Calcium-binding proteins S100A8, S100A9, and S100A12: expression and regulation at the maternal-conceptus interface in pigs

Among the many calcium-binding proteins, S100A8, S100A9, and S100A12 play important roles in inflammation, innate immunity, and antimicrobial function, but their expression, regulation, and function at the maternal-conceptus interface in pigs are not fully understood. Therefore, we determined the expression and regulation of S100A8, S100A9, S100A12, and their receptor AGER at the maternal-conceptus interface in pigs. We found that S100A8, S100A9, and S100A12 mRNAs were expressed in the endometrium during the estrous cycle and pregnancy, with the greatest levels on Day (D) 12 of pregnancy, and AGER appeared at greater levels on D15 and D30 of pregnancy than on other days. The expression of S100A8, S100A9, and S100A12 was predominantly localized to epithelial cells in the endometrium, and they were detected in early-stage conceptus and later chorioallantoic tissues during pregnancy. AGER expression was localized to endometrial epithelial and stromal cells and chorionic epithelial cells. In endometrial explant tissues, the expression of S100A8, S100A9, and S100A12 was induced by estrogen, S100A8 by interleukin-1β, and AGER by interferon-γ. We further found that on D12 of pregnancy, the expression of S100A8, S100A9, and S100A12 decreased significantly in the endometria of gilts carrying conceptuses derived from somatic cell nuclear transfer. These results indicate that the expression of S100A8, S100A9, and S100A12 is dynamically regulated in response to conceptus-derived signals at the maternal-conceptus interface, suggesting that S100A8, S100A9, and S100A12 could play a critical role in regulating endometrial epithelial cell function and conceptus implantation to support the establishment and maintenance of pregnancy in pigs.