PLATELET-DERIVED GROWTH-FACTOR EXPRESSION IN NORMALLY HEALING HUMAN FRACTURES

Platelet-derived growth factor (PDGF) has been shown to have effects o n bone and cartilage cells in vitro, but its role in vivo in bone repa ir is not clear. We studied biopsy material from 16 normally healing f ractures at a variety of times after injury, using immunohistochemistr y for PDGF and in situ hybridization for PDGF A and B chains. PDGF A-c hain gene was found to be expressed by many cell types over a prolonge d 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 exp ression was more restricted, being detected principally in osteoblasts at the stage of bone formation, PDGF was detected using immunohistoch emistry in the cell types expressing PDGF A. These findings indicate t hat PDGF is expressed during normal human fracture repair, and the in vitro data also suggest that PDGF is likely to be an important local r egulator in this process.