Journal
CALCIFIED TISSUE INTERNATIONAL
Volume 87, Issue 6, Pages 513-524Publisher
SPRINGER
DOI: 10.1007/s00223-010-9408-6
Keywords
Biosilica; SaOS-2 cell; Bone morphogenetic protein-2; Osteogenic index; Hydroxyapatite; Nodule
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Funding
- German Bundesministerium fur Bildung und Forschung, Center of Excellence BIOTECmarin
- Deutsche Forschungsgemeinschaft [Schr 277/10-1]
- International Human Frontier Science Program
- European Commission [244967-Mem-S]
- Johannes Gutenberg-University Research Center for Complex Matter (COMATT)
- International S & T Cooperation Program of China [2008DFA00980]
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Biosilica is a natural polymer, synthesized by the poriferan enzyme silicatein from monomeric silicate substrates. Biosilica stimulates mineralizing activity and gene expression of SaOS-2 cells. To study its effect on the formation of hydroxyapatite (HA), SaOS-2 cells were grown on different silicatein/biosilica-modified substrates (bone slices, Ca-P-coated coverslips, glass coverslips). Growth on these substrates induced the formation of HA nodules, organized in longitudinal arrays or spherical spots. Nodules of sizes above 1 mu m were composed of irregularly arranged HA prism-like nanorods, formed by aggregates of three to eight SaOS-2 cells. Moreover, growth on silicatein/biosilica-modified substrates elicited increased [H-3]dT incorporation into DNA, indicative of enhanced cell proliferation. Consequently, an in vitro-based bioassay was established to determine the ratio between [H-3]dT incorporation and HA formation. This ratio was significantly higher for cells that grew on silicatein/biosilica-modified substrates than for cells on Ca-P-coated coverslips or plain glass slips. Hence, we propose that this ratio of in vitro-determined parameters reflects the osteogenic effect of different substrates on bone-forming cells. Finally, qRT-PCR analyses demonstrated that growth of SaOS-2 cells on a silicatein/biosilica matrix upregulated BMP2 (bone morphogenetic protein 2, inducer of bone formation) expression. In contrast, TRAP (tartrate-resistant acid phosphatase, modulator of bone resorption) expression remained unaffected. We conclude that biosilica shows pronounced osteogenicity in vitro, qualifying this material for studies of bone replacement also in vivo.
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