Proliferation Of Neural Precursor Cells Research Articles

Fluoxetine rescues impaired hippocampal neurogenesis in a transgenic A53T synuclein mouse model

The accumulation of alpha-synuclein in Lewy bodies and Lewy neurites of different neuronal populations is one of the neuropathological hallmarks in Parkinson disease (PD). Overexpression of human wildtype or mutant alpha-synuclein affects the generation of new neurons in the adult dentate gyrus (DG) of the hippocampus in models of PD. Hippocampal dysfunction with reduced neurogenesis plays an important role in the pathogenesis of depression, an important non-motor symptom in PD. Moreover, effective antidepressant treatment is still an unmet need in PD. The present study explored if impaired hippocampal neurogenesis in the A53T transgenic animal model of PD may be restored by chronic oral application of the selective serotonin reuptake inhibitor (SSRI) fluoxetine. First, we determined the expression pattern of transgenic mutant A53T synuclein in developing DG neurons and showed early expression of the transgene linked to a severely impaired neurogenesis. After chronic fluoxetine treatment we observed an increased adult neurogenesis in the hippocampus of more than threefold in treated A53T mice compared with controls. The pro-neurogenic effect of chronic fluoxetine application is predominantly related to an increased proliferation of neural precursor cells in the DG, and to a lesser extent by induction of differentiation into mature neurons. Analysis of the underlying mechanisms revealed an induction of brain-derived and glial cell-derived neurotrophic factor levels as a result of fluoxetine treatment. This study underlines the large potential of SSRI-dependent mechanisms to stimulate adult hippocampal neurogenesis in alpha-synuclein models and may lead to novel means to improve neuropsychiatric symptoms in PD.

Functional improvement and neurogenesis after collagen-GAG matrix implantation into surgical brain trauma

Surgical or traumatic brain injury often leads to loss of cerebral parenchyma but there is as yet no clinically effective strategy for neural regeneration. Collagen glycosaminoglycan (collagen-GAG, CG) scaffolds have previously been used in many tissues in vivo but have never been utilized in the brain. Using an animal model, we investigated the effects of the implantation of CG scaffold matrix following surgical brain trauma. Results indicated that implantation of CG scaffold could significantly promote functional recovery following surgical brain trauma. The CG scaffold was found to facilitate proliferation, differentiation and migration of endogenous neural precursor cells (NPCs) both in the intra-matrix zone (IMZ) and lesion boundary zone (LBZ). The tissue concentration of brain-derived neurotrophic factor (BDNF) and glia-derived neurotrophic factor (GDNF) in the cortex demonstrated a sustained increase after implantation of CG scaffold following surgical brain trauma. These results suggest that the utilization of CG scaffolds can be considered as a potential clinical strategy for tissue regeneration and functional recovery after brain injury.

Cycling or not cycling: cell cycle regulatory molecules and adult neurogenesis.

The adult brain most probably reaches its highest degree of plasticity with the lifelong generation and integration of new neurons in the hippocampus and olfactory system. Neural precursor cells (NPCs) residing both in the subgranular zone of the dentate gyrus and in the subventricular zone of the lateral ventricles continuously generate neurons that populate the dentate gyrus and the olfactory bulb, respectively. The regulation of NPC proliferation in the adult brain has been widely investigated in the past few years. Yet, the intrinsic cell cycle machinery underlying NPC proliferation remains largely unexplored. In this review, we discuss the cell cycle components that are involved in the regulation of NPC proliferation in both neurogenic areas of the adult brain.

Septic metastatic encephalitis: coexistence of brain damage and repair

Septic metastatic encephalitis (SME) arises from systemic bacterial infections and is a severe complication of sepsis with a high mortality. In this study, we examined the neuropathological findings in humans suffering from SME including white matter pathology and proliferation of neural precursor cells in the hippocampal dentate gyrus. The brains of 10 autopsy cases with SME and 10 control cases after sudden death from non-neurological causes were studied by means of immunohistochemistry. We found diffuse axonal injury and demyelination in the frontal cortex (P = 0.01) as well as increased numbers of recently generated TUC-4 expressing neurones in the hippocampal dentate gyrus in SME cases (P = 0.01). The median density of apoptotic granule cells in the dentate gyrus also was higher in SME cases, the difference, however, failed to reach statistical significance (P = 0.25). The coexistence of degenerative processes predominantly in the neocortex and regenerative activity in the hippocampal formation known from bacterial meningitis also characterizes the pathology of SME.

Nuclear Factor of Activated T Cells (NFAT) Proteins Repress Canonical Wnt Signaling via Its Interaction with Dishevelled (Dvl) Protein and Participate in Regulating Neural Progenitor Cell Proliferation and Differentiation

The Ca(2+) signaling pathway appears to regulate the processes of the early development through its antagonism of canonical Wnt/β-catenin signaling pathway. However, the underlying mechanism is still poorly understood. Here, we show that nuclear factor of activated T cells (NFAT), a component of Ca(2+) signaling, interacts directly with Dishevelled (Dvl) in a Ca(2+)-dependent manner. A dominant negative form of NFAT rescued the inhibition of the Wnt/β-catenin pathway triggered by the Ca(2+) signal. NFAT functioned downstream of β-catenin without interfering with its stability, but influencing the interaction of β-catenin with Dvl by its competitively binding to Dvl. Furthermore, we demonstrate that NFAT is a regulator in the proliferation and differentiation of neural progenitor cells by modulating canonical Wnt/β-catenin signaling pathway in the neural tube of chick embryo. Our findings suggest that NFAT negatively regulates canonical Wnt/β-catenin signaling by binding to Dvl, thereby participating in vertebrate neurogenesis.

Chemokines and Inflammatory Mediators Interact to Regulate Adult Murine Neural Precursor Cell Proliferation, Survival and Differentiation

Adult neural precursor cells (NPCs) respond to injury or disease of the CNS by migrating to the site of damage or differentiating locally to replace lost cells. Factors that mediate this injury induced NPC response include chemokines and pro-inflammatory cytokines, such as tumor necrosis factor-α (TNFα) and interferon-γ (IFNγ), which we have shown previously promotes neuronal differentiation. RT-PCR was used to compare expression of chemokines and their receptors in normal adult mouse brain and in cultured NPCs in response to IFNγ and TNFα. Basal expression of many chemokines and their receptors was found in adult brain, predominantly in neurogenic regions, with OB≫SVZ>hippocampus and little or no expression in non-neurogenic regions, such as cortex. Treatment of SVZ-derived NPCs with IFNγ and TNFα (alone and in combination) resulted in significant upregulation of expression of specific chemokines, with CXCL1, CXCL9 and CCL2 most highly upregulated and CCL19 downregulated. Unlike IFNγ, chemokine treatment of NPCs in vitro had little or no effect on survival, proliferation or migration. Neuronal differentiation was promoted by CXCL9, CCL2 and CCL21, while astrocyte and total oligodendrocyte differentiation was not affected. However, IFNγ, CXCL1, CXCL9 and CCL2 promoted oligodendrocyte maturation. Therefore, not only do NPCs express chemokine receptors, they also produce several chemokines, particularly in response to inflammatory mediators. This suggests that autocrine or paracrine production of specific chemokines by NPCs in response to inflammatory mediators may regulate differentiation into mature neural cell types and may alter NPC responsiveness to CNS injury or disease.

Glucocorticoid Regulation of Astrocytic Fate and Function

Glial loss in the hippocampus has been suggested as a factor in the pathogenesis of stress-related brain disorders that are characterized by dysregulated glucocorticoid (GC) secretion. However, little is known about the regulation of astrocytic fate by GC. Here, we show that astrocytes derived from the rat hippocampus undergo growth inhibition and display moderate activation of caspase 3 after exposure to GC. Importantly, the latter event, observed both in situ and in primary astrocytic cultures is not followed by either early- or late-stage apoptosis, as monitored by stage I or stage II DNA fragmentation. Thus, unlike hippocampal granule neurons, astrocytes are resistant to GC-induced apoptosis; this resistance is due to lower production of reactive oxygen species (ROS) and a greater buffering capacity against the cytotoxic actions of ROS. We also show that GC influence hippocampal cell fate by inducing the expression of astrocyte-derived growth factors implicated in the control of neural precursor cell proliferation. Together, our results suggest that GC instigate a hitherto unknown dialog between astrocytes and neural progenitors, adding a new facet to understanding how GC influence the cytoarchitecture of the hippocampus.

Dopaminergic Modulation of Cortical Inputs during Maturation of Adult-Born Dentate Granule Cells

Adult neurogenesis, a particular form of plasticity in the adult brain, is under dynamic control of neuronal activity mediated by various neurotransmitters. Despite accumulating evidence suggesting that the neurotransmitter dopamine (DA) regulates proliferation of neural precursor cells in the neurogenic zones, whether and how it acts on newly generated neurons that integrate into the established network remains unknown. Using patch-clamp recordings from retrovirus-labeled newborn hippocampal dentate granule cells (DGCs) in acute mouse brain slices, we found that DA not only caused a long-lasting attenuation of medial perforant path (MPP) inputs to the young DGCs, but also decreased their capacity to express long-term potentiation (LTP). In contrast, DA suppressed MPP transmission to mature DGCs to a similar extent but did not influence their LTP expression. This difference was linked to activation of distinct subtypes of DA receptors in DGCs at different developmental stages. Our observations suggest that DA is particularly effective in modulating the activities of hyperexcitable young neurons, which may have important implications for the dentate function as a filter for incoming information to the hippocampus.

Proneural transcription factors Dlx2 and Pax6 are altered in adult SVZ neural precursor cells following striatal cell loss

Compensatory replacement of neurons by endogenous subventricular zone (SVZ)-derived neural precursor cells has been demonstrated in the adult brain following striatal cell loss. Such cell replacement is associated with increased SVZ cell proliferation and neuroblast expansion in the rostral migratory stream (RMS). SVZ-derived neural precursor cells co-express multiple transcription factors involved in lineage restriction and cell fate determination. We propose that compensatory neurogenesis in response to striatal cell loss will alter the temporal expression of transcription factors in discrete populations of SVZ-derived neural precursor cells. We therefore examined the expression of Mash1, Dlx2, Pax6 and Olig2 in SVZ-derived neural precursor cell populations across a range of times following quinolinic acid (QA) induced striatal cell death. We have identified a heterogeneous population of SVZ-derived neural precursor cells that respond independently to striatal cell loss. In both the anterior SVZ (aSVZ) and RMS we observed an increase in a sub-population of Dlx2+ transit amplifying precursor (TAP) cells and neuroblasts following QA lesioning when compared to controls. Subsequently, the number of Pax6+ TAPs and neuroblasts in the QA lesioned aSVZ and RMS was also increased. Olig2 expression was not however altered in response to QA-induced cell loss. Our results suggest Dlx2 and Pax6 may play a prominent role in directing neural precursor cell proliferation and neuroblast generation following striatal cell loss. Selective alteration of specific transcription factors in the SVZ and during migration through the RMS in response to cell loss may predetermine the subsequent generation of specific neuronal subclasses for endogenous replacement.

Lithium promotes neural precursor cell proliferation: evidence for the involvement of the non-canonical GSK-3β-NF-AT signaling

Lithium, a drug that has long been used to treat bipolar disorder and some other human pathogenesis, has recently been shown to stimulate neural precursor growth. However, the involved mechanism is not clear. Here, we show that lithium induces proliferation but not survival of neural precursor cells. Mechanistic studies suggest that the effect of lithium mainly involved activation of the transcription factor NF-AT and specific induction of a subset of proliferation-related genes. While NF-AT inactivation by specific inhibition of its upstream activator calcineurin antagonized the effect of lithium on the proliferation of neural precursor cells, specific inhibition of the NF-AT inhibitor GSK-3β, similar to lithium treatment, promoted neural precursor cell proliferation. One important function of lithium appeared to increase inhibitory phosphorylation of GSK-3β, leading to GSK-3β suppression and subsequent NF-AT activation. Moreover, lithium-induced proliferation of neural precursor cells was independent of its role in inositol depletion. These findings not only provide mechanistic insights into the clinical effects of lithium, but also suggest an alternative therapeutic strategy for bipolar disorder and other neural diseases by targeting the non-canonical GSK-3β-NF-AT signaling.

Acute Hepatocyte Growth Factor Treatment Induces Long-Term Neuroprotection and Stroke Recovery via Mechanisms Involving Neural Precursor Cell Proliferation and Differentiation

Hepatocyte growth factor (HGF) is an interesting candidate for acute stroke treatment as shown by continuous infusion or gene delivery protocols. However, little is known about HGF-mediated long-term effects. The present study therefore analyzed long-term effects of an acute intrastriatal HGF treatment (5 μg) after a 45-minute stroke, with regard to brain injury and neurologic recovery. Hepatocyte growth factor induced long-term neuroprotection as assessed by infarct volume and neuronal cell death analysis for as long as 4 weeks after stroke, which was associated with sustained neurologic recovery as evidenced by corner-turn and tight-rope tests. Analyzing underlying mechanisms of HGF-induced sustained neuroprotection, enhanced cell proliferation followed by increased neuronal differentiation of neural precursor cells (NPCs) was observed in the ischemic striatum of HGF-treated mice, which persisted for up to 4 weeks. In line with this, HGF promoted neurosphere formation as well as proliferation of NPC and decreased caspase-3-dependent hypoxic injury in vitro. Preservation of blood-brain barrier integrity 24 hours after stroke was furthermore noticed in animals receiving HGF, which was associated with the inhibition of matrix metalloproteases (MMP)-2 and MMP-9 at 4 and 24 hours, respectively. We suggest that sustained recruitment of proliferating cells together with improved neurovascular remodeling provides an explanation for HGF-induced long-term neuroprotection.

Intravenous Hedgehog Agonist Induces Proliferation of Neural and Oligodendrocyte Precursors in Rodent Spinal Cord Injury

Sonic hedgehog (Shh) is a glycoprotein molecule that upregulates the transcription factor gli-1 and plays a critical role in the proliferation of endogenous neural precursor cells when directly injected into adult rodent spinal cords after injury. To use small-molecule agonists of the hedgehog pathway in an attempt to replicate these findings with intravenous administration. Forty Sprague-Dawley rats were randomly divided into 4 groups. Saline treatment control groups were divided into a contusion injury group and a noninjury sham group; Shh agonist treatment groups were divided into an injury group and a noninjury sham group. Shh agonist Ag11.1 was administered to the treatment groups and saline to the control groups. Injections were performed on days 1 and 4 after surgery. On day 14, 1 group was sacrificed, and injured spinal cord portions were removed for explant cultures. After 7 days in culture, specimens were fixed for immunostaining neural precursor cells, and cell counts were taken. Histological analysis demonstrated cystic cavitary lesions with a rim of white-matter sparing in all specimens. In animals treated with hedgehog agonist for a contusion injury, a significant increase in the number of nestin- and musashi-1-positive neural precursor cells at the rim of the cavity was noted. There was a significant increase in the number of O4-positive oligodendrocyte precursors compared with uninjured controls and BrdU-positive cells, reproducing the findings of previous studies using direct Shh protein injection, which demonstrated spared white matter and increased recovery.

Functional Expression and Subcellular Localization of the Taurine Transporter TauT in Murine Neural Precursors

Taurine addition to cultured embryonic neural precursor cells (NPC) significantly increased cell proliferation [Hernández-Benítez et al., 2010]. The medium used for NPC growing and proliferation is a fetal serum-free medium, and therefore, NPC become taurine depleted. Addition of taurine to the cultured medium fully replenished the cell taurine pool, suggesting the functional expression of a taurine transporter (TauT) in these cells. In the present study, TauT in NPC was functionally characterized and its protein expression and the subcellular distribution of immunoreactivity were determined. ³H-taurine uptake in NPC could be separated into a non-saturable component and a Na⁺/Cl^–-dependent, saturable component. The saturable component showed an apparent 2:1:1 Na⁺/Cl^–/taurine stoichiometry, a V_max of 0.39 ± 0.04 nmol/mg protein/min, and a K_m of 21.7 ± 2.6 µM. TauT in NPC was strongly inhibited by hypotaurine and β-alanine (92 and 79%, respectively) and reduced (71%) by γ-aminobutyric acid. TauT protein is expressed in NPC as a single band of about 70 kDa. Essentially all (98.8%) of the neurosphere-forming cells were positive to TauT immunoreactivity. Immunolocalization visualized by confocal microscopy localized TauT predominantly at the cell membrane. TauT was also found at the cytosol and only occasionally at the nuclear membrane. This study represents the first characterization of TauT in NPC.

Neural precursor cell proliferation and differentiation: Looking at the redox environment and cell defense mechanisms

International Journal of Developmental NeuroscienceVolume 28, Issue 8 p. 657-658 Article [P1.08]: Neural precursor cell proliferation and differentiation: Looking at the redox environment and cell defense mechanisms E. Torrado, Corresponding Author E. Torrado n/[email protected] University of Lisbon, PortugalSearch for more papers by this authorA.R. Vaz, A.R. Vaz University of Lisbon, PortugalSearch for more papers by this authorA. Fernandes, A. Fernandes University of Lisbon, PortugalSearch for more papers by this authorC. Bellarosa, C. Bellarosa Fondazione Italiana Fegato, ItalySearch for more papers by this authorC. Tiribelli, C. Tiribelli Fondazione Italiana Fegato, ItalySearch for more papers by this authorA.S. Falcão, A.S. Falcão University of Lisbon, PortugalSearch for more papers by this author et al E. Torrado, Corresponding Author E. Torrado n/[email protected] University of Lisbon, PortugalSearch for more papers by this authorA.R. Vaz, A.R. Vaz University of Lisbon, PortugalSearch for more papers by this authorA. Fernandes, A. Fernandes University of Lisbon, PortugalSearch for more papers by this authorC. Bellarosa, C. Bellarosa Fondazione Italiana Fegato, ItalySearch for more papers by this authorC. Tiribelli, C. Tiribelli Fondazione Italiana Fegato, ItalySearch for more papers by this authorA.S. Falcão, A.S. Falcão University of Lisbon, PortugalSearch for more papers by this author et al First published: 01 November 2010 https://doi.org/10.1016/j.ijdevneu.2010.07.049Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. Volume28, Issue8Abstracts to the 18th Biennial Meeting of the International Society for Developmental Neuroscience, 6‐9 June 2010, Estoril, PortugalDecember 2010Pages 657-658 RelatedInformation

TAp73 Acts via the bHLH Hey2 to Promote Long-Term Maintenance of Neural Precursors

Increasing evidence suggests that deficits in adult stem cell maintenance cause aberrant tissue repair and premature aging [1]. While the mechanisms regulating stem cell longevity are largely unknown, recent studies have implicated p53 and its family member p63. Both proteins regulate organismal aging [2-4] as well as survival and self-renewal of tissue stem cells [5-9]. Intriguingly, haploinsufficiency for a third family member, p73, causes age-related neurodegeneration [10]. While this phenotype is at least partially due to loss of the ΔNp73 isoform, a potent neuronal prosurvival protein [11-16], a recent study showed that mice lacking the other p73 isoform, TAp73, have perturbations in the hippocampal dentate gyrus [17], a major neurogenic site in the adult brain. These findings, and the link between the p53 family, stem cells, and aging, suggest that TAp73 might play a previously unanticipated role in maintenance of neural stem cells. Here, we have tested this hypothesis and show that TAp73 ensures normal adult neurogenesis by promoting the long-term maintenance of neural stem cells. Moreover, we show that TAp73 does this by transcriptionally regulating the bHLH Hey2, which itself promotes neural precursor maintenance by preventing premature differentiation.

Effects of mood stabilizers on adult dentate gyrus-derived neural precursor cells

Neurogenesis in the adult dentate gyrus (DG) is considered to be partly involved in the action of mood stabilizers. However, it remains unclear how mood stabilizers affect neural precursor cells in adult DG. We have established a culture system of adult rat DG-derived neural precursor cells (ADP) and have shown that lithium, a mood stabilizer, and dexamethasone, an agonist of glucocorticoid receptor, reciprocally regulate ADP proliferation. Neurogenesis constitutes not only proliferation of neural precursor cells but also apoptosis and differentiation. To develop further understanding of mood stabilizer effects on neural precursor cells in adult DG, we investigated and compared the effects of four common mood stabilizers—lithium, valproate, carbamazepine, and lamotrigine—on ADP proliferation, apoptosis, and differentiation. ADP proliferation, decreased by dexamethasone, was examined using Alamar Blue assay. Using TUNEL assay, ADP apoptosis induced by staurosporine was examined. The differentiated ADP induced by retinoic acid was characterized by immunostaining with anti-GFAP or anti-Tuj1 antibody. Lithium and valproate, but not carbamazepine and lamotrigine, recovered ADP proliferation decreased by dexamethasone. All four mood stabilizers decreased ADP apoptosis. Retinoic acid differentiated ADP into both neurons and astrocytes. Lithium and carbamazepine increased the ratio of neurons and decreased that of astrocytes. However, valproate and lamotrigine increased the ratio of astrocytes and decreased that of neurons. Therefore, these four stabilizers exhibited both common and differential effects on ADP proliferation, apoptosis, and differentiation.

Dyrk1A Phosphorylates p53 and Inhibits Proliferation of Embryonic Neuronal Cells

Down syndrome (DS) is associated with many neural defects, including reduced brain size and impaired neuronal proliferation, highly contributing to the mental retardation. Those typical characteristics of DS are closely associated with a specific gene group "Down syndrome critical region" (DSCR) on human chromosome 21. Here we investigated the molecular mechanisms underlying impaired neuronal proliferation in DS and, more specifically, a regulatory role for dual-specificity tyrosine-(Y) phosphorylation-regulated kinase 1A (Dyrk1A), a DSCR gene product, in embryonic neuronal cell proliferation. We found that Dyrk1A phosphorylates p53 at Ser-15 in vitro and in immortalized rat embryonic hippocampal progenitor H19-7 cells. In addition, Dyrk1A-induced p53 phosphorylation at Ser-15 led to a robust induction of p53 target genes (e.g. p21(CIP1)) and impaired G(1)/G(0)-S phase transition, resulting in attenuated proliferation of H19-7 cells and human embryonic stem cell-derived neural precursor cells. Moreover, the point mutation of p53-Ser-15 to alanine rescued the inhibitory effect of Dyrk1A on neuronal proliferation. Accordingly, brains from embryonic DYRK1A transgenic mice exhibited elevated levels of Dyrk1A, Ser-15 (mouse Ser-18)-phosphorylated p53, and p21(CIP1) as well as impaired neuronal proliferation. These findings suggest that up-regulation of Dyrk1A contributes to altered neuronal proliferation in DS through specific phosphorylation of p53 at Ser-15 and subsequent p21(CIP1) induction.

Human immunodeficiency virus type 1 Tat modulates proliferation and differentiation of human neural precursor cells: implication in NeuroAIDS

Human immunodeficiency virus type 1 (HIV-1) and viral proteins affect neuronal survival and neuron-glial cell interactions, which culminate in neurological disorders. HIV-1 infects regions of neurogenesis in human adult and pediatric brain. However, little is known about the effect of HIV-1 or viral proteins on the properties of human neural precursor cells (hNPCs), particularly neurogenesis, hence a detailed investigation on these lines is warranted. Human neural precursor cells were cultured in presence and absence of HIV-1B transactivating protein Tat to investigate if HIV-1 viral protein alters the properties of human neural precursor cells. Cellular and molecular approaches were adopted to study the effect of HIV-1B transactivating protein Tat on proliferation and differentiation potential of human fetal brain-derived NPCs. Cell proliferation assays such as BrdU and Ki67 staining and pathway-specific cDNA and protein arrays were used in the study. Data reveal that HIV-1B Tat protein severely affects proliferation of hNPCs, as evident by lower incorporation of BrdU and Ki67 staining as well as neurosphere assay. HIV-1 Tat substantially attenuated neurogenesis, as evident by the smaller numbers of Tuj-1- and doublecortin-positive cells differentiated from hNPCs, without affecting their viability. These data suggest that HIV-1 Tat alters the properties of human neural precursor cells via attenuation of the cell cycle regulatory unit cyclin D1 and the mitogen-activated protein kinase (MAPK) pathway, particularly extracellular signal-related kinase 1/2 (ERK1/2). The study provides new insights into cellular and molecular mechanisms that may modulate human neural precursor cell properties in HIV/AIDS (acquired immunodeficiency syndrome) individuals. Validation with autopsy brain samples is necessary to further substantiate these important observations.

Neural Precursor Cell Proliferation Is Disrupted Through Activation of the Aryl Hydrocarbon Receptor by 2,3,7,8-Tetrachlorodibenzo-p-Dioxin

Neurogenesis involves the proliferation of multipotent neuroepithelial stem cells followed by differentiation into lineage-restricted neural precursor cells (NPCs) during the embryonic period. Interestingly, these progenitor cells express robust levels of the aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor that regulates expression of genes important for growth regulation, and xenobiotic metabolism. Upon binding 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a pervasive environmental contaminant and potent AhR ligand, AhR, is activated and disrupts gene expression patterns to produce cellular toxicity. Because of its widespread distribution in the brain during critical proliferative phases of neurogenesis, it is conceivable that AhR participates in NPC expansion. Therefore, this study tested the hypothesis that AhR activation by TCDD disrupts signaling events that regulate NPC proliferation. The C17.2 NPC line served as a model system to (1) assess whether NPCs are targets for TCDD-induced neurotoxicity and (2) characterize the effects of TCDD on NPC proliferation. We demonstrated that C17.2 NPCs express an intact AhR signaling pathway that becomes transcriptionally active after TCDD exposure. (3)H-thymidine and alamar blue reduction assays indicated that TCDD suppresses NPC proliferation in a concentration-dependent manner without the loss of cell viability. Cell cycle distribution analysis by flow cytometry revealed that TCDD-induced growth arrest results from an impaired G1 to S cell cycle transition. Moreover, TCDD exposure altered p27( kip1) and cyclin D1 cell cycle regulatory protein expression levels consistent with a G1 phase arrest. Initial studies in primary NPCs isolated from the ventral forebrain of embryonic mice demonstrated that TCDD reduced cell proliferation through a G1 phase arrest, corroborating our findings in the C17.2 cell line. Together, these observations suggest that the inappropriate or sustained activation of AhR by TCDD during neurogenesis can interfere with signaling pathways that regulate neuroepithelial stem cell/NPC proliferation, which could adversely impact final cell number in the brain and lead to functional impairments.

Lipopolysaccharide acutely inhibits proliferation of neural precursor cells in the dentate gyrus in adult rats

Lipopolysaccharide (LPS), a bacterial endotoxin released during infection, is known to suppress neurogenesis in the dentate gyrus (DG) in mature rats. The present study aimed to elucidate acute effect of LPS, as well as possible mechanisms involved in the effect, on the neurogenesis in the DG of adult rats. In the first experiment, proliferating cells in the DG were labeled with bromodeoxyuridine (BrdU). Double-labeled immunohistochemistry performed 28 days after the BrdU incorporation revealed co-expression of NeuN, a marker of mature neurons, in most of the BrdU-positive cells in the DG. The rat was injected intraperitoneally with LPS or saline at various intervals after the BrdU incorporation, and BrdU-positive cells were examined 24 h thereafter. The endotoxin reduced the number of BrdU-positive cells that were labeled 24 h before, but not 7 or 28 days before sacrifice, suggesting rapid LPS actions on precursor cells during proliferation, but not after mitosis. In the second experiment, cells in the DG positively stained with BrdU or serine10 phosphorylated histone H3 (pHH3) were examined 5 h after the injection of LPS or saline. BrdU was incorporated 2 h before sacrifice. In these rats, LPS reduced the number of BrdU- or pHH3-positive cells. LPS did not affect the number of terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL)-positive cells within 5, 8 or 24 h. These results indicate that the endotoxin acutely suppresses neurogenesis in the DG in adult rats, presumably by inhibiting proliferation of neural precursor cells, but not by increasing cell death.