Collagen XXIV null mice have osteoporotic bones

Collagen XXIV, discovered as a cDNA, has a typical C‐propeptide domain, indicating the molecule is a member of the fibrillar collagens. The amino terminal non‐collagenous domain is large, similar to those of fibrillar collagen alpha1(V), alpha1(XI) and alpha1(XI) chains. The triple helical domain is about 100 amino acids shorter than other fibrillar collagen chains and contains an imperfection (Koch et al., JBC 278: 43236, 2003). The gene is activated late in the osteoblast differentiation program, and is regulated by CREB‐AP1 (Matsuo et al., JBC 281:5445, 2006; Matsuo et al., Conn Tiss Res 49:68, 2008). Our objective was to evaluate the importance of collagen XXIV to the architecture of bone by examining null mice. MicroCT analysis of the femurs of 5 month old null mice were compared with those of age matched wild type mice. The cortical bone was less dense in the null mice and cross sections through the distal femur displayed fewer trabeculae. 3D reconstructions indicated that the femurs of the null mice had the same bone volume as the wild type femurs, but that the bone was less dense, having an osteoporotic appearance. Conclusion: Collagen XXIV is important for proper bone density.