Mechanisms of Synaptic Depression: Focus on Rap Signaling Pathways

持续性突触的两种形式--长期突触抑制(LTD)和去增强 反复突触活动期后的抑郁，是广泛研究的脊椎动物突触的例子 可塑性。导致LTD和去增强的细胞和分子机制很可能 阐明神经发育、适应、学习和发育的生理和病理现象 记忆。 现在有令人信服的证据表明，重复的突触活动会导致NMDA- 敏感谷氨酸受体与突触后AMPA敏感谷氨酸受体的去除 (AMPA-Rs)来自兴奋性突触在LTD和去增强。然而，生化途径 NMDA-R活动与AMPA-R贩运之间的联系在很大程度上是未知的。我们之前已经报道过， 小GTP酶RAPL通过激活p38MAPK控制LTD。在初步研究中，我们观察到 小的GTPase Rap2通过激活JNK来控制去增强。基于这些发现，我提出了一个新的 模拟RAP1和RAP2通过两条独立的信号通路传递突触抑制信号。我们将测试 在这个模型中，有三个假设，分别有三个目的，使用器官类型培养的海马片 准备工作。这种准备使我们能够操纵突触活动和信号分子的活动 采用生理学、药理学和重组蛋白递送方法。我们将分析其影响 这些操作通过检查电生理标记的重组AMPA-R介导的电流， 测量GluR1和GluR2基因敲除小鼠的突触反应，以及量化磷酸化或 活跃的内源信号分子和谷氨酸受体。结合这些方法，我们将 确定：(目标1)RAPL-p38MAPK信号有限，而Rap2-JNK信号去增强；(目标1) 2)不同的下游信号分子传递RAPL-p38MAPK和Rap2-JNK通路；以及(目标3) 不同的上游信号分子控制着RAPL-p38MAPK和Rap2-JNK通路。 因为控制Rap信号通路的信号分子或酶的遗传缺陷会导致 严重的精神发育迟缓，这项研究的发现也应该表明更多的分子靶点 新的遗传和药理学策略可能有效地治疗这些潜伏的精神疾病。

Long-term synaptic depression (LTD) and depotentiation, the two forms of sustained synaptic depression after periods of repetitive synaptic activity, are extensively studied examples of vertebrate synaptic plasticity. The cellular and molecular mechanisms responsible for LTD and depotentiation will likely elucidate physiological and pathological phenomena of neural development, adaptation, learning and memory. There is now compelling evidence that repetitive synaptic activity leads to activation of NMDA- sensitive glutamate receptors (NMDA-Rs) and removal of postsynaptic AMPA-sensitive glutamate receptors (AMPA-Rs) from excitatory synapses during LTD and depotentiation. However, the biochemical pathways that link NMDA-R activity to AMPA-R trafficking are largely unknown. We have previously reported that small GTPase Rapl controls LTD via activation of p38MAPK. In a preliminary study, we observed that small GTPase Rap2 controls depotentiation via activation of JNK. Based on these findings, I proposed a new model that Rapl and Rap2 signal synaptic depression via two independent signaling pathways. We will test three hypotheses in this model with three aims, respectively, using an organotypic culture hippocampal slice preparation. This preparation allows us to manipulate synaptic activity and signaling molecules' activity using physiology, pharmacology and recombinant protein delivery methods. We will assay the effects of these manipulations by examining electrophysiologically tagged recombinant AMPA-R-mediated currents, measuring synaptic responses in GluRl and GluR2 knockout mice, as well as quantifying phosphorylated or active endogenous signaling molecules and glutamate receptors. Combining these approaches, we will determine whether: (Aim 1) Rapl-p38MAPK signals LTD whereas Rap2-JNK signals depotentiation; (Aim 2) different downstream signaling molecules relay Rapl-p38MAPK and Rap2-JNK pathways; and (Aim 3) different upstream signaling molecules control Rapl-p38MAPK and Rap2-JNK pathways. Because genetic defects in signaling molecules or enzymes controlling Rap signaling pathways lead to severe mental retardation, the findings from this study should also suggest additional molecular targets for novel genetic and pharmacological strategies that may efficaciously treat these insidious mental diseases.