The Orthopaedic Unit has developed a research program conducting basic investigation at the cellular and molecular levels into the pathophysiology of bone formation, remodeling, and repair. Initial investigations have focused on the structure and function of bone and cartilage extracellular matrix proteins and the regulation of gene expression in fracture healing. Additional efforts are directed towards the study of wound healing in other musculoskeletal tissues. In FY88 we published the nucleotide and amino acid sequence of osteonectin, a major protein component of the bone extracellular matrix, and suggested a model for osteonectin structure. Surprisingly, we found identity between osteonectin and a protein secreted by basement membranes, called SPARC, that is found in blood vessels, lung, and cartilage. We have developed monoclonal antibodies to osteonectin, and are using them to elucidate the function of this molecule. Using recombinant DNA technology we have found that a temporal sequence of gene activity is observable during repair of bone injury, and that this sequence is altered in models of abnormal healing, including diabetes and after adriamycin administration, and in fractures that heal by intermembranous bone formation. We have demonstrated that in impaired fracture healing this alteration in gene expression correlates with abnormalities in protein content and mechanical strength. We developed methods for organ culture of fracture callus, and have demonstrated the effects of growth factors on the expression of structural protein genes during normal fracture repair. We have identified expression of TGF-B, IGF-2 but not IGF-l, and both aFGF and bFGF in the fracture callus. High levels of TGF-beta were localized to areas of endochondral ossification, where osteoblasts, osteoid, and hypertrophic chondrocytes immediately adjacent to regions of calcified cartilage showed strong staining with anti-TGF-beta antibody. The correlation of of growth factor expression with certain histological events and distinct changes in structural.
