Decreased expression of osteocalcin and osteonectin in relation to high strains and decreased mineralization in mandibular distraction osteogenesis

In a rabbit model of mandibular distraction osteogenesis, high strains resu lted in a substantial reduction in the expression rate of the two osteogeni c marker proteins, osteocalcin and osteocalcin, In non-distracted samples a nd mandibles exposed to 2000 microstrains, staining for osteocalcin in the osteotomized area was detected in osteoblasts and diffusely dispersed in th e mineralized matrix of the surrounding bone. However, in osteotomized mand ibles distracted at strains above physiological levels (200000 and 300000 m u strains, respectively) the majority of osteoblast-like cells failed to ex press immunodetectable amounts of osteocalcin, Similarly, in the extracellu lar matrix of the distraction area the expression of osteonectin decreased by applying higher strains. Ultrastructural analyses of mandibular samples exposed to hyperphysiological strains revealed that the reduced expression rate of osteocalcin and osteonectin was paralleled by a significant loss of crystal formation, suggesting a functional role of both proteins related t o mechanical loading.