TPA MEDIATED NEURODEGENERATION AND MICROGLIA ACTIVATION

神经细胞死亡既发生在正常发育过程中，也发生在各种病理情况下，如癫痫、阿尔茨海默病和脑缺血。我们已经发现，组织纤溶酶原激活物(TPA)是一种将纤溶酶原转化为纤溶酶的丝氨酸蛋白酶，它介导了海马神经细胞的死亡。此外，tPA还调节小胶质细胞的激活，小胶质细胞是大脑的“免疫”细胞。TPA很早就被认为是神经元在基础条件下表达的。然而，在兴奋性毒性损伤后，我们发现海马区tPA的主要来源是新激活的小胶质细胞。我们建议：1.鉴定介导生理功能的纤溶酶原激活剂/纤溶酶底物(S)。TPA在生理条件下在哺乳动物的大脑中表达，并在神经元重塑过程中分泌。初步数据表明，tPA/纤溶酶参与了刺激神经元活动后苔藓纤维的萌发。硫酸软骨素蛋白多糖代表着很有希望的候选物质，并将被进一步分析。此外，趋化因子将被评估为tPA/纤溶酶作用的潜在靶点。2.解剖tPA介导的神经细胞死亡途径。我们的初步证据表明，tPA通过细胞凋亡介导了海马区的兴奋性死亡。我们将证实这一观察结果，并确定信号通路，包括小胶质细胞所扮演的潜在角色(S)。3.在相关环境中确定神经退行性变是否需要tPA。表现出自发性神经元变性的突变小鼠将与纯合子tPA-/-小鼠杂交。他们的后代将被用来确定tPA的缺失是否为突变基因中处于危险状态的神经元提供了保护。4.探讨组织型纤溶酶原激活剂在人类神经退变中的作用。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，以及神经变性。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变途径的必要部分，或者可能单独作为疾病进展的标志。其目的将包括通过将tPA活性水平的变化与疾病进展相关联来验证该模型，并操纵tPA活动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.