A novel action of follicle-stimulating hormone in the ovary promotes estradiol production without inducing excessive follicular growth before puberty

Charlotte M. François,Alain Gougeon,Florence Petit,Frank Giton,Solange Magre,Joëlle Cohen-Tannoudji,Célia Ravel,Céline J. Guigon

doi:10.1038/srep46222

Abstract

In cyclic females, FSH stimulates ovarian estradiol (E2) production and follicular growth up to the terminal stage. A transient elevation in circulating FSH and E2 levels occurs shortly after birth. But what could be the action of FSH on the ovary during this period, and in particular how it stimulates ovarian steroidogenesis without supporting terminal follicular maturation is intriguing. By experimentally manipulating FSH levels, we demonstrate in mice that the mid-infantile elevation in FSH is mandatory for E2 production by the immature ovary, but that it does not stimulate follicle growth. Importantly, FSH increases aromatase expression to stimulate E2 synthesis, however it becomes unable to induce cyclin D2, a major driver of granulosa cell proliferation. Besides, although FSH prematurely induces luteinizing hormone (LH) receptor expression in granulosa cells, LH pathway is not functional in these cells to induce their terminal differentiation. In line with these results, supplying infantile mice with a superovulation regimen exacerbates E2 production, but it does not stimulate the growth of follicles and it does not induce ovulation. Overall, our findings unveil a regulation whereby high postnatal FSH concentrations ensure the supply of E2 required for programming adult reproductive function without inducing follicular maturation before puberty.

Highlights

In hypophysectomized rats[17,18,19]
By using the gold standard method for steroid measurement, i.e., gas chromatography coupled with mass spectrometry (GC-MS), we found that E2 production increased concomitantly to the rise in gonadotropin levels to attain a peak at 14 dpn (Fig. 1C)
Supplying equine Chorionic gonadotropin (eCG) prevented the effects of the Ganirelix treatment on both Cyp19a1 and Ccnd[2] expression (Fig. 3B and C). To determine whether these alterations in follicle-stimulating hormone (FSH)-regulated Ccnd[2] expression had an impact on granulosa cell proliferation in preantral/early antral follicles, we examined by immunohistochemistry the expression of a mitosis marker, i.e., phosphorylated histone H3 (p-HH3)[32] and the incorporation of BrdU under these experimental conditions (Fig. 3D)

Summary

Introduction

In hypophysectomized rats[17,18,19]. FSH regulation of early follicular growth in infantile mice has been demonstrated in vitro[20]. Despite the important elevation in circulating FSH in prepubertal females and the associated production of E2, follicles do not grow beyond the antral stage and no ovulation occurs[21,22,23,24,25] These latter observations are intriguing given the well-documented stimulatory action of FSH on the growth of follicles[13]. The current study clearly shows that the marked elevation in FSH levels occurring during the postnatal period is mandatory for the significant production of E2 by the immature ovary. It does not stimulate preantral/ early antral follicle growth and it does not stimulate terminal follicular maturation. Our studies provide some molecular cues to explain this unprecedented uncoupling in FSH-mediated regulation of ovarian steroidogenesis and follicular growth during the prepubertal period

Methods

Results

Conclusion