So how do those first generation stem cell therapies work? Stem cells, often from the patient, are delivered to a damaged heart and seem to be making a measurable difference - but it has taken a few years to understand just how this process works:
In 2003, the researchers demonstrated that adult stem cells circulating in blood can be used to repair hearts, and that it is not necessary to take the stem cells from bone marrow. In 2004, they found stem cells use different methods to morph into the two kinds of cells needed to restore heart function. In animal studies, they showed that to make new heart muscle cells, the human stem cells fuse onto cardiac cells to produce new muscle (myocyte) cells. But to form new blood vessel cells, the stem cells "differentiate" or mature by themselves to provide new endothelial cells that patch vessel damage.
In this study, they looked into the mechanism by which stem cells fuse to cardiac myocytes.
Heart muscle cells do not divide, so the researchers did not know whether the new fused cells were an endpoint in themselves, designed to replace dying cardiac muscle, or whether they could give rise to other new cells. They discovered that fused cells took on some "stemness" - they divided, and continued to do so as long as new tissue is needed, but not long enough to produce a tumor.
The accepted dogma is that heart cells cannot divide, but we show that fusing stem cells onto muscle cells bestows these cells with a new and wonderful ability to divide again to repair the heart.
Meanwhile, scientists continue to document the ever more evident complexity of human tissue: the closer you look, the more there is to see, and biochemistry is always more complex than you'd like to think it is. Stem cells, for example, do much more than just act as a source of new cells:
"We found that stem cells can participate actively in determining what type of cell their daughters will become right at the moment of stem cell division," said Embryology director and study co-author Allan Spradling. "This suggests that tissue stem cells might not just be a source of new cells, but could actually be the ‘brains' of the tissue - the cells that figure out what type of new cell is needed at any given moment."
"Each individual stem cell seems to have a great degree of independence from the rest of the animal's body," Spradling explained. "On one hand, the [intestinal stem cells] can respond quickly to the needs of the gut lining as it loses cells. On the other hand, they seem rather vulnerable to losing control of cell division."
Deconstructing these mechanisms will lead to better control over cells - if scientists can accurately reproduce the natural environment of biochemical signals, they can start to control the growth of cell populations to therapeutic ends. The body builds and repairs organs; so will we, in due course - but better, deliberately, and to save and extend lives.
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