The complex process of osteoblast differentiation involves many systemic, paracrine and autocrine factors. Among the most critical are the bone morphogenetic proteins (BMPs). BMPs are a family of locally active growth and differentiation factors, with most members capable of inducing and modulating bone cell differentiation. The applicants' study of the glucocorticoid (GC) enhancement of early osteoblast differentiation has led to the hypothesis that BMP-6 has a uniquely important role. The present proposal focuses on understanding mechanisms involved in the role and regulation of BMP-6 expression during early osteoblast differentiation. It is hypothesized that: (1) BMP-6 expression is required for initiation of osteoblast differentiation; (2) the GC regulation of the BMP-6 expression occurs primarily via pretranslational mechanisms; and (3) a specific region of the BMP-6 promoter is required to convey the GC regulation of BMP-6 gene expression. The requirement for BMP-6 to initiate osteoblast differentiation will be tested by demonstrating that BMP-6 antisense oligonucleotides block GC-induced differentiation; it is suggested that addition of exogenous BMP-6 should restore normal differentiation of cultures treated with BMP-6 antisense oligonucleotides. Pretranslational regulation of BMP-6 expression will be examined by measuring GC-induced changes in BMP-6 mRNA synthesis and stability. Finally, the promoter of the BMP-6 gene will be identified and the specific region that is required for GC-enhancement of BMP-6 transcription determined. This region will be compared with the region of the BMP-6 promoter which is required for increased BMP-6 expression in other contexts, including spontaneous osteoblast differentiation and induction by other BMPs. Clinical application of the BMP-induced bone formation could increase successful healing of bone in challenging orthopedic applications, such as spine fusions, fracture nonunions and segmental long bone defects. Despite encouraging results with BMPs in lower vertebrate animal models, bone formation in nonhuman primates has required larger BMP doses, making certain clinical applications very expensive. An improved understanding of the regulation of specific BMPs, and development of strategies to enhance the in vivo expression or activity of the most critical osteoinductive factors, would have great clinical value. An increased understanding of the BMP-6 promoter may lead to strategies involving oligonucleotide therapy or viral-mediated delivery of factors to enhance expression of BMP-6 locally, or in a targeted population of cells.
| Liu, Yunshan; Titus, Louisa; Barghouthi, Mejd et al. (2004) Glucocorticoid regulation of human BMP-6 transcription. Bone 35:673-81 |
