Nephrogenic diabetes insipidus in mice lacking aquaporin-3 water channels

Abstract

Aquaporin-3 (AQP3) is a water channel expressed at the basolateral plasma membrane of kidney collecting-duct epithelial cells. The mouse AQP3 cDNA was isolated and encodes a 292-amino acid water͞glycerol-transporting glycoprotein expressed in kidney, large airways, eye, urinary bladder, skin, and gastrointestinal tract. The mouse AQP3 gene was analyzed, and AQP3 null mice were generated by targeted gene disruption. The growth and phenotype of AQP3 null mice were grossly normal except for polyuria. AQP3 deletion had little effect on AQP1 or AQP4 protein expression but decreased AQP2 protein expression particularly in renal cortex. Fluid consumption in AQP3 null mice was more than 10-fold greater than that in wild-type litter mates, and urine osmolality (<275 milliosmol) was much lower than in wild-type mice (>1,200 milliosmol). After 1-desamino-8-D-arginine-vasopressin administration or water deprivation, the AQP3 null mice were able to concentrate their urine partially to Ϸ30% of that in wild-type mice. Osmotic water permeability of cortical collecting-duct basolateral membrane, measured by a spatial filtering optics method, was >3-fold reduced by AQP3 deletion. To test the hypothesis that the residual concentrating ability of AQP3 null mice was due to the inner medullary collecting-duct water channel AQP4, AQP3͞AQP4 double-knockout mice were generated. The double-knockout mice had greater impairment of urinary-concentrating ability than did the AQP3 single-knockout mice. Our findings establish a form of nephrogenic diabetes insipidus produced by impaired water permeability in collecting-duct basolateral membrane. Basolateral membrane aquaporins may thus provide blood-accessible targets for drug discovery of aquaretic inhibitors.water transport ͉ AQP3 ͉ kidney ͉ urinary-concentrating mechanism ͉ polyuria A quaporin-3 (AQP3, originally called glycerol intrinsic protein, GLIP, based on its glycerol-transport function) was cloned from rat kidney by our laboratory (1) as well as by Ishibashi et al. (2) and Echevarria et al. (3). AQP3 is a relatively weak transporter of water but functions as an efficient glycerol transporter (4). Reflection coefficient measurements (5) and mutagenesis studies (6) suggested that water and glycerol share a common pathway through the AQP3 protein, although inhibition experiments were interpreted as suggesting different pathways (7). Immunocytochemistry in rat showed AQP3 protein expression in basolateral membrane of kidney collecting duct and large airways, as well as in several tissues that are thought not to have an important water-transporting role including urinary bladder, conjunctiva, and epidermis (8-11). Recent studies report strong AQP3 expression in various regions of the gastrointestinal tract including small intestine (12). Another unique feature of AQP3 is its gene structure, which is different from the water-selective mammalian aquaporins (13). AQP3, AQP7, and AQP9 have been called ''aquaglyceroporins'' because of their relatively broad solute specificity and sequence ho...

Defective water and glycerol transport in the proximal tubules of AQP7 knockout mice

“…In fact, AQP1 knockout mice were found to develop polyuria due to both a defective water reabsorption mechanism in the proximal tubules and a dysfunctional countercurrent mechanism in the inner medulla (26). Other renal AQPs, such as AQP2, AQP3, and AQP4, are all present in the collecting ducts and are directly involved in water reabsorption to produce the final concentrated urine (2,13,14). Very recently, Maeda et al (16) generated AQP7 knockout mice and reported on the phenotype characteristics only in the adipocytes, where AQP7 constitutes a glycerol-releasing pathway without which hypoglycemia occurs after starvation.…”

Aquaporins in sperm osmoadaptation: an emerging role for volume regulation

“…Alternatively, we hypothesize that AQP3 may function as a part of the membrane osmosensing/mechanosensing system for the initial sensing of cell swelling and therefore, may "trigger" subsequent RVD events such as solute transport and cytoskeleton reconstruction. This hypothesis is supported by the fact that AQP3 is strongly expressed in many organs, such as the bladder, trachea and esophagus, and in olfactory cells [18,28,29] , where they seem to have no obvious requirements for rapid water movement but need sensitive perception of tension, shear stress and so on. Moreover, this hypothesis is supported by the recent discovery that AQP5 is actively involved in salivary gland cell RVD by coordinating with TRPV4, a volume sensitive calcium channel, to concertedly regulate cell volume under hypotonic stimulation [23] .…”

“…However, genetic deletion of AQP7 and 8 in mice did not result in obvious abnormalities in sperm morphology and function [11,16,17] , Review www.nature.com/aps Chen Q et al Acta Pharmacologica Sinica npg suggesting that these AQPs are not essential for mouse sperm function or that they can be functionally substituted by other aquaporin members. After a previous study identified Aquaporin-3 (AQP3) expression in mouse testes [18] , we demonstrated that AQP3 was present in both mouse and human sperm and was located in the plasma membrane of the principle piece of fl agellum [3] ( Figure 1A). Further functional studies using AQP3 knockout mice have shown that upon exposure to physiological hypotonic stress, AQP3 mutant sperm show normal initial motility but display increased vulnerability to hypotonic cell swelling characterized by increased tail bending after entering the uterus [3] .…”

Dissecting the Roles of Aquaporins in Renal Pathophysiology Using Transgenic Mice

“…In contrast to AQP1 null mice, countercurrent multiplication and exchange mechanisms in AQP3/AQP4 null mice are basically intact. The polyuria in AQP3 null mice results in large part from the more than three-fold reduction in P f of cortical collecting duct basolateral membrane (16). In addition, AQP2 expression is reduced in AQP3 null mice, which appears to be a maladaptive renal response seen in various forms of acquired polyuria.…”

“…Deletion of AQP1 and/or AQP3 in mice results in marked polyuria, as seen in 24 hour urine collections (Fig. 1B) (15,16). Fig.…”