Androgen receptor signaling regulates follicular growth and steroidogenesis in interaction with gonadotropins in the ovary during mini-puberty in mice.

In females, androgens contribute to ovarian diseases such as polycystic ovarian syndrome (PCOS), but their action is also crucial for ovarian physiology, i.e., follicular growth and estradiol (E2) synthesis during reproductive life, in interaction with the gonadotropins LH and FSH. However, it is unclear whether androgens already play a role in the ovary at mini-puberty, a phase of postnatal development with active follicular growth and high E2 levels. Therefore, we analyzed the potential actions of androgens on the ovary and their possible interaction with gonadotropins during this period in mice. We used molecular-based studies and pharmacological approaches in vivo and on cultured ovaries. We found that mini-pubertal ovaries produce significant amounts of testosterone and display androgen receptor (AR) expression in growing follicles, both under the control of LH. By blocking AR signaling either in vivo or in ovarian cultures, we found that this pathway may participate in the regulation of prepubertal E2 synthesis and follicular growth, possibly by regulating the expression of a number of key intra-ovarian regulators, including FSH receptor (Fshr), the aromatase enzyme converting androgens into estrogens (Cyp19a1) and the cell cycle inhibitor p27KIP1 (Cdkn1b). We further showed that AR may stimulate FSH-mediated regulation of Cyp19a1 through its action on Fshr mRNA abundance. Overall, this work supports the idea that AR signaling is already activated in mini-pubertal ovaries to regulate E2 synthesis and follicular growth, at the interplay with LH and FSH signaling. Its early action may, thus, contribute to the implementation of early ovarian function with possible impacts on reproductive function.

Estradiol promotes cell survival and induces Greb1 expression in granulosa cell tumors of the ovary through an ERα-dependent mechanism.

Granulosa cell tumor (GCT) is a form of ovarian tumor characterized by its tendency to recur years after surgical ablation. Little is known about the mechanisms involved in GCT development and progression. GCTs can produce estradiol (E2), but whether this hormone could play a role in this cancer through its nuclear receptors, i.e. ERα and ERß, remains unknown. Here, we addressed this issue by cell-based and molecular studies on human GCTs and GCT cell lines. Importantly, we observed that E2 significantly increased the growth of GCT cells by promoting cell survival. The use of selective agonists of each type of receptor, together with Esr1 (ERα) or Esr2 (ERß)-deleted GCT cells, revealed that E2 mediated its effects through ERα-dependent genomic mechanisms and ERß/ERα-dependent extra-nuclear mechanisms. Notably, the expression of Greb1, a prototypical ER target gene, was dose-dependently upregulated by E2 specifically through ERα in GCT cells. Accordingly, using GCTs from patients, we found that GREB1 mRNA abundance was positively correlated to intra-tumoral E2 concentrations. Tissue microarray analyses showed that there were various combinations of ER expression in primary and recurrent GCTs, and that ERα expression persisted only in combination with ERß in ~40% of recurrent tumors. Altogether, this study demonstrates that E2 can promote the progression of GCTs, with a clear dependence on ERα. In addition to demonstrating that GCTs can be classified as a hormone-related cancer, our results also highlight that the nature of ER forms present in recurrent GCTs could underlie the variable efficiency of endocrine therapies. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Estradiol Regulates mRNA Levels of Estrogen Receptor Beta 4 and Beta 5 Isoforms and Modulates Human Granulosa Cell Apoptosis.

Estrogen receptor beta (ERß) plays a critical role in granulosa cell (GC) functions. The existence of four human ERß splice isoforms in the ovary suggests their differential implication in 17ß-estradiol (E2) actions on GC apoptosis causing follicular atresia. In this study, we investigated whether E2 can regulate ERß isoforms expression to fine tune its apoptotic activities in human GC. For this purpose, we measured by RT-qPCR the expression of ERß isoforms in primary culture of human granulosa cells (hGCs) collected from patients undergoing in vitro fertilization, before and after E2 exposure. Besides, we assessed the potential role of ERß isoforms on cell growth and apoptosis after their overexpression in a human GC line (HGrC1 cells). We confirmed that ERß1, ERß2, ERß4, and ERß5 isoform mRNAs were predominant over that of ERα in hGCs, and found that E2 selectively regulates mRNA levels of ERß4 and ERß5 isoforms in these cells. In addition, we demonstrated that overexpression of ERß1 and ERß4 in HGrC1 cells increased cell apoptosis by 225% while ERß5 or ERß2 had no effect. Altogether, our study revealed that E2 may influence GC fate by specifically regulating the relative abundance of ERß isoforms mRNA to modulate the balance between pro-apoptotic and non-apoptotic ERß isoforms.

Aberrant granulosa cell-fate related to inactivated p53/Rb signaling contributes to granulosa cell tumors and to FOXL2 downregulation in the mouse ovary.

Ovarian granulosa cell tumors (GCTs) are indolent tumors of the ovary affecting women at all ages and potentially displaying late recurrence. Even if there is still little information regarding the mechanisms involved in GCT development and progression, FOXL2 would be a major tumor suppressor gene in granulosa cells. We analyzed the mechanisms underlying GCT initiation and progression by using mice with targeted expression of SV40 large T-antigen in granulosa cells (AT mouse), which develop GCTs. Consistent with patients, AT mice with developing GCTs displayed increased levels in circulating anti-Müllerian hormone (AMH), estradiol and androgens, as well as decreased FOXL2 protein abundance. Very few mice developed metastases (1 out of 30). In situ analyses revealed that GCT initiation resulted from both increased granulosa cell survival and proliferation in large antral follicles. Tumorigenesis was associated with the combined inactivation of p53 and Rb pathways, as shown by the impaired expression of respective downstream targets regulating cell apoptosis and proliferation, i.e., Bax, Bak, Gadd45a, Ccna2, Ccne1, E2f1, and Orc1. Importantly, the expression of FOXL2 was still present in newly developed GCTs and its downregulation only started during GCT growth. Collectively, our experiments provide evidence that disrupted p53/Rb signaling can drive tumor initiation and growth. This model challenges the current paradigm that impaired FOXL2 signaling is a major switch of granulosa cell tumorigenesis, albeit possibly contributing to tumor growth.

FSH inhibits AMH to support ovarian estradiol synthesis in infantile mice.

Anti-Müllerian hormone (AMH) regulates ovarian function in cyclic females, notably by preventing premature follicle-stimulating hormone (FSH)-mediated follicular growth and steroidogenesis. Its expression in growing follicles is controlled by FSH and by estradiol (E2). In infantile females, there is a transient increase in the activity of the gonadotrope axis, as reflected by elevated levels of both gonadotropins and E2. We previously demonstrated in mice that elevated FSH concentrations are necessary to induce E2 production by preantral/early antral follicles through the stimulation of aromatase expression without supporting their growth. However, whether this action of FSH could involve AMH is unknown. Here, we show that Amh mRNA and protein abundance and serum AMH levels are elevated in infantile mouse females, compared with those in adults. By experimentally manipulating FSH and E2 levels in infantile mice, we demonstrate that high FSH concentrations lower Amh expression specifically in preantral/early antral follicles, whereas E2 has no effect. Importantly, treatment of infantile ovaries in organotypic cultures with AMH decreases FSH-mediated expression of Cyp19a1 aromatase, but it does not alter the expression of cyclin D2-mediating granulosa cell proliferation. Overall, our data indicate that the infantile elevation in FSH levels suppresses Amh expression in preantral/early antral follicles, thereby favoring Cyp19a1 aromatase expression and E2 production. Together with recent discoveries that AMH can act on both the hypothalamus and the pituitary to increase gonadotropin levels, this work suggests that AMH is a critical regulator of the gonadotrope axis during the infantile period, thereby contributing to adult reproductive function programming.