scholarly journals Molecular mechanisms regulating aquaporin-2 in kidney collecting duct

2016 ◽  
Vol 311 (6) ◽  
pp. F1318-F1328 ◽  
Author(s):  
Hyun Jun Jung ◽  
Tae-Hwan Kwon

The kidney collecting duct is an important renal tubular segment for regulation of body water homeostasis and urine concentration. Water reabsorption in the collecting duct principal cells is controlled by vasopressin, a peptide hormone that induces the osmotic water transport across the collecting duct epithelia through regulation of water channel proteins aquaporin-2 (AQP2) and aquaporin-3 (AQP3). In particular, vasopressin induces both intracellular translocation of AQP2-bearing vesicles to the apical plasma membrane and transcription of the Aqp2 gene to increase AQP2 protein abundance. The signaling pathways, including AQP2 phosphorylation, RhoA phosphorylation, intracellular calcium mobilization, and actin depolymerization, play a key role in the translocation of AQP2. This review summarizes recent data demonstrating the regulation of AQP2 as the underlying molecular mechanism for the homeostasis of water balance in the body.

Author(s):  
Mikkel R. Holst ◽  
Louis Gammelgaard ◽  
Jesse Aaron ◽  
Frédéric H. Login ◽  
Sampavi Rajkumar ◽  
...  

Regulated vesicle exocytosis is a key response to extracellular stimuli in diverse physiological processes; including hormone regulated short-term urine concentration. In the renal collecting duct, the water channel aquaporin-2 localizes to the apical plasma membrane as well as small, sub-apical vesicles. In response to stimulation with the antidiuretic hormone, arginine vasopressin, aquaporin-2 containing vesicles fuse with the plasma membrane, which increases collecting duct water reabsorption and thus, urine concentration. The nano-scale size of these vesicles has limited analysis of their 3D organization. Using a cell system combined with 3D super resolution microscopy, we provide the first direct analysis of the 3D network of aquaporin-2 containing exocytic vesicles in a cell culture system. We show that aquaporin-2 vesicles are 43 ± 3nm in diameter, a size similar to synaptic vesicles, and that one fraction of AQP2 vesicles localized with the sub-cortical F-actin layer and the other localized in between the F-actin layer and the plasma membrane. Aquaporin-2 vesicles associated with F-actin and this association was enhanced in a serine 256 phospho-mimic of aquaporin-2, whose phosphorylation is a key event in antidiuretic hormone-mediated aquaporin-2 vesicle exocytosis.


2017 ◽  
Vol 312 (4) ◽  
pp. F744-F747 ◽  
Author(s):  
Emma T. B. Olesen ◽  
Robert A. Fenton

The targeting of the water channel aquaporin-2 (AQP2) to the apical plasma membrane of kidney collecting duct principal cells is regulated mainly by the antidiuretic peptide hormone arginine vasopressin (AVP). This process is of crucial importance for the maintenance of body water homeostasis. In this brief review we assess the role of cyclic adenosine monophosphate (cAMP) and discuss the emerging concept that type 2 AVP receptor (V2R)-mediated AQP2 trafficking is cAMP-independent.


2010 ◽  
Vol 298 (2) ◽  
pp. F266-F278 ◽  
Author(s):  
G. Procino ◽  
C. Barbieri ◽  
M. Carmosino ◽  
F. Rizzo ◽  
G. Valenti ◽  
...  

Vasopressin causes the redistribution of the water channel aquaporin-2 (AQP2) from cytoplasmic storage vesicles to the apical plasma membrane of collecting duct principal cells, leading to urine concentration. The molecular mechanisms regulating the selective apical sorting of AQP2 are only partially uncovered. In this work, we investigate whether AQP2 sorting/trafficking is regulated by its association with membrane rafts. In both MCD4 cells and rat kidney, AQP2 preferentially associated with Lubrol WX-insoluble membranes regardless of its presence in the storage compartment or at the apical membrane. Block-and-release experiments indicate that 1) AQP2 associates with detergent-resistant membranes early in the biosynthetic pathway; 2) strong cholesterol depletion delays the exit of AQP2 from the trans-Golgi network. Interestingly, mild cholesterol depletion promoted a dramatic accumulation of AQP2 at the apical plasma membrane in MCD4 cells in the absence of forskolin stimulation. An internalization assay showed that AQP2 endocytosis was clearly reduced under this experimental condition. Taken together, these data suggest that association with membrane rafts may regulate both AQP2 apical sorting and endocytosis.


1998 ◽  
Vol 9 (12) ◽  
pp. 2181-2193 ◽  
Author(s):  
J H Earm ◽  
B M Christensen ◽  
J Frøkiaer ◽  
D Marples ◽  
J S Han ◽  
...  

Hypercalcemia is frequently associated with a urinary concentrating defect and overt polyuria. The molecular mechanisms underlying this defect are poorly understood. Dysregulation of aquaporin-2 (AQP2), the predominant vasopressin-regulated water channel, is known to be associated with a range of congenital and acquired water balance disorders including nephrogenic diabetes insipidus and states of water retention. This study examines the effect of hypercalcemia on the expression of AQP2 in rat kidney. Rats were treated orally for 7 d with dihydrotachysterol, which produced significant hypercalcemia with a 15 +/- 2% increase in plasma calcium concentration. Immunoblotting and densitometry of membrane fractions revealed a significant decrease in AQP2 expression in kidney inner medulla of hypercalcemic rats to 45.7 +/- 6.8% (n = 11) of control levels (100 +/- 12%, n = 9). A similar reduction in AQP2 expression was seen in cortex (36.9 +/- 4.2% of control levels, n = 6). Urine production increased in parallel, from 11.3 +/- 1.4 to a maximum of 25.3 +/- 1.9 ml/d (P < 0.01), whereas urine osmolality decreased from 2007 +/- 186 mosmol/kg x H2O to 925 +/- 103 mosmol/kg x H2O (P < 0.01). Immunocytochemistry confirmed a decrease in total AQP2 labeling of collecting duct principal cells from kidneys of hypercalcemic rats, and reduced apical labeling. Immunoelectron microscopy demonstrated a significant reduction in AQP2 labeling of the apical plasma membrane, consistent with the development of polyuria. In summary, the results strongly suggest that AQP2 downregulation and reduced apical plasma membrane delivery of AQP2 play important roles in the development of polyuria in association with hypercalcemia.


2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
Yong Pyo Lee ◽  
Yun Jung Lee ◽  
So Min Lee ◽  
Jung Joo Yoon ◽  
Hye Yoom Kim ◽  
...  

Edema is a symptom that results from the abnormal accumulation of fluid in the body. The cause of edema is related to the level of aquaporin (AQP)2 protein expression, which regulates the reabsorption of water in the kidney. Edema is caused by overexpression of the AQP2 protein when the concentration of Na+in the blood increases. The rhizome ofAtractylodes macrocephalahas been used in traditional oriental medicine as a diuretic drug; however, the mechanism responsible for the diuretic effect of the aqueous extract fromA. macrocephalarhizomes (AAMs) has not yet been identified. We examined the effect of the AAM on the regulation of water channels in the mouse inner medullary collecting duct (mIMCD)-3 cells under hypertonic stress. Pretreatment of AAM attenuates a hypertonicity-induced increase in AQP2 expression as well as the trafficking of AQP2 to the apical plasma membrane. Tonicity-responsive enhancer binding protein (TonEBP) is a transcription factor known to play a central role in cellular homeostasis by regulating the expression of some proteins, including AQP2. Western immunoblot analysis demonstrated that the protein and mRNA expression levels of TonEBP also decrease after AAM treatment. These results suggest that the AAM has a diuretic effect by suppressing water reabsorption via the downregulation of the TonEBP-AQP2 signaling pathway.


2020 ◽  
Vol 319 (1) ◽  
pp. C1-C10 ◽  
Author(s):  
Robert A. Fenton ◽  
Sathish K. Murali ◽  
Hanne B. Moeller

In mammals, conservation of body water is critical for survival and is dependent on the kidneys’ ability to minimize water loss in the urine during periods of water deprivation. The collecting duct water channel aquaporin-2 (AQP2) plays an essential role in this homeostatic response by facilitating water reabsorption along osmotic gradients. The ability to increase the levels of AQP2 in the apical plasma membrane following an increase in plasma osmolality is a rate-limiting step in water reabsorption, a process that is tightly regulated by the antidiuretic hormone arginine vasopressin (AVP). In this review, the focus is on the role of the carboxyl-terminus of AQP2 as a key regulatory point for AQP2 trafficking. We provide an overview of AQP2 structure, disease-causing mutations in the AQP2 carboxyl-terminus, the role of posttranslational modifications such as phosphorylation and ubiquitylation in the tail domain, and their implications for balanced trafficking of AQP2. Finally, we discuss how various modifications of the AQP2 tail facilitate selective protein-protein interactions that modulate the AQP2 trafficking mechanism.


Endocrinology ◽  
2008 ◽  
Vol 149 (11) ◽  
pp. 5803-5810 ◽  
Author(s):  
Hidetaka Suga ◽  
Hiroshi Nagasaki ◽  
Taka-aki Kondo ◽  
Yoshiki Okajima ◽  
Chizuko Suzuki ◽  
...  

Congenital nephrogenic diabetes insipidus (NDI) is a chronic disorder involving polyuria and polydipsia that results from unresponsiveness of the renal collecting ducts to the antidiuretic hormone vasopressin. Either of the genetic defects in vasopressin V2 receptor or the water channel aquaporin 2 (AQP2) cause the disease, which interfere the water reabsorption at the epithelium of the collecting duct. An unconscious state including a perioperative situation can be life threatening because of the difficulty to regulate their water balance. The Sendai virus (SeV) vector system deleting fusion protein (F) gene (SeV/ΔF) is considered most suitable because of the short replication cycle and nontransmissible character. An animal model for NDI with reduced AQP2 by lithium chloride was used to develop the therapy. When the SeV/ΔF vector carrying a human AQP2 gene (AQP2-SeV/ΔF) was administered retrogradely via ureter to renal pelvis, AQP2 was expressed in the renal collecting duct to reduce urine output and water intake by up to 40%. In combination with the retorograde administration to pelvis, this system could be the cornerstone for the applicable therapies on not only NDI patients but also other diseases associate with the medullary collecting duct.


1996 ◽  
Vol 7 (3) ◽  
pp. 403-409 ◽  
Author(s):  
S Elliot ◽  
P Goldsmith ◽  
M Knepper ◽  
M Haughey ◽  
B Olson

The vasopressin-sensitive water channel (aquaporin 2; AQP-2) mediates water transport across the apical plasma membrane of the renal collecting ducts and is excreted in human urine. This study presents the hypothesis that measurements of the AQP-2 excretion rate might be used as a marker of collecting-duct responsiveness to vasopressin, and therefore could be useful in the clinical evaluation of various water-balance disorders. This study presents information about the development of an antibody to human AQP-2, and measures the urinary excretion of AQP-2 by quantitative Western analysis. A standard curve of band densities was generated by using known quantities of the modified immunizing peptide to derive the amount of AQP-2 contained in aliquots of urine. AQP-2 urinary excretion changed with short-term alterations in hydration status produced either by water loading (76% decrease, P < 0.01) or by 3% sodium chloride (760% increase, P < 0.01). Steady-state 24-h urinary excretion of AQP-2 was 43 +/- 10 nmol/24 h (or 28.5 +/- 6.9 pmol/mg creatinine), and 20 +/- 6 nmol/24 h (or 18.3 +/- 7.9 pmol/mg creatinine) in men and women, respectively. Therefore, urinary AQP-2 excretion can be quantified by using Western analysis, and may serve as a marker of collecting-duct responsiveness to vasopressin in different physiologic settings.


2000 ◽  
Vol 278 (4) ◽  
pp. C791-C802 ◽  
Author(s):  
Anna L. Stevens ◽  
Sylvie Breton ◽  
Corinne E. Gustafson ◽  
Richard Bouley ◽  
Raoul D. Nelson ◽  
...  

Aquaporin 2 (AQP2), the vasopressin-regulated water channel, was originally identified in renal collecting duct principal cells. However, our recent description of AQP2 in the vas deferens indicated that this water channel may have extra-renal functions, possibly related to sperm concentration in the male reproductive tract. In this study, we have examined the regulation and membrane insertion pathway of AQP2 in the vas deferens. The amino acid sequence of vas deferens AQP2 showed 100% identity to the renal protein. AQP2 was highly expressed in the distal portion (ampulla) of the vas deferens, but not in the proximal portion nearest the epididymis. It was concentrated on the apical plasma membrane of vas deferens principal cells, and very little was detected on intracellular vesicles. Protein expression levels and cellular localization patterns were similar in normal rats and vasopressin-deficient Brattleboro homozygous rats, and were not changed after 36 h of dehydration, or after 3 days of vasopressin infusion into Brattleboro rats. AQP2 was not found in apical endosomes (labeled with Texas Red-dextran) in vas deferens principal cells, indicating that it is not rapidly recycling in this tissue. Finally, vasopressin receptors were not detectable on vas deferens epithelial cell membranes using a [3H]vasopressin binding assay. These data indicate that AQP2 is a constitutive apical membrane protein in the vas deferens, and that it is not vasopressin-regulated in this tissue. Thus AQP2 contains targeting information that can be interpreted in a cell-type-specific fashion in vivo.


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