Osteocytes play an important role in experimental periodontitis in healthy and diabetic mice through expression of RANKL

Aim: Periodontitis results from bacteria-induced inflammation. A key cytokine, RANKL, is produced by a number of cell types. The cellular source of RANKL critical for periodontitis has not been established. Methods: We induced periodontal bone loss by oral inoculation of Porphyromonas gingivalis and Fusobacterium nucleatum in both normoglycaemic and streptozotocin-induced type 1 diabetic mice. Experimental transgenic mice had osteocyte-specific deletion of floxed receptor activator of nuclear factor kappa-B ligand (RANKL) mediated by DMP-1-driven Cre recombinase. Outcomes were assessed by micro-CT, histomorphometric analysis, immunofluorescent analysis of RANKL and tartrate-resistant acid phosphatase staining for osteoclasts and osteoclast activity. Results: Oral infection stimulated RANKL expression in osteocytes of wild-type mice, which was increased by diabetes and blocked in transgenic mice. Infected wild-type mice had significant bone loss and increased osteoclast numbers and activity, which were further enhanced by diabetes. No bone loss or increase in osteoclastogenesis or activity was detected in transgenic mice with RANKL deletion in osteocytes that were normoglycaemic or diabetic. Conclusions: This study demonstrates for the first time the essential role of osteocytes in bacteria-induced periodontal bone loss and in diabetes-enhanced periodontitis.