Abstract
Estrogen receptor-α gene deficiency enhances androgen biosynthesis in the mouse Leydig cell
Akingbemi,Benson T.; Ge,Renshan; Rosenfeld,Cheryl S.; Newton,Leslie G.; Hardy,Dianne O.; Catterall,James F.; Lubahn,Dennis B.; Korach,Kenneth S.; Hardy,Matthew P.
Endocrinology 144(1): 84-93
Publication date: 2003
Leydig cells, which produce the primary male steroid hormonetestosterone (T), express the two estrogen receptor (ER) subtypes,ER and ERß, and have the capacity to convert testosteroneto the natural estrogen 17ß-estradiol. Thus, Leydigcells are subject to estrogen action. The development of transgenicmice that are homozygous for targeted deletion of genes encodingthe ER subtypes provides an opportunity to examine the roleof estrogen in Leydig cell function. In this study androgenbiosynthesis was analyzed in Leydig cells from mice that werehomozygous for targeted deletion of the ER gene (ERKO). T productionby ERKO Leydig cells was 2-fold higher than that in wild-type(WT) cells. Serum T levels were accordingly higher in ERKO comparedwith WT mice (5.1 ± 1.1 vs. 2.2 ± 0.4 ng/ml; P0.01) as were serum LH levels (1.31 ± 0.3 vs. 0.45 ±0.08 ng/ml; P 0.01). Mice that were treated with the pure antiestrogenICI 182,780 at 100 µg/kg·d for 7 d, effectivelyabrogating ER-mediated activity, also had 2-fold elevationsin the serum levels of LH (1.15 ± 0.3 vs. 0.45 ±0.2 ng/ml) and T (4.3 ± 1.1 vs. 2.2 ± 0.2 ng/ml;P 0.01). Increased androgen biosynthesis by ERKO Leydig cellswas associated with higher steroidogenic enzyme activity, especiallyof cytochrome P450 17-hydroxylase/17-20 lyase (P450)and 17ß-hydroxysteroid dehydrogenase (17ß-HSD),as measured by conversion of radiolabeled steroid substratesto T or its precursors. The largest increases in enzymatic activitywere observed for P450 (423 ± 45 pmol/min·10cells in ERKO Leydig cells vs. 295 ± 27 pmol/min·10cells in WT cells; P < 0.01). Consistent with steroidogenicenzyme activity, the testis of ERKO mice expressed higher steadystate mRNA levels for steroidogenic acute regulatory proteinand two enzymes involved in androgen biosynthesis, P450 and17ß-HSD type III, as determined by semiquantitativeRT-PCR. Compared with the controls, higher steady state mRNAlevels for steroidogenic acute regulatory protein and P450were also measured in the testis of ICI 182,780-treated mice.In a second set of experiments estrogen administration reducedserum LH and T levels in WT controls, whereas ERKO mice wereunaffected. Although exposure of WT and ERKO Leydig cells toestrogen in vitro did not affect androgen biosynthesis, incubationwith ICI 182,780 reduced T production by WT, but not ERKO, Leydigcells. These observations indicate that abrogation of the ERgene by targeted deletion or treatment with an antiestrogenincreases Leydig cell steroidogenesis in association with elevationsin the serum levels of LH, which presumably is the result ofestrogen insensitivity at the level of the hypothalamus and/orpituitary gonadotropes. Furthermore, the decrease in T productionby WT Leydig cells and not ERKO Leydig cells occasioned by incubationwith ICI 182,780 suggests that of the ER subtypes, ER has aregulatory role in Leydig cell steroidogenic function.
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