title: BMP-non-responsive Sca1+ CD73+ CD44+ mouse bone marrow derived osteoprogenitor cells respond to combination of VEGF and BMP-6 to display enhanced osteoblastic differentiation and ectopic bone formation.
abstract: Clinical trials on fracture repair have challenged the effectiveness of bone morphogenetic proteins (BMPs) but suggest that delivery of mesenchymal stem cells (MSCs) might be beneficial. It has also been reported that BMPs could not increase mineralization in several MSCs populations, which adds ambiguity to the use of BMPs. However, an exogenous supply of MSCs combined with vascular endothelial growth factor (VEGF) and BMPs is reported to synergistically enhance fracture repair in animal models. To elucidate the mechanism of this synergy, we investigated the osteoblastic differentiation of cloned mouse bone marrow derived MSCs (D1 cells) in vitro in response to human recombinant proteins of VEGF, BMPs (-2, -4, -6, -9) and the combination of VEGF with BMP-6 (most potent BMP). We further investigated ectopic bone formation induced by MSCs pre-conditioned with VEGF, BMP-6 or both. No significant increase in mineralization, phosphorylation of Smads 1/5/8 and expression of the ALP, COL1A1 and osterix genes was observed upon addition of VEGF or BMPs alone to the cells in culture. The lack of CD105, Alk1 and Alk6 expression in D1 cells correlated with poor response to BMPs indicating that a greater care in the selection of MSCs is necessary. Interestingly, the combination of VEGF and BMP-6 significantly increased the expression of ALP, COL1A1 and osterix genes and D1 cells pre-conditioned with VEGF and BMP-6 induced greater bone formation in vivo than the non-conditioned control cells or the cells pre-conditioned with either VEGF or BMP-6 alone. This enhanced bone formation by MSCs correlated with higher CADM1 expression and OPG/RANKL ratio in the implants. Thus, combined action of VEGF and BMP on MSCs enhances osteoblastic differentiation of MSCs and increases their bone forming ability, which cannot be achieved through use of BMPs alone. This strategy can be effectively used for bone repair.
authors.affiliation: Orthopaedic Research Laboratories, Department of Orthopaedic Surgery, University of Virginia, Charlottesville, Virginia, United States of America.
authors.forename: Vedavathi
authors.initials: V
authors.lastname: Madhu
authors.affiliation: Orthopaedic Research Laboratories, Department of Orthopaedic Surgery, University of Virginia, Charlottesville, Virginia, United States of America.
authors.forename: Ching-Ju
authors.initials: CJ
authors.lastname: Li
authors.affiliation: Orthopaedic Research Laboratories, Department of Orthopaedic Surgery, University of Virginia, Charlottesville, Virginia, United States of America.
authors.forename: Abhijit S
authors.initials: AS
authors.lastname: Dighe
authors.affiliation: Orthopaedic Research Laboratories, Department of Orthopaedic Surgery, University of Virginia, Charlottesville, Virginia, United States of America.
authors.forename: Gary
authors.initials: G
authors.lastname: Balian
authors.affiliation: Orthopaedic Research Laboratories, Department of Orthopaedic Surgery, University of Virginia, Charlottesville, Virginia, United States of America.
authors.forename: Quanjun
authors.initials: Q
authors.lastname: Cui
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000187:drug effects* / Q000378:metabolism; D055418:Bone Morphogenetic Protein 6 / Q000494:pharmacology*; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D051379:Mice; D010012:Osteogenesis / Q000187:drug effects* / Q000502:physiology; D042461:Vascular Endothelial Growth Factor A / Q000494:pharmacology*
chemical_list: D055418:Bone Morphogenetic Protein 6; D019485:Bone Morphogenetic Proteins; D042461:Vascular Endothelial Growth Factor A