Endocrine Abstracts (2004) 7 P56

Testosterone regulates renal expression of the alpha-subunit of the epithelial sodium channel (alpha-ENaC)

M Quinkler, IJ Bujalska, K Kaur, S Hughes, M Hewison & PM Stewart

Department of Medicine, Queen Elizabeth Hospital, University of Birmingham, Birmingham, UK.

Studies in rats suggest that androgens are involved in sex-specific differences in blood pressure. In human studies there is no difference in blood pressure between boys and girls, but following puberty, men present with a higher blood pressure than women. Modulation of sodium reabsorption through the ENaC is an important component in the control of sodium balance. This is clearly demonstrated by rare genetic disorders of sodium-channel activity (Liddle's syndrome and pseudohypoaldosteronism type 1), associated with contrasting effects on blood pressure. We investigated the androgen-dependent regulation of alpha-ENaC using the human renal cell line HKC-8 as a model. Using RT-PCR and Western Blots we investigated expression of the androgen receptor (AR) in HKC-8 cells and male human kidney. Androgen metabolism was investigated using radiolabeled androstenedione, testosterone or DHEA. We used Affymetrix microarray techniques to look at androgen-dependent gene regulation. For verification we used Taq Man quantitative RT-PCR. In addition the promoter region of alpha-ENaC was mapped from GeneBank and analysed for AR binding sites. The AR was expressed in male kidney and HKC-8 cells at both the mRNA and protein level. HKC-8 cells did not inactivate testosterone to androstenedione. The Affymetrix assay showed a 2.14-fold increase in alpha-ENaC, but no changes in beta- or gamma-ENaC mRNA expression by testosterone. Taq Man PCR revealed the highest alpha-ENaC induction (over 3-fold) with 50nM testosterone at 48h. This induction was blocked completely by adding 10-5 M of the AR antagonist flutamide. Mapping of alpha-ENaC promoter showed an AR response element located 1.5 kb upstream the translation start codon in exon 2. We have shown for the first time that alpha-ENaC mRNA expression is directly upregulated by testosterone. This could be an important mechanism to explain the higher blood pressure in men compared to women and their increased susceptibility to hypertension.

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