Activity-Dependent Regulation of Kv4 Channels

Kv 4通道已被证明在调节神经活动中起重要作用： 整合突触输入的高频序列，调节反向传播动作电位，以及 有助于长时程增强。因此，影响Kv 4功能/可用性的突变已经被发现。 显示出导致空间学习缺陷、癫痫发作行为以及颞叶癫痫。在过去 资助期间，我们发现Kv 4通道的表达和营业额在三个新的背景下受到影响： 调节胆碱能突触稳态，响应于人Aβ42的过度表达，以及 正常老化。在所提出的研究中，我们研究了Kv 4表达的机制， 胆碱能突触稳态突触稳态/缩放是一种可塑性形式， 在过去的十年中，研究了作为一种保护机制，平衡全球神经活动的变化; 这可能发生在生理过程中，如学习/记忆和发育，以及在 病理条件。我们以果蝇中枢神经元为模型， （Dα7）nAChR在胆碱能阻断后上调，从而增强突触电流并提供 自我平衡反应我们发现这种自我平衡反应触发了一种新的调节机制- Kv 4通道的上调，我们显示防止了稳态响应的“过冲”。 我们进一步表明，Kv 4通道的上调被转录抑制剂阻断， 依赖于Dα7 nAChRs和Ca 2+内流。果蝇仍然是一个理想的模型系统， 研究，因为它的胆碱能中枢神经系统，它提供的遗传工具，其冗余较少的基因组（例如，只有 单个果蝇NFAT和Kv 4基因，每个基因代表哺乳动物中的多基因家族），并且 从基因调控机制到完整大脑中的生理相关性的能力，最终， 整个动物行为。拟议的研究将应用新的光遗传学方法来诱导胆碱能 体内突触稳态（Aim-1）-尚未在任何系统中探索， 目前在哺乳动物系统中不可行。我们将研究潜在的分子机制，包括 α7 nAChRs和Kv 4通道（Aim-2）之间的新关系，以及Kv 4的失活诱导转录 （Aim-3），由NFAT（Aim-4）介导。我们还将测试所有的分子机制，为他们的生理 与完整大脑中已识别神经元的相关性。我们的研究可能会揭示重要的见解， 胆碱能突触稳态的潜在机制。

Kv4 channels have been shown to play important roles in modulating neural activity: regulating the integration of high-frequency trains of synaptic input, regulating backpropagating action potentials, and contributing to long-term potentiation. Consequently, mutations that affect Kv4 function/availability have been shown to result in spatial learning defects, seizure behavior, as well as temporal lobe epilepsy. In the last funding period, we showed that expression and turnover of Kv4 channels are affected in three new contexts: in modulating cholinergic synaptic homeostasis, in response to over-expression of human Aβ42, and during normal aging. In the proposed studies, we investigate the mechanisms underlying Kv4 expression during cholinergic synaptic homeostasis. Synaptic homeostasis/scaling is a form of plasticity that has been heavily studied in the last decade as a protective mechanism that counterbalances changes in global neural activity; this likely occurs during physiological processes, such as learning/memory and development, as well as during pathological conditions. We used Drosophila central neurons as a model, and showed that Drosophila α7 (Dα7) nAChRs are up-regulated after cholinergic blockade, thereby enhancing synaptic currents and providing a homeostatic response. We found that this homeostatic response triggered a novel regulatory mechanism – the up-regulation of Kv4 channels, which we showed prevents an “overshoot” of the homeostatic response. We further showed that the up-regulation of Kv4 channels is blocked by transcriptional inhibitors, and is dependent on Dα7 nAChRs and Ca2+ influx. Drosophila continues to be an ideal model system for these studies because of its cholinergic CNS, the genetic tools it offers, its less redundant genome (eg. there is only a single Drosophila NFAT and Kv4 gene, each of which represents a multi-gene family in mammals), and the ability to go from mechanisms of gene regulation to physiological relevance in the intact brain, and eventually, whole animal behavior. The proposed studies will apply new optogenetic approaches to elicit cholinergic synaptic homeostasis in vivo (Aim-1) –something that has not been explored in any system, and which would currently not be feasible in mammalian systems. We will examine underlying molecular mechanisms, including a novel relationship between α7 nAChRs and Kv4 channels (Aim-2), and inactivity-induced transcription of Kv4 (Aim-3) that is mediated by NFAT (Aim-4). We will also test all molecular mechanisms for their physiological relevance in identified neurons in the intact brain. Our studies are likely to reveal important insights into the underlying mechanisms of cholinergic synaptic homeostasis.