Americans consider excess fat a curse - a health culprit. But now scientists have discovered that fat may actually play a beneficial role in tissue regeneration.

Led by Marc Hedrick, assistant professor in residence at the School of Medicine, researchers at UCLA and the University of Pittsburgh have identified fat as the first plentiful source of stem cells - immature and unspecified cells crucial to the body's ability to renew and repair its own tissues. By manipulating stem cell environments, researchers can grow a variety of human tissues, such as bone, cartilage and muscle.

"We were looking at fat tissues for other reasons and noticed some cells behaving oddly," explained Hedrick of the Division of Plastic and Reconstructive Surgery. "They were making muscle cells, making bone nodules. So we began trying to push them in one direction or another, and they seemed to be responding."

Scientists have been harvesting stem cells for tissue engineering research from bone marrow and brain and fetal tissue. But the use of fetal cells, taken from aborted fetuses, is highly controversial. Scientists are also concerned that the cells could form tumors or prove hard to control, and that the engineered tissue might be rejected by the recipient, said Hedrick.

With the discovery of an abundance of stem cells in fat, which the researchers acquired from cosmetic surgery patients in Beverly Hills, harvesting stem cells from other sources will be unnecessary. And the potential to use a patient's own stem cells to grow tissue will reduce the likelihood that the tissue will be rejected, added Hedrick.

The scientists are now looking at practical applications for their findings, published in this month's edition of the journal Tissue Engineering. This includes tissue regeneration for breast reconstruction, osteoporosis problems and muscle loss due to trauma.

"There is potential for regenerating a lot of different tissues, perhaps some day solid organs, glands, nerves or brain tissue," said Hedrick, who expects practical uses for laboratory-grown tissues to enter the medical marketplace within five years or so.