Localization of RANK, RANKL and osteoprotegerin during healing of surgically created periodontal defects in sheep.

BACKGROUND AND OBJECTIVE Modeling of periodontal bone regeneration in a large animal enables better examination of the spatial and temporal regulation of osteogenesis and the remodeling of the healing defect. RANK, RANKL and osteoprotegerin (OPG) are known to be important regulators of bone healing. The aim of this study was to create periodontal defects surgically in a large animal model and to examine bone regeneration and the expression of RANK, RANKL and OPG proteins in the defect site during bone regeneration. MATERIAL AND METHODS Periodontal defects were made in the furcation of the second mandibular premolar of sheep. Wound healing was examined 6 h, and 1, 4 and 6 wk after surgery and in control tissue. The teeth and defect region were decalcified and paraffin embedded. Immunohistochemistry for RANK, RANKL and OPG was conducted. Osteoclasts were identified using TRAP staining. RESULTS The defects were examined at different time points after surgery and by 6 wk the defect region had fully regenerated with new bone, albeit less dense than that in the unwounded controls. RANK-positive osteoclasts were present at the edge of the wound from week 1 and were found within the defect at week 6, corresponding to osteoclast activation and bone remodeling. RANKL staining increased from week 1 compared with unwounded tissue, and peaked at 4 and 6 wk, as the osteoblast numbers increased. At the same time, OPG immunostaining was high in controls and at week 6, suggesting that it may act to block RANKL and control the bone remodeling within the defect. CONCLUSION Distinctive temporal and spatial expression patterns for RANK, RANKL and OPG proteins were observed during healing of surgically created periodontal wounds in a sheep model. The research identifies possible therapeutic approaches to periodontal bone repair via modulation of these members of the tumor necrosis factor family.