The role of non-collagenous proteins, in particular, osteocalcin and osteopontin, in the determination of bone matrix quality

Abstract

Non-collagenous proteins (NCP) like osteocalcin and osteopontin form a smaller fraction of bone's organic material. While osteocalcin binds strongly to bone mineral, osteopontin has been described as `bone glue'. Both are associated with bone mineral. The structural and mechanical properties of four genotypes; wild type (WT), osteocalcin deficient (OC-/-), osteopontin deficient (OPN-/-) and OC-OPN-/- or double knock-out mouse model were investigated in this study. Results show that OC and OPN regulate bone structure and mechanical competency - two vital characteristics of the vertebrate skeleton. They also complemented each other in determining bone length. In contrast to their synergistic role in bone size, they were inter-dependent in the maintenance of matrix quality. These findings highlight that OC and OPN function in both independent and dependent ways to regulate various aspects of the skeleton. Using small angle x-ray scattering and wavelength dispersive spectroscopy, this work also shows that OC and OPN play key roles in the regulation of bone mineral crystal size, morphology, organization and mineral composition, thereby regulating bone matrix quality.