Engineering glutamate metabolism

描述（由申请人提供）：这项工作的目的是建立一个转基因小鼠模型，研究谷氨酸可用性在调节体内氮分配中的作用。谷氨酸占膳食蛋白质的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，谷氨酸在体内氮代谢中起着重要作用，在骨骼肌中，谷氨酰胺是谷氨酰胺的直接前体，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。补充谷氨酰胺越来越多地被用于各种各样的患者，尤其是那些消化功能受损和/或肌肉萎缩的患者。由于谷氨酰胺是由来源于肌肉蛋白分解的氨基酸合成的，因此补充谷氨酰胺的理由是它将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，骨骼肌也显示丙氨酸和氨的净生产，但对这一过程的调节知之甚少。有证据表明，在分解代谢状态下，细胞内谷氨酸限制了谷氨酰胺的合成，这项工作将检验谷氨酸可用性是氮分配为谷氨酰胺、丙氨酸和氨的主要决定因素的假设。在骨骼肌中表达谷氨酸脱氢酶的转基因小鼠模型将被开发，这将使我们能够通过饮食手段操纵肌内谷氨酸水平。我们假设肌内谷氨酸含量的改变会改变该组织对膳食氨基酸和分解代谢应激的反应，从而改变其合成和释放谷氨酰胺、丙氨酸和氨的比例。这项工作的长期目标是制定氨基酸和蛋白质的最佳递送，以提高蛋白质的增加和限制蛋白质的浪费，在治疗和预防疾病。

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.