The bone marrow-derived human mesenchymal stem cell: potential progenitor of the endometrial stromal fibroblast

Endometrial regeneration and endometrial stem/progenitor cells

The functional layer of the human endometrium is a highly regenerative tissue undergoing monthly cycles of growth, differentiation and shedding during a woman's reproductive years. Fluctuating levels of circulating estrogen and progesterone orchestrate this dramatic remodeling of human endometrium. The thin inactive endometrium of postmenopausal women which resembles the permanent basal layer of cycling endometrium retains the capacity to respond to exogenous sex steroid hormones to regenerate into a thick functional endometrium capable of supporting pregnancy. Endometrial regeneration also follows parturition and endometrial resection. In non menstruating rodents, endometrial epithelium undergoes rounds of proliferation and apoptosis during estrus cycles. The recent identification of adult stem cells in both human and mouse endometrium suggests that epithelial progenitor cells and the mesenchymal stem/stromal cells have key roles in the cyclical regeneration of endometrial epithelium and stroma. This review will summarize the evidence for endometrial stem/progenitor cells, examine their role in mouse models of endometrial epithelial repair and estrogen-induced endometrial regeneration, and also describe the generation of endometrial-like epithelium from human embryonic stem cells. With markers now available for identifying endometrial mesenchymal stem/stromal cells, their possible role in gynecological diseases associated with abnormal endometrial proliferation and their potential application in cell-based therapies to regenerate reproductive and other tissues will be discussed.

Induction of IGFBP-1 expression by cAMP is associated with histone acetylation status of the promoter region in human endometrial stromal cells

Many genes are up- or down-regulated in human endometrial stromal cells (ESCs) undergoing decidualization. IGF-binding protein-1 (IGFBP-1) and prolactin (PRL) are preferentially expressed during decidualization and are recognized as specific markers of decidualization. This study investigated the involvement of epigenetic mechanisms in the regulation of IGFBP-1 and PRL induction by decidualization in ESCs. ESCs isolated from the proliferative phase endometrium were incubated with cAMP to induce decidualization. Human dermal fibroblasts (HDFs) were used as a nonendometrial control. cAMP induced the expressions of both genes in ESCs but induced the expression of only PRL in HDFs. Histone acetylation levels of the IGFBP-1 promoter region evaluated by chromatin immunoprecipitation assay were higher in ESCs than in HDFs. The IGFBP-1 promoter regions in the two cell types showed similar levels of DNA hypomethylation. The histone acetylation levels and DNA methylation status of the PRL promoter and enhancer regions were similar in the two cell types. cAMP had no significant effects on the histone acetylation levels and DNA methylation status of the IGFBP-1 promoter and the PRL promoter and enhancer regions in ESCs. Cotreatment of HDF with cAMP and histone deacetylase inhibitors induced IGFBP-1 expression, which was accompanied by an increased histone acetylation level and recruitment of CCAAT/enhancer-binding protein-β to the promoter region. These results show that, during decidualization in ESCs, high histone acetylation status of the promoter regions of IGFBP-1 and PRL is associated with the induction of the IGFBP-1 and PRL genes by making the promoter regions accessible to transcriptional factors.

Increased expression of importin13 in endometriosis and endometrial carcinoma

Background

Importin13 (IPO13) is a novel potential marker of corneal epithelial progenitor cells. We investigated the expression and localization of IPO13 in endometrial, endometriotic and endometrial carcinoma tissue.

Material/Methods

IPO13 expression in endometrial, endometriotic and endometrial carcinoma tissue was examined by immunohistochemistry, qPCR and Western blot.

Results

Immunohistochemistry studies showed that IPO13 protein was expressed mainly in cytoplasm of glandular epithelial cell and stromal cells. The rate of importin13-positive cells in proliferative phase endometrium was higher (by about 6-fold) than that in secretory endometrium (P<0.05) and the rate of importin13-positive cells in endometriosis and endometrial carcinoma was higher than that in normal secretory phase endometrial tissues (by about 4- and 9-fold, respectively). Immunofluorescence microscopy revealed co-localization of IPO13 with CD34, CD45, c-kit, telomerase, CD90 and CD146. QPCR revealed significantly increased IPO13 mRNA in endometriosis and endometrial carcinoma versus secretory phase endometrium (by about 2- and 10-fold, respectively). Western blot analysis showed that IPO13 protein is enhanced in endometriosis and endometrial carcinoma versus secretory phase endometrium (p<0.05).

Conclusions

These results demonstrate an increased expression of IPO13 in endometriosis and endometrial carcinoma, which could be involved in the pathogenesis of endometriosis and endometrial carcinoma; IPO13 can serve as an endometrial progenitor/stem cell marker.

Human oral mucosa and gingiva: a unique reservoir for mesenchymal stem cells

Mesenchymal stem cells (MSCs) represent a heterogeneous population of progenitor cells with self-renewal and multipotent differentiation potential. Aside from their regenerative role, extensive in vitro and in vivo studies have demonstrated that MSCs are capable of potent immunomodulatory effects on a variety of innate and adaptive immune cells. In this article, we will review recent experimental studies on the characterization of a unique population of MSCs derived from human oral mucosa and gingiva, especially their immunomodulatory and anti-inflammatory functions and their application in the treatment of several in vivo models of inflammatory diseases. The ease of isolation, accessible tissue source, and rapid ex vivo expansion, with maintenance of stable stem-cell-like phenotypes, render oral mucosa- and gingiva-derived MSCs a promising alternative cell source for MSC-based therapies.

Optimization and scale-up culture of human endometrial multipotent mesenchymal stromal cells: potential for clinical application

We have previously identified and purified multipotent mesenchymal stromal cell (MSC)-like cells in the highly regenerative endometrial lining of the human uterus (eMSC) as CD140b⁺CD146⁺ cells. Due to ease of accessibility with minimal morbidity via biopsy, we are proposing to use eMSC in cell-based therapies; however, culture conditions compliant with Good Manufacturing Practice have not been established for eMSC. The aim of this study was to optimize serum-free and xeno-free culture conditions for expansion of eMSC for potential clinical use. Real-time cell assessment (Xcelligence) and MTS viability assays were used to measure attachment and proliferation of freshly isolated, flow cytometry-sorted CD140b⁺CD146⁺ eMSC cultured in several commercially available and in-house serum-free and xeno-free media in combination with five attachment matrices (fibronectin, collagen, gelatin, laminin, and Cell Start-XF®). Comparisons were made with a standard serum-containing medium, DMEM/F-12/10% fetal bovine serum. Under all conditions examined, eMSC attachment and proliferation was greatest using a fibronectin matrix, with Lonza TP-SF® and our in-house DMEM/SF/FGF2/EGF serum-free xeno-product-containing medium similar to serum-containing medium. Hypoxia increased eMSC proliferation in the DMEM/SF/FGF2/EGF serum-free medium. Culture of eMSC for 7 days on a fibronectin matrix in DMEM/SF/FGF2/EGF serum-free media in 5% O₂ maintained greater numbers of undifferentiated eMSC expressing CD140b, CD146, and W5C5 compared to culture under similar conditions in Lonza TP-SF medium. However, the percentage of cells expressing typical MSC phenotypic markers, CD29, CD44, CD73, and CD105, were similar for both media. EMSC showed greater expansion in 2D compared to 3D culture on fibronectin-coated microbeads using the optimized DMEM/SF/FGF2/EGF medium in 5% O₂. In the optimized 2D culture conditions, eMSC retained CFU activity, multipotency, and MSC surface phenotype, representing the first steps in their preparation for potential clinical use.

Endometrial reconstruction from stem cells

Adult stem cells have been identified in the highly regenerative human endometrium on the basis of their functional attributes. They can reconstruct endometrial tissue in vivo suggesting their possible use in treating disorders associated with inadequate endometrium. The identification of specific markers for endometrial mesenchymal stem cells and candidate markers for epithelial progenitor cells enables the potential use of endometrial stem/progenitor cells in reconstructing endometrial tissue in Asherman syndrome and intrauterine adhesions.

Perivascular human endometrial mesenchymal stem cells express pathways relevant to self-renewal, lineage specification, and functional phenotype

Human endometrium regenerates on a cyclic basis from candidate stem/progenitors whose genetic programs are yet to be determined. A subpopulation of endometrial stromal cells, displaying key properties of mesenchymal stem cells (MSCs), has been characterized. The endometrial MSC (eMSC) is likely the precursor of the endometrial stromal fibroblast. The goal of this study was to determine the transcriptome and signaling pathways in the eMSC to understand its functional phenotype. Endometrial stromal cells from oocyte donors (n = 20) and patients undergoing benign gynecologic surgery (n = 7) were fluorescence-activated cell sorted into MCAM (CD146)(+)/PDGFRB(+) (eMSC), MCAM (CD146)(-)/PDGFRB(+) (fibroblast), and MCAM (CD146)(+)/PDGFRB(-) (endothelial) populations. The eMSC population contained clonogenic cells with a mesenchymal phenotype differentiating into adipocytes when cultured in adipogenic medium. Gene expression profiling using Affymetrix Human Gene 1.0 ST arrays revealed 762 and 1518 significantly differentially expressed genes in eMSCs vs. stromal fibroblasts and eMSCs vs. endothelial cells, respectively. By principal component and hierarchical clustering analyses, eMSCs clustered with fibroblasts and distinctly from endothelial cells. Endometrial MSCs expressed pericyte markers and were localized by immunofluorescence to the perivascular space of endometrial small vessels. Endometrial MSCs also expressed genes involved in angiogenesis/vasculogenesis, steroid hormone/hypoxia responses, inflammation, immunomodulation, cell communication, and proteolysis/inhibition, and exhibited increased Notch, TGFB, IGF, Hedgehog, and G-protein-coupled receptor signaling pathways, characteristic of adult tissue MSC self-renewal and multipotency. Overall, the data support the eMSC as a clonogenic, multipotent pericyte that displays pathways of self-renewal and lineage specification, the potential to respond to conditions during endometrial desquamation and regeneration, and a genetic program predictive of its differentiated lineage, the stromal fibroblast.

Comparative transcriptome analysis of human trophectoderm and embryonic stem cell-derived trophoblasts reveal key participants in early implantation

The implantation process begins with attachment of the trophectoderm (TE) of the blastocyst to the maternal endometrial epithelium. Herein we have investigated the transcriptome of mural TE cells from 13 human blastocysts and compared these with those of human embryonic stem cell (hESC)-derived-TE (hESC(troph)). The transcriptomes of hESC(troph) at Days 8, 10, and 12 had the greatest consistency with TE. Among genes coding for secreted proteins of the TE of human blastocysts and of hESC(troph) are several molecules known to be involved in the implantation process, as well as novel ones, such as CXCL12, HBEGF, inhibin A, DKK3, WNT5A, and follistatin. The similarities between the two lineages underscore some of the known mechanisms and offer discovery of new mechanisms and players in the process of the very early stages of human implantation. We propose that the hESC(troph) is a viable functional model of human trophoblasts to study trophoblast-endometrial interactions. Furthermore, the data derived herein offer the promise of novel diagnostics and therapeutics aimed at practical challenges in human infertility and pregnancy disorders associated with abnormal embryonic implantation.

Endometrial stem cells and reproduction

Abnormal endometrial function remains a significant cause of implantation failure, recurrent pregnancy loss, and other pathologies responsible for female infertility. The development of novel therapies to treat infertility due to endometrial dysfunction requires an understanding of the latest advancements in endometrial cell biology, such as the role of endometrial stem cells. The remarkable regenerative capacity of the human endometrium is absolutely essential for successful reproduction and likely requires a population of stem cells in the endometrium. The purpose of this review is to provide an introduction to some of the newest concepts in endometrial stem cell biology.

Plasticity of human menstrual blood stem cells derived from the endometrium

Stem cells can be obtained from women's menstrual blood derived from the endometrium. The cells display stem cell markers such as Oct-4, SSEA-4, Nanog, and c-kit (CD117), and have the potent ability to differentiate into various cell types, including the heart, nerve, bone, cartilage, and fat. There has been no evidence of teratoma, ectopic formation, or any immune response after transplantation into an animal model. These cells quickly regenerate after menstruation and secrete many growth factors to display recurrent angiogenesis. The plasticity and safety of the acquired cells have been demonstrated in many studies. Menstrual blood-derived stem cells (MenSCs) provide an alternative source of adult stem cells for research and application in regenerative medicine. Here we summarize the multipotent properties and the plasticities of MenSCs and other endometrial stem cells from recent studies conducted both in vitro and in vivo.

Decreased expression of c-kit and telomerase in a rat model of chronic endometrial ischemia

BACKGROUND

It was unclear whether chronic endometrial ischemia contributed to the pathogenesis of thin endometrium and was associated with decreased endometrial stem/progenitor cell. Thus, we explored the role of chronic endometrial ischemia in the pathogenesis of thin endometrium and its effect on endometrial stem/progenitor cells apoptosis.

MATERIAL/METHODS

In vitro, endometrial side population (ESP) cell apoptosis models were built, and apoptosis was quantified by fluorescence-activated cell sorter (FACS) analysis, pou5f1, and c-kit mRNA was detected by qPCR. In vivo, a rat model of chronic endometrial ischemia was induced by performing bilateral uterine artery ligation. TERT and caspase3 were detected by immunohistochemistry. Pou5f1and c-kit mRNA was examined by qPCR. C-kit, caspase3 and telomerase were detected by Western blot.

RESULTS

In the in vitro endometrial SP (ESP) cells apoptosis model, we found that the apoptotic rate was gradually increased with time, prolonging the expression of TERT, and c-kit mRNA was gradually decreased. In the in vivo endometrial SP (ESP) cells apoptosis model, we found that endometrial thickness, luminal epithelium thickness, gland epithelium thickness and the number of glands in the experiment group were significantly decreased compared with those in the control group (P<0.05). The expression levels of c-kit, pou5f1 and telomerase was significantly lower in the experimental group than those in the control group (P<0.05). The expression level of caspase3 was significantly higher in the experimental group compared with that in the control group (P<0.05).

CONCLUSIONS

The present work shows that chronic ischemia and chronic endometrial ischemia-associated stem/progenitor cells apoptosis may be responsible for the pathogenesis of thin endometrium.

Cigarette smoke inhibits recruitment of bone-marrow-derived stem cells to the uterus

Cigarette smoking leads to female infertility and a decreased incidence of endometriosis. Bone marrow derived stem cells are recruited to uterine endometrium and endometriosis. The effect of cigarette smoking on stem cell recruitment to any organ is uncharacterized. We hypothesized that bone marrow-derived mesenchymal stem cell recruitment to the uterus and differentiation would be diminished by cigarette smoke. We used human mesenchymal stem cells (hMSC) in vitro and a mouse model of cigarette smoke exposure. After myeloablation female C57BL/6J received bone marrow cells from males. Mice were exposed to room air or smoke from unfiltered cigarettes. Immunofluorescence and Y-FISH was performed on uterine sections. In vitro hMSCs were treated with 8-Br-cAMP to induce endometrial cell differentiation with or without cigarette smoke extract (CSE) and decidualization assessed morphologically and by prolactin expression. After 4 weeks the total number of Y-chromosome cells in the uterus was reduced by 68% in the smoke exposed mice. Both leukocytes and bone marrow derived endometrial cells were reduced by 60% and 73%, respectively. Differentiation of bone marrow derived cell to endometrial epithelial cells was reduced by 84%. hMSC treated with CSE failed to show cytological characteristics of decidualization. mRNA levels of the decidualization marker prolactin were decreased by 90% in CSE treated cells. Smoking inhibits both recruitment of bone marrow derived stem cells to uterus and stem cell differentiation. Inhibition of stem cells recruitment may be a general mechanism by which smoking leads to long term organ damage through inability to repair or regenerate multiple tissues.

Adult stem cells in the endometrium

Rare cells with adult stem cell activity were recently discovered in human endometrium. Endometrial stem/progenitor cell candidates include epithelial, mesenchymal and endothelial cells, and all may contribute to the rapid endometrial regeneration following menstruation, rather than a single candidate. Endometrial mesenchymal stem-like cells (eMSC) are prospectively isolated as CD146(+)PDGF-Rβ(+) cells and are found in both basalis and functionalis as perivascular cells. Epithelial progenitor cells are detected in colony forming unit assays but their identity awaits elucidation. They are postulated to reside in the basalis in gland bases. Endometrial stem/progenitor cells may be derived from endogenous stem cells, but emerging evidence suggests a bone marrow contribution. Endometrial endothelial progenitor cells are detected as side population cells, which express several endothelial cell markers and differentiate into endometrial glandular epithelial, stromal and endothelial cells. Investigating endometrial stem cell biology is crucial to understanding normal endometrial physiology and to determine their roles in endometrial proliferative diseases. The nature of endometriosis suggests that initiation of ectopic endometrial lesions involves endometrial stem/progenitor cells, a notion compatible with Sampson's retrograde menstruation theory and supported by the demonstration of eMSC in menstrual blood. Evidence of cancer stem cells (CSC) in endometrial cancer indicates that new avenues for developing therapeutic options targeting CSC may become available. We provide an overview of the accumulating evidence for endometrial stem/progenitor cells and their possible roles in endometrial proliferative disorders, and discuss the unresolved issues.