Gene expression of transforming growth factor-beta 3 and tissue inhibitor of metalloproteinase type 1 during membranous bone healing in rats

A number of growth factors have been implicated in fracture repair. Transfo rming growth factor-beta3 (TGF-beta3) is believed to be involved in osteobl ast proliferation, chemotaxis, and collagen synthesis. The collagens act as the scaffolding for new bone matrix formation, whereas tissue inhibitors o f metalloproteinases (TIMPs) may help regulate matrix remodeling in bone re pair. Despite their hypothesized integral role in fracture repair, the temp oral expression of these molecules in membranous bone fracture healing rema ins 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 fractur e healing. Twenty-eight adult male Sprague-Dawley rats underwent a mandibul ar osteotomy, and the healing regenerate was harvested on postoperative day s 3, 5,7,9, 23, and 37. Total cellular ribonucleic acid was isolated, and N orthern analysis was performed. TGF-beta3 expres sion was downregulated dra matically 3 days after the osteotomy and remained less than 20% of control levels throughout repair. In marked contrast, TIMP-1 gene expression, low d uring early repair, increased more than twofold over control at later time points. Understanding the temporal pattern of gene expression during membra nous fracture heating has important clinical implications because elucidati ng these mechanisms may lead to appropriate biomolecular approaches to augm ent membranous bone fracture healing.