Stem Cells May Be Building Blocks of Genitourinary Repairs

CLAYTON, Australia, Sept. 13 -- A small number of special cells that resemble mesenchymal stem cells, bearing the possible application for major anatomic repairs, have been found in human endometrium, investigators have found.

Examining endometrial tissues from 17 women in their 30s and 40s, Caroline E. Gargett, Ph.D. and Kjiana E. Schwab, of Monash Medical Center here identified two markers that allowed them to pinpoint and isolate mesenchymal stem-like-cells, they reported online in Human Reproduction.

"The most exciting property of mesenchymal stem cells is their in vivo differentiation capacity, as they can repair or induce repair of damaged muscles and ischemic heart muscle, and survive and differentiate into astrocytes in the brain," they wrote. "Thus, mesenchymal stem cells have immense therapeutic potential."

The most likely early therapeutic application of the discovery would involve the use of autologous mesenchymal stem cells for anatomic repair of conditions such as pelvic floor prolapse, Dr. Gargett speculated.

"We believe that using a combination of biological scaffold and a woman's own mesenchymal stem cells might provide a solution that would ensure a longer lasting firm natural tissue that would be a superior support for the prolapsed uterus," she said.

Observation of the impressive regenerative properties of endometrium - it grows 4 to 7 mm within four to 10 days of every menstrual cycle -led Dr. Gargett and Schwab, a Ph.D. candidate working in her lab, to explore the possibility of isolating mesenchymal stems cells from the tissue.

But to do so, they first had to figure out how to find them -- no mean feat, because many of the surface receptors in mesenchymal stem cells expanded in culture, such as CD29 or CD105, are not unique to the cells, and can be found as markers on many other cell types, the authors noted.

"We had previously detected that mesenchymal stem cells were present in the human endometrium but we were unable to isolate the mesenchymal stem cells, which was a big drawback in studying their properties," said Dr. Gargett. "The major finding of this study was the identification of two markers which enabled the prospective isolation of mesenchymal stem cell-like cells from human endometrial tissue."

They focused on two perivascular cell markers in endometrial tissue -- platelet-derived growth factor-receptor b (PDGF-b), which is expressed that colony-forming endometrial stromal cells, and CD146, a member of the immunoglobulin superfamily, which is also an endothelial cell marker.

Using high-speed fluorescence activated cell sorting of endometrial tissue, they found that only 1.5% of the cells expressed both markers and were therefore likely candidates for being the elusive endometrial mesenchymal stem cells.

To determine whether the isolated cells, found in endometrial stroma, were capable of differentiation into multiple cell types, they tested them for mesenchymal stem cell-like properties using functional assays. They found that the sorted cells bearing both receptors had a greater than 15-fold enrichment of colony-forming endometrial stromal cells compared with cells that had neither receptor on their surfaces.

In addition, when colonies of the cells were pooled, expanded in culture, and exposed to induction factors for osteocytes, adipocytes, myocytes and chondrocytes, they differentiated into the corresponding cell types.

In the final step, the investigators attempted to nail down the location of the cells with immunohistochemistry of hysterectomy samples, and found evidence that they are located perivascularly in the endometrium.

"The fact that the cells expressing the two markers were located in the perivascular region strengthens our case that we have isolated mesenchymal stem cells, because mesenchymal stem cells from bone marrow and fat are found around blood vessels too," Dr. Gargett said. "It also gives us clues as to how they might function in repairing and regenerating new endometrium each month."

Curettage or biopsy is likely to be the most efficient means of mesenchymal stem cell-collection for use in autologous tissue repair. Postmenopausal women could be given a short course of hormone replacement therapy to expand the endometrium prior to harvesting, Dr. Gargett said.

"We also believe that the identification of the mesenchymal stem cells in human endometrium gives us the opportunity to investigate their possible role in the development and pathogenesis of common gynecological disorders associated with abnormal endometrial growth, such as endometriosis and adenomyosis," she added.

The authors noted that because their differentiation assays used pooled clonally derived cells rather than clones expanded from a single cell, they were not able to determine the true differentiation potential of a single cell carrying both the CD146 and PDGF-b receptors. They are not quite ready, therefore, to definitively declare that the cells they had identified are true mesenchymal stem cells.