Stem cells in neurodevelopment and plasticity

Identification of novel NRF2-dependent genes as regulators of lead and arsenic toxicity in neural progenitor cells

Lead (Pb) and arsenic (As) are prevalent metal contaminants in the environment. Exposures to these metals are associated with impaired neuronal functions and adverse effects on neurodevelopment in children. However, the molecular mechanisms by which Pb and As impair neuronal functions remain poorly understood. Here, we identified F2RL2, TRIM16L, and PANX2 as novel targets of Nuclear factor erythroid 2-related factor 2 (NRF2)-the master transcriptional factor for the oxidative stress response-that are commonly upregulated with both Pb and As in human neural progenitor cells (NPCs). Using a ChIP (Chromatin immunoprecipitation)-qPCR assay, we showed that NRF2 directly binds to the promoter region of F2RL2, TRIM16L, and PANX2 to regulate expression of these genes. We demonstrated that F2RL2, PANX2, and TRIM16L have differential effects on cell death, proliferation, and differentiation of NPCs in both the presence and absence of metal exposures, highlighting their roles in regulating NPC function. Furthermore, the analyses of the transcriptomic data on NPCs derived from autism spectrum disorder (ASD) patients revealed that dysregulation of F2RL2, TRIM16L, and PANX2 was associated with ASD genetic backgrounds and ASD risk genes. Our findings revealed that Pb and As induce a shared NRF2-dependent transcriptional response in NPCs and identified novel genes regulating NPC function. While further in vivo studies are warranted, this study provides a novel mechanism linking metal exposures to NPC function and identifies potential genes of interest in the context of neurodevelopment.

Gold and silver nanoparticles in Alzheimer's and Parkinson's diagnostics and treatments

Neurodegenerative diseases (NDs) impose substantial medical and public health burdens on people worldwide and represent one of the major threats to human health. The prevalence of these age-dependent disorders is dramatically increasing over time, a process intrinsically related to a constantly rising percentage of the elderly population in recent years. Among all the NDs, Alzheimer's and Parkinson's are considered the most debilitating as they cause memory and cognitive loss, as well as severely affecting basic physiological conditions such as the ability to move, speak, and breathe. There is an extreme need for new and more effective therapies to counteract these devastating diseases, as the available treatments are only able to slow down the pathogenic process without really stopping or resolving it. This review aims to elucidate the current nanotechnology-based tools representing a future hope for NDs treatment. Noble metal nano-systems, that is, gold and silver nanoparticles (NPs), have indeed unique physicochemical characteristics enabling them to deliver any pharmacological treatment in a more effective way within the central nervous system. This can potentially make NPs a new hope for reversing the actual therapeutic strategy based on slowing down an irreversible process into a more effective and permanent treatment.

Self-Assembling Hydrogel Structures for Neural Tissue Repair

Hydrogel materials have been employed as biological scaffolds for tissue regeneration across a wide range of applications. Their versatility and biomimetic properties make them an optimal choice for treating the complex and delicate milieu of neural tissue damage. Aside from finely tailored hydrogel properties, which aim to mimic healthy physiological tissue, a minimally invasive delivery method is essential to prevent off-target and surgery-related complications. The specific class of injectable hydrogels termed self-assembling peptides (SAPs), provide an ideal combination of in situ polymerization combined with versatility for biofunctionlization, tunable physicochemical properties, and high cytocompatibility. This review identifies design criteria for neural scaffolds based upon key cellular interactions with the neural extracellular matrix (ECM), with emphasis on aspects that are reproducible in a biomaterial environment. Examples of the most recent SAPs and modification methods are presented, with a focus on biological, mechanical, and topographical cues. Furthermore, SAP electrical properties and methods to provide appropriate electrical and electrochemical cues are widely discussed, in light of the endogenous electrical activity of neural tissue as well as the clinical effectiveness of stimulation treatments. Recent applications of SAP materials in neural repair and electrical stimulation therapies are highlighted, identifying research gaps in the field of hydrogels for neural regeneration.

The role of fibroblast growth factors and their receptors in gliomas: the mutations involved

The central nervous system (CNS) comprises of neurons, which are responsible for impulse transmission, and glial cells, which surround neurons providing protection and nutrition. Glial cells are categorized into astrocytes, oligodendrocytes, microglial cells, and ependymal cells. Tumors forming from glial cells are called gliomas, and they are classified accordingly into astrocytomas, oligodendrogliomas, and ependymomas. Gliomas are characterized by high mortality rates and degree of malignancy, heterogeneity, and resistance to treatment. Among the molecular players implicated in glioma pathogenesis are members of the fibroblast growth factor (FGF) superfamily as well as their receptors (FGFRs). In the present study, we provide a review of the literature on the role of FGFs and FGFRs in glioma pathogenesis. We also demonstrate that FGFs, and particularly FGF1 and FGF2, bear a variety of mutations in gliomas, while FGFRs are also crucially involved. In fact, several studies show that in gliomas, FGFRs bear mutations, mainly in the tyrosine kinase domains. Specifically, it appears that FGFR1-TACC1 and FGFR3-TACC3 fusions are common in these receptors. A better understanding of the mutations and the molecular players involved in glioma formation will benefit the scientific community, leading to the development of more effective and innovative therapeutic approaches.

Olive oil-enriched diet reduces brain oxidative damages and ameliorates neurotrophic factor gene expression in different life stages of rats

Our aim was to assess the influence of maternal diet rich in monounsaturated fatty acids on oxidative and molecular parameters in brains of mouse pups as well as their body weight during their lifetime. Female rats received a diet containing 20% of olive oil-enriched diet (OOED) and a standard diet control diet (CD) in different periods: pregnancy, lactation and after weaning until pups' adulthood. On the last prenatal day (Group 1), embryos from OOED group showed smaller body weight, brain weight and lower levels of sulphydryl groups glutathione reduced (GSH) in the brain. On postnatal delay-21 (PND21) (Group 2), pups from OOED group showed higher body weight and brain weight, reduced brain weight/body weight ratio and lower brain lipid peroxidation (LP). On PND70 (Group 3), pups from OOED group showed lower brain LP and higher levels of GSH in prefrontal cortex and lower brain levels of reactive species in the hippocampus. Interestingly, the group of animals whose diet was modified from OOED to CD on PND21 showed greater weight gain compared to the group that remained in the same original diet (OOED) until adulthood. Furthermore, OOED consumption during pregnancy and lactation significantly increased BDNF only, as well as its main transcripts exon IV and VI mRNA levels in the prefrontal cortex. In addition, OOED significantly up-regulated FGF-2 mRNA levels in the prefrontal cortex. These findings open a pioneering line of investigation about dietary adjunctive therapeutic strategies and the potential of healthy dietary habits to prevent neonatal conditions and their influence on adulthood.

Convergent regulation of neuronal differentiation and Erk and Akt kinases in human neural progenitor cells by lysophosphatidic acid, sphingosine 1-phosphate, and LIF: specific roles for the LPA1 receptor

The bioactive lysophospholipids lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) have diverse effects on the developing nervous system and neural progenitors, but the molecular basis for their pleiotropic effects is poorly understood. We previously defined LPA and S1P signaling in proliferating human neural progenitor (hNP) cells, and the current study investigates their role in neuronal differentiation of these cells. Differentiation in the presence of LPA or S1P significantly enhanced cell survival and decreased expression of neuronal markers. Further, the LPA receptor antagonist Ki16425 fully blocked the effects of LPA, and differentiation in the presence of Ki16425 dramatically enhanced neurite length. LPA and S1P robustly activated Erk, but surprisingly both strongly suppressed Akt activation. Ki16425 and pertussis toxin blocked LPA activation of Erk but not LPA inhibition of Akt, suggesting distinct receptor and G-protein subtypes mediate these effects. Finally, we explored cross talk between lysophospholipid signaling and the cytokine leukemia inhibitory factor (LIF). LPA/S1P effects on neuronal differentiation were amplified in the presence of LIF. Similarly, the ability of LPA/S1P to regulate Erk and Akt was impacted by the presence of LIF; LIF enhanced the inhibitory effect of LPA/S1P on Akt phosphorylation, while LIF blunted the activation of Erk by LPA/S1P. Taken together, our results suggest that LPA and S1P enhance survival and inhibit neuronal differentiation of hNP cells, and LPA1 is critical for the effect of LPA. The pleiotropic effects of LPA may reflect differences in receptor subtype expression or cross talk with LIF receptor signaling.

Neurobiology meets genomic science: the promise of human-induced pluripotent stem cells

The recent introduction of the induced pluripotent stem cell technology has made possible the derivation of neuronal cells from somatic cells obtained from human individuals. This in turn has opened new areas of investigation that can potentially bridge the gap between neuroscience and psychopathology. For the first time we can study the cell biology and genetics of neurons derived from any individual. Furthermore, by recapitulating in vitro the developmental steps whereby stem cells give rise to neuronal cells, we can now hope to understand factors that control typical and atypical development. We can begin to explore how human genes and their variants are transcribed into messenger RNAs within developing neurons and how these gene transcripts control the biology of developing cells. Thus, human-induced pluripotent stem cells have the potential to uncover not only what aspects of development are uniquely human but also variations in the series of events necessary for normal human brain development that predispose to psychopathology.

Mcl-1 regulates the survival of adult neural precursor cells

Since the discovery of neural precursor cells (NPCs) in the adult mammalian brain, there has been a lot of excitement surrounding the potential for regeneration in the adult brain. For instance, many studies have shown that a significant number of NPCs will migrate to a site of injury and differentiate into all of the neural lineages. However, one of the main challenges affecting endogenous neural regeneration is that many of the NPCs that migrate to the injury site ultimately undergo apoptosis. Therefore, we sought to determine whether myeloid cell leukemia-1 (Mcl-1), an anti-apoptotic Bcl-2 protein, would promote the survival of adult NPCs by impeding apoptosis. To do this, we first confirmed that Mcl-1 is endogenously expressed within the adult NPC population using BrdU labeling assays. Next, we conditionally deleted Mcl-1 in adult NPCs using cre/lox technology and expressed Cre from the NPC-specific promoter Nestin. In vitro, cells that had Mcl-1 conditionally deleted had a 2-fold increase in apoptosis when compared to controls. In vivo, we used electroporation to conditionally delete Mcl-1 in adult NPCs and assessed apoptosis at 72h. after electroporation. As in our in vitro results, there was a 2-fold increase in apoptosis when Mcl-1 was conditionally deleted. Finally, we found that Mcl-1 over-expression reduced the endogenous rate of adult NPC apoptosis 2-fold in vitro. Collectively, these results demonstrate that Mcl-1 is crucial for the survival of adult NPCs and may be a promising target for future neural regeneration therapies.

Annual Research Review: The promise of stem cell research for neuropsychiatric disorders

The study of the developing brain has begun to shed light on the underpinnings of both early and adult onset neuropsychiatric disorders. Neuroimaging of the human brain across developmental time points and the use of model animal systems have combined to reveal brain systems and gene products that may play a role in autism spectrum disorders, attention deficit hyperactivity disorder, obsessive compulsive disorder and many other neurodevelopmental conditions. However, precisely how genes may function in human brain development and how they interact with each other leading to psychiatric disorders is unknown. Because of an increasing understanding of neural stem cells and how the nervous system subsequently develops from these cells, we have now the ability to study disorders of the nervous system in a new way - by rewinding and reviewing the development of human neural cells. Induced pluripotent stem cells (iPSCs), developed from mature somatic cells, have allowed the development of specific cells in patients to be observed in real time. Moreover, they have allowed some neuronal-specific abnormalities to be corrected with pharmacological intervention in tissue culture. These exciting advances based on the use of iPSCs hold great promise for understanding, diagnosing and, possibly, treating psychiatric disorders. Specifically, examination of iPSCs from typically developing individuals will reveal how basic cellular processes and genetic differences contribute to individually unique nervous systems. Moreover, by comparing iPSCs from typically developing individuals and patients, differences at stem cell stages, through neural differentiation, and into the development of functional neurons may be identified that will reveal opportunities for intervention. The application of such techniques to early onset neuropsychiatric disorders is still on the horizon but has become a reality of current research efforts as a consequence of the revelations of many years of basic developmental neurobiological science.

Fgfr2 is required for the development of the medial prefrontal cortex and its connections with limbic circuits

To understand the role of specific fibroblast growth factor receptors (FGFRs) in cortical development, we conditionally inactivated Fgfr2 or both Fgfr1 and Fgfr2 [Fgfr2 conditional knock-out (cKO) or double knock-out mice, respectively] in radial glial cells of the dorsal telencephalon. Fgfr1 and Fgfr2 are necessary for the attainment of a normal number of excitatory neurons in the cerebral cortex. The action of FGF receptors appears to be through increasing self-renewal of neuronal precursors within the ventricular zone. Volume measurements, assessments of excitatory neuron number, and areal marker expression suggested that the proper formation of the medial prefrontal cortex (mPFC) depends on the function of Fgfr2, whereas Fgfr1 together with Fgfr2 control excitatory cortical neuron development within the entire cerebral cortex. Fgfr2 cKO mice had fewer and smaller glutamate synaptic terminals in the bed nuclei of the stria terminalis (BST), a projection area for mPFC cortical neurons. Furthermore, Fgfr2 cKO mice showed secondary decreases in GABAergic neurons in the BST and septum. These data demonstrate that FGFR2 signaling expands the number of excitatory neurons in the mPFC and secondarily influences target neurons in subcortical stations of the limbic system.

Selective regulation of growth factor expression in cultured cortical astrocytes by neuro-pathological toxins

Astrocytes are integrated in the complex regulation of neurodegeneration and neuronal damage in the CNS. It is well-known that astroglia produces a plethora of growth factors which might be protective for neurons. Growth factors prevent neurons from cell death and promote proliferation and differentiation of precursor cells. Previous data suggest that astrocytes may respond to toxic stimuli by a selective mobilization of guarding molecules. In the present study, we have investigated the potency of different pathological stimuli such as lipopolysaccharides, tumor necrosis factor alpha, glutamate, and hydrogen peroxide to activate cultured cortical astroglia and stimulate growth factor expression. Astroglial cultures were exposed to the above factors for 24h at non-toxic concentrations for astrocytes. Growth factor expression was analyzed by real-time PCR, oligo-microarray technique, and ELISA. Insulin-like growth factor-1 was selectively down-regulated by lipopolysaccharides and tumor necrosis factor alpha, bone morphogenetic protein 6 by all stimuli. In contrast, lipopolysaccharides, tumor necrosis factor alpha, and glutamate increased leukemia inhibitory factor. Fibroblast growth factor 2 was up-regulated by lipopolysaccharides and tumor necrosis factor alpha and down-regulated by hydrogen peroxide. Besides hydrogen peroxide, all other stimuli promoted vascular epithelial growth factor A mRNA and protein expression. It appears that lipopolysaccharides but not tumor necrosis factor alpha effects on vascular epithelial growth factor A depend on the classic NFkappaB pathway. Our data clearly demonstrate that astroglia actively responses to diverse pathological compounds by a selective expression pattern of growth factors. These findings make astrocytes likely candidates to participate in disease-specific characteristics of neuronal support or damage.

Fgfr1 is required for cortical regeneration and repair after perinatal hypoxia

Chronic postnatal hypoxia causes an apparent loss of cortical neurons that is reversed during recovery (Fagel et al., 2006). The cellular and molecular mechanisms underlying this plasticity are not understood. Here, we show that chronic hypoxia from postnatal days 3 (P3) to 10 causes a 30% decrease in cortical neurons and a 24% decrease in cortical volume. T-brain-1 (Tbr1)(+) and SMI-32(+) excitatory neuron numbers were completely recovered 1 month after the insult, but the mice showed a residual deficit in Parvalbumin(+) and Calretinin(+) GABAergic interneurons. In contrast, hypoxic mice carrying a disrupted fibroblast growth factor receptor-1 (Fgfr1) gene in GFAP+ cells [Fgfr1 conditional knock-out (cKO)], demonstrated a persistent loss of excitatory cortical neurons and a worsening of the interneuron defect. Labeling proliferating progenitors at P17 revealed increased generation of cortical NeuN(+) and Tbr1(+) excitatory neurons in wild-type mice subjected to hypoxic insult, whereas Fgfr1 cKO failed to mount a cortical neurogenetic response. Hypoxic wild-type mice also demonstrated a twofold increase in cell proliferation in the subventricular zone (SVZ) at P17 and a threefold increase in neurogenesis in the olfactory bulb (OB) at P48, compared with normoxic mice. In contrast, Fgfr1 cKO mice had decreased SVZ cell proliferation and curtailed reactive neurogenesis in the OB. Thus, the activation of FGFR-1 in GFAP+ cells is required for neuronal recovery after neonatal hypoxic injury, which is attributable in part to enhanced cortical and OB neurogenesis. In contrast, there is incomplete recovery of inhibitory neurons after injury, which may account for persistent behavioral deficits.

Short-term withdrawal of mitogens prior to plating increases neuronal differentiation of human neural precursor cells

Background

Human neural precursor cells (hNPC) are candidates for neural transplantation in a wide range of neurological disorders. Recently, much work has been done to determine how the environment for NPC culture in vitro may alter their plasticity. Epidermal growth factor (EGF) and fibroblast growth factor-2 (FGF-2) are used to expand NPC; however, it is not clear if continuous exposure to mitogens may abrogate their subsequent differentiation. Here we evaluated if short-term removal of FGF-2 and EGF prior to plating may improve hNPC differentiation into neurons.

Principal Findings

We demonstrate that culture of neurospheres in suspension for 2 weeks without EGF-FGF-2 significantly increases neuronal differentiation and neurite extension when compared to cells cultured using standard protocols. In this condition, neurons were preferentially located in the core of the neurospheres instead of the shell. Moreover, after plating, neurons presented radial rather than randomly oriented and longer processes than controls, comprised mostly by neurons with short processes. These changes were followed by alterations in the expression of genes related to cell survival.

Conclusions

These results show that EGF and FGF-2 removal affects NPC fate and plasticity. Taking into account that a three dimensional structure is essential for NPC differentiation, here we evaluated, for the first time, the effects of growth factors removal in whole neurospheres rather than in plated cell culture.

Production, characterization, and efficient transfection of highly pure oligodendrocyte precursor cultures from mouse embryonic neural progenitors

Much current knowledge of oligodendrocyte biology, the myelin-forming cells in the central nervous system, comes from cell culture studies mainly from postnatal rat tissue but mouse cells have been much more difficult to produce in large quantities. We have developed a high yield protocol for production of oligodendrocyte precursor cells from mouse embryonic neural progenitors grown as neurospheres. Neurospheres can be maintained and expanded for long periods in culture in the presence of epidermal growth factor (EGF). When floating neurospheres were plated on substrate-coated dishes in media supplemented with platelet derived growth factor (PDGF) and basic fibroblast growth factor (bFGF), the spheres attached and generated migrating cells that were predominantly oligodendrocyte-lineage cells. Furthermore, cells in spheres could be shifted to the oligodendrocyte phenotype prior to plating on substrate, by incubation in suspension with PDGF/bFGF. Single cell suspensions plated after dissociation of either EGF-treated neurospheres or PDGF/bFGF-treated oligospheres had the bipolar, elongated morphology characteristic of oligodendrocyte precursor cells. mRNA and protein expression analysis of the cells generated by this method confirmed their oligodendrocyte lineage. Oligodendrocyte precursors generated by this method matured in response to ciliary neurotrophic factor treatment, producing cells with multiple processes and myelin-like membranes. The most important aspect of this protocol is the ability to generate very high numbers of relatively pure mouse oligodendrocyte progenitor cells, which can be easily transfected. These studies open up many kinds of investigations on transgenic and mutant mouse oligodendrocytes, thereby providing a valuable tool to study oligodendrocyte biology and development.

Deletion of lysophosphatidic acid receptor LPA1 reduces neurogenesis in the mouse dentate gyrus

Neurogenesis persists in certain regions of the adult brain including the subgranular zone of the hippocampal dentate gyrus wherein its regulation is essential, particularly in relation to learning, stress and modulation of mood. Lysophosphatidic acid (LPA) is an extracellular signaling phospholipid with important neural regulatory properties mediated by specific G protein-coupled receptors, LPA(1-5). LPA(1) is highly expressed in the developing neurogenic ventricular zone wherein it is required for normal embryonic neurogenesis, and, by extension may play a role in adult neurogenesis as well. By means of the analyses of a variant of the original LPA(1)-null mutant mouse, termed the Malaga variant or "maLPA(1)-null," which has recently been reported to have defective neurogenesis within the embryonic cerebral cortex, we report here a role for LPA(1) in adult hippocampal neurogenesis. Proliferation, differentiation and survival of newly formed neurons are defective in the absence of LPA(1) under normal conditions and following exposure to enriched environment and voluntary exercise. Furthermore, analysis of trophic factors in maLPA(1)-null mice demonstrated alterations in brain-derived neurotrophic factor and insulin growth factor 1 levels after enrichment and exercise. Morphological analyses of doublecortin positive cells revealed the anomalous prevalence of bipolar cells in the subgranular zone, supporting the operation of LPA(1) signaling pathways in normal proliferation, maturation and differentiation of neuronal precursors.

Injury and recovery in the developing brain: evidence from functional MRI studies of prematurely born children

Functional MRI (fMRI) might provide important insights into emerging data that suggest that recovery from injury can occur in the brains of children born prematurely. Strategies employing auditory stimulation demonstrate blood-oxygen-level-dependent (BOLD) activation in preterm infants as young as 33 weeks' gestational age, and reliable BOLD signal in response to visual stimulation occurs at term-equivalent age. Strategies based on fMRI are particularly suited to the study of language and memory, and emerging data are likely to provide insights into perplexing reports that have demonstrated improving cognitive scores but persistent volumetric and microstructural changes in frontotemporal language systems in the prematurely born. Even when sex, gestational age and early medical and environmental interventions are taken into account, fMRI data from several investigators suggest the engagement of alternative neural networks for language and memory in the developing preterm brain.

The neural progenitor-specifying activity of FoxG1 is antagonistically regulated by CKI and FGF

FoxG1 is an evolutionarily conserved, winged-helix transcriptional repressor that maintains progenitor cells in the vertebrate forebrain. How the activity of FoxG1 is regulated is not known. Here, we report that in the developing Xenopus and mouse forebrain, FoxG1 is nuclear in progenitor cells but cytoplasmic in differentiating cells. The subcellular localisation of FoxG1 is regulated at the post-translational level by casein kinase I (CKI) and fibroblast growth factor (FGF) signalling. CKI phosphorylation of Ser 19 of FoxG1 promotes nuclear import, whereas FGF-induced phosphorylation of Thr 226 promotes nuclear export. Interestingly, FGF-induced phosphorylation of FoxG1 is mediated Akt kinase (also known as protein B kinase, PKB) kinase, rather than the MAPK pathway. Phosphorylation of endogenous FoxG1 is blocked by CKI and Akt inhibitors. In the mouse olfactory placode cell line OP27, and in cortical progenitors, increased FGF signalling causes FoxG1 to exit the nucleus and promotes neuronal differentiation, whereas FGF and Akt inhibitors block this effect. Thus, CKI and FGF signalling converge on an antagonistic regulation of FoxG1, which in turn controls neurogenesis in the forebrain.

Interferon-gamma promotes differentiation of neural progenitor cells via the JNK pathway

It has been reported that interferon-gamma (IFN-gamma) facilitates differentiation of PC-12 cells and murine adult neural stem cells. Here we show that IFN-gamma promotes the differentiation of C17.2 neural progenitor cells (NPC) into a neuronal phenotype characterized by neurite outgrowth and the expression of the neuronal marker protein beta-III tubulin. IFN-gamma induced an increase in the activity c-jun N-terminal kinase (JNK) without affecting activities of extracellular signal-regulated kinases (ERKs 1 and 2). An inhibitor of JNK blocked the ability of IFN-gamma to promote differentiation of NPC into neurons, whereas an inhibitor of ERKs 1 and 2 did not. Our findings show that the pro-inflammatory cytokine, IFN-gamma has the potential to stimulate neurogenesis, suggesting roles for this cytokine in development and repair of the nervous system.

Secreted factors from ventral telencephalon induce the differentiation of GABAergic neurons in cortical cultures

It is widely believed that the pyramidal cells and interneurons of the cerebral cortex are distinct in their origin, lineage and genetic make up. In view of these findings, the current thesis is that the phenotype determination of cortical neurons is primarily directed by genetic mechanisms. Using in vitro assays, the present study demonstrates that secreted factors from ganglionic eminence (GE) of the ventral telencephalon have the potency to induce the differentiation of a subset of cortical neurons towards gamma-aminobutyric acid (GABA)ergic lineage. Characterization of cortical cultures that were exposed to medium derived from GE illustrated a significant increase in the number of GABA-, calretinin- and calbindin-positive neurons. Calcium imaging together with pharmacological studies showed that the application of exogenous medium significantly elevated the intracellular calcium transients in cortical neurons through the activation of ionotropic glutamate receptors. The increase in GABA+ neurons appeared to be associated with the elevated calcium activity; treatment with blockers specific for glutamate receptors abolished both the synchronized transients and reduced the differentiation of GABAergic neurons. Such studies demonstrate that although intrinsic mechanisms determine the fate of cortical interneurons, extrinsic factors have the potency to influence their neurochemical differentiation and contribute towards their molecular diversity.

Plasticity of 5‐HT1Areceptor‐mediated signaling during early postnatal brain development

The presence of serotonin 1A receptor (5-HT(1A)-R) in the hippocampus, amygdala, and most regions of the frontal cortex is essential between postnatal day-5-21 (P5-21) for the expression of normal anxiety levels in adult mice. Thus, the 5-HT(1A)-R plays a crucial role in this time window of brain development. We show that the 5-HT(1A)-R-mediated stimulation of extracellular signal-regulated kinases 1 and 2 (Erk1/2) in the hippocampus undergoes a transition between P6 and P15. At P6, a protein kinase C (PKC) isozyme is required for the 5-HT(1A)-R -->Erk1/2 cascade, which causes increased cell division in the dentate gyrus. By contrast, at P15, PKC alpha participates downstream of Erk1/2 to augment synaptic transmission through the Schaffer Collateral pathway but does not cause increased cell division. Our data demonstrate that the 5-HT(1A)-R -->Erk1/2 cascade uses PKC isozymes differentially, first boosting the cell division to form new hippocampal neurons at P6 and then undergoing a plastic change in mechanism to strengthen synaptic connections in the hippocampus at P15.

Emerging role of the FGF system in psychiatric disorders

Fibroblast growth factors (FGFs) comprise several peptides that, by interacting with a family of FGF receptors, participate in brain development and contribute to neuronal repair and plasticity. Recent evidence suggests that the expression of FGFs is altered in mood disorders and can be regulated by psychotropic drugs. This provides further support to the notion that neurotrophic molecules might have a role in the etiology and treatment of mental disorders.

Fibroblast growth factor 2 is required for maintaining the neural stem cell pool in the mouse brain subventricular zone

Cells within the subventricular zone (SVZ) express basic Fgf (Fgf2) and Fgf receptor proteins. We show that the absence of Fgf2 gene products reduces by 50% the dividing progenitor population of the anterior SVZ (SVZa) without changing their cell cycle time. Every 2-3 cell cycles of the SVZa progenitor cell population, 30,000 newly generated neurons capable of long-term survival are added to the glomerular layer of the olfactory bulb. Fgf2 knockout mice have smaller olfactory bulbs due to decreased output of these newly generated cells into the bulbs. A population of slow-dividing neural stem cells (NSCs) residing in the SVZa is identified by its slow cell cycle kinetics (cell cycle approx. 20 days); these cells, called 'S' cells, are negative for glial fibrillary acidic protein and occasionally express brain-lipid-binding protein, a molecular marker of radial glia. The number of these dividing NSCs is reduced from about 13,000 in wild-type to 8,500 cells in Fgf2 knockout mice. Thus, FGF2 regulates the number of proliferative cells and olfactory bulb neurogenesis by maintaining a slow-dividing stem cell pool within the SVZa.

Neural stem cells redefined: a FACS perspective

Using the generally accepted ontogenetic definition, neural stem cells (NSCs) are characterized as undifferentiated cells originating from the neuroectoderm that have the capacity both to perpetually self-renew without differentiating and to generate multiple types of lineage-restricted progenitors (LRP). LRPs can themselves undergo limited self-renewal, then ultimately differentiate into highly specialized cells that compose the nervous system. However, this physiologically delimited definition of NSCs has been increasingly blurred in the current state of the field, as the great majority of studies have retrospectively inferred the existence of NSCs based on their deferred functional capability rather than prospectively identifying the actual cells that created the outcome. Further complicating the matter is the use of a wide variety of neuroepithelial or neurosphere preparations as a source of putative NSCs, without due consideration that these preparations are themselves composed of heterogeneous populations of both NSCs and LRPs. This article focuses on recent attempts using FACS strategies to prospectively isolate NSCs from different types of LRPs as they appear in vivo and reveals the contrasting differences among these populations at molecular, phenotypic, and functional levels. Thus, the strategies presented here provide a framework for more precise studies of NSC and LRP cell biology in the future.

Umbilical cord blood stem cells can expand hematopoietic and neuroglial progenitors in vitro

The ability of hematopoietic tissue-derived adult stem cells to transdifferentiate into neural progenitor cells offers an interesting alternative to central nervous system (CNS)- or embryonic-derived stem cells as a viable source for cellular therapies applied to brain regeneration. Umbilical cord blood (CB) due to its primitive nature and it unproblematic collection appears as a promising candidate for multipotent stem cell harvest. We developed a negative immunomagnetic selection method that depletes CB from hematopoietic lineage marker-expressing cells, hence isolating a discrete lineage negative (LinNeg) stem cell population (0.1% of CB mononucleated cell [MCN] population). In liquid culture supplemented with thrombopoietin, flt-3 ligand, and c-kit ligand (TPOFLK), CB LinNeg stem cells could expand primitive nonadherent hematopoietic progenitors (up to 47-fold) and simultaneously produce slow-dividing adherent cells with neuroglial progenitor cell morphology over 8 weeks. Laser scanning confocal microscopy analysis identified these adherent cells to express glial fibrillary acidic protein (GFAP). Gene expression analysis showed upregulation of primitive neuroglial progenitor cell markers including, GFAP, nestin, musashi-1, and necdin. ELISA quantification of liquid culture supernatant revealed the in vitro release of transforming growth factor beta-1 (TGFbeta1), glial cell line-derived neurotrophic factor (GDNF) suggesting their contribution to CB LinNeg stem cell transdifferentiation into neuroglial progenitors. Our study supports that a single CB specimen can be pre-expanded in TPOFLK to produce both primitive hematopoietic and neuropoietic progenitors, hence widening CB clinical potential for cellular therapies.

Simulated apoptosis/neurogenesis regulates learning and memory capabilities of adaptive neural networks

Characterization of neuronal death and neurogenesis in the adult brain of birds, humans, and other mammals raises the possibility that neuronal turnover represents a special form of neuroplasticity associated with stress responses, cognition, and the pathophysiology and treatment of psychiatric disorders. Multilayer neural network models capable of learning alphabetic character representations via incremental synaptic connection strength changes were used to assess additional learning and memory effects incurred by simulation of coordinated apoptotic and neurogenic events in the middle layer. Using a consistent incremental learning capability across all neurons and experimental conditions, increasing the number of middle layer neurons undergoing turnover increased network learning capacity for new information, and increased forgetting of old information. Simulations also showed that specific patterns of neural turnover based on individual neuronal connection characteristics, or the temporal-spatial pattern of neurons chosen for turnover during new learning impacts new learning performance. These simulations predict that apoptotic and neurogenic events could act together to produce specific learning and memory effects beyond those provided by ongoing mechanisms of connection plasticity in neuronal populations. Regulation of rates as well as patterns of neuronal turnover may serve an important function in tuning the informatic properties of plastic networks according to novel informational demands. Analogous regulation in the hippocampus may provide for adaptive cognitive and emotional responses to novel and stressful contexts, or operate suboptimally as a basis for psychiatric disorders. The implications of these elementary simulations for future biological and neural modeling research on apoptosis and neurogenesis are discussed.

A glance into somatic stem cell biology: basic principles, new concepts, and clinical relevance

Somatic stem cells are undifferentiated cells with a high capacity for self-renewal that can give rise to one or more specialized cell types with specific functions in the body. Profound characterization of these cells has been difficult due to the fact that their frequency in different tissues of the body is extremely low; furthermore, their identification is not based on their morphology but on immunophenotypic and functional assays. Nevertheless, significant advances in the study of these cells at both cellular and molecular levels have been achieved during the last decade. The majority of what we know concerning somatic stem cell biology has come from work on hematopoietic stem cells. More recently, however, there has been a great amount of information on neural and epithelial stem cells. The importance of stem cell research has gone beyond basic biology and is currently contributing to the development of new medical approaches for treatment of hematologic, neurologic, autoimmune, and metabolic disorders (cellular therapy).

Chronic hypoxia up-regulates fibroblast growth factor ligands in the perinatal brain and induces fibroblast growth factor-responsive radial glial cells in the sub-ependymal zone

A number of signaling molecules have been implicated in the acute response to hypoxia/ischemia in the adult brain. In contrast, the reaction to chronic hypoxemia is largely unexplored. We used a protocol of chronic hypoxia in rat pups during the first three postnatal weeks, encompassing the period of cellular plasticity in the cerebral cortex. We find that the levels of fibroblast growth factor 1 (FGF1) and FGF2, two members of the FGF family, increase after 2 weeks of chronic hypoxia. In contrast, members of the neurotrophin family are unaffected. FGF2 is normally expressed in the nucleus of mature, glial fibrillary acidic protein (GFAP)-containing astrocytes. Under hypoxia, most FGF2-containing cells do not express detectable levels of GFAP, suggesting that chronic low O(2) induces their transformation into more immature glial phenotypes. Remarkably, hypoxia promotes the appearance of radial glia throughout the sub-ventricular and ependymal zones. Most of these cells express vimentin and brain lipid binding protein. A subset of these radial glial cells expresses FGF receptor 1, and are in close contact with FGF2-positive cells in the sub-ventricular zone. Thus, FGF receptor signaling in radial glia may foster cell genesis after chronic hypoxic damage. From the results of this study we suggest that after the chronic exposure to low levels of oxygen during development, the expression of radial glia increases in the forebrain periventricular region. We envision that astroglia, which are the direct descendants of radial glia, are reverting back to immature glial cells. Alternatively, hypoxia hinders the normal maturation of radial glia into GFAP-expressing astrocytes. Interestingly, hypoxia increases the levels of expression of FGF2, a factor that is essential for neuronal development. Furthermore, chronic hypoxia up-regulated FGF2's major receptor in the periventricular region. Because radial glia have been suggested to play a key role in neurogenesis and cell migration, our data suggests that hypoxia-induced FGF signaling in radial glia may represent part of a conserved program capable of regenerating neurons in the brain after injury.

REN: a novel, developmentally regulated gene that promotes neural cell differentiation

Expansion and fate choice of pluripotent stem cells along the neuroectodermal lineage is regulated by a number of signals, including EGF, retinoic acid, and NGF, which also control the proliferation and differentiation of central nervous system (CNS) and peripheral nervous system (PNS) neural progenitor cells. We report here the identification of a novel gene, REN, upregulated by neurogenic signals (retinoic acid, EGF, and NGF) in pluripotent embryonal stem (ES) cells and neural progenitor cell lines in association with neurotypic differentiation. Consistent with a role in neural promotion, REN overexpression induced neuronal differentiation as well as growth arrest and p27Kip1 expression in CNS and PNS neural progenitor cell lines, and its inhibition impaired retinoic acid induction of neurogenin-1 and NeuroD expression. REN expression is developmentally regulated, initially detected in the neural fold epithelium of the mouse embryo during gastrulation, and subsequently throughout the ventral neural tube, the outer layer of the ventricular encephalic neuroepithelium and in neural crest derivatives including dorsal root ganglia. We propose that REN represents a novel component of the neurogenic signaling cascade induced by retinoic acid, EGF, and NGF, and is both a marker and a regulator of neuronal differentiation.

Fibroblast growth factor 2 is necessary for the growth of glutamate projection neurons in the anterior neocortex

Basic fibroblast growth factor (Fgf2) is required for the generation of founder cells within the dorsal pseudostratified ventricular epithelium, which will generate the cerebral cortex, but the ganglionic eminences are not affected. We report here that the Fgf2 null mutant mice show an approximately 40% decrease in cortical glutamatergic pyramidal neurons. In contrast, no change in pyramidal or granule cell number is detected in the hippocampus of Fgf2 -/- mice. In addition, the soma of the pyramidal cells in the frontal and parietal cortices are smaller in Fgf2 knock-out mice. The decrease in the number and size of glutamatergic neuronal population affects all cortical layers but is restricted to the frontal and parietal cortices without any change in the occipital cortex, indicating that Fgf2 is necessary to regulate cell number and size in the anterior cerebral cortex. In contrast to pyramidal neurons, cortical GABA interneurons are unaffected by the lack of Fgf2. The resulting imbalance between the excitatory and inhibitory neurotransmission in the cerebral cortex is reflected by an increased duration of sleep when the animals receive a GABA receptor agonist. Thus, Fgf2 signaling may contribute to the regional specification of the cerebral cortex and may play a role in increasing the size of anterior cortical regions during vertebrate evolution.