Osteocalcin and osteopontin influence bone morphology and mechanical properties

Osteocalcin (OC) and osteopontin (OPN) are major non-collagenous proteins (NCPs) involved in bone matrix organization and deposition. In spite of this, it is currently unknown whether OC and OPN alter bone morphology and consequently affect bone fracture resistance. The goal of this study is to establish the role of OC and OPN in the determination of cortical bone size, shape, and mechanical properties. Our results show that Oc(-/-) and Opn(-/-) mice were no different from each other or wild type (WT) with respect to bone morphology (P > 0.1). Bones from mice lacking both NCPs (Oc(-/-)Opn(-/-)) were shorter, with thicker cortices and larger cortical areas, compared with the WT, Oc(-/-), and Opn(-/-) groups (P < 0.05), suggesting a synergistic role for NCPs in the determination of bone morphology. Maximum bending load was significantly different among the groups (P = 0.024), while tissue mineral density and measures of stiffness and strength were not different (P > 0.1). We conclude that the removal of both OC and OPN from bone matrix induces morphological adaptation at the structural level to maintain bone strength.