TISSUE SPECIFIC NUTRITIONAL ADAPTATIONS IN RENAL FAILURE

必需支链氨基酸(BCAA)起着至关重要的作用 在维持正常蛋白质动态平衡中的作用及其影响 调节代谢功能的细胞内信号通路。正常情况下 个体对减少的饮食蛋白质摄入量的营养适应(例如， 禁食，一种低蛋白质饮食处方)减少不可逆转的降解 BCAA的。分解代谢疾病，如慢性肾功能衰竭(CRF)或急性 糖尿病损害了这些保护蛋白质质量的适应性反应，因此 导致瘦体重的损失。普莱斯博士和 同事们要了解调节细胞活动的机制 限速酶--支链α-酮酸脱氢酶 在支链氨基酸降解中，在支链氨基酸分解的主要组织中， 确定在不同的分解代谢状态下是否存在共同的信号 调节BCKAD活性，从而调节BCAA水平。为了实现这些目标， 研究人员将评估三个假说：1)酸化和 糖皮质激素通过特异性途径影响BCKAD亚单位基因转录 顺势作用的反应元件。调查人员将识别特定的DNA BCKAD E2基因中对酸化有反应的启动子元件 和糖皮质激素。2)慢性肾衰大鼠支链氨基酸利用异常 由组织特异性的BCKAD活性改变所致， 生化水平。研究人员将定义CRF如何影响 BCKAD和抑制BCKAD的独特激酶BCKAD的活性 在一种成熟的大鼠模型中，肌肉、肝脏和肾脏的活动。他们 将测量BCKAD活性、BCKAD亚基和激酶蛋白以及 3)胰岛素调节BCKAD和/或BCKAD活性 不同的组织通过一种需要关键信号酶的机制 磷脂酰肌醇3-激酶。调查人员将确定生化指标 提高大鼠肌肉、肝脏和肾脏BCKAD活性的机制(S) 对急性糖尿病(即胰岛素不足)的反应，然后 研究胰岛素调节BCKAD和BCKAD的信号机制 培养的L6肌细胞中的激酶。调查人员的调查结果将定义 尿毒症、急性糖尿病和糖尿病中调节支链氨基酸降解的细胞机制 其他分解代谢情况。

The essential branched-chain amino acids (BCAA) play critical roles in maintaining normal protein homeostasis and they influence critical intracellular signaling pathways that regulate metabolic functions. In normal individuals, nutritional adaptations to a reduced dietary protein intake (e.g., fasting, a low protein diet prescription) decrease the irreversible degradation of BCAA. Catabolic conditions like chronic renal failure (CRF) or acute diabetes impair these adaptive responses that preserve protein mass, thus contributing to the loss of lean body mass. The goals of Dr. Price and colleagues are to understand the mechanisms that regulate the activity of branched-chain alpha-ketoacid dehydrogenase (BCKAD), the rate-limiting enzyme in BCAA degradation, in the major tissues where BCAA are catabolized, and to determine if there are common signals in different catabolic states that regulate BCKAD activity, and hence, BCAA levels. To address these goals, the investigators will evaluate three hypotheses: 1) Acidification and glucocorticoids influence transcription of BCKAD subunit genes through specific cis-acting response elements. The investigators will identify specific DNA promoter elements in the BCKAD E2 gene that confer responses to acidification and glucocorticoids. 2) Abnormalities in BCAA utilization in rats with CRF result from tissue-specific alterations in BCKAD activity at both genetic and biochemical levels. The investigators will define how CRF influences the activities of BCKAD and BCKAD kinase, a unique kinase that inhibits BCKAD activity, in muscle, liver and kidney in a well-established rat model. They will measure BCKAD activity, BCKAD subunit and kinase proteins and amounts of subunit and kinase mRNAs 3) Insulin modulates BCKAD and/or BCKAD activities in different tissues by a mechanism requiring the critical signaling enzyme phosphatidylinositol 3-kinase. The investigators will determine the biochemical mechanism(s) that increase BCKAD activity in rat muscle, liver and kidney in response to acute diabetes mellitus (i.e., insulin insufficiency) and then examine the signaling mechanisms by which insulin regulates BCKAD and BCKAD kinase in cultured L6 muscle cells. The investigators findings will define cellular mechanisms regulating BCAA degradation in uremia, acute diabetes and other catabolic conditions.