Secretory leukocyte protease inhibitor (SLPI), also known as neutrophil elastase and cathepsin-G protease inhibitor, functions in protection of epithelial cells from proteases. SLPI is expressed and secreted by many mucosal tissues, including lungs, seminal vesicles and cervix in women. SLPI plays an important role in protection of endometrial epithelial cells during pregnancy from degradation by degradation by proteases derived from trophoblast at the maternal-conceptus interface. In pigs, SLPI mRNA is known to be expressed in endometrial tissues, but the expression of SLPI in the endometrium throughout the estrous cycle and pregnancy has not been determined. Therefore, we analyzed the expression and regulation of SLPI mRNA in the endometrium throughout the whole stages of the estrous cycle and pregnancy in pigs. We obtained endometrial tissues from gilts on Days 0 (day of estrus), 3, 6, 9, 12, 15, and 18 of the estrous cycle and on Days 10, 12, 15, 30, 60, 90, and 114 of pregnancy. Real-time RT-PCR analysis showed that the expression of SLPI mRNA in the endometrium increases during midt-o late pregnancy. During the estrous cycle, levels of SLPPI mRNA in estrus and proestrus were higher than those in diestrus and metestrus. In situ hybridization analysis showed that SLPI mRNA was specifically localized to the glandular epithelial cells in the endometrium during pregnancy with strong signal intensity during mid-to late pregnancy. SLPI mRNA was not detectable in conceptus tissues on Days 12 and 15 of pregnancy, but SLPI mRNA was expressed in chorioallantoic tissues during mid-to term pregnancy with increasing levels toward term pregnancy. To determine the effects of steroid hormones, estrogen and progesterone, on the expression of SLPI mRNA, endometrial explant tissues from immature pigs were treated with increasing doses of estradiol-17β (E2) and progesterone (P4). Increasing doses of E2 and P4 increased the expression of SLPI mRNA in endometrial tissues. These results showed that SLPI was expressed in the endometrium in a pregnancy stage-and cell type-specific manner and the expression of SLPI was regulated by E2 and P4 in endometrial tissues, suggesting that SLPI may play an important role in regulating the endometrial epithelial cell function during mid-to late pregnancy in pigs. Further analysis to determine the roles of SLPI at the maternal-conceptus interface is still needed.

Caspases are a family of cysteine protease enzymes composed of more than 10 members that play essential roles in apoptosis and inflammation. It has been reported that caspases play a critical role in regulating apoptosis at the maternal-conceptus interface in many species. However, the expression and regulation of caspases have not been determined in the endometrium in pigs. Therefore, we analyzed the expression, localization, and regulation of caspases in the endometrium during the estrous cycle and pregnancy in pigs. Real-time RT-PCR analysis showed that caspases were expressed in the endometrium during the estrous cycle and pregnancy. The expression of CASP6, CASP7, and CASP8 during the estrous cycle and CASP3, CASP6, CASP7, and CASP10 changed during pregnancy. Levels of CASP3 mRNA in the endometrium were higher on Day 12 of pregnancy than the estrous cycle and levels of CASP7 mRNAs were highest on Day 15 of estrous cycle and pregnancy. Immunohistochemistry analysis showed that CASP3 protein was localized to endometrial epithelial cells on Days 12 and 15 the estrous cycle and pregnancy, but cleaved CASP3 was localized only to luminal epithelial (LE) cells on Days 12 and 15 of pregnancy in the endometrium. CASP7 protein was localized to endometrial LE cells only on Day 15 of pregnancy. CASP3, CASP6, CASP7, CASP8, and CASP10 mRNAs were detectable in conceptus on D12 and D15 of pregnancy, and chorioallantoic tissues expressed CASP3, CASP6, CASP7, CASP8, CASP8, and CASP10 with increasing levels toward term pregnancy, except CASP3 mRNA. The effect of steroid hormones and interleukin-1βß (IL1B) on CASP3 expression and the effect of interferon-γ(IFNG) on CASP7 expression was determined by endometrial explant cultures and we found that CASP3 expression was increased by IL1B and CASP7 expression was increased by IFNG in a dose-dependent manner. These results showed that caspases were expressed in the endometrium during the estrous cycle and pregnancy in a stage- and/or pregnancy-specific dependent manner and some caspases were regulated by IL1B or IFNG in the endometrial tissues, suggesting that caspase may play an important role in regulating apoptosis for the establishment and maintenance of pregnancy at the maternal-conceptus interface in pigs.