Circulating cells in the blood have the ability to form bone at sites distant from the original skeleton, according to a new research.
It is believed that bone-forming cells, derived from the body's connective tissue, are the only cells able to form the skeleton.
But the new study has shown that specialized cells in the blood share a common origin with white blood cells derived from the bone marrow, and that these bloodstream cells are capable of forming bone outside the normal skeleton.
This study represents the first example of how circulating cells may contribute to abnormal bone formation.
The discovery was made while studying a rare genetic disease of misplaced bone growth, fibrodysplasia ossificans progressiva (FOP).
"Identifying circulating cells with bone-forming potential in humans has important implications for FOP, as well as more common disorders where bone is formed outside the skeleton, such as in end-stage aortic valve disease, following head and spinal cord injury, and after hip and knee replacements," said senior author Dr. Robert J. Pignolo.
He added: "This type of aberrant bone growth also occurs after severe trauma, such as blast injuries suffered by Iraqi war veterans, and its study may help us understand how bone forms after the development of the skeleton has ceased, with possible applications in bone diseases where only scarce or poor quality bone forms."
The researchers analyzed blood samples from patients with FOP and unaffected individuals, and isolated cells that could form bone when transplanted subcutaneously into animals.
The isolated cells were characterized using surface and other markers, which identified them as being derived from bone marrow.
They also examined tissue from FOP patients that had formed new bone, and found that these cells had migrated into the early sites of the lesion.
"This study provides an explanation for how bone-forming cells could seed sites of injury and inflammation that subsequently develop ossifications outside the skeleton," said Dr. Frederick S. Kaplan.
The study has been published in the online edition of the journal Stem Cells.