RANKL, RANK And OPG Expression In Surgically Created Periodontal Defects

Background: Three members of the tumour necrosis factor (TNF) family play important roles in bone healing: RANK (receptor activator of nuclear factor kappa-B), RANKL (RANK ligand) and the inhibitor Osteoprotegerin (OPG). The expression of these cytokines during periodontal wound healing is poorly understood. It has been suggested that expression of these proteins in chronic periodontitis, may alter their expression during subsequent bone healing. Objective: To characterise the spatio-temporal relationship of RANKL, RANK and OPG proteins during healing during healing of surgically-created periodontal defects. Methods: A sheep periodontal furcation model was used. Two control animals were sacrificed at baseline without surgical intervention. In the test group, 10 sheep had Class II furcation defects surgically created on the buccal of mandibular second premolars. Two test animals per time interval were sacrificed at 6 hours, 1, 2, 4 and 6 weeks post-surgery. Formalin-fixed, demineralised, paraffin-embedded serial sections were examined using immunohistochemical (IHC) staining for RANKL, RANK and OPG, matched to step-serial H&E sections. Osteoclasts were identified using Tartrate Resistant Acid Phosphatase (TRAP) staining. Results: After six weeks, the test furcations filled with new bones that appeared less dense than the unwounded controls. Osteoclasts were prominent at 6 hours, whilst osteoblasts began to populate the wounds from 2 weeks post-operatively. RANK staining was most intense after 6 hours, corresponding to osteoclast activation. RANKL increased from 4 weeks and peaked after 6 weeks, as osteoblasts numbers increased. OPG, a negative regulator of the RANKL/RANK pathway, was highest in the unwounded controls. Conclusions: The distinctive spatial and temporal expression of RANKL, RANK and OPG proteins during healing of a surgical periodontal wound was characterised in the sheep. Future investigations will examine the expression of these cytokines during healing following the induction of chronic periodontitis. Acknowledgements: Funded by the NZDARF and the Government of Malaysia