Symposium 10: Differentiation Plasticity of Stem Cells. Direct differentiation of radial glial cells from embryonic stem cells

The major role of radial glial cells in neuronal development is to provide support and guidance for neuronal migration. In vitro, neurons, astrocytes and oligodendrocytes have also been generated from neural stem cells and embryonic stem cells, but the generation of radial glial cells in vitro has not yet been reported. Since radial glial cells can lead to neurons and astrocytes during brain development, neurogenesis and gliogenesis of stem cells in vitro may at least in part also utilize the same mechanisms. To test this hypothesis, we utilized five different clones of embryonic (ES) and embryonal carcinoma (EC) stem cell lines to investigate the differentiation of radial glial cells during in vitro neural differentiation. Here, we demonstrate that radial glial cells can be generated from ES/EC cell lines. These ES/EC cell‐derived radial glial cells are similar in morphology to radial glial cells in vivo. They also express several cytoskeletal markers that are characteristics of radial glial cells in vivo. The processes of these in vitro‐generated radial glial cells are organized into scaffolds that appear to support the migration of newly generated neurons in culture. Like radial glial cells in vivo, they appear to differentiate subsequently into astrocytes. Differentiation of radial glial cells may be a common pathway during in vitro neural differentiation of ES cells. This novel in vitro model system may facilitate the investigation of regulation of radial glial cell differentiation and its biological function. Acknowledgements: Supported by USPHS Grant NS11853 and a grant from the Children's Medical Research Foundation.     

Neuronal-glial interactions in central nervous system neurogenesis: the neural stem cell perspective

Essentially, three neuroectodermal-derived cell types make up the complex architecture of the adult CNS: neurons, astrocytes and oligodendrocytes. These elements are endowed with remarkable morphological, molecular and functional heterogeneity that reaches its maximal expression during development when stem/progenitor cells undergo progressive changes that drive them to a fully differentiated state. During this period the transient expression of molecular markers hampers precise identification of cell categories, even in neuronal and glial domains. These issues of developmental biology are recapitulated partially during the neurogenic processes that persist in discrete regions of the adult brain. The recent hypothesis that adult neural stem cells (NSCs) show a glial identity and derive directly from radial glia raises questions concerning the neuronal-glial relationships during pre- and post-natal brain development. The fact that NSCs isolated in vitro differentiate mainly into astrocytes, whereas in vivo they produce mainly neurons highlights the importance of epigenetic signals in the neurogenic niches, where glial cells and neurons exert mutual influences. Unravelling the mechanisms that underlie NSC plasticity in vivo and in vitro is crucial to understanding adult neurogenesis and exploiting this physiological process for brain repair. In this review we address the issues of neuronal/glial cell identity and neuronal-glial interactions in the context of NSC biology and NSC-driven neurogenesis during development and adulthood in vivo, focusing mainly on the CNS. We also discuss the peculiarities of neuronal-glial relationships for NSCs and their progeny in the context of in vitro systems.     

Brg1 is required for murine neural stem cell maintenance and gliogenesis

Epigenetic alterations in cell-type-specific gene expression control the transition of neural stem cells (NSCs) from predominantly neurogenic to predominantly gliogenic phases of differentiation, but how this switch occurs is unclear. Here, we show that brahma-related gene 1 (Brg1), an ATP-dependent chromatin remodeling factor, is required for the repression of neuronal commitment and the maintenance of NSCs in a state that permits them to respond to gliogenic signals. Loss of Brg1 in NSCs in conditional brg1 mutant mice results in precocious neuronal differentiation, such that cells in the ventricular zone differentiate into post-mitotic neurons before the onset of gliogenesis. As a result, there is a dramatic failure of astrocyte and oligodendrocyte differentiation in these animals. The ablation of brg1 in gliogenic progenitors in vitro also prevents growth-factor-induced astrocyte differentiation. Furthermore, proteins implicated in the maintenance of stem cells, including Sox1, Pax6 and Musashi-1, are dramatically reduced in the ventricular zones of brg1 mutant mice. We conclude that Brg1 is required to repress neuronal differentiation in NSCs as a means of permitting glial cell differentiation in response to gliogenic signals, suggesting that Brg1 regulates the switch from neurogenesis to gliogenesis.     

MiR-615在平行培养的神经干细胞与运动神经元的表达比较

目的探讨MiR-615在脊髓源性神经干细胞与运动神经元间的表达特征。方法通过免疫磁珠法分离纯化胚胎大鼠脊髓运动神经元;通过神经克隆球形成技术分离纯化胚胎大鼠脊髓源性神经干细胞。采用TaqMan miR-615Assay定量检测培养的脊髓源性神经干细胞与运动神经元中miR-615的表达差异。结果通过平行培养技术分别获得了纯化的脊髓源性神经干细胞与运动神经元。定量检测结果显示,miR-615在分离的运动神经元中较在脊髓源性神经干细胞中显著高表达。结论本文提示miR-615可能在神经干细胞定向分化为运动神经元过程中发挥重要的调节作用。     

Defective Self-Renewal and Differentiation of GBA-Deficient Neural Stem Cells Can Be Restored By Macrophage Colony-Stimulating Factor

Gaucher disease (GD) is an autosomal recessive lysosomal storage disorder caused by mutations in the glucocerebrosidase gene (GBA), which encodes the lysosomal enzyme glucosylceramidase (GCase). Deficiency in GCase leads to characteristic visceral pathology and lethal neurological manifestations in some patients. Investigations into neurogenesis have suggested that neurodegenerative disorders, such as GD, could be overcome or at least ameliorated by the generation of new neurons. Bone marrow-derived mesenchymal stem cells (BM-MSCs) are potential candidates for use in the treatment of neurodegenerative disorders because of their ability to promote neurogenesis. Our objective was to examine the mechanism of neurogenesis by BM-MSCs in GD. We found that neural stem cells (NSCs) derived from a neuronopathic GD model exhibited decreased ability for self-renewal and neuronal differentiation. Co-culture of GBA-deficient NSCs with BM-MSCs resulted in an enhanced capacity for self-renewal, and an increased ability for differentiation into neurons or oligodendrocytes. Enhanced proliferation and neuronal differentiation of GBA-deficient NSCs was associated with elevated release of macrophage colony-stimulating factor (M-CSF) from BM-MSCs. Our findings suggest that soluble M-CSF derived from BM-MSCs can modulate GBA-deficient NSCs, resulting in their improved proliferation and neuronal differentiation.     

Regulation of neural stem cell by bone morphogenetic protein (BMP) signaling during brain development

Neurogenesis is the process in which neurons are generated from neural stem/progenitor cells (NSCs/NPCs). It involves the proliferation and neuronal fate specification/differentiation of NSCs, as well as migration, maturation and functional integration of the neuronal progeny into neuronal network. NSCs exhibit the two essential properties of stem cells: self-renewal and multipotency. Contrary to previous dogma that neurogenesis happens only during development, it is generally accepted now that neurogenesis can take place throughout life in mammalian brains. This raises a new therapeutic potential of applying stem cell therapy for stroke, neurodegenerative diseases and other diseases. However, the maintenance and differentiation of NSCs/NPCs are tightly controlled by the extremely intricate molecular networks. Uncovering the underlying mechanisms that drive the differentiation, migration and maturation of specific neuronal lineages for use in regenerative medicine is, therefore, crucial for the application of stem cell for clinical therapy as well as for providing insight into the mechanisms of human neurogenesis. Here, we focus on the role of bone morphogenetic protein (BMP) signaling in NSCs during mammalian brain development.     

Effects of the monomeric, oligomeric, and fibrillar Abeta42 peptides on the proliferation and differentiation of adult neural stem cells from subventricular zone

The incidence of amyloid plaques, composed mainly of beta-amyloid peptides (Abeta), does not correlate well with the severity of neurodegeneration in patients with Alzheimer's disease (AD). The effects of Abeta(42) on neurons or neural stem cells (NSCs) in terms of the aggregated form remain controversial. We prepared three forms of oligomeric, fibrillar, and monomeric Abeta(42) peptides and investigated their effects on the proliferation and neural differentiation of adult NSCs, according to the degree of aggregation or concentration. A low micromolar concentration (1 micromol/L) of oligomeric Abeta(42) increased the proliferation of adult NSCs remarkably in a neurosphere assay. It also enhanced the neuronal differentiation of adult NSCs and their ability to migrate. These results provide us with valuable information regarding the effects of Abeta(42) on NSCs in the brains of patients with AD.     

Embryonic stem cell neurogenesis and neural specification

The prospect of using embryonic stem cell (ESC)‐derived neural progenitors and neurons to treat neurological disorders has led to great interest in defining the conditions that guide the differentiation of ESCs, and more recently induced pluripotent stem cells (iPSCs), into neural stem cells (NSCs) and a variety of neuronal and glial subtypes. Over the past decade, researchers have looked to the embryo to guide these studies, applying what we know about the signaling events that direct neural specification during development. This has led to the design of a number of protocols that successfully promote ESC neurogenesis, terminating with the production of neurons and glia with diverse regional addresses and functional properties. These protocols demonstrate that ESCs undergo neural specification in two, three, and four dimensions, mimicking the cell–cell interactions, patterning, and timing that characterizes the in vivo process. We therefore propose that these in vitro systems can be used to examine the molecular regulation of neural specification. J. Cell. Biochem. 111: 535–542, 2010. © 2010 Wiley‐Liss, Inc.     

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.     

Radial glial cells defined and major intermediates between embryonic stem cells and CNS neurons

Radial glial cells have been identified as a major source of neurons during development. Here, we review the evidence for the distinct "glial" nature of radial glial cells and contrast these cells with their progenitors, the neuroepithelial cells. Recent results also suggest that not only during neurogenesis in vivo, but also during the differentiation of cultured embryonic stem cells toward neurons, progenitors with clear glial antigenic characteristics act as cellular intermediates.     

溶血磷脂酸促进离体大鼠胚胎神经干细胞的增殖及其向胆碱能神经元分化

溶血磷脂酸（1ysophosphatidic acid,LPA）是一种细胞外磷脂信号。本研究用[^3H]-胸腺嘧啶掺入法、免疫细胞化学和Western blot等技术,观察了LPA对体外培养的大鼠胚胎神经干细胞（neural stem cells,NSCs）的增殖以及向MAF2标记的一般神经元和ChAT标记的胆碱能神经元的分化的影响。结果显示：（1）在特殊的无血清培养基中加入低浓度的LPA（0．01-1．0μmol/L）后,NSCs对【^3H】-胸腺嘧啶的摄入呈剂量依赖性增加,表明LPA对NSCs有显著的促增殖作用;（2）在培养基中加入胎牛血清以诱导NSCs的分化,发现低浓度的LPA增加MAF2阳性和ChAT阳性神经元的比例,0．1μmol／L LPA引起的增加达到峰值;（3）Western blot分析显示LPA促进了MAP2和ChAT的表达;（4）在诱导NSCs出现分化早期,用倒置显微镜观察到低浓度的LPA明显促进细胞突起的生长和细胞的迁移。以上结果表明,低浓度LPA在一定范围内可以促进NSCs的增殖、并分化为一般的MAP2阳性神经元和特殊的胆碱能神经元,而且LPA可以促进在分化早期出现的神经元或神经胶质细胞前体细胞的迁移和突起生长。     

Neural stem cells: involvement in adult neurogenesis and CNS repair

Recent advances in stem cell research, including the selective expansion of neural stem cells (NSCs) in vitro, the induction of particular neural cells from embryonic stem cells in vitro, the identification of NSCs or NSC-like cells in the adult brain and the detection of neurogenesis in the adult brain (adult neurogenesis), have laid the groundwork for the development of novel therapies aimed at inducing regeneration in the damaged central nervous system (CNS). There are two major strategies for inducing regeneration in the damaged CNS: (i) activation of the endogenous regenerative capacity and (ii) cell transplantation therapy. In this review, we summarize the recent findings from our group and others on NSCs, with respect to their role in insult-induced neurogenesis (activation of adult NSCs, proliferation of transit-amplifying cells, migration of neuroblasts and survival and maturation of the newborn neurons), and implications for therapeutic interventions, together with tactics for using cell transplantation therapy to treat the damaged CNS.     

A novel role for Gab2 in bFGF-mediated cell survival during retinoic acid-induced neuronal differentiation

Gab proteins amplify and integrate signals stimulated by many growth factors. In culture and animals, retinoic acid (RA) induces neuronal differentiation. We show that Gab2 expression is detected in neurons in three models of neuronal differentiation: embryonic carcinoma (EC) stem cells, embryonic stem cells, and primary neural stem cells (NSCs). RA treatment induces apoptosis, countered by basic FGF (bFGF). In EC cells, Gab2 silencing results in hypersensitivity to RA-induced apoptosis and abrogates the protection by bFGF. Gab2 suppression reduces bFGF-dependent activation of AKT but not ERK, and constitutively active AKT, but not constitutively active MEK1, reverses the hypersensitization. Thus, Gab2-mediated AKT activation is required for bFGF's protection. Moreover, Gab2 silencing impairs the differentiation of EC cells to neurons. Similarly, in NSCs, Gab2 suppression reduces bFGF-dependent proliferation as well as neuronal survival and production upon differentiation. Our findings provide the first evidence that Gab2 is an important player in neural differentiation, partly by acting downstream of bFGF to mediate survival through phosphoinositide 3 kinase-AKT.     

大鼠胚胎神经干细胞纹状体内移植后特性

观察大鼠胚胎神经干细胞移植入成年大鼠纹状体后的存活、迁移和分化状况。自14天胎鼠脑室下区分离获得神经干细胞,利用无血清培养基培养扩增并进行鉴定。经4～5代的扩增后,以BrdU标记的神经干细胞通过脑立体定位注射移植入成年大鼠纹状体内,然后分别于移植后2周、4周、6周和8周时做脑冰冻切片,通过免疫组织化学和免疫荧光方法检测移植细胞的数量、定位和分化情况。8周后移植细胞的检出率约16%;移植细胞向周围宿主组织有广泛的迁移表现,尤以沿着白质束向头尾方向的迁移最为显著,最远向后侧达到内囊;纹状体中移植细胞主要分化为神经元和星形胶质细胞。星形胶质细胞数量最多,主要位于移植区与宿主组织临界部位,而神经元处于移植区中央。培养的大鼠胚胎神经干细胞可以作为移植替代治疗神经退行性疾病研究的供体细胞源,而移植中的迁移现象值得注意。     

Effects of Oxygen Concentration on the Proliferation and Differentiation of Mouse Neural Stem Cells In Vitro

Background and purpose Cerebral ischemia is known to elicit the activation of neural stem cells (NSCs); however its mechanism is not fully determined. Although oxygen concentration is known to mediate many ischemic actions, there has been little attention given to the role of pathological oxygen changes under cerebral ischemia on the activation of NSCs. We investigated the effects of various oxygen concentrations on mouse neural stem cells in vitro. Methods NSCs were cultured from the ganglionic eminence of fetal ICR mice on embryonic day 15.5 using a neurosphere method. The effects of oxygen concentrations on proliferation, differentiation, and cell death of NSCs were evaluated by bromodeoxyuridine (BrdU) incorporation, immunocytochemistry, and TUNEL assay, respectively. Results The highest proliferation and the neuronal differentiation of the NSCs were observed in 2% oxygen, which yielded significantly higher proportions of both BrdU-labeled cells and Tuj1-positive cells when compared with 20% and 4% oxygen. On the other hand, the differentiation to the astrocytes was not affected by oxygen concentrations, except in the case of anoxia (0% oxygen). The cell death of the NSCs increased in lower oxygen conditions and peaked at anoxia. Furthermore, the switching of the neuronal subtype differentiation from GABA-positive to glutamate-positive neurons was observed in lower oxygen conditions. Conclusions These findings raise the possibility that reduced oxygen levels occurring with cerebral ischemia enhance NSC proliferation and neural differentiation, and that mild hypoxia (2% oxygen), which is known to occur in the ischemic penumbra, is suitable for abundant neuronal differentiation.