Expression of Neutral and Cationic Amino Acid Transporters in the Uterine Endometrium, Peri-Implantation Conceptus and Placenta in Pigs.

Abstract

Amino acids, nitric oxide (NO) and polyamines play an important role in implantation and development of conceptus (embryos/fetuses and associated extraembryonic membranes), but mechanisms for endometrial transport and conceptus uptake of the nutrients are not understood in pigs. In this study, we investigated expression of genes that encode transporters for neutral (SLC1A1, SLC1A5 and ASCT1) and cationic amino acids (SLC7A1, SLC7A2, SLC7A7 and SLC7A9) and ornithine decarboxylase (ODC1), a key enzyme for synthesis of polyamines from L-arginine, in the uterine endometrium, peri-implantation conceptus and chorioallantoic placenta in pigs. Uterine endometrial tissues were collected from Days (D) 12 and 15 of the estrous cycle and D12, 15, 30, 60, 90, and 114 of pregnancy. Placental tissues were collected on D30, 60, 90 and 114 of pregnancy. Realtime RT-PCR analyses showed that SLC1A1 and SLC1A5 mRNAs were expressed in the uterine endometrium. Expression of SLC1A1 mRNA increased on D15 of pregnancy and decreased at term, while expression of SLC1A5 and ASCT1 mRNAs increased during mid- to late pregnancy. The abundance of SLC7A1, SLC7A2 and SLC7A9 mRNAs was highest on D12, but maintained at low levels thereafter during pregnancy. Expression of SLC7A7 mRNA was high during early pregnancy, and then low during mid- to late pregnancy. Expression of ODC1 did not change during pregnancy. In situ hybridization analyses determined that SLC1A1, SLC7A7, SLC7A9 and ODC1 mRNAs were localized to luminal and glandular epithelial cells and the chorion of the placenta during pregnancy. To determine whether conceptuses on D12 and D15 of pregnancy express neutral and cationic amino acid transporters and ODC1, we performed RT-PCR analysis and found that ASCT1, SLC1A1, SLC1A5, SLC7A1, SLC7A7 and SLC7A9 mRNAs were detected in conceptuses on D12 and D15 of pregnancy. Further, we analyzed expression of neutral and cationic amino acid transporters and ODC1 in the placenta on D30, 60, 90, and 114 of pregnancy. Realtime RT-PCR analyses revealed that expression of ASCT1 mRNA were biphasic with highest levels on D30 and at term, while expression of SLC7A2, SLC7A9 and ODC1 mRNAs was highest on D30, and then decreased to term. Expression of SLC1A1, SLC1A5, SLC7A1 and SLC7A7 did not change during pregnancy. These results indicate that dynamic changes in expression of amino acid transporters in the endometrium, conceptus and placenta may be critical for survival, growth, and development of pig conceptuses. This research was supported by the Next Generation BioGreen 21 program (#PJ007997), RDA, Republic of Korea.