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Endometrial regeneration has long been proposed to be mediated by stem cells, but the isolation of endometrial stem cells has been hampered by a lack of validated markers. Specific markers would enable isolation of these stem cells, thereby promoting advancements in regenerative medicine for the treatment of endometrial diseases and dysfunctions. We sought to investigate the regenerative ability of human endometrial positive for sushi domain containing 2/intercellular adhesion molecule 1 (SUSD2 + /ICAM1 + ) cells and Side Population cell lines in a xenograft mice model. The injection of total endometrial cell suspensions and Side Population cell lines under kidney capsules induced neoformation of human endometrium verified by the presence of typical endometrial markers (vimentin, cytokeratin 18, and progesterone receptor) by immunofluorescence. Total endometrial cell types promoted a better reconstitution in comparison to injecting ICAM1 + and SUSD2 + cells alone. The endometrial fraction is probably acting as a niche, resulting in increased reconstruction efficiency of pure fractions. Human engrafted cells were localized near blood vessels and induced the proliferation of surrounding cells. Our results suggest that human endometrial Side Population, a heterogeneous population possibly harboring endometrial stem cells, has the optimum capacity to regenerate endometrial-like tissue. In contrast, cells positive for single stem cell markers SUSD2 and ICAM1 have minimally functional regenerative capacities in the absence of niche-like cells.

Objective: To study, isolate and characterize leucine-rich repeat-containing heterotrimeric guanine nucleotide-binding protein-coupled receptor 5 (LGR5)-positive cells from human endometrium to determine their functional relevance., Design: Prospective experimental animal study., Setting: University research laboratories., Animal(s): Nonobese diabetic mice (NOD-SCID) (strain code 394; NOD.CB17-Prkdc scid /NcrCrl)., Intervention(s): Human LGR5 + cells were labeled with superparamagnetic iron oxide nanoparticles (SPIOs) and injected under the kidney capsule in immunocompromised mice., Main Outcome Measure(s): Epithelial and stromal LGR5 + cells were isolated from human endometrium by means of fluorescence-activated cell sorting, and phenotypic characterization was performed by means of flow cytometry with the use of hematopoietic and mesenchymal markers. Engrafted SPIO-labeled LGR5 + cells were localized with the use of Prussian blue staining and immunohistochemistry against CD9 and Vimentin. Deep transcriptomic profiling of LGR5 + cells was performed with the use of microarrays and RNA sequencing., Result(s): The percentage of LGR5 + cells in human endometrium represented 1.08 ± 0.73% and 0.82 ± 0.76% of total cells in the epithelial and stromal compartments, respectively. LGR5 + cells were phenotypically characterized by abundant expression of CD45 hematopoietic marker and no expression of surface markers CD31, CD34, CD133, CD73, and CD90. Coexpression with the macrophage marker CD163 was detected. Xenotransplantation of labeled LGR5 + cells into the kidney capsules of immunocompromised mice resulted in a weak endometrial reconstitution from this cell of origin. Transcriptomic profiling revealed new attributes for LGR5 + cells related to their putative hematopoietic origin., Conclusion(s): These data suggest that endometrial LGR5 is not an endogenous stem cell marker. Instead, LGR5 + cells appear to be recruited from blood to be part of the stem cell niche at the perivascular microenvironment to activate the endogenous niche., (Copyright © 2016 American Society for Reproductive Medicine. Published by Elsevier Inc. All rights reserved.)

Objective: To study the involvement of seven types of bone marrow-derived cells (BMDCs) in the endometrial regeneration in mice after total body irradiation., Design: Prospective experimental animal study., Setting: University research laboratories., Animal(s): β-Actin-green fluorescent protein (GFP) transgenic C57BL/6-Tg (CAG-EGFP) and C57BL/6J female mice., Intervention(s): The BMDCs were isolated from CAG-EGFP mice: unfractionated bone marrow cells, hematopoietic progenitor cells, endothelial progenitor cells (EPCs), and mesenchymal stem cells (MSCs). In addition three murine GFP(+) cell lines were used: mouse Oct4 negative BMDC multipotent adult progenitor cells (mOct4(-)BM-MAPCs), BMDC hypoblast-like stem cells (mOct4(+) BM-HypoSCs), and MSCs. All cell types were injected through the tail vein of 9 Gy-irradiated C57BL/6J female mice., Main Outcome Measure(s): Flow cytometry, cell culture, bone marrow transplantation assays, histologic evaluation, immunohistochemistry, proliferation, apoptosis, and statistical analysis., Result(s): After 12 weeks, histologic analysis revealed that uteri of mice with mOct4(-)BM-MAPCs and MSC line were significantly smaller than uteri of mice with uncultured BMDCs or mOct4(+) BM-HypoSCs. The percentage of engrafted GFP(+) cells ranged from 0.13%-4.78%. Expression of Ki-67 was lower in all uteri from BMDCs treated mice than in the control, whereas TUNEL(+) cells were increased in the EPCs and mOct4(+)BM-HypoSCs groups., Conclusion(s): Low number of some BMDCs can be found in regenerating endometrium, including stromal, endotelial, and epithelial compartments. Freshly isolated MSCs and EPCs together with mOct4(+) BM-HypoSCs induced the greatest degree of regeneration, whereas culture isolated MSCs and mOct4(-)BM-MAPCs transplantation may have an inhibitory effect on endometrial regeneration., (Copyright © 2015 American Society for Reproductive Medicine. Published by Elsevier Inc. All rights reserved.)

Objective: To provide a detailed summary of current scientific knowledge of somatic stem cells (SSCs) in murine and human myometrium and their putative implication in leiomyoma formation, as well as to establish new therapeutic options., Design: Pubmed and Scholar One manuscripts were used to identify the most relevant studies on SSCs and their implications in human myometrium and leiomyomas., Setting: University research laboratory-affiliated infertility clinic., Patient(s): Not applicable., Intervention(s): Not applicable., Main Outcome Measure(s): Not applicable., Result(s): Despite numerous publications on SSCs, it was not until 2007 that scientific evidence based on the use of 5-bromo-2'-deoxyuridine (BrdU) and side population (SP) methods in murine and human myometrium were first published. Recently, it has been reported that SP cells are present in human leiomyomas; however, to date the pathogenesis of this benign tumor remains unclear. Besides many genetic/epigenetic alterations, changes to steroid hormones and growth factors may also be associated with the impaired function, proliferation, and differentiation of a subset of putative SSCs in human myometrium., Conclusion(s): These findings open up new possibilities for understanding the origin of this benign tumor and help to develop new nonsurgical approaches for their management., (Copyright © 2014 American Society for Reproductive Medicine. Published by Elsevier Inc. All rights reserved.)

The existence of human endometrial somatic stem cells was proposed in the mid-20th century for the first time. This hypothesis became stronger and was revised by two authors between 1978 and 1989. Nevertheless, it was not until 2004 that scientific evidence was first published. As we describe here, the great regenerative capability of the human endometrium has been finally questioned in the last 8 years, and this period can be considered the most productive in endometrial stem cell biology given the new scientific information recapitulated to date. We provide a detailed summary based on the actual scientific knowledge obtained about (1) the existence of somatic stem cells in murine (detected with label-retaining cell methods) and human (cells isolated by different methods) endometria, (2) the involvement of bone marrow as a putative extrauterine source of endometrial somatic stem cells, (3) the implication and biological pathways of these cells in several pathologies like endometriosis and endometrial cancer, and (4) the future of endometrial somatic stem cells in regenerative medicine to provide new strategies in autologous transplant and bioengineering., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)

Accumulated evidence demonstrates the existence of bone marrow-derived cells origin in the endometria of women undergoing bone marrow transplantation (BMT). In these reports, cells of a bone marrow (BM) origin are able to differentiate into endometrial cells, although their contribution to endometrial regeneration is not yet clear. We have previously demonstrated the functional relevance of side population (SP) cells as the endogenous source of somatic stem cells (SSC) in the human endometrium. The present work aims to understand the presence and contribution of bone marrow-derived cells to the endometrium and the endometrial SP population of women who received BMT from male donors. Five female recipients with spontaneous or induced menstruations were selected and their endometrium was examined for the contribution of XY donor-derived cells using fluorescent in situ hybridization (FISH), telomapping and SP method investigation. We confirm the presence of XY donor-derived cells in the recipient endometrium ranging from 1.7% to 2.62%. We also identify 0.45-0.85% of the donor-derived cells in the epithelial compartment displaying CD9 marker, and 1.0-1.83% of the Vimentin-positive XY donor-derived cells in the stromal compartment. Although the percentage of endometrial SP cells decreased, possibly being due to chemotherapy applied to these patients, they were not formed by XY donor-derived cells, donor BM cells were not associated with the stem cell (SC) niches assessed by telomapping technique, and engraftment percentages were very low with no correlation between time from transplant and engraftment efficiency, suggesting random terminal differentiation. In conclusion, XY donor-derived cells of a BM origin may be considered a limited exogenous source of transdifferentiated endometrial cells rather than a cyclic source of BM donor-derived stem cells.

Endometrial regeneration is mediated, at least in part, by the existence of a specialized somatic stem cell (SSC) population recently identified by several groups using the side population (SP) technique. We previously demonstrated that endometrial SP displays genotypic, phenotypic and the functional capability to develop human endometrium after subcutaneous injection in NOD-SCID mice. We have now established seven human endometrial SP (hESP) cell lines (ICE 1-7): four from the epithelial and three from the stromal fraction, respectively. SP cell lines were generated under hypoxic conditions based on their cloning efficiency ability, cultured for 12-15 passages (20 weeks) and cryopreserved. Cell lines displayed normal 46XX karyotype, intermediate telomerase activity pattern and expressed mRNAs encoding proteins that are considered characteristic of undifferentiated cells (Oct-4, GDF3, DNMT3B, Nanog, GABR3) and those of mesodermal origin (WT1, Cardiac Actin, Enolase, Globin, REN). Phenotype analysis corroborated their epithelial (CD9+) or stromal (vimentin+) cell origin and mesenchymal (CD90+, CD73+ and CD45⁻) attributes. Markers considered characteristic of ectoderm or endoderm were not detected. Cells did not express either estrogen receptor alpha (ERα) or progesterone receptor (PR). The hESP cell lines were able to differentiate in vitro into adipocytes and osteocytes, which confirmed their mesenchymal origin. Finally, we demonstrated their ability to generate human endometrium when transplanted beneath the renal capsule of NOD-SCID mice. These findings confirm that SP cells exhibit key features of human endometrial SSC and open up new possibilities for the understanding of gynecological disorders such as endometriosis or Asherman syndrome. Our cell lines can be a valuable model to investigate new targets for endometrium proliferation in endometriosis.

During reproductive life, the human endometrium undergoes around 480 cycles of growth, breakdown and regeneration should pregnancy not be achieved. This outstanding regenerative capacity is the basis for women's cycling and its dysfunction may be involved in the etiology of pathological disorders. Therefore, the human endometrial tissue must rely on a remarkable endometrial somatic stem cells (SSC) population. Here we explore the hypothesis that human endometrial side population (SP) cells correspond to somatic stem cells. We isolated, identified and characterized the SP corresponding to the stromal and epithelial compartments using endometrial SP genes signature, immunophenotyping and characteristic telomerase pattern. We analyzed the clonogenic activity of SP cells under hypoxic conditions and the differentiation capacity in vitro to adipogenic and osteogenic lineages. Finally, we demonstrated the functional capability of endometrial SP to develop human endometrium after subcutaneous injection in NOD-SCID mice. Briefly, SP cells of human endometrium from epithelial and stromal compartments display genotypic, phenotypic and functional features of SSC.