Local Mechanisms Underlying Synaptic Plasticity

描述（由申请人提供）：了解突触为长期记忆存储而改变的机制对于解释正常的大脑功能以及大脑疾病和紊乱至关重要。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基础上的突触变化至关重要。最近的研究表明，泛素-蛋白酶体途径的蛋白水解在突触的长期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期突触可塑性中的时空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合适的哺乳动物长期突触可塑性模型系统，即海马的后期长期增强（L-LTP）。我们的研究结果表明，抑制蛋白酶体增强了L-LTP早期翻译依赖的诱导部分，但抑制了L-LTP转录依赖的维持阶段。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，但在后期阶段干扰局部翻译。我们的研究结果还表明，抑制蛋白酶体可阻断脑源性神经营养因子（BDNF）的转录，BDNF是一种camp反应元件结合蛋白（CREB）诱导基因。此外，我们的研究结果表明，蛋白酶体抑制剂可阻断ATF4的降解，ATF4是一种CREB抑制因子，已知可抑制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，并鉴定由蛋白酶体稳定的新合成蛋白。在我们的第二个目标下，我们将测试这样一种观点，即蛋白酶体的阻断会导致可塑性的负调节因子（如翻译抑制因子）的积累，并阻碍细胞核中的转录，从而损害L-LTP的维持。利用蛋白质组学、分子生物学和电生理学研究的强大结合，提出的实验将解决长期突触可塑性中蛋白质水解和蛋白质合成之间关系的重要问题。与公共健康相关：当神经细胞之间的突触连接发生变化时，记忆就形成了。最近的发现表明，神经细胞中蛋白质的降解调节在记忆中起着重要作用。当蛋白质被一种叫做泛素的小分子标记时，它们会被细胞中一个叫做蛋白酶体的部分降解。蛋白质降解在许多疾病和大脑紊乱中是不正常的。这项研究可以帮助解释大脑疾病导致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.