Developmental stage-dependent self-regulation of embryonic cortical precursor cell survival and differentiation by leukemia inhibitory factor

Microglia Colonization Associated with Angiogenesis and Neural Cell Development

The temporal and spatial pattern of microglia colonization of the nervous system implies a role in early stages of organ development including cell proliferation, differentiation, and neurovascularization. As microglia colonize and establish within the developing nervous system, they assume a neural-specific identity and contribute to key developmental events. Their association around blood vessels implicates them in development of the vascular system or vice versa. A similar association has been reported for neural cell proliferation and associated phenotypic shifts and for cell fate differentiation to neuronal or glial phenotypes. These processes are accomplished by phagocytic activities, cell-cell contact relationships, and secretion of various factors. This chapter will present data currently available from studies evaluating the dynamic and interactive nature of these processes throughout the progression of nervous system development.

Vitamin C-Induced Epigenetic Modifications in Donor NSCs Establish Midbrain Marker Expressions Critical for Cell-Based Therapy in Parkinson's Disease

Cultured neural stem/precursor cells (NSCs) are regarded as a potential systematic cell source to treat Parkinson's disease (PD). However, the therapeutic potential of these cultured NSCs is lost during culturing. Here, we show that treatment of vitamin C (VC) enhances generation of authentic midbrain-type dopamine (mDA) neurons with improved survival and functions from ventral midbrain (VM)-derived NSCs. VC acted by upregulating a series of mDA neuron-specific developmental and phenotype genes via removal of DNA methylation and repressive histone code (H3K9m3, H3K27m3) at associated gene promoter regions. Notably, the epigenetic changes induced by transient VC treatment were sustained long after VC withdrawal. Accordingly, transplantation of VC-treated NSCs resulted in improved behavioral restoration, along with enriched DA neuron engraftment, which faithfully expressed midbrain-specific markers in PD model rats. These results indicate that VC treatment to donor NSCs could be a simple, efficient, and safe therapeutic strategy for PD in the future.

•

Vitamin C (VC) potentiates therapeutic capacity of donor NSCs to treat PD

•

Long-lasting epigenetic activation of VM-specific genes underlies the VC effects

•

The VC effects enhanced mDA neuron engraftment

MicroRNA profiling reveals unique miRNA signatures in IGF-1 treated embryonic striatal stem cell fate decisions in striatal neurogenesis in vitro

The striatum is considered to be the central processing unit of the basal ganglia in locomotor activity and cognitive function of the brain. IGF-1 could act as a control switch for the long-term proliferation and survival of EGF+bFGF-responsive cultured embryonic striatal stem cell (ESSC), while LIF imposes a negative impact on cell proliferation. The IGF-1-treated ESSCs also showed elevated hTERT expression with demonstration of self-renewal and trilineage commitment (astrocytes, oligodendrocytes, and neurons). In order to decipher the underlying regulatory microRNA (miRNA)s in IGF-1/LIF-treated ESSC-derived neurogenesis, we performed in-depth miRNA profiling at 12 days in vitro and analyzed the candidates using the Partek Genome Suite software. The annotated miRNA fingerprints delineated the differential expressions of miR-143, miR-433, and miR-503 specific to IGF-1 treatment. Similarly, the LIF-treated ESSCs demonstrated specific expression of miR-326, miR-181, and miR-22, as they were nonsignificant in IGF-treated ESSCs. To elucidate the possible downstream pathways, we performed in silico mapping of the said miRNAs into ingenuity pathway analysis. Our findings revealed the important mRNA targets of the miRNAs and suggested specific interactomes. The above studies introduced a new genre of miRNAs for ESSC-based neuroregenerative therapeutic applications.

Leukemia inhibitory factor enhances bovine oocyte maturation and early embryo development

The present study was conducted to examine the effects of leukemia inhibitory factor (LIF) on bovine oocyte maturation and early embryo development in vitro. Results showed that LIF supplementation (25 ng/ml) enhanced nuclear maturation of intact cumulus-oocyte complexes (COCs) compared to the vehicle control. Similar results were observed in denuded oocytes, indicating that LIF directly influences oocyte development. LIF-treated oocytes showed a higher cortical-granule-migration rate and increased expression of CD9, a tetraspanin transmembrane protein essential for fertilization. After in vitro fertilization, oocytes receiving LIF supplementation exhibited a higher cleavage rate and yielded a significantly higher number of blastocysts. To further dissect the molecular mechanism underlying this LIF-induced bovine oocyte maturation phenotype, we examined the involvement of two signaling cascades, mitogen-activated protein kinases (MAPK3/1)- and the signal transducer and activator of transcription 3 (STAT3)-dependent pathways. Western blot results revealed that LIF phosphorylated MAPK3/1 and STAT3. Inhibition of MAPK3/1 activation with MEK inhibitor U0126 only partially blocked LIF-induced nuclear maturation, although it attenuated oocyte cytoplasmic maturation. Inhibition of JAK/STAT3 activation with a specific pharmacological inhibitor completely abolished the LIF-response in bovine oocyte. In summary, these data revealed a novel role for LIF in bovine oocyte maturation subsequent embryonic development.

Immunopharmacological intervention for successful neural stem cell therapy: New perspectives in CNS neurogenesis and repair

The pharmacological support and stimulation of endogenous and transplanted neural stem cells (NSCs) is a major challenge in brain repair. Trauma to the central nervous system (CNS) results in a distinct inflammatory response caused by local and infiltrating immune cells. This makes NSC-supported regeneration difficult due to the presence of inhibitory immune factors which are upregulated around the lesion site. The continual and dual role of the neuroinflammatory response leaves it difficult to decipher upon a single modulatory strategy. Therefore, understanding the influence of cytokines upon regulation of NSC self-renewal, proliferation and differentiation is crucial when designing therapies for CNS repair. There is a plethora of partially conflicting data in vitro and in vivo on the role of cytokines in modulating the stem cell niche and the milieu around NSC transplants. This is mainly due to the pleiotropic role of many factors. In order for cell-based therapy to thrive, treatment must be phase-specific to the injury and also be personalized for each patient, i.e. taking age, sex, neuroimmune and endocrine status as well as other key parameters into consideration. In this review, we will summarize the most relevant information concerning interleukin (IL)-1, IL-4, IL-10, IL-15, IFN-γ, the neuropoietic cytokine family and TNF-α in order to extract promising therapeutic approaches for further research. We will focus on the consequences of neuroinflammation on endogenous brain stem cells and the transplantation environment, the effects of the above cytokines on NSCs, as well as immunopharmacological manipulation of the microenvironment for potential therapeutic use.

Role of cytokine signaling during nervous system development

Cytokines are signaling proteins that were first characterized as components of the immune response, but have been found to have pleiotropic effects in diverse aspects of body function in health and disease. They are secreted by numerous cells and are used extensively in intercellular communications to produce different activities, including intricate processes engaged in the ontogenetic development of the brain. This review discusses factors involved in brain growth regulation and recent findings exploring cytokine signaling pathways during development of the central nervous system. In view of existing data suggesting roles for neurotropic cytokines in promoting brain growth and repair, these molecules and their signaling pathways might become targets for therapeutic intervention in neurodegenerative processes due to diseases, toxicity, or trauma.

TNF-α affects human cortical neural progenitor cell differentiation through the autocrine secretion of leukemia inhibitory factor

Proinflammatory cytokine tumor necrosis factor-alpha (TNF-α) is a crucial effector of immune responses in the brain that participates in the pathogenesis of several acute and chronic neurodegenerative disorders. Accumulating evidence has suggested that TNF-α negatively regulates embryonic and adult neurogenesis. However, the effect of TNF-α on cell fate decision in human neural progenitor cells (NPCs) has rarely been studied. Our previous studies have shown that recombinant TNF-α enhances astrogliogenesis and inhibits neurogenesis of human NPCs through the STAT3 (signal transducer and activator of transcription 3) pathway. In the current study, we further elucidated the specific mechanism involved in TNF-α-induced astrogliogenesis. We found that TNF-α activated STAT3 at delayed time points (6 h and 24 h), whereas conditioned medium collected from TNF-α-treated NPCs induced an immediate STAT3 activation. These data suggest TNF-α plays an indirect role on STAT3 activation and the subsequent NPC differentiation. Further, we showed that TNF-α induced abundant amounts of the IL-6 family cytokines, including Leukemia inhibitory factor (LIF) and Interleukin 6 (IL-6), in human NPCs. TNF-α-induced STAT3 phosphorylation and astrogliogenesis were abrogated by the addition of neutralizing antibody for LIF, but not for IL-6, revealing a critical role of autocrine secretion of LIF in TNF-α-induced STAT3 activation and astrogliogenesis. This study generates important data elucidating the role of TNF-α in neurogenesis and may provide insight into new therapeutic strategies for brain inflammation.

Stromal cell-secreted factors promote the survival of embryonic stem cell-derived early neural stem/progenitor cells via the activation of MAPK and PI3K-Akt pathways

Neural stem/progenitor cells (NS/PCs) have been studied extensively with the hope of using them clinically to repair the damaged central nervous system. However, little is known about the signals that regulate the proliferation, survival, and differentiation of NS/PCs in early development. To clarify the underlying mechanisms, we took advantage of an in vitro ES cell differentiation system from which we can obtain neurospheres containing NS/PCs with characteristics of the early caudal neural tube, by treating embryoid bodies (EBs) with a low concentration of retinoic acid (RA). We found that conditioned medium from the PA6 stromal cell line (PA6CM) increased the efficiency of neurosphere formation by suppressing apoptosis and promoting the survival of the NS/PCs. PA6CM also induced the phosphorylation of Erk1/2 and Akt1 in cells derived from the EBs. Furthermore, inhibitors of the MAPK and PI3K-Akt signaling pathways, U0126 and LY294002, attenuated the effects of PA6CM, significantly increasing the number of apoptotic cells and decreasing the number of viable cells among the ES cell-derived NS/PCs. Thus, PA6CM appears to contain soluble factors that promote the survival of ES cell-derived early NS/PCs through the activation of the MAPK and PI3K-Akt pathways.

O-linked beta-N-acetylglucosaminylation in mouse embryonic neural precursor cells

In neural stem cells (NSCs), glycoconjugates and carbohydrate antigens are known not only to serve as excellent cell surface biomarkers for cellular differentiation and development but also to play important functional roles in determining cell fate. O-linked beta-N-acetylglucosamine (O-GlcNAc), which modifies nuclear and cytoplasmic proteins on the serine and threonine residues, is also expected to play an important regulatory role. It is not known, however, whether O-GlcNAc is expressed in NSCs or what the function of this expression is. In this study, we evaluated the patterns and possible functions of O-GlcNAcylation in mouse embryonic neuroepithelial cells (NECs), which are known to be rich in NSCs. We confirmed the expression of O-GlcNAc transferase, O-GlcNAcase, and several O-GlcNAcylated proteins in NECs. Treatment of NECs with O-GlcNAcase inhibitors, PUGNAc and streptozotocin, induced robust accumulation of O-GlcNAc in NECs and reduction of number of NECs. In O-GlcNAcase inhibitor-treated NECs, the Ras-mitogen-activated protein kinase pathway and the phosphatidylinositol 3-kinase-Akt pathway, important for proliferation and survival, respectively, were intact, but caspase-3, an executioner for cell death, was activated. These results suggest the possibility that O-GlcNAc is involved in cell death signaling in NECs. Furthermore, in NECs, we identified an O-GlcNAc-modified protein, Sp1 transcription factor. Our study is the first to evaluate expression and functions of O-GlcNAc in NECs.

Cytokines and CNS development

Cytokines are pleotrophic proteins that coordinate the host response to infection as well as mediate normal, ongoing signaling between cells of nonimmune tissues, including the nervous system. As a consequence of this dual role, cytokines induced in response to maternal infection or prenatal hypoxia can profoundly impact fetal neurodevelopment. The neurodevelopmental roles of individual cytokine signaling pathways are being elucidated through gain- and loss-of-function studies in cell culture and model organisms. We review this work with a particular emphasis on studies where cytokines, their receptors, or components of their signaling pathways have been altered in vivo. The extensive and diverse requirements for properly regulated cytokine signaling during normal nervous system development revealed by these studies sets the foundation for ongoing and future work aimed at understanding how cytokines induced normally and pathologically during critical stages of fetal development alter nervous system function and behavior later in life.

Leukemia inhibitory factor favours neurogenic differentiation of long-term propagated human midbrain precursor cells

There is a lot of excitement about the potential use of multipotent neural stem cells for the treatment of neurodegenerative diseases. However, the strategy is compromised by the general loss of multipotency and ability to generate neurons after long-term in vitro propagation. In the present study, human embryonic (5 weeks post-conception) ventral mesencephalic (VM) precursor cells were propagated as neural tissue-spheres (NTS) in epidermal growth factor (EGF; 20 ng/ml) and fibroblast growth factor 2 (FGF2; 20 ng/ml). After more than 325 days, the NTS were transferred to media containing either EGF+FGF2, EGF+FGF2+heparin or leukemia inhibitory factor (LIF; 10 ng/ml)+FGF2+heparin. Cultures were subsequently propagated for more than 180 days with NTS analyzed at various time-points. Our data show for the first time that human VM neural precursor cells can be long-term propagated as NTS in the presence of EGF and FGF2. A positive effect of heparin was found only after 150 days of treatment. After switching into different media, only NTS exposed to LIF contained numerous cells positive for markers of newly formed neurons. Besides of demonstrating the ability of human VM NTS to be long-term propagated, our study also suggests that LIF favours neurogenic differentiation of human VM precursor cells.

N-glycans modulate the activation of gp130 in mouse embryonic neural precursor cells

gp130 is a ubiquitously expressed glycoprotein and signal transducer of interleukin 6 family of cytokines. It has been reported that gp130 has 11 potential N-glycosylation sites in the extracellular domain, and nine of them are actually N-glycosylated. However, the structure and functional role of the carbohydrate chains carried by gp130 are totally unknown. In this study, we examined the functional role of N-glycans of gp130 in mouse neuroepithelial cells. In neuroepithelial cells treated with tunicamycin, an N-glycosylation inhibitor, unglycosylated form of gp130 was detected. The unglycosylated gp130 was not phosphorylated in response to leukemia inhibitory factor stimulation. Although the unglycosylated gp130 was found to be expressed on the cell surface, it could not form a heterodimer with leukemia inhibitory factor receptor. These results suggest that N-glycans are required for the activation, but not for the localization, of gp130 in neuroepithelial cells.

Leukemia inhibitory factor promotes olfactory sensory neuronal survival via phosphoinositide 3-kinase pathway activation and Bcl-2

Leukemia inhibitory factor (LIF), a neuropoietic cytokine, has been implicated in the control of neuronal development. We previously reported that LIF plays a critical role in regulating the terminal differentiation of olfactory sensory neurons (OSNs). Here, we demonstrate that LIF plays a complementary role in supporting the survival of immature OSNs. Mature OSNs express LIF, which may be elaborated in a paracrine manner to influence adjacent neurons. LIF null mice display more apoptotic immature neurons than do their wild-type littermates. LIF treatment of dissociated OSNs in vitro significantly reduces the apoptosis of immature OSNs. Double immunocytochemical analysis indicates that the survival of immature OSNs is dependent on the presence of LIF. LIF activates the phosphoinositide 3-kinase (PI3K) pathways and induces the expression of the antiapoptotic molecule Bcl-2 in OSNs, whereas inhibition of the PI3K pathway blocks LIF-dependent OSN survival and Bcl-2 induction. Thus, LIF plays a central role in maintaining the size and integrity of the population of immature neurons within the olfactory epithelium; this population is critical to the rapid recovery of olfactory function after injury. LIF may play a similar role elsewhere in the CNS and thus be important for manipulation of stem cell populations for therapeutic interventions.

Mash1 and neurogenin 2 enhance survival and differentiation of neural precursor cells after transplantation to rat brains via distinct modes of action

Neural precursor cells (NPCs) are regarded as a promising source of donor cells in transplantation-based therapies for neurodegenerative disorders. However, poor survival and limited neuronal differentiation of the transplanted NPCs remain critical limitations for developing therapeutic strategies. In this study, we investigated the effects of the proneural basic helix-loop-helix (bHLH) transcription factors Mash1 and Neurogenin 2 (Ngn2) in neuronal differentiation and survival of NPCs. Induction of Mash1 or Ngn2 expression strikingly enhanced neuronal differentiation of cultured NPCs in vitro. Ngn2-transduced NPCs underwent a rapid cell cycle arrest, which often accompanies differentiation. In contrast, cells continuously expanded upon Mash1 expression during NPC differentiation. Notably, sonic hedgehog (SHH) was upregulated by Mash1 and mediated the proliferative and survival effects of Mash1 on NPCs. Upon transplantation into adult rat brains, Mash1-expressing NPCs yielded large grafts enriched with neurons compared to control LacZ-transduced NPCs. Interestingly, enhancements in neuronal yield, as well as in donor cell survival, were also achieved by transplanting Ngn2-transduced NPCs. We show that a differentiation stage- and cell density-dependent survival effect of Ngn2 involves neurotrophin3 (NT3)/TrkC-mediated signaling. Together, these findings suggest potential benefits of bHLH gene manipulation to develop successful transplantation strategies for brain disorders.

In vitro neuronal and glial differentiation from embryonic or adult neural precursor cells are differently affected by chronic or acute activation of microglia

The contribution of microglia to the modulation of neurogenesis under pathological conditions is unclear. Both pro- and anti-neurogenic effects have been reported, likely reflecting the complexity of microglial activation process. We previously demonstrated that prolonged (72 hr) in vitro exposure to lipopolysaccharide (LPS) endows microglia with a potentially neuroprotective phenotype, here referred as to "chronic". In the present study we further characterized the chronic phenotype and investigated whether it might differently regulate the properties of embryonic and adult neural precursor cells (NPC) with respect to the "acute" phenotype acquired following a single (24 hr) LPS stimulation. We show that the LPS-dependent induction of the proinflammatory cytokines interleukin (IL)-1 alpha, IL-1 beta, IL-6, and tumor necrosis factor (TNF)-alpha was strongly reduced after chronic stimulation of microglia, as compared with acute stimulation. Conversely, the synthesis of the anti-inflammatory cytokine IL-10 and the immunomodulatory prostaglandin E2 (PGE2) was still elevated or further increased, after chronic LPS exposure, as revealed by real time PCR and ELISA techniques. Acutely activated microglia, or their conditioned medium, reduced NPC survival, prevented neuronal differentiation and strongly increased glial differentiation, likely through the release of proinflammatory cytokines, whereas chronically activated microglia were permissive to neuronal differentiation and cell survival, and still supported glial differentiation. Our data suggest that, in a chronically altered environment, persistently activated microglia can display protective functions that favor rather than hinder brain repair processes.

Leukemia inhibitory factor induces cumulus expansion in immature human and mouse oocytes and improves mouse two-cell rate and delivery rates when it is present during mouse in vitro oocyte maturation

OBJECTIVE

To examine the role of leukemia inhibitory factor (LIF) during in vitro maturation (IVM) on human and mice cumulus expansion and mice oocyte competence by in vitro fertilization (IVF), culture, and embryo transfer (ET).

DESIGN

Prospective animal and human study.

SETTING

Serono laboratories and IVF clinic.

PATIENT(S)

Healthy women volunteers and 8-week-old female mice.

INTERVENTION(S)

Cumulus compacted human and mice oocytes were matured in IVM media with and without recombinant follicle-stimulating hormone (FSH) and with and without LIF. Mice IVM oocytes with and without 0.2 IU/mL of recombinant FSH; or with and without recombinant FSH + LIF (0.1, 1.0, 1000.0 ng/mL) and ovulated oocytes were in vitro fertilized and cultured. We transferred 395 blastocysts to the uterine horn of 2.5-day pseudopregnant female mice.

MAIN OUTCOME MEASURE(S)

Cumulus expansion in human and mice oocytes, and two-cell rate, blastocyst rate, and delivered rate of live pups in mice.

RESULT(S)

In human and mouse oocytes, LIF induced cumulus expansion. When 1000 ng/mL of LIF was added in combination with recombinant FSH, a statistically significant increase in cleavage rate, embryo development rate, and birth rate was observed when compared with oocytes matured with FSH alone.

CONCLUSION(S)

Leukemia inhibitory factor induced cumulus expansion similarly in human and mouse cumulus-oocyte complexes, and recombinant FSH plus LIF supplementation during mouse IVM significantly improved oocyte competence as measured by cleavage rate, blastocyst development, and birth rate.

Contrasting and brain region-specific roles of neurogenin2 and mash1 in GABAergic neuron differentiation in vitro

We have cultivated highly uniform populations of neural precursor cells, which retain their region-specific identities, from various rat embryonic brain regions. The roles of the proneural basic-helix-loop-helix (bHLH) factors neurogenin2 (Ngn2) and Mash1 in gamma-aminobutyric acid (GABA) neuron differentiation were explored in the region-specific cultures. Consistent with previous in vivo studies, forced expression of Mash1 promoted GABA neuron formation from the precursors derived from the developing forebrains, whereas Ngn2 displayed an inhibitory role in forebrain GABA neuron differentiation. Functional analyses of mutant bHLH proteins indicated that the helix-loop-helix domains of Mash1 and Ngn2, known as the structures for protein-protein interactions, impart the distinct activities. Intriguingly, the regulatory activities of Mash1 and Ngn2 in GABA neuron differentiation from the hindbrain- and spinal cord-derived precursor cells were completely opposite of those observed in the forebrain-derived cultures: increased GABA neuron yield by Ngn2 and decreased yield by Mash1 were shown in the precursors of those posterior brain regions. No clear difference that depended on dorsal-ventral brain regions was observed in the bHLH-mediated activities. Finally, we demonstrated that Otx2, the expression of which is developmentally confined to the regions anterior to the isthmus, is a factor responsible for the anterior-posterior region-dependent opposite effects of the bHLH proteins.

Bcl-XL/Bax proteins direct the fate of embryonic cortical precursor cells

In the developing mouse brain, the highest Bcl-X(L) expression is seen at the peak of neurogenesis, whereas the peak of Bax expression coincides with the astrogenic period. While such observations suggest an active role of the Bcl-2 family proteins in the generation of neurons and astrocytes, no definitive demonstration has been provided to date. Using combinations of gain- and loss-of-function assays in vivo and in vitro, we provide evidence for instructive roles of these proteins in neuronal and astrocytic fate specification. Specifically, in Bax knockout mice, astrocyte formation was decreased in the developing cortices. Overexpression of Bcl-X(L) and Bax in embryonic cortical precursors induced neural and astrocytic differentiation, respectively, while inhibitory RNAs led to the opposite results. Importantly, inhibition of caspase activity, dimerization, or mitochondrial localization of Bcl-X(L)/Bax proteins indicated that the differentiation effects of Bcl-X(L)/Bax are separable from their roles in cell survival and apoptosis. Lastly, we describe activation of intracellular signaling pathways and expression of basic helix-loop-helix transcriptional factors specific for the Bcl-2 protein-mediated differentiation.

The neuropoietic cytokine family in development, plasticity, disease and injury

Neuropoietic cytokines are well known for their role in the control of neuronal, glial and immune responses to injury or disease. Since this discovery, it has emerged that several of these proteins are also involved in nervous system development, in particular in the regulation of neurogenesis and stem cell fate. Recent data indicate that these proteins have yet more functions, as key modulators of synaptic plasticity and of various behaviours. In addition, neuropoietic cytokines might be a factor in the aetiology of psychiatric disorders.

The expression and functions of glycoconjugates in neural stem cells

The mammalian central nervous system is organized by a variety of cells such as neurons and glial cells. These cells are generated from a common progenitor, the neural stem cell (NSC). NSCs are defined as undifferentiated neural cells that are characterized by their high proliferative potential while retaining the capacity for self-renewal and multipotency. Glycoconjugates carrying carbohydrate antigens, including glycoproteins, glycolipids, and proteoglycans, are primarily localized on the plasma-membrane surface of cells and serve as excellent biomarkers at various stages of cellular differentiation. Moreover, they also play important functional roles in determining cell fate such as self-renewal, proliferation, and differentiation. In the present review, we discuss the expression pattern and possible functions of glycoconjugates and carbohydrate antigens in NSCs, with an emphasis on stage-specific embryonic antigen-1, human natural killer antigen-1, polysialic acid-neural cell-adhesion molecule, prominin-1, gp130, chondroitin sulfate proteoglycans, heparan sulfate proteoglycans, cystatin C, galectin-1, glycolipids, and Notch.

Microglia-derived interleukin-6 and leukaemia inhibitory factor promote astrocytic differentiation of neural stem/progenitor cells

Neural stem/progenitor cells (NSPCs) proliferate and differentiate depending on their intrinsic properties and local environment. It has been recognized that astrocytes promote neurogenic differentiation of NSPCs, suggesting the importance of cell-cell interactions between glial cells and NSPCs. Recent studies have demonstrated that microglia, one type of glial cells, play an important role in neurogenesis. However, little is known about how activated microglia control the proliferation and differentiation of NSPCs. In this study, we investigated the possibility that microglia-derived soluble factors regulate the behaviour of NSPCs. To this end, NSPCs and microglial cultures were obtained from rat embryonic day 16 subventricular zone (SVZ) and rat postnatal 1 day cortex, respectively, and the conditioned medium from microglia was prepared. Microglial-conditioned medium had no significant effect on the proliferation of NSPCs. In contrast, it increased the percentage of cells positive for a marker of astrocytes, glial fibrillary acidic protein (GFAP) during differentiation. The induction of astrocytic differentiation by microglial-conditioned medium was reduced by the inhibition of the Janus kinase/signal transducer and activation of transcription (JAK/STAT) and mitogen-activated protein kinase (MAPK) pathways. Furthermore, microglia-derived interleukin (IL)-6 and leukaemia inhibitory factor (LIF) were identified as essential molecules for this astrocytic differentiation using neutralizing antibodies and recombinant cytokines. Our results suggest that microglia as well as astrocytes contribute to the integrity of the local environment of NSPCs, and at least IL-6 and LIF released by activated microglia promote astrocytic differentiation of NSPCs via the activation of the JAK/STAT and MAPK pathways.

Leukemia inhibitory factor promotes neural stem cell self-renewal in the adult brain

Although neural stem cells (NSCs) persist in various areas of the adult brain, their contribution to brain repair after injury is very limited. Treatment with exogenous growth factors can mitigate this limitation, suggesting that the brain environment is normally deficient in permissive cues and that it may be possible to stimulate the latent regenerative potential of endogenous progenitors with appropriate signals. We analyzed the effects of overexpressing the cytokine leukemia inhibitory factor (LIF) on adult neurogenesis in the normal brain. We found that LIF reduces neurogenesis in the olfactory bulb and subventricular zone by acting directly on NSCs. LIF appears to promote NSC self-renewal, preventing the emergence of more differentiated cell types. This ultimately leads to an expansion of the NSC pool. Our results have implications for the development of therapeutic strategies for brain repair and suggest that LIF may be useful, in combination with other factors, in promoting regeneration in the adult brain.

The role of leptin in the development of the cerebral cortex in mouse embryos

Leptin is detected in the sera, and leptin receptors are expressed in the cerebrum of mouse embryos, suggesting that leptin plays a role in cerebral development. Compared with the wild type, leptin-deficient (ob/ob) mice had fewer cells at embryonic day (E) 16 and E18 and had fewer 5-bromo-2'-deoxyuridine(+) cells at E14 and E16 in the neuroepithelium. Intracerebroventricular leptin injection in E14 ob/ob embryos increased the number of neuroepithelium cells at E16. In cultured neurosphere cells, leptin treatment increased Hes1 mRNA expression and maintained neural progenitors. Astrocyte differentiation was induced by low-dose (0.1 microg/ml) but not high-dose (1 microg/ml) leptin. High-dose leptin decreased Id mRNA and increased Ngn1 mRNA in neurosphere cells. The neuropeptide Y mRNA level in the cortical plate was lower in ob/ob than the wild type at E16 and E18. These results suggest that leptin maintains neural progenitors and is related to glial and neuronal development in embryos.