Mitogen-Activated Protein Kinase 8 (MAP3K8) Mediates the Signaling Pathway of Estradiol Stimulating Progesterone Production Through G Protein-Coupled Receptor 30 (GPR30) in Mouse Corpus Luteum

The corpus luteum (CL) is a transient endocrine gland developed from the ovulated follicles, and the most important function is to synthesize and secrete progesterone (P4), a key hormone to maintain normal pregnancy and estrous cycle in most mammals. It is known that estrogen has a vital role in stimulating P4 synthesis in CL, but it still remains unclear about the mechanism of estradiol (E2) regulating P4 production in CL. Our results here first show that all of the CL cells express MAPK 8 (MAP3K8), and the MAP3K8 level is much higher at the midstage than at the early and late stages during CL development. The further functional studies show that the forced inhibition of endogenous MAP3K8 by using MAP3K8 small interfering RNA and MAP3K8 signaling inhibitor (MAP3K8i) in the luteal cells significantly block the P4 synthesis and neutralize the enhancing effect of E2 on P4 production in the CL. In addition, our results here demonstrate that the stimulating effect of E2 on P4 synthesis relies on the estrogen no-classical protein-coupled receptor 30, and MAP3K8 is involved in mediating the protein-coupled receptor 30signaling of E2 affecting P4 synthesis via stimulating ERK phosphorylation. These novel findings are critical for our understanding the ovary physiology and pathological mechanism.