Vasopressin-Independent Regulation of Aquaporin-2 by Tamoxifen in Kidney Collecting Ducts.

Lene N Nejsum,Stine Julie Tingskov,Hyo-Jung Choi,Weidong Wang,Shan Hu,Chunling Li,Rikke Nørregaard,Mikkel R Holst,Tae-Hwan Kwon,Jørgen Frøkiær

doi:10.3389/fphys.2019.00948

Lene N Nejsum, Stine Julie Tingskov + Show 8 more

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https://doi.org/10.3389/fphys.2019.00948

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Abstract

Arginine vasopressin (AVP) mediates water reabsorption in the kidney collecting ducts through regulation of aquaporin-2 (AQP2). Also, estrogen has been known to regulate AQP2. Consistently, we previously demonstrated that tamoxifen (TAM), a selective estrogen receptor modulator, attenuates the downregulation of AQP2 in lithium-induced nephrogenic diabetes insipidus (NDI). In this study, we investigated the AVP-independent regulation of AQP2 by TAM and the therapeutic effect of TAM on the dysregulation of AQP2 and impaired urinary concentration in a unilateral ureteral obstruction (UUO) model. Primary cultured inner medullary collecting duct (IMCD) cells from kidneys of male Sprague-Dawley rats were treated with TAM. Rats subjected to 7 days of UUO were treated with TAM by oral gavage. Changes of intracellular trafficking and expression of AQP2 were evaluated by quantitative PCR, Western blotting, and immunohistochemistry. TAM induced AQP2 protein expression and intracellular trafficking in primary cultured IMCD cells, which were independent of the vasopressin V2 receptor (V2R) and cAMP activation, the critical pathways involved in AVP-stimulated regulation of AQP2. TAM attenuated the downregulation of AQP2 in TGF-β treated IMCD cells and IMCD suspensions prepared from UUO rats. TAM administration in vivo attenuated the downregulation of AQP2, associated with an improvement of urinary concentration in UUO rats. In addition, TAM increased CaMKII expression, suggesting that calmodulin signaling pathway is likely to be involved in the TAM-mediated AQP2 regulation. In conclusion, TAM is involved in AQP2 regulation in a vasopressin-independent manner and improves urinary concentration by attenuating the downregulation of AQP2 and maintaining intracellular trafficking in UUO.

Highlights

The kidney collecting duct is a critical tubular segment for the arginine vasopressin (AVP)mediated water reabsorption and regulation of body water homeostasis
We determined the effect of dDAVP and TAM treatment on expression of total AQP2 and AQP2 phosphorylated at serine 256 in the primary inner medullary collecting duct (IMCD) cells using semiquantitative immunoblotting (Figure 1)
In order to investigate a possible pathway for the regulation of AQP2 after TAM treatment, we measured the expression of calmodulin-dependent protein kinase II (CaMKII) in the inner medulla of the kidneys from rats subjected to sham or ureteral obstruction (UUO)

Summary

Introduction

The kidney collecting duct is a critical tubular segment for the arginine vasopressin (AVP)mediated water reabsorption and regulation of body water homeostasis. AVP binds to its receptor, vasopressin type-2 receptor (V2R), localized in the basolateral plasma membrane of collecting duct principal cells This initiates a cascade leading to an increase in cAMP levels and activation of protein kinase A (PKA)-dependent phosphorylation of AQP2 at the serine 256 residue (pS256-AQP2). This is the main pathway of AQP2 trafficking to the apical plasma membrane of the collecting duct principal cells, which increases the osmotic water permeability (Katsura et al, 1997; Kortenoeven and Fenton, 2014; Jung and Kwon, 2016, 2019). CAMP/ PKA signaling is a critical regulatory pathway in the AVP-mediated AQP2 expression and trafficking, it has been discovered that modulation of calmodulin, Wnt, prostaglandin E2, and cGMP pathways influences AQP2 regulation and trafficking (Bouley et al, 2005; Hoffert et al, 2005; Olesen et al, 2011; Jung and Kwon, 2016, 2019)

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