脑梗死后神经干细胞的活化和移植

脑梗死后，缺血核心神经细胞的死亡不可避免。成年哺乳动物脑室下层（SVZ）和海马齿状回颗粒下层（SGZ）等保持着神经发生。脑梗死可促进神经发生。存在于这些部位的神经干细胞（NSC）具有自我更新和多向分化潜能。近年来，NSC的激活和向梗死灶周围迁移等机制逐渐为人们所认识，采取适当的措施激活脑内自然的神经发生、移植外源性NSC治疗脑梗死的研究，给脑梗死后缺损组织结构和功能的修复带来了希望。     

神经干细胞与脑缺血

神经干细胞(NSC)在脑缺血时发生增殖、迁移和分化,以修复损伤的神经功能,NSC移植可用于防治脑缺血。     

缺血缺氧性脑损伤治疗的新方法--神经干细胞移植

神经干细胞(NSC)是一群较原始的、能自我更新并具有多种分化潜能的细胞,可分化成神经元、少突胶质细胞和星形细胞.在生理条件下,体内的NSC通常保持静息状态;神经损伤后,内源性NSC可因微环境的改变而被激活、迁移和分化,以替代损伤的细胞和重建神经环路;遗传修饰后,外源性NSC移植显示了很大的治疗潜力,为今后缺血缺氧性脑损伤的治疗提供了新的手段.     

神经干细胞及其在缺血性脑损伤中的研究进展

神经干细胞(NSC)的迁移现象是指细胞在生长过程中有规律地发生位移的现象。NSC迁移是当前NSC研究的核心问题,阐明其机制对发展神经生物学和临床应用NSC治疗中枢神经系统疾病具有重要意义。目前应用NSC治疗缺血性脑损伤包括运用外源性NSC移植和内源性NSC两种方法。本文对比了两种方法的优缺点,介绍了NSC的来源、分离纯化、特征、迁移现象及其机制,以及NSC应用于治疗缺血性脑损伤存在的问题和展望。     

神经干细胞的增殖与分化调控机制

神经干细胞(NSC)是具有高度自我更新能力并能分化为神经元、星形胶质细胞和少突胶质细胞的神经前体细胞。从胚胎和成年哺乳动物脑内均可分离出NSC。干细胞的增殖和分化受微环境和基因的双重调控,现已发现多种细胞因子和基因可调节NSC的增殖并决定其分化方向。对NSC增殖和分化机制认识的加深将会促进NSC的临床应用。     

缺血缺氧性脑损伤治疗的新方法——神经干细胞移植

神经干细胞（NSC）是一群较原始的，能自我更新并具有多种分化潜能的细胞，可分化成神经元，少突胶质细胞和星形细胞。在生理条件下，体现人的NSC通常保持静息状态；神经损伤后，内源性NSC可因微环境的改变而被激活，迁移和分化 。以替代损伤的细胞和重建神经环路；遗传修饰后，外源性NSC移植显示了很大的治疗潜力，为今后缺血缺氧性脑损伤的治疗提供了新的手段。     

中枢神经系统的免疫学特性与神经干细胞移植的免疫排斥问题

中枢神经系统被认为是免疫特免器官,但其免疫特免性并不完全,组织移植后也可发生免疫排斥反应。神经干细胞(NSC)移植为治疗多种中枢神经系统疾病开辟了崭新的途径。尽管NSC具有低免疫原性,但也存在免疫排斥反应的困扰。文章就中枢神经系统的免疫学特征、中枢神经系统内免疫应答及免疫排斥反应的机制和NSC移植的免疫排斥问题进行了综述。     

脑缺血后的神经和血管发生

成年脑内存在神经干细胞(NSC),脑缺血后室管膜、室下区和海马齿状回的NSC因微环境改变而被激活,并参与机体的损伤修复反应。同时,作为对缺血的另一种代偿反应,半暗带内的骨髓源性内皮细胞、脑血管内皮细胞增殖迁移,巨噬细胞浸润增加,并使新生血管形成。两个过程密切相关,共同完成缺血后的脑组织修复。     

神经干细胞与神经营养因子

神经干细胞（NSC）增殖是神经发育早期阶段的主要事件，在此阶段，NSC通过10—12次分裂进行增殖，为后期神经发生提供足够的细胞来源。此外，当脑组织受损时，内源性NSC也可增殖并分化，补偿缺失的神经细胞，部分修复神经功能。神经营养因子（NTF）是一类对神经元有特异性保护作用的内分泌多肽，它可促进体内、外培养神经元存活及突起生长。1952年Levi—Montalcini在研究鸡胚的神经发育过程中发现了神经生长因子（NGF），此后几十年，新的NTF不断被发现，并形成了NTF大家族。它们来源于靶细胞逆向营养神经元，促进和维持神经细胞生长、存活，修复神经细胞功能。在胚胎发育早期，NTF如碱性成纤维细胞生长因子（bFGF）、表皮生长因子（EGF）等能显著促进NSC的增殖与分化。     

神经干细胞与脑缺血

神经干细胞（NSC）在脑缺血时发生增殖，迁移和分化，以修复损伤的神经功能，NSC移植可用于防治脑缺血。     

经鼻导入rhG—CSF后脑梗死大鼠内源性神经干细胞的增殖与迁移

目的 探讨人重组粒细胞集落刺激因子（rhG-CSF）经鼻靶向中枢给药对脑梗死大鼠内源性神经干细胞增殖与迁移的调节作用。方法线栓法制作大脑中动脉阻塞模型（MCAO）,皮下或鼻腔给予rhG-CSF（60μg／kg）。运用5-溴脱氧尿苷嘧啶（BrdU）标记及免疫组织化学法检测局灶性脑梗死大鼠室管膜及脑室下层（SVZ）神经干细胞的增殖。结果正常组及假手术对照组大鼠SVZ区域散在少量BrdU阳性细胞;术后7d和14d,脑梗死组大鼠SVZ区BrdU阳性细胞数明显增加;rhG-CSF组BrdU阳性细胞数进一步增加;经鼻给药组的BrdU阳性细胞数明显高于相应时间点的皮下用药组（P〈0．01）。结论rhG-CSF鼻腔给药可以促进脑梗死后大鼠内源性神经干细胞的增殖和靶向迁移。     

Ephrins as negative regulators of adult neurogenesis in diverse regions of the central nervous system

In the central nervous system (CNS) of adult mammals, neurogenesis occurs in only two restricted areas, the subgranular zone (SGZ) of the hippocampus and the subventricular zone (SVZ). Isolation of multipotent progenitor cells from other CNS regions suggests that their neurogenic potential is dictated by local environmental cues. Here, we report that astrocytes in areas outside of the SGZ and SVZ of adult mice express high levels of ephrin-A2 and -A3, which present an inhibitory niche, negatively regulating neural progenitor cell growth. Adult mice lacking both ephrin-A2 and -A3 display active ongoing neurogenesis throughout the CNS. These findings suggest that neural cell replacement therapies for neurodegeneration or injury in the adult CNS may be achieved by manipulating ephrin signaling pathways.     

Growth hormone receptor immunoreactivity is increased in the subventricular zone of juvenile rat brain after focal ischemia: A potential role for growth hormone in injury-induced neurogenesis

BackgroundDuring recovery from an ischemic brain injury, a cerebral growth hormone (GH) axis is activated. Whilst GH has been demonstrated to be neuroprotective both in vitro and in vivo, a role for GH in neuro-restorative processes after brain injury has yet to be studied.ObjectiveTo explore a role for GH in injury-induced neurogenesis by examining GH receptor (GH-R) immunoreactivity within the subventricular zone (SVZ) of juvenile rats after brain injury and by testing the proliferative capacity of GH on embryonic mouse neural stem cells.DesignTwenty-one day old rats were subjected to unilateral hypoxic-ischemia of the brain and sacrificed 1–15 days later. Coronal brain sections from these animals and age-matched naïve controls were immunostained for GH-R and cell markers of neurogenesis. The level of GH-R immunoreactivity in the ipsilateral and contralateral SVZ of each animal was semi-quantified both by independent blinded scoring by two examiners and blinded image analysis. To examine the effect of GH on proliferation of embryonic mouse neural stem cells, cells were treated with increasing concentrations of rat pituitary GH for 48 h in the presence of 5′-bromo-2′-deoxyuridine.ResultsThe level of GH-R immunoreactivity in the ipsilateral SVZ was significantly increased 5 days after injury vs. the contralateral SVZ, coinciding both spatially and temporally with injury-induced neurogenesis. The population of GH-R immunopositive cells in the ipsilateral SVZ at this time was found to include proliferating cells (Ki67 immunopositive), neural progenitor cells (nestin immunopositive) and post-proliferative migratory neuroblasts (doublecortin immunopositive). Stimulation of embryonic mouse NSCs with physiological concentrations of rat pituitary GH elicited a dose-dependent proliferative response.ConclusionThese results indicate a novel role for GH and its receptor in injury-induced neurogenesis, and suggest that GH treatment may potentiate endogenous neuro-restorative processes after brain injury.     

星形细胞在神经再生中的作用

神经干细胞和骨髓间质细胞具有增殖及分化为神经元的潜能,作为替代细胞为脑损伤后的神经再生带来了希望。最近的研究发现,成年颗粒下层和脑室下带等脑区的星形细胞具有干细胞的特性,在一定条件下可分化为神经元,并能提高神经的可塑性。探讨星形细胞对神经再生的影响,有助于重新认识星形细胞的功能及其在神经再生中的作用。     

脑缺血后的神经发生与凋亡

研究表明 ,成年哺乳动物脑内存在神经干细胞 ,具有神经发生的能力。在脑缺血后 ,神经干细胞被激活 ,分化为神经元并可替代丢失的神经细胞 ,发挥一定的代偿功能 ,同时其他一些细胞却发生凋亡。文章介绍了脑缺血后神经发生和凋亡的研究新进展 ,而促进神经发生 ,减少凋亡会是一条新的治疗新思路     

大鼠脑梗死后内源性神经干细胞的增殖及迁移

目的研究成年大鼠脑梗死后内源性神经干细胞增殖及迁移。 方法制作大鼠脑梗死模型,将其分成梗死后1、3、7、14、28 d组,对照组为假手术组。免疫组织化学方法动态检测大鼠脑内5-溴脱氧尿苷嘧啶(BrdU)、巢蛋白(Nestin)的表达。 结果与正常对照组相比,室下区及海马BrdU和Nestin阳性细胞在脑梗死后1 d开始增加(P<0.05),7d达到高峰,14 d后开始下降,但仍高于正常水平(P<0.05),28 d后接近正常水平;室下区及海马BrdU和Nestin阳性细胞经胼胝体向对侧迁移。 结论脑梗死可激活内源性神经干细胞原位增殖及迁移。     

人参皂甙Rg1对大鼠局灶性脑缺血后侧脑室下区神经干细胞增殖分化的影响

目的观察人参皂甙Rg1对大鼠局灶性脑缺血后侧脑室下区神经干细胞增殖分化的影响,探讨其促进神经发生的作用。方法将60只Wistar大鼠随机分为假手术组、单纯缺血组及人参皂甙Rg1治疗组。用Longa线栓法制作成年大鼠大脑中动脉闭塞模型。腹腔注射5-溴脱氧尿苷(BrdU)标记处于增殖状态的神经干细胞,用免疫单标及双标免疫荧光技术观察人参皂甙Rg1对局灶性脑缺血后侧脑室下区BrdU免疫活性及BrdU/神经元特异性烯醇化酶和BrdU/胶质纤维酸性蛋白双标免疫活性的影响,并计数作定量分析。结果脑缺血后侧脑室下区存在BrdU阳性细胞分布;应用人参皂甙Rg1后,上述部位及周边脑区BrdU阳性细胞数及双标阳性细胞明显增多(P<0.01)。结论人参皂甙Rg1能诱导侧脑室下区神经干细胞增殖、分化,提示其具有促进神经发生的能力。     

局灶性脑缺血后神经干细胞增殖及GDNF表达变化的实验研究

目的研究局灶性脑缺血后大鼠脑内神经干细胞(NSCs)增殖情况及与胶质细胞源性神经营养因子(GDNF)表达变化的关系。方法将24只SD大鼠随机分为假手术组和模型1组、模型2组、模型3组各6只,后三组用大脑中动脉栓塞法(MCAO)制备局灶性脑缺血模型,分别于术后3、7、14 d处死;假手术组除不以尼龙线阻塞大脑中动脉起始部外,其他操作与模型1组相同。采用免疫组化染色法观察5-溴脱氧尿嘧啶核苷(BrdU)标记的细胞及巢蛋白(Nestin)、GDNF阳性细胞表达,BrdU/Nestin免疫荧光双标法观察NSCs变化。结果模型2组损伤侧脑室下层(SVZ)BrdU阳性细胞显著多于假手术组(P<0.05),模型3组与假手术组相似;模型2、3组皮层梗死灶周围BrdU阳性细胞均显著多于假手术组(P<0.01、0.05);模型1、2组皮层梗死灶周围Nestin阳性细胞均显著多于假手术组(P均<0.01),BrdU/Nestin免疫荧光双标显示BrdU阳性细胞几乎均为Nestin阳性;模型2、3组皮层梗死灶周围GDNF阳性细胞均显著多于假手术组(P均<0.05)。结论大鼠局灶性脑缺血后3～14 d内源性NSCs增殖加快,GDNF表达增加可能对其起促进作用。     

Essential role of Shp2-binding sites on FRS2alpha for corticogenesis and for FGF2-dependent proliferation of neural progenitor cells

Mammalian corticogenesis occurs through a complex process that includes neurogenesis, in which neural progenitor cells proliferate, differentiate, and migrate. It has been reported recently that neurogenesis occurs in the subventricular zone (SVZ), a region previously thought to be the primary site of gliogenesis. It has been recognized that in the SVZ, intermediate progenitor cells, derived from radial glial cells that are multipotent neural stem cells, produce only neurons. However, the molecular mechanisms underlying the regulation of neural stem cells and intermediate progenitor cells as well as their contribution to overall corticogenesis remain unknown. The docking protein FRS2alpha is a major mediator of signaling by means of FGFs and neurotrophins. FRS2alpha mediates many of its pleiotropic cellular responses by recruiting the adaptor protein Grb2 and the protein tyrosine phosphatase Shp2 upon ligand stimulation. Here, we report that targeted disruption of Shp2-binding sites in FRS2alpha leads to severe impairment in cerebral cortex development in mutant mice. The defect in corticogenesis appears to be due at least in part to abnormalities in intermediate progenitor cells. Genetic evidence is provided that FRS2alpha plays critical roles in the maintenance of intermediate progenitor cells and in neurogenesis in the cerebral cortex. Moreover, FGF2-responsive neurospheres, which are cell aggregates derived from neural stem/progenitor cells (NSPCs), from FRS2alpha mutant mice were smaller than those of WT mice. However, mutant NSPCs were able to self-renew, demonstrating that Shp2-binding sites on FRS2alpha play an important role in NSPC proliferation but are dispensable for NSPC self-renewing capacity after FGF2 stimulation.     

Vascular endothelial growth factor (VEGF) stimulates neurogenesis in vitro and in vivo

Vascular endothelial growth factor (VEGF) is an angiogenic protein with neurotrophic and neuroprotective effects. Because VEGF promotes the proliferation of vascular endothelial cells, we examined the possibility that it also stimulates the proliferation of neuronal precursors in murine cerebral cortical cultures and in adult rat brain in vivo. VEGF (>10 ng/ml) stimulated 5-bromo-2'-deoxyuridine (BrdUrd) incorporation into cells that expressed immature neuronal marker proteins and increased cell number in cultures by 20-30%. Cultured cells labeled by BrdUrd expressed VEGFR2/Flk-1, but not VEGFR1/Flt-1 receptors, and the effect of VEGF was blocked by the VEGFR2/Flk-1 receptor tyrosine kinase inhibitor SU1498. Intracerebroventricular administration of VEGF into rat brain increased BrdUrd labeling of cells in the subventricular zone (SVZ) and the subgranular zone (SGZ) of the hippocampal dentate gyrus (DG), where VEGFR2/Flk-1 was colocalized with the immature neuronal marker, doublecortin (Dcx). The increase in BrdUrd labeling after the administration of VEGF was caused by an increase in cell proliferation, rather than a decrease in cell death, because VEGF did not reduce caspase-3 cleavage in SVZ or SGZ. Cells labeled with BrdUrd after VEGF treatment in vivo include immature and mature neurons, astroglia, and endothelial cells. These findings implicate the angiogenesis factor VEGF in neurogenesis as well.