星形胶质细胞在脊髓损伤中的研究进展

<正>近年来,脊髓损伤(spinal cord injury,SCI)的发病率在我国乃至世界呈明显上升趋势。脊髓损伤后的神经再生问题,一直是科研人员和临床工作者研究的一个重点和难点。脊髓损伤后,阻碍轴突再生的主要的因素是小胶质细胞激活、星形胶质细胞(astrocyte,AS)增殖活化和胶质瘢痕的形成[1]。而AS的增殖活化后并分泌多种细胞外基质共同形成神经胶质瘢痕是抑制脊髓损伤修复的最主要障碍。最近研究显示,星     

Nrf2基因敲除对小鼠颅脑损伤后神经功能障碍和胶质细胞活化的影响

目的研究Nrf2基因对小鼠颅脑损伤的保护作用及可能机制。方法利用PCR方法确认Nrf2(+/+)型和Nrf2(-/-)型小鼠遗传背景,建立小鼠闭合性颅脑损伤模型。用神经功能缺损评分(NSS)和病死率评估致伤程度和伤后神经功能状态,用免疫组化方法观察致伤灶周围小胶质细胞和星形胶质细胞活化情况。结果与Nrf2(+/+)型小鼠比较,Nrf2(-/-)型小鼠伤后神经功能障碍明显严重(P<0.01);伤后1 d,Nrf2(-/-)型小鼠挫伤灶周围小胶质细胞活化明显增强,3 d时差异更显著,直到7 d仍有统计学差别(P<0.05)。此外,伤后1、3、7 d,Nrf2(-/-)型小鼠挫伤灶周围星形胶质细胞活化亦增强,但仅3 d时有统计学意义(P<0.05)。结论 Nrf2基因敲除可加重小鼠颅脑损伤后神经功能障碍,且这种变化可能是通过影响胶质细胞活化实现的。     

β-淀粉样蛋白对AD大鼠脑内胶质细胞的影响作用研究

目的　探讨Meynert核注射 β 淀粉样蛋白 (Aβ)后对大鼠脑神经胶质细胞超微结构的影响及其可能机制。方法　将 1μLAB1-40 (10 μg/ μL)在立体定向仪下注入大鼠右侧Meynert核 ,分别于 1周、4周时用透射电镜观察脑组织中神经胶质细胞超微结构变化。结果　实验组Meynert核、海马区和皮层区均可见神经胶质细胞增生 ,其中以小胶质细胞为主 ,星形胶质细胞次之 ;小胶质细胞聚集并吞噬变性神经细胞以及血管周围可见增生活跃的小胶质细胞聚集 ;神经元胞体皱缩 ,胞浆浓缩 ,核染色质固缩成团块状并见边聚现象 ,核膜尚完整 ,有发生凋亡的趋势 ;正常对照组和假手术组无上述变化。结论　Aβ能引发CNS神经胶质细胞增生并活化 ,免疫炎性反应在AD记忆障碍和痴呆形成过程中可能具有重要作用。     

细胞周期依赖激酶抑制剂Olomoucine对活化星形胶质细胞神经蛋白聚糖、短蛋白聚糖表达的抑制作用

目的研究细胞周期依赖激酶抑制剂Olomoucine对星形胶质细胞活化后神经蛋白聚糖(Neurocan)、短蛋白聚糖(Brevican)表达的抑制作用。方法应用睫状神经营养因子(CNTF)刺激法建立体外培养星形胶质细胞的活化模型,实验分3组:对照组、活化组与抑制组。对照组:正常培养的星形胶质细胞;活化组:星形胶质细胞加入20 ng/ml睫状神经营养因子(CNTF)处理24 h;抑制组:星形胶质细胞用20 ng/ml睫状神经营养因子预处理24 h,加入100μmol/L Olomoucine。应用ELISA法检测不同时间点(12 h、24 h、48 h)各组细胞上清液中Neurocan、Brevican含量变化,半定量RT-PCR检测各组细胞GFAP mRNA及Neurocanm RNA、Brevican mRNA的表达变化。结果(1)活化组上清液中Neurocan、Brevican的含量在12 h、24 h、48 h随着时间的延长逐渐增加,与对照组比较差异有显著性(P0.01);抑制组上清液中Neurocan、Brevican含量随着时间的延长较活化组明显降低,与对照组、活化组比较差异有显著性(P0.01)。(2)活化组细胞GFAP mRNA、Neurocan mRNA、Brevican mRNA表达明显增加,与对照组比较差异有显著性(P0.01);抑制组细胞GFAP mRNA、Neurocan mRNA、Brevican mRNA表达均明显下调,与活化组比较差异有显著性(P0.01)。结论细胞周期依赖激酶抑制剂Olomoucine可抑制活化星形胶质细胞神经蛋白聚糖、短蛋白聚糖表达。     

水通道蛋白4抗体对体外培养大鼠皮层神经细胞的毒性作用

目的 观察水通道蛋白4(AQP4)抗体对体外培养的大鼠皮层神经细胞的毒性作用,探讨其在视神经脊髓炎发病机制中的作用.方法 选取孕16～19 d Wistar大鼠胚胎皮层神经细胞培养3d,采用随机数字表法分为2组:对照组、AQP4抗体阳性患者血清组(抗体组).对照组以10％的比例加入正常人血清,抗体组加入等量AQP4抗体阳性患者血清培养.2h、4h、6h后使用免疫组织化学荧光染色观察星形胶质细胞、神经元和小胶质细胞形态及数量的变化.结果 对照组不同时间点3种神经细胞形态和数目无任何变化:抗体组2h后就出现星形胶质细胞肿胀、小胶质细胞体积增大以及神经元轴突断裂等形态学的改变,但3种细胞数量无明显变化:4h后星形胶质细胞和神经元比例分别为(24.73+5.27)％和(35.49+8.43)％,明显少于对照组[(30.34±4.53)％和(48.60±1 0.99)％],差异有统计学意义(p＜0.05);小胶质细胞比例较对照组明显增多[分别为(27.35±13.17)％和(16.44±2.70)％],差异有统计学意义(P＜0.05);6 h后3种细胞数量变化更为明显(P＜0.05).结论 AQP4抗体能导致体外培养的大鼠皮层星形胶质细胞和神经元死亡以及小胶质细胞的活化,推测其在视神经脊髓炎的发病机制中发挥一定作用.     

小胶质细胞在出血性脑卒中发病机制中的研究进展

出血性脑卒中(intracerebral haemorrhage,ICH)是脑卒中致死率最高的类型,目前临床对其仍缺乏有效的治疗方法。小胶质细胞是ICH后第一个产生免疫应答的中枢神经系统细胞。ICH急性期脑损伤后,小胶质细胞可被诱导为经典的M1型(促炎作用)或补充替代的M2型(抗炎作用),其中,M1型抑制中枢神经系统的修复,M2型通过分泌抗炎因子和神经营养因子来促进组织的再生和修复。同时,小胶质细胞与星形胶质细胞、神经元、少突胶质细胞以及T淋巴细胞生理病理上具有紧密联系,其M1型和M2型极化与其他神经细胞产生不同的交互作用,这些均在ICH的病理过程中具有至关重要的作用。基于此,本文对ICH后小胶质细胞和其他神经细胞的相互作用的关键分子机制进行综述。     

星形胶质细胞对脑缺血后神经元的保护作用

神经元和神经胶质细胞共同构成中枢神经系统。而其中星形胶质细胞(astrocytes,AS)在数量上占有绝对优势,其数量是神经元的10～50倍,约占脑体积的一半。AS长期以来被认为是脑组织中简单的堆积物,发     

髓样细胞触发受体2调控小胶质细胞功能及参与阿尔茨海默病发病机制的研究进展

阿尔茨海默病(AD)是一种以细胞外β淀粉样蛋白(Aβ)沉积形成的淀粉样斑块、细胞内过度磷酸化tau蛋白形成的纤维缠结及神经炎症为特征性病理表现的神经退行性病变。近年来研究发现,髓样细胞触发受体2(TREM2)基因突变显著增加阿尔茨海默病的发病风险。TREM2在中枢神经系统(CNS)中仅表达于小胶质细胞,小胶质细胞作为CNS中最主要的一道免疫防线,吞噬中枢神经系统特异性碎片及Aβ和tau等异常聚集蛋白,还可调节可溶性炎症介质的释放,以应对中枢神经系统损伤。本文对小胶质细胞TREM2在AD中的作用进行综述。     

星形胶质细胞在多发性硬化发病中的作用机制

星形胶质细胞是中枢神经系统中数量最多的胶质细胞,其生理功能为支持和营养神经元,参与免疫调节和神经递质代谢,支持血-脑脊液屏障,调节神经细胞内、外离子浓度等。星形胶质细胞在多发性硬化(multiple sclerosis,MS)中反应性增生,此现象称为星形胶质细胞活化。活化的星形胶质细胞一方面产生一些具有神经损伤的细胞因子,另一方面能分泌有利于神经系统恢复的因子来促进神经生长和修复。因而星形胶质细胞在MS中具有双重角色。在MS发病机制中明确星形胶质细胞在不同发病阶段的作用倾向,可能为MS的治疗提供新的治疗策略。     

兔外伤性视神经损伤后不同时期减压的形态学观察

目的观察视神经损伤模型在损伤后不同时期减压的形态学改变,了解其与手术时机的关系。方法建立家兔外伤性视神经损伤模型,将损伤分为正常对照组、损伤48h减压组、7d减压组、14d减压组及损伤不减压组,在光镜下观察各组视神经的组织形态学改变。结果正常对照组视神经纵切面胶质细胞基本呈柱形均匀排列,神经纤维排列整齐。损伤48h减压组纵切面胶质细胞排列基本均匀,损伤处可见空泡样变性,可见少量胶质细胞增生。损伤7d减压组纵切面胶质细胞排列紊乱,大部分区域出现多个大小不等的空泡,部分区域出现脱髓鞘样变,胶质细胞增生明显。损伤14d减压组纵切面胶质细胞完全丧失柱形排列,胶质细胞明显增生,视神经脱髓鞘样变明显。损伤不减压组可见大片神经纤维坏死,视神经脱髓鞘样变明显,胶质细胞增生。结论神经元继发性损伤是视功能进行性下降的重要原因,视神经减压术有利于减轻视神经的间接损伤,较早期进行减压(48h)可阻止轴突继发性损伤。     

Insight into astrocyte activation after optic nerve injury

In response to optic nerve damage, astrocytes become reactive. This reactivity can be identified by the presence of morphological and molecular changes throughout the retina and optic nerve as well as the formation of a glial scar. The process of astrocyte activation exhibits spatial and temporal characteristics, and it is finely regulated by complex signaling mechanisms. Excessive astrocyte activation plays a crucial role in progressive optic nerve injury. This review focuses on the spatial and temporal characteristics and mechanisms of astrocyte activation and discusses the modulation of astrocyte activation. Further insight into astrocyte activation might provide targets for future therapeutic interventions. © 2014 Wiley Periodicals, Inc.     

Endothelin B receptors are expressed by astrocytes and regulate astrocyte hypertrophy in the normal and injured CNS

The ability of mammalian central nervous system (CNS) neurons to survive and/or regenerate following injury is influenced by surrounding glial cells. To identify the factors that control glial cell function following CNS injury, we have focused on the endothelin B receptor (ET(B)R), which we show is expressed by the majority of astrocytes that are immunoreactive for glial acid fibrillary protein (GFAP) in both the normal and crushed rabbit optic nerve. Optic nerve crush induces a marked increase in ET(B)R and GFAP immunoreactivity (IR) without inducing a significant increase in the number of GFAP-IR astrocytes, suggesting that the crush-induced astrogliosis is due primarily to astrocyte hypertrophy. To define the role that endothelins play in driving this astrogliosis, artificial cerebrospinal fluid (CSF), ET-1 (an ET(A)R and ET(B)R agonist), or Bosentan (a mixed ET(A)R and ET(B)R antagonist) were infused via osmotic minipumps into noninjured and crushed optic nerves for 14 days. Infusion of ET-1 induced a hypertrophy of ET(B)R/GFAP-IR astrocytes in the normal optic nerve, with no additional hypertrophy in the crushed nerve, whereas infusion of Bosentan induced a significant decrease in the hypertrophy of ET(B)R/GFAP-IR astrocytes in the crushed but not in the normal optic nerve. These data suggest that pharmacological blockade of astrocyte ET(B)R receptors following CNS injury modulates glial scar formation and may provide a more permissive substrate for neuronal survival and regeneration.     

Activation of epidermal growth factor receptor causes astrocytes to form cribriform structures

Epidermal growth factor receptor (EGFR) is expressed in reactive astrocytes following injury in the CNS. However, the effects of activation of the EGFR pathway in astrocytes are not well established. In the present study, we demonstrate that activation of EGFR causes optic nerve astrocytes, as well as brain astrocytes, to form cribriform structures with cavernous spaces. Formation of the cribriform structures is dependent on new protein synthesis and cell proliferation. Platelet-derived growth factor and basic fibroblast growth factor were not effective. Smooth muscle cells and epithelial cells do not form cribriform structures in response to EGFR activation. The formation of the cribriform structures appears to be related to a guided migration of astrocytes and the expression of integrin beta1 and extracellular fibronectin in response to activation of EGFR. The EGFR pathway may be a specific, signal transduction pathway that regulates reactive astrocytes to form cavernous spaces in the glial scars following CNS injury and in the compressed optic nerve in glaucomatous optic nerve neuropathy.     

Lesion-induced changes in the expression of ciliary neurotrophic factor and its receptor in rat optic nerve

There is evidence that ciliary neurotrophic factor (CNTF) is involved in reactive changes following lesions of the nervous system. To investigate, whether differences in the regulation of CNTF and CNTF receptor α (CNTFRα) contribute to the differences in PNS and CNS responses to injury, we have studied their expression on the mRNA and protein level in the rat optic nerve following a crush lesion to compare them with the situation in peripheral nerve. Seven days after the lesion, CNTF mRNA and protein levels were markedly decreased at the lesion site, concommitant with the disappearance of GFAP- and CNTF-immunopositive astrocytes. CNTF levels in proximal and distal parts were less affected. This was in contrast to the situation in the PNS, where CNTF was downregulated at and distal to the lesion site. Different from other CNS regions, optic nerve astrocytes expressed CNTFRα mRNA under normal conditions. Following lesion, CNTFRα was reduced substantially only in distal and proximal parts of the optic nerve but continued to be expressed at high levels at the lesion site, suggesting that GFAP-negative, CNTF-responsive cells are present there. Our results suggest that differences in lesion-induced changes in the optic and sciatic nerve reflect differences in the response to injury of astrocytes and Schwann cells. In the light of the known actions of CNTF in inducing astrogliosis, the expression pattern observed in the optic nerve indicates that CNTF and CNTFRα are involved in glial scar formation in the lesion area. GLIA 23:239–248, 1998. © 1998 Wiley-Liss, Inc.     

Effects of axotomy on the expression of NADPH-diaphorase in the visual pathway of the tench

The distribution of NADPH-diaphorase (ND) positive elements was analyzed throughout the visual pathway of the tench in normal conditions and after optic nerve transection. In the control retina, ND-labeled elements were observed in the photoreceptor, inner nuclear, outer nuclear and ganglion cell layers. In the optic nerve of control animals, small and numerous ND-positive glial cells that were identified as presumably astrocyte-like cells were observed. In the optic tracts and optic tectum, a different type of ND-positive glial cell was detected. Axotomy induced severe changes in the ND staining pattern in the visual pathway. A decrease in the number of ND-stained cells was detected in the retina. In the optic nerve of lesioned animals, the number of small cells gradually decreased, whereas the number of large cells did not change. Two new ND-positive cell populations were observed after the lesion: microglial-like cells appeared close to the lesioned area from 24 h to 7 days after transection, and astrocyte-like cells were found throughout the optic nerve from 14 days up to at least 120 days. The total number of ND-stained glial cells increased at 30 and 60 days and returned to control parameters at 120 days. In addition, the number of ND-positive cells increased at the same survival times in the optic tracts and in the retinorecipient strata of the optic tectum with respect to control animals. Thus, degenerative/regenerative processes in the fish visual pathway are accompanied by an increase in the number of ND-positive cells. Synthesis of nitric oxide is elicited in microglial-like cells as a response to axon injury, whereas the expression in astrocyte-like cells seems to be associated with both normal processes under physiological conditions and with the regenerative phase after the lesion.     

Temporal regulation of EphA4 in astroglia during murine retinal and optic nerve development

Eph receptors and their ephrin ligands play important roles in many aspects of visual system development. In this study, we characterized the spatial and temporal expression pattern of EphA4 in astrocyte precursor cell (APC) and astrocyte populations in the murine retina and optic nerve. EphA4 is expressed by immotile optic disc astrocyte precursor cells (ODAPS), but EphA4 is downregulated as these cells migrate into the retina. Surprisingly, mature astrocytes in the adult retina re-express EphA4. Within the optic nerve, EphA4 is expressed in specialized astrocytes that form a meshwork at the optic nerve head (ONH). Our in vitro and in vivo data indicate that EphA4 is dispensable for retinal ganglion cell (RGC) axon growth and projections through the chiasm. While optic stalk structure, APC proliferation and migration, retinal vascularization, and oligodendrocyte migration appear normal in EphA4 mutants, the expression of EphA4 in APCs and in the astrocyte meshwork at the ONH has implications for optic nerve pathologies.     

Morphological and functional analysis of an incomplete CNS fiber tract lesion: graded crush of the rat optic nerve

Fiber tract lesions in the central nervous system (CNS) often induce delayed retrograde neuronal degeneration, a phenomenon that represents an important therapeutic challenge in clinical neurotraumatology. In the present study, we report an in vivo trauma model of graded axonal lesion of CNS neurons. Controlled by a newtonmeter device, we induced retrograde degeneration of adult rat retinal ganglion cells (RGCs) by graded crush of the optic nerve. The extent of secondary RGC death increased linearly with the applied crush force. Moreover, visually evoked potentials were used to characterize the consequences of controlled optic nerve lesion on the functional integrity of the visual projection. The presented model of fiber tract lesion closely resembles the clinical conditions of traumatic brain injury and could prove useful to screen for neuroprotective drugs based on both a morphological and functional read-out.     

Increased adenine nucleotide translocator 1 in reactive astrocytes facilitates glutamate transport

A hallmark of central nervous system (CNS) pathology is reactive astrocyte production of the chronic glial scar that is inhibitory to neuronal regeneration. The reactive astrocyte response is complex; these cells also produce neurotrophic factors and are responsible for removal of extracellular glutamate, the excitatory neurotransmitter that rises to neurotoxic levels in injury and disease. To identify genes expressed by reactive astrocytes, we employed an in vivo model of the glial scar and differential display PCR and found an increase in the level of Ant1, a mitochondrial ATP/ADP exchanger that facilitates the flux of ATP out of the mitochondria. Ant1 expression in reactive astrocytes is regulated by transforming growth factor-beta1, a pluripotent CNS injury-induced cytokine. The significance of increased Ant1 is evident from the observation that glutamate uptake is significantly decreased in astrocytes from Ant1 null mutant mice while a specific Ant inhibitor reduces glutamate uptake in wild-type astrocytes. Thus, the astrocytic response to CNS injury includes an apparent increase in energy mobilization capacity by Ant1 that contributes to neuroprotective, energy-dependent glutamate uptake.     

Mechanism of acute ischemic injury of oligodendroglia in early myelinating white matter: the importance of astrocyte injury and glutamate release

In developing CNS white matter (WM), the period of early myelination is characterized by a heightened sensitivity to ischemic injury. Using an in situ (isolated) preparation, we show that the mechanism of acute ischemic injury of immature WM oligodendroglial involves Ca2+ influx though non-NMDA type glutamate receptors (GluRs). The Ca2+-influx and acute cell death that was evoked by ischemic conditions (oxygen and glucose withdrawal) in identified P10 rat optic nerve oligodendroglia were blocked by removing extracellular Ca2+ or by CNQX, a selective non-NMDA GluR antagonist. The selective Na-K-Cl cotransport (NKCC) inhibitor bumetanide was also highly protective, even though NKCC expression is restricted to astrocytes in this tissue. Bumetanide largely prevented the non-NMDA GluR-mediated [Ca2+]i rise evoked by ischemia in oligodendroglia, suggesting that it interfered with ischemic glutamate release. In control WM, glutamate-like reactivity was located mainly in astrocytes and oligodendroglia identified using ultrastructural criteria. In ischemic WM, astrocyte glutamate-like reactivity was reduced, an effect countered by bumetanide. We suggest a model in which NKCC-dependent injury and release of glutamate from astrocytes activates glutamate receptors on oligodendroglia, resulting in Ca2+-influx and acute cell death.