The cycling and aging mouse female reproductive tract at single-cell resolution.

The female reproductive tract (FRT) undergoes extensive remodeling during reproductive cycling. This recurrent remodeling and how it shapes organ-specific aging remains poorly explored. Using single-cell and spatial transcriptomics, we systematically characterized morphological and gene expression changes occurring in ovary, oviduct, uterus, cervix, and vagina at each phase of the mouse estrous cycle, during decidualization, and into aging. These analyses reveal that fibroblasts play central-and highly organ-specific-roles in FRT remodeling by orchestrating extracellular matrix (ECM) reorganization and inflammation. Our results suggest a model wherein recurrent FRT remodeling over reproductive lifespan drives the gradual, age-related development of fibrosis and chronic inflammation. This hypothesis was directly tested using chemical ablation of cycling, which reduced fibrotic accumulation during aging. Our atlas provides extensive detail into how estrus, pregnancy, and aging shape the organs of the female reproductive tract and reveals the unexpected cost of the recurrent remodeling required for reproduction.

Embryo-uterine interaction coordinates mouse embryogenesis during implantation.

Embryo implantation into the uterus marks a key transition in mammalian development. In mice, implantation is mediated by the trophoblast and is accompanied by a morphological transition from the blastocyst to the egg cylinder. However, the roles of trophoblast-uterine interactions in embryo morphogenesis during implantation are poorly understood due to inaccessibility in utero and the remaining challenges to recapitulate it ex vivo from the blastocyst. Here, we engineer a uterus-like microenvironment to recapitulate peri-implantation development of the whole mouse embryo ex vivo and reveal essential roles of the physical embryo-uterine interaction. We demonstrate that adhesion between the trophoblast and the uterine matrix is required for in utero-like transition of the blastocyst to the egg cylinder. Modeling the implanting embryo as a wetting droplet links embryo shape dynamics to the underlying changes in trophoblast adhesion and suggests that the adhesion-mediated tension release facilitates egg cylinder formation. Light-sheet live imaging and the experimental control of the engineered uterine geometry and trophoblast velocity uncovers the coordination between trophoblast motility and embryo growth, where the trophoblast delineates space for embryo morphogenesis.

Regional specialization, polyploidy, and seminal fluid transcripts in the Drosophila female reproductive tract.

Sexual reproduction requires the choreographed interaction of female cells and molecules with sperm and seminal fluid. In internally fertilizing animals, these interactions are managed by specialized tissues within the female reproductive tract (FRT), such as a uterus, glands, and sperm storage organs. However, female somatic reproductive tissues remain understudied, hindering insight into the molecular interactions that support fertility. Here, we report the identification, molecular characterization, and analysis of cell types throughout the somatic FRT in the premier Drosophila melanogaster model system. We find that the uterine epithelia is composed of 11 distinct cell types with well-delineated spatial domains, likely corresponding to functionally specialized surfaces that interact with gametes and reproductive fluids. Polyploidy is pervasive: More than half of lower reproductive tract cells are ≥4C. While seminal fluid proteins (SFPs) are typically thought of as male products that are transferred to females, we find that specialized cell types in the sperm storage organs heavily invest in expressing SFP genes. Rates of amino acid divergence between closely related species indicate heterogeneous evolutionary processes acting on male-limited versus female-expressed seminal fluid genes. Together, our results emphasize that more than 40% of annotated seminal fluid genes are better described as shared components of reproductive transcriptomes, which may function cooperatively to support spermatozoa. More broadly, our work provides the molecular foundation for improved technologies to catalyze the functional characterization of the FRT.

Single-cell insights into epithelial morphogenesis in the neonatal mouse uterus.

The uterus is vital for successful reproduction in mammals, and two different types of epithelia (luminal and glandular) are essential for embryo implantation and pregnancy establishment. However, the essential cellular and molecular factors and pathways governing postnatal epithelium maturation, determination, and differentiation in developing uterus are yet to be elucidated. Here, the epithelium of the neonatal mouse uterus was isolated and subjected to single-cell transcriptome (scRNA-seq) analysis. Both the undifferentiated epithelium and determined luminal epithelium were heterogeneous and contained several different cell clusters based on single-cell transcription profiles. Substantial gene expression differences were evident as the epithelium matured and differentiated between postnatal days 1 to 15. Two new glandular epithelium-expressed genes (Gas6 and Cited4) were identified and validated by in situ hybridization. Trajectory analyses provided a framework for understanding epithelium maturation, lineage bifurcation, and differentiation. A candidate set of transcription factors and gene regulatory networks were identified that potentially direct epithelium lineage specification and morphogenesis. This atlas provides a foundation important to discover intrinsic cellular and molecular mechanisms directing uterine epithelium morphogenesis during a critical window of postnatal development.

Uterus Transplantation: the Translational Evolution of a Clinical Breakthrough.

Women suffering from absolute uterine factor infertility (AUFI), due to either lack of a uterus or one unable to sustain neonatal viability, presented as one of the last frontiers in conquering infertility. Following systematic animal research for over a decade, uterus transplantation was tested as a treatment for AUFI in 2012, which culminated in the first human live birth in 2014. The development of uterus transplantation from mouse to human has followed both the Moore criteria for introduction of a surgical innovation and the IDEAL concept for evaluation of a novel major surgical procedure. In this article we review the important preclinical animal and human studies that paved the way for the successful introduction of human uterus transplantation a decade ago. We discuss this in the context of the Moore criteria and describe the different procedures of preparation, surgeries, postoperative monitoring, and use of assisted reproduction in human uterus transplantation. We review the worldwide activities and associated results in the context of the IDEAL concept for evaluation of surgical innovation and appraise the ethical considerations relevant to uterus transplantation. We conclude that rigorous application of the Moore criteria and strict alignment with the IDEAL concept have resulted in the establishment of uterus transplantation as a novel, safe, and effective infertility therapy that is now being used worldwide for the treatment of women suffering from AUFI.

Uterine Immunoprivileged Cells Restore Cardiac Function of Male Recipients After Myocardial Infarction.

It has been documented that the uterus plays a key cardio-protective role in pre-menopausal women, which is supported by uterine cell therapy, to preserve cardiac functioning post-myocardial infarction, being effective among females. However, whether such therapies would also be beneficial among males is still largely unknown. In this study, we aimed to fill in this gap in knowledge by examining the effects of transplanted uterine cells on infarcted male hearts. We identified, based on major histocompatibility complex class I (MHC-I) expression levels, 3 uterine reparative cell populations: MHC-I(neg), MHC-I(mix), and MHC-I(pos). In vitro, MHC-I(neg) cells showed higher levels of pro-angiogenic, pro-survival, and anti-inflammatory factors, compared to MHC-I(mix) and MHC-I(pos). Furthermore, when cocultured with allogeneic mixed leukocytes, MHC-I(neg) had lower cytotoxicity and leukocyte proliferation. In particular, CD8+ cytotoxic T cells significantly decreased, while CD4+CD25+ Tregs and CD4-CD8- double-negative T cells significantly increased when cocultured with MHC-I(neg), compared to MHC-I(mix) and MHC-I(pos) cocultures. In vivo, MHC-I(neg) as well as MHC-I(mix) were found under both syngeneic and allogeneic transplantation in infarcted male hearts, to significantly improve cardiac function and reduce the scar size, via promoting angiogenesis in the infarcted area. All of these findings thus support the view that males could also benefit from the cardio-protective effects observed among females, via cell therapy approaches involving the transplantation of immuno-privileged uterine reparative cells in infarcted hearts.

Single-cell transcriptomic profiling of the neonatal oviduct and uterus reveals new insights into upper Müllerian duct regionalization.

The upper Müllerian duct (MD) is patterned and specified into two morphologically and functionally distinct organs, the oviduct and uterus. It is known that this regionalization process is instructed by inductive signals from the adjacent mesenchyme. However, the interaction landscape between epithelium and mesenchyme during upper MD development remains largely unknown. Here, we performed single-cell transcriptomic profiling of mouse neonatal oviducts and uteri at the initiation of MD epithelial differentiation (postnatal day 3). We identified major cell types including epithelium, mesenchyme, pericytes, mesothelium, endothelium, and immune cells in both organs with established markers. Moreover, we uncovered region-specific epithelial and mesenchymal subpopulations and then deduced region-specific ligand-receptor pairs mediating mesenchymal-epithelial interactions along the craniocaudal axis. Unexpectedly, we discovered a mesenchymal subpopulation marked by neurofilaments with specific localizations at the mesometrial pole of both the neonatal oviduct and uterus. Lastly, we analyzed and revealed organ-specific signature genes of pericytes and mesothelial cells. Taken together, our study enriches our knowledge of upper MD development, and provides a manageable list of potential genes, pathways, and region-specific cell subtypes for future functional studies.

Effects of intrauterine extracellular vesicle microRNAs on embryonic gene expression in low-fertility cows.

Embryo survival and pre-implantation development depend on uterine luminal fluid, which is believed to play a role in early embryonic death and infertility in cows. Extracellular vesicles (EVs) in the uterine luminal fluid contain microRNAs (miRNAs), crucial mediators of intercellular communication. miRNAs regulate conceptus-maternal interactions and participate in embryonic development by suppressing gene expression. Therefore, we hypothesized that miRNAs in the intrauterine EVs of low-fertility cows would hinder embryonic survival and development. EVs were collected from the bovine uterine luminal fluid of both normal- and low-fertility cows 7 days post-estrus. Small RNA-sequencing analysis of miRNAs isolated from these EVs identified eight miRNAs that were highly expressed in normal-fertility cows (normal-fertility miRNAs) and eight with elevated expression in low-fertility cows (low-fertility miRNAs). These two sets of miRNAs were transfected into hatched blastocysts via lipofection. RNA-seq following lipofection with low-fertility miRNAs identified 424 differentially expressed genes (DEGs) relative to the control; in contrast, following lipofection with normal-fertility miRNAs, seven DEGs were identified. Pathway analysis of the DEGs identified following lipofection with low-fertility miRNAs revealed substantial enrichment of mitogen-activated protein kinase (MAPK) signaling. Expression of activator protein 1 (AP1) and interferon-tau (IFNT) mRNA was significantly lower in the low-fertility miRNA transfection group than in the control. IFNT is essential for maternal pregnancy recognition. Therefore, miRNAs in intrauterine EVs from low-fertility cows at 7 days post-estrus may inhibit embryo development and suppress IFNT expression by altering MAPK signaling.

Spatially restricted ecto-5'-nucleotidase expression promotes the growth of uterine leiomyomas by modulating Akt activity.

Found in as many as 80% of women, uterine leiomyomas are a frequent cause of abnormal uterine bleeding, pelvic pain, and infertility. Despite their significant clinical impact, the mechanisms responsible for driving leiomyoma growth remain poorly understood. After obtaining IRB permission, expression of ecto-5'-nucleotidase (NT5E, CD73) was assessed in matched specimens of myometrium and leiomyoma by real-time qPCR, Western blot, and immunohistochemistry (IHC). Adenosine concentrations were measured by enzyme-linked assay. Primary cultures were used to assess the impact of adenosine and/or adenosine receptor agonists on proliferation, apoptosis, and patterns of intracellular signaling in vitro. When compared to matched specimens of healthy myometrium, uterine leiomyomas were characterized by reduced CD73 expression. Largely limited to thin-walled vascular structures and the pseudocapsule of leiomyomas despite diffuse myometrial distribution. Restricted intra-tumoral CD73 expression was accompanied by decreased levels of intra-tumoral adenosine. In vitro, incubation of primary leiomyoma cultures with adenosine or its hydrolysis-resistant analog 2-chloro-adenosine (2-CL-AD) inhibited proliferation, induced apoptosis, and reduced proportion of myocytes in S- and G2-M phases of the cell cycle. Decreased proliferation was accompanied by reduced expression of phospho-Akt, phospho-Cdk2-Tyr15, and phospho-Histone H3. Enforced expression of the A2B adenosine receptor (ADORA2B) and ADORA2B-selective agonists similarly suppressed proliferation and inhibited Akt phosphorylation. Collectively, these observations broadly implicate CD73 and reduced extracellular concentrations of adenosine as key regulators of leiomyoma growth and potentially identify novel strategies for clinically managing these common tumors.

Bovine and human endometrium-derived hydrogels support organoid culture from healthy and cancerous tissues.

Organoid technology has provided unique insights into human organ development, function, and diseases. Patient-derived organoids are increasingly used for drug screening, modeling rare disorders, designing regenerative therapies, and understanding disease pathogenesis. However, the use of Matrigel to grow organoids represents a major challenge in the clinical translation of organoid technology. Matrigel is a poorly defined mixture of extracellular matrix proteins and growth factors extracted from the Engelbreth-Holm-Swarm mouse tumor. The extracellular matrix is a major driver of multiple cellular processes and differs significantly between tissues as well as in healthy and disease states of the same tissue. Therefore, we envisioned that the extracellular matrix derived from a native healthy tissue would be able to support organoid growth akin to organogenesis in vivo. Here, we have developed hydrogels from decellularized human and bovine endometrium. These hydrogels supported the growth of mouse and human endometrial organoids, which was comparable to Matrigel. Organoids grown in endometrial hydrogels were proteomically more similar to the native tissue than those cultured in Matrigel. Proteomic and Raman microspectroscopy analyses showed that the method of decellularization affects the biochemical composition of hydrogels and, subsequently, their ability to support organoid growth. The amount of laminin in hydrogels correlated with the number and shape of organoids. We also demonstrated the utility of endometrial hydrogels in developing solid scaffolds for supporting high-throughput, cell culture-based applications. In summary, endometrial hydrogels overcome a major limitation of organoid technology and greatly expand the applicability of organoids to understand endometrial biology and associated pathologies.

Development and characterization of human fetal female reproductive tract organoids to understand Müllerian duct anomalies.

Müllerian ducts are paired tubular structures that give rise to most of the female reproductive organs. Any abnormalities in the development and differentiation of these ducts lead to anatomical defects in the female reproductive tract organs categorized as Müllerian duct anomalies. Due to the limited access to fetal tissues, little is understood of human reproductive tract development and the associated anomalies. Although organoids represent a powerful model to decipher human development and disease, such organoids from fetal reproductive organs are not available. Here, we developed organoids from human fetal fallopian tubes and uteri and compared them with their adult counterparts. Our results demonstrate that human fetal reproductive tract epithelia do not express some of the typical markers of adult reproductive tract epithelia. Furthermore, fetal organoids are grossly, histologically, and proteomically different from adult organoids. While external supplementation of WNT ligands or activators in culture medium is an absolute requirement for the adult reproductive tract organoids, fetal organoids are able to grow in WNT-deficient conditions. We also developed decellularized tissue scaffolds from adult human fallopian tubes and uteri. Transplantation of fetal organoids onto these scaffolds led to the regeneration of the adult fallopian tube and uterine epithelia. Importantly, suppression of Wnt signaling, which is altered in patients with Müllerian duct anomalies, inhibits the regenerative ability of human fetal organoids and causes severe anatomical defects in the mouse reproductive tract. Thus, our fetal organoids represent an important platform to study the underlying basis of human female reproductive tract development and diseases.

Generation of a Wt1 conditional deletion, nuclear red fluorescent protein reporter allele in the mouse.

A Wt1 conditional deletion, nuclear red fluorescent protein (RFP) reporter allele was generated in the mouse by gene targeting in embryonic stem cells. Upon Cre-mediated recombination, a deletion allele is generated that expresses RFP in a Wt1-specific pattern. RFP expression was detected in embryonic and adult tissues known to express Wt1, including the kidney, mesonephros, and testis. In addition, RFP expression and WT1 co-localization was detected in the adult uterine stroma and myometrium, suggesting a role in uterine function. Crosses with Wnt7a-Cre transgenic mice that express Cre in the Müllerian duct epithelium activate Wt1-directed RFP expression in the epithelium of the oviduct but not the stroma and myometrium of the uterus. This new mouse strain should be a useful resource for studies of Wt1 function and marking Wt1-expressing cells.

Uterine prostaglandin DP receptor-induced upon implantation contributes to decidualization together with EP4 receptor.

To investigate the yet-unknown roles of prostaglandins (PGs) in the uterus, we analyzed the expression of various PG receptors in the uterus. We found that three types of Gs-coupled PG receptors, DP, EP2, and EP4, were expressed in luminal epithelial cells from the peri-implantation period to late pregnancy. DP expression was also induced in stromal cells within the mesometrial region, whereas EP4 was expressed in stromal cells within the anti-mesometrial region during the peri-implantation period. The timing of DP induction after embryo attachment correlated well with that of cyclooxygenase-2 (COX-2); however, COX-2-expressing stromal cells were located in the vicinity of the embryo, whereas DP-expressing stromal cells surrounded these cells on the mesometrial side. Specific [3H]PGD2-binding activity was detected in the decidua of uteri, with PGD2 synthesis comparable to that of PGE2 detected in the uteri during the peri-implantation period. Administration of the COX-2-specific inhibitor celecoxib caused adverse effects on decidualization, as demonstrated by the attenuated weight of the implantation sites, which was recovered by the simultaneous administration of a DP agonist. Such a rescuing effect of the DP agonist was mimicked by an EP4 agonist, but not an EP2 agonist. While the importance of DP signaling was shown pharmacologically, DP/EP2 double deficiency did not affect implantation and decidualization, suggesting the contribution of EP4 to these processes. Indeed, administration of an EP4 antagonist substantially affected decidualization in DP/EP2-deficient mice. These results suggest that COX-2-derived PGD2 and PGE2 contribute to decidualization via a coordinated pathway of DP and EP4 receptors.

An update on pacemaking in the myometrium.

Timely and efficient contractions of the smooth muscle of the uterus - the myometrium - are crucial to a successful pregnancy outcome. These episodic contractions are regulated by spontaneous action potentials changing cell and tissue electrical excitability. In this short review we will document and discuss current knowledge of these processes. Those seeking a conclusive account of myometrial pacemaking mechanisms, or indeed a definitive description of the anatomical site of uterine pacemaking, may be disappointed. Rather, after almost a century of investigation, and in spite of promising studies in the last decade or so, there remain many gaps in our knowledge. We review the progress that has been made using recent technologies including in vivo and ex vivo imaging and electrophysiology and computational modelling, taking evidence from studies of animal and human myometrium, with particular emphasis on what may occur in the latter. We have prioritized physiological studies that bring us closer to understanding function. From our analyses we suggest that in human myometrium there is no fixed pacemaking site, but rather mobile, initiation sites produce the connectivity for synchronizing electrical and contractile activity. We call for more studies and funding, as physiological understanding of pacemaking gives hope to being better able to treat clinical conditions such as preterm and dysfunctional labours.

A Potential Role of CD82/KAI1 during Uterine Decidualization in Mice.

The tumor metastasis suppressor gene CD82/KAI1 has been demonstrated to impact human trophoblast invasion and migration. Communication between trophoblasts and decidual stromal cells plays a crucial role in controlling the normal invasiveness of trophoblasts. However, whether CD82/KAI1 is involved in decidualization and what role it plays remain unclear. CD82/KAI1 demonstrates specific spatiotemporal expression patterns in stromal cells undergoing decidualization during pregnancy. This is observed in both naturally pregnant females post-implantation and pseudopregnant mice undergoing induced decidualization, as detected through in situ hybridization and immunofluorescence. CD82/KAI1 expression showed a significant time-dependent increase in cultured stromal cells after 24 and 48 h of progesterone (P4) and estrogen (E2) treatment. This was accompanied by a notable upregulation of decidualization markers, including cyclin D3 and PR. After transducing stromal cells with the adenovirus-overexpressing CD82/KAI1 for 48 h, the expression of cyclin D3 protein increased. Meanwhile, there was an attenuated expression of CD82/KAI1 due to an adenovirus siRNA knockdown, whereas cyclin D3 and PR expressions were not affected. Our findings suggest a potential role of CD82/KAI1 in regulating the process of decidualization, providing insights into stromal cell differentiation.

Transcript analysis of uterus transplant cervical biopsies using the Banff Human Organ Transplant panel.

Uterus transplantation is being more widely implemented in clinical practice. Monitoring of rejection is routinely done for cervical biopsies and is dependent on histopathological assessment, as rejections are clinically silent and nonhistological biomarkers are missing. Until this gap is filled, it is important to corroborate the histopathological diagnosis of rejection through independent methods such as gene expression analysis. In this study, we compared our previously published scoring system for grading rejection in uterus transplant cervical biopsies to the gene expression profile in the same biopsy. For this, we used the Banff Human Organ Transplant gene panel to analyze the expression of 788 genes in 75 paraffin-embedded transplant cervical biopsies with a spectrum of histologic findings, as well as in 24 cervical biopsies from healthy controls. We found that gene expression in borderline changes did not differ from normal transplants, whereas the genes with increased expression in mild rejections overlapped with previously published rejection-associated transcripts. Moderate/severe rejection samples showed a gene expression pattern characterized by a mixture of rejection-associated and tissue injury-associated genes and a decrease in epithelial transcripts. In summary, our findings support our proposed scoring system for rejection but argue against the treatment of borderline changes.

Protease-activated receptor 2: a promising therapeutic target for women's cancers.

Cancers affecting women, such as breast, uterine, ovarian, endometrial and cervical cancers, have become increasingly prevalent. The growing incidence and death rates associated with these cancers warrant the development of innovative and alternative approaches to current treatments. This article investigates the association of women's cancers with a molecular target known as protease-activated receptor 2 (PAR2), a G-protein coupled receptor that is expressed on the surface of cancer cells. Expression levels of the PAR2 gene were curated from publicly available databases and were found to be significantly overexpressed in tissues from patients with breast, uterine, ovarian, endometrial or cervical cancer compared to normal tissues. PAR2 overexpression has been previously linked to tumor progression and, in some cases, tumor growth. Activation of PAR2 by either endogenous proteases or synthetic agonists triggers certain downstream intracellular signaling pathways that have been associated with tumor progression, cell migration and invasion, angiogenesis and apoptosis of cancer cells. While recent advances have led to the identification of several PAR2 antagonists, none has yet been developed for human use. Additionally, PAR2 inhibition has been shown also to increase the efficacy of chemotherapeutic drugs, allowing them to be potentially used at less toxic doses in combination therapies for cancer. The present work briefly summarizes the current status of PAR2 as a potential therapeutic target for treating women's cancers. Significance Statement This article highlights potential roles for PAR2 in cancers affecting women. Overexpression of the PAR2 gene in women's cancers is associated with various oncogenic processes such as tumor progression, cell migration and invasion, ultimately contributing to poorer patient prognoses. Given the increasing incidence of women's cancers, there is an urgent need to develop novel therapeutic drugs and PAR2 represents a promising target for developing new treatments.

Ovarian sex steroid and epithelial control of immune responses in the uterus and oviduct: human and animal models†.

The female reproductive tract (FRT), including the uterus and oviduct (Fallopian tube), is responsible for maintaining an optimal microenvironment for reproductive processes, such as gamete activation and transportation, sperm capacitation, fertilization, and early embryonic and fetal development. The mucosal surface of the FRT may be exposed to pathogens and sexually transmitted microorganisms due to the opening of the cervix during mating. Pathogens and endotoxins may also reach the oviduct through the peritoneal fluid. To maintain an optimum reproductive environment while recognizing and killing pathogenic bacterial and viral agents, the oviduct and uterus should be equipped with an efficient and rigorously controlled immune system. Ovarian sex steroids can affect epithelial cells and underlying stromal cells, which have been shown to mediate innate and adaptive immune responses. This, in turn, protects against potential infections while maintaining an optimal milieu for reproductive events, highlighting the homeostatic involvement of ovarian sex steroids and reproductive epithelial cells. This article will discuss how ovarian sex steroids affect the immune reactions elicited by the epithelial cells of the non-pregnant uterus and oviduct in the bovine, murine, and human species. Finally, we propose that there are regional and species-specific differences in the immune responses in FRT.

Evidence for metabolism of creatine by the conceptus, placenta, and uterus for production of adenosine triphosphate during conceptus development in pigs†.

In pigs, the majority of embryonic mortality occurs when free-floating conceptuses (embryos/fetuses and associated placental membranes) elongate, and the uterine-placental interface undergoes folding and develops areolae. Both periods involve proliferation, migration, and changes in morphology of cells that require adenosine triphosphate (ATP). We hypothesize that insufficient ATP in conceptus and uterine tissues contributes to conceptus loss in pigs. Creatine is stored in cells as phosphocreatine for ATP regeneration through the creatine-creatine kinase- phosphocreatine pathway. However, the expression of components of this pathway in pigs has not been examined throughout gestation. Results of qPCR analyses indicated increases in AGAT, GAMT, CKM, CKB, and SLC6A8 mRNAs in elongating porcine conceptuses, and immunofluorescence microscopy localized guanidinoacetate N-methyltransferase, creatine kinase M, and creatine kinase B proteins to the trophectoderm of elongating conceptuses, to the columnar chorionic epithelial cells at the bottom of chorioallantoic troughs, and to endometrial luminal epithelium at the tops of the endometrial ridges of uterine-placental folds on Days 40, 60, and 90 of gestation. Guanidinoacetate N-methyltransferase protein is expressed in endometrial luminal epithelium at the uterine-placental interface, but immunostaining is more intense in luminal epithelium at the bottoms of the endometrial ridges. Results of this study indicate that key elements of the pathway for creatine metabolism are expressed in cells of the conceptus, placenta, and uterus for potential production of ATP during two timepoints in pregnancy with a high demand for energy; elongation of the conceptus for implantation and development of uterine-placental folding during placentation.

Metabolic pathways for glucose and fructose: I synthesis and metabolism of fructose by ovine conceptuses†.

Fructose, the most abundant hexose sugar in fetal fluids and the blood of sheep and other ungulates and cetaceans, is synthesized from glucose via the polyol pathway in trophectoderm and chorion. However, the cell-specific and temporal expression of enzymes for the synthesis and metabolism of fructose in sheep conceptuses (embryo and placental membranes) and placentomes has not been characterized. This study characterized key enzymes involved in fructose synthesis and metabolism by ovine conceptuses throughout pregnancy. Day 17 conceptuses expressed mRNAs for the polyol pathway (SORD and AKR1B1) and glucose and fructose metabolism (HK1, HK2, G6PD, OGT, and FBP), but not those required for gluconeogenesis (G6Pase or PCK). Ovine placentomes also expressed mRNAs for SORD, AKR1B1, HK1, and OGT. Fructose can be metabolized via the ketohexokinase (KHK) pathway, and isoforms, KHK-A and KHK-C, were expressed in ovine conceptuses from Day 16 of pregnancy and placentomes during pregnancy in a cell-specific manner. The KHK-A protein was more abundant in the trophectoderm and cotyledons of placentomes, while KHK-C protein was more abundant in the endoderm of Day 16 conceptuses and the chorionic epithelium in placentomes. Expression of KHK mRNAs in placentomes was greatest at Day 30 of pregnancy (P < 0.05), but not different among days later in gestation. These results provide novel insights into the synthesis and metabolism of fructose via the uninhibited KHK pathway in ovine conceptuses to generate ATP via the tricarboxylic cycle, as well as substrates for the pentose cycle, hexosamine biosynthesis pathway, and one-carbon metabolism required for conceptus development throughout pregnancy.