Local Mechanisms Underlying Synaptic Plasticity

描述（由申请人提供）：了解突触被修饰用于长期记忆存储的机制对于解释正常的脑功能以及脑疾病和障碍至关重要。许多研究已经证实，新的基因表达和新的蛋白质合成对于长期记忆的基础突触变化至关重要。最近的研究表明，泛素-蛋白酶体途径的蛋白水解在长时程突触可塑性中起着关键作用。本研究的目的是阐明蛋白酶体在长时程突触可塑性中的空间和时间作用以及蛋白质合成和降解之间的相互作用。我们将使用一个非常适合哺乳动物长时程突触可塑性的模型系统，海马中的晚期长时程增强（L-LTP）。我们的研究结果表明，蛋白酶体的抑制增强了L-LTP的早期，抑制依赖于诱导的L-LTP的一部分，但抑制转录依赖的L-LTP的维持阶段。蛋白酶体介导的L-LTP早期增强依赖于NMDA受体和cAMP依赖性蛋白激酶。我们的数据表明，蛋白酶体抑制通过稳定树突中局部合成的蛋白质来增加L-LTP的诱导，但在后期干扰局部翻译。我们的研究结果还表明，抑制蛋白酶体阻断脑源性神经营养因子（BDNF），这是一个cAMP反应元件结合蛋白（CREB）诱导基因的转录。此外，我们的研究结果表明，蛋白酶体抑制剂阻断ATF 4的降解，ATF 4是一种CREB阻遏物，已知其抑制L-LTP和记忆。因此，蛋白酶体抑制似乎通过阻碍CREB介导的转录来阻断L-LTP的维持。我们的第一个目的是研究蛋白酶体抑制增强L-LTP诱导的机制，并确定新合成的蛋白质稳定的蛋白酶体。在我们的第二个目标下，我们将测试蛋白酶体的阻断通过引起可塑性的负调节因子（如翻译抑制因子）的积累和通过阻碍细胞核中的转录来损害L-LTP的维持的想法。使用蛋白质组学，分子生物学和电生理学研究的强大组合，拟议的实验将解决重要的，悬而未决的问题，有关蛋白质水解和蛋白质合成之间的关系，在长期突触可塑性。公共卫生相关性：当神经细胞之间的连接（称为突触）发生变化时，记忆就形成了。最近的发现表明，通过降解调节神经细胞中的蛋白质在记忆中起作用。当蛋白质被一种叫做泛素的小分子标记时，它们被细胞中一种叫做蛋白酶体的部分降解。蛋白质降解在大脑的许多疾病和紊乱中是异常的。这项研究可以帮助解释大脑疾病中发生的记忆丧失和老年时发生的记忆丧失。

Description (provided by applicant): Understanding mechanisms by which synapses are modified for long-term memory storage is crucial for explaining normal brain function as well as diseases and disorders of the brain. Many studies have established that new gene expression and new protein synthesis are critical for synaptic changes that underlie long-term memory. Recent studies indicate that proteolysis by the ubiquitin-proteasome pathway plays a critical role in long-term synaptic plasticity. The goal of this proposal is to elucidate the spatial and temporal roles of the proteasome and the interplay between protein synthesis and degradation in long-term synaptic plasticity We will use a highly suitable model system of mammalian long-term synaptic plasticity, late phase long-term potentiation (L-LTP) in the hippocampus. Our results show that inhibition of the proteasome enhances the early, translation-dependent induction part of L-LTP but inhibits the transcription-dependent maintenance phase of L-LTP. Proteasome-mediated enhancement of early part of L-LTP depends on NMDA receptor and cAMP-dependent protein kinase. Our data indicate that proteasome inhibition increases induction of L-LTP by stabilizing the locally synthesized proteins in the dendrites but interferes with local translation at later stages. Our results also show that inhibition of proteasome blocks transcription of brain-derived neurotrophic factor (BDNF), which is a cAMP-responsive element binding protein (CREB)-inducible gene. Furthermore, our results show that proteasome inhibitors block degradation of ATF4, a CREB repressor that is known to suppress L-LTP and memory. Thus, proteasome inhibition appears to block maintenance of L-LTP by hindering CREB-mediated transcription. Our first aim is to investigate the mechanism by which L-LTP induction is enhanced by proteasome inhibition and to identify the newly synthesized proteins stabilized by the proteasome. Under our second aim, we will test the idea that blockade of the proteasome impairs the maintenance of L-LTP by causing a buildup of negative regulators of plasticity such as translation repressors and by hindering transcription in the nucleus. Using a powerful combination of proteomic, molecular biological and electrophysiological studies the proposed experiments will address important, unanswered questions pertaining to the relationship between proteolysis and protein synthesis in long-term synaptic plasticity. PUBLIC HEALTH RELEVANCE: Memories form when connections between nerve cells called synapses change. Recent discoveries show that regulation of proteins in the nerve cells by degradation plays a role in memory. Proteins are degraded by a part of the cell named proteasome when they are tagged by a little molecule called ubiquitin. Protein degradation is abnormal in many diseases and disorders of the brain. This research could help explain the memory loss that occurs in brain diseases and memory loss that happens in old age.