The chemokine receptor CXCR4 and its ligand CXCL12 are activated during implantation and placentation in sheep

Role of chemokines in regulating luteal and uterine functions in pregnant cows

Pregnancy is intricately regulated by the interactions between various bioactive substances secreted by the conceptus, uterus, and corpus luteum (CL). Interferon-τ, synthesized and secreted by the conceptus, plays a central role in the interaction mechanism of maternal recognition in cows. Chemokines, chemotaxis mediators that are primarily secreted by immune cells, regulate various reproductive responses in various species. Although there are scattered reports on the potential roles of chemokines in the bovine CL and the uterus during the estrous cycle, there is little information on chemokines in these organs during pregnancy. Therefore, in this review, we discuss the possible physiological roles of chemokines in the CL and uterus of pregnant cows, focusing on our recent findings on chemokines and changes in their receptor expression in the CL and endometrium of cows at some stages of pregnancy.

LncRNA STAT3-AS regulates endometrial receptivity via the STAT3 signaling pathway

Endometrial receptivity is critical for the successful establishment of pregnancy in ruminants. Interferon tau (IFNT) plays a key role in promoting embryo attachment by activating the Janus kinase/signal transducer and activator of transcription pathway, which induces the expression of a series of interferon-stimulated genes (ISGs). In our previous study, sequencing analysis of goat endometrial epithelial cells (gEECs) treated with 20 ng/mL IFNT revealed a differentially expressed long non-coding RNA located on the STAT3 antisense chain, which we designated STAT3-AS. The aim of this study was to investigate the role and mechanism of STAT3-AS in establishing endometrial receptivity in goats. The results showed that STAT3-AS was expressed in both the nucleus and cytoplasm of gEECs, and its expression increased significantly in the uterus on day 15 of pregnancy. STAT3-AS expression was upregulated in gEECs treated with IFNT alone or in combination with progesterone and estradiol. Knockdown of STAT3-AS using specific short interfering RNA significantly inhibited the expression of classical ISGs such as interferon-stimulated gene 15 and 2',5'-oligodenylate synthetase 2, as well as uterine endometrial receptivity-related genes including homeobox gene A11, integrin beta 3, and vascular endothelial growth factor. Moreover, gEEC proliferation and the STAT3 pathway were suppressed in the absence of STAT3-AS. However, pretreatment with the STAT3 activator RO8191 restored the effect of silencing STAT3-AS on endometrial receptivity. Overall, these results suggest that STAT3-AS is an important regulator of endometrial receptivity in goats and that it regulates endometrial receptivity through the STAT3 pathway.

Placental insufficiency and heavier placentas in sheep after suppressing CXCL12/CXCR4 signaling during implantation†

During implantation, trophoblast cell invasion and differentiation is predominantly important to achieving proper placental formation and embryonic development. The chemokine, C-X-C motif chemokine ligand 12 (CXCL12) working through its receptor C-X-C motif chemokine receptor 4 (CXCR4) is implicated in implantation and placentation but precise roles of this axis are unclear. Suppressing CXCL12/CXCR4 signaling at the fetal-maternal interface in sheep reduces trophoblast invasion, disrupts uterine remodeling, and diminishes placental vascularization. We hypothesize these negative impacts during implantation will manifest as compromised fetal and placental growth at midgestation. To test, on day 12 postbreeding, osmotic pumps were surgically installed in 30 ewes and delivered intrauterine CXCR4 inhibitor or saline for 7 or 14 days. On day 90, fetal/maternal tissues were collected, measured, weighed, and maternal (caruncle) and fetal (cotyledon) placenta components separated and analyzed. The objectives were to determine if (i) suppressing CXCL12/CXCR4 during implantation results in reduced fetal and placental growth and development and (ii) if varying the amount of time CXCL12/CXCR4 is suppressed impacts fetal/placental development. Fetal weights were similar; however greater placental weight and placentome numbers occurred when CXCL12/CXCR4 was suppressed for 14 days. In caruncles, greater abundance of fibroblast growth factor 2, vascular endothelial growth factor A, vascular endothelial growth factor A receptor 1 (FLT-1), and placental growth factor were observed after suppressing CXCL12/CXCR4. Similar results occurred in cotyledons except less vascular endothelial growth factor in 7 day group and less fibroblast growth factor in 14 day group. Our data underscore the importance of CXCL12/CXCR4 signaling during placentation and provide strong evidence that altering CXCL12-mediated signaling induces enduring placental effects manifesting later in gestation.

Maternal CXCR4 deletion results in placental defects and pregnancy loss mediated by immune dysregulation

CXCR4 is a key regulator of the development of NK cells and DCs, both of which play an important role in early placental development and immune tolerance at the maternal-fetal interface. However, the role of CXCR4 in pregnancy is not well understood. Our study demonstrates that adult-induced global genetic CXCR4 deletion, but not uterine-specific CXCR4 deletion, was associated with increased pregnancy resorptions and decreased litter size. CXCR4-deficient mice had decreased NK cells and increased granulocytes in the decidua, along with increased leukocyte numbers in peripheral blood. We found that CXCR4-deficient mice had abnormal decidual NK cell aggregates and NK cell infiltration into trophoblast areas beyond the giant cell layer. This was associated with low NK cell expression of granzyme B, a NK cell granule effector, indicative of NK cell dysfunction. Pregnancy failure in these mice was associated with abnormalities in placental vascular development and increased placental expression of inflammatory genes. Importantly, adoptive BM transfer of WT CXCR4+ BM cells into CXCR4-deficient mice rescued the reproductive deficits by normalizing NK cell function and mediating normal placental vascular development. Collectively, our study found an important role for maternal CXCR4 expression in immune cell function, placental development, and pregnancy maintenance.

USP18 promotes endometrial receptivity via the JAK/STAT1 and the ISGylation pathway

Interferon-tau (IFNT), a pregnancy recognition signal in ruminants, promotes the establishment of endometrial receptivity by inducing the expression of interferon-stimulated genes (ISGs) via the Janus kinase/signal transducer and activator of transcription (JAK/STATs) signaling pathway. However, the precise mechanisms remain largely unknown. Ubiquitin-specific protease 18 (USP18) acts specifically on the ISGylation modification system to exert deubiquitination and participates in the regulation of the type I IFN signaling pathway. The purpose of this study was to determine the role and mechanism of USP18 on endometrial receptivity in goat. USP18 was mainly localized in the uterine luminal and glandular epithelium, and its expression levels were significantly increased from days 5-18 of early pregnancy. Progesterone (P₄), estradiol (E₂), and IFNT significantly stimulated USP18 expression in goat endometrial epithelial cells (gEECs) cultured in vitro. Meanwhile, the markers of endometrial receptivity HOXA11, ITGB1, ITGB3, and ITGB5 were significantly upregulated after USP18 overexpression in gEECs. However, USP18 interference significantly inhibited the expression of HOXA10, ITGB1, ITGB3, and ITGB5 in gEECs. In addition, both the phosphorylation levels of STAT1 and the expression of ISGylation-modified proteins were significantly increased after USP18 silencing in gEECs. Furthermore, pretreatment with the STAT1 inhibitor Fludara markedly restored the effect of USP18 interference in gEECs. In summary, USP18 may play an important role in promoting goat endometrial receptivity by regulating the JAK/STAT1 pathway and ISGylation.

Regulation and Function of Chemokines at the Maternal–Fetal Interface

Successful pregnancy requires the maternal immune system to tolerate the semi-allogeneic embryo. A good trophoblast function is also essential for successful embryo implantation and subsequent placental development. Chemokines are initially described in recruiting leukocytes. There are rich chemokines and chemokine receptor system at the maternal–fetal interface. Numerous studies have reported that they not only regulate trophoblast biological behaviors but also participate in the decidual immune response. At the same time, the chemokine system builds an important communication network between fetally derived trophoblast cells and maternally derived decidual cells. However, abnormal functions of chemokines or chemokine receptors are involved in a series of pregnancy complications. As growing evidence points to the roles of chemokines in pregnancy, there is a great need to summarize the available data on this topic. This review aimed to describe the recent research progress on the regulation and function of the main chemokines in pregnancy at the maternal–fetal interface. In addition, we also discussed the potential relationship between chemokines and pregnancy complications.

Ruminant conceptus-maternal interactions: interferon-tau and beyond

Embryonic or fetal loss in cattle is associated with problems that occur during oocyte maturation, early embryonic development, conceptus elongation, maternal recognition of pregnancy (MRP), and/or placental attachment and implantation. Many of these problems manifest as inadequate or asynchronous communication between the developing conceptus and endometrium, resulting in pregnancy failure. This review will provide an overview of how various conceptus-endometrial paracrine signaling systems control the fate of early pregnancy in cattle and other ruminants. We begin by summarizing the actions of interferon-tau, the classic MRP signal in ruminates, and then explore how other secretory factors derived from either the conceptus or endometrium influence establishment and maintenance of pregnancy. Insight into how the endometrium responds to male vs. female conceptuses or conceptuses produced by in vitro methods will also be described. Specific focus will be placed on describing how "omic" technologies and other cutting-edge techniques have assisted with identifying novel conceptus and/or endometrial factors and their functions. Recent findings indicate that the endometrial transcriptome and histotroph are altered by conceptus sex, quality, and origin, suggesting that the endometrium is a sensor of conceptus biochemistry. Although the endometrium has a certain level of flexibility in terms of conceptus-maternal interactions, this interplay is not sufficient to retain some pregnancies. However, new information inspires us to learn more and will help develop technologies that mitigate early embryonic loss and reproductive failure in ruminants and other animals.

Chemokine C-X-C receptor 4 mediates recruitment of bone marrow-derived nonhematopoietic and immune cells to the pregnant uterus†

Bone marrow-derived progenitor cells (BMDPCs) are mobilized to the circulation in pregnancy and get recruited to the pregnant decidua where they contribute functionally to decidualization and successful implantation. However, the molecular mechanisms underlying BMDPCs recruitment to the decidua are unknown. CXCL12 ligand and its CXCR4 receptor play crucial roles in the mobilization and homing of stem/progenitor cells to various tissues. To investigate the role of CXCL12-CXCR4 axis in BMDPCs recruitment to decidua, we created transgenic GFP mice harboring CXCR4 gene susceptible to tamoxifen-inducible Cre-mediated ablation. These mice served as BM donors into wild-type C57BL/6 J female recipients using a 5-fluorouracil-based nongonadotoxic submyeloablation to achieve BM-specific CXCR4 knockout (CXCR4KO). Successful CXCR4 ablation was confirmed by RT-PCR and in vitro cell migration assays. Flow cytometry and immunohistochemistry showed a significant increase in GFP+ BM-derived cells (BMDCs) in the implantation site as compared to the nonpregnant uterus of control (2.7-fold) and CXCR4KO (1.8-fold) mice. This increase was uterus-specific and was not observed in other organs. This pregnancy-induced increase occurred in both hematopoietic (CD45+) and nonhematopoietic (CD45-) uterine BMDCs in control mice. In contrast, in CXCR4KO mice there was no increase in nonhematopoietic BMDCs in the pregnant uterus. Moreover, decidual recruitment of myeloid cells but not NK cells was diminished by BM CXCR4 deletion. Immunofluorescence showed the presence of nonhematopoietic GFP+ cells that were negative for CD45 (panleukocyte) and DBA (NK) markers in control but not CXCR4KO decidua. In conclusion, we report that CXCR4 expression in nonhematopoietic BMDPCs is essential for their recruitment to the pregnant decidua.

Transcriptome study of receptive endometrium in overweight and obese women shows important expression differences in immune response and inflammatory pathways in women who do not conceive

Obesity and being overweight are growing worldwide health problems that also affect women of reproductive age. They impair women’s fertility and are associated with lower IVF success rates. The mechanism by which increased body weight disrupts fertility has not yet been established. One possibility is that it affects the process of embryo implantation on the endometrial level. The purpose of our study was to determine the differences in enriched biological pathways in the endometrium of overweight and obese women undergoing IVF procedures. For this purpose, 14 patients (5 pregnant, 9 non-pregnant) were included in the study. Endometrial samples were obtained during the window of implantation and RNA sequencing was performed. There were no differences in general patient’s and IVF cycle characteristics between pregnant and non-pregnant women. In the endometrial samples of women who did not conceive, pathways related to the immune response, inflammation, and reactive oxygen species production were over-expressed. Our findings show that the reason for implantation failure in overweight and obese women could lie in the excessive immune and inflammatory response at the endometrial level.

CXCL12 May Drive Inflammatory Potential in the Ovine Corpus Luteum During Implantation

Adequate corpus luteum (CL) function is paramount to successful pregnancy. Structural and functional CL integrity is controlled by diverse cell types that contribute and respond to the local cytokine milieu. The chemokine ligand 12 (CXCL12) and receptor, CXCR4, are modulators of inflammation and cell survival, but little is understood about CXCL12-CXCR4 axis and CL functional regulation. Corpora lutea from control nonpregnant ewes (n = 5; day 10 estrous cycle (D10C)) and pregnant ewes (n = 5/day) on days 20 (D20P) and 30 (D30P) post-breeding were analyzed for gene and protein expression of CXCL12, CXCR4, and select inflammatory cytokines. In separate cell culture studies, cytokine production was evaluated following CXCL12 treatment. Abundance of CXCL12 and CXCR4 increased (P < 0.05) in pregnant ewes compared to nonpregnant ewes, as determined by a combination of quantitative PCR, immunoblot, and immunofluorescence microscopy. CXCR4 was detected in steroidogenic and nonsteroidogenic cells in ovine CL, and select pro-inflammatory mediators were greater in CL from pregnant ewes. In vitro studies revealed greater abundance of tumor necrosis factor (TNF) following CXCL12 administration (P = 0.05), while P4 levels in cell media were unchanged. Fully functional CL of pregnant ewes is characterized by increased abundance of inflammatory cytokines which may function in a luteotropic manner. We report concurrent increases in CXCL12, CXCR4, and select inflammatory mediators in ovine CL as early pregnancy progresses. We propose CXCL12 stimulates production of select cytokines, rather than P4 in the CL to assist in CL establishment and survival.

Inhibition of the C-X-C Motif Chemokine 12 (CXCL12) and Its Receptor CXCR4 Reduces Utero-Placental Expression of the VEGF System and Increases Utero-Placental Autophagy

The placenta, a unique organ that only develops during pregnancy, is essential for nutrient, oxygen, and waste exchange between offspring and mother. Yet, despite its importance, the placenta remains one of the least understood organs and knowledge of early placental formation is particularly limited. Abnormalities in placental development result in placental dysfunction or insufficiency whereby normal placental physiology is impaired. Placental dysfunction is a frequent source of pregnancy loss in livestock, inflicting serious economic impact to producers. Though the underlying causes of placental dysfunction are not well-characterized, initiation of disease is thought to occur during establishment of functional fetal and placental circulation. A comprehensive understanding of the mechanisms controlling placental growth and vascularization is necessary to improve reproductive success in livestock. We propose chemokine C-X-C motif ligand 12 (CXCL12) signaling through its receptor CXCR4 functions as a chief coordinator of vascularization through direct actions on fetal trophoblast and maternal endometrial and immune cells. To investigate CXCL12–CXCR4 signaling on uteroplacental vascular remodeling at the fetal–maternal interface, we utilized a CXCR4 antagonist (AMD3100). On day 12 post-breeding in sheep, osmotic pumps were surgically installed and delivered either AMD3100 or saline into the uterine lumen ipsilateral to the corpus luteum for 14 days. On day 35 of ovine pregnancy, fetal/placental and endometrial tissues were collected, snap-frozen in liquid nitrogen, and uterine horn cross sections were preserved for immunofluorescent analysis. Suppressing CXCL12–CXCR4 at the fetal–maternal interface during initial placental vascularization resulted in diminished abundance of select angiogenic factors in fetal and maternal placenta on day 35. Compared to control, less vascular endothelial growth factor (VEGF) and VEFG receptor 2 (KDR) were observed in endometrium when CXCL12–CXCR4 was diminished. Less VEGF was also evident in fetal placenta (cotyledons) in ewes receiving AMD3100 infusion compared to control. Suppressing CXCL12–CXCR4 at the fetal–maternal interface also resulted in greater autophagy induction in fetal and maternal placenta compared to control, suggestive of CXCL12–CXCR4 impacting cell survival. CXCL12–CXCR4 signaling may govern placental homeostasis by serving as a critical upstream mediator of vascularization and cell viability, thereby ensuring appropriate placental development.

CXCR4 signaling at the fetal-maternal interface may drive inflammation and syncytia formation during ovine pregnancy†

Early pregnancy features complex signaling between fetal trophoblast cells and maternal endometrium directing major peri-implantation events including localized inflammation and remodeling to establish proper placental development. Proinflammatory mediators are important for conceptus attachment, but a more precise understanding of molecular pathways regulating this process is needed to understand how the endometrium becomes receptive to implantation. Both chemokine ligand 12 (CXCL12) and its receptor CXCR4 are expressed by fetal and maternal tissues. We identified this pair as a critical driver of placental angiogenesis, but their additional importance to inflammation and trophoblast cell survival, proliferation, and invasion imply a role in syncytia formation at the fetal-maternal microenvironment. We hypothesized that CXCL12 encourages both endometrial inflammation and conceptus attachment during implantation. We employed separate ovine studies to (1) characterize endometrial inflammation during early gestation in the ewe, and (2) establish functional implications of CXCL12 at the fetal-maternal interface through targeted intrauterine infusion of the CXCR4 inhibitor AMD3100. Endometrial tissues were evaluated for inflammatory mediators, intracellular signaling events, endometrial modifications, and trophoblast syncytialization using western blotting and immunohistochemistry. Endometrial tissue from ewes receiving CXCR4 inhibitor demonstrated dysregulated inflammation and reduced AKT and NFKB, paired with elevated autophagic activity compared to control. Immunohistochemical observation revealed an impairment in endometrial surface remodeling and diminished trophoblast syncytialization following localized CXCR4 inhibition. These data suggest CXCL12-CXCR4 regulates endometrial inflammation and remodeling for embryonic implantation, and provide insight regarding mechanisms that, when dysregulated, lead to pregnancy pathologies such as intrauterine growth restriction and preeclampsia.

Expression and Functional Analysis of CXCL12 and Its Receptors in Human Term Trophoblast Cells

Chemokine CXCL12 and its receptors CXCR4/CXCR7 play a pivotal role in many physiological and pathological situations, while the expression and function in human term trophoblast cells remain largely unknown. In the study, the expression and function of CXCL12 and its receptors CXCR4/CXCR7 in human term trophoblast cells were investigated. Immunocytochemistry and flow cytometry showed that the expression of CXCL12/CXCR4/CXCR7 could be detected in term trophoblast cells while expression level differed. The secretion of CXCL12 in human term trophoblast cells was confirmed by enzyme-linked immunosorbent assay (ELISA). In order to reveal the function of CXCL12, exogenetic recombinant human CXCL12 protein (rhCXCL12) was added to the cultured term trophoblast cells; results showed that cell proliferation ability was increased while cell apoptosis rate was decreased. Moreover, the effects of rhCXCL12 on term trophoblast cells could be diminished or attenuated by antibodies against CXCL12, CXCR4, or CXCR7, respectively. Therefore, these results revealed the important role of CXCL12 on human term trophoblast cells. Our study will provide new insights into understanding the role of CXCL12 on human term trophoblast cells.

Human Endometrial Extracellular Vesicles Functionally Prepare Human Trophectoderm Model for Implantation: Understanding Bidirectional Maternal-Embryo Communication

Embryo implantation into maternal endometrium is critical for initiation and establishment of pregnancy, requiring developmental synchrony between endometrium and blastocyst. However, factors regulating human endometrial-embryo cross talk and facilitate implantation remain largely unknown. Extracellular vesicles (EVs) are emerging as important mediators of this process. Here, a trophectoderm spheroid-based in vitro model mimicking the pre-implantation human embryo is used to recapitulate important functional aspects of blastocyst implantation. Functionally, human endometrial EVs, derived from hormonally treated cells synchronous with implantation, are readily internalized by trophectoderm cells, regulating adhesive and invasive capacity of human trophectoderm spheroids. To gain molecular insights into mechanisms underpinning endometrial EV-mediated enhancement of implantation, quantitative proteomics reveal critical alterations in trophectoderm cellular adhesion networks (cell adhesion molecule binding, cell-cell adhesion mediator activity, and cell adherens junctions) and metabolic and gene expression networks, and the soluble secretome from human trophectodermal spheroids. Importantly, transfer of endometrial EV cargo proteins to trophectoderm to mediate changes in trophectoderm function is demonstrated. This is highlighted by correlation among endometrial EVs, the trophectodermal proteome following EV uptake, and EV-mediated trophectodermal cellular proteome, important for implantation. This work provides an understanding into molecular mechanisms of endometrial EV-mediated regulation of human trophectoderm functions-fundamental in understanding human endometrium-embryo signaling during implantation.

Cysteine-X-cysteine motif chemokine ligand 12 and its receptor CXCR4: expression, regulation, and possible function at the maternal-conceptus interface during early pregnancy in pigs

Cysteine-X-cysteine (CXC) motif chemokine ligand 12 (CXCL12) and its receptor, CXC chemokine receptor type 4 (CXCR4), are involved in regulating the proliferation, migration, and survival of trophoblast cells and the maternal immune response in humans and mice. The present study examined the expression, regulation, and function of CXCL12 and CXCR4 at the maternal-conceptus interface during pregnancy in pigs. The endometrium expressed CXCL12 and CXCR4 mRNAs with the greatest CXCL12 abundance on Day 15 of pregnancy. CXCL12 protein was localized mainly in endometrial epithelial cells, while CXCR4 protein was localized in subepithelial stromal cells, vascular endothelial cells, and immune cells in blood vessels in the endometrium during the estrous cycle and pregnancy. CXCL12 protein was detected in uterine flushing on Day 15 of pregnancy. The conceptus during early pregnancy and chorioallantoic tissues during mid-to-late pregnancy expressed CXCL12 and CXCR4. Interferon-γ increased the abundance of CXCL12, but not CXCR4 mRNA in endometrial explants. Recombinant CXCL12 (rCXCL12) protein dose-dependently increased migration of cultured porcine trophectoderm cells and peripheral blood mononuclear cells (PBMCs). Furthermore, rCXCL12 caused migration of T cells, but not natural killer cells, in PBMCs. This study revealed that interferon-γ-induced CXCL12 and its receptor, CXCR4, were expressed at the maternal-conceptus interface and increased the migration of trophectoderm cells and T cells at the time of implantation in pigs. These results suggest that CXCL12 may be critical for the establishment of pregnancy by regulating trophoblast migration and T cell recruitment into the endometrium during the implantation period in pigs.

Chemokines as the modulators of endometrial epithelial cells remodelling

Previous studies highlighted chemokines as potential factors regulating changes in the endometrium during early pregnancy. The current study aimed to screen the effects of a broad range of chemokines and indicate those that are involved in porcine luminal epithelial (LE) cell remodelling. Messenger RNA expression of chemokines (CCL2, CCL4, CCL5, CCL8, CXCL2, CXCL8, CXCL10 and CXCL12) and both the mRNA and protein expression of their receptors (CCR1, CCR2, CCR3, CCR5, CXCR2, CXCR3, CXCR4) were detected in LE cells. Exogenous CCL8 enhanced the proliferative and migration potential of LE cells and their motility in the environment with its stable concentration. The adhesive properties of LE cells were negatively affected by CCL8. However, CXCL12 positively affected the proliferation, motility and adhesion of LE cells as well as caused a decrease in MUC1 mRNA expression. To conclude, our studies determined that exogenous chemokines affected critical endometrial epithelial cell functions in the context of embryo implantation. We suggest that of all the examined factors, chemokine CCL8 participates in the establishment of a proper environment for embryo implantation, whereas CXCL12, apart from participation in endometrial receptivity, promotes embryo attachment.

Intrauterine inhibition of chemokine receptor 4 signaling modulates local and systemic inflammation in ovine pregnancy

PROBLEM

Chemokines help coordinate inflammation within the fetal-maternal microenvironment during gestation. The chemokine CXCL12 signaling through its receptor CXCR4 regulates inflammatory activity, but this phenomenon is not well understood during pregnancy, and there are no reports exploring the role of this pair in peripheral immune tolerance during gestation. Herein, we hypothesize that intrauterine CXCL12-CXCR4 signaling governs local and systemic immunomodulatory dynamics during early gestation in ewes.

METHOD OF STUDY

Osmotic pumps were surgically installed for intrauterine infusion of a CXCR4 inhibitor, AMD3100, beginning on day 12 post-breeding in sheep. Endometrial tissues were collected on day 35 of gestation and evaluated for inflammatory potential, Akt pathway activation, and autophagy induction. Demonstrative of peripheral immune activity, levels of select cytokines were assessed in daily blood samples collected throughout the study, as well as in corpus luteum and spleen on day 35.

RESULTS

Anti-inflammatory IL10 was primarily localized to endometrial glandular epithelium with lower abundance when CXCR4 was antagonized. Inhibition of CXCR4 at the fetal-maternal interface resulted in less activation of Akt in endometrium, while evidence of autophagy induction was greater. Corpora lutea from ewes receiving intrauterine AMD3100 exhibited lower interferon-gamma (IFNG) expression. Blood inflammatory potential was differentially altered in a temporal fashion throughout infusion. IL10 abundance in spleen was greater following CXCR4 inhibition at the fetal-maternal interface, while IFNG was less.

CONCLUSION

Intrauterine CXCL12-CXCR4 signaling governs endometrial and systemic inflammation; disruption of this axis may have detrimental impacts on offspring and maternal health.

CXCR4 signaling at the ovine fetal-maternal interface regulates vascularization, CD34+ cell presence, and autophagy in the endometrium†

Placenta development is characterized by extensive angiogenesis and vascularization but if these processes are compromised placental dysfunction occurs, which is the underlying cause of pregnancy complications such as preeclampsia and intrauterine growth restriction. Dysregulation of placental angiogenesis has emerged as one of the main pathophysiological features in the development of placental insufficiency and its clinical consequences. The signaling axis initiated by chemokine ligand 12 (CXCL12) and its receptor CXCR4 stimulates angiogenesis in other tissues, and may be central to placental vascularization. We hypothesized that CXCL12-CXCR4 signaling governs the pro-angiogenic placental microenvironment by coordinating production of central angiogenic factors and receptors and regulates endometrial cell survival essential for placental function and subsequent fetal longevity. The CXCR4 antagonist, AMD3100, was used to elucidate the role of CXCL12-CXCR4 signaling regarding uteroplacental vascular remodeling at the fetal-maternal interface. On day 12 postbreeding, osmotic pumps were surgically installed and delivered either AMD3100 or PBS into the uterine lumen ipsilateral to the corpus luteum. On day 20, endometrial tissues were collected, snap-frozen in liquid nitrogen, and uterine horn cross sections preserved for immunofluorescent analysis. In endometrium from ewes receiving AMD3100 infusion, the abundance of select angiogenic factors was diminished, while presence of CD34+ cells increased compared to control ewes. Ewes receiving AMD3100 infusion also exhibited less activation of Akt/mTOR signaling, and elevated LC3B-II, a marker of cellular autophagy in endometrium. This study suggests that CXCL12-CXCR4 signaling governs placental homeostasis by serving as a critical upstream mediator of vascularization and cell viability, thereby ensuring appropriate placental development.

Variable chemokine expression in porcine trophoblasts and endometrium during the peri-implantation period

Successful embryo implantation and its further development depends on appropriate endometrial remodelling. Porcine early pregnancy is associated with intensive endometrial angiogenesis and establishment of an immunotolerant environment for the embryo. An increasing number of factors are believed to participate in endometrial remodelling. The aim of this study was to elucidate the involvement of selected chemokines at the porcine maternal-foetal interface during the peri-implantation period. Real-time PCR analysis revealed several upregulated chemokines during the time of implantation, and Western blot/ELISA analyses and immunohistochemical staining confirmed their presence at the protein level. The gene expression of several chemokines and receptors was also confirmed in early porcine trophoblasts. The results indicated that IFNG, a porcine trophoblast signal, positively influenced the expression of some chemokines in endometrial cells. In conclusion, we suggest that some of the examined chemokines may be involved in endometrial communication with the trophoblast (CCL2, CCL5, CCL11, CXCL12), whereas others are implicated in the recruitment of immune cells and establishment of an immunotolerant environment for the embryo (CXCL9, CXCL10).

CXCL12 expression in aborted mouse uteri induced by IFN-γ: Potential anti-inflammatory effect involves in endometrial restoration after abortion in mice

Anti-inflammation is a key process to restore tissue integrity and function. CXCL12 is a homeostasis chemokine, which plays a coordinating role in organogenesis, tumorigenesis and regeneration. In the present study we found that the uterus of abortion mice showed different histo-morphological changes with the development of abortion. The expression of chemokine CXCL12 and its receptor CXCR4 in abortion uterus showed a time-dependent pattern. Compared with normal pregnancy, the expression of CXCL12 and CXCR4 did not change in the uterus of GD7 abortion mice, but increased significantly in the uterus of GD8 and GD10 abortion mice. However, the expression of IFN-γ increased significantly in the uterus of GD7 abortion mice, while there was no significant change detected in GD8 aborted mice uterus. Our further data show that the expression of CXCL12 is not regulated by IFN-γ in endometrial stromal cell culture system in vitro. The treatment of CXCL12 significantly inhibits the expression of IFN-γ in in vitro cultured stromal cells and splenic monocytes. This suggests that CXCL12 may play an anti-inflammatory role in the uterus of abortion mice to promote the process of endometrial restoration after abortion, rather than participate in the process of abortion as a response molecule of IFN-γ.

Mechanisms for the establishment and maintenance of pregnancy: synergies from scientific collaborations

Research on the functions of interferon tau (IFNT) led to the theory of pregnancy recognition signaling in ruminant species. But IFNT does much more as it induces expression of interferon regulatory factor 2 (IRF2) in uterine luminal (LE), superficial glandular (sGE), but not glandular (GE) epithelia. First, IRF2 silences transcription of the estrogen receptor alpha gene and, indirectly, transcription of the oxytocin receptor gene to abrogate development of the luteolytic mechanism to prevent regression of the corpus luteum and its production of progesterone for establishing and maintaining pregnancy. Second, IRF2 silences expression of classical interferon-stimulated genes in uterine LE and sGE; however, uterine LE and sGE respond to progesterone (P4) and IFNT to increase expression of genes for transport of nutrients into the uterine lumen such as amino acids and glucose. Other genes expressed by uterine LE and sGE encode for adhesion molecules such as galectin 15, cathepsins, and cystatins for tissue remodeling, and hypoxia-inducible factor relevant to angiogenesis and survival of blastocysts in a hypoxic environment. IFNT is also key to a servomechanism that allows uterine epithelia, particularly GE, to proliferate and to express genes in response to placental lactogen and placental growth hormone in sheep. The roles of secreted phosphoprotein 1 are also discussed regarding its role in implantation in sheep and pigs, as well as its stimulation of expression of mechanistic target of rapamycin mRNA and protein which is central to proliferation, migration, and gene expression in the trophectoderm cells.

Effect of metabolic status on conceptus-maternal interactions on day 19 in dairy cattle: II. Effects on the endometrial transcriptome

The aim of this study was to test the hypothesis that the metabolic stresses associated with lactation alter the ability of the endometrium to respond appropriately to the conceptus by examining endometrial gene expression on day 19 of pregnancy. Immediately after calving, primiparous Holstein cows with similar production and fertility estimated breeding values were randomly divided into two groups and either dried off (i.e. never milked) immediately or milked twice daily. Approximately 65-75 days postpartum, grade 1 blastocysts recovered from superovulated Holstein heifer donors (n = 5) were transferred (1 per recipient) into lactating (n = 11) and nonlactating (n = 11) recipients. Control nulliparous Holstein heifers (n = 6) were artificially inseminated. RNA-sequencing was performed on intercaruncular endometrial samples recovered at slaughter from confirmed pregnant animals on day 19 (n = 5 lactating and nonlactating cows; n = 4 heifers). Differentially expressed genes (DEGs) were identified between both postpartum groups compared to heifers and between lactating and nonlactating cows. Functional annotation of DEGs between cows and heifers revealed over-representation of categories, including endosome, cytoplasmic vesicle, endocytosis, regulation of exocytosis, and cytokine receptor activity. Functional categories including transcription factor binding sites, cell motility, and cell migration were enriched for DEGs between endometria from lactating and nonlactating cows. In conclusion, while the evidence for a major effect of lactation on the endometrial transcriptome is relatively weak, these data suggest that the metabolic status of the animal (heifer vs cow) modulates the response of the endometrium to the developing conceptus.

Cell-specific expression and signal transduction of C-C motif chemokine ligand 2 and atypical chemokine receptors in the porcine endometrium during early pregnancy

Chemokines and atypical chemokine receptors (ACKRs; also known as chemokine decoy receptors) play an important role in reproductive immunology by recruiting leukocytes during early pregnancy. The aim of this study was to determine the expression of C-C motif chemokine ligand 2 (CCL2) and ACKRs in the endometrium during estrous cycle and early pregnancy, and to investigate the functional effects of CCL2 on porcine uterine luminal epithelial (pLE) cells. Our results indicated that CCL2, ACKR1, ACKR3, and ACKR4 were strongly detected in the glandular and luminal epithelium of the endometrium during early pregnancy compared to that in non-pregnant pigs. Recombinant CCL2 improved pLE cell proliferation via activation of the PI3K and MAPK pathways and suppression of endoplasmic reticulum (ER) stress by reducing the expression of ER stress regulatory genes. Collectively, these results provide novel insights into CCL2-mediated signaling mechanisms in the porcine endometrium at the maternal-fetal interface during early pregnancy.

Modulatory effects of trophoblast-secreted CXCL12 on the migration and invasion of human first-trimester decidual epithelial cells are mediated by CXCR4 rather than CXCR7

BACKGROUND

Maternal-fetal crosstalk during embryo implantation is complex and regulated by local signaling molecules. Chemokines and their receptors are critical signaling components required for implantation and the process of pregnancy. This study aimed to explore whether human first-trimester trophoblast cells (TCs) were capable of modulating the migration and invasion of human first-trimester decidual epithelial cells (DECs) via CXCL12/CXCR4/CXCR7 signaling.

METHOD

The expression of CXCR4 and CXCR7 in DECs was examined by immunohistochemistry, immunocytochemistry, immunofluorescence, flow cytometry, real-time polymerase chain reactions and western blotting. The effects of recombinant human CXCL12 (rhCXCL12) and TC-conditioned medium (TC-CM) on DEC viability in vitro were explored using a viability assay. The modulatory effects of rhCXCL12 and TC/DEC co-cultures on DEC migration and invasion were examined with migration/invasion assays.

RESULT

CXCR4 and CXCR7 were co-expressed in human first-trimester DECs. Human rhCXCL12 and TC-CM had no effects on DEC viability in vitro (P > 0.05). Both exogenous CXCL12 and co-culture with TCs significantly increased the migration and invasion of DECs (P < 0.05). Neutralizing antibodies against CXCR4 (P < 0.05) or CXCL12 (P < 0.05), but not CXCR7 (P > 0.05), significantly blocked the enhanced migration and invasion of DECs induced by exogenous CXCL12 or TC co-culture.

CONCLUSIONS

CXCR4 and CXCR7 were co-expressed in human first-trimester DECs. TC-derived CXCL12 promoted the migration and invasion of DECs via CXCR4, but not CXCR7, in a paracrine manner during early pregnancy.

In the ovine pituitary, CXCR4 is localized in gonadotropes and somatotropes and increases with elevated serum progesterone

The pituitary is the central endocrine regulator of reproduction and in addition to various hormones regulating its actions, other molecules, such as chemokines, influence pituitary physiology as well. Despite reports over 2 decades ago that chemokines regulate the pituitary, much of the basic biology discerning chemokine action in the pituitary is unclear. A small number of chemokines and their receptors have been localized to the pituitary, yet chemokine ligand 12 (CXCL12) and its receptor, CXCR4, have received the most attention as both are increased in human pituitary adenomas. This chemokine duo was also reported in normal human and rat pituitary, suggestive of a functional role and that this chemokine axis might function in pituitaries from other mammalian species. To date, reports of CXCL12 and CXCR4 in pituitary from livestock are lacking, and research on pituitary during pregnancy in any mammalian species is limited. Moreover, progesterone regulates CXCR4 expression in a tissue-dependent manner, but whether differing concentrations of progesterone reaching the pituitary modulate CXCL12 or CXCR4 is not known. To address these gaps, our first objective was to determine if CXCL12 and CXCR4 expression and protein abundance differ in sheep pituitary during early gestation (days 20, 25, and 30 of gestation) compared to nonpregnant ewes. The second objective was to determine if CXCL12 or CXCR4 production was altered in the ovine pituitary when circulating progesterone concentrations are elevated. The expression of CXCL12 messenger RNA decreased on day 20 of gestation compared to nonpregnant ewes; CXCL12 protein was similar across all days tested. In nonpregnant and pregnant ewes, CXCR4 was localized to somatotropes and gonadotropes on all days tested. Abundance of CXCR4 increased in the pituitary tissue of pregnant ewes with elevated circulating progesterone compared with pregnant ewes with normal circulating progesterone concentrations (control). The present study details CXCL12 and CXCR4 in normal ovine pituitary and reveals that gonadotropes and somatotropes may be regulated by CXCL12/CXCR4, underscoring this signaling axis as a potential new class of modulator in endocrine functions.

Paracrine and endocrine actions of interferon tau (IFNT)

This review focuses on the paracrine and endocrine actions of interferon tau (IFNT) during pregnancy recognition and establishment in ruminants. Pregnancy recognition involves the suppression of the endometrial luteolytic mechanism by the conceptus to maintain progesterone production by the corpus luteum (CL). The paracrine antiluteolytic effects of conceptus-derived IFNT inhibit upregulation of oxytocin receptors in the endometrial epithelia of the uterus, thereby preventing the production of luteolytic prostaglandin F2 alpha (PGF2α) pulses. In the endometrium, IFNT induces or upregulates a large number of classical IFN-stimulated genes (ISGs) and regulates expression of many other genes in a cell-specific manner that are likely important for conceptus elongation, implantation and establishment of pregnancy. Further, IFNT has endocrine effects on extrauterine cells and tissues. In sheep, IFNT induces luteal resistance to PGF2α, thereby ensuring survival of the CL for maintenance of pregnancy. The ISGs induced in circulating peripheral blood mononuclear cells by IFNT may also be useful as an indicator of pregnancy status in cattle. An increased knowledge of IFNT and ISGs is important to improve the reproductive efficiency in ruminants.

Differential expression and functional roles of chemokine (C-C motif) ligand 23 and its receptor chemokine (C-C motif) receptor type 1 in the uterine endometrium during early pregnancy in pigs

Many chemokines expressed by cells of the uterine endometrium of mammals are involved in cell-cell interactions. However, little is known about expression and functional roles of chemokine (C-C motif) ligand 23 (CCL23) in the uterine endometrium. Results of this study demonstrated that CCL23 and its receptor, chemokine (C-C motif) receptor type 1 (CCR1), are up-regulated in porcine endometria during pregnancy. CCL23 and CCR1 mRNAs were strongly expressed in endometrial glandular (GE) and luminal (LE) epithelial cells. Treatment of porcine uterine luminal epithelial (pLE) cells with recombinant CCL23 increased the abundances of PCNA and cyclin D1, and enhanced proliferation and cell cycle progression in pLE cells. CCL23 also stimulated phosphorylation of cell signaling molecules including AKT and MAPKs in pLE cells. Furthermore, ER stress-related molecules were reduced by CCL23. These results suggest that CCL23-CCR1 signaling is important for endometrial development and establishment of pregnancy in pigs.

Inhibition of chemokine (C-X-C motif) receptor four (CXCR4) at the fetal-maternal interface during early gestation in sheep: alterations in expression of chemokines, angiogenic factors and their receptors

Chemokine (C-X-C motif) ligand 12 (CXCL12) and its receptor, chemokine (C-X-C motif) receptor 4 (CXCR4), are involved in significant biological processes associated with early pregnancy including increasing trophoblast invasion and stimulating placental vascularization. To further elucidate functions of CXCL12-CXCR4 signaling during early gestation, our objective was to inhibit CXCR4 in vivo using a CXCR4 antagonist, AMD3100. We hypothesized that inhibition of CXCR4 would negatively affect chemokine and angiogenic factor regulation imperative for placental development in sheep. Osmotic pumps containing PBS (control) or AMD3100 (CXCR4 antagonist) were surgically installed ipsilateral to the corpus luteum on d 12 of gestation and administered treatments directly into the uterine lumen. Maternal (caruncle and intercaruncle) and fetal membrane tissues were collected on d 23 of gestation and mRNA and protein expression were analyzed for vascular endothelial growth factor (VEGF), kinase insert domain receptor (KDR), fms related tyrosine kinase 1 (FLT1), fibroblast growth factor 2 (FGF2), angiopoietin 1 (ANGPT1), hypoxia inducible factor 1 ɑ subunit (HIF1A), CXCL12, and its corresponding receptors (CXCR4 and CXCR7). Immunohistochemical procedures were performed for analysis of CXCL12 and cell proliferation. In caruncle tissue ipsilateral to the pump, mRNA for KDR, ANGPT1, HIF1A, and CXCL12 increased (P < 0.05) in treated ewes compared to control, whereas caruncle tissue contralateral to the pump had increased expression (P < 0.05) of KDR, and CXCL12 in treated ewes. In fetal membrane, CXCR4 mRNA and protein decreased (P < 0.05), while VEGF protein decreased (P < 0.05) in caruncle and fetal membrane tissue from treated ewes. Results from this study highlight the importance of CXCL12-CXCR4 signaling at the fetal-maternal interface. Inhibiting this axis may disrupt typical regulation of angiogenic factors needed for placental development and embryo growth.

Insights into conceptus elongation and establishment of pregnancy in ruminants

This review integrates established and new information on the factors and pathways regulating conceptus–endometrial interactions, conceptus elongation and establishment of pregnancy in sheep and cattle. Establishment of pregnancy in domestic ruminants begins at the conceptus stage (embryo or fetus and associated extra-embryonic membranes) and includes pregnancy recognition signalling, implantation and the onset of placentation. Survival and growth of the preimplantation blastocyst and elongating conceptus require embryotrophic factors (amino acids, carbohydrates, proteins, lipids and other substances) provided by the uterus. The coordinated and interactive actions of ovarian progesterone and conceptus-derived factors (interferon-τ and prostaglandins) regulate expression of elongation- and implantation-related genes in the endometrial epithelia that alter the uterine luminal milieu and affect trophectoderm proliferation, migration, attachment, differentiation and function. A comparison of sheep and cattle finds both conserved and non-conserved embryotrophic factors in the uterus; however, the overall biological pathways governing conceptus elongation and establishment of pregnancy are likely conserved. Given that most pregnancy losses in ruminants occur during the first month of pregnancy, increased knowledge is necessary to understand why and provide a basis for new strategies to improve pregnancy outcome and reproductive efficiency.

Characterization of exosomal release in bovine endometrial intercaruncular stromal cells

BACKGROUND

Cell-to-cell communication between the blastocyst and endometrium is critical for implantation. In recent years, evidence has emerged from studies in humans and several other animal species that exosomes are secreted from the endometrium and trophoblast cells and may play an important role in cell-to-cell communication maternal-fetal interface during early pregnancy. Exosomes are stable extracellular lipid bilayer vesicles that encapsulate proteins, miRNAs, and mRNAs, with the ability to deliver their cargo to near and distant sites, altering cellular function(s). Furthermore, the exosomal cargo can be altered in response to environmental cues (e.g. hypoxia). The current study aims to develop an in vitro system to evaluate maternal-embryo interactions via exosomes (and exosomal cargo) produced by bovine endometrial stromal cells (ICAR) using hypoxia as a known stimulus associated with the release of exosomes and alterations to biological responses (e.g. cell proliferation).

METHODS

ICAR cells cultured under 8 % O₂ or 1 % O₂ for 48 h and changes in cell function (i.e. migration, proliferation and apoptosis) were evaluated. Exosome release was determined following the isolation (via differential centrifugation) and characterization of exosomes from ICAR cell-conditioned media. Exosomal proteomic content was evaluated by mass spectrometry.

RESULTS

Under hypoxic conditions (i.e. 1 % O₂), ICAR cell migration and proliferation was decreased (~20 and ~32 %, respectively) and apoptotic protein caspase-3 activation was increased (∼1.6 fold). Hypoxia increased exosome number by ~3.6 fold compared with culture at 8 % O₂. Mass spectrometry analysis identified 128 proteins unique to exosomes of ICAR cultured at 1 % O₂ compared with only 46 proteins unique to those of ICAR cultured at 8 % O₂. Differential production of proteins associated with specific biological processes and molecular functions were identified, most notably ADAM10, pantetheinase and kininogen 2.

CONCLUSIONS

In summary, we have shown that a stimulus such as hypoxia can alter both the cellular function and exosome release of ICAR cells. Alterations to exosome release and exosomal content in response to stimuli may play a crucial role in maternal-fetal crosstalk and could also affect placental development.

Spontaneous Preterm Delivery, Particularly with Reduced Fetal Growth, is Associated with DNA Hypomethylation of Tumor Related Genes

Background

Preterm delivery and sub-optimal fetal growth are associated with each other and affect both mother and infant. Our aim was to determine (i) whether there are detectable differences in DNA methylation between early and late gestation and (ii) whether changes in DNA methylation from entry are associated with spontaneous preterm delivery with and without reduced fetal growth.

Methods

We conducted a case-control study nested within a large prospective cohort. Gene specific methylation was measured by Methyl-Profiler PCR Array in a Human Breast Cancer Signature Panel of 24 genes from maternal peripheral leukocytes genomic DNA at entry and 3^rd trimester (sampled at 16 and 30 weeks of gestation, respectively). Clonal bisulfite DNA sequencing was performed to confirm the changes in selected genes (CYP1B1, GADD45A and CXCL12). Multivariable analysis was used for data analysis.

Results

There was significantly decrease in DNA methylation in 15 of 24 genes during the 3^rd trimester in cases of spontaneous preterm delivery (n=23) as compared to the controls (n=19) (p<0.05–p<0.01 for each gene). Similar results were observed by bisulfite sequencing for 3 genes. The change in DNA methylation between late and early gestation was significantly different in cases (overall decrease in methylation was −4.0 ± 1.5%) compared to the controls (overall increase in methylation was 12.6 ± 2.19%, p<0.0001). A graded pattern of DNA methylation was observed in 15 genes. Cases who delivered preterm with reduced fetal growth had the lowest level of methylation, cases delivering preterm without reduced fetal growth were next and term controls were highest in methylation (p for trend <0.05 to p<0.01 for each gene). Cases of preterm delivery also had significantly lower dietary choline intake.

Conclusions

These data suggest that epigenetic modification is associated with an increased risk of spontaneous preterm delivery, spontaneous preterm delivery with reduced fetal growth in particular.

Human chorionic gonadotropin increases serum progesterone, number of corpora lutea and angiogenic factors in pregnant sheep

Early gestation is a critical period when implantation and placental vascularization are established, processes influenced by progesterone (P4). Although human chorionic gonadotropin (hCG) is not endogenously synthesized by livestock, it binds the LH receptor, stimulating P4 synthesis. We hypothesized treating pregnant ewes with hCG would increase serum P4, number of corpora lutea (CLs) and concepti, augment steroidogenic enzymes, and increase membrane P4 receptors (PAQRs) and angiogenic factors in reproductive tissues. The objective was to determine molecular alterations induced by hCG in pregnant sheep that may promote pregnancy. Ewes received either 600 IU of hCG or saline i.m. on day 4 post mating. Blood samples were collected daily from day 0 until tissue collection for serum P4 analysis. Reproductive tissues were collected on either day 13 or 25 of gestation and analyzed for PAQRs, CXCR4, proangiogenic factors and steroidogenic enzymes. Ewes receiving hCG had more CL and greater serum P4, which remained elevated. On day 25, StAR protein production decreased in CL from hCG-treated ewes while HSD3B1 was unchanged; further, expression of CXCR4 significantly increased and KDR tended to increase. PAQR7 and CXCR4 protein was increased in caruncle tissue from hCG-treated ewes. Maternal hCG exposure influenced fetal extraembryonic tissues, as VEGFA, VEGFB, FLT1, and ANGPT1 expression increased. Our results indicate hCG increases serum P4 due to augmented CL number per ewe. hCG treatment resulted in greater PAQR7 and CXCR4 in maternal endometrium and promoted expression of proangiogenic factors in fetal extraembryonic membranes. Supplementing livestock with hCG may boost P4 levels and improve reproductive efficiency.

Uterine vasculature remodeling in human pregnancy involves functional macrochimerism by endothelial colony forming cells of fetal origin

The potency of adult-derived circulating progenitor endothelial colony forming cells (ECFCs) is drastically surpassed by their fetal counterparts. Human pregnancy is associated with robust intensification of blood flow and vascular expansion in the uterus, crucial for placental perfusion and fetal supply. Here, we investigate whether fetal ECFCs transmigrate to maternal bloodstream and home to locations of maternal vasculogenesis, primarily the pregnant uterus. In the first instance, endothelial-like cells, originating from mouse fetuses expressing paternal eGFP, were identified within uterine endothelia. Subsequently, LacZ or enhanced green fluorescent protein (eGFP)-labeled human fetal ECFCs, transplanted into immunodeficient (NOD/SCID) fetuses on D15.5 pregnancy, showed similar integration into the mouse uterus by term. Mature endothelial controls (human umbilical vein endothelial cells), similarly introduced, were unequivocally absent. In humans, SRY was detected in 6 of 12 myometrial microvessels obtained from women delivering male babies. The copy number was calculated at 175 [IQR 149-471] fetal cells per millimeter square endothelium, constituting 12.5% of maternal vessel lumina. Cross-sections of similar human vessels, hybridized for Y-chromosome, positively identified endothelial-associated fetal cells. It appears that through ECFC donation, fetuses assist maternal uterine vascular expansion in pregnancy, potentiating placental perfusion and consequently their own fetal supply. In addition to fetal growth, this cellular mechanism holds implications for materno-fetal immune interactions and long-term maternal vascular health.

Activation of the CXCL12/CXCR4 signaling axis may drive vascularization of the ovine placenta

Early pregnancy, when most embryonic losses occur, is a critical period in which vital placental vascularization is established. Vascular endothelial growth factor (VEGF) is a potent inducer of angiogenesis, and factors that regulate VEGF function, expression, or both may ultimately affect vascularization. Activation of the C-X-C chemokine receptor type 4 (CXCR4) by its cognate ligand, C-X-C chemokine ligand 12 (CXCL12), increases VEGF synthesis and secretion, which in turn stimulates CXCL12 and CXCR4 production and this synergistic regulation may influence placental vascularization. We hypothesized that expression of CXCL12, CXCR4, select angiogenic factors, and their receptors would increase in placental tissues during early pregnancy and that treatment of ovine trophectoderm cells with CXCL12 would increase production of angiogenic factors. To test this hypothesis, maternal caruncle (CAR) and fetal extraembryonic membrane (FM) tissues were collected on days 18, 20, 22, 25, 26, and 30 of pregnancy and on day 10 of the estrous cycle (control, NP) to determine relative mRNA or protein expression of CXCL12 and CXCR4 and selected angiogenic factors. In CAR, expression of mRNA for CXCR4 increased on day 18, 20, 22, and 25 and CXCL12 increased on day 18 and 20 compared with NP ewes. CXCL12 protein followed a similar pattern in CAR tissue, with greater levels on day 20 than in NP tissue. Greater levels of fibroblast growth factor 2 (FGF2) mRNA was observed in CAR on day 20 of gestation than on day 30. In FM, CXCL12, CXCR4, angiopoietin 1, VEGF, and VEGF receptor 1 were enhanced with advancing pregnancy, whereas FGF2 and kinase insert domain receptor (or VEGF receptor 2) peaked on day 25. An increase in protein levels occurred on day 25 compared with day 20 in FM for CXCL12 and CXCR4, as well as a similar tendency for FGF2 protein. Both CXCL12 and CXCR4 are specifically localized to trophoblast cells and to the uterine luminal and glandular epithelium. Treatment of ovine trophectoderm cells with CXCL12 increased mRNA expression for VEGF and FGF2. The relationship between VEGF, FGF2, and the CXCL12/CXCR4 signaling underscores the potential role for this chemokine axis in driving placentation.