Regulation of Tight Junctions by Sex Hormones in Goat Mammary Epithelial Cells.

The sex hormones of estrogen and progesterone (P 4 ) play a vital role in mammary gland development and milk lactation in ruminants. The tight junction (TJ) between adjacent secretory epithelial cells is instrumental in establishing the mammary blood-milk barrier. However, whether estrogen and P 4 exert their effect on mammary function via regulating TJ remain unclear. Here, to clarify the role of 17-β estradiol (E 2 ) and P 4 in the regulation of TJ in goat mammary gland, we first explored the relationships between the concentrations of E 2 , P 4 , and the protein expression of claudin-1, claudin-3, occludin, and ZO-1 during the mammary gland development in goat. Then, we further explored the mRNA and protein expression of claudin-1, claudin-3, occludin, and ZO-1 in the goat mammary epithelial cells (GMECs) in vitro under different concentrations of E 2 and P 4 . The results demonstrated that the protein expression of claudin-1 decreased, but occludin and ZO-1 increased with the decline in E 2 and P 4 during the transition from pregnancy to lactation. In the in vitro studies, E 2 exerted a positive effect on the mRNA expression of claudin-1, and accelerated the proteins' expression of claudin-1 and ZO-1 in GMECs; P 4 upregulated the mRNA expression of claudin-1, claudin-3, occludin, and ZO-1, and also improved the protein expression of claudin-1, claudin-3, and ZO-1 in the GMECs. The results demonstrated that E 2 and P 4 play an important role in regulating the expression of the mammary TJ components, which may ultimately affect the mammary gland development and milk lactation.