Circulating osteogentic precursor cells in non-hereditary heterotopic ossification.

Area of Science:

• Cell Biology
• Pathology
• Regenerative Medicine

Background:

• Non-hereditary heterotopic ossification (NHHO) is abnormal bone formation outside the skeleton, often following trauma, CNS injury, or surgery.
• Circulating osteogenic precursor (COP) cells, a subpopulation of bone marrow-derived mononuclear cells (Type 1 collagen+, CD45+), have been previously identified with the capacity for extraskeletal ossification.

Purpose of the Study:

• To systematically evaluate the presence and localization of COP cells in various forms of NHHO.
• To investigate the role of COP cells in the histopathology of NHHO secondary to diverse clinical conditions.

Main Methods:

• Tissue analysis of bone specimens from patients with NHHO resulting from traumatic brain injury, spinal cord injury, cerebrovascular accident, trauma without neurological injury, and joint arthroplasty.
• Histopathological examination to identify and quantify COP cells within lesions and assess their proximity to blood vessels.

Main Results:

• COP cells were consistently identified in all examined bone specimens of NHHO, with an average of 2-14 cells per high power field.
• COP cells were predominantly found in early fibroproliferative and neovascular lesions associated with NHHO.
• The presence of COP cells near blood vessels supported their circulatory status and migratory potential.

Conclusions:

• This study provides the first systematic histopathological evidence linking COP cells to multiple forms of NHHO.
• Data suggest that circulating, hematopoietic-derived cells with osteogenic potential can migrate to inflammatory sites, including soft tissue injuries.
• COP cells are likely involved in seeding extraskeletal ossification, potentially at sites distant from the initial central nervous system (CNS) injury.