Transcriptional characterization of bone morphogenetic proteins (BMPs)-mediated osteogenic signaling

Bone formation is presumably a complex and well-orchestrated process of osteoblast lineage-specific differentiation. As members of the TGFbeta superfamily, bone morphogenetic proteins (BMPs) play an important role in regulating osteoblast differentiation and subsequent bone formation. Several BMPs are able to induce de novo bone formation. Although significant progress has recently been made about the transcriptional control of osteoblast differentiation, detailed molecular events underlying the osteogenic process remain to be elucidated. In order to identify potentially important signaling mediators activated by osteogenic BMPs but not by non-osteogenic BMPs, we sought to determine the transcriptional differences between three osteogenic BMPs (i.e., BMP-2, BMP-6, and BMP-9) and two inhibitory/non-osteogenic BMPs (i.e., BMP-3 and BMP-12). Through the microarray analysis of approximately 12,000 genes in pre-osteoblast progenitor cells, we found that expression level of 203 genes (105 up-regulated and 98 down-regulated) was altered >2-fold upon osteogenic BMP stimulation. Gene ontology analysis revealed that osteogenic BMPs, but not inhibitory/non-osteogenic BMPs, activate genes involved in the proliferation of pre-osteoblast progenitor cells towards osteoblastic differentiation, and simultaneously inhibit myoblast-specific gene expression. BMP-regulated expression of the selected target genes was confirmed by RT-PCR, as well as by the CodeLink Bioarray analysis. Our findings are consistent with the notion that osteogenesis and myogenesis are two divergent processes. Further functional characterization of these downstream target genes should provide important insights into the molecular mechanisms behind BMP-mediated bone formation.