Heterotopic ossification (HO) or bone formation in non-skeletal sites is very rare but can occur in cases of central nervous system (CNS) inhury or amputation/hip replacement surgery where skeletal bone is removed or replaced. However, our own data suggests that peripheral nerves may also be contributing to this process. We recently showed that release of neurogenic inflammatory mediator's substance P and CGRP, led to recruitment and degranulation of mast cells and nerve remodeling. This remodeling involved expansion of nerve associated cells, as well as their release and migration in the soft tissues. We observed the expression of osteogenic protein osterix, brown adipocyte protein UCP1, and the primitive stem cell factors, Klf4 and nanog. The data collectively have led us to hypothesize that peripheral nerves possess progenitors/stem cells, which expand in response to BMP2 for contribution to the newly forming heterotopic bone. However, the exact nature and origin of these stem/progenitors is unclear. Our own data suggests that p75 positive cells are either progenitor cells, or perhaps de-differentiating Schwann cells, that undergo osteogenesis. We have devised a series of aims to isolate and characterize these cells and demonstrate their functional contribution, either directly or indirectly to heterotopic ossification.
Our overarching hypothesis is that heterotopic bone is formed from nerve progenitor/stem cells that reside in peripheral nerves, which are released by neurologic inflammation caused directly by BMP2. These findings would provide a novel mechanism for the development of both diagnostics and therapuetics for the treatment of this disease.