Expression Of L-selectin And Its Ligand On Maternal-Fetal Interface And Their Impact On Implantation

At the molecular level, there are close links between processes that are key to reproductive, immune, and vascular functions. L-selectin, and its ligands, a pair of important adhesion molecules involved in immune and inflammatory process, have been found on the maternal-fetal interface during mammal implantation. The binding of L-selectin and its ligands, peripheral lymph node addressin (PNAd), mediates lymphocyte homing and adhesion between leukocyte and vascular endothelium. They also function as signal-transducing receptors. Genbacev et al. have found that the binding of L-selectin and its ligands might function as an initiative step in human embryo implantation. During the implantation window, both L-selectin on embryo's surface and its ligands on endometrium seem to undergo upregulation. Up to date, four glycoprotein ligands have been identified for L-selectin, including CD34, mucosal addressin cell adhesion molecule-1 (MAdCAM-1), glycosylation-dependent cell adhesion molecule-1 (GlyCAM-1), and Sgp200 (the latter has not been cloned yet). They were firstly identified on lymph node high endothelial venules of mouse, and collectively termed as peripheral lymph node addressin (PNAd). Sulfatedcarbohydrate structures in ligands are the major domain recognized by L-selectin. N-acetylglucosamine-6-O-sulfotransferase (GlcNAc6ST) functions as a key enzyme in the synthesis of functional ligands for L-selectin.Although L-selectin and its ligands have been found on maternal-fetal interface, there are few reports about their spatial and temporal expression pattern during normal menstrual cycle and early pregnancy. Whether their expression level is associated with successful implantation? Whether they have functional importance in implantation in vivo? These questions are still need to be clarified.In this study, we estimate the expression characteristics of L-selectin on human peri-implantation embryos and its ligands on endometrium throughout the menstrual cycle and during the first trimester of pregnancy. To explore their effect on implantation, we compare the L-selectin ligands (PNAd) and GlcNAc6ST mRNA expression level in secretory phase endometrium between pregnant and nonpregnant patients who underwent in vitro fertilization and embryo transfer (IVF-ET). On the basis of this, we investigate the importance of L-selectin in mouse embryo implantation in vivo.Part One: L-Selectin and Its Ligands (PNAd) Expression on Human Maternal-Fetal InterfaceObjective: To explore the distribution of L-selectin in human peri-implantation embryo and chorion during the first trimester and investigate the spatial and temporal expression of L-selectin ligands (PNAd) in endometrium and deciduas.Methods: (1) L-selectin expression was examined by immunofluorescence in 20 peri-implantation embryos from IVF-ET program (morula, n=8; blastocyst, n=12) and 5 cases of chorion during the first trimester from pregnant women whounderwent induced abortion without medical indications. (2) Immunohistochemistry and Western Blotting were used to examine PNAd expression in endometrium from 76 women (12 from healthy women, in proliferative phase; 64 from sterile women suffering from tubal or male factor, among them, 28 in early-secretory, 36 in mid-secretory phase) and deciduas from 13 women during the first trimester of pregnancy.Results: (1) L-selectin was expressed in membrane and cytoplasma of morula (8/8), blastocyst (12/12, including inner cell mass and trophoblast) and chorion (5/5) in the first trimester, and no significant difference was observed among the above three stages (P>0.05). (2) PNAd localized to the membrane and cytoplasm of luminal and glandular epithelia. Staining was patchy and much less intense during the proliferative phase and deciduas than the secretory phase. In Western Blotting of PNAd, four bands appeared, which were Sgp200, CD34, MAdCAM-1, and GlyCAM-1 respectively, and each was positively correlated with the others significantly (r=0.340~0.718, .P<0.05). The former three molecule levels were significantly higher during secreto...