GABA transporter type 1 (GAT1) function in epilepsy

GABA 转运蛋白 1 型 (GAT1) 在癫痫中的功能

• 批准号: 8598049
• 负责人: Christopher Bruce Ransom
• 金额: --
• 依托单位: VA PUGET SOUND HEALTHCARE SYSTEM
• 依托单位国家: 美国
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-01-01 至 2014-12-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8598049
• 关键词: 3-aminobutyric acid; Acute; Affect; Afghanistan; Aging; American; Animals; Anions; Anticonvulsants; Antiepileptic Agents; Biological Assay; Brain; Caring; Cell physiology; Characteristics; Chemicals; Conflict (Psychology); Connexins; Data; Disease; Dose; Down-Regulation; Drug effect disorder; Electric Stimulation; Electroconvulsive Shock; Epilepsy; Extracellular Space; Failure; Frequencies; GABA Transporter 1; GABA transporter; Genetic; High Pressure Liquid Chromatography; Hippocampus (Brain); Iraq; Kainic Acid; Knock-out; Measurement; Mediating; Membrane Transport Proteins; Mentorship; Modeling; Molecular; Mus; Neurons; Neurotransmitters; Patients; Pentylenetetrazole; Pharmaceutical Preparations; Process; Publishing; Recurrence; Refractory; Research; Research Personnel; Residual state; Seizures; Severities; Signal Transduction; Slice; Status Epilepticus; Stroke; Surface; Synapses; Synaptic Vesicles; Testing; Therapeutic; Traumatic Brain Injury; Veratridine; Veterans; Vigabatrin; base; design; extracellular; gabapentin; gamma-Aminobutyric Acid; improved; in vivo; neuronal excitability; postsynaptic; receptor; relating to nervous system; research study; response; skills; synaptic inhibition; tiagabine; uptake

DESCRIPTION (provided by applicant): Epilepsy affects nearly 3 million Americans and approximately 30% of these patients continue to have seizures despite treatment with multiple antiepileptic drugs. Improved understanding of the cellular and molecular changes underlying seizures, and antiepileptic drug action, is essential to advance the care of veterans suffering from medically refractory epilepsy. Among the changes seen in epilepsy is a reduction of neuronal membrane transporters for the inhibitory neurotransmitter 3-aminobutyric acid (GABA) [GABA transporter type 1 (GAT1)] (During et al., 1995; Patrylo et al., 2001). Classically, GABA transporters were thought to function by removing GABA from the extracellular space, thereby terminating GABA actions. It is now clear that GABA transporters can also operate in the reverse direction to release GABA into the extracellular space, a process termed nonvesicular release. Nonvesicular GABA release is augmented by neuronal depolarization and alterations of ionic gradients, conditions that exist during epileptic seizures. Nonvesicular GABA release may be particularly important during prolonged seizures when vesicular GABA release at synapses is compromised by reductions in extracellular [Ca2+], GABA packaging into synaptic vesicles is limited by energy failure, and GABA synthesis is stimulated by low [ATP], causing an increase in cytoplasmic [GABA] that favors nonvesicular release (Erecinska et al., 1984; Hablitz and Heinemann, 1987; Allen et al., 2004). This proposal will test the hypothesis that nonvesicular GABA release has an important antiepileptic action and GAT1 downregulation in epilepsy is maladaptive. Specifically, it is hypothesized that the loss of nonvesicular GABA release mediated by GAT1 will exacerbate seizures despite elevated basal concentrations of ambient GABA. Consistent with this, studies on animals with genetic deletion of GABA transporter type 1 [GAT1 knockout (GAT1 KO)] have identified a heightened sensitivity to chemoconvulsants (Chiu et al., 2005). GAT1 function in epilepsy will be evaluated by three specific aims: Specific Aim 1 will test the hypothesis that nonvesicular GABA release in brain slices from GAT1 KO animals is reduced compared to wild type littermates. Specific Aim 2 will test the hypothesis that AEDs that increase GABA concentration or GAT1 surface expression will enhance nonvesicular release from wild type but not GAT1 KO neurons. Specific Aim 3 will test the hypothesis that nonvesicular release mediated by GAT1 affects seizure threshold in vivo and limits seizure frequency/severity in epileptic mice. Identification of changes in nonvesicular release in GAT1 knockout neurons and determination of AED effects on nonvesicular release in Specific Aims 1-2 will provide a basis for interpretation of in vivo data.

描述(由申请人提供)： 癫痫影响着近300万美国人，其中约30%的患者尽管接受了多种抗癫痫药物的治疗，但仍有癫痫发作。更好地了解癫痫发作背后的细胞和分子变化以及抗癫痫药物的作用，对于推进患有药物难治性癫痫的退伍军人的护理至关重要。癫痫的变化之一是抑制性神经递质3-氨基丁酸(GABA)的神经细胞膜转运体减少[GABA转运体1型(GAT1)](在等人，1995年期间；帕特瑞罗等人，2001年)。传统上，GABA转运体的功能被认为是通过将GABA从细胞外空间移除，从而终止GABA的作用。现在很清楚，GABA转运体也可以反向操作，将GABA释放到细胞外空间，这一过程被称为非囊泡释放。癫痫发作期间存在的神经元去极化和离子梯度的改变增加了非囊泡性GABA的释放。在长时间的癫痫发作中，非囊泡性GABA释放可能特别重要，此时突触的囊泡性GABA释放受到细胞外[Ca2+]减少的影响，GABA进入突触小泡的包装受到能量衰竭的限制，GABA合成受到低[ATP]的刺激，导致有利于非囊泡性释放的细胞质[GABA]增加(Erecinska等人，1984；Hablitz和Heinemann，1987；Allen等人，2004)。这一建议将检验这样一种假设，即非囊泡性GABA释放具有重要的抗癫痫作用，而GAT1在癫痫中的下调是不适应的。具体地说，假设GAT1介导的非囊泡性GABA释放的丢失将加剧癫痫发作，尽管环境中GABA的基础浓度升高。与此一致的是，对GABA转运体1型基因缺失的动物[GAT1基因敲除(GAT1 KO)]的研究发现，对化学惊厥药物的敏感性增加(Chiu等人，2005年)。GAT1在癫痫中的功能将通过三个特定目标进行评估：特定目标1将测试GAT1 KO动物脑片中非囊泡性GABA释放比野生型小鼠减少的假设。特定目标2将验证这样的假设，即增加GABA浓度或GAT1表面表达的AEDs将促进野生型GAT1 KO神经元的非囊泡释放。特异性目标3将验证GAT1介导的非囊泡释放在体内影响癫痫阈值并限制癫痫小鼠癫痫发作频率/严重程度的假设。识别GAT1基因敲除神经元中非囊泡释放的变化，并确定AED对特定目标1-2中非囊泡释放的影响，将为体内数据的解释提供基础。