Gonadotropin Surge-Induced Expression of Progesterone Receptor Serves the Ovary as a Trigger of Ovulation and a Terminator of Ovulatory Inflammation

Ovulation is triggered by the gonadotropin surge that induces the expression of two key genes, progesterone receptor (Pgr) and prostaglandin-endoperoxide synthase 2 (Ptgs2) in the granulosa cells of preovulatory follicles. Their gene products PGR and PTGS2 activate two separate pathways that are both essential for successful ovulation. Here we show that the PGR plays an additional essential role; attenuate ovulatory inflammation by ending the gonadotropin surge-induced Ptgs2 expression. PGR indirectly terminates Ptgs2expression by inhibiting the NF-κB, a transcription factor required for Ptgs2 expression. When the expression of PGR was ablated in the granulosa cells, the ovary undergoes hyperinflammatory condition manifested by excessive PGE2 synthesis, immune cell infiltration, and oxidative damage. Despite the ovary undergoes ovulations dozens or hundreds of times in one’s lifetime, the repetitive ovulatory inflammations do not leave significant tissue damage in the ovary. The PGR-driven termination of PTGS2 expression may protect ovary from the ovulatory inflammation.