Mechanical and signaling mechanisms that guide pre-implantation embryo movement

Uterine stromal but not epithelial PTGS2 is critical for murine pregnancy success

Use of non-steroidal anti-inflammatory drugs that target prostaglandin synthase (PTGS) enzymes have been implicated in miscarriage. Further, PTGS2-derived prostaglandins are reduced in the endometrium of patients with a history of implantation failure. However, in the mouse model of pregnancy, peri-implantation PTGS2 function is controversial. Some studies suggest that Ptgs2 -/- mice display deficits in ovulation, fertilization, and implantation, while other studies suggest a role for PTGS2 only in ovulation but not implantation. Further, the uterine cell type responsible for PTGS2 function and role of PTGS2 in regulating implantation chamber formation is not known. To address this we generated tissue-specific deletion models of Ptgs2 . We observed that PTGS2 ablation from the epithelium alone in Ltf cre/+ ; Ptgs2 f/f mice and in both the epithelium and endothelium of the Pax2 cre/+ ; Ptgs2 f/f mice does not affect embryo implantation. Further, deletion of PTGS2 in the ovary, oviduct, and the uterus using Pgr cre/+ ; Ptgs2 f/f does not disrupt pre-implantation events but instead interferes with post-implantation chamber formation, vascular remodeling and decidualization. While all embryos initiate chamber formation, more than half of the embryos fail to transition from blastocyst to epiblast stage, resulting in embryo death and resorbing decidual sites at mid-gestation. Thus, our results suggest no role for uterine epithelial PTGS2 in early pregnancy but instead highlight a role for uterine stromal PTGS2 in modulating post-implantation embryo and implantation chamber growth. Overall, our study provides clarity on the compartment-specific role of PTGS2 and provides a valuable model for further investigating the role of stromal PTGS2 in post-implantation embryo development.

Dysregulated miR-124-3p in endometrial epithelial cells reduces endometrial receptivity by altering polarity and adhesion

The endometrium undergoes substantial remodeling in each menstrual cycle to become receptive to an implanting embryo. Abnormal endometrial receptivity is one of the major causes of embryo implantation failure and infertility. MicroRNA-124-3p is elevated in both the serum and endometrial tissue of women with chronic endometritis, a condition associated with infertility. MicroRNA-124-3p also has a role in cell adhesion, a key function during receptivity to allow blastocysts to adhere and implant. In this study, we aimed to determine the function of microRNA-124-3p on endometrial epithelial adhesive capacity during receptivity and effect on embryo implantation. Using a unique inducible, uterine epithelial-specific microRNA overexpression mouse model, we demonstrated that elevated uterine epithelial microRNA-124-3p impaired endometrial receptivity by altering genes associated with cell adhesion and polarity. This resulted in embryo implantation failure. Similarly in a second mouse model, increasing microRNA-124-3p expression only in mouse uterine surface (luminal) epithelium impaired receptivity and led to implantation failure. In humans, we demonstrated that microRNA-124-3p was abnormally increased in the endometrial epithelium of women with unexplained infertility during the receptive window. MicroRNA-124-3p overexpression in primary human endometrial epithelial cells (HEECs) impaired primary human embryo trophectoderm attachment in a 3-dimensional culture model of endometrium. Reduction of microRNA-124-3p in HEECs from infertile women normalized HEEC adhesive capacity. Overexpression of microRNA-124-3p or knockdown of its direct target IQGAP1 reduced fertile HEEC adhesion and its ability to lose polarity. Collectively, our data highlight that microRNA-124-3p and its protein targets contribute to endometrial receptivity by altering cell polarity and adhesion.

Spatiotemporally distinct roles of cyclooxygenase-1 and cyclooxygenase-2 at fetomaternal interface in mice

Embryo implantation is crucial for ensuring a successful pregnancy outcome and subsequent child health. The intrauterine environment during the peri-implantation period shows drastic changes in gene expression and cellular metabolism in response to hormonal stimuli and reciprocal communication with embryos. Here, we performed spatial transcriptomic analysis to elucidate the mechanisms underlying embryo implantation. Transcriptome data revealed that lipid metabolism pathways, especially arachidonic acid-related (AA-related) ones, were enriched in the embryo-receptive luminal epithelia. Cyclooxygenases (COXs), rate-limiting enzymes involved in prostaglandin production by AA, were spatiotemporally regulated in the vicinity of embryos during implantation, but the role of each COX isozyme in the uterus for successful pregnancy was unclear. We established uterine-specific COX2-knockout (uKO) and COX1/uterine COX2-double-KO (COX1/COX2-DKO) mice. COX2 uKO caused deferred implantation with failed trophoblast invasion, resulting in subfertility with reduced pregnancy rates and litter sizes. COX1/COX2 DKO induced complete infertility, owing to abrogated embryo attachment. These results demonstrate that both isozymes have distinct roles during embryo implantation. Spatial transcriptome and lipidome analyses revealed unique profiles of prostaglandin synthesis by each COX isozyme and spatiotemporal expression patterns of downstream receptors throughout the endometrium. Our findings reveal previously unappreciated roles of COXs at the fetomaternal interface to establish early pregnancy.

Monoamine oxidases activity maintains endometrial monoamine homeostasis and participates in embryo implantation and development

BACKGROUND

Monoamine oxidases (MAOs) is an enzyme that catalyzes the deamination of monoamines. The current research on this enzyme is focused on its role in neuropsychiatric, neurodevelopmental, and neurodegenerative diseases. Indeed, MAOs with two isoforms, namely, A and B, are located on the outer mitochondrial membrane and are widely distributed in the central nervous system and peripheral tissues. Several reports have described periodic changes in the levels of this enzyme in the human endometrial tissue.

RESULTS

The novel role of MAOs in endometrial receptivity establishment and embryonic development by maintaining monoamine homeostasis was investigated in this study. MAOs activity was observed to be enhanced during the first trimester in both humans and mice under normal conditions. However, under pathological conditions, MAOs activity was reduced and was linked to early pregnancy failure. During the secretory phase, the endometrial stromal cells differentiated into decidual cells with a stronger metabolism of monoamines by MAOs. Excessive monoamine levels cause monoamine imbalance in decidual cells, which results in the activation of the AKT signal, decreased FOXO1 expression, and decidual dysfunction.

CONCLUSIONS

The findings suggest that endometrial receptivity depends on the maintenance of monoamine homeostasis via MAOs activity and that this enzyme participates in embryo implantation and development.

Multi-omics analyses and machine learning prediction of oviductal responses in the presence of gametes and embryos

The oviduct is the site of fertilization and preimplantation embryo development in mammals. Evidence suggests that gametes alter oviductal gene expression. To delineate the adaptive interactions between the oviduct and gamete/embryo, we performed a multi-omics characterization of oviductal tissues utilizing bulk RNA-sequencing (RNA-seq), single-cell RNA-sequencing (scRNA-seq), and proteomics collected from distal and proximal at various stages after mating in mice. We observed robust region-specific transcriptional signatures. Specifically, the presence of sperm induces genes involved in pro-inflammatory responses in the proximal region at 0.5 days post-coitus (dpc). Genes involved in inflammatory responses were produced specifically by secretory epithelial cells in the oviduct. At 1.5 and 2.5 dpc, genes involved in pyruvate and glycolysis were enriched in the proximal region, potentially providing metabolic support for developing embryos. Abundant proteins in the oviductal fluid were differentially observed between naturally fertilized and superovulated samples. RNA-seq data were used to identify transcription factors predicted to influence protein abundance in the proteomic data via a novel machine learning model based on transformers of integrating transcriptomics and proteomics data. The transformers identified influential transcription factors and correlated predictive protein expressions in alignment with the in vivo-derived data. In conclusion, our multi-omics characterization and subsequent in vivo confirmation of proteins/RNAs indicate that the oviduct is adaptive and responsive to the presence of sperm and embryos in a spatiotemporal manner.

Effects of blastocyst elongation and implantation chamber formation on the alignment of the embryonic axis and uterine axis in mice

Embryo implantation involves a series of events that bring the embryo and maternal tissues into contact to support post-implantation development in mammals. During implantation, alignment of the embryonic-abembryonic (E-Ab) axis of the blastocyst with the mesometrial-antimesometrial (M-AM) axis of the uterus precedes post-implantation embryonic development and placentation. In the present study, we observed the morphological changes in blastocysts and the endometrial luminal epithelium (LE) that occur during the alignment of the embryonic and the uterine axes. We found that at the time that the blastocysts attached to the LE at the mural trophectoderm, the embryonic axis was not aligned with the uterine axis. Alignment of the embryonic E-Ab axis with the uterine M-AM axis occurred after E4.0, and the embryo was significantly elongated during the process. The depth of the implantation chamber (IC) correlated with the degree of alignment, suggesting that elongated embryos are oriented along the M-AM axis during IC formation. Transplantation of the Concanavalin A (Con A)-coated beads induced IC formation, and the alignment of two Con A-coated beads present in the same IC in the M-AM direction suggested that elongated materials can align along the M-AM axis. These data suggest that an elongated shape of the embryo and IC formation coordinate the alignment of the embryonic and uterine axes.

Imaging the dynamics of murine uterine contractions in early pregnancy†

Uterine muscle contractility is essential for reproductive processes including sperm and embryo transport, and during the uterine cycle to remove menstrual effluent. Even still, uterine contractions have primarily been studied in the context of preterm labor. This is partly due to a lack of methods for studying the uterine muscle contractility in the intact organ. Here, we describe an imaging-based method to evaluate mouse uterine contractility of both the longitudinal and circular muscles in the cycling stages and in early pregnancy. By transforming the image-based data into three-dimensional spatiotemporal contractility maps, we calculate waveform characteristics of muscle contractions, including amplitude, frequency, wavelength, and velocity. We report that the native organ is highly contractile during the progesterone-dominant diestrus stage of the cycle when compared to the estrogen-dominant proestrus and estrus stages. We also observed that during the first phase of uterine embryo movement when clustered embryos move toward the middle of the uterine horn, contractions are dynamic and non-uniform between different segments of the uterine horn. In the second phase of embryo movement, contractions are more uniform and rhythmic throughout the uterine horn. Finally, in Lpar3-/- uteri, which display faster embryo movement, we observe global and regional increases in contractility. Our method provides a means to understand the wave characteristics of uterine smooth muscle in response to modulators and in genetic mutants. Better understanding uterine contractility in the early pregnancy stages is critical for the advancement of artificial reproductive technologies and a possibility of modulating embryo movement during clinical embryo transfers.

Yes Associated Transcriptional Regulator 1 (YAP1) and WW Domain Containing Transcription Regulator (WWTR1) are required for murine pregnancy initiation

Endometrial stromal cell decidualization is required for pregnancy success. Although this process is integral to fertility, many of the intricate molecular mechanisms contributing to decidualization remain undefined. One pathway that has been implicated in endometrial stromal cell decidualization in humans in vitro is the Hippo signaling pathway. Two previously conducted studies showed that the effectors of the Hippo signaling pathway, YAP1 and WWTR1, were required for decidualization of primary stromal cells in culture. To investigate the in vivo role of YAP1 and WWTR1 in decidualization and pregnancy initiation, we generated a Progesterone Cre mediated partial double knockout (pdKO) of Yap1 and Wwtr1. Female pdKOs exhibited subfertility, a compromised decidualization response, partial interruption in embryo transport, blunted endometrial receptivity, delayed implantation and subsequent embryonic development, and a unique transcriptional profile. Bulk mRNA sequencing revealed aberrant maternal remodeling evidenced by significant alterations in extracellular matrix proteins at 7.5 days post-coitus in pdKO dams and enrichment for terms associated with fertility-compromising diseases like pre-eclampsia and endometriosis. Our results indicate a required role for YAP1 and WWTR1 for successful mammalian uterine function and pregnancy success.

The impact of ovarian stimulation on the human endometrial microenvironment

STUDY QUESTION

How does ovarian stimulation (OS), which is used to mature multiple oocytes for ART procedures, impact the principal cellular compartments and transcriptome of the human endometrium in the periovulatory and mid-secretory phases?

SUMMARY ANSWER

During the mid-secretory window of implantation, OS alters the abundance of endometrial immune cells, whereas during the periovulatory period, OS substantially changes the endometrial transcriptome and impacts both endometrial glandular and immune cells.

WHAT IS KNOWN ALREADY

Pregnancies conceived in an OS cycle are at risk of complications reflective of abnormal placentation and placental function. OS can alter endometrial gene expression and immune cell populations. How OS impacts the glandular, stromal, immune, and vascular compartments of the endometrium, in the periovulatory period as compared to the window of implantation, is unknown.

STUDY DESIGN, SIZE, DURATION

This prospective cohort study carried out between 2020 and 2022 included 25 subjects undergoing OS and 25 subjects in natural menstrual cycles. Endometrial biopsies were performed in the proliferative, periovulatory, and mid-secretory phases.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Blood samples were processed to determine serum estradiol and progesterone levels. Both the endometrial transcriptome and the principal cellular compartments of the endometrium, including glands, stroma, immune, and vasculature, were evaluated by examining endometrial dating, differential gene expression, protein expression, cell populations, and the three-dimensional structure in endometrial tissue. Mann-Whitney U tests, unpaired t-tests or one-way ANOVA and pairwise multiple comparison tests were used to statistically evaluate differences.

MAIN RESULTS AND THE ROLE OF CHANCE

In the periovulatory period, OS induced high levels of differential gene expression, glandular-stromal dyssynchrony, and an increase in both glandular epithelial volume and the frequency of endometrial monocytes/macrophages. In the window of implantation during the mid-secretory phase, OS induced changes in endometrial immune cells, with a greater frequency of B cells and a lower frequency of CD4 effector T cells.

LARGE SCALE DATA

The data underlying this article have been uploaded to the Genome Expression Omnibus/National Center for Biotechnology Information with accession number GSE220044.

LIMITATIONS, REASONS FOR CAUTION

A limited number of subjects were included in this study, although the subjects within each group, natural cycle or OS, were homogenous in their clinical characteristics. The number of subjects utilized was sufficient to identify significant differences; however, with a larger number of subjects and additional power, we may detect additional differences. Another limitation of the study is that proliferative phase biopsies were collected in natural cycles, but not in OS cycles. Given that the OS cycle subjects did not have known endometrial factor infertility, and the comparisons involved subjects who had a similar and robust response to stimulation, the findings are generalizable to women with a normal response to OS.

WIDER IMPLICATIONS OF THE FINDINGS

OS substantially altered the periovulatory phase endometrium, with fewer transcriptomic and cell type-specific changes in the mid-secretory phase. Our findings show that after OS, the endometrial microenvironment in the window of implantation possesses many more similarities to that of a natural cycle than does the periovulatory endometrium. Further investigation of the immune compartment and the functional significance of this cellular compartment under OS conditions is warranted.

STUDY FUNDING/COMPETING INTERESTS

Research reported in this publication was supported by the National Institute of Allergy and Infectious Diseases (R01AI148695 to A.M.B. and N.C.D.), Eunice Kennedy Shriver National Institute of Child Health and Human Development (R01HD109152 to R.A.), and the March of Dimes (5-FY20-209 to R.A.). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health or March of Dimes. All authors declare no conflict of interest.

Epigenomic analysis of the myometrium during late implantation revealed regulatory elements in genes related to the cellular zinc homeostasis pathway in pigs

The myometrium, composed of the inner circular muscle (CM) and outer longitudinal muscle (LM), is crucial in establishing and maintaining early pregnancy. However, the molecular mechanisms involved are not well understood. In this study, we identified the transcriptomic features of the CM and LM collected from the mesometrial (M) and anti-mesometrial (AM) sides of the pig uterus on day 18 of pregnancy during the placentation initiation phase. Some genes in the cellular zinc ion level regulatory pathways (MT-1A, MT-1D, MT-2B, SLC30A2, and SLC39A2) were spatially and highly enriched in uterine CM at the mesometrial side. In addition, the histone modification profiles of H3K27ac and H3K4me3 in uterine CM and LM collected from the mesometrial side were characterized. Genomic regions associated with the expression of genes regulating the cellular zinc ion level were detected. Moreover, six highly linked variants in the H3K27ac-enriched region of the pig SLC30A2 gene were identified and found to be significantly associated with the total number born at the second parity (P < 0.05). In conclusion, the genes in the pathways of cellular zinc homeostasis and their regulatory elements identified have implications for pig reproduction trait improvement and warrant further investigations.

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.

Cysteine-rich intestinal protein 1 is a novel surface marker for human myometrial stem/progenitor cells

Myometrial stem/progenitor cells (MyoSPCs) have been proposed as the cells of origin for uterine fibroids, but the identity of the MyoSPC has not been well established. We previously identified SUSD2 as a possible MyoSPC marker, but the relatively poor enrichment in stem cell characteristics of SUSD2+ over SUSD2- cells compelled us to find better markers. We combined bulk RNA-seq of SUSD2+/- cells with single cell RNA-seq to identify markers for MyoSPCs. We observed seven distinct cell clusters within the myometrium, with the vascular myocyte cluster most highly enriched for MyoSPC characteristics and markers. CRIP1 expression was found highly upregulated by both techniques and was used as a marker to sort CRIP1+/PECAM1- cells that were both enriched for colony forming potential and able to differentiate into mesenchymal lineages, suggesting that CRIP1+/PECAM1- cells could be used to better study the etiology of uterine fibroids.

Vascular changes in the cycling and early pregnant uterus

Uterine vascular remodeling is intrinsic to the cycling and early pregnant endometrium. Maternal regulatory factors such as ovarian hormones, VEGF, angiopoietins, Notch, and uterine natural killer cells significantly mediate these vascular changes. In the absence of pregnancy, changes in uterine vessel morphology and function correlate with different stages of the human menstrual cycle. During early pregnancy, vascular remodeling in rodents and humans results in decreased uterine vascular resistance and increased vascular permeability necessary for pregnancy success. Aberrations in these adaptive vascular processes contribute to increased risk of infertility, abnormal fetal growth, and/or preeclampsia. This Review comprehensively summarizes uterine vascular remodeling in the human menstrual cycle, and in the peri- and post-implantation stages in rodent species (mice and rats).

Cysteine-Rich Intestinal Protein 1 is a Novel Surface Marker for Myometrial Stem/Progenitor Cells

Myometrial stem/progenitor cells (MyoSPCs) have been proposed as the cells of origin for uterine fibroids, which are benign tumors that develop in the myometrium of most reproductive age women, but the identity of the MyoSPC has not been well established. We previously identified SUSD2 as a possible MyoSPC marker, but the relatively poor enrichment in stem cell characteristics of SUSD2+ over SUSD2- cells compelled us to find better discerning markers for more rigorous downstream analyses. We combined bulk RNA-seq of SUSD2+/- cells with single cell RNA-seq to identify markers capable of further enriching for MyoSPCs. We observed seven distinct cell clusters within the myometrium, with the vascular myocyte cluster most highly enriched for MyoSPC characteristics and markers, including SUSD2. CRIP1 expression was found highly upregulated in both techniques and was used as a marker to sort CRIP1+/PECAM1- cells that were both enriched for colony forming potential and able to differentiate into mesenchymal lineages, suggesting that CRIP1+/PECAM1- cells could be used to better study the etiology of uterine fibroids.

Pre-implantation mouse embryo movement under hormonally altered conditions

Pre-implantation embryo movement is crucial to pregnancy success, but the role of ovarian hormones in modulating embryo movement is not understood. We ascertain the effects of altered hormonal environment on embryo location using two delayed implantation mouse models: natural lactational diapause (ND); and artificially induced diapause (AD), a laboratory version of ND generated by ovary removal and provision of supplemental progesterone (P4). Previously, we showed that embryos in a natural pregnancy (NP) first display unidirectional clustered movement, followed by bidirectional scattering and spacing movement. In the ND model, we discovered that embryos are present as clusters near the oviductal-uterine junction for ∼24 h longer than NP, followed by locations consistent with a unidirectional scattering and spacing movement. Intriguingly, the AD model resembles embryo location in NP and not ND. When measuring serum hormone levels, unlike the popular paradigm of reduced estrogen (E2) levels in diapause, we observed that E2 levels are comparable across NP, ND and AD. P4 levels are reduced in ND and highly increased in AD when compared to NP. Further, exogenous administration of E2 or P4 modifies embryo location during the unidirectional phase, while E2 treatment also affects embryo location in the bidirectional phase. Taken together, our data suggest that embryo movement can be modulated by both P4 and E2. Understanding natural hormonal adaptation in diapause provides an opportunity to determine key players that regulate embryo location, thus impacting implantation success. This knowledge can be leveraged to understand pregnancy survival and implantation success in hormonally altered conditions in the clinic.

Integrating Transcriptomic and ChIP-Seq Reveals Important Regulatory Regions Modulating Gene Expression in Myometrium during Implantation in Pigs

The myometrium is the outer layer of the uterus. Its contraction and steroidogenic activities are required for embryo implantation. However, the molecular mechanisms underlying its functions remain unknown in pigs. The myometrium includes the inner circular muscle (CM) and the outer longitudinal muscle (LM) layers. In this study, we collected the CM and LM samples from the mesometrial side (named M) of the uterus on days 12 (pre-implantation stage) and 15 (implantation stage) of pregnancy and day 15 of the estrous cycle. The transcriptomic results revealed distinct differences between the uterine CM and LM layers in early pregnancy: the genes expressed in the LM layer were mainly related to contraction pathways, whereas the transcriptional signatures in the CM layer on day 15 of pregnancy were primarily involved in the immune response processes. Subsequent comparisons in the CM layer between pregnant and cyclic gilts show that the transcriptional signatures of the CM layer are implantation-dependent. Next, we investigated the genome-wide profiling of histone H3 lysine 27 acetylation (H3K27ac) and histone H3 lysine 4 trimethylation (H3K4me3) in pig uterine CM and LM layers. The genomic regions that had transcriptional activity and were associated with the expression of genes in the two layers were characterized. Taken together, the regulatory regions identified in the study may contribute to modulating the gene expression in pig uterine CM and LM layers during implantation.

Developmental and mechanical roles of Reichert's membrane in mouse embryos

Embryonic development and growth in placental mammals proceeds in utero with the support of exchanges of gases, nutrients and waste products between maternal tissues and offspring. Murine embryos are surrounded by several extraembryonic membranes, parietal and visceral yolk sacs, and amnion in the uterus. Notably, the parietal yolk sac is the most outer membrane, consists of three layers, trophoblasts and parietal endoderm (PaE) cells, and is separated by a thick basal lamina termed Reichert's membrane (RM). RM is composed of extracellular matrix (ECM) initially formed as the basement membrane of the trophectoderm of pre-implanted embryos and followed by the heavy deposition of ECM mainly produced in PaE cells of post-implanted embryos. In addition to the physiological roles of RM, such as gas and nutrient exchange, it also plays a crucial role in cushioning and dispersing intrauterine pressures exerted on embryos for normal egg-cylinder morphogenesis. Mechanistically, such intrauterine pressures generated by uterine smooth muscle contractions appear to be involved in the elongation of the egg-cylinder shape, along with primary axis formation, as an important biomechanical element in utero. This review focuses on our current views of the roles of RM in properly buffering intrauterine mechanical forces for mouse egg-cylinder morphogenesis. This article is part of the theme issue 'Extraembryonic tissues: exploring concepts, definitions and functions across the animal kingdom'.

Kisspeptin Is Upregulated at the Maternal-Fetal Interface of the Preeclamptic-like BPH/5 Mouse and Normalized after Synchronization of Sex Steroid Hormones

Insufficient invasion of conceptus-derived trophoblast cells in the maternal decidua is a key event in the development of early-onset preeclampsia (PE), a subtype of PE associated with high maternal and fetal morbidity and mortality. Kisspeptins, a family of peptides previously shown to inhibit trophoblast cell invasion, have been implicated in the pathogenesis of early-onset PE. However, a role of kisspeptin signaling during the genesis of this syndrome has not been elucidated. Herein, we used the preeclamptic-like BPH/5 mouse model to investigate kisspeptin expression and potential upstream regulatory mechanisms in a PE-like syndrome. Expression of the kisspeptin encoding gene, Kiss1, and the 10-amino-acid kisspeptide (Kp-10), are upregulated in the non-pregnant uterus of BPH/5 females during diestrus and in the maternal-fetal interface during embryonic implantation and decidualization. Correspondingly, the dysregulation of molecular pathways downstream to kisspeptins also occurs in this mouse model. BPH/5 females have abnormal sex steroid hormone profiles during early gestation. In this study, the normalization of circulating concentrations of 17β-estradiol (E2) and progesterone (P4) in pregnant BPH/5 females not only mitigated Kiss1 upregulation, but also rescued the expression of multiple molecules downstream to kisspeptin and ameliorated adverse fetoplacental outcomes. Those findings suggest that uterine Kiss1 upregulation occurs pre-pregnancy and persists during early gestation in a PE-like mouse model. Moreover, this study highlights the role of sex steroid hormones in uteroplacental Kiss1 dysregulation and the improvement of placentation by normalization of E2, P4 and Kiss1.

The people behind the papers – Manoj Madhavan and Ripla Arora

The 3D architecture of the uterus plays a key role in determine pregnancy outcome. A new paper in Development reveals the dynamic changes in luminal folding pattern that occur during the preimplantation period in mice. To hear more about the story, we caught up with first author Manoj Madhavan and corresponding author Ripla Arora, Assistant Professor at Michigan State University.

Aberrant uterine folding in mice disrupts implantation chamber formation and alignment of embryo-uterine axes

The uterine luminal epithelium folds characteristically in mammals, including humans, horses and rodents. Improper uterine folding in horses results in pregnancy failure, but the precise function of folds remains unknown. Here, we uncover dynamic changes in the 3D uterine folding pattern during early pregnancy with the entire lumen forming pre-implantation transverse folds along the mesometrial-antimesometrial axis. Using a time course, we show that transverse folds are formed before embryo spacing, whereas implantation chambers form as the embryo begins attachment. Thus, folds and chambers are two distinct structures. Transverse folds resolve to form a flat implantation region, after which an embryo arrives at its center to attach and form the post-implantation chamber. Our data also suggest that the implantation chamber facilitates embryo rotation and its alignment along the uterine mesometrial-antimesometrial axis. Using WNT5A- and RBPJ-deficient mice that display aberrant folds, we show that embryos trapped in longitudinal folds display misalignment of the embryo-uterine axes, abnormal chamber formation and defective post-implantation morphogenesis. These mouse models with disrupted uterine folding provide an opportunity to understand uterine structure-based mechanisms that are crucial for implantation and pregnancy success.

This article has an associated ‘The people behind the papers’ interview.

Disruption of Folate Metabolism Causes Poor Alignment and Spacing of Mouse Conceptuses for Multiple Generations

Abnormal uptake or metabolism of folate increases risk of human pregnancy complications, though the mechanism is unclear. Here, we explore how defective folate metabolism influences early development by analysing mice with the hypomorphic Mtrr^gt mutation. MTRR is necessary for methyl group utilisation from folate metabolism, and the Mtrr^gt allele disrupts this process. We show that the spectrum of phenotypes previously observed in Mtrr^gt/gt conceptuses at embryonic day (E) 10.5 is apparent from E8.5 including developmental delay, congenital malformations, and placental phenotypes. Notably, we report misalignment of some Mtrr^gt conceptuses within their implantation sites from E6.5. The degree of misorientation occurs across a continuum, with the most severe form visible upon gross dissection. Additionally, some Mtrr^gt/gt conceptuses display twinning. Therefore, we implicate folate metabolism in blastocyst orientation and spacing at implantation. Skewed growth likely influences embryo development since developmental delay and heart malformations (but not defects in neural tube closure or trophoblast differentiation) associate with severe misalignment of Mtrr^gt/gt conceptuses. Typically, the uterus is thought to guide conceptus orientation. To investigate a uterine effect of the Mtrr^gt allele, we manipulate the maternal Mtrr genotype. Misaligned conceptuses were observed in litters of Mtrr^+/+, Mtrr^+/gt, and Mtrr^gt/gt mothers. While progesterone and/or BMP2 signalling might be disrupted, normal decidual morphology, patterning, and blood perfusion are evident at E6.5 regardless of conceptus orientation. These observations argue against a post-implantation uterine defect as a cause of conceptus misalignment. Since litters of Mtrr^+/+ mothers display conceptus misalignment, a grandparental effect is explored. Multigenerational phenotype inheritance is characteristic of the Mtrr^gt model, though the mechanism remains unclear. Genetic pedigree analysis reveals that severe conceptus skewing associates with the Mtrr genotype of either maternal grandparent. Moreover, the presence of conceptus skewing after embryo transfer into a control uterus indicates that misalignment is independent of the peri- and/or post-implantation uterus and instead is likely attributed to an embryonic mechanism that is epigenetically inherited. Overall, our data indicates that abnormal folate metabolism influences conceptus orientation over multiple generations with implications for subsequent development. This study casts light on the complex role of folate metabolism during development beyond a direct maternal effect.