Truncated tyrosine kinase B brain-derived neurotrophic factor receptor directs cortical neural stem cells to a glial cell fate by a novel signaling mechanism

During development of the mammalian cerebral cortex neural stem cells (NSC) first generate neurons and subsequently produce glial cells. The mechanism(s) responsible for this developmental shift from neurogenesis to gliogenesis is unknown. Brain-derived neurotrophic factor (BDNF) is believed to play important roles in the development of the mammalian cerebral cortex; it enhances neurogenesis and promotes the differentiation and survival of newly generated neurons. Here, we provide evidence that a truncated form of the BDNF receptor tyrosine kinase B (trkB-t) plays a pivotal role in directing embryonic mouse cortical NSC to a glial cell fate. Expression of trkB-t promotes differentiation of NSC toward astrocytes while inhibiting neurogenesis both in cell culture and in vivo. The mechanism by which trkB-t induces astrocyte genesis is not simply the result of inhibition of full-length receptor with intrinsic tyrosine kinase activity signaling. Instead, binding of BDNF to trkB-t activates a signaling pathway (involving a G-protein and protein kinase C) that induced NSC to become glial progenitors and astrocytes. Thus, the increased expression of trkB-t in the embryonic cerebral cortex that occurs coincident with astrocyte production plays a pivotal role in the developmental transition from neurogenesis to gliogenesis. Our findings suggest a mechanism by which a single factor (BDNF) regulates the production of the two major cell types in the mammalian cerebral cortex.     

Lithium enhances the neuronal differentiation of neural progenitor cells in vitro and after transplantation into the avulsed ventral horn of adult rats through the secretion of brain-derived neurotrophic factor

This study was undertaken to elucidate the molecular mechanisms by which lithium regulates the development of spinal cord-derived neural progenitor cells (NPCs) in vitro and after transplanted in vivo . Our results show that lithium at the therapeutic concentration significantly increases the proliferation and neuronal differentiation of NPCs in vitro. Specific ELISAs, western blotting, and quantitative real-time RT-PCR assays demonstrate that lithium treatment significantly elevates the expression and production of brain-derived neurotrophic factor (BDNF) by NPCs in culture. Application of a BDNF neutralizing antibody in culture leads to a marked reduction in the neurogenesis of lithium-treated NPCs to the control level. However, it shows no effects on the proliferation of lithium-treated NPCs. These findings suggest that the BDNF pathway is possibly involved in the supportive role of lithium in inducing NPC neurogenesis but not proliferation. This study also provides evidence that lithium is able to elevate the neuronal generation and BDNF production of NPCs after transplantation into the adult rat ventral horn with motoneuron degeneration because of spinal root avulsion, which highlights the therapeutic potential of lithium in cell replacement strategies for spinal cord injury because of its ability to promote neuronal differentiation and BDNF production of grafted NPCs in the injured spinal cord.     

Stabilization of the retinal vascular network by reciprocal feedback between blood vessels and astrocytes

Development of the retinal vasculature is controlled by a hierarchy of interactions among retinal neurons, astrocytes and blood vessels. Retinal neurons release platelet-derived growth factor (PDGFA) to stimulate proliferation of astrocytes, which in turn stimulate blood vessel growth by secreting vascular endothelial cell growth factor (VEGF). Presumably, there must be counteractive mechanisms for limiting astrocyte proliferation and VEGF production to prevent runaway angiogenesis. Here, we present evidence that the developing vessels provide feedback signals that trigger astrocyte differentiation--marked by cessation of cell division, upregulation of glial fibrillary acidic protein (GFAP) and downregulation of VEGF. We prevented retinal vessel development by raising newborn mice in a high-oxygen atmosphere, which leads, paradoxically, to retinal hypoxia (confirmed by using the oxygen-sensing reagent EF5). The forced absence of vessels caused prolonged astrocyte proliferation and inhibited astrocyte differentiation in vivo. We could reproduce these effects by culturing retinal astrocytes in a low oxygen atmosphere, raising the possibility that blood-borne oxygen itself might induce astrocyte differentiation and indirectly prevent further elaboration of the vascular network.     

Brain-derived neurotrophic factor expression is repressed during myogenic differentiation by miR-206

Brain-derived neurotrophic factor (BDNF) is required for efficient skeletal-muscle regeneration and perturbing its expression causes abnormalities in the proliferation and differentiation of skeletal muscle cells. In this study, we investigated the mechanism of BDNF suppression that occurs during myogenic differentiation. BDNF is expressed at the mRNA level as two isoforms that differ in the length of their 3'UTRs as a result of alternative cleavage and polyadenylation. Sequence analysis revealed the presence of three miR-206 target sites in the long BDNF 3'UTR (BDNF-L), whereas only one site was found in the short mRNA BDNF 3'UTR (BDNF-S). miR-206 is known to regulate the differentiation of C2C12 myoblasts and its expression is induced during the transition from myoblasts to myotubes. We thus examined whether miR-206-mediated suppression is responsible for the expression pattern of BDNF during myogenic differentiation. BDNF-L was suppressed to a greater extent than BDNF-S during differentiation of C2C12 myoblasts. Transfection of a miR-206 precursor decreased activity of reporters representative of the BDNF-L 3'UTR, but not BDNF-S 3'UTR, and repressed endogenous BDNF mRNA levels. This suppression was found to be dependent on the presence of multiple miR-206 target sites in the BDNF-L 3'UTR. Conversely, suppression of miR-206 levels resulted in de-repression of BDNF 3'UTR reporter activity and increased endogenous BDNF-L mRNA levels. A receptor for BDNF, p75(NTR) , was also suppressed during differentiation and in response to miR-206, but this appeared to not be entirely mediated via a miR-206 target site its 3'UTR. Based on these observations, BDNF represents a novel target through which miR-206 controls the initiation and maintenance of the differentiated state of muscle cells. These results further suggest that miR-206 might play a role in regulating retrograde signaling of BDNF at the neuromuscular junction.     

Nitric oxide acts in a positive feedback loop with BDNF to regulate neural progenitor cell proliferation and differentiation in the mammalian brain

Nitric oxide (NO) is believed to act as an intercellular signal that regulates synaptic plasticity in mature neurons. We now report that NO also regulates the proliferation and differentiation of mouse brain neural progenitor cells (NPCs). Treatment of dissociated mouse cortical neuroepithelial cluster cell cultures with the NO synthase inhibitor L-NAME or the NO scavenger hemoglobin increased cell proliferation and decreased differentiation of the NPCs into neurons, whereas the NO donor sodium nitroprusside inhibited NPC proliferation and increased neuronal differentiation. Brain-derived neurotrophic factor (BDNF) reduced NPC proliferation and increased the expression of neuronal NO synthase (nNOS) in differentiating neurons. The stimulatory effect of BDNF on neuronal differentation of NPC was blocked by L-NAME and hemoglobin, suggesting that NO produced by the latter cells inhibited proliferation and induced neuronal differentiation of neighboring NPCs. A similar role for NO in regulating the switch of neural stem cells from proliferation to differentiation in the adult brain is suggested by data showing that NO synthase inhibition enhances NPC proliferation and inhibits neuronal differentiation in the subventricular zone of adult mice. These findings identify NO as a paracrine messenger stimulated by neurotrophin signaling in newly generated neurons to control the proliferation and differentiation of NPC, a novel mechanism for the regulation of developmental and adult neurogenesis.     

Adenoviral Astrocyte-Specific Expression of BDNF in the Striata of Mice Transgenic for Huntington’s Disease Delays the Onset of the Motor Phenotype

Huntington’s disease (HD) is a neurodegenerative disorder characterized by motor, cognitive, and psychiatric symptoms. The most characteristic structural feature of this disease is neurodegeneration accompanied by gliosis in the striatum. BDNF has been proposed to protect striatal neurons from degeneration, because it is an important survival factor for these neurons from development to adulthood. Considering the extensive gliosis and the survival effects of BDNF, we constructed an adenovirus to express a BDNF cDNA in astrocyte cells using a promoter of the glial fibrillary acidic protein gene. Cells stably transfected in vitro with a BDNF cDNA driven by this promoter expressed BDNF and responded to external stimuli increasing BDNF production. When the vector was applied into the striata of mice transgenic for HD, long-term expression of the transgene was observed, associated with a delay of onset of the motor phenotype of the R6/2 HD transgenic mice. The present data indicate that the striatal expression of BDNF is a potential adjuvant for the treatment of HD.     

A Time-Dependent Increase in Glial Fibrillary Acidic Protein Expression and Glutamine Synthetase Activity in Long-Term Subculture of the GL15 Glioma Cell Line

1. Astrocytes are the most numerous cellular elements in the central nervous tissue, where they play a critical role in physiological and pathological events. The biological signals regulating astrocyte growth and differentiation are relevant for both physiology and pathology, but they are still little understood.2. Using a poorly differentiated glioma cell line, GL15, we investigated whether, in long-term subculture, this could upregulate the expression of glial fibrillary acidic protein (GFAP), as described in some rodent astrocyte cell lines. Under the same culture conditions, we investigated glutamine synthetase (GS) activity, growth-associated protein (GAP)-43 expression, and expression of several neutrotrophic factors.3. A dramatic increase in GFAP expression was evidenced by Western blotting during progressive in vitro growth of GL15 cells. GS specific activity was also upregulated in long-term culture. The time spent in vitro by GL15 cells did not affect GAP-43 and neutrophic factor BDNF and NT3 expression as revealed by RT-PCR analysis.4. Our results suggest that, in GL15, GFAP and GS genes may have common or integrated regulatory mechanisms elicited at the cell confluency which could be relevant for both astrocyte physiology and astrocyte pathology. These mechanisms are not involved in GAP-43 and neutrophic factor BDNF and NT3 expression.     

BDNF alters ERK/p38 MAPK activity ratios to promote differentiation in growth plate chondrocytes

The ERK and p38 MAPK pathways are well-known transducers of signals that regulate proliferation and differentiation, but precisely how these pathways control growth plate chondrocyte development is unclear. For example, the ERK pathway has been reported to be required by some investigators but inhibitory to chondrocyte development by others. Moreover, how these two pathways interact to regulate chondrocyte development is even less clear. Using primary bovine growth plate chondrocytes and murine ATDC5 cells, we demonstrate that the ERK and p38 pathways have opposing effects on proliferation but are both absolutely required for differentiation. Two factors that promote chondrocyte differentiation, brain-derived neurotrophic factor (BDNF) and C-type natriuretic peptide, increase p38 activity while decreasing, but not completely inhibiting, ERK activity. The attenuation of ERK activity by BDNF occurs via p38-dependent raf-1 inhibition. The inhibition of raf-1 by p38 is direct, because purified p38 protein inhibits the kinase activity of purified active raf-1 as well as raf-1 immunoprecipitated from chondrocyte lysates. Moreover, IGF-I, which stimulates proliferation, suppresses p38 activation. This work describes a model wherein unopposed IGF-I promotes high ERK/p38 activity ratios favoring proliferation, whereas BDNF signals a transition to differentiation by decreasing the ERK/p38 activity ratio without completely inhibiting ERK, which involves the direct inhibition of raf-1 by p38.     

Melatonin Regulates the Viability and Differentiation of Rat Midbrain Neural Stem Cells

(1) Neurogenesis driven by neural stem cells (NSCs) is regulated by physiological and pathological factors. Melatonin (MT) has profound neurotrophic and neuroprotective effects. Hence, we studied the role of MT in regulating the viability and differentiation of NSCs derived from rat ventral midbrain. (2) NSCs were isolated from the rat ventral midbrain. The viability of NSCs was determined by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-ulfophenyl)-2H-tetrazolium assay. The differentiation of NSCs was examined by analyzing the expression of the neural markers, MT receptors, brain derived neurotropic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) with semi-quantitative RT-PCR, immunofluorescence cytochemistry, and Western blot. (3) Our results showed that MT could promote the viability of NSCs. In addition, MT could significantly elevate the mRNA and protein levels of tyroxine hydroxylase (TH), a marker of dopaminergic neurons, and decrease the expression of the astrocytes maker glial fibrillary acidic protein (GFAP). MT also increased the production of BDNF and GDNF in the cultured NSCs. Meanwhile, we first found that two subtypes of MT receptors, MT1 and MT2, were expressed in the ventral midbrain NSCs. (4) These results demonstrated that MT could induce NSCs to differentiate into dopaminergic neurons and decrease astrocyte production. These findings also suggest that MT could offer a beneficial tool in guiding directional differentiation of NSCs.     

Astrocytes from acyclic female rats exhibit lowered capacity for neuronal differentiation

Astrocytes comprise a large proportion of the central nervous system support cells and play a critical role in neural injury and repair. The present study examined the impact of ovarian aging using an ex vivo model system, where astrocytes were derived from the olfactory bulb of young, reproductively competent females and reproductive senescent females. Cellular morphology and the spatial pattern of laminin deposition was altered in astrocyte cultures derived from reproductive senescent females. Young adult astrocytes had a flattened polygonal shape with actin bundles at the cell edges, while reproductive senescent astrocytes had a contractile appearance with thick stress fibers visible throughout the cell. Moreover, in reproductive senescent astrocytes, BDNF was elevated with a concomitant reduction in expression of the BDNF receptor, TrkB. To examine the ability of astrocytes derived from young adult and reproductive senescent females to promote neuronal differentiation, neural progenitor cells (NPCs) were co-cultured with astrocytes derived from these groups. At day 4 in vitro, MAP-2(+) NPCs were located in smaller clusters when co-cultured with young adult astrocytes and in large clusters when co-cultured with older astrocytes. At days 6 and 10, neuronal differentiation was significantly reduced in reproductive senescent astrocyte-NPC co-cultures, as determined by NeuN(+) cell numbers and MAP-2(+) process lengths. Furthermore, estrogen only enhanced neuronal differentiation in young adult-NPC co-cultures. The ovarian age-related astrocyte phenotype thus limits the ability of this cell to promote neuronal differentiation in NPC populations and suggests that the astrocyte-mediated microenvironment in older acyclic females is less conducive to repair following neurovascular injury.     

博尔纳病病毒核蛋白调控神经干细胞存活增殖及ERK1／2信号通路的实验研究

目的观察博尔纳病病毒核蛋白（Borna disease virus p40,BDV p40）对大鼠海马源性神经干细胞（Neural stem cells,NSCs）增殖、存活、分化及ERK1／2信号通路的影响,揭示BDV引起神经精神疾病的部分发病机制。方法（1）分别用pEGFP—N1—p40及pEGFP—N1质粒转染NSCs,观察转染效率并鉴定BDVp40在NSCs中的表达。（2）实验设置3组：未转染组、pEGFP—N1空转对照组及pEGFP—N1—p40转染组,用CCK-8试剂盒、Brdu摄入实验及免疫组化分别检测细胞存活、增殖及分化为神经元、星型胶质细胞、少突胶质细胞的比例的变化,并经Western Blot检测ERK1／2磷酸化的改变。结果（1）成功建立表达BDVp40的NSCs模型;PCR结果显示只有pEGFP—N1-p40转染组细胞有BDVp40基因表达。（2）BDVp40抑制NSCs的存活、增殖,但对于转染后贴壁分化14d时3组细胞分化为神经元、星型胶质细胞、少突胶质细胞的比例未见显著差异。WesternBlot结果显示BDVp40下调了磷酸化ERK1／2在蛋白水平的表达。结论BDVp40抑制NSCs的存活、增殖,但是对NSCs的分化方向没有明显的影响。BDVp40有可能通过下调磷酸化ERK1／2活性对NSCs的存活、增殖起抑制作用。     

Possible involvement of brain-derived neurotrophic factor in eating disorders

Eating disorders (EDs) manifest as abnormal patterns of eating behavior and weight regulation driven by low self-esteem due to weight preoccupation and perceptions toward body weight and shape. Two major groups of such disorders are anorexia nervosa (AN) and bulimia nervosa (BN). The etiology of EDs is complex and evidence indicates that both biological/genetic and psychosocial factors are involved. Several lines of evidence indicate that brain-derived neurotrophic factor (BDNF) plays a critical role in regulating eating behaviors and cognitive impairments in the EDs. BDNF is involved in neuronal proliferation, differentiation, and survival during development. BDNF and its tyrosine kinase receptor (TrkB) are expressed in hypothalamic nuclei associated with eating behaviors. A series of studies using BDNF knockout mice and the human BDNF gene indicate an association of BDNF and EDs with predisposition and vulnerability. In the previous studies, serum BDNF levels in subjects with EDs are reduced significantly compared with healthy controls, hence, we proposed that levels of serum BDNF would be a useful diagnostic indicator for EDs.     

Numb links extracellular cues to intracellular polarity machinery to promote chemotaxis

Cell polarization is essential throughout development for proliferation, migration, and differentiation. However, it is not known how extracellular cues correctly orient cell polarity at distinct stages of development. Here, we show that the endocytic adaptor protein Numb, previously characterized for its role in cell proliferation, subsequently plays an important role in cell migration. In neural precursors stimulated with the chemotactic factor BDNF, Numb binds to activated TrkB, the BDNF receptor, and functions both as an endocytic regulator for TrkB and as a scaffold for aPKC (aPKC). Thus, Numb promotes BDNF-dependent aPKC activation. Interestingly, Numb is also a substrate of aPKC. When phosphorylated, Numb exhibits increased efficacy in binding TrkB and in promoting a chemotactic response to BDNF. Therefore, Numb functions in a feed-forward loop to promote chemotaxis of neural precursors, linking BDNF, an extracellular cue, to aPKC, a critical component of the intrinsic polarity machinery.     

Neurotrophin channeling of neural progenitor cell differentiation

The act of defining neuropoietic progenitor/stem cells is still in its early phases. Epidermal growth factor (EGF) stimulates extended proliferation of aggregates of subventricular striatal cells, taken from E15 mouse striatum, termed neurospheres in liquid culture. We have shown here and in previous work, using either immunohistochemistry or RT-PCR, that neurosphere cells express 13 cytokines (32 tested) and 20 cytokine receptors (28 tested), with 11 potential paracrine and nine potential autocrine loops. The neurotrophin receptors, Trk A, B, and C, were all expressed. Using a newly developed FACS single cell deposition technique, we evaluated the capacity of single EGF stimulated neurosphere cells to respond to the ligands for Trk A and B, nerve growth factor (NGF), and brain-derived neurotrophin factor (BDNF). Addition of NGF or BDNF to EGF for 14 days had no effect, but removal of EGF at day 14 with subsequent addition of BDNF or NGF resulted in an increase in neuronal and astroglial, but not oligodendrocyte, colony cells at 21 and 28 days of culture for BDNF, and of both cell types at 28 days for NGF. Tri-lineage colonies increased at day 21 with BDNF and at day 28 for both NGF and BDNF. Gross colony morphology also showed changes with neurotrophin addition, forming multiple individual cell balls or filamentous spreads. When EGF was withdrawn, a threshold effect was observed, with small, but not large, colonies ceasing growth. BDNF and NGF showed no effects on cell proliferation when compared to EGF controls, as determined by 5'-bromo-2-deoxyuridine (BrdU) incorporation and thus, they appear to affect differentiation of progenitor cells. These data indicate a sequential action of cytokines with EGF maintaining viability and proliferation and blocking differentiation. Removal of EGF is then permissive for the differentiating effects of BDNF and NGF. These data further indicate that the majority of EGF neurosphere clones have neurotrophin dependent tri-lineage potential.     

In vivo induction of glial cell proliferation and axonal outgrowth and myelination by brain-derived neurotrophic factor

Brain-derived neurotrophic factor (BDNF) belongs to the neurotrophin family of neuronal cell survival and differentiation factors but is thought to be involved in neuronal cell proliferation and myelination as well. To explore the role of BDNF in vivo, we employed the intermediate pituitary melanotrope cells of the amphibian Xenopus laevis as a model system. These cells mediate background adaptation of the animal by producing high levels of the prohormone proopiomelanocortin (POMC) when the animal is black adapted. We used stable X. transgenesis in combination with the POMC gene promoter to generate transgenic frogs overexpressing BDNF specifically and physiologically inducible in the melanotrope cells. Intriguingly, an approximately 25-fold overexpression of BDNF resulted in hyperplastic glial cells and myelinated axons infiltrating the pituitary, whereby the transgenic melanotrope cells became located dispersed among the induced tissue. The infiltrating glial cells and axons originated from both peripheral and central nervous system sources. The formation of the phenotype started around tadpole stage 50 and was induced by placing white-adapted transgenics on a black background, i.e. after activation of transgene expression. The severity of the phenotype depended on the level of transgene expression, because the intermediate pituitaries from transgenic animals raised on a white background or from transgenics with only an approximately 5-fold BDNF overexpression were essentially not affected. In conclusion, we show in a physiological context that, besides its classical role as neuronal cell survival and differentiation factor, in vivo BDNF can also induce glial cell proliferation as well as axonal outgrowth and myelination.     

Regulated temporal-spatial astrocyte precursor cell proliferation involves BRAF signalling in mammalian spinal cord

Expansion of astrocyte populations in the central nervous system is characteristic of evolutionarily more complex organisms. However, regulation of mammalian astrocyte precursor proliferation during development remains poorly understood. Here, we used Aldh1L1-GFP to identify two morphologically distinct types of proliferative astrocyte precursors: radial glia (RG) in the ventricular zone and a second cell type we call an 'intermediate astrocyte precursor' (IAP) located in the mantle region of the spinal cord. Astrogenic RG and IAP cells proliferated in a progressive ventral-to-dorsal fashion in a tight window from embryonic day 13.5 until postnatal day 3, which correlated precisely with the pattern of active ERK signalling. Conditional loss of BRAF function using BLBP-cre resulted in a 20% decrease in astrocyte production, whereas expression of activated BRAFV600E resulted in astrocyte hyperproliferation. Interestingly, BRAFV600E mitogenic effects in astrocytes were restricted, in part, by the function of p16INK4A-p19(ARF), which limited the temporal epoch for proliferation. Together, these findings suggest that astrocyte precursor proliferation involves distinct RG and IAP cells; is subjected to temporal and spatial control; and depends in part on BRAF signalling at early stages of mammalian spinal cord development.     

Aggrecan is expressed by embryonic brain glia and regulates astrocyte development

Determination of the molecules that regulate astrocyte development has been hindered by the paucity of markers that identify astrocytic precursors in vivo. Here we report that the chondroitin sulfate proteoglycan aggrecan both regulates astrocyte development and is expressed by embryonic glial precursors. During chick brain development, the onset of aggrecan expression precedes that of the astrocytic marker GFAP and is concomitant with detection of the early glial markers GLAST and glutamine synthetase. In co-expression studies, we established that aggrecan-rich cells contain the radial glial markers nestin, BLBP and GLAST and later in embryogenesis, the astroglial marker GFAP. Parallel in vitro studies showed that ventricular zone cultures, enriched in aggrecan-expressing cells, could be directed to a GFAP-positive fate in G5-supplemented differentiation media. Analysis of the chick aggrecan mutant nanomelia revealed marked increases in the expression of the astrocyte differentiation genes GFAP, GLAST and GS in the absence of extracellular aggrecan. These increases in astrocytic marker gene expression could not be accounted for by changes in precursor proliferation or cell death, suggesting that aggrecan regulates the rate of astrocyte differentiation. Taken together, these results indicate a major role for aggrecan in the control of glial cell maturation during brain development.     

Extracellular matrix-associated molecules collaborate with ciliary neurotrophic factor to induce type-2 astrocyte development

O-2A progenitor cells give rise to both oligodendrocytes and type-2 astrocytes in vitro. Whereas oligodendrocyte differentiation occurs constitutively, type-2 astrocyte differentiation requires extracellular signals, one of which is thought to be ciliary neurotrophic factor (CNTF). CNTF, however, is insufficient by itself to induce the development of stable type-2 astrocytes. In this report we show the following: (a) that molecules associated with the extracellular matrix (ECM) cooperate with CNTF to induce stable type-2 astrocyte differentiation in serum-free cultures. The combination of CNTF and the ECM-associated molecules thus mimics the effect of FCS, which has been shown previously to induce stable type-2 astrocyte differentiation in vitro. (b) Both the ECM-associated molecules and CNTF act directly on O-2A progenitor cells and can induce them to differentiate prematurely into type-2 astrocytes. (c) ECM-associated molecules also inhibit oligodendrocyte differentiation, even in the absence of CNTF, but this inhibition is not sufficient on its own to induce type-2 astrocyte differentiation. (d) Whereas the effect of ECM on oligodendrocyte differentiation is mimicked by basic fibroblast growth factor (bFGF), the effect of ECM on type-2 astrocyte differentiation is not. (e) The ECM-associated molecules that are responsible for inhibiting oligodendrocyte differentiation and for cooperating with CNTF to induce type-2 astrocyte differentiation are made by non-glial cells in vitro. (f) Molecules that have these activities and bind to ECM are present in the optic nerve at the time type-2 astrocytes are thought to be developing.     

The p75 receptor is required for BDNF-induced differentiation of neural precursor cells

Epidermal growth factor (EGF)-treated neurospheres from fetal forebrain contain multipotential cells capable of neuronal, astrocytic, and oligodendroglial differentiation. These neural precursor cells express the TrkB as well as the neurotrophin receptor p75 (p75NTR), suggesting that they are BDNF responsive. In this study, we test whether the p75NTR plays a role in the differentiation of these neural precursor cells in vitro. Activation of the TrkB and the p75NTR by the addition of BDNF facilitates neuronal commitment and marked neurite genesis. However, no promotion of neuronal commitment by BDNF was observed in the neural precursor cells from mice carrying a mutation in the p75NTR gene. In addition, we observed a significant increase in the number of nestin-positive cells and the proliferation of the cells lacking functional p75NTR. These findings suggest that the p75NTR is required for proper neuronal fate decision as well as the differentiation of the neural precursor cells.     

Melatonin antagonizes interleukin‐18‐mediated inhibition on neural stem cell proliferation and differentiation

Neural stem cells (NSCs) are self‐renewing, pluripotent and undifferentiated cells which have the potential to differentiate into neurons, oligodendrocytes and astrocytes. NSC therapy for tissue regeneration, thus, gains popularity. However, the low survivals rate of the transplanted cell impedes its utilities. In this study, we tested whether melatonin, a potent antioxidant, could promote the NSC proliferation and neuronal differentiation, especially, in the presence of the pro‐inflammatory cytokine interleukin‐18 (IL‐18). Our results showed that melatonin per se indeed exhibited beneficial effects on NSCs and IL‐18 inhibited NSC proliferation, neurosphere formation and their differentiation into neurons. All inhibitory effects of IL‐18 on NSCs were significantly reduced by melatonin treatment. Moreover, melatonin application increased the production of both brain‐derived and glial cell‐derived neurotrophic factors (BDNF, GDNF) in IL‐18‐stimulated NSCs. It was observed that inhibition of BDNF or GDNF hindered the protective effects of melatonin on NSCs. A potentially protective mechanism of melatonin on the inhibition of NSC's differentiation caused IL‐18 may attribute to the up‐regulation of these two major neurotrophic factors, BNDF and GNDF. The findings indicate that melatonin may play an important role promoting the survival of NSCs in neuroinflammatory diseases.