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 of 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 protein, is part of the transduction mechanism between force as applied to bone during orthodontic tooth movement and bone remodeling. To test this hypothesis, we examined connexin 43 expression in a rat model system of experimental tooth movement. To establish the model, we extracted maxillary first molars to initiate supra-eruption of opposing mandibular molars. The rats were killed at 0, 6, 12, 24, and 48 hrs post-extraction. The mandibles were removed, demineralized, and embedded in paraffin. To localize connexin 43 protein and mRNA, we used a specific antibody 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, respectively. We found connexin 43 protein expressed by osteoclasts (++++) and periodontal ligament cells (+++) in compression zones, and by osteoblasts (++++) and osteocytes (++++) in tension zones of the periodontal ligament. In addition, connexin 43 mRNA was found in some bone and periodontal 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 expressing connexin 43 48 hrs after molar extraction was also significantly greater in bone subjected to tension when compared with controls (P < 0.001). The results of this study support the hypothesis that connexin 43 plays a role in the coordination of events during experimentally induced alveolar bone remodeling.