Gene expression of TGF-β superfamily during healing of bone fracture

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BMPs play a fundamental role in bone regeneration. Localization of BMP and BMPR (BMP receptor) was investigated during healing of mandibular fractures in rats.The immunoreactivities of BMP and receptors showed the same distributions. The immunoreactions were observed in fibroblast-like cells in bone fissures with blood clots and connective tissue cells in muscular tissue from 1 to 2 days after the bone fracture. Fibrosis was found from 3 days, and intense immunoreactions were found in the fibroblasts. Cartilage formation started from 4 days, and the immunoreactions were found in the chondroblasts, proliferative and resting chondrocytes, but not in hypertrophic chondrocytes. Bone resorption in osteoclasts was observed in the region of the bone fracture, and intense immunoreactions were found in the osteoclasts. Bone formation was observed from 7 days and cartilage was gradually replaced by bone. Intense immunoreactions were found in osteoblasts along newly formed bone trabeculae. Immunoreactions of osteoblasts were gradually decreased after 14 days, and they were not found at 28 days.The immunohistochemical localization of BMPR-IB showed the same distribution patterns as those with BMPR-IA and II. These results suggest that BMPs play a central role in cartilage and bone formation during healing of bone fractures, particularly in bone resorption by osteoclasts.