Nestin-expressing Neural Progenitor Cells Research Articles

Deltamethrin Exposure Inhibits Adult Hippocampal Neurogenesis and Causes Deficits in Learning and Memory in Mice.

Deficits in learning and memory are often associated with disruption of hippocampal neurogenesis, which is regulated by numerous processes, including precursor cell proliferation, survival, migration, and differentiation to mature neurons. Recent studies demonstrate that adult born neurons in the dentate gyrus (DG) in the hippocampus can functionally integrate into the existing neuronal circuitry and contribute to hippocampal-dependent learning and memory. Here, we demonstrate that relatively short-term deltamethrin exposure (3 mg/kg every 3 days for 1 month) inhibits adult hippocampal neurogenesis and causes deficits in learning and memory in mice. Hippocampal-dependent cognitive functions were evaluated using 2 independent hippocampal-dependent behavioral tests, the novel object recognition task and Morris water maze. We found that deltamethrin-treated mice exhibited profound deficits in novel object recognition and learning and memory in water maze. Deltamethrin exposure significantly decreased bromodeoxyuridine (BrdU)-positive cells (39%) and Ki67+ cells (47%) in the DG of the hippocampus, indicating decreased cellular proliferation. In addition, deltamethrin-treated mice exhibited a 44% decrease in nestin-expressing neural progenitor cells and a 38% reduction in the expression of doublecortin (DCX), an early neuronal differentiation marker. Furthermore, deltamethrin-exposed mice exhibited a 25% reduction in total number of granule cells in the DG. These findings indicate that relatively short-term exposure to deltamethrin causes significant deficits in hippocampal neurogenesis that is associated with impaired learning and memory.

Somatic cell transfer of c-Myc and Bcl-2 induces large-cell anaplastic medulloblastomas in mice

A highly aggressive subgroup of the pediatric brain tumor medulloblastoma is characterized by overexpression of the proto-oncogene c-Myc, which encodes a transcription factor that normally maintains neural progenitor cells in an undifferentiated, proliferating state during embryonic development. Myc-driven medulloblastomas typically show a large-cell anaplastic (LCA) histological pattern, in which tumor cells display large, round nuclei with prominent nucleoli. This subgroup of medulloblastoma is therapeutically challenging because it is associated with a high rate of metastatic dissemination, which is a powerful predictor of short patient survival times. Genetically engineered mouse models have revealed important insights into the pathogenesis of medulloblastoma and served as preclinical testing platforms for new therapies. Here we report a new mouse model of Myc-driven medulloblastoma, in which tumors arise in situ after retroviral transfer and expression of Myc in Nestin-expressing neural progenitor cells in the cerebella of newborn mice. Tumor induction required concomitant loss of Tp53 or overexpression of the antiapoptotic protein Bcl-2. Like Myc-driven medulloblastomas in humans, the tumors induced in mice by Myc + Bcl-2 and Myc - Tp53 showed LCA cytoarchitecture and a high rate of metastatic dissemination to the spine. The fact that Myc - Tp53 tumors arose only in Tp53(-/-) mice, coupled with the inefficient germline transmission of the Tp53-null allele, made retroviral transfer of Myc + Bcl-2 a more practical method for generating LCA medulloblastomas. The high rate of spinal metastasis (87% of brain tumor-bearing mice) will be an asset for testing new therapies that target the most lethal aspect of medulloblastoma.

HD iPSC-derived neural progenitors accumulate in culture and are susceptible to BDNF withdrawal due to glutamate toxicity.

Huntington's disease (HD) is a fatal neurodegenerative disease, caused by expansion of polyglutamine repeats in the Huntingtin gene, with longer expansions leading to earlier ages of onset. The HD iPSC Consortium has recently reported a new in vitro model of HD based on the generation of induced pluripotent stem cells (iPSCs) from HD patients and controls. The current study has furthered the disease in a dish model of HD by generating new non-integrating HD and control iPSC lines. Both HD and control iPSC lines can be efficiently differentiated into neurons/glia; however, the HD-derived cells maintained a significantly greater number of nestin-expressing neural progenitor cells compared with control cells. This cell population showed enhanced vulnerability to brain-derived neurotrophic factor (BDNF) withdrawal in the juvenile-onset HD (JHD) lines, which appeared to be CAG repeat-dependent and mediated by the loss of signaling from the TrkB receptor. It was postulated that this increased death following BDNF withdrawal may be due to glutamate toxicity, as the N-methyl-d-aspartate (NMDA) receptor subunit NR2B was up-regulated in the cultures. Indeed, blocking glutamate signaling, not just through the NMDA but also mGlu and AMPA/Kainate receptors, completely reversed the cell death phenotype. This study suggests that the pathogenesis of JHD may involve in part a population of 'persistent' neural progenitors that are selectively vulnerable to BDNF withdrawal. Similar results were seen in adult hippocampal-derived neural progenitors isolated from the BACHD model mouse. Together, these results provide important insight into HD mechanisms at early developmental time points, which may suggest novel approaches to HD therapeutics.

The notch signaling pathway: its role in focal CNS demyelination and apotransferrin‐induced remyelination

Oligodendroglial damage and demyelination are common pathological features characterizing white matter and neurodegenerative disorders. Identifying the signaling pathways involved in myelin repair through oligodendroglial progenitor maturation is essential for the development of new therapies. This article investigated the role of the Notch signaling pathway in CNS demyelination and apotransferrin-induced remyelination in a focal lysolecithin-induced demyelination model in rats. Notch was found activated in Nestin-expressing neural progenitor cells and in NG2-expressing oligodendroglial precursor cells in the subventricular zone and corpus callosum of lysolecithin-demyelinated rats. Notch activation seemed to be driven by Jagged1, which led to a high expression of downstream gene Hes5 in the subventricular zone of demyelinated rats. Apotransferrin injection induced remyelination, while the injection of the γ-secretase inhibitor reversed this effect. In addition, 24 h after apotransferrin injection, evidence showed Notch activation concomitantly with an increase in F3/contactin levels and the up-regulation of the myelin-associated glycoprotein gene in the subventricular zone and corpus callosum of demyelinated rats. Collected evidence supports the participation of both canonical and non-canonical Notch signaling pathways in demyelination/remyelination. Notch activation was found to trigger Hes5 expression as a consequence of focal demyelination, which might promote oligodendroglial precursor cell proliferation. During apotransferrin-induced remyelination, Notch activation seemed to be mediated by the expression of F3/contactin, which might induce apotransferrin-mediated oligodendroglial maturation. Evidence of the participation of Notch signaling in the demyelination/remyelination process will help further understand demyelinating disorders such as Multiple Sclerosis and the use of aTf should be taken into consideration as a possible therapeutic intervention.

Deletion or activation of the aryl hydrocarbon receptor alters adult hippocampal neurogenesis and contextual fear memory

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates the toxicity of dioxin and serves multiple developmental roles. In the adult brain, while we now localize AhR mRNA to nestin-expressing neural progenitor cells in the dentate gyrus (DG) of the hippocampus, its function is unknown. This study tested the hypothesis that AhR participates in hippocampal neurogenesis and associated functions. AhR deletion and activation by the potent environmental toxicant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), adversely impacted neurogenesis and cognition. Adult AhR-deficient mice exhibited impaired hippocampal-dependent contextual fear memory while hippocampal-independent memory remained intact. AhR-deficient mice displayed reduced cell birth, decreased cell survival, and diminished neuronal differentiation in the DG. Following TCDD exposure, wild-type mice exhibited impaired hippocampal-dependent contextual memory, decreased cell birth, reduced neuronal differentiation, and fewer mature neurons in the DG. Glial differentiation and apoptosis were not altered in either TCDD-exposed or AhR-deficient mice. Finally, defects observed in TCDD-exposed mice were dependent on AhR, as TCDD had no negative effects in AhR-deficient mice. Our findings suggest that AhR should be further evaluated as a potential transcriptional regulator of hippocampal neurogenesis and function, although other sites of action may also warrant consideration. Moreover, TCDD exposure should be considered as an environmental risk factor that disrupts adult neurogenesis and potentially related memory processes.

Neural progenitors generated from the mesenchymal stem cells of first-trimester human placenta matured in the hypoxic-ischemic rat brain and mediated restoration of locomotor activity

Term placenta is a great reservoir of mesenchymal stem cells (MSCs), however, the potential of the earlier placenta is largely unknown. In this report, we established 17 MSC lines from 19 first-trimester human placenta (fPMSC). fPMSC proliferated for 90–150 days in vitro and by enhanced cellular interaction, fPMSC differentiated into nestin-expressing neural progenitor cells (fPMSC-NP), accompanied by inductions of immature neuron-specific genes. Therapeutic effect of the fPMSC-NP was tested in the animal model of hypoxia-ischemia (HI) which was devastating to dopaminergic neurons and to locomotor activity. Improvement of motor activity was evident as early as 2 weeks after transplantation of the fPMSC-NP into bilateral striatum and became indistinguishable from that of the age-matched normal animals by 8 weeks but no spontaneous recovery was observed in the control-grafted animals. Immunohistochemical analyses revealed that the implanted fPMSC-NP matured into ectodermal cells including the tyrosine hydroxylase (TH)-expressing neurons in the recipient striatum. So, the improved motor behavior was likely due to the dopaminergic differentiation of the implanted fPMSC-NP in the dopaminergic-denervated host brain. Based on this result, we propose that progenitors may be more advantageous than the terminally differentiated cells for the purpose of cell replacement therapies since the progenitors are easily obtainable and are expected to be more pliable to the new environment.

Depletion of the neural precursor cell pool by glucocorticoids

Glucocorticoids (GCs) are indicated for a number of conditions in obstetrics and perinatal medicine; however, the neurodevelopmental and long-term neurological consequences of early-life GC exposure are still largely unknown. Preclinical studies have demonstrated that GCs have a major influence on hippocampal cell turnover by inhibiting neurogenesis and stimulating apoptosis of mature neurons. Here we examined the fate of the limited pool of neural progenitor cells (NPCs) after GC administration during neonatal development; the impact of this treatment on hippocampal structure was also studied. Phenotype-specific genetic and antigenic markers were used to identify cultured NPCs at various developmental stages; the survival of these cells was monitored after exposure to the synthetic glucocorticoid dexamethasone (DEX). In addition, the effects of neonatal DEX treatment on the neurogenic potential of the rat hippocampus were examined by monitoring the incorporation of bromodeoxyuridine and expression of Ki67 antigen at various postnatal ages. Multipotent nestin-expressing NPCs and Talpha1-tubulin-expressing immature neurons succumb to GC-induced apoptosis in primary hippocampal cultures. Neonatal GC treatment results in marked apoptosis among the proliferating population of cells in the dentate gyrus, depletes the NPC pool, and leads to significant and sustained reductions in the volume of the dentate gyrus. Both NPCs and immature neurons in the hippocampus are sensitive to the proapoptotic actions of GCs. Depletion of the limited NPC pool during early life retards hippocampal growth, thus allowing predictions about the potential neurological and psychiatric consequences of neonatal GC exposure.

Activated BRAF induces gliomas in mice when combined with Ink4a/Arf loss or Akt activation

Mutations in receptor tyrosine kinase (RTK) growth factor receptors (epidermal growth factor receptor, platelet-derived growth factor receptor, MET and ERBB2), which result in downstream activation of the RAS/RAF/MEK/ERK mitogen-activated protein kinase (MAPK) pathway and PI(3)K/Akt pathway, are found in almost all high-grade gliomas and MAPK signaling is necessary for continued glioma maintenance. In addition, BRAF is mutated in the majority of low-grade gliomas and its expression and activity is significantly increased in the majority of high-grade gliomas. Although the importance of RTKs and RAS signaling in glioma development has been shown, the role of BRAF has yet to be characterized. We evaluated the effect of activated BRAF in glioma formation using the retroviral replication-competent avian leukosis virus long terminal repeat, splice acceptor (RCAS)/TVA system to transfer genes encoding activated forms of BRAF, KRas, Akt and Cre to nestin-expressing neural progenitor cells in Ink4a/Arf(lox/lox) mice in vivo. Although expression of activated BRAF alone is not sufficient for tumorigenesis, the combination of activated BRAF and Akt or BRAF with Ink4a/Arf loss is transforming. Interestingly, activated BRAF generates gliomas with characteristics similar to activated KRas in the context of Akt but not Ink4a/Arf loss. Our studies show a role for BRAF activation and signaling in glioma development and as potential target for glioma therapy.

Neuregulin induces proliferation of neural progenitor cells via PLC/PKC pathway

Nestin-expressing neural progenitor cells (NPCs) have been isolated from hippocampus of brains and propagated with epidermal growth factor and basic fibroblast growth factor (bFGF). However, the underlying signaling mechanisms regulating NPC proliferation remain elusive. Here we showed that neuregulinβ1 (NRG), like bFGF, effectively promoted the proliferation of hippocampus-derived NPCs and maintained the progenitor states of NPCs. Activation of protein kinase C (PKC), a downstream effector of phospholipase C (PLC), with 12-O-tetradecanoylphorbol-13-acetate (TPA) mimicked the NRG-induced proliferation of NPCs. The synergic effect of TPA plus NRG on neurosphere growth further prompted us to find that NRG induced NPC propagation through PLC/PKC signaling pathway. ErbB4, an important functional receptor of NRG, had an interaction with PLCγ1 protein. In addition, inactivation of PLC pathway led to severe proliferative suppression of NPCs. Our study suggests that activation of PLC/PKC pathway plays an essential role in the NRG-induced proliferation of hippocampus-derived NPCs.

C-Myc Enhances Sonic Hedgehog-Induced Medulloblastoma Formation from Nestin-Expressing Neural Progenitors in Mice

Medulloblastomas are malignant brain tumors that arise in the cerebella of children. The presumed cellsof-origin are undifferentiated precursors of granule neurons that occupy the external granule layer (EGL) of the developing cerebellum. The overexpression of proteins that normally stimulate proliferation of neural progenitor cells may initiate medulloblastoma formation. Two known mitogens for neural progenitors are the c-Myc oncoprotein and Sonic hedgehog (Shh), a crucial determinant of embryonic pattern formation in the central nervous system. We modeled the ability of c-Myc and Shh to induce medulloblastoma in mice using the RCAS/tv-a system, which allows postnatal gene transfer and expression in a cell type-specific manner. We targeted the expression of Shh and c-Myc to nestin-expressing neural progenitor cells by injecting replication-competent ALV splice acceptor (RCAS) vectors into the cerebella of newborn mice. Following injection with RCAS-Shh alone, 3/32 (9%) mice developed medulloblastomas and 5/32 showed multifocal hyperproliferation of the EGL, possibly a precursor stage of medulloblastoma. Following injection with RCAS-Shh plus RCAS-Myc, 9/39 (23%) mice developed medulloblastomas. We conclude that nestin-expressing neural progenitors, present in the cerebellum at birth, can act as the cells-of-origin for medulloblastoma, and that c-Myc cooperates with Shh to enhance tumorigenicity.

Inhibition of mitogen-activated protein kinase kinase blocks proliferation of neural progenitor cells

Nestin-expressing neural progenitor (NP) cells have been isolated from the subventricular zone (SVZ) of the brain and propagated with epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF). In other neural cell types it has been shown that EGF and bFGF activate cell surface receptors involved in the mitogen-activated protein kinase (MAPK) signal pathway. To examine this issue in NP cells, we isolated primary SVZ cells and stimulated them with EGF and bFGF and then used a phosphorylation-specific antibody to detect activated MAPK by immunofluorescent staining or Western blotting. The addition of growth factors activated MAPK transiently in cells that co-expressed nestin. A distinct phospho-MAPK signal was also detected in nestin-positive cells with mitotic chromosomes. A novel MAPK kinase (MEK1) inhibitor U0126 blocked the activation of MAPK and the proliferation of primary cells more effectively than the same concentration of PD98059. After exposure of cells to U0126 for 10 days, we noted that there was a significant reduction in the number of cells that expressed nestin and an increase in the percentage of apoptotic cells. These data provide evidence that activation of MAPK by MEK1 is important for the proliferation of NP cells.