TPA MEDIATED NEURODEGENERATION AND MICROGLIA ACTIVATION

神经元细胞死亡发生在正常发育过程中和各种病理条件下，如癫痫，阿尔茨海默病和脑缺血。 我们已经发现，组织纤溶酶原激活剂（tPA），丝氨酸蛋白酶，纤溶酶原转化为纤溶酶，介导海马神经元细胞死亡。 此外，tPA介导小胶质细胞（大脑的“免疫”细胞）的活化。 长期以来，人们都知道tPA在基础条件下由神经元表达。 然而，在兴奋性毒性损伤后，我们发现海马tPA的主要来源变成了新激活的小胶质细胞。 我们建议：1. 鉴定介导生理功能的tPA/纤溶酶底物。 tPA在生理条件下在哺乳动物脑中表达，并在神经元重塑期间分泌。 初步数据表明，tPA/纤溶酶参与苔藓纤维发芽后刺激神经元的活动。 硫酸软骨素蛋白聚糖代表有前途的候选人，并将进一步分析。 此外，将评价趋化因子作为tPA/纤溶酶作用的潜在靶标。2. 剖析tPA介导的神经元细胞死亡途径。 我们的初步证据表明，tPA介导兴奋性死亡海马通过凋亡。 我们将证实这一观察结果，并确定信号转导途径，包括小胶质细胞发挥的潜在作用。 3. 确定在相关环境中神经变性是否需要tPA。 显示自发性神经元变性的突变小鼠将与纯合tPA-/-小鼠异交。 然后将使用它们的后代来确定tPA的缺乏是否对突变基因型中处于风险中的神经元提供保护。 4. 研究tPA在人类神经退行性变中的作用。 自身免疫性疾病多发性硬化（MS）的部分特征在于活化的小胶质细胞的显著增加、反映疾病进展的高水平tPA活性和神经变性。 我们建议使用MS动物模型来评估tPA在MS中的潜在作用，以确定它是否可能是神经退行性通路的必要部分，或者可能仅用作疾病进展的标志物。 目的将包括通过将tPA活性水平的变化与疾病进展相关联来验证模型，并操纵tPA活性水平以确定疾病进展是否可以改变。

Neuronal cell death takes place both during normal development and in various pathological conditions such as epilepsy, Alzheimer's disease, and brain ischemia. We have found that tissue plasminogen activator (tPA), a serine protease that converts plasminogen to plasmin, mediates neuronal cell death in the hippocampus. In addition, tPA mediates activation of microglia, the "immune" cells of the brain. tPA has long been known to be expressed under basal conditions by neurons. After excitotoxic injury, however, we have found that the primary source of hippocampal tPA becomes newly activated microglia. We propose to: 1. Identify tPA/plasmin substrate(s) that mediate physiological function. tPA is expressed in the mammalian brain under physiological conditions and is secreted during neuronal remodeling. Preliminary data suggest that tPA/plasmin are involved in mossy fiber sprouting after stimulation of neuronal activity. Chondroitin sulfate proteoglycans represent promising candidates and will be analyzed further. In addition, chemokines will be evaluated as potential targets for tPA/plasmin action. 2. Dissect the neuronal cell death pathway mediated by tPA. Our preliminary evidence suggests that tPA mediates excitotoxic death in the hippocampus via apoptosis. We will confirm this observation and define the pathway of signaling, including potential role(s) played by microglia. 3. Determine whether tPA is required for neurodegeneration in a related setting. A mutant mouse that displays spontaneous neuronal degeneration will be outcrossed to homozygous tPA-/- mice. Their progeny will then be used to determine whether the absence of tPA confers protection to the neurons at risk in the mutant genotype. 4. Investigate the involvement of tPA in human neurodegeneration. The autoimmune disease multiple sclerosis (MS) is characterized in part by a marked increase in activated microglia, high levels of tPA activity that mirror disease progression, and neurodegeneration. We propose to use an MS animal model to evaluate the potential role of tPA in MS, in order to determine whether it is likely to be a requisite part of the neurodegenerative pathway, or is likely to be useful solely as a marker for disease progression. The aim will include validating the model by correlating changes in levels of tPA activity with the disease progression, and manipulating tPA activity levels to determine if the disease progression can be altered.