title: Osteopontin mediates mineralization and not osteogenic cell development in vitro.
abstract: Biomineralization is a complex process in the development of mineralized tissues such as bone and pathological calcifications such as atherosclerotic plaques, kidney stones and gout. Osteopontin (OPN), an anionic phosphoprotein, is expressed in mineralizing tissues and has previously been demonstrated to be a potent inhibitor of hydroxyapatite formation. The OPN-deficient (Opn-/-) mouse displays a hypermineralized bone phenotype starting at 12 weeks postnatally. By isolating and culturing Opn-/- and wild-type (WT) osteoblasts, we sought to determine the role of OPN and two of its functional peptides in osteoblast development and mineralization. Opn-/- osteoblasts had significantly increased mineral deposition relative to their WT counterparts, with no physiologically relevant change in gene expression of osteogenic markers. Supplementation with bovine milk OPN (mOPN) led to a dramatic reduction in mineral deposition by the Opn-/- osteoblasts. Treatment with OPN-derived peptides corresponding to phosphorylated OPN-(220-235) (P3) and non-phosphorylated OPN-(65-80) (OPAR) also rescued the hypermineralization phenotype of Opn-/- osteogenic cultures. Supplementation with mOPN or the OPN-derived peptides did not alter the expression of terminal osteogenic markers. These data suggest that OPN plays an important role in the regulation of biomineralization, but that OPN does not appear to affect osteoblast cell development in vitro.
authors.affiliation: *Department of Biochemistry, Schulich School of Medicine & Dentistry, University of Western Ontario, London, Ontario, Canada, N6A 5C1.
authors.forename: Erik
authors.initials: E
authors.lastname: Holm
authors.affiliation: *Department of Biochemistry, Schulich School of Medicine & Dentistry, University of Western Ontario, London, Ontario, Canada, N6A 5C1.
authors.forename: Jared S
authors.initials: JS
authors.lastname: Gleberzon
authors.affiliation: *Department of Biochemistry, Schulich School of Medicine & Dentistry, University of Western Ontario, London, Ontario, Canada, N6A 5C1.
authors.forename: Yinyin
authors.initials: Y
authors.lastname: Liao
authors.affiliation: †Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 10, DK-8000 Aarhus, Denmark.
authors.forename: Esben S
authors.initials: ES
authors.lastname: Sørensen
authors.affiliation: §Department of Physiology and Pharmacology, Schulich School of Medicine & Dentistry, University of Western Ontario, London, Ontario, Canada, N6A 5C1.
authors.forename: Frank
authors.initials: F
authors.lastname: Beier
authors.affiliation: *Department of Biochemistry, Schulich School of Medicine & Dentistry, University of Western Ontario, London, Ontario, Canada, N6A 5C1.
authors.forename: Graeme K
authors.initials: GK
authors.lastname: Hunter
authors.affiliation: *Department of Biochemistry, Schulich School of Medicine & Dentistry, University of Western Ontario, London, Ontario, Canada, N6A 5C1.
authors.forename: Harvey A
authors.initials: HA
authors.lastname: Goldberg
mesh_terms: D000818:Animals; D002113:Calcification, Physiologic / Q000187:drug effects*; D002454:Cell Differentiation / Q000187:drug effects*; D002478:Cells, Cultured; D059630:Mesenchymal Stem Cells / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010006:Osteoblasts / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology; D010012:Osteogenesis / Q000187:drug effects*; D053495:Osteopontin / Q000235:genetics / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology
chemical_list: D010446:Peptide Fragments; C506896:Spp1 protein, mouse; D053495:Osteopontin