TAC1 and injury: Mediate HO formation via substance P and calcitonin gene-related peptide. BMP2 may induce neurogenic inflammation to remodel nerve and release HO precursor cells. May explain how HO occurs following traumatic brain injury. Mice lacking sensory neurons cells do not develop HO. Tie2+ endoneurial progenitors the major HO cell contributors in a mice model; however, Tie2 marker is also expressed in endothelial and mesenchymal cells.