Isolation and characterization of side population cells in the postpartum murine endometrium.

Endometrium is a highly active organ that is periodically remodeled during the life span. Previous studies have indicated the presence of an adult stem or progenitor cell population in this tissue. In this study, side population (SP) cells were isolated from the endometrium of postpartum murine uterus but not from the endometrium of a uterus undergoing a normal estrus cycle. Phenotype analysis showed that SP cells were negative for hematopoietic, endothelial, and mesenchymal stem cell (MSC) markers, but they expressed stem cell antigen 1 (Sca-1) and c-kit at various degrees. Side population cell is a heterogeneous population of endometrial stem/progenitor cells that have colony-forming capacity. They were found to reside in quiescence in the stroma but not in the luminal epithelium. These data suggest that, like other tissues and organs, the murine endometrium also contains SP cells. Their specific role in the regeneration of the endometrium warrants further study.