Role of Astrocyte Injury in Neuroprotection

描述(申请人提供)：星形胶质细胞是神经束的重要组成部分，它们的功能障碍与多种特发性和遗传性疾病有关，包括阿尔茨海默氏症和帕金森氏病，以及能量缺乏综合征，如硫胺素缺乏和抗代谢中毒。健康的星形胶质细胞-神经元相互作用的主流模式是相邻膜之间持续而密切的物理接触，促进神经元的动态平衡。虽然神经纤维中星形胶质细胞的丢失通常被认为是一种负面事件，但我们在此提出，在中毒的急性阶段，星形胶质细胞的丢失可能会保护神经元免受腺苷释放所介导的进一步损伤。具体地说，在这个方案中，我们假设DNB诱导的星形胶质细胞氧化应激诱导腺苷释放，腺苷通过旁分泌机制激活神经元中的A1受体，并自我调节受损星形胶质细胞上的A2受体。由于氧化应激是沉淀事件，这一假设的推论是，在神经元中，氧化应激聚集在PI3K/ERK上，调节bc1蛋白的活性，促进线粒体融合和细胞稳定。额外的神经元保护是通过A1介导的AKT激活，阻断促死亡的Bcl蛋白和激活存活的Bcl-蛋白来实现的。相反，在星形胶质细胞中，A2受体的激活会加剧钙控制的丧失、肿胀和细胞死亡。星形胶质细胞在保护神经元免受氧化应激诱导的细胞死亡中的作用这一假设将通过解决以下具体问题来检验。目的1：星形胶质细胞释放的腺苷能沉默神经元并保护它们免受1，3-DNB的影响吗？目的2：A1受体是否通过PI3K、AKT和/或ERK介导的信号传导阻断神经元中与死亡相关的蛋白家族成员？目的3：线粒体融合或分裂的过程是由Mfn1/2、Bax/Bad/Bclxl和DRP1的结合决定的还是依赖于它们的结合？目的4：改变线粒体形态的蛋白质结合是否也改变了膜的电位和功能？二硝基苯(DNB)提供了选择性损伤星形胶质细胞的能量剥夺综合征的极佳模型。这一实验方法将使我们能够剖析bc1蛋白、丝裂原蛋白和DRP-1在协调线粒体功能丧失中的作用，并可能为形成致病基础的神经元/神经胶质相互作用提供新的见解，或为选择性细胞对环境神经毒物的敏感性提供新的见解。与公共健康相关的星形胶质细胞是中枢神经系统的支持细胞。我们实验室的数据显示，它们是许多环境化学品的主要目标，这些化学品会导致中枢神经系统功能障碍。随着星形胶质细胞损伤的进展，ATP被转化为腺苷，并释放到细胞外空间，在那里它可以与神经元上的A1受体(保护性)和星形胶质细胞上的A2受体(损伤)相互作用。我们认为，在中枢神经系统损伤的急性期，腺苷引起神经元功能丧失(沉默)，并可能使神经元免受氧化应激和兴奋性毒性的有害影响。

DESCRIPTION (provided by applicant): Astrocytes are an important component of the neuropil and their dysfunction has been associated with a variety of idiopathic and genetic diseases including Alzheimer's and Parkinson's disease and in energy deprivation syndromes such as thiamine deficiency and antimetabolite poisoning. The prevailing model of healthy astrocyte-neuron interaction is one of continuous and intimate physical contact between adjacent membranes that promotes neuronal homeostasis. While the loss of astrocytes in the neuropil is generally viewed as a negative event, we propose here that in the acute phases of intoxication loss of astrocytes may protect neurons against further injury mediated by release of adenosine. Specifically, in this proposal we hypothesize that DNB-induced oxidative stress in astrocytes induces the release of adenosine which in turn activates A1 receptors in neurons via paracrine mechanisms and self-regulates A2 receptors on injured astrocytes. Since oxidative stress is the precipitating event, the corollary to this hypothesis is that in neurons, oxidative stress converges on PI3K/ERK to regulate the activity of BCL proteins that promote mitochondrial fusion and stabilization of the cell. Additional neuronal protection is achieved via A1-mediated activation of AKT with blockage of pro-death Bcl proteins and activation of survival Bcl-proteins. Conversely, in astrocytes, activation of the A2 receptor exacerbates loss of calcium control, swelling and cell death. This hypothesis for the role of astrocytes in the protection of neurons from oxidative stress-induced cell death will be tested by addressing the following specific questions. AIM 1: Can adenosine released by astrocytes silence neurons and protect them from the effects of exposure to 1,3-DNB? Aim 2: Does A1 receptor mediated signaling through PI3K, AKT and/or ERK block death- related members of the Bcl-family of proteins in neurons? Aim 3: Is the course of mitochondrial fusion or fission determined by or dependent upon binding of Mfn1/2, Bax/Bad/Bcl-XL and Drp 1? Aim 4: Does binding of proteins that alter mitochondrial morphology also alter membrane potential and function? Dinitrobenzene (DNB) provides and excellent model of energy deprivation syndromes with selective damage to astrocytes. This experimental approach will enable dissection of the role of BCL-proteins, mitofusins and Drp-1 in coordinating the loss of mitochondrial function and may provide new insights into neuronal/glial interactions that form the foundation for pathoclisis, or selective cellular susceptibility to environmental neurotoxicants. PUBLIC HEALTH RELEVANCE Astrocytes are supporting cells in the central nervous system. Data from our laboratories show that they are a primary target of many environmental chemicals that result in dysfunction of the central nervous system. As injury to the astrocyte progresses, ATP is converted to adenosine and is released into the extracellular space where it can interact with A1 receptors on neurons (protective) and A2 receptors on astrocytes (injurious). We propose here that in the acute phases of CNS injury, loss of neuronal function (silencing) is elicited by adenosine and may spare the neuron from the deleterious effects of oxidative stress and excitotoxicity.