Erk信号途径在B104 CM诱导神经干细胞向少突胶质细胞前体分化中的作用

目的探讨细胞外信号调节激酶(Erk)信号途径及下游转录因子cf-os、cj-un等在神经母细胞瘤B104细胞系来源的条件培养基(B104 CM)诱导神经干细胞(NSCs)向少突胶质细胞前体(OPCs)分化中的作用。方法从形态学上观察Erk1/2特异性抑制剂U0126阻断对B104 CM诱导NSCs向OPCs分化的影响;分别以Western blotting和RT-PCR法检测对照组、B104 CM诱导组和U0126预孵组NSCs中Erk的磷酸化和转录因子cf-os、cj-un、c-myc的表达情况。结果U0126预孵可阻断B104 CM诱导的NSCs向OPCs分化;B104 CM可引起NSCs中Erk1/2迅速磷酸化和cf-os、cj-unmRNA表达上调,该作用可被U0126阻断。结论B104 CM通过活化Erk信号途径及其随后上调转录因子cf-os、cj-un的表达诱导NSCs向OPCs分化。     

Rho GTPases mediate the mechanosensitive lineage commitment of neural stem cells

Adult neural stem cells (NSCs) play important roles in learning and memory and are negatively impacted by neurological disease. It is known that biochemical and genetic factors regulate self-renewal and differentiation, and it has recently been suggested that mechanical and solid-state cues, such as extracellular matrix (ECM) stiffness, can also regulate the functions of NSCs and other stem cell types. However, relatively little is known of the molecular mechanisms through which stem cells transduce mechanical inputs into fate decisions, the extent to which mechanical inputs instruct fate decisions versus select for or against lineage-committed blast populations, or the in vivo relevance of mechanotransductive signaling molecules in native stem cell niches. Here we demonstrate that ECM-derived mechanical signals act through Rho GTPases to activate the cellular contractility machinery in a key early window during differentiation to regulate NSC lineage commitment. Furthermore, culturing NSCs on increasingly stiff ECMs enhances RhoA and Cdc42 activation, increases NSC stiffness, and suppresses neurogenesis. Likewise, inhibiting RhoA and Cdc42 or downstream regulators of cellular contractility rescues NSCs from stiff matrix- and Rho GTPase-induced neurosuppression. Importantly, Rho GTPase expression and ECM stiffness do not alter proliferation or apoptosis rates indicating that an instructive rather than selective mechanism modulates lineage distributions. Finally, in the adult brain, RhoA activation in hippocampal progenitors suppresses neurogenesis, analogous to its effect in vitro. These results establish Rho GTPase-based mechanotransduction and cellular stiffness as biophysical regulators of NSC fate in vitro and RhoA as an important regulatory protein in the hippocampal stem cell niche.     

叶酸通过调节p53/p21(waf1/cip1)信号途径促进小鼠神经干细胞增殖和分化

目的:研究叶酸对体外培养小鼠神经干细胞(neural stem cells,NSCs)增殖和分化的影响及作用机制。方法:采用无血清悬浮培养方法分离培养新生小鼠脑NSCs,通过MTT法检测叶酸对NSCs增殖的影响;撤除生长因子后,用含10%胎牛血清的培养基诱导分化培养6 d后,采用Tuj1(神经元标记物)和GFAP(胶质细胞标记物)免疫荧光双标记法检测叶酸对NSCs分化的影响;并应用流式细胞术、RT-PCR法检测给予叶酸对NSCs细胞周期、p53和p21(waf1/cip1)mRNA水平的影响。结果:与对照组相比,MTT法测定结果显示,叶酸组NSCs增殖能力明显增强;分化后免疫荧光双标法测定显示,叶酸组Tuj1阳性细胞的比率明显增加,且差异具有显著性(P<0.01);流式细胞仪测定结果显示,叶酸组NSCs在G0/G1期细胞数量明显减少(P<0.01),而G2/M期细胞数量明显增多(P<0.01);RT-PCR结果显示,叶酸组NSCs中p53和p21 mRNA表达量明显降低。结论:叶酸能促进NSCs增殖及向神经元分化;叶酸对NSCs增殖和分化的影响与调节NSCs细胞周期及p53/p21(waf1/cip1)信号转导途径相关。     

NANOS2 acts downstream of glial cell line-derived neurotrophic factor signaling to suppress differentiation of spermatogonial stem cells

Stem cells are maintained by both stem cell-extrinsic niche signals and stem cell-intrinsic factors. During murine spermatogenesis, glial cell line-derived neurotrophic factor (GDNF) signal emanated from Sertoli cells and germ cell-intrinsic factor NANOS2 represent key regulators for the maintenance of spermatogonial stem cells. However, it remains unclear how these factors intersect in stem cells to control their cellular state. Here, we show that GDNF signaling is essential to maintain NANOS2 expression, and overexpression of Nanos2 can alleviate the stem cell loss phenotype caused by the depletion of Gfra1, a receptor for GDNF. By using an inducible Cre-loxP system, we show that NANOS2 expression is downregulated upon the conditional knockout (cKO) of Gfra1, while ectopic expression of Nanos2 in GFRA1-negative spermatogonia does not induce de novo GFRA1 expression. Furthermore, overexpression of Nanos2 in the Gfra1-cKO testes prevents precocious differentiation of the Gfra1-knockout stem cells and partially rescues the stem cell loss phenotypes of Gfra1-deficient mice, indicating that the stem cell differentiation can be suppressed by NANOS2 even in the absence of GDNF signaling. Taken together, we suggest that NANOS2 acts downstream of GDNF signaling to maintain undifferentiated state of spermatogonial stem cells.     

Gli1 induces G2/M arrest and apoptosis in hippocampal but not tumor-derived neural stem cells

Sonic hedgehog (Shh) is necessary for sustaining the proliferation of neural stem cells (NSCs), yet little is known about its mechanisms. Whereas Gli1, Gli2, and Gli3, the primary mediators of Shh signaling, were all expressed in hippocampal neural progenitors, Shh treatment of NSCs induced only Gli1 expression. Acute depletion of Gli1 in postnatal NSCs by short-hairpin RNA decreased proliferation, whereas germline deletion of Gli1 did not affect NSC proliferation, suggesting a difference in mechanisms of Gli1 compensation that may be developmentally dependent. To determine whether Gli1 was sufficient to enhance NSC proliferation, we overexpressed this mitogen and were surprised to find that Gli1 resulted in decreased proliferation, accumulation of NSCs in the G2/M phase of cell cycle, and apoptosis. In contrast, Gli1-expressing lineage-restricted neural precursors demonstrated a 4.5-fold proliferation enhancement. Expression analyses of Gli1-expressing NSCs identified significant induction of Gadd45a and decreased cyclin A2 and Stag1 mRNA, genes involved in the G2-M transition and apoptosis. Furthermore, Gadd45a overexpression was sufficient to partially recapitulate the Gli1-induced G2/M accumulation and cell death of NSCs. In contrast to normal stem cells, tumor-derived stem cells had markedly higher basal Gli1 expression and did not undergo apoptosis with further elevation of Gli1. Our data suggest that Gli1-induced apoptosis may serve as a protective mechanism against premature mitosis and may give insight into mechanisms by which nonmalignant stem cells restrain hyperproliferation in the context of potentially transforming mitogenic signals. Tumor-derived stem cells apparently lack these mechanisms, which may contribute to their unrestrained proliferation and malignant potential.     

Effects of granulocyte colony-stimulating factor on the proliferation and cell-fate specification of neural stem cells

Granulocyte-colony stimulating factor (G-CSF) is a growth factor that regulates proliferation, differentiation and survival of hematopoietic progenitor cells. There is growing evidence to suggest that G-CSF exerts a powerful neuroprotective effect in different neurological disorders. However, it has remained to be elucidated if G-CSF has a direct effect on neural stem cells (NSCs). Here, we show that G-CSF could stimulate the proliferation of NSCs and promote their differentiation in vitro. Additionally, we have shown that G-CSF-induced proliferation of NSCs is associated with phosphorylation of STAT3, and the differentiation is linked to altered expression of differentiation-related genes. Remarkably, G-CSF could not initiate the differentiation of NSCs. The added roles of G-CSF in regulating proliferation and differentiation of NSCs as shown in this study would serve as a useful reference in designing new stem cell therapy strategies for promoting brain recovery and repair.     

Hypoxia stimulates proliferation of rat neural stem cells with influence on the expression of cyclin D1 and c-Jun N-terminal protein kinase signaling pathway in vitro

Ischemia/hypoxia is known to induce the neural stem cells proliferation and neural differentiation in rodent and human brain; however its mechanisms remain largely unknown. In this study we investigated the effect of hypoxia on neural stem cells (NSCs) proliferation with the expression of cyclin D1 and the phosphorylation of mitogen-activated protein kinases (MAPK) signaling molecules. NSCs were cultured from cortex of fetal Sprague–Dawley rats on embryonic day 5.5. The hypoxia was made using a microaerophilic incubation system. The NSCs proliferation was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, diameter measurement of neurospheres, bromodeoxyuridine (BrdU) incorporation assay and cell cycle analysis. The cell death of NSCs was evaluated by terminal dUTP nick-end labeling (TUNEL) assay. The expression of cyclin D1, phosphorylated extracellular signal regulated kinase (ERK), c-Jun N-terminal protein kinase (JNK) and p38 were analyzed by immunoblotting assay. The results showed that hypoxia increased NSCs proliferation in cell amount, diameter of neurospheres, BrdU incorporation and cell division, and the highest proliferation of the NSCs was observed with 12 h hypoxic treatment; hypoxia did not decrease cell death of NSCs; after hypoxic treatment, the expression of cyclin D1 increased, meanwhile P-JNK2 level increased, P-p38 decreased, and no significant change in P-ERK2 level compared to normoxic cultures. JNK inhibitor SP600125 attenuated the increase of cyclin D1 induced by hypoxia. These findings propose that hypoxia increases cyclin D1 expression through activation of JNK in NSCs of rat in vitro, suggesting a novel possible mechanism for hypoxia-induced proliferation of NSCs.     

The influence of fiber diameter of electrospun substrates on neural stem cell differentiation and proliferation

Neural stem/progenitor cells (NSCs) are capable of self-renewal and differentiation into all types of neural lineage under different biochemical and topographical cues. In this study, we cultured rat hippocampus-derived adult NSCs (rNSCs) on laminin-coated electrospun Polyethersulfone (PES) fiber meshes with average fiber diameters of 283+/-45 nm, 749+/-153 nm and 1452+/-312 nm; and demonstrated that fiber diameter of PES mesh significantly influences rNSC differentiation and proliferation. Under the differentiation condition (in the presence of 1 microM retinoic acid and 1% fetal bovine serum), rNSCs showed a 40% increase in oligodendrocyte differentiation on 283-nm fibers and 20% increase in neuronal differentiation on 749-nm fibers, in comparison to tissue culture polystyrene surface. SEM imaging revealed that cells stretched multi-directionally to follow underlying 283-nm fibers, but extended along a single fiber axis on larger fibers. When cultured on fiber meshes in serum free medium in the presence of 20 ng/mL of FGF-2, rNSCs showed lower proliferation and more rounded morphology compared to that cultured on laminin-coated 2D surface. As the fiber diameter decreased, higher degree of proliferation and cell spreading and lower degree of cell aggregation were observed. This collective evidence indicates fiber topography can play a vital role in regulating differentiation and proliferation of rNSCs in culture.     

Tetramethylpyrazine promotes proliferation and differentiation of neural stem cells from rat brain in hypoxic condition via mitogen-activated protein kinases pathway in vitro

This study investigated the effects of tetramethylpyrazine (TMP), an active element of traditional Chinese medicine Ligusticum Chuanxiong, on proliferation and differentiation of neural stem cells (NSCs) from rat brain in hypoxia condition and the activation of mitogen-activated protein kinases (MAPKs) signaling pathway during the processes. The results showed that TMP promoted the proliferation and differentiation of the NSCs into neurons. TMP increased the phosphorylation of ERK1/2 and decreased the phosphorylation of p38 at different time points. ERK inhibitor (U0126) in part blocked the differentiation of the NSCs into neurons induced by TMP. Our findings demonstrated that TMP enhanced the proliferation and differentiation of NSCs of rat after hypoxia in vitro, in which the phosphorylation of ERK and p38 was involved.     

Polydopamine-mediated surface modification of scaffold materials for human neural stem cell engineering

Surface modification of tissue engineering scaffolds and substrates is required for improving the efficacy of stem cell therapy by generating physicochemical stimulation promoting proliferation and differentiation of stem cells. However, typical surface modification methods including chemical conjugation or physical absorption have several limitations such as multistep, complicated procedures, surface denaturation, batch-to-batch inconsistencies, and low surface conjugation efficiency. In this study, we report a mussel-inspired, biomimetic approach to surface modification for efficient and reliable manipulation of human neural stem cell (NSC) differentiation and proliferation. Our study demonstrates that polydopamine coating facilitates highly efficient, simple immobilization of neurotrophic growth factors and adhesion peptides onto polymer substrates. The growth factor or peptide-immobilized substrates greatly enhance differentiation and proliferation of human NSCs (human fetal brain-derived NSCs and human induced pluripotent stem cell-derived NSCs) at a level comparable or greater than currently available animal-derived coating materials (Matrigel) with safety issues. Therefore, polydopamine-mediated surface modification can provide a versatile platform technology for developing chemically defined, safe, functional substrates and scaffolds for therapeutic applications of human NSCs.     

Energy metabolism in adult neural stem cell fate

The adult mammalian brain contains a population of neural stem cells that can give rise to neurons, astrocytes, and oligodendrocytes and are thought to be involved in certain forms of memory, behavior, and brain injury repair. Neural stem cell properties, such as self-renewal and multipotency, are modulated by both cell-intrinsic and cell-extrinsic factors. Emerging evidence suggests that energy metabolism is an important regulator of neural stem cell function. Molecules and signaling pathways that sense and influence energy metabolism, including insulin/insulin-like growth factor I (IGF-1)-FoxO and insulin/IGF-1-mTOR signaling, AMP-activated protein kinase (AMPK), SIRT1, and hypoxia-inducible factors, are now implicated in neural stem cell biology. Furthermore, these signaling modules are likely to cooperate with other pathways involved in stem cell maintenance and differentiation. This review summarizes the current understanding of how cellular and systemic energy metabolism regulate neural stem cell fate. The known consequences of dietary restriction, exercise, aging, and pathologies with deregulated energy metabolism for neural stem cells and their differentiated progeny will also be discussed. A better understanding of how neural stem cells are influenced by changes in energy availability will help unravel the complex nature of neural stem cell biology in both the normal and diseased state.     

Neurofibromatosis-1 regulates neuroglial progenitor proliferation and glial differentiation in a brain region-specific manner

Recent studies have shown that neuroglial progenitor/stem cells (NSCs) from different brain regions exhibit varying capacities for self-renewal and differentiation. In this study, we used neurofibromatosis-1 (NF1) as a model system to elucidate a novel molecular mechanism underlying brain region-specific NSC functional heterogeneity. We demonstrate that Nf1 loss leads to increased NSC proliferation and gliogenesis in the brainstem, but not in the cortex. Using Nf1 genetically engineered mice and derivative NSC neurosphere cultures, we show that this brain region-specific increase in NSC proliferation and gliogenesis results from selective Akt hyperactivation. The molecular basis for the increased brainstem-specific Akt activation in brainstem NSCs is the consequence of differential rictor expression, leading to region-specific mammalian target of rapamycin (mTOR)/rictor-mediated Akt phosphorylation and Akt-regulated p27 phosphorylation. Collectively, these findings establish mTOR/rictor-mediated Akt activation as a key driver of NSC proliferation and gliogenesis, and identify a unique mechanism for conferring brain region-specific responses to cancer-causing genetic changes.     

内源性神经干细胞与缺血性脑损伤

神经干细胞具有自我更新和多向分化潜能。成年脑内存在神经干细胞为脑损伤后的自我修复提供了可能。脑缺血能激活内源性神经干细胞,诱导其增殖、迁移、分化,参与损伤后结构修复和功能重建。 兴奋性氨基酸、一氧化氮合酶、细胞因子等诸多因素参与调控内源泉性神经干细胞的激活。进一步了解内源性神经干细胞的活化机制,对其临床应用具有重要意义。     

Aβ1-42作用的小胶质细胞对体外培养的神经干细胞生存的影响

目的: 探讨β-淀粉样蛋白(Aβ_1-42)作用的小胶质细胞对体外培养的神经干细胞(NSCs)生存的影响。方法: 利用Transwell小室在体外建立NSCs与小胶质细胞共培养体系,检测Aβ_1-42蛋白作用小胶质细胞前后NSCs增殖、分化及凋亡情况。结果: 与单纯共培养组相比,Aβ_1-42干预共培养组的增殖率降低,且微管相关蛋白2(MAP-2)和胆碱乙酰转化酶(CHAT)阳性表达率也均降低。结论: Aβ_1-42介导的炎症反应抑制了神经干细胞的增殖,促进其凋亡,并能显著降低其分化成神经元尤其是胆碱能神经元的能力。     

PF-127-LV-NTFs三维复合支架培养大鼠神经干细胞

目的观察Pluronic F-127(PF-127)水凝胶负载编码慢病毒LINGO-1 shRNA(LV)及神经营养因子混合物(NTFs)(PF-127-LV-NTFs)三维复合支架对大鼠神经干细胞(NSCs)增殖分化的影响。方法构建慢病毒(LV)后以不同感染复数(MOI)感染NSCs,用RT-qPCR及Western blot检测NSCs中LINGO-1的表达;按照一定比例将脑源性神经营养因子(BDNF)、神经营养素-3(NT-3)、血小板衍生生长因子(PDGF)、胰岛素样生长因子-1(IGF-1)、表皮生长因子(EGF)、碱性成纤维细胞生长因子(bFGF)、神经胶质细胞来源的神经营养因子(GDNF)配制成NTFcocktail(NTFs),PF-127水凝胶负载LV和NTFcocktail并分组培养NSCs;用CCK-8法检测NSCs的细胞活力,LIVE/DEAD染色检测NSCs的存活率,免疫荧光染色检测NSCs增殖和分化情况。结果 LV感染NSCs的最适MOI=5;PF-127对NSCs的细胞活力没有影响;PF-127+LV+NTFs组NSCs存活、增殖及神经元分化比例较高(P&...