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

Critical points for optimizing long-term culture and neural differentiation capacity of rodent and human neural stem cells to facilitate translation into clinical settings

Despite several decades of research on the nature and functional properties of neural stem cells, which brought great advances in regenerative medicine, there is still a plethora of ambiguous protocols and interpretations linked to their applications. Here, we present a whole spectrum of protocol elements that should be standardized in order to obtain viable cell cultures and facilitate their translation into clinical settings. Additionally, this review also presents outstanding limitations and possible problems to be encountered when dealing with protocol optimization. Most importantly, we also outline the critical points that should be considered before starting any experiments utilizing neural stem cells or interpreting their results.

Cannabidiol induces autophagy via ERK1/2 activation in neural cells

Autophagy is a lysosomal catabolic process essential to cell homeostasis and is related to the neuroprotection of the central nervous system. Cannabidiol (CBD) is a non-psychotropic phytocannabinoid present in Cannabis sativa. Many therapeutic actions have been linked to this compound, including autophagy activation. However, the precise underlying molecular mechanisms remain unclear, and the downstream functional significance of these actions has yet to be determined. Here, we investigated CBD-evoked effects on autophagy in human neuroblastoma SH-SY5Y and murine astrocyte cell lines. We found that CBD-induced autophagy was substantially reduced in the presence of CB1, CB2 and TRPV1 receptor antagonists, AM 251, AM 630 and capsazepine, respectively. This result strongly indicates that the activation of these receptors mediates the autophagic flux. Additionally, we demonstrated that CBD activates autophagy through ERK1/2 activation and AKT suppression. Interestingly, CBD-mediated autophagy activation is dependent on the autophagy initiator ULK1, but mTORC1 independent. Thus, it is plausible that a non-canonical pathway is involved. Our findings collectively provide evidence that CBD stimulates autophagy signal transduction via crosstalk between the ERK1/2 and AKT kinases, which represent putative regulators of cell proliferation and survival. Furthermore, our study sheds light on potential therapeutic cannabinoid targets that could be developed for treating neurodegenerative disorders.

Epidermal Growth Factor in the CNS: A Beguiling Journey from Integrated Cell Biology to Multiple Sclerosis. An Extensive Translational Overview

This article reviews the wealth of papers dealing with the different effects of epidermal growth factor (EGF) on oligodendrocytes, astrocytes, neurons, and neural stem cells (NSCs). EGF induces the in vitro and in vivo proliferation of NSCs, their migration, and their differentiation towards the neuroglial cell line. It interacts with extracellular matrix components. NSCs are distributed in different CNS areas, serve as a reservoir of multipotent cells, and may be increased during CNS demyelinating diseases. EGF has pleiotropic differentiative and proliferative effects on the main CNS cell types, particularly oligodendrocytes and their precursors, and astrocytes. EGF mediates the in vivo myelinotrophic effect of cobalamin on the CNS, and modulates the synthesis and levels of CNS normal prions (PrP^Cs), both of which are indispensable for myelinogenesis and myelin maintenance. EGF levels are significantly lower in the cerebrospinal fluid and spinal cord of patients with multiple sclerosis (MS), which probably explains remyelination failure, also because of the EGF marginal role in immunology. When repeatedly administered, EGF protects mouse spinal cord from demyelination in various experimental models of autoimmune encephalomyelitis. It would be worth further investigating the role of EGF in the pathogenesis of MS because of its multifarious effects.

The sphingosine-1-phosphate analogue, FTY-720, promotes the proliferation of embryonic neural stem cells, enhances hippocampal neurogenesis and learning and memory abilities in adult mice

BACKGROUND AND PURPOSE

Fingolimod (FTY-720) is the first oral therapeutic drug approved for the relapsing-remitting forms of multiple sclerosis. Neural stem cells (NSCs) are capable of continuous self-renewal and differentiation. The dentate gyrus of the hippocampus in the adult mammalian brain contains a population of NSCs and is one of the regions where neurogenesis takes place. FTY-720 has been shown to have neuroprotective effects in several model systems, so we investigated the direct effects of FTY-720 on NSCs and adult neurogenesis.

EXPERIMENTAL APPROACHES

We assessed the effects of FTY-720 on the proliferation and differentiation of cultured embryonic hippocampal NSCs using the 5-bromo-2-deoxyuridine incorporation assay, the neurosphere formation assay and western blot analysis. Receptor selective agonists and antagonists were used to identify the mechanisms involved. Neurogenesis in the hippocampus of C57BL/6 mice was also assessed by immunohistochemistry. The Morris water maze and fear conditioning tests were used to detect the learning and memory abilities of mice.

KEY RESULTS

FTY-720 promoted the proliferation of embryonic hippocampal NSCs probably via the activation of ERK signalling, Gi/o proteins and S1P1 receptors. However, FTY-720 did not affect the differentiation of cultured hippocampal NSCs. In vivo, chronic treatment with FTY-720 promoted hippocampal neurogenesis in adult C57BL/6 mice and enhanced their learning and memory abilities.

CONCLUSIONS AND IMPLICATIONS

Our results suggest a new target for the activation of NSCs and provide an insight into the therapeutic effects of FTY-720 in neuropsychiatric disorders, neurodegenerative diseases and age-related cognitive decline where hippocampal neurogenesis is compromised.

Ghrelin regulates cell cycle-related gene expression in cultured hippocampal neural stem cells

We have previously demonstrated that ghrelin stimulates the cellular proliferation of cultured adult rat hippocampal neural stem cells (NSCs). However, little is known about the molecular mechanisms by which ghrelin regulates cell cycle progression. The purpose of this study was to investigate the potential effects of ghrelin on cell cycle regulatory molecules in cultured hippocampal NSCs. Ghrelin treatment increased proliferation assessed by CCK-8 proliferation assay. The expression levels of proliferating cell nuclear antigen and cell division control 2, well-known cell-proliferating markers, were also increased by ghrelin. Fluorescence-activated cell sorting analysis revealed that ghrelin promoted progression of cell cycle from G0/G1 to S phase, whereas this progression was attenuated by the pretreatment with specific inhibitors of MEK/extracellular signal-regulated kinase 1/2, phosphoinositide 3-kinase/Akt, mammalian target of rapamycin, and janus kinase 2/signal transducer and activator of transcription 3. Ghrelin-induced proliferative effect was associated with increased expression of E2F1 transcription factor in the nucleus, as determined by Western blotting and immunofluorescence. We also found that ghrelin caused an increase in protein levels of positive regulators of cell cycle, such as cyclin A and cyclin-dependent kinase (CDK) 2. Moreover, p27(KIP1) and p57(KIP2) protein levels were reduced when cell were exposed to ghrelin, suggesting downregulation of CDK inhibitors may contribute to proliferative effect of ghrelin. Our data suggest that ghrelin targets both cell cycle positive and negative regulators to stimulate proliferation of cultured hippocampal NSCs.

Differential responses of Trans-Resveratrol on proliferation of neural progenitor cells and aged rat hippocampal neurogenesis

The plethora of literature has supported the potential benefits of Resveratrol (RV) as a life-extending as well as an anticancer compound. However, these two functional discrepancies resulted at different concentration ranges. Likewise, the role of Resveratrol on adult neurogenesis still remains controversial and less understood despite its well documented health benefits. To gather insight into the biological effects of RV on neurogenesis, we evaluated the possible effects of the compound on the proliferation and survival of neural progenitor cells (NPCs) in culture, and in the hippocampus of aged rats. Resveratrol exerted biphasic effects on NPCs; low concentrations (10 μM) stimulated cell proliferation mediated by increased phosphorylation of extracellular signal-regulated kinases (ERKs) and p38 kinases, whereas high concentrations (>20 μM) exhibited inhibitory effects. Administration of Resveratrol (20 mg/kg body weight) to adult rats significantly increased the number of newly generated cells in the hippocampus, with upregulation of p-CREB and SIRT1 proteins implicated in neuronal survival and lifespan extension respectively. We have successfully demonstrated that Resveratrol exhibits dose dependent discrepancies and at a lower concentration can have a positive impact on the proliferation, survival of NPCs and aged rat hippocampal neurogenesis implicating its potential as a candidate for restorative therapies against age related disorders.

Methylglyoxal Causes Cell Death in Neural Progenitor Cells and Impairs Adult Hippocampal Neurogenesis

Methylglyoxal (MG) is formed during normal metabolism by processes like glycolysis, lipid peroxidation, and threonine catabolism, and its accumulation is associated with various degenerative diseases, such as diabetes and arterial atherogenesis. Furthermore, MG has also been reported to have toxic effects on hippocampal neurons. However, these effects have not been studied in the context of neurogenesis. Here, we report that MG adversely affects hippocampal neurogenesis and induces neural progenitor cell (NPC) death. MG significantly reduced C17.2 NPC proliferation, and high concentration of MG (500 μM) induced cell death and elevated oxidative stress. Further, MG was found to activate the ERK signaling pathway, indicating elevated stress response. To determine the effects of MG in vivo, mice were administrated with vehicle or MG (0.5 or 1 % in drinking water) for 4 weeks. The numbers of BrdU-positive cells in hippocampi were significantly lower in MG-treated mice, indicating impaired neurogenesis, but MG did not induce neuronal damage or glial activations. Interestingly, MG reduced memory retention when administered to mice at 1 % but not at 0.5 %. In addition, the levels of hippocampal BDNF and synaptophysin were significantly lower in the hippocampi of mice treated with MG at 1 %. Collectively, our findings suggest MG could be harmful to NPCs and to hippocampal neurogenesis.

Platelet-derived growth factor-BB restores HIV Tat -mediated impairment of neurogenesis: role of GSK-3β/β-catenin

Our previous study demonstrated that platelet-derived growth factor-BB (PDGF-BB) increased the cell proliferation of primary rat neuronal progenitor cells (NPCs). However, whether PDGF-BB regulates neurogenesis in HIV-associated neurological disorder (HAND) remains largely unknown. In this study we demonstrated that pre-treatment of NPCs with PDGF-BB restored Tat-mediated impairment of cell proliferation via activation of p38 and JNK MAPK pathways. Moreover, treatment with PDGF-BB induced inactivation of glycogen synthase kinase-3β (GSK-3β), evidenced by its phosphorylation at Ser9, this effect was significantly inhibited by the p38 and JNK inhibitors. Level of nuclear β-catenin, the primary substrate of GSK-3β, was also concomitantly increased following PDGF-BB treatment, suggesting that PDGF-BB stimulates NPC proliferation via acting on GSK-3β to promote nuclear accumulation of β-catenin. This was further validated by gain and loss of function studies using cells transfected with either the wild type or mutant GSK-3β constructs. Together these data underpin the role of GSK-3β/β-catenin as a novel target that regulates NPC proliferation mediated by PDGF-BB with implications for therapeutic intervention for reversal of impaired neurogenesis inflicted by Tat.

Involvement of miR-9/MCPIP1 axis in PDGF-BB-mediated neurogenesis in neuronal progenitor cells

Highly conserved microRNA-9 (miR-9) has a critical role in various cellular processes including neurogenesis. However, its regulation by neurotropins that are known to mediate neurogenesis remains poorly defined. In this study, we identify platelet-derived growth factor-BB (PDGF-BB)-mediated upregulation of miR-9, which in turn downregulates its target gene monocyte chemotactic protein-induced protein 1 (MCPIP1), as a key player in modulating proliferation, neuronal differentiation as well as migration of neuronal progenitor cells (NPCs). Results indicate that miR-9-mediated NPC proliferation and neuronal differentiation involves signaling via the nuclear factor-kappa B (NF-κB) and cAMP response element-binding protein (CREB) pathways, and that NPC migration involves CREB but not the NF-κB signaling. These findings thus suggest that miR-9-mediated downregulation of MCPIP1 acts as a molecular switch regulation of neurogenesis.

Multiple signaling pathways mediate ghrelin-induced proliferation of hippocampal neural stem cells

Ghrelin, an endogenous ligand for the GH secretagogue receptor (GHS-R) receptor 1a (GHS-R1a), has been implicated in several physiologic processes involving the hippocampus. The aim of this study was to investigate the molecular mechanisms of ghrelin-stimulated neurogenesis using cultured adult rat hippocampal neural stem cells (NSCs). The expression of GHS-R1a was detected in hippocampal NSCs, as assessed by western blot analysis and immunocytochemistry. Ghrelin treatment increased the proliferation of cultured hippocampal NSCs assessed by BrdU incorporation. The exposure of cells to the receptor-specific antagonist d-Lys-3-GHRP-6 abolished the proliferative effect of ghrelin. By contrast, ghrelin showed no significant effect on cell differentiation. The expression of GHS-R1a was significantly increased by ghrelin treatment. The analysis of signaling pathways showed that ghrelin caused rapid activation of ERK1/2 and Akt, which were blocked by the GHS-R1a antagonist. In addition, ghrelin stimulated the phosphorylation of Akt downstream effectors, such as glycogen synthase kinase (GSK)-3β, mammalian target of rapamycin (mTOR), and p70(S6K). The activation of STAT3 was also caused by ghrelin treatment. Furthermore, pretreatment of cells with specific inhibitors of MEK/ERK1/2, phosphatidylinositol-3-kinase (PI3K)/Akt, mTOR, and Jak2/STAT3 attenuated ghrelin-induced cell proliferation. Taken together, our results support a role for ghrelin in adult hippocampal neurogenesis and suggest the involvement of the ERK1/2, PI3K/Akt, and STAT3 signaling pathways in the mediation of the actions of ghrelin on neurogenesis. Our data also suggest that PI3K/Akt-mediated inactivation of GSK-3β and activation of mTOR/p70(S6K) contribute to the proliferative effect of ghrelin.

Activation of type 1 cannabinoid receptor (CB1R) promotes neurogenesis in murine subventricular zone cell cultures

The endocannabinoid system has been implicated in the modulation of adult neurogenesis. Here, we describe the effect of type 1 cannabinoid receptor (CB1R) activation on self-renewal, proliferation and neuronal differentiation in mouse neonatal subventricular zone (SVZ) stem/progenitor cell cultures. Expression of CB1R was detected in SVZ-derived immature cells (Nestin-positive), neurons and astrocytes. Stimulation of the CB1R by (R)-(+)-Methanandamide (R-m-AEA) increased self-renewal of SVZ cells, as assessed by counting the number of secondary neurospheres and the number of Sox2+/+ cell pairs, an effect blocked by Notch pathway inhibition. Moreover, R-m-AEA treatment for 48 h, increased proliferation as assessed by BrdU incorporation assay, an effect mediated by activation of MAPK-ERK and AKT pathways. Surprisingly, stimulation of CB1R by R-m-AEA also promoted neuronal differentiation (without affecting glial differentiation), at 7 days, as shown by counting the number of NeuN-positive neurons in the cultures. Moreover, by monitoring intracellular calcium concentrations ([Ca²⁺]_i) in single cells following KCl and histamine stimuli, a method that allows the functional evaluation of neuronal differentiation, we observed an increase in neuronal-like cells. This proneurogenic effect was blocked when SVZ cells were co-incubated with R-m-AEA and the CB1R antagonist AM 251, for 7 days, thus indicating that this effect involves CB1R activation. In accordance with an effect on neuronal differentiation and maturation, R-m-AEA also increased neurite growth, as evaluated by quantifying and measuring the number of MAP2-positive processes. Taken together, these results demonstrate that CB1R activation induces proliferation, self-renewal and neuronal differentiation from mouse neonatal SVZ cell cultures.

Angiotensin II increased neuronal stem cell proliferation: role of AT2R

Angiotensin II (Ang II), known a potent vasoactive substance in the renin-angiotensin system in the brain, plays a critical role in systemic blood pressure control. However, increasing evidence indicated that the physiological role of Ang II go beyond its vasoactive effect. In the present study, we demonstrated that Ang II type-1 receptor (AT1R) and type-2 receptor (AT2R) were expressed in primary rat hippocampal neuronal stem cells (NSCs). Treatment of rat hippocampal NSCs with Ang II increased cell proliferation. Pretreatment of NSCs with specific AT2R, but not AT1R, antagonist significantly suppressed Ang II-induced cell proliferation. Furthermore, Ang II stimulated ERK and Akt phosphorylation in NSCs. Pretreatment of MEK inhibitor, but not PI3K inhibitor, inhibited Ang II-induced ERK phosphorylation as well as cell proliferation. In addition, stimulation of NSCs with Ang II decreased expression of K_V 1.2/K_V 3.1 channels and blocked K⁺ currents which lie downstream of ERK activation. Taken together, these findings underpin the role of AT2R as a novel target that regulates cell proliferation mediated by Ang II with implications for therapeutic intervention for regulation of neurogenesis.

Ghrelin-induced hippocampal neurogenesis and enhancement of cognitive function are mediated independently of GH/IGF-1 axis: lessons from the spontaneous dwarf rats

We recently have reported that ghrelin modulates adult hippocampal neurogenesis. However, there is a possibility that the action of ghrelin on hippocampal neurogenesis could be, in part, due to the ability of ghrelin to stimulate the GH/insulin-like growth factor (IGF)-1 axis, where both GH and IGF-1 infusions are known to increase hippocampal neurogenesis. To explore this possibility, we assessed the impact of ghrelin on progenitor cell proliferation and differentiation in the dentate gyrus (DG) of spontaneous dwarf rats (SDRs), a dwarf strain with a mutation of the GH gene resulting in total loss of GH. Double immunohistochemical staining revealed that Ki-67-positive progenitor cells and doublecortin (DCX)-positive neuroblasts in the DG of the SDRs expressed ghrelin receptors. We found that ghrelin treatment in the SDRs significantly increased the number of proliferating cell nuclear antigen- and BrdU-labeled cells in the DG. The number of DCX-labeled cells in the DG of ghrelin-treated SDRs was also significantly increased compared with the vehicle-treated controls. To test whether ghrelin has a direct effect on cognitive performance independently of somatotropic axis, hippocampus-dependent learning and memory were assessed using the Y-maze and novel object recognition (NOR) test in the SDRs. Ghrelin treatment for 4 weeks by subcutaneous osmotic pump significantly increased alternation rates in the Y-maze and exploration time for novel object in the NOR test compared to vehicle-treated controls. Our results indicate that ghrelin-induced adult hippocampal neurogenesis and enhancement of cognitive function are mediated independently of somatotropic axis.

Lessons from the embryonic neural stem cell niche for neural lineage differentiation of pluripotent stem cells

Pluripotent stem cells offer an abundant and malleable source for the generation of differentiated cells for transplantation as well as for in vitro screens. Patterning and differentiation protocols have been developed to generate neural progeny from human embryonic or induced pluripotent stem cells. However, continued refinement is required to enhance efficiency and to prevent the generation of unwanted cell types. We summarize and interpret insights gained from studies of embryonic neuroepithelium. A multitude of factors including soluble molecules, interactions with the extracellular matrix and neighboring cells cooperate to control neural stem cell self-renewal versus differentiation. Applying these findings and concepts to human stem cell systems in vitro may yield more appropriately patterned cell types for biomedical applications.

Mitogen- and stress-activated kinases regulate progenitor cell proliferation and neuron development in the adult dentate gyrus

The neurogenic niche within the subgranular zone (SGZ) of the dentate gyrus is a source of new neurons throughout life. Interestingly, SGZ proliferative capacity is regulated by both physiological and pathophysiological conditions. One outstanding question involves the molecular mechanisms that regulate both basal and inducible adult neurogenesis. Here, we examined the role of the MAPK-regulated kinases, mitogen- and stress-activated kinase (MSK)1 and MSK2. as regulators of dentate gyrus SGZ progenitor cell proliferation and neurogenesis. Under basal conditions, MSK1/2 null mice exhibited significantly reduced progenitor cell proliferation capacity and a corollary reduction in the number of doublecortin (DCX)-positive immature neurons. Strikingly, seizure-induced progenitor proliferation was totally blocked in MSK1/2 null mice. This blunting of cell proliferation in MSK1/2 null mice was partially reversed by forskolin infusion, indicating that the inducible proliferative capacity of the progenitor cell population was intact. Furthermore, in MSK1/2 null mice, DCX-positive immature neurons exhibited reduced neurite arborization. Together, these data reveal a critical role for MSK1/2 as regulators of both basal and activity-dependent progenitor cell proliferation and morphological maturation in the SGZ.

Resveratrol inhibits the proliferation of neural progenitor cells and hippocampal neurogenesis

Resveratrol is a phytoalexin and natural phenol that is present at relatively high concentrations in peanuts and red grapes and wine. Based upon studies of yeast and invertebrate models, it has been proposed that ingestion of resveratrol may also have anti-aging actions in mammals including humans. It has been suggested that resveratrol exerts its beneficial effects on health by activating the same cellular signaling pathways that are activated by dietary energy restriction (DR). Some studies have reported therapeutic actions of resveratrol in animal models of metabolic and neurodegenerative disorders. However, the effects of resveratrol on cell, tissue and organ function in healthy subjects are largely unknown. In the present study, we evaluated the potential effects of resveratrol on the proliferation and survival of neural progenitor cells (NPCs) in culture, and in the hippocampus of healthy young adult mice. Resveratrol reduced the proliferation of cultured mouse multi-potent NPCs, and activated AMP-activated protein kinase (AMPK), in a concentration-dependent manner. Administration of resveratrol to mice (1-10 mg/kg) resulted in activation of AMPK, and reduced the proliferation and survival of NPCs in the dentate gyrus of the hippocampus. Resveratrol down-regulated the levels of the phosphorylated form of cyclic AMP response element-binding protein (pCREB) and brain-derived neurotrophic factor (BDNF) in the hippocampus. Finally, resveratrol-treated mice exhibited deficits in hippocampus-dependent spatial learning and memory. Our findings suggest that resveratrol, unlike DR, adversely affects hippocampal neurogenesis and cognitive function by a mechanism involving activation of AMPK and suppression of CREB and BDNF signaling.

Platelet-derived growth factor-BB restores human immunodeficiency virus Tat-cocaine-mediated impairment of neurogenesis: role of TRPC1 channels

Platelet-derived growth factor-BB (PDGF-BB) has been reported to provide tropic support for neurons in the CNS. However, whether PDGF-BB regulates neurogenesis, especially in the context of HIV-associated neurological disorder and drug abuse, remains essentially unknown. In this study, we demonstrate that pretreatment of rat hippocampal neuronal progenitor cells (NPCs) with PDGF-BB restored proliferation that had been impaired by HIV Tat-cocaine via the cognate receptors. We identify the essential role of transient receptor potential canonical (TRPC) channels in PDGF-BB-mediated proliferation. Parallel but distinct ERK/CREB, phosphatidylinositol 3-kinase/Akt signaling pathways with downstream activation of mammalian target of rapamycin (mTOR)/eukaryotic translation initiation factor 4E-binding protein (4E-BP)-p70S6K and nuclear factor-κB were critical for proliferation. Blocking TRPC1 channel suppressed PDGF-mediated proliferation as well as PDGF-BB-induced ERK/CREB and mTOR/4E-BP-p70S6K activation, thereby underscoring its role in this process. In vivo relevance of these findings was further corroborated in Tat transgenic mice wherein hippocampal injection of recombinant AAV2-PDGF-B restored impaired NPC proliferation that was induced by Tat-cocaine. Together, these data underpin the role of TRPC1 channel as a novel target that regulates cell proliferation mediated by PDGF-BB with implications for therapeutic intervention for reversal of impaired neurogenesis inflicted by Tat and cocaine.

The molecular basis of the cooperation between EGF, FGF and eCB receptors in the regulation of neural stem cell function

Adult neurogenesis relies on EGF and FGF receptor (EGFR/FGFR) function and endocannabinoid (eCB) signalling. Here we have used a neural stem cell (NSC) line to determine how these systems cooperate to regulate neurogenesis. The results show the EGFR to be solely responsible for maintaining PI3K activation explaining its dominant role in promoting NSC survival. The EGFR and FGFR synergistically regulate the ERK/MAPK pathway, and this explains the requirement for both for optimal cell proliferation. The eCB receptors did not contribute to activation of the PI3K or ERK/MAPK pathways, highlighting the importance of another major proliferation pathway. The EGFR plays the dominant role in maintaining the transcriptome, with significant changes in the expression of over 3500 transcripts seen within hours of inhibition or activation of this receptor. The FGFR has a more modest effect on transcription with evidence for nodal integration with EGFR signalling at the level of the ERK/MAPK pathway. A common set of transcripts are regulated by the CB1 and CB2 receptors, with cooperation between these receptors and the EGFR apparent in the regulation of a pool of transcripts, most likely representing signal integration downstream from an as yet to be identified node. Finally, a first level molecular analysis of the transcriptional response shows regulation of a number of key growth factors, growth factor receptors and GPCRs to be under the control of the EGFR.

The opiate analgesic buprenorphine decreases proliferation of adult hippocampal neuroblasts and increases survival of their progeny

Although opiate drugs of abuse have been shown to decrease adult hippocampal neurogenesis, the impact of opiate analgesics has not been tested. North American regulatory boards governing the ethical treatment of experimental animals require the administration of analgesics, such as buprenorphine, following minor surgical interventions. Here, we show that two commonly used post-operative buprenorphine dosing regimes significantly inhibit the proliferation of doublecortin-positive neuroblasts but not other hippocampal stem and progenitor cell populations in adult mice. Buprenorphine, administered in schedules of three 0.05 mg/kg subcutaneous injections over a single day or seven 0.05 mg/kg injections over a 3-day period decreased the number of actively proliferating 5-iodo-2'-deoxyuridine-labeled doublecortin-positive cells for up to 6 days after opiate withdrawal. The minimal (three injection), but not standard (seven injection), analgesic paradigm also reduced basal indices of hippocampal progenitor cell apoptosis and enhanced survival of newly born cells for up to 28 days. Taken together, these data provide the first evidence that the routine administration of opiate analgesics has transient but long-lasting effects on neurogenesis and further emphasize that analgesic dosage and schedule should be reported and considered when interpreting the magnitude of neural stem and progenitor cell activation in response to in vivo intervention.

Soluble amyloid precursor protein: a novel proliferation factor of adult progenitor cells of ectodermal and mesodermal origin

INTRODUCTION

Soluble amyloid precursor protein α (sAPPα) is a proteolyte of APP cleavage by α-secretase. The significance of the cleavage and the physiological role of sAPPα are unknown. A crystal structure of a region of the amino terminal of sAPPα reveals a domain that is similar to cysteine-rich growth factors. While a previous study implicates sAPPα in the regulation of neural progenitor cell proliferation in the subventricular zone of adult mice, the ubiquitous expression of APP suggests that its role as a growth factor might be broader.

METHODS

sAPPα and α-secretase activities were determined in neural progenitor cells (NPCs), mesenchymal stem cells (MSC) and human decidua parietalis placenta stem cells (hdPSC). Inhibition of α-secretase was achieved by treatment with the matrixmetalloproteinase inhibitor GM6001, and proliferation was determined using clonogenic and immunocytochemical analysis of cell-lineage markers. Recovery of proliferation was achieved by supplementing GM6001-treated cells with recombinant soluble APPα. Expression of APP and its cellular localization in the subventricular zone was determined by Western blot and immunohistochemical analyses of APP wild type and knockout tissue. Alterations in pERK and pAKT expression as a function of soluble APPα production and activity in NPCs were determined by Western blot analysis.

RESULTS

Here we show that sAPPα is a proliferation factor of adult NPCs, MSCs and hdpPSC. Inhibition of α-secretase activity reduces proliferation of these stem cell populations in a dose-dependent manner. Stem cell proliferation can be recovered by the addition of sAPPα in a dose-dependent manner, but not of media depleted of sAPPα. Importantly, sAPPα operates independently of the prominent proliferation factors epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF), but in association with ERK signaling and MAP-kinase signaling pathways. Levels of sAPPα and putative α-secretase, ADAM10, are particularly high in the subventricular zone of adult mice, suggesting a role for sAPPα in regulation of NPCs in this microenvironment.

CONCLUSIONS

These results determine a physiological function for sAPPα and identify a new proliferation factor of progenitor cells of ectodermal and mesodermal origin. Further, our studies elucidate a potential pathway for sAPPα signaling through MAP kinase activation.

cAMP response element-binding protein (CREB) is required for epidermal growth factor (EGF)-induced cell proliferation and serum response element activation in neural stem cells isolated from the forebrain subventricular zone of adult mice

Neurogenesis, which occurs not only in the developing brain but also in restricted regions in the adult brain including the forebrain subventricular zone (SVZ), is regulated by a variety of environmental factors, extracellular signals, and intracellular signal transduction pathways. We investigated whether the transcription factor cAMP response element (CRE)-binding protein (CREB) is involved in the regulation of cell proliferation of neural stem cells (NSCs) isolated from the SVZ of adult mice. Treatment of NSCs with the protein kinase A (PKA) inhibitors H89 and KT5720 inhibited epidermal growth factor (EGF)-stimulated NSC proliferation. Similar inhibition was observed when a dominant-negative mutant of CREB (MCREB) was expressed. EGF treatment increased CRE-mediated transcriptional activity, but this increase was much less than that caused by treatment with the adenylate cyclase activator forskolin, which changed neither basal nor EGF-stimulated proliferation of NSCs. Neither PKA inhibitors nor MCREB expression blocked EGF-induced phosphorylation of extracellular signal-regulated kinase (ERK), a protein kinase mediating EGF's mitogenic action. However, MCREB suppressed EGF-induced expression of several immediately early genes including c-fos, c-jun, jun-B, and fra-1 and subsequent AP-1 transcriptional activation. MCREB expression also inhibited the ability of EGF to stimulate transcriptional activation mediated by the serum response element (SRE), a promoter sequence regulating c-fos gene expression. These results suggest that basal activity of CREB is required for the mitogenic signaling of EGF in NSCs at a level between ERK activation and SRE-mediated transcriptional activation.

HNK-1 epitope-carrying tenascin-C spliced variant regulates the proliferation of mouse embryonic neural stem cells

Neural stem cells (NSCs) possess high proliferative potential and the capacity for self-renewal with retention of multipotency to differentiate into neuronal and glial cells. NSCs are the source for neurogenesis during central nervous system development from fetal and adult stages. Although the human natural killer-1 (HNK-1) carbohydrate epitope is expressed predominantly in the nervous system and involved in intercellular adhesion, cell migration, and synaptic plasticity, the expression patterns and functional roles of HNK-1-containing glycoconjugates in NSCs have not been fully recognized. We found that HNK-1 was expressed in embryonic mouse NSCs and that this expression was lost during the process of differentiation. Based on proteomics analysis, it was revealed that the HNK-1 epitopes were almost exclusively displayed on an extracellular matrix protein, tenascin-C (TNC), in the mouse embryonic NSCs. Furthermore, the HNK-1 epitope was found to be present only on the largest isoform of the TNC molecules. In addition, the expression of HNK-1 was dependent on expression of the largest TNC variant but not by enzymes involved in the biosynthesis of HNK-1. By knocking down HNK-1 sulfotransferase or TNC by small interfering RNA, we further demonstrated that HNK-1 on TNC was involved in the proliferation of NSCs via modulation of the expression level of the epidermal growth factor receptor. Our finding provides insights into the function of HNK-1 carbohydrate epitopes in NSCs to maintain stemness during neural development.

Novel embryonic neuronal migration and proliferation defects in Dcx mutant mice are exacerbated by Lis1 reduction

Heterozygous LIS1 mutations and males with loss of the X-linked DCX result in lissencephaly, a neuronal migration defect. LIS1 regulates nuclear translocation and mitotic division of neural progenitor cells, while the role of DCX in cortical development remains poorly understood. Here, we uncovered novel neuronal migration and proliferation defects in the Dcx mutant embryonic brains. Although cortical organization was fairly well preserved, Dcx(ko/Y) neurons displayed defective migration velocities similar to Lis1(+/ko) neurons when characterized by time-lapse video-microscopy of embryonic cortical slices. Dcx(ko/Y) migrating neurons displayed novel multidirectional movements with abnormal morphology and increased branching. Surprisingly, Dcx(ko/Y) radial glial cells displayed spindle orientation abnormalities similar to Lis1(+/ko) cells that in turn lead to moderate proliferation defects both in vivo and in vitro. We found functional genetic interaction of the two genes, with the combined effects of Lis1 haploinsufficiency and Dcx knock-out leading to more severe neuronal migration and proliferation phenotypes in the Lis1(+/ko);Dcx(ko/Y) male double mutant compared with the single mutants, resulting in cortical disorganization and depletion of the progenitor pool. Thus, we provide definitive evidence for a critical role for Dcx in neuronal migration and neurogenesis, as well as for the in vivo genetic interaction of the two genes most commonly involved in human neuronal migration defects.

The angiogenic factor angiopoietin-1 is a proneurogenic peptide on subventricular zone stem/progenitor cells

In the adult mammalian brain, the subventricular zone (SVZ) hosts stem cells constantly generating new neurons. Angiopoietin-1 (Ang-1) is an endothelial growth factor with a critical role in division, survival, and adhesion of endothelial cells via Tie-2 receptor activity. Expression of Tie-2 in nonendothelial cells, especially neurons and stem cells, suggests that Ang-1 may be involved in neurogenesis. In the present work, we investigated the putative role of Ang-1 on SVZ neurogenesis. Immature cells from SVZ-derived neurospheres express Ang-1 and Tie-2 mRNA, suggesting a role for the Ang-1/Tie-2 system in the neurogenic niche. Moreover, we also found that Tie-2 protein expression is retained on differentiation in neurons and glial cells. Ang-1 triggered proliferation via activation of the ERK1/2 (extracellular signal-regulated kinase 1/2) mitogen-activated protein kinase (MAPK) kinase pathway but did not induce cell death. Accordingly, coincubation with an anti-Tie-2 neutralizing antibody prevented the pro-proliferative effect of Ang-1. Furthermore, Ang-1 increased the number of NeuN (neuronal nuclear protein)-positive neurons in cultures treated for 7 d, as well as the number of functional neurons, as assessed by monitoring [Ca(2+)](i) rises after application of specific stimuli for neurons and immature cells. The proneurogenic effect of Ang-1 is mediated by Tie-2 activation and subsequent mTOR (mammalian target of rapamycin kinase) mobilization. In agreement, neuronal differentiation significantly decreased after exposure to an anti-Tie-2 neutralizing antibody and to rapamycin. Moreover, Ang-1 elicited the activation of the SAPK (stress-activated protein kinase)/JNK (c-Jun N-terminal kinase) MAPK, involved in axonogenesis. Our work shows a proneurogenic effect of Ang-1, highlighting the relevance of blood vessel/stem cell cross talk in health and disease.

Involvement of beta1-integrin up-regulation in basic fibroblast growth factor- and epidermal growth factor-induced proliferation of mouse neuroepithelial cells

In neural stem cells, basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF) promote cell proliferation and self-renewal. In the bFGF- and EGF-responsive neural stem cells, beta1-integrin also plays important roles in crucial cellular processes, including proliferation, migration, and apoptosis. The cross-talk of the signaling pathways mediated by these growth factors and beta1-integrin, however, has not been fully elucidated. Here we report a novel molecular mechanism through which bFGF or EGF promotes the proliferation of mouse neuroepithelial cells (NECs). In the NECs, total beta1-integrin expression levels and proliferation were dose-dependently increased by bFGF but not by EGF. EGF rather than bFGF strongly induced the increase of beta1-integrin localization on the NEC surface. bFGF- and EGF-induced beta1-integrin up-regulation and proliferation were inhibited after treatment with a mitogen-activated protein kinase kinase inhibitor, U0126, which indicates the dependence on the mitogen-activated protein kinase pathway. Involvement of beta1-integrin in bFGF- and EGF-induced proliferation was confirmed by the finding that NEC proliferation and adhesion to fibronectin-coated dishes were inhibited by knockdown of beta1-integrin using small interfering RNA. On the other hand, apoptosis was induced in NECs treated with RGD peptide, a small beta1-integrin inhibitor peptide with the Arg-Gly-Asp motif, but it was independent of beta1-integrin expression levels. Those results suggest that regulation of beta1-integrin expression/localization is involved in cellular processes, such as proliferation, induced by bFGF and EGF in NECs. The mechanism underlying the proliferation through beta1-integrin would not be expected to be completely identical, however, for bFGF and EGF.

A role for the MAPK/ERK pathway in oligodendroglial differentiation in vitro: stage specific effects on cell branching

The mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway is important for both long-term survival and timing of the progression of oligodendrocyte differentiation. Oligodendroglial cells treated with MEK inhibitor were distinguished by using stage specific markers: NG2 proteoglycan, A2B5, 2'3'nucleotide-cyclic 3'phosphodiesterase (CNPase) and myelin basic protein (MBP), and classified according to their morphology into different developmental stages. Treatment significantly increased the number of cells with more immature morphologies and decreased the number of mature cells. Furthermore, it increased the number of rounded cells that could not be classified into any of the oligodendroglial developmental stages. The strongest effects were usually observed shortly after treatment. Rounded cells were CNPase/MBP positive and they were not stained by anti-NG2 or A2B5, indicating that they were mature cells unable either to extend and/or to maintain their processes. These data showed an effect of the MAPK/ERK pathway on oligodendroglial branching, with possible consequences for the formation of the myelin sheath.

Endogenous hepatocyte growth factor is a niche signal for subventricular zone neural stem cell amplification and self-renewal

Neural stem cells persist in the adult mammalian brain, within the subventricular zone (SVZ). The endogenous mechanisms underpinning SVZ neural stem cell proliferation, self-renewal, and differentiation are not fully elucidated. In the present report, we describe a growth-stimulatory activity of liver explant-conditioned media on SVZ cell cultures and identify hepatocyte growth factor (HGF) as a major player in this effect. HGF exhibited a mitogenic activity on SVZ cell cultures in a mitogen-activated protein kinase (MAPK) (ERK1/2)-dependent manner as U0126, a specific MAPK inhibitor, blocked it. Combining a functional neurosphere forming assay with immunostaining for c-Met, along with markers of SVZ cells subtypes, demonstrated that HGF promotes the expansion of neural stem-like cells that form neurospheres and self-renew. Immunostaining, HGF enzyme-linked immunosorbent assay and Madin-Darby canine kidney cell scattering assay indicated that SVZ cell cultures produce and release HGF. SVZ cell-conditioned media induced proliferation on SVZ cell cultures, which was blocked by HGF-neutralizing antibodies, hence implying that endogenously produced HGF accounts for a major part in SVZ mitogenic activity. Brain sections immunostaining revealed that HGF is produced by nestin-expressing cells and c-Met is expressed within the SVZ by immature cells. HGF intracerebroventricular injection promoted SVZ cell proliferation and increased the ability of these cells exposed in vivo to HGF to form neurospheres in vitro, whereas intracerebroventricular injection of HGF-neutralizing antibodies decreased SVZ cell proliferation. The present study unravels a major role, both in vitro and in vivo, for endogenous HGF in SVZ neural stem cell growth and self-renewal.

Human neural progenitors express functional lysophospholipid receptors that regulate cell growth and morphology

Background

Lysophospholipids regulate the morphology and growth of neurons, neural cell lines, and neural progenitors. A stable human neural progenitor cell line is not currently available in which to study the role of lysophospholipids in human neural development. We recently established a stable, adherent human embryonic stem cell-derived neuroepithelial (hES-NEP) cell line which recapitulates morphological and phenotypic features of neural progenitor cells isolated from fetal tissue. The goal of this study was to determine if hES-NEP cells express functional lysophospholipid receptors, and if activation of these receptors mediates cellular responses critical for neural development.

Results

Our results demonstrate that Lysophosphatidic Acid (LPA) and Sphingosine-1-phosphate (S1P) receptors are functionally expressed in hES-NEP cells and are coupled to multiple cellular signaling pathways. We have shown that transcript levels for S1P1 receptor increased significantly in the transition from embryonic stem cell to hES-NEP. hES-NEP cells express LPA and S1P receptors coupled to G_i/o G-proteins that inhibit adenylyl cyclase and to G_q-like phospholipase C activity. LPA and S1P also induce p44/42 ERK MAP kinase phosphorylation in these cells and stimulate cell proliferation via G_i/o coupled receptors in an Epidermal Growth Factor Receptor (EGFR)- and ERK-dependent pathway. In contrast, LPA and S1P stimulate transient cell rounding and aggregation that is independent of EGFR and ERK, but dependent on the Rho effector p160 ROCK.

Conclusion

Thus, lysophospholipids regulate neural progenitor growth and morphology through distinct mechanisms. These findings establish human ES cell-derived NEP cells as a model system for studying the role of lysophospholipids in neural progenitors.

Fibroblast growth factor-2 and -4 promote the proliferation of bone marrow mesenchymal stem cells by the activation of the PI3K-Akt and ERK1/2 signaling pathways

Bone marrow mesenchymal stem cells (BMMSCs) have the capacity for self-renewal, and differentiation into a variety of cell types. They thus represent an attractive source of material for cell therapy. However, little is known about the mechanisms underlying the proliferation of BMMSCs. The purpose of this study was to identify the factors and signaling pathways involved in the proliferation of stem cell antigen-1(+) (Sca-1(+)) BMMSCs. Among the cytokines and growth factors examined in this study, fibroblast growth factor-2 (FGF-2) and FGF-4 significantly stimulated the proliferation of Sca-1(+) BMMSCs, as determined by bromodeoxyuridine incorporation. PI3K-Akt, ERK1/2, and JAK/STAT3 pathways were investigated after stimulation with FGF-2 or FGF-4 via Western blot analysis. No changes were observed in the total ERK1/2 and Akt; however, the pERK1/2 and pAkt levels were upregulated early within 15 min in the FGF-2- or FGF-4-treated Sca-1(+) BMMSCs. Moreover, the pERK1/2 and pAkt upregulation induced by FGF-2 and -4 were completely abolished by treatment with the MEK1/2 inhibitor, U0126 and the PI3K inhibitor, LY294002. However, no change in pJAK2 or total JAK2 levels was observed in the Sca-1(+) BMMSCs induced by FGF-2 or FGF-4. As a consequence of PI3K-Akt and ERK1/2, the upregulation of c-Jun in the Sca-1(+) BMMSCs, after stimulation with FGF-2 or FGF-4, was observed after 12 and 24 h. Moreover, the activation of c-Jun in FGF-2- and FGF-4-treated Sca-1(+) BMMSCs was significantly reduced by U0126. Taken together, these data suggest that FGF-2 and -4 promote the proliferation of Sca-1(+) BMMSCs by activation of the ERK1/2 and PI3K-Akt signaling pathways.

Stabilized beta-catenin functions through TCF/LEF proteins and the Notch/RBP-Jkappa complex to promote proliferation and suppress differentiation of neural precursor cells

The proliferation and differentiation of neural precursor cells are mutually exclusive during brain development. Despite its importance for precursor cell self renewal, the molecular linkage between these two events has remained unclear. Fibroblast growth factor 2 (FGF2) promotes neural precursor cell proliferation and concurrently inhibits their differentiation, suggesting a cross talk between proliferation and differentiation signaling pathways downstream of the FGF receptor. We demonstrate that FGF2 signaling through phosphatidylinositol 3 kinase activation inactivates glycogen synthase kinase 3beta (GSK3beta) and leads to the accumulation of beta-catenin in a manner different from that in the Wnt canonical pathway. The nuclear accumulated beta-catenin leads to cell proliferation by activating LEF/TCF transcription factors and concurrently inhibits neuronal differentiation by potentiating the Notch1-RBP-Jkappa signaling pathway. beta-Catenin and the Notch1 intracellular domain form a molecular complex with the promoter region of the antineurogenic hes1 gene, allowing its expression. This signaling interplay is especially essential for neural stem cell maintenance, since the misexpression of dominant-active GSK3beta completely inhibits the self renewal of neurosphere-forming stem cells and prompts their neuronal differentiation. Thus, the GSK3beta/beta-catenin signaling axis regulated by FGF and Wnt signals plays a pivotal role in the maintenance of neural stem/precursor cells by linking the cell proliferation to the inhibition of differentiation.

Inhibitors of p38 mitogen-activated protein kinase enhance proliferation of mouse neural stem cells

The p38 mitogen-activated protein kinase (MAPK) is induced in response to environmental stress. Although p38 MAPK has been implicated in diverse cellular processes, including cell proliferation, differentiation, and survival of differentiated cells in the central nervous system (CNS), the expression profile and roles of p38 MAPK in the developing brain remain largely unknown. In the present study, we demonstrate that p38 MAPK is expressed predominantly in nestin-positive cells in the cerebral cortex in embryonic day 10 (E10) brain and that expression of the protein decreases gradually during development. To investigate the roles of p38 MAPK in the embryonic brain, two selective p38 MAPK inhibitors, SB202190 and SB203580, were added to the primary neuronal cultures from E10-E14 brains. After 7 days of exposure to these inhibitors, but not SB202474, a negative analog of SB203580, numerous large neurospheres were present. MAPK inhibitors also selectively increased the growth rate of neural stem cells (NSCs) purified from secondary neurospheres and the number of bromodeoxyuridine-positive NSCs. Thus, p38 MAPK inhibitors are potent stimulators of NSC proliferation, and p38 MAPK may be an intrinsic negative regulator of NSC proliferation during early brain development.

Leptin increases adult hippocampal neurogenesis in vivo and in vitro

Leptin, an adipose-derived hormone, has been implicated in several physiological processes involving the hippocampus. However, the role of leptin in adult hippocampal neurogenesis remains unknown. Here we show that leptin regulates neurogenesis in the dentate gyrus of adult mice as well as in cultured adult hippocampal progenitor cells. Chronic administration of leptin to adult mice increased cell proliferation without significant effects on the differentiation and the survival of newly proliferated cells in the dentate gyrus. The expression of the long form leptin receptor, LepRb, was detected in hippocampal progenitor cells by reverse transcription-PCR and immunohistochemistry. Leptin treatment also increased proliferation of cultured adult hippocampal progenitor cells. Analysis of signal transduction pathways revealed that leptin stimulated phosphorylation of Akt and STAT3 but not ERK1/2. Furthermore, pre-treating the cells with specific inhibitors of Akt or STAT3 attenuated leptin-induced cell proliferation in a dose-dependent manner. Taken together, our results support a role for leptin in adult hippocampal neurogenesis and suggest the involvement of the Akt and STAT3 signaling pathways in mediating the actions of leptin on neurogenesis.

Oxygen glucose deprivation inhibits the growth and ERK phosphorylation of neural progenitor cells in vitro

The neurogenic regions such as subventricular zone of the lateral ventricles could become ischemic in some clinical situations due to the blockage of blood vessels by blood clots. Hence the aim of this study is to investigate the effects of OGD on the growth of neural progenitor cells and the phosphorylation of ERK, which plays an important role in the growth of these cells. Oxygen glucose deprivation (OGD) for 4h decreased the growth of neural progenitor cells in vitro and also decreased the phosphorylation of extracellular signal regulated kinase (ERK). Inhibition of the ERK pathway for 4h using U0126 (10 microM) also decreased the growth of progenitor cells. These data suggest that a decline in the phospho-ERK content might decrease the growth of progenitor cells following OGD.

Mechanism of insulin-like growth factor I-mediated proliferation of adult neural progenitor cells: role of Akt

Insulin-like growth factor I (IGF-I) is involved in the proliferation and differentiation of adult neural progenitor cells; however, the underlying mechanism is not clear. We analysed the involvement of the phosphatidylinositol 3-kinase/Akt and MEK/extracellular signal-regulated kinase (ERK) pathways in the IGF-I-mediated proliferation of rat neural progenitor cells. Stimulation of neural progenitor cells with IGF-I enhanced the phosphorylation of Akt but not ERK. Cell proliferation assay demonstrated that 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (phosphoinositide 3-kinase inhibitor) but not 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)-butadiene (U0126) (ERK inhibitor) inhibited the IGF-I-induced survival of cells, whereas fibroblast growth factor 2 (FGF-2) enhanced the IGF-I-mediated survival of cells. Consistent with the cell proliferation assay, 5'bromo-2-deoxy-uridine incorporation studies established a negative role for IGF-I in proliferation. However, FGF-2 (ERK activator) in the presence of IGF-I (Akt activator) increased the proliferation of cells. Accordingly, stimulation of the ERK pathway by FGF-2 induced the expression of cyclin D1, which is essential for the entry of cells into cell cycle, and IGF-I in the presence of FGF-2 up-regulated the expression of cyclin D1. IGF-I in the absence or presence of FGF-2 increased the phosphorylation of glycogen synthase kinase, thus supporting its role in the survival of neural progenitor cells. To further confirm the role of ERK activation in the proliferation, we cultured cells in FGF-2 + IGF-I-containing medium in the presence and absence of U0126 (ERK inhibitor), and showed the inhibition of nestin expression in U0126-treated cells. The decrease in the cyclin D1 content in conjunction with the inhibition of nestin expression by ERK inhibitor confirms the role of ERK in the proliferation of cells.

Caspase inhibition increases survival of neural stem cells in the gastrointestinal tract

Neural stem cell (NSC) transplantation is a promising tool for the restoration of the enteric nervous system in a variety of motility disorders. Post-transplant survival represents a critical limiting factor for successful repopulation. The aim of this study was to determine the role of both immunological as well as non-immune-mediated mechanisms on post-transplant survival of NSC in the gut. Mouse CNS-derived NSC (CNS-NSC) were transplanted into the pylorus of recipient mice with and without the addition of a caspase-1 inhibitor (Ac-YVAD-cmk) in the injection media. In a separate experiment, CNS-NSC were transplanted in the pylorus of mice that were immunosuppressed by administration of cyclosporin A (CsA). Apoptosis and proliferation of the implanted cells was assessed 1 and 7 days post-transplantation. Survival was assessed 1 week post-transplantation. The degree of immunoresponse was also measured. The addition of a caspase-1 inhibitor significantly reduced apoptosis, increased proliferation and enhanced survival of CNS-NSC. CsA-treatment did not result in improved survival. Our results indicate that caspase-1 inhibition, but not immunosuppression, improves survival of CNS-NSC in the gut. Pre-treatment with a caspase-1 inhibitor may be a practical method to enhance the ability of transplanted CNS-NSC to survive in their new environment.

NT3 inhibits FGF2-induced neural progenitor cell proliferation via the PI3K/GSK3 pathway

Neurotrophin 3 (NT3), a member of the neurotrophin family, antagonizes the proliferative effect of fibroblast growth factor 2 (FGF2) on cortical precursors. However, the mechanism by which NT3 inhibits FGF2-induced neural progenitor (NP) cell proliferation is unclear. Here, using an FGF2-dependent rat neurosphere culture system, we found that NT3 inhibits both FGF2-induced neurosphere growth and bromodeoxyuridine (BrdU) incorporation in a dose-dependent manner. U0126, a mitogen-activated protein kinase kinase 1/2 (MEK1/2) inhibitor, and LY294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor, both inhibited FGF2-induced BrdU incorporation, suggesting that the extracellular signal-regulated kinase1/2 (ERK1/2) and PI3K pathways are required for FGF2-induced NP cell proliferation. NT3 significantly inhibited FGF2-induced phosphorylation of Akt and glycogen synthase kinase 3beta (GSK3beta), a downstream kinase of Akt, whereas phosphorylation of ERK1/2 was unaffected. The inhibitory effect of NT3 on FGF2-induced NP cell proliferation was abolished by LY294002, and treatment with SB216763, a specific GSK3 inhibitor, antagonized the NT3 effect, rescuing both neurosphere growth and BrdU incorporation. Moreover, experiments with anti-NT3 antibody revealed that endogenous NT3 also plays a role in inhibiting FGF2-induced NP cell proliferation, and that anti-NT3 antibody enhanced phospho-Akt and phospho-GSK3beta levels in the presence of FGF2. These findings indicate that FGF2-induced NP cell proliferation is inhibited by NT3 via the PI3K/GSK3 pathway.

Glutamate and Regulation of Proliferation in the Developing Mammalian Telencephalon

Increasing evidence suggests that classical neurotransmitters play an important morphogenetic role during development of the mammalian central nervous system. Using in vitro and in vivo models, we have previously identified a role for the N-methyl-D-aspartate (NMDA) subclass of glutamate receptors in the proliferation of striatal progenitors. Here, we compare the roles of ionotropic glutamate receptors in the proliferation of either striatal or cortical progenitors. In culture, glutamate receptor activation promoted proliferation of both striatal and cortical neuroblasts. However, cortical and striatal neuroblasts responded to distinct ionotropic receptors. Cortical cultures were sensitive to AMPA/KA receptor blockade, whereas striatal neuroblast proliferation was altered by NMDA antagonists. In vivo, BrdU uptake in the proliferative ventricular zone was reduced in embryos following acute administration of ionotropic glutamate receptor antagonists. In keeping with in vitro observations, proliferation in cortical and striatal ventricular regions was reduced, respectively, by either AMPA/KA or NMDA receptor blockade. We also determined whether forebrain-derived progenitors expanded as neurospheres in the presence of growth factors show similar ionotropic glutamatergic responses. Cells in neither dorsal nor ventral telencephalon-derived neurospheres showed altered proliferation following exposure to either class of ionotropic glutamate receptor antagonist. Together, these findings suggest that glutamate influences the proliferation of forebrain neuronal progenitors, but not more primitive populations represented in multipotential progenitors expanded in vitro. The effects on neuroblast proliferation in different forebrain domains are heterogeneous and are mediated by distinct subclasses of ionotropic glutamate receptors.

LIF receptor signaling modulates neural stem cell renewal

Activation of the leukemia inhibitory factor (LIF) receptor has been reported to promote gliogenesis and also to support neural stem cell (NSC) renewal. To investigate this paradox, we isolated NSCs and generated neurospheres from embryonic mice either wild-type, heterozygous, or homozygous null for LIF receptor (LIFR)-beta. Exogenous LIF abrogated neurosphere formation and promoted expression of GFAP by all cells in wild-type and heterozygous cultures. LIF also stimulated a twofold increase in the number of multipotential clones generated from these cultures in comparison with those pretreated with EGF and FGF-2 (E+F) alone. In contrast, the clonogenicity of low-density cultures of LIFR knockout cells was reduced in comparison with that of wild-type cells grown in E+F and was unaffected by LIF. Thus, although LIFR signaling is not necessary for NSC self-renewal, it enhances both the clonogenicity and the expression of GFAP by these multipotential cells.

Defective adult neurogenesis in CB1 cannabinoid receptor knockout mice

Pharmacological studies suggest a role for CB1 cannabinoid receptors (CB1R) in regulating neurogenesis in the adult brain. To investigate this possibility, we measured neurogenesis by intraperitoneal injection of bromodeoxyuridine (BrdU), which labels newborn neurons, in wild-type and CB1R-knockout (CB1R-KO) mice. CB1R-KO mice showed reductions in the number of BrdU-labeled cells to approximately 50% of wild-type (WT) levels in dentate gyrus and subventricular zone (SVZ), suggesting that CB1R activation promotes neurogenesis. To test this further, WT mice were given the CB1R antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboximide hydrochloride (SR141716A) before measuring neurogenesis with BrdU. SR141716A paradoxically increased the number of BrdU-labeled cells by approximately 50% in SVZ; another CB1R antagonist, 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-1-piperidinyl-1H-pyrazole-3-carboxamide (AM251), had a similar effect. To investigate this discrepancy, SR141716A was given to CB1R-KO mice, in which it still stimulated neurogenesis, indicating involvement of a non-CB1 receptor. Action at one such non-CB1, SR141716A-sensitive site, the VR1 vanilloid receptor, was tested by administering SR141716A to VR1-KO mice, in which the ability of SR141716A to enhance neurogenesis was abolished. Thus, CB1 and VR1 receptors both seem to have roles in regulating adult neurogenesis.

Beta1 integrins activate a MAPK signalling pathway in neural stem cells that contributes to their maintenance

The emerging evidence that stem cells develop in specialised niches highlights the potential role of environmental factors in their regulation. Here we examine the role of beta1 integrin/extracellular matrix interactions in neural stem cells. We find high levels of beta1 integrin expression in the stem-cell containing regions of the embryonic CNS, with associated expression of the laminin alpha2 chain. Expression levels of laminin alpha2 are reduced in the postnatal CNS, but a population of cells expressing high levels of beta1 remains. Using neurospheres - aggregate cultures, derived from single stem cells, that have a three-dimensional architecture that results in the localisation of the stem cell population around the edge of the sphere - we show directly that beta1 integrins are expressed at high levels on neural stem cells and can be used for their selection. MAPK, but not PI3K, signalling is required for neural stem cell maintenance, as assessed by neurosphere formation, and inhibition or genetic ablation of beta1 integrin using cre/lox technology reduces the level of MAPK activity. We conclude that integrins are therefore an important part of the signalling mechanisms that control neural stem cell behaviour in specific areas of the CNS.

Chemokines promote quiescence and survival of human neural progenitor cells

Many cell types in the brain express chemokines and chemokine receptors under homeostatic conditions, arguing for a role of these proteins in normal brain processes. Because chemokines have been shown to regulate hematopoietic progenitor cell proliferation, we hypothesized that chemokines would regulate neural progenitor cell (NPC) proliferation as well. Here we show that chemokines activating CXCR4 or CCR3 reversibly inhibit NPC proliferation in isolated cells, neurospheres, and in hippocampal slice cultures. Cells induced into quiescence by chemokines maintain their multipotential ability to form both neurons and astrocytes. The mechanism of chemokine action appears to be a reduction of extracellular signal-related kinase phosphorylation as well as an increase in Reelin expression. The inhibitory effects of chemokines are blocked by heparan sulfate and apolipoprotein E3 but not apolipoprotein E4, suggesting a regulatory role of these molecules on the effects of chemokines. Additionally, we found that the chemokine fractalkine promotes survival of NPCs. In addition to their role in chemotaxis, chemokines affect both the survival and proliferation of human NPCs in vitro. The presence of constitutively expressed chemokines in the brain argues that under homeostatic conditions, chemokines promote survival but maintain NPCs in a quiescent state. Our studies also suggest a link between inflammatory chemokine production and the inhibition of neurogenesis.

Gap junctional communication is required to maintain mouse cortical neural progenitor cells in a proliferative state

The mechanisms that determine whether neural stem cells remain in a proliferative state or differentiate into neurons or glia are largely unknown. Here we establish a pivotal role for gap junction-mediated intercellular communication in determining the proliferation and survival of mouse neural progenitor cells (NPCs). When cultured in the presence of basic fibroblast growth factor (bFGF), NPCs express the gap junction protein connexin 43 and are dye-coupled. Upon withdrawal of bFGF, levels of connexin 43 and dye coupling decrease, and the cells cease proliferating and differentiate into neurons; the induction of gap junctions by bFGF is mediated by p42/p44 mitogen-activated protein kinases. Inhibition of gap junctions abolishes the ability of bFGF to maintain NPCs in a proliferative state resulting in cell differentiation or cell death, while overexpression of connexin 43 promotes NPC self-renewal in the absence of bFGF. In addition to promoting their proliferation, gap junctions are required for the survival of NPCs. Gap junctional communication is therefore both necessary and sufficient to maintain NPCs in a self-renewing state.

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 neuregulinbeta1 (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 PLCgamma1 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.