Regulation of endogenous neural stem/progenitor cells for neural repair-factors that promote neurogenesis and gliogenesis in the normal and damaged brain

Primitive and Definitive Neural Precursor Cells Are Present in Human Cerebral Organoids

Activation of neural stem cells (NSCs) correlates with improved functional outcomes in mouse models of injury. In the murine brain, NSCs have been extensively characterized and comprise (1) primitive NSCs (pNSCs) and (2) definitive NSCs (dNSCs). pNSCs are the earliest cells in the NSC lineage giving rise to dNSCs in the embryonic and adult mouse brain. pNSCs are quiescent under baseline conditions and can be activated upon injury. Herein, we asked whether human pNSCs and dNSCs can be isolated during the maturation of human cerebral organoids (COs) and activated by drugs known to regulate mouse NSC behavior. We demonstrate that self-renewing, multipotent pNSC and dNSC populations are present in human COs and express genes previously characterized in mouse NSCs. The drug NWL283, an inhibitor of apoptosis, reduced cell death in COs but did not improve NSC survival. Metformin, a drug used to treat type II diabetes that is known to promote NSC activation in mice, was found to expand human NSC pools. Together, these findings are the first to identify and characterize human pNSCs, advancing our understanding of the human NSC lineage and highlighting drugs that enhance their activity.

A three-dimensional tissue-engineered rostral migratory stream as an in vitro platform for subventricular zone-derived cell migration

In the brains of most adult mammals, neural precursor cells (NPCs) from the subventricular zone (SVZ) migrate through the rostral migratory stream (RMS) to replace olfactory bulb interneurons. Following brain injury, published studies have shown that NPCs can divert from the SVZ-RMS-OB route and migrate toward injured brain regions, but the quantity of arriving cells, the lack of survival and terminal differentiation of neuroblasts into neurons, and their limited capacity to re-connect into circuitry are insufficient to promote functional recovery in the absence of therapeutic intervention. Our lab has fabricated a biomimetic tissue-engineered rostral migratory stream (TE-RMS) that replicates some notable structural and functional components of the endogenous rat RMS. Based on the design attributes for the TE-RMS platform, it may serve as a regenerative medicine strategy to facilitate sustained neuronal replacement into an injured brain region or an in vitro tool to investigate cell-cell communication and neuroblast migration. Previous work has demonstrated that the TE-RMS replicates the basic structure, unique nuclear shape, cytoskeletal arrangement, and surface protein expression of the endogenous rat RMS. Here, we developed an enhanced TE-RMS fabrication method in hydrogel microchannels that allowed more robust and high-throughput TE-RMS assembly. We report unique astrocyte behavior, including astrocyte bundling into the TE-RMS, the presence of multiple TE-RMS bundles, and observations of discontinuities in TE-RMS bundles, when microtissues are fabricated in agarose microchannels containing different critical curved or straight geometric features. We also demonstrate that we can harvest NPCs from the SVZ of adult rat brains and that EGFP+ cells migrate in chain formation from SVZ neurospheres through the TE-RMS in vitro. Overall, the TE-RMS can be utilized as an in vitro platform to investigate the pivotal cell-cell signaling mechanisms underlying the synergy of molecular cues involved in immature neuronal migration and differentiation.

Adult Neurogenesis of Teleost Fish Determines High Neuronal Plasticity and Regeneration

Studying the properties of neural stem progenitor cells (NSPCs) in a fish model will provide new information about the organization of neurogenic niches containing embryonic and adult neural stem cells, reflecting their development, origin cell lines and proliferative dynamics. Currently, the molecular signatures of these populations in homeostasis and repair in the vertebrate forebrain are being intensively studied. Outside the telencephalon, the regenerative plasticity of NSPCs and their biological significance have not yet been practically studied. The impressive capacity of juvenile salmon to regenerate brain suggests that most NSPCs are likely multipotent, as they are capable of replacing virtually all cell lineages lost during injury, including neuroepithelial cells, radial glia, oligodendrocytes, and neurons. However, the unique regenerative profile of individual cell phenotypes in the diverse niches of brain stem cells remains unclear. Various types of neuronal precursors, as previously shown, are contained in sufficient numbers in different parts of the brain in juvenile Pacific salmon. This review article aims to provide an update on NSPCs in the brain of common models of zebrafish and other fish species, including Pacific salmon, and the involvement of these cells in homeostatic brain growth as well as reparative processes during the postraumatic period. Additionally, new data are presented on the participation of astrocytic glia in the functioning of neural circuits and animal behavior. Thus, from a molecular aspect, zebrafish radial glia cells are seen to be similar to mammalian astrocytes, and can therefore also be referred to as astroglia. However, a question exists as to if zebrafish astroglia cells interact functionally with neurons, in a similar way to their mammalian counterparts. Future studies of this fish will complement those on rodents and provide important information about the cellular and physiological processes underlying astroglial function that modulate neural activity and behavior in animals.

Neuroblasts migration under control of reactive astrocyte-derived BDNF: a promising therapy in late neurogenesis after traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) is a disease with high mortality and morbidity, which leads to severe neurological dysfunction. Neurogenesis has provided therapeutic options for treating TBI. Brain derived neurotrophic factor (BDNF) plays a key role in neuroblasts migration. We aimed to investigate to the key regulating principle of BDNF in endogenous neuroblasts migration in a mouse TBI model.

METHODS

In this study, controlled cortical impact (CCI) mice (C57BL/6J) model was established to mimic TBI. The sham mice served as control. Immunofluorescence staining and enzyme-linked immunosorbent assay were performed on the CCI groups (day 1, 3, 7, 14 and 21 after CCI) and the sham group. All the data were analyzed with Student's t-test or one-way or two-way analysis of variance followed by Tukey's post hoc test.

RESULTS

Our results revealed that neuroblasts migration initiated as early as day 1, peaking at day 7, and persisted till day 21. The spatiotemporal profile of BDNF expression was similar to that of neuroblasts migration, and BDNF level following CCI was consistently higher in injured cortex than in subventricular zone (SVZ). Reactive astrocytes account for the major resource of BDNF along the migrating path, localized with neuroblasts in proximity. Moreover, injection of exogenous CC chemokine ligand 2 (CCL2), also known as monocyte chemoattractant protein-1, at random sites promoted neuroblasts migration and astrocytic BDNF expression in both normal and CCI mice (day 28). These provoked neuroblasts can also differentiate into mature neurons. CC chemokine ligand receptor 2 antagonist can restrain the neuroblasts migration after TBI.

CONCLUSIONS

Neuroblasts migrated along the activated astrocytic tunnel, directed by BDNF gradient between SVZ and injured cortex after TBI. CCL2 might be a key regulator in the above endogenous neuroblasts migration. Moreover, delayed CCL2 administration may provide a promising therapeutic strategy for late neurogenesis post-trauma.

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

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

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

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

Regulation of Neurogenesis and Neuronal Differentiation by Natural Compounds

Neuronal damage or degeneration is the main feature of neurological diseases. Regulation of neurogenesis and neuronal differentiation is important in developing therapies to promote neuronal regeneration or synaptic network reconstruction. Neurogenesis is a multistage process in which neurons are generated and integrated into existing neuronal circuits. Neuronal differentiation is extremely complex because it can occur in different cell types and can be caused by a variety of inducers. Recently, natural compounds that induce neurogenesis and neuronal differentiation have attracted extensive attention. In this paper, the potential neural induction effects of medicinal plant-derived natural compounds on neural stem/progenitor cells (NS/PCs), the cultured neuronal cells, and mesenchymal stem cells (MSCs) are reviewed. The natural compounds that are efficacious in inducing neurogenesis and neuronal differentiation include phenolic acids, polyphenols, flavonoids, glucosides, alkaloids, terpenoids, quinones, coumarins, and others. They exert neural induction effects by regulating signal factors and cell-specific genes involved in the process of neurogenesis and neuronal differentiation, including specific proteins (β-tubulin III, MAP-2, tau, nestin, neurofilaments, GFAP, GAP-43, NSE), related genes and proteins (STAT3, Hes1, Mash1, NeuroD1, notch, cyclin D1, SIRT1, reggie-1), transcription factors (CREB, Nkx-2.5, Ngn1), neurotrophins (BDNF, NGF, NT-3) and signaling pathways (JAK/STAT, Wnt/β-catenin, MAPK, PI3K/Akt, GSK-3β/β-catenin, Ca2+/CaMKII/ATF1, Nrf2/HO-1, BMP). The natural compounds with neural induction effects are of great value for neuronal regenerative medicine and provide promising prevention and treatment strategies for neurological diseases.

Combination of Stem Cells and Rehabilitation Therapies for Ischemic Stroke

Stem cell transplantation with rehabilitation therapy presents an effective stroke treatment. Here, we discuss current breakthroughs in stem cell research along with rehabilitation strategies that may have a synergistic outcome when combined together after stroke. Indeed, stem cell transplantation offers a promising new approach and may add to current rehabilitation therapies. By reviewing the pathophysiology of stroke and the mechanisms by which stem cells and rehabilitation attenuate this inflammatory process, we hypothesize that a combined therapy will provide better functional outcomes for patients. Using current preclinical data, we explore the prominent types of stem cells, the existing theories for stem cell repair, rehabilitation treatments inside the brain, rehabilitation modalities outside the brain, and evidence pertaining to the benefits of combined therapy. In this review article, we assess the advantages and disadvantages of using stem cell transplantation with rehabilitation to mitigate the devastating effects of stroke.

Kv1.1 channels regulate early postnatal neurogenesis in mouse hippocampus via the TrkB signaling pathway

In the postnatal brain, neurogenesis occurs only within a few regions, such as the hippocampal sub-granular zone (SGZ). Postnatal neurogenesis is tightly regulated by factors that balance stem cell renewal with differentiation, and it gives rise to neurons that participate in learning and memory formation. The Kv1.1 channel, a voltage-gated potassium channel, was previously shown to suppress postnatal neurogenesis in the SGZ in a cell-autonomous manner. In this study, we have clarified the physiological and molecular mechanisms underlying Kv1.1-dependent postnatal neurogenesis. First, we discovered that the membrane potential of neural progenitor cells is highly dynamic during development. We further established a multinomial logistic regression model for cell-type classification based on the biophysical characteristics and corresponding cell markers. We found that the loss of Kv1.1 channel activity causes significant depolarization of type 2b neural progenitor cells. This depolarization is associated with increased tropomyosin receptor kinase B (TrkB) signaling and proliferation of neural progenitor cells; suppressing TrkB signaling reduces the extent of postnatal neurogenesis. Thus, our study defines the role of the Kv1.1 potassium channel in regulating the proliferation of postnatal neural progenitor cells in mouse hippocampus.

Interleukin-17A promotes the differentiation of bone marrow mesenchymal stem cells into neuronal cells

Ischemia or hemorrhagic stroke is one of the leading causes of death and permanent disability in the worldwide population. As a consequence of the potential increasing in stroke, stem cell therapy is currently an area of intense focus. However, there are less data available regarding the promotion of healing efficacy after stroke. The present study aimed to investigate whether the cytokine interleukin-17A (IL-17A) could have a role in promoting the neuronal differentiation of mesenchymal stem cells (MSCs) and to investigate the associated molecular mechanism. Firstly, different concentration of IL-17A at range from 5-40 ng/mL was applied to stimulate bone marrow MSCs (BMSCs) during the course of neurogenic differentiation. Then reverse transcription-PCR, histological analyses and immunofluorescence assays were used to determine the optimum concentration of IL-17A in promoting the neuronal differentiation of BMSCs, which was 20 ng/mL. Mechanistically, Wnt signaling pathway was activated and Notch signaling pathway was suppressed. In addition, there were antergic effect of these two signaling pathways modulating the neurogenic differentiation of BMSCs induced by IL-17A. The present study demonstrated the potential role of IL-17A-based BMSCs strategy for promoting neuronal differentiation in vitro. However, the treatment efficacy could be considerably confirmed in animals with ischemia stroke. Therefore, a more sophisticated strategy that addresses the complicated treatment associated with stroke is needed.

Post-stroke Neurogenesis: Friend or Foe?

The substantial clinical burden and disability after stroke injury urges the need to explore therapeutic solutions. Recent compelling evidence supports that neurogenesis persists in the adult mammalian brain and is amenable to regulation in both physiological and pathological situations. Its ability to generate new neurons implies a potential to contribute to recovery after brain injury. However, post-stroke neurogenic response may have different functional consequences. On the one hand, the capacity of newborn neurons to replenish the damaged tissue may be limited. In addition, aberrant forms of neurogenesis have been identified in several insult settings. All these data suggest that adult neurogenesis is at a crossroads between the physiological and the pathological regulation of the neurological function in the injured central nervous system (CNS). Given the complexity of the CNS together with its interaction with the periphery, we ultimately lack in-depth understanding of the key cell types, cell-cell interactions, and molecular pathways involved in the neurogenic response after brain damage and their positive or otherwise deleterious impact. Here we will review the evidence on the stroke-induced neurogenic response and on its potential repercussions on functional outcome. First, we will briefly describe subventricular zone (SVZ) neurogenesis after stroke beside the main evidence supporting its positive role on functional restoration after stroke. Then, we will focus on hippocampal subgranular zone (SGZ) neurogenesis due to the relevance of hippocampus in cognitive functions; we will outline compelling evidence that supports that, after stroke, SGZ neurogenesis may adopt a maladaptive plasticity response further contributing to the development of post-stroke cognitive impairment and dementia. Finally, we will discuss the therapeutic potential of specific steps in the neurogenic cascade that might ameliorate brain malfunctioning and the development of post-stroke cognitive impairment in the chronic phase.

Niche Cells Crosstalk In Neuroinflammation After Traumatic Brain Injury

Traumatic brain injury (TBI) is recognized as the disease with high morbidity and disability around world in spite of the work ongoing in neural protection. Due to heterogeneity among the patients, it's still hard to acquire satisfying achievements in clinic. Neuroinflammation, which exists since primary injury occurs, with elusive duality, appear to be of significance from recovery of injury to neurogenesis. In recent years, studied have revealed that communication in neurogenic niche is more than “cell to cell” communication, and study on NSCs represent it as central role in the progress of neural regeneration. Hence, the neuroinflammation-affecting crosstalk after TBI, and clarifying definitive role of NSCs in the course of regeneration is a promising subject for researchers, for its great potential in overcoming the frustrating status quo in clinic, promoting welfare of TBI patient.

Understanding Abnormal SMO-SHH Signaling in Autism Spectrum Disorder: Potential Drug Target and Therapeutic Goals

Autism is a multifactorial neurodevelopmental condition; it demonstrates some main characteristics, such as impaired social relationships and increased repetitive behavior. The initiation of autism spectrum disorder is mostly triggered during brain development by the deregulation of signaling pathways. Sonic hedgehog (SHH) signaling is one such mechanism that influences neurogenesis and neural processes during the development of the central nervous system. SMO-SHH signaling is also an important part of a broad variety of neurological processes, including neuronal cell differentiation, proliferation, and survival. Dysregulation of SMO-SHH signaling leads to many physiological changes that lead to neurological disorders such as ASD and contribute to cognitive decline. The aberrant downregulation of SMO-SHH signals contributes to the proteolytic cleavage of GLI (glioma-associated homolog) into GLI3 (repressor), which increases oxidative stress, neuronal excitotoxicity, neuroinflammation, and apoptosis by suppressing target gene expression. We outlined in this review that SMO-SHH deregulation plays a crucial role in the pathogenesis of autism and addresses the current status of SMO-SHH pathway modulators. Additionally, a greater understanding of the SHH signaling pathway is an effort to improve successful treatment for autism and other neurological disorders.

Multimodal treatment for spinal cord injury: a sword of neuroregeneration upon neuromodulation

Spinal cord injury is linked to the interruption of neural pathways, which results in irreversible neural dysfunction. Neural repair and neuroregeneration are critical goals and issues for rehabilitation in spinal cord injury, which require neural stem cell repair and multimodal neuromodulation techniques involving personalized rehabilitation strategies. Besides the involvement of endogenous stem cells in neurogenesis and neural repair, exogenous neural stem cell transplantation is an emerging effective method for repairing and replacing damaged tissues in central nervous system diseases. However, to ensure that endogenous or exogenous neural stem cells truly participate in neural repair following spinal cord injury, appropriate interventional measures (e.g., neuromodulation) should be adopted. Neuromodulation techniques, such as noninvasive magnetic stimulation and electrical stimulation, have been safely applied in many neuropsychiatric diseases. There is increasing evidence to suggest that neuromagnetic/electrical modulation promotes neuroregeneration and neural repair by affecting signaling in the nervous system; namely, by exciting, inhibiting, or regulating neuronal and neural network activities to improve motor function and motor learning following spinal cord injury. Several studies have indicated that fine motor skill rehabilitation training makes use of residual nerve fibers for collateral growth, encourages the formation of new synaptic connections to promote neural plasticity, and improves motor function recovery in patients with spinal cord injury. With the development of biomaterial technology and biomechanical engineering, several emerging treatments have been developed, such as robots, brain-computer interfaces, and nanomaterials. These treatments have the potential to help millions of patients suffering from motor dysfunction caused by spinal cord injury. However, large-scale clinical trials need to be conducted to validate their efficacy. This review evaluated the efficacy of neural stem cells and magnetic or electrical stimulation combined with rehabilitation training and intelligent therapies for spinal cord injury according to existing evidence, to build up a multimodal treatment strategy of spinal cord injury to enhance nerve repair and regeneration.

Neurorestoration Approach by Biomaterials in Ischemic Stroke

Ischemic stroke (IS) is the leading cause of disability in the western world, assuming a high socio-economic cost. One of the most used strategies in the last decade has been biomaterials, which have been initially used with a structural support function. They have been perfected, different compounds have been combined, and they have been used together with cell therapy or controlled release chemical compounds. This double function has driven them as potential candidates for the chronic treatment of IS. In fact, the most developed are in different phases of clinical trial. In this review, we will show the ischemic scenario and address the most important criteria to achieve a successful neuroreparation from the point of view of biomaterials. The spontaneous processes that are activated and how to enhance them is one of the keys that contribute to the success of the therapeutic approach. In addition, the different routes of administration and how they affect the design of biomaterials are analyzed. Future perspectives show where this broad scientific field is heading, which advances every day with the help of technology and advanced therapies.

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

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

Targeting Purinergic Signaling and Cell Therapy in Cardiovascular and Neurodegenerative Diseases

Extracellular purines exert several functions in physiological and pathophysiological mechanisms. ATP acts through P2 receptors as a neurotransmitter and neuromodulator and modulates heart contractility, while adenosine participates in neurotransmission, blood pressure, and many other mechanisms. Because of their capability to differentiate into mature cell types, they provide a unique therapeutic strategy for regenerating damaged tissue, such as in cardiovascular and neurodegenerative diseases. Purinergic signaling is pivotal for controlling stem cell differentiation and phenotype determination. Proliferation, differentiation, and apoptosis of stem cells of various origins are regulated by purinergic receptors. In this chapter, we selected neurodegenerative and cardiovascular diseases with clinical trials using cell therapy and purinergic receptor targeting. We discuss these approaches as therapeutic alternatives to neurodegenerative and cardiovascular diseases. For instance, promising results were demonstrated in the utilization of mesenchymal stem cells and bone marrow mononuclear cells in vascular regeneration. Regarding neurodegenerative diseases, in general, P2X7 and A_2A receptors mostly worsen the degenerative state. Stem cell-based therapy, mainly through mesenchymal and hematopoietic stem cells, showed promising results in improving symptoms caused by neurodegeneration. We propose that purinergic receptor activity regulation combined with stem cells could enhance proliferative and differentiation rates as well as cell engraftment.

Interaction between Angiotensin Type 1, Type 2, and Mas Receptors to Regulate Adult Neurogenesis in the Brain Ventricular-Subventricular Zone

The renin-angiotensin system (RAS), and particularly its angiotensin type-2 receptors (AT2), have been classically involved in processes of cell proliferation and maturation during development. However, the potential role of RAS in adult neurogenesis in the ventricular-subventricular zone (V-SVZ) and its aging-related alterations have not been investigated. In the present study, we analyzed the role of major RAS receptors on neurogenesis in the V-SVZ of adult mice and rats. In mice, we showed that the increase in proliferation of cells in this neurogenic niche was induced by activation of AT2 receptors but depended partially on the AT2-dependent antagonism of AT1 receptor expression, which restricted proliferation. Furthermore, we observed a functional dependence of AT2 receptor actions on Mas receptors. In rats, where the levels of the AT1 relative to those of AT2 receptor are much lower, pharmacological inhibition of the AT1 receptor alone was sufficient in increasing AT2 receptor levels and proliferation in the V-SVZ. Our data revealed that interactions between RAS receptors play a major role in the regulation of V-SVZ neurogenesis, particularly in proliferation, generation of neuroblasts, and migration to the olfactory bulb, both in young and aged brains, and suggest potential beneficial effects of RAS modulators on neurogenesis.

Role of bone morphogenetic protein-2/4 in astrocyte activation in neuropathic pain

Background

Bone morphogenetic protein-2/4 (BMP2/4) has been recognized as promoters of astrocyte activity. Substantial evidence suggests that BMP2/4 may be elevated and plays a critical role in astrocyte activation upon spinal cord injury. Although neuropathic pain is similarly associated with astrocyte activation, the participation of BMP2/4 in this regard still remains unclear.

Methods

A rat model of neuropathic pain achieved by spinal nerve ligation at L5 was used to evaluate the expression of glial fibrillary acidic protein and BMP2/4 in the spinal cord in days 1, 4, 7, 10, and 14. Next, normal rats received intrathecal exogenous BMP2/4 and the antagonist Noggin to assess the effect of BMP2/4 on astrocyte activation. In both experiments, von Frey filaments were used to evaluate the changes in paw withdrawal threshold. In addition, Western blotting and immunofluorescence were performed to assess the expression of glial fibrillary acidic protein, BMP2/4, p-Smad 1/5/8, and phospho-signal transducer and activator of transcription-3 (p-STAT3) in the spinal cord.

Results

Firstly, spinal nerve ligation caused a significant increase in the expression of BMP4, while BMP2 levels remained unchanged. Secondly, exogenous BMP4 but not BMP2 induced a significant decrease in paw withdrawal threshold, along with the upregulation of glial fibrillary acidic protein. Moreover, exogenous BMP4 stimulated both p-Smad 1/5/8 and p-STAT3, while BMP2 only upregulated p-Smad 1/5/8. Finally, exogenous Noggin alleviated the decrease in paw withdrawal threshold induced by BMP4 and reduced astrocyte activation, as well as p-STAT3 upregulation.

Conclusions

Our results indicate only BMP4—and not BMP2—intervened in allodynia in rats by eliciting glial activation probably through both p-Smad 1/5/8 and p-STAT3 signaling.

Thyroid Hormones in the Brain and Their Impact in Recovery Mechanisms After Stroke

Thyroid hormones are of fundamental importance for brain development and essential factors to warrant brain functions throughout life. Their actions are mediated by binding to specific intracellular and membranous receptors regulating genomic and non-genomic mechanisms in neurons and populations of glial cells, respectively. Among others, mechanisms include the regulation of neuronal plasticity processes, stimulation of angiogenesis and neurogenesis as well modulating the dynamics of cytoskeletal elements and intracellular transport processes. These mechanisms overlap with those that have been identified to enhance recovery of lost neurological functions during the first weeks and months after ischemic stroke. Stimulation of thyroid hormone signaling in the postischemic brain might be a promising therapeutic strategy to foster endogenous mechanisms of repair. Several studies have pointed to a significant association between thyroid hormones and outcome after stroke. With this review, we will provide an overview on functions of thyroid hormones in the healthy brain and summarize their mechanisms of action in the developing and adult brain. Also, we compile the major thyroid-modulated molecular pathways in the pathophysiology of ischemic stroke that can enhance recovery, highlighting thyroid hormones as a potential target for therapeutic intervention.

Impact of Mesenchymal Stromal Cell Delivery Through Cardiopulmonary Bypass on Postnatal Neurogenesis

BACKGROUND

Neurodevelopmental impairment is an important challenge for survivors after neonatal surgery with cardiopulmonary bypass (CPB). The subventricular zone, where most neural stem/progenitors originate, plays a critical role in cortical maturation of the frontal lobe. Promoting neurogenesis in the subventricular zone is therefore a potential therapeutic target for preserving cortical growth. Mesenchymal stromal cells (MSCs) promote endogenous regeneration in the rodent brain. We investigated the impact of MSC delivery through CPB on neural stem/progenitor cells and neuroblasts (ie, young neurons) in the piglet subventricular zone.

METHODS

Two-week-old piglets (n = 12) were randomly assigned to one of three groups: (1) control, (2) deep hypothermic circulatory arrest, and (3) circulatory arrest, followed by MSC administration. MSCs (10 × 10⁶ per kg) were delivered through CPB during the rewarming period. Neural stem/progenitors, proliferating cells, and neuroblasts were identified with immunohistochemistry at 3 hours after CPB.

RESULTS

CPB-induced insults caused an increased proliferation of neural stem/progenitors (P < .05). MSC delivery reduced the acute proliferation. MSC treatment increased the number of neuroblasts in the outer region of the subventricular zone (P < .05) where they form migrating chains toward the frontal lobe. Conversely, the thickness of the neuroblast-dense band along the lateral ventricle was reduced after treatment (P < .05). These findings suggest that MSC treatment changes neuroblast distribution within the subventricular zone.

CONCLUSIONS

MSC delivery through CPB has the potential to mitigate effects of CPB on neural stem/progenitor cells and to promote migration of neuroblasts. Further investigation is necessary to determine the long-term effect of MSC treatment during CPB on postnatal neurogenesis.

L-type voltage-gated calcium channels in stem cells and tissue engineering

L-type voltage-gated calcium ion channels (L-VGCCs) have been demonstrated to be the mediator of several significant intracellular activities in excitable cells, such as neurons, chromaffin cells and myocytes. Recently, an increasing number of studies have investigated the function of L-VGCCs in non-excitable cells, particularly stem cells. However, there appear to be no systematic reviews of the relationship between L-VGCCs and stem cells, and filling this gap is prescient considering the contribution of L-VGCCs to the proliferation and differentiation of several types of stem cells. This review will discuss the possible involvement of L-VGCCs in stem cells, mainly focusing on osteogenesis mediated by mesenchymal stem cells (MSCs) from different tissues and neurogenesis mediated by neural stem/progenitor cells (NSCs). Additionally, advanced applications that use these channels as the target for tissue engineering, which may offer the hope of tissue regeneration in the future, will also be explored.

A Nerve Growth Factor Dipeptide Mimetic Stimulates Neurogenesis and Synaptogenesis in the Hippocampus and Striatum of Adult Rats with Focal Cerebral Ischemia

The nerve growth factor (NGF) and its mimetics, which have neuroprotective and neuroregenerative properties, are attractive candidates for developing new drugs for brain injury therapy. A dipeptide mimetic of NGF loop 4, bis(N-succinyl-L-glutamyl-L-lysine) hexamethylenediamide (GK-2), developed at the Zakusov Research Institute of Pharmacology, has the NGF-like ability to activate TrkA receptors, but unlike NGF, GK-2 activates mainly the PI3K/AKT pathway associated with neuroprotection and has no effect on the MAPK cascade associated with hyperalgesia, the main side effect of NGF. That GK-2 possesses neuroprotective activity has been observed in various models of cerebral ischemia. GK-2 was found to statistically significantly reduce the cerebral infarct volume in experimental stroke, even at treatment onset 24 h after injury. This suggests that GK-2 possesses neuroregenerative properties, which may be associated with the activation of neurogenesis and/or synaptogenesis. We studied the effect of GK-2 on neurogenesis and synaptogenesis in experimental ischemic stroke caused by transient occlusion of the middle cerebral artery in rats. GK-2 was administered 6 or 24 h after surgery and then once a day for 7 days. One day after the last administration, proliferative activity in the hippocampus and striatum of the affected hemisphere was assessed using Ki67 and synaptogenesis in the striatum was evaluated using synaptophysin and PSD-95. Ki67 immunoreactivity, both in the striatum and in the hippocampus of the ischemic rats, was found to have dropped by approximately 30% compared to that in the sham-operated controls. Synaptic markers - synaptophysin and PSD-95 - were also statistically significantly reduced, by 14 and 29%, respectively. GK-2 in both administration schedules completely restored the level of Ki67 immunoreactivity in the hippocampus and promoted its increase in the striatum. In addition, GK-2 restored the level of the postsynaptic marker PSD-95, with the therapeutic effect amounting to 70% at the start of its administration after 6 h, and promoted restoration of the level of this marker at the start of administration 24 h after an experimental stroke. GK-2 had no effect on the synaptophysin level. These findings suggest that the neurotrophin mimetic GK-2, which mainly activates one of the main Trk receptor signaling pathways PI3K/ AKT, has a stimulating effect on neurogenesis (and, probably, gliogenesis) and synaptogenesis in experimental cerebral ischemia. This effect may explain the protective effect observed at the start of dipeptide administration 24 h after stroke simulation.

Tracking Neural Progenitor Cell Migration in the Rodent Brain Using Magnetic Resonance Imaging

The study of neurogenesis and neural progenitor cells (NPCs) is important across the biomedical spectrum, from learning about normal brain development and studying disease to engineering new strategies in regenerative medicine. In adult mammals, NPCs proliferate in two main areas of the brain, the subventricular zone (SVZ) and the subgranular zone, and continue to migrate even after neurogenesis has ceased within the rest of the brain. In healthy animals, NPCs migrate along the rostral migratory stream (RMS) from the SVZ to the olfactory bulb, and in diseased animals, NPCs migrate toward lesions such as stroke and tumors. Here we review how MRI-based cell tracking using iron oxide particles can be used to monitor and quantify NPC migration in the intact rodent brain, in a serial and relatively non-invasive fashion. NPCs can either be labeled directly in situ by injecting particles into the lateral ventricle or RMS, where NPCs can take up particles, or cells can be harvested and labeled in vitro, then injected into the brain. For in situ labeling experiments, the particle type, injection site, and image analysis methods have been optimized and cell migration toward stroke and multiple sclerosis lesions has been investigated. Delivery of labeled exogenous NPCs has allowed imaging of cell migration toward more sites of neuropathology, which may enable new diagnostic and therapeutic opportunities for as-of-yet untreatable neurological diseases.

Systemic Factors Trigger Vasculature Cells to Drive Notch Signaling and Neurogenesis in Neural Stem Cells in the Adult Brain

It is well documented that adult neural stem cells (NSCs) residing in the subventricular zone (SVZ) and the subgranular zone (SGZ) are induced to proliferate and differentiate into new neurons after injury such as stroke and hypoxia. However, the role of injury‐related cues in driving this process and the means by which they communicate with NSCs remains largely unknown. Recently, the coupling of neurogenesis and angiogenesis and the extensive close contact between vascular cells and other niche cells, known as the neurovascular unit (NVU), has attracted interest. Further facilitating communication between blood and NSCs is a permeable blood‐brain‐barrier (BBB) present in most niches, making vascular cells a potential conduit between systemic signals, such as vascular endothelial growth factor (VEGF), and NSCs in the niche, which could play an important role in regulating neurogenesis. We show that the leaky BBB in stem cell niches of the intact and stroke brain can respond to circulating VEGF₁₆₅ to drive induction of the Notch ligand DLL4 (one of the most important cues in angiogenesis) in endothelial cells (ECs), pericytes, and further induce significant proliferation and neurogenesis of stem cells. Stem Cells2019;37:395–406

Delayed and Abbreviated Environmental Enrichment after Brain Trauma Promotes Motor and Cognitive Recovery That Is Not Contingent on Increased Neurogenesis

Environmental enrichment (EE) confers motor and cognitive recovery in pre-clinical models of traumatic brain injury (TBI), and neurogenesis has been attributed to mediating the benefits. Whether that ascription is correct has not been fully investigated. Hence, the goal of the current study is to further clarify the possible role of learning-induced hippocampal neurogenesis on functional recovery after cortical impact or sham injury by utilizing two EE paradigms (i.e., early + continuous, initiated immediately after TBI and presented 24 h/day; and delayed + abbreviated, initiated 4 days after TBI for 6 h/day) and comparing them to one another as well as to standard (STD) housed controls. Motor and cognitive performance was assessed on post-operative Days 1-5 and 14-19, respectively, for the STD and early + continuous EE groups and on Days 4-8 and 17-22, for the delayed + abbreviated EE groups. Rats were injected with bromodeoxyuridine (BrdU, 500 mg/ kg; intraperitoneally) for 3 days (12 h apart) before cognitive training and sacrificed 1 week later for quantification of BrdU+ and doublecortin (DCX+) labeled cells. Both early + continuous and delayed + abbreviated EE promoted motor and cognitive recovery after TBI, relative to STD (p < 0.05), and did not differ from one another (p > 0.05). However, only early + continuous EE increased DCX+ cells beyond the level of STD-housed controls (p < 0.05). No effect of EE on non-injured controls was observed. Based on these data, two novel conclusions emerged. First, EE does not need to be provided early and continuously after TBI to confer benefits, which lends credence to the delayed + abbreviated EE paradigm as a relevant pre-clinical model of neurorehabilitation. Second, the functional recovery observed after TBI in the delayed + abbreviated EE paradigm is not contingent on increased hippocampal neurogenesis. Future studies will elucidate alternate viable mechanisms mediating the benefits induced by EE.

Depression and adult neurogenesis: Positive effects of the antidepressant fluoxetine and of physical exercise

Of wide interest for health is the relation existing between depression, a very common psychological illness, accompanied by anxiety and reduced ability to concentrate, and adult neurogenesis. We will focus on two neurogenic stimuli, fluoxetine and physical exercise, both endowed with the ability to activate adult neurogenesis in the dentate gyrus of the hippocampus, known to be required for learning and memory, and both able to counteract depression. Fluoxetine belongs to the class of selective serotonin reuptake inhibitor (SSRI) antidepressants, which represent the most used pharmacological therapy; physical exercise has also been shown to effectively counteract depression symptoms in rodents as well as in humans. While there is evidence that the antidepressant effect of fluoxetine requires its pro-neurogenic action, exerted by promoting proliferation, differentiation and survival of progenitor cells of the hippocampus, on the other hand fluoxetine exerts also neurogenesis-independent antidepressant effects by influencing the plasticity of the new neurons generated. Similarly, the antidepressant action of running also correlates with an increase of hippocampal neurogenesis and plasticity, although the gene pathways involved are only partially coincident with those of fluoxetine, such as those involved in serotonin metabolism and synapse formation. We further discuss how extra-neurogenic actions are also suggested by the fact that, unlike running, fluoxetine is unable to stimulate neurogenesis during aging, but still displays antidepressant effects. Moreover, in specific conditions, fluoxetine or running activate not only progenitor but also stem cells, which normally are not stimulated; this fact reveals how stem cells have a long-term, hidden ability to self-renew and, more generally, that neurogenesis is subject to complex controls that may play a role in depression, such as the type of neurogenic stimulus or the state of the local niche. Finally, we discuss how fluoxetine or running are effective in counteracting depression originated from stress or neurodegenerative diseases.

Hydroxybutyrate promotes the recovery from cerebral infarction by activating Amp-activated protein kinase signaling

Recent studies have shown that hydroxybutyrate (GHB) is effective for protection against ischemia/brain damage in rat models. However, the specific underlying mechanism is poorly understood. In line with the previous studies, the present data showed that GHB improves cerebral blood flow (CBF) and physiological variables, including pH, pCO₂ and pO₂. Using CD31-immunofluorescence staining, a reduction of blood vessel density was indicated in the middle cerebral artery occlusion (MCAO) group; however, GHB treatment enhanced the cerebral vascular density in the ischemic area. In addition, GHB treatment increased the number of BrdU/lectin double-positive cells. Furthermore, the reduction of nestin-positive cells was identified in the brain of MCAO rats, while the number of nestin-positive cells was significantly increased after GHB administration. Compared with the sham group, the activation of Amp-activated protein kinase (AMPK) was identified in MCAO rats, suggesting stress-mediated AMPK activation after ischemia. Furthermore, the western blot assay showed that GHB treatment resulted in further activation of AMPK and endothelial nitric oxide synthase (eNOS), suggesting an enhanced energy supply. In summary, the present novel data indicates that GHB promotes the recovery from cerebral infarction mainly by activating AMPK and eNOS signaling, thereby enhancing angiogenesis and neuron regeneration.

Inhibition of Notch1 Signaling at the Subacute Stage of Stroke Promotes Endogenous Neurogenesis and Motor Recovery After Stroke

Background and Purpose: It is still not clear whether Notch1 signaling inhibition can promote functional outcomes after stroke, given that it plays time-dependent roles in the sequential process of endogenous neurogenesis. The purpose of this study was to identify the appropriate time frame for Notch1 signaling inhibition according to the temporal evolution of Notch1 signaling activation and the responses of neural stem cells (NSCs), in order to target it for therapeutic intervention and stimulate neurorestorative strategies after stroke.

Methods: Sprague-Dawley (SD) rats were subjected to 90-min of middle cerebral artery occlusion (MCAO). Rats were sacrificed before, and at day 1, day 2, day 3, day 4, and day 7 after ischemia for immunohistochemical analysis of the Notch intracellular domain (NICD), Nestin and doublecortin (Dcx). Next, MCAO rats were treated with the γ-secretase inhibitor N-[N-(3,5-di uorophenacetyl)-1-alanyl]-S-phenylglycine t-butylester (DAPT) or with saline at day 4 after ischemia, and subsequently evaluated with behavioral test analysis and magnetic resonance imaging (MRI). The rat brains were then harvested for immunohistochemical analysis of Dcx, NeuN and myelin basic protein (MBP) at 2, 3, 4, and 8 weeks.

Results: Notch1 signaling was maximally activated at day 3 after ischemia in parallel with the temporal evolution of NSCs. Inhibiting Notch1 signaling at day 4 after reperfusion with DAPT further promoted recovery of MRI parameters of the corticospinal tract (CST) and the functional outcomes, concomitantly with an increase in neuroblasts, their migration to the ischemic boundary, and potential differentiation to mature neurons, as well as the amelioration of axonal bundle integrity.

Conclusion: Inhibition of Notch1 signaling at the subacute stage of stroke could maximally promote endogenous neurogenesis and axonal reorganization.

Enhancing endogenous capacity to repair a stroke-damaged brain: An evolving field for stroke research

Stroke represents a severe medical condition that causes stroke survivors to suffer from long-term and even lifelong disability. Over the past several decades, a vast majority of stroke research targets neuroprotection in the acute phase, while little work has been done to enhance stroke recovery at the later stage. Through reviewing current understanding of brain plasticity, stroke pathology, and emerging preclinical and clinical restorative approaches, this review aims to provide new insights to advance the research field for stroke recovery. Lifelong brain plasticity offers the long-lasting possibility to repair a stroke-damaged brain. Stroke impairs the structural and functional integrity of entire brain networks; the restorative approaches containing multi-components have great potential to maximize stroke recovery by rebuilding and normalizing the stroke-disrupted entire brain networks and brain functioning. The restorative window for stroke recovery is much longer than previously thought. The optimal time for brain repair appears to be at later stage of stroke rather than the earlier stage. It is expected that these new insights will advance our understanding of stroke recovery and assist in developing the next generation of restorative approaches for enhancing brain repair after stroke.

Mild Fluid Percussion Injury Induces Diffuse Axonal Damage and Reactive Synaptic Plasticity in the Mouse Olfactory Bulb

Despite the regenerative capacity of the olfactory bulb (OB), head trauma causes olfactory disturbances in up to 30% of patients. While models of olfactory nerve transection, olfactory receptor neuron (ORN) ablation, or direct OB impact have been used to examine OB recovery, these models are severe and not ideal for study of OB synaptic repair. We posited that a mild fluid percussion brain injury (mFPI), delivered over mid-dorsal cortex, would produce diffuse OB deafferentation without confounding pathology. Wild type FVB/NJ mice were subjected to mFPI and OB probed for ORN axon degeneration and onset of reactive synaptogenesis. OB extracts revealed 3 d postinjury elevation of calpain-cleaved 150-kDa αII-spectrin, an indicator of axon damage, in tandem with reduced olfactory marker protein (OMP), a protein specific to intact ORN axons. Moreover, mFPI also produced a 3-d peak in GFAP+ astrocyte and IBA1+ microglial reactivity, consistent with postinjury inflammation. OB glomeruli showed disorganized ORN axons, presynaptic degeneration, and glial phagocytosis at 3 and 7 d postinjury, all indicative of deafferentation. At 21 d after mFPI, normal synaptic structure re-emerged along with OMP recovery, supporting ORN afferent reinnervation. Robust 21 d postinjury upregulation of GAP-43 was consistent with the time course of ORN axon sprouting and synapse regeneration reported after more severe olfactory insult. Together, these findings define a cycle of synaptic degeneration and recovery at a site remote to non-contusive brain injury. We show that mFPI models diffuse ORN axon damage, useful for the study of time-dependent reactive synaptogenesis in the deafferented OB.

Abnormal neurogenesis and cortical growth in congenital heart disease

Long-term neurological deficits due to immature cortical development are emerging as a major challenge in congenital heart disease (CHD). However, cellular mechanisms underlying dysregulation of perinatal corticogenesis in CHD remain elusive. The subventricular zone (SVZ) represents the largest postnatal niche of neural stem/progenitor cells (NSPCs). We show that the piglet SVZ resembles its human counterpart and displays robust postnatal neurogenesis. We present evidence that SVZ NSPCs migrate to the frontal cortex and differentiate into interneurons in a region-specific manner. Hypoxic exposure of the gyrencephalic piglet brain recapitulates CHD-induced impaired cortical development. Hypoxia reduces proliferation and neurogenesis in the SVZ, which is accompanied by reduced cortical growth. We demonstrate a similar reduction in neuroblasts within the SVZ of human infants born with CHD. Our findings demonstrate that SVZ NSPCs contribute to perinatal corticogenesis and suggest that restoration of SVZ NSPCs' neurogenic potential is a candidate therapeutic target for improving cortical growth in CHD.

Functional Reintegration of Sensory Neurons and Transitional Dendritic Reduction of Mitral/Tufted Cells during Injury-Induced Recovery of the Larval Xenopus Olfactory Circuit

Understanding the mechanisms involved in maintaining lifelong neurogenesis has a clear biological and clinical interest. In the present study, we performed olfactory nerve transection on larval Xenopus to induce severe damage to the olfactory circuitry. We surveyed the timing of the degeneration, subsequent rewiring and functional regeneration of the olfactory system following injury. A range of structural labeling techniques and functional calcium imaging were performed on both tissue slices and whole brain preparations. Cell death of olfactory receptor neurons and proliferation of stem cells in the olfactory epithelium were immediately increased following lesion. New olfactory receptor neurons repopulated the olfactory epithelium and once again showed functional responses to natural odorants within 1 week after transection. Reinnervation of the olfactory bulb (OB) by newly formed olfactory receptor neuron axons also began at this time. Additionally, we observed a temporary increase in cell death in the OB and a subsequent loss in OB volume. Mitral/tufted cells, the second order neurons of the olfactory system, largely survived, but transiently lost dendritic tuft complexity. The first odorant-induced responses in the OB were observed 3 weeks after nerve transection and the olfactory network showed signs of major recovery, both structurally and functionally, after 7 weeks.

Specific Features of SVZ Neurogenesis After Cortical Ischemia: a Longitudinal Study

Stroke is a devastating disease with an increasing prevalence. Part of the current development in stroke therapy is focused in the chronic phase, where neurorepair mechanisms such as neurogenesis, are involved. In the adult brain, one of the regions where neurogenesis takes place is the subventricular zone (SVZ) of the lateral ventricles. Given the possibility to develop pharmacological therapies to stimulate this process, we have performed a longitudinal analysis of neurogenesis in a model of cortical ischemia in mice. Our results show an initial decrease of SVZ proliferation at 24 h, followed by a recovery leading to an increase at 14d and a second decrease 28d after stroke. Coinciding with the 24 h proliferation decrease, an increase in the eutopic neuroblast migration towards the olfactory bulb was observed. The analysis of the neuroblast ectopic migration from the SVZ toward the lesion showed an increase in this process from day 14 after the insult. Finally, our data revealed an increased number of new cortical neurons in the peri-infarct cortex 65d after the insult. In summary, we report here critical check-points about post-stroke neurogenesis after cortical infarcts, important for the pharmacological modulation of this process in stroke patients.

CXCR7 Participates in CXCL12-mediated Cell Cycle and Proliferation Regulation in Mouse Neural Progenitor Cells

Background:

Cell cycle regulation of neural progenitor cells (NPCs) is an essential process for neurogenesis, neural development, and repair after brain trauma. Stromal cell-derived factor-1 (SDF-1, CXCL12) and its receptors CXCR4 and CXCR7 are well known in regulating the migration and survival of NPCs. The effects of CXCL12 on NPCs proliferation, cell cycle regulation, and their associated signaling pathways remain unclear. Cyclin D1 is a protein required for progression through the G1 phase of the cell cycle and a known downstream target of β-catenin. Therefore, cyclin D1 plays critical roles of cell cycle regulation, proliferation, and survival in NPCs.

Methods:

Primary mouse NPCs (mNPCs) were derived from brain tissues of wild-type, Cxcr4 knockout, or Cxcr7 knockout mice at mouse embryonic day 13.5 (E13.5). Flow cytometry was used to perform cell cycle analysis by quantitation of DNA content. Real-time PCR and Western blot were used to evaluate mRNA and protein expressions, respectively. Ki67 immunostaining and TUNEL assay were used to assess the proliferation and survival of mNPCs, respectively.

Results:

CXCL12 pretreatment led to the shortening of G0/G1 phase and lengthening of S phase, suggesting that CXCL12 regulates cell cycle progression in mNPCs. Consistently, CXCL12 treatment increased the expression of CyclinD1 and β-catenin, and promoted proliferation and survival of mNPCs. Cxcr7 knockout of mNPCs blocked CXCL12-mediated mNPCs proliferation, whereas Cxcr4 knockout mNPC did not significantly effect CXCL12- mediated mNPCs proliferation.

Conclusion:

CXCR7 plays an important role in CXCL12-mediated mNPC cell cycle regulation and proliferation.

Dentate granule progenitor cell properties are rapidly altered soon after birth

Neurogenesis occurs during the embryonic period and ceases soon after birth in the neocortex, but continues to occur in the hippocampus even in the adult. The embryonic neocortex has radial glia or progenitor cells expressing brain lipid-binding protein (BLBP), whereas the adult hippocampus has radial granule progenitor cells expressing BLBP and glial fibrillary acidic protein (GFAP) in the subgranular zone. We previously found that embryonic hippocampal granule progenitor cells express GFAP, but not BLBP, indicating that these cells are different from both embryonic neocortical and adult granule progenitor cells. In the present study, as the first step towards understanding the mechanism of persistent hippocampal neurogenesis, we aimed to determine the stage at which embryonic-type granule progenitors become adult-type progenitors using mouse Gfap-GFP transgenic mice. During the embryonic stages, Gfap-GFP-positive (Gfap-GFP+) cells were distributed in the entire developing dentate gyrus (DG), whereas BLBP-positive (BLBP+) cells were mainly present in the fimbria and subpial region, and to some extent in the DG. Up to postnatal day 0 (P0), double-positive cells were scarcely detected. However, at P1, one-third of the Gfap-GFP+ cells in the DG suddenly began to weakly express BLBP. Thereafter, Gfap-GFP+/BLBP+ cells rapidly increased in number, and extended their radial processes in the inner granular cell layer. At P14 and in the adult, two-thirds of the Gfap-GFP+ cells in the subgranular zone showed BLBP immunoreactivity. These results suggest that the properties of hippocampal granule progenitor cells are rapidly altered from an embryonic to adult type soon after birth.

Spatiotemporal presentation of exogenous SDF-1 with PLGA nanoparticles modulates SDF-1/CXCR4 signaling axis in the rodent cortex

Stromal cell-derived factor-1 (SDF-1) and its key receptor CXCR4 have been implicated in directing cellular recruitment for several pathological/disease conditions thus also gained considerable attention for regenerative medicine. One regenerative approach includes sustained release of SDF-1 to stimulate prolonged stem cell recruitment. However, the impact of SDF-1 sustained release on the endogenous SDF-1/CXCR4 signaling axis is largely unknown as auto-regulatory mechanisms typically dictate cytokine/receptor signaling. We hypothesize that spatiotemporal presentation of exogenous SDF-1 is a key factor in achieving long-term manipulation of endogenous SDF-1/CXCR4 signaling. Here in the present study, we sought to probe our hypothesis using a transgenic mouse model to contrast the spatial activation of endogenous SDF-1 and CXCR4 in response to exogenous SDF-1 injected in bolus or controlled release (PLGA nanoparticles) form in the adult rodent cortex. Our data suggests that the manner of SDF-1 presentation significantly affected initial CXCR4 cellular activation/recruitment despite having similar protein payloads over the first 24 h (∼30 ng for both bolus and sustained release groups). Yet, one week post-injection, this response was negligible. Therefore, the transient nature CXCR4 recruitment/activation in response to bolus or controlled release SDF-1 indicated that cytokine/receptor auto-regulatory mechanisms may demand more complex release profiles (i.e. delayed and/or pulsed release) to achieve sustained cellular response.

TRPV4 Activation Contributes Functional Recovery from Ischemic Stroke via Angiogenesis and Neurogenesis

The endothelial transient receptor potential cation channel subfamily V member 4 (TRPV4) plays a crucial role in vascular remodeling; however, TRPV4-mediated angiogenesis after ischemic neuronal death as a neurorestorative strategy has not yet been thoroughly examined. In this study, we first tested whether TRPV4 activation can improve functional recovery in rats subjected to transient brain ischemia. The possible mechanisms for TRPV4 activation-promoted functional recovery were explored. A TRPV4 agonist, 4α-phorbol 12,13-didecanoate (4α-PDD), was intravenously injected via the tail vein at 6 h and 1, 2, 3, 4 days after ischemic stroke. The treatment reduced infarct volume by almost 50% (14.7 ± 3.7 vs. 29.2 ± 6.2%; p < 0.0001) and improved functional outcomes (p = 0.03) on day 5. To explore the therapeutic mechanism, we measured endothelial nitric oxide synthase (eNOS) expression and phosphorylation, vascular endothelial growth factor A (VEGFA) signaling, and neural stem/progenitor cells (NPCs). TRPV4 activation significantly increased eNOS expression and phosphorylation (serine 1177) by more than 2-fold in the ischemic region. The expressions of VEGFA and VEGF receptor-2 were significantly higher in the treated animals, especially an increase of the proangiogenic VEGFA_164a isoform while a decrease of the antiangiogenic VEGFA_165b isoform. We evaluated angiogenesis by detecting microvessel density in ischemic region. Using the immunohistochemistry staining, we found that 4α-PDD treatment caused a 3.4-fold increase of microvessel density (p < 0.0001). In addition, NPC proliferation and migration in the ischemic hemisphere were increased by 3-fold and 5-fold, respectively. In conclusion, our data suggest that TRPV4 activation by 4α-PDD may improve poststroke functional improvement through angiogenesis and neurogenesis.

Physical exercise rescues defective neural stem cells and neurogenesis in the adult subventricular zone of Btg1 knockout mice

Adult neurogenesis occurs throughout life in the dentate gyrus (DG) and the subventricular zone (SVZ), where glia-like stem cells generate new neurons. Voluntary running is a powerful neurogenic stimulus triggering the proliferation of progenitor cells in the DG but, apparently, not in the SVZ. The antiproliferative gene Btg1 maintains the quiescence of DG and SVZ stem cells. Its ablation causes intense proliferation of DG and SVZ stem/progenitor cells in young mice, followed, during adulthood, by progressive decrease of the proliferative capacity. We have previously observed that running can rescue the deficit of DG Btg1-null neurogenesis. Here, we show that in adult Btg1-null SVZ stem and neuroblast cells, the reduction of proliferation is associated with a longer cell cycle and a more frequent entry into quiescence. Notably, running increases proliferation in Btg1-null SVZ stem cells highly above the levels of sedentary wild-type mice and restores normal values of cell cycle length and quiescence in stem and neuroblast cells, without affecting wild-type cells. Btg1-null SVZ neuroblasts show also increased migration throughout the rostral migratory stream and a deficiency of differentiated neurons in the olfactory bulb, possibly a consequence of premature exit from the cycle; running, however, normalizes migration and differentiation, increasing newborn neurons recruited to the olfactory circuitry. Furthermore, running increases the self-renewal of Btg1-null SVZ-derived neurospheres and, remarkably, in aged Btg1-null mice almost doubles the proliferating SVZ stem cells. Altogether, this reveals that SVZ stem cells are endowed with a hidden supply of self-renewal capacity, coupled to cell cycle acceleration and emerging after ablation of the quiescence-maintaining Btg1 gene and following exercise.

High-Frequency Repetitive Transcranial Magnetic Stimulation (rTMS) Improves Functional Recovery by Enhancing Neurogenesis and Activating BDNF/TrkB Signaling in Ischemic Rats

Repetitive transcranial magnetic stimulation (rTMS) has rapidly become an attractive therapeutic approach for stroke. However, the mechanisms underlying this remain elusive. This study aimed to investigate whether high-frequency rTMS improves functional recovery mediated by enhanced neurogenesis and activation of brain-derived neurotrophic factor (BDNF)/tropomyosin-related kinase B (TrkB) pathway and to compare the effect of conventional 20 Hz rTMS and intermittent theta burst stimulation (iTBS) on ischemic rats. Rats after rTMS were sacrificed seven and 14 days after middle cerebral artery occlusion (MCAO), following evaluation of neurological function. Neurogenesis was measured using specific markers: Ki67, Nestin, doublecortin (DCX), NeuN and glial fibrillary acidic protein (GFAP), and the expression levels of BDNF were visualized by Western blotting and RT-PCR analysis. Both high-frequency rTMS methods significantly improved neurological function and reduced infarct volume. Moreover, 20 Hz rTMS and iTBS significantly promoted neurogenesis, shown by an increase of Ki67/DCX, Ki67/Nestin, and Ki67/NeuN-positive cells in the peri-infarct striatum. These beneficial effects were accompanied by elevated protein levels of BDNF and phosphorylated-TrkB. In conclusion, high-frequency rTMS improves functional recovery possibly by enhancing neurogenesis and activating BDNF/TrkB signaling pathway and conventional 20 Hz rTMS is better than iTBS at enhancing neurogenesis in ischemic rats.

Selective lesion of the hippocampus increases the differentiation of immature neurons in the monkey amygdala

A large population of immature neurons is present in the ventromedial portion of the adult primate amygdala, a region that receives substantial direct projections from the hippocampal formation. Here, we show the effects of neonatal (n = 8) and adult (n = 6) hippocampal lesions on the populations of mature and immature neurons in the paralaminar, lateral, and basal nuclei of the adult monkey amygdala. Compared with unoperated controls (n = 7), the number of mature neurons was about 70% higher in the paralaminar nucleus of neonate- and adult-lesioned monkeys, and 40% higher in the lateral and basal nuclei of neonate-lesioned monkeys. The number of immature neurons in the paralaminar nucleus was 40% higher in neonate-lesioned monkeys and 30% lower in adult-lesioned monkeys. Similar changes in neuron numbers were also found in two monkeys with nonexperimental, selective, bilateral hippocampal damage. These changes in neuron numbers following hippocampal lesions appear to reflect the differentiation of immature neurons present in the paralaminar nucleus. After adult lesions, the differentiation of immature neurons was essentially restricted to the paralaminar nucleus and was associated with a decrease in the population of immature neurons. In contrast, after neonatal lesions, the differentiation of immature neurons involved the paralaminar, lateral, and basal nuclei. It was associated with an increase in the population of immature neurons in the paralaminar nucleus. Such lesion-induced neuronal plasticity sheds new light on potential mechanisms that may facilitate functional recovery following focal brain injury.

Optogenetic stimulation of glutamatergic neuronal activity in the striatum enhances neurogenesis in the subventricular zone of normal and stroke mice

Neurogenesis in the subventricular zone (SVZ) of the adult brain may contribute to tissue repair after brain injuries. Whether SVZ neurogenesis can be upregulated by specific neuronal activity in vivo and promote functional recovery after stroke is largely unknown. Using the spatial and cell type specific optogenetic technique combined with multiple approaches of in vitro, ex vivo and in vivo examinations, we tested the hypothesis that glutamatergic activation in the striatum could upregulate SVZ neurogenesis in the normal and ischemic brain. In transgenic mice expressing the light-gated channelrhodopsin-2 (ChR2) channel in glutamatergic neurons, optogenetic stimulation of the glutamatergic activity in the striatum triggered glutamate release into SVZ region, evoked membrane currents, Ca²⁺ influx and increased proliferation of SVZ neuroblasts, mediated by AMPA receptor activation. In ChR2 transgenic mice subjected to focal ischemic stroke, optogenetic stimuli to the striatum started 5days after stroke for 8days not only promoted cell proliferation but also the migration of SVZ neuroblasts into the peri-infarct cortex with increased neuronal differentiation and improved long-term functional recovery. These data provide the first morphological and functional evidence showing a unique striatum-SVZ neuronal regulation via a semi-phasic synaptic mechanism that can boost neurogenic cascades and stroke recovery. The benefits from stimulating endogenous glutamatergic activity suggest a novel regenerative strategy after ischemic stroke and other brain injuries.

Traceable microRNA-124 loaded nanoparticles as a new promising therapeutic tool for Parkinson's disease

Parkinson's disease (PD), a neurodegenerative disorder characterized by the selective degeneration of the nigrostriatal dopaminergic pathway, is a major socio-economic burden in modern society. While there is presently no cure for PD, enhancing the number of neural stem cells (NSCs) and/or stimulating their differentiation into new neurons are promising therapeutic strategies. Many proneurogenic factors have been implicated in controlling NSCs activity, including the microRNA (miR)-124. However, current strategies described for the intracellular delivery of miR involve mostly unspecific or inefficient platforms. In Saraiva et al. we developed miR-124 loaded nanoparticles (NPs) able to efficiently deliver miR-124 into neural stem/progenitor cells and boost neuronal differentiation and maturation in vitro. In vivo, the intracerebroventricular injection of miR-124 NPs increased the number of new neurons in the olfactory bulb of healthy and 6-hydroxidopamine (6-OHDA) lesioned mice, a model for PD. Importantly, miR-124 NPs enhanced the migration of new neurons into the 6-OHDA lesioned striatum, culminating in motor function improvement. Given the recent advent of clinical trials for miR-based therapies and the theranostic applications of our NPs, we expect to support the clinical translation of our delivery platform in the context of PD and other neurodegenerative diseases which may benefit from enhancing miR levels.

Subarachnoid Hemorrhage Promotes Proliferation, Differentiation, and Migration of Neural Stem Cells via BDNF Upregulation

Patients who suffer from subarachnoid hemorrhage (SAH) usually have long-term neurological impairments. Endogenous neurogenesis might play a potential role in functional recovery after SAH; however, the underlying neurogenesis mechanism is still unclear. We assessed the extent of neurogenesis in the subventricular zone (SVZ) to better understand the neurogenesis mechanism after SAH. We performed a rat model of SAH to examine the extent of neurogenesis in the SVZ and assessed functional effects of the neurotrophic factors in the cerebrospinal fluid (CSF) on neural stem cells (NSCs) after SAH. In this study, the proliferation, differentiation, and migratory capacities of NSCs in the SVZ were significantly increased on days 5 and 7 post SAH. Furthermore, treatment of cultured rat fetal NSCs with the CSF collected from rats on days 5 and 7 post SAH enhanced their proliferation, differentiation, and migration. Enzyme-linked immunosorbent assay (ELISA) of the CSF detected a marked increase in the concentration of brain-derived neurotrophic factor (BDNF). Treating the cultured NSCs with recombinant BDNF (at the same concentration as that in the CSF) or with CSF from SAH rats, directly, stimulated proliferation, differentiation, and migration to a similar extent. BDNF expression was upregulated in the SVZ of rats on days 5 and 7 post SAH, and BDNF release occurred from NSCs, astrocytes, and microglia in the SVZ. These results indicate that SAH triggers the expression of BDNF, which promotes the proliferation, differentiation, and migration of NSCs in the SVZ after SAH.

Demyelination-Induced Inflammation Attracts Newly Born Neurons to the White Matter

There is compelling evidence that microglial activation negatively impacts neurogenesis. However, microglia have also been shown to promote recruitment of newly born neurons to injured areas of the gray matter. In the present study, we explored whether demyelination-triggered inflammation alters the process of neurogenesis in the white matter. A 2-μl solution of 0.04 % ethidium bromide was stereotaxically injected into the corpus callosum of adult male rats. Brain inflammation was dampened by daily injections of progesterone (5 mg/kg, s.c.) for 14 days. Control rats received oil (s.c.). Newly born neurons (DCX and Tbr2), microglia (Iba-1), astrocytes (vimentin or GFAP), oligodendrocyte progenitor cells (OPCs; NG2), and mature oligodendrocytes (CC-1) were monitored in the vicinity of demyelination site using immunofluorescent staining. Western blot was used to explore microglial polarization using M1 (iNOS) and M2 (arginase-1) markers. Focal demyelination elicited strong microglial and astroglial activation and reduced the number of OPCs at the site of demyelination. This inflammatory response was associated with enhanced number of newly born neurons in the white matter and the subventricular zone (SVZ). A proportion of newly born neurons within the white matter showed features of OPCs. Interestingly, blunting brain inflammation led to reduced neurogenesis around the demyelination area and in the SVZ. These data suggest that the white matter inflammation creates a conducive environment for the recruitment of newly born neurons. The fact that a sizable fraction of these newly born neurons adopt OPC features suggests that they could contribute to the remyelination process.

Critical role of astrocytic interleukin-17 A in post-stroke survival and neuronal differentiation of neural precursor cells in adult mice

The brain and the immune system interact in complex ways after ischemic stroke, and the long-term effects of immune response associated with stroke remain controversial. As a linkage between innate and adaptive immunity, interleukin-17 A (IL-17 A) secreted from gamma delta (γδ) T cells has detrimental roles in the pathogenesis of acute ischemic stroke. However, to date, the long-term actions of IL-17 A after stroke have not been investigated. Here, we found that IL-17 A showed two distinct peaks of expression in the ischemic hemisphere: the first occurring within 3 days and the second on day 28 after stroke. Our data also showed that astrocyte was the major cellular source of IL-17 A that maintained and augmented subventricular zone (SVZ) neural precursor cells (NPCs) survival, neuronal differentiation, and subsequent synaptogenesis and functional recovery after stroke. IL-17 A also promoted neuronal differentiation in cultured NPCs from the ischemic SVZ. Furthermore, our in vitro data revealed that in primary astrocyte cultures activated astrocytes released IL-17 A via p38 mitogen-activated protein kinase (MAPK). Culture media from reactive astrocytes increased neuronal differentiation of NSCs in vitro. Blockade of IL-17 A with neutralizing antibody prevented this effect. In addition, after screening for multiple signaling pathways, we revealed that the p38 MAPK/calpain 1 signaling pathway was involved in IL-17 A-mediated neurogenesis in vivo and in vitro. Thus, our results reveal a previously uncharacterized property of astrocytic IL-17 A in the maintenance and augment of survival and neuronal differentiation of NPCs, and subsequent synaptogenesis and spontaneous recovery after ischemic stroke.

Treatment of traumatic brain injury in rats with N-acetyl-seryl-aspartyl-lysyl-proline

OBJECTIVE The authors' previous studies have suggested that thymosin beta 4 (Tβ4), a major actin-sequestering protein, improves functional recovery after neural injury. N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP) is an active peptide fragment of Tβ4. Its effect as a treatment of traumatic brain injury (TBI) has not been investigated. Thus, this study was designed to determine whether AcSDKP treatment improves functional recovery in rats after TBI. METHODS Young adult male Wistar rats were randomly divided into the following groups: 1) sham group (no injury); 2) TBI + vehicle group (0.01 N acetic acid); and 3) TBI + AcSDKP (0.8 mg/kg/day). TBI was induced by controlled cortical impact over the left parietal cortex. AcSDKP or vehicle was administered subcutaneously starting 1 hour postinjury and continuously for 3 days using an osmotic minipump. Sensorimotor function and spatial learning were assessed using a modified Neurological Severity Score and Morris water maze tests, respectively. Some of the animals were euthanized 1 day after injury, and their brains were processed for measurement of fibrin accumulation and neuroinflammation signaling pathways. The remaining animals were euthanized 35 days after injury, and brain sections were processed for measurement of lesion volume, hippocampal cell loss, angiogenesis, neurogenesis, and dendritic spine remodeling. RESULTS Compared with vehicle treatment, AcSDKP treatment initiated 1 hour postinjury significantly improved sensorimotor functional recovery (Days 7-35, p < 0.05) and spatial learning (Days 33-35, p < 0.05), reduced cortical lesion volume, and hippocampal neuronal cell loss, reduced fibrin accumulation and activation of microglia/macrophages, enhanced angiogenesis and neurogenesis, and increased the number of dendritic spines in the injured brain (p < 0.05). AcSDKP treatment also significantly inhibited the transforming growth factor-β1/nuclear factor-κB signaling pathway. CONCLUSIONS AcSDKP treatment initiated 1 hour postinjury provides neuroprotection and neurorestoration after TBI, indicating that this small tetrapeptide has promising therapeutic potential for treatment of TBI. Further investigation of the optimal dose and therapeutic window of AcSDKP treatment for TBI and the associated underlying mechanisms is therefore warranted.

Suppressor of Cytokine Signaling-2 (SOCS2) Regulates the Microglial Response and Improves Functional Outcome after Traumatic Brain Injury in Mice

Traumatic brain injury (TBI) is frequently characterized by neuronal, axonal and myelin loss, reactive gliosis and neuroinflammation, often associated with functional deficits. Endogenous repair mechanisms include production of new neurons from precursor cells, but usually the new neurons fail to integrate and survive more than a few weeks. This is in part mediated by the toxic and inflammatory environment present in the injured brain which activates precursor cells to proliferate and differentiate but limits survival of the newborn progeny. Therefore, an understanding of mechanisms that regulate production and survival of newborn neurons and the neuroinflammatory response after brain injury may lead to therapeutic options to improve outcomes. Suppressor of Cytokine Signaling 2 (SOCS2) promotes hippocampal neurogenesis and survival of newborn neurons in the adult brain and regulates anti-inflammatory responses in the periphery, suggesting it may be a useful candidate to improve outcomes of TBI. In this study the functional and cellular responses of SOCS2 over-expressing transgenic (SOCS2Tg) mice were compared to wildtype littermates following mild or moderately severe TBI. Unlike wildtype controls, SOCS2Tg mice showed functional improvement on a ladder test, with a smaller lesion volume at 7d post injury and increased numbers of proliferative CD11b⁺ microglia/macrophages at 35d post-injury in the mild injury paradigm. At 7d post-moderately severe injury there was an increase in the area covered by cells expressing an anti-inflammatory M2 phenotype marker (CD206⁺) but no difference in cells with a pro-inflammatory M1 phenotype marker (CD16/32⁺). No effect of SOCS2 overexpression was observed in production or survival of newborn neurons, even in the presence of the neuroprotective agent erythropoietin (EPO). Therefore, SOCS2 may improve outcome of TBI in mice by regulating aspects of the neuroinflammatory response, promoting a more anti-inflammatory environment, although this was not sufficient to enhance survival of newborn cortical neurons.

Aberrant Adult Neurogenesis in the Subventricular Zone-Rostral Migratory Stream-Olfactory Bulb System Following Subchronic Manganese Exposure

Adult neurogenesis occurs in brain subventricular zone (SVZ). Our recent data reveal an elevated proliferation of BrdU(+) cells in SVZ following subchronic manganese (Mn) exposure in rats. This study was designed to distinguish Mn effect on the critical stage of adult neurogenesis, ie, proliferation, migration, survival and differentiation from the SVZ via the rostral migratory stream to the olfactory bulb (OB). Adult rats received a single ip-dose of BrdU at the end of 4-week Mn exposure to label proliferating cells. Immunostaining and cell-counting showed a 48% increase of BrdU(+) cells in Mn-exposed SVZ than in controls (P< .05). These BrdU(+) cells were identified as a mixed population of mainly GFAP(+) type-B neural stem cells, Nestin(+) type-C transit progenitor cells, DCX(+) migratory neuroblasts and Iba1(+) microglial cells. Another group of adult rats received 3 daily ip-injections of BrdU followed by subchronic Mn exposure. By 4-week post BrdU labeling, most of the surviving BrdU(+) cells in the OB were differentiated into NeuN(+) matured neurons. However, survival rates of BrdU/NeuN/DAPI triple-labeled cells in OB were 33% and 64% in Mn-exposed and control animals, respectively (P< .01). Infusion of Cu directly into the lateral ventricle significantly decreased the cell proliferation in the SVZ. Taken together, these results suggest that Mn exposure initially enhances the cell proliferation in adult SVZ. In the OB, however, Mn exposure significantly reduces the surviving adult-born cells and markedly inhibits their differentiation into mature neurons, resulting in an overall decreased adult neurogenesis in the OB.