Generation Of New Neurons Research Articles

Adult Neural Stem Cell Multipotency and Differentiation Are Directed by the Methyl-CpG-Binding Protein MBD1.

The generation of new neurons in the subventricular zone of the dentate gyrus during adulthood is indispensable to hippocampal-dependent learning and memory formation ([Goncalves et al., 2016][1]). A decrease in neurogenesis is associated with increased anxiety, depression, and other

Synergic Functions of miRNAs Determine Neuronal Fate of Adult Neural Stem Cells.

SummaryAdult neurogenesis requires the precise control of neuronal versus astrocyte lineage determination in neural stem cells. While microRNAs (miRNAs) are critically involved in this step during development, their actions in adult hippocampal neural stem cells (aNSCs) has been unclear. As entry point to address that question we chose DICER, an endoribonuclease essential for miRNA biogenesis and other RNAi-related processes. By specific ablation of Dicer in aNSCs in vivo and in vitro, we demonstrate that miRNAs are required for the generation of new neurons, but not astrocytes, in the adult murine hippocampus. Moreover, we identify 11 miRNAs, of which 9 have not been previously characterized in neurogenesis, that determine neurogenic lineage fate choice of aNSCs at the expense of astrogliogenesis. Finally, we propose that the 11 miRNAs sustain adult hippocampal neurogenesis through synergistic modulation of 26 putative targets from different pathways.

Spinal Cord Injury Impairs Neurogenesis and Induces Glial Reactivity in the Hippocampus.

The incorporation of newborn neurons with increased synaptic remodeling and activity-dependent plasticity in the dentate gyrus enhances hippocampal-dependent learning performances. Astrocytes and microglial cells are components of the neurogenic niche and regulate neurogenesis under normal and neurophatological conditions leading to functional consequences for learning and memory. Although cognitive impairments were reported in patients after spinal cord injury (SCI), only few studies have considered remote changes in brain structures which are not related with sensory and motor cortex. Thus, we examined neurogenesis and glial reactivity by stereological assessment in dentate gyrus sub-regions after three different intensities of thoracic spinal cord compression in rats. Sixty days after injury we observed a decrease in the Basso-Bresnahan-Beattie locomotor scale scores, rotarod performance and volume of spare tissue that correlated with the severity of the compression. Regarding the hippocampus, we observed that neurogenesis and hilar neurons were reduced after severe SCI, while only neurogenesis decreased in the moderately injured group. In addition, severe SCI induced reactive microglia and astrogliosis in all dentate gyrus sub-regions. Furthermore, the density of reactive microglia increased in the hilus whereas astrogliosis developed in the molecular layer after moderate SCI. No changes were observed in the mildly injured rats. These results suggest glial response and neurogenesis are associated with injury intensity. Interestingly, hippocampal neurogenesis is more sensitive to SCI than astrocytes or microglia reaction, as moderate injury impairs the generation of new neurons without changing glial response in the subgranular zone.

Huatuo Zaizao pill promotes functional recovery and neurogenesis after cerebral ischemia-reperfusion in rats

BackgroundIschemic stroke is the third leading cause of death in adults worldwide and is the first leading cause of long-term disability. Neurogenesis plays an important role in promoting behavioral recovery after stroke. Huatuo Zaizao pill (HT), a traditional Chinese medicine, has been used clinically in China to promote the rehabilitation after stroke, but the underlying mechanism of action was still unclear. This study is to investigate the effects of HT on the functional recovery in a rat model of cerebral ischemia-reperfusion (I/R) injury, and the potential molecular mechanisms.MethodsRats were randomly divided into sham, model with cerebral I/R injury, or HT-treated groups, then administered orally with vehicle (for the sham and model group) or HT (0.5, 1.0, or 2.0 mg/kg) respectively, for 3 or 7 days. Functional recovery was assessed by cylinder test, beam walking test, and adhesive test. Neurogenesis was investigated by double immunofluorescence staining for 5-ethynyl-2-deoxyuridine (EdU) and neuronal nuclear protein (NeuN). The proteins of kinase A (PKA), cAMP response element-binding protein (CREB), and brain-derived neurotrophic factor (BDNF) were assayed by western blotting. The level of BDNF mRNA was evaluated by RT-PCR.ResultsCompared with the model group, treatment with HT significantly promoted functional recovery in I/R injured rats (p < 0.05 or p < 0.01). The generation of new neurons was increased in the HT groups. HT treatment for 3 days increased the level of BDNF mRNA in I/R injured rats. Expression of PKA, phosphorylated CREB, and BDNF were significantly (p < 0.05) increased with the 7-day HT treatment.ConclusionsThese results indicated that HT treatment could promote functional recovery after stroke. HT enhanced the expression of BDNF and increased the level of neurogenesis in cerebral I/R animal, which might be associated with the functional recovery.

Single-Cell Transcriptomic Analysis Defines Heterogeneity and Transcriptional Dynamics in the Adult Neural Stem Cell Lineage

Neural stem cells (NSCs) in the adult mammalian brain serve as a reservoir for the generation of new neurons, oligodendrocytes, and astrocytes. Here, we use single-cell RNA sequencing to characterize adult NSC populations and examine the molecular identities and heterogeneity of invivo NSC populations. We find that cells in the NSC lineage exist on a continuum through the processes of activation and differentiation. Interestingly, rare intermediate states with distinct molecular profiles can be identified and experimentally validated, and our analysis identifies putative surface markers and key intracellular regulators for these subpopulations of NSCs. Finally, using the power of single-cell profiling, we conduct a meta-analysis to compare invivo NSCs and invitro cultures, distinct fluorescence-activated cell sorting strategies, and different neurogenic niches. These data provide a resource for the field and contribute to an integrative understanding of the adult NSC lineage.

Detecting Neuronal Differentiation Markers in Newborn Cells of the Adult Brain.

Adult neurogenesis is the lifelong generation of new neurons that occurs into restricted regions of the adult mammalian brain, namely the dentate gyrus of the hippocampus and the olfactory bulb. In this chapter, we describe the procedures aimed to investigate adult neurogenesis in the murine brain. Specifically, we explain how to inject into animals exogenous markers of proliferation (i.e., BrdU) and prepare brain tissues to perform immunofluorescence reactions for neuronal markers in combination with BrdU staining. As BrdU is incorporated in the DNA during the S-phase of the cell cycle of proliferating cells and is then inherited by daughter cells, by coupling BrdU-immunoreactivity together with the immunolabeling for neuronal markers, we provide the general procedures that can be applied to identify adult-born neurons and to characterize their specific phenotypes in different brain regions, under physiological condition or in pathological states.

Functions of Maternally-Derived Taurine in Fetal and Neonatal Brain Development.

Taurine (2-aminoethanesulfonic acid) is a sulfur-containing organic acid, which has various physiological functions, including membrane stabilization, cell-volume regulation, mitochondrial protein translocation, anti-oxidative activity, neuroprotection against neurotoxicity and modulation of intracellular calcium levels. Taurine also activates GABAA receptors and glycine receptors. Mammalian fetuses and infants are dependent on taurine delivered from their mothers via either the placenta or their mother's milk. Taurine is a molecule that links mother-fetus or mother-infant bonding.This review describes the functions of taurine and the mechanisms of action of taurine in fetal and brain development. Taurine is involved in regulating the proliferation of neural progenitors, migration of newly-generated neurons, and the synapse formation of neurons after migration during fetal and neonatal development. In this review, we also discuss the environmental factors that might influence the functional roles of taurine in neural development.

Neurogenesis and pattern separation: time for a divorce.

The generation of new neurons in the adult mammalian brain has led to numerous theories as to their functional significance. One of the most widely held views is that adult neurogenesis promotes pattern separation, a process by which overlapping patterns of neural activation are mapped to less overlapping representations. While a large body of evidence supports a role for neurogenesis in high interference memory tasks, it does not support the proposed function of neurogenesis in mediating pattern separation. Instead, the adult-generated neurons seem to generate highly overlapping and yet distinct distributed representations for similar events. One way in which these immature, highly plastic, hyperactive neurons may contribute to novel memory formation while avoiding interference is by virtue of their extremely sparse connectivity with incoming perforant path fibers. Another intriguing proposal, awaiting empirical confirmation, is that the young neurons' recruitment into memory formation is gated by a novelty/mismatch mechanism mediated by CA3 or hilar back-projections. Ongoing research into the intriguing link between neurogenesis, stress-related mood disorders, and age-related neurodegeneration may lead to promising neurogenesis-based treatments for this wide range of clinical disorders. WIREs Cogn Sci 2017, 8:e1427. doi: 10.1002/wcs.1427 For further resources related to this article, please visit the WIREs website.

Brain-Derived Neurotrophic Factor Induces Cell Survival and the Migration of Murine Adult Hippocampal Precursor Cells During Differentiation In Vitro.

The generation of new neurons during adulthood involves local precursor cell migration and terminal differentiation in the dentate gyrus. These events are influenced by the hippocampal microenvironment. Brain-derived neurotrophic factor (BDNF) is relevant for hippocampal neuronal development and behavior. Interestingly, studies that have been performed in controlled in vitro systems that involve isolated precursor cells that were derived from the dentate gyrus (AHPCs) have shown that BDNF induces the activation of the TrkB receptor and, consequentially, might activate signaling pathways that favor survival and neuronal differentiation. Based on the fact that the cellular events of AHPCs that are induced by single factors can be studied in this controlled in vitro system, we investigated the ability of BDNF and the involvement of protein kinase C (PKC), as one of the TrkB-downstream activated signaling proteins, in the regulation of migration, here reflected by motility, of AHPCs. Precursor cells were cultured following a concentration-response curve (1-640ng/ml) for 24 or 96h. We found that BDNF favored cell survival without altering the viability under culture proliferative conditions of the AHPCs. Concomitantly, glial- and neuronal-differentiated precursor cells increased as a consequence of survival promoted by BDNF. Additionally, pharmacological approaches showed that BDNF (40ng/ml)-induced migration of AHPCs was blocked with the compounds K252a and GF109203x, which prevent the activation of TrkB and PKC, respectively. The results indicate that in the in vitro migration of differentiated AHPCs it is involved the BDNF and TrkB cascade. Our results provide additional information about the mechanism by which BDNF impacts adult neurogenesis in the hippocampus.

A new role for the P2Y-like GPR17 receptor in the modulation of multipotency of oligodendrocyte precursor cells in vitro.

Oligodendrocyte precursor cells (OPCs, also called NG2 cells) are scattered throughout brain parenchyma, where they function as a reservoir to replace lost or damaged oligodendrocytes, the myelin-forming cells. The hypothesis that, under some circumstances, OPCs can actually behave as multipotent cells, thus generating astrocytes and neurons as well, has arisen from some in vitro and in vivo evidence, but the molecular pathways controlling this alternative fate of OPCs are not fully understood. Their identification would open new opportunities for neuronal replace strategies, by fostering the intrinsic ability of the brain to regenerate. Here, we show that the anti-epileptic epigenetic modulator valproic acid (VPA) can promote the generation of new neurons from NG2+ OPCs under neurogenic protocols in vitro, through their initial de-differentiation to a stem cell-like phenotype that then evolves to "hybrid" cell population, showing OPC morphology but expressing the neuronal marker βIII-tubulin and the GPR17 receptor, a key determinant in driving OPC transition towards myelinating oligodendrocytes. Under these conditions, the pharmacological blockade of the P2Y-like receptor GPR17 by cangrelor, a drug recently approved for human use, partially mimics the effects mediated by VPA thus accelerating cells' neurogenic conversion. These data show a co-localization between neuronal markers and GPR17 in vitro, and suggest that, besides its involvement in oligodendrogenesis, GPR17 can drive the fate of neural precursor cells by instructing precursors towards the neuronal lineage. Being a membrane receptor, GPR17 represents an ideal "druggable" target to be exploited for innovative regenerative approaches to acute and chronic brain diseases.

Brain repair and reprogramming: the route to clinical translation

The adult brain has a very limited capacity for generation of new neurons, and neurogenesis only takes place in restricted regions. Some evidence for neurogenesis after injury has been reported, but few, if any, neurons are replaced after brain injury or degeneration, and the permanent loss of neurons leads to long-term disability and loss of brain function. For decades, researchers have been developing cell transplantation using exogenous cell sources for brain repair, and this method has now been shown to successfully restore lost function in experimental and clinical trials. Here, we review the development of cell-replacement strategies for brain repair in Parkinson's disease using the example of human foetal brain cells being successfully translated from preclinical findings to clinical trials. These trials demonstrate that cell-replacement therapy is a viable option for patients with Parkinson's disease, but more importantly also show how the limited availability of foetal cells calls for development of novel cell sources and methods for generating new neurons for brain repair. We focus on new stem cell sources that are on the threshold of clinical application for brain repair and discuss emerging cellular reprogramming technologies. Reviewing the current status of direct neural conversion, both invitro and invivo, where somatic cells are directly reprogrammed into functional neurons without passing through a stem cell intermediate, we conclude that both methods result in the successful replacement of new neurons that mature and integrate into the host brain. Thus, this new field shows great promise for future brain repair, although much work is still needed in preclinical animal models before it can be seriously considered for clinical applications.

Understanding adult neurogenesis beyond its role in learning and memory formation

There has been a shift in the understanding of brain, neurons, and their functional role over the last two decades. Earlier it was believed that the brain was a static organ and was not subject to any change throughout life. An understanding was developed later that brain reorganizes its structure by a specific property called neuroplasticity. Recent research shows that the brain generates new neurons even in the adult stage, and this process is called adult neurogenesis. Although researchers still not have all the answers about the newborn neurons, and why and how they are generated, and what is their role, some have highlighted the importance of these in learning and memory formation, and even in memories of fear and spatial navigation. A wide range of environmental experience influences the generation of newborn neurons and their functional variability. There are questions about how different environmental experiences cause the differences in the generation of new neurons. Recently the field of optogenetics attempted to answer the questions on adult neurogenesis. However there are still questions about adult neurogenesis which needs a more naturalistic approach, for their better understanding.

Decreased adult neurogenesis in hibernating Syrian hamster

Generation of new neurons from adult neural stem cells occurs in the dentate gyrus (DG) of the hippocampus and the lateral walls of the lateral ventricles. In this article, we study the neurogenesis that takes place during the hibernation of the Syrian hamster (Mesocricetus auratus). Using a variety of standard neurogenesis markers and 5-bromo-2-deoxyuridine (BrdU) incorporation, we describe a preferential decrease in the proliferation of newborn neurons in the subventricular zone (SVZ) of the hibernating hamsters (torpor) rather than in the hippocampus. Furthermore, we demonstrate that the proliferative capacity is recovered after 3–4days of torpor when arousal is triggered under natural conditions (i.e., not artificially provoked). In addition, we show that tau3R, a tau isoform with three microtubule-binding domains, is a suitable marker to study neurogenesis both in the SVZ and subgranular zone (SGZ) of the Syrian hamster brain.

Acute deep brain stimulation in the thalamic reticular nucleus protects against acute stress and modulates initial events of adult hippocampal neurogenesis

Deep brain stimulation (DBS) is used as an alternative therapeutic procedure for pharmacoresistant psychiatric disorders. Recently the thalamic reticular nucleus (TRN) gained attention due to the description of a novel pathway from the amygdala to this nucleus suggesting that may be differentially disrupted in mood disorders. The limbic system is implicated in the regulation of these disorders that are accompanied by neuroplastic changes. The hippocampus is highly plastic and shows the generation of new neurons, process affected by stress but positively regulated by antidepressant drugs. We explored the impact of applying acute DBS to the TRN (DBS-TRN) in male Wistar rats exposed to acute stress caused by the forced-swim Porsolt’s test (FST) and on initial events of hippocampal neurogenesis. After the first session of forced-swim, rats were randomly subdivided in a DBS-TRN and a Sham group. Stimulated rats received 10min of DBS, thus the depressant-like behavior reflected as immobility was evaluated in the second session of forced-swim. Locomotricity was evaluated in the open field test. Cell proliferation and doublecortin-associated cells were quantified in the hippocampus of other cohorts of rats. No effects of electrode implantation were found in locomotricity. Acute DBS-TRN reduced immobility in comparison to the Sham group (p<0.001). DBS-TRN increased cell proliferation (Ki67 or BrdU-positive cells; p=0.02, p=0.02) and the number of doublecortin-cells compared to the Sham group (p<0.02). Similar effects were found in rats previously exposed to the first session of forced-swim. Our data could suggest that TRN brain region may be a promising target for DBS to treat intractable depression.

Editorial: 50th Anniversary of Adult Neurogenesis: Olfaction, Hippocampus, and Beyond.

Editorial: 50th Anniversary of Adult Neurogenesis: Olfaction, Hippocampus, and Beyond.

Allergy Enhances Neurogenesis and Modulates Microglial Activation in the Hippocampus.

Allergies and their characteristic TH2-polarized inflammatory reactions affect a substantial part of the population. Since there is increasing evidence that the immune system modulates plasticity and function of the central nervous system (CNS), we investigated the effects of allergic lung inflammation on the hippocampus—a region of cellular plasticity in the adult brain. The focus of the present study was on microglia, the resident immune cells of the CNS, and on hippocampal neurogenesis, i.e., the generation of new neurons. C57BL/6 mice were sensitized with a clinically relevant allergen derived from timothy grass pollen (Phl p 5). As expected, allergic sensitization induced high serum levels of allergen-specific immunoglobulins (IgG1 and IgE) and of TH2 cytokines (IL-5 and IL-13). Surprisingly, fewer Iba1+ microglia were found in the granular layer (GL) and subgranular zone (SGZ) of the hippocampal dentate gyrus and also the number of Iba1+MHCII+ cells was lower, indicating a reduced microglial surveillance and activation in the hippocampus of allergic mice. Neurogenesis was analyzed by labeling of proliferating cells with bromodeoxyuridine (BrdU) and determining their fate 4 weeks later, and by quantitative analysis of young immature neurons, i.e., cells expressing doublecortin (DCX). The number of DCX+ cells was clearly increased in the allergy animals. Moreover, there were more BrdU+ cells present in the hippocampus of allergic mice, and these newly born cells had differentiated into neurons as indicated by a higher number of BrdU+NeuN+ cells. In summary, allergy led to a reduced microglia presence and activity and to an elevated level of neurogenesis in the hippocampus. This effect was apparently specific to the hippocampus, as we did not observe these alterations in the subventricular zone (SVZ)/olfactory bulb (OB) system, also a region of high cellular plasticity and adult neurogenesis.

Can the Brain Benefits of Exercise Be Enhanced Without Additional Exercise?

Exercise has long been considered a useful means by which to maintain brain health and treat brain diseases. Yet many of the neural benefits of exercise, such as enhanced hippocampal neurogenesis, take weeks to manifest. Moreover, the brains most in need of the restorative effects of exercise are often paired with bodies that can tolerate very little physical activity, such as those deconditioned by stroke. It would therefore be of great utility to pinpoint ways in which the brain benefits of exercise could be augmented without adding additional exercise time. Exercise represents a significant challenge to the brain because of the heat produced by exercising muscles, but physical activity in the cold attenuates this physiological burden. Using a rat model of voluntary exercise, we recently tested the hypothesis that exercise in cold ambient temperature (4.5°C) would stimulate hippocampal neurogenesis more effectively than exercise at room temperature. We found that, compared to animals that ran at room temperature, animals that exercised in the cold ran a shorter distance and for less total time. Nonetheless, they had more significantly more newly generated neurons in the hippocampal dentate gyrus, indicating that running in the cold may be an effective means by which to maximize brain exercise benefits, yet minimize exercise time. Exercise is increasingly becoming accepted as “medicine” for diseases of both brain and body1. For the brain, exercise offers chemical, cellular and structural benefits, including enhanced generation of new neurons, glia and blood vessels2-5, increased expression of neurotrophins (such as brain-derived neurotrophic factor (BDNF)6,7), dendritic remodeling8,9 and stabilization of stress responses10 and inflammatory signaling11. These mechanisms of action directly counteract those present in disease states. For example, the depressed brain is characterized by decreased synaptic plasticity, hippocampal neurogenesis and BDNF12, all of which can be reversed by exercise.

X Irradiation Induces Acute Cognitive Decline via Transient Synaptic Dysfunction.

Cranial X irradiation can severely impair higher brain function, resulting in neurocognitive deficits. Radiation-induced brain injury is characterized by acute, early and late delayed changes, and morbidity is evident more than 6 months after irradiation. While the acute effects of radiation exposure on the brain are known, the underlying mechanisms remain unclear. In this study, we examined the acute effect of X radiation on synaptic function using behavioral analysis and immunohistochemistry. We found that 10 Gy whole-brain irradiation immediately after conditioning (within 30 min) impaired the formation of fear memory, whereas irradiation 24 h prior to conditioning did not. To investigate the mechanisms underlying these behavioral changes, we irradiated one hemisphere of the brain and analyzed synaptic function and adult neurogenesis immunohistochemically. We focused on drebrin, whose loss from dendritic spines is a surrogate marker of synaptopathy. The intensity of drebrin immunoreactivity started to decrease in the irradiated hemisphere 2 h after exposure. The immunostaining intensity recovered to preirradiation levels by 24 h, indicating that X radiation induced transient synaptic dysfunction. Interestingly, the number of newly generated neurons was not changed at 2 h postirradiation, whereas it was significantly decreased at 8 and 24 h postirradiation. Because irradiation 24 h prior to conditioning had no effect on fear memory, our findings suggest that radiation-induced death of newly-generated neurons does not substantially impact fear memory formation. The radiation-induced synaptic dysfunction likely caused a transient memory deficit during the critical period for fear memory formation (approximately 1-3 h after conditioning), which coincides with a change in drebrin immunostaining in the hippocampus, a structure critical for fear memory formation.

Abstract WP96: The Role of T-Lymphocytes in Neuroregeneration After Cerebral Ischemia

Introduction: Inflammation plays a critical role in the pathogenesis of ischemic stroke. The CNS responds to ischemic injury with an inflammatory process, characterized by an infiltration of inflammatory cells. Particularly T cells exhibit a great impact on early stroke outcome as recent studies showed that ablation of these cells decrease infarct size and improve neurological deficits in the acute phase after stroke. However, the role of T cells in the sub-acute and chronic phase after stroke is unknown. T cells are essential for effective neurogenesis and angiogenesis, mechanisms that are integral for successful regeneration after stroke. We assessed the hypothesis that T cells influence cellular mechanisms of post-ischemic neuroregeneration and consequently affect functional and structural recovery. Methods: 24 wild type (wt) and 11 RAG1 -/- mice were subjected to photothrombotic ischemia, a subset of 12 wt and 6 RAG1 -/- animals underwent training in motorized running wheels starting at day 3 following ischemia until the end of the experiment on day 28. Sensorimotor and cognitive testing was applied to quantify the recovery process. To label newly generated neurons, 5-Chloro-2′-deoxyuridine (CldU) and iododeoxyuridine (IdU) were administered at days 1 and 2 (CldU) and once weekly until day 28 (IdU) after ischemia. In a subsequent experiment, 17 RAG1 -/- mice were subjected to photothrombotic ischemia and underwent training, a subset of 10 animals received an adoptive transfer of T cells. Functional testing and cellular labeling were carried out in analogy to the first experiment. Results: Training improved recovery from sensorimotor and cognitive deficits following cortical ischemia in wt animals and increased the generation of new neurons in the ischemic brain. Rehabilitative training did not induce functional recovery in RAG1 -/- animals and had no effect on the generation of neurons. Adoptive transfer of T cells into the immunodeficient mice restored the ability for regeneration. Conclusion: T cells play an essential role in the functional and structural regeneration following ischemic brain injury. These results provide new clues on the complex mechanism by which immune cells impact different stages of the pathogenesis of ischemic stroke.

Editorial: Molecular Mechanisms for Reprogramming Hippocampal Development and Function by Early-Life Stress.

Editorial: Molecular Mechanisms for Reprogramming Hippocampal Development and Function by Early-Life Stress.