Engineering glutamate metabolism

描述(由申请人提供)：这项工作的目的是制造一个转基因小鼠模型，以研究谷氨酸在调节体内氮分配中的作用。谷氨酸占食物蛋白质的10%-15%，但大多数摄入的谷氨酸是由小肠的肠细胞代谢的。然而，谷氨酸在体内的氮代谢中起主要作用，在骨骼肌中是谷氨酰胺的直接前体，谷氨酰胺被许多组织(肠粘膜、肝脏、肾脏和免疫细胞)利用，特别是在分解代谢状态下。越来越多的患者服用补充谷氨酰胺，尤其是那些消化功能受损和/或肌肉萎缩的患者。由于谷氨酰胺是由肌肉蛋白质分解产生的氨基酸合成的，补充谷氨酰胺的理由是它会减少内源性谷氨酰胺的合成，从而维持肌肉质量。除了谷氨酰胺，骨骼肌还显示出丙氨酸和氨的净产生，但对这一过程的调节知之甚少。有证据表明，细胞内谷氨酸对分解代谢状态下谷氨酰胺的合成是有限的，这项工作将检验这样一种假设，即谷氨酸的可用性是将氮分配到谷氨酰胺、丙氨酸和氨中的主要决定因素。将建立一个在骨骼肌中表达谷氨酸脱氢酶的转基因小鼠模型，这将使我们能够通过饮食手段来调控肌肉中的谷氨酸水平。我们假设，改变肌肉中谷氨酸的含量将改变该组织对饮食氨基酸和分解代谢应激所合成和释放的谷氨酰胺、丙氨酸和氨的比率。这项工作的长期目标是制定氨基酸和蛋白质的最佳输送方案，以促进蛋白质的积累，并在疾病的治疗和预防中限制蛋白质的浪费。

DESCRIPTION (provided by applicant): The aim of this work is to produce a transgenic mouse model to study the role of glutamate availability in the regulation of nitrogen partitioning within the body. Glutamate makes up to 10-15% of dietary protein but most ingested glutamate is metabolized by the enterocytes of the small intestine. However, glutamate plays a major role in nitrogen metabolism within the body and, in skeletal muscle, is the direct precursor of glutamine which is utilized by a number of tissues (intestinal mucosa, liver, kidneys and immune cells) particularly in catabolic states. Supplemental glutamine is increasingly being given to a variety of patients, most notably those with impaired digestive function and/or muscle wasting. Since glutamine is synthesized from amino acids derived from muscle protein breakdown the rationale for glutamine supplementation is that it will decrease endogenous glutamine synthesis and thereby maintain muscle mass. In addition to glutamine, skeletal muscle also shows net production of alanine and ammonia but little is known about the regulation of this process. There is evidence that intracellular glutamate is limiting for glutamine synthesis in catabolic states and this work will test the hypothesis that glutamate availability is a prime determinant in the partitioning of nitrogen into glutamine, alanine and ammonia. A transgenic mouse model expressing glutamate dehydrogenase in skeletal muscle will be developed which will enable us to manipulate intramuscular glutamate levels through dietary means. We hypothesize that changing intramuscular glutamate content will change the ratio of glutamine, alanine and ammonia synthesized and released by this tissue in response to dietary amino acids and catabolic stress. The long term goals of the work are to formulate optimal delivery of amino acids and protein to enhance protein accretion and limit protein wasting in the treatment, and prevention, of disease.