SOX9: A Novel Mediator of the Ovulatory Process in the Human Ovary

Abstract Ovarian disorders in women, including defects in ovulation and subsequent corpus luteum (CL) development, account for up to 30% of all infertility cases. Understanding the mechanism underlying these processes is critically important, as this knowledge provides a foundation for our ability to aid or manage female fertility. The mid-cycle gonadotropin surge triggers dramatic changes in the dominant follicle, culminating in ovulation and transformation into the CL. One essential step elicited by the gonadotropin surge is the induction of specific transcription factors that directly control the transcription of genes crucial for successful ovulation and luteinization. However, our knowledge of regulatory actions of LH/hCG-induced ovulatory transcription factors remains limited, especially in humans. Our preliminary data shed light on SOX9 (sex-determining region Y (SRY)-box transcription factor 9) as a critical transcriptional regulator involved in periovulatory processes. It has long been accepted that SOX9 is expressed at a low level or repressed in the developing ovary. This active suppression of SOX9 in granulosa cells is crucial for maintaining ovarian phenotype. Challenging this belief, our preliminary data showed that SOX9 expression was markedly up-regulated in granulosa cells of dominant follicles after an ovulatory bolus of hCG administration and was directly regulated by progesterone/progesterone receptor (PGR), an essential mediator of the ovulatory process. Furthermore, our pilot study showed that SOX9 regulated the expression of STAR and CYP11A1 and progesterone production in human granulosa/lutein cells. Based on these data, we hypothesize that SOX9 expression is increased in follicular cells of dominant follicles by the LH surge/hCG- P4/PGR pathway, and the up-regulated SOX9 regulates the transcription of genes crucial for successful ovulation and luteinization in the human ovary. This hypothesis will be tested utilizing in vivo ovarian tissue samples obtained from normally cycling women during various ovulatory phases and a primary human granulosa/lutein cell culture model that can mimic in vivo changes in ovulatory gene expression and hormone profiles. In Aim 1, we will determine the expression pattern of SOX9 and its downstream genes in follicular cells isolated from dominant follicles and whole dominant follicles obtained from normally cycling women throughout the periovulatory period. In Aim 2, we will identify SOX9-regulated downstream genes and assess the impact of SOX9 knockdown on granulosa/lutein cell function. The proposed is in line with R21 mechanisms, as it will not only, for the first time, demonstrate the ovulatory up-regulation of SOX9 in human ovulatory follicles but also enhance our understanding of how the LH surge/hCG - P4/PGR - SOX9 pathway controls the human-specific ovulatory process and luteinization in the ovary. This fundamental knowledge could be directly applied in designing a diagnostic marker(s) for anovulatory disorders or luteal insufficiency and developing strategies to manage female fertility.