神经干细胞修复脊髓损伤

背景：神经生物学和干细胞技术的发展．使通过细胞移植增加脊髓神经数量、减少胶质瘢痕和空洞的形成成为可能。 目的：复习相关文献,就神经干细胞的鉴定及特性、神经干细胞修复脊髓损伤的可能机制、临床前研究及临床应用方面进行综述。 方法：以 “neural stem cells,transplant,spinal cord injury”为英文检索词,以“神经干细胞,移植,脊髓损伤” 为中文检索词,由第一作者检索1997/2010 PubMed数据库及万方数据库有关神经干细胞鉴定、特性、神经干细胞修复脊髓损伤的可能机制、临床前研究及临床应用方面等方面的文章。排除发表时间较早、重复及类似研究,对29篇符合标准的文献进行归纳总结。 结果与结论：神经干细胞有产生神经元、少突胶质细胞、星形胶质细胞,并替代受损的神经细胞功能等。文章从神经干细胞的鉴定及特性,神经干细胞修复脊髓损伤的可能机制,神经干细胞治疗脊髓损伤的实验研究及临床应用等方面进行了讨论。关于干细胞来源的神经元或胶质细胞移植后的长期生存及表型稳定性,以及逃脱分化及选择性程序的很少部分胚胎干细胞,可能会自在移植后的移植位点扩增并形成肿瘤等问题有待进一步解决。     

小胶质细胞的概述及其与脑缺血的关系

炎症反应在脑缺血损伤中扮演着重要角色,主要表现在免疫细胞的激活,其中最主要的是小胶质细胞的激活。小胶质细胞的激活受到严格控制。脑缺血后小胶质细胞被激活,活化后的小胶质细胞形态和功能发生改变。小胶质细胞在脑缺血中发挥脑保护和神经毒性双重作用。因此,抑制小胶质细胞过度活化,拮抗神经毒性因子、促进神经保护因子、阻断小胶质细胞的炎症反应将为缺血性脑血管病的治疗提供新思路。     

脊髓损伤后神经炎症反应的研究现状

脊髓损伤会造成严重的神经病理损害,且功能康复十分有限.最初的机械性损伤固然能迅速破坏神经元及神经胶质,但随后迟发的二次病理损伤破坏性更大.二次损伤可表现为神经元及胶质细胞的凋亡,血一脊髓屏障的通透性增加及复杂的神经炎症反应,其中神经炎症反应可持续到损伤后数月甚至数年,而我们对神经炎症发生的机制目前却知之甚少~([1-2]).     

胶质细胞在癫癎发病机制中的作用研究进展

癫癎是神经系统疾病中的一种严重危害人类健康的常见病、多发病,患病率约为1%,发病机制非常复杂.胶质细胞是神经系统的重要组成部分,胶质细胞占脑细胞总数的约90%,包括星形胶质细胞、少突胶质细胞和小胶质细胞,其在生理与病理状态下对维护神经系统功能的作用至今未明.胶质细胞不仅与脑的正常生理活动、发育以及神经病理过程有明显关系,而且与神经元的功能活动以及损伤与修复过程有千丝万缕的联系.近年来研究表明胶质细胞在癫癎的发病机制中扮演重要角色.本文就癎性发作时胶质细胞功能改变(细胞形态改变、免疫表型改变和细胞增殖活动)、胶质细胞与神经元之间物质、信息交流方面的研究进展进行综述.     

胶质细胞在癫痫发病机制中的作用研究进展

癫痫是神经系统疾病中的一种严重危害人类健康的常见病、多发病，患病率约为1％，发病机制非常复杂。胶质细胞是神经系统的重要组成部分，胶质细胞占脑细胞总数的约90％，包括星形胶质细胞、少突胶质细胞和小胶质细胞，其在生理与病理状态下对维护神经系统功能的作用至今未明。胶质细胞不仅与脑的正常生理活动、发育以及神经病理过程有明显关系，而且与神经元的功能活动以及损伤与修复过程有千丝万缕的联系。近年来研究表明胶质细胞在癫痫的发病机制中扮演重要角色。本文就痫性发作时胶质细胞功能改变（细胞形态改变、免疫表型改变和细胞增殖活动）、胶质细胞与神经元之间物质、信息交流方面的研究进展进行综述。     

针刺对MCAO大鼠脑组织小胶质细胞活化及炎症介质含量的影响

目的研究针刺对MCAO大鼠脑组织小胶质细胞活化及TNF-α、IL-1β、IL-6含量的影响。方法建立MCAO大鼠模型,分别针刺内关、曲池后进行神经体征评分,HE染色检测神经元坏死率,ELISA法检测脑组织炎症介质含量,IBA1免疫荧光染色检测小胶质细胞活化。结果与假手术对照组相比,模型对照组大鼠神经体征评分、脑海马神经元坏死率、脑组织TNF-α、IL-1β、IL-6含量、IBA1表达均明显升高(P<0.01);与模型对照组相比,内关组、曲池组神经体征评分、脑海马神经元坏死率、IL-1含量、IBA1表达明显降低,曲池组TNF-α、IL-6含量明显降低(P<0.05)。结论针刺内关、曲池能改善MCAO大鼠的神经功能损伤,抑制小胶质细胞活化,降低炎症介质含量,提示针刺可能通过影响小胶质细胞活化从而调控脑缺血继发的炎症反应。     

细胞周期机制在创伤性脑损伤中的研究进展

创伤性脑损伤后诱导继发性损伤,导致神经元凋亡、神经炎症和神经功能障碍,一个重要的损伤机制是细胞周期激活。细胞周期再进入机制可能是神经元凋亡性细胞死亡的共同通路,通路可能是p53依赖性或p53非依赖性的。创伤性脑损伤也导致星形胶质细胞和小胶质细胞中细胞周期激活。细胞周期抑制剂,在创伤性脑损伤后可以提供强有力的神经保护作用,为颅脑损伤的治疗提供新的研究靶点。     

反应性星形胶质细胞对脑缺血神经元的保护

近年来研究发现星形胶质细胞在脑缺血后异常活跃。它可通过分泌生长因子、细胞因子、识别分子等修复损伤的神经元，促进轴突再生及诱导再生神经元的迁移。起到恢复神经系统正常功能的作用。现综述如下。1 星形胶质细胞损伤对神经元的影响近10年研究表明神经胶质细胞在神经系统发育、突触传递、神经组织的修复与再生、神经免疫及多种神经疾病的病理机制中都起着十分重要的作用。用选择性胶质毒素Fluorocitrate(FC)注射入无损伤的鼠脑，造成早期胶质细胞功能紊乱，而产生类似缺血半影区的改变，而且发现在缺乏正常胶质细胞时神经元对扩散性…     

小胶质细胞与脑缺血

目前许多研究均支持免疫性炎症反应参与了缺血性中风后的脑损伤。脑缺血后数小时，受损脑区域的炎症反应开始启动，持续数天，使脑缺血所致的迟发性脑损伤加重、神经细胞的生物学功能预后更差，而中枢神经系统（CNS）最主要的免疫效应细胞小胶质细胞则是免疫性炎症反应的重要角色，尤其在半月带，小胶质细胞的活化异常活跃，活化的小胶质细胞与白细胞一样，会释放和分泌大量的前炎症因子、酶和神经营养因子，因此小胶质细胞在脑缺血损伤中的作用逐渐受到关注。深入研究小胶质细胞在脑缺血过程中的作用，将为临床治疗脑缺血提供新的途径。现将小胶质细胞在脑缺血病理过程中的功能、来源及免疫反应综述如下。     

帕金森病炎症/免疫异常细胞模型的建立

目的 观察小胶质细胞激活后形态和功能的变化。以探讨活化的小胶质细胞对多巴胺能神经元产生损伤作用的可能机制。阐明帕金森病发病的免疫机制。方法 建立原代小胶质细胞培养。筛选和鉴定的方法，以细菌细胞壁脂多糖为工具药激活小胶质细胞，通过免疫组化，MTT，ELISA等方法观察小胶质细胞形态，数量和功能的文化。结果 LPS激活的小胶质细胞体积增大，OX-42表达上调，释放一氧化氮（NitricOxide,NO)，合成超氧阴离子（O2）及分泌细胞因子TNF-α量显著增多，而细胞数量无明显改变。结论 激活的小胶质细胞对多巴胺能神经元的损伤作用。可能与释放NO，O2^-及细胞因子TNF-α等细胞毒性物质有关。     

IL‐4 drives microglia and macrophages toward a phenotype conducive for tissue repair and functional recovery after spinal cord injury

Macrophages and microglia play a key role in the maintenance of nervous system homeostasis. However, upon different challenges, they can adopt several phenotypes, which may lead to divergent effects on tissue repair. After spinal cord injury (SCI), microglia and macrophages show predominantly pro‐inflammatory activation and contribute to tissue damage. However, the factors that hamper their conversion to an anti‐inflammatory state after SCI, or to other protective phenotypes, are poorly understood. Here, we show that IL‐4 protein levels are undetectable in the spinal cord after contusion injury, which likely favors microglia and macrophages to remain in a pro‐inflammatory state. We also demonstrate that a single delayed intraspinal injection of IL‐4, 48 hours after SCI, induces increased expression of M2 marker in microglia and macrophages. We also show that delayed injection of IL‐4 leads to the appearance of resolution‐phase macrophages, and that IL‐4 enhances resolution of inflammation after SCI. Interestingly, we provide clear evidence that delayed administration of IL‐4 markedly improves functional outcomes and reduces tissue damage after contusion injury. It is possible that these improvements are mediated by the presence of macrophages with M2 markers and resolution‐phase macrophages. These data suggest that therapies aimed at increasing IL‐4 levels could be valuable for the treatment of acute SCI, for which there are currently no effective treatments. GLIA 2016;64:2079–2092     

Neuroprotective effects of nitidine against traumatic CNS injury via inhibiting microglia activation

Glial cell response to injury has been well documented in the pathogenesis after traumatic brain injury (TBI) and spinal cord injury (SCI). Although microglia, the resident macrophages in the central nervous system (CNS), are responsible for clearing debris and toxic substances, excessive activation of these cells will lead to exacerbated secondary damage by releasing a variety of inflammatory and cytotoxic mediators and ultimately influence the subsequent repair after CNS injury. In fact, inhibition of microgliosis represents a therapeutic strategy for CNS trauma. We here showed that nitidine, a benzophenanthridine alkaloid, restricted reactive microgliosis and promoted CNS repair after traumatic injury. Nitidine was shown to prevent cultured microglia from LPS-induced reactive activation by regulation of ERK and NF-κB signaling pathway. Furthermore, the nitidine-mediated inhibition of microgliosis was also shown in injured brain and spinal cord, which significantly increased neuronal survival and decreased neural tissue damage after injury. Importantly, behavioral analysis revealed that nitidine-treated mice with SCI had improved functional recovery as assessed by Basso Mouse Scale and swimming test. Together, these findings indicated that nitidine increased CNS tissue sparing and improved functional recovery by attenuating reactive microgliosis, suggestive of the potential therapeutic benefit for CNS injury.     

Optimising plasticity: environmental and training associated factors in transplant-mediated brain repair

With progressively ageing populations, degeneration of nerve cells of the brain, due to accident or disease, represents one of the major problems for health and welfare in the developed world. The molecular environment in the adult brain promotes stability limiting its ability to regenerate or to repair itself following injury. Cell transplantation aims to repair the nervous system by introducing new cells that can replace the function of the compromised or lost cells. Alternatives to primary embryonic tissue are actively being sought but this is at present the only source that has been shown reliably to survive grafting into the adult brain and spinal cord, connect with the host nervous system, and influence behaviour. Based on animal studies, several clinical trials have now shown that embryonic tissue grafts can partially alleviate symptoms in Parkinson's disease, and related strategies are under evaluation for Huntington's disease, spinal cord injury, stroke and other CNS disorders. The adult brain is at its most plastic in the period following injury, offering a window of opportunity for therapeutic intervention. Enriched environment, behavioural experience and grafting can each separately influence neuronal plasticity and recovery of function after brain damage, but the extent to which these factors interact is at present unknown. To improve the outcome following brain damage, transplantation must make use of the endogenous potential for plasticity of both the host and the graft and optimise the external circumstances associated with graft-mediated recovery. Our understanding of mechanisms of brain plasticity subsequent to brain damage needs to be associated with what we know about enhancing intrinsic recovery processes in order to improve neurobiological and surgical strategies for repair at the clinical level. With the proof of principle beginning to emerge from clinical trials, a rich area for innovative research with profound therapeutic application, even broader than the specific context of transplantation, is now opening for investigation.     

Human umbilical cord blood (HUCB) cells for central nervous system repair

Cellular therapy is a compelling and potential treatment for certain neurological and neurodegenerative diseases as well as a viable treatment for acute injury to the spinal cord and brain. The hematopoietic system offers alternative sources for stem cells compared to those of fetal or embryonic origin. Bone marrow stromal and umbilical cord cells have been used in pre-clinical models of brain injury, directed to differentiate into neural phenotypes, and have been related to functional recovery after engraftment in central nervous system (CNS) injury models. This paper reviews the advantages, utilization and progress of human umbilical cord blood (HUCB) cells in the neural cell transplantation and repair field.     

Potent pro-inflammatory actions of leukemia inhibitory factor in the spinal cord of the adult mouse

Injury in the peripheral or central nervous systems causes a significant rise in the levels of the pleiotropic cytokine leukemia inhibitory factor (LIF). This increase influences cell survival, reactive gliosis and inflammatory responses. Since prior work has focused primarily on peripheral nerve and brain, little is known about the role of LIF in the spinal cord injury response. We address this issue by examining the effects of injury in the LIF knockout (KO) mouse, as well as using an adenoviral vector to over-express LIF in the spinal cord of adult mice. We find that LIF over-expression results in a dramatic rise in cell proliferation, primarily in microglia/macrophages. Astrocytes are not stimulated to proliferate but are activated by the elevated LIF. LIF over-expression also causes the development of severe hindlimb motor dysfunction, an effect mediated by the enhanced activation of microglia/macrophages, as inhibiting microglial activation with minocycline attenuates these motor deficits. Conversely, proliferation is significantly diminished and the microglial/macrophage response to spinal cord injury is much less in the LIF KO compared to wild type (WT). Thus, LIF is a potent pro-inflammatory factor in the adult spinal cord and represents a potential target for the manipulation of inflammatory reactions after spinal cord injury.     

Effect of glial cells on remyelination after spinal cord injury

Remyelination plays a key role in functional recovery of axons after spinal cord injury. Glial cells are the most abundant cells in the central nervous system. When spinal cord injury occurs, many glial cells at the lesion site are immediately activated, and different cells differentially affect inflammatory reactions after injury. In this review, we aim to discuss the core role of oligodendrocyte precursor cells and crosstalk with the rest of glia and their subcategories in the remyelination process. Activated astrocytes influence prolif-eration, differentiation, and maturation of oligodendrocyte precursor cells, while activated microglia alter remyelination by regulating the inflammatory reaction after spinal cord injury. Understanding the interac-tion between oligodendrocyte precursor cells and the rest of glia is necessary when designing a therapeutic plan of remyelination after spinal cord injury.     

Spinal Cord Injury Scarring and Inflammation: Therapies Targeting Glial and Inflammatory Responses

Deficits in neuronal function are a hallmark of spinal cord injury (SCI) and therapeutic efforts are often focused on central nervous system (CNS) axon regeneration. However, secondary injury responses by astrocytes, microglia, pericytes, endothelial cells, Schwann cells, fibroblasts, meningeal cells, and other glia not only potentiate SCI damage but also facilitate endogenous repair. Due to their profound impact on the progression of SCI, glial cells and modification of the glial scar are focuses of SCI therapeutic research. Within and around the glial scar, cells deposit extracellular matrix (ECM) proteins that affect axon growth such as chondroitin sulfate proteoglycans (CSPGs), laminin, collagen, and fibronectin. This dense deposition of material, i.e., the fibrotic scar, is another barrier to endogenous repair and is a target of SCI therapies. Infiltrating neutrophils and monocytes are recruited to the injury site through glial chemokine and cytokine release and subsequent upregulation of chemotactic cellular adhesion molecules and selectins on endothelial cells. These peripheral immune cells, along with endogenous microglia, drive a robust inflammatory response to injury with heterogeneous reparative and pathological properties and are targeted for therapeutic modification. Here, we review the role of glial and inflammatory cells after SCI and the therapeutic strategies that aim to replace, dampen, or alter their activity to modulate SCI scarring and inflammation and improve injury outcomes.     

The therapeutic potential of targeting exchange protein directly activated by cyclic adenosine 3′,5′-monophosphate (Epac) for central nervous system trauma

Millions of people worldwide are affected by traumatic spinal cord injury, which usually results in permanent sensorimotor disability. Damage to the spinal cord leads to a series of detrimental events including ischaemia, haemorrhage and neuroinflammation, which over time result in further neural tissue loss. Eventually, at chronic stages of traumatic spinal cord injury, the formation of a glial scar, cystic cavitation and the presence of numerous inhibitory molecules act as physical and chemical barriers to axonal regrowth. This is further hindered by a lack of intrinsic regrowth ability of adult neurons in the central nervous system. The intracellular signalling molecule, cyclic adenosine 3′,5′-monophosphate (cAMP), is known to play many important roles in the central nervous system, and elevating its levels as shown to improve axonal regeneration outcomes following traumatic spinal cord injury in animal models. However, therapies directly targeting cAMP have not found their way into the clinic, as cAMP is ubiquitously present in all cell types and its manipulation may have additional deleterious effects. A downstream effector of cAMP, exchange protein directly activated by cAMP 2 (Epac2), is mainly expressed in the adult central nervous system, and its activation has been shown to mediate the positive effects of cAMP on axonal guidance and regeneration. Recently, using ex vivo modelling of traumatic spinal cord injury, Epac2 activation was found to profoundly modulate the post-lesion environment, such as decreasing the activation of astrocytes and microglia. Pilot data with Epac2 activation also suggested functional improvement assessed by in vivo models of traumatic spinal cord injury. Therefore, targeting Epac2 in traumatic spinal cord injury could represent a novel strategy in traumatic spinal cord injury repair, and future work is needed to fully establish its therapeutic potential.     

Arginase-1 is expressed exclusively by infiltrating myeloid cells in CNS injury and disease

Resident microglia and infiltrating myeloid cells play important roles in the onset, propagation, and resolution of inflammation in central nervous system (CNS) injury and disease. Identifying cell type-specific mechanisms will help to appropriately target interventions for tissue repair. Arginase-1 (Arg-1) is a well characterised modulator of tissue repair and its expression correlates with recovery after CNS injury. Here we assessed the cellular localisation of Arg-1 in two models of CNS damage. Using microglia specific antibodies, P2ry12 and Fc receptor-like S (FCRLS), we show the LysM-EGFP reporter mouse is an excellent model to distinguish infiltrating myeloid cells from resident microglia. We show that Arg-1 is expressed exclusively in infiltrating myeloid cells but not microglia in models of spinal cord injury (SCI) and experimental autoimmune encephalomyelitis (EAE). Our in vitro studies suggest that factors in the CNS environment prevent expression of Arg-1 in microglia in vivo. This work suggests different functional roles for these cells in CNS injury and repair and shows that such repair pathways can be switched on in infiltrating myeloid cells in pro-inflammatory environments.     

Microglia in neurodegenerative diseases

A major feature of neurodegeneration is disruption of central nervous system homeostasis, during which microglia play diverse roles. In the central nervous system, microglia serve as the first line of immune defense and function in synapse pruning, injury repair, homeostasis maintenance, and regulation of brain development through scavenging and phagocytosis. Under pathological conditions or various stimulations, microglia proliferate, aggregate, and undergo a variety of changes in cell morphology, immunophenotype, and function. This review presents the features of microglia, especially their diversity and ability to change dynamically, and reinterprets their role as sensors for multiple stimulations and as effectors for brain aging and neurodegeneration. This review also summarizes some therapeutic approaches for neurodegenerative diseases that target microglia.