Role of claudin-2 in Calcium Homeostasis and Kidney Stone Disease

项目总结/摘要 肾结石影响9%的人口，特发性高钙尿症是主要的致病危险因素。我们 长期目标是阐明特发性高钙尿症的发病机制并开发新的治疗方法。的 肾近端小管重吸收70%的过滤钙，这被认为是通过细胞旁途径发生的。 Claudin-2是一种细胞旁阳离子通道，在近端肾小管和肠上皮细胞中表达。 上皮在初步的研究中，我们发现claudin-2基因敲除小鼠的肾脏和吸收功能， 高钙尿症，导致严重的乳头状肾钙质沉着症。此外，我们发现claudin-2基因变异是 与人类肾结石疾病有关。我们推测claudin-2介导钙重吸收 近端小管和结肠中的钙分泌。claudin-2的损失增加了钙递送到 髓袢，易发生内髓钙沉积，从而导致肾结石病。的 检验这一假设的具体目的是：（1）检验claudin-2是否介导细胞旁钙重吸收 在肾近端小管我们将使用claudin-2全基因敲除小鼠的小管微穿刺， 用肾特异性条件性敲除小鼠近端小管的贡献，测试claudin-2在近端小管中的作用。 噻嗪类药物的降尿钙作用，并探讨其性别效应。(2)测试claudin-2是否介导肠 钙的分泌。我们将产生特异性的claudin-2敲除小鼠，并进行示踪通量测定 在外翻肠囊和尤辛室制备中。(3)检测人类claudin-2基因变异 和蛋白表达与尿钙和肾结石有关。我们将进行基因关联 一项在3个美国人群队列中进行的研究，旨在检测claudin-2基因多态性与病史的相关性 肾结石和钙的排泄。在一个单独的肾结石患者队列和匹配的正常对照组中， 志愿者，我们将测试尿外泌体中claudin-2蛋白丰度与高钙尿症的相关性。 肾结石

PROJECT SUMMARY/ABSTRACT Kidney stones affect 9% of the population and idiopathic hypercalciuria is the major pathogenic risk factor. Our long-term goal is to elucidate the pathogenesis of idiopathic hypercalciuria and develop novel therapies. The renal proximal tubule reabsorbs 70% of filtered calcium, which is believed to occur via the paracellular pathway. Claudin-2 is a paracellular cation channel that is expressed in the proximal renal tubule and in intestinal epithelium. In preliminary studies, we show that claudin-2 knockout mice have renal and absorptive hypercalciuria, leading to severe papillary nephrocalcinosis. Moreover, we find that claudin-2 gene variants are associated with kidney stone disease in humans. We hypothesize that claudin-2 mediates calcium reabsorption in the proximal tubule and calcium secretion in the colon. Loss of claudin-2 increases calcium delivery to the loop of Henle, and predisposes to inner medullary calcium deposition and hence kidney stone disease. The specific aims to test this hypothesis are: (1) Test whether claudin-2 mediates paracellular calcium reabsorption in the renal proximal tubule. We will use tubule micropuncture of claudin-2 global knockout mice, determine the contribution of the proximal tubule with kidney-specific conditional knockout mice, test the role of claudin-2 in the hypocalciuric effect of thiazides, and explore the effect of sex. (2) Test whether claudin-2 mediates intestinal secretion of calcium. We will generate intestine-specific claudin-2 knockout mice and perform tracer flux assays in everted intestinal sacs and Ussing chamber preparations. (3) Test whether human claudin-2 gene variants and protein expression are associated with urine calcium and kidney stones. We will conduct a gene association study in 3 U.S. population-based cohorts to test the association of claudin-2 gene polymorphisms with a history of kidney stones and calcium excretion. In a separate cohort of kidney stone formers and matched normal volunteers, we will test the association of claudin-2 protein abundance in urinary exosomes with hypercalciuric kidney stone disease.