Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center , Nijmegen , The Netherlands.
Department of Medicine, University of Minnesota Medical School , Minneapolis, Minnesota.
Am J Physiol Renal Physiol. 2018 Jul 1;315(1):F27-F35. doi: 10.1152/ajprenal.00601.2017. Epub 2018 Mar 21.
Mutations in hepatocyte nuclear factor 1β (HNF1β) cause autosomal dominant tubulointerstitial kidney disease (ADTKD-HNF1β), and patients tend to develop renal cysts, maturity-onset diabetes of the young (MODY), and suffer from electrolyte disturbances, including hypomagnesemia, hypokalemia, and hypocalciuria. Previous HNF1β research focused on the renal distal convoluted tubule (DCT) to elucidate the ADTKD-HNF1β electrolyte phenotype, although 70% of Mg is reabsorbed in the thick ascending limb of Henle's loop (TAL). An important regulator of Mg reabsorption in the TAL is the calcium-sensing receptor (CaSR). This study used several methods to elucidate the role of HNF1β in electrolyte reabsorption in the TAL. HNF1β ChIP-seq data revealed a conserved HNF1β binding site in the second intron of the CaSR gene. Luciferase-promoter assays displayed a 5.8-fold increase in CaSR expression when HNF1β was present. Expression of the HNF1β p.Lys156Glu mutant, which prevents DNA binding, abolished CaSR expression. Hnf1β knockdown in an immortalized mouse kidney TAL cell line (MKTAL) reduced expression of the CaSR and Cldn14 (claudin 14) by 56% and 48%, respectively, while Cldn10b expression was upregulated 5.0-fold. These results were confirmed in a kidney-specific HNF1β knockout mouse, which exhibited downregulation of the Casr by 81%. Cldn19 and Cldn10b expression levels were also decreased by 37% and 83%, respectively, whereas Cldn3 was upregulated by 4.6-fold. In conclusion, HNF1β is a transcriptional activator of the CaSR. Consequently, patients with HNF1β mutations may have reduced CaSR activity in the kidney, which could explain cyst progression and hyperabsorption of Ca and Mg in the TAL resulting in hypocalciuria.
肝细胞核因子 1β（HNF1β）突变导致常染色体显性遗传性肾小管间质性肾病（ADTKD-HNF1β），患者易发生肾囊肿、青少年发病的成年型糖尿病（MODY），并伴有电解质紊乱，包括低镁血症、低钾血症和低钙尿症。先前的 HNF1β 研究主要集中在肾脏远曲小管（DCT）上，以阐明 ADTKD-HNF1β 电解质表型，尽管 70%的镁在亨利氏袢升支粗段（TAL）中被重吸收。TAL 中镁重吸收的一个重要调节因子是钙敏感受体（CaSR）。本研究采用多种方法阐明 HNF1β 在 TAL 中电解质重吸收中的作用。HNF1β ChIP-seq 数据显示 CaSR 基因第二内含子中有一个保守的 HNF1β 结合位点。当存在 HNF1β 时，荧光素酶启动子测定显示 CaSR 表达增加了 5.8 倍。表达不能与 DNA 结合的 HNF1β p.Lys156Glu 突变体，使 CaSR 表达完全缺失。在永生化的小鼠肾脏 TAL 细胞系（MKTAL）中敲低 Hnf1β，使 CaSR 和 Cldn14（紧密连接蛋白 14）的表达分别降低了 56%和 48%，而 Cldn10b 的表达上调了 5.0 倍。在肾脏特异性 HNF1β 敲除小鼠中也得到了证实，Casr 的表达下调了 81%。Cldn19 和 Cldn10b 的表达水平也分别降低了 37%和 83%，而 Cldn3 的表达上调了 4.6 倍。综上所述，HNF1β 是 CaSR 的转录激活因子。因此，HNF1β 突变患者的肾脏中 CaSR 活性可能降低，这可以解释囊肿的进展以及 TAL 中 Ca 和 Mg 的过度吸收导致低钙尿症。
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