Subcellular localization of L-selectin ligand in the endometrium implies a novel function for pinopodes in endometrial receptivity

Abstract

BackgroundApical surfaces of human endometrial epithelium and endothelium are key elements for the initiation of molecular interactions to capture the blastocyst or leukocyte, respectively. The L-selectin adhesion system has been strongly proposed to play an important role in the initial steps of trophoblast adhesion and promotion of integrin-dependent processes, ultimately culminating in the establishment of the embryo-maternal interface. On the basis of these facts, we hypothesized a novel role for pinopodes as the first embryo-fetal contact sites to contain the highest subcellular expression of L-selectin ligand suggesting its role in early adhesion as predicted. Thus, the objective of this study was therefore to determine the subcellular pattern of distribution of the L-selectin ligand (MECA-79) in human endometrial apical membrane region during the window of implantation.MethodsEndometrial biopsies of secretory phases from fertile females ranging in age between 25 and 42years were studied using several approaches, including scanning electron microscopy (SEM), immunostaining for light microscopy and transmission electron microscopy (TEM), and immunoblotting as well as statistical analysis of the area-related numerical densities of immunoreactive MECA-79-bound nanogolds to detect the expression pattern and the subcellular distribution pattern of L-selectin ligand (MECA-79) in human endometrium during the window of implantation.ResultsThe endometrial biopsies were scored according the dating criteria of Noyes et al. by an experienced histologist. The SEM images of the midluteal phase specimens revealed that fully developed pinopodes were abundant in our samples. HRP-immunostaining and immunofluorescent staining as well as immunoblotting revealed that MECA-79 was expressed in the midluteal phase specimens. The results of immunogold TEM illustrated the expression of MECA-79 in human pinopodes in the midluteal phase and a higher area-relate numerical density in pinopodes compared to that of the uterodome-free areas.ConclusionsThis is the first demonstration of the subcellular localization of MECA-79 in the human pinopodes which may indicate a novel role for pinopodes to be capable of shear-stress-dependent tethering-type adhesion in the initial phases of human embryo implantation.

Decreased expression of aquaporin 2 is associated with impaired endometrial receptivity in controlled ovarian stimulation

“…the maternal-fetal interface and impairs endometrial receptivity (Nejatbakhsh et al 2012;Rashidi et al 2012). Our results suggest that COS has an adverse effect on water movement and balance of uterine luminal epithelial cells.…”

Physiological and molecular determinants of embryo implantation

“…L-selectin was previously thought to be expressed only in hematopoietic cells due to its essential role in adhesion between lymphocytes and high endothelial venules (Berg et al, 1993). Intriguingly, human trophoblasts also express functional L-selectin, while its ligand oligosaccharides are detected mainly in pinopodes, the apical cellular protrusions of the endometrial epithelium where blastocyst adhesion initiates (Genbacev et al, 2003; Nejatbakhsh et al, 2012). These findings indicate a potential interaction between L-selectin in human blastocysts and oligosaccharide ligands on the endometrial epithelium as an initial step in human implantation.…”

Embryo–epithelium interactions during implantation at a glance

“…Embryos initially form tenuous and reversible attachments to epithelial cells. The mucin-associated fucosylated glycans sulpho-sialyl Lewis X, Lewis Y (SsLe x and Le y , respectively) and H type 1 are candidates for mediating this interaction, either by direct binding of H type 1 to Le y or by binding of SsLe x to L-selectin on the embryo (Aplin and Jones, 2012;Aplin and Kimber, 2004;Jones and Aplin, 2009;Genbacev et al, 2003;Kimber et al, 2001;Nejatbakhsh et al, 2012;Zhang et al, 2009;Lindenberg et al, 1988;Wang et al, 1998;Zhu et al, 1995). Le y appears to have a role in embryo attachment after the clearance of mucin from the glycocalyx , including in the modulation of signalling through the epidermal growth factor receptor (EGFR) and/or mitogen-activated protein kinase (MAPK) pathway .…”