Neural stem cells: involvement in adult neurogenesis and CNS repair

Unraveling the intricate link between cell death and neuroinflammation using Drosophila as a model

Protein aggregation is a common pathological occurrence in neurodegenerative diseases. This often leads to neuroinflammation, which exacerbates the aggregation and progression of diseases like Parkinson's and Alzheimer's. Here, we focus on immune responses and neurotoxicity in a Parkinson's disease model in Drosophila. Mutations in the SNCA gene that encodes the alpha (α)-Synuclein protein have been linked to familial Parkinson's disease, disrupting autophagy regulation in neuronal cells and promoting the formation of Lewy bodies, a hallmark of Parkinson's pathology. This results in the loss of dopaminergic neurons, manifesting as movement disorders. α-Synuclein aggregation triggers innate immune responses by activating microglial cells, leading to phagocytic activity and the expression of neuroprotective antimicrobial peptides (AMPs). However, sustained AMP expression or chronic inflammation resulting from inadequate microglial phagocytosis can induce neuronal toxicity and apoptosis, leading to severe dopaminergic neuron loss. This review underscores the mechanistic connection between immune response pathways and α-Synuclein-mediated neurodegeneration using Drosophila models. Furthermore, we extensively explore factors influencing neuroinflammation and key immune signaling pathways implicated in neurodegenerative diseases, particularly Parkinson's disease. Given the limited success of traditional treatments, recent research has focused on therapies targeting inflammatory signaling pathways. Some of these approaches have shown promising results in animal models and clinical trials. We provide an overview of current therapeutic strategies showing potential in treating neurodegenerative diseases, offering new avenues for future research and treatment development.

Nucleoporin 153 deficiency in adult neural stem cells defines a pathological protein-network signature and defective neurogenesis in a mouse model of AD

BACKGROUND

Reduction of adult hippocampal neurogenesis is an early critical event in Alzheimer's disease (AD), contributing to progressive memory loss and cognitive decline. Reduced levels of the nucleoporin 153 (Nup153), a key epigenetic regulator of NSC stemness, characterize the neural stem cells isolated from a mouse model of AD (3×Tg) (AD-NSCs) and determine their altered plasticity and gene expression.

METHODS

Nup153-regulated mechanisms contributing to NSC function were investigated: (1) in cultured NSCs isolated from AD and wild type (WT) mice by proteomics; (2) in vivo by lentiviral-mediated delivery of Nup153 or GFP in the hippocampus of AD and control mice analyzing neurogenesis and cognitive function; (3) in human iPSC-derived brain organoids obtained from AD patients and control subjects as a model of neurodevelopment.

RESULTS

Proteomic approach identified Nup153 interactors in WT- and AD-NSCs potentially implicated in neurogenesis regulation. Gene ontology (GO) analysis showed that Nup153-bound proteins in WT-NSCs were involved in RNA metabolism, nuclear import and epigenetic mechanisms. Nup153-bound proteins in AD-NSCs were involved in pathways of neurodegeneration, mitochondrial dysfunction, proteasomal processing and RNA degradation. Furthermore, recovery of Nup153 levels in AD-NSCs reduced the levels of oxidative stress markers and recovered proteasomal activity. Lentiviral-mediated delivery of Nup153 in the hippocampal niche of AD mice increased the proliferation of early progenitors, marked by BrdU/DCX and BrdU/PSANCAM positivity and, later, the integration of differentiating neurons in the cell granule layer (BrdU/NeuN+ cells) compared with GFP-injected AD mice. Consistently, Nup153-injected AD mice showed an improvement of cognitive performance in comparison to AD-GFP mice at 1 month after virus delivery assessed by Morris Water Maze. To validate the role of Nup153 in neurogenesis we took advantage of brain organoids derived from AD-iPSCs characterized by fewer neuroepithelial progenitor loops and reduced differentiation areas. The upregulation of Nup153 in AD organoids recovered the formation of neural-like tubes and differentiation.

CONCLUSIONS

Our data suggest that the positive effect of Nup153 on neurogenesis is based on a complex regulatory network orchestrated by Nup153 and that this protein is a valuable disease target.

The activation of dormant ependymal cells following spinal cord injury

Ependymal cells, a dormant population of ciliated progenitors found within the central canal of the spinal cord, undergo significant alterations after spinal cord injury (SCI). Understanding the molecular events that induce ependymal cell activation after SCI represents the first step toward controlling the response of the endogenous regenerative machinery in damaged tissues. This response involves the activation of specific signaling pathways in the spinal cord that promotes self-renewal, proliferation, and differentiation. We review our current understanding of the signaling pathways and molecular events that mediate the SCI-induced activation of ependymal cells by focusing on the roles of some cell adhesion molecules, cellular membrane receptors, ion channels (and their crosstalk), and transcription factors. An orchestrated response regulating the expression of receptors and ion channels fine-tunes and coordinates the activation of ependymal cells after SCI or cell transplantation. Understanding the major players in the activation of ependymal cells may help us to understand whether these cells represent a critical source of cells contributing to cellular replacement and tissue regeneration after SCI. A more complete understanding of the role and function of individual signaling pathways in endogenous spinal cord progenitors may foster the development of novel targeted therapies to induce the regeneration of the injured spinal cord.

Influence of SARS-CoV-2 on Adult Human Neurogenesis

Infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is associated with the onset of neurological and psychiatric symptoms during and after the acute phase of illness. Inflammation and hypoxia induced by SARS-CoV-2 affect brain regions essential for fine motor function, learning, memory, and emotional responses. The mechanisms of these central nervous system symptoms remain largely unknown. While looking for the causes of neurological deficits, we conducted a study on how SARS-CoV-2 affects neurogenesis. In this study, we compared a control group with a group of patients diagnosed with COVID-19. Analysis of the expression of neurogenesis markers showed a decrease in the density of neuronal progenitor cells and newborn neurons in the SARS-CoV-2 group. Analysis of COVID-19 patients revealed increased microglial activation compared with the control group. The unfavorable effect of the inflammatory process in the brain associated with COVID-19 disease increases the concentration of cytokines that negatively affect adult human neurogenesis.

Adult hypothalamic neurogenesis and sleep-wake dysfunction in aging

In the mammalian brain, adult neurogenesis has been extensively studied in the hippocampal sub-granular zone and the sub-ventricular zone of the anterolateral ventricles. However, growing evidence suggests that new cells are not only "born" constitutively in the adult hypothalamus, but many of these cells also differentiate into neurons and glia and serve specific functions. The preoptic-hypothalamic area plays a central role in the regulation of many critical functions, including sleep-wakefulness and circadian rhythms. While a role for adult hippocampal neurogenesis in regulating hippocampus-dependent functions, including cognition, has been extensively studied, adult hypothalamic neurogenic process and its contributions to various hypothalamic functions, including sleep-wake regulation are just beginning to unravel. This review is aimed at providing the current understanding of the hypothalamic adult neurogenic processes and the extent to which it affects hypothalamic functions, including sleep-wake regulation. We propose that hypothalamic neurogenic processes are vital for maintaining the proper functioning of the hypothalamic sleep-wake and circadian systems in the face of regulatory challenges. Sleep-wake disturbance is a frequent and challenging problem of aging and age-related neurodegenerative diseases. Aging is also associated with a decline in the neurogenic process. We discuss a hypothesis that a decrease in the hypothalamic neurogenic process underlies the aging of its sleep-wake and circadian systems and associated sleep-wake disturbance. We further discuss whether neuro-regenerative approaches, including pharmacological and non-pharmacological stimulation of endogenous neural stem and progenitor cells in hypothalamic neurogenic niches, can be used for mitigating sleep-wake and other hypothalamic dysfunctions in aging.

Expression of NLRP3 Inflammasomes in Neurogenic Niche Contributes to the Effect of Spatial Learning in Physiological Conditions but Not in Alzheimer's Type Neurodegeneration

A common feature of neurodegenerative disorders, in particular Alzheimer's disease (AD), is a chronic neuroinflammation associated with aberrant neuroplasticity. Development of neuroinflammation affects efficacy of stem and progenitor cells proliferation, differentiation, migration, and integration of newborn cells into neural circuitry. However, precise mechanisms of neurogenesis alterations in neuroinflammation are not clear yet. It is well established that expression of NLRP3 inflammasomes in glial cells marks neuroinflammatory events, but less is known about contribution of NLRP3 to deregulation of neurogenesis within neurogenic niches and whether neural stem cells (NSCs), neural progenitor cells (NPCs) or immature neuroblasts may express inflammasomes in (patho)physiological conditions. Thus, we studied alterations of neurogenesis in rats with the AD model (intra-hippocampal injection of Aβ1-42). We found that in Aβ-affected brain, number of CD133+ cells was elevated after spatial training in the Morris water maze. The number of PSA-NCAM+ neuroblasts diminished by Aβ injection was completely restored by subsequent spatial learning. Spatial training leads to elevated expression of NLRP3 inflammasomes in the SGZ (subgranular zones): CD133+ and PSA-NCAM+ cells started to express NLRP3 in sham-operated, but not AD rats. Taken together, our data suggest that expression of NLRP3 inflammasomes in CD133+ and PSA-NCAM+ cells may contribute to stimulation of adult neurogenesis in physiological conditions, whereas Alzheimer's type neurodegeneration abolishes stimuli-induced overexpression of NLRP3 within the SGZ neurogenic niche.

Slit1 Protein Regulates SVZ-Derived Precursor Mobilization in the Adult Demyelinated CNS

Slit1 is a secreted axon guidance molecule, also involved in adult neurogenesis. In physiological conditions, Slit1 loss promotes ectopic dispersal of SVZ-derived neural precursors (SVZ-NPCs) into periventricular structures such as the corpus callosum. Demyelination of the corpus callosum triggers SVZ-NPC migration to ectopic locations and their recruitment by the lesion, suggesting a possible role for Slit1 in SVZ-NPCs ectopic dispersal regulation in pathological conditions. Here, we have investigated the function of Slit1 protein in the recruitment of SVZ-NPCs after CNS demyelination. We find that the dynamics of oligodendrogenesis and temporal profile of developmental myelination in Slit1^–/– mice are similar to Slit1^+/− controls. SVZ micro-dissection and RT-PCR from wild-type mice, show that Slits and Robos are physiologically regulated at the transcriptional level in response to corpus callosum demyelination suggesting their role in the process of SVZ-NPC ectopic migration in demyelinating conditions. Moreover, we find that the number of SVZ-NPCs recruited by the lesion increases in Sli1^–/– mice compared to Slit1^+/− mice, leading to higher numbers of Olig2⁺ cells within the lesion. Time-lapse video-microscopy of immuno-purified NPCs shows that Slit1-deficient cells migrate faster and make more frequent directional changes than control NPCs, supporting a cell-autonomous mechanism of action of Slit1 in NPC migration. In conclusion, while Slit1 does not affect the normal developmental process of oligodendrogenesis and myelination, it regulates adult SVZ-NPC ectopic migration in response to demyelination, and consequently oligodendrocyte renewal within the lesion.

Current understanding of adult neurogenesis in the mammalian brain: how does adult neurogenesis decrease with age?

Adult neurogenesis occurs throughout life in restricted brain regions in mammals. However, the number of neural stem cells (NSCs) that generate new neurons steadily decreases with age, resulting in a decrease in neurogenesis. Transplantation of mesenchymal cells or cultured NSCs has been studied as a promising treatment in models of several brain injuries including cerebral infarction and cerebral contusion. Considering the problems of host-versus-graft reactions and the tumorigenicity of transplanted cells, the mobilization of endogenous adult NSCs should be more feasible for the treatment of these brain injuries. However, the number of adult NSCs in the adult brain is limited, and their mitotic potential is low. Here, we outline what we know to date about why the number of NSCs and adult neurogenesis decrease with age. We also discuss issues applicable to regenerative medicine.

4D Self-Morphing Culture Substrate for Modulating Cell Differentiation

As the most versatile and promising cell source, stem cells have been studied in regenerative medicine for two decades. Currently available culturing techniques utilize a 2D or 3D microenvironment for supporting the growth and proliferation of stem cells. However, these culture systems fail to fully reflect the supportive biological environment in which stem cells reside in vivo, which contain dynamic biophysical growth cues. Herein, a 4D programmable culture substrate with a self-morphing capability is presented as a means to enhance dynamic cell growth and induce differentiation of stem cells. To function as a model system, a 4D neural culture substrate is fabricated using a combination of printing and imprinting techniques keyed to the different biological features of neural stem cells (NSCs) at different differentiation stages. Results show the 4D culture substrate demonstrates a time-dependent self-morphing process that plays an essential role in regulating NSC behaviors in a spatiotemporal manner and enhances neural differentiation of NSCs along with significant axonal alignment. This study of a customized, dynamic substrate revolutionizes current stem cell therapies, and can further have a far-reaching impact on improving tissue regeneration and mimicking specific disease progression, as well as other impacts on materials and life science research.

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

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

Neural stem cell heterogeneity in the mammalian forebrain

The brain was long considered an organ that underwent very little change after development. It is now well established that the mammalian central nervous system contains neural stem cells that generate progeny that are capable of making new neurons, astrocytes, and oligodendrocytes throughout life. The field has advanced rapidly as it strives to understand the basic biology of these precursor cells, and explore their potential to promote brain repair. The purpose of this review is to present current knowledge about the diversity of neural stem cells in vitro and in vivo, and highlight distinctions between neural stem cell populations, throughout development, and within the niche. A comprehensive understanding of neural stem cell heterogeneity will provide insights into the cellular and molecular regulation of neural development and lifelong neurogenesis, and will guide the development of novel strategies to promote regeneration and neural repair.

Vascularization of the Damaged Nerve under the Effect of Experimental Cell Therapy

Quantitative analysis of blood vessels in the distal segment of rat sciatic nerve after its ligation for 40 sec and subperineurial administration of mesenchymal stem cells or dissociated cells of rat embryonic spinal cord was carried our by immunohistochemical tracing of von Willebrand factor, a marker of endothelial cells of blood vessels. It was found that the number of blood vessels per unit area of the nerve trunk in 21 days after injury and administration of mesenchymal stem cells increased by more than 1.5 times in comparison with the control (damaged nerve). After administration of dissociated cells of the embryonic spinal cord, this effect was not observed. It is assumed that mesenchymal stem cells stimulate the growth of vessels of the damaged nerve via production of angiogenic factors.

Neural Stem Cell Transplantation Is Associated with Inhibition of Apoptosis, Bcl-xL Upregulation, and Recovery of Neurological Function in a Rat Model of Traumatic Brain Injury

Traumatic brain injury (TBI) is a common disease that usually causes severe neurological damage, and current treatment is far from satisfactory. The neuroprotective effects of neural stem cell (NSC) transplantation in the injured nervous system have largely been known, but the underlying mechanisms remain unclear, and their limited sources impede their clinical application. Here, we established a rat model of TBI by dropping a weight onto the cortical motor area of the brain and explored the effect of engrafted NSCs (passage 3, derived from the hippocampus of embryonic 12- to 14-d green fluorescent protein transgenic mice) on TBI rats. Moreover, RT-PCR and Western blotting were employed to investigate the possible mechanism associated with NSC grafts. We found rats with TBI exhibited a severe motor and equilibrium dysfunction, while NSC transplantation could partly improve the motor function and significantly reduce cell apoptosis and increase B-cell lymphoma–extra large (Bcl-xL) expression at 7 d postoperation. However, other genes including Bax, B-cell lymphoma 2, Fas ligand, and caspase3 did not exhibit significant differences in expression. Moreover, to test whether Bcl-xL could be used as a therapeutic target, herpes simplex virus (HSV) 1 carrying Bcl-xL recombinant was constructed and injected into the pericontusional cortices. Bcl-xL overexpression not only resulted in a significant improvement in neurological function but also inhibits cell apoptosis, as compared with the TBI rats, and exhibits the same effects as the administration of NSC. The present study therefore indicated that NSC transplantation could promote the recovery of TBI rats in a manner similar to that of Bcl-xL overexpression. Therefore, Bcl-xL overexpression, to some extent, could be considered as a useful strategy to replace NSC grafting in the treatment of TBI in future clinical practices.

Human dental stem cell derived transgene-free iPSCs generate functional neurons via embryoid body-mediated and direct induction methods

Induced pluripotent stem cells (iPSCs) give rise to neural stem/progenitor cells, serving as a good source for neural regeneration. Here, we established transgene-free (TF) iPSCs from dental stem cells (DSCs) and determined their capacity to differentiate into functional neurons in vitro. Generated TF iPSCs from stem cells of apical papilla and dental pulp stem cells underwent two methods-embryoid body-mediated and direct induction, to guide TF-DSC iPSCs along with H9 or H9 Syn-GFP (human embryonic stem cells) into functional neurons in vitro. Using the embryoid body-mediated method, early stage neural markers PAX6, SOX1, and nestin were detected by immunocytofluorescence or reverse transcription-real time polymerase chain reaction (RT-qPCR). At late stage of neural induction measured at Weeks 7 and 9, the expression levels of neuron-specific markers Nav1.6, Kv1.4, Kv4.2, synapsin, SNAP25, PSD95, GAD67, GAP43, and NSE varied between stem cells of apical papilla iPSCs and H9. For direct induction method, iPSCs were directly induced into neural stem/progenitor cells and guided to become neuron-like cells. The direct method, while simpler, showed cell detachment and death during the differentiation process. At early stage, PAX6, SOX1 and nestin were detected. At late stage of differentiation, all five genes tested, nestin, βIII-tubulin, neurofilament medium chain, GFAP, and Nav, were positive in many cells in cultures. Both differentiation methods led to neuron-like cells in cultures exhibiting sodium and potassium currents, action potential, or spontaneous excitatory postsynaptic potential. Thus, TF-DSC iPSCs are capable of undergoing guided neurogenic differentiation into functional neurons in vitro, thereby may serve as a cell source for neural regeneration.

Cross-talk between blood vessels and neural progenitors in the developing brain

The formation of the central nervous system (CNS) involves multiple cellular and molecular interactions between neural progenitor cells (NPCs) and blood vessels to establish extensive and complex neural networks and attract a vascular supply that support their function. In this review, we discuss studies that have performed genetic manipulations of chick, fish and mouse embryos to define the spatiotemporal roles of molecules that mediate the reciprocal regulation of NPCs and blood vessels. These experiments have highlighted core functions of NPC-expressed ligands in initiating vascular growth into and within the neural tube as well as establishing the blood-brain barrier. More recent findings have also revealed indispensable roles of blood vessels in regulating NPC expansion and eventual differentiation, and specific regional differences in the effect of angiocrine signals. Accordingly, NPCs initially stimulate blood vessel growth and maturation to nourish the brain, but blood vessels subsequently also regulate NPC behaviour to promote the formation of a sufficient number and diversity of neural cells. A greater understanding of the molecular cross-talk between NPCs and blood vessels will improve our knowledge of how the vertebrate nervous system forms and likely help in the design of novel therapies aimed at regenerating neurons and neural vasculature following CNS disease or injury.

Stem Cell Pathology

Rapid advances in stem cell biology and regenerative medicine have opened new opportunities for better understanding disease pathogenesis and the development of new diagnostic, prognostic, and treatment approaches. Many stem cell niches are well defined anatomically, thereby allowing their routine pathological evaluation during disease initiation and progression. Evaluation of the consequences of genetic manipulations in stem cells and investigation of the roles of stem cells in regenerative medicine and pathogenesis of various diseases such as cancer require significant expertise in pathology for accurate interpretation of novel findings. Therefore, there is an urgent need for developing stem cell pathology as a discipline to facilitate stem cell research and regenerative medicine. This review provides examples of anatomically defined niches suitable for evaluation by diagnostic pathologists, describes neoplastic lesions associated with them, and discusses further directions of stem cell pathology.

Effects of ginsenoside‑Rg1 on the proliferation and glial‑like directed differentiation of embryonic rat cortical neural stem cells in vitro

Ginsenoside-Rg1, the main active component of Panax notoginseng, exhibits a number of pharmacological functions, including promoting protein synthesis in the brain, increasing the number of synapses, improving memory and promoting recovery of brain function following injury. The effect of ginsenoside-Rg1 on proliferation and glial-like-directed differentiation in the cortical neural stem cells (NSCs) of embryonic rat brain was investigated. The present study used MTS assays to identify the optimum dose and window time of ginsenoside-Rg1 administration to stimulate the proliferation of cortical NSCs in the rat embryonic tissue. The oxygen glucose deprivation (OGD) set-up was used as a cell injury model. Immunofluorescent staining was used for identification of NSCs and subsequent observation of their proliferation and glial-like directed differentiation. Nestin expression was the marker for the presence of NSCs among the cortical cells of embryonic rat brain. The optimum dose of ginsenoside-Rg1 for proliferation of NSCs was 0.32 µg/ml. The optimum window time of 0.32 µg/ml ginsenoside-Rg1 administration on proliferation of NSCs was 6 h. Ginsenoside-Rg1 at 0.32 µg/ml concentration promoted incorporation of bromo-2-deoxyuridine, and expression of nestin and vimentin in primary and passaged NSCs, and NSCs following OGD. Ginsenoside-Rg1 had a role in promoting proliferation and glial-like-directed differentiation of cortical NSCs. The plausible explanation for these responses is that ginsenoside-Rg1 acts similarly to the growth factors to promote the proliferation and differentiation of NSCs.

Directed differentiation of postnatal hippocampal neural stem cells generates nuclear receptor related‑1 protein‑ and tyrosine hydroxylase‑expressing cells

Parkinson's disease (PD) is a severe neurodegenerative disorder. Although the detailed underlying molecular mechanism remains to be elucidated, the major pathological feature of PD is the loss of dopaminergic (DA) neurons of the substantia nigra. The use of donor stem cells to replace DA neurons may be a key breakthrough in the treatment of PD. In the present study, the growth kinetics of hippocampal neural stem cells (Hip-NSCs) isolated from postnatal mice and cultured in vitro were observed, specifically the generation of cells expressing DA neuronal markers nuclear receptor related-1 protein (Nurr1) and tyrosine hydroxylase (TH). It was revealed that Hip-NSCs differentiated primarily into astrocytes when cultured in serum-containing medium. However, in low serum conditions, the number of βIII tubulin-positive neurons increased markedly. The proportion of Nurr1-positive cells and TH-positive neurons, significantly increased with increasing duration of directed differentiation of Hip-NSCs (P=0.0187 and 0.0254, respectively). The results of the present study reveal that Hip-NSCs may be induced to differentiate in vitro into neurons expressing Nurr1 and TH, known to be critical regulators of DA neuronal fate. Additionally, their expression may be necessary to facilitate neuronal maturation in vitro. These data suggest that Hip-NSCs may serve as a source of DA neurons for cell therapy in patients diagnosed with PD.

Accelerating skin wound healing by M-CSF through generating SSEA-1 and -3 stem cells in the injured sites

Wound healing is a complicated process requiring the collaborative efforts of different cell lineages. Our recent studies have found that one subset of hematopoietic cells can be induced to dedifferentiate into multipotent stem cells by means of a proliferating fibroblast releasable factor, M-CSF. Understanding the importance of stem cells on skin wound healing, here we evaluate the biological significance of M-CSF on skin wound healing. In an in vivo mouse skin excisional wound model, we found that SSEA-positive stem cells were present in wounded but not normal skin. After isolating skin cells from either normal or wounded skin by collagenase digestion, and analyzing the SSEA-1 positive cells by flow cytometry, we found a significant increase in the number of SSEA-1 positive cells in wounded skin. Topical application of M-CSF in skin wounds accelerated healing remarkably, while application of M-CSF-neutralizing antibody slowed wound healing. Furthermore, injection of EGFP-labeled hematopoietic cell-derived stem cells generated from M-CSF treated splenocytes resulted in EGFP-labeled cells being enriched in the skin wound site and further differentiated into functional organ-specific cells. Together, these data demonstrated that M-CSF makes a significant contribution to the healing process by inducing hematopoietic cell dedifferentiation into stem cells.

Purines in neurite growth and astroglia activation

The mammalian nervous system is a complex, functional network of neurons, consisting of local and long-range connections. Neuronal growth is highly coordinated by a variety of extracellular and intracellular signaling molecules. Purines turned out to be an essential component of these processes. Here, we review the current knowledge about the involvement of purinergic signaling in the regulation of neuronal development. We particularly focus on its role in neuritogenesis: the formation and extension of neurites. In the course of maturation mammals generally lose their ability to regenerate the central nervous system (CNS) e.g. after traumatic brain injury; although, spontaneous regeneration still occurs in the peripheral nervous system (PNS). Thus, it is crucial to translate the knowledge about CNS development and PNS regeneration into novel approaches to enable neurons of the mature CNS to regenerate. In this context we give a general overview of growth-inhibitory and growth-stimulatory factors and mechanisms involved in neurite growth. With regard to neuronal growth, astrocytes are an important cell population. They provide structural and metabolic support to neurons and actively participate in brain signaling. Astrocytes respond to injury with beneficial or detrimental reactions with regard to axonal growth. In this review we present the current knowledge of purines in these glial functions. Moreover, we discuss organotypic brain slice co-cultures as a model which retains neuron-glia interactions, and further presents at once a model for CNS development and regeneration. In summary, the purinergic system is a pivotal factor in neuronal development and in the response to injury. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.

Premature aging of the hippocampal neurogenic niche in adult Bmal1-deficient mice

Hippocampal neurogenesis undergoes dramatic age-related changes. Mice with targeted deletion of the clock geneBmal1 (Bmal1(-/-)) show disrupted regulation of reactive oxygen species homeostasis, accelerated aging, neurodegeneration and cognitive deficits. As proliferation of neuronal progenitor/precursor cells (NPCs) is enhanced in young Bmal1(-/-) mice, we tested the hypothesis that this results in premature aging of hippocampal neurogenic niche in adult Bmal1(-/-) mice as compared to wildtype littermates. We found significantly reduced pool of hippocampal NPCs, scattered distribution, enhanced survival of NPCs and an increased differentiation of NPCs into the astroglial lineage at the expense of the neuronal lineage. Immunoreaction of the redox sensitive histone deacetylase Sirtuine 1, peroxisomal membrane protein at 70 kDa and expression of the cell cycle inhibitor p21(Waf1/CIP1) were increased in adult Bmal1(-/-) mice. In conclusion, genetic disruption of the molecular clockwork leads to accelerated age-dependent decline in adult neurogenesis presumably as a consequence of oxidative stress.

Cross-talk between human neural stem/progenitor cells and peripheral blood mononuclear cells in an allogeneic co-culture model

Transplantation of human neural stem/progenitor cells (hNSCs) as a regenerative cell replacement therapy holds great promise. However, the underlying mechanisms remain unclear. We, here, focused on the interaction between hNSCs and allogeneic peripheral blood mononuclear cells (PBMCs) in a co-culture model. We found that hNSCs significantly decrease the CD3⁺ and CD8⁺ T cells, reduce the gamma delta T cells and increase the regulatory T cells, along with reduced pro-inflammatory cytokines and increased anti-inflammatory cytokines after co-culture. We also found that PBMCs, in turn, significantly promote the proliferation and differentiation of hNSCs. Our data suggest that hNSCs cross-talk with immune cells.

The selective antagonism of P2X7 and P2Y1 receptors prevents synaptic failure and affects cell proliferation induced by oxygen and glucose deprivation in rat dentate gyrus

Purinergic P2X and P2Y receptors are broadly expressed on both neurons and glial cells in the central nervous system (CNS), including dentate gyrus (DG). The aim of this research was to determine the synaptic and proliferative response of the DG to severe oxygen and glucose deprivation (OGD) in acute rat hippocampal slices and to investigate the contribution of P2X₇ and P2Y₁ receptor antagonism to recovery of synaptic activity after OGD. Extracellular field excitatory post-synaptic potentials (fEPSPs) in granule cells of the DG were recorded from rat hippocampal slices. Nine-min OGD elicited an irreversible loss of fEPSP and was invariably followed by the appearance of anoxic depolarization (AD). Application of MRS2179 (selective antagonist of P2Y₁ receptor) and BBG (selective antagonist of P2X₇ receptor), before and during OGD, prevented AD appearance and allowed a significant recovery of neurotransmission after 9-min OGD. The effects of 9-min OGD on proliferation and maturation of cells localized in the subgranular zone (SGZ) of slices prepared from rats treated with 5-Bromo-2′-deoxyuridine (BrdU) were investigated. Slices were further incubated with an immature neuron marker, doublecortin (DCX). The number of BrdU⁺ cells in the SGZ was significantly decreased 6 hours after OGD. This effect was antagonized by BBG, but not by MRS2179. Twenty-four hours after 9-min OGD, the number of BrdU⁺ cells returned to control values and a significant increase of DCX immunofluorescence was observed. This phenomenon was still evident when BBG, but not MRS2179, was applied during OGD. Furthermore, the P2Y₁ antagonist reduced the number of BrdU⁺ cells at this time. The data demonstrate that P2X₇ and P2Y₁ activation contributes to early damage induced by OGD in the DG. At later stages after the insult, P2Y₁ receptors might play an additional and different role in promoting cell proliferation and maturation in the DG.

Interleukin-17 inhibits adult hippocampal neurogenesis

Interleukin 17(A) (IL-17) is a potent pro-inflammatory cytokine that acts as a central regulator of inflammatory response within the brain, but its physiological roles under non-inflammatory conditions remain elusive. Here we report that endogenous IL-17 ablates neurogenesis in the adult dentate gyrus (DG) of hippocampus. Genetic deletion of IL-17 increased the number of adult-born neurons in the DG. Further, we found that IL-17 deletion altered cytokine network, facilitated basal excitatory synaptic transmission, enhanced intrinsic neuronal excitability, and increased expression of proneuronal genes in neuronal progenitor cells (NPCs). Our findings suggest a profound role of IL-17 in the negative regulation of adult hippocampal neurogenesis under physiology conditions.

Autophagy-related gene Atg5 is essential for astrocyte differentiation in the developing mouse cortex

Astrocyte differentiation is essential for late embryonic brain development, and autophagy is active during this process. However, it is unknown whether and how autophagy regulates astrocyte differentiation. Here, we show that Atg5, which is necessary for autophagosome formation, regulates astrocyte differentiation. Atg5 deficiency represses the generation of astrocytes in vitro and in vivo. Conversely, Atg5 overexpression increases the number of astrocytes substantially. We show that Atg5 activates the JAK2-STAT3 pathway by degrading the inhibitory protein SOCS2. The astrocyte differentiation defect caused by Atg5 loss can be rescued by human Atg5 overexpression, STAT3 overexpression, and SOCS2 knockdown. Together, these data demonstrate that Atg5 regulates astrocyte differentiation, with potential implications for brain disorders with autophagy deficiency.

Neuroprotective effect of buyang huanwu decoction on rat ischemic/reperfusion brain damage by promoting migration of neural precursor cells

Buyang Huanwu Decoction (BYHWD) is a classic formula widely used for treating stroke-induced disability, the highest morbidity of neurological disorders in China. However, the mechanism of its neuroprotection has not been fully clarified. Previous reports indicated that BYHWD may promote growth and differentiation of neural precursor cells (NPCs). The present study focused on the effects of BYHWD on migration of NPCs in rats with middle cerebral artery occlusion (MCAO). Rats were treated with different doses of BYHWD (12 and 24 grams/kg) from day 1 to day 21 after model building. BYHWD could increase the survival rate and decrease neurological scores and infarct volume as compared with the vehicle-treated MCAO rats. Moreover, BYHWD treatment significantly increased 5-bromo-2-deoxyuridine (BrdU)-positive cells in the subventricular zone (SVZ), subgranular zone (SGZ), and corpus striatum (CS) of the infarct brain. Interestingly, BYHWD could markedly enhance BrdU(+)/doublecortin(+) cells not only in the SVZ and SGZ but also in CS, by up-regulating the protein expression of migration activators, including stromal cell derived factor-1, CXC chemokine receptor 4, vascular endothelial growth factor, Reelin, and brain-derived neurotrophic factor in the ipsilateral infarct area after MCAO. In addition, BYHWD treatment was able to promote the neuronal differentiation, which was closely related to the migratory process of NPCs in MCAO rats. These findings offer evidence for the first time that BYHWD may exert its neuroprotective effects partially by promotion of NPCs migration to ischemic brain areas.

Hypothalamic subependymal niche: a novel site of the adult neurogenesis

The discovery of undifferentiated, actively proliferating neural stem cells (NSCs) in the mature brain opened a brand new chapter in the contemporary neuroscience. Adult neurogenesis appears to occur in specific brain regions (including hypothalamus) throughout vertebrates’ life, being considered an important player in the processes of memory, learning, and neural plasticity. In the adult mammalian brain, NSCs are located mainly in the subgranular zone (SGZ) of the hippocampal dentate gyrus and in the subventricular zone (SVZ) of the lateral ventricle ependymal wall. Besides these classical regions, hypothalamic neurogenesis occurring mainly along and beneath the third ventricle wall seems to be especially well documented. Neurogenic zones in SGZ, SVZ, and in the hypothalamus share some particular common features like similar cellular cytoarchitecture, vascularization pattern, and extracellular matrix properties. Hypothalamic neurogenic niche is formed mainly by four special types of radial glia-like tanycytes. They are characterized by distinct expression of some neural progenitor and stem cell markers. Moreover, there are numerous suggestions that newborn hypothalamic neurons have a significant ability to integrate into the local neural pathways and to play important physiological roles, especially in the energy balance regulation. Newly formed neurons in the hypothalamus can synthesize and release food intake regulating neuropeptides and they are sensitive to the leptin. On the other hand, high-fat diet positively influences hypothalamic neurogenesis in rodents. The nature of this intriguing new site of adult neurogenesis is still so far poorly studied and requires further investigations.

Neuroregeneration in the nucleus ambiguus after recurrent laryngeal nerve avulsion in rats

OBJECTIVES

The objective was to investigate neuroregeneration, the origins of newborn cells and the proliferation of neuronal and glial cells in the nucleus ambiguus (NA) after ipsilateral recurrent laryngeal nerve (RLN) avulsion.

METHODS

All of the animals received a CM-Dil injection in the left lateral ventricle. Forty-five adult rats were subjected to a left RLN avulsion injury, while 9 rats were used as controls. 5-Bromo-2-deoxyuridine (BrdU) was injected intraperitoneally. Neuron quantification and immunohistochemical analysis were performed in the brain stems at different time points after RLN injury.

RESULTS

After RLN avulsion, CM-Dil labeled neural progenitor cells (NPCs) migrated to the ipsilateral NA and differentiated into astrocytes but not into neurons. In the NA, the neuronal cells re-expressed nestin. Only a small number of neuronal and glial cells in the NA showed BrdU immunoreactivity.

CONCLUSIONS

After RLN avulsion, the NPCs in the ependymal layer of the fourth ventricle or central canal are activated, migrate to the lesion in the NA and differentiate exclusively into astrocytes. The newborn neural stem cells in the NA may arise from the mature region neurons. The presence of both cell types in the NA may play a role in repairing RLN injuries.

The proliferation study of hips cell-derived neuronal progenitors on poly-caprolactone scaffold

INTRODUCTION

The native inability of nervous system to regenerate, encourage researchers to consider neural tissue engineering as a potential treatment for spinal cord injuries. Considering the suitable characteristics of induced pluripotent stem cells (iPSCs) for tissue regeneration applications, in this study we investigated the adhesion, viability and proliferation of neural progenitors (derived from human iPSCs) on aligned poly-caprolactone (PCL) nanofibers.

METHODS

Aligned poly-caprolactone nanofibrous scaffold was fabricated by electrospinning and characterized by scanning electron microscopy (SEM). Through neural induction, neural progenitor cells were derived from induced pluripotent stem cells. After cell seeding on the scaffolds, their proliferation was investigated on different days of culture.

RESULTS

According to the SEM micrographs, the electrospun PCL scaffolds were aligned along with uniformed morphology. Evaluation of adhesion and viability of neural progenitor cells on plate (control) and PCL scaffold illustrated increasing trends in proliferation but this rate was higher in scaffold group. The statistical analyses confirmed significant differences between groups on 36h and 48h.

DISCUSSION

Evaluation of cell proliferation along with morphological assessments, staining and SEM finding suggested biocompatibility of the PCL scaffolds and suitability of the combination of the mentioned scaffold and human iPS cells for neural regeneration.

Glioblastoma multiforme therapy and mechanisms of resistance

Glioblastoma multiforme (GBM) is a grade IV brain tumor characterized by a heterogeneous population of cells that are highly infiltrative, angiogenic and resistant to chemotherapy. The current standard of care, comprised of surgical resection followed by radiation and the chemotherapeutic agent temozolomide, only provides patients with a 12–14 month survival period post-diagnosis. Long-term survival for GBM patients remains uncommon as cells with intrinsic or acquired resistance to treatment repopulate the tumor. In this review we will describe the mechanisms of resistance, and how they may be overcome to improve the survival of GBM patients by implementing novel chemotherapy drugs, new drug combinations and new approaches relating to DNA damage, angiogenesis and autophagy.

In vitro and in vivo neuronal electrotaxis: a potential mechanism for restoration?

Electrical brain stimulation used to treat a variety of neurological and psychiatric diseases is entering a new period. The technique is well established and the potential complications are well known and generally manageable. Recent studies demonstrated that electrical fields (EFs) can enhance neuroplasticity-related processes. EFs applied in the physiological range induce migration of different neural cell types from different species in vitro. There are some evidences that also the speed and directedness of cell migration are enhanced by EFs. However, it is still unclear how electrical signals from the extracellular space are translated into intracellular actions resulting in the so-called electrotaxis phenomenon. Here, we aim to provide a comprehensive review of the data on responses of cells to electrical stimulation and the relation to functional recovery.

Dynamics of focal adhesions and reorganization of F-actin in VEGF-stimulated NSCs under varying differentiation states

Precise migration of neural stem/progenitor cells (NSCs) is crucially important for neurogenesis and repair in the nervous system. However, the detailed mechanisms are not clear. Our previous results showed that NSCs in varying differentiation states possess different migratory ability to vascular endothelial growth factor (VEGF). In this study, we demonstrate the different dynamics of focal adhesions (FAs) and reorganization of F-actin in NSCs during spreading and migration stimulated by VEGF. We found that the migrating NSCs of 0.5 and 1 day differentiation possess more FAs at leading edge than cells of other states. Moreover, the phosphorylation of focal adhesion kinase (FAK) and paxillin in NSCs correlates closely with their differentiation states. VEGF promotes FA formation with broad lamellipodium generation at the leading edge in chemotaxing cells of 0, 0.5, and 1 day differentiation, but not in cells of 3 days differentiation. Furthermore, cells of 1 day differentiation show a maximal asymmetry of FAs between lamella and cell rear, orchestrating cell polarization and directional migration. Time-lapse video analysis shows that the disassembly of FAs and the cell tail detachment in NSCs of 1 day differentiation are more rapid, along with the concurrent enlarged size of FAs at the leading edge, leading to the most effective chemotactic response to VEGF. Collectively, these results indicate that the dynamics of FAs and reorganization of F-actin in NSCs that undergo directional migration correlate closely with their differentiation states, contributing to the different chemotactic responses of these cells to VEGF.

Steps toward safe cell therapy using induced pluripotent stem cells

The enthusiasm for producing patient-specific human embryonic stem cells using somatic nuclear transfer has somewhat abated in recent years because of ethical, technical, and political concerns. However, the interest in generating induced pluripotent stem cells (iPSCs), in which pluripotency can be obtained by transcription factor transduction of various somatic cells, has rapidly increased. Human iPSCs are anticipated to open enormous opportunities in the biomedical sciences in terms of cell therapies for regenerative medicine and stem cell modeling of human disease. On the other hand, recent reports have emphasized the pitfalls of iPSC technology, including the potential for genetic and epigenetic abnormalities, tumorigenicity, and immunogenicity of transplanted cells. These constitute serious safety-related concerns for iPSC-based cell therapy. However, preclinical data supporting the safety and efficacy of iPSCs are also accumulating. In this Review, recent achievements and future tasks for safe iPSC-based cell therapy are summarized, using regenerative medicine for repair strategies in the damaged central nervous system (CNS) as a model. Insights on safety and preclinical use of iPSCs in cardiovascular repair model are also discussed.

Subventricular zone-derived oligodendrogenesis in injured neonatal white matter in mice enhanced by a nonerythropoietic erythropoietin derivative

Perinatal hypoxia-ischemia (HI) frequently causes white-matter injury, leading to severe neurological deficits and mortality, and only limited therapeutic options exist. The white matter of animal models and human patients with HI-induced brain injury contains increased numbers of oligodendrocyte progenitor cells (OPCs). However, the origin and fates of these OPCs and their potential to repair injured white matter remain unclear. Here, using cell-type- and region-specific genetic labeling methods in a mouse HI model, we characterized the Olig2-expressing OPCs. We found that after HI, Olig2+ cells increased in the posterior part of the subventricular zone (pSVZ) and migrated into the injured white matter. However, their oligodendrocytic differentiation efficiency was severely compromised compared with the OPCs in normal tissue, indicating the need for an intervention to promote their differentiation. Erythropoietin (EPO) treatment is a promising candidate, but it has detrimental effects that preclude its clinical use for brain injury. We found that long-term postinjury treatment with a nonerythropoietic derivative of EPO, asialo-erythropoietin, promoted the maturation of pSVZ-derived OPCs and the recovery of neurological function, without affecting hematopoiesis. These results demonstrate the limitation and potential of endogenous OPCs in the pSVZ as a therapeutic target for treating neonatal white-matter injury.

Neural stem cells, adult neurogenesis, and galectin-1: from bench to bedside

Neural stem cells (NSCs) in the adult brain have been a consistent focus of biomedical research largely because of their potential clinical application. To fully exploit this potential, the molecular mechanisms that regulate NSCs must be clarified. Several lines of evidence show that a multifunctional protein, Galectin-1, is expressed and has a functional role in a subset of adult NSCs. Researchers, including our group, have explored the physiological role of Galectin-1 in NSCs and its application in the treatment of animal models of neurological disorders such as brain ischemia and spinal cord injury. Here, we summarize what is currently known regarding the role of Galectin-1 in adult NSCs. Furthermore, we discuss current issues in researching the role of Galectin-1 in adult NSCs under both physiological and pathological conditions.

Growth factors released from gelatin hydrogel microspheres increase new neurons in the adult mouse brain

Recent studies have shown that new neurons are continuously generated by endogenous neural stem cells in the subventricular zone (SVZ) of the adult mammalian brain. Some of these new neurons migrate to injured brain tissues and differentiate into mature neurons, suggesting that such new neurons may be able to replace neurons lost to degenerative disease or injury and improve or repair neurological deficits. Here, we tested whether delivering growth factors via gelatin hydrogel microspheres would support neurogenesis in the SVZ. Insulin-like growth factor-1 (IGF-1)-containing microspheres increased the number of new neurons in the SVZ. Hepatocyte growth factor (HGF)-containing microspheres increased the number of new neurons migrating from the SVZ towards the injured striatum in a stroke model in mouse. These results suggest that the strategy of using gelatin hydrogel microspheres to achieve the sustained release of growth factors holds promise for the clinical regeneration of damaged brain tissues from endogenous neural stem cells in the adult SVZ.

Purinergic signaling promotes proliferation of adult mouse subventricular zone cells

In adult mammalian brains, neural stem cells (NSCs) exist in the subventricular zone (SVZ), where persistent neurogenesis continues throughout life. Those NSCs produce neuroblasts that migrate into the olfactory bulb via formation of transit-amplifying cells, which are committed precursor cells of the neuronal lineage. In this SVZ niche, cell-cell communications conducted by diffusible factors as well as physical cell-cell contacts are important for the regulation of the proliferation and fate determination of NSCs. Previous studies have suggested that extracellular purinergic signaling, which is mediated by purine compounds such as ATP, plays important roles in cell-cell communication in the CNS. Purinergic signaling also promotes the proliferation of adult NSCs in vitro. However, the in vivo roles of purinergic signaling in the neurogenic niche still remain unknown. In this study, ATP infusion into the lateral ventricle of the mouse brain resulted in an increase in the numbers of rapidly dividing cells and Mash1-positive transit-amplifying cells (Type C cells) in the SVZ. Mash1-positive cells express the P2Y1 purinergic signaling receptor and infusion of the P2Y1 receptor-specific antagonist MRS2179 decreased the number of rapidly dividing bromodeoxyuridine (BrdU)-positive cells and Type C cells. Moreover, a 17% reduction of rapidly dividing BrdU-positive cells and a 19% reduction of Mash1-positive cells were observed in P2Y1 knock-out mice. Together, these results suggest that purinergic signaling promotes the proliferation of rapidly dividing cells and transit-amplifying cells, in the SVZ niche through the P2Y1 receptor.

Functional recovery of the dentate gyrus after a focal lesion is accompanied by structural reorganization in the adult rat

The adult brain is highly plastic and tends to undergo substantial reorganization after injury to compensate for the lesion effects. It has been shown that such reorganization mainly relies on anatomical and biochemical modifications of the remaining cells which give rise to a network rewiring without reinstating the original morphology of the damaged region. However, few studies have analyzed the neurorepair potential of a neurogenic structure. Thus, the aim of this work was to analyze if the DG could restore its original morphology after a lesion and to establish if the structural reorganization is accompanied by behavioral and electrophysiological recovery. Using a subepileptogenic injection of kainic acid (KA), we induced a focal lesion in the DG and assessed in time (1) the loss and recovery of dependent and non dependent DG cognitive functions, (2) the anatomical reorganization of the DG using a stereological probe and immunohistochemical markers for different neuronal maturation stages and, (3) synaptic plasticity as assessed through the induction of in vivo long-term potentiation (LTP) in the mossy fiber pathway (CA3-DG). Our results show that a DG focal lesion with KA leads to a well delimited region of neuronal loss, disorganization of the structure, the loss of associated mnemonic functions and the impairment to elicit LTP. However, behavioral and synaptic plasticity expression occurs in a time dependent fashion and occurs along the morphological restoration of the DG. These results provide novel information on neural plasticity events associated to functional reorganization after damage.

Controlling the stem cell compartment and regeneration in vivo: the role of pluripotency pathways

Since the realization that embryonic stem cells are maintained in a pluripotent state through the interplay of a number of key signal transduction pathways, it is becoming increasingly clear that stemness and pluripotency are defined by the complex molecular convergence of these pathways. Perhaps this has most clearly been demonstrated by the capacity to induce pluripotency in differentiated cell types, so termed iPS cells. We are therefore building an understanding of how cells may be maintained in a pluripotent state, and how we may manipulate cells to drive them between committed and pluripotent compartments. However, it is less clear how cells normally pass in and out of the stem cell compartment under normal and diseased physiological states in vivo, and indeed, how important these pathways are in these settings. It is also clear that there is a potential "dark side" to manipulating the stem cell compartment, as deregulation of somatic stem cells is being increasingly implicated in carcinogenesis and the generation of "cancer stem cells." This review explores these relationships, with a particular focus on the role played by key molecular regulators of stemness in tissue repair, and the possibility that a better understanding of this control may open the door to novel repair strategies in vivo. The successful development of such strategies has the potential to replace or augment intervention-based strategies (cell replacement therapies), although it is clear they must be developed with a full understanding of how such approaches might also influence tumorigenesis.