Stanford Report, August 23, 2006

Quick study: Boning up on fat

THE QUESTION: What signals instruct fat cells to turn into bone?

THE BACKGROUND: Fat contains a population of cells that can turn into bone or cartilage. In the past, Michael Longaker, MD, the Deane P. and Louise Mitchell Professor in the School of Medicine, used these cells to repair bone in rats; others have had success using them to repair bone in humans. By learning what signals tell the fat cells to turn into bone, researchers could have even better luck using the cells to heal damaged bone.

THE STUDY: The researchers grew fat cells in a lab dish with combinations of molecules called retinoic acid and bone morphogenic protein, or BMP. They then analyzed those cells to see if either chemical enhanced fat's ability to turn into bone. They also examined the genes being used by fat cells and newly formed bone cells.

THE FINDINGS: Fat cells exposed to retinoic acid with or without BMP convert into bone at a higher rate than cells without retinoic acid exposure. Those cells grown with both retinoic acid and BMP convert at the highest rate.

Fat cells that develop into bone also produce a protein on their cell surface that detects BMP in the environment. It appears that retinoic acid causes fat cells to produce the BMP receptor, which in turn allows those cells to receive bone-forming instruction from BMP in the environment.

WHY IT MATTERS: In the future, researchers may be able to add retinoic acid and BMP to fat cells as a way of enhancing their conversion into bone. Likewise, putting these chemicals on a synthetic scaffold covering a bone break or irregularity could help the fat cells' ability to repair the damage.

WHAT THE RESEARCHER SAYS: "In a baby boomer population, aches and pains associated with bones and joints are an enormous problem, and fat is a readily available resource," said Longaker.

FIND THIS STUDY: It was published in the Aug. 15 issue of the Proceedings of the National Academy of Sciences and is available online at http://www.pnas.org/cgi/content/full/103/33/12335.