Osteogenic gene expression correlates with development of heterotopic ossification in war wounds

Heterotopic ossification (HO) is a frequent complication of modern wartime extremity injuries. The biological mechanisms responsible for the development of HO in traumatic wounds remain elusive.

The aims of our study were to (1) characterize the expression profile of osteogenesis-related gene transcripts in traumatic war wounds in which HO developed; and (2) determine whether expression at the mRNA level correlated with functional protein expression and HO formation.

Biopsy specimens from 54 high-energy penetrating extremity wounds obtained at the initial and final surgical débridements were evaluated. The levels of selected osteogenic-related gene transcripts from RNA extracts were assessed by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. As a result of its key role in osteogenesis, the concentration of BMP-2 in the effluent of 29 wounds also was determined.

The transcripts of 13 genes (ALPL [p = 0.006], BMP-2 [p < 0.001], BMP-3 [p = 0.06], COL2A1 [p < 0.001], COLL10A1 [p < 0.001], COL11A1 [p = 0.006], COMP [p = 0.02], CSF2 [p = 0.003], CSF3 [p = 0.012], MMP8 [p < 0.001], MMP9 [p = 0.014], SMAD1 [p = 0.024], and VEGFA [p = 0.017]) were upregulated greater than twofold in wounds in which HO developed compared with wounds in which it did not develop. Gene transcript expression of BMP-2 also correlated directly with functional protein expression in the wounds that formed HO (p = 0.029).

Important differences exist in the osteogenic gene expression profile of wounds in which HO developed compared with wounds in which it did not develop. The upregulation of multiple osteogenesis-related gene transcripts indicates the presence of a proosteogenic environment necessary for ectopic bone formation in traumatic wounds.

Understanding the osteogenic environment associated with war wounds may allow for the development of novel therapeutic strategies for HO.