Controversy doesn't derail stem cell progress
— -- Almost unnoticed amid the revival of stem cell politics this year, progress and peril in the science behind the controversy continues to hum along.
Human embryonic stem cells, with their ability to turn into every kind of organ tissue in the body, have tantalized biomedical researchers ever since their 1998 isolation by University of Wisconsin scientists. Organ replacement tissues free from immune system rejection, grown from embryonic stem cells or from more recently discovered "induced" stem cells grown from skin cells, have been envisioned for a decade.
"At this moment, the full promise of stem cell research remains unknown, and it should not be overstated," President Obama said in March while announcing a lifting of the previous administration's restrictions of federal funding on human embryonic stem cell research. He added, "Scientists believe these tiny cells may have the potential to help us understand, and possibly cure, some of our most devastating diseases and conditions."
In a study in the current Nature journal, a team led by George Daley of Children's Hospital Boston offered fresh insight into reaching that goal, demonstrating a novel, purely physical way to make stem cells turn into, or "differentiate" into, blood cells. Without using chemicals to trigger differentiation, the usual approach, the team placed mouse embryonic stem cells into a rotating "flow device," essentially between the inner ring and outer ring of a record-player. The viscous flow, or shear stress, on the cells caused by rotating the rings at different speeds for two days triggered the transformation from unspecialized stem cell to blood cell.
"By itself, the shear stress did it," said study team member William Lensch, in an interview conducted while we were both changing planes last week at Boston's Logan Airport (a small world, science reporting). "We tried all sorts of ways to push a flow along on the cells and they all gummed up, until the rotation method."
Shear flow alone on the cells triggered a jump in the expression of a blood cell gene and blood cell chemicals and limited the stem cells' production of nitric acid, which blocks their differentiation. "Collectively, these data reveal a critical role for biomechanical forces in haematopoietic (blood cell) development," says the study.
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