Mesenchymal stem cells collected from patients are still stem cells.

With aging or disease mesenchymal stem cells located in the bone marrow can default to a fat cell phenotype versus a bone cell phenotype. When we speak of stem cells ability to become many different types of cells, we call that the stem cells are multipotent. Therefore one test for determining that a stem cell remains functionally a stem cell is to show that it can become different cell types. We usually bone cells and fat cells when studying bone biology since both are located in bone. These images show MSC induced to become fat cells (in an earlier post bone cells were shown). Fat vacuoles (lipid droplets) stain green while cell nuclei stain blue. Both the primary and revision patient MSC were able to form fat cells (and as I discussed in an earlier post, we quantified that there were fewer fat cells). However, in these images you can see more clearly that in addition to having fewer fat cells there are fewer lipid droplets and that those droplets are also smaller.

The loss of bone formation that we observed should normally result in an increase in fat cells. One reason we reached the conclusion that the mesenchymal stem cells are deficient is that they neither form bone cells or fat cells. Nevertheless, the remain capable of forming both a bone cell or a fat cell, which lead us to conclude that they remain stem cells.