Androgen Receptor–Mediated Regulation of the α-Subunit of the Epithelial Sodium Channel in Human Kidney

Abstract

Abstract-Rodents studies suggest that androgens are involved in sex-specific differences in blood pressure. In humans, there is no difference in blood pressure between boys and girls, but after puberty, blood pressure increases more in men than in women. We investigated androgen-dependent regulation of the ␣-subunit of the epithelial sodium channel (␣EnaC) in human kidney and in the human renal cell line immortalized human renal proximal tubular cell line (HKC-8).We used microarray technique to analyze androgen-dependent gene regulation and performed quantitative RT-PCR for verification. Promoter constructs for human ␣ENaC were used in transfection studies to analyze the regulation by testosterone. We investigated the in vivo effect of testosterone on ␣ENaC in a rat model and used the mouse collecting duct cell line M-1 for transepithelial electrophysiological measurements. The androgen receptor (AR) was expressed in male kidney and HKC-8 cells. ␣ENaC mRNA expression increased 2-to 3-fold after treatment with testosterone in HKC-8 cells. The induction by testosterone was completely blocked by adding the AR antagonist flutamide. Analysis of the ␣ENaC promoter sequence identified a putative AR response element (ARE) located 140 nucleotides upstream from the transcription start site. HKC-8 cell transfection studies showed that testosterone directly upregulated gene expression via this ARE. In vivo, testosterone treatment of orchiectomized rats resulted in an increased renal ␣ENaC mRNA expression. In testosterone-treated mouse M-1 cells, amiloride caused a significant stronger decrease in short circuit current than in control cells. These data show that ␣ENaC expression is directly regulated by androgens in vitro and in vivo and highlight a potential mechanism explaining the reported gender differences in blood pressure. Key Words: blood pressure Ⅲ gender Ⅲ kidney Ⅲ sodium channels A ndrogens are known to play an important role in renal tubular epithelial cell growth, hypertrophy, and erythropoetin production, and may be important determinants of sex-specific differences in blood pressure. 1 In spontaneously hypertensive rats, males have higher blood pressures than females, 2 an effect that is reversed by male castration. Furthermore, increases in blood pressure were observed in castrated male and female rats after the administration of testosterone, 2,3 whereas administration of the androgen receptor (AR) antagonist flutamide attenuated hypertension. 4 These studies strongly implicate androgens in the regulation of blood pressure in the rat, but the mechanisms for this are still unknown.In humans, there is no difference in blood pressure between boys and girls, but during and after puberty, boys show higher blood pressure than age-matched girls, 5,6 and men have a higher overall mean arterial pressure than women, 7 regardless of ethnic origin. 8 The higher blood pressure and stronger progression of hypertension in men is associated with a higher risk and mortality for cardiovascular diseases than in women. 9,10 Alt...

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