179 EFFECTS OF DEHYDROEPIANDROSTERONE ON SPERM FERTILIZABILITY IN VITRO AND TESTICULAR GENE EXPRESSION

Abstract

Strain differences of in vitro fertilizability still constitute a serious problem in mouse reproduction. To improve the in vitro fertilizability of mouse sperm, we examined the effects of implanting time-release pellets of dehydroepiandrosterone (DHEA), a testosterone precursor, on sperm fertilizability and testicular gene expression. DHEA pellets (5 mg pellet^–1, 21-day release form; Innovative Research of America) or placebo pellets were implanted subcutaneously in 9-week-old male mice from 2 strains: C57BL/6CrNSlc (B6) and 129X1/SvJJmsSlc (129X1). After 21 days, in vitro fertilization was conducted using epididymal sperm from these males and oocytes from superovulated 4-week-old Slc:ICR females. The percentages of 2-cell embryo formation in the placebo and DHEA groups were 78.2 ± 14.2% vs 89.3 ± 2.5%, respectively (mean ± standard error of the mean, n = 4 per group) using B6 sperm and 40.9 ± 8.8% vs 41.3 ± 3.1%, respectively (n = 4 per group) using 129X1 sperm, indicating no significant effect of DHEA treatment (P > 0.05 by 2-way ANOVA). However, a strain difference was quite evident (P < 0.05 by 2-way ANOVA). Quantitative Western blotting using testicular protein extracts with glyceraldehyde-3-phosphate dehydrogenase as an internal control showed that the expression of androgen receptor protein (AR) was significantly higher in B6 than in 129X1 males (P < 0.05 by 2-way ANOVA), whereas there was no significant effect of DHEA on the amount of AR in either strain (P > 0.05 by 2-way ANOVA). In B6 testes, 2-dimensional electrophoresis indicated that 1 protein spot was denser in DHEA-treated males than in placebo-treated males. In 129X1 testes, DHEA did not change the density of the corresponding spot. Mass spectrometry of the spot suggested that it was Cu/Zn superoxide dismutase (SOD1). Thus, 21-day-release pellets of 5 mg DHEA had no significant effect on sperm fertilizability in vitro in 2 strains, but the DHEA pellets induced a strain-dependent testicular protein expression, which might be because of the differential AR expression. Although DHEA treatment of male mice has the potential to improve sperm fertilizability in vitro, a more detailed study is needed to determine the optimal dose, age and duration of DHEA treatment.

This work was supported by a grant from the Ministry of Health, Labour and Welfare, Japan.