Sclerostin is essential for alveolar bone loss in occlusal hypofunction

Bone loss is caused by occlusal hypofunction and is a serious health concern. This is particularly true of tooth loss, which is common in the elderly. However, the cellular and molecular mechanisms underlying bone loss have yet to be fully elucidated. Sclerostin and Wnt/β-catenin signaling have previously been reported to serve important roles in regulating bone remodeling. Therefore, the present study aimed to investigate the involvement of sclerostin and Wnt/β-catenin signaling in occlusal hypofunction-induced alveolar bone remodeling. The unilateral maxillary molars of 14 male Sprague-Dawley rats were extracted in order to establish a model of occlusal hypofunction. For each rat, the non-extraction side was treated as the control group for comparisons with the extraction side. At 8 weeks after tooth extraction, the rats were sacrificed and alveolar bone specimens were harvested for X-ray radiography, micro-computed tomography (CT) and histological and immunohistochemical examinations. Bone loss and architecture deterioration were observed at the occlusal hypofunction side. The bone mineral density was markedly decreased and the ratio of bone volume to total volume was significantly decreased at the hypofunction side, as compared with the control side (P<0.001). In addition, the number of osteoclasts at the hypofunction side were significantly increased compared with that in the control side (P<0.001), as demonstrated using tartrate-resistant acid phosphatase staining. Furthermore, the protein expression levels of sclerostin and receptor activator of nuclear factor-κB ligand were increased, whereas those of β-catenin were decreased, at the hypofunction side when compared with the control side. In conclusion, the results of the present study suggested that occlusal hypofunction-induced bone loss may be associated with upregulated expression of sclerostin, which, in turn, may inhibit the activity of the Wnt/β-catenin signaling pathway.