Impaired expression of an organic cation transporter, IMPT1 , in a knockout mouse model for kidney stone disease (original) (raw)
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The molecular basis of renal tubular transport disorders
Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2000
Sodium and water homeostasis are key to the survival of organisms. Reabsorption of sodium and water occurs throughout the tubule structure of the nephron, the basic functional unit of the kidney, by various transport mechanisms. Altered transport protein function can lead to renal tubular disorders resulting in metabolic alkalosis, hypokalemia, hypertension, and decreased capacity to concentrate urine, for instance. However, recent advances in molecular physiology, molecular genetics and expression cloning systems have aided in unraveling the molecular basis of some renal tubular disorders. This review will examine the molecular basis of Bartter's syndrome, Gitelman's syndrome, Liddle's syndrome, and autosomal nephrogenic diabetes insipidus. An understanding of the molecular basis of these disorders of the human kidney can give us a better understanding of basic renal function of lower mammals and other vertebrates.
Kidney-specific expression of a novel mouse organic cation transporter-like protein
FEBS Letters, 1997
Using the signal sequence trap method, we have cloned a novel 12-membrane-spanning transporter-like protein, termed renal-specific transporter (RST), from the mouse kidney. RST is a 553-amino-acid protein highly homologous to recently cloned organic cation transporters, e.g. it is 30% identical to rat organic cation transporter 1 at the amino acid level. Northern blot analysis has revealed that the RST gene is expressed abundantly and specifically in the kidney. In situ hybridization analysis has shown that RST gene expression is restricted to the renal proximal tubule, where various organic cations such as endogenous catecholamines and choline or clinically used cationic drugs are known to be actively excreted.
Chronic renal failure in a mouse model of human adenine phosphoribosyltransferase deficiency
American Journal of Physiology-Renal Physiology, 1998
In humans, adenine phosphoribosyltransferase (APRT, EC 2.4.2.7 ) deficiency can manifest as nephrolithiasis, interstitial nephritis, and chronic renal failure. APRT catalyzes synthesis of AMP from adenine and 5-phosphoribosyl-1-pyrophosphate. In the absence of APRT, 2,8-dihydroxyadenine (DHA) is produced from adenine by xanthine dehydrogenase (XDH) and can precipitate in the renal interstitium, resulting in kidney disease. Treatment with allopurinol controls formation of DHA stones by inhibiting XDH activity. Kidney disease in APRT-deficient mice resembles that seen in humans. By age 12 wk, APRT-deficient male mice are, on average, mildly anemic and smaller than normal males. They have extensive renal interstitial damage (assessed by image analysis) and elevated blood urea nitrogen (BUN), and their creatinine clearance rates, which measure excretion of infused creatinine as an estimate of glomerular filtration rate (GFR), are about half that of wild-type males. APRT-deficient males ...
NDT Plus, 2010
Adenine phosphoribosyltransferase (APRT) deficiency, a rare inborn error inherited as an autosomic recessive trait, presents with 2,8-dihydroxyadenine (2,8-DHA) crystal nephropathy. We describe clinical, biochemical and molecular findings in a renal transplant recipient with renal failure, 2,8-DHA stones and no measurable erythrocyte APRT activity. Homozygous C>G substitution at −3 in the splicing site of exon 2 (IVS2 −3 c>g) was found in the APRT gene. The patient's asymptomatic brother was heterozygous for such mutation, and his APRT activity was 23% of controls. A splicing alteration leading to incorrect gene transcription and virtually absent APRT activity is seemingly associated with the newly identified mutation.
Orphan Transporter SLC6A18 Is Renal Neutral Amino Acid Transporter B0AT3
Journal of Biological Chemistry, 2009
The orphan transporter Slc6a18 (XT2) is highly expressed at the luminal membrane of kidney proximal tubules and displays ϳ50% identity with Slc6a19 (B 0 AT1), which is the main neutral amino acid transporter in both kidney and small intestine. As yet, the amino acid transport function of XT2 has only been experimentally supported by the urinary glycine loss observed in xt2 null mice. We report here that in Xenopus laevis oocytes, co-expressed ACE2 (angiotensin-converting enzyme 2) associates with XT2 and reveals its function as a Na ؉-and Cl ؊-dependent neutral amino acid transporter. In contrast to its association with ACE2 observed in Xenopus laevis oocytes, our experiments with ace2 and collectrin null mice demonstrate that in vivo it is Collectrin, a smaller homologue of ACE2, that is required for functional expression of XT2 in kidney. To assess the function of XT2 in vivo, we reanalyzed its knockout mouse model after more than 10 generations of backcrossing into C57BL/6 background. In addition to the previously published glycinuria, we observed a urinary loss of several other amino acids, in particular -branched and small neutral ones. Using telemetry, we confirmed the previously described link of XT2 absence with hypertension but only in physically restrained animals. Taken together, our data indicate that the formerly orphan transporter XT2 functions as a sodium and chloride-dependent neutral amino acid transporter that we propose to rename B 0 AT3.
Proceedings of The National Academy of Sciences, 2006
Mutations in the alanine-glyoxylate amino transferase gene (AGXT) are responsible for primary hyperoxaluria type I, a rare disease characterized by excessive hepatic oxalate production that leads to renal failure. We generated a null mutant mouse by targeted mutagenesis of the homologous gene, Agxt, in embryonic stem cells. Mutant mice developed normally, and they exhibited hyperoxaluria and crystalluria. Approximately half of the male mice in mixed genetic background developed calcium oxalate urinary stones. Severe nephrocalcinosis and renal failure developed after enhancement of oxalate production by ethylene glycol administration. Hepatic expression of human AGT1, the protein encoded by AGXT, by adenoviral vector-mediated gene transfer in Agxt ؊/؊ mice normalized urinary oxalate excretion and prevented oxalate crystalluria. Subcellular fractionation and immunofluorescence studies revealed that, as in the human liver, the expressed wild-type human AGT1 was predominantly localized in mouse hepatocellular peroxisomes, whereas the most common mutant form of AGT1 (G170R) was localized predominantly in the mitochondria.
Developmental changes in multispecific organic anion transporter 1 expression in the rat kidney1
Kidney International, 2000
Developmental changes in multispecific organic anion transsuch as the urine concentrating capacity, acidification abilporter 1 expression in the rat kidney. ity, and glucose transport activity, are also poorly devel-Background. The cDNA of the multispecific organic anion oped at birth [2]. Physiological studies have demonstrated transporter 1 (OAT1) responsible for the tubular secretion of that some of these renal functions mature rapidly during organic anions was recently isolated. In the current study, we investigated the developmental changes in OAT1 expression the perinatal period. For example, the GFR increases in the rat kidney. by twofold during the first two weeks of life [3]. Because Methods. Ontogenic expression of rat OAT1 was investithe kidney is the organ central to the maintenance of gated by Northern blot, in situ hybridization, Western blot, homeostasis, the perinatal maturation of renal functions and immunohistochemical analysis. In addition, para-aminohippurate (PAH) accumulation was measured using fetal, neo-is rational for the body to adapt to extrauterine life. natal, and adult rat kidney slices. Using the molecular cloning technique, a variety of Results. In Northern blot analysis, OAT1 was detected as cDNA encoding transporters and channels existing in early as on embryonic day 18 in the fetal kidney. The expression the renal tubules have been identified, and the ontogenic level of OAT1 mRNA increased remarkably just after birth (postnatal day 0). In situ hybridization revealed OAT1 expres-expression of several of these, such as the facilitated sion on embryonic day 19. In both the fetal and neonatal kidglucose transporters (GLUTs) [4, 5], sodium-dependent neys, OAT1 mRNA was localized in a relatively deep region glucose transporters (SGLTs) [6], sodium/phosphate in the cortex. Western blot analysis detected OAT1 protein transporters (Na/Pi transporters) [7], and water channels on embryonic day 20, and the expression level increased after birth. Immunohistochemical analysis did not reveal OAT1 1 See Editorial by Sasaki, p. 1772. therefore, the renal organic anion transport pathway plays a key role in the pharmacokinetics of these drugs
Analysis of regulatory polymorphisms in organic ion transporter genes (SLC22A) in the kidney
Journal of Human Genetics, 2008
Organic cation transporters (OCTs) and organic anion transporters (OATs) (SLC22A family) play crucial roles in the renal secretion of various drugs. Messengar ribonucleic acid (mRNA) expression of transporters can be a key factor regulating interindividual differences in drug pharmacokinetics. However, the source of variations in mRNA levels of transporters is unclear. In this study, we focused on single nucleotide polymorphisms (SNP) in the promoter region [regulatory SNPs (rSNPs)] as candidates for the factor regulating mRNA levels of SLC22A. We sequenced the promoter regions of OCT2 and OAT1-4 in 63 patients and investigated the effects of the identified rSNPs on transcriptional activities and mRNA expression. In the OCT2 promoter region, one deletion polymorphism (-578_-576delAAG) was identified; -578_-576delA-AG significantly reduced OCT2 promoter activity (p \ 0.05), and carriers of -578_-576delAAG tend to have lower OCT2 mRNA levels, but the difference is not significant. There was no rSNP in the OAT1 and OAT2 genes. The five rSNPs of OAT3 and one rSNP of OAT4 were unlikely to influence mRNA expression and promoter activity. This is the first study to investigate the influences of rSNPs on mRNA expression of SLC22A in the kidney and to identify a regulatory polymorphism affecting OCT2 promoter activity.
Molecular characterization of a new urea transporter in the human kidney
FEBS Letters, 1996
A eDNA clone (HUT2) sharing 61.1% and 89.9% sequence identity with the human erythroid (HUTll) and the rabbit (UT2) urea transporters, respectively, was isolated by homology cloning from a human kidney library. HUT2 transcripts were restricted to the kidney and the HUT2 polypeptide was not immunoprecipitated with blood group Kidd-related antibodies (anti-Jk3) in coupled transcriptiontranslation assays. Functional expression studies in Xenopus oocytes demonstrated that HUT2-mediated urea transport was not inhibited by p-chloromercuribenzene sulfonate (pCMBS) which, however, inhibited the urea flux mediated by HUTll. These findings demonstrate that at least two distinct urea transporters are present in human tissues. By in situ hybridization, the gene encoding HUT2 has been assigned to chromosome 18q12.l-q21-1, as found previously for the Kidd/urea transporter HUT11, suggesting that both genes evolved from duplication of a common ancestor.
Update on the genetics of nephrolithiasis
Clinical cases in mineral and bone metabolism : the official journal of the Italian Society of Osteoporosis, Mineral Metabolism, and Skeletal Diseases, 2008
Genetic studies of calcium kidney stones evidenced the possible involvement of calcium-sensing receptor gene, vitamin D receptor gene and bicarbonate-sensitive adenylate cyclase gene, but it is uncertain which specific polymorphisms could be responsible. Thus, further studies are required to better assess the involvement of these or other genes and the interactions between different genes and between genes and environment. In addition to research in humans, the study of different strains of knock-out mice let us include the gene of phosphate reabsorption carrier NPT2, caveolin-1, protein NHERF-1, osteopontin and Tamm-Horsfall protein among the possible determinants. Further steps in the knowledge of calcium stone causes may be done using the instruments that the modern biotechnology and bioinformatics have made available to the researchers.