Endometrial Injury and Its Rescue by Mesenchymal Stem Cells Is Dependent on Estrous Cycle Phase

Asherman Syndrome (AS) is caused by injury to the endometrium leading to uterine scarring, decreased menstruation and infertility; it typically occurs after surgical curettage of the uterus. AS is treated surgically albeit with limited success. Administration of bone marrow-derived mesenchymal stem cells (MSCs) has recently been demonstrated to restore uterine function in AS; however, there is no data available on the role of the estrous cycle phase on outcomes. Here, we describe endometrial injury during estrus or diestrus, its differential effect on fertility, and its response after bone marrow MSC treatment to reverse the infertility in a murine model. Endometrial injury in the estrus phase did not affect fertility outcomes whereas injury in the diestrus phase resulted in infertility. Bone marrow (BM)-derived MSC treatment without injury in the estrus or diestrus phase did not affect the pregnancy outcomes. BM MSC treatment following endometrial injury in the diestrus phase restored fertility. Immunofluorescence analysis revealed that vimentin or cytokeratin-positive BM-derived cells in the uterus were extremely rare. BM MSC treatment after injury increased CD45⁺ cells, indicating a role for immunomodulation in endometrial repair. Finally, qRT-PCR showed that Ccl3, Il-1β and Mmp3 gene expression was significantly higher in the endometrium of the injury + BM MSC group than in other groups. In summary, injury to the endometrium during the diestrus phase results in infertility that can be restored by the treatment of BM MSCs. The therapeutic effect of BM MSCs on the endometrium appears to be mediated primarily by immunomodulation rather than BM MSC engraftment.