VE-cadherin enables trophoblast endovascular invasion and spiral artery remodeling during placental development

DOCK1 deficiency drives placental trophoblast cell dysfunction by influencing inflammation and oxidative stress, hallmarks of preeclampsia

Preeclampsia (PE) is a globally prevalent obstetric disorder, pathologically characterized by abnormal placental development. Dysfunctions of angiogenesis, vasculogenesis and spiral artery remodeling are demonstrated to be involved in PE pathogenesis; however, the underlying mechanisms remain largely unknown. Here, we investigated the role of the dedicator of cytokinesis 1 (DOCK1), crucial molecule in various cellular processes, in PE progression using HTR-8 cells derived from first-trimester placental extravillous trophoblasts. Our analysis revealed an aberrant DOCK1 expression in the placental villi of PE patients and its impact on essential cellular functions for vascular network formation. A deficiency of DOCK1 in HTR-8 cells impaired the vascular network formation, exacerbated the expression of anti-angiogenic factor ENG, and reduced VEGF levels. Moreover, DOCK1 knockout amplified apoptosis, as indicated by an altered BCL2: BAX ratio and enhanced levels of cleaved PARP. DOCK1 depletion also boosted NF-κB activation and pro-inflammatory cytokine production (IL-6 and TNF-α). Furthermore, the mice treated with DOCK1 inhibitor, TBOPP, exhibited PE-like symptoms. These findings highlight the multifaceted roles of DOCK1 in the pathophysiology of PE, demonstrating that its deficiency can lead to placental dysfunction by orchestrating inflammatory responses and oxidative stress. These insights emphasize the pathogenic role of DOCK1 in PE development and suggest potential treatment strategies that require further exploration. In the graphical abstract, a split image of placental villi contrasts the effects of normal and reduced DOCK1 expression on preeclampsia. The left side illustrates adequate DOCK1 levels supporting healthy trophoblast function and effective spiral artery remodeling. The right side highlights the consequences of DOCK1 deficiency, leading to trophoblast dysfunction and impaired spiral artery remodeling, accompanied by angiogenic imbalance, increased inflammation, oxidative stress, and apoptosis, contributing to placental dysfunction and the development of preeclampsia.

Single-cell RNA sequencing of estrual mice reveals PM2.5-induced uterine cell heterogeneity and reproductive toxicity

Fine particulate matter (PM2.5) exposure has been extensively linked to reproductive and developmental dysfunctions, yet the underlying mechanisms remain elusive. This study employed single-cell RNA sequencing (scRNA-seq) to investigate PM2.5-induced changes in uterine cell populations and gene expression profiles in mice during estrus and early pregnancy. Methodologically, we intranasally inoculated mice with 20 μL of 4.0 mg/mL PM2.5 suspension during their estrus and early pregnancy periods. Utilizing scRNA-seq analysis, we revealed significant alterations in cell type composition following PM2.5 exposure. Notably, we observed a marked decrease in the proportion of natural killer (NK) cells in PM2.5-exposed mice (2.00 % vs. 8.97 % in controls). Further functional enrichment analysis identified suppression of the IL-17 signaling pathway in NK cells as a key mechanism of PM2.5-induced toxicity. GSEA analysis showed in-depth details of the downregulated genes in this pathway, including Fosb, S100a8, Tnfaip3, IL-17a, and S100a9. PM2.5 exposure also disrupted intercellular communication within the uterine microenvironment, with the number of cell interactions decreasing from 483 to 315 and interaction strength reducing from 12.43 to 6.78 compared to controls. Histological examination revealed that PM2.5 exposure led to thinning of the endometrium and less prominent main branches in uterine tissues, and immunofluorescence assays corroborated the altered expression of IL-17 pathway components, showing enhanced Hsp90ab1 expression and reduced FOSB, S100A8, and S100A9 expression in PM2.5-exposed uterine tissues. These findings provide novel insights into the cellular mechanisms of PM2.5-induced reproductive toxicity, highlighting the IL-17 signaling pathway in uterine NK cells as a potential target for therapeutic interventions. Our results underscore the need for air quality regulations and open new avenues for developing biomarkers and targeted therapies to mitigate the reproductive risks associated with PM2.5 exposure.

Temporal BMP4 effects on mouse embryonic and extraembryonic development

The developing placenta, which in mice originates through the extraembryonic ectoderm (ExE), is essential for mammalian embryonic development. Yet unbiased characterization of the differentiation dynamics of the ExE and its interactions with the embryo proper remains incomplete. Here we develop a temporal single-cell model of mouse gastrulation that maps continuous and parallel differentiation in embryonic and extraembryonic lineages. This is matched with a three-way perturbation approach to target signalling from the embryo proper, the ExE alone, or both. We show that ExE specification involves early spatial and transcriptional bifurcation of uncommitted ectoplacental cone cells and chorion progenitors. Early BMP4 signalling from chorion progenitors is required for proper differentiation of uncommitted ectoplacental cone cells and later for their specification towards trophoblast giant cells. We also find biphasic regulation by BMP4 in the embryo. The early ExE-originating BMP4 signal is necessary for proper mesoendoderm bifurcation and for allantois and primordial germ cell specification. However, commencing at embryonic day 7.5, embryo-derived BMP4 restricts the primordial germ cell pool size by favouring differentiation of their extraembryonic mesoderm precursors towards an allantois fate. ExE and embryonic tissues are therefore entangled in time, space and signalling axes, highlighting the importance of their integrated understanding and modelling in vivo and in vitro.

Rational Design of Nanomedicine for Placental Disorders: Birthing a New Era in Women's Reproductive Health

The placenta is a transient organ that forms during pregnancy and acts as a biological barrier, mediating exchange between maternal and fetal circulation. Placental disorders, such as preeclampsia, fetal growth restriction, placenta accreta spectrum, and gestational trophoblastic disease, originate in dysfunctional placental development during pregnancy and can lead to severe complications for both the mother and fetus. Unfortunately, treatment options for these disorders are severely lacking. Challenges in designing therapeutics for use during pregnancy involve selectively delivering payloads to the placenta while protecting the fetus from potential toxic side effects. Nanomedicine holds great promise in overcoming these barriers; the versatile and modular nature of nanocarriers, including prolonged circulation times, intracellular delivery, and organ-specific targeting, can control how therapeutics interact with the placenta. In this review, nanomedicine strategies are discussed to treat and diagnose placental disorders with an emphasis on understanding the unique pathophysiology behind each of these diseases. Finally, prior study of the pathophysiologic mechanisms underlying these placental disorders has revealed novel disease targets. These targets are highlighted here to motivate the rational design of precision nanocarriers to improve therapeutic options for placental disorders.

Reduced syncytin-1 regulates trophoblast invasion and apoptosis in preeclampsia

INTRODUCTION

Preeclampsia is a pregnancy-specific disorder characterized by de novo development of hypertension and proteinuria over 20 weeks gestation that has been associated with the dysfunction of trophoblasts. Current evidence suggests that syncytin-1 plays an important role in the non-fusogenic biological activity of trophoblasts, except for specific fusogenic function. However, the underlying mechanism remains unclear.

METHODS

The expression and location of syncytin-1 in normal and the late-onset preeclampsia placentas were detected by quantitative real-time PCR, western blotting and immunofluorescence. Morphological and apoptosis analysis were processed in placentas. The ex vivo extravillous explant culture model was used to explore the effect of syncytin-1 on EVT outgrowths. Real-time quantitative PCR and immunoblotting were used to calculate syncytin-1 levels in the trophoblast cells before and after syncytin-1 knockdown or overexpression. CCK-8 assay was used to detect the cell viability. TUNEL staining and immunoblotting were processed in trophoblast cells. Transwell assays and wound healing assays were utilize to assess the invasion and migration of trophoblastic cells. Conditional knockout of syncytin-a mouse model was conducted to present the change of placentas in vivo. The ex vivo extravillous explant culture model was used to explore the effect of syncytin-1 on EVT outgrowths. Western blotting was used to identify the key proteins of PI3K/Akt pathways and invasion-related proteins in trophoblast cells.

RESULTS AND DISCUSSION

Here, reduced syncytin-1 was identified in the late-onset preeclampsia placentas. Reduced syncytin-1 may attenuates the EMT process by promoting apoptosis, inhibiting proliferation and invasion by suppressed PI3K/Akt pathway in trophoblast cells. Our findings provide novel insights into the non-fusogenic biological function of reduced syncytin-1 that may be involves in the pathogenesis of preeclampsia.

YAP/TAZ signaling in allantois-derived cells is required for placental vascularization

Normal placental development and angiogenesis are crucial for fetal growth and maternal health during pregnancy. However, molecular regulation of placental angiogenesis has been difficult to study due to a lack of specific genetic tools that isolate the placenta from the embryo and yolk sac. To address this gap in knowledge we recently developed Hoxa13 Cre mice in which Cre is expressed in allantois-derived cells, including placental endothelial and stromal cells. Mice lacking the transcriptional regulators Yes-associated protein (YAP) and PDZ-binding motif (TAZ) in allantois-derived cells exhibit embryonic lethality at midgestation with compromised placental vasculature. snRNA-seq analysis revealed transcriptional changes in placental stromal cells and endothelial cells. YAP/TAZ mutants exhibited significantly reduced placental stromal cells prior to the endothelial architectural change, highlighting the role of these cells in placental vascular growth. These results reveal a central role for YAP/TAZ signaling during placental vascular growth and implicate Hoxa13 -derived placental stromal cells as a critical component of placental vascularization.

Preeclampsia in the Context of COVID-19: Mechanisms, Pathophysiology, and Clinical Outcomes

The emergence of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has led to the global COVID-19 pandemic, significantly impacting the health of pregnant women. Obstetric populations, already vulnerable, face increased morbidity and mortality related to COVID-19, aggravated by preexisting comorbidities. Recent studies have shed light on the potential correlation between COVID-19 and preeclampsia (PE), a leading cause of maternal and perinatal morbidity worldwide, emphasizing the significance of exploring the relationship between these two conditions. Here, we review the pathophysiological similarities that PE shares with COVID-19, with a particular focus on severe COVID-19 cases and in PE-like syndrome cases related with SARS-CoV-2 infection. We highlight cellular and molecular mechanistic inter-connectivity between these two conditions, for example, regulation of renin-angiotensin system, tight junction and barrier integrity, and the complement system. Finally, we discuss how COVID-19 pandemic dynamics, including the emergence of variants and vaccination efforts, has shaped the clinical scenario and influenced the severity and management of both COVID-19 and PE. Continued research on the mechanisms of SARS-CoV-2 infection during pregnancy and the potential risk of developing PE from previous infections is warranted to delineate the complexities of COVID-19 and PE interactions and to improve clinical management of both conditions.

Tissue module discovery in single-cell-resolution spatial transcriptomics data via cell-cell interaction-aware cell embedding

Computational methods are desired for single-cell-resolution spatial transcriptomics (ST) data analysis to uncover spatial organization principles for how individual cells exert tissue-specific functions. Here, we present ST data analysis via interaction-aware cell embedding (SPACE), a deep-learning method for cell-type identification and tissue module discovery from single-cell-resolution ST data by learning a cell representation that captures its gene expression profile and interactions with its spatial neighbors. SPACE identified spatially informed cell subtypes defined by their special spatial distribution patterns and distinct proximal-interacting cell types. SPACE also automatically discovered "cell communities"-tissue modules with discernible boundaries and a uniform spatial distribution of constituent cell types. For each cell community, SPACE outputs a characteristic proximal cell-cell interaction network associated with physiological processes, which can be used to refine ligand-receptor-based intercellular signaling analyses. We envision that SPACE can be used in large-scale ST projects to understand how proximal cell-cell interactions contribute to emergent biological functions within cell communities. A record of this paper's transparent peer review process is included in the supplemental information.

High-throughput methylome analysis reveals differential methylation for early and late onset preeclampsia for mothers and their children

Preeclampsia is a hypertensive disorder of pregnancy that affects ∼2%-5% of all pregnancies, contributes to 4 of the top 10 causes of pregnancy-related deaths, and remains a long-term risk factor for cardiometabolic diseases. Yet, little is still known about the molecular mechanisms that lead to this disease. There is evidence that some cases have a genetic cause. However, it is well appreciated that harmful factors in the environment, such as poor nutrition, stress, and toxins, may lead to epigenetics changes that can contribute to this disease. DNA methylation is one of the epigenetic modifications known to be fairly stable and impact gene expression. Using DNA from buccal swabs, we analyzed global DNA methylation among three groups of individuals: mothers who experienced 1) early-stage preeclampsia (<32 wk), 2) late-stage preeclampsia (>37 wk), or 3) no complications during their pregnancies, as well as the children from these three groups. We found significant differentially methylated regions (DMRs) between mothers who experienced preeclampsia compared with those with no complications adjacent or within genes that are important for placentation, embryonic development, cell adhesion, and inflammation (e.g., the cadherin pathway). A significant portion of DMR genes showed expression in tissues relevant to preeclampsia (i.e., the brain, heart, kidney, uterus, ovaries, and placenta). As this study was performed on DNA extracted from cheek swabs, this opens the way to future studies in different tissues, aimed at identifying possible biomarkers of risk and early detection, developing targeted interventions, and reducing the progression of this life-threatening disease.NEW & NOTEWORTHY Preeclampsia is a life-threatening hypertensive disorder, affecting 2%-5% of pregnancies, that remains poorly understood. This study analyzed DNA methylation from buccal swabs from mothers who experienced early and late-stage preeclampsia and those with uncomplicated pregnancies, along with their children. Differentially methylated regions were found near and within genes crucial for placental function, embryonic development, and inflammation. Many of these genes are expressed in preeclampsia-related tissues, offering hope for future biomarker development for this condition.

Fibronectin mediates activin A-promoted human trophoblast migration and acquisition of endothelial-like phenotype

BACKGROUND

During human early placentation, a proportion of extravillous trophoblasts (EVTs) migrate to the maternal decidua, differentiating into endovascular EVTs to remodel spiral arteries and ensure the establishment of blood circulation at the maternal-fetal interface. Inadequate EVT migration and endovascular differentiation are closely associated with adverse pregnancy outcomes such as miscarriage. Activin A and fibronectin are both secretory molecules abundantly expressed at the maternal-fetal interface. Activin A has been reported to regulate EVT biological functions. However, whether fibronectin mediates activin A-promoted EVT migration and acquisition of endothelial-like phenotype as well as the underlying molecular mechanisms remain unknown. Additionally, the role of fibronectin in pregnancy establishment and maintenance warrants further investigation.

METHODS

Primary and immortalized (HTR8/SVneo) human EVTs were used as in vitro study models. Cultured human first-trimester chorionic villous explants were utilized for ex vivo validation. A local fibronectin knockdown model in ICR mouse uteri, achieved by nonviral in vivo transfection with small interfering RNA (siRNA) targeting fibronectin 1 (si-Fn1), was employed to explore the roles of fibronectin in the establishment and maintenance of early pregnancy.

RESULTS

Our results showed that activin A treatment significantly induced fibronectin 1 (FN1) mRNA expression and fibronectin protein production, which is essential for human trophoblast migration and endothelial-like tube formation. Both basal and activin A-upregulated fibronectin expression were abolished by the TGF-β type I receptor inhibitor SB431542 or siRNA-mediated knockdown of activin receptor-like kinase (ALK4) or SMAD4. Moreover, activin A-increased trophoblast migration and endothelial-like tube formation were attenuated following the depletion of fibronectin. Fibronectin knockdown via intrauterine siRNA administration reduced CD31 and cytokeratin 8 (CK8) expression at the maternal-fetal interface, resulting in a decrease in the number of implantation sites and embryos.

CONCLUSIONS

Our study demonstrates that activin A promotes trophoblast cell migration and acquisition of endothelial-like phenotype via ALK4-SMAD2/3-SMAD4-mediated fibronectin upregulation. Furthermore, through a local fibronectin knockdown model in mouse uteri, we found that the absence of fibronectin at the maternal-fetal interface impedes endovascular migration of trophoblasts and decidual vascularization, thereby interfering with early embryo implantation and the maintenance of pregnancy. These findings provide novel insights into placental development during early pregnancy establishment and contribute to the advancement of therapeutic approaches for managing pregnancy complications related to trophoblast dysfunction.

Fetoplacental Disposition and Toxicity of Cadmium in Mice Lacking the Bcrp Transporter

The environmental toxicant cadmium (Cd) impairs the growth of rodents and humans in utero which in turn heightens susceptibility to diseases later in life. We previously demonstrated that the maternal-facing efflux transporter, breast cancer resistance protein (human BCRP/ABCG2, mouse Bcrp/Abcg2) confers resistance against Cd toxicity in human trophoblasts. In the current study, we sought to determine whether the absence of Bcrp alters the fetoplacental disposition and toxicity of Cd in mice. Pregnant female wild-type (WT) and Bcrp-null mice (n = 9-10/group) were administered a single injection of saline (5 ml/kg) or CdCl2 (5 mg/kg) on gestational day (GD) 9. Following Cd treatment, Bcrp-null offspring were shorter and accumulated more Cd in their placentas on GD 17 compared to WT mice. Because Cd can adversely impact placentation and transplacental nutrient delivery in mice, multiple pathways were assessed using morphometrics and immunohistochemistry including placenta zonation, vasculature development, and nutrient transporter expression. Most notably, the placentas of Bcrp-null mice had reduced immunostaining of the cell adhesion marker, β-catenin, and the trophoblast marker, cytokeratin, as well as decreased expression of divalent metal nutrient transporters (Dmt1, Zip14, and ZnT1) following Cd treatment. In summary, the absence of Bcrp expression increased placental concentrations of Cd which was associated with shorter fetal size that may be related to differential changes in molecular patterns of placental development and nutrition.

Trophoblast Cell Function in the Antiphospholipid Syndrome

Antiphospholipid syndrome (APS) is a complex thrombo-inflammatory autoimmune disease characterized by the presence of antiphospholipid antibodies (aPL). Women with APS are at high risk of recurrent early pregnancy loss as well as late obstetrical complications-premature birth due to placental insufficiency or severe preeclampsia. Accumulating evidence implies that vascular thrombosis is not the only pathogenic mechanism in obstetric APS, and that the direct negative effect of aPL on the placental cells, trophoblast, plays a major role. In this review, we summarize the current findings regarding the potential mechanisms involved in aPL-induced trophoblast dysfunction. Introduction on the APS and aPL is followed by an overview of the effects of aPL on trophoblast-survival, cell function and aPL internalization. Finally, the implication of several non-coding RNAs in pathogenesis of obstetric APS is discussed, with special emphasis of their possible role in trophoblast dysfunction and the associated mechanisms.

GPR65 inhibits human trophoblast cell adhesion through upregulation of MYLK and downregulation of fibronectin via cAMP-ERK signaling in a low pH environment

BACKGROUND

Extravillous trophoblasts (EVTs) are essential cells during the formation of the placenta, with the major function of invading the maternal decidua, anchoring the developing placenta to the uterus, remodeling uterine arteries, and regulating immune responses to prevent rejection. During early pregnancy, the decidua undergoes a hypoxic and acidic microenvironment, which has been shown to participate in tumor cell migration, invasion, growth, and angiogenesis. Nevertheless, the mechanisms by which EVTs sense and respond to the acidic microenvironment, thereby executing their functions, remain poorly understood.

METHODS

The effects of G protein-coupled receptor 65 (GPR65) on cell adhesion and other cellular functions were tested using JAR spheroids, mouse blastocysts, and HTR-8/SVneo cells. Specifically, we employed HTR-8/SVneo cells for gene overexpression and silencing to investigate the underlying mechanism of GPR65's impact on trophoblast cell function under acidic conditions. Additionally, villus tissue samples obtained from early pregnancy loss patients were utilized to explore the potential association between GPR65 and its related signaling pathway molecules with the disease.

RESULTS

This study identified GPR65 expression widely in trophoblasts, with the highest level in EVTs. Importantly, optimal GPR65 levels are required for maintaining normal adhesion, migration, and invasion, whereas overexpression of GPR65 inhibits these functions by activating the cAMP-ERK signaling pathway, upregulating myosin light chain kinase (MYLK) and MYLK3 expression, and subsequently downregulating fibronectin. Consistently, elevated expression of GPR65, MYLK, and MYLK3 is observed in patients suffering from early pregnancy loss.

CONCLUSIONS

This work offers insights into the suppressive effects of GPR65 on EVT function under acidic conditions and highlights a putative target for therapeutic intervention in early pregnancy complications. Video Abstract.

Variable Cre Recombination Efficiency in Placentas of Cyp19-Cre ROSAmT/mG Transgenic Mice

The aromatase-Cre recombinase (Cyp19-Cre) transgenic mouse model has been extensively used for placenta-specific gene inactivation. In a pilot study, we observed unexpected phenotypes using this mouse strain, which prompted an extensive characterization of Cyp19-Cre placental phenotypes using ROSAmT/mG transgenic reporter mice. The two strains were mated to generate bi-transgenic Cyp19-Cre;ROSAmT/mG mice following a standard transgenic breeding scheme, and placental and fetal tissues were analyzed on embryonic day 17.5. Both maternal and paternal Cre inheritance were analyzed by mating the respective Cyp19-Cre and ROSAmT/mG males and females. The genotype results showed the expected percentage of Cyp19-Cre;ROSAmT/mG fetuses (73%) and Cre mRNA was expressed in all of the Cyp19-Cre placentas. However, surprisingly, only about 50% of the Cyp19-Cre;ROSAmT/mG placentas showed Cre-mediated recombinase activity as demonstrated by placental enhanced green fluorescent protein (EGFP) expression. Further genetic excision analysis of the placentas revealed consistent results showing the absence of excision of the tdTomato in all of the Cyp19-Cre;ROSAmT/mG placentas lacking EGFP expression. Moreover, among the EGFP-expressing placentas, there was wide variability in recombination efficiency, even in placentas from the same litter, leading to a mosaic pattern of EGFP expression in different zones and cell types of the placentas. In addition, we observed a significantly higher percentage of Cre recombination activity in placentas with maternal Cre inheritance. Our results show frequent mosaicism, inconsistent recombination activity, and parent-of-origin effects in placentas from Cyp19-Cre;ROSAmT/mG mice, suggesting that tail-biopsy genotype results may not necessarily indicate the excision of floxed genes in Cyp19-Cre positive placentas. Thus, placenta-specific mutagenesis studies using the Cyp19-Cre model require extensive characterization and careful interpretation of the placental phenotypes for each floxed allele.

Molecular mechanism of VE-cadherin in regulating endothelial cell behaviour during angiogenesis

Vascular endothelial (VE)-cadherin, an endothelium-specific adhesion protein, is found in the junctions between endothelial cells (ECs). It's crucial to maintain the homogeneity of ECs. Keeping and controlling the contact between ECs is essential. In addition to its adhesive function, VE-cadherin plays important roles in vascular development, permeability, and tumour angiogenesis. Signal transfer, cytoskeletal reconstruction, and contractile integrating, which are crucial for constructing and maintaining monolayer integrity as well as for repair and regeneration, are the foundation of endothelial cell (EC) junctional dynamics. The molecular basis of adhesion junctions (AJs), which are closely related and work with actin filaments, is provided by the VE-cadherin-catenin complex. They can activate intracellular signals that drive ECs to react or communicate structural changes to junctions. An increasing number of molecules, including the vascular endothelial growth factor receptor 2 (VEGFR2) and vascular endothelial protein tyrosine phosphatase (VE-PTP), have been connected to VE-cadherin in addition to the conventional VE-cadherin-catenin complex. This review demonstrates significant progress in our understanding of the molecular mechanisms that affect VE-cadherin's function in the regulation of EC behaviour during angiogenesis. The knowledge of the molecular processes that control VE-cadherin's role in the regulation of EC behaviour during angiogenesis has recently advanced, as shown in this review.

Trans-differentiation of trophoblast stem cells: implications in placental biology

Trophoblast invasion is a hallmark of hemochorial placentation. Invasive trophoblast cells replace the endothelial cells of uterine spiral arteries. The mechanism by which the invasive trophoblast cells acquire this phenotype is unknown. Here, we demonstrate that, during differentiation, a small population of trophoblast stem (TS) cells trans-differentiate into a hybrid cell type expressing markers of both trophoblast (TC) and endothelial (EC) cells. In addition, a compendium of EC-specific genes was found to be associated with TS cell differentiation. Using functional annotation, these genes were categorized into angiogenesis, cell adhesion molecules, and apoptosis-related genes. HES1 repressed transcription of EC genes in TS cells. Interestingly, differentiated TCs secrete TRAIL, but its receptor DR4 is expressed only in ECs and not in TCs. TRAIL induced apoptosis in EC but not in TC. Co-culture of ECs with TC induced apoptosis in ECs via extrinsic apoptotic pathway. These results highlight that (a) TS cells possess the potential to trans-differentiate into "trophendothelial" phenotype, regulated by HES1 and (b) trophoblast differentiation-induced TRAIL secretion directs preferential demise of ECs located in their vicinity.

Endometrial small extracellular vesicles regulate human trophectodermal cell invasion by reprogramming the phosphoproteome landscape

A series of cyclical events within the uterus are crucial for pregnancy establishment. These include endometrial regeneration following menses, under the influence of estrogen (proliferative phase), then endometrial differentiation driven by estrogen/progesterone (secretory phase), to provide a microenvironment enabling attachment of embryo (as a hatched blastocyst) to the endometrial epithelium. This is followed by invasion of trophectodermal cells (the outer layer of the blastocyst) into the endometrium tissue to facilitate intrauterine development. Small extracellular vesicles (sEVs) released by endometrial epithelial cells during the secretory phase have been shown to facilitate trophoblast invasion; however, the molecular mechanisms that underline this process remain poorly understood. Here, we show that density gradient purified sEVs (1.06-1.11 g/ml, Alix⁺ and TSG101⁺, ∼180 nm) from human endometrial epithelial cells (hormonally primed with estrogen and progesterone vs. estrogen alone) are readily internalized by a human trophectodermal stem cell line and promote their invasion into Matrigel matrix. Mass spectrometry-based proteome analysis revealed that sEVs reprogrammed trophectoderm cell proteome and their cell surface proteome (surfaceome) to support this invasive phenotype through upregulation of pro-invasive regulators associated with focal adhesions (NRP1, PTPRK, ROCK2, TEK), embryo implantation (FBLN1, NIBAN2, BSG), and kinase receptors (EPHB4/B2, ERBB2, STRAP). Kinase substrate prediction highlighted a central role of MAPK3 as an upstream kinase regulating target cell proteome reprogramming. Phosphoproteome analysis pinpointed upregulation of MAPK3 T204/T202 phosphosites in hTSCs following sEV delivery, and that their pharmacological inhibition significantly abrogated invasion. This study provides novel molecular insights into endometrial sEVs orchestrating trophoblast invasion, highlighting the microenvironmental regulation of hTSCs during embryo implantation.