Mechanisms underlying activity-dependent modulation of GABA(A) receptor expressio

描述（由申请方提供）：3-氨基丁酸（GABAA）受体是CNS中突触抑制的主要部位，是多种药物如苯二氮卓类、巴比妥类、全身麻醉剂和神经类固醇的药物靶点。受损的GABA能传递是许多神经和精神疾病如癫痫、焦虑、睡眠障碍、成瘾、自闭症、精神发育迟滞、抑郁症和精神分裂症的促成因素之一。突触后GABAA受体的数量受到高度调节，并且是调节突触抑制强度的主要决定因素。神经元活动的慢性双向变化可导致兴奋性和抑制性突触强度的全局补偿性调整;这一过程称为稳态突触缩放。调节突触后部位GABAA受体的数量是抑制性突触传递中活动依赖性变化的潜在机制之一。我以前已经表明，神经元活动的慢性变化调节内质网（ER）相关的GABAA受体的降解，介导的Ca 2+内流通过L型电压门控Ca 2+通道，调节受体细胞表面的数量和突触抑制的功效。然而，连接神经元活动的变化，以调节GABAA受体的营业额和丰度在抑制性突触的信号通路是未知的。这些现象与我的初步研究一起，使我能够产生一个中心假设，推动本提案中的实验：CaMKII对丝氨酸383上GABAA受体3亚基的活性依赖性磷酸化，调节这些受体的插入，从而调节它们在抑制性突触上的丰度，改变突触抑制的功效。我的工作将集中在3个可区分但互补的实验目标：1）测试GABAA受体3亚基（S383）内的CaMKII磷酸化位点调节这些受体的突触表达水平和突触抑制的假设。2)检验[Ca 2 +]i的变化调节3S 383的CaMKII依赖性磷酸化和细胞表面GABAA受体数量的假设。3)检验神经元活动变化调节3S 383的CaMKII磷酸化并调节细胞表面GABAA受体的插入和丰度的假设。 公共卫生相关性：神经递质既可以兴奋也可以抑制神经元的活动，GABA是脑中主要的抑制性神经递质，而谷氨酸是兴奋性神经递质。GABA与GABAA受体结合，然后GABAA受体打开并允许带负电荷的离子进入神经元，抑制其电活动。改变神经元表面GABAA受体的数量可以调节其电活动，了解神经元如何调节GABAA受体的数量对于了解癫痫和精神分裂症等脑疾病非常重要，其中电活动失调，GABAA受体的数量改变。

DESCRIPTION (provided by applicant): 3-aminobutyric acid (GABAA) receptors are the major sites of synaptic inhibition in the CNS and are drug targets for a variety of pharmacotherapeutic agents such as benzodiazepines, barbiturates, general anesthetics and neurosteroids. Compromised GABAergic transmission is one of the contributing factors in a number of neurological and psychiatric diseases such as epilepsy, anxiety, sleep disorders, addiction, autism, mental retardation, depression and schizophrenia. The number of post-synaptic GABAA receptors is highly regulated and is a major determinant in modulating the strength of synaptic inhibition. Chronic bi-directional changes in neuronal activity can lead to global, compensatory adjustments in excitatory and inhibitory synaptic strengths; a process known as homeostatic synaptic scaling. Modulating the number of GABAA receptors at post-synaptic sites is one of the mechanisms underlying activity dependent changes in inhibitory synaptic transmission. I have previously shown that chronic changes in neuronal activity regulate the endoplasmic reticulum (ER)-associated degradation of GABAA receptors, mediated by Ca2+ influx through L-type voltage gated Ca2+channels, modulating receptor cell surface number and efficacy of synaptic inhibition. However, the signaling pathways linking changes in neuronal activity to the modulation of GABAA receptor turnover and abundance at inhibitory synapses is unknown. These phenomena together with my preliminary studies have allowed me to generate a central hypothesis driving the experiments in this proposal: Activity dependent phosphorylation of the GABAA receptor ¿3 subunit on serine 383 by CaMKII, modulates the insertion of these receptors and consequently their abundance at inhibitory synapses, modifying the efficacy of synaptic inhibition. My work will focus on 3 distinguishable but complimentary experimental goals: 1) To test the hypothesis that the CaMKII phosphorylation site within the GABAA receptor ¿3 subunit (S383) modulates the synaptic expression levels of these receptors and synaptic inhibition. 2) To test the hypothesis that changes in [Ca2+]i regulate the CaMKII dependent phosphorylation of ¿3S383 and the numbers of GABAA receptors at the cell surface. 3) To test the hypothesis that changes in neuronal activity modulate the CaMKII phosphorylation of ¿3S383 and regulates the insertion and abundance of cell surface GABAA receptors. PUBLIC HEALTH RELEVANCE: Neurotransmitters can either excite or inhibit the activity of neurons, and GABA is the main inhibitory neurotransmitter in the brain while glutamate is an excitatory neurotransmitter. GABA binds to the GABAA receptor, which then opens and allows negatively charged ions into the neuron, inhibiting its electrical activity. Altering the numbers of GABAA receptors on the surface of a neuron modulates its electrical activity, and understanding how neurons regulate the numbers of GABAA receptors is important for understanding a number of brain diseases like epilepsy and Schizophrenia, where electrical activity is deregulated and the number of GABAA receptors is altered.