MICROGLIAL ACTIVATION IN TRAUMATIC BRAIN INJURY

描述(摘自申请者摘要)：创伤性脑损伤(TBI) 诱导小胶质细胞激活，小胶质细胞是大脑的免疫效应细胞。这个 小胶质细胞在颅脑损伤中的作用是一把双刃剑，兼有两者 神经保护和神经退行性变的作用。因此，一个治疗目标 将最大限度地减少负面的、神经毒性的小胶质细胞活动，同时最大化 神经保护。小胶质细胞与其他脑细胞相互作用的解剖 小胶质细胞参与的生化途径的类型和鉴定 颅脑损伤后的激活很难在体内完成。许多海流 体外小胶质细胞损伤模型不能复制主要成分 脑损伤，即组织拉伤或拉伸。这项提议的目标是 探讨脑损伤诱导小胶质细胞的信号转导途径 激活并确定激活对神经元损伤的后果， 采用一种具有良好特性的体外牵张损伤模型。我们最近的研究 证明小胶质细胞不是被牵张损伤直接激活的，而是 是由拉伸损伤的星形胶质细胞释放的可溶性因子激活的。 激活的小胶质细胞形态改变，花生四烯酸增加 释放，并增强细胞内钙信号，符合 巨噬细胞激活。我们第一次发现了一种 激活的小胶质细胞中谷氨酸介导的钙信号通路，这可能是 构成小胶质细胞和受损星形胶质细胞之间的信号网络 神经元。我们还发现拉伸损伤的星形胶质细胞和严重 受损的神经元将三磷酸腺苷释放到细胞外空间。我们假设 创伤后星形胶质细胞和神经元释放谷氨酸和三磷酸腺苷 启动小胶质细胞趋化激活。在目前的建议中，我们将 继续剖析牵张诱导的信号通路 通过检测谷氨酸介导的花生四烯酸释放来激活小胶质细胞 钙信号、形态变化、增殖、主要 组织相容抗原表达、吞噬和趋化作用。我们会 还确定了拉伸激活的小胶质细胞改变的机制 神经元钙信号或发挥神经毒性作用。使用血管紧张素转换酶抑制剂 花生四烯酸级联反应、钙信号、嘌呤能和谷氨酸能 受体，我们将尝试中和小胶质细胞的神经毒性。离体 神经保护和神经毒性机制的剖析 创伤后的小胶质细胞可以允许更有效的发展 减少颅脑损伤后继发性损伤的策略 从神经毒性到神经保护的小胶质细胞效应的平衡。

DESCRIPTION (adapted from applicant's abstract): Traumatic brain injury (TBI) induces activation of microglia, the immune effector cells of the brain. The role of microglia in TBI is one of double-edged sword, having both neuroprotective and neurodegenerative effects. Therefore, a treatment goal would be to minimize negative, neurotoxic microglial actions while maximizing neuroprotection. Dissection of microglial interactions with other brain cell types and identification of biochemical pathways involved in microglial activation after TBI is difficult to accomplish in vivo. Many of the current models of in vitro microglial injury do not reproduce the major component of TBI, that being tissue strain or stretch. The goal of this proposal is to examine the signal transduction pathways responsible for TBI-induced microglial activation and determine the consequences of activation on neuronal injury, using a well-characterized in vitro stretch-injury model. Our recent studies demonstrate that microglia are not directly activated by stretch injury, but are activated by soluble factors released from stretch-injured astrocytes. Activated microglia had morphological alterations, increased arachidonic acid release, and enhanced intracellular calcium signaling consistent with macrophage activation. For the first time, we have identified upregulation of a glutamate-mediated calcium-signaling pathway in activated microglia, which may constitute a signaling network between microglia and injured astrocytes and neurons. We have also found that stretch-injured astrocytes and severely injured neurons release ATP into the extracellular space. We hypothesize that glutamate and ATP released by traumatically injured astrocytes and neurons initiates microglial chemotaxis activation. In the present proposal, we will continue to dissect the signaling pathways involved in stretch-induced microglial activation by examining arachidonic acid release, glutamate-mediated calcium signaling, morphological changes, proliferation, major histocompatibility antigen expression, phagocytosis, and chemotaxis. We will also determine the mechanisms through which stretch-activated microglia alter neuronal calcium signaling or exert neurotoxic effects. Using inhibitors of the arachidonic acid cascade, calcium signaling, purinergic and glutamatergic receptors, we will attempt to counteract microglial neurotoxicity. In vitro dissection of the mechanisms involved in the neuroprotection and neurotoxicity of microglia after trauma could permit the development of more effective strategies aimed at reduction of secondary injury after TBI by shifting the balance of microglial effects from neurotoxic to neuroprotective.