Regulation of androgen receptor signaling by ubiquitination during folliculogenesis and its possible dysregulation in polycystic ovarian syndrome

Jung Jin Lim,Patricia D A Lima,Reza Salehi,Dong Ryul Lee,Benjamin K Tsang

doi:10.1038/s41598-017-09880-0

Abstract

Although chronic hyperandrogenism suppresses antral follicular development, a phenomenon often observed in polycystic ovarian syndrome (PCOS), whether and how deregulation of androgen receptor (AR) signaling is involved, is not well understood. In the present study, we examined the role of ring finger protein 6 (RNF6) in AR ubiquitination and the possible dysregulation in the expression and actions of growth differentiation factor 9 (GDF9) and kit-ligand (Kitlg) in a chronic androgenized PCOS rat model. 5α-dihydrotestosterone (DHT) treatment in vivo inhibited antral follicle growth, a response mediated through increased RNF6 content, suppressed K63- but increased K48-linked AR ubiquitination as well as the mRNA expression and content of soluble KIT-L (sKitlg) and content of GDF9. These androgenic responses were attenuated by gonadotropin treatment in vivo. Growth of antral follicles from DHT-treated rats in vitro was significantly slower when compared to those of control but was significantly enhanced by exogenous GDF9, suggesting the DHT-induced antral follicular growth arrest is in part the results of GDF9 suppression. Our findings indicate how hyperandrogenism modulates RNF6 content and subsequently AR ubiquitination, resulting in antral follicle growth arrest in a chronically androgenized PCOS rat model.

Highlights

Androgens stimulate granulosa cell proliferation and promote preantral follicle growth in the mammalian ovary[1,2,3,4], but suppress later stages of follicular development through induction of granulosa cell apoptosis, symptoms often associated with ovarian dysregulation evident in hyperandrogenic anovulation[5, 6]
Our studies suggest that antral follicle growth arrest observed in polycystic ovarian syndrome (PCOS) may in part be associated with androgen-induced, Ring finger protein 6 (RNF6)-mediated Androgen receptor (AR) (K48) polyubiquitination and degradation and loss of granulosa cell proliferative response
Using a chronically androgenized rat model, we have investigated in the present study the role of RNF6-mediated site-specific AR ubiquitination in androgen-induced antral follicular growth arrest

Summary

Introduction

Androgens stimulate granulosa cell proliferation and promote preantral follicle growth in the mammalian ovary[1,2,3,4], but suppress later stages of follicular development through induction of granulosa cell apoptosis, symptoms often associated with ovarian dysregulation evident in hyperandrogenic anovulation[5, 6]. GDF9 and Kitlg are known to mediate androgen action on follicular development, the cellular mechanisms involved in the AR ubiquitination induced by androgen are not completely understood. We hypothesized that androgen-induced ovarian follicular growth is dependent on site-specific RNF6-mediated AR polyubiquitination, which determines AR transcriptional activity (K63; Kitlg mRNA expression) and AR stability and abundance (K48). During chronic androgenization, increased RNF6-mediated AR ubiquitination (K48) results in enhanced AR degradation and decreased Kitlg expression, GDF9 down-regulation and antral follicular growth arrest. Our studies suggest that antral follicle growth arrest observed in PCOS may in part be associated with androgen-induced, RNF6-mediated AR (K48) polyubiquitination and degradation and loss of granulosa cell proliferative response

Methods

Results

Conclusion