Endometrial Stem Cells.

The endometrium is a dynamic tissue that undergoes repeated cycles of growth and regression with each estrous or menstrual cycle. Adult progenitor stem cells are responsible for this remarkable regenerative capacity; these same progenitor stem cells also have an enhanced capacity to generate endometriosis if shed in a retrograde fashion. The progenitor stem cells reside in the uterus; however, less-committed mesenchymal stem cells may also travel from other tissues such as bone marrow to repopulate the progenitor population. Mesenchymal stem cells are also involved in the pathogenesis of endometriosis and may be the principle source of endometriosis outside of the peritoneal cavity when they differentiate into endometriosis in ectopic locations. The flux of mesenchymal stem cells to the uterus is regulated by uterine injury and disease and does not appear to be directly regulated by sex steroids; recruitment of extra-uterine mesenchymal stem cell is not the source of cycle endometrial regeneration in each estrus or menstrual cycle. Enhanced stem cell availability appears to treat uterine injury such as Asherman's syndrome. Finally, besides progenitor stem cells, we have recently identified multipotent stem cells in the endometrium. These multipotent stem cells are a readily available source of cells that are useful in tissue engineering and regenerative medicine. Endometrial stem cells have been used to generate chondrocytes, myocytes, neurons, and adiposites in vitro as well as to replace dopaminergic neurons in a murine model of Parkinson's disease and pancreatic beta cells in a murine diabetes model.