Structure and characterization of the mouse UT-A gene (<i>Slc14a2</i>)

Fenton, Robert A.; Cottingham, C.A.; Stewart, Gavin; Howorth, A.; Hewitt, Jeff; Smith, Craig P.

doi:10.1152/ajprenal.00264.2001

Cited by 77 publications

(72 citation statements)

References 31 publications

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“…Deletion of this segment selectively disrupted a region encoding segments of two IMCD isoforms of UT-A, namely UT-A1 and UT-A3 (17). Successful deletion of these transporters was confirmed by immunoblotting and immunocytochemistry, demonstrating that UT-A1 and UT-A3 proteins were absent from the IM of UT-A1͞3 Ϫ/Ϫ mice, and by isolated perfused tubule studies showing an absence of phloretin-sensitive and vasopressinregulated urea transport in IMCD segments.…”

Section: Discussionmentioning

confidence: 91%

Urinary concentrating defect in mice with selective deletion of phloretin-sensitive urea transporters in the renal collecting duct

Fenton

Chou

Stewart

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

225

230

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To investigate the role of inner medullary collecting duct (IMCD) urea transporters in the renal concentrating mechanism, we deleted 3 kb of the UT-A urea transporter gene containing a single 140-bp exon (exon 10). Deletion of this segment selectively disrupted expression of the two known IMCD isoforms of UT-A, namely UT-A1 and UT-A3, producing UT-A1͞3 ؊/؊ mice. In isolated perfused IMCDs from UT-A1͞3 ؊/؊ mice, there was a complete absence of phloretin-sensitive or vasopressin-stimulated urea transport. On a normal protein intake (20% protein diet), UT-A1͞ 3 ؊/؊ mice had significantly greater fluid consumption and urine flow and a reduced maximal urinary osmolality relative to wildtype controls. These differences in urinary concentrating capacity were nearly eliminated when urea excretion was decreased by dietary protein restriction (4% by weight), consistent with the 1958 Berliner hypothesis stating that the chief role of IMCD urea transport in the concentrating mechanism is the prevention of ureainduced osmotic diuresis. Analysis of inner medullary tissue after water restriction revealed marked depletion of urea in UT-A1͞3 ؊/؊ mice, confirming the concept that phloretin-sensitive IMCD urea transporters play a central role in medullary urea accumulation. However, there were no significant differences in mean inner medullary Na ؉ or Cl ؊ concentrations between UT-A1͞3 ؊/؊ mice and wild-type controls, indicating that the processes that concentrate NaCl were intact. Thus, these results do not corroborate the predictions of passive medullary concentrating models stating that NaCl accumulation in the inner medulla depends on rapid vasopressin-regulated urea transport across the IMCD epithelium.UT-A ͉ isolated perfused tubule ͉ vasopressin ͉ concentrating mechanism F or survival remote from water sources, terrestrial animals require effective water-conservation mechanisms. In birds and mammals, water conservation depends on specialized urinary concentrating mechanisms that reduce water excretion while maintaining solute excretion. This concentrating function is carried out in the renal medulla. In mammals, the medulla is divided into two regions, the outer medulla and the inner medulla (IM), both of which manifest increased tissue osmolality relative to the blood plasma (1). In these regions, high interstitial osmolality draws water from the renal collecting duct via aquaporin water channels, resulting in a concentrated final urine. In the outer medulla, the interstitial space is concentrated through the classic countercurrent multiplication mechanism (2) in which water and solute are separated by active NaCl transport from the water-impermeable thick ascending limb of Henle (3, 4). However, in the IM the ascending portion of Henle's loop is incapable of high rates of active transport (5, 6), implying that solute concentration in the IM occurs by a different, yet unknown mechanism.One important feature of the IM that distinguishes it from the outer medulla is its ability to accumulate large amounts of urea. Berliner ...

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Section: Discussionmentioning

confidence: 91%

Urinary concentrating defect in mice with selective deletion of phloretin-sensitive urea transporters in the renal collecting duct

Fenton

Chou

Stewart

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

225

230

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“…There are two distinct but closely related urea transporter genes: UT-A (Slc14a2) and UT-B (Slc14a1) (15)(16)(17). Several urea transporter isoforms are derived from the UT-A gene via alternative splicing and alternative promotors ( Figure 2) (15).…”

Section: Urea Transportersmentioning

confidence: 99%

“…Use of an alternative exon inserts a stop codon that terminates UT-A3 after amino acid 460 (an aspartic acid). UT-A2 is identical to the terminal 397 amino acids of UT-A1 and is driven by an alternative promoter in intron 13 of the mouse gene (15). Illustration by Josh basolateral membrane domains (32).…”

Section: Urea Transportersmentioning

confidence: 99%

“…Illustration by Josh basolateral membrane domains (32). UT-A3 mRNA abundance can be upregulated by the prolonged action of AVP (15). In contrast to the multiple UT-A isoforms, the mouse UT-B gene encodes only a single protein that is expressed throughout the kidney medulla in the basolateral and apical regions of the descending vasa recta (DVR) endothelial cells (Figures 1 and 3) (33)(34)(35).…”

Section: Urea Transportersmentioning

confidence: 99%

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Urea and Renal Function in the 21st Century

Fenton¹,

Knepper²

2007

Journal of the American Society of Nephrology

115

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Since the turn of the 21st century, gene knockout mice have been created for all major urea transporters that are expressed in the kidney: the collecting duct urea transporters UT-A1 and UT-A3, the descending thin limb isoform UT-A2, and the descending vasa recta isoform UT-B. This article discusses the new insights that the results from studies in these mice have produced in the understanding of the role of urea in the urinary concentrating mechanism and kidney function. Following is a summary of the major findings: (1) Urea accumulation in the inner medullary interstitium depends on rapid transport of urea from the inner medullary collecting duct (IMCD) lumen via UT-A1 and/or UT-A3; (2) as proposed by Robert Berliner and colleagues in the 1950s, the role of IMCD urea transporters in water conservation is to prevent a urea-induced osmotic diuresis; (3) the absence of IMCD urea transport does not prevent the concentration of NaCl in the inner medulla, contrary to what would be predicted from the passive countercurrent multiplier mechanism in the form proposed by Kokko and Rector and Stephenson; (4) deletion of UT-B (vasa recta isoform) has a much greater effect on urinary concentration than deletion of UT-A2 (descending limb isoform), suggesting that the recycling of urea between the vasa recta and the renal tubules quantitatively is less important than classic countercurrent exchange; and (5) urea reabsorption from the IMCD and the process of urea recycling are not important elements of the mechanism of protein-induced increases in GFR. In addition, the clinical relevance of these studies is discussed, and it is suggested that inhibitors that specifically target collecting duct urea transporters have the potential for clinical use as potassium-sparing diuretics that function by creation of urea-dependent osmotic diuresis.

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“…When both UT-A1 and UT-A3 were genetically deleted from the IMCD UT-A1/3 Ϫ/Ϫ , the mice showed the urine-concentrating defect that is caused by a failure of urea transport from the IMCD lumen to the inner medullary interstitium, resulting in osmotic diuresis. Mouse UT-A1 expression is controlled under UT-A␣ promoter, which contains tonicity-responsive enhancer (TonE) (22). A putative TonEBP consensus sequence is also present in the promoter region of aqp2 gene (23).…”

Section: Discussionmentioning

confidence: 99%

Pax Transactivation-Domain Interacting Protein Is Required for Urine Concentration and Osmotolerance in Collecting Duct Epithelia

Kim¹,

Wang²,

Cai³

et al. 2007

Journal of the American Society of Nephrology

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Pax transactivation-domain interacting protein (PTIP) is a widely expressed nuclear protein that is essential for early embryonic development. PTIP was first identified on the basis of its interactions with the developmental regulator Pax2 but can also bind to other nuclear transcription factors. The Pax2 protein is essential for development of the renal epithelia and for regulating the response of mature collecting ducts to hyperosmotic stress. For determination of whether PTIP also functions in more differentiated cell types, the Cre-LoxP system was used to delete the ptip gene in the renal collecting ducts using Ksp-Cre driver mice. Collecting duct-specific ptip knockout mice were viable with little discernible phenotype under normal physiologic conditions. However, collecting duct-specific ptip mutants were unable to concentrate urine after the treatment of desamino-cis, D-arginine vasopressin, an antidiuretic hormone. Furthermore, aquaporin-2 (AQP2) expression in the inner medulla of the ptip knockout mice was decreased approximately 10-fold compared with that of wild-type littermates. Expression level of tonicity responsive enhancer binding protein, a transcription factor of AQP2, is not altered in the mutant mice, but its nuclear localization in the inner medulla is unresponsive after treatment with vasopressin agonists. This was due, at least in part, to decreased expression of the arginine vasopressin receptor 2 in ptip mutants. Furthermore, ptip null inner medullary collecting duct cells were sensitive to hyperosmolality in vitro. Thus, ptip is required for the urine concentration mechanism by modulating arginine vasopressin receptor 2 and AQP2 expression in the inner medulla. The data suggest an essential role for ptip in regulating urine concentration and in controlling survival of collecting duct epithelial cells in high osmolality.

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Structure and characterization of the mouse UT-A gene (Slc14a2)

Cited by 77 publications

References 31 publications

Urinary concentrating defect in mice with selective deletion of phloretin-sensitive urea transporters in the renal collecting duct

Urinary concentrating defect in mice with selective deletion of phloretin-sensitive urea transporters in the renal collecting duct

Urea and Renal Function in the 21st Century

Pax Transactivation-Domain Interacting Protein Is Required for Urine Concentration and Osmotolerance in Collecting Duct Epithelia

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