Androgens regulate ovarian follicular development by increasing follicle stimulating hormone receptor and microRNA-125b expression

Abstract

Although androgen excess is considered detrimental to women's health and fertility, global and ovarian granulosa cell-specific androgen-receptor (AR) knockout mouse models have been used to show that androgen actions through ARs are actually necessary for normal ovarian function and female fertility. Here we describe two AR-mediated pathways in granulosa cells that regulate ovarian follicular development and therefore female fertility. First, we show that androgens attenuate follicular atresia through nuclear and extranuclear signaling pathways by enhancing expression of the microRNA (miR) miR-125b, which in turn suppresses proapoptotic protein expression. Second, we demonstrate that, independent of transcription, androgens enhance follicle-stimulating hormone (FSH) receptor expression, which then augments FSHmediated follicle growth and development. Interestingly, we find that the scaffold molecule paxillin regulates both processes, making it a critical regulator of AR actions in the ovary. Finally, we report that low doses of exogenous androgens enhance gonadotropin-induced ovulation in mice, further demonstrating the critical role that androgens play in follicular development and fertility. These data may explain reported positive effects of androgens on ovulation rates in women with diminished ovarian reserve. Furthermore, this study demonstrates mechanisms that might contribute to the unregulated follicle growth seen in diseases of excess androgens such as polycystic ovary syndrome. O ther than the obligatory role of androgens as estrogen precursors in steroidogenesis (1), little is known about the direct involvement of androgens in the female ovary. For many decades, excess androgens in women have been considered detrimental to women's health, as diseases such as polycystic ovary syndrome (PCOS) are associated with reduced fertility. In the past, these negative effects of androgens on female fertility were thought to occur primarily at the level of the hypothalamus and pituitary (2, 3), although important data across different species (4-7) suggested that androgens could also directly promote follicle growth (8, 9). Attitudes about androgen actions in female fertility changed with the development of global androgenreceptor knockout (ARKO) mice (10-12). The female ARKO mice had considerable reproductive defects, with decreased fertility, defective follicular development, reduced ovulation, and premature ovarian failure. In other words, the phenotype of these ARKO mice suggested that androgen signaling might actually be important for normal female reproductive health. Intriguingly, through the generation of granulosa cell (GC)-specific ARKO mice, we (13) and then others (14) demonstrated that essentially all the observed reproductive phenotypes in the complete AR-null mice are caused by androgen actions in GCs. These results highlighted that, with regard to fertility, androgen signaling in the ovary is at least as important as androgen signaling in the pituitary or hypothalamus. By using this GC-specific ARK...

Androgen receptor and miRNA-126* axis controls follicle-stimulating hormone receptor expression in porcine ovarian granulosa cells

“…As the most physiologically important nuclear receptor and cell surface receptor in ovarian follicles, respectively, AR and FSHR are considered to be essential regulators of GC biology (Wang et al 2015). Many recent publications demonstrated that AR and FSHR mRNA levels are tightly correlated (Catteau-Jonard et al 2008, Nielsen et al 2011 and that androgens can regulate FSHR expression in GCs (Sen et al 2014, (I) Luciferase activity assays. miR-126* or NC mimic was co-transfected with pmirGLO-FSHR-3′-UTR mut.…”

“…Because miR-126* expression is regulated by AR, we postulated that AR regulates FSHR expression via miRNAs. One downstream target of AR is miR-125b, which represses p53 expression; this miRNA cooperates with AR to synergistically inhibit the p53 function in mGCs (Sen et al 2014). Similarly, Ribas et al (2009) showed that androgen-bound AR up-regulates expression of miR-21, and the AR/miR-21 axis exerts oncogenic effects in prostate tumors by down-regulating TGFBR2 (Mishra et al 2014).…”

“…FSH can synergize with androgens to regulate FSHR expression in follicles (Sen et al 2014, Walters 2015. Previous studies have shown that low-to-moderate doses of testosterone, a principal androgen, significantly increase FSHR mRNA levels in human luteinized GCs, whereas higher doses of testosterone do not further increase the FSHR mRNA levels and have no effect on FSHR protein expression (Garcia-Velasco et al 2012).…”

“…Previous studies have shown that low-to-moderate doses of testosterone, a principal androgen, significantly increase FSHR mRNA levels in human luteinized GCs, whereas higher doses of testosterone do not further increase the FSHR mRNA levels and have no effect on FSHR protein expression (Garcia-Velasco et al 2012). Sen et al (2014) demonstrated that androgens, including testosterone and its metabolite dihydrotestosterone (DHT), regulate FSHR protein expression independent of transcription in primary mouse GCs. Androgens exert their biological activities via the androgen receptor (AR), a 110 kDa protein of the nuclear receptor superfamily .…”

“…microRNAs (miRNAs), small non-coding RNAs of 20-22 nucleotides in length, play crucial roles in ovarian function and GC apoptosis (Imbar & Eisenberg 2014, Zhou et al 2015, Liu et al 2016. A recent study demonstrated that androgens attenuate follicular atresia by increasing expression of miR-125b, which in turn suppresses the expression of proapoptotic proteins (Sen et al 2014). Several studies also showed that androgens and AR control their target genes by regulating the expression of miRNAs (Ma et al 2013, Lyu et al 2014, Pasqualini et al 2015.…”