Spatiotemporal expression and regulation of peptidase inhibitor 3 and secretory leukocyte protease inhibitor at the maternal–fetal interface in pigs

OBJECTIVE: Two serine protease inhibitors, peptidase inhibitor 3 (PI3) and secretory leukocyte protease inhibitor (SLPI), play important roles in protease inhibition and antimicrobial activity, but their expression, regulation, and function at the maternal–fetal interface in pigs are not fully understood. Therefore, we determined the expression and regulation of PI3 and SLPI in the endometrium throughout the estrous cycle and at the maternal–fetal interface in pigs. METHODS: Endometrial tissues during the estrous cycle and pregnancy, conceptus tissues during early pregnancy, and chorioallantoic tissues during mid to late pregnancy were obtained, and the expression of PI3 and SLPI was analyzed. The effects of the steroid hormones estradiol-17β (E2) and progesterone (P4) on the expression of PI3 and SLPI were determined in endometrial explant cultures. RESULTS: PI3 and SLPI were expressed in the endometrium during the estrous cycle and pregnancy, with higher levels during mid to late pregnancy than during the estrous cycle and early pregnancy. Early-stage conceptuses and chorioallantoic tissues during mid to late pregnancy also expressed PI3 and SLPI. PI3 protein and SLPI mRNA were primarily localized to endometrial epithelia. In endometrial explant cultures, the expression of PI3 was induced by increasing doses of P4, and the expression of SLPI was induced by increasing doses of E2 and P4. CONCLUSION: These results suggest that the PI3 and SLPI expressed in the endometrium and conceptus tissues play an important role in antimicrobial activity for fetal protection against potential pathogens and in blocking protease actions to allow epitheliochorial placenta formation.