Overexpressed osteoactivin reduced osteoclastic callus resorption during distraction osteogenesis in mice

Distraction osteogenesis is a widely used surgical technique to treat bone deformity and shortening. Several biological treatments have been studied to enhance bone formation during distraction osteogenesis in animals. However, role of osteoactivin in the osseous tissues during distraction osteogenesis remains poorly understood. In this animal experimental study, we investigated the spatiotemporal expression of osteoactivin by immunohistochemistry and real-time PCR using a mouse model for tibial lengthening. Furthermore, to address the role of osteoactivin in bone lengthening, we subjected the osteoactivin-transgenic mice to distraction osteogenesis model. During the lag phase, the fibroblast-like cells (possible progenitors of the osteoblasts or chondrocytes), which mainly express osteoactivin, were infiltrated into the osteotomy site. Osteoactivin was ubiquitously expressed in the lengthened segment during the distraction and consolidation phases. Consistent with the immunohistochemical analysis, the levels of the osteoactivin transcripts in the tibias were significantly increased throughout the distraction osteogenesis process. The bone mineral content in the osteoactivin-transgenic mice calculated using peripheral quantitative computed tomography was also significantly increased at the remodeling zone. The histomorphometric analysis revealed that newly formed callus resorption in the remodeling zone was significantly reduced but bone formation was not altered in the osteoactivin-transgenic mice. We conclude that osteoactivin functions as an inhibitor of callus resorption during the consolidation phase of distraction osteogenesis.