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

SIMPLE SUMMARY: How ovarian hormones affect goat lactation by regulating cell–cell junctions is still unclear. Through the in vivo and in vitro assays, we found that ovarian hormones could elevate cell–cell junction protein expression, which may affect the intercellular space and molecule transportation between the goat mammary epithelial cells. Our assessment suggests that ovarian hormones may affect goat milk production by regulating the cell–cell junction protein expression between mammary epithelial cells. ABSTRACT: 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.