In the rare disease fibrodysplasia ossificans progressiva (FOP), a mutation in the Alk2 gene results in the formation of bone in soft tissues. Now researchers show that the bone cells derive from others that form the inner lining of blood vessels, called endothelial cells. These become stem-like cells before re-differentiating into bone. This process could be important in normal tissue repair, suggest Damian Medici at Harvard Medical School and Bjorn Olsen at the Harvard School of Dental Medicine, both in Boston, Massachusetts, and their colleagues.
The team found that cells from bony lesions in patients with FOP expressed marker proteins specific for endothelium. And when mutant Alk2 was introduced into normal human endothelial cells, it conferred characteristics of mesenchymal stem cells. When cultured in appropriate conditions, the endothelial-derived 'stem cells' transformed into bone, cartilage and fat cells.