Studies of Motoneuorn Death-Insight into SMAs and ALS

描述（申请人提供）：神经元死亡是发育和病理中枢神经系统（CNS）的一个突出特征。在过去的十年中，这位研究者和许多其他研究者提供了有价值的信息，概述了神经元死亡的几个关键特征。以小鸡脊髓运动神经元为模型系统，我们采用了两种方法来确定营养支持不足导致的运动神经元死亡的生化和分子机制。在第一种方法中，我们研究了在非神经元死亡中起作用的因素是否也参与运动神经元死亡。为此，我们确定了促凋亡分子Bax从细胞质到细胞器膜（线粒体和细胞核）的易位，与细胞死亡的承诺一致。随后，细胞色素c从线粒体中释放出来，特定的半胱天冬酶被激活。在第二种方法中，我们进行了减法杂交筛选，以明确识别当运动神经元致力于细胞死亡时差异表达的信息。通过这种方法，我们发现淀粉样蛋白前体蛋白（APP）在缺乏营养支持的运动神经元中的表达比有营养支持的健康运动神经元的表达增加。令人惊讶的是，我们发现APP是半胱天冬酶的底物，这种相互作用实际上可能促进神经元的死亡。在这个竞争性更新应用程序中，实验的目标有两个。

DESCRIPTION (provided by applicant): Neuronal death is a prominent feature of the developing and pathological central nervous system (CNS). During the past decade work from this investigator and many others has provided valuable information outlining several of the key features of neuronal death. Using chick spinal motoneurons as our model system, we have taken two approaches to identify biochemical and molecular mechanisms underlying motoneuron death resulting from insufficient trophic support. In the first approach, we have investigated if factors identified to have a role in nonneuronal deaths are also involved in motoneuron death. To this end, we identified a translocation of the pro-apoptotic molecule Bax from location in cytoplasm to organelle membrane (mitochondria and nuclear) coincident with the cells commitment to death. Following this event, cytochrome c is released from mitochondria and specific caspases are activated. In the second approach, we performed a subtractive hybridization screen to specifically identify messages that are differentially expressed when motoneurons are committed to cell death. With this approach we found that the amyloid precursor protein (APP) has increased expression in motoneurons deprived of trophic support as compared to healthy counterparts supplied with support. Surprisingly, we identified that APP is a substrate of for caspases and that this interaction may actually promote the neurons commitment to death. The goals of the experiments in this competing renewal application are two fold. First, many of the events that we have identified during the previous period are associated with the execution phase of cell death. We will extend our studies to identify those events that link insult (e.g., loss of trophic support) with the cell's apparent commitment to the death cascade. In the second aim, experiments are plan to examine how neurons respond to the stress of trophic factor deprivation by exploring the roles of exogenous and endogenous Hsps, ubiquitin and the proteasome pathways have in promoting death in the absence of trophic support. Results of these experiments will provide information regarding how motoneurons respond to adverse changes in their environment. These type of data may provide novel insight as to why this neuronal population is susceptible to destruction in amyotrophic lateral Sclerosis (ALS) and the spinal muscular atrophies (SMAs).