Collecting Duct-Specific Inactivation of HNF-1β Leads to Fibrocystic Disease and Impaired Urinary Concentration

Hepatocyte nuclear factor-1β (HNF-1β) is an essential transcription factor that regulates tissue-specific gene expression in the kidney, liver, pancreas and genitourinary tract. In humans, mutations of HNF-1β cause renal cysts and diabetes (RCAD) and congenital anomalies of the kidney and urinary tract (CAKUT). Inactivation of Hnf-1β in tubular epithelial cells throughout the nephron leads to early-onset cyst formation and postnatal lethality. Here, we used Pkhd1/Cre mice to delete Hnf-1β specifically in renal collecting ducts (CD). Hnf-1β mutant mice survived long-term and developed slowly progressive cystic kidney disease, renal fibrosis, and hydronephrosis. Compared with wild-type littermates, Hnf-1β mutant mice had higher urine volume, lower urine osmolality, and higher water intake. Differences were seen at baseline, following 24h water restriction, and following administration of dDAVP. Circulating ADH levels were similar in wild type and mutant mice. Polyuria, polydipsia, and decreased urine osmolality were present prior to the onset of cyst formation and hydronephrosis. These findings indicated that Hnf-1β mutant mice have a primary defect in urinary concentrating ability. Studies using in vitro hypertonicity response experiments identified NR1H4 (FXR), a transcription factor previously shown to regulate water homeostasis, as a novel HNF-1β target. mIMCD3 cells exposed to hypertonic medium robustly upregulated Fxr mRNA levels; this upregulation was lost in Hnf-1β mutant cells. HNF-1β was bound to the Fxr promoter region in vivo, and Fxr mRNA was significantly downregulated in mutant mice. FXR protein localized to CD in wild-type mice and was almost undetectable in the cyst epithelium of mutant mice. These findings highlight a new and critical role for HNF-1β in urinary concentration and hypertonicity by regulating the transcription of FXR in the CD. Cultured cells were treated with two conditions, each in triplicate for a total of twelve RNA-Seq samples