Tissue distribution, ontogeny, and hormonal regulation of xenobiotic transporters in mouse kidneys

Abstract

Kidneys play important roles in the elimination of numerous endogenous and exogenous chemicals. In recent years, at least 37 xenobiotic transporters have been identified in mammalian kidneys. Although much progress has been made, information on 14 of these transporters (ATP-binding cassette [Abc] a1, apical sodium bile acid transporter [Asbt], breast cancer resistance protein, concentrative nucleoside transporter 1, equilibrative nucleoside transporter [Ent] 2, Ent3, sodium-phosphate cotransporter [Npt] 1, Npt2a, Npt2b, Npt2c, organic anion transporter [Oat] 5, organic anion-transporting polypeptide [Oatp] 4c1, peptide transporter 2, and uric acid transporter [Urat] 1) in kidneys is quite limited. Therefore, the purpose of the present study was to examine the tissue distribution, ontogeny, and hormonal regulation of these 14 transporters in kidneys of mice. Other than in kidneys, Npt2b is also highly expressed in liver and lung, Npt2c in liver and colon, Asbt in ileum, and Abca1 in liver, lung, testis, ovary, and placenta of mice. Most of these (13 of 14) transporters are lowly expressed in mouse kidneys until 15 days of age, which in part contributes to the immaturity of excretory function in fetal and newborn kidneys. One exception is Ent2, which is highly expressed before birth and gradually decreases after birth until reaching adult levels at 15 days of age. Gender-divergent expression of male-predominant (Urat1 and Oatp4c1) and female-predominant (Oat5) transporters in mouse kidneys is primarily due to stimulatory effects of androgens and estrogens, respectively. In conclusion, the mRNA expression of xenobiotic transporters in kidneys is determined by tissue, age, and sex hormones.

Fig. 1.

Diagram of cellular localization and transport direction of known transporters in kidneys. Excretion transporters from basolateral and apical membranes are depicted in the proximal tubular cells (PTCs) of kidneys (left). Reabsorption transporters from basolateral and apical membranes are shown in the PTCs of kidneys (right). Transporters labeled in gray are transporters for which there are previously published data concerning tissue distribution, ontogeny, and gender difference. Transporters labeled in black are transporters that were not fully characterized previously and are addressed in the present study.

Fig. 2.

Tissue distribution of Npt1, 2a, 2b, and 2c. Total RNA from male and female C57BL/6 mouse tissues (n = 6/gender) was analyzed by the bDNA assay for mRNA expression of each Npt. Data are presented as mean ± S.E.M. *, statistically significant difference between male and female mice (p < 0.05). RLU, relative light units.

Fig. 3.

Tissue distribution of Abca1, Asbt, Oat5, and Urat1. Total RNA from male and female C57BL/6 mouse tissues (n = 6/gender) was analyzed by the bDNA assay for mRNA expression of each transporter. Data are presented as mean ± S.E.M. *, statistically significant difference between male and female mice (p < 0.05). RLU, relative light units.

Fig. 4.

Ontogenic expression of Npt1, 2a, and 2c mRNA in mouse kidneys. Total RNA from C57BL/6 mice of each age (n = 5/gender/age) was analyzed by the bDNA assay. Data are presented as mean ± S.E.M. *, statistically significant difference between male and female mice (p < 0.05). RLU, relative light units.

Fig. 5.

Ontogenic expression of Asbt, Cnt1, Pept2, Oat5, and Urat1 mRNA in mouse kidneys. Total RNA from C57BL/6 mice of each age (n = 5/gender/age) was analyzed by the bDNA assay. Data are presented as mean ± S.E.M. *, statistically significant difference between male and female mice (p < 0.05). RLU, relative light units.

Fig. 6.

Ontogenic expression of Ent2, Ent3, Oatp4c1, and Bcrp mRNA in mouse kidneys. Total RNA from C57BL/6 mice of each age (n = 5/gender/age) was analyzed by the bDNA assay. Data are presented as mean ± S.E.M. *, statistically significant difference between male and female mice (p < 0.05). RLU, relative light units.

Fig. 7.

Effects of sex hormones on the gender-divergent mRNA expression of Oat5, Urat1, and Oatp4c1 in kidneys of naive and gonadectomized (GNX) mice. Total kidney RNA was isolated and analyzed by the bDNA signal amplification assay for mRNA expression of each transporter. The data are presented as mean ± S.E.M. (n = 6–7/group). The treatments were separated into groups: GNX (placebo administered to gonadectomized mice), GNX + DHT (5α-dihydroxytestosterone administered to gonadectomized mice), and GNX + E2 (17β-estradiol administered to gonadectomized mice). *, statistical difference (p < 0.05) between male and female mice; †, statistically significant difference (p < 0.05) between naive mice and the same gender, placebo-treated gonadectomized mice; ‡, statistically significant difference (p < 0.05) between placebo-treated gonadectomized mice and the same gender gonadectomized mice after sex hormone replacement.

Fig. 8.

Effects of growth hormone on the gender-divergent mRNA expression of Oat5, Urat1, and Oatp4c1 in kidneys of naive and lit/lit mice. Total kidney RNA was isolated and analyzed by the bDNA signal amplification assay for mRNA expression of each transporter. The data are presented as mean ± S.E.M. (n = 6–7/group). The treatments were separated into groups: Lit (placebo administered to lit/lit mice), Lit + GH_MP (rat GH twice daily administered by intraperitoneal injection to lit/lit mice mimicking male-pattern GH secretion), and Lit + GH_FP (continuous infusion to lit/lit mice via a subcutaneous implanted 21-day-release 1-mg rat GH pellet mimicking female-pattern GH secretion). *, statistical difference (p < 0.05) between male and female mice; †, statistically significant difference (p < 0.05) between naive mice and the same gender, placebo-treated lit/lit mice; ‡, statistically significant difference (p < 0.05) between placebo-treated lit/lit mice and the same gender lit/lit mice after growth hormone replacement.