RENAL BASIS OF HYPOCITRATURIA

描述：(直接取自应用程序)硝酸尿症是肾结石的重要原因。柠檬酸在肾小球中自由过滤，尿中柠檬酸的排泄主要受近端肾小管柠檬酸重吸收和代谢速率的调节。重吸收是由NADC-1基因编码的顶膜3NA/柠檬酸共转运体介导的，代谢由两条途径之一介导：一条线粒体途径，介导三羧酸循环中的柠檬酸代谢；一条细胞质途径，ATP柠檬酸裂解酶将柠檬酸代谢成乙酰辅酶A和草酰乙酸酯。拟议的研究将检查负责调节柠檬酸重吸收和代谢的分子机制，重点是NADC-1。目标1的研究将探讨NADC-1在慢性代谢性酸中毒、缺钾、碱喂养和饥饿大鼠中的调节分子机制。AIM 2的研究将进一步探讨酸性细胞外液对培养的近端小管细胞NADC-1调节的分子机制。这些研究将利用表达天然NADC-1的细胞，以及表达稳定转染的标记NADC-1的细胞，以及瞬时转染的报告构建体。目标1和目标2将共同解决NADC-1的调节问题。目标3中的研究将解决已知的酸中毒激活的信号通路在调节NADC-1中的作用。这些途径包括：1)酪氨酸激酶和MAP激酶途径；2)糖皮质激素；3)内皮素。AIM 4中的研究将使用13C核磁共振波谱对肾近端小管线粒体和细胞质途径中的柠檬酸代谢进行定量。最后，目标5中的研究将探讨高钾血症是否会导致高柠檬酸尿症，从而导致高钾性肾小管远端酸中毒患者不容易患肾结石。这些研究将使我们能够继续了解肾近端小管柠檬酸盐处理的调节机制。

Description: (Taken directly from the application) Hypocitraturia is an important cause of kidney stones. Citrate is freely filtered in the glomerulus, and urinary citrate excretion is regulated principally by the rate of citrate reabsorption and metabolism in the proximal tubule. Reabsorption is mediated by an apical membrane 3Na+/citrate cotransporter encoded by the NaDC-1 gene, and metabolism is mediate by one of two pathways: a mitochondrial pathway that mediates citrate metabolism in the tricarboxylic acid cycle; and a cytoplasmic pathway in which ATP citrate lyase metabolizes citrate to acetyl CoA and oxaloacetate. The proposed studies will examine the molecular mechanisms responsible for regulation of citrate reabsorption and metabolism, focusing on NaDC-1. Studies in Aim 1 will address the molecular mechanisms of NaDC-1 regulation in rats with chronic metabolic acidosis, K+ deficiency, alkali feeding, and starvation. Studies in Aim 2 will further address the molecular mechanisms of NaDC-1 regulation in cultured proximal tubule cells exposed to acidic extracellular fluid. These studies will utilize cells expressing native NaDC-1, as well as cells expressing stably transfected tagged NaDC-1, and transiently transfected reporter constructs. Aim 1 and 2 together will address the regulation of NaDC-1. Studies in Aim 3 will address the role of signaling pathways known to be activated by acidosis in the regulation of NaDC-1. These pathways include: 1) tyrosine kinase and MAP kinase pathways; 2) glucocorticoids; and 3) endothelin. Studies in Aim 4 will quantitate citrate metabolism in mitochondrial and cytoplasmic pathways of the renal proximal tubule using 13C NMR spectroscopy. Lastly, studies in Aim 5 will address whether hyperkalemia causes hypercitraturia and thus is responsible for the lack of predisposition to nephrolithiasis in hyperkalemic renal distal tubular acidosis. These studies will allow us to continue to pursue an understanding of the mechanisms of regulation of renal citrate handling in the proximal tubule.