Normal human endometrium in cell culture. I. Separation and characterization of epithelial and stromal components in vitro

Scar matrix drives Piezo1 mediated stromal inflammation leading to placenta accreta spectrum

Scar tissue formation is a hallmark of wound repair in adults and can chronically affect tissue architecture and function. To understand the general phenomena, we sought to explore scar-driven imbalance in tissue homeostasis caused by a common, and standardized surgical procedure, the uterine scar due to cesarean surgery. Deep uterine scar is associated with a rapidly increasing condition in pregnant women, placenta accreta spectrum (PAS), characterized by aggressive trophoblast invasion into the uterus, frequently necessitating hysterectomy at parturition. We created a model of uterine scar, recapitulating PAS-like invasive phenotype, showing that scar matrix activates mechanosensitive ion channel, Piezo1, through glycolysis-fueled cellular contraction. Piezo1 activation increases intracellular calcium activity and Protein kinase C activation, leading to NF-κB nuclear translocation, and MafG stabilization. This inflammatory transformation of decidua leads to production of IL-8 and G-CSF, chemotactically recruiting invading trophoblasts towards scar, initiating PAS. Our study demonstrates aberrant mechanics of scar disturbs stroma-epithelia homeostasis in placentation, with implications in cancer dissemination.

Injectable "Homing-Like" Bioactive Short-Fibers for Endometrial Repair and Efficient Live Births

The prevalence of infertility caused by endometrial defects is steadily increasing, posing a significant challenge to women's reproductive health. In this study, injectable "homing-like" bioactive decellularized extracellular matrix short-fibers (DEFs) of porcine skin origin are innovatively designed for endometrial and fertility restoration. The DEFs can effectively bind to endometrial cells through noncovalent dipole interactions and release bioactive growth factors in situ. In vitro, the DEFs effectively attracted endometrial cells through the "homing-like" effect, enabling cell adhesion, spreading, and proliferation on their surface. Furthermore, the DEFs effectively facilitated the proliferation and angiogenesis of human primary endometrial stromal cells (HESCs) and human umbilical vein endothelial cells (HUVECs), and inhibited fibrosis of pretreated HESCs. In vivo, the DEFs significantly accelerated endometrial restoration, angiogenesis, and receptivity. Notably, the deposition of endometrial collagen decreased from 41.19 ± 2.16% to 14.15 ± 1.70% with DEFs treatment. Most importantly, in endometrium-injured rats, the use of DEFs increased the live birth rate from 30% to an impressive 90%, and the number and development of live births close to normal rats. The injectable "homing-like" bioactive DEFs system can achieve efficient live births and intrauterine injection of DEFs provides a new promising clinical strategy for endometrial factor infertility.

Pre-clinical models to study abnormal uterine bleeding (AUB)

Abnormal Uterine Bleeding (AUB) is a common debilitating condition that significantly reduces quality of life of women across the reproductive age span. AUB creates significant morbidity, medical, social, and economic problems for women, their families, workplace, and health services. Despite the profoundly negative effects of AUB on public health, advancement in understanding the pathophysiology of AUB and the discovery of novel effective therapies is slow due to lack of reliable pre-clinical models. This review discusses currently available laboratory-based pre-clinical scientific models and how they are used to study AUB. Human and animal in vitro, ex vivo, and in vivo models will be described along with advantages and limitations of each method.

Three-dimensional culture models of human endometrium for studying trophoblast-endometrium interaction during implantation

During implantation, a symphony of interaction between the trophoblast originated from the trophectoderm of the implanting blastocyst and the endometrium leads to a successful pregnancy. Defective interaction between the trophoblast and endometrium often results in implantation failure, pregnancy loss, and a number of pregnancy complications. Owing to ethical concerns of using in vivo approaches to study human embryo implantation, various in vitro culture models of endometrium were established in the past decade ranging from two-dimensional cell-based to three-dimensional extracellular matrix (ECM)/tissue-based culture systems. Advanced organoid systems have also been established for recapitulation of different cellular components of the maternal-fetal interface, including the endometrial glandular organoids, trophoblast organoids and blastoids. However, there is no single ideal model to study the whole implantation process leaving more research to be done pursuing the establishment of a comprehensive in vitro model that can recapitulate the biology of trophoblast-endometrium interaction during early pregnancy. This would allow us to have better understanding of the physiological and pathological process of trophoblast-endometrium interaction during implantation.

Organoids of the female reproductive tract

Healthy functioning of the female reproductive tract (FRT) depends on balanced and dynamic regulation by hormones during the menstrual cycle, pregnancy and childbirth. The mucosal epithelial lining of different regions of the FRT-ovaries, fallopian tubes, uterus, cervix and vagina-facilitates the selective transport of gametes and successful transfer of the zygote to the uterus where it implants and pregnancy takes place. It also prevents pathogen entry. Recent developments in three-dimensional (3D) organoid systems from the FRT now provide crucial experimental models that recapitulate the cellular heterogeneity and physiological, anatomical and functional properties of the organ in vitro. In this review, we summarise the state of the art on organoids generated from different regions of the FRT. We discuss the potential applications of these powerful in vitro models to study normal physiology, fertility, infections, diseases, drug discovery and personalised medicine.

Methods for Studying Endometrial Pathology and the Potential of Atomic Force Microscopy in the Research of Endometrium

The endometrium lines the uterine cavity, enables implantation of the embryo, and provides an environment for its development and growth. Numerous methods, including microscopic and immunoenzymatic techniques, have been used to study the properties of the cells and tissue of the endometrium to understand changes during, e.g., the menstrual cycle or implantation. Taking into account the existing state of knowledge on the endometrium and the research carried out using other tissues, it can be concluded that the mechanical properties of the tissue and its cells are crucial for their proper functioning. This review intends to emphasize the potential of atomic force microscopy (AFM) in the research of endometrium properties. AFM enables imaging of tissues or single cells, roughness analysis, and determination of the mechanical properties (Young’s modulus) of single cells or tissues, or their adhesion. AFM has been previously shown to be useful to derive force maps. Combining the information regarding cell mechanics with the alternations of cell morphology or gene/protein expression provides deeper insight into the uterine pathology. The determination of the elastic modulus of cells in pathological states, such as cancer, has been proved to be useful in diagnostics.

A Novel Molecule in Human Cyclic Endometrium: LncRNA TUNAR Is Involved in Embryo Implantation

Embryo implantation rate remains an inefficient process in in vitro fertilization and embryo transfer (IVF-ET) cycles. The role long non-coding RNA (lncRNA) plays in embryo implantation remains unclear. We aimed to investigate the expression pattern of lncRNA TCL1 upstream neural differentiation-associated RNA (TUNAR) in human cyclic endometrium and clarify the role of TUNAR in the development of endometrial receptivity. Endometrial biopsies were collected at the late proliferative phase, luteinizing hormone (LH) + 2 and LH + 7, from patients with or without recurrent implantation failure (RIF). Real-time RT PCR was performed to detect the level of lncRNAs. After pZW1-snoVector-TUNAR transfection, multiple function of TUNAR in endometrial epithelial cells (EECs) and endometrial stromal cells (ESCs) was investigated. The expression of TUNAR in endometrium was found down-regulated at LH + 7 and up-regulated in RIF patients. In proliferative phase, TUNAR was overwhelmingly more abundant in ESCs and regulated its proliferation. In LH + 7, the difference in the expression of TUNAR between ESCs and EECs was narrowed. Overexpression of TUNAR not only impaired spheroid attachment to EECs, but also inhibited decidualization of ESCs. TUNAR was found expressed in human endometrium for the first time, which might be involved in embryo implantation by modulating the blastocyst attachment to the endometrial epithelium and regulating the proliferation and decidualization of ESCs. Our study helps us to better understand the molecular mechanisms of embryo implantation and may provide a promising biomarker of endometrial receptivity.

In vitro models of the human endometrium: evolution and application for women's health

The endometrium is the inner lining of the uterus that undergoes complex regeneration and differentiation during the human menstrual cycle. The process of endometrial shedding, regeneration, and differentiation is driven by ovarian steroid hormones and prepares the endometrium and intrauterine environment for embryo implantation and pregnancy establishment. Endometrial glands and their secretions are essential for pregnancy establishment, and cross talk between the glandular epithelium and stromal cells appears vital for decidualization and placental development. Despite being crucial, the biology of the human endometrium during pregnancy establishment and most of pregnancy is incomplete, given the ethical and practical limitations of obtaining and studying endometrium from pregnant women. As such, in vitro models of the human endometrium are required to fill significant gaps in understanding endometrial biology. This review is focused on the evolution and development of in vitro three-dimensional models of the human endometrium and provides insight into the challenges and promises of those models to improve women's reproductive health.

Progesterone modulates adhesion molecules in uterine epithelial cells and in vitro embryo production in buffalo

This study was undertaken to evaluate the role of progesterone (P4) in modulation of the expression profile of adhesion-related molecules in uterine epithelial cells (UECs) and in vitro blastocyst production in buffalo. UECs were isolated from slaughterhouse-derived uteri by enzymatic treatment, and cells were characterized by immunocytochemistry (ICC) and PCR assays. The well-characterized UECs were exposed to different concentrations of P4 (0, 0.314, 3.14 and 6.28 ng/ml) along with the basal level of oestradiol for 6 days. Thereafter, the relative mRNA expression of different biomolecules such as mucin 1 (MUC1), osteopontin, integrin alpha (α3, α6 and αV) and beta (β1 and β3) subunits, progesterone receptor (PR) and oestrogen receptor, was evaluated. Further, day 2 post-insemination embryos were cultured in mSOF supplemented with or without P4. UECs were found positive for cytokeratin expression and negative for vimentin expression. Progesterone treatment significantly enhanced the mRNA expression of most of the transcripts compared with the control group, and correspondingly, the immunofluorescence depicted higher protein expression of all these molecules. Further, the long-term exposure of UECs to P4 downregulated the expression of PR and, concomitantly, MUC1. Progesterone supplementation to embryo culture medium significantly (p < .05) improved the blastocyst rate. The study demonstrates the role of P4 hormone in modulation of the expression of early implantation-related biomolecules in uterine epithelial cells; hence, adequate level of steroids is crucial for normal embryo development and its implantation.

Local Cortisol Elevation Contributes to Endometrial Insulin Resistance in Polycystic Ovary Syndrome

CONTEXT

Endometrial insulin resistance (IR) may account for the endometrial dysfunction in polycystic ovary syndrome (PCOS). The underlying mechanism remains to be elucidated.

OBJECTIVE

To investigate whether the abundance of 11β-hydroxysteroid dehydrogenases (11β-HSDs) 1 and 2 and cortisol as well as the insulin signaling pathway are altered in PCOS endometrium and to clarify the relationship between endometrial IR and local cortisol.

DESIGN

We measured cortisol and cortisone concentrations, 11β-HSD1 and 11β-HSD2, and core insulin signaling molecules in endometrial biopsies collected from non-PCOS and PCOS with or without IR patients on the seventh day after human chorionic gonadotropin injection. We also studied the effects of cortisol on glucose uptake and the insulin signaling pathway in primary cultured endometrial epithelial cells (EECs).

RESULTS

The cortisol concentration was elevated, whereas 11β-HSD2 expression was diminished in endometrial biopsies obtained from PCOS with IR patients compared with those from non-PCOS and PCOS without IR patients. The implantation rate was relatively impaired and the endometrial insulin signaling pathway was defective in PCOS with IR patients. In addition, cortisol attenuated insulin-stimulated glucose uptake in EECs, which was mediated by inhibition of Akt phosphorylation and glucose transporter type 4 translocation via induction of phosphatase and tensin homolog deleted on chromosome ten (PTEN).

CONCLUSIONS

Decreased oxidation of cortisol and defects of insulin signaling in endometrium were observed in PCOS with IR patients. The excessive cortisol level, derived from the reduction of 11β-HSD2, might contribute to the development of endometrial IR by inhibiting the insulin signaling pathway via induction of PTEN expression in EECs.

Cryopreservation and recovery of human endometrial epithelial cells with high viability, purity, and functional fidelity

OBJECTIVE

To develop a protocol for cryopreservation and recovery of human endometrial epithelial cells (eECs) retaining molecular and functional characteristics of endometrial epithelium in vivo.

DESIGN

In vitro study using human endometrial cells.

SETTING

University research laboratory.

PATIENT(S)

Endometrial biopsies were obtained from premenopausal women undergoing benign gynecologic procedures.

INTERVENTION(S)

Primary eECs were cryopreserved in 1% fetal bovine serum/10% dimethylsulfoxide in Defined Keratinocyte Serum-Free Medium (KSFM). Recovered cells were observed for endometrial stromal fibroblast (eSF) contamination and subsequently evaluated for morphology, gene expression, and functional characteristics of freshly cultured eECs and in vivo endometrial epithelium.

MAIN OUTCOME MEASURE(S)

Analysis of eEC morphology and the absence of eSF contamination; evaluation of epithelial-specific gene and protein expression; assessment of epithelial polarity.

RESULT(S)

Endometrial epithelial cells recovered after cryopreservation (n = 5) displayed epithelial morphology and expressed E-cadherin (CDH1), occludin (OCLN), claudin1 (CLDN1), and keratin18 (KRT18). Compared with eSF, recovered eECs displayed increased (P<.05) expression of epithelial-specific genes AREG, CDH1, DEFB4A, MMP7, and WNT7A, while exhibiting low-to-undetectable (P<.05) stromal-specific genes COL6A3, HOXA11, MMP2, PDGFRB, and WNT5A. Recovered eECs secreted levels of cytokines and growth factors similarly to freshly cultured eECs. Recovered eECs could form a polarized monolayer with high transepithelial electrical resistance (TER) and impermeability to small molecules, and expressed apical/basolateral localization of CDH1 and apical localization of OCLN.

CONCLUSION(S)

We have developed a protocol for cryopreservation of eECs in which recovered cells after thawing demonstrate morphologic, transcriptomic, and functional characteristics of human endometrial epithelium in vivo.

Microarray analysis on gene regulation by estrogen, progesterone and tamoxifen in human endometrial stromal cells

Epithelial stromal cells represent a major cellular component of human uterine endometrium that is subject to tight hormonal regulation. Through cell-cell contacts and/or paracrine mechanisms, stromal cells play a significant role in the malignant transformation of epithelial cells. We isolated stromal cells from normal human endometrium and investigated the morphological and transcriptional changes induced by estrogen, progesterone and tamoxifen. We demonstrated that stromal cells express appreciable levels of estrogen and progesterone receptors and undergo different morphological changes upon hormonal stimulation. Microarray analysis indicated that both estrogen and progesterone induced dramatic alterations in a variety of genes associated with cell structure, transcription, cell cycle, and signaling. However, divergent patterns of changes, and in some genes opposite effects, were observed for the two hormones. A large number of genes are identified as novel targets for hormonal regulation. These hormone-responsive genes may be involved in normal uterine function and the development of endometrial malignancies.

Isolation and Culture of Human Endometrial Epithelial Cells and Stromal Fibroblasts

Purification and culture of endometrial epithelial cells (eEC) and stromal fibroblasts (eSF) from endometrial biopsies allows for downstream cell-specific in vitro studies. The utility of this protocol is the ease with which cells are purified without contamination from unwanted cell types, and the ability to use patient-paired eEC and eSF in experiments. These methods have been previously published, but here the protocol has been updated for maximum efficiency.

Seminal plasma induces global transcriptomic changes associated with cell migration, proliferation and viability in endometrial epithelial cells and stromal fibroblasts

STUDY QUESTION

How does seminal plasma (SP) affect the transcriptome of human primary endometrial epithelial cells (eEC) and stromal fibroblasts (eSF)?

SUMMARY ANSWER

Exposure of eEC and eSF to SP in vitro increases expression of genes and secreted proteins associated with cellular migration, proliferation, viability and inhibition of cell death.

WHAT IS KNOWN ALREADY

Studies in both humans and animals suggest that SP can access and induce physiological changes in the upper female reproductive tract (FRT), which may participate in promoting reproductive success.

STUDY DESIGN, SIZE, DURATION

This is a cross sectional study involving control samples versus treatment. SP (pooled from twenty donors) was first tested for dose- and time-dependent cytotoxic effects on eEC and eSF (n = 4). As exposure of eEC or eSF to 1% SP for 6 h proved to be non-toxic, a second set of eEC/eSF samples (n = 4) was treated under these conditions for transcriptome, protein and functional analysis. With a third set of samples (n = 3), we further compared the transcriptional response of the cells to SP versus fresh semen.

PARTICIPANTS/MATERIALS, SETTING, METHODS

eEC and eSF were isolated from endometrial biopsies from women of reproductive age undergoing benign gynecologic procedures and maintained in vitro. RNA was isolated and processed for microarray studies to analyze global transcriptomic changes. Secreted factors in conditioned media from SP-treated cells were analyzed by Luminex and for the ability to stimulate migration of CD14+ monocytes and CD4+ T cells.

MAIN RESULTS AND THE ROLE OF CHANCE

Pathway identifications were determined using the Z-scoring system in Ingenuity Pathways Analysis (Z scores ≥|1.5|). SP induced transcriptomic changes (P < 0.05) associated with promoting leukocyte and endothelial cell recruitment, and proliferation of eEC and eSF. Cell viability pathways were induced, while those associated with cell death were suppressed (P < 0.05). SP and fresh semen induced similar sets of pathways, suggesting that SP can model the signaling effects of semen in the endometrium. SP also induced secretion of pro-inflammatory and pro-chemotactic cytokines, as well as pro-angiogenic and proliferative growth factors (P < 0.05) in both eEC and eSF. Finally, functional assays revealed that conditioned media from SP-treated eEC and eSF significantly increased (P < 0.05) chemotaxis of CD14+ monocytes and CD4+ T cells.

LIMITATIONS, REASONS FOR CAUTION

This study is limited to in vitro analyses of the effects of SP on endometrial cells. In addition, the measured response to SP was conducted in the absence of the ovarian hormones estradiol and progesterone, as well as epithelial-stromal paracrine signaling. While this study focused on establishing the baseline cellular response of endometrial cells to SP, future work should assess how hormone signaling in the presence of appropriate paracrine interactions affects SP-induced genes in these cells.

WIDER IMPLICATIONS OF THE FINDINGS

The results of this study support previous findings that SP and semen contain bioactive factors capable of eliciting chemotactic responses in the uterus, which can lead to recruitment of leukocytes to the endometrium. Future directions will explore if similar changes in gene expression do indeed occur after coitus in vivo, and how the signaling cascades initiated by SP in the endometrium can affect reproductive success, female reproductive health and susceptibility to sexually transmitted diseases. The gene list provided by the transcriptome analysis reported here should prove a valuable resource for understanding the response of the upper FRT to SP exposure.

STUDY FUNDING/COMPETING INTEREST(S)

This project was supported by NIH AI083050-04 (W.C.G./L.C.G.); NIH U54HD 055764 (L.C.G.); NIH 1F32HD074423-02 (J.C.C.); DOD W81XWH-11-1-0562 (W.C.G.); NIH 5K12-DK083021-04, NIH 1K99AI104262-01A1, The UCSF Hellman Award (N.R.R.). The authors have nothing to disclose.

Coculturing human endometrial epithelial cells and stromal fibroblasts alters cell-specific gene expression and cytokine production

OBJECTIVE

To determine the effects of coculturing endometrial epithelial cells (eEC) with paired endometrial stromal fibroblasts (eSF) on cell-specific gene expression and cytokine secretion patterns.

DESIGN

In vitro study.

SETTING

University research laboratory.

PATIENT(S)

Endometrial biopsies were obtained from premenopausal women.

INTERVENTION(S)

Polarized eEC and subject-paired eSF were cultured for 12.5 hours alone (monoculture) or combined in a two-chamber coculture system without cell-cell contact. Cells and conditioned media were analyzed for global gene expression and cytokine secretion, respectively. Purified, endometrial tissue-derived eEC and eSF isolated by fluorescent activated cell sorting (FACS) were used as noncultured controls.

MAIN OUTCOME MEASURE(S)

Cell-specific global gene expression profiling and analysis of secreted cytokines in eEC/eSF cocultures and respective monocultures.

RESULT(S)

Transepithelial resistance, diffusible tracer exclusion, expression of tight junction proteins, and apical/basolateral vectorial secretion confirmed eEC structural and functional polarization. Distinct transcriptomes of eEC and eSF were consistent with their respective lineages and their endometrial origin. Coculture of eEC with eSF resulted in altered cell-specific gene expression and cytokine secretion.

CONCLUSION(S)

This coculture model provides evidence that interactions between endometrial functionally polarized epithelium and stromal fibroblasts affect cell-specific gene expression and cytokine secretion underscoring their relevance when modeling endometrium in vitro.

Steroid receptors in canine endometrial cells can be regulated by estrogen and progesterone under in vitro conditions

The expression of estrogen (ER) and progesterone receptors (PR) in the endometrium is regulated by steroid hormones. An increase in plasma estrogen leads to upregulation of the number of both steroid receptors, whereas a decrease in both receptors population is due to high concentration of plasma progesterone. To study the exact effect of different concentrations of beta-estradiol and progesterone on canine epithelial and stromal endometrial cells an in vitro model from dog uterus was developed and kept for 20 days. Material was obtained from healthy dogs, undergoing ovariohysterectomy. Endometrial epithelial and stromal cells were gained after collagenase treatment, followed by filtration steps. Electron microscopy and immunolabeling were used to study cell morphology and differentiation. Immunocytochemistry was used to determine proliferation rate (Ki-67), ER and PR status on Days 3, 8, 10, 13, and 20. Mitotic activity of both cells was stimulated with different concentrations of steroids and revealed high values until cells reached confluency. ER and PR expression in confluent layer from epithelial and stromal cells was upregulated with beta-estradiol. In addition progesterone significant downregulated both receptors population in stromal cells, whereas the reduction was less pronounced in epithelial cells. Results showed that our in vitro system is a useful tool to study the influence of beta-estradiol and progesterone on cell proliferation rate, ER and PR expression. The primary cell culture model helps to avoid experiments on living animals.

Messenger ribonucleic acid for the mouse decidual prolactin is present and induced during in vitro decidualization of endometrial stromal cells

Although decidualization of endometrial stromal cells is crucial for blastocyst implantation and maintenance of pregnancy, its complex mechanism still remains largely unknown. To explore the mechanisms of decidualization, we have established an in vitro decidualization model in mice. Through extraction of mRNA from endometrial stromal cells for subsequent reverse transcriptase polymerase chain reaction analysis, we found that two ovarian hormones, 17 beta-estradiol and progesterone, induced morphological changes and expression of mRNA for prolactin (PRL) and the decidual/trophoblastic PRL-related protein (d/tPRP) in cultured mouse endometrial stromal cells. The expression of mRNA for the decidual PRL was also detected in the mouse decidua in vitro. In conclusion, mouse mRNA for decidual PRL is present and induced by estradiol and progesterone through in vitro decidualization of endometrial stromal cells.

Endometrial stromal cells regulate epithelial cell growth in vitro: a new co-culture model

The regulation of epithelial cell function and morphogenesis by the paracrine effectors from the mesenchyme or stroma has been well established using in-vivo studies. A more complete understanding of these relationships has been delayed due, in part, to a lack of appropriate co-culture models. In this study, we describe a co-culture model which demonstrates that normal paracrine relationships can be reconstituted in vitro and that human endometrial stromal cells regulate both growth and differentiation of primary human endometrial epithelial cells. Interesting differences in the proliferation of stromal and epithelial cells were noted in response to the basement membrane extract, Matrigel((R)). Exposure of stromal cells to Matrigel((R)) enhanced the paracrine capacity of these cells in vitro. When epithelial cells were co-cultured in contact with stromal cells embedded in Matrigel((R)), epithelial cell growth was inhibited by 65-80% compared to controls. Stromal cells in contact with Matrigel((R)) also regulated epithelial cell differentiation, as shown by induction of glycodelin expression. These co-culture studies show great promise as a method to investigate the cellular interactions between endometrial stromal and epithelial cells and their environment and to understand the molecular basis for the regulation of normal growth and differentiation of cells within complex tissues such as the endometrium.

Paracrine regulation of menstruation

Endometrial proliferation, secretion, vascular neoformation and modification to shedding is under direct and/or indirect control of steroid hormones. The progressive modification of the endometrial architecture is due to its growth and differentiation. The new tissue regenerates monthly from a 2-5 mm to a 12-18 mm of complex tissue until it sheds under a co-ordinated network of bioactive molecules produced and activated during the menstrual cycle. The steroid hormones, the HLA-DR and integrin molecules, the intense production of several proteins, the vascular damage, and the disconnection of cell-cell and cell-matrix interaction are participating in both the endometrial preparation for embryonic implantation and the shedding and bleeding of the tissue itself. Menstruation is a process associated with damage to the epithelium, endothelium and extracellular matrix, ending on controlled bleeding, tissue dissolution and repair. Endometrial proteinases and tissue factor (TF) contribute to systemic factors to control the mechanisms of regulation of tissue dissolution, tissue shedding, and vascular bleeding during menstruation.

The isolation and long-term culture of normal human endometrial epithelium and stroma. Expression of mRNAs for angiogenic polypeptides basally and on oestrogen and progesterone challenges

A highly reproducible and technically straightforward technique for the isolation and long-term culture of normal human endometrial epithelial cells is described. The essential conditions for long-term culture are that the cells be seeded onto a gelatin matrix and that ‘endothelial cell growth supplement’ be present in the culture medium. Normal endometrial epithelial cells express cytokeratins and oestrogen receptors. They may be passaged five to six times without change in properties. Growth of normal endometrial epithelial cells was stimulated by 17-beta-oestradiol and epidermal growth factor. Expression of the mRNA coding for seven polypeptide angiogenic factors, by normal endometrial epithelial, stromal and three endometrial carcinoma lines, was examined. The endometrial epithelial and stromal cells express mRNA for the polypeptide angiogenic factors, basic fibroblast growth factor, vascular endothelial cell growth factor, transforming growth factor-beta 1 and pleiotrophin, as well as the cytokine midkine. Expression of the mRNA for both vascular endothelial growth factor and midkine by normal endometrial epithelial cells showed a 2-fold increase on treatment with a physiological dose of 17-beta-oestradiol (10(−10) M) while, in contrast, the mRNA of transforming growth factor-beta 1 decreased 4-fold on treatment with 17-beta-oestradiol (10(−10) M) and was abolished by exposure to progesterone (5 × 10(−9) M). Expression of the mRNAs for angiogenic polypeptides by the endometrial carcinoma lines was more restricted.

Culture characteristics of human endometrial glandular epithelium throughout the menstrual cycle: modulation of deoxyribonucleic acid synthesis by 17 beta-estradiol and medroxyprogesterone acetate

OBJECTIVE

The purpose of this study was to evaluate the culture characteristics and cell proliferation of human endometrial glandular epithelial cells in primary culture on extracellular matrix and to evaluate sex steroid modulation of this process.

STUDY DESIGN

We examined the culture characteristics in 53 endometrial gland preparations obtained throughout the menstrual cycle and determined the incorporation of tritiated thymidine in endometrial epithelial cells as a measure of deoxyribonucleic acid synthesis (cell proliferation) in the presence and absence of 17 beta-estradiol and medroxyprogesterone acetate.

RESULTS

Good culture maintenance of endometrial epithelial monolayers on extracellular matrix was observed from glands derived from proliferate phase endometrium (21 of 23), whereas poor adherence and culture maintenance was observed in all 30 of specimens from the secretory phase. With 17 beta-estradiol treatment for 22 hours, tritiated thymidine incorporation was not different from control, but medroxyprogesterone acetate treatment for 22 hours was associated with diminished tritiated thymidine incorporation by 36% (p < 0.004). When 17 beta-estradiol (10(-8) mol/L) was included in the incubation medium from the time of initial culture, tritiated thymidine incorporation on day 4 was 40% of control (p < 0.006), and tritiated thymidine was not suppressed further by 22 hours of treatment with medroxyprogesterone acetate (10(-7) mol/L). In spite of cellular spread of endometrial epithelial cells to subconfluence, deoxyribonucleic acid content per well did not increase over time in culture.

CONCLUSIONS

We conclude that exposure of endometrial glands to progesterone in vivo inhibits adherence and the establishment of cell monolayers cultured on a thin layer of extracellular matrix. Because 17 beta-estradiol treatment in culture for 22 hours does not increase tritiated thymidine incorporation, it is possible that 17 beta-estradiol exerts its proliferative effect on the endometrial epithelium by an indirect action mediated by stromal cells. The effects of 17 beta-estradiol and medroxyprogesterone acetate on deoxyribonucleic acid synthesis in endometrial epithelial cells may represent an action on a stem cell population of dividing cells or a terminally differentiated cell population that undergoes programmed cell death.

Effect of platelet-derived growth factor on endometrial stromal cell proliferation in vitro: a model for endometriosis?

OBJECTIVE

To assess the direct effects of platelet-derived growth factor (PDGF), a macrophage secretory product structurally and functionally similar to substances released by peritoneal macrophages isolated from endometriosis patients, on endometrial cell proliferation.

DESIGN

Prospective analysis of cell proliferation in vitro.

SETTING

Proliferative phase endometrial stromal cells isolated from biopsy specimens were grown in short-term culture and served as a model for stromal components of endometriotic implants.

PATIENTS

Biopsies were obtained from regularly cycling volunteers without endometrial pathology.

INTERVENTIONS

Platelet-derived growth factor was added to nutrient medium in both the presence and absence of suboptimal (2.5%) calf serum (CS) supplements and a physiological estradiol (E2) concentration (10(-9) M).

MAIN OUTCOME MEASURES

Cumulative [3H]-thymidine incorporation as a reflection of cell proliferation.

RESULTS

Platelet-derived growth factor exerted a significant dose-dependent effect on stromal cell proliferation in both the presence and absence of CS (P less than 0.01). This effect was enhanced in, at best, an additive but not synergistic manner by E2 10(-9) M.

CONCLUSION

These data imply that macrophage secretory products such as PDGF may play a significant role in the maintenance or proliferation of endometriosis.

Isolation and monolayer culture of human fallopian tube epithelial cells

In the present study we have established a pure monolayer culture system of human fallopian tube epithelial cells. The cells were isolated using collagenase digestion, and were cultured in Medium 199 supplemented with 15% fetal bovine serum. The epithelial cells derived from primary and secondary culture were characterized using immunocytochemical staining and electron microscopy. The cells continued to grow for 2 to 3 wk once the monolayer culture of the cells was established. It is currently possible to maintain the cultures until the third generation. Proliferation of these cells was enhanced by epidermal growth factor but not by basic-fibroblast growth factor, insulin, transferrin, estradiol-17 beta, or progesterone. This culture system offers a good model for determining characteristics of the tubal epithelium and would permit effective study of co-culture with embryos.

Culture of human endometrial cells under polarizing conditions

Glandular epithelial and stromal cells were isolated from human endometrial biopsies and cultured in a dual-chambered system (Millicell; Millipore, Bedford, Ma., USA) that provides access of the medium to both sides of a membrane coated with reconstituted basement membrane material (Matrigel; Collaborative Research Inc., Bedford, Ma., USA). Examination by electron microscopy revealed that the epithelial cells formed a polarized cuboidal-columnar monolayer on the Matrigel surface. The cells exhibited apical microvilli, basal nuclei, and numerous cytoplasmic structures consistent with a well-differentiated cytoplasm; they were joined basally by interdigitating processes and apically by tight junctions and desmosomes. In contrast, epithelial cells cultured in parallel on plastic dishes were flattened, had fewer microvilli and cytoplasmic structures, and no junctional complexes.

Development of a method to isolate and culture highly purified populations of stromal and epithelial cells from human endometrial biopsy specimens

Appropriate endometrial maturation is of paramount importance to achieve reproductive success. Practical and ethical considerations require that in vitro methods be available to evaluate regulation of human endometrial function. Additionally, tissue complexity requires separation of individual cell populations. This report describes an improved method for isolation of endometrial epithelial and stromal cells, using biopsy specimens as a tissue source. Separated cells were obtained using selective enzymatic digestion in conjunction with physical separation procedures. Isolated populations exhibited over 95% homogeneity, ascertained immunocytochemically. Using this system, isolated cells from normal endometrium can readily be obtained for in vitro studies. Within the defined conditions of a culture system, important areas of current concern in the endometrium such as ectopic endometrial growth and implantation can be addressed.

Establishment and characterization of a human cell line from a serous papillary endometrial carcinoma

The cell line SPEC-1, derived from a human serous papillary endometrial carcinoma (SPEC), has been established and repetitively subcultured for over 18 months. SPEC is a clinically aggressive histologic variant of endometrial adenocarcinoma with a significantly poorer prognosis. The SPEC cells exhibit morphologic and ultrastructural characteristics of transformed epithelial cells. The cells were further characterized with regard to growth kinetics, histochemistry, karyotype, and tumorigenicity. These studies indicate that several properties of the SPEC cells in culture contrast markedly with those of both typical endometrial adenocarcinoma cell lines and normal endometrial epithelia, as described in the literature. The most significant of these differences concern cytogenetic and ultrastructural features. The implications of these unique characteristics are discussed with regard to the relationship they may have to the unusually aggressive biological behavior of this tumor cell type in vivo. This SPEC cell line should prove useful in future studies designed to determine important factors in the biological behavior of human tumor cells.

Indication of selective growth of human endometrial epithelial cells on extracellular matrix

The culturing of human endometrium in conventional plastic dishes and media is only partially successful, mainly because a growth of a heterogeneous population of cells is achieved. Naturally produced extracellular matrix closely resembles the subepithelial basement membrane and seems to affect both growth and differentiation of cells. These qualities of the extracellular matrix (ECM) were applied for obtaining endometrial epithelial cultures. Endometrial tissue specimens were plated after slicing on ECM-coated dishes and kept for up to 8 d. The growth of a confluent homogeneous tissue composed of polygonal epithelial-like cells was demonstrated. To further characterize these cells, cultures were examined by scanning electron microscopy and transmission electron microscopy. Scanning electron microscopy revealed flattened polygonal cells covered with microvilli, among which ciliated cells were observed. By transmission electron microscopy the cells were seen as a monolayer, with some cells overlapping, closely adherent to the matrix. Microvilli, as well as intracellular vacuoles and glycogen granules were observed. Cell type specific cytoskeletal markers were demonstrated by antibodies to intermediate filament proteins (keratin and epithelial membrane antigen). Taken together, the morphologic and immunohistochemical studies indicate that a selective growth of the epithelial component of endometrial tissue was obtained after plating unprocessed endometrial tissue fragments on ECM-coated culture dishes.

Gland formation from human endometrial epithelial cells in vitro

We have developed methods for the culture of human endometrial glandular epithelia in vitro. The culture medium is serum-free and is used in combination with Matrigel, an extracellular matrix material applied as a coating on cell culture plates. Cell growth begins as a monolayer, but the cells subsequently form glandular or organoid structures. The glands are composed of polar columnar cells facing a central lumen, which is enclosed by the apical surfaces of cells displaying numerous microvilli and sealed by tight junction complexes. The ability to study in vitro the complex process of glandular morphogenesis represents an important new tool in cell biology which may be used to investigate growth regulation, hormone production and dependency, and cellular recognition and interactions. Ultimately, these characteristics may be applied to study the alterations of glandular epithelia associated with neoplasia.

Progesterone in vitro stimulates secretion of a specific protein by ovine epithelial endometrial cells

Cultured ovine epithelial endometrial cells from oestrogen-treated ovariectomized ewes were treated in vitro with combinations of oestradiol-17 beta (E), progesterone (P) and the P-receptor antagonist RU486 (each 10(-6) to 10(-9) M), in the presence of [35S]methionine. Neither DNA content of dishes nor total protein were increased in treatment compared with control dishes. Incorporation of [35S] into secreted protein was lower from cells treated in vitro with P or E + P (10(-9) M) than from those treated with E (10(-9) M, P less than 0.01). Incorporation of [35S] into cellular protein was decreased by P (10(-9) M, P less than 0.025). SDS-PAGE analysis of secreted proteins enabled measurement of levels of a 46K protein which is secreted maximally following E + P administration in vivo. In vitro, P either alone or with E (each 10(-7) M) increased the abundance of the 46K protein in cell secretions by a factor of 1.5 +/- 0.1 (N = 9) or 1.8 +/- 0.3 (N = 10) respectively (P less than 0.01) compared with controls. The administration of E (10(-7) M) or either or both steroids at 10(-9) M, was without effect. RU486 alone (10(-6) to 10(-8) M) was also without effect but in the presence of E + P or P, blocked the increase in the 46K protein, suggesting this effect is mediated via binding of P to its receptor.

Inhibition of fibroblast proliferation in a culture of human endometrial stromal cells using a medium containing D-valine

A nutrient medium in which D-valine was substituted for L-valine inhibited fibroblast proliferation in a culture of human endometrial stromal cells. Fibroblasts were not killed by D-valine and were able to grow again when D-valine was replaced by L-valine. The stromal cells proliferate in the D-valine medium only when seeded at high density. They were distinguished from fibroblasts by their morphology in light microscopy, their surface characteristics at scanning electron microscopy and their lower staining with fibronectin antibodies.

Morphologically stable epithelial vesicles cultured from normal human endometrium in defined media

Epithelium from normal human endometrium was cultured as morphologically stable vesicular structures in a defined, hormone-supplemented PFMR-4 medium. The structures consisted of a single layer of polarized epithelial cells with the apical surface facing the external culture medium, and the basal surface resting on a well-defined basal lamina adjacent to the internal lumen. Vesicles were shown to retain their viability for up to 3 mo. in culture, to actively synthesize DNA after being cultured for over a month in a defined medium, and to respond to steroid hormones. When embedded within a collagen gel, the vesicles reversed their epithelial polarity and formed branching, pseudoglandular structures. It was concluded that the three-dimensional shape of the epithelial vesicles had a critical role to play in their morphological stability, nutrient requirement, and hormone sensitivity.

Basally located epithelial cell surface component identified by a novel monoclonal antibody technique

Tubular aggregates of glandular epithelial cells (gland fragments) were isolated from human endometrium by collagenase digestion of surrounding stroma, thus exposing the basal surfaces of the cells. Using these aggregates as immunogen, monoclonal antibodies could be derived that recognized basally located antigens. One such antibody, G71, is described, that binds to a basal epithelial cell antigen present in a variety of human epithelia. Epitope-bearing molecules in the range Mr 60 000-180 000 are present in two of the tissues studied, amnion and endometrium. The epitope is associated with areas of epithelial cell-extracellular matrix contact.

Activities of glycogen synthetase and glycogen phosphorylase in the human endometrium: relative distribution in isolated glands and stroma

The activities of glycogen synthetase and glycogen phosphorylase were studied in endometrial samples obtained from 51 premenopausal women during the menstrual cycle. The total activities of glycogen synthetase and glycogen phosphorylase and the activity of the active form of glycogen phosphorylase increased gradually from the proliferative phase to the secretory phase and reached a maximum during the midsecretory phase, while the activity of the active form of glycogen synthetase increased slightly. In 30 of the 51 women, the relative distribution of glycogen synthetase and glycogen phosphorylase activities in isolated glands and stromal cells was determined following collagenase digestion of the endometrial specimens. The results indicated that the activities of the active form of glycogen synthetase and glycogen phosphorylase in the isolated glands during the secretory phase were more than threefold and twofold, respectively, greater than those present in the isolated stromal cells and that the levels of these enzymes in the glands and stromal cells changed in parallel with those in the undissociated endometrium observed during the menstrual cycle. In addition, histochemical studies revealed the presence of glycogen phosphorylase activity in both the glands and the stromal cells, whereas the glycogen synthetase activity was present only in the glands. These findings suggest that the stromal cells of the human endometrium as well as the glands may play an important role in the nutrition of the implanting blastocyst.

Prostaglandin production from homogenates of separated glandular epithelium and stroma from human endometrium

The biosynthesis of prostaglandins by isolated epithelial glandular and stromal cells was studied after collagenase digestion of endometrium collected from women at various stages of the menstrual cycle. Homogenates of the separate cell types were incubated for 60 minutes with 2.08 micrograms 1(14)C arachidonic acid and the products separated by thin layer chromatography. Both glandular and stromal homogenates synthesised PGF2 alpha. More PGF2 alpha was synthesised by glandular epithelium separated from both proliferative and secretory endometrium than by stroma. The ratio of PGF2 alpha/PGE2 was greater in glands and stroma isolated from secretory than proliferative endometrium. Small but significant amounts of 6-keto-PGF1 alpha were produced by all cell types. These results suggest that the increased synthesis of PGF2 alpha from secretory endometrium is due, at least in part, to increased activity of cyclo-oxygenase enzyme in the glandular epithelium.

Establishment and morphologic characterization of normal human endometrium in vitro

Tissue culture offers a model system with which to study the endocrine-mediated growth, differentiation, and metabolic activities of the endometrium. We have established and continue to maintain monolayer cultures of normal human endometrial epithelial cells from each phase of the menstrual cycle. At present, eight proliferative, two secretory, and two menstrual phase cultures have been established. These have been passed at least three times. One proliferative phase culture has been growing for 18 mo, and passed 10 times. Colonies of epithelioid cells as well as single cells appear in the cultures within 2 to 8 h of initial culture and maintain this appearance throughout long-term growth. The cells are periodic acid Schiff positive for carbohydrates and positive for keratin, an immunochemical marker for epithelial tissues. Studies comparing the ultrastructure of the cultures with fresh endometrial tissue revealed morphologic features common to both, including prominent nucleoli, Golgi, mitochondria-rough endoplasmic reticulum complexes, and abundant glycogen. The cells are not tumorigenic in the nude mouse and do not form colonies on soft agarose, confirming the nonneoplastic identity of the cells.

A comparison of developmental changes in surface charge in mouse blastocysts and uterine epithelium using DEAE beads and dextran sulfate in vitro

The ability of 3.5-day mouse blastocysts and vesicles prepared from maternal uterine epithelium to adhere to surfaces by charge interactions was compared by observing their adhesion to DEAE-Sephadex beads in the presence of increasing concentrations of dextran sulfate. The adhesion frequency for both the blastocysts and epithelium declined in a manner suggesting that predominantly ionic sites were being titrated, but differences between the two tissues in characteristics of the titration curve and susceptibility to neuraminidase digestion indicated that nonionic interactions were relatively more important for blastocysts. Because the threshold concentration of dextran sulfate required to initiate displacement of uterine epithelium from the DEAE beads was at least 4X that required to initiate the displacement of blastocysts, we argue that the uterine epithelium had at least 4X more interactive charged groups on its surface than the blastocysts. These differences were even more pronounced 4.5 days after mating, a time when attachment to the uterine epithelium is normally first seen in vivo. Blastocysts isolated at this time showed a marked increase in resistance to polyanion competition, but the epithelium showed a nearly 50% decline in surface negative charge that was not compensated by nonionic mechanisms. These observations support the conclusion that the initial adhesion of blastocysts in vivo is accompanied by a reduction in negativity of the uterine epithelial surface and by the formation of new trophoblast cell surfaces that adhere by nonelectrostatic interactions.

Enzymatic dissociation of ovarian and uterine tissues

A method is described for the preparation of high yields of viable, dissociated cells from porcine theca interna and corpus luteum and from human and bovine endometrium. The tissues were dissociated by incubation at 37 degrees C in a mixture of 0.5% collagenase, 0.1% hyaluronidase and 0.1% pronase in balanced salt solution containing 1% chicken serum. This procedure consistently provided high yields of structurally and metabolically intact dispersed cells after a digestion period of 60 min. The procedure is superior to methods previously reported in the literature.

Human endometrium in cell culture: a new method for culturing human endometrium as separate epithelial and stromal components

The present study describes a simple method for culturing human endometrium as separate epithelial and stromal components. Fifty-two samples of normal human endometrium have been initiated in tissue culture: endometrium from both the proliferative and luteal phases of the menstrual cycle showed satisfactory growth in vitro with a success rate of about 94%. Epithelial cultures remained viable for 60 days, while from stromal cells it was possible to establish cell lines. Both cell types possessed estrogen receptors. Epithelial cells showed no clear estrogen or progesterone response. Our observations suggest that this simple method for culturing human endometrium may serve as a tool in further investigations.

Characterization of a new human endometrial carcinoma (RL95-2) established in tissue culture

A new human endometrial cell line, RL95-2, derived from a Grade 2 moderately differentiated adenosquamous carcinoma of the endometrium has been passaged successfully in cell culture for more than 2 yr. The cells are characteristically epithelioid with well-defined junctional complexes, tonofilaments, filopodialike extensions, and surface microvilli. Nuclei are large, irregular, and invaginated frequently with multiple, prominent, lamellar nucleoli. The cells have a log phase doubling time of 22 to 34 h followed by continued growth at a reduced rate with no apparent plateau phase. They exhibit a strong tendency for piling up as well as for the formation of glandlike dome structures. Karyotypically the line is trisomic 8 (47,XX,+8) and has an 8% frequency of polyploidization. Both cytoplasmic and nuclear estrogen receptors are present. Antihuman alpha-keratin characterizes the cell line as epithelial, nonstromal. The RL95-2 cell line may provide a useful in vitro system for the investigation of the endocrine regulation of endometrial neoplasia.

Morphology and growth potential of stromal cell cultures derived from human endometrium

Propagable cell cultures derived from human endometrial tissue were determined to contain cells predominantly of stromal cell origin based on their morphologic resemblance to endometrial stromal cells. These features included nexi, solitary cilia, and predecidual cytology. In addition to morphology the cell cultures retained a normal karyotype and responded to steroid hormones as evidenced by cellular aggregation. The stromal cells were evaluated for a variety of characteristics associated with transformed cells and seemed to be biologically normal without neoplastic phenotypes. Growth potential of the stromal cell cultures was also characterized in normal maintenance medium, in nutritionally depleted medium with reduced levels of calcium or serum, and in medium with increased levels of serum. The prolonged survival of the stromal cells in vitro coupled with the retention of in vivo characteristics and an absence of neoplastic phenotype provides a human cell system that is amenable to a variety of long-term experimental analyses.

Monolayer culture of human endometrium: methods of culture and identification of cell types

Monolayer cultures can be established from human endometrial tissue after enzymatic dispersal into isolated glands or single cells. Three cell types that have distinct morphology by light and electron microscopy are observed in the resulting primary cultures. One cell type, an elongated spindle cell, is similar in appearance to fibroblasts derived from other tissues. A second cell type forms colonies of tightly cohesive cells, ranging in shape from oval to polygonal. These cells have typical organelles and junctional complexes characteristic of epithelial cells from the endometrium. The third cell type assumes a pavement-like appearance composed of polygonal cells when viewed by phase contrast microscopy, but lacks distinctive ultrastructural features of epithelial cells. These cells in culture resemble the endometrial stromal cell, the predominant cell type of the human endometrium in vivo. The epithelial cell does not survive subculturing but the other two cell types can be passaged through several generations and can be stored in liquid nitrogen and subsequently returned to culture.

Growth characteristics of primary cultures of stromal cells from human endometrium

The growth rate of stromal cells derived from 23 specimens of human endometrial tissue taken at various phases of the cycle was measured during the first seven days of primary culture. The stromal cells were found to differ radically in their ability to grow in culture according to the phase of the cycle at which the tissue was obtained. Early and mid proliferative stromal cells were capable of proliferation but that capacity was lost in late proliferative tissue. Growth at significant rates reappeared at days 21--22 and persisted in cells from late secretory tissue. Following plating, a 2--4 day lag period preceded proliferation of all but the most rapidly growing cultures. Subcultures showed a shorter lag period and faster maximal growth rate than the primary cultures from which they were derived. Estradiol, 10(-9) M. inhibition stromal cell growth in primary culture and this effect was prevented by 10(-8) M progesterone. These observations indicate that proliferative characteristics of stromal cells in primary culture are strongly influenced by the hormonal environment of the endometrium at the time of biopsy.