title: Nanoparticle labeling identifies slow cycling human endometrial stromal cells.
abstract: BACKGROUND
  Evidence suggests that the human endometrium contains stem or progenitor cells that are responsible for its remarkable regenerative capability. A common property of somatic stem cells is their quiescent state. It remains unclear whether slow-cycling cells exist in the human endometrium. We hypothesized that the human endometrium contains a subset of slow-cycling cells with somatic stem cell properties. Here, we established an in vitro stem cell assay to isolate human endometrial-derived mesenchymal stem-like cells (eMSC).
  
  
  METHODS
  Single-cell stromal cultures were initially labeled with fluorescent nanoparticles and a small population of fluorescent persistent cells (FPC) remained after culture of 21 days. Two populations of stromal cells, namely FPC and non-FPC were sorted.
  
  
  RESULTS
  Quantitative analysis of functional assays demonstrated that the FPC had higher colony forming ability, underwent more rounds of self-renewal and had greater enrichment of phenotypically defined prospective eMSC markers: CD146+/CD140b+ and W5C5+ than the non-FPC. They also differentiate into multiple mesenchymal lineages and the expression of lineage specific markers was lower than that of non-FPC. The FPC exhibit low proliferation activities. A proliferation dynamics study revealed that more FPC had a prolonged G1 phase.
  
  
  CONCLUSIONS
  With this study we present an efficient method to label and isolate slow-proliferating cells obtained from human endometrial stromal cultures without genetic modifications. The FPC population could be easily maintained in vitro and are of interest for tissue-repair and engineering perspectives. In summary, nanoparticle labeling is a promising tool for the identification of putative somatic stem or progenitor cells when their surface markers are undefined.
authors.forename: Lina
authors.initials: L
authors.lastname: Xiang
authors.forename: Rachel W S
authors.initials: RW
authors.lastname: Chan
authors.forename: Ernest H Y
authors.initials: EH
authors.lastname: Ng
authors.forename: William S B
authors.initials: WS
authors.lastname: Yeung
mesh_terms: D000328:Adult; D002454:Cell Differentiation; D019070:Cell Lineage; D049109:Cell Proliferation; D004717:Endometrium / Q000166:cytology*; D005260:Female; D005434:Flow Cytometry; D016193:G1 Phase; D006801:Humans; D007150:Immunohistochemistry; D008875:Middle Aged; D053758:Nanoparticles / Q000032:analysis; D017154:Stromal Cells; D059008:Time-Lapse Imaging