Progesterone-regulated Hsd11b2 as a barrier to balance mouse uterine corticosterone

Glucocorticoids (GCs) are essential for mouse embryo implantation and decidualization. Excess GCs are harmful for mouse embryo implantation and decidualization. 11β-Hydroxysteroid dehydrogenases type I and II (Hsd11b1/Hsd11b2) are main enzymes for regulating local level of GCs. Hsd11b2 acts as the placental glucocorticoid barrier to protect the fetus from excessive exposure. Although effects of GCs on the fetus and placenta in late pregnancy have been extensively studied, the effects of these adrenal corticosteroids in early pregnancy are far less well defined. Therefore, we examined the expression, regulation and function of Hsd11b1/Hsd11b2 in mouse uterus during early pregnancy. We found that Hsd11b2 is highly expressed in endometrial stromal cells on days 3 and 4 of pregnancy and mainly upregulated by progesterone (P4). In both ovariectomized mice and cultured stromal cells, P4 significantly stimulates Hsd11b2 expression. P4 stimulation of Hsd11b2 is mainly mediated by the Ihh pathway. The uterine level of corticosterone (Cort) is regulated by Hsd11b2 during preimplantation. Embryo development and the number of inner cell mass cells are suppressed by Cort treatment. These results indicate that P4 should provide a low Cort environment for the development of preimplantation mouse embryos by promoting the expression of uterine Hsd11b2.