Gene expression of transforming growth factor-β3 and tissue inhibitor of metalloproteinase type 1 during membranous bone healing in rats

A number of growth factors have been implicated in fracture repair. Transforming growth factor-beta3 (TGF-beta3) is believed to be involved in osteoblast proliferation, chemotaxis, and collagen synthesis. The collagens act as the scaffolding for new bone matrix formation, whereas tissue inhibitors of metalloproteinases (TIMPs) may help regulate matrix remodeling in bone repair. Despite their hypothesized integral role in fracture repair, the temporal expression of these molecules in membranous bone fracture healing remains unknown. The objective of this study was to assess the temporal pattern of TGF-beta3 and TIMP type 1 (TIMP-1) expression in rat mandibular fracture healing. Twenty-eight adult male Sprague-Dawley rats underwent a mandibular osteotomy, and the healing regenerate was harvested on postoperative days 3, 5,7,9, 23, and 37. Total cellular ribonucleic acid was isolated, and Northern analysis was performed. TGF-beta3 expres sion was downregulated dramatically 3 days after the osteotomy and remained less than 20% of control levels throughout repair. In marked contrast, TIMP-1 gene expression, low during early repair, increased more than twofold over control at later time points. Understanding the temporal pattern of gene expression during membranous fracture heating has important clinical implications because elucidating these mechanisms may lead to appropriate biomolecular approaches to augment membranous bone fracture healing.