Mesenchymal stem cells (MSCs) are perhaps the most versatile type of stem cell known in adults, capable of forming bone, cartilage, fat and muscle. Though hard to identify definitively, these colony-forming cells can be found in bone marrow and around blood vessels in fat. Now, researchers led by Caroline Gargett from Monash University in Melbourne have tentatively identified a new and potentially richer source: the lining of the uterus.

The researchers had previously identified colony-forming cells among the loose connective tissue (stroma) of the endometrium but had not been able to isolate probable MSCs. To do so, the researchers sorted cells for expression of two markers (CD146 and PDGF-Rb) associated with MSCs. Cells with these markers accounted for only 1.5% of stromal cells sorted, but they were 15 times more likely to form colonies. The study also showed, for the first time, that these endometrial cells were able to differentiate into bone, cartilage, fat and muscle lineages1. Although further characterization is necessary, these results, in addition to the cells' occurrence around blood vessels, indicate that they are probably MSCs.

Only 8% of the sorted cells were able to form colonies, but this was a 6-fold enrichment over unsorted stromal cells, and the authors note that MSCs from other tissues are enriched 2- to 100-fold for colony-forming cells by similar cell sorting.

Studying these cells could aid understanding of diseases like endometriosis. Moreover, because the endometrium is so proliferative—the outer layer sheds and replaces itself every 4 weeks—this population of cells could be useful for tissue-engineering therapies. In fact, the percentage of colony-forming MSCs in the endometrial stroma seems to be more than 10 times, and perhaps more than 100 times, that collected in bone marrow. Gargett believes that collecting tissue from the inner layer of the endometrium, where the MSCs are expected to reside, would not be any more invasive than a biopsy of the bone marrow.

Initial therapeutic applications would probably be for the women from whom the endometrial MSCs were collected and could be used for a condition called pelvic floor prolapse, common in women who have given birth. Gargett believes that work in humans is probably a decade away. Closer at hand, these cells could aid understanding in diseases like endometriosis, as well as the biological function of MSCs.