Platelet-derived growth factor expression in normally healing human fractures

Platelet-derived growth factor (PDGF) has been shown to have effects on bone and cartilage cells in vitro, but its role in vivo in bone repair is not clear. We studied biopsy material from 16 normally healing fractures at a variety of times after injury, using immunohistochemistry for PDGF and in situ hybridization for PDGF A and B chains. PDGF A-chain gene was found to be expressed by many cell types over a prolonged period during fracture healing. These cells included endothelial and mesenchymal cells in granulation tissue and osteoblasts, chondrocytes, and osteoclasts later during fracture healing. PDGF B-chain gene expression was more restricted, being detected principally in osteoblasts at the stage of bone formation. PDGF was detected using immunohistochemistry in the cell types expressing PDGF A. These findings indicate that PDGF is expressed during normal human fracture repair, and the in vitro data also suggest that PDGF is likely to be an important local regulator in this process.