Source of aberrant bone growth discovered

PHILADELPHIA, March 5 (UPI) -- A U.S. study has identified the source of immature cells that spur heterotopic ossification -- misplaced bone growth.

Researchers at the University of Pennsylvania School of Medicine and the University of Connecticut said they discovered the major repository of bone-forming cells originates in blood vessels deep within skeletal muscle and other connective tissues, and not from muscle stem cells themselves.

That finding, said the scientists, shows cells important in the inflammatory response to injury trigger skeleton-stimulating proteins to transform muscle tissue into bone. Understanding that process, they said, has important implications for understanding the formation of bone, not only in fibrodysplasia ossificans progressive -- a rare disease known as FOP in which patients' muscle cells literally metamorphose to bone -- but also in many common disorders of misplaced bone growth such as thouse following head, athletic and spinal cord injuries.

"We always knew that heterotopic, or misplaced, bone growth was supplied by a rich vasculature, but we never suspected that cells from the blood vessels … could undergo a metamorphosis that becomes a second skeleton," said Dr. Frederick Kaplan, the study's senior author. "When these components interact pathologically, as in the rare disease FOP, devastating results occur. We want to fix that."

The findings are reported in the Journal of Bone & Joint Surgery.