Temporal and spatial expression of osteoprotegerin and receptor activator of nuclear factor-κB ligand during mandibular distraction in rats

Purpose: The expression profiles of osteoprotegerin and receptor activator of nuclear factor-K13 ligand (RANKL) were investigated in the distraction region to reveal bone remodelling characters during mandibular distraction osteogenesis. Material and Methods: Osteotomies were performed and external distractors were used on the mandibles of 42 adult mate SD rats. After a 5-day latency period, the distractors were activated at a rate of 0.4 mm/day for 6 days, followed by a 4-week consolidation period. Radiographs were taken, and specimens were harvested at the end of the latency period, when distraction was completed, and at the end of 1, 2, 3 and 4 weeks of the consolidation period. Tartrate-resistant acid phosphatase staining was used to detect activated osteoclasts. Temporospatial expression of osteoprotegerin and RANKL was investigated by using immunohistochemistry, in situ hybridization and reverse transcription polymerase chain reaction. Semi-quantitative analysis was used to characterize osteoprotegerin (OPG). RANKL and RANKL/OPG ratio. Results: In all time points, osteoprotegerin and RANKL were co-localized in bone marrow lining cells, osteoblasts and newly embedded osteocytes. Osteoprotegerin mRNA expression increased to a peak when distraction was completed and maintained this level until the end of week 2 of the consolidation period. RANKL mRNA expression increased steadily until the end of week 1 of the consolidation period and maintained a peak level until the end of week 3, with a slight decrease at the end of week 2. The RANKL/OPG ratio increased continuously and reached its highest level at the end of weeks 3 and 4 of the consolidation period. Tartrate-resistant acid phosphatase staining positive osteoclasts were mainly detected at weeks 2, 3 and 4 of the consolidation period in bone marrow cavities and bone surfaces. Conclusions: The temporospatial expression patterns of osteoprotegerin and RANKL suggest that the osteoblast lineage cell network orchestrates bone remodelling during distraction osteogenesis and most activated bone resorption takes place during weeks 3 and 4 of the consolidation phase. (c) 2007 European Association for Cranio-Maxillofacial Surgery.