Insulin-like growth factors studied

ANN ARBOR, Mich., March 15 (UPI) -- U.S. scientists say their discovery of how hormones known as insulin-like growth factors work may lead to new treatments for muscle-wasting diseases.

The researchers, led by University of Michigan Professor Cunming Duan, say they've resolved a long-standing mystery about the workings of the growth factors and that finding might also lead to new ways of preventing muscle loss that accompanies aging.

Insulin-like growth factors work by binding to receptors on the cells they target. During muscle formation, Duan said, the binding can prompt either of two responses from myoblasts -- immature cells that develop into muscle tissue. Some cells are stimulated to divide while others interpret the same signal as an order to differentiate (become specialized).

"These are opposite and mutually exclusive cellular events -- once a muscle cell divides, it can't differentiate, and once it differentiates, it can never divide again," Duan said.

Now he and his team have solved the question of how activation of the same receptor by the same hormone can elicit two such distinctly different responses.

"The myoblasts' response is controlled by oxygen availability," Duan said. When oxygen levels are normal, muscle cell differentiation occurs; when oxygen levels are below normal, the growth factor promotes muscle cell division.

The study that included former graduate student Hongxia Ren and Columbia University Professor Domenico Accili appears in the early online edition of the Proceedings of the National Academy of Sciences.