Transcription factor HNF1β regulates expression of the calcium-sensing receptor in the thick ascending limb of the kidney

Abstract

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.

Urinary proteome signature of Renal Cysts and Diabetes syndrome in children

“…It is important to notice that mutations in UMOD, MUC1, and HNF1B are responsible for ADTKD, showing a strict correlation between these proteins and RCAD along with ADTKD phenotypes 42 . Considering the acknowledged role of HNF1B in regulating kidney transports and also calcium-sensing receptor CaSR 16,43 , it was interesting to notice that several peptides associated with calcium binding or calcium regulating properties might be changed in RCAD patients. The disruption of multiple calcium regulators may be one of the bases of the renal cysts formation as observed previously 44,45 .…”

Pathophysiological aspects of the thick ascending limb and novel genetic defects: HELIX syndrome and transient antenatal Bartter syndrome

“…Second, expression of CaSR is regulated by the transcription factor HNF1B: Using promoter assays Kompatscher et al, showed an increase in CaSR expression in presence of HNF1beta and a decrease of its expression when the DNA binding was blocked. They also observed a down regulation of the CaSR as well as of claudin-19 and of claudin-10b in hnf1b-knockout mice [69]. This likely contributes to the tubular phenotypes observed in patients with HNF1B mutations.…”

Bifunctional protein PCBD2 operates as a co‐factor for hepatocyte nuclear factor 1β and modulates gene transcription

“…35 Transcriptional targets of HNF1β in the TAL involved in electrolyte transport and cystogenesis are calcium-sensing receptor (CASR), PKHD1 and KCNJ16. 4,6,45 In the DCT, FXYD2 and KCNJ16 are the main transcriptional targets. Interestingly, while both PCBD2 and PCBD1 are expressed in the DCT, our luciferase experiments show that PCBD1 enhances the activation of the FXYD2 promoter by HNF1β while PCBD2 does not.…”

“…Transcriptional targets of HNF1β in the TAL involved in electrolyte transport and cystogenesis are calcium‐sensing receptor (CASR), PKHD1 and KCNJ16 4,6,45 . In the DCT, FXYD 2 and KCNJ16 are the main transcriptional targets.…”