IGF-I, IGF-IR and IRS1 expression as an early reaction of PDL cells to experimental tooth movement in the rat

Objective: To characterize in vivo the role of IGF-I and its signalling, as an early reaction in the mechanotransduction process and to analyse changes of the local expression related to the magnitude of the applied force. Materials and methods: Forces of 0.1 N, 0.25 N and 0.5 N were applied to move the right upper first molars of 12 anaesthetized rats mesially. These forces were kept constant for 4 h. The untreated contralateral side served as a control. Paraffin-embedded sections of the resected jaws were prepared for immunohistochemistry to localize insulin-like growth factor-I (IGF-I), its receptor (IGF-IR), and insulin receptor substrate 1 (IRS1). Histomorphometric analysis was performed to count the percentage of immunoreactive cells in different parts of the periodontal ligament. Results: IGF-I, IGF-IR and IRS1 positive cells were observed in the periodontal tissues of the control and loaded teeth. In the experimental group, the number of IGF-I-, IGF-IR- and IRS1-positive cells increased significantly on the tension side and decreased on the compression side. Conclusions: These data indicate a close relationship between mechanical loading of the PDL and the autocrine/paracrine expression of IGF components as an early step in the mechanotransduction process leading in the long term to an organized remodelling of the alveolar bone. (C) 2010 Elsevier Ltd. All rights reserved.