Estrogen receptor alpha regulates uterine epithelial lineage specification and homeostasis

Revolutionizing Implantation Studies: Uterine-Specific Models and Advanced Technologies

Implantation is a complex and tightly regulated process essential for the establishment of pregnancy. It involves dynamic interactions between a receptive uterus and a competent embryo, orchestrated by ovarian hormones such as estrogen and progesterone. These hormones regulate proliferation, differentiation, and gene expression within the three primary uterine tissue types: myometrium, stroma, and epithelium. Advances in genetic manipulation, particularly the Cre/loxP system, have enabled the in vivo investigation of the role of genes in a uterine compartmental and cell type-specific manner, providing valuable insights into uterine biology during pregnancy and disease. The development of endometrial organoids has further revolutionized implantation research. They mimic the native endometrial structure and function, offering a powerful platform for studying hormonal responses, implantation, and maternal-fetal interactions. Combined with omics technologies, these models have uncovered the molecular mechanisms and signaling pathways that regulate implantation. This review provides a comprehensive overview of uterine-specific genetic tools, endometrial organoids, and omics. We explore how these advancements enhance our understanding of implantation biology, uterine receptivity, and decidualization in reproductive research.

Retinoic acid antagonizes estrogen signaling to maintain adult uterine cell fate

Classical tissue recombination experiments demonstrate that cell-fate determination along the anterior-posterior axis of the Müllerian duct occurs prior to postnatal day 7 in mice. However, little is known about how these cell types are maintained in adults. In this study, we provide genetic evidence that a balance between antagonistic retinoic acid (RA) and estrogen signaling activity is required to maintain simple columnar cell fate in adult uterine epithelium. Transdifferentiation of simple columnar uterine epithelium into stratified cervicovaginal-like epithelium was observed in three related mouse genetic models, in which RA signaling was perturbed in the postnatal uterus. Single-cell RNA sequencing analysis identified the transformed epithelial cell populations and revealed extensive immune cell infiltration resulting from loss of RA signaling. Surprisingly, disruption of RA signaling led to dysregulated expression of a substantial number of estrogen target genes, suggesting that these two pathways may functionally oppose each other in determining and maintaining uterine epithelial cell fate. Consistent with this model, neonatal exposure to the strong synthetic estrogen, diethylstilbestrol, downregulated expression of a group of RA target genes and led to epithelial stratification and immune cell infiltration in wild-type uterus. Treating RA receptor triple conditional knockout pups with fulvestrant, an estrogen antagonist, reestablished the balance between the two signaling pathways, and effectively prevented the transformation of mutant simple columnar epithelia to metaplastic stratified epithelia. These findings implicate an essential role for RA signaling in maintaining uterine cytodifferentiation by antagonizing estrogen signaling in the postnatal uterus.

Uterine organoids reveal insights into epithelial specification and plasticity in development and disease

Understanding how epithelial cells in the female reproductive tract (FRT) differentiate is crucial for reproductive health, yet the underlying mechanisms remain poorly defined. At birth, FRT epithelium is highly malleable, allowing differentiation into various epithelial types, but the regulatory pathways guiding these early cell fate decisions are unclear. Here, we use neonatal mouse endometrial organoids and assembloid coculture models to investigate how innate cellular plasticity and external mesenchymal signals influence epithelial differentiation. Our findings demonstrate that uterine epithelium undergoes marked age-dependent changes, transitioning from a highly plastic state capable of forming both monolayered and multilayered structures to a more restricted fate as development progresses. Interestingly, parallels emerge between the developmental plasticity of neonatal uterine epithelium and pathological conditions such as endometrial cancer, where similar regulatory mechanisms may reactivate, driving abnormal epithelial differentiation and tumorigenesis. These results not only deepen our understanding of early uterine development but also offer a valuable model for studying the progression of reproductive diseases and cancers.

Decoding Müllerian Duct Epithelial Regionalization

Müllerian ducts (MD), also known as paramesonephric ducts, are the primordial anlage of the female reproductive tract organs including the oviduct, uterus, cervix and upper vagina along the craniocaudal axis. Although the general architecture of MD-derived organs is conserved, each organ possesses their unique epithelial structures and cell types to confer their region-specific functions, which collectively coordinate successful fertilization and pregnancy. MD epithelial fate decisions and differentiation along the craniocaudal axis is dependent on spatiotemporal regulation of intrinsic transcription factors and extrinsic signals derived from the mesenchyme. Findings from genetic mouse models, single-cell sequencing studies, and organoid cultures have significantly advanced our understanding of the cellular and molecular mechanisms of MD regionalization. In this review, we first discuss the diversity of epithelial morphologies and cell types in the female reproductive tract organs. Then, we discuss the roles of key transcription factors (Hox, transcriptional cascade driving multiciliogenesis, Foxa2, and P63), signaling pathways (estrogen/ESR1, Wnt/β-catenin, hedgehog, and retinoic acid), and epigenetic factors (microRNAs, chromatin remodeling factors, and histone modification enzymes) in region-specific MD differentiation. Further deciphering molecular mechanisms of MD craniocaudal patterning will open new avenues to improve our strategies for prevention, diagnosis, and treatment of Müllerian anomalies and female reproductive tract disorders.

Biosynthetic pathway for leukotrienes is stimulated by lipopolysaccharide and cytokines in pig endometrial stromal cells

An inflammatory response is related to different inflammatory mediators generated by immune and endometrial cells. The links between lipopolysaccharide (LPS), cytokines, and leukotrienes (LTs) in endometrial stromal cells remain unclear. This study aimed to examine the influence of LPS, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-4 and IL-10 on 5-lipooxygenase (5-LO), LTA4 hydrolase (LTAH) and LTC4 synthase (LTCS) mRNA and protein abundances, and LTB4 and cysteinyl (cys)-LTs release including LTC4, by the cultured pig endometrial stromal cells, as well as on cell viability. 24-hour exposure to LPS, TNF-α, IL-4 and IL-10 up-regulated 5-LO mRNA and protein abundances. LPS increased LTAH mRNA abundance, while TNF-α, IL-1β and IL-10 augmented LTAH mRNA and protein abundances. TNF-α and IL-4 increased LTCS mRNA and protein abundances. In addition, LTCS mRNA abundance was enhanced by LPS and IL-4, while LTCS protein abundance was increased by IL-1β. Cells responded to LPS, TNF-α, IL-1β and IL-10 with increased LTB4 release. TNF-α, IL-1β and IL-4 stimulated LTC4 release. Cys-LTs release was up-regulated by LPS, TNF-α, IL-1β and IL-4. All studied cytokines augmented cell viability. In summary, LPS, TNF-α, IL-1β, IL-4 and IL-10 are potential LTs immunomodulatory agents in endometrial stromal cells. These functional interactions could be one of the mechanisms responsible for local orchestrating events in inflamed and healthy endometrium.

Protocol for the establishment and characterization of an endometrial-derived epithelial organoid and stromal cell co-culture system

Postnatal development of the uterus involves the specification of undifferentiated epithelium into uterine-type epithelium. That specification is regulated by stromal-epithelial interactions as well as intrinsic cell-specific transcription factors and gene regulatory networks. Here, we present a co-culture system to study the effects of stromal-derived factors on epithelial cell growth and differentiation into organoids. First, we describe epithelial cell isolation and organoid growth characterization. Second, we detail a co-culture system that allows the study of stromal-derived paracrine factors on epithelial development. For complete details on the use and execution of this protocol, please refer to Rizo et al.1.

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.