The Role of Endometrial Selectins and Their Ligands on Bovine Conceptus Attachment to the Uterine Epithelium During Peri-Implantation Period1

Abstract

A successful pregnancy depends on the blastocyst's implantation to the maternal endometrium; however, the initial interaction between blastocyst and uterine epithelium has not been well characterized. The objectives of this study were to determine if selectins and their ligands were expressed in the bovine conceptus and/or uterus during the periattachment period and to study whether selectins were associated with conceptus attachment to the uterine epithelium. Through the RNA-sequence analysis of bovine conceptuses on Days 17, 20, and 22 (Day 0 = day of estrus), only the SELL ligand, podocalyxin (PODXL), and P-selectin (SELP) ligand, SELPLG, were found. Quantitative PCR analysis confirmed the presence of PODXL and SELPLG in these conceptuses and revealed that SELL, mRNA and protein, detected in the uterine epithelium but not in conceptuses increased during the periattachment period. In the cultured endometrial epithelial cells (EECs), SELL transcript was up-regulated when uterine flushings from Day 20 pregnant animals were placed onto these cells. SELL was also up-regulated when cultured EECs were treated with progesterone, EGF, or bFGF, but not with IFNT. In the coculture system with EECs and bovine trophoblast CT-1 cells, SELL expression in EECs was effectively reduced by its small interfering RNA; however, IFNT, a marker for CT-1 cell attachment to EECs, was not reduced, nor was a transcription factor of IFNT, CDX2. These observations suggest that the conceptus could attach to the uterine epithelium through the use of endometrial SELL and embryonic selectin ligands, possibly initiating the conceptus attachment process in the bovine species.

Continuous model of conceptus implantation to the maternal endometrium

“…In the human placenta, SELL adhesion system is identified to be essential for forming and maintaining cell columns during early stages of placenta development and mediating cytotrophoblast migration (Prakobphol et al 2006). In our study (Bai et al 2015), SELL expression was detected in bovine endometrial epithelia, not in trophoblasts, and its ligands, P-selectin glycoprotein ligand (SELPLG) and podocalyxin (PODXL), were found in both conceptus and endometrium. Although endometrial epithelial SELL expression is not orthologous to that in humans (Prakobphol et al 2006), cessation of conceptus movement and/or apposition through SELL and PODXL expression is required for the implantation processes in humans as well as bovine species.…”

“…In our studies, although timing of events was not determined precisely, both cell-cell adhesion and EMT-like cell loosening/movement occurred on day 22 of bovine gestation (Yamakoshi et al 2012, Bai et al 2015, Kusama et al 2016b). The treatment with activin A or P22 UF in cocultured CT-1 cells induced characteristics similar to those of EMT (Kusama et al 2016b), which involves downregulation of apicobasal polarity, loss of cell-cell adhesion and expression of MMPs (Moustakas & Heldin 2014).…”

Bovine P-selectin mediates leukocyte adhesion and is highly polymorphic in dairy breeds

“…been implicated in the process of bovine conceptus attachment during which SELL mRNA and protein are both up-regulated on uterine epithelial cells and uterine SELP expression also increases from Day 20 (Bai et al, 2015). In humans, SELL ligand appears to play a key role in blastocyst attachment (Wang et al, 2008) while low levels of uterine expression are associated with implantation failure and infertility (Foulk et al, 2007;Margarit et al, 2009).…”

“…Endometrial SELP expression in the cow increases from Day 20 of gestation (Bai et al, 2015) and SELP polymorphisms in women are associated with recurrent pregnancy losses (Dendana et al, 2012). The precise role of SELP during embryo and placental development remains to be determined.…”

Polymorphisms in the selectin gene cluster are associated with fertility and survival time in a population of Holstein Friesian cows

“…A similar attachment system may be important in the cow as the SELL ligand podocalyxin and PSGL1 were both expressed in the pre-implantation cow conceptus, while SELL and SELP (but not SELE ) were up-regulated in the uterine endometrium between days 17–20 after insemination [42]. Knock-out of the SELL gene or SELL-ligand does not interfere with implantation in mice [43].…”