Nanomechanics of Knockout Mouse Bones

Abstract

ABSTRACTOsteocalcin (OC) and osteopontin (OPN) are among the most abundant non-collagenous bone matrix proteins. Both have drawn interest from investigators studying their function in osteoporosis and it is known that mutations of these proteins can also have dramatic effects on the properties of bone. Other proteins including fibrillin 1 and 2 (FBN2) have been less widely studied, but can be mutated in some individuals resulting in connective tissue disorders. It has been reported that abnormal fibrillin may play a role in decreased bone mass. In this study bones from osteopontin (OPN), osteocalcin (OC) and fibrillin-2 (FBN2) knockout mice have been investigated. The study has identified how these proteins affect the bone's nanomechanical properties (hardness and elastic modulus). Nanoindentation tests were performed on the radial axis of cortical femora bones from the knockout mice and their wildtype controls. The results showed that young (age< 12 weeks) OPN knock-out bones have significantly lower mechanical properties than wild-type bones indicate a crucial role for OPN in early bone mineralization. After 12 weeks of age, the OPN knockout and wild-type control bones did not show any statistical difference. In OC deficient mice the mechanical properties were found to increase in the cortical mid-shaft of femora from 1 year old mice, suggesting an increase in bone mineralization, but 3 month old FBN2 deficient mice bones showed a decrease in mechanical properties across the cortical radial axis of the mid- femora.