title: Cross-Talk Between VEGF and BMP-6 Pathways Accelerates Osteogenic Differentiation of Human Adipose-Derived Stem Cells.
abstract: Deficiency in vascular endothelial growth factor (VEGF) or bone morphogenetic proteins (BMPs) results in fracture non-unions. Therefore, it is indispensable to comprehend the combined effect of VEGF and BMPs on the osteogenic differentiation of osteoprogenitor mesenchymal stem cells (MSCs) that are either naturally occurring at the fracture repair site or exogenously added to enhance the bone repair. We found that the combination of VEGF and BMP-6 enhanced COL1A2 expression, which correlated with upregulated expression of osterix, Dlx5, and Msx2 in human adipose-derived stem cells (hADSCs). Cross-talk between VEGF and BMP-6 pathways upregulated activation of p38 mitogen-activated kinase (p38 MAPK) and inhibited activation of protein kinase B (PKB, also known as Akt), whereas phosphorylation of "mothers against decapentaplegic" homologs 1/5/8 (Smads 1/5/8) and extracellular signal-regulated kinases 1 and 2 (ERK 1/2) was not affected. Consistent with these findings, p38 inhibitor SB203580, or siRNA knockdown of osterix, abrogated crosstalk between the VEGF and BMP-6 pathways and significantly reduced the observed upregulation of COL1A2. Nuclear translocation of the phosphorylated form of osterix was also inhibited by SB203580. Although crosstalk between the VEGF-BMP-6 pathways did not show an effect on the extent of mineralization, inhibition of any one of the three components that were upregulated through the cross-talk, i.e., osterix, Dlx5, and p38 activation, led to a complete inhibition of mineralization. Inhibition of PKB/Akt activation, which is attenuated through the cross-talk, significantly enhanced ALP gene expression. These observations imply that crosstalk between the VEGF and BMP-6 signaling pathways enhances osteogenic differentiation of MSCs.
authors.affiliation: Orthopaedic Research Laboratories, Department of Orthopaedic Surgery, University of Virginia, Charlottesville, Virginia.
authors.forename: Ching-Ju
authors.initials: CJ
authors.lastname: Li
authors.affiliation: Orthopaedic Research Laboratories, Department of Orthopaedic Surgery, University of Virginia, Charlottesville, Virginia.
authors.forename: Vedavathi
authors.initials: V
authors.lastname: Madhu
authors.affiliation: Orthopaedic Research Laboratories, Department of Orthopaedic Surgery, University of Virginia, Charlottesville, Virginia.
authors.forename: Gary
authors.initials: G
authors.lastname: Balian
authors.affiliation: Orthopaedic Research Laboratories, Department of Orthopaedic Surgery, University of Virginia, Charlottesville, Virginia.
authors.forename: Abhijit S
authors.initials: AS
authors.lastname: Dighe
authors.affiliation: Orthopaedic Research Laboratories, Department of Orthopaedic Surgery, University of Virginia, Charlottesville, Virginia.
authors.forename: Quanjun
authors.initials: Q
authors.lastname: Cui
mesh_terms: D017667:Adipocytes / Q000166:cytology / Q000378:metabolism; D055418:Bone Morphogenetic Protein 6 / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation / Q000235:genetics*; D024042:Collagen Type I / Q000096:biosynthesis; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000378:metabolism*; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism; D010012:Osteogenesis / Q000235:genetics*; D015398:Signal Transduction; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000096:biosynthesis
chemical_list: C525816:BMP6 protein, human; D055418:Bone Morphogenetic Protein 6; C000601279:COL1A2 protein, human; D024042:Collagen Type I; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; D048051:p38 Mitogen-Activated Protein Kinases