Hypercalciuria and TRPV6-mediated Active Calcium Reabsorption in the Proximal Tubule

项目总结 高钙尿症发生在5-10%的人群中，是导致钙(钙)肾结石的最常见原因 疾病。CA重吸收发生在不同的肾单位段；然而，来自人类受试者的证据 提示结石患者近端肾小管钙重吸收减少。此外，在这两个方面的研究 动物和人类认为近端肾小管钙重吸收增加是低钙尿症的原因 治疗高钙尿症的一线药物--噻嗪类利尿剂的疗效。与远端钙重吸收的比较 关于近端小管钙重吸收的机制，人们知之甚少。一系列证据 来自经典生理学的研究表明，在近端存在一条活跃的钙转运途径 直小管，近端小管的最后一部分，在小管液体进入肾小管之前，钙可以在这里被重新吸收。 亨勒环，由于水的提取，可能会发生磷酸钙的过饱和。活性钙重吸收 在肾单位的这一段，可以将肾小管液中的钙排出到低于血浆中的水平。这个 本研究的目的是阐明一条新的主动钙转运通路在近侧直肠肌中的作用。 肾小管在引起和治疗高钙尿中的作用。中心假说是体内活跃的钙重吸收。 近端小管被餐后胰岛素激增和高胰岛素血症破坏，并通过 噻嗪类药物。此外，近端直管顶侧的钙通道可作为钙感受器 调节整体钙动态平衡。研究表明，餐后胰岛素的分泌和钙的排泄都是 高钙尿性结石患者增加。我们的初步研究表明，TRPV6是细胞内的一个关键钙通道。 跨细胞钙转运途径，分布于近端直小管，TRPV6活性受抑制 在TRPV6基因缺失的小鼠中，氢氯噻嗪的降钙尿作用显著降低。这些 观察结果支持我们的假设，这意味着胰岛素对TRPV6的抑制有助于餐后 胰岛素抵抗引起的代偿性高胰岛素血症引起的高钙尿和高钙尿。我们会 通过追求以下具体目标来检验我们的假设并实现我们的研究目标。1.确定 胰岛素对近曲小管活性钙重吸收的抑制作用2.确定TRPV6的程度 介导了噻嗪类药物的降钙尿作用。3.确定TRPV6在牙周近端的钙敏感作用 调节维生素D合成和细胞旁钙运输的直管。各种方法，从案例 利用TRPV6缺失小鼠的新陈代谢研究的人近端小管细胞的流入将被用来完成 我们的研究目标。在成功完成拟议的研究后，我们预计将揭开分子的面纱 近端小管主动钙重吸收调节钙重吸收和钙的机制 动态平衡。胰岛素对活性钙重吸收的抑制作用提供了分子基础 许多结石患者出现餐后高钙尿，糖尿病前期患者钙排泄增加。这些结果 将有助于制定预防高钙尿症和肾结石疾病的新策略。

PROJECT SUMMARY Hypercalciuria occurs in 5-10% of the population and is the most common cause of calcium (Ca) kidney stone disease. Ca reabsorption takes place in different nephron segments; however, evidence from human subjects indicates that proximal tubule Ca reabsorption is decreased in stone formers. Furthermore, studies in both animals and humans suggest that increased proximal tubule Ca reabsorption accounts for the hypocalciuric effect of thiazide diuretics, the first line medication for hypercalciuria. Compared to Ca reabsorption in the distal tubule, much less is known about the mechanism of Ca reabsorption in the proximal tubule. Lines of evidence from classical physiological studies indicate the existence of an active Ca transport pathway in the proximal straight tubule, the last portion of the proximal tubule where Ca can be reabsorbed before tubular fluid enters the loop of Henle where supersaturation of Ca phosphate may occur due to water extraction. Active Ca reabsorption in this segment of the nephron may remove Ca in the tubular fluid to a level below that in the plasma. The objective of this proposal is to elucidate the roles of a novel active Ca transport pathway in the proximal straight tubule in causing and treating hypercalciuria. The central hypothesis is that active Ca reabsorption in the proximal tubule is disrupted by postprandial insulin surge and under hyperinsulinemia and is enhanced by thiazides. In addition, a Ca channel in the apical side of proximal straight tubule may act as a Ca sensor to regulate overall Ca homeostasis. It has been shown that postprandial insulin secretion and Ca excretion are both increased in hypercalciuric stone formers. Our preliminary studies indicate that TRPV6, a key Ca channel in the transcellular Ca transport pathway, is distributed to the proximal straight tubule, and TRPV6 activity is inhibited by insulin, and the hypocalciuric effect of hydrochlorothiazide is significantly reduced in TRPV6 null mice. These observations support our hypothesis, which implies that inhibition of TRPV6 by insulin contributes to postprandial hypercalciuria and hypercalciuria due to compensatory hyperinsulinemia as a result of insulin resistance. We will test our hypothesis and achieve our research objective by pursuing the following specific aims. 1. Determine the inhibitory effect of insulin on active Ca reabsorption in the proximal tubule. 2. Determine to what extent TRPV6 mediates the hypocalciuric effect of thiazides. 3. Determine the Ca-sensor roles of TRPV6 in the proximal straight tubule that regulate vitamin D synthesis and paracellular Ca transport. Approaches ranging from Ca influx in human proximal tubule cells to metabolic studies using TRPV6 null mice will be employed to accomplish our research goals. Upon successful completion of the proposed research, we expect to unveil the molecular mechanism for the active Ca reabsorption in the proximal tubule that regulates Ca reabsorption and Ca homeostasis. The inhibition of the active Ca reabsorption by insulin provides a molecular basis for the postprandial hypercalciuria in many stone formers and elevated Ca excretion in prediabetes. These outcomes will help to develop a new strategy to prevent hypercalciuria and kidney stone disease.