Differential properties of adult rat and mouse brain-derived neural stem/progenitor cells

Enhancing Cognitive Functions and Neuronal Growth through NPY1R Agonist and Ketamine Co-Administration: Evidence for NPY1R-TrkB Heteroreceptor Complexes in Rats

This study investigates the combined effects of the neuropeptide Y Y1 receptor (NPY1R) agonist [Leu31-Pro34]NPY at a dose of 132 µg and Ketamine at 10 mg/Kg on cognitive functions and neuronal proliferation, against a backdrop where neurodegenerative diseases present an escalating challenge to global health systems. Utilizing male Sprague-Dawley rats in a physiological model, this research employed a single-dose administration of these compounds and assessed their impact 24 h after treatment on object-in-place memory tasks, alongside cellular proliferation within the dorsal hippocampus dentate gyrus. Methods such as the in situ proximity ligation assay and immunohistochemistry for proliferating a cell nuclear antigen (PCNA) and doublecortin (DCX) were utilized. The results demonstrated that co-administration significantly enhanced memory consolidation and increased neuronal proliferation, specifically neuroblasts, without affecting quiescent neural progenitors and astrocytes. These effects were mediated by the potential formation of NPY1R-TrkB heteroreceptor complexes, as suggested by receptor co-localization studies, although further investigation is required to conclusively prove this interaction. The findings also highlighted the pivotal role of brain-derived neurotrophic factor (BDNF) in mediating these effects. In conclusion, this study presents a promising avenue for enhancing cognitive functions and neuronal proliferation through the synergistic action of the NPY1R agonist and Ketamine, potentially via NPY1R-TrkB heteroreceptor complex formation, offering new insights into therapeutic strategies for neurodegenerative diseases.

Long interspersed nuclear elements safeguard neural progenitors from precocious differentiation

Long interspersed nuclear element-1 (L1 or LINE-1) is a highly abundant mobile genetic element in both humans and mice, comprising almost 20% of each genome. L1s are silenced by several mechanisms, as their uncontrolled expression has the potential to induce genomic instability. However, L1s are paradoxically expressed at high levels in differentiating neural progenitor cells. Using in vitro and in vivo techniques to modulate L1 expression, we report that L1s play a critical role in both human and mouse brain development by regulating the rate of neural differentiation in a reverse-transcription-independent manner.

Neuropeptide Y receptor 1 and galanin receptor 2 (NPY1R-GALR2) interactions in the dentate gyrus and their relevance for neurogenesis and cognition

Introduction

This study may unveil novel insights into the interactions between neuropeptide Y receptor 1 (NPY1R) and galanin receptor 2 (GALR2), in the dentate gyrus of the dorsal hippocampus, shedding light on their role in neurogenesis and cognitive functions. Existing literature highlights the potential of these interactions in enhancing learning and memory, yet detailed mechanisms remain underexplored.

Methods

Utilizing intracerebroventricular injections of GALR2 and NPY1R agonists in Sprague-Dawley male rats, we examined neurogenesis via markers PCNA and DCX, and memory consolidation through the object-in-place task over a three-week period.

Results

Significant increases in NPY1R-GALR2 co-localization and neuroblast proliferation were observed, alongside enhanced memory consolidation. These findings suggest a synergistic effect of NPY1R and GALR2 activation on cognitive functions.

Discussion

Our findings may foster the development of novel heterobivalent or multitargeting drugs, affecting NPY1R-GALR2 interaction, and suggest a future pharmacogical strategy for improving learning and memory found in many brain diseases. Further research is encouraged to explore these mechanisms in pathological models.

Isolation and Culture of Neural Stem/Progenitor Cells from the Hippocampal Dentate Gyrus of Young Adult and Aged Rats

Adult neural stem/progenitor cells (NSPCs) in two neurogenic areas of the brain, the dentate gyrus and the subventricular zone, are major players in adult neurogenesis. Addressing specific questions regarding NSPCs outside of their niche entails in vitro studies through isolation and culture of these cells. As there is heterogeneity in their morphology, proliferation, and differentiation capacity between these two neurogenic areas, NSPCs should be isolated from each area through specific procedures and media. Identifying region-specific NPSCs provides an accurate pathway for assessing the effects of extrinsic factors and drugs on these cells and investigating the mechanisms of neurogenesis in both healthy and pathologic conditions. A great number of isolation and expansion techniques for NSPCs have been reported. The growth and expansion of NSPCs obtained from the dentate gyrus of aged rats are generally difficult. There are relatively limited data and protocols about NSPCs isolation and their culture from aged rats. Our approach is an efficient and reliable strategy to isolate and expand NSPCs obtained from young adult and aged rats. NSPCs isolated by this method maintain their self-renewal and multipotency. Key features • NSPCs isolated from the hippocampal dentate gyrus of young adult and aged rats, based on Kempermann et al. (2014) and Aligholi et al. (2014). • Maintenance of NSPCs isolated from the dentate gyrus of aged rats (20-24 months) in our culture condition is feasible. • According to our protocol, maximum growth of primary neurospheres obtained from isolated NSPCs of young and aged rats took 15 and 35 days, respectively.

mRNA Abundance of Neurogenic Factors Correlates with Hearing Capacity in Auditory Brainstem Nuclei of the Rat

Neural stem cells (NSCs) have previously been described up to the adult stage in the rat cochlear nucleus (CN). A decreasing neurogenic potential was observed with critical changes around hearing onset. A better understanding of molecular factors affecting NSCs and neurogenesis is of interest as they represent potential targets to treat the cause of neurologically based hearing disorders. The role of genes affecting NSC development and neurogenesis in CN over time on hearing capacity has remained unclear. This study investigated the mRNA abundance of genes influencing NSCs and neurogenesis in rats' CN over time. The CN of rats on postnatal days 6, 12, and 24 were examined. Real-time quantitative polymerase chain reaction arrays were used to compare mRNA levels of 84 genes relevant to NSCs and neurogenesis. Age- and hearing-specific patterns of changes in mRNA abundance of neurogenically relevant genes were detected in the rat CN. Additionally, crucial neurogenic factors with significant and relevant influence on neurogenesis were identified. The results of this work should contribute to a better understanding of the molecular mechanisms underlying the neurogenesis of the auditory pathway.

Apolipoprotein E Recognizes Alzheimer's Disease Associated 3-O Sulfation of Heparan Sulfate

Apolipoprotein E (ApoE)'s ϵ4 alle is the most important genetic risk factor for late onset Alzheimer's Disease (AD). Cell-surface heparan sulfate (HS) is a cofactor for ApoE/LRP1 interaction and the prion-like spread of tau pathology between cells. 3-O-sulfo (3-O-S) modification of HS has been linked to AD through its interaction with tau, and enhanced levels of 3-O-sulfated HS and 3-O-sulfotransferases in the AD brain. In this study, we characterized ApoE/HS interactions in wildtype ApoE3, AD-linked ApoE4, and AD-protective ApoE2 and ApoE3-Christchurch. Glycan microarray and SPR assays revealed that all ApoE isoforms recognized 3-O-S. NMR titration localized ApoE/3-O-S binding to the vicinity of the canonical HS binding motif. In cells, the knockout of HS3ST1-a major 3-O sulfotransferase-reduced cell surface binding and uptake of ApoE. 3-O-S is thus recognized by both tau and ApoE, suggesting that the interplay between 3-O-sulfated HS, tau and ApoE isoforms may modulate AD risk.

Dying transplanted neural stem cells mediate survival bystander effects in the injured brain

Neural stem and progenitor cell (NSPC) transplants provide neuroprotection in models of acute brain injury, but the underlying mechanisms are not fully understood. Here, we provide evidence that caspase-dependent apoptotic cell death of NSPCs is required for sending survival signals to the injured brain. The secretome of dying NSPCs contains heat-stable proteins, which protect neurons against glutamate-induced toxicity and trophic factor withdrawal in vitro, and from ischemic brain damage in vivo. Our findings support a new concept suggesting a bystander effect of apoptotic NSPCs, which actively promote neuronal survival through the release of a protective "farewell" secretome. Similar protective effects by the secretome of apoptotic NSPC were also confirmed in human neural progenitor cells and neural stem cells but not in mouse embryonic fibroblasts (MEF) or human dopaminergic neurons, suggesting that the observed effects are cell type specific and exist for neural progenitor/stem cells across species.

Critical points for optimizing long-term culture and neural differentiation capacity of rodent and human neural stem cells to facilitate translation into clinical settings

Despite several decades of research on the nature and functional properties of neural stem cells, which brought great advances in regenerative medicine, there is still a plethora of ambiguous protocols and interpretations linked to their applications. Here, we present a whole spectrum of protocol elements that should be standardized in order to obtain viable cell cultures and facilitate their translation into clinical settings. Additionally, this review also presents outstanding limitations and possible problems to be encountered when dealing with protocol optimization. Most importantly, we also outline the critical points that should be considered before starting any experiments utilizing neural stem cells or interpreting their results.

Galanin and Neuropeptide Y Interaction Enhances Proliferation of Granule Precursor Cells and Expression of Neuroprotective Factors in the Rat Hippocampus with Consequent Augmented Spatial Memory

Dysregulation of hippocampal neurogenesis is linked to several neurodegenereative diseases, where boosting hippocampal neurogenesis in these patients emerges as a potential therapeutic approach. Accumulating evidence for a neuropeptide Y (NPY) and galanin (GAL) interaction was shown in various limbic system regions at molecular-, cellular-, and behavioral-specific levels. The purpose of the current work was to evaluate the role of the NPY and GAL interaction in the neurogenic actions on the dorsal hippocampus. We studied the Y1R agonist and GAL effects on: hippocampal cell proliferation through the proliferating cell nuclear antigen (PCNA), the expression of neuroprotective and anti-apoptotic factors, and the survival of neurons and neurite outgrowth on hippocampal neuronal cells. The functional outcome was evaluated in the object-in-place task. We demonstrated that the Y1R agonist and GAL promote cell proliferation and the induction of neuroprotective factors. These effects were mediated by the interaction of NPYY1 (Y1R) and GAL2 (GALR2) receptors, which mediate the increased survival and neurites' outgrowth observed on neuronal hippocampal cells. These cellular effects are linked to the improved spatial-memory effects after the Y1R agonist and GAL co-injection at 24 h in the object-in-place task. Our results suggest the development of heterobivalent agonist pharmacophores, targeting Y1R-GALR2 heterocomplexes, therefore acting on the neuronal precursor cells of the DG in the dorsal hippocampus for the novel therapy of neurodegenerative cognitive-affecting diseases.

Hippocampal cytogenesis abrogation impairs inter-regional communication between the hippocampus and prefrontal cortex and promotes the time-dependent manifestation of emotional and cognitive deficits

Impaired ability to generate new cells in the adult brain has been linked to deficits in multiple emotional and cognitive behavioral domains. However, the mechanisms by which abrogation of adult neural stem cells (NSCs) impacts on brain function remains controversial. We used a transgenic rat line, the GFAP-Tk, to selectively eliminate NSCs and assess repercussions on different behavioral domains. To assess the functional importance of newborn cells in specific developmental stages, two parallel experimental timeframes were adopted: a short- and a long-term timeline, 1 and 4 weeks after the abrogation protocol, respectively. We conducted in vivo electrophysiology to assess the effects of cytogenesis abrogation on the functional properties of the hippocampus and prefrontal cortex, and on their intercommunication. Adult brain cytogenesis abrogation promoted a time-specific installation of behavioral deficits. While the lack of newborn immature hippocampal neuronal and glial cells elicited a behavioral phenotype restricted to hyperanxiety and cognitive rigidity, specific abrogation of mature new neuronal and glial cells promoted the long-term manifestation of a more complex behavioral profile encompassing alterations in anxiety and hedonic behaviors, along with deficits in multiple cognitive modalities. More so, abrogation of 4 to 7-week-old cells resulted in impaired electrophysiological synchrony of neural theta oscillations between the dorsal hippocampus and the medial prefrontal cortex, which are likely to contribute to the described long-term cognitive alterations. Hence, this work provides insight on how newborn neurons and astrocytes display different functional roles throughout different maturation stages, and establishes common ground to reconcile contrasting results that have marked this field.

Improved Method for Efficient Generation of Functional Neurons from Murine Neural Progenitor Cells

Neuronal culture was used to investigate neuronal function in physiological and pathological conditions. Despite its inevitability, primary neuronal culture remained a gold standard method that requires laborious preparation, intensive training, and animal resources. To circumvent the shortfalls of primary neuronal preparations and efficiently give rise to functional neurons, we combine a neural stem cell culture method with a direct cell type-conversion approach. The lucidity of this method enables the efficient preparation of functional neurons from mouse neural progenitor cells on demand. We demonstrate that induced neurons (NPC-iNs) by this method make synaptic connections, elicit neuronal activity-dependent cellular responses, and develop functional neuronal networks. This method will provide a concise platform for functional neuronal assessments. This indeed offers a perspective for using these characterized neuronal networks for investigating plasticity mechanisms, drug screening assays, and probing the molecular and biophysical basis of neurodevelopmental and neurodegenerative diseases.

AAV ablates neurogenesis in the adult murine hippocampus

Recombinant adeno-associated virus (rAAV) has been widely used as a viral vector across mammalian biology and has been shown to be safe and effective in human gene therapy. We demonstrate that neural progenitor cells (NPCs) and immature dentate granule cells (DGCs) within the adult murine hippocampus are particularly sensitive to rAAV-induced cell death. Cell loss is dose dependent and nearly complete at experimentally relevant viral titers. rAAV-induced cell death is rapid and persistent, with loss of BrdU-labeled cells within 18 hr post-injection and no evidence of recovery of adult neurogenesis at 3 months post-injection. The remaining mature DGCs appear hyperactive 4 weeks post-injection based on immediate early gene expression, consistent with previous studies investigating the effects of attenuating adult neurogenesis. In vitro application of AAV or electroporation of AAV2 inverted terminal repeats (ITRs) is sufficient to induce cell death. Efficient transduction of the dentategyrus (DG)- without ablating adult neurogenesis- can be achieved by injection of rAAV2-retro serotyped virus into CA3. rAAV2-retro results in efficient retrograde labeling of mature DGCs and permits in vivo two-photon calcium imaging of dentate activity while leaving adult neurogenesis intact. These findings expand on recent reports implicating rAAV-linked toxicity in stem cells and other cell types and suggest that future work using rAAV as an experimental tool in the DG and as a gene therapy for diseases of the central nervous system should be carefully evaluated.

REV-ERB Agonist SR9009 Regulates the Proliferation and Neurite Outgrowth/Suppression of Cultured Rat Adult Hippocampal Neural Stem/Progenitor Cells in a Concentration-Dependent Manner

REV-ERBs are heme-binding nuclear receptors that regulate the circadian rhythm and play important roles in the regulation of proliferation and the neuronal differentiation process in neuronal stem/progenitor cells in the adult brain. However, the effects of REV-ERB activation in the adult brain remain unclear. In this study, SR9009, a synthetic REV-ERB agonist that produces anxiolytic effects in mice, was used to treat undifferentiated and neuronally differentiated cultured rat adult hippocampal neural stem/progenitor cells (AHPs). The expression of Rev-erbβ was upregulated during neurogenesis in cultured rat AHPs, and Rev-erbβ knockdown analysis indicated that REV-ERBβ regulates the proliferation and neurite outgrowth of cultured rat AHPs. The application of a low concentration (0.1 µM) of the REV-ERB agonist SR9009 enhanced neurite outgrowth during neurogenesis in cultured rat AHPs, whereas the addition of a high concentration (2.5 µM) of SR9009 suppressed neurite outgrowth. Further examination of the SR9009 regulatory mechanism showed that the expressions of downstream target genes of REV-ERBβ, including Ccna2 and Sez6, were modulated by SR9009. The results of this study indicated that REV-ERBβ activity in cultured rat AHPs was regulated by SR9009 in a concentration-dependent manner. Furthermore, SR9009 inhibited the growth of cultured rat AHPs through various pathways, which may provide insight into the multifunctional mechanisms of action associated with SR9009. The findings of this study may provide an improved understanding of proliferation and neuronal maturation mechanisms in cultured rat AHPs through SR9009-regulated REV-ERBβ signaling pathways.

Lamin B1 decline underlies age-related loss of adult hippocampal neurogenesis

Neurogenesis in the adult hippocampus declines with age, a process that has been implicated in cognitive and emotional impairments. However, the mechanisms underlying this decline have remained elusive. Here, we show that the age-dependent downregulation of lamin B1, one of the nuclear lamins in adult neural stem/progenitor cells (ANSPCs), underlies age-related alterations in adult hippocampal neurogenesis. Our results indicate that higher levels of lamin B1 in ANSPCs safeguard against premature differentiation and regulate the maintenance of ANSPCs. However, the level of lamin B1 in ANSPCs declines during aging. Precocious loss of lamin B1 in ANSPCs transiently promotes neurogenesis but eventually depletes it. Furthermore, the reduction of lamin B1 in ANSPCs recapitulates age-related anxiety-like behavior in mice. Our results indicate that the decline in lamin B1 underlies stem cell aging and impacts the homeostasis of adult neurogenesis and mood regulation.

Ascorbic acid can promote the generation and expansion of neuroepithelial-like stem cells derived from hiPS/ES cells under chemically defined conditions through promoting collagen synthesis

INTRODUCTION

Spinal cord injury (SCI) is a neurological, medically incurable disorder. Human pluripotent stem cells (hPSCs) have the potential to generate neural stem/progenitor cells (NS/PCs), which hold promise in the treatment of SCI by transplantation. In our study, we aimed to establish a chemically defined culture system using serum-free medium and ascorbic acid (AA) to generate and expand long-term self-renewing neuroepithelial-like stem cells (lt-NES cells) differentiated from hPSCs effectively and stably.

METHODS

We induced human embryonic stem cells (hESCs)/induced PSCs (iPSCs) to neurospheres using a newly established in vitro induction system. Moreover, lt-NES cells were derived from hESC/iPSC-neurospheres using two induction systems, i.e., conventional N2 medium with gelatin-coated plates (coated) and N2+AA medium without pre-coated plates (AA), and were characterized by reverse transcription polymerase chain reaction (RT-PCR) analysis and immunocytochemistry staining. Subsequently, lt-NES cells were induced to neurons. A microelectrode array (MEA) recording system was used to evaluate the functionality of the neurons differentiated from lt-NES cells. Finally, the mechanism underlying the induction of lt-NES cells by AA was explored through RNA-seq and the use of inhibitors.

RESULTS

HESCs/iPSCs were efficiently induced to neurospheres using a newly established induction system in vitro. lt-NES cells derived from hESC/iPSC-neurospheres using the two induction systems (coated vs. AA) both expressed the neural pluripotency-associated genes PAX6, NESTIN, SOX1, and SOX2. After long-term cultivation, we found that they both exhibited long-term expansion for more than a dozen generations while maintaining neuropluripotency. Moreover, the lt-NES cells retained the ability to differentiate into general functional neurons that express β-tubulin at high levels. We also demonstrated that AA promotes the generation and long-term expansion of lt-NES cells by promoting collagen synthesis via the MEK-ERK1/2 pathway.

CONCLUSIONS

This new chemically defined culture system was stable and effective regarding the generation and culture of lt-NES cells induced from hESCs/iPSCs using serum-free medium combined with AA. The lt-NES cells induced under this culture system maintained their long-term expansion and neural pluripotency, with the potential to differentiate into functional neurons.

Apolipoprotein E expression pattern in human induced pluripotent stem cells during in vitro neural induction

Apolipoprotein E (APOE) is a multifunctional protein that plays significant roles in important cellular mechanisms in peripheral tissues and is as well expressed in the central nervous system, notably by adult neural stem cells (NSCs) in the hippocampus. Evidence from animal studies suggest that APOE is critical for adult NSC maintenance. However, whether APOE has the potential to play a similar role in human NSCs has not been directly investigated. To address this question, we conducted a focused study characterising APOE gene and protein expression in an in vitro model of neural differentiation utilising human induced pluripotent stem cells. We found that APOE gene expression was dramatically decreased as the cells became more differentiated, indicating that APOE expression levels reflect the degree of cellular differentiation during neural induction. Furthermore, qualitative analysis results of immunocytochemistry showed that intracellular localisation of APOE protein becomes more pronounced as neural differentiation progresses. Taken together, our findings suggest a potential role for APOE in human NSC maintenance and justify further investigations being carried out to understand whether changes in APOE levels can directly impact the neurogenic capacity of human stem cells.

Apolipoprotein E expression pattern in human induced pluripotent stem cells during in vitro neural induction

Apolipoprotein E (APOE) is a multifunctional protein that plays significant roles in important cellular mechanisms in peripheral tissues and is as well expressed in the central nervous system, notably by adult neural stem cells (NSCs) in the hippocampus. Evidence from animal studies suggest that APOE is critical for adult NSC maintenance. However, whether APOE has the potential to play a similar role in human NSCs has not been directly investigated. To address this question, we conducted a focused study characterising APOE gene and protein expression in an in vitro model of neural differentiation utilising human induced pluripotent stem cells. We found that APOE gene expression was dramatically decreased as the cells became more differentiated, indicating that APOE expression levels reflect the degree of cellular differentiation during neural induction. Furthermore, qualitative analysis results of immunocytochemistry showed that intracellular localisation of APOE protein becomes more pronounced as neural differentiation progresses. Taken together, our findings suggest a potential role for APOE in human NSC maintenance and justify further investigations being carried out to understand whether changes in APOE levels can directly impact the neurogenic capacity of human stem cells.

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.

In Vitro Monolayer Culture of Dispersed Neural Stem Cells on the E-Cadherin-Based Substrate with Long-Term Stemness Maintenance

Neural stem cells (NSCs) play an important role in neural tissue engineering because of their capacity of self-renewal and differentiation to multiple cell lineages. The in vitro conventional neurosphere culture protocol has some limitations such as limited nutrition and oxygen penetration and distribution causing the heterogeneity of cells inside, inaccessibility of internal cells, and inhomogeneous cellular morphology and properties. As a result, cultivation as a monolayer is a better way to study NSCs and obtain a homogeneous cell population. The cadherins are a classical family of homophilic cell adhesion molecules mediating cell-cell adhesion. Here, we used a recombinant human E-cadherin mouse IgG Fc chimera protein that self-assembles on a hydrophobic polystyrene surface via hydrophobic interaction to obtain an E-cadherin-coated culture plate (ECP). The rat fetal NSCs were cultured on the ECP and routine tissue culture plate (TCP) from passage 2 to passage 5. NSCs on TCP formed uniform floating neurospheres and grew up over time, while cells on the ECP adhered on the bottom of the plate and exhibited individual cells with scattering morphology, forming intercellular connections between cells. The cell proliferation and differentiation behaviors that were evaluated by Cell Counting Kit-8 assay (CCK-8), immunofluorescence staining, and real-time quantitative polymerase chain reaction showed NSCs could maintain the capacity for self-renewal and ability to differentiate into neurons, oligodendrocytes, and astrocytes after the long-term in vitro cell culture and passaging. Therefore, our study indicated that hE-cad-Fc could provide a homogeneous environment for individual cells in monolayer conditions to maintain the capacity of self-renewal and differentiation by mimicking the cell-cell interaction.

The role of adult hippocampal neurogenesis in brain health and disease

Adult neurogenesis in the dentate gyrus of the hippocampus is highly regulated by a number of environmental and cell-intrinsic factors to adapt to environmental changes. Accumulating evidence suggests that adult-born neurons may play distinct physiological roles in hippocampus-dependent functions, such as memory encoding and mood regulation. In addition, several brain diseases, such as neurological diseases and mood disorders, have deleterious effects on adult hippocampal neurogenesis, and some symptoms of those diseases can be partially explained by the dysregulation of adult hippocampal neurogenesis. Here we review a possible link between the physiological functions of adult-born neurons and their roles in pathological conditions.

Modeling Reveals the Dependence of Hippocampal Neurogenesis Radiosensitivity on Age and Strain of Rats

Cognitive dysfunction following radiation treatment for brain cancers in both children and adults have been correlated to impairment of neurogenesis in the hippocampal dentate gyrus. Various species and strains of rodent models have been used to study radiation-induced changes in neurogenesis and these investigations have utilized only a limited number of doses, dose-fractions, age and time after exposures conditions. In this paper, we have extended our previous mathematical model of radiation-induced hippocampal neurogenesis impairment of C57BL/6 mice to delineate the time, age, and dose dependent alterations in neurogenesis of a diverse strain of rats. To the best of our knowledge, this is the first predictive mathematical model to be published about hippocampal neurogenesis impairment for a variety of rat strains after acute or fractionated exposures to low linear energy transfer (low LET) radiation, such as X-rays and γ-rays, which are conventionally used in cancer radiation therapy. We considered four compartments to model hippocampal neurogenesis and its impairment following radiation exposures. Compartments include: (1) neural stem cells (NSCs), (2) neuronal progenitor cells or neuroblasts (NB), (3) immature neurons (ImN), and (4) glioblasts (GB). Additional consideration of dose and time after irradiation dependence of microglial activation and a possible shift of NSC proliferation from neurogenesis to gliogenesis at higher doses is established. Using a system of non-linear ordinary differential equations (ODEs), characterization of rat strain and age-related dynamics of hippocampal neurogenesis for unirradiated and irradiated conditions is developed. The model is augmented with the description of feedback regulation on early and late neuronal proliferation following radiation exposure. Predictions for dose-fraction regimes compared to acute radiation exposures, along with the dependence of neurogenesis sensitivity to radiation on age and strain of rats are discussed. A major result of this work is predictions of the rat strain and age dependent differences in radiation sensitivity and sub-lethal damage repair that can be used for predictions for arbitrary dose and dose-fractionation schedules.

Long-Term Labeling of Hippocampal Neural Stem Cells by a Lentiviral Vector

Using a lentivirus-mediated labeling method, we investigated whether the adult hippocampus retains long-lasting, self-renewing neural stem cells (NSCs). We first showed that a single injection of a lentiviral vector expressing a green fluorescent protein (LV PGK-GFP) into the subgranular zone (SGZ) of the adult hippocampus enabled an efficient, robust, and long-term marking of self-renewing NSCs and their progeny. Interestingly, a subset of labeled cells showed the ability to proliferate multiple times and give rise to Sox2⁺ cells, clearly suggesting the ability of NSCs to self-renew for an extensive period of time (up to 6 months). In addition, using GFP⁺ cells isolated from the SGZ of mice that received a LV PGK-GFP injection 3 months earlier, we demonstrated that some GFP⁺ cells displayed the essential properties of NSCs, such as self-renewal and multipotency. Furthermore, we investigated the plasticity of NSCs in a perforant path transection, which has been shown to induce astrocyte formation in the molecular layer of the hippocampus. Our lentivirus (LV)-mediated labeling study revealed that hippocampal NSCs are not responsible for the burst of astrocyte formation, suggesting that signals released from the injured perforant path did not influence NSC fate determination. Therefore, our studies showed that a gene delivery system using LVs is a unique method to be used for understanding the complex nature of NSCs and may have translational impact in gene therapy by efficiently targeting NSCs.

Sirt1 protects neural stem cells from apoptosis by decreasing acetylation of histone 3K9

Objective

To explore the role and mechanism of Sirt1 in protecting neural stem cells (NSCs) from apoptosis.

Materials and methods

Transfection was used to overexpress Sirt1 in rat NSCs. The effect of Sirt1 overexpression on camptothecin-induced apoptosis of NSCs was evaluated. Western blotting was used to examine the expression of Sirt1, cleaved caspase-3, and acetylated histone 3K9.

Results

Overexpression of Sirt1 in NSCs decreased the cleavage of caspase-3 and acetylation of histone 3K9.

Conclusion

Sirt1 may protect NSCs from apoptosis by decreasing the acetylation of histone 3 on K9.

Grafting Neural Stem and Progenitor Cells Into the Hippocampus of Juvenile, Irradiated Mice Normalizes Behavior Deficits

The pool of neural stem and progenitor cells (NSPCs) in the dentate gyrus of the hippocampus is reduced by ionizing radiation. This explains, at least partly, the learning deficits observed in patients after radiotherapy, particularly in pediatric cases. An 8 Gy single irradiation dose was delivered to the whole brains of postnatal day 9 (P9) C57BL/6 mice, and BrdU-labeled, syngeneic NSPCs (1.0 × 10⁵ cells/injection) were grafted into each hippocampus on P21. Three months later, behavior tests were performed. Irradiation impaired novelty-induced exploration, place learning, reversal learning, and sugar preference, and it altered the movement pattern. Grafting of NSPCs ameliorated or even normalized the observed deficits. Less than 4% of grafted cells survived and were found in the dentate gyrus 5 months later. The irradiation-induced loss of endogenous, undifferentiated NSPCs in the dentate gyrus was completely restored by grafted NSPCs in the dorsal, but not the ventral, blade. The grafted NSPCs did not exert appreciable effects on the endogenous NSPCs; however, more than half of the grafted NSPCs differentiated. These results point to novel strategies aimed at ameliorating the debilitating late effects of cranial radiotherapy, particularly in children.

A Fatty Acid Oxidation-Dependent Metabolic Shift Regulates Adult Neural Stem Cell Activity

Hippocampal neurogenesis is important for certain forms of cognition, and failing neurogenesis has been implicated in neuropsychiatric diseases. The neurogenic capacity of hippocampal neural stem/progenitor cells (NSPCs) depends on a balance between quiescent and proliferative states. Here, we show that the rate of fatty acid oxidation (FAO) regulates the activity of NSPCs. Quiescent NSPCs show high levels of carnitine palmitoyltransferase 1a (Cpt1a)-dependent FAO, which is downregulated in proliferating NSPCs. Pharmacological inhibition and conditional deletion of Cpt1a in vitro and in vivo leads to altered NSPC behavior, showing that Cpt1a-dependent FAO is required for stem cell maintenance and proper neurogenesis. Strikingly, manipulation of malonyl-CoA, the metabolite that regulates levels of FAO, is sufficient to induce exit from quiescence and to enhance NSPC proliferation. Thus, the data presented here identify a shift in FAO metabolism that governs NSPC behavior and suggest an instructive role for fatty acid metabolism in regulating NSPC activity.

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A metabolic shift defines NSPC quiescence versus proliferation

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Quiescent NSPCs require high levels of FAO

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Changing levels of a single metabolite is sufficient to induce NSPC proliferation

Involvement of Nuclear Receptor REV-ERBβ in Formation of Neurites and Proliferation of Cultured Adult Neural Stem Cells

Neural stem cells (NSCs) serve as the source of both neurons and support cells, and neurogenesis is reportedly linked to the circadian clock. This study aimed to clarify the functional role of the circadian rhythm-related nuclear receptor, REV-ERBβ, in neurogenesis of NSCs from adult brain. Accordingly, Rev-erbβ expression and the effect of Rev-erbβ gene-specific knockdown on neurogenesis in vitro was examined in adult rodent NSCs. Initial experiments confirmed REV-ERBβ expression in cultured adult NSCs, while subsequent gene expression and gene ontogeny analyses identified functional genes upregulated or downregulated by REV-ERBβ. In particular, expression levels of factors associated with proliferation, stemness, and neural differentiation were affected. Knockdown of Rev-erbβ showed involvement of REV-ERBβ in regulation of cellular proliferation and self-renewal of cultured adult NSCs. Moreover, Rev-erbβ-knockdown cells formed neurons with a slightly shrunken morphology, fewer new primary neurites, and reduced length and branch formation of neurites. Altogether, this suggests that REV-ERBβ is involved in neurite formation during neuronal differentiation of cultured adult NSCs. In summary, REV-ERBβ is a known circadian regulatory protein that appears to be involved in neurogenesis via regulation of networks for cell proliferation and neural differentiation/maturation in adult NSCs.

Review: adult neurogenesis contributes to hippocampal plasticity

Adult hippocampal neurogenesis is the process by which new functional neurons are added to the adult dentate gyrus of the hippocampus. Animal studies have shown that the degree of adult hippocampal neurogenesis is regulated by local environmental cues as well as neural network activities. Furthermore, accumulating evidence has suggested that adult hippocampal neurogenesis plays prominent roles in hippocampus-dependent brain functions. In this review, we summarize the mechanisms underlying the regulation of adult hippocampal neurogenesis at various developmental stages and propose how adult-born neurons contribute to structural and functional hippocampal plasticity.

CD60b: Enriching Neural Stem/Progenitor Cells from Rat Development into Adulthood

CD60b antigens are highly expressed during development in the rat nervous system, while in the adult their expression is restricted to a few regions, including the subventricular zone (SVZ) around the lateral ventricles—a neurogenic niche in the adult brain. For this reason, we investigated whether the expression of C60b is associated with neural stem/progenitor cells in the SVZ, from development into adulthood. We performed in vitro and in vivo analyses of CD60b expression at different stages and identified the presence of these antigens in neural stem/progenitor cells. We also observed that CD60b could be used to purify and enrich a population of neurosphere-forming cells from the developing and adult brain. We showed that CD60b antigens (mainly corresponding to ganglioside 9-O-acetyl GD3, a well-known molecule expressed during central nervous system development and mainly associated with neuronal migration) are also present in less mature cells and could be used to identify and isolate neural stem/progenitor cells during development and in the adult brain. A better understanding of molecules associated with neurogenesis may contribute not only to improve the knowledge about the physiology of the mammalian central nervous system, but also to find new treatments for regenerating tissue after disease or brain injury.

Nup153 Interacts with Sox2 to Enable Bimodal Gene Regulation and Maintenance of Neural Progenitor Cells

Neural progenitor cells (NeuPCs) possess a unique nuclear architecture that changes during differentiation. Nucleoporins are linked with cell-type-specific gene regulation, coupling physical changes in nuclear structure to transcriptional output; but, whether and how they coordinate with key fate-determining transcription factors is unclear. Here we show that the nucleoporin Nup153 interacts with Sox2 in adult NeuPCs, where it is indispensable for their maintenance and controls neuronal differentiation. Genome-wide analyses show that Nup153 and Sox2 bind and co-regulate hundreds of genes. Binding of Nup153 to gene promoters or transcriptional end sites correlates with increased or decreased gene expression, respectively, and inhibiting Nup153 expression alters open chromatin configurations at its target genes, disrupts genomic localization of Sox2, and promotes differentiation in vitro and a gliogenic fate switch in vivo. Together, these findings reveal that nuclear structural proteins may exert bimodal transcriptional effects to control cell fate.

HSPB1 mutations causing hereditary neuropathy in humans disrupt non-cell autonomous protection of motor neurons

Heat shock protein beta-1 (HSPB1), is a ubiquitously expressed, multifunctional protein chaperone. Mutations in HSPB1 result in the development of a late-onset, distal hereditary motor neuropathy type II (dHMN) and axonal Charcot-Marie Tooth disease with sensory involvement (CMT2F). The functional consequences of HSPB1 mutations associated with hereditary neuropathy are unknown. HSPB1 also displays neuroprotective properties in many neuronal disease models, including the motor neuron disease amyotrophic lateral sclerosis (ALS). HSPB1 is upregulated in SOD1-ALS animal models during disease progression, predominately in glial cells. Glial cells are known to contribute to motor neuron loss in ALS through a non-cell autonomous mechanism. In this study, we examined the non-cell autonomous role of wild type and mutant HSPB1 in an astrocyte-motor neuron co-culture model system of ALS. Astrocyte-specific overexpression of wild type HSPB1 was sufficient to attenuate SOD1(G93A) astrocyte-mediated toxicity in motor neurons, whereas, overexpression of mutHSPB1 failed to ameliorate motor neuron toxicity. Expression of a phosphomimetic HSPB1 mutant in SOD1(G93A) astrocytes also reduced toxicity to motor neurons, suggesting that phosphorylation may contribute to HSPB1 mediated-neuroprotection. These data provide evidence that astrocytic HSPB1 expression may play a central role in motor neuron health and maintenance.

Loss of PINK1 leads to metabolic deficits in adult neural stem cells and impedes differentiation of newborn neurons in the mouse hippocampus

Emerging evidence suggests that mitochondrial dynamics regulates adult hippocampal neurogenesis (AHN). Although abnormal AHN has been linked to depression, anxiety, and cognitive dysfunction, which are features of neurodegenerative conditions, including Parkinson's disease (PD), the impact of mitochondrial deficits on AHN have not been explored previously in a model of neurodegeneration. Here, we used PTEN-induced kinase 1-deficient (PINK1^-/- ) mice that lacked a mitochondrial kinase mutated in recessive familial PD. We show that mitochondrial defects, elevated glycolysis, and increased apoptosis are associated with impaired but not abrogated differentiation of PINK1-deficient neural stem cells (NSCs) in culture. In the dentate gyrus of PINK1^-/- mice, newly generated doublecortin-positive neurons show aberrant dendritic morphology, and their maturation is compromised compared with wild-type mice. In addition, in vivo labeling of NSCs with 5-ethynyl-2'-deoxyuridine shows that proliferating NSC numbers are normal, but the differentiation of NSCs to doublecortin-positive neuroblasts and mature NeuN⁺ neurons is impeded in PINK1^-/- mice. Finally, we demonstrate that home cage activity and corticosterone levels of PINK1^-/- mice are normal, thereby excluding reduced physical activity and increased stress as causes of neurogenesis defects. Our results reveal a new and important relationship between mitochondrial dysfunction and impaired AHN in a genetic PD model. Targeting mitochondrial function and metabolism to increase AHN may hold promise for the treatment of affective disorders and the mitigation of related symptoms in PD and other neurodegenerative conditions.-Agnihotri, S. K., Shen, R., Li, J., Gao, X., Büeler, H. Loss of PINK1 leads to metabolic deficits in adult neural stem cells and impedes differentiation of newborn neurons in the mouse hippocampus.

Ten-Eleven Translocation 1 and 2 Confer Overlapping Transcriptional Programs for the Proliferation of Cultured Adult Neural Stem Cells

Adult neurogenesis originates from neural stem cells (NSCs) in specific regions of the adult brain. The molecular mechanisms that control the self-renewal and multipotency of NSCs have not been fully elucidated. In recent years, emerging evidence has revealed that ten-eleven translocation (TET) family DNA dioxygenases TET1 and TET2 play important roles in the central nervous system. Here, I present evidence that Tet1 and Tet2 are expressed in cultured NSCs derived from adult mouse brain and play an important role in the proliferative self-renewal of NSCs in an undifferentiated state. The investigation of intracellular molecular networks involving both Tet1 and Tet2 by gene knockdown and comprehensive genetic analyses showed that overlapping molecular mechanisms involving TET1 and TET2 regulate the expression of at least 16 genes required for DNA replication and cell cycle control. Interestingly, transcriptional regulation of the selected gene through TET1 and TET2 did not correlate with direct CpG demethylation of the gene promoter. These findings suggest that TET1 and TET2 play an important role in the proliferation of NSCs in the adult mouse brain by specifically regulating common genes for DNA replication and the cell cycle.

The pharmacological stimulation of Nurr1 improves cognitive functions via enhancement of adult hippocampal neurogenesis

The nuclear receptor related-1 (Nurr1) protein plays an important role in both the development of neural precursor cells (NPCs) and cognitive functions. Despite its relevance, the effects of Nurr1 on adult hippocampal neurogenesis have not been thoroughly investigated. Here we used RT-PCR, western blot, and immunocytochemistry to show that adult hippocampal NPCs abundantly express Nurr1. We then examined the effect of Nurr1 activation on adult hippocampal NPCs using amodiaquine (AQ), an anti-malarial drug that was recently discovered to be a Nurr1 agonist. Cell proliferation assay showed that AQ significantly increased cell proliferation. AQ-treated NPCs showed increased levels of phosphorylation of Akt and ERK1/2 whereas AQ-treated Nurr1 siRNA-transfected NPCs showed no changes in those levels. Further immunocytochemical and immunohistochemical analyses confirmed the stimulating effect of Nurr1 agonist on the proliferation and differentiation of adult hippocampal NPCs both in vivo and in vitro. In addition to its effects on proliferation and differentiation of NPCs, AQ-treated mice showed a significant enhancement of both short- and long-term memory in the Y-maze and the novel object recognition test. These data suggest that activation of Nurr1 may enhance cognitive functions by increasing adult hippocampal neurogenesis and also indicate that Nurr1 may be used as a therapeutic target for the treatment of memory disorders and cognitive impairment observed in neurodegenerative diseases.

Long-Term Estrogen Receptor Beta Agonist Treatment Modifies the Hippocampal Transcriptome in Middle-Aged Ovariectomized Rats

Estradiol (E2) robustly activates transcription of a broad array of genes in the hippocampal formation of middle-aged ovariectomized rats via estrogen receptors (ERα, ERβ, and G protein-coupled ER). Selective ERβ agonists also influence hippocampal functions, although their downstream molecular targets and mechanisms are not known. In this study, we explored the effects of long-term treatment with ERβ agonist diarylpropionitrile (DPN, 0.05 mg/kg/day, sc.) on the hippocampal transcriptome in ovariectomized, middle-aged (13 month) rats. Isolated hippocampal formations were analyzed by Affymetrix oligonucleotide microarray and quantitative real-time PCR. Four hundred ninety-seven genes fulfilled the absolute fold change higher than 2 (FC > 2) selection criterion. Among them 370 genes were activated. Pathway analysis identified terms including glutamatergic and cholinergic synapse, RNA transport, endocytosis, thyroid hormone signaling, RNA degradation, retrograde endocannabinoid signaling, and mRNA surveillance. PCR studies showed transcriptional regulation of 58 genes encoding growth factors (Igf2, Igfb2, Igf1r, Fgf1, Mdk, Ntf3, Bdnf), transcription factors (Otx2, Msx1), potassium channels (Kcne2), neuropeptides (Cck, Pdyn), peptide receptors (Crhr2, Oprm1, Gnrhr, Galr2, Sstr1, Sstr3), neurotransmitter receptors (Htr1a, Htr2c, Htr2a, Gria2, Gria3, Grm5, Gabra1, Chrm5, Adrb1), and vesicular neurotransmitter transporters (Slc32a1, Slc17a7). Protein-protein interaction analysis revealed networking of clusters associated with the regulation of growth/troph factor signaling, transcription, translation, neurotransmitter and neurohormone signaling mechanisms and potassium channels. Collectively, the results reveal the contribution of ERβ-mediated processes to the regulation of transcription, translation, neurogenesis, neuromodulation, and neuroprotection in the hippocampal formation of ovariectomized, middle-aged rats and elucidate regulatory channels responsible for DPN-altered functional patterns. These findings support the notion that selective activation of ERβ may be a viable approach for treating the neural symptoms of E2 deficiency in menopause.

Cell type-dependent Erk-Akt pathway crosstalk regulates the proliferation of fetal neural progenitor cells

Neural progenitor (NP) cells are the multipotent cells that produce neurons and glia in the central nervous system. Compounds regulating their proliferation are key to both understanding brain development and unlocking their potential in regenerative repair. We discuss a chemical screen that unexpectedly identified inhibitors of Erk signaling potently promoting the self-renewing divisions of fetal NP cells. This occurred through crosstalk between Erk and Akt signaling cascades. The crosstalk mechanism is cell type-specific, and is not detected in adult NP cells as well as brain tumor cells. The mechanism was also shown to be independent from the GSK-3 signaling pathway, which has been reported to be a major regulator of NP cell homeostasis and inhibitors to which were also identified in the screen. In vitro Erk inhibition led to the prolonged rapid expansion of fetal NP cells while retaining their multipotency. In vivo inhibitor administration significantly inhibited the neuronal differentiation, and resulted in increased proliferative progenitor cells in the ventricular/subventricular zone (VZ/SVZ) of the embryonic cortex. Our results uncovered a novel regulating pathway for NP cell proliferation in the developing brain. The discovery provides a pharmacological basis for in vitro expansion and in vivo manipulation of NP cells.

Major histocompatibility complex class I molecules protect motor neurons from astrocyte-induced toxicity in amyotrophic lateral sclerosis

Astrocytes isolated from individuals with amyotrophic lateral sclerosis (ALS) are toxic to motor neurons (MNs) and play a non-cell autonomous role in disease pathogenesis. The mechanisms underlying the susceptibility of MNs to cell death remain unclear. Here we report that astrocytes derived from either mice bearing mutations in genes associated with ALS or human subjects with ALS reduce the expression of major histocompatibility complex class I (MHCI) molecules on MNs; reduced MHCI expression makes these MNs susceptible to astrocyte-induced cell death. Increasing MHCI expression on MNs increases survival and motor performance in a mouse model of ALS and protects MNs against astrocyte toxicity. Overexpression of a single MHCI molecule, HLA-F, protects human MNs from ALS astrocyte-mediated toxicity, whereas knockdown of its receptor, the killer cell immunoglobulin-like receptor KIR3DL2, on human astrocytes results in enhanced MN death. Thus, our data indicate that, in ALS, loss of MHCI expression on MNs renders them more vulnerable to astrocyte-mediated toxicity.

Dibutyl Phthalate Inhibits the Effects of Follicle-Stimulating Hormone on Rat Granulosa Cells Through Down-Regulation of Follicle-Stimulating Hormone Receptor

Dibutyl phthalate (DBP) is used worldwide in solvents and plasticizers. The cytotoxicity and potential tumorigenic effect of DBP have been reported. DBP has also been shown to impact reproductive function. In this study, to further evaluate the effects of DBP on granulosa cells (GCs), we treated rat GCs in vitro with DBP before evaluation of the biological alterations of these GCs. We found that DBP did not induce significant GC death at the tested concentrations. However, follicle-stimulating hormone (FSH)-induced KIT ligand (KITLG) expression in GCs was significantly reduced at both mRNA and protein levels by DBP treatment in a dose-dependent manner. The down-regulation of KITLG was due to the down-regulation of expression of FSH receptor (FSHR) in GCs. Down-regulation of FSHR impaired FSH-induced intracellular signaling in GCs, demonstrated by decreased phosphorylation of AKT and mechanistic target of rapamycin (mTOR). Furthermore, DBP treatment also reduced FSH-induced expression of hypoxia-inducible factor 1-alpha (HIF1A), which is an important signaling component for KITLG expression. Other FSH-induced biological effects, such as production of estradiol and progesterone, as well as GC proliferation, were also suppressed by DBP. Therefore, our study discovered a unique mechanism underlying the toxicity of DBP on GCs. These findings may initiate the development of novel therapeutic interventions for DBP-induced damage to GCs.

REST Regulates Non-Cell-Autonomous Neuronal Differentiation and Maturation of Neural Progenitor Cells via Secretogranin II

RE-1 silencing transcription factor (REST), a master negative regulator of neuronal differentiation, controls neurogenesis by preventing the differentiation of neural stem cells. Here we focused on the role of REST in the early steps of differentiation and maturation of adult hippocampal progenitors (AHPs). REST knockdown promoted differentiation and affected the maturation of rat AHPs. Surprisingly, REST knockdown cells enhanced the differentiation of neighboring wild-type AHPs, suggesting that REST may play a non-cell-autonomous role. Gene expression analysis identified Secretogranin II (Scg2) as the major secreted REST target responsible for the non-cell-autonomous phenotype. Loss-of-function of Scg2 inhibited differentiation in vitro, and exogenous SCG2 partially rescued this phenotype. Knockdown of REST in neural progenitors in mice led to precocious maturation into neurons at the expense of mushroom spines in vivo. In summary, we found that, in addition to its cell-autonomous function, REST regulates differentiation and maturation of AHPs non-cell-autonomously via SCG2.

SIGNIFICANCE STATEMENT

Our results reveal that REST regulates differentiation and maturation of neural progenitor cells in vitro by orchestrating both cell-intrinsic and non-cell-autonomous factors and that Scg2 is a major secretory target of REST with a differentiation-enhancing activity in a paracrine manner. In vivo, REST depletion causes accelerated differentiation of newborn neurons at the expense of spine defects, suggesting a potential role for REST in the timing of the maturation of granule neurons.

An electrically resistive sheet of glial cells for amplifying signals of neuronal extracellular recordings

Electrical signals of neuronal cells can be recorded non-invasively and with a high degree of temporal resolution using multielectrode arrays (MEAs). However, signals that are recorded with these devices are small, usually 0.01%-0.1% of intracellular recordings. Here, we show that the amplitude of neuronal signals recorded with MEA devices can be amplified by covering neuronal networks with an electrically resistive sheet. The resistive sheet used in this study is a monolayer of glial cells, supportive cells in the brain. The glial cells were grown on a collagen-gel film that is permeable to oxygen and other nutrients. The impedance of the glial sheet was measured by electrochemical impedance spectroscopy, and equivalent circuit simulations were performed to theoretically investigate the effect of covering the neurons with such a resistive sheet. Finally, the effect of the resistive glial sheet was confirmed experimentally, showing a 6-fold increase in neuronal signals. This technique feasibly amplifies signals of MEA recordings.

A mechanism for the segregation of age in mammalian neural stem cells

Throughout life, neural stem cells (NSCs) generate neurons in the mammalian brain. Using photobleaching experiments, we found that during cell division in vitro and within the developing mouse forebrain, NSCs generate a lateral diffusion barrier in the membrane of the endoplasmic reticulum, thereby promoting asymmetric segregation of cellular components. The diffusion barrier weakens with age and in response to impairment of lamin-associated nuclear envelope constituents. Weakening of the diffusion barrier disrupts asymmetric segregation of damaged proteins, a product of aging. Damaged proteins are asymmetrically inherited by the nonstem daughter cell in embryonic and young adult NSC divisions, whereas in the older adult brain, damaged proteins are more symmetrically distributed between progeny. Thus, these data identify a mechanism of how damage that accumulates with age is asymmetrically distributed during somatic stem cell division.

RNA interference machinery-mediated gene regulation in mouse adult neural stem cells

Background

Neurogenesis in the brain of adult mammals occurs throughout life in two locations: the subventricular zone of the lateral ventricle and the subgranular zone of the dentate gyrus in the hippocampus. RNA interference mechanisms have emerged as critical regulators of neuronal differentiation. However, to date, little is known about its function in adult neurogenesis.

Results

Here we show that the RNA interference machinery regulates Doublecortin levels and is associated with chromatin in differentiating adult neural progenitors. Deletion of Dicer causes abnormal higher levels of Doublecortin. The microRNA pathway plays an important role in Doublecortin regulation. In particular miRNA-128 overexpression can reduce Doublecortin levels in differentiating adult neural progenitors.

Conclusions

We conclude that the RNA interference components play an important role, even through chromatin association, in regulating neuron-specific gene expression programs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-015-0198-7) contains supplementary material, which is available to authorized users.

Aging and Exercise Affect Hippocampal Neurogenesis via Different Mechanisms

The rate of neurogenesis is determined by 1) the number of neural stem/progenitor cells (NSCs), 2) proliferation of NSCs, 3) neuron lineage specification, and 4) survival rate of the newborn neurons. Aging lowers the rate of hippocampal neurogenesis, while exercise (Ex) increases this rate. However, it remains unclear which of the determinants are affected by aging and Ex. We characterized the four determinants in different age groups (3, 6, 9, 12, 21 months) of mice that either received one month of Ex training or remained sedentary. Bromodeoxyuridine (BrdU) was injected two hours before sacrificing the mice to label the proliferating cells. The results showed that the number of newborn neurons massively decreased (>95%) by the time the mice reached nine months of age. The number of NSC was mildly reduced during aging, while Ex delayed such decline. The proliferation rates were greatly decreased by the time the mice were 9-month-old and Ex could not improve the rates. The rates of neuron specification were decreased during aging, while Ex increased the rates. The survival rate was not affected by age or Ex. Aging greatly reduced newborn neuron maturation, while Ex potently enhanced it. In conclusion, age-associated decline of hippocampal neurogenesis is mainly caused by reduction of NSC proliferation. Although Ex increases the NSC number and neuron specification rates, it doesn't restore the massive decline of NSC proliferation rate. Hence, the effect of Ex on the rate of hippocampal neurogenesis during aging is limited, but Ex does enhance the maturation of newborn neurons.

Optimizing culture medium composition to improve oligodendrocyte progenitor cell yields in vitro from subventricular zone-derived neural progenitor cell neurospheres

Neural Stem and Progenitor Cells (NSC/NPC) are gathering tangible recognition for their uses in cell therapy and cell replacement therapies for human disease, as well as a model system to continue research on overall neural developmental processes in vitro. The Subventricular Zone is one of the largest NSC/NPC niches in the developing mammalian Central Nervous System, and persists through to adulthood. Oligodendrocyte progenitor cell (OPC) enriched cultures are usefull tools for in vitro studies as well as for cell replacement therapies for treating demyelination diseases. We used Subventricular Zone-derived NSC/NPC primary cultures from newborn mice and compared the effects of different growth factor combinations on cell proliferation and OPC yield. The Platelet Derived Growth Factor-AA and BB homodimers had a positive and significant impact on OPC generation. Furthermore, heparin addition to the culture media contributed to further increase overall culture yields. The OPC generated by this protocol were able to mature into Myelin Basic Protein-expressing cells and to interact with neurons in an in vitro co-culture system. As a whole, we describe an optimized in vitro method for increasing OPC.

Melatonin ameliorates dexamethasone-induced inhibitory effects on the proliferation of cultured progenitor cells obtained from adult rat hippocampus

Glucocorticoids, hormones that are released in response to stress, induce neuronal cell damage. The hippocampus is a primary target of glucocorticoids in the brain, the effects of which include the suppression of cell proliferation and diminished neurogenesis in the dentate gyrus. Our previous study found that melatonin, synthesized primarily in the pineal, pretreatment prevented the negative effects of dexamethasone, the glucocorticoid receptor agonist, on behavior and neurogenesis in rat hippocampus. In the present study, we attempted to investigate the interrelationship between melatonin and dexamethasone on the underlying mechanism of neural stem cell proliferation. Addition of dexamethasone to hippocampal progenitor cells from eight-week old rats resulted in a decrease in the number of neurospheres; pretreatment with melatonin precluded these effects. The immunocytochemical analyses indicated a reduction of Ki67 and nestin-positive cells in the dexamethasone-treated group, which was minimized by melatonin pretreatment. A reduction of the extracellular signal-regulated kinase 1 and 2 (ERK1/2) phosphorylation and G1-S phase cell cycle regulators cyclin E and CDK2 in dexamethasone-treated progenitor cells were prevented by pretreatment of melatonin. Moreover, luzindole, a melatonin receptor antagonist blocked the positive effect of melatonin whereas RU48, the glucocorticoid receptor antagonist blocked the negative effect of dexamethasone on the number of neurospheres. Moreover, we also found that dexamethasone increased the glucocorticoid receptor protein but decreased the level of MT1 melatonin receptor, whereas melatonin increased the level of MT1 melatonin receptor but decreased the glucocorticoid receptor protein. These suggest the crosstalk and cross regulation between the melatonin receptor and the glucocorticoid receptor on hippocampal progenitor cell proliferation.

Regulation of later neurogenic stages of adult-derived neural stem/progenitor cells by L-type Ca2+ channels

In the adult hippocampus, new neurons are continuously generated and incorporated into the local circuitry in a manner dependent on the network activity. Depolarization evoked by neurotransmitters has been assumed to activate L-type Ca2+ channels (LTCC) which regulate the intracellular Ca2+ -dependent signaling cascades. The process of neurogenesis contains several stages such as proliferation, fate determination, selective death/survival and maturation. Here, we investigated which stage of neurogenesis is under the regulation of LTCC using a clonal line of neural stem/progenitor cells, PZ5, which was derived from adult rat hippocampus. Although undifferentiated PZ5 cells were type 1-like cells expressing both nestin and glial fibrillary acidic protein, they generated neuronal, astrocytic and oligodendrocytic populations in differentiation medium containing retinoic acid. Proliferation of undifferentiated PZ5 cells was dependent on neither the LTCC antagonist, nimodipine (Nimo) nor the LTCC agonists, Bay K 8644 (BayK) or FPL 64176 (FPL), whereas the fraction of neuronal population that expressed both βIII-tubulin and MAP2 was reduced by Nimo but increased by BayK or FPL. At an earlier period of differentiation (e.g., day 4), the fraction of PZ5 cells expressing HuC/D, pan-neuronal marker, was not affected either by the LTCC activation or inhibition. At a later period of differentiation (e.g., day 9), the fraction of dying neurons was decreased by LTCC activation and increased by LTCC inhibition. It is suggested that the LTCC activation facilitates the survival and maturation of immature neurons, and that its inhibition facilitates the neuronal death.

Sox2 transcription network acts as a molecular switch to regulate properties of neural stem cells

Neural stem cells (NSCs) contribute to ontogeny by producing neurons at the appropriate time and location. Neurogenesis from NSCs is also involved in various biological functions in adults. Thus, NSCs continue to exert their effects throughout the lifespan of the organism. The mechanism regulating the core functional properties of NSCs is governed by intra- and extracellular signals. Among the transcription factors that serve as molecular switches, Sox2 is considered a key factor in NSCs. Sox2 forms a core network with partner factors, thereby functioning as a molecular switch. This review discusses how the network of Sox2 partner and target genes illustrates the molecular characteristics of the mechanism underlying the self-renewal and multipotency of NSCs.

A small molecule p75(NTR) ligand protects neurogenesis after traumatic brain injury

The p75 neurotrophin receptor (p75(NTR)) influences the proliferation, survival, and differentiation of neuronal precursors and its expression is induced in injured brain, where it regulates cell survival. Here, we test the hypotheses that pharmacologic modulation of p75(NTR) signaling will promote neural progenitor survival and proliferation, and improve outcomes of traumatic brain injury (TBI). LM11A-31, an orally available, blood-brain barrier-permeant small-molecule p75(NTR) signaling modulator, significantly increased proliferation and survival, and decreased JNK phosphorylation, in hippocampal neural stem/progenitor cells in culture expressing wild-type p75(NTR), but had no effect on cells expressing a mutant neurotrophin-unresponsive form of the receptor. The compound also enhanced the production of mature neurons from adult hippocampal neural progenitors in vitro. In vivo, intranasal administration of LM11A-31 decreased postinjury hippocampal and cortical neuronal death, neural progenitor cell death, gliogenesis, and microglial activation, and enhanced long-term hippocampal neurogenesis and reversed spatial memory impairments. LM11A-31 diminished the postinjury increase of SOX2-expressing early progenitor cells, but protected and increased the proliferation of endogenous polysialylated-neural cell adhesion molecule positive intermediate progenitors, and restored the long-term production of mature granule neurons. These findings suggest that modulation of p75(NTR) actions using small molecules such as LM11A-31 may constitute a potent therapeutic strategy for TBI.