title: BMP2 and mechanical loading cooperatively regulate immediate early signalling events in the BMP pathway.
abstract: BACKGROUND
  Efficient osteogenic differentiation is highly dependent on coordinated signals arising from growth factor signalling and mechanical forces. Bone morphogenetic proteins (BMPs) are secreted proteins that trigger Smad and non-Smad pathways and thereby influence transcriptional and non-transcriptional differentiation cues. Crosstalk at multiple levels allows for promotion or attenuation of signalling intensity and specificity. Similar to BMPs, mechanical stimulation enhances bone formation. However, the molecular mechanism by which mechanical forces crosstalk to biochemical signals is still unclear.
  
  
  RESULTS
  Here, we use a three-dimensional bioreactor system to describe how mechanical forces are integrated into the BMP pathway. Time-dependent phosphorylation of Smad, mitogen-activated protein kinases and Akt in human fetal osteoblasts was investigated under loading and/or BMP2 stimulation conditions. The phosphorylation of R-Smads is increased both in intensity and duration under BMP2 stimulation with concurrent mechanical loading. Interestingly, the synergistic effect of both stimuli on immediate early Smad phosphorylation is reflected in the transcription of only a subset of BMP target genes, while others are differently affected. Together this results in a cooperative regulation of osteogenesis that is guided by both signalling pathways.
  
  
  CONCLUSIONS
  Mechanical signals are integrated into the BMP signalling pathway by enhancing immediate early steps within the Smad pathway, independent of autocrine ligand secretion. This suggests a direct crosstalk of both mechanotransduction and BMP signalling, most likely at the level of the cell surface receptors. Furthermore, the crosstalk of both pathways over longer time periods might occur on several signalling levels.
authors.affiliation: Institute for Chemistry/Biochemistry, FU Berlin, Berlin, Germany.
authors.forename: Jessica
authors.initials: J
authors.lastname: Kopf
authors.forename: Ansgar
authors.initials: A
authors.lastname: Petersen
authors.forename: Georg N
authors.initials: GN
authors.lastname: Duda
authors.forename: Petra
authors.initials: P
authors.lastname: Knaus
mesh_terms: D019149:Bioreactors; D015153:Blotting, Western; D055396:Bone Morphogenetic Protein 2 / Q000378:metabolism*; D005333:Fetus / Q000166:cytology; D006801:Humans; D040542:Mechanotransduction, Cellular; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D010012:Osteogenesis; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D020239:Receptor Cross-Talk; D015398:Signal Transduction; D051902:Smad5 Protein / Q000378:metabolism
chemical_list: D055396:Bone Morphogenetic Protein 2; D051902:Smad5 Protein; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases