TPA MEDIATED NEURODEGENERATION AND MICROGLIA ACTIVATION

神经细胞死亡既发生在正常发育过程中，也发生在各种病理条件下，如癫痫、阿尔茨海默病和脑缺血。我们发现组织纤溶酶原激活剂（tPA），一种将纤溶酶原转化为纤溶酶的丝氨酸蛋白酶，介导海马神经元细胞死亡。此外，tPA还能激活小胶质细胞，即大脑的“免疫”细胞。早就知道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tPA/纤溶酶底物介导生理功能。tPA在哺乳动物大脑生理状态下表达，并在神经元重塑过程中分泌。初步数据表明，tPA/纤溶酶参与了苔藓纤维在神经元活动刺激后发芽的过程。硫酸软骨素蛋白聚糖代表了有希望的候选人，将进一步分析。此外，趋化因子将被评估为tPA/纤溶酶作用的潜在靶点。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通过凋亡介导海马的兴奋性毒性死亡。我们将证实这一观察结果，并确定信号通路，包括小胶质细胞发挥的潜在作用。3. 确定是否需要tPA治疗相关的神经退行性疾病。显示自发性神经元变性的突变小鼠将与纯合子tPA-/-小鼠异交。他们的后代将被用来确定tPA的缺失是否能保护突变基因型中处于危险中的神经元。4. 探讨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症（MS）的部分特征是激活的小胶质细胞显著增加，反映疾病进展的高水平tPA活性和神经退行性变。我们建议使用多发性硬化症动物模型来评估tPA在多发性硬化症中的潜在作用，以确定它是否可能是神经退行性途径的必要部分，或者可能仅作为疾病进展的标记物。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活性水平以确定是否可以改变疾病进展。

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.