The beating of the heart inside an embryo doesn’t just circulate blood through the developing creature, it also triggers the formation of blood stem cells, the cells that give rise to all other forms of blood cells, according to two new studies. The surprising findings show that the physical force of the heartbeat and blood flowing through the aorta cause embryonic stem cells to differentiate–although researchers don’t yet understand quite how this is accomplished.
The findings could eventually have practical applications for people with blood cancers and other diseases that are treated with transplants of bone marrow, the site of blood stem cell production. Scientists can make red and white blood cells easily in the laboratory, but bone marrow patients need blood stem cells to constantly replenish their blood supply. Producing these cells, also called hematopoietic stem cells, is much more difficult…. Only about a third of patients who require bone marrow transplants have matching donors. “Basically we cannot offer optimal therapy to two-thirds of patients” [Science News], says Leonard Zon, coauthor of one of the new studies. If researchers can learn how the body stimulates blood stem cell production, they may be able to duplicate the process in the lab, says Zon.
The two studies, published in Nature and Cell, examined the phenomenon in mice and zebrafish, respectively. In the mouse study, the research team placed mouse embryonic stem cells in a centrifuge-like device that mimics sheer stress — the frictional force blood creates when it flows over cells — in a mouse’s aorta. In early embryos, blood stem cells first form on the floor of the aorta. Later in development, they migrate to the bone marrow. Embryonic stem cells exposed to the same magnitude of sheer stress as found in the mouse aorta produced hematopoietic stem cells [Science News]. Different magnitudes of stess, like the amount of force found in a human aorta, showed no such result. Zon’s team found similar results in the zebrafish study, and also showed that a mutant type of embryo that never develops a heart beat, known as a “silent heart” embryo, had fewer blood stem cells.
Both studies also found that levels of nitric oxide, which is known to play a key role in blood vessel formation, increase when blood is flowing…. Researchers think nitric oxide may work as a type of signal to start the process of blood stem cell production [Reuters].
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Image: Luigi Adamo and Guillermo Garcia-Cardena. A blood cell colony emerges in response to blood flow.