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

项目摘要 高钙尿症发生在5 - 10%的人口，是最常见的原因钙（钙）肾结石 疾病钙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表明， 表明结石形成者近端小管钙重吸收减少。此外，两项研究 动物和人类表明，近端小管钙重吸收增加， 噻嗪类利尿剂的作用，高钙尿症的一线药物。与远端的Ca重吸收相比 近端小管钙重吸收的机制尚不清楚。条证据 从经典的生理学研究表明，存在一个积极的钙转运途径，在近端 直小管，近端小管的最后一部分，在小管液体进入前钙可以被重吸收。 Henle袢，由于水提取，可能发生磷酸钙过饱和。活性钙重吸收 在肾单位的这一部分中，可以将管状流体中的Ca去除到低于血浆中的水平。的 本研究的目的是阐明近端直肌中一种新的主动钙转运途径的作用， 肾小管在引起和治疗高钙尿症中的作用。中心假设是，在细胞中的活性钙重吸收， 近端小管被餐后胰岛素峰和高胰岛素血症破坏， 噻嗪类。此外，近端直小管顶侧的钙通道可能作为钙传感器， 调节整体Ca稳态。已经表明，餐后胰岛素分泌和钙排泄都是 在高钙尿石形成者中增加。我们的初步研究表明，TRPV6，一个关键的钙通道，在细胞膜上， TRPV6通过跨细胞Ca转运途径被分布到近端直小管，并且TRPV6活性被 在TRPV6缺失小鼠中，氢氯噻嗪的低钙尿效应显著降低。这些 观察结果支持我们的假设，这意味着胰岛素对TRPV 6的抑制有助于餐后 高钙尿和由于胰岛素抵抗引起的代偿性高胰岛素血症引起的高钙尿。我们将 通过追求以下具体目标来验证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在多大程度上 介导噻嗪类的低钙尿效应。3.确定TRPV6在近端细胞中的Ca传感器作用 调节维生素D合成和细胞旁钙转运直小管。方法包括： 将采用人近端小管细胞中的流入来进行使用TRPV 6缺失小鼠的代谢研究， 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 近端小管中活性钙重吸收的机制，调节钙重吸收和钙 体内平衡胰岛素对活性钙重吸收的抑制作用，为钙离子的释放提供了分子基础。 许多结石形成者的餐后高钙尿和糖尿病前期的钙排泄升高。这些结果 将有助于开发一种新的策略来预防高钙尿症和肾结石疾病。

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.