Estradiol regulates Osteopontin mRNA expression in bovine endometrial gland cells (BEGC) in vitro

Osteopontin (OPN) is an extracellular matrix protein secreted by endometrial glands during early pregnancy and is required for adhesion and signal transduction at the uterine-placental surface. In sheep, endometrial OPN secretion is mediated by progesterone (P4) through downregulation of its own nuclear receptor (PR). In our in vitro study, we evaluated the regulation of OPN in the bovine endometrium.

Bovine endometrial gland cells (BEGC) were stimulated with P4, estradiol (E2) and the ruminant pregnancy recognition signal interferon tau (IFNτ) both alone and in combination to simulate the hormonal situation in early pregnancy. After stimulation, the mRNA expression of PR and OPN was analyzed by quantitative real-time PCR. Additionally, OPN protein expression was analyzed by immunofluorescence and Western blot.

Stimulation with P4 alone as well as a combination of P4 and IFNτ had no effect on the PR and OPN mRNA expression. The addition of E2 to the stimulation media led to a significant increase in PR mRNA expression, but only stimulation with E2 alone led to a significant increase in OPN mRNA expression. After combined E2/P4 stimulation, the stimulating effect of E2 was no longer detectable. None of the stimulations affected OPN protein expression.

OPN regulation by P4 could not be demonstrated but stimulation with E2 led to an increase in OPN gene expression. As E2 does not play a major role during implantation in cattle, this result suggests that OPN may play a less prominent role in cattle as it does in sheep.