Vojdani et al. Hum Cell. 2011 Mar;24(1):35-42
One of the major debates in the area of stem cell therapy is whether adult stem cells are capable of directly transforming (differentiating) into new tissue, or whether the therapeutic effects of administered stem cells occur because of growth factors produced by the injected stem cells. There are supporting data for both possibilities. The direct differentiation of adult stem cells into damaged tissue is supported by studies showing donor-derived adult tissue formed in patients treated. However in many situations that amount of new tissue found is relatively small. Supporting the “growth factor” hypothesis are numerous studies showing that administration of the tissue culture media that the stem cells have been grown in is capable of eliciting therapeutic effects.
Besides adult stem cells differentiating into other cells, there is some belief that other cells of the body are capable of this “transdifferenetiation” ability. For example, there was some work suggesting that B cells are capable of transforming into monocytes. There is some similarity between memory T and B cells with stem cells in that both of them express telomerase in a similar manner as stem cells. Therefore it would be interesting to see if B or T cells may express potential for differentiation into other cells. This is what was investigated in a recent paper (Vojdani et al. Cardiomyocyte marker expression in a human lymphocyte cell line using mouse cardiomyocyte extract. Hum Cell. 2011 Mar;24(1):35-42)
The investigators used a human B cell line called Raji. These cells are immortalized, therefore they may express some of the properties associated with pluripotency. What I mean is that generally cancer cells seem to start reexpressing proteins associated with “earlier” cells and possibly stem cells. For example, cancer cells are known to start re-expressing embryonic stem cell markers such as Oct-4 (Huang et al. Med Oncol. 2011 May 1).
Usually stem cells are made to differentiate into various tissues by exposing them to extracts of the cells that you want them to become. By extracts is usually meant the protein content of the cells after breaking up the cells either through freeze-thaw, sonication, or hypotonic lysis. In the current experiment the Raji cells were “retrodifferentiated” by treatment with 5-azacytidine, which is a DNA methylase inhibitor, as well as the HDAC inhibitor trichostatin A. These chemicals act to remove methylation of the cells, as well as to “open up” the histones by allowing for histone acetylation, respectively. To these undifferentiated cells the extracts from mouse heart cells were added. An interesting method of adding the extracts was used. The cell membrane was temporarily permeabilized and the extracts were added.
After 10 days, 3, and 4 weeks the cells started adhering and expressed a morphology similar to heart cells. Interestingly the cells stated expressing myosin heavy chain, α-actinin and cardiac troponin T after 3 and 4 weeks. Flow cytometry confirmed these data. In cells exposed to trichostatin A and 5-aza-2-deoxycytidine and permeabilized in the presence of the cardiomyocyte extract, troponin T expression was seen in 3.53% of the cells and 3.11% of them expressed α-actinin. These data suggest that pluripotency may be expressed by cells other than conventional stem cells. These experiments are similar to those performed by Collas’ group who demonstrated that administration of cytoplasm from Jurkat T cells to fibroblasts is capable of inducing the transdifferentiation of fibroblasts into cells that express T cell receptor and are capable of secreting IL-2 in response to ligation of the T cell receptor. This reminds us of the opposite of reprogramming by nuclear transfer (eg cloning).
Making Blood Cells into Heart Cells
PRECISE: Adipose-derived stem cells show utility as therapy
Cardiology Today
PRECISE is The Randomized Clinical Trial of Adipose-Derived Stem Cells in Treatment of Non Revascularizable Ischemic Myocardium, a double blind, placebo-controlled trial involving 27 patients with chronic ischemic heart disease with HF, angina or both, who were not eligible for percutaneous or surgical revascularization. The patients in the study underwent a liposuction to remove adipose tissue from their abdomen, the stem cells were separated and then reinjected directly into the heart. Placebo patients received the same treatment however were injected with placebo in place of stem cells. “These patients were not even able to be transplanted. So these were very high-risk, no-option patients,” said Francisco Fernández-Avilés, MD, with the department of cardiology, Hospital General Universitario Gregorio Marañón, Madrid, and PRECISE investigator.
The patients who were treated with stem cells had improved infarct size at 6 months and peak oxygen consumption compared to the placebo patients. “In my opinion, the results of the PRECISE trial are good enough to reconsider the possibility to start a larger scale randomized trial comparing cells to placebo in terms of left ventricular function, mainly clinical outcomes [like] mortality, HF and ischemia,” Fernández-Avilés said. For the years ahead, Fernández-Avilés said in patients with chronic HF and viability, the answer for stem cell therapy is adipose tissue, “and for patients with no viability, in my opinion, we need more basic investigation to find more effective cells.”
Membrane Voltage Changes Control Timing of Stem Cell Differentiation
Researchers at Tufts University have discovered that changes in voltage which naturally occur across adult human stem cell membranes act as a powerful control mechanism which determines the timing of stem cell differentiation.
Led by Dr. Michael Levin, the scientists have shed new light on the role that electrophysiology plays in the differentiation and proliferation of stem cells. According to Dr. Levin, “We have found that voltage changes act as a signal to delay or accelerate the decision of a stem cell to drop out of a stem state and differentiate into a specific cell type. This discovery gives scientists in regenerative medicine a new set of control knobs to use in ongoing efforts to shape the behavior of adult stem cells. In addition, by uncovering a new mechanism by which these cells are controlled in the human body, this research suggests potential future diagnostic applications.”
Using human mesenchymal stem cells (hMSCs), the researchers examined naturally occurring changes in membrane potential (voltage) in the hMSCs, which were harvested from donor bone marrow. As the hMSCs were differentiating into fat and bone cells, the scientists discovered unique voltage patterns that correspond to each stage of the differentiation process. For example, hyperpolarization, in which the difference between the interior and exterior voltages of a cell increases, was found to be characteristic of cells that had already differentiated, but not of cells that still remained undifferentiated. Additionally, the hMSCs were found to exhibit different membrane potentials depending upon whether they were differentiating into bone or fat cells.
When the researchers depolarized the hMSCs by exposing them to high levels of extracellular ions such as potassium, the artificially induced depolarization was found to disrupt the increase in negative voltage that would otherwise naturally occur during differentiation, which resulted in suppressed differentiation as measured by suppressed fat and bone cell differentiation markers. Converseley, when the researchers treated the hMSCs with hyperpolarizing reagents, the various differentiation markers were found to be upregulated.
All cells throughout the human body are, by their very nature, electrical, and terms which are usually reserved for electronics or electrical engineering, such as “current” and “voltage”, are also directly relevant to human physiology. Although biologists do not generally focus much attention on the electrochemistry, nor on the electrophysics, of cellular processes, such electrical phenomena are undeniably at the very essence of organic life. As this study clearly demonstrates, a simple change in voltage across the membrane of a stem cell is all that is required to constitute the “command” that determines whether a stem cell will or will not differentiate.
The Tufts researchers plan to continue further studies to examine in further detail the extent to which hyperpolarization determines the specific types of cells into which a stem cell will differentiate. Ultimately, if scientists could control such electrical processes, cellular differentiation could be used as a therapeutic tool with much greater precision and specificity. Regardless of what, exactly, such future discoveries might reveal, however, the electrodynamics of stem cells is already recognized as playing a vital role in the field of regenerative medicine.
The study was funded in part by the National Science Foundation, the National Institutes of Health, and the U.S. Defense Advanced Research Projects Agency (DARPA). The publication appeared in PLoS ONE, a peer-reviewed, open-access resource of the Public Library of Science.
