Klotho (KL) is a single transmembrane protein composed of KL1 and KL2 repeats possessing β-glucuronidase activity and maintains calcium homeostasis in physiological state. It has been implicated in pigs that calcium is important for the establishment and maintenance of pregnancy, and our previous study has shown that transient receptor potential vanilloid type 6 (TRPV6), a calcium ion transporter, is predominantly expressed in the uterine endometrium during pregnancy in pigs. However, expression and function of KL in the uterine endometrium has not been determined in pigs. Thus, the present study determined expression and regulation of KL in the uterine endometrium during the estrous cycle and pregnancy in pigs. Real-time RT-PCR analysis showed that levels of KL mRNA decreased between Days 12 to 15 of the estrous cycle, and its expression showed a biphasic manner during pregnancy. KL mRNA was expressed in conceptuses and in chorioallantoic tissues during pregnancy. Explant culture study showed that expression levels of KL were not affected by treatment of steroid hormones or interleukin-1beta during the implantation period. Furthermore, levels of KL mRNA in the uterine endometrium from gilts carrying somatic cell nuclear transfer (SCNT)- derived embryos were significantly lower than those from gilts carrying natural mating-derived embryos on Day 12 of pregnancy. These results exhibited that KL was expressed at the maternal-conceptus interface in a pregnancy statusand stage-specific manner, and its expression was affected by SCNT procedure, suggesting that KL may play an important role in the establishment and maintenance of pregnancy in pigs.

For successful embryo implantation, the communication of the maternal endometrium with the conceptus trophec-toderm is required essentially. In pigs, conceptuses undergo morphological change in length to enlarge the physical contact area with the maternal endometrium and secrete estrogen to induce the maternal recognition of pregnancy during the peri-implantation period. Conceptus-derived estrogen prevents luteolysis by conversion in direction of PGF2α secretion from the uterine vasculature to the uterine lumen as well as it affects on expression of the uterine endo-metrial genes. In addition to estrogen, conceptuses release various signaling molecules, including cytokines, growth factors, and proteases, and, in response to these signaling molecules, the maternal uterine endometrium also syn-thesizes many signaling molecules, including hormones, cytokines, growth factors, lipid molecules, and utilizes ions such as calcium ion by calcium regulatory molecules. These reciprocal interactions of the conceptus trophectoderm with the maternal uterine endometrium make development and successful implantation of embryos possible. Thus, signaling molecules at the maternal-conceptus interface may play an important role in the implantation process. This review summarized syntheses and functions of signaling molecules at the maternal-conceptus interface to further understand mechanisms of the embryo implantation process in pigs.

Prostaglandins (PGs), especially PGE2 and PGF2α, are critical local mediators that play important role in luteolysis and maternal recognition of pregnancy in pigs. Luteolysis during the estrous cycle in pigs is induced by PGF2α synthesized and secreted by the uterine endometrium. In pregnant pigs, PG synthesis is changed in favor of PGE2 synthesis. However, molecular and cellular mechanisms by which PGE2 and PGF2α are produced in the uterine endometrium during pregnancy are poorly understood. Therefore, we determined immunolocalization of PTGES, AKR1B1, CBR1, and HPGD that are involved in synthesis and catabolism of PGE2 and PGF2α in the uterine endometrium during the estrous cycle and pregnancy in pigs. Uterine endometrial tissue samples were collected from day (D) 12 and D15 of the estrous cycle and from D12, D15, D30, D60, D90, and D114 of pregnancy. Spatial expression of all proteins studied was analyzed by immunohistochemistry. PTGES were localized primarily to luminal and glandular epithelial cells. AKR1B1 were localized to luminal epithelial cells during early pregnancy and chorionic membrane during mid- to late pregnancy. CBR1 and HPGD were localized to luminal epithelial cells. Our results showed that expression of proteins responsible for synthesis and catabolism of PGE2 and PGF2α were dynamically regulated in the uterine endometrium during the estrous cycle and pregnancy in pigs. These results indicate that PGs play critical roles to support the establishment and maintenance of pregnancy at the maternal-fetal interface in pigs. This research was supported by the Next Generation BioGreen 21 program (#PJ007997), RDA, Republic of Korea.

Cathepsins (CTSs), a family of lysosomal cysteine proteases, and their inhibitors (CSTs) play a critical role in remodeling of the uterine endometrium and placenta for the establishment and maintenance of pregnancy in many animal species including rodents, sheep, cow and pigs. It has been shown that the high rate of pregnancy failure by somatic cell nuclear transfer (SCNT) is associated with abnormal placental development. Our previous study has shown that CST6 is highly expressed in the uterine endometrium from mid to late pregnancy in pigs. In this study, to understand whether appropriate endometrial and placental tissue remodeling occurs in the uterine endometrium from gilts with conceptuses derived from SCNT during pregnancy in pigs, we investigated expression of CST6 in the uterine endometrium. Uterine endometrial tissues were obtained from gilts that carried SCNT-derived normal conceptuses (NT-No) and abnormal conceptuses (NT-Ab), and from gilts carrying conceptuses from natural mating (Non-NT) on D114 of pregnancy. Immunoblot analysis showed that CST6 protein levels in the endometrial tissues of gilts carrying NT-No were lower than those of gilts carrying Non-NT. The levels of CST6 protein in the endometrial tissues of gilts carrying NT-Ab decreased even more than those of gilts carrying NT-No. These results indicate that decreased expression of CST6 in the endometrium with NT-No and NT-Ab reflects inappropriate endometrial tissue remodeling and pregnancy failure of pigs with SCNT derived conceptuses and that CST6 plays an important role for the maintenance of pregnancy in pigs. * This work was supported by the Next Generation BioGreen 21 program (#PJ007997), RDA, Republic of Korea.

Na+/K+-ATPase, an energy-transducing ion pump, is responsible for maintenance of relatively high concentrations of potassium ions but low concentrations of sodium ions in the cell by transport of these ions across the plasma membrane and participates in transport of various nutrients including glucose, amino acids. and ions. Na+/K+-ATPase consists of α, β, and FXYD subunits, but only α and β subunits are needed for basic functions. FXYD subunit is an auxiliary protein for αβ complex of Na+/K+-ATPase. Our recent study has shown that α (ATP1A1-4) and β (ATP1B1-3) subunits of Na+/K+-ATPase are expressed in the uterine endometrium during the estrous cycle and pregnancy in pigs. In this study, we further determined expression of FXYD (FXYD1-7) subunits of Na+/K+-ATPase in the uterine endometrium during the estrous cycle and pregnancy in pigs. Real-time RT-PCR analysis showed that mRNAs for all subtypes of FXYD subunit were expressed in the uterine endometrium during the estrous cycle and pregnancy in a pregnancy status- and stage-specific fashion. In situ hybridization analysis exhibited that transcripts of all subtypes of FXYD subunit were primarily localized to luminal (LE) and glandular epithelia (GE) during the estrous cycle and early pregnancy and to chorionic membrane (CM) during mid to term pregnancy. RT-PCR analysis showed that FXYD subunits were expressed in conceptuses on D12 and D15 of pregnancy. These results indicate that all subtypes of FXYD subunit are expressed in the uterine endometrium and conceptuses during the estrous cycle and pregnancy in a pregnancy status- and stagespecific manner. These suggest that FXYD may be involved in the establishment and maintenance of pregnancy by regulating the activity of Na+/K+-ATPase in nutrient transport at the maternal-fetal interface in pigs. * This work was supported by the Next Generation BioGreen 21 program (#PJ007997), RDA and the National Research Foundation (NRF #2010-0012304) funded by the Korean Government, Republic of Korea.

Na+/K+-ATPase, an energy-transducing ion pump, is responsible for maintenance of relatively high concentrations of potassium ions but low concentrations of sodium ions in the cell by transport of these ions across the plasma membrane. Na+/K+-ATPase consists of α, β, and γ subunits, but only α and β subunits are needed for basic functions. Na+/K+-ATPase is also involved in regulation of intracellular calcium ion concentration by coupling with Na+/Ca2+ exchanger involved in intracellular calcium extrusion. Our previous study showed that calcium regulatory molecules including Na+/Ca2+ exchanger are expressed in the uterine endometrium during the estrous cycle and pregnancy in pigs, however, expression of Na+/K+-ATPase in the uterine endometrium has not been determined. Thus, we examined expression of α1 (ATP1A1) and β1 (ATP1- B1) subunits of Na+/K+-ATPase in the uterine endometrium during the estrous cycle and pregnancy in pigs. Real-time RT-PCR analysis showed that levels of ATP1A1 m- RNA in the uterine endometrium during the estrous cycle and early pregnancy were higher than those during mid and term pregnancy, and that levels of ATP1B1 mRNA were highest on day (D) 12 of the estrous cycle. In situ hybridization analysis revealed that ATP1A1 and ATP1B1 mRNAs were localized to luminal (LE) and glandular epithelia (GE) in the endometrium. During mid to term pregnancy, localization of ATP1A1 mRNA was confined to LE, GE, and chorionic membrane (CM) of areolae and ATP1- B1 mRNA was localized to LE, GE and CM with the strongest intensity in LE of areolae. Signal intensity of ATP1B1 mRNA in LE was slightly stronger than that in GE. RT-PCR analysis showed that ATP1A1 and ATP1B1 mRNAs were expressed in conceptuses on D12 and D15 of pregnancy. These results showed that ATP1A1 and ATP1B1 were expressed in the uterine endometrium and conceptuses during the estrous cycle and pregnancy in a pregnancy status- and stage-specific manner. These suggest that Na+/K+-ATPase may play a key role in the establishment and maintenance of pregnancy by regulating intracellular concentrations of various ions including calcium at the maternal-fetal interface in pigs.

Proteases and their inhibitors are involved in the process of pregnancy by remodeling uterine endometrium and placenta in many mammals. During placentation, proteases and their inhibitors contribute to formation of epitheliochorial type placentation in pigs. Our previous study showed that LGMN and CST6 were expressed in the uterine endometrium and localized mainly to glandular epithelial cells (GE) and chorionic membrane (CM) during mid to late pregnancy. In this study, we investigated expression of LGMN and CST6 in the uterine endometrium and fetal membrane during pregnancy in pigs. Uterine endometrial tissue samples and fetal membrane samples were collected from D30, D60, D90, and D114 of pregnancy. Real-time RT-PCR analysis showed that both LGMN and CST6 mRNAs were detected in the uterine endometrium and fetal membrane in all samples with higher levels during mid to late stage of pregnancy. Analysis by immunoblotting revealed that LGMN protein was present in the porcine uterine endometrium and fetal membrane. Based on the placental and endometrial distribution of proteases and their inhibitors, we examined LGMN mRNA and LGMN protein expression in the neonatal pigs. In situ hybridization analysis using the intestine from D90 of piglet revealed that LGMN mRNA was highly expressed in the absorptive epithelium of the intestinal villi. Immunohistochemical experiments demonstrated that LGMN protein was localized to epithelial villi. These results suggest a possible role of LGMN in modification of proteins that are transported through the fetal membrane from the uterine for successful transport and utilization in the fetus.

Prostaglandins (PGs) are critical lipid mediators involved in many reproductive processes including luteolysis, maternal recognition of pregnancy, and implantation in domestic animals. In pigs, PGs, especially PGE2 and PGF2α, are produced in the uterine endometrium. The actions of PGE2 and PGF2α are mediated by signaling receptors, PTGERs and PTGFR, respectively, but their expression in the uterine endometrium is not well elucidated. In this study, we determined expression of PTGERs and PTGFR in the uterine endometrium during the estrous cycle and pregnancy in pigs. Uterine endometrial tissue samples were collected from Day (D) 12 and D15 of the estrous cycle and from D12, D15, D30, D60, D90, and D114 of pregnancy. Temporal expression of all genes studied was analyzed by real-time RT-PCR. PTGERs except for PTGER1 were expressed in the uterine endometrium during the estrous cycle and pregnancy. Levels of PTGER2 and PTGER3 mRNA increased during early pregnancy and late pregnancy, respectively, and levels of PTGER4 mRNA were not changed during pregnancy. Levels of PTGFR mRNA were highest on D90 of pregnancy. Results of this study showed that expression of PG receptors was dynamically regulated in the uterine endometrium during pregnancy in pigs. These results indicate that actions of PGs are dependent on types of receptors and is critical to support the establishment and maintenance of pregnancy at the maternal-fetal interface in pigs.

Successful pregnancy requires suppression of maternal immune response to the implanting conceptus, which acts as a semiallograft. During the implantation period in humans and rodents, various immune modulators are produced at the maternal-fetal interface and regulate functions of cytotoxic T cells and NK cells for protection of conceptuses from the maternal immune system. However, maternal immune responses to the conceptuses during the establishment and maintenance of pregnancy are not much understood in pigs which show true epitheliochorial type placentation. Previously, we reported that SLA-DQ molecule, a type of MHC class II molecules, is expressed in the uterine endometrium during pregnancy in a stage- and cell type specific manner, and that SLA-DQ expression is essential for the maintenance of pregnancy. Thus, to understand the role of SLA-DQ and maternal-fetal immune interaction, we examined expression of CD80 and CD86, co-stimulators for T cell activation, in the uterine endometrium during pregnancy. We also measured levels of CD80 and CD86 mRNAs in the uterine endometrium of pigs carrying conceptuses derived from somatic cell nuclear transfer (SCNT) and those from natural mating on Day 12 of pregnancy. Expression of endometrial CD80 mRNA was affected by day of pregnancy, and levels of CD80 mRNA were significantly higher on Day 15 of pregnancy than those of the estrous cycle. Expression of CD86 mRNA did not change during pregnancy. Levels of CD80 and CD86 mRNAs were not different in the uterine endometrium of pigs carrying SCNT derived conceptuses on D12 of pregnancy compared to those with conceptuses derived from natural mating. These findings suggest that CD80 and CD86 are involved in immune interactions at the maternal-fetal interface during pregnancy for the establishment and maintenance of pregnancy in pigs.

Successful pregnancy requires well-coordinated interactions between the maternal uterus and the developing embryo in pigs. In pigs, implantation begins around Day 12 of pregnancy. During this period, conceptus undergoes a dramatic morphological change and secretes various factors such as estrogens, interleukin-1 beta (IL1B), and interferons. Estrogens produced by conceptuses act as the signal for maternal recognition of pregnancy, and the mechanism of estrogen action is explained by the endocrine and exocrine theory. The uterine endometrium becomes receptive to the conceptus by changing cell adhesion molecules, polarizing epithelial cells and increasing secretory activity. Some changes of uterine activity are affected by the ovarian hormone, progesterone, but the presence of conceptus in the uterus also induces changes of endometrial functions, including most importantly maternal recognition of pregnancy. Many factors, such as hormones, cytokines, enzymes, extracellular matrix proteins, and transport proteins are reported to be present at the maternal-fetal interface and function in the establishment of pregnancy in pigs. However, understanding of the cellular and molecular events occurring in the endometrium is not complete. In recent studies we made some progress on understanding of expression and function of genes involved in maternal-fetal interaction for the establishment and maintenance of pregnancy in the uterine endometrium in pigs. Firstly, we found that lysophosphatidic acid (LPA) was present at the maternal-and fetal interface at the time of implantation and LPA receptor 3 was uniquely expressed in the endometrium during early pregnancy. Secondly, we observed that salivary lipocalin (SAL1), a lipid-binding protein, was uniquely expressed in the uterine endometrium at the time of embryo implantation, and its expression was regulated by IL1B. Furthermore, expression of IL1B receptors are regulated by estrogen and IL1B, and IL1B functions in expression of genes related to prostaglandin synthesis and transport. Thirdly, we found that calcium regulatory molecules TRPV6 and S100G were dynamically regulated in the uterine endometrium during pregnancy, suggesting that regulation of calcium ion concentration may important for the embryo implantation and the maintenance of pregnancy. Finally, we observed that an MHC class II molecule, SLA-DQ, is expressed in the uterine endometrium at the time of conceptus implantation and its expression is essential for successful pregnancy, indicating that appropriate maternal-fetal immune interaction is required for the maintenance of pregnancy. Further analysis of these molecules will provide insights into the cellular and molecular basis of maternal-and fetal interaction during pregnancy in pigs.