Stem Cells on Their Way to Becoming Smooth Muscle Tissue: ?We Can Say We Are Midway There?

You used mesenchymal stem cells instead of embryonic stem cells [1]. What are the difference between these 2 kinds of stem cells?

The embryonic stem cells are found only in developing embryos and there’s a lot of controversy about them, specifically ethical controversy, in that an embryo would have to be destroyed in order to obtain these stem cells. However, they are more valuable than adult stem cells because they have the potential to turn into any kind of cell in the body, whereas some of the types of stem cells you would find in the adult body, like the mesenchymal stem cells, have more limited potential. They can only turn into certain kinds of things, so they can not turn into everything.

Traditionally, the differentiation of cells is prompted by chemical signals, but you used mechanical stimulation. What was your process?

The process is to put the mesenchymal stem cells onto an elastic substrate—which is basically a silicone membrane—and the cells can actually feel this membrane and they will physically attach themselves to it; they grip the silicone when the silicone gets stretched that will get transmitted to the cell as well. It is very similar to how cells would feel forces in the body because the body is made of both cells and non-cellular materials and when the materials get stretched, the cells attached get stretched as well. That’s the process.

Your findings indicate that the stem cells were well on their way to becoming smooth muscle tissue. Can you elaborate on this?

We are guessing we are about 50% there. When people talk about smooth muscle tissue, they typically talk about early, intermediate, and late markers of differentiation. One of the most interesting findings from our study is that we found this intermediate marker called Calponin 1—which is involved in the contraction and relaxation of these muscle cells—go way up after we stretched these muscle cells. We found an important intermediate marker there, but we didn’t necessarily see some of the significant late differentiation markers. We can say we are midway there, but we are not quite there yet.

How do you foresee the development of tissue engineering?

The mechanical stimulation is very important. There are certain things you can do with chemical stimulation alone, but when you think about the body it doesn’t just feel chemical stimulation. There are some things that chemical stimulation alone will not do, so in this particular study, we were interested in focusing only on the mechanical stimulation and seeing how much you can do with it. In terms of the stimulation that we were looking at, like I said, it may only be halfway there, so there may be the need to add additional chemical factors. Sometimes chemical factors and mechanical factors can interact with each other and you would get a greater response than from either one alone. It is important to look at each method separately, and as you progress down your research, to also look at them together.

In terms of embryonic versus adult stem cells there is still a lot of controversy and of course because of that, there is a lot of difficulty to obtain funding or to even obtain the stem cells in the first place. If you can get a good result from adult stem cells, it may not even be necessary to use embryonic stem cells. Now, if you can’t get the result with adult stem cells, then it is good to look into the embryonic research. But if you can get the tissue type that you want for tissue engineering from only using adult stems, then there’s really no problem with it. It may actually be better [to use adult stem cells], so as not to upset the ethical issues and also in terms of ease of getting the cells, which can be obtained from adult bone marrow, but obtaining the embryonic stem cells is a lot more difficult.

[1] Kurpinski K. et al, PNAS, 103, 16095 (2006); published online before print

Kyle Kurpinski is a graduate student in bioengineering at University of California Berkeley.

Interview by Thanh Tam Candice Vu