased cell proliferation and neurogenesis in the hippocampal DG and SVZ. Our findings show a dissociation between behavioral and proliferative effects of repeated CBD and suggest that the antidepressant-like effects of CBD may occur independently of adult neurogenesis in non-stressed Swiss mice.

Control of the Cell Cycle in Adult Neurogenesis and its Relation with Physical Exercise

In the adult brain the neurogenesis is mainly restricted to two neurogenic regions: newly generated neurons arise at the subventricular zone (SVZ) of the lateral ventricle and at the subgranular zone of the hippocampal subregion named the dentate gyrus. The hippocampus is involved in learning and memory paradigms and the generation of new hippocampal neurons has been hypothesized to be a pivotal form of plasticity involved in the process. Moreover the dysregulation of hippocampal adult neurogenesis has been recognized and could anticipate several varieties of brain disease such as Alzheimer disease, epilepsy and depression. Over the last few decades numerous intrinsic, epigenetic and environmental factors have been revealed to deeply influence the process of adult neurogenesis, although the underlying mechanisms remain largely unknown. Growing evidence indicates that physical exercise represents one of the main extrinsic factor able to profoundly increase hippocampal adult neurogenesis, by altering neurochemistry and function of newly generated neurons. The present review surveys how neurogenesis can be modulated by cell cycle kinetics and highlights the putative role of the cell cycle length as a key component of the beneficial effect of running for hippocampal adult neurogenesis, both in physiological conditions and in the presence of defective neurogenesis.

Nrf2 regulates neurogenesis and protects neural progenitor cells against Aβ toxicity

Neural stem/progenitor cells (NPCs) proliferate and produce new neurons in neurogenic areas throughout the lifetime. While these cells represent potential therapeutic treatment of neurodegenerative diseases, regulation of neurogenesis is not completely understood. We show that deficiency of nuclear factor erythroid 2-related factor (Nrf2), a transcription factor induced in response to oxidative stress, prevents the ischemia-induced increase in newborn neurons in the subgranular zone of the dentate gyrus. Consistent with this finding, the growth of NPC neurospheres was increased by lentivirus-mediated overexpression of Nrf2 gene or by treatment with pyrrolidine dithiocarbamate (PDTC), an Nrf2 activating compound. Also, neuronal differentiation of NPCs was increased by Nrf2 overexpression or PDTC treatment but reduced by Nrf2 deficiency. To investigate the impact of Nrf2 on NPCs in Alzheimer's disease (AD), we treated NPCs with amyloid beta (Aβ), a toxic peptide associated with neurodegeneration and cognitive abnormalities in AD. We found that Aβ1-42-induced toxicity and reduction in neurosphere proliferation were prevented by Nrf2 overexpression, while Nrf2 deficiency enhanced the Aβ1-42-induced reduction of neuronal differentiation. On the other hand, Aβ1-40 had no effect on neurosphere proliferation in wt NPCs but increased the proliferation of Nrf2 overexpressing neurospheres and reduced it in Nrf2-deficient neurospheres. These results suggest that Nrf2 is essential for neuronal differentiation of NPCs, regulates injury-induced neurogenesis and provides protection against Aβ-induced NPC toxicity.

S-Nitrosylation in neurogenesis and neuronal development

BACKGROUND

Nitric oxide (NO) is a pleiotropic messenger molecule. The multidimensional actions of NO species are, in part, mediated by their redox nature. Oxidative posttranslational modification of cysteine residues to regulate protein function, termed S-nitrosylation, constitutes a major form of redox-based signaling by NO.

SCOPE OF REVIEW

S-Nitrosylation directly modifies a number of cytoplasmic and nuclear proteins in neurons. S-Nitrosylation modulates neuronal development by reaction with specific proteins, including the transcription factor MEF2. This review focuses on the impact of S-nitrosylation on neurogenesis and neuronal development.

MAJOR CONCLUSIONS

Functional characterization of S-nitrosylated proteins that regulate neuronal development represents a rapidly emerging field. Recent studies reveal that S-nitrosylation-mediated redox signaling plays an important role in several biological processes essential for neuronal differentiation and maturation.

GENERAL SIGNIFICANCE

Investigation of S-nitrosylation in the nervous system has elucidated new molecular and cellular mechanisms for neuronal development. S-Nitrosylated proteins in signaling networks modulate key events in brain development. Dysregulation of this redox-signaling pathway may contribute to neurodevelopmental disabilities such as autism spectrum disorder (ASD). Thus, further elucidation of the involvement of S-nitrosylation in brain development may offer potential therapeutic avenues for neurodevelopmental disorders. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.

Mice with ablated adult brain neurogenesis are not impaired in antidepressant response to chronic fluoxetine

The neurogenesis hypothesis of major depression has two main facets. One states that the illness results from decreased neurogenesis while the other claims that the very functioning of antidepressants depends on increased neurogenesis. In order to verify the latter, we have used cyclin D2 knockout mice (cD2 KO mice), known to have virtually no adult brain neurogenesis, and we demonstrate that these mice successfully respond to chronic fluoxetine. After unpredictable chronic mild stress, mutant mice showed depression-like behavior in forced swim test, which was eliminated with chronic fluoxetine treatment, despite its lack of impact on adult hippocampal neurogenesis in cD2 KO mice. Our results suggest that new neurons are not indispensable for the action of antidepressants such as fluoxetine. Using forced swim test and tail suspension test, we also did not observe depression-like behavior in control cD2 KO mice, which argues against the link between decreased adult brain neurogenesis and major depression.

How to make a hippocampal dentate gyrus granule neuron

Granule neurons in the hippocampal dentate gyrus (DG) receive their primary inputs from the cortex and are known to be continuously generated throughout adult life. Ongoing integration of newborn neurons into the existing hippocampal neural circuitry provides enhanced neuroplasticity, which plays a crucial role in learning and memory; deficits in this process have been associated with cognitive decline under neuropathological conditions. In this Primer, we summarize the developmental principles that regulate the process of DG neurogenesis and discuss recent advances in harnessing these developmental cues to generate DG granule neurons from human pluripotent stem cells.

Sleep and adult neurogenesis: implications for cognition and mood

The hippocampal dentate gyrus plays a critical role in learning and memory throughout life, in part by the integration of adult-born neurons into existing circuits. Neurogenesis in the adult hippocampus is regulated by numerous environmental, physiological, and behavioral factors known to affect learning and memory. Sleep is also important for learning and memory. Here we critically examine evidence from correlation, deprivation, and stimulation studies that sleep may be among those factors that regulate hippocampal neurogenesis. There is mixed evidence for correlations between sleep variables and rates of hippocampal cell proliferation across the day, the year, and the lifespan. There is modest evidence that periods of increased sleep are associated with increased cell proliferation or survival. There is strong evidence that disruptions of sleep exceeding 24 h, by total deprivation, selective REM sleep deprivation, and chronic restriction or fragmentation, significantly inhibit cell proliferation and in some cases neurogenesis. The mechanisms by which sleep disruption inhibits neurogenesis are not fully understood. Although sleep disruption procedures are typically at least mildly stressful, elevated adrenal corticosterone secretion is not necessary for this effect. However, procedures that prevent both elevated corticosterone and interleukin 1β signaling have been found to block the effect of sleep deprivation on cell proliferation. This result suggests that sleep loss impairs hippocampal neurogenesis by the presence of wake-dependent factors, rather than by the absence of sleep-specific processes. This would weigh against a hypothesis that regulation of neurogenesis is a function of sleep. Nonetheless, impaired neurogenesis may underlie some of the memory and mood effects associated with acute and chronic sleep disruptions.