Stretching transforms bone marrow stem cells

Using special laboratory dishes to 'stretch' bone marrow stem cells could help them transform into smooth muscle tissue, says US bioengineering researcher Kyle Kurpinski. He told delegates attending a meeting of the American Chemical Society that physical manipulation of stem cells might be an important step in coaxing them to develop into other types of cell. Kurpinski, from the University of California, says that by adding chemical 'signals' to the stretched cells, it may be possible to produce a layer of tissue that could be rolled up to form new blood vessels.

Finding ways of getting stem cells to grow into other, more specialised cell types is crucial for the development of new, cell-based therapies for a wide range of conditions. So far, scientists have concentrated on identifying the chemical growth factors, or signals, that direct a cell down a particular developmental pathway. But Kurpinski's work shows that physical methods might be useful too. The cells were grown on an elastic membrane, which had microscopic grooves in it to get the cells facing the right way. The membrane was then repeatedly stretched and relaxed for several days, after which the cells started to resemble smooth muscle cells.

Kurpinski told a press conference that in the body, stem cells attach to the walls of blood vessels, where they naturally stretch and contract as blood is pumped through the arteries. 'Governor Schwarzenegger got big biceps by lifting dumbbells', he said, adding 'it works the same way for stem cells to become smooth muscle cells. They have to sit in culture day in and day out lifting weights'.

Another study presented at the meeting suggested that bone marrow stem cells might also be persuaded to turn into nerve, muscle or bone tissue, simply by growing them on different types of gel-like materials in a dish - soft like a brain, stiff like muscle or hard like bone. Lead researcher Dennis Discher, of the University of Pennsylvania, explained that when stem cells sense the elasticity of the material that surround them, they might develop into cells that mimic that environment.

This work could have important clinical implications, for example, in work aiming to heal damaged heart muscle with injections of stem cells. Since dead and scarred heart tissue is more rigid than healthy heart tissue, it may not be providing the right growth cues for the injected stem cells. 'In a rigid environment of scar tissue, the stem cell cannot flex its muscles', said Discher, adding that it would be like trying to grow them on a table.

Another study presented at the meeting, which took place in San Francisco, California last week, suggested that a specialised type of blood stem cell could be persuaded to grow other types of cell. Terry Papoutsakis, of Northwestern University, Illinois, said that human megakaryocytes - blood cells that normally produce platelets - could be 'reprogrammed' into neutrophil-like cells that fight infections.