围产期缺氧缺血性脑损伤中星形胶质细胞的病理生理改变

转产期缺氧因性脑损的研究焦点集中在神经元上,但是,星形胶持细胞也参与缺氧缺血过程并起着关键作用。星形胶质细胞在缺氧缺血损伤中的改变是中枢神经系统中最早和最显著的,这种参与对缺氧缺血变为以及中枢神经系统是损伤还是修复这一最终发展有重要影响。目前,星形胶质细胞的作用越来越受到重视,对脑缺氧缺血过程中星形胶质细胞的病理生理变化也有了深入的研究。     

缺血缺氧对体外培养星形胶质细胞细胞活化和细胞周期的影响

目的观察缺血缺氧损伤对星形胶质细胞细胞活化和细胞周期的影响。方法用流式细胞仪及BrdU掺入法检测缺血缺氧后不同时间点星形胶质细胞细胞周期变化和细胞的增殖活力;用荧光免疫细胞化学技术测定胶质细胞纤维酸性蛋白(GFAP)及细胞周期蛋白cyclinD1的表达水平。结果体外缺血缺氧损伤后星形胶质细胞S期较正常组明显增高,6h达高峰,BrdU掺入法显示损伤后6h星形胶质细胞的增殖活力最高,而随后S期细胞数目及细胞增殖活力都呈下降趋势。在缺血缺氧早期,GFAP阳性染色增强,6h最高;缺血缺氧12h后GFAP阳性染色变弱,而cyclinD1的表达在损伤后逐渐增加,在24h时达高峰。结论缺血缺氧损伤激活星形胶质细胞,使其进入新的细胞周期,出现细胞的增殖反应;cyclinD1参与了损伤后星形胶质细胞的修复和增殖;细胞周期事件与星形胶质细胞的增殖活化密切相关。     

星形胶质细胞的兴奋对神经元树突丝运动的调节机制

神经元树突上树突丝(filopodia)的形成及其运动,是神经元探索胞外环境、寻找突触前膜结构的一种方式.为研究星形胶质细胞的兴奋对神经元树突上树突丝运动的调节机制,在与神经元混合培养的星形胶质细胞中转染光敏感通道(channelrhodopsin-2).Channelrhodopsin-2是一种可表达于细胞膜表面的非选择性阳离子通道,可被特定模式的蓝光激活,导致大量钙离子内流并进一步诱发星形胶质细胞产生钙波,从而实现了选择性激活星形胶质细胞的目的.研究结果显示,在混合培养的神经元与星形胶质细胞模型中,激活的星形胶质细胞可以抑制神经元filopodia的运动,与外源性ATP、谷氨酸的作用效果一致.这表明星形胶质细胞激活后可能通过释放ATP和谷氨酸等递质来抑制神经元filopodia的运动.     

星形胶质细胞在脊髓损伤中的研究展望

近年来星形胶质细胞(astrocyte,AS)已经逐渐成为中枢神经系统(CNS)疾病研究中的热点之一。激活星形胶质细胞会产生和释放神经递质、神经营养因子和促炎因子等,对神经元既有保护作用也有毒性作用。现综述星形胶质细胞的形态、功能以及与脊髓损伤(spinal cord injury,SCI)的联系等,为进一步研究星形胶质细胞和脊髓损伤提供依据。     

脑缺血后大鼠神经元和星形胶质细胞P21cip1表达的研究

目的研究大鼠局灶性脑缺血再灌注损伤后细胞周期蛋白依赖性激酶抑制因子P21cip1在神经元和星形胶质细胞的表达。方法建立大鼠大脑中动脉阻塞(MCAo)再灌注模型,应用流式细胞术检测各组MCAo再灌注后不同时期神经元和星形胶质细胞中的P21cip1的表达。结果缺血侧皮层区星形胶质细胞和神经元中的P21cip1的表达在再灌注3d、7d、14d后表达下调,与假手术组比较有显著性差异(P<0.05);神经元中的P21cip1的表达和星形胶质细胞中的P21cip1的表达无显著性差异(P>0.05)。结论局灶性脑缺血再灌注损伤后,缺血侧皮层区星形胶质细胞和神经元的p21cip1表达下调。     

基于单细胞转录组的基因富集方法分析星形胶质细胞与阿尔茨海默病的关系*

目的:通过生物信息学方法分析阿尔茨海默病(Alzheimer disease, AD)中与星形胶质细胞相关的糖代谢通路,为揭示AD患者的星形胶质细胞在大脑中的糖代谢过程提供理论基础。方法:首先根据细胞特异性表达基因将AD患者和健康人脑组织单细胞转录组学测序结果进行降维分析,再根据星形胶质细胞不同亚型的基因表达特征进行细胞分群,对星形胶质细胞差异表达基因进行基因注释(Gene Ontology. GO)、信号通路分析(Kyoto Encyclopedia of Genes and Genomes, KEGG)以及基因集富集分析(Gene Set Enrichment Analysis, GSEA),采用转录调控网络分析与AD的星形胶质细胞相关的转录辅助因子。结果:所有细胞降维分析结果显示AD患者脑内星形胶质细胞和兴奋性神经元数量显著减少;星形胶质细胞降维分析结果显示其可以被进一步分为6个亚群,其中在AD患者中减少的星形胶质细胞主要为RASGEF1B⁺SLC26A3⁺亚群和NRGN⁺CALM1⁺亚群;GO分析结果显示AD患者与健康对照星形胶质细胞差异表达基因主要与轴突发生、神经元的迁移、胶质细胞分化、体内锌离子稳态、突触传递的正调控、血管运输有关。KEGG结果显示,上述差异基因主要与PI3K-Akt信号通路、AMPK信号通路、钙信号通路有关。GSEA分析结果显示,AD患者差异基因在糖酵解/糖异生通路中得到富集,其中丙酮酸激酶PKM、PFKL、ACSS1、乳酸脱氢酶LDHB在AD患者星形胶质细胞中下调。转录调控网络分析结果显示,星形胶质细胞中差异表达转录辅助因子有5个,其中PKM、SOX2、SOX9在AD患者星形胶质细胞中下调。SREBF1和BCL6在AD患者星形胶质细胞中上调。结论:AD患者脑内兴奋性神经元和星形胶质细胞数量降低,以及星形胶质细胞糖酵解相关基因下调。结合星形胶质细胞作为神经元的主要乳酸供应细胞,其数量减少和糖酵解能力减低提示星形胶质细胞供能不足可能是AD发生的机制之一。     

靶向星形胶质细胞治疗缺血性脑卒中的研究进展

缺血性脑卒中(ischemic stroke, IS)发生后,缺血区星形胶质细胞(astrocyte)活化,这些反应性星形胶质细胞对缺血区神经元发挥有利和有害双重作用。星形胶质细胞与IS诱导的谷氨酸功能障碍、线粒体功能障碍和胶质瘢痕形成密切相关,并且在IS后神经元网络重构中发挥重要调节作用。现重点探讨如何利用星形胶质细胞对IS发挥保护作用的研究进展。     

疼痛研究的新亮点:星形胶质细胞

一直以来疼痛被认为仅仅是由神经元调节的。目前的研究表明,星形胶质细胞与疼痛有密切的关系。星形胶质细胞通过许多重要功能如参与信号转导、被激活而表现出激活的特性,如释放促炎性因子、神经营养因子等,在疼痛调节过程中发挥重要作用。对星形胶质细胞与疼痛关系的研究,必将为疼痛机制的阐明及疼痛治疗提供新的思路。     

星形胶质细胞糖代谢对神经元的支持及保护作用

脑组织有着极其复杂的功能,这些功能的完成有赖于神经元细胞与胶质细胞之间的广泛合作。星形胶质细胞作为人脑内数量最多的细胞,其与神经元细胞之间的相互作用就显得十分重要。葡萄糖代谢途径包括糖酵解,有氧氧化及磷酸戊糖三条途径。其为脑组织维持其正常功能的前提。研究表明星形胶质细胞和神经元在糖代谢方面有着各自的特点,神经元在能量底物及抗氧化应激中对星形胶质细胞糖代谢途径存在一定的依赖性,干扰星形胶质细胞与神经元之间的代谢过程会导致疾病的发生。本综述主要从糖酵解及磷酸戊糖两条糖代谢途径阐述了星形胶质细胞与神经元的关系。这或许会对研究脑的代谢,脑疾病中神经元的损伤机制及如何保护神经元提供全新的视角,并可能为一些疾病的治疗开辟了新的途径。     

大鼠脑缺血再灌注损伤后神经元和星形胶质细胞的动态变化及Cyclin D1表达的差异

目的研究大鼠局灶性脑缺血再灌注损伤后神经元和星形胶质细胞表达量的动态演变及各自cyclin D1的表达差异。方法建立大鼠大脑中动脉阻塞（MCAO）再灌注模型,随机分为再灌注后1d组,3d组,7d组,14d组和假手术组,应用流式细胞术检测各组再灌注后不同时间点神经元和星形胶质细胞数量变化及各自cyclin D1的表达。结果缺血侧梗死边缘区皮质星形胶质细胞的表达增加,而神经元的表达下降,与假手术组比较有明显差异（P〈0．05）;神经元和星形胶质细胞中各自cyclin D1的表达在再灌注7d、14d后表达上调,且星形胶质细胞中的cyclinD1增加更明显,与假手术组比较有统计学差异（P〈0．05）。结论大鼠脑缺血再灌注后,缺血侧梗死边缘区皮质星形胶质细胞和神经元的cyclinD1表达均有不同程度的上调,星形胶质细胞的cyclin D1表达上调比神经元的更为显著。     

Mitogen-activated protein kinases and cerebral ischemia

Mitogen-activated protein kinases (MAPKs) have crucial roles in signal transduction from the cell surface to the nucleus and regulate cell death and survival. Recent papers support the hypothesis that neuronal apoptosis and cerebral ischemia induce the robust activation of MAPK cascades. Although extracellular signal-regulated kinases pathways promote cell survival and proliferation, and c-Jun N-terminal protein kinases/p38 pathways induce apoptosis in general, the roles of MAPK cascades in neuronal death and survival seem to be complicated and altered by the type of cells and the magnitude and timing of insults. Some specific inhibitors of MAPK cascades provide important information in clarifying the roles of each molecule in neuronal death and survival, but the results are still controversial. Further studies are necessary to elucidate the activated signal transduction upstream and downstream of the cascades in cerebral ischemia, and to define the crosstalk between the cascades and other signaling pathways, before MAPK cascades can be candidate molecules in the treatment of cerebral ischemia.     

Expression of TNF and TNF receptors (p55 and p75) in the rat brain after focal cerebral ischemia.

Cerebral ischemia induces a rapid and dramatic up-regulation of tumor necrosis factor (TNF) protein and mRNA, but the cellular sources of TNF in the ischemic brain have not been defined. The diverse activities of TNF are mediated via ligand interaction with two distinct receptors, p55 and p75, which activate separate intracellular signal transduction pathways, leading to distinct biological effects. Since the effects of cerebral ischemia on TNF receptor (TNFR) expression are unknown, we examined the cellular localization and protein expression of TNF and its two receptors in the rat cerebral cortex in response to permanent middle cerebral artery (MCA) occlusion. The results indicate that focal. cerebral ischemia up-regulates expression of TNF and both TNFRs within the ischemic cortex. The most abundant type of TNF immunoreactivity (IR) was a punctate and filamentous pattern of transected cellular processes; however, cell bodies of neurons, astrocytes, and microglia, as well as infiltrating polymorphonuclear (PMN) leukocytes also showed TNF IR. Brain vasculature displayed TNF IR not only within endothelial cells but also in the perivascular space. MCA occlusion induced significant up-regulation of TNF receptors, with p55 IR appearing within 6 hr, significantly before the appearance of p75 IR at 24 hr after the onset of ischemia. Since p55 has been implicated in transducing cytotoxic signalling of TNF, these results support the proposed injurious role of excessive TNF produced during the acute response to cerebral ischemia.     

Three distinct roles of aquaporin-4 in brain function revealed by knockout mice

Aquaporin-4 (AQP4) is expressed in astrocytes throughout the central nervous system, particularly at the blood-brain and brain-cerebrospinal fluid barriers. Phenotype analysis of transgenic mice lacking AQP4 has provided compelling evidence for involvement of AQP4 in cerebral water balance, astrocyte migration, and neural signal transduction. AQP4-null mice have reduced brain swelling and improved neurological outcome in models of (cellular) cytotoxic cerebral edema including water intoxication, focal cerebral ischemia, and bacterial meningitis. However, brain swelling and clinical outcome are worse in AQP4-null mice in models of vasogenic (fluid leak) edema including cortical freeze-injury, brain tumor, brain abscess and hydrocephalus, probably due to impaired AQP4-dependent brain water clearance. AQP4 deficiency or knock-down slows astrocyte migration in response to a chemotactic stimulus in vitro, and AQP4 deletion impairs glial scar progression following injury in vivo. AQP4-null mice also manifest reduced sound- and light-evoked potentials, and increased threshold and prolonged duration of induced seizures. Impaired K⁺ reuptake by astrocytes in AQP4 deficiency may account for the neural signal transduction phenotype. Based on these findings, we propose modulation of AQP4 expression or function as a novel therapeutic strategy for a variety of cerebral disorders including stroke, tumor, infection, hydrocephalus, epilepsy, and traumatic brain injury.     

Three distinct roles of aquaporin-4 in brain function revealed by knockout mice

Aquaporin-4 (AQP4) is expressed in astrocytes throughout the central nervous system, particularly at the blood-brain and brain-cerebrospinal fluid barriers. Phenotype analysis of transgenic mice lacking AQP4 has provided compelling evidence for involvement of AQP4 in cerebral water balance, astrocyte migration, and neural signal transduction. AQP4-null mice have reduced brain swelling and improved neurological outcome in models of (cellular) cytotoxic cerebral edema including water intoxication, focal cerebral ischemia, and bacterial meningitis. However, brain swelling and clinical outcome are worse in AQP4-null mice in models of vasogenic (fluid leak) edema including cortical freeze-injury, brain tumor, brain abscess and hydrocephalus, probably due to impaired AQP4-dependent brain water clearance. AQP4 deficiency or knock-down slows astrocyte migration in response to a chemotactic stimulus in vitro, and AQP4 deletion impairs glial scar progression following injury in vivo. AQP4-null mice also manifest reduced sound- and light-evoked potentials, and increased threshold and prolonged duration of induced seizures. Impaired K+ reuptake by astrocytes in AQP4 deficiency may account for the neural signal transduction phenotype. Based on these findings, we propose modulation of AQP4 expression or function as a novel therapeutic strategy for a variety of cerebral disorders including stroke, tumor, infection, hydrocephalus, epilepsy, and traumatic brain injury.     

Enteric neurons show a primary cilium

The primary cilium is a non‐motile cilium whose structure is 9+0. It is involved in co‐ordinating cellular signal transduction pathways, developmental processes and tissue homeostasis. Defects in the structure or function of the primary cilium underlie numerous human diseases, collectively termed ciliopathies. The presence of single cilia in the central nervous system (CNS) is well documented, including some choroid plexus cells, neural stem cells, neurons and astrocytes, but the presence of primary cilia in differentiated neurons of the enteric nervous system (ENS) has not yet been described in mammals to the best of our knowledge. The enteric nervous system closely resembles the central nervous system. In fact, the ultrastructure of the ENS is more similar to the CNS ultrastructure than to the rest of the peripheral nervous system. This research work describes for the first time the ultrastructural characteristics of the single cilium in neurons of rat duodenum myenteric plexus, and reviews the cilium function in the CNS to propose the possible role of cilia in the ENS cells.     

Thrombin signaling in the brain: the role of protease-activated receptors

Signaling by the protease thrombin has started to be appreciated in cell biology, especially since the gene for protease-activated receptor-1 (PAR-1) has been cloned. Apart from the central role of thrombin in blood coagulation and wound healing, thrombin also regulates cellular functions in a large variety of cells through PAR-1, PAR-3 and PAR-4. Receptors are activated by a proteolytic cleavage mechanism via G protein-coupled signaling pathways. Accumulating evidence shows that thrombin changes the morphology of neurons and astrocytes, induces glial cell proliferation, and even exerts, depending on the concentration applied, either cytoprotective or cytotoxic effects on neural cells. These effects may be mediated, through either distinct or overlapping signal transduction cascades, by activation of PARs. This review focuses on the underlying signaling events initiated by thrombin in neuronal and glial cells, to summarize our understanding of the intracellular signaling machinery linking thrombin receptors to their potential physiological and pathological functions in the CNS.     

Neuron‐specific non‐classical release of prothymosin alpha: a novel neuroprotective damage‐associated molecular patterns

Prothymosin alpha (ProTα), a nuclear protein devoid of signal sequence, has been shown to possess a number of cellular functions including cell survival. Most recently, we demonstrated that ProTα is localized in the nuclei of neurons, while it is found in both nuclei and cytoplasm in the astrocytes and microglia of adult brain. However, the cell type‐specific non‐classical release of ProTα under cerebral ischemia is yet unknown. In this study, we report that ProTα is non‐classically released along with S100A13 from neurons in the hippocampus, striatum and somatosensory cortex at 3 h after cerebral ischemia, but amlexanox (an anti‐allergic compound) reversibly blocks this neuronal ProTα release. We found that none of ProTα is released from astrocytes and microglia under ischemic stress. Indeed, ProTα intensity is increased gradually in astrocytes and microglia through 24 h after the cerebral ischemia. Interestingly, Z‐Val‐Ala‐Asp fluoromethyl ketone, a caspase 3 inhibitor, pre‐treatment induces ProTα release from astrocytes in the ischemic brain, but this release is reversibly blocked by amlexanox. However, Z‐Val‐Ala‐Asp fluoromethyl ketone as well as amlexanox has no effect on ProTα distribution in microglia upon cerebral ischemia. Taken together, these results suggest that only neurons have machineries to release ProTα upon cerebral ischemic stress in vivo.     

Inductin of neuron-derived orphan receptor-1 in the dentate gyrus of the hippocampal formation following transient global ischemia in the rat

Neuron-derived orphan receptor (NOR-1) is a member of the thyroid/steroid receptor superfamily that was originally identified in forebrain neuronal cells undergoing apoptosis. In addition to apoptotic stimuli, activation of several signal transduction pathways including direct neuronal depolarization regulates the expression of NOR-1. In this study we tested whether the expression of NOR-1 is changed following transient ischemic injury in the adult rat brain. NOR-1 mRNA increased rapidly in the dentate gyrus of the hippocampal formation and piriform cortex 3 h after transient global ischemia and returned to basal level at 6 h. On the other hand, oxygen-glucose deprivation of cultured cerebral cortical neurons did not alter the expression of NOR-1. These results suggest that expression of NOR-1 is differentially regulated in different brain regions in response to globally applied brain ischemia, but that hypoxia is not sufficient to induce its expression.     

Interleukin-1 beta-induced expression of the prostaglandin E-receptor subtype EP3 in U373 astrocytoma cells depends on protein kinase C and nuclear factor-kappaB

Both interleukin-1beta (IL-1beta) and prostaglandins (PGs) are important mediators of physiological and pathophysiological processes in the brain. PGE2 exerts its effects by binding to four different types of PGE2 receptors named EP1-EP4. EP3 has found to be expressed in neurons, whereas expression of EP3 in glial cells has not been reported in the brain yet. Here we describe IL-1beta-induced EP3 receptor expression in human astrocytoma cells, primary astrocytes of rat and human origin and in rat brain. Using western blot, we found a marked up-regulation of EP3 receptor synthesis in human and rat primary glial cells. Intracerebroventricular administration of IL-1beta stimulated EP3 receptor synthesis in rat hippocampus. The analysis of involved signal transduction pathways by pathway-specific inhibitors revealed an essential role of protein kinase C and nuclear factor-kappaB in astrocytic IL-1beta-induced EP3 synthesis. Our data suggest that PGE2 signaling in the brain may be altered after IL-1beta release due to up-regulation of EP3 receptors. This might play an important role in acute and chronic conditions such as cerebral ischemia, traumatic brain injury, HIV-encephalitis, Alzheimer's disease and prion diseases in which a marked up-regulation of IL-1beta is followed by a prolonged increase of PGE2 levels in the brain.