An immunohistochemical study of human endometrial extracellular matrix during the menstrual cycle and first trimester of pregnancy

Photo-Cross-linked Gelatin Methacryloyl Hydrogels Enable the Growth of Primary Human Endometrial Stromal Cells and Epithelial Gland Organoids

In vitro three-dimensional (3D) models are better able to replicate the complexity of real organs and tissues than 2D monolayer models. The human endometrium, the inner lining of the uterus, undergoes complex changes during the menstrual cycle and pregnancy. These changes occur in response to steroid hormone fluctuations and elicit crosstalk between the epithelial and stromal cell compartments, and dysregulations are associated with a variety of pregnancy disorders. Despite the importance of the endometrium in embryo implantation and pregnancy establishment, there is a lack of in vitro models that recapitulate tissue structure and function and as such a growing demand for extracellular matrix hydrogels that can support 3D cell culture. To be physiologically relevant, an in vitro model requires mechanical and biochemical cues that mimic those of the ECM found in the native tissue. We report a semisynthetic gelatin methacryloyl (GelMA) hydrogel that combines the bioactive properties of natural hydrogels with the tunability and reproducibility of synthetic materials. We then describe a simple protocol whereby cells can quickly be encapsulated in GelMA hydrogels. We investigate the suitability of GelMA hydrogel to support the development of an endometrial model by culturing the main endometrial cell types: stromal cells and epithelial cells. We also demonstrate how the mechanical and biochemical properties of GelMA hydrogels can be tailored to support the growth and maintenance of epithelial gland organoids that emerge upon 3D culturing of primary endometrial epithelial progenitor cells in a defined chemical medium. We furthermore demonstrate the ability of GelMA hydrogels to support the viability of stromal cells and their function measured by monitoring decidualization in response to steroid hormones. This study describes the first steps toward the development of a hydrogel matrix-based model that recapitulates the structure and function of the native endometrium and could support applications in understanding reproductive failure.

Current Strategies of Modeling Human Trophoblast Using Human Pluripotent Stem Cells in vitro

We previously established a trophoblast differentiation protocol from primed human pluripotent stem cells (PSC). To induce this lineage, we use a combination of Bone Morphogenetic Protein-4 (BMP4) and the WNT inhibitor IWP2. This protocol has enabled us to obtain a pure population of trophectoderm (TE)-like cells that could subsequently be terminally differentiated into syncytiotrophoblasts (STB) and extravillous trophoblasts (EVT). However, the resulting TE-like cells could only be terminally differentiated to a variable mixture of STB and EVT, with a bias toward the STB lineage. Recently, methods have been developed for derivation and culture of self-renewing human trophoblast stem cells (TSC) from human embryos and early gestation placental tissues. These primary TSCs were further able to differentiate into either STB or EVT with high efficiency using the lineage specific differentiation protocols. Based partly on these protocols, we have developed methods for establishing self-renewing TSC-like cells from PSC, and for efficient lineage-specific terminal differentiation. Here, we describe in detail the protocols to derive and maintain PSC-TSC, from both embryonic stem cells (ESC) and patient-derived induced pluripotent stem cells (iPSC), and their subsequent terminal differentiation to STB and EVT. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Trophoblast Differentiation into TE-like Cells Basic Protocol 2: Conversion of PSC-Derived TE-like Cells to TSC Basic Protocol 3: Passaging PSC-Derived TSC in iCTB Complete Medium Basic Protocol 4: STB Differentiation from PSC-derived TSC Basic Protocol 5: EVT Differentiation from PSC-derived TSC Support Protocol 1: Geltrex-coated tissue culture plate preparation Support Protocol 2: Collagen IV-coated tissue culture plate preparation Support Protocol 3: Fibronectin-coated tissue culture plate preparation.

Endometrial extracellular matrix components do not change over the course of embryonic diapause and reactivation in the roe deer (Capreolus capreolus)

The modification of the endometrial extracellular matrix (ECM) is a crucial step for embryo implantation in many mammalian species. The embryo of the European roe deer (Capreolus capreolus) displays a 4-5 months long temporary reduction of developmental pace termed embryonic diapause. A reduction of epithelial cell height during diapause has previously been described. Co-occurring ECM modifications may contribute to the changes of the intra-uterine milieu during reactivation at which the embryo regains developmental velocity. We assessed the localization of five ECM proteins (collagen I and IV, fibronectin, laminin, and extracellular matrix protein 1) using immunohistochemistry in animals with early, late, and post-diapause (elongating) embryos. While our results confirmed the reduction of epithelial height during diapause, we only detected marginal differences in localization and staining intensities of the selected ECM proteins. Major ECM remodelling events in the roe deer endometrium are thus likely to occur only at implantation.

Inflammation-Related Molecules at the Maternal–Fetal Interface during Pregnancy and in Pathologically Altered Endometrium

The blastocyst expresses paternally derived alloantigens and induces inflammation during implantation. However, it is necessary for the onset of pregnancy. An abnormal response might result in a pathological course of pregnancy or pregnancy failure. On the other hand, a state of maternal immune tolerance is necessary to ensure the normal development of pregnancy by suppressing inflammatory processes. This article discusses recognized mechanisms and the significance of inflammatory processes for embryo implantation and pregnancy establishment. We would also like to present disorders involving excessive inflammatory response and their influence on events occurring during embryo implantation. The chain of correlation between the processes responsible for embryo implantation and the subsequent physiological course of pregnancy is complicated. Many of those interrelationships are still yet to be discovered. Undoubtedly, their recognition will give hope to infertile couples for the emergence of new treatments that will increase the chance of giving birth to a healthy child.

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.

Interactions between Macrophages and Mast Cells in the Female Reproductive System

Mast cells (MCs) and macrophages (Mϕs) are innate immune cells that differentiate from early common myeloid precursors and reside in all body tissues. MCs have a unique capacity to neutralize/degrade toxic proteins, and they are hypothesized as being able to adopt two alternative polarization profiles, similar to Mϕs, with distinct or even opposite roles. Mϕs are very plastic phagocytic cells that are devoted to the elimination of senescent/anomalous endogenous entities (to maintain tissue homeostasis), and to the recognition and elimination of exogenous threats. They can adopt several functional phenotypes in response to microenvironmental cues, whose extreme profiles are the inflammatory/killing phenotype (M1) and the anti-inflammatory/healing phenotype (M2). The concomitant and abundant presence of these two cell types and the partial overlap of their defensive and homeostatic functions leads to the hypothesis that their crosstalk is necessary for the optimal coordination of their functions, both under physiological and pathological conditions. This review will examine the relationship between MCs and Mϕs in some situations of homeostatic regulation (menstrual cycle, embryo implantation), and in some inflammatory conditions in the same organs (endometriosis, preeclampsia), in order to appreciate the importance of their cross-regulation.

Human Endometrial Organoids: Recent Research Progress and Potential Applications

Since traditional two-dimensional (2D) cell culture cannot meet the demand of simulating physiological conditions in vivo, three-dimensional (3D) culture systems have been developed. To date, most of these systems have been applied for the culture of gastrointestinal and neural tissue. As for the female reproductive system, the culture of endometrial and oviductal tissues in Matrigel has also been performed, but there are still some problems that remain unsolved. This review highlights recent progress regarding endometrial organoids, focusing on the signal for organoid derivation and maintenance, the coculture of the epithelium and stroma, the drug screening using organoids from cancer patients, and provides a potential guideline for genome editing in endometrial organoids.

Modelling the impact of decidual senescence on embryo implantation in human endometrial assembloids

Decidual remodelling of midluteal endometrium leads to a short implantation window after which the uterine mucosa either breaks down or is transformed into a robust matrix that accommodates the placenta throughout pregnancy. To gain insights into the underlying mechanisms, we established and characterized endometrial assembloids, consisting of gland-like organoids and primary stromal cells. Single-cell transcriptomics revealed that decidualized assembloids closely resemble midluteal endometrium, harbouring differentiated and senescent subpopulations in both glands and stroma. We show that acute senescence in glandular epithelium drives secretion of multiple canonical implantation factors, whereas in the stroma it calibrates the emergence of anti-inflammatory decidual cells and pro-inflammatory senescent decidual cells. Pharmacological inhibition of stress responses in pre-decidual cells accelerated decidualization by eliminating the emergence of senescent decidual cells. In co-culture experiments, accelerated decidualization resulted in entrapment of collapsed human blastocysts in a robust, static decidual matrix. By contrast, the presence of senescent decidual cells created a dynamic implantation environment, enabling embryo expansion and attachment, although their persistence led to gradual disintegration of assembloids. Our findings suggest that decidual senescence controls endometrial fate decisions at implantation and highlight how endometrial assembloids may accelerate the discovery of new treatments to prevent reproductive failure.

How Mechanical Forces Change the Human Endometrium during the Menstrual Cycle in Preparation for Embryo Implantation

The human endometrium is characterized by exceptional plasticity, as evidenced by rapid growth and differentiation during the menstrual cycle and fast tissue remodeling during early pregnancy. Past work has rarely addressed the role of cellular mechanics in these processes. It is becoming increasingly clear that sensing and responding to mechanical forces are as significant for cell behavior as biochemical signaling. Here, we provide an overview of experimental evidence and concepts that illustrate how mechanical forces influence endometrial cell behavior during the hormone-driven menstrual cycle and prepare the endometrium for embryo implantation. Given the fundamental species differences during implantation, we restrict the review to the human situation. Novel technologies and devices such as 3D multifrequency magnetic resonance elastography, atomic force microscopy, organ-on-a-chip microfluidic systems, stem-cell-derived organoid formation, and complex 3D co-culture systems have propelled the understanding how endometrial receptivity and blastocyst implantation are regulated in the human uterus. Accumulating evidence has shown that junctional adhesion, cytoskeletal rearrangement, and extracellular matrix stiffness affect the local force balance that regulates endometrial differentiation and blastocyst invasion. A focus of this review is on the hormonal regulation of endometrial epithelial cell mechanics. We discuss potential implications for embryo implantation.

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.

The role of extracellular matrix in normal and pathological pregnancy: Future applications of microphysiological systems in reproductive medicine

IMPACT STATEMENT

Extracellular matrix in the womb regulates the initiation, progression, and completion of a healthy pregnancy. The composition and physical properties of extracellular matrix in the uterus and at the maternal-fetal interface are remodeled at each gestational stage, while maladaptive matrix remodeling results in obstetric disease. As in vitro models of uterine and placental tissues, including micro-and milli-scale versions of these organs on chips, are developed to overcome the inherent limitations of studying human development in vivo, we can isolate the influence of cellular and extracellular components in healthy and pathological pregnancies. By understanding and recreating key aspects of the extracellular microenvironment at the maternal-fetal interface, we can engineer microphysiological systems to improve assisted reproduction, obstetric disease treatment, and prenatal drug safety.

Maternal Obesity and the Uterine Immune Cell Landscape: The Shaping Role of Inflammation

Inflammation is often equated to the physiological response to injury or infection. Inflammatory responses defined by cytokine storms control cellular mechanisms that can either resolve quickly (i.e., acute inflammation) or remain prolonged and unabated (i.e., chronic inflammation). Perhaps less well-appreciated is the importance of inflammatory processes central to healthy pregnancy, including implantation, early stages of placentation, and parturition. Pregnancy juxtaposed with disease can lead to the perpetuation of aberrant inflammation that likely contributes to or potentiates maternal morbidity and poor fetal outcome. Maternal obesity, a prevalent condition within women of reproductive age, associates with increased risk of developing multiple pregnancy disorders. Importantly, chronic low-grade inflammation is thought to underlie the development of obesity-related obstetric and perinatal complications. While diverse subsets of uterine immune cells play central roles in initiating and maintaining healthy pregnancy, uterine leukocyte dysfunction as a result of maternal obesity may underpin the development of pregnancy disorders. In this review we discuss the current knowledge related to the impact of maternal obesity and obesity-associated inflammation on uterine immune cell function, utero-placental establishment, and pregnancy health.

The role of mesenchymal-epithelial transition in endometrial function

BACKGROUND

The human uterine endometrium undergoes significant remodeling and regeneration on a rapid and repeated basis, after parturition, menstruation, and in some cases, injury. The ability of the adult endometrium to undergo cyclic regeneration and differentiation/decidualization is essential for successful human reproduction. Multiple key physiologic functions of the endometrium require the cells of this tissue to transition between mesenchymal and epithelial phenotypes, processes known as mesenchymal-epithelial transition (MET) and epithelial-mesenchymal transition (EMT). Although MET/EMT processes have been widely characterized in embryonic development and in the context of malignancy, mounting evidence demonstrates the importance of MET/EMT in allowing the endometrium the phenotypic and functional flexibility necessary for successful decidualization, regeneration/re-epithelialization and embryo implantation.

OBJECTIVE AND RATIONALE

The objective of this review is to provide a comprehensive summary of the observations concerning MET and EMT and their regulation in physiologic uterine functions, specifically in the context of endometrial regeneration, decidualization and embryo implantation.

SEARCH METHODS

Using variations of the search terms 'mesenchymal-epithelial transition', 'mesenchymal-epithelial transformation', 'epithelial-mesenchymal transition', 'epithelial-mesenchymal transformation', 'uterus', 'endometrial regeneration', 'endometrial decidualization', 'embryo implantation', a search of the published literature between 1970 and 2018 was conducted using the PubMed database. In addition, we searched the reference lists of all publications included in this review for additional relevant original studies.

OUTCOMES

Multiple studies demonstrate that endometrial stromal cells contribute to the regeneration of both the stromal and epithelial cell compartments of the uterus, implicating a role for MET in mechanisms responsible for endometrial regeneration and re-epithelialization. During decidualization, endometrial stromal cells undergo morphologic and functional changes consistent with MET in order to accommodate embryo implantation. Under the influence of estradiol, progesterone and multiple other factors, endometrial stromal fibroblasts acquire epithelioid characteristics, such as expanded cytoplasm and rough endoplasmic reticulum required for greater secretory capacity, rounded nuclei, increased expression of junctional proteins which allow for increased cell-cell communication, and a reorganized actin cytoskeleton. During embryo implantation, in response to both maternal and embryonic-derived signals, the maternal luminal epithelium as well as the decidualized stromal cells acquire the mesenchymal characteristics of increased migration/motility, thus undergoing EMT in order to accommodate the invading trophoblast.

WIDER IMPLICATIONS

Overall, the findings support important roles for MET/EMT in multiple endometrial functions required for successful reproduction. The endometrium may be considered a unique wound healing model, given its ability to repeatedly undergo repair without scarring or loss of function. Future studies to elucidate how MET/EMT mechanisms may contribute to scar-free endometrial repair will have considerable potential to advance studies of wound healing mechanisms in other tissues.

Development of the human placenta

The placenta is essential for normal in utero development in mammals. In humans, defective placental formation underpins common pregnancy disorders such as pre-eclampsia and fetal growth restriction. The great variation in placental types across mammals means that animal models have been of limited use in understanding human placental development. However, new tools for studying human placental development, including 3D organoids, stem cell culture systems and single cell RNA sequencing, have brought new insights into this field. Here, we review the morphological, molecular and functional aspects of human placental formation, with a focus on the defining cell of the placenta - the trophoblast.

A gelatin hydrogel to study endometrial angiogenesis and trophoblast invasion

The endometrium is the lining of the uterus and site of blastocyst implantation. Each menstrual cycle, the endometrium cycles through rapid phases of growth, remodelling and breakdown. Significant vascular remodelling is also driven by trophoblast cells that form the outer layer of the blastocyst. Trophoblast invasion and remodelling enhance blood flow to the embryo ahead of placentation. Understanding the mechanisms of endometrial vascular remodelling and trophoblast invasion would provide key insights into endometrial physiology and cellular interactions critical for establishment of pregnancy. The objective of this study was to develop a tissue engineering platform to investigate the processes of endometrial angiogenesis and trophoblast invasion in a three-dimensional environment. We report adaptation of a methacrylamide-functionalized gelatin hydrogel that presents matrix stiffness in the range of the native tissue, supports the formation of endometrial endothelial cell networks with human umbilical vein endothelial cells and human endometrial stromal cells as an artificial endometrial perivascular niche and the culture of an endometrial epithelial cell layer, enables culture of a hormone-responsive stromal compartment and provides the capacity to monitor the kinetics of trophoblast invasion. With these studies, we provide a series of techniques that will instruct researchers in the development of endometrial models of increasing complexity.

Prostaglandin F2α stimulates adhesion, migration, invasion and proliferation of the human trophoblast cell line HTR-8/SVneo

INTRODUCTION

The amount of prostaglandin F_2α (PGF_2α) in the uterine lumen increases during the window of implantation in many mammals, including humans. We hypothesized that PGF_2α regulates processes related to human embryo implantation.

METHODS

The effect of PGF_2α was studied using an in vitro model of human extravillous trophoblast (EVT) cell line (HTR-8/SVneo). Adhesion, proliferation, invasion and migration assays, zymography for metalloproteinases (MMP) activity, and gene/protein expression analyses were applied. Doses of 100 nM and/or 1 μM of PGF_2α and fluprostenol were used. PGF_2α receptor (PTGFR), MMP9 and MMP2 proteins in the human first trimester placenta were localized by immunohistochemistry and immunofluorescence.

RESULTS

This study is the first reporting the expression of PTGFR protein in the first trimester placenta, as well as in HTR-8/SVneo cells. PGF_2α and fluprostenol increased HTR-8/SVneo cell proliferation and adhesion to extracellular matrix protein (P < 0.05). This effect was abolished by mitogen activated protein kinases (MAPK) inhibitor. PGF_2α induced phosphorylation of focal adhesion kinase and MAPK1/3 (P < 0.05). PGF_2α increased mRNA content and protein activity of MMP9, and gene and protein expression of interleukin-6 (P < 0.05). EVT cell migration and invasiveness were stimulated by PGF_2α (P < 0.05). The PGF_2α effect on cell invasion was reduced by inhibitors of MMP2, MMP9 and mTOR. In all experiments, the stimulatory effects of PGF_2α were diminished by using a PTGFR antagonist.

DISCUSSION

Our findings suggest a significant role for PGF_2α in mechanisms associated with implantation. PGF_2α acting by PTGFR in HTR-8/SVneo cells stimulates their adhesion and proliferation through the MAPK signaling pathway and increases invasiveness inducing MMP proteolytic activity and mTOR signaling.

Establishment of a three-dimensional model to study human uterine angiogenesis

STUDY QUESTION

Can primary human uterine microvascular endothelial cells (UtMVECs) be used as a model to study uterine angiogenic responses in vitro that are relevant in pregnancy?

SUMMARY ANSWER

UtMVECs demonstrated angiogenic responses when stimulated with proangiogenic factors, including sphingosine 1-phosphate (S1P), vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), physiological levels of wall shear stress (WSS), human chorionic gonadotropin (hCG) and various combinations of estrogen and progesterone.

WHAT IS KNOWN ALREADY

During sprouting angiogenesis, signaling from growth factors and cytokines induces a monolayer of quiescent endothelial cells (ECs) lining the vasculature to degrade the extracellular matrix and invade the surrounding tissue to form new capillaries. During pregnancy and the female reproductive cycle, the uterine endothelium becomes activated and undergoes sprouting angiogenesis to increase the size and number of blood vessels in the endometrium.

STUDY DESIGN, SIZE, DURATION

The study was designed to examine the angiogenic potential of primary human UtMVECs using the well-characterized human umbilical vein EC (HUVEC) line as a control to compare angiogenic potential. ECs were seeded onto three-dimensional (3D) collagen matrices, supplemented with known proangiogenic stimuli relevant to pregnancy and allowed to invade for 24 h. Sprouting responses were analyzed using manual and automated methods for quantification.

PARTICIPANTS/MATERIALS, SETTING, METHODS

RT-PCR, Western blot analysis and immunostaining were used to characterize UtMVECs. Angiogenic responses were examined using 3D invasion assays. Western blotting was used to confirm signaling responses after proangiogenic lipid, pharmacological inhibitor, and recombinant lentiviral treatments. All experiments were repeated at least three times.

MAIN RESULTS AND THE ROLE OF CHANCE

After ensuring that UtMVECs expressed the proper endothelial markers, we found that UtMVECs invade 3D collagen matrices dose-dependently in response to known proangiogenic stimuli (e.g. S1P, VEGF, bFGF, hCG, estrogen, progesterone and WSS) present during early pregnancy. Invasion responses were positively correlated with phosphorylation of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) and p42/p44 mitogen-activated protein kinase (ERK). Inhibition of these second messengers significantly impaired sprouting (P < 0.01). Gene silencing of membrane type 1-matrix metalloproteinase using multiple approaches completely abrogated sprouting (P < 0.001). Finally, UtMVECs displayed a unique ability to undergo sprouting in response to hCG, and combined estrogen and progesterone treatment.

LARGE SCALE DATA

Not applicable.

LIMITATIONS, REASONS FOR CAUTION

The study of uterine angiogenesis in vitro has limitations and any findings many not fully represent the in vivo state. However, these experiments do provide evidence for the ability of UtMVECs to be used in functional sprouting assays in a 3D environment, stimulated by physiological factors that are produced locally within the uterus during early pregnancy.

WIDER IMPLICATIONS OF THE FINDINGS

We show that UtMVECs can be used reliably to investigate how growth factors, hormones, lipids and other factors, such as flow, affect angiogenesis in the uterus.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by NIH award HL095786 to K.J.B. The authors have no conflicts of interest.

Endometrial vascular development in heavy menstrual bleeding: altered spatio-temporal expression of endothelial cell markers and extracellular matrix components

STUDY QUESTION

Are there any phenotypic and structural/architectural changes in the vessels of endometrium and superficial myometrium during the normal menstrual cycle in healthy women and those with heavy menstrual bleeding (HMB)?

SUMMARY ANSWER

Spatial and temporal differences in protein levels of endothelial cell (EC) markers and components of the extracellular matrix (ECM) were detected across the menstrual cycle in healthy women and these are altered in HMB.

WHAT IS KNOWN ALREADY

HMB affects 30% of women of reproductive age with ~50% of cases being idiopathic. We have previously shown that the differentiation status of endometrial vascular smooth muscle cells (VSMCs) is altered in women with HMB, suggesting altered vessel maturation compared to controls. Endometrial arteriogenesis requires the co-ordinated maturation not only of the VSMCs but also the underlying ECs and surrounding ECM. We hypothesized that there are spatial and temporal patterns of protein expression of EC markers and vascular ECM components in the endometrium across the menstrual cycle, which are altered in women with HMB.

STUDY DESIGN, SIZE, DURATION

Biopsies containing endometrium and superficial myometrium were taken from hysterectomy specimens from both healthy control women without endometrial pathology and women with subjective HMB in the proliferative (PP), early secretory (ESP), mid secretory (MSP) and late secretory (LSP) phases (N = 5 for each cycle phase and subject group). Samples were fixed in formalin and embedded in paraffin wax.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Serial sections (3μm thick) were immunostained for EC markers (factor VIII related antigen (F8RA), CD34, CD31 and ulex europaeus-agglutinin I (UEA-1) lectin), structural ECM markers (osteopontin, laminin, fibronectin and collagen IV) and for Ki67 to assess proliferation. Immunoreactivity of vessels in superficial myometrium, endometrial stratum basalis, stratum functionalis and luminal region was scored using either a modified Quickscore or by counting the number of positive vessels.

MAIN RESULTS AND THE ROLE OF CHANCE

In control samples, all four EC markers showed a dynamic expression pattern according to the menstrual cycle phase, in both endometrial and myometrial vessels. EC protein marker expression was altered in women with HMB compared with controls, especially in the secretory phase in the endometrial luminal region and stratum functionalis. For example, in the LSP expression of UEA-1 and CD31 in the luminal region decreased in HMB (mean quickscore: 1 and 5, respectively) compared with controls (3.2 and 7.4, respectively) (both P = 0.008), while expression of F8RA and CD34 increased in HMB (1.4 and 8, respectively) compared with controls (0 and 5.8, respectively) (both P = 0.008). There was also a distinct pattern of expression of the vascular structural ECM protein components osteopontin, laminin, fibronectin and collagen IV in the superficial myometrium, stratum functionalis and stratum basalis during the menstrual cycle, which was altered in HMB. In particular, compared with controls, osteopontin expression in HMB was higher in stratum functionalis in the LSP (7.2 and 11.2, respectively P = 0.008), while collagen IV expression was reduced in stratum basalis in the MSP (4.6 and 2.8, respectively P = 0.002) and in stratum functionalis in the ESP (7 and 3.2, respectively P = 0.008).

LIMITATIONS, REASONS FOR CAUTION

The protein expression of vascular EC markers and ECM components was assessed using a semi-quantitative approach in both straight and spiral arterioles. In our hospital, HMB is determined by subjective criteria and levels of blood loss were not assessed.

WIDER IMPLICATIONS OF THE FINDINGS

Variation in the protein expression pattern between the four EC markers highlights the importance of choice of EC marker for investigation of endometrial vessels. Differences in expression of the different EC markers may reflect developmental stage dependent expression of EC markers in endometrial vessels, and their altered expression in HMB may reflect dysregulated vascular development. This hypothesis is supported by altered expression of ECM proteins within endometrial vessel walls, as well as our previous data showing a dysregulation in VSMC contractile protein expression in the endometrium of women with HMB. Taken together, these data support the suggestion that HMB symptoms are associated with weaker vascular structures, particularly in the LSP of the menstrual cycle, which may lead to increased and extended blood flow during menstruation.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by Wellbeing of Women (RG1342) and Newcastle University. There are no competing interests to declare.

TRIAL REGISTRATION NUMBER

Not applicable.

Regulation of Placental Extravillous Trophoblasts by the Maternal Uterine Environment

During placentation invasive extravillous trophoblasts (EVTs) migrate into the maternal uterus and modify its vessels. In particular, remodeling of the spiral arteries by EVTs is critical for adapting blood flow and nutrient transport to the developing fetus. Failures in this process have been noticed in different pregnancy complications such as preeclampsia, intrauterine growth restriction, stillbirth, or recurrent abortion. Upon invasion into the decidua, the endometrium of pregnancy, EVTs encounter different maternal cell types such as decidual macrophages, uterine NK (uNK) cells and stromal cells expressing a plethora of growth factors and cytokines. Here, we will summarize development of the EVT lineage, a process occurring independently of the uterine environment, and formation of its different subtypes. Further, we will discuss interactions of EVTs with arteries, veins and lymphatics and illustrate how the decidua and its different immune cells regulate EVT differentiation, invasion and survival. The present literature suggests that the decidual environment and its soluble factors critically modulate EVT function and reproductive success.

Distribution of extracellular matrix molecules in human uterine tubes during the menstrual cycle: a histological and immunohistochemical analysis

The uterine tube (UT) is an important and complex organ of the women's reproductive system. In general, the anatomy and basic histology of this organ are well-known. However, the composition and function of the extracellular matrix (ECM) of the UT is still poorly understood. The ECM is a complex supramolecular material produced by cells which is commonly restricted to the basement membrane and interstitial spaces. ECM molecules play not only a structural role, they are also important for cell growth, survival and differentiation in all tissues. In this context, the aim of this study was to evaluate the deposition and distribution of type I and III collagens and proteoglycans (decorin, biglycan, fibromodulin and versican) in human UT during the follicular and luteal phases by using histochemical and immunohistochemical techniques. Our results showed a broad synthesis of collagens (I and III) in the stroma of the UT. The analysis by regions showed, in the mucosa, a specific distribution of versican and fibromodulin in the epithelial surface, whereas decorin and fibromodulin were observed in the lamina propria. Versican and decorin were found in the stroma of the muscular layer, whereas all studied proteoglycans were identified in the serosa. Curiously, biglycan was restricted to the wall of the blood vessels of the serosa and muscular layers. Furthermore, there was an immunoreaction for collagens, decorin, versican and fibromodulin in the UT peripheral nerves. The differential distribution of these ECM molecules in the different layers of the UT could be related to specific structural and/or biomechanical functions needed for the oviductal transport, successful fertilization and early embryogenesis. However, further molecular studies under physiological and pathological conditions are still needed to elucidate the specific role of each molecule in the human UT.

Uterine responses to early pre-attachment embryos in the domestic dog and comparisons with other domestic animal species

In the dog, there is no luteolysis in the absence of pregnancy. Thus, this species lacks any anti-luteolytic endocrine signal as found in other species that modulate uterine function during the critical period of pregnancy establishment. Nevertheless, in the dog an embryo-maternal communication must occur in order to prevent rejection of embryos. Based on this hypothesis, we performed microarray analysis of canine uterine samples collected during pre-attachment phase (days 10-12) and in corresponding non-pregnant controls, in order to elucidate the embryo attachment signal. An additional goal was to identify differences in uterine responses to pre-attachment embryos between dogs and other mammalian species exhibiting different reproductive patterns with regard to luteolysis, implantation, and preparation for placentation. Therefore, the canine microarray data were compared with gene sets from pigs, cattle, horses, and humans. We found 412 genes differentially regulated between the two experimental groups. The functional terms most strongly enriched in response to pre-attachment embryos related to extracellular matrix function and remodeling, and to immune and inflammatory responses. Several candidate genes were validated by semi-quantitative PCR. When compared with other species, best matches were found with human and equine counterparts. Especially for the pig, the majority of overlapping genes showed opposite expression patterns. Interestingly, 1926 genes did not pair with any of the other gene sets. Using a microarray approach, we report the uterine changes in the dog driven by the presence of embryos and compare these results with datasets from other mammalian species, finding common-, contrary-, and exclusively canine-regulated genes.

Molecular and Cellular Pathogenesis of Endometriosis

BACKGROUND

A substantial body of studies supports the view that molecular and cellular features of endometriotic lesions differ from those of eutopic endometrium. Apart from that, evidence exists that the eutopic endometrium from pa-tients with endometriosis differs from that of females without endometriosis.

OBJECTIVE

Aberrant expression profiles include a number of non-steroid signaling pathways that exert their putative influ-ence on the pathogenesis of endometriosis at least in part via crosstalk(s) with estrogen-mediated mechanisms. A rational to focus research on non-steroid signal pathways is that they might be remunerative targets for the development and selection of novel therapeutics to treat endometriosis possibly without affecting estrogen levels.

RESULTS AND CONCLUSION

In this article, we describe molecular and cellular features of endometriotic lesions and focus on the canonical WNT/β-signaling pathway, a key regulatory system in biology (including stem cell homeostasis) and often in pathophysiological conditions such as endometriosis. Recently emerged novel biological concepts in signal transduction and gene regulation like exosomes and microRNAs are discussed in their putative role in the pathogenesis of endometriosis.

Uterine and placental distribution of selected extracellular matrix (ECM) components in the dog

For many years, modifications of the uterine extracellular matrix (ECM) during gestation have not been considered as critical for successful canine (Canis lupus familiaris) pregnancy. However, previous reports indicated an effect of free-floating blastocysts on the composition of the uterine ECM. Here, the expression of selected genes involved in structural functions, cell-to-cell communication and inhibition of matrix metalloproteinases were targeted utilizing qPCR and immunohistochemistry. We found that canine free-floating embryos affect gene expression of FN1, ECM1 and TIMP4 This seems to be associated with modulation of trophoblast invasion, and proliferative and adhesive functions of the uterus. Although not modulated at the beginning of pregnancy, the decrease of structural ECM components (i.e. COL1, -3, -4 and LAMA2) from pre-implantation toward post-implantation at placentation sites appears to be associated with softening of the tissue in preparation for trophoblast invasion. The further decrease of these components at placentation sites at the time of prepartum luteolysis seems to be associated with preparation for the release of fetal membranes. Reflecting a high degree of communication, intercellular cell adhesion molecules are induced following placentation (Cx26) or increase gradually toward prepartum luteolysis (Cx43). The spatio-temporal expression of TIMPs suggests their active involvement in modulating fetal invasiveness, and together with ECM1, they appear to protect deeper endometrial structures from trophoblast invasion. With this, the dog appears to be an interesting model for investigating placental functions in other species, e.g. in humans in which Placenta accreta appears to share several similarities with canine subinvolution of placental sites (SIPS). In summary, the canine uterine ECM is only moderately modified in early pregnancy, but undergoes vigorous reorganization processes in the uterus and placenta following implantation.

Local remodeling of synthetic extracellular matrix microenvironments by co-cultured endometrial epithelial and stromal cells enables long-term dynamic physiological function

Mucosal barrier tissues, comprising a layer of tightly-bonded epithelial cells in intimate molecular communication with an underlying matrix-rich stroma containing fibroblasts and immune cells, are prominent targets for drugs against infection, chronic inflammation, and other disease processes. Although human in vitro models of such barriers are needed for mechanistic studies and drug development, differences in extracellular matrix (ECM) needs of epithelial and stromal cells hinder efforts to create such models. Here, using the endometrium as an example mucosal barrier, we describe a synthetic, modular ECM hydrogel suitable for 3D functional co-culture, featuring components that can be remodeled by cells and that respond dynamically to sequester local cell-secreted ECM characteristic of each cell type. The synthetic hydrogel combines peptides with off-the-shelf reagents and is thus accessible to cell biology labs. Specifically, we first identified a single peptide as suitable for initial attachment of both endometrial epithelial and stromal cells using a 2D semi-empirical screen. Then, using a co-culture system of epithelial cells cultured on top of gel-encapsulated stromal cells, we show that inclusion of ECM-binding peptides in the hydrogel, along with the integrin-binding peptide, leads to enhanced accumulation of basement membrane beneath the epithelial layer and more fibrillar collagen matrix assembly by stromal cells over two weeks in culture. Importantly, endometrial co-cultures composed of either cell lines or primary cells displayed hormone-mediated differentiation as assessed by morphological changes and secretory protein production. A multiplex analysis of apical cytokine and growth factor secretion comparing cell lines and primary cells revealed strikingly different patterns, underscoring the importance of using primary cell models in analysis of cell-cell communication networks. In summary, we define a "one-size-fits-all" synthetic ECM that enables long-term, physiologically responsive co-cultures of epithelial and stromal cells in a mucosal barrier format.

Endometrial Stromal Decidualization Responds Reversibly to Hormone Stimulation and Withdrawal

Human endometrial stromal decidualization is required for embryo receptivity, angiogenesis, and placentation. Previous studies from our laboratories established that connexin (Cx)-43 critically regulates endometrial stromal cell (ESC) differentiation, whereas gap junction blockade prevents it. The current study evaluated the plasticity of ESC morphology and Cx43 expression, as well as other biochemical markers of cell differentiation, in response to decidualizing hormones. Primary human ESC cultures were exposed to 10 nM estradiol, 100 nM progesterone, and 0.5 mM cAMP for up to 14 days, followed by hormone withdrawal for 14 days, mimicking a biphasic ovulatory cycle. Reversible differentiation was documented by characteristic changes in cell shape. Cx43 was reversibly up- and down-regulated after the estradiol, progesterone, and cAMP treatment and withdrawal, respectively, paralleled by fluctuations in prolactin, vascular endothelial growth factor, IL-11, and glycodelin secretion. Markers of mesenchymal-epithelial transition (MET), and its counterpart epithelial-mesenchymal transition, followed reciprocal patterns corresponding to the morphological changes. Incubation in the presence of 18α-glycyrrhetinic acid, an inhibitor of gap junctions, partially reversed the expression of decidualization and MET markers. In the absence of hormones, Cx43 overexpression promoted increases in vascular endothelial growth factor and IL-11 secretion, up-regulated MET markers, and reduced N-cadherin, an epithelial-mesenchymal transition marker. The combined results support the hypothesis that Cx43-containing gap junctions and endocrine factors cooperate to regulate selected biomarkers of stromal decidualization and MET and suggest roles for both phenomena in endometrial preparation for embryonic receptivity.

Human Decidual Stromal Cells as a Component of the Implantation Niche and a Modulator of Maternal Immunity

The human decidua is a specialized tissue characterized by embryo-receptive properties. It is formed during the secretory phase of menstrual cycle from uterine mucosa termed endometrium. The decidua is composed of glands, immune cells, blood and lymph vessels, and decidual stromal cells (DSCs). In the process of decidualization, which is controlled by oestrogen and progesterone, DSCs acquire specific functions related to recognition, selection, and acceptance of the allogeneic embryo, as well as to development of maternal immune tolerance. In this review we discuss the relationship between the decidualization of DSCs and pathological obstetrical and gynaecological conditions. Moreover, the critical influence of DSCs on local immune cells populations as well as their relationship to the onset and maintenance of immune tolerance is described.

GnRH regulates trophoblast invasion via RUNX2-mediated MMP2/9 expression

STUDY HYPOTHESIS

We hypothesized that Runt-related transcription factor 2 (RUNX2), matrix metalloproteinase (MMP)2 and MMP9 are involved in basal and gonadotrophin-releasing hormone (GnRH)-induced human extravillous trophoblast (EVT) cell invasion.

STUDY FINDING

Our finding indicates that GnRH-induced RUNX2 expression enhances the invasive capacity of EVT cells by modulating the expression of MMP2 and MMP9.

WHAT IS KNOWN ALREADY

GnRH is expressed in first-trimester placenta and exerts pro-invasive effects on EVT cells in vitro. RUNX2 regulates MMP2 and MMP9 expression and is often associated with invasive phenotypes.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

First-trimester human placenta (n = 9) was obtained from women undergoing elective termination of pregnancy. The localization of RUNX2, MMP2 and MMP9 in first-trimester human placenta was examined by immunohistochemistry. Primary or immortalized (HTR-8/SVneo) EVT cells were treated alone or in combination with GnRH, GnRH antagonist Antide, MAPK kinase inhibitor PD98095, phosphatidylinositol 3-kinase inhibitor LY294002, MMP2/9 inhibitor or small interfering RNAs (siRNAs) targeting RUNX2, MMP2 and/or MMP9. Protein and mRNA levels were measured by western blot and RT-PCR, respectively. Cell invasiveness was evaluated by transwell Matrigel or collagen I invasion assays.

MAIN RESULTS AND THE ROLE OF CHANCE

RUNX2, MMP2 and MMP9 were detected in the cell column regions of human first-trimester placental villi. GnRH treatment increased RUNX2 mRNA and protein levels in HTR-8/SVneo cells and primary EVTs, and these effects were attenuated by co-treatment with Antide, PD98095 or LY294002. Down-regulation of RUNX2 by siRNA reduced basal and GnRH-induced MMP2/9 expression and cell invasion. Moreover, pharmacological inhibition or siRNA-mediated knockdown of MMP2/9 reduced basal and GnRH-induced cell invasion.

LIMITATIONS, REASONS FOR CAUTION

The lack of an in vivo model is the major limitation of our in vitro study.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings provide important insight into the functions of the GnRH - GnRH receptor system in early implantation and placentation.

LARGE SCALE DATA

Not applicable.

STUDY FUNDING AND COMPETING INTERESTS

This research was supported by Canadian Institutes of Health Research (Grant #143317) to P.C.K.L. The authors have nothing to disclose.

Strain-specific induction of endometrial periglandular fibrosis in mice exposed during adulthood to the endocrine disrupting chemical bisphenol A

The aim of this study was to compare effects of bisphenol A (BPA) on collagen accumulation in uteri of two mouse strains. Adult C57Bl/6N and CD-1 mice were exposed to dietary BPA (0.004-40mg/kg/day) or 17α-ethinyl estradiol (0.00002-0.001mg/kg/day) as effect control. An equine endometrosis-like phenotype with increased gland nesting and periglandular collagen accumulation was characteristic of unexposed C57Bl/6N, but not CD-1, endometrium. BPA non-monotonically increased gland nest density and periglandular collagen accumulation in both strains. Increased collagen I and III expression, decreased matrix metalloproteinase 2 (MMP2) and MMP14 expression, and increased immune response were associated with the endometrosis phenotype in the C57Bl/6N strain and the 30ppm BPA CD-1 group. The association between the pro-collagen shift in increased collagen expression and decreased MMP2 expression and activity implies that strain differences and BPA exposure alter regulation of endometrial remodeling and contribute to increased fibrosis, a component of several human uterine diseases.

Effect of ovarian hormones on the healthy equine uterus: a global gene expression analysis

The physiological changes associated with the varying hormonal environment throughout the oestrous cycle are linked to the different functions the uterus needs to fulfil. The aim of the present study was to generate global gene expression profiles for the equine uterus during oestrus and Day 5 of dioestrus. To achieve this, samples were collected from five horses during oestrus (follicle >35 mm in diameter) and dioestrus (5 days after ovulation) and analysed using high-throughput RNA sequencing techniques (RNA-Seq). Differentially expressed genes between the two cycle stages were further investigated using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses. The expression of 1577 genes was found to be significantly upregulated during oestrus, whereas 1864 genes were expressed at significantly higher levels in dioestrus. Most genes upregulated during oestrus were associated with the extracellular matrix, signal interaction and transduction, cell communication or immune function, whereas genes expressed at higher levels in early dioestrus were most commonly associated with metabolic or transport functions, correlating well with the physiological functions of the uterus. These results allow for a more complete understanding of the hormonal influence on gene expression in the equine uterus by functional analysis of up- and downregulated genes in oestrus and dioestrus, respectively. In addition, a valuable baseline is provided for further research, including analyses of changes associated with uterine inflammation.

Collagen type IV at the fetal-maternal interface

Introduction

Extracellular matrix proteins play a crucial role in influencing the invasion of trophoblast cells. However the role of collagens and collagen type IV (col-IV) in particular at the implantation site is not clear.

Methods

Immunohistochemistry was used to determine the distribution of collagen types I, III, IV and VI in endometrium and decidua during the menstrual cycle and the first trimester of pregnancy. Expression of col-IV alpha chains during the reproductive cycle was determined by qPCR and protein localisation by immunohistochemistry. The structure of col-IV in placenta was examined using transmission electron microscopy. Finally, the expression of col-IV alpha chain NC1 domains and collagen receptors was localised by immunohistochemistry.

Results

Col-IV alpha chains were selectively up-regulated during the menstrual cycle and decidualisation. Primary extravillous trophoblast cells express collagen receptors and secrete col-IV in vitro and in vivo, resulting in the increased levels found in decidua basalis compared to decidua parietalis. A novel expression pattern of col-IV in the mesenchyme of placental villi, as a three-dimensional network, was found. NC1 domains of col-IV alpha chains are known to regulate tumour cell migration and the selective expression of these domains in decidua basalis compared to decidua parietalis was determined.

Discussion

Col-IV is expressed as novel forms in the placenta. These findings suggest that col-IV not only represents a structural protein providing tissue integrity but also influences the invasive behaviour of trophoblast cells at the implantation site.

•

Our data suggest that progesterone might regulate collagen type IV.

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Primary extravillous trophoblast cells secrete collagen type IV.

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A novel three-dimensional network of collagen type IV in placenta is presented.

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Trophoblast cells express integrin alpha 10, integrin alpha 11 and collagen receptors DDR-1 and DDR-2.

Interferon-γ protects first-trimester decidual cells against aberrant matrix metalloproteinases 1, 3, and 9 expression in preeclampsia

Human extravillous trophoblast (EVT) invades the decidua via integrin receptors and subsequently degrades extracellular matrix proteins. In preeclampsia (PE), shallow EVT invasion elicits incomplete spiral artery remodeling, causing reduced uteroplacental blood flow. Previous studies show that preeclamptic decidual cells, but not interstitial EVTs, display higher levels of extracellular matrix-degrading matrix metalloproteinase (MMP)-9, but not MMP-2. Herein, we extend our previous PE-related assessment of MMP-2 and MMP-9 to include MMP-1, which preferentially degrades fibrillar collagens, and MMP-3, which can initiate a local proteolytic cascade. In human first-trimester decidual cells incubated with estradiol, tumor necrosis factor-α (TNF-α) significantly enhanced MMP-1, MMP-3, and MMP-9 mRNA and protein levels and activity measured by real-time quantitative RT-PCR, ELISA, immunoblotting, and zymography, respectively. In contrast, interferon γ (IFN-γ) reversed these effects and medroxyprogesterone acetate elicited further reversal. Immunoblotting revealed that p38 mitogen-activated protein kinase signaling mediated TNF-α enhancement of MMP-1, MMP-3, and MMP-9, whereas IFN-γ inhibited p38 mitogen-activated protein kinase phosphorylation. Unlike highly regulated MMP-1, MMP-3, and MMP-9, MMP-2 mRNA and protein expression was constitutive in decidual cells. Because inflammation underlies PE-associated shallow EVT invasion, these results suggest that excess macrophage-derived TNF-α augments expression of MMP-1, MMP-3, and MMP-9 in decidual cells to interfere with normal stepwise EVT invasion of the decidua. In contrast, decidual natural killer cell-derived IFN-γ reverses such TNF-α-induced MMPs to protect against PE.

Differences in collagen ultrastructure of human first trimester decidua basalis and parietalis: implications for trophoblastic invasion of the placental bed

AIM

The human embryo-maternal interface in the first trimester of pregnancy is an area of extensive tissue remodeling. Because collagen is the most abundant constituent of the extracellular matrix of the placental bed, successful invasion must involve its rapid turnover. We compared the nature and distribution of collagen fibrils in decidua basalis and parietalis.

METHODS

We used a direct-vision hysteroscopic technique to obtain biopsies of the decidua basalis and parietalis from 11 women undergoing pregnancy termination in the first trimester. The biopsies were subjected to light, transmission and scanning electron microscopy, and immunohistochemical studies using mouse monoclonal antibodies against cytokeratin 7 and collagen types I, III and V.

RESULTS

Collagen fibrils in the stroma of decidua basalis were significantly thicker when compared to those in decidua parietalis (56.48 ± 1.37 nm vs 45.64 ± 0.85 nm; P < 0.0001 [mean ± standard error]) between 9 and 12 weeks gestation, but this difference in thickness was not observed at gestations below 9 weeks. In basalis, the fibrils appeared disrupted at most places surrounding the decidual/trophoblast cells while a uniform regular arrangement was preserved throughout most of parietalis.

CONCLUSION

There are differences in the ultrastructure of collagen fibrils between basalis and parietalis, with thicker and disrupted fibrils within abundant amorphous tissue in basalis, and thinner uniform fibrils in parietalis. These differences may reflect an adaptive response by decidua or a direct consequence of the invading trophoblast cells.

Border patrol: insights into the unique role of perlecan/heparan sulfate proteoglycan 2 at cell and tissue borders

The extracellular matrix proteoglycan (ECM) perlecan, also known as heparan sulfate proteoglycan 2 or HSPG2, is one of the largest (>200 nm) and oldest (>550 M years) extracellular matrix molecules. In vertebrates, perlecan's five-domain structure contains numerous independently folding modules with sequence similarities to other ECM proteins, all connected like cars into one long, diverse complex train following a unique N-terminal domain I decorated with three long glycosaminoglycan chains, and an additional glycosaminoglycan attachment site in the C-terminal domain V. In lower invertebrates, perlecan is not typically a proteoglycan, possessing the majority of the core protein modules, but lacking domain I where the attachment sites for glycosaminoglycan chains are located. This suggests that uniting the heparan sulfate binding growth factor functions of domain I and the core protein functions of the rest of the molecule in domains II-V occurred later in evolution for a new functional purpose. In this review, we surveyed several decades of pertinent literature to ask a fundamental question: Why did nature design this protein uniquely as an extraordinarily long multifunctional proteoglycan with a single promoter regulating expression, rather than separating these functions into individual proteins that could be independently regulated? We arrived at the conclusion that the concentration of perlecan at functional borders separating tissues and tissue layers is an ancient key function of the core protein. The addition of the heparan sulfate chains in domain I likely occurred as an additional means of binding the core protein to other ECM proteins in territorial matrices and basement membranes, and as a means to reserve growth factors in an on-site depot to assist with rapid repair of those borders when compromised, such as would occur during wounding. We propose a function for perlecan that extends its role from that of an extracellular scaffold, as we previously suggested, to that of a critical agent for establishing and patrolling tissue borders in complex tissues in metazoans. We also propose that understanding these unique functions of the individual portions of the perlecan molecule can provide new insights and tools for engineering of complex multi-layered tissues including providing the necessary cues for establishing neotissue borders.

Estradiol induces transcriptional and posttranscriptional modifications in versican expression in the mouse uterus

We have previously shown the differential expression of versican in the mouse uterus under ovarian hormone influence. We also demonstrated there is not a direct correlation between mRNA levels and protein expression, suggesting posttranscriptional events, such as alteration in mRNA stability. This posttranscriptional effect may result in the elongation and stabilization of transcripts poly(A) tail. Thus, the aim of this study was to analyze whether estradiol (E2) regulates versican mRNA stability and expression in a dose-related and time-dependent manner. For this purpose female mice were ovariectomized and treated with a single injection of 0.1 or 10 μg E2. To block transcription a group of females received a single injection of alpha-amanitin before hormone administration. Uterine tissues were collected 30 min, 1, 3, 6, 12 and 24 h after treatments and processed for quantitative real time PCR (qPCR), RACE-PAT Assay and immunohistochemistry. qPCR showed that versican mRNA levels are higher than control from 3 to 24 h after E2 administration, whereas after transcription inhibition versican mRNA unexpectedly increases within 3 h, which can be explained when transcriptional blockers alter the degradation rate of the transcript, resulting in the superinduction of this mRNA. Accordingly, analysis of versican transcript poly(A) tail evidenced a longer product 3 h after treatment, but not after 12 h. Versican immunoreaction becomes conspicuous in the superficial stroma only 3 h after E2 injection, whereas the whole stroma is immunoreactive from 6 h onward. These results demonstrate that E2 modulates versican at the transcriptional and posttranscriptional levels in a time-dependent manner.

Transforming growth factor β1 (TGFβ1) and progesterone regulate matrix metalloproteinases (MMP) in human endometrial stromal cells

CONTEXT

Menstruation is preceded by progesterone withdrawal and endometrial matrix remodeling predominantly through induction of matrix metalloproteinases (MMP) and recruitment of invading neutrophils.

DESIGN

Using endometrial tissues from women during various phases of the menstrual cycle, we found that MMP2, MMP9, and MMP11 were up-regulated in the late secretory phase/premenstrual phase. Because TGFβ-responsive genes were also up-regulated in endometrium during this time, we tested the hypothesis that TGFβ1 and progesterone regulate expression of MMP in human endometrial stromal cells (HESC).

RESULTS

Treatment of HESC with TGFβ1 resulted in marked increases in MMP2 and MMP11 mRNA and pro- and active MMP2 activity. Progesterone inhibited TGFβ1-induced stimulation of MMP2 and MMP11 through its nuclear hormone receptors. Interestingly, TGFβ1 also decreased progesterone receptor (PR)-A and PR-B in HESC with a more pronounced effect on PR-A.

CONCLUSIONS

These data support the hypothesis that TGFβ1 has endogenous anti-progestational effects in HESC and that the opposing effects of progesterone and TGFβ1 are important in regulation of matrix integrity in human endometrium.

Transforming growth factor-α mRNA expression and its possible roles in mouse endometrial stromal cells

Transforming growth factor-α (TGFα) is thought to be involved in the regulation of endometrial cells. We investigated Tgfa mRNA expression, and the effects of TGFα on DNA-synthesis and gene expression of insulin-like growth factor 1 (IGF1), IGF binding protein-3 (IGFBP3) and IGF1 receptor in the mouse endometrial cells, because IGF1 is involved in estrogen-induced growth of endometrial cells. We also investigated the role of TGFα on matrix metalloproteinase (MMP) expression, as MMPs are involved both in tissue remodeling during cell proliferation and in enhancement of IGF1 signaling through the degradation of IGFBP3. Tgfa mRNA expression was detected in endometrial luminal and glandular epithelial cells, and stromal cells. Tgfa mRNA signals did not appear to change in endometrial luminal epithelial cells, but signals in glandular epithelial cells were higher at diestrus 1, 2 and proestrus, and the number of stromal cells showing strong signals appeared to increase at diestrus 1 and 2. Endometrial epithelial and stromal cells were treated with estradiol-17β (E2) or progesterone (P4). E2 or P4 stimulated Tgfa mRNA expression in stromal cells. TGFα stimulated DNA synthesis in endometrial epithelial and stromal cells, while E2 and P4 stimulated DNA synthesis in stromal cells. In stromal cells, TGFα, at as low as 1 ng/ml, decreased Igfbp3 and Mmp9 mRNA levels, while high dose (10 ng/ml) of TGFα decreased Igf1 mRNA level and increased Mmp3 mRNA level. These results imply that TGFα stimulates proliferation of endometrial stromal cells through multiple mechanisms, including its regulation of Igfbp3 and Mmp3 transcription.

Trophoblast-derived chemokine CXCL12 promotes CXCR4 expression and invasion of human first-trimester decidual stromal cells

BACKGROUND

The aim of this study was to investigate the role of the chemokine (C-X-C motif) ligand 12/chemokine (C-X-C motif) receptor 4 (CXCL12/CXCR4) axis on the crosstalk between human first-trimester trophoblast cells (TCs) and decidual stromal cells (DSCs), to contribute to a better understanding of the molecular mechanisms on the interaction between the mother and embryo during pregnancy.

METHODS

CXCR4 on human first-trimester DSC membranes was detected by flow cytometry. The effects of exogenous CXCL12 or TC-conditioned medium (TCM) on proliferation and invasion of DSCs were examined by measuring proliferating cell nuclear antigen (PCNA) and an invasion assay, respectively. Finally, a co-culture model was established to investigate the effect of CXCL12 secreted from TCs on motility of DSCs.

RESULTS

The mean (±SEM) percentage of DSCs positive for CXCR4 was 32.32 ± 7.18%. Human recombinant CXCL12 induced an increase in CXCR4 levels on DSCs via binding to CXCR4 (P < 0.01) but had no effect on the PCNA expression of DSCs. Moreover, both exogenous CXCL12 and TCM reinforced the invasive ability of DSCs via CXCR4 ligation. A co-culture model further confirmed that the enhanced invasiveness of DSCs in co-culture with TCs was inhibited by anti-CXCR4 or anti-CXCL12 neutralizing antibody (both P< 0.01).

CONCLUSIONS

Human first-trimester DSCs express membrane CXCR4 and TC-derived CXCL12 promotes CXCR4 expression and invasion of DSCs via ligation with CXCR4. Our data highlight the role of CXCL12/CXCR4 axis on the co-operation between TCs and DSCs during human first-trimester pregnancy.

Regulation of matrix metalloproteinases activity studied in human endometrium as a paradigm of cyclic tissue breakdown and regeneration

When abundant and activated, matrix metalloproteinases (MMPs, or matrixins) degrade most, if not all, constituents of the extracellular matrix (ECM). The resulting massive tissue breakdown is best exemplified in humans by the menstrual lysis and shedding of the endometrium, the mucosa lining the uterus. After menstruation, MMP activity needs to be tightly controlled as the endometrium regenerates and differentiates to avoid abnormal tissue breakdown while allowing tissue repair and fine remodelling to accommodate implantation of a blastocyst. This paper reviews how MMPs are massively present and activated in the endometrium at menstruation, and how their activity is tightly controlled at other phases of the cycle. Progesterone represses expression of many but not all MMPs. Its withdrawal triggers focal expression of MMPs specifically in the areas undergoing lysis, an effect mediated by local cytokines such as interleukin-1α, LEFTY-2, tumour necrosis factor-α and others. MMP-3 is selectively expressed at that time and activates proMMP-9, otherwise present in latent form throughout the cycle. In addition, a large number of neutrophils loaded with MMPs are recruited at menstruation through induction of chemokines, such as interleukin-8. At the secretory phase, progesterone repression of MMPs is mediated by transforming growth factor-β. Tissue inhibitors of metalloproteinases (TIMPs) are abundant at all phases of the cycle to prevent any undue MMP activity, but are likely overwhelmed at menstruation. At other phases of the cycle, MMPs can elude TIMP inhibition as exemplified by recruitment of active MMP-7 to the plasma membrane of epithelial cells, allowing processing of membrane-associated growth factors needed for epithelial repair and proliferation. Finally, receptor-mediated endocytosis through low density lipoprotein receptor-related protein-1 (LRP-1) efficiently clears MMP-2 and -9 at the proliferative and secretory phases. This mechanism is probably essential to prevent any excessive ECM degradation by the active form of MMP-2 that is permanently present. However, shedding of the ectodomain of LRP-1 specifically at menstruation prevents endocytosis of MMPs allowing full degradation of the ECM. Thus endometrial MMPs are regulated at the levels of transcription, release from infiltrating neutrophils, activation, binding to the cell membrane, inhibition by TIMPs and endocytic clearance by LRP-1. This allows tight control during endometrial growth and differentiation but results in a burst of activity for menstrual tissue breakdown. This article is part of a Special Issue entitled: Proteolysis 50 years after the discovery of lysosome.

Functional SNP -1562C/T in the promoter region of MMP9 and recurrent early pregnancy loss

Angiogenesis, invasion and decidualization play an important role in uterine preparation and embryo development. Matrix metalloproteinases (MMP) are crucial for the degradation/remodelling of the extracellular matrix and are involved in spiral artery formation and invasion of endometrium during implantation. A functional single-nucleotide polymorphism (SNP) in the MMP9 promoter, 1562C/T, is known to influence expression in an allele-specific manner. The present study evaluated the association between maternal genotype of SNP 1562C/T of MMP9 and recurrent early pregnancy loss (REPL) risk. This case–control study was comprised of REPL patients (n = 106) and women having one healthy child as controls (n = 111). Genotyping for SNP 1562C/T of MMP9 was performed by PCR/restriction fragment length polymorphism followed by DNA sequencing. Allele and genotype distribution did not differ significantly between patients and controls (by allele, chi-squared 0.228, odds ratio 1.12, 95% confidence interval 0.695–1.816; by genotype, chi-squared 0.893). Thus SNP 1562C/T of MMP9 was not associated with REPL risk in this population and further study in other populations will verify whether it is associated with REPL risk or not. REPL is a multifactorial pathology and other genetic or environmental factors may be contributing to the complex aetiology of REPL.

Extracellular matrix remodelling in rat endometrium during early pregnancy: the role of fibronectin and laminin

The endometrial extracellular matrix (ECM) remodelling has a crucial role in the establishment of a successful pregnancy. In addition to its basic function such as regulation of cell function, differentiation, migration, proliferation, the substantial alterations in the endometrial ECM may play a specific role in the trophoblast invasion, placentation, cell death and formation of the proper and functional implantation chamber around the embryo. In the present study, immunolocalizations of fibronectin and laminin were determined using avidin-biotin complex-peroxidase in rat implantation sites during 7-10 days of pregnancy. Both proteins were present in the basal membrane of blood vessels and in decidual matrix whereas they were absent or had very weak reactivity in the primary decidual zone on day 7. When placentation has begun, the immunoreactivity of both proteins was increased in the placental bed and in the basal membrane of blood vessels of the mesometrial region. The immunolocalization of both proteins seemed to be decreased in the antimesometrial decidua, however, it was increased in the mesometrial decidual matrix on days 9 and 10. Therefore, it could be suggested laminin and fibronectin demonstrating dynamic expressions in relation with the morphological differentiation of endometrial stroma may play crucial roles in the control of trophoblast adhesion and invasion, in placentation and angiogenesis, in the determination of cell shape and fate thus contributing the endometrial receptivity and a successful pregnancy.

Altered spatiotemporal expression of collagen types I, III, IV, and VI in Lpar3-deficient peri-implantation mouse uterus

Lpar3 is upregulated in the preimplantation uterus, and deletion of Lpar3 leads to delayed uterine receptivity in mice. Microarray analysis revealed that there was higher expression of Col3a1 and Col6a3 in the Preimplantation Day 3.5 Lpar3(-/-) uterus compared to Day 3.5 wild-type (WT) uterus. Since extracellular matrix (ECM) remodeling is indispensable during embryo implantation, and dynamic spatiotemporal alteration of specific collagen types is part of this process, this study aimed to characterize the expression of four main uterine collagen types: fibril-forming collagen (COL) I and COL III, basement membrane COL IV, and microfibrillar COL VI in the peri-implantation WT and Lpar3(-/-) uterus. An observed delay of COL III and COL VI clearance in the Lpar3(-/-) uterus may be associated with higher preimplantation expression of Col3a1 and Col6a3. There was also delayed clearance of COL I and delayed deposition of COL IV in the decidual zone in the Lpar3(-/-) uterus. These changes were different from the effects of 17beta-estradiol and progesterone on uterine collagen expression in ovariectomized WT uterus, indicating that the altered collagen expression in Lpar3(-/-) uterus is unlikely to be a result of alterations in ovarian hormones. Decreased expression of several genes encoding matrix-degrading metallo- and serine proteinases was observed in the Lpar3(-/-) uterus. These results demonstrate that pathways downstream of LPA3 are involved in the dynamic remodeling of ECM in the peri-implantation uterus.

Lymphatics in the human endometrium disappear during decidualization

BACKGROUND

The mammalian placenta plays a central role in maternal tolerance of the semi-allogeneic fetus and fluid balance between the maternal and fetal compartments. The lymphatics play a role in both these function. The aim of this study was to describe the distribution of lymphatic vessels in human decidua, with particular focus on the lymphatics that surround remodelling spiral arteries during decidualization and trophoblast invasion.

METHODS

Placental bed and non-placental bed (decidua parietalis) biopsies were obtained from 41 women undergoing elective termination of pregnancy at 6-18 weeks gestational age as well as placental bed biopsies from 5 women undergoing elective Caesarean section at term. In addition to routine haematoxylin and eosin staining, double immunohistochemical labelling was performed on serial 3-µm sections to identify lymphatic vessels in conjunction with one of the following: blood vessels, smooth muscle, epithelial and trophoblast cells or proliferating cells. Representative photomicrographs of all sections were obtained from a total of 273 areas (46 samples, average 6 range 3-15 areas per sample). Descriptive findings of the organization of lymphatics in human placental bed and decidua parietalis were made from a total of 1638 images.

RESULTS

Lymphatic vessels positive for podoplanin were abundant in non-decidualized hypersecretory endometrium at all stages of gestation. By contrast, the decidua was nearly always devoid of lymphatics. In some samples, structures that appeared to be regressing lymphatics could be observed at the boundary between non-decidualized hypersecretory and decidualized endometrium. Lymphatic vessels were notably absent from the vicinity of spiral arteries that were surrounded by decidualized stromal cells. Lymphatic vessels in non-decidualized hypersecretory endometrium appeared larger and more elongated as gestation progressed. Proliferating lymphatic vascular endothelial cells were identified in both large vessels, and in streaks of D2-40 positive cells that could have been newly forming lymphatic vessels. Placental bed lymphatics exhibited limited and variable staining with LYVE-1 at all stages of pregnancy apart from term.

CONCLUSIONS

We have made novel observations on lymphatics in the placental bed and their relationship with other structures throughout pregnancy. Endometrial stromal cell decidualization results in a loss of lymphatics, with this phenomenon being particularly apparent around the spiral arteries.

Hormone-regulated expression and distribution of versican in mouse uterine tissues

BACKGROUND

Remodeling of the extracellular matrix is one of the most striking features observed in the uterus during the estrous cycle and after hormone replacement. Versican (VER) is a hyaluronan-binding proteoglycan that undergoes RNA alternative splicing, generating four distinct isoforms. This study analyzed the synthesis and distribution of VER in mouse uterine tissues during the estrous cycle, in ovariectomized (OVX) animals and after 17beta-estradiol (E2) and medroxyprogesterone (MPA) treatments, either alone or in combination.

METHODS

Uteri from mice in all phases of the estrous cycle, and animals subjected to ovariectomy and hormone replacement were collected for immunoperoxidase staining for versican, as well as PCR and quantitative Real Time PCR.

RESULTS

In diestrus and proestrus, VER was exclusively expressed in the endometrial stroma. In estrus and metaestrus, VER was present in both endometrial stroma and myometrium. In OVX mice, VER immunoreaction was abolished in all uterine tissues. VER expression was restored by E2, MPA and E2+MPA treatments. Real Time PCR analysis showed that VER expression increases considerably in the MPA-treated group. Analysis of mRNA identified isoforms V0, V1 and V3 in the mouse uterus.

CONCLUSION

These results show that the expression of versican in uterine tissues is modulated by ovarian steroid hormones, in a tissue-specific manner. VER is induced in the myometrium exclusively by E2, whereas MPA induces VER deposition only in the endometrial stroma.