Wojciechowski Daniel, Kovalchuk Elena, Yu Lan, Tan Hua, Fahlke Christoph, Stölting Gabriel, Alekov Alexi K
Institute for Neurophysiology, Hannover Medical School, Hanover, Germany.
Institute of Complex Systems 4 (ICS-4) - Zelluläre Biophysik, Forschungszentrum Jülich, Jülich, Germany.
Front Physiol. 2018 Oct 23;9:1490. doi: 10.3389/fphys.2018.01490. eCollection 2018.
Dent disease 1 (DD1) is a renal salt-wasting tubulopathy associated with mutations in the Cl/H antiporter ClC-5. The disease typically manifests with proteinuria, hypercalciuria, nephrocalcinosis, and nephrolithiasis but is characterized by large phenotypic variability of no clear origin. Several DD1 cases have been reported lately with additional atypical hypokalemic metabolic alkalosis and hyperaldosteronism, symptoms usually associated with another renal disease termed Bartter syndrome (BS). Expression of the Bartter-like DD1 mutant ClC-5 G261E in HEK293T cells showed that it is retained in the ER and lacks the complex glycosylation typical for ClC-5 WT. Accordingly, the mutant abolished CLC ionic transport. Such phenotype is not unusual and is often observed also in DD1 ClC-5 mutants not associated with Bartter like phenotype. We noticed, therefore, that one type of BS is associated with mutations in the protein barttin that serves as an accessory subunit regulating the function and subcellular localization of ClC-K channels. The overlapping symptomatology of DD1 and BS, together with the homology between the proteins of the CLC family, led us to investigate whether barttin might also regulate ClC-5 transport. In HEK293T cells, we found that barttin cotransfection impairs the complex glycosylation and arrests ClC-5 in the endoplasmic reticulum. As barttin and ClC-5 are both expressed in the thin and thick ascending limbs of the Henle's loop and the collecting duct, interactions between the two proteins could potentially contribute to the phenotypic variability of DD1. Pathologic barttin mutants differentially regulated trafficking and processing of ClC-5, suggesting that the interaction between the two proteins might be relevant also for the pathophysiology of BS. Our findings show that barttin regulates the subcellular localization not only of kidney ClC-K channels but also of the ClC-5 transporter, and suggest that ClC-5 might potentially play a role not only in kidney proximal tubules but also in tubular kidney segments expressing barttin. In addition, they demonstrate that the spectrum of clinical, genetic and molecular pathophysiology investigation of DD1 should be extended.
1型丹特病（DD1）是一种与氯离子/氢离子反向转运体ClC-5突变相关的肾性失盐性肾小管病。该病通常表现为蛋白尿、高钙尿症、肾钙质沉着症和肾结石，但具有来源不明的显著表型变异性。最近报道了几例DD1病例，伴有额外的非典型低钾性代谢性碱中毒和醛固酮增多症，这些症状通常与另一种称为巴特综合征（BS）的肾脏疾病相关。在HEK293T细胞中表达类似巴特综合征的DD1突变体ClC-5 G261E，结果显示它滞留在内质网中，并且缺乏ClC-5野生型典型的复杂糖基化。因此，该突变体消除了CLC离子转运。这种表型并不罕见，在与类似巴特综合征表型无关的DD1 ClC-5突变体中也经常观察到。因此，我们注意到一种类型的BS与barttin蛋白的突变有关，barttin作为辅助亚基调节ClC-K通道的功能和亚细胞定位。DD1和BS重叠的症状学，以及CLC家族蛋白之间的同源性，促使我们研究barttin是否也可能调节ClC-5的转运。在HEK293T细胞中，我们发现共转染barttin会损害复杂糖基化，并使ClC-5在内质网中滞留。由于barttin和ClC-5都在髓袢升支细段和粗段以及集合管中表达，这两种蛋白之间的相互作用可能潜在地导致了DD1的表型变异性。病理性barttin突变体对ClC-5的转运和加工有不同的调节作用，这表明这两种蛋白之间的相互作用可能也与BS的病理生理学相关。我们的研究结果表明，barttin不仅调节肾脏ClC-K通道的亚细胞定位，还调节ClC-5转运体的亚细胞定位，并表明ClC-5可能不仅在肾近端小管中发挥作用，还可能在表达barttin的肾小管节段中发挥作用。此外，它们还表明，DD1的临床、遗传和分子病理生理学研究范围应扩大。
