Mutual Regulation of Follicle-Stimulating Hormone Signaling and Bone Morphogenetic Protein System in Human Granulosa Cells1

Abstract

Bone morphogenetic proteins (BMPs) play critical roles in folliculogenesis by modulating the actions of follicle-stimulating hormone (FSH) in the ovary. However, the effects of FSH on the BMP system remain unknown. Here, we have investigated the effects of FSH on BMP signaling using the human granulosa-like tumor cell line KGN. KGN cells express BMP type I and type II receptors and the BMP signaling molecules SMADs. FSH administration upregulated BMP type IA (BMPR1A) and IB (BMPR1B) receptors, activin type II receptor (ACVR2), and BMP type II receptor (BMPR2). FSH also augmented SMAD1 and SMAD5 expression, and conversely, FSH suppressed the expression of the inhibitory SMADs, SMAD6 and SMAD7. Bioassays revealed that FSH enhances BMP-induced SMAD1/5/8 phosphorylation and cellular DNA synthesis induced by BMP6 and BMP7. Since overexpression of BMPR1A and BMPR1B, but not SMADs, significantly enhanced the BMP responses, these type I receptors were revealed to be limiting factors for BMP signaling in KGN cells. BMPs significantly suppressed progesterone synthesis induced by forskolin and dibutyryl-cAMP (BtcAMP) but had no effect on estradiol induced by the same factors. KGN cAMP levels induced by forskolin were not altered by BMPs, suggesting that BMPs regulate steroidogenesis at a level downstream of cAMP synthesis in KGN cells. In this regard, BMPs specifically reduced the STAR transcription, whereas the levels of CYP11A, HSD3B2, and CYP19 stimulated by forskolin as well as BtcAMP were not altered. Collectively, the two major factors, FSH-cAMP pathway and BMP system, are reciprocally and functionally linked. Given that BMPs downregulate FSH receptors in KGN cells, this interaction may contribute to fine-tuning of the mutual sensitivity toward BMP ligands and FSH.

Single-cell expression analysis of BMP15 and GDF9 in mature oocytes and BMPR2 in cumulus cells of women with polycystic ovary syndrome undergoing controlled ovarian hyperstimulation

“…In bovine granulosa cells, estrogen used alone and in combination with FSH has been shown to up-regulate BMPR2 mRNA expression [22,24]. Supporting this finding, a study using a human granulosa-like tumor cell line showed that FSH up-regulated BMPR2 in GCs [23]. Our results indicate the likelihood that BMPR2 expression might be up-regulated by rFSH alone or in combination with steroids in PCOS cumulus cells.…”

“…However, a positive correlation was observed between mRNA expression of BMPR2 in PCOS cumulus cells and levels of testosterone and androstenedione in FF from pre-ovulatory follicles. In fact, several studies have shown that BMP receptors are hormonally regulated [22][23][24]. PCOS-related hyperandrogenism can exerts complex effects on the ovarian follicle.…”

“…Gene expression profiles of BMP receptors in cumulus cells have only been fragmentally reported, and their results showed that BMPR2 is hormonally regulated [22][23][24]. However, evaluation of transcripts of this gene in cumulus cells from PCOS women undergoing COH for IVF has not been thoroughly examined.…”

Changes in granulosa cells' gene expression associated with increased oocyte competence in bovine

“…BMPR1B is a BMP family member that regulates follicular development by affecting granulosa cell proliferation and steroidogenesis. BMPs modulate FSH actions in the ovary and reciprocally (Miyoshi et al 2006). BMPR1B is expressed from secondary to atretic follicles and is the receptor for BMP2, -4, -6, and -7.…”

Interference RNA-based silencing of endogenous SMAD4 in porcine granulosa cells resulted in decreased FSH-mediated granulosa cells proliferation and steroidogenesis

“…In addition, FSH increased the expression levels of SMAD1/ 5 and decreased the expression of inhibitory SMADs, SMAD6/7. Thus, it is most likely that FSH augments the bioavailability of BMP signaling in human granulosa (Miyoshi et al 2006).…”