One growth factor that potentially plays a role in fracture healing is midkine (Mdk). Previous findings suggest that Mdk is a negative regulator of osteoblast activity and bone formation, thereby raising the possibility that a specific Mdk-antagonist might improve fracture healing. The aim of the present study was to evaluate the effects of a monoclonal anti-Mdk antibody (Mdk-Ab) on bone repair in vivo and on osteoblasts in vitro. Forty-two C57BL/6J mice received a diaphyseal femur osteotomy stabilised with an external fixator. Half of the animals were injected with vehicle (PBS) or Mdk-Ab twice per week for three weeks. The mice were sacrificed at day 10, 21 or 28 and fracture healing was assessed by 3-point-bending test, micro-computed tomography, histomorphometric and immunohistochemical analysis. For in vitro experiments, preosteogenic cells were differentiated for 5 days and recombinant Mdk and the Mdk-Ab were added for 6 h to the culture medium. Gene and protein expression was analysed using qPCR and western blotting. (n=6-8; p<0.05; Mann-Whitney-U test). During fracture healing, treatment with Mdk-Ab led to a significantly increased relative flexural rigidity after 21 and 28 days. Bone mineral density and bone volume ratio were significantly increased in the fracture callus at day 21. Histomorphometric analysis revealed that the bone content in the fracture callus was significantly increased after 10 and 21 days. Osteoblast surface as well as beta-catenin expression were also significantly increased. In vitro experiments confirmed a negative influence of Mdk on osteoblast differentiation and beta-catenin signalling that was abolished by Mdk-Ab treatment. Antagonising Mdk seemed to improve osteoblast function based on an increased beta-catenin signalling, leading to a faster callus mineralisation and therefore to an accelerated bone repair. The findings of the present study indicate that there is a therapeutic potential for the Mdk-Ab to enhance fracture healing in patients with orthopaedic complications.
Disclosure: The authors declared no competing interests. This work was supported by the German Research Foundation (IG18-3/3).