Expression Of Organic Anion Transporter Research Articles

Gender-Specific and Developmental Influences on the Expression of Rat Organic Anion Transporters

Rat organic anion transporter 1 (Oat1), Oat2, and Oat3, members of the organic anion transporter family, transport some organic anions across cellular membranes. Previously, highest Oat1 and Oat3 mRNA expression was reported in kidney and Oat2 in liver. However, gender and developmental differences in Oat expression remain unknown. This study describes gender- and age-specific patterns of rat organic anion transporter expression in various tissues. Oat mRNA expression was evaluated in adult male and female Sprague-Dawley rat tissues, and developmental expression was also determined in kidneys of Sprague-Dawley rats ranging in age from days 0 through 45. Expression was quantified using branched-DNA signal amplification. Oat1 mRNA expression was primarily observed in kidney. Surprisingly, Oat2 mRNA expression was also highest in kidney rather than in liver. Moreover, considerably higher Oat2 levels were seen in female kidney as compared with male. Finally, Oat3 mRNA expression was highest in kidney of both genders, whereas a male-predominant pattern was observed in liver. At birth, all kidney Oat mRNA levels were low. Renal Oat1 expression gradually increased throughout development, approaching adult levels at 30 days of age, where at days 40 and 45 Oat1 levels were greater in males than females. Oat2 expression in kidney was minimal through day 30 but increased dramatically at day 35 in females only. Lastly, Oat3 mRNA expression in kidney matured earliest, rapidly increasing from birth through day 10. These data indicate that Oat mRNA expression is primarily localized to the kidney, and observed expression patterns may explain some previously recognized age- and gender-dependent toxicities associated with chemical exposure.

Differential Gene Expression of Organic Anion Transporters in Male and Female Rats

Sex-related differential gene expression of organic anion transporters (rOAT1, rOAT2, and rOAT3) in rat brain, liver, and kidney was investigated. There were no sex differences in the expression of rOAT1 mRNA. rOAT2 mRNA was abundant in the liver and weakly expressed in the kidney of male rats; however, the OAT2 gene was strongly expressed in both organs of females. The abundance of rOAT2 mRNA markedly increased in castrated male rat kidney; however, treatment of castrated male rats with testosterone led to a decrease of rOAT2 mRNA. Expression of rOAT3 mRNA in intact female rats was found in the kidney and brain, whereas in males rOAT3 mRNA was also found in the liver. rOAT3 mRNA markedly decreased in the liver of castrated male rats but increased in testosterone-treated castrated male rats. Moreover, rOAT3 mRNA increased in the hypophysectomized female rat liver, indicating that rOAT3 is an inducible isoform. The present findings suggest that sex steroids play an important role in the expression and maintenance of OAT2/3 isoforms in the rat liver and kidney. Our results provide information on the differential gene expression of OAT isoforms with sex hormone dependency.

The organic anion transporter family: from physiology to ontogeny and the clinic.

The organic anion transporter (OAT) family handles a wide variety of clinically important compounds (antibiotics, nonsteriodal anti-inflammatory drugs, etc.) and toxins. However, little is known about their appearance during development despite documented differences in the handling of anionic drugs among neonates, children, and adults. A similar spatiotemporal pattern of mRNA expression of the OATs (OAT1-4) during kidney development suggests that OAT genes may be useful in understanding the mechanisms of proximal tubule maturation. Moreover, OAT expression in unexpected extrarenal sites (e.g., spinal cord, bone, skin) has also been detected during development, possibly indicating a role for these transporters in the formation or preservation of extrarenal tissues. The cloning of these transporters also paves the way for computer-based modeling of drug-transporter interactions at the molecular level, potentially aiding in the design and assessment of new drugs. Additionally, increased understanding of single nucleotide polymorphisms in OATs and other transporters may eventually allow the use of a patient's expression profile and polymorphisms to individualize drug therapy.

Effect of phenobarbital on the expression of bile salt and organic anion transporters of rat liver

Background/Aims : The hepatic clearance of drugs and cholephilic organic anions is stimulated by phenobarbital (PB). Our aim was to analyze the effects of PB on the expression of hepatocellular bile salt and organic anion transporters. Methods : Male Sprague–Dawley rats were treated intraperitoneally with PB (80 mg/kg/d) or saline for 5 days. Transporter expression was quantified by northern and western blot analysis and initial uptake rates of bromosulphophthalein (BSP) and digoxin were measured in isolated hepatocytes. Results : Compared to control rats, PB treatment increased expression of the organic anion transporting polypeptide 2 (Oatp2; Slc21a5 ) more than 2-fold on the RNA ( P<0.05 ) and protein ( P<0.001 ) levels. Expression of Oatp1 ( Slc21a1 ), Oatp4 ( Slc21a6 ) and the Na +-taurocholate cotransporting polypeptide (Ntcp; Slc10a1 ) was unaltered. At the canalicular pole, expression of the bile salt export pump (Bsep; ABCB11 ) and of the multidrug resistance proteins 2 (Mrp2; ABCC2 ) and 6 (Mrp6; ABCC6 ) was not significantly changed. Whereas hepatocellular BSP uptake was unaffected by PB, digoxin uptake was stimulated 4-fold. Conclusions : The induction of digoxin uptake by PB correlates with Oatp2 expression. In contrast, the lack of increase of Oatp1 and Oatp4 expression is in accordance with unchanged BSP uptake. These data challenge the previously held view that PB induces hepatocellular BSP uptake systems.

Altered gene expression in kidneys of mice with 2,8-dihydroxyadenine nephrolithiasis

We have developed a knockout mouse model for adenine phosphoribosyltransferase (APRT) deficiency, a condition that often leads to 2,8-dihydroxyadenine (DHA) nephrolithiasis in humans. Aprt knockout male mice develop severe renal damage by three months of age, but this is strain specific. Renal damage in female mice is less pronounced than in males. The gene level changes that promote renal injury in APRT-deficient mice are not known. We used mRNA differential display polymerase chain reaction (DD-PCR) to analyze renal gene expression changes in APRT-deficient male and female mice (strain C3H) compared with age- and sex-matched Aprt heterozygote controls. The differentially amplified bands were reamplified, cloned, sequenced, and queried against the National Center for Biotechnology Information nonredundant databases using the Basic Alignment Search Tool. Relative quantitative reverse transcription-polymerase chain reaction was used to confirm the results of DD-PCR for a selected number of genes in one-, three-, and six-month-old male and female mice. Sixty-three differentially amplified bands were identified, including 21 for known genes, and 8 of these were examined further. In three-month-old APRT-deficient male mice, the expression of C10 was increased tenfold, and there was a fourfold to sevenfold increase in the expression of a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS-1), MGP (matrix Gla protein), and lysyl oxidase (LOX). The expression of cholecystokinin-A receptor (CCKAR), imprinted multimembrane-spanning polyspecific transporter-like gene 1 (IMPT-1), and kidney androgen-regulated protein (KAP) was diminished twofold to fourfold, but there was little or no change in the expression of organic anion transporter (OATP). Except for a more than tenfold increase in C10 expression and up to tenfold decrease in KAP expression, APRT-deficient female mice did not show significant changes in gene expression compared with controls. These findings suggest that (1) there are sex-related differences in gene expression in DHA lithiasis, possibly caused by increased deposition of DHA crystals in male compared with female kidneys; and (2) the expression of certain genes (for example, C10) may simply be an indication of nonspecific cellular stimulation and may not be related to renal injury.

Developmental changes in multispecific organic anion transporter 1 expression in the rat kidney

The cDNA of the multispecific organic anion transporter 1 (OAT1) responsible for the tubular secretion of organic anions was recently isolated. In the current study, we investigated the developmental changes in OAT1 expression in the rat kidney. Ontogenic expression of rat OAT1 was investigated by Northern blot, in situ hybridization, Western blot, and immunohistochemical analysis. In addition, para-aminohippurate (PAH) accumulation was measured using fetal, neonatal, and adult rat kidney slices. In Northern blot analysis, OAT1 was detected as early as on embryonic day 18 in the fetal kidney. The expression level of OAT1 mRNA increased remarkably just after birth (postnatal day 0). In situ hybridization revealed OAT1 expression on embryonic day 19. In both the fetal and neonatal kidneys, OAT1 mRNA was localized in a relatively deep region in the cortex. Western blot analysis detected OAT1 protein on embryonic day 20, and the expression level increased after birth. Immunohistochemical analysis did not reveal OAT1 staining in the fetal kidneys. A faint signal of OAT1 protein was detected on postnatal day 0; thereafter, the expression level increased. In the functional study using kidney slices, low but definite probenecid-sensitive PAH accumulation was noted in fetal rat kidney on embryonic day 20. After birth, probenecid-sensitive PAH uptake was increased. The present study consistently demonstrates the remarkable increase of OAT1 expression after birth, and the immature excretory capacity of the proximal tubules of the neonatal kidney can be attributed, at least in part, to the low expression level of OAT1.