FSH Modulates The Expression Of Inhibin-α And The Secretion Of Inhibins Via Orphan Nuclear Receptor Nur77in Ovarian Granulosa Cells

Inhibins are closely associated with female ovarian follicle development. The altered expression levels of the inhibin subunits during follicle development and their regulation by extrinsic and intra-ovarian factors suggest that these proteins may have important roles in folliculogenesis, oocyte maturation and corpus lutea function. Previous studys showed that women with primary ovarian failure (POF) have lower serum levels of Inhibin A and B. As the unique subunit of inhibins, the expression of inhibin-α subunit can be regulated by FSH in human granulosa cells, but the precise molecular pathway remains unknown.The orphan nuclear receptor Nur77(also known as NR4A1, NGFI-B, TR3or NAK-1) is a member of the NR4A family. Nur77is expressed in several tissues, including the ovary. Nur77can bind to DNA as a monomer through a regulatory element, called the NGFI-B response element (NBRE), which is present in a subset of genes. Nur77activates steroidogenic gene expression during luteinization, indicating that the stage-specific expression of Nur77may have functional relevance in follicular maturation.In the present study, we investigated the role of the orphan nuclear receptor, Nur77, in both the transcriptional regulation of the inhibin α-subunit gene and the secretion of inhibins. Our results showed that in a human GCT-derived cell line, KGN, FSH induced the expression of Nur77and inhibin-a. In the ovarian granulosa cells of the Nur77knockout mice, the mRNA levels of inhibin-a decreased relative to wild-type mice. Furthermore, the overexpression or reduction of Nur77affected the expression of inhibin-a. Nur77overexpression also improved the secretion of Inhibin A and B in human granulosa-lutein cells. However, inhibin-a expression was not increased following the FSH treatment if Nur77was knocked down. In addition, ChlP-PCR, ABCD and luciferase reporter assays confirmed that Nur77directly regulated the transcription of inhibin-a gene through the specific NBRE site located in the promoter.These data indicate a role of Nur77in both the regulation of inhibin-a and the secretion of inhibins in ovarian granulosa cells. We suppose that Nur77may be one of the key regulator for ovarian follicular development and participating in the process of female fertility.