Renal expression of organic anion transporter OAT2 in rats and mice is regulated by sex hormones

Abstract

The renal reabsorption and/or excretion of various organic anions is mediated by specific organic anion transporters (OATs). OAT2 (Slc22a7) has been identified in rat kidney, where its mRNA expression exhibits gender differences [females (F) > males (M)]. The exact localization of OAT2 protein in the mammalian kidney has not been reported. Here we studied the expression of OAT2 mRNA by RT-PCR and its protein by Western blotting (WB) and immunocytochemistry (IC) in kidneys of adult intact and gonadectomized M and F, sex hormone-treated castrated M, and prepubertal M and F rats, and the protein in adult M and F mice. In adult rats, the expression of OAT2 mRNA was predominant in the outer stripe (OS) tissue, exhibiting 1) gender dependency (F > M), 2) upregulation by castration and downregulation by ovariectomy, and 3) strong downregulation by testosterone and weak upregulation by estradiol and progesterone treatment. A polyclonal antibody against rat OAT2 on WB of isolated renal membranes labeled a approximately 66-kDa protein band that was stronger in F. By IC, the antibody exclusively stained brush border (BB) of the proximal tubule S3 segment (S3) in the OS and medullary rays (F > M). In variously treated rats, the pattern of 66-kDa band density in the OS membranes and the staining intensity of BB in S3 matched the mRNA expression. The expression of OAT2 protein in prepubertal rats was low and gender independent. In mice, the expression pattern largely resembled that in rats. Therefore, OAT2 in rat (and mouse) kidney is localized to the BB of S3, exhibiting gender differences (F > M) that appear in puberty and are caused by strong androgen inhibition and weak estrogen and progesterone stimulation.

Organic anion transporters: discovery, pharmacology, regulation and roles in pathophysiology

“…In contrast, intermittent secretion, such as that seen in males, yields relatively low rOat2 mRNA levels in the kidney. In mice, although one study found no sex differences in renal mOat2 mRNA expression [56], two other groups showed a female predominance in either mOat2 message [55] or protein [126] that was consistent with rat studies.…”

“…As alluded to above, renal Oat2 mRNA and protein was reported to be predominant in female rats and mice [56,[124][125][126][127]. Castration of male rats markedly increased renal rOat2 mRNA and protein [126,127], whereas ovariectomy in females resulted in a relatively weak reduction in rOat2 mRNA and protein [126]. Consistent with these findings, administration of estradiol or progesterone to castrated or noncastrated male rats weakly stimulated renal rOat2 mRNA and protein expression [126,127].…”

“…Castration of male rats markedly increased renal rOat2 mRNA and protein [126,127], whereas ovariectomy in females resulted in a relatively weak reduction in rOat2 mRNA and protein [126]. Consistent with these findings, administration of estradiol or progesterone to castrated or noncastrated male rats weakly stimulated renal rOat2 mRNA and protein expression [126,127]. In addition, it has been shown that the growth hormone secretion pattern is an important determinant of rOat2 message expression [125].…”

“…In such a case, it will be of interest to determine the mechanism supporting this organ-specific gender-dependent regulation. As alluded to above, renal Oat2 mRNA and protein was reported to be predominant in female rats and mice [56,[124][125][126][127]. Castration of male rats markedly increased renal rOat2 mRNA and protein [126,127], whereas ovariectomy in females resulted in a relatively weak reduction in rOat2 mRNA and protein [126].…”

“…That is, testosterone is a major inhibitory steroid, and the continuous growth hormone secretion pattern, which is characteristic of females, is an important stimulatory factor. The importance of gender difference in renal Oat2 expression is difficult to predict, as it remains unclear whether this transporter is expressed in the proximal tubule, loop of Henle, or collecting duct [58,126,128]. In addition, Oat2's relative involvement in reabsorption versus secretion, and endogenous homeostasis versus xenobiotic disposition remains ambiguous.…”