Synapse to Nuclear Signaling During Long-Lasting Neuronal Plasticity

突触可塑性的赫布形式和稳态形式需要新的基因表达来维持。为了使刺激诱导的转录改变发生，信号必须从突触刺激部位传递到细胞核。这种长距离的逆行运输给神经元带来了一系列独特的挑战，因为神经元中的突触可能位于离细胞索马和细胞核很远的地方。电化学和钙依赖性过程允许在神经元的亚细胞区室之间极其快速的信号传导。在许多系统中的研究还表明，可溶性信号分子可以从突触转运到细胞核，以影响转录的变化。本研究旨在阐明小鼠海马神经元在长期学习相关突触可塑性过程中突触到核信号传导的细胞生物学机制。在过去的资助周期中，我们的特点是在海马长时程增强过程中，突触局部转录的输入蛋白介导的主动核输入的作用。转录因子的突触到核转运提供了将突触活性与基因表达变化偶联的直接手段。我们专注于这个延续的建议，在活动依赖性可塑性的突触核运输的CREB调节转录辅激活因子CRTC 1。我们已经证明，CRTC 1追踪兴奋性神经元中的谷氨酸能活动，以向细胞核通报突触事件。它从受刺激的突触主动转运到细胞核中，并在翻译后修饰中对刺激做出反应而发生深刻变化。此外，虽然多巴胺能刺激触发CRTC 1核输入，神经调节输入，提高细胞内cAMP调节CRTC 1在细胞核中的持久性。我们已经产生了一些试剂来研究和操纵神经元中的CRTC 1，现在建议使用这些试剂来深入分析小鼠海马神经元长期突触可塑性过程中的细胞生物学和突触核信号传导功能。为此，我们提出了三个具体的目标，旨在回答三组问题：1）CRTC 1如何从突触到细胞核旅行; 2）CRTC 1核输入如何改变基因表达？刺激诱导的CRTC 1磷酸化改变如何改变其核转运和下游转录？神经调节如何调节CRTC 1介导的基因表达？这些问题的答案将提供深入了解学习相关基因表达的细胞生物学，以及CRTC 1的特殊功能。我们的研究结果与一系列神经精神障碍和认知障碍（如精神发育迟滞、阿尔茨海默病和与年龄相关的记忆丧失）有关，其中长期记忆受损。

Hebbian and homeostatic forms of synaptic plasticity require new gene expression for their persistence. For stimulus-induced alterations in transcription to occur, signals must be relayed from sites of synaptic stimulation to the nucleus. Such long-distance retrograde transport poses a unique set of challenges in neurons, where synapses can be located at great distances from the cell soma and nucleus. Electrochemical and calcium- dependent processes allow for extremely rapid signaling between subcellular compartments in neurons. Studies in a number of systems have also indicated that soluble signaling molecules can be transported from the synapse to the nucleus to effect changes in transcription. This proposal is aimed at elucidating the cell biology of synapse to nuclear signaling during long-lasting, learning-related synaptic plasticity in mouse hippocampal neurons. During the past funding cycle, we characterized a role for importin-mediated active nuclear import of synaptically localized transcription during hippocampal long-term potentiation. Synapse to nuclear transport of transcription factors provides a direct means of coupling synaptic activity with changes in gene expression. We focus this continuation proposal on the synapse to nuclear transport of the CREB regulated transcriptional coactivator CRTC1 during activity-dependent plasticity. We have shown that CRTC1 tracks glutamatergic activity in excitatory neurons to inform the nucleus about synaptic events. It is actively transported into the nucleus from stimulated synapses, and undergoes profound changes in post-translational modification in response to stimulation. Moreover, while glutamatergic stimuli trigger CRTC1 nuclear import, neuromodulatory inputs that elevate intracellular cAMP regulate the persistence of CRTC1 in the nucleus. We have generated a number of reagents to study and manipulate CRTC1 in neurons and now propose to use these to perform an in-depth analysis of the cell biology and function of its synapse to nuclear signaling during long-term synaptic plasticity of mouse hippocampal neurons. Towards this end we propose three specific aims directed at answering three sets of questions: 1) How does CRTC1 travel from synapse to nucleus; 2) How does CRTC1 nuclear import alter gene expression? How do stimulus-induced change in CRTC1 phosphorylation alter its nuclear transport and downstream transcription? and 3) How does neuromodulation regulate CRTC1-mediated gene expression? The answers to these questions will provide insight into the cell biology of learning-related gene expression, and into the particular function of CRTC1. The results of our studies are relevant to a spectrum of neuropsychiatric disorders, and to cognitive disorders (such as mental retardation, Alzheimer's Disease and age-related memory loss) in which long-term memory is impaired.