Bone Sialoprotein Deficiency Impairs Osteoclastogenesis and Mineral Resorption In Vitro

Université de Lyon, Saint-Etienne, France.
Journal of bone and mineral research: the official journal of the American Society for Bone and Mineral Research (Impact Factor: 6.83). 12/2010; 25(12):2669-79. DOI: 10.1002/jbmr.245
Source: PubMed


Bone sialoprotein (BSP) and osteopontin (OPN) belong to the small integrin-binding ligand N-linked glycoprotein (SIBLING) family, whose members interact with bone cells and bone mineral. Previously, we showed that BSP knockout (BSP(-/-) ) mice have a higher bone mass than wild type (BSP(+/+) ) littermates, with very low bone-formation activity and reduced osteoclast surfaces and numbers. Here we report that approximately twofold fewer tartrate-resistant acid phosphatase (TRACP)-positive cells and approximately fourfold fewer osteoclasts form in BSP(-/-) compared with BSP(+/+) spleen cell cultures. BSP(-/-) preosteoclast cultures display impaired proliferation and enhanced apoptosis. Addition of RGD-containing proteins restores osteoclast number in BSP(-/-) cultures to BSP(+/+) levels. The expression of osteoclast-associated genes is markedly altered in BSP(-/-) osteoclasts, with reduced expression of cell adhesion and migration genes (αV integrin chain and OPN) and increased expression of resorptive enzymes (TRACP and cathepsin K). The migration of preosteoclasts and mature osteoclasts is impaired in the absence of BSP, but resorption pit assays on dentine slices show no significant difference in pit numbers between BSP(+/+) and BSP(-/-) osteoclasts. However, resorption of mineral-coated slides by BSP(-/-) osteoclasts is markedly impaired but is fully restored by coating the mineral substrate with hrBSP and partly restored by hrOPN coating. In conclusion, lack of BSP affects both osteoclast formation and activity, which is in accordance with in vivo findings. Our results also suggest at least some functional redundancy between BSP and OPN that remains to be clarified.

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Available from: Mh Lafage-Proust, Oct 13, 2014
    • "Analysis of the Bsp -/-mouse, during development and repair, revealed decreased growth and mineralization of long bones (Malaval et al. 2008; Malaval et al. 2009; Holm et al. 2015). Lack of BSP also affected osteoclast formation and recruitment negatively, leading to reduced long bone turnover (Malaval et al. 2008; Boudiffa et al. 2010). Previously, we reported that loss of BSP causes inhibition of functional acellular cementum on molar and incisor tooth roots, hypomineralization of cellular cementum, and detachment and disorganization of the periodontal ligament (PDL; Foster et al. 2013). "
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    ABSTRACT: Bone sialoprotein (BSP) is an acidic phosphoprotein with collagen-binding, cell attachment, and hydroxyapatite-nucleating properties. BSP expression in mineralized tissues is upregulated at onset of mineralization. Bsp-null (Bsp(-/-)) mice exhibit reductions in bone mineral density, bone turnover, osteoclast activation, and impaired bone healing. Furthermore, Bsp(-/-) mice have marked periodontal tissue breakdown, with a lack of acellular cementum leading to periodontal ligament detachment, extensive alveolar bone and tooth root resorption, and incisor malocclusion. We hypothesized that altered mechanical stress from mastication contributes to periodontal destruction observed in Bsp(-/-) mice. This hypothesis was tested by comparing Bsp(-/-) and wild-type mice fed with standard hard pellet diet or soft powder diet. Dentoalveolar tissues were analyzed using histology and micro-computed tomography. By 8 wk of age, Bsp(-/-) mice exhibited molar and incisor malocclusion regardless of diet. Bsp(-/-) mice with hard pellet diet exhibited high incidence (30%) of severe incisor malocclusion, 10% lower body weight, 3% reduced femur length, and 30% elevated serum alkaline phosphatase activity compared to wild type. Soft powder diet reduced severe incisor malocclusion incidence to 3% in Bsp(-/-) mice, supporting the hypothesis that occlusal loading contributed to the malocclusion phenotype. Furthermore, Bsp(-/-) mice in the soft powder diet group featured normal body weight, long bone length, and serum alkaline phosphatase activity, suggesting that tooth dysfunction and malnutrition contribute to growth and skeletal defects reported in Bsp(-/-) mice. Bsp(-/-) incisors also erupt at a slower rate, which likely leads to the observed thickened dentin and enhanced mineralization of dentin and enamel toward the apical end. We propose that the decrease in eruption rate is due to a lack of acellular cementum and associated defective periodontal attachment. These data demonstrate the importance of BSP in maintaining proper periodontal function and alveolar bone remodeling and point to dental dysfunction as causative factor of skeletal defects observed in Bsp(-/-) mice. © International & American Associations for Dental Research 2015.
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    • "Parenthetically, because of the critical importance of OC in mineralization and other biological processes or functions, if OC is reduced or absent (as in OC knock-out mice), it is very likely that some other molecule is redundant to OC to mitigate an overt change in bone phenotype. In the case of the BSP knock-out model, replacement of one SIBLING family member protein by another can lead to normal bone function and phenotype [40] [41]. "
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    ABSTRACT: Mineralization of vertebrate tissues such as bone, dentin, cementum, and calcifying tendon involves type I collagen, which has been proposed as a template for calcium and phosphate ion binding and subsequent nucleation of apatite crystals. Type I collagen thereby has been suggested to be responsible for the deposition of apatite mineral without the need for non-collagenous proteins or other extracellular matrix molecules. Based on studies in vitro, non-collagenous proteins, including osteocalcin and bone sialoprotein, are thought to mediate vertebrate mineralization associated with type I collagen. These proteins, as possibly related to mineral deposition, have not been definitively localized in vivo. The present study has reexamined their localization in the leg tendons of avian turkeys, a representative model of vertebrate mineralization. Immunocytochemistry of osteocalcin demonstrates its presence at the surface of, outside and within type I collagen while that of bone sialoprotein appears to be localized at the surface of or outside type I collagen. The association between osteocalcin and type I collagen structure is revealed optimally when calcium ions are added to the antibody solution in the methodology. In this manner, osteocalcin is found specifically located along the a4-1, b1, c2 and d bands defining in part the hole and overlap zones within type I collagen. From these data, while type I collagen itself may be considered a stereochemical guide for intrafibrillar mineral nucleation and subsequent deposition, osteocalcin bound to type I collagen may also possibly mediate nucleation, growth and development of platelet-shaped apatite crystals. Bone sialoprotein and osteocalcin as well, each immunolocalized at the surface of or outside type I collagen, may affect mineral deposition in these portions of the avian tendon.
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    • "Interestingly, the expression of osteocalcin, the most important noncollagenic bone matrix protein, was significantly decreased only in cells exposed to sera of OO patients (P < 0.05, Figure 1(d)), strongly suggesting that the presence of different amount of muscle and adipose tissues can differently interfere with osteoblast biology. Finally, the expression of osteopontin (OPN), a highly phosphorylated bone matrix sialoprotein [31–35], was also significantly inhibited in osteoblasts incubated with sera of all groups of obese patients as compared to CTL (Figure 1(e), P < 0.05). "
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