Regulation of Brain Neurotransmitter Synthesis

描述(申请人提供)：这项提案的总体目标是了解调节谷氨酸代谢的机制，以及它与中枢神经系统(CNS)中谷氨酸神经传递的相互关系。谷氨酸和天冬氨酸是哺乳动物大脑中主要的兴奋性神经递质。这些氨基酸是不同寻常的，因为它们有双重作用，首先是神经递质，其次是氮和能量代谢的重要中间体。它们在外周组织中的代谢作用已得到很好的认识，但它们在大脑中的代谢与神经递质功能之间的关系却鲜有人关注。神经传递过程中谷氨酸的释放会导致神经元中谷氨酸的损失。如果留在突触间隙，谷氨酸是兴奋毒性的。在这项提案中，我们将确定改变星形胶质细胞和神经元中复杂的代谢过程的效果，这些过程可以解毒和补充释放的谷氨酸。我们的目标是确定支链氨基酸(BCAA)氮和支链氨基转移酶(SCAT)同工酶对谷氨酸合成的贡献。我们将在体外通过特定的BCAT同工酶在海马片上测试阻断支链氨基酸氮转移的神经学后果，并在体内降低大鼠脑内BCAT同工酶的表达。我们还将测试代谢假说，了解神经活性药物加巴喷丁的作用机制。我们将研究抑制丙酮酸羧化酶(PC)催化的谷氨酸/丙酮酸循环的碳调节步骤的神经学后果。我们将确定降低PC表达对海马区谷氨酸合成和神经传递的影响。我们将验证生酮饮食治疗顽固性癫痫的疗效是通过PC降低丙酮酸羧化而产生的假设。我们将在体内测试代谢理论，用于使用核磁共振波谱计算通过PC途径的通量的电流模型。我们最近的研究揭示了Magistretti假说的分子基础和视网膜胶质细胞中高比率的有氧糖酵解。我们将确定这项观察是否提供了一种机制，将谷氨酸神经传递联系到谷氨酸丙酮酸循环的逆境臂上。这项研究的结果将为目前癫痫饮食治疗的潜在机制提供洞察，并洞察影响这些途径(枫糖浆尿病和丙酮酸羧基酶缺乏)的先天性代谢错误的神经后果的生化基础，从而可能导致更好的治疗方案。

DESCRIPTION (provided by applicant): The overall goal of this proposal is to understand mechanisms that regulate glutamate metabolism and how it interrelates with glutamate neurotransmission in the central nervous system (CNS). Glutamate and aspartate are the major excitatory neurotransmitters in the mammalian brain. These amino acids are unusual, because they have dual roles, first as neurotransmitters, and second as important intermediates in nitrogen and energy metabolism. Their metabolic roles in peripheral tissues are well recognized, but the relationship between their metabolism and neurotransmitter function in the brain has received much less attention. Release of glutamate during neurotransmission generates a loss of glutamate from the neuron. If left in the synaptic space, the glutamate is excitotoxic. In the proposal we will determine the effect of altering the complex metabolic processes in astroglia and neurons that operate to detoxify and replenish the released glutamate. Our goal is to define the contribution of branched chain amino acid (BCAA) nitrogen and the branched chain aminotransferas.e (SCAT) isozymes to the synthesis of glutamate. We will test the neurological consequences of blocking nitrogen transfer from BCAAs via specific BCAT isozymes in vitro in hippocampal slices and after lowering expression of BCAT isozymes in vivo in rat brain. We will also test the metabolic hypothesis for the mechanism of action of neuroactive drug gabapentin. We will examine neurological consequences of inhibiting the carbon regulatory step of the glutamate/pyruvate cycle catalyzed by pyruvate carboxylase (PC). We will determine the consequences of lowering PC expression on de novo glutamate synthesis and neurotransmission in hippocampus. We will test the hypothesis that the efficacy of the ketogenic diet in treating intractable epilepsy results from lowering pyruvate carboxylation by PC. We will test, in vivo, the metabolic theory underlying current models for calculating flux through PC pathway using nuclear magnetic resonance spectroscopy. Our recent studies reveal the molecular basis for the Magistretti hypothesis and the high rates of aerobic glycolysis in retinal glia. We will determine if this observation provides a mechanism for tying glutamate neurotransmission to the anaplerotic arm of the glutamate pyruvate cycle Results from this study will provide insight into mechanisms underling current dietary treatments for epilepsy and insight into the biochemical basis of the neurological consequences of inborn errors of metabolism that affect these pathways (Maple Syrup Urine Disease and Pyruvate Carboxylase deficiency) that may lead to better treatment regimens.