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

描述(申请人提供)：3-氨基丁酸(GABAA)受体是中枢神经系统中突触抑制的主要部位，也是各种药物治疗的药物靶点，如苯二氮卓类药物、巴比妥酸盐、全身麻醉药和神经类固醇。GABA能传递受损是许多神经和精神疾病的促成因素之一，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。突触后GABAA受体的数量受到高度调控，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以导致兴奋性和抑制性突触强度的全局代偿性调整；这一过程被称为动态平衡突触缩放。调节突触后部位GABAA受体的数量是抑制性突触传递活动依赖变化的机制之一。我以前已经证明，神经元活动的慢性变化调节内质网(ER)相关的GABA受体的降解，通过L型电压门控钙通道介导钙内流，调节受体细胞表面数量和突触抑制的效果。然而，将神经元活性的变化与抑制性突触的GABAA受体周转和丰度调节联系起来的信号通路尚不清楚。这些现象加上我的初步研究，使我能够产生一个中心假说，推动这一提议中的实验：CaMKII对丝氨酸383上GABAA受体3亚单位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的丰度，改变突触抑制的效果。我的工作将集中在三个可区分但互补的实验目标上：1)检验GABAA受体3亚单位(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)验证[Ca~(2+)]_i变化对CaMKII依赖性的3S383磷酸化和细胞表面GABAA受体数目的调节作用。3)验证神经元活动改变调节CaMKII磷酸化3S383并调节细胞表面GABAA受体插入和丰度的假设。 与公共健康相关：神经递质可以兴奋或抑制神经元的活动，GABA是大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受体的数量对于理解癫痫和精神分裂症等脑部疾病非常重要，这些疾病的电活动被解除调控，GABAA受体的数量发生变化。

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.