Uromodulin Regulates Murine Aquaporin−2 Activity via Thick Ascending Limb–Collecting Duct Cross−Talk during Water Deprivation

Abstract

Uromodulin, a urinary protein synthesized and secreted from the thick ascending limb (TAL) of the loop of Henle, is associated with hypertension through the activation of sodium reabsorption in the TAL. Uromodulin is a potential target for hypertension treatment via natriuresis. However, its biological function in epithelial cells of the distal nephron segment, particularly the collecting duct, remains unknown. Herein, we examined the regulation of uromodulin production during water deprivation in vivo as well as the effect of uromodulin on the activity of the water channel aquaporin−2 (AQP2) in vitro and in vivo using transgenic mice. Water deprivation upregulated uromodulin production; immunofluorescence experiments revealed uromodulin adhesion on the apical surface of the collecting duct. Furthermore, the activation of AQP2 was attenuated in mice lacking uromodulin. Uromodulin enhanced the phosphorylation and apical trafficking of AQP2 in mouse collecting duct cells treated with the vasopressin analog dDAVP. The uromodulin-induced apical trafficking of AQP2 was attenuated via endocytosis inhibitor treatment, suggesting that uromodulin activates AQP2 through the suppression of endocytosis. This study provides novel insights into the cross−talk between TAL and the collecting duct, and indicates that the modulation of uromodulin is a promising approach for diuresis and hypertension treatment.

Five-Aminolevulinic Acid (5-ALA) Induces Heme Oxygenase-1 and Ameliorates Palmitic Acid-Induced Endoplasmic Reticulum Stress in Renal Tubules

“…Gene expression was analyzed by real-time RT-PCR as previously described [ 44 ]. Total RNA was extracted after a brief wash in phosphate-buffered saline from cells using a miRNeasy Mini Kit (QIAGEN, Tokyo, Japan) according to the manufacturer’s protocol.…”

“…Thirty micrograms of protein were loaded for SDP-PAGE gel and transferred to nitrocellulose membranes. Western blotting was performed using established protocols [ 44 ]. Densitometry analysis was performed using ImageJ software 1.52a (National Institute of Health, Bethesda, MD, USA).…”

The Versatile Role of Uromodulin in Renal Homeostasis and Its Relevance in Chronic Kidney Disease

“…Because vasopressin is a hormone secreted during dehydration or volume depletion, upregulated uromodulin secretion by vasopressin is considered a reasonable physiological response. Furthermore, urinary uromodulin secretion increases under dehydration condition and, conversely, activates AQP2 in collecting duct cells ( 43 ). These findings suggest that the TAL and collecting duct work cooperatively to retain sodium and water through cross-talk with uromodulin ( Fig.…”

“…Uromodulin stimulates the expression of apical TRPV5 by inhibiting endocytosis ( 52 ). Uromodulin upregulates membrane proteins, such as TRPV5 and AQP2, by inhibiting endocytosis ( 43 , 52 ). Interestingly, the regulatory effect of uromodulin on apical membrane proteins is executed in a segment distant from its production, suggesting an autocrine-like function of uromodulin.…”

The role of uromodulin in cardiovascular disease: a review

“…In addition, it has been shown that UMOD enhances AQP2 phosphorylation and apical transport in mouse collecting duct cells treated with vasopressin analog dDAVP. The uromodulin-induced apicaltrafficking of AQP2 was attenuated via endocytosis inhibitor treatment, suggesting that uromodulin activates AQP2 through the suppression of endocytosis ( 87 ). Moreover, NKCC2 phosphorylation and activity are also regulated by the dDAVP-V2R-cAMP-PKA pathway, in which dDAVP promotes salt reabsorption by upregulating NKCC2 ( 88 ).…”