Role For Inflammatory Cytokines In Neurodegeneration

趋化因子已被证明参与脑发育，维持正常的脑内稳态，以及神经胶质细胞和神经细胞的迁移、分化和增殖。炎症介质可促进趋化因子及其受体的表达，并与多种神经炎性疾病和神经系统疾病有关，包括多发性硬化症、创伤、中风、阿尔茨海默病、肿瘤进展和艾滋病痴呆。趋化因子作用的一个新兴领域是神经内分泌和免疫系统之间的通讯。现在很明显，趋化因子及其受体代表着一个多功能的蛋白质家族，其对中枢神经系统的作用并不局限于神经炎症。这些分子构成了生理和发育过程中细胞通讯的关键调节器。我们之前已经证明，人类神经细胞表达许多细胞表面趋化因子受体，这些受体似乎介导神经细胞迁移和细胞内钙的增加。此外，我们还发现SDF-1a和HIV蛋白gp120能够与神经元表面的CXCR4结合，导致神经细胞程序性死亡。尽管有这些发现，但关于神经元和神经胶质细胞表面其他趋化因子受体的生物学作用仍然知之甚少。在这项研究中，我们研究了各种趋化因子的直接和间接作用，尤其是MCP-1和MIP-2(我们已经证明了神经元上存在细胞表面受体)，以诱导神经细胞死亡或存活。我们发现MCP-1和MIP-2通过特定的细胞表面趋化因子受体，通过产生活性氧物种(如一氧化氮或一氧化氮)，通过激活caspase和释放谷氨酸，直接和特异性地诱导海马神经元分化死亡。此外，我们还发现，这些趋化因子直接激活星形胶质细胞，产生一些似乎对人类和啮齿动物分化的神经元有毒的炎性细胞因子和分子。事实上，趋化因子诱导的星形胶质细胞神经毒性似乎部分是由于代谢活跃的星形胶质细胞和小胶质细胞释放谷氨酸所致。我们认为中枢神经系统趋化因子在神经炎症的发生以及与创伤和神经系统疾病相关的各种病理后遗症中起着重要作用。趋化因子在急性和慢性神经退行性变和神经炎症过程中是否有共同的潜在生化和分子机制仍有待确定。更多的研究集中在趋化因子和各种炎症介质在阿尔茨海默病(AD)发生中的作用。这种疾病的显著病理特征是b-淀粉样蛋白(Ab)斑块的积聚，继而导致AD患者大脑内的神经变性和神经炎症。有几种形式的抗体，包括AB1-40和1-42，每种都表现出不同的细胞结合和神经毒性效力。例如，Ab1-40主要与反应性星形胶质细胞有关，而Ab1-42与激活的小胶质细胞/巨噬细胞有关，表现出比Ab1-40更强的神经毒性。在这两种情况下，激活的胶质细胞的存在都会导致趋化因子和炎性细胞因子的产生，我们认为这可能介导并加剧了抗体诱导的神经毒性。利用基因芯片技术，我们分析了两种形式的抗体肽对神经元和星形胶质细胞群体的影响及其诱导差异基因表达的能力。许多促炎症(包括趋化因子和几个CCR)、凋亡和谷氨酸受体相关基因在人类星形胶质细胞和神经细胞中上调。我们目前正在研究这些基因在抗体介导的激活和细胞死亡中的特定作用，并检查对照、老年和AD脑组织的组织切片，以寻找相关基因的RNA和蛋白质表达。我们相信这些研究可能阐明神经胶质细胞直接和间接介导神经炎症、神经退行性变和AD病理的途径。除了上述工作，我们最近还从AD患者和年龄匹配的同龄人那里获得了高度明确的海马区组织，希望建立一个确定AD的炎症机制以及抗体和趋化因子诱导的神经毒性和星形胶质细胞激活的模型。本项目的目标是利用基因芯片分析技术，对急性(创伤)和慢性(AD)疾病损伤过程中获得的中枢神经系统组织的基因表达谱进行表征和比较。我们已经进行了这些研究，目前正在处理数据。目前正在进行免疫组织学分析和聚合酶链式反应确认，以证实我们的发现。总体而言，我们认为在急性和慢性神经退行性变和神经炎症过程中都有共同的潜在生化和分子机制。该项目的最终目标是：1)利用基因芯片技术分析急性(创伤)和慢性(AD)疾病损伤过程中获得的中枢神经系统组织的基因图谱；2)确定特定的炎症标志物在神经退行性变的急性期和慢性期是否受到调节，这可能是诊断或表型的；以及3)确定特定的信号通路是否被用于各种神经退行性变过程，特别是神经胶质细胞。

Chemokines have been shown to be involved in brain development, in the maintenance of normal brain homeostasis, and in the migration, differentiation, and proliferation of glial and neuronal cells. Chemokine and chemokine receptor expression can be increased by inflammatory mediators and have been associated with a number of neuroinflammatory and neurological disorders including multiple sclerosis, trauma, stroke, Alzheimer's disease, tumor progression, and AIDS dementia. An emerging area of interest for chemokine action is represented by the communication between the neuroendocrine and the immune system. It is now evident that chemokines and their receptors represent a multifunctional pluripotent family of proteins whose actions on the CNS are not restricted to neuroinflammation. These molecules constitute crucial regulators of cellular communication in physiological and developmental processes. We have previously shown that human neuronal cells express a number of cell surface chemokine receptors, which appear to mediate neuronal cell migration and increases in intracellular calcium. In addition, we have found that SDF-1a and the HIV protein, gp120, are able to bind to CXCR4 on the surface of neurons resulting in a programmed neuronal cell death. Despite these findings, there is still very little known about the biological role of other chemokine receptors on the surface of neurons and glia cells. In this study, we have examined the direct and indirect effects of a variety of chemokines, more specifically here MCP-1 and MIP-2 (for which we have demonstrated the presence of cell surface receptors on neurons), to induce neuronal cell death or survival. We have found that the MCP-1 and MIP-2 directly and specifically induce differentiated hippocampal neuron death via specific cell surface chemokine receptors, through the generation of reactive oxygen species production (e.g., nitric oxide or NO), through caspase activation, and glutamate release. In addition, we have also found that these chemokines directly activate astrocytes to produce a number of inflammatory cytokines and molecules that appear to be toxic to human and rodent differentiated neurons. In fact, chemokine-induced astrocyte neurotoxicity appears to be partially due to the release of glutamate by metabolically active astrocytes and microglia. We believe that CNS chemokines play an important role in the genesis of neuroinflammation and the various pathological sequelae associated with trauma and neurological diseases. Whether there are common underlying biochemical and molecular mechanisms in which chemokines mediate their effects in both acute and chronic neurodegenerative and neuroinflammatory processes remains to be determined. Additional studies have focused on chemokines and various inflammatory mediators in the development of Alzheimers Disease (AD). The hallmark pathological feature of this disease is the accumulation of b-amyloid (Ab) plaques, the ensuing neurodegeneration and neuroinflammation within the brains of AD patients. There are several forms of Ab, including Ab1-40 and 1-42, each exhibiting differing cellular associations as well as neurotoxic potency. For example, Ab 1-40 is primarily associated with reactive astrocytes, while Ab 1-42 is associated with activated microglia/macrophages and exhibits greater neurotoxic potency than Ab 1-40. The presence of activated glia in both cases results in the production of chemokines and inflammatory cytokines, which we believe may mediate as well as exacerbate Ab-induced neurotoxicity. Using cDNA microarray technology, we have analyzed the effect of the two forms of Ab peptide on neuronal and astroglial populations and their ability to induce differential gene expression. A number of proinflammatory (including chemokines and several CCRs), apoptotic, and glutamate receptor-associated genes were found to be upregulated in human astrocytes and neuronal cells. We are currently examining the specific role of these genes in Ab-mediated activation and cell death as well as examining histological sections of control aged and AD brain tissue for the RNA and protein expression of the genes in question. We believe these studies may elucidate the pathways via which glia cells may directly and indirectly mediate neuroinflammation, neurodegeneration and AD pathology. In addition to the work above, we have recently acquired highly defined hippocampal tissue from AD patients along with age-matched counterparts with the hope of building a model defining the inflammatory mechanisms of AD as well as Ab- and chemokine-induced neurotoxicity and astrocyte activation. The goals of this project are to characterize and compare the gene expression profile of CNS tissue obtained from acute (trauma) and chronic (AD) disease-injury processes using cDNA microarray analysis. We have already performed these studies and are currently processing the data. Immunohistological analyses and PCR confirmations are currently underway to confirm our findings. Overall, we believe there are common underlying biochemical and molecular mechanisms involved in both acute and chronic neurodegenerative and neuroinflammatory processes. The ultimate goals of this project are: 1) to characterize and compare the genetic profile of CNS tissue obtained from acute (trauma) and chronic (AD) disease-injury processes using cDNA microarray analysis; 2) to determine whether specific inflammatory markers are modulated during acute and chronic phases of neurodegeneration that may be diagnostic or phenotypic; and 3) to determine whether specific signaling pathways are being utilized in various neurodegenerative processes with specific emphasis on neuroglia.