The urea transporter UT-A1 plays a predominant role in a urea-dependent urine-concentrating mechanism

Xiaoqiang Geng,Shun Zhang,Jinzhao He,Ang Ma,Yingjie Li,Min Li,Hong Zhou,Guangping Chen,Baoxue Yang

doi:10.1074/jbc.ra120.013628

Abstract

Urea transporters are a family of urea-selective channel proteins expressed in multiple tissues that play an important role in the urine-concentrating mechanism of the mammalian kidney. Previous studies have shown that knockout of urea transporter (UT)-B, UT-A1/A3, or all UTs leads to urea-selective diuresis, indicating that urea transporters have important roles in urine concentration. Here, we sought to determine the role of UT-A1 in the urine-concentrating mechanism in a newly developed UT-A1-knockout mouse model. Phenotypically, daily urine output in UT-A1-knockout mice was nearly 3-fold that of WT mice and 82% of all-UT-knockout mice, and the UT-A1-knockout mice had significantly lower urine osmolality than WT mice. After 24-h water restriction, acute urea loading, or high-protein (40%) intake, UT-A1-knockout mice were unable to increase urine-concentrating ability. Compared with all-UT-knockout mice, the UT-A1-knockout mice exhibited similarly elevated daily urine output and decreased urine osmolality, indicating impaired urea-selective urine concentration. Our experimental findings reveal that UT-A1 has a predominant role in urea-dependent urine-concentrating mechanisms, suggesting that UT-A1 represents a promising diuretic target.

Highlights

Urea is the main end product of protein metabolism in mammals and plays a critical role in the urine-concentrating and water-conservation mechanism [1]
Western blotting analysis showed that urea transporter (UT)-A1 and UT-A3 were expressed in the renal inner medulla, and UT-A2 was expressed in the renal outer medulla in WT mice
UT-A1 was deleted in the inner medullary collecting duct (IMCD), UT-A2 and UT-A3 expressions were not affected in UT-A1–KO mice (Fig. 1, B and C)

Summary

Introduction

Urea is the main end product of protein metabolism in mammals and plays a critical role in the urine-concentrating and water-conservation mechanism [1]. UT-A1–KO mice are a suitable model to determine the role of UT-A1 in intrarenal urea recycling and the urine-concentrating mechanism. The average urine osmolality of UT-A1–KO mice was markedly lower than that of WT mice and was similar to all-UT–KO mice (Fig. 2C and Table S1).

Results

Conclusion