The histone methyltransferase EZH2 is required for normal uterine development and function in mice†

The histone methyltransferase KMT2D is essential for embryo implantation via regulating precise differentiation of endometrial cells

Embryo implantation failures are a major challenge in reproductive medicine, but the underlying mechanism remains poorly understood. Successful implantation requires dynamic remodeling of the endometrium through integrated proliferation and differentiation of endometrial cells including luminal epithelial, glandular epithelial, and stromal cells. Conversely, their disruption causes infertility. Spatiotemporal control of transcription is required for these processes; however, the underlying epigenetic regulation is largely unknown. In this study, we examined expression data from the human endometrium during implantation and discovered that expression of the histone lysine methyltransferase KMT2D was significantly suppressed in patients with recurrent implantation failure. Further study revealed that uterine deletion of Kmt2d in mice caused infertility due to implantation failure. Morphological analysis discovered a reduction in the number of uterine glands and aberrant differentiation of the luminal and glandular epithelium into stratified phenotypes in Kmt2d knockout uteri. Administration of leukemia inhibitory factor protein, which is expressed in uterine glands and is essential for implantation, did not rescue implantation failure in Kmt2d knockout mice, suggesting that infertility was not solely due to uterine gland dysfunction. RNA sequencing analysis revealed that Kmt2d knockout uteri displayed suppressed expression of genes involved in ion homeostasis, which may affect the uterine luminal morphology. Our study suggests that KMT2D plays an essential role in facilitating successful embryo implantation by regulating the coordinated differentiation of endometrial cells, providing valuable insights into unexplained implantation failures in women.

Transcription Factor 23 is an Essential Determinant of Murine Term Parturition

Pregnancy involving intricate tissue transformations governed by the progesterone hormone (P4). P4 signaling via P4 receptors (PRs) is vital for endometrial receptivity, decidualization, myometrial quiescence, and labor initiation. This study explored the role of TCF23 as a downstream target of PR during pregnancy. TCF23 was found to be expressed in female reproductive organs, predominantly in uterine stromal and smooth muscle cells. Tcf23 expression was high during midgestation and was specifically regulated by P4, but not estrogen. The Tcf23 knockout (KO) mouse was generated and analyzed. Female KO mice aged 4-6 months exhibited subfertility, reduced litter size, and defective parturition. Uterine histology revealed disrupted myometrial structure, altered collagen organization, and disarrayed smooth muscle sheets at the conceptus sites of KO mice. RNA-Seq analysis of KO myometrium revealed dysregulation of genes associated with cell adhesion and extracellular matrix organization. TCF23 potentially modulates TCF12 activity to mediate cell-cell adhesion and matrix modulation in smooth muscle cells. Overall, TCF23 deficiency leads to impaired myometrial remodeling, causing parturition delay and fetal demise. This study sheds light on the critical role of TCF23 as a dowstream mediator of PR in uterine remodeling, reflecting the importance of cell-cell communication and matrix dynamics in myometrial activation and parturition.

Multiple tissue-specific epigenetic alterations regulate persistent gene expression changes following developmental DES exposure in mouse reproductive tissues

Clinically, developmental exposure to the endocrine disrupting chemical, diethylstilboestrol (DES), results in long-term male and female infertility. Experimentally, developmental exposure to DES results in abnormal reproductive tract phenotypes in male and female mice. Previously, we reported that neonatal DES exposure causes ERα-mediated aberrations in the transcriptome and in DNA methylation in seminal vesicles (SVs) of adult mice. However, only a subset of DES-altered genes could be explained by changes in DNA methylation. We hypothesized that alterations in histone modification may also contribute to the altered transcriptome during SV development. To test this idea, we performed a series of genome-wide analyses of mouse SVs at pubertal and adult developmental stages in control and DES-exposed wild-type and ERα knockout mice. Neonatal DES exposure altered ERα-mediated mRNA and lncRNA expression in adult SV, including genes encoding chromatin-modifying proteins that can impact histone H3K27ac modification. H3K27ac patterns, particularly at enhancers, and DNA methylation were reprogrammed over time during normal SV development and after DES exposure. Some of these reprogramming changes were ERα-dependent, but others were ERα-independent. A substantial number of DES-altered genes had differential H3K27ac peaks at nearby enhancers. Comparison of gene expression changes, H3K27ac marks and DNA methylation marks between adult SV and adult uterine tissue from ovariectomized mice neonatally exposed to DES revealed that most of the epigenetic changes and altered genes were distinct in the two tissues. These findings indicate that the effects of developmental DES exposure cause reprogramming of reproductive tract tissue differentiation through multiple epigenetic mechanisms.

Epigenetic Dysregulation in Endometriosis: Implications for Pathophysiology and Therapeutics

Endometriosis is a prevalent gynecological condition associated with pelvic pain and infertility. Despite more than a century of research, the etiology of endometriosis still eludes scientific consensus. This lack of clarity has resulted in suboptimal prevention, diagnosis, and treatment options. Evidence of genetic contributors to endometriosis is interesting but limited; however, significant progress has been made in recent years in identifying an epigenetic role in the pathogenesis of endometriosis through clinical studies, in vitro cell culture experiments, and in vivo animal models. The predominant findings include endometriosis-related differential expression of DNA methyltransferases and demethylases, histone deacetylases, methyltransferases, and demethylases, and regulators of chromatin architecture. There is also an emerging role for miRNAs in controlling epigenetic regulators in the endometrium and endometriosis. Changes in these epigenetic regulators result in differential chromatin organization and DNA methylation, with consequences for gene expression independent of a genetic sequence. Epigenetically altered expression of genes related to steroid hormone production and signaling, immune regulation, and endometrial cell identity and function have all been identified and appear to play into the pathophysiological mechanisms of endometriosis and resulting infertility. This review summarizes and critically discusses early seminal findings, the ever-growing recent evidence of epigenetic contributions to the pathophysiology of endometriosis, and implications for proposed epigenetically targeted therapeutics.

Dissecting mammalian reproduction with spatial transcriptomics

BACKGROUND

Mammalian reproduction requires the fusion of two specialized cells: an oocyte and a sperm. In addition to producing gametes, the reproductive system also provides the environment for the appropriate development of the embryo. Deciphering the reproductive system requires understanding the functions of each cell type and cell-cell interactions. Recent single-cell omics technologies have provided insights into the gene regulatory network in discrete cellular populations of both the male and female reproductive systems. However, these approaches cannot examine how the cellular states of the gametes or embryos are regulated through their interactions with neighboring somatic cells in the native tissue environment owing to tissue disassociations. Emerging spatial omics technologies address this challenge by preserving the spatial context of the cells to be profiled. These technologies hold the potential to revolutionize our understanding of mammalian reproduction.

OBJECTIVE AND RATIONALE

We aim to review the state-of-the-art spatial transcriptomics (ST) technologies with a focus on highlighting the novel biological insights that they have helped to reveal about the mammalian reproductive systems in the context of gametogenesis, embryogenesis, and reproductive pathologies. We also aim to discuss the current challenges of applying ST technologies in reproductive research and provide a sneak peek at what the field of spatial omics can offer for the reproduction community in the years to come.

SEARCH METHODS

The PubMed database was used in the search for peer-reviewed research articles and reviews using combinations of the following terms: 'spatial omics', 'fertility', 'reproduction', 'gametogenesis', 'embryogenesis', 'reproductive cancer', 'spatial transcriptomics', 'spermatogenesis', 'ovary', 'uterus', 'cervix', 'testis', and other keywords related to the subject area. All relevant publications until April 2023 were critically evaluated and discussed.

OUTCOMES

First, an overview of the ST technologies that have been applied to studying the reproductive systems was provided. The basic design principles and the advantages and limitations of these technologies were discussed and tabulated to serve as a guide for researchers to choose the best-suited technologies for their own research. Second, novel biological insights into mammalian reproduction, especially human reproduction revealed by ST analyses, were comprehensively reviewed. Three major themes were discussed. The first theme focuses on genes with non-random spatial expression patterns with specialized functions in multiple reproductive systems; The second theme centers around functionally interacting cell types which are often found to be spatially clustered in the reproductive tissues; and the thrid theme discusses pathological states in reproductive systems which are often associated with unique cellular microenvironments. Finally, current experimental and computational challenges of applying ST technologies to studying mammalian reproduction were highlighted, and potential solutions to tackle these challenges were provided. Future directions in the development of spatial omics technologies and how they will benefit the field of human reproduction were discussed, including the capture of cellular and tissue dynamics, multi-modal molecular profiling, and spatial characterization of gene perturbations.

WIDER IMPLICATIONS

Like single-cell technologies, spatial omics technologies hold tremendous potential for providing significant and novel insights into mammalian reproduction. Our review summarizes these novel biological insights that ST technologies have provided while shedding light on what is yet to come. Our review provides reproductive biologists and clinicians with a much-needed update on the state of art of ST technologies. It may also facilitate the adoption of cutting-edge spatial technologies in both basic and clinical reproductive research.

Histone modifications in embryo implantation and placentation: insights from mouse models

Embryo implantation and placentation play pivotal roles in pregnancy by facilitating crucial maternal-fetal interactions. These dynamic processes involve significant alterations in gene expression profiles within the endometrium and trophoblast lineages. Epigenetics regulatory mechanisms, such as DNA methylation, histone modification, chromatin remodeling, and microRNA expression, act as regulatory switches to modulate gene activity, and have been implicated in establishing a successful pregnancy. Exploring the alterations in these epigenetic modifications can provide valuable insights for the development of therapeutic strategies targeting complications related to pregnancy. However, our current understanding of these mechanisms during key gestational stages remains incomplete. This review focuses on recent advancements in the study of histone modifications during embryo implantation and placentation, while also highlighting future research directions in this field.

Uterine-specific Ezh2 deletion enhances stromal cell senescence and impairs placentation, resulting in pregnancy loss

Maternal uterine remodeling facilitates embryo implantation, stromal cell decidualization and placentation, and perturbation of these processes may cause pregnancy loss. Enhancer of zeste homolog 2 (EZH2) is a histone methyltransferase that epigenetically represses gene transcription; loss of uterine EZH2 affects endometrial physiology and induces infertility. We utilized a uterine Ezh2 conditional knockout (cKO) mouse to determine EZH2's role in pregnancy progression. Despite normal fertilization and implantation, embryo resorption occurred mid-gestation in Ezh2cKO mice, accompanied by compromised decidualization and placentation. Western blot analysis revealed Ezh2-deficient stromal cells have reduced amounts of the histone methylation mark H3K27me3, causing upregulation of senescence markers p21 and p16 and indicating that enhanced stromal cell senescence likely impairs decidualization. Placentas from Ezh2cKO dams on gestation day (GD) 12 show architectural defects, including mislocalization of spongiotrophoblasts and reduced vascularization. In summary, uterine Ezh2 loss impairs decidualization, increases decidual senescence, and alters trophoblast differentiation, leading to pregnancy loss.

The EZH2-PRC2-H3K27me3 axis governs the endometrial cell cycle and differentiation for blastocyst invasion

Infertility occurs in 15% of couples worldwide. Recurrent implantation failure (RIF) is one of the major problems in in vitro fertilization and embryo transfer (IVF-ET) programs, and how to manage patients with RIF to achieve successful pregnancy outcomes remains unresolved. Here, a uterine polycomb repressive complex 2 (PRC2)-regulated gene network was found to control embryo implantation. Our RNA-seq analyses of the human peri-implantation endometrium obtained from patients with RIF and fertile controls revealed that PRC2 components, including its core enzyme enhancer of zeste homolog 2 (EZH2)-catalyzing H3K27 trimethylation (H3K27me3) and their target genes are dysregulated in the RIF group. Although fertility of uterine epithelium-specific knockout mice of Ezh2 (eKO mice) was normal, Ezh2-deleted mice in the uterine epithelium and stroma (uKO mice) exhibited severe subfertility, suggesting that stromal Ezh2 plays a key role in female fertility. The RNA-seq and ChIP-seq analyses revealed that H3K27me3-related dynamic gene silencing is canceled, and the gene expression of cell-cycle regulators is dysregulated in Ezh2-deleted uteri, causing severe epithelial and stromal differentiation defects and failed embryo invasion. Thus, our findings indicate that the EZH2-PRC2-H3K27me3 axis is critical to preparing the endometrium for the blastocyst invasion into the stroma in mice and humans.

MLL1:EZH2 Ratio in Uterine Secretions and Endometrial Receptivity in Patients with Endometriosis

OBJECTIVE

To establish a novel approach for diagnosing endometriosis (EM) in patients with impaired endometrial receptivity.

METHOD

Mixed lineage leukemia 1 (MLL1) and enhancer of zeste homolog 2 (EZH2) levels were analyzed. The MLL1:EZH2 ratio in identifying impaired endometrial receptivity has been established and validated.

RESULTS

In normal endometrial tissue, the MLL1:EZH2 ratio increased significantly in the midsecretory phase, compared with that in the proliferative phase. In the midsecretory phase, the MLL1:EZH2 ratio in endometrial tissues and uterine secretions accurately identifies patients with EM who have impaired endometrial receptivity. In the validation group, the sensitivity and specificity of the MLL1:EZH2 ratio in the uterine secretions of the midsecretory phase, in diagnosing patients EM who have impaired endometrial receptivity, were 100% and 96.55%, respectively.

CONCLUSIONS

The MLL1:EZH2 ratio in uterine secretions of the midsecretory phase may serve as a marker to diagnose EM in patients with impaired endometrial receptivity.

Role of EZH2 in Uterine Gland Development

Enhancer of zeste homolog 2 (EZH2) is a core component of polycomb repressive complex 2 that plays a vital role in transcriptional repression of gene expression. Conditional ablation of EZH2 using progesterone receptor (Pgr)-Cre in the mouse uterus has uncovered its roles in regulating uterine epithelial cell growth and stratification, suppressing decidual myofibroblast activation, and maintaining normal female fertility. However, it is unclear whether EZH2 plays a role in the development of uterine glands, which are required for pregnancy success. Herein, we created mice with conditional deletion of Ezh2 using anti-Mullerian hormone receptor type 2 (Amhr2)-Cre recombinase that is expressed in mesenchyme-derived cells of the female reproductive tract. Strikingly, these mice showed marked defects in uterine adenogenesis. Unlike Ezh2 Pgr-Cre conditional knockout mice, deletion of Ezh2 using Amhr2-Cre did not lead to the differentiation of basal-like cells in the uterus. The deficient uterine adenogenesis was accompanied by impaired uterine function and pregnancy loss. Transcriptomic profiling using next generation sequencing revealed dysregulation of genes associated with signaling pathways that play fundamental roles in development and disease. In summary, this study has identified an unrecognized role of EZH2 in uterine gland development, a postnatal event critical for pregnancy success and female fertility.

SWI/SNF Antagonism of PRC2 Mediates Estrogen-Induced Progesterone Receptor Expression

Endometrial cancer (EC) is characterized by high estrogen levels unopposed by progesterone. Treatment with progestins is standard for early EC, but the response to progestins is dependent on progesterone receptor (PGR) expression. Here, we show that the expression of PGR in endometrial epithelial cells is dependent on ARID1A, a DNA-binding subunit of the SWI/SNF chromatin-remodeling complex that is commonly mutated in EC. In endometrial epithelial cells with estrogen receptor overexpression, we find that ARID1A promotes estrogen signaling and regulates common gene expression programs. Normally, endometrial epithelial cells expressing estrogen receptors respond to estrogen by upregulating the PGR. However, when ARID1A expression is lost, upregulation of PGR expression is significantly reduced. This phenomenon can also occur following the loss of the SWI/SNF subunit BRG1, suggesting a role for ARID1A- and BRG1-containing complexes in PGR regulation. We find that PGR is regulated by a bivalent promoter, which harbors both H3K4me3 and H3K27me3 histone tail modifications. H3K27me3 is deposited by EZH2, and inhibition of EZH2 in the context of ARID1A loss results in restoration of estrogen-induced PGR expression. Our results suggest a role for ARID1A deficiency in the loss of PGR in late-stage EC and a therapeutic utility for EZH2 inhibitors in this disease.

EZH2 and Endometrial Cancer Development: Insights from a Mouse Model

Enhancer of zeste homolog 2 (EZH2), a core component of polycomb repressive complex 2, plays an important role in cancer development. As both oncogenic and tumor suppressive functions of EZH2 have been documented in the literature, the objective of this study is to determine the impact of Ezh2 deletion on the development and progression of endometrial cancer induced by inactivation of phosphatase and tensin homolog (PTEN), a tumor suppressor gene frequently dysregulated in endometrial cancer patients. To this end, we created mice harboring uterine deletion of both Ezh2 and Pten using Cre recombinase driven by the progesterone receptor (Pgr) promoter. Our results showed reduced tumor burden in Pten^d/d; Ezh2^d/d mice compared with that of Pten^d/d mice during early carcinogenesis. The decreased Ki67 index in EZH2 and PTEN-depleted uteri versus that in PTEN-depleted uteri indicated an oncogenic role of EZH2 during early tumor development. However, mice harboring uterine deletion of both Ezh2 and Pten developed unfavorable disease outcome, accompanied by exacerbated epithelial stratification and heightened inflammatory response. The observed effect was non-cell autonomous and mediated by altered immune response evidenced by massive accumulation of intraluminal neutrophils, a hallmark of endometrial carcinoma in Pten^d/d; Ezh2^d/d mice during disease progression. Hence, these results reveal dual roles of EZH2 in endometrial cancer development.

Gene silencing by EZH2 suppresses TGF-β activity within the decidua to avert pregnancy-adverse wound healing at the maternal-fetal interface

A little-appreciated feature of early pregnancy is that embryo implantation and placental outgrowth do not evoke wound-healing responses in the decidua, the specialized endometrial tissue that surrounds the conceptus. Here, we provide evidence that this phenomenon is partly due to an active program of gene silencing mediated by EZH2, a histone methyltransferase that generates repressive histone 3 lysine 27 trimethyl (H3K27me3) histone marks. We find that pregnancies in mice with EZH2-deficient decidual stromal cells frequently fail by mid-gestation, with the decidua showing ectopic myofibroblast formation, peri-embryonic collagen deposition, and gene expression profiles associated with transforming growth factor β (TGF-β)-driven fibroblast activation and fibrogenic extracellular matrix (ECM) remodeling. Analogous responses are observed when the mutant decidua is surgically wounded, while blockade of TGF-β receptor signaling inhibits the defects and improves reproductive outcomes. Together, these results highlight a critical feature of reproductive success and have implications for the context-specific control of TGF-β-mediated wound-healing responses elsewhere in the body.

Regulation of AKT Signaling in Mouse Uterus

17β-estradiol (E2) treatment of ovariectomized adult mice stimulates the uterine PI3K-AKT signaling pathway and epithelial proliferation through estrogen receptor 1 (ESR1). However, epithelial proliferation occurs independently of E2/ESR1 signaling in neonatal uteri. Similarly, estrogen-independent uterine epithelial proliferation is seen in adulthood in mice lacking Ezh2, critical for histone methylation, and in wild-type (WT) mice treated neonatally with estrogen. The role of AKT in estrogen-independent uterine epithelial proliferation was the focus of this study. Expression of the catalytically active phosphorylated form of AKT (p-AKT) and epithelial proliferation were high in estrogen receptor 1 knockout and WT mice at postnatal day 6, when E2 concentrations were low, indicating that neither ESR1 nor E2 are essential for p-AKT expression and epithelial proliferation in these mice. However, p-AKT levels and proliferation remained estrogen responsive in preweaning WT mice. Expression of p-AKT and proliferation were both high in uterine luminal epithelium of mice estrogenized neonatally and ovariectomized during adulthood. Increased expression of phosphorylated (inactive) EZH2 was also observed. Consistent with this, Ezh2 conditional knockout mice show ovary-independent uterine epithelial proliferation and high epithelial p-AKT. Thus, adult p-AKT expression is constitutive and E2/ESR1 independent in both model systems. Finally, E2-induced p-AKT expression and normal uterine proliferation did not occur in mice lacking membrane (m)ESR1, indicating a key role for membrane ESR1 in AKT activation. These findings emphasize the importance of AKT activation in promoting uterine epithelial proliferation even when that proliferation is not E2/ESR1 dependent and further indicate that p-AKT can be uncoupled from E2/ESR1 signaling in several experimental scenarios.

Downregulation of EZH2 in Trophoblasts Induces Decidual M1 Macrophage Polarization: a Potential Cause of Recurrent Spontaneous Abortion

Macrophages are known to be pivotal for ensuring the establishment of the immune tolerance microenvironment at the maternal–fetal interface. In particular, trophoblasts stay in close contact with decidual macrophages (DMs), which have been reported to play an active role in the modulation of the polarization of DMs. Thus, any dysfunction of trophoblasts might be associated with certain pregnancy‐related complications, such as recurrent spontaneous abortion (RSA). Enhancer of zeste homolog 2 (EZH2) is an important epigenetic regulatory gene that has been previously shown to be related to immune regulation. The present study assessed the expression of EZH2 in villi tissue obtained from healthy controls and RSA patients. Trophoblasts conditioned medium was collected to incubate macrophages differentiated from the THP‐1 cell line. The expression and function of EZH2 in trophoblasts were knocked down either by the use of siRNA or GSK126 as an inhibitor. Our results show a significant decrease in the expression of EZH2 in villi tissue from RSA patients as compared to healthy controls. Further, the inhibition of expression or function of EZH2 in trophoblasts promoted M1 macrophage polarization, which might be involved in the pathogenesis of RSA. Moreover, the suppression of EZH2 was found to affect the secretion of immune and inflammatory cytokines in trophoblasts. Altogether, these results indicated the importance of EZH2 in the regulation of immune functions of trophoblasts and thus highlighted its potential to be explored as a therapeutic target to prevent and treat pregnancy loss.

Spatial Transcriptomics analysis of uterine gene expression in enhancer of Zeste homolog 2 (Ezh2) conditional knockout mice

Histone proteins undergo various modifications that alter chromatin structure, including addition of methyl groups. Enhancer of homolog 2 (EZH2), is a histone methyltransferase that methylates lysine residue 27, and thereby, suppresses gene expression. EZH2 plays integral role in the uterus and other reproductive organs. We have previously shown that conditional deletion of uterine EZH2 results in increased proliferation of luminal and glandular epithelial cells, and RNAseq analyses reveal several uterine transcriptomic changes in Ezh2 conditional (c) knockout (KO) mice that can affect estrogen signaling pathways. To pinpoint the origin of such gene expression changes, we used the recently developed spatial transcriptomics (ST) method with the hypotheses that Ezh2cKO mice would predominantly demonstrate changes in epithelial cells and/or ablation of this gene would disrupt normal epithelial/stromal gene expression patterns. Uteri were collected from ovariectomized adult WT and Ezh2cKO mice and analyzed by ST. Asb4, Cxcl14, Dio2, and Igfbp5 were increased, Sult1d1, Mt3, and Lcn2 were reduced in Ezh2cKO uterine epithelium vs. WT epithelium. For Ezh2cKO uterine stroma, differentially expressed key hub genes included Cald1, Fbln1, Myh11, Acta2, and Tagln. Conditional loss of uterine Ezh2 also appears to shift the balance of gene expression profiles in epithelial vs. stromal tissue toward uterine epithelial cell and gland development and proliferation, consistent with uterine gland hyperplasia in these mice. Current findings provide further insight into how EZH2 may selectively affect uterine epithelial and stromal compartments. Additionally, these transcriptome data might provide the mechanistic understanding and valuable biomarkers for human endometrial disorders with epigenetic underpinnings.

Role of nuclear and membrane estrogen signaling pathways in the male and female reproductive tract

Estrogen signaling through the main estrogen receptor, estrogen receptor 1 (ESR1; also known as ERα), is essential for normal female and male reproductive function. Historically, studies of estrogen action have focused on the classical genomic pathway. Although this is clearly the major pathway for steroid hormone actions, these hormones also signal through rapid non-classical effects involving cell membrane actions. Reports of rapid effects of estrogens extend for more than half a century, but recent results have expanded understanding of the identity, structure, function and overall importance of membrane receptors in estrogen responses. Key findings in this field were the immunohistochemical detection of ESR1 in cell membranes and demonstration that a portion of newly synthesized ESR1 is routed to the membrane by palmitoylation. These receptors in the membrane can then signal through protein kinases and other mechanisms following ligand binding to alter cell function. Another crucial advance in the field was development of transgenic mice expressing normal amounts of functional nuclear ESR1 (nESR1) but lacking membrane ESR1 (mESR1). Both male and female transgenic mice lacking mESR1 were infertile as adults, and both sexes had extensive reproductive abnormalities. Transgenic mice lacking mESR1 were highly protected from deleterious effects of neonatal estrogen administration, and estrogen effects on the histone methyltransferase Enhancer of Zeste homolog 2 that are mediated through mESR1 could have significant effects on epigenetic imprinting. In summary, signaling through mESR1 is essential for normal male and female reproductive function and fertility, and is a critical enabler of normal estrogen responses in vivo. Although the precise role of mESR1 in estrogen responses remains to be established, future research in this area should clarify its mechanism of action and lead to a better understanding of how mESR1 signaling works with classical genomic signaling through nESR1 to promote full estrogenic responses.

Mice lacking membrane estrogen receptor 1 are protected from reproductive pathologies resulting from developmental estrogen exposure†

Both membrane and nuclear fractions of estrogen receptor 1 (ESR1) mediate 17β-estradiol (E2) actions. Mice expressing nuclear (n)ESR1 but lacking membrane (m)ESR1 (nuclear-only estrogen receptor 1 [NOER] mice) show reduced E2 responsivity and reproductive abnormalities culminating in adult male and female infertility. Using this model, we investigated whether reproductive pathologies caused by the synthetic estrogen diethylstilbestrol (DES) are mitigated by mESR1 ablation. Homozygous and heterozygous wild-type (WT and HET, respectively) and NOER male and female mice were subcutaneously injected with DES (1 mg/kg body weight [BW]) or vehicle daily from postnatal day (PND) 1-5. Uterine histology was assessed in select DES-treated females at PND 5, whereas others were ovariectomized at PND 60 and treated with E2 (10 μg/kg BW) or vehicle 2 weeks later. Neonatal DES exposure resulted in ovary-independent epithelial proliferation in the vagina and uterus of WT but not NOER females. Neonatal DES treatment also induced ovary-independent adult expression of classical E2-induced transcripts (e.g., lactoferrin [Ltf] and enhancer of zeste homolog 2 [Ezh2]) in WT but not NOER mice. At PND 90, DES-treated WT and HET males showed smaller testes and a high incidence of bacterial pyogranulomatous inflammation encompassing the testes, epididymis and occasionally the ductus deferens with spread to lumbar lymph nodes; such changes were largely absent in NOER males. Results indicate that male and female NOER mice are protected from deleterious effects of neonatal DES, and thus mESR1 signaling is required for adult manifestation of DES-induced reproductive pathologies in both sexes.

The Endometrial Transcription Landscape of MRKH Syndrome

The Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome (OMIM 277000) is characterized by agenesis of the uterus and upper part of the vagina in females with normal ovarian function. While genetic causes have been identified for a small subset of patients and epigenetic mechanisms presumably contribute to the pathogenic unfolding, too, the etiology of the syndrome has remained largely enigmatic. A comprehensive understanding of gene activity in the context of the disease is crucial to identify etiological components and their potential interplay. So far, this understanding is lacking, primarily due to the scarcity of samples and suitable tissue. In order to close this gap, we profiled endometrial tissue of uterus rudiments in a large cohort of MRKH patients using RNA-seq and thereby provide a genome-wide view on the altered transcription landscape of the MRKH syndrome. Differential and co-expression analyses of the data identified cellular processes and candidate genes that converge on a core network of interconnected regulators that emerge as pivotal for the perturbed expression space. With these results and browsable access to the rich data through an online tool we seek to accelerate research to unravel the underlying biology of the syndrome.

The Roles of the Histone Protein Modifier EZH2 in the Uterus and Placenta

Epigenetic modifications regulate normal physiological, as well as pathological processes in various organs, including the uterus and placenta. Both organs undergo dramatic and rapid restructuring that depends upon precise orchestration of events. Epigenetic changes that alter transcription and translation of gene-sets regulate such responses. Histone modifications alter the chromatin structure, thereby affecting transcription factor access to gene promoter regions. Binding of histones to DNA is regulated by addition or removal of subunit methyl and other groups, which can inhibit or stimulate transcription. Enhancer of zeste homolog 2 (EZH2) is the catalytic subunit of polycomb repressive complex 2 (PRC2) that catalyzes tri-methylation of histone H3 at Lys 27 (H3K27me3) and subsequently suppresses transcription of genes bound by such histones. Uterine EZH2 expression exerts a critical role in development and function of this organ with deletion of this gene resulting in uterine hyperplasia and expression of cancer-associated transcripts. Elucidating the roles of EZH2 in uterus and placenta is essential as EZH2 dysregulation is associated with several uterine and placental pathologies. Herein, we discuss EZH2 functions in uterus and placenta, emphasizing its physiological and pathological importance.

Peri- and Postpubertal Estrogen Exposures of Female Mice Optimize Uterine Responses Later in Life

At birth, all female mice, including those that either lack estrogen receptor α (ERα-knockout) or that express mutated forms of ERα (AF2ERKI), have a hypoplastic uterus. However, uterine growth and development that normally accompany pubertal maturation does not occur in ERα-knockout or AF2ERKI mice, indicating ERα-mediated estrogen (E2) signaling is essential for this process. Mice that lack Cyp19 (aromatase knockout, ArKO mice), an enzyme critical for E2 synthesis, are unable to make E2 and lack pubertal uterine development. A single injection of E2 into ovariectomized adult (10 weeks old) females normally results in uterine epithelial cell proliferation; however, we observe that although ERα is present in the ArKO uterine cells, no proliferative response is seen. We assessed the impact of exposing ArKO mice to E2 during pubertal and postpubertal windows and observed that E2-exposed ArKO mice acquired growth responsiveness. Analysis of differential gene expression between unexposed ArKO samples and samples from animals exhibiting the ability to mount an E2-induced uterine growth response (wild-type [WT] or E2-exposed ArKO) revealed activation of enhancer of zeste homolog 2 (EZH2) and heart- and neural crest derivatives-expressed protein 2 (HAND2) signaling and inhibition of GLI Family Zinc Finger 1 (GLI1) responses. EZH2 and HAND2 are known to inhibit uterine growth, and GLI1 is involved in Indian hedgehog signaling, which is a positive mediator of uterine response. Finally, we show that exposure of ArKO females to dietary phytoestrogens results in their acquisition of uterine growth competence. Altogether, our findings suggest that pubertal levels of endogenous and exogenous estrogens impact biological function of uterine cells later in life via ERα-dependent mechanisms.

Mice lacking uterine enhancer of zeste homolog 2 have transcriptomic changes associated with uterine epithelial proliferation

Enhancer of zeste homolog 2 (EZH2) is a histone methyltransferase that suppresses gene expression. Previously, we developed a conditional null model where EZH2 is knocked out in uterus. Deletion of uterine EZH2 increased proliferation of luminal and glandular epithelial cells. Herein, we used RNA-Seq in wild-type (WT) and EZH2 conditional knockout (Ezh2cKO) uteri to obtain mechanistic insights into the gene expression changes that underpin the pathogenesis observed in these mice. Ovariectomized adult Ezh2cKO mice were treated with vehicle (V) or 17β-estradiol (E2; 1 ng/g). Uteri were collected at postnatal day (PND) 75 for RNA-Seq or immunostaining for epithelial proliferation. Weighted gene coexpression network analysis was used to link uterine gene expression patterns and epithelial proliferation. In V-treated mice, 88 transcripts were differentially expressed (DEG) in Ezh2cKO mice, and Bmp5, Crabp2, Lgr5, and Sprr2f were upregulated. E2 treatment resulted in 40 DEG with Krt5, Krt15, Olig3, Crabp1, and Serpinb7 upregulated in Ezh2cKO compared with control mice. Transcript analysis relative to proliferation rates revealed two module eigengenes correlated with epithelial proliferation in WT V vs. Ezh2cKO V and WT E2 vs. Ezh2cKO E2 mice, with a positive relationship in the former and inverse in the latter. Notably, the ESR1, Wnt, and Hippo signaling pathways were among those functionally enriched in Ezh2cKO females. Current results reveal unique gene expression patterns in Ezh2cKO uterus and provide insight into how loss of this critical epigenetic regulator assumingly contributes to uterine abnormalities.

Reproductive tract biology: Of mice and men

The study of male and female reproductive tract development requires expertise in two separate disciplines, developmental biology and endocrinology. For ease of experimentation and economy, the mouse has been used extensively as a model for human development and pathogenesis, and for the most part similarities in developmental processes and hormone action provide ample justification for the relevance of mouse models for human reproductive tract development. Indeed, there are many examples describing the phenotype of human genetic disorders that have a reasonably comparable phenotype in mice, attesting to the congruence between mouse and human development. However, anatomic, developmental and endocrinologic differences exist between mice and humans that (1) must be appreciated and (2) considered with caution when extrapolating information between all animal models and humans. It is critical that the investigator be aware of both the similarities and differences in organogenesis and hormone action within male and female reproductive tracts so as to focus on those features of mouse models with clear relevance to human development/pathology. This review, written by a team with extensive expertise in the anatomy, developmental biology and endocrinology of both mouse and human urogenital tracts, focusses upon the significant human/mouse differences, and when appropriate voices a cautionary note regarding extrapolation of mouse models for understanding development of human male and female reproductive tracts.

Progesterone and Estrogen Signaling in the Endometrium: What Goes Wrong in Endometriosis?

In the healthy endometrium, progesterone and estrogen signaling coordinate in a tightly regulated, dynamic interplay to drive a normal menstrual cycle and promote an embryo-receptive state to allow implantation during the window of receptivity. It is well-established that progesterone and estrogen act primarily through their cognate receptors to set off cascades of signaling pathways and enact large-scale gene expression programs. In endometriosis, when endometrial tissue grows outside the uterine cavity, progesterone and estrogen signaling are disrupted, commonly resulting in progesterone resistance and estrogen dominance. This hormone imbalance leads to heightened inflammation and may also increase the pelvic pain of the disease and decrease endometrial receptivity to embryo implantation. This review focuses on the molecular mechanisms governing progesterone and estrogen signaling supporting endometrial function and how they become dysregulated in endometriosis. Understanding how these mechanisms contribute to the pelvic pain and infertility associated with endometriosis will open new avenues of targeted medical therapies to give relief to the millions of women suffering its effects.