RANK-RANKL-OPG expression after gingival mesenchymal stem cell hypoxia preconditioned application in an orthodontic tooth movement animal model

BACKGROUND: The expression of receptor activator of Nuclear Factor Kappa Beta (RANK) and its ligand (RANKL), as well as osteoprotegrin (OPG), in the alveolar bone (AB), may improve bone remodeling during orthodontic tooth movement (OTM). It is hypothesized that hypoxia-preconditioned gingival mesenchymal stem cells (GMSC) may be more effective than normoxia-preconditioned GMSC in this regard. This study aims to investigate the expression of RANK, RANKL, and OPG in the compression and tension sides of AB after allogeneic administration of GMSC that were normoxia or hypoxia-preconditioned in rabbits (Oryctolagus cuniculus) undergoing OTM. METHODS: Twenty-four healthy young male rabbits were divided into two groups: T1, which underwent OTM and received normoxia-preconditioned GMSC, and T2, which underwent OTM and received hypoxia-preconditioned GMSC. A ligature wire was attached to the mandibular first molar and connected to a 50 g/mm(2) closed coil spring, exerting force on the central incisor and left mandibular molar of the experimental animals. After 24 h of OTM, either normoxia- or hypoxia-preconditioned GMSC were injected into the gingiva of the samples in a single dose of 20 μl of phosphate-buffered saline (PBS). All samples were sacrificed on days 7, 14, and 28, and immunohistochemistry was performed to analyze the expression of RANK, RANKL, and OPG on the tension and compression sides. RESULTS: The expressions of RANK-RANKL-OPG in the alveolar bone of the compression and tension sides were significantly different during the 14-day period of OTM following allogeneic administration of GMSC that were normoxia or hypoxia-preconditioned (p < 0.05). CONCLUSION: The expression of RANK-RANKL was significantly increased on the compression side of the alveolar bone during OTM after the administration of hypoxia-preconditioned allogeneic GMSC but not on the tension side. Conversely, RANKL-OPG expression was enhanced on the tension side but not on the compression side, as observed through immunohistochemical analysis in vivo.