Stem Cell-Like Differentiation Potentials of Endometrial Side Population Cells as Revealed by a Newly Developed In Vivo Endometrial Stem Cell Assay

Abstract

BackgroundEndometrial stem/progenitor cells contribute to the cyclical regeneration of human endometrium throughout a woman's reproductive life. Although the candidate cell populations have been extensively studied, no consensus exists regarding which endometrial population represents the stem/progenitor cell fraction in terms of in vivo stem cell activity. We have previously reported that human endometrial side population cells (ESP), but not endometrial main population cells (EMP), exhibit stem cell-like properties, including in vivo reconstitution of endometrium-like tissues when xenotransplanted into immunodeficient mice. The reconstitution efficiency, however, was low presumably because ESP cells alone could not provide a sufficient microenvironment (niche) to support their stem cell activity. The objective of this study was to establish a novel in vivo endometrial stem cell assay employing cell tracking and tissue reconstitution systems and to examine the stem cell properties of ESP through use of this assay.Methodology/Principal FindingsESP and EMP cells isolated from whole endometrial cells were infected with lentivirus to express tandem Tomato (TdTom), a red fluorescent protein. They were mixed with unlabeled whole endometrial cells and then transplanted under the kidney capsule of ovariectomized immunodeficient mice. These mice were treated with estradiol and progesterone for eight weeks and nephrectomized. All of the grafts reconstituted endometrium-like tissues under the kidney capsules. Immunofluorescence revealed that TdTom-positive cells were significantly more abundant in the glandular, stromal, and endothelial cells of the reconstituted endometrium in mice transplanted with TdTom-labeled ESP cells than those with TdTom-labeled EMP cells.Conclusions/SignificanceWe have established a novel in vivo endometrial stem cell assay in which multi-potential differentiation can be identified through cell tracking during in vivo endometrial tissue reconstitution. Using this assay, we demonstrated that ESP cells differentiated into multiple endometrial lineages in the niche provided by whole endometrial cells, indicating that ESP cells are genuine endometrial stem/progenitor cells.

The Endometrium as a Source of Mesenchymal Stem Cells for Regenerative Medicine1

“…Human endometrial SP cells formed glandular, stromal, and endothelial structures when transplanted under the kidney capsule of immunodeficient NOD/SCIDγ mice [45]. In vivo studies have also suggested that human endometrial SP cells may be able to differentiate to a smooth muscle cell-like phenotype [47]. Reconstitution of endothelial cells was not observed in other studies [43], which may result from the heterogeneity of SP cells.…”

The endometrium as a source of mesenchymal stem cells in domestic animals and possible applications in veterinary medicine

“…48 In vivo assays have demonstrated that endometrial side population cells may be genuine stem cells. 40,42,49 These assays transplanted these cells under the renal capsules of immunodeficient ovariectomized mice administered oestradiol and progesterone for eight weeks who were subsequently subjected to nephrectomy. The results showed that all grafts reconstituted tissue similar to the endometrium under the renal capsules.…”

“…The results showed that all grafts reconstituted tissue similar to the endometrium under the renal capsules. 49 …”

Regeneration capacity of the endometrium: endometrial stem cells

“…Yapılan çalımalarda endometrial mezenkimal kök hücrelerin in vitro olarak kondrosit, [20] adiposit [21] ve hematopoetik [22] farklılama gösterebil-dikleri saptanmıtır. Yapılan bir baka çalımada endometrial mezenkimal kök hücrelerin insülin ve glukagon sekrete eden endodermal pankreatik hücrelere farklılabildikleri ve bu hücrelerin immün sistemi baskılanmı farelerde oluturulan diyabet modelinde kan ekerini düürdükleri tespit edilmitir.…”