Bone Abstracts

Collagen XV is a secreted proteoglycan localized in the outermost layer of the basement membrane and in the fibrillar matrix. Previously, the collagen XV gene (COL15A1) has been linked to osteogenic differentiation, being identified mainly in mature osteoblasts forming new bone tissue or lining bone trabeculae. Our previous data on collagen XV knockout fetuses reports subtle skeletal changes. The aim of this study was to analyse skeletal changes in adult mice lacking collagen XV. To this end, we compared a control group of C57BL/6 male mice (n=8) with littermates lacking Col15a1 (n=8). Formalin fixed left tibias and femurs were scanned by micro-computed tomography with 6.7 μm pixel size. Right hind limbs were tested for mechanical properties in three point bending and axial loading of the femoral neck. Lack of Col15a1 decreased the trabecular bone volume fraction by 44 and 60%, mainly due to 40 and 58% decreases in the trabecular number in tibias and femurs respectively. Additionally, the distance between trabeculae was increased by 26% in the femurs. There were no changes in cortical bone morphometric parameters but increased mechanical strength was observed in the tibias and the femurs as well as in the femoral neck. Confocal laser scanning microscopy of rhodamin 6G stained osteocytic networks revealed less organized cortical bone in the Col15a1 knockout mice. Our results suggest a novel role for collagen XV as a matrix organizer during osteoblastic bone formation.