Uterine Receptivity For Blastocyst Implantation Research Articles

Uterine glands impact uterine receptivity, luminal fluid homeostasis and blastocyst implantation.

Uterine glands are essential for pregnancy in mice and likely humans, because they secrete or transport bioactive substances that regulate uterine receptivity for blastocyst implantation. In mice, the uterus becomes receptive to blastocyst implantation on day 4, but is refractory by day 5. Here, blastocysts could be recovered from progesterone-induced uterine gland (PUGKO) but not wildtype (WT) mice on day 5 post-mating. Anti-adhesive Muc1 protein and microvilli were present on the luminal epithelium of PUGKO but not WT uteri. A number of known uterine receptivity genes and gland-specific genes were altered in the PUGKO uterus. Next, the uterus and uterine luminal fluid (ULF) were obtained from WT and PUGKO mice on day 3, 4 and 5. Transcriptome analysis revealed that 580 genes were decreased in the PUGKO uterus, however ULF secrotome analysis revealed that many proteins and several amino acids were increased in the PUGKO ULF. Of note, many proteins encoded by many gland-specific genes were not identified in the ULF of WT mice. These results support the ideas that uterine glands secrete factors that regulate ULF homeostasis and interact with other cell types in the uterus to influence uterine receptivity and blastocyst implantation for the establishment of pregnancy.

Angiogenesis and Hormonal Regulation on Uterine Receptivity for Blastocyst Implantation

Abstract: Synchronization of embryonic development and differentiation of specific uterine cell types to a receptive state is essential for a successful pregnancy. The period of uterine receptivity for implantation is limited. Increased vascular permeability and angiogenesis are hallmarks of the implantation process. Although implantation involves the interaction of numerous signaling molecules, the hierarchical mechanisms that coordinate the embryo—uterine dialog remain poorly understood. This review highlights our knowledge about angiogenesis, uterine receptivity, and hormonal regulation for blastocyst implantation in the mouse. A better understanding of uterine biology during the peri-implantation period would facilitate the further development of reproductive technology.

Uterine epithelial cells: Serving two masters

Uterine epithelial cells are unique cells in that they are both epithelial in the typical barrier sense but in many mammalian species, they characteristically allow the blastocyst to penetrate them from the apical surface. Here we examine how these cells subserve both functions and in particular we synthesize recent evidence on focal adhesions and how these membrane structures contribute to uterine receptivity for blastocyst implantation. Focal adhesions emerge as a dynamic new player in the ‘plasma membrane transformation’ of early pregnancy and uterine receptivity in that they disassemble at the time of implantation in common with many other structures on the basolateral plasma membrane of these cells.

Extended uterine receptivity for blastocyst implantation and full-term fetal development in mice with vitrified-warmed ovarian tissue autotransplantation.

Our previous study demonstrated that vitrified-warmed ovarian tissue autotransplantation (VOAT) into estrus cycle-ceased ovariectomized mice restored fertility to achieve full-term fetal development for transferred embryos, while less steroidogenesis in the corpus luteum was observed in VOAT mice. It has been reported that the window of uterine receptivity for blastocyst implantation is extended at lower estrogen levels. Therefore, we hypothesized that duration of the window in VOAT mice could be extended. Blastocysts were transferred into VOAT mice on day 5 of pseudopregnancy. Immunohistochemical analysis was performed to examine the potential in VOAT ovarian tissues. The rate of live birth pups from embryos transferred on day 5 of pseudopregnant VOAT mice was not different from that of embryos transferred on day 4 of pseudopregnancy in VOAT mice, while embryo transfer on day 5 into intact mice showed no pregnancy. Immunohistochemical analysis of the corpus luteum of day 8 pseudopregnant VOAT mice with uteri having decidualization induced on day 5 showed less steroidogenesis and blood vessel formation as compared to intact mice. Uterine receptivity was extended in VOAT mice. Less steroidogenesis and blood vessel formation in the transferred ovarian tissues may be associated with the extended uterine receptivity.

Insights from Mechanism Involved in Uterine Receptivity for Blastocyst Implantation in Mouse

Insights from Mechanism Involved in Uterine Receptivity for Blastocyst Implantation in Mouse

Progesterone supplementation extends uterine receptivity for blastocyst implantation in mice

We previously showed that blastocyst can initiate implantation beyond the normal 'window' of uterine receptivity on day 5 of pregnancy and pseudopregnancy (PSP) in mice. In this study, we investigated whether uterine receptivity for blastocyst implantation can be further extended on day 6 of PSP and the role of progesterone (P(4)) on this event. Embryo transfers, experimentally induced decidualization, in situ hybridization and [(3)H]thymidine incorporation were performed. Blastocysts initiate attachment reaction within 48 h when transferred on day 5, but not on day 6 of PSP. Likewise, decidualization reaction occurred on days 4 and 5 of PSP, but completely failed on day 6. However, P(4) supplementation partially retains uterine receptivity for blastocyst implantation and decidualization on day 6 of PSP. In addition, certain indicators of uterine receptivity, such as cell proliferation profile and expression patterns of implantation-related genes were similarly observed on days 4 and 5 of PSP, but not on day 6. Consistent with embryo transfer and decidualization, exogenous administration of P(4) partially restores these indicators on day 6 of PSP. We concluded that critical physiological changes occur between days 4 and 5 of PSP, leading to uterine non-receptivity on day 6, but P(4) is able to extend the uterine receptivity through day 6.

Redistribution of aquaporins 1 and 5 in the rat uterus is dependent on progesterone: a study with light and electron microscopy

During early pregnancy in the rat there is a dramatic reduction in luminal fluid which is associated with uterine receptivity for blastocyst implantation. This study investigates the presence and distributional changes of several members of the aquaporin (AQP) family in the rat uterus in response to hormonal regime. An increase in apical AQP5 protein expression was found in response to progesterone alone or in combination with oestrogen, which is similar to that seen at the time of implantation. AQP1 was found in endothelial cells of the endometrium and in the inner circular layer of smooth muscle, with maximal protein expression seen after three doses of progesterone plus 8 hr of oestrogen treatment. These results, for the first time, show that the up-regulation of AQP5 in the apical plasma membrane of uterine epithelial cells and AQP1 in the inner circular layer of myometrium, is dependent on progesterone. Furthermore, unlike during normal pregnancy, there is no differential gradient of AQP5 expression between mesometrial and antimesometrial poles of the progesterone treated uterus. Hence it is suggested that the differential gradient of AQP5 is dependent on the presence of a blastocyst, in addition to the appropriate hormonal environment.

Physiological Effects of Dietary Phytoestrogens

In the mouse, the coordinated effects of ovarian estrogen (estradiol-17β, E 2 ) and progesterone (P 4 ) regulate uterine cell proliferation and differentiation, thereby determining the timing of uterine receptivity for blastocyst implantation. After relocation of their research program, Wang et al . noted variability in responses to ovarian hormones and undertook an investigation of the role of diet-derived phytoestrogens in modulating the uterine response to endogenous steroid hormones. Mice were fed with one of two brands of mouse chow with similar composition but different isoflavone content, 5V00 [less than 50 parts per million (ppm) isoflavones] or 5001 (more than 400 ppm isoflavones). When maintained on these diets for 8 weeks and ovariectomized 2 weeks before sacrifice, mice on the 5001 diet had higher uterine weight compared with 5V00 mice, exhibited bromodeoxyuridine incorporation into uterine epithelial cells, and showed an enhanced response (increased uterine weight) to treatment with E 2 or P 4 . The authors used reverse transcription polymerase chain reaction (RT-PCR) to show that 5001 mice had increased abundance of mRNAs encoding the estrogen target genes PR (nuclear progesterone receptor), LF (lactoferrin), and LIF (leukemia inhibitory factor) and decreased abundance of ERα (nuclear estrogen receptor α) and sFRP2 (secreted frizzled related protein 2). Consistent with this, immunohistochemical analysis indicated that 5001 mice had increased PR abundance and decreased ERα abundance compared with the 5V00 mice. Finally, the authors observed that the temporal window during which blastocyst implantation occurred was advanced by about 4 hours in nonovariectomized mice fed the high-phytoestrogen diet. Thus, the authors conclude that, at least in mice, dietary phytoestrogens can modulate the response to endogenous hormones and influence their physiological effects. H. Wang, S. Tranguch, H. Xie, G. Hanley, S. K. Das, S. K. Dey, Variation in commercial rodent diets induces disparate molecular and physiological changes in the mouse uterus. Proc. Natl. Acad. Sci. U.S.A. 102 , 9960-9965 (2005). [Abstract] [Full Text]

Cytoskeletal proteins in uterine epithelial cells only partially return to the pre-receptive state after the period of receptivity

Immunohistochemical staining of 5 cytoskeletal proteins (actin, alpha-actinin, gelsolin, plectin and plakoglobin) was used to investigate changes in distribution patterns of these proteins after the period of uterine receptivity for blastocyst implantation in the rat. Actin was found throughout the cytoplasm but it was concentrated along the apical plasma membrane on day 1 of pregnancy, decreased by day 6 and then increased again at day 9. Alpha-actinin and gelsolin were localized in distinctive bands along the apical plasma membrane at day 6 of pregnancy but became diffusely distributed at day 9. Plectin was localized along the apical and basal plasma membranes at day 6 but in higher amounts apically and at day 9, it was concentrated in apical and basal zones in the cells. Plakoglobin was found along the lateral and basal membranes with increased intensity along the apical third of the lateral plasma membrane from day 6 to day 9 of pregnancy. These results show that all 5 cytoskeletal proteins redistributed after the period of uterine receptivity: some exhibited a similar pattern of labelling to that found during the prereceptive state, whereas others only partially returned to the pre-receptive state. This change in distribution patterns may reflect differences in the epithelial barrier function before and after the period of receptivity.

Models for the study of uterine receptivity for blastocyst implantation.

A variety of models have been developed to study endometrial receptivity which involves normal, appropriately timed endometrial development and remodeling for blastocyst attachment and trophoblast invasion during the luteal phase of the menstrual cycle. Due to species differences, the human is by far the best model per se by which to study human endometrial receptivity. Techniques have evolved to obtain in vivo data on endometrial receptivity using hysteroscopy, ultrasonography or magnetic resonance imaging. Despite species differences, comparative studies of mammalian models and tissue- and cell culture models using endometrial tissue or cells harvested at particular phases of the reproductive cycle, or following experimental manipulation, have been used productively to study endometrial function. Differences as well as similarities have proven to be instructive. Such models have been used to study a variety of entities, such as homotypic and heterotypic cell-cell interaction, the role of steroids, cytokines, growth factors, immunomodulatory agents and pharmacological substances. These models have also been used to study cellular, biochemical and molecular mechanisms involved with uterine receptivity. This chapter was designed to provide a critical review of contemporary literature relating to in vivo models and laboratory strategies and paradigms for the study of uterine receptivity for blastocyst implantation.

Coordination of Differential Effects of Primary Estrogen and Catecholestrogen on Two Distinct Targets Mediates Embryo Implantation in the Mouse**This work was supported, in part, by NIH Grant HD-12304 and as part of the National Cooperative Program on Markers of Uterine Receptivity for Blastocyst Implantation [NIH Grants HD-29968 (to S.K.D.), HD-35114 (to B.C.P.), and ES-07814 (to S.K.D.)]. A center grant in

In the mouse, estrogen is essential for blastocyst implantation in the progesterone (P4)-primed uterus. The mechanism(s) by which estrogen initiates this response still remains elusive. The present investigation, using delayed implantation in the mouse, examined the differential role of estradiol-17beta (E2) and its catechol metabolite 4-hydroxy-E2 (4-OH-E2) in uterine and blastocyst activation for implantation. The conditions of delayed implantation were induced by ovariectomizing mice on day 4 (day 1 = vaginal plug) of pregnancy or pseudopregnancy and maintaining them with P4 from days 5-7. The binding of EGF to blastocysts was used as a marker for blastocyst activation. Our results show that whereas E2 fails to activate dormant blastocysts (with respect to EGF binding in vitro), 4-OH-E2, cAMP, or prostaglandin E2, is effective in this response. Further, whereas 4-OH-E2 induced-activation is not blocked by an antiestrogen, an inhibitor of PG synthesis, adenylyl cyclase or protein kinase A effectively blocks this activation. These results suggest that 4-OH-E2 effects on blastocysts are mediated by PGs, which, in turn, stimulate cAMP production and thus activation of protein kinase A. Two-fluoro-E2 is a poor substrate and an inhibitor of catecholestrogen synthesis, but it is estrogenic, with respect to uterine growth and gene expression. Using blastocyst transfer experiments, we observed that dormant blastocysts incubated with 4-OH-E2 in vitro, but not with E2, are capable of implanting in P4-treated delayed implanting mice receiving two-fluoro-E2. The results suggest that whereas E2 is necessary for preparation of the uterus, uterine-derived catecholestrogen is important for blastocyst activation for implantation. Indeed, the receptive uterus has the capacity to synthesize 4-OH-E2. Collectively, we demonstrate that the primary ovarian estrogen E2, via its interaction with nuclear estrogen receptors, participates in the preparation of the P4-primed uterus to the receptive state in an endocrine manner, whereas its metabolite 4-OH-E2, produced from E2 in the uterus, mediates blastocyst activation for implantation in a paracrine manner. Our results also establish that these target-specific effects of primary estrogen and catecholestrogen are both essential for implantation and that successful implantation occurs only when the activated stage of the blastocyst coincides with the receptive state of the uterus.

Endometrial prostaglandin E2 binding: characterization in rats sensitized for the decidual cell reaction and changes during pseudopregnancy.

As an initial step in testing the hypothesis that uterine receptivity for blastocyst implantation and sensitivity for decidualization are controlled in part by the presence of functional receptors for prostaglandin E2 (PGE2) in the endometrium, we have characterized the high-affinity binding of [3H]PGE2 to an endometrial membrane preparation from ovariectomized rats treated with progesterone and estradiol so that their uteri were sensitized for the decidual cell reaction. As determined by Scatchard analysis, a single class of [3H]PGE2 binding sites with an apparent Kd ranging from 2 to 6 nM and a capacity of approximately 100 fmol/mg protein was found. Prostaglandins E1 and E2 competed equally for binding while relative cross-reactivity of other prostanoids and compounds tested was less than 3%. Binding was temperature-dependent and reversible. Under the assay conditions used, no metabolism of [3H]PGE2 was detectable. Pretreatment of the membrane preparation with proteolytic enzymes, or by heating, reduced subsequent specific [3H]PGE2 binding. These data are consistent with the presence of endometrial PGE receptors in the sensitized endometrium. The binding of [3H]PGE2 to endometrial membrane preparations from rats on Days 2 to 7 pseudopregnancy was determined. No specific binding could be detected on Day 2. A low binding capacity was found on Days 3 and 4; this increased markedly on Day 5 and reached a maximum on Day 6. These data indicate that the onset of uterine receptivity/sensitivity is temporally correlated with the appearance of endometrial PGE binding sites.