Copine1 regulates neural stem cell functions during brain development

Copine 1 (CPNE1) is a well-known phospholipid binding protein in plasma membrane of various cell types. In brain cells, CPNE1 is closely associated with AKT signaling pathway, which is important for neural stem cell (NSC) functions during brain development. Here, we investigated the role of CPNE1 in the regulation of brain NSC functions during brain development and determined its underlying mechanism. In this study, abundant expression of CPNE1 was observed in neural lineage cells including NSCs and immature neurons in human. With mouse brain tissues in various developmental stages, we found that CPNE1 expression was higher at early embryonic stages compared to postnatal and adult stages. To model developing brain in vitro, we used primary NSCs derived from mouse embryonic hippocampus. Our in vitro study shows decreased proliferation and multi-lineage differentiation potential in CPNE1 deficient NSCs. Finally, we found that the deficiency of CPNE1 downregulated mTOR signaling in embryonic NSCs. These data demonstrate that CPNE1 plays a key role in the regulation of NSC functions through the activation of AKT-mTOR signaling pathway during brain development.     

Upregulation of Flk-1 by bFGF via the ERK pathway is essential for VEGF-mediated promotion of neural stem cell proliferation

Neural stem cells （NSCs） constitute the cellular basis for embryonic brain development and neurogenesis. The process is regulated by NSC niche including neighbor cells such as vascular and glial cells. Since both vascular and glial cells secrete vascular endothelial growth factor （VEGF） and basic fibroblast growth factor （bFGF）, we assessed the effect of VEGF and bFGF on NSC proliferation using nearly homogeneous NSCs that were differentiated from mouse embryonic stem cells. VEGF alone did not have any significant effect. When bFGF was added, however, VEGF stimulated NSC proliferation in a dose-dependent manner, and this stimulation was inhibited by ZM323881, a VEGF receptor （Flk-1）- specific inhibitor. Interestingly, ZM323881 also inhibited cell proliferation in the absence of exogenous VEGF, suggesting that VEGF autocrine plays a role in the proliferation of NSCs. The stimulatory effect of VEGF on NSC proliferation depends on bFGF, which is likely due to the fact that expression of Flk-1 was upregulated by bFGF via phosphorylation of ERK1/2. Collectively, this study may provide insight into the mechanisms by which microenvironmental niche signals regulate NSCs.     

Upregulation of FIk-1 by bFGF via the ERK pathway is essential for VEGF-mediated promotion of neural stem cell proliferation

Neural stem cells (NSCs) constitute the cellular basis for embryonic brain development and neurogenesis.The processis regulated by NSC niche including neighbor cells such as vascular and glial cells.Since both vascular and glial cellssecrete vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF),we assessed the effect ofVEGF and bFGF on NSC proliferation using nearly homogeneous NSCs that were differentiated from mouse embryonicstem cells.VEGF alone did not have any significant effect.When bFGF was added,however,VEGF stimulated NSCproliferation in a dose-dependent manner,and this stimulation was inhibited by ZM323881,a VEGF receptor (Flk-1)-specific inhibitor.Interestingly,ZM323881 also inhibited cell proliferation in the absence of exogenous VEGF,suggestingthat VEGF autocrine plays a role in the proliferation of NSCs.The stimulatory effect of VEGF on NSC proliferationdepends on bFGF,which is likely due to the fact that expression of Flk-1 was upregulated by bFGF via phosphoryla-tion of ERK1/2.Collectively,this study may provide insight into the mechanisms by which mieroenvironmental nichesignals regulate NSCs.     

Circular RNA expression profiles during the differentiation of mouse neural stem cells

Background

Circular RNAs (circRNAs) have recently been found to be expressed in human brain tissue, and many lines ofevidence indicate that circRNAs play regulatory roles in neurodevelopment. Proliferation and differentiation of neural stem cells (NSCs) are critical parts during development of central nervous system (CNS).To date, there have been no reports ofcircRNA expression profiles during the differentiation of mouse NSCs. We hypothesizethat circRNAs mayregulate gene expression in the proliferation anddifferentiation of NSCs.

Results

In this study, we obtained NSCs from the wild-type C57BL/6 J mouse fetal cerebral cortex. We extracted total RNA from NSCs in different differentiation stagesand then performed RNA-seq. By analyzing the RNA-Seq data, we found 37circRNAs and 4182 mRNAs differentially expressedduringthe NSC differentiation. Gene Ontology (GO) enrichment analysis of thecognate linear genes of these circRNAsrevealed that some enriched GO terms were related to neural activity. Furthermore, we performed a co-expression network analysis of these differentially expressed circRNAs and mRNAs. The result suggested a stronger GO enrichmentin neural features for both the cognate linear genes of circRNAs and differentially expressed mRNAs.

Conclusion

We performed the first circRNA investigation during the differentiation of mouse NSCs. Wefound that12 circRNAs might have regulatory roles duringthe NSC differentiation, indicating that circRNAs might be modulated during NSC differentiation.Our network analysis suggested the possible complex circRNA-mRNA mechanisms during differentiation, and future experimental workis need to validate these possible mechanisms.

     

Akhirin regulates the proliferation and differentiation of neural stem cells/progenitor cells at neurogenic niches in mouse brain

Specialized microenvironment, or neurogenic niche, in embryonic and postnatal mouse brain plays critical roles during neurogenesis throughout adulthood. The subventricular zone (SVZ) and the dentate gyrus (DG) of hippocampus in the mouse brain are two major neurogenic niches where neurogenesis is directed by numerous regulatory factors. Now, we report Akhirin (AKH), a stem cell maintenance factor in mouse spinal cord, plays a pivotal regulatory role in the SVZ and in the DG. AKH showed specific distribution during development in embryonic and postnatal neurogenic niches. Loss of AKH led to abnormal development of the ventricular zone and the DG along with reduction of cellular proliferation in both regions. In AKH knockout mice (AKH^−/−), quiescent neural stem cells (NSCs) increased, while proliferative NSCs or neural progenitor cells decreased at both neurogenic niches. In vitro NSC culture assay showed increased number of neurospheres and reduced neurogenesis in AKH^−/−. These results indicate that AKH, at the neurogenic niche, exerts dynamic regulatory role on NSC self-renewal, proliferation and differentiation during SVZ and hippocampal neurogenesis.     

Peroxisome proliferator-activated receptor gamma-mediated regulation of neural stem cell proliferation and differentiation

Peroxisome proliferator-activated receptor gamma (PPARgamma) plays an important role in insulin sensitivity, tissue homeostasis, and regulating cellular functions. We found high-level expression of PPARgamma in embryo mouse brain and neural stem cells (NSCs), in contrast to extremely low levels in adult mouse brain. Here, we show that PPARgamma mediates the proliferation and differentiation of murine NSCs via up-regulation of the epidermal growth factor receptor and activation of the ERK pathway. Cell growth rates of NSCs prepared from heterozygous PPARgamma-deficient mouse brains, PPARgamma-RNA-silenced NSCs, and PPARgamma dominant-negative NSCs were significantly decreased compared with those of wild-type NSCs. Physiological concentrations of PPARgamma agonists, rosiglitazone and pioglitazone, stimulated NSC growth, whereas antagonists caused cell death in a concentration-dependent manner via activation of the caspase cascade. The stimulation of cell growth by PPARgamma was associated with a rapid activation of the ERK pathway by phosphorylation and up-regulation of epidermal growth factor receptor and cyclin B protein levels. In contrast, activation of PPARgamma by agonists inhibited the differentiation of NSCs into neurons. The inhibition of differentiation was associated with an activation of STAT3. These data indicate that PPARgamma regulates the development of the central nervous system during early embryogenesis via control of NSC proliferation.     

A novel, brain-specific mouse drebrin: cDNA cloning, chromosomal mapping, genomic structure, expression, and functional characterization

Drebrin A, a major neuronal actin-binding protein, regulates the dendritic spine shapes of neurons. Here, we have cloned and characterized a novel mouse cDNA clone encoding a truncated form of drebrin A, named s-drebrin A. Analysis of the genomic organization of the mouse drebrin gene (Dbn1), which mapped to the central portion of chromosome 13, revealed that isoforms including s-drebrin A are generated by alternative splicing from a single drebrin gene. The s-drebrin A mRNA was expressed in the brain, but not in non-neuronal tissues. The s-drebrin A expression was barely detected in the embryonic brain, but was upregulated during postnatal development of the brain. Overexpression of GFP-tagged s-drebrin A in fibroblasts showed it to be associated with actin filaments and with changes in actin cytoskeleton organization. These findings suggest that s-drebrin A has a role in spine morphogenesis, possibly by competing the actin-binding activity with drebrin A.     

Lewis X-carrying N-glycans regulate the proliferation of mouse embryonic neural stem cells via the Notch signaling pathway

Neural stem cells (NSCs) possess high proliferative potential and the capacity for self-renewal with retention of multipotency to differentiate into brain-forming cells. Several signaling pathways have been shown to be involved in the fate determination process of NSCs, but the molecular mechanisms underlying the maintenance of neural cell stemness remain largely unknown. Our previous study showed that human natural killer carbohydrate epitopes expressed specifically by mouse NSCs modulate the Ras-MAPK pathway, raising the possibility of regulatory roles of glycoprotein glycans in the specific signaling pathways involved in NSC fate determination. To address this issue, we performed comparative N-glycosylation profiling of NSCs before and after differentiation in a comprehensive and quantitative manner. We found that Lewis X-carrying N-glycans were specifically displayed on undifferentiated cells, whereas pauci-mannose-type N-glycans were predominantly expressed on differentiated cells. Furthermore, by knocking down a fucosyltransferase 9 with short interfering RNA, we demonstrated that the Lewis X-carrying N-glycans were actively involved in the proliferation of NSCs via modulation of the expression level of Musashi-1, which is an activator of the Notch signaling pathway. Our findings suggest that Lewis X carbohydrates, which have so far been characterized as undifferentiation markers, actually operate as activators of the Notch signaling pathway for the maintenance of NSC stemness during brain development.     

Expansion of Embryonic and Adult Neural Stem Cells by In Utero Electroporation or Viral Stereotaxic Injection

Somatic stem cells can divide to generate additional stem cells (expansion) or more differentiated cell types (differentiation), which is fundamental for tissue formation during embryonic development and tissue homeostasis during adulthood ¹. Currently, great efforts are invested towards controlling the switch of somatic stem cells from expansion to differentiation because this is thought to be fundamental for developing novel strategies for regenerative medicine ^1,2. However, a major challenge in the study and use of somatic stem cell is that their expansion has been proven very difficult to control.Here we describe a system that allows the control of neural stem/progenitor cell (altogether referred to as NSC) expansion in the mouse embryonic cortex or the adult hippocampus by manipulating the expression of the cdk4/cyclinD1 complex, a major regulator of the G1 phase of the cell cycle and somatic stem cell differentiation ^3,4. Specifically, two different approaches are described by which the cdk4/cyclinD1 complex is overexpressed in NSC in vivo. By the first approach, overexpression of the cell cycle regulators is obtained by injecting plasmids encoding for cdk4/cyclinD1 in the lumen of the mouse telencephalon followed by in utero electroporation to deliver them to NSC of the lateral cortex, thus, triggering episomal expression of the transgenes ^5-8. By the second approach, highly concentrated HIV-derived viruses are stereotaxically injected in the dentate gyrus of the adult mouse hippocampus, thus, triggering constitutive expression of the cell cycle regulators after integration of the viral construct in the genome of infected cells ⁹. Both approaches, whose basic principles were already described by other video protocols ^10-14, were here optimized to i) reduce tissue damage, ii) target wide portions of very specific brain regions, iii) obtain high numbers of manipulated cells within each region, and iv) trigger high expression levels of the transgenes within each cell. Transient overexpression of the transgenes using the two approaches is obtained by different means i.e. by natural dilution of the electroporated plasmids due to cell division or tamoxifen administration in Cre-expressing NSC infected with viruses carrying cdk4/cyclinD1 flanked by loxP sites, respectively ^9,15.These methods provide a very powerful platform to acutely and tissue-specifically manipulate the expression of any gene in the mouse brain. In particular, by manipulating the expression of the cdk4/cyclinD1 complex, our system allows the temporal control of NSC expansion and their switch to differentiation, thus, ultimately increasing the number of neurons generated in the mammalian brain. Our approach may be critically important for basic research and using somatic stem cells for therapy of the mammalian central nervous system while providing a better understanding of i) stem cell contribution to tissue formation during development, ii) tissue homeostasis during adulthood, iii) the role of adult neurogenesis in cognitive functions, and perhaps, iv) better using somatic stem cells in models of neurodegenerative diseases.     

Type-1 (CB1) Cannabinoid Receptor Promotes Neuronal Differentiation and Maturation of Neural Stem Cells

Neural stem cells (NSCs) are self-renewing cells that can differentiate into multiple neural lineages and repopulate regions of the brain after injury. We have investigated the role of endocannabinoids (eCBs), endogenous cues that modulate neuronal functions including neurogenesis, and their receptors CB₁ and CB₂ in mouse NSCs. Real-time PCR and Western blot analyses indicated that CB₁ is present at higher levels than CB₂ in NSCs. The eCB anandamide (AEA) or the CB₁-specific agonist ACEA enhanced NSC differentiation into neurons, but not astrocytes and oligodendrocytes, whereas the CB₂-specific agonist JWH133 was ineffective. Conversely, the effect of AEA was inhibited by CB₁, but not CB₂, antagonist, corroborating the specificity of the response. CB₁ activation also enhanced maturation of neurons, as indicated by morphometric analysis of neurites. CB₁ stimulation caused long-term inhibition of the ERK1/2 pathway. Consistently, pharmacological inhibition of the ERK1/2 pathway recapitulated the effects exerted by CB₁ activation on neuronal differentiation and maturation. Lastly, gene array profiling showed that CB₁ activation augmented the expression of genes involved in neuronal differentiation while decreasing that of stemness genes. These results highlight the role of CB₁ in the regulation of NSC fate and suggest that its activation may represent a pro-neuronal differentiation signal.     

Pattern of expression of the podocalyxin gene in the mouse brain during development

We studied the expression pattern of the major renal protein Podocalyxin during the development of mouse brain using in situ hybridization. Podocalyxin mRNA was widely expressed at least from E14, the first age we studied, and expression remained high until adulthood. The highest levels of expression were postnatal. Podocalyxin expression was particularly elevated in the cortical plate, the hippocampus and cerebellum, and in several basal forebrain nuclei.     

Arctigenin protects against neuronal hearing loss by promoting neural stem cell survival and differentiation

Neuronal hearing loss has become a prevalent health problem. This study focused on the function of arctigenin (ARC) in promoting survival and neuronal differentiation of mouse cochlear neural stem cells (NSCs), and its protection against gentamicin (GMC) induced neuronal hearing loss. Mouse cochlea was used to isolate NSCs, which were subsequently cultured in vitro. The effects of ARC on NSC survival, neurosphere formation, differentiation of NSCs, neurite outgrowth, and neural excitability in neuronal network in vitro were examined. Mechanotransduction ability demonstrated by intact cochlea, auditory brainstem response (ABR), and distortion product optoacoustic emissions (DPOAE) amplitude in mice were measured to evaluate effects of ARC on GMC‐induced neuronal hearing loss. ARC increased survival, neurosphere formation, neuron differentiation of NSCs in mouse cochlear in vitro. ARC also promoted the outgrowth of neurites, as well as neural excitability of the NSC‐differentiated neuron culture. Additionally, ARC rescued mechanotransduction capacity, restored the threshold shifts of ABR and DPOAE in our GMC ototoxicity murine model. This study supports the potential therapeutic role of ARC in promoting both NSCs proliferation and differentiation in vitro to functional neurons, thus supporting its protective function in the therapeutic treatment of neuropathic hearing loss in vivo.     

Tsukushi is essential for proper maintenance and terminal differentiation of mouse hippocampal neural stem cells

Secreted proteoglycan molecule Tsukushi (TSK) regulates various developmental processes, such as early body patterning and neural plate formation by interacting with major signaling pathways like Wnt, BMP, Notch etc. In central nervous system, TSK inhibits Wnt signaling to control chick retinal development. It also plays important roles for axon guidance and anterior commissure formation in mouse brain. In the present study, we investigated the role of TSK for the development and proper functioning of mouse hippocampus. We found that TSK expression is prominent at hippocampal regions of early postnatal mouse until postnatal day 15 and gradually declines at later stages. Hippocampal dimensions are affected in TSK knockout mice (TSK-KO) as shown by reduced size of hippocampus and dentate gyrus (DG). Interestingly, neural stem cell (NSC) density at the neural niche of DG was higher in TSK-KO compared with wild-type. The ratio of proliferating NSCs as well as the rate of overall cell proliferation was also higher in TSK-KO hippocampus. Our in vitro study also suggests an increased number of neural stem/progenitor cells residing in TSK-KO hippocampus. Finally, we found that the terminal differentiation of NSCs in TSK-KO was disturbed as the differentiation to neuronal cell lineage was increased while the percentages of astrocytes and oligodendrocytes were decreased. Overall, our study establishes the involvement of TSK in hippocampal development, NSC maintenance and terminal differentiation at perinatal stages.     

Periostin Promotes Neural Stem Cell Proliferation and Differentiation following Hypoxic-Ischemic Injury

Neural stem cell (NSC) proliferation and differentiation are required to replace neurons damaged or lost after hypoxic-ischemic events and recover brain function. Periostin (POSTN), a novel matricellular protein, plays pivotal roles in the survival, migration, and regeneration of various cell types, but its function in NSCs of neonatal rodent brain is still unknown. The purpose of this study was to investigate the role of POSTN in NSCs following hypoxia-ischemia (HI). We found that POSTN mRNA levels significantly increased in differentiating NSCs. The proliferation and differentiation of NSCs in the hippocampus is compromised in POSTN knockout mice. Moreover, NSC proliferation and differentiation into neurons and astrocytes significantly increased in cultured NSCs treated with recombinant POSTN. Consistently, injection of POSTN into neonatal hypoxic-ischemic rat brains stimulated NSC proliferation and differentiation in the subventricular and subgranular zones after 7 and 14 days of brain injury. Lastly, POSTN treatment significantly improved the spatial learning deficits of rats subjected to HI. These results suggest that POSTN significantly enhances NSC proliferation and differentiation after HI, and provides new insights into therapeutic strategies for the treatment of hypoxic-ischemic encephalopathy.     

The injured brain interacts reciprocally with neural stem cells supported by scaffolds to reconstitute lost tissue

Hypoxic-ischemic injury is a prototype for insults characterized by extensive tissue loss. Seeding neural stem cells (NSCs) onto a polymer scaffold that was subsequently implanted into the infarction cavities of mouse brains injured by hypoxia-ischemia allowed us to observe the multiple reciprocal interactions that spontaneously ensue between NSCs and the extensively damaged brain: parenchymal loss was dramatically reduced, an intricate meshwork of many highly arborized neurites of both host- and donor-derived neurons emerged, and some anatomical connections appeared to be reconstituted. The NSC-scaffold complex altered the trajectory and complexity of host cortical neurites. Reciprocally, donor-derived neurons were seemingly capable of directed, target-appropriate neurite outgrowth (extending axons to the opposite hemisphere) without specific external instruction, induction, or genetic manipulation of host brain or donor cells. These "biobridges" appeared to unveil or augment a constitutive reparative response by facilitating a series of reciprocal interactions between NSC and host, including promoting neuronal differentiation, enhancing the elaboration of neural processes, fostering the re-formation of cortical tissue, and promoting connectivity. Inflammation and scarring were also reduced, facilitating reconstitution.     

人神经干细胞的体外生物学特性

本实验利用有丝分裂因子,体外诱导生成人神 经干细胞(NSCs),观察其生长特性并进行鉴定。取胎龄10-22周的大脑半球,分散细胞后种于添加表皮生长因子(EGF,20ng/ml)和/或碱性成纤维生长因子(bFGF,20ng/ml)的培养基中。利用免疫组织化学方法鉴定分化后的细胞类型。同时,进行细胞克隆分析、传代培养及端粒酶活性检测。结果显示:NSCs呈悬浮生长的干细胞球,其特异性抗原nestin阳性。NSCs具有增殖能力,可连续传代而不丢失其增殖和多分化潜能的干细胞特性。撤除EGF和bFGF的作用,细胞停止分裂,并分化为神经元、星形胶质细胞和少突胶质细胞。克隆分析显示NSCs生长呈密度依赖性。人NSCs表达较低的端粒酶水平,并随培养时间延长而下调。研究表明,利用有丝分裂因子,可在体外成功诱导生成人NSCs,其生长,分化受内外源因素的调节,相关的机制还有待阐明。     

Mash-1在大鼠SVZa神经干细胞迁移流的发育学表达

目的了解在大鼠脑发育过程中,mash-1在SVZa神经干细胞迁移流通路中三个不同脑区内的表达模式。方法用RT-PCR和免疫荧光染色的方法观察在胚胎14d(E14),出生后0d(P0),生后7d(P7)3个不同发育阶段大鼠SVZa、RMS、OB3个区域mash-1的表达情况。结果RT-PCR显示在大鼠脑发育过程中SVZa、RMS、OB三个区域mash-1的mRNA均有不同程度的表达,在出生前后(P0)表达最高;免疫组化显示在大鼠脑发育成熟过程中,mash-1表达水平呈现复杂的时空表达模式,在胚胎期SVZa神经干细胞迁移流通路中表达密集,P0时期在嗅球有较高的表达,P7以后mash-1的表达水平普遍下降。结论mash-1可能主要参与调节大鼠SVZa神经干细胞分化过程,对其迁移和增殖也可能具有积极影响。     

Mammalian neural stem-cell renewal: nature versus nurture

Recent data show that the final events of mammalian brain organogenesis may depend in part on the direct control of neural stem cell (NSC) proliferation and survival. Environmental and intrinsic factors play a role throughout development and during adulthood to regulate NSC proliferation. The NSCs acquire new competences throughout development, including adulthood, and this change in competence is region-specific. The factors controlling NSC survival, undifferentiated state, proliferation, and cell-cycle number are beginning to be identified, but the links between them remain unclear. However, current knowledge should help to formulate an understanding of how a stem cell can generate a new stem cell.