Progesterone antagonist, RU486, represses LHCGR expression and LH/hCG signaling in cultured luteinized human mural granulosa cells

Progesterone, the main steroid synthesized by the corpus luteum (CL), prepares the uterus for implantation, maintains the CL survival, and induces progesterone auto-secretion. However, the molecular mechanisms involving the progesterone auto-secretion pathways at the luteal phase are not fully understood, especially in humans. We aim to study the molecular mechanism of the progesterone pathway in human granulosa cells. Our model system consists of luteinized human-mural-granulosa-cells (hmGCs) obtained from follicles aspirated during in vitro fertilization (IVF) procedures. hmGCs were seeded in culture and were subjected to different hormonal treatments. mRNA levels were analyzed by quantitative real-time PCR (qRT-PCR). Progesterone levels were measured by enzyme immunoassay (EIA). We show that exposure of luteinized hmGCs to the progesterone receptor antagonist, RU486 (mifepristone), resulted in inhibition of LHCGR, LH/hCG target genes and progesterone secretion. Exposure of hmGCs to medium that was incubated with hmGCs for 4 d-conditioned medium (CM), which contain 150 ± 7.5 nM progesterone, resulted in induction of LHCGR and LH/hCG target genes, which was blocked by RU486. In addition, RU486 inhibited some of the progesterone biosynthesis pathway genes. Our results revealed a novel mechanism of the progesterone antagonist pathway in the luteal granulosa cells and emphasis the fundamental role of progesterone in the early luteal phase.