Bone formation is a complex process regulated by hormones and by systemic and local growth factors. The goal of this laboratory has been to study the effects of systemic and local growth factors on bone formation. Our recetn efforts have focused on the local regulators of bone growth. We discovered that cultured fetal rat calvariae secrete at least two growth factors; these were originally termed bone-derived growth factor (BDGF) I and II. We have now shown that BDGF-I is a transforming growth factor of the beta class (TGF-beta), has a relative molecular mass (Mr) of 23,000 and stimulates preosteoblastic cell replication. We also showed that BDGF II (presently termed BDGF) is a distinct factor, has a Mr of 11-12,000 and stimulates, simultaneously, bone DNA and collagen synthesis. The biochemical and some of the biological properties of TGF-beta have been characterized but the amino acid sequence and many of the biological effects of BDGF are unknown. Over the next five years we intend to determine the amino acid sequence of BDGF by the use of gas phase sequencing and by establishing the structure of a complementary (c) DNA clone for BDGF. We also plan to investigate the effects of TGF-beta and BDGF on bone formation, examine their interactions with hormones an study their receptors. Our studies will include the development of sensitive and specific assays for TGF-beta and BDGF which will be useful to study the synthesis of these factors by bone cells and its regulation by systemic hormones and growth factors. To complement these experiments, we will examine mRNA expression of TGF-beta and BDGF in bone tissue and cells. For this purpose, we obtained a mouse cDNA clone for TGF-beta and we will develop a rat cDNA clone for BDGF by constructing a bone cell library which will be probed with a labeled synthetic oligonucleotide made in accordance with the structure of BDGF. Our research will provide information about the biochemical and biological properties of bone-derived TGF-beta and BDGF and how these factors interact with hormones and other growth factors which may modulate their synthesis or effects. These studies are valuable because local factors are likely to have an important effect on bone remodelling and mediation of the effects of hormones on bone. Our current understanding of bone cell physiology and metabolic bone disease is limited and this research may provide future diagnostic and therapeutic alternatives for metabolic bone disorders.
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