The molecular mechanisms of bone formation and repair are not well understood. One of the goals of our laboratory is in the elucidation of the contributions of polypeptide growth factors in bone matrix formation and calcification. We are currently using a fetal bovine osteoblast in vitro culture system. To evaluate endogenous growth factor expression in bone cells, several techniques in cell and molecular biology are being utilized. Present studies involve mitogenic analysis, immunofluorescence and in situ hybridization. To further characterize these cells, bone - specific histologic procedures as well as alkaline phosphatase and osteoclacin expression will be evaluated through the mineralization process. At this time, we have focused our attention on the bone cell mitogen platelet-derived growth factor (PDGF). PDGF as well as bFGF and TGF-beta have been shown to be sequestered in bone matrix and are released during periods of bone resorption. In future studies we plan to find the source of the PDGF-like molecules (i.e. (1) sequestered PDGF released during depletion of media, and (2) endogenous release of PDGF from osteoblasts at various time points of mineralization. Preliminary results are prompting us to consider different growth factors as well as novel growth factors with PDGF-like activity. These factors may play an important role in the rapid bone formation of the fetal osteoblast. Our group intends to further characterize the role of PDGF utilizing radioimmunoassay and western blot analysis to quantitate PDGF in conditioned media and bone matrix. Future studies will follow to evaluate other polypeptide growth factors (i.e. TGF- beta, a&bFGF, IGF-I & II, EGF, TGF-alpha) as well as other factors potentially responsible for eliciting effects in bone mineralization. By elucidating the roles of bone growth factors during mineralization, delivery of targeted factors at a wounds site may optimize osseous repair with therapeutic regimens for treatment.
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