EXPRESSION OF CONNEXIN-43 IN RAT MANDIBULAR BONE AND PERIODONTAL-LIGAMENT (PDL) CELLS DURING EXPERIMENTAL TOOTH MOVEMENT

Bone remodeling in response to force requires the coordinated action o f osteoblasts, osteoclasts, osteocytes, and periodontal ligament cells . Coordination among these cells may be mediated, in part, by cell-to- cell communication via gap junctions. This study tests the hypothesis that the regulation of expression of connexin 43, a gap junction prote in, is part of the transduction mechanism between force as applied to bone during orthodontic tooth movement and bone remodeling. To test th is hypothesis, we examined connexin 43 expression in a rat model syste m of experimental tooth movement. To establish the model, we extracted maxillary first molars to initiate supra-eruption of opposing mandibu lar molars. The rats were killed at 0, 6, 12, 24, and 48 hrs post-extr action. The mandibles were removed, demineralized, and embedded in par affin. To localize connexin 43 protein and mRNA, we used a specific an tibody for immunohistochemistry and a specific cDNA probe for in situ hybridization. Western and Northern blot analyses were used to assess the specificity of the connexin 43 antibody and cDNA probe, respective ly. We found connexin 43 protein expressed by osteoclasts (++++) and p eriodontal ligament cells (+++) in compression zones, and by osteoblas ts (++++) and osteocytes (++++) in tension zones of the periodontal li gament. In addition, connexin 43 mRNA was found in some bone and perio dontal ligament cells. Connexin 43 protein was found, by densitometric analysis, to be higher in the periodontal ligament after exposure to force compared with controls (P < 0.001). The number of osteocytes exp ressing connexin 43 48 hrs after molar extraction was also significant ly greater in bone subjected to tension when compared with controls (P < 0.001). The results of this study support the hypothesis that conne xin 43 plays a role in the coordination of events during experimentall y induced alveolar bone remodeling.