Down-regulation of brush border efflux transporter expression in the kidneys of pregnant mice

Abstract

Pregnancy increases the urinary excretion of chemicals in women and rodents. It is unknown whether the enhanced clearance of drugs during pregnancy involves changes in the expression of transporters that mediate chemical secretion and reabsorption. The purpose of this study was to quantify the mRNA and protein expression of efflux transporters in kidneys from virgin and pregnant mice on gestational days 7, 11, 14, and 17 and postnatal days 1, 15, and 30 with use of quantitative polymerase chain reaction, Western blot, and immunofluorescence. Multidrug resistance protein (Mdr) 1b mRNA, multidrug resistance-associated protein (Mrp) 4 mRNA, and protein levels decreased significantly by 25-75% throughout pregnancy and lactation. Similarly, Mrp2 and multidrug and toxin extrusion transporter (Mate) 1 mRNA expression were down-regulated 20-40% during mid to late gestation but returned to control levels by postnatal day 15. In contrast, Mrp3 mRNA and protein increased 225% and 31%, respectively, at gestational day 14. Coordinated down-regulation of brush border transporters Mate1, Mrp2, and Mrp4 and up-regulation of the basolateral Mrp3 transporter would reduce chemical secretion into urine.

Fig. 1.

Renal mRNA expression of efflux transporters in pregnant and lactating mice. Total RNA was isolated from kidneys, and mRNA levels were quantified using quantitative PCR. mRNA expression of (A) apical and (B) basolateral efflux transporters is shown. Data were normalized to virgin controls at each time point (set to 1.0) and presented as mean relative expression ± S.E.M. Light gray bars represent pregnant mice and dark gray bars represent lactating mice. *Statistical difference, compared with time-matched virgin mice (P ≤ 0.05).

Fig. 2.

Renal protein expression of efflux transporters in pregnant mice. Protein expression of (A) apical and (B) basolateral efflux transporters on GD14 is shown. Immunoblots are presented in the upper portion, and equal protein loading was confirmed using β-actin. Protein band intensity was quantified using densitometry. Data were normalized to virgin controls and presented as mean relative protein expression ± S.E.M. *Statistical difference, compared with time-matched virgin mice (P ≤ 0.05).

Fig. 3.

Immunofluorescent detection of renal efflux transporters in pregnant mice. Immunofluorescent detection of (A) apical and (B) basolateral efflux transporters in renal tissues of virgin and pregnant mice at GD14. Indirect immunofluorescence of transporters (green) was conducted on kidney cryosections (6 μm) obtained from GD14 pregnant mice and time-matched virgin controls. Images of cortical regions are shown at 10× magnification. Images were cropped, enlarged, and provided as insets.