MOLECULAR MECHANISMS OF GALLIUM ON BONE FORMATION

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Decreased bone formation is an important component of the pathophysiology that leads to Type II osteoporosis and, ultimately, hip fractures. A more complete understanding of the cellular and molecular events which control bone formation will lead to new therapeutic approaches for osteoporosis. Gallium nitrate is a new U.S.F.D.A.- approved drug with proven efficacy for the treatment of disordered bone metabolism. Recent studies show that gallium nitrate can transcriptionally regulate the expression of two bone matrix proteins, bone Gla protein (BGP or osteocalcin) and type (I) collagen, in a manner that mimics naturally occurring growth factors and that would be expected to favor new bone formation. We propose to study at the cellular and molecular levels the mechanism(s) of action of gallium on bone formation. The specific objectives of this proposal are: AIM 1) to characterize the effects of gallium nitrate on osteogenic cultures of normal rat calvarial cells. Primary osteogenic cells which undergo a reproducible developmental sequence will be exposed to gallium at different stages of intramembranous ossification to examine gallium effects on cell proliferation, differentiation and gene expression; AIM 2) to delineate the DNA sequence(s) (response elements) on the BGP and type (I) collagen genes which are the target(s) of action of gallium nitrate. A series of 5'-flanking deletions of the BGP and type (I) collagen gene promoter regions that have been stably and transiently transfected into bone cell cultures will be analyzed for gallium responsiveness; AIM 3) to identify sequences in the type (I) collagen gene responsible for the transcriptional response to gallium nitrate in transgenic mouse models in order to study gallium effects on the respective promoter regions in intact animals. Type (I) collagen gene responsiveness to gallium will be examined in cells exposed to normal developmental cues and tissue interactions; AIM 4) to identify the transcription factor(s) which interact with the gallium nitrate regulatory element(s) on the BGP and type (I) collagen genes to transcriptionally regulate these genes. The results of these studies will provide insight into molecular events which are critical for new bone formation, and how gallium nitrate modulates these events.