Loss of transcriptional activation of the potassium channel Kir5.1 by HNF1β drives autosomal dominant tubulointerstitial kidney disease

Abstract

HNF1β is an essential transcription factor for the development and functioning of the kidney. Mutations in HNF1β cause autosomal dominant tubulointerstitial kidney disease (ADTKD-HNF1β), which is characterized by renal cysts and maturity-onset diabetes of the young (MODY). Moreover, patients suffer from a severe electrolyte phenotype consisting of hypomagnesemia and hypokalemia. Until now, genes that are regulated by HNF1β are only partially known and do not fully explain the phenotype of the patients. Therefore, we conducted chIP-seq in immortalized mouse kidney cells (mpkDCT) to identify HNF1β binding sites at a genome-wide scale. In total 7,421 HNF1β binding sites were identified, including several genes involved in electrolyte transport and diabetes. A highly specific and conserved HNF1β 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 HNF1β was present. Expression of the Hnf1β p.Lys156Glu mutant that was previously identified in a ADTKD-HNF1β patient, did not activate Kcnj16 expression. Knock down of Hnf1β in mpkDCT cells significantly reduced the expression of Kcnj16 (Kir5.1) and Kcnj10 (Kir4.1) by 38% and 37%, respectively. These results were confirmed in a HNF1β renal knockout mouse, exhibiting downregulation of Kcnj16, Kcnj10 and Slc12a3 transcripts in the kidney by 78%, 83% and 76%, respectively, compared to HNF1β wild-type mice. In conclusion, HNF1β has been identified as a transcriptional activator of Kcnj16. Consequently patients with HNF1β mutations may have a reduced Kir5.1 activity in the kidney, resulting in hypokalemia and hypomagnesemia.

Essential role of Kir5.1 channels in renal salt handling and blood pressure control

“…Mutations in Kcnj16 gene are also associated with nonfamilial Brugada syndrome that causes arrhythmias including sudden cardiac death (26); in addition, genome-wide association studies of metabolite quantitative traits identified Kcnj16 as a candidate gene (27). Furthermore, it was proposed that loss of activation of Kcnj16 by transcriptional factor HNF1β might result in the development of autosomal dominant tubulointerstitial kidney disease (28). Despite these important findings, the mechanistic role of K ir 4.1/K ir 5.1 (Kcnj10/Kcnj16) basolateral K + channels in the development of salt-sensitive (SS) hypertension and control of electrolyte balance is largely unknown.…”

Mechanism of Fibrosis in HNF1B-Related Autosomal Dominant Tubulointerstitial Kidney Disease

“…14,18,19 Recent chromatin immunoprecipitation sequencing (ChIP-seq) experiments have shown that HNF-1b regulates cholesterol metabolism through transcriptional activation of Srebp2 and Pcsk9, 20 urinary concentration through activation of Fxr, 21 and potassium and magnesium homeostasis through activation of Kir5.1. 22 However, the complete gene network governed by HNF-1b in the kidney and the mechanisms whereby human mutations lead to a broad spectrum of clinical phenotypes remain to be fully elucidated. Constitutive ablation of Hnf1b in mice results in embryonic lethality due to failure of endoderm development, 23 and kidney-specific deletion of Hnf1b using the Ksp/Cre deleter strain results in postnatal kidney failure.…”

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

“…Immunohistochemistry. Immunohistochemistry (IHC) was performed as previously described (36). In short, stainings for HNF1␤ were achieved on 4-m sections of mouse kidney samples fixed in formalin and embedded in paraffin.…”

“…HNF1␤ is ubiquitously expressed in the epithelial cells of all nephron segments (14). In the distal convoluted tubule (DCT), HNF1␤ regulates the expression of the Kir4.1-Kir5.1 K ϩ channel and the ␥-subunit of the Na ϩ -K ϩ -ATPase (FXYD2) (23,36). Kidney-specific (Ksp) HNF1␤ knockout (KO) mice display reduced Kcnj10 (Kir4.1) and Kcnj16 (Kir5.1) expression levels, resulting in lower Na ϩ -Cl Ϫ -cotransporter (NCC) transcript levels (15).…”

“…Here, HNF1␤ regulates the expression of uromodulin (UMOD), which is a cystic disease gene responsible for ADTKD-UMOD (OMIM: 191845) (30). The TAL plays a dominant role in Na ϩ , Ca 2ϩ , and Mg 2ϩ reabsorption (17,36). In this segment, the furosemide-sensitive Na ϩ -K ϩ -2Cl Ϫ -cotransporter (NKCC2) facilitates transcellular Na ϩ reabsorption.…”