Endocrine Abstracts

Estradiol (E2) plays an essential role in woman fertility. E2, locally produced by granulosa cells (GCs) of ovarian antral follicles, controls follicular development and selection, and triggers the gonadotropin surge that leads to ovulation. Dysovulation arising from the arrest of antral follicle growth and maturation occurs in up to 10 % of reproductive-aged women suffering polycystic ovary syndrome (PCOS). Although the diagnostic criteria for PCOS are clearly established, the molecular etiology of this syndrome is still under debate. Given the high importance of E2 in follicular growth and selection, our study aimed at identifying the possible disturbances of E2 signaling, predominantly mediated by estrogen receptors ERα and ERβ, that could impact GCs steroidogenic function and participate in PCOS. For this purpose, we performed primary cultures of GCs from follicles of 30 patients undergoing in vitro fertilization either for male factor infertility (control) or for PCOS. First, we analyzed by RT-qPCR the expression level of the two transcription factors ERα and ERβ in GCs, and demonstrated that they exhibited the same level of expression in control and PCOS patients. Strikingly, E2 treatment significantly regulated the expression of genes involved in various biological processes (steroid biosynthesis: Cyp19a1 and Cyp11A1; cell survival: Bcl-2) in primary cultures of control GCs, whereas in PCOS cells, E2 was ineffective despite the presence of ERα and ERβ. Then, we characterized the steroidogenic activity of GCs from control and PCOS, by measuring steroid hormone concentrations in both cells and follicular fluids (FF) using GC/MS. Our analyses demonstrated that E2, pregnenolone (P5) and progesterone (P4) concentrations were significantly lower (by 27 %, 41 % and 45 % respectively) in PCOS FF when compared to control. They also revealed that contrary to P5, the reduction of concentrations of E2 and P4 in FF did not correlate with a decrease in their intracellular biosynthesis. Indeed, intracellular concentrations of E2 and P4 were similar in both groups, whereas that of P5 was significantly reduced (by 59 %) in PCOS, probably through the down-regulation of Cyp11A1 expression that we observed. Altogether, our study provides a novel signature of PCOS by revealing an impairment in E2 signaling that may contribute to follicular growth dysregulations. In addition, our results suggest the existence of a selective steroid degradation in FF of PCOS patients that may explain lower levels of anti-inflammatory steroids P4 and P5, and enhance the local ovarian inflammation contributing to unsuccessful oocyte maturation.