Ex vivo effects of bisphenol A or zearalenone on the prepubertal rat testis.

Bisphenol A (BPA) and zearalenone (ZEA) are two widespread xenoestrogens involved in male reproductive disorders. Few studies investigated the effects of these compounds on the prepubertal testis, which is highly sensitive to endocrine disruptors such as xenoestrogens. An ex vivo approach was performed to evaluate the effects of BPA or ZEA (10-11, 10-9, 10-6 M) on the testes of 20 and 25 dpp rats. To investigate the involvement of classical nuclear ER-mediated estrogen signaling in these effects, pre-incubation with an antagonist (ICI 182.780 10-6 M) was performed. BPA and ZEA have similar effects on spermatogenesis- and steroidogenesis-related endpoints in the immature testis, but our study highlights different age-dependent patterns of sensitivity to each compound during the prepubertal period. Moreover, our results indicate that the effects of BPA are likely to be induced by nuclear ER, whereas those of ZEA appear to involve other mechanisms.

Deoxynivalenol enhances estrogen receptor alpha-induced signaling by ligand-independent transactivation.

Deoxynivalenol (DON), which is one of the prevalent mycotoxins in food and feeds, exerts adverse effects on animal and human health. These effects are mainly associated with its ribotoxic properties, although few studies suggest the involvement of other mechanisms of action. To assess the ability of DON to disrupt estrogen signaling, we conducted an in vitro study using MCF-7 and MDA-MB-231 cells. After 72h, DON reduced cell viability in both cell lines, thus highlighting its well-known cytotoxic effect. However, after 6h, DON increased the expression of estrogen-responsive genes, hence demonstrating the stimulation of estrogen signaling by this mycotoxin after a short-term exposure. This effect was partially reversed by siRNA-mediated silencing of ERα expression and by 4-hydroxytamoxifen (ERα antagonist), but neither by G36 (GPER antagonist) nor by the siRNA-mediated silencing of PPARγ2 expression. Moreover, DON exposure induced an increase in the level of ERα phosphorylation at serine 167. Furthermore, when combined with zearalenone (a naturally co-occurring mycotoxin recognized as an endocrine disruptor), DON increased the expression of estrogen-responsive genes to a greater extent than each individual compound taken separately. Taken together, our results suggest, for the first time, that DON can disrupt estrogen signaling through the ligand-independent activation of ERα.

Caspase-2 involvement during ionizing radiation-induced oocyte death in the mouse ovary.

In mammals, the pool of primordial follicles at birth is determinant for female fertility. Exposure to IR during oogonia proliferation and the diplotene stages of ovarian development induced the virtual disappearance of primordial follicles in the postnatal ovary, while half the follicular reserve remained present after irradiation during the zygotene/pachytene stages. This sensitivity difference was correlated with the level of caspase-2 expression evaluated by immunohistochemistry. At the diplotene stage, Western blot and caspase activity analysis revealed that caspase-2 was activated 2 h after irradiation and a significant increase in the number of oocytes expressing cleaved caspase-9 and -3 occurred 6 h after treatment. Inhibition of caspase-2 activity prevented the cleavage of caspase-9 and partially prevented the loss of oocytes in response to irradiation. Taken together, our results show that caspase-2-dependent activation of the mitochondrial apoptotic pathway is one of the mechanisms involved in the genotoxic stress-induced depletion of the primordial follicle pool.

Quantification of cytochrome P450 aromatase transcripts before and during luteal phase in rabbit.

The aim of the present study was to quantify the promoter II- and I.r-derived transcripts of p450 aromatase gene during follicular stages and during corpus luteum formation in the rabbit. An ovulatory dose of hCG induced, first the disappearance of 90% of aromatase transcripts since 6 h before ovulation, and second a gradual decrease during pseudopregnancy. Individual quantification of both the promoter-derived transcripts showed that promoter II-derived transcript was the main transcript expressed both during follicular phase and pseudopregnancy, but kinetics of disappearance were not similar between both the promoter-derived transcripts. Moreover, hCG up-regulates aromatase expression in vitro in luteal tissue but estradiol, which was without effect on aromatase expression in preovulatory granulosa cells, down-regulates this expression in luteal tissue. In conclusion, the regulation of P450 aromatase in rabbit is mainly under control of promoter II regardless of which cyclic stage is studied. Moreover, we reported an opposite effect of estradiol on aromatase expression in vitro between follicular and luteal cells.

Expression of the rabbit cytochrome P450 aromatase encoding gene uses alternative tissue-specific promoters.

The aim of the present study was to analyse the tissue-specific expression of various promoter-derived transcripts from the gene encoding rabbit aromatase cytochrome P450. A new promoter, named I.r, was identified, and promoters II and I.r were sequenced. Promoter I.r-derived transcripts were found in preovulatory granulosa cells, corpus luteum, placenta and adipose tissue. An alternative splice variant of this transcript was found with tissue-specific preference. Tissue-specific expression of promoter-derived variants was studied in the ovary before and after ovulation. While the level of promoter II-derived transcript decreased dramatically after ovulation, that of promoter I.r-derived transcript remained unchanged, indicating that promoter II and promoter I.r were not controlled by a single regulation system. The existence of this dual system of regulation suggests that the rabbit ovary could be a useful model to study the promoter-specific regulation of aromatase.