Functionally improved bone in calbindin-D28k knockout mice.

Abstract

In vitro studies indicate that Calbindin-D28k, a calcium binding protein, is important in regulating the life span of osteoblasts as well as the mineralization of bone extracellular matrix. The recent creation of a Calbindin-D28k knockout mouse has provided the opportunity to study the physiological effects of the Calbindin-D28k protein on bone remodeling in vivo. In this experiment, histomorphometry, microCT, and bend testing were used to characterize bones in Calbindin-D28k KO (knockout) mice. The femora of Calbindin-D28k KO mice had significantly increased cortical bone volume (60.4% +/- 3.1) compared to wild-type (WT) mice (45.4% +/- 4.6). The increased bone volume was due to a decrease in marrow cavity area, and significantly decreased endosteal perimeters (3.397 mm +/- 0.278 in Calbindin-D28k KO mice, and 4.046 mm +/- 0.450 in WT mice). Similar changes were noted in the analysis of the tibias in both mice. The bone formation rates were similar in the femoral and tibial cortical bones of both mice. microCT analysis of the trabecular bone in the tibial plateau indicated that Calbindin-D28k KO mice had an increased bone volume (35.2% +/- 3.1) compared to WT mice (24.7% +/- 4.9) which was primarily due to increased trabecular number (8.99 mm(-1) +/- 0.94 in Calbindin-D28k KO mice compared to 6.75 mm(-1) +/- 0.85 in WT mice). Bone mineral content analysis of the tibias indicated that there is no difference in the calcium or phosphorus content between the Calbindin-D28k KO and WT mice. Cantilever bend testing of the femora demonstrated significantly lower strains in the bones of Calbindin-D28k KO mice (4135 micro strain/kg +/- 1266) compared to WT mice (6973 micro strain/kg +/- 998) indicating that the KO mice had stiffer bones. Three-point bending demonstrated increased failure loads in bones of Calbindin-D28k KO mice (31.6 N +/- 2.1) compared to WT mice (15.0 N +/- 1.7). In conclusion, Calbindin-D28k KO mice had increased bone volume and stiffness indicating that Calbindin-D28k plays an important role in bone remodeling.