| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2005: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2004: ¥2,400,000 (Direct Cost: ¥2,400,000)
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| Research Abstract |
A new congenic mouse, P6.P2-13, was constructed by backcrossing SAMP2 (a strain with high peak bone mass) consecutively to SAMP6 (a strain with low peak bone mass). P6.P2-13 carried a segregated SAMP2-derived 2.4Mb interval of chromosome 13 on the SAMP6 background. In the morphometrical analysis using micro-CT, P6.P2-13 showed increased bone area fraction at the diaphysial cortex, and increased trabecular bone volume at metaphysis when compared to SAMP6. In the dynamic histomorphometrical study at 2 months of age, P6.P2-13 exhibited a 40% higher bone formation rate, and a 40% enlarged mineralizing surface in the periosteal surface of the femoral mid-shaft than that of SAMP6. Primarily cultured osteoblasts harvested from P6.P2-13 showed a higher osteoblastic activity than those from SAMP6, in the condition without systemic factors. Secreted frizzled-related protein 4 (Sfrp4),one of the candidate genes within the segregated 2.4Mb interval, showed approximately 40-fold higher level of expression in calvaria tissue in SAMP6 than in P6.P2-13. Recombinant Sfrp4 suppressed the proliferation of osteoblasts. TCF/β-catenin dependent-reporter activity in the osteoblasts derived from SAMP6 showed lower responsiveness for Wnt ligand, Wnt3A, than those from P6.P2-13. Fourteen single nucleotide polymorphisms (SNPs) were found in the putative promoter sequences of Sfrp4 in SAMP2 compared to SAMP6. The transcriptional activity of the SAMP6-type promoter construct was 40% higher than that of the SAMP2-type one. These results presented Sfrp4 as a negative regulator of bone formation in SAMP6 and a candidate gene regulating bone mass.
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