Transcriptional control of synaptic plasticity by class IIa HDACs

描述（由申请人提供）：在哺乳动物脑中，神经元活动控制着回路发育和突触可塑性所必需的许多基因。然而，潜在的分子机制尚未完全了解。HDAC 4是IIa类组蛋白去乙酰化酶核阻遏物家族的成员，其在细胞核和细胞质之间穿梭并以信号调节的方式与组织特异性转录因子（TF）相互作用。人类遗传学研究表明，HDAC 4基因座的突变会导致智力迟钝，但HDAC 4缺陷对神经回路的影响仍然难以捉摸。我们最近令人兴奋的研究结果支持一个假设，HDAC 4是一个分子底物的NMDA受体依赖性转录控制突触强度。我们提供的证据表明，在培养的神经元中，HDAC 4抑制多个突触相关基因，从而影响中枢突触的结构组织及其生理特性。此外，我们发现，NMDA受体阻止HDAC 4的神经元染色质和TF的结合，并且在小鼠前脑中这种转录途径的失调损害神经传递和空间记忆。我们开发了一个全面的遗传工具箱，并组建了一个合格的研究人员团队，以严格研究小鼠模型中核HDAC 4信号的结果。在SA 1中，突触输入和HDAC 4阻遏物活性之间的相互作用将在缺乏NMDA受体的突变动物中进行测试，并在一种新的独特的小鼠品系中进行测试，该小鼠品系能够对体内特定神经元类型的突触神经递质释放进行急性药物诱导操纵。在SA 2中，我们将使用遗传丧失和获得功能的方法来定义HDAC 4在调节齿状回（DG）中的基础神经传递和经验依赖性形式的突触可塑性中的作用，齿状回（DG）是将皮质信息中继到海马体并促进若干认知任务的脑区域。为此，我们将询问由于条件性基因沉默而缺乏天然HDAC 4或在野生型背景中表达组成型核阻遏物突变体的小鼠。最后，针对SA 3的成像实验将测试核HDAC 4信号传导如何影响DG中兴奋性和抑制性神经元之间的连接，以及它们的功能性突触的结构。这些研究将为大脑中经验依赖性转录沉默/去抑制机制提供重要的新见解，阐明HDAC 4在控制突触功能中的作用，并为罕见的人类疾病提供分子解释。

DESCRIPTION (provided by applicant): In the mammalian brain, a number of genes essential for circuit development and synaptic plasticity are controlled by neuronal activity. However, the underlying molecular mechanisms are incompletely understood. HDAC4 is a member of the class IIa histone deacetylase family of nuclear repressors that shuttle between the nucleus and cytoplasm and interact with tissue-specific transcription factors (TFs) in a signal-regulated manner. Human genetic studies have shown that mutations in the HDAC4 locus cause mental retardation, but the consequences of HDAC4 deficiency on neural circuits remain elusive. Our recent exciting findings support a hypothesis that HDAC4 is a molecular substrate for NMDA receptor-dependent transcriptional control of synaptic strength. We provide evidence that, in cultured neurons, HDAC4 represses multiple synapse-related genes thereby affecting the structural organization of central synapses and their physiological properties. Furthermore, we show that NMDA receptors prevent the binding of HDAC4 to neuronal chromatin and TFs, and that misregulation of this transcriptional pathway in the mouse forebrain impairs neurotransmission and spatial memory. We have developed a comprehensive genetic toolbox and assembled a team of qualified investigators to rigorously investigate the outcomes of nuclear HDAC4 signaling in mouse models. In SA1, the interplay between synaptic inputs and HDAC4 repressor activity will be tested in mutant animals that are deficient for NMDA receptors, and in a new unique mouse strain that enables acute drug-inducible manipulation of synaptic neurotransmitter release from specific neuronal types in vivo. In SA2, we will use both genetic loss- and gain- of-function approaches to define the role of HDAC4 in regulating basal neurotransmission and experience- dependent forms of synaptic plasticity in the Dentate Gyrus (DG), a brain region that relays cortical information into the hippocampus and promotes several cognitive tasks. To this end, we will interrogate mice that either lack native HDAC4 due to conditional gene silencing, or express a constitutively nuclear repressor mutant in the wildtype background. Finally, imaging experiments directed towards SA3 will test how nuclear HDAC4 signaling impacts the connectivity between excitatory and inhibitory neurons in the DG, and the architectures of their functional synapses. These studies will gain significant new insights into the mechanisms of experience-dependent transcriptional silencing/de-repression in the brain, elucidate the role of HDAC4 in controlling synaptic function, and provide a molecular explanation for a rare human disease.