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Kidney Week

Abstract: SA-OR063

Transcriptional Activation of Kir5.1 by HNF1B – Implications for Autosomal Dominant Tubulo-Interstitial Kidney Disease

Session Information

Category: Fluid, Electrolytes, and Acid-Base

  • 704 Fluid, Electrolyte, Acid-Base Disorders

Authors

  • Hoenderop, Joost, Radboud University Medical Center, Nijmegen, Netherlands
  • Kompatscher, Andreas, Radboud University Medical Center, Nijmegen, Netherlands
  • Aboudehen, Karam S., University of Minnesota, Minneapolis, Minnesota, United States
  • Igarashi, Peter, University of Minnesota, Minneapolis, Minnesota, United States
  • De Baaij, Jeroen H.F., Radboud University Medical Center, Nijmegen, Netherlands
  • Bindels, René J., Radboud University Medical Center, Nijmegen, Netherlands
Background

Hepatocyte nuclear factor 1 homeobox B (HNF1B) is an essential transcription factor for the development and functioning of the kidney. Mutations in HNF1b cause autosomal dominant tubulointerstitial kidney disease (ADTKD-HNF1B). Patients often suffer from a severe electrolyte phenotype consisting of hypomagnesemia and hypokalemia. Until now, known genes regulated by HNF1B do not fully explain the phenotype of the patients.

Methods

Therefore, a chromatin immunoprecipitation and sequencing (chIP-seq) was conducted in immortalized mouse kidney cells (mpkDCT) to identify HNF1B binding sites at a genome-wide scale. Luciferase-promoter assays, siRNA-mediated knockdown of Hnf1b in DCT cells and RT-qPCR on HNF1B mutant mouse kidneys were performed to assess the transcriptional regulation of Hnf1b on candidate genes in vitro and in vivo.

Results

In total 7,421 HNF1B binding sites were identified, including several genes involved in electrolyte transport and diabetes. A highly conserved HNF1B site was identified in the promoter of Kcnj16, encoding the potassium channel Kir5.1. Luciferase-promoter assays showed a 2.2 fold increase in Kcnj16 expression when HNF1B was present. Expression of the Hnf1b p.Lys156Glu mutant that was identified in a ADTKD-HNF1B patient, did not activate Kcnj16 expression. Knockdown of Hnf1b in mpkDCT cells significantly reduced the expression of Kcnj16 (Kir5.1) and Kcnj10 (Kir4.1) by 38% and 37%. These results were confirmed in a HNF1B renal knockout mouse, exhibiting downregulation of Kcnj16, Kcnj10 and Slc12a3 transcripts in the kidney by 78%, 83% and 76%, respectively, compared to HNF1B wild-type mice.

Conclusion

HNF1B has been identified as a transcriptional activator of Kcnj16. Consequently patients with HNF1B mutations may have reduced Kir5.1 activity in the kidney, resulting in hypokalemia and hypomagnesemia.

Funding

  • Government Support - Non-U.S.