title: Loss of bone sialoprotein leads to impaired endochondral bone development and mineralization.
abstract: Bone sialoprotein (BSP) is an anionic phosphoprotein in the extracellular matrix of mineralized tissues, and a promoter of biomineralization and osteoblast development. Previous studies on the Bsp-deficient mouse (Bsp(-/-)) have demonstrated a significant bone and periodontal tissue phenotype in adulthood. However, the role of BSP during early long bone development is not known. To address this, early endochondral ossification in the Bsp(-/-) mouse was studied. Embryonic day 15.5 (E15.5) wild-type (WT) tibiae showed early stages of ossification that were absent in Bsp(-/-) mice. At E16.5, mineralization had commenced in the Bsp(-/-) mice, but staining for mineral was less intense and more dispersed compared with that in WT controls. Tibiae from Bsp(-/-) mice also demonstrated decreased mineralization and shortened length at postnatal day 0.5 (P0.5) compared to WT bones. There was no detectable difference in the number of tartrate-resistant acid phosphatase-positive foci at P0.5, although the P0.5 Bsp(-/-) tibiae had decreased Vegfα expression compared with WT tissue. Due to the shortened tibiae the growth plates were examined and determined to be of normal overall length. However, the length of the resting zone was increased in P0.5 Bsp(-/-) tibiae whereas that of the proliferative zone was decreased, with no change in the hypertrophic zone length of Bsp(-/-) mice. A reduction in cells positive for Ki-67, an S-phase cell-cycle marker, was noted in the proliferative zone. Decreased numbers of TUNEL-positive hypertrophic chondrocytes were also apparent in the Bsp(-/-) tibial growth plates, suggesting decreased apoptosis. Expression of the osteogenic markers Alp1, Col1a1, Sp7, Runx2, and Bglap was reduced in the endochondral bone of the neonatal Bsp(-/-) compared to WT tibiae. These results suggest that BSP is an important and multifaceted protein that regulates both chondrocyte proliferation and apoptosis as well as transition from cartilage to bone during development of endochondral bone.
authors.affiliation: Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada N6A 5C1. Electronic address: eholm@uwo.ca.
authors.forename: Erik
authors.initials: E
authors.lastname: Holm
authors.affiliation: Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada M5S 1A8. Electronic address: jane.aubin@utoronto.ca.
authors.forename: Jane E
authors.initials: JE
authors.lastname: Aubin
authors.affiliation: Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada N6A 5C1; School of Dentistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada N6A 5C1. Electronic address: graeme.hunter@schulich.uwo.ca.
authors.forename: Graeme K
authors.initials: GK
authors.lastname: Hunter
authors.affiliation: Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada, N6A 5C1. Electronic address: fbeier@uwo.ca.
authors.forename: Frank
authors.initials: F
authors.lastname: Beier
authors.affiliation: Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada N6A 5C1; School of Dentistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada N6A 5C1. Electronic address: hagoldbe@uwo.ca.
authors.forename: Harvey A
authors.initials: HA
authors.lastname: Goldberg
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D015415:Biomarkers / Q000378:metabolism; D001846:Bone Development / Q000235:genetics; D016723:Bone Remodeling; D002113:Calcification, Physiologic / Q000235:genetics; D019902:Chondrocytes / Q000378:metabolism; D005786:Gene Expression Regulation; D018507:Gene Expression Regulation, Developmental; D006132:Growth Plate / Q000473:pathology / Q000503:physiopathology; D058574:Integrin-Binding Sialoprotein / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D051379:Mice; D042282:Microdissection; D060888:Real-Time Polymerase Chain Reaction; D013977:Tibia / Q000254:growth & development / Q000378:metabolism / Q000503:physiopathology
chemical_list: D015415:Biomarkers; D058574:Integrin-Binding Sialoprotein
keywords: Bone sialoprotein; Development; Endochondral bone; Growth plate; Mineralization; SIBLINGs