Mechanisms for Extracellular Glutamate Formation in Brai

Brai 细胞外谷氨酸形成机制

• 批准号: 7013462
• 负责人: H. Ronald Zielke
• 金额: $ 27.3万
• 依托单位: UNIVERSITY OF MARYLAND BALTIMORE
• 依托单位国家: 美国
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-02-17 至 2009-01-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7013462
• 关键词: aminoacid transport; astrocytes; bioenergetics; brain metabolism; branched chain aminoacid; catecholamines; cerebellum; corpus striatum; dicarboxylate; enzyme activity; gamma aminobutyrate; glutamate dehydrogenase; glutamates; glutamine; granule cell; human tissue; intracellular transport; ketoacid; laboratory rat; membrane transport proteins; microdialysis; neurons; nitrogen metabolism; serotonin; tissue /cell culture

It has been postulated that glutamate levels in the interstitial space are maintained at low levels to prevent excitotoxicity. This is critical since the developing brain has increased sensitivity to excitotoxicity due to up regulation of excitatory amino acid receptors. Elevated extracellular glutamate in perinatal hypoxia/ischemia increases only about 3 fold, yet is a major cause of mortality and morbidity. Survivors are often left with severe, permanent neurological impairment. However, we postulate that a low level of glutamate is necessary in the interstitial space. Baseline levels of glutamate have been shown to interact with metabotropic receptors. This project will examine mechanisms by which extracellular glutamate is generated in both perinatal and adult brain in the normal and in the traumatized perinatal brain following an episode of hypoxia/ischemia. Preliminary results indicate that infusion of glutamine into the rat and mouse brain by microdialysis markedly increases the concentration of extracellular glutamate to excitotoxic levels and that it is synthesized in the extracellular space from glutamine. The concentration of extracellular glutamine in brain is normally 200 -300 mu M providing a ready precursor. We hypothesize that under normal conditions the primary mechanism for extracellular glutamate synthesis is maleate activated glutaminase (MAG), a side reaction of the ectoenzyme gamma-glutamyl transpeptidase (gamma-GTP). We hypothesize a second mechanism predominates in trauma. We propose that intramitochondrial phosphate dependent glutaminase (PDG) is released (or exposed) from damaged cells and converts glutamine to glutamate resulting in excitotoxicity and cell death days after the initial traumatic event. These enzymes may also play a role in conditions such as elevated ammonia. We will determine the enzymatic mechanism for extracellular glutamate formation in normal and 7-day old hypoxic-ischemic rat brain, adult rats under conditions of ammonia toxicity, mice deficient in the enzyme gamma-GTP, and in neuronal cell cultures. Studies will utilize microdialysis and cell culture in the presence and absence of effectors of the enzymes involved. It is anticipated that these studies will lead to new approaches in the care of infants that have experienced hypoxic or ischemic injury during infancy.

据推测，细胞间隙中的谷氨酸水平保持在较低水平以防止兴奋性毒性。这是至关重要的，因为由于兴奋性氨基酸受体的上调，发育中的大脑对兴奋性毒性的敏感性增加。围产期缺氧/缺血时细胞外谷氨酸含量升高仅增加约 3 倍，但却是死亡率和发病率的主要原因。幸存者常常留下严重的、永久性的神经损伤。然而，我们假设间隙空间中需要低水平的谷氨酸。谷氨酸的基线水平已被证明与代谢受体相互作用。该项目将研究正常的围产期大脑和缺氧/缺血后受损的围产期大脑中细胞外谷氨酸的产生机制。初步结果表明，向大鼠和小鼠输注谷氨酰胺 通过微透析显着地将细胞外谷氨酸浓度提高到兴奋性毒性水平，并且它是在细胞外空间由谷氨酰胺合成的。脑中细胞外谷氨酰胺的浓度通常为200 -300 μM，提供现成的前体。我们假设在正常条件下，细胞外谷氨酸合成的主要机制是马来酸激活的谷氨酰胺酶（MAG），它是胞外酶γ-谷氨酰转肽酶（γ-GTP）的副反应。我们假设第二种机制在创伤中占主导地位。我们提出线粒体内磷酸盐依赖性谷氨酰胺酶 (PDG) 从受损细胞中释放（或暴露），并将谷氨酰胺转化为谷氨酸，导致最初创伤事件后几天的兴奋性毒性和细胞死亡。这些酶也可能在氨升高等情况下发挥作用。我们将确定正常和 7 日龄缺氧缺血大鼠大脑、氨中毒条件下的成年大鼠、缺乏 γ-GTP 酶的小鼠以及神经元细胞培养物中细胞外谷氨酸形成的酶促机制。研究将在存在或不存在相关酶效应子的情况下利用微透析和细胞培养。预计这些研究将为护理婴儿期经历过缺氧或缺血性损伤的婴儿带来新的方法。