Mandibular repositioning modulates IGFBP-3,-4,-5 and -6 expression in the mandibular condylar cartilage of young rats

Abstract

Functional orthopedic appliances correct dental malocclusion partially by exerting indirect mechanical stimulus on the condylar cartilage, modulating growth and the adaptation of orofacial structures. However, the exact nature of the biological responses to this therapy is not well understood. Insulin-like growth factors I and II (IGF-I and II) are important local factors during growth and differentiation in the condylar cartilage [D. Hajjar, M.F. Santos and E.T. Kimura, Propulsive appliance stimulates the synthesis of insulin-like growth factors I and II in the mandibular condylar cartilage of young rats, Arch. Oral Biol. 48 (2003), 635–642]. The bioefficacy of IGFs at the cellular level is modulated by IGF binding proteins (IGFBP). The aim of this study was to verify the mRNA and protein expression of IGFBP-3, IGFBP-4, IGFBP-5 and IGFBP-6 in the condylar cartilage of young male Wistar rats that used a mandibular propulsive appliance for 3, 9, 15, 20, 30 or 35 days. For this purpose, sagittal sections of decalcified and paraffin-embedded condyles were submitted to immunohistochemistry and the condylar cartilage to RT–PCR. The control group showed a gradual increase in the protein expression of all IGFBPs, except IGFBP-4. Following use of the appliance, IGFBP-3 and IGFBP-6 expression decreased in the early stage of the treatment. At 20 days of treatment there was a decline in the IGFs and IGFBP-3, IGFBP-4 and IGFBP-5 expression and at 30 days there was a peak in the IGFs and all IGFBPs expression except for IGFBP-3 where the peak was observed in the control animals. The expression patterns of all IGFBPs in the condylar cartilage were similar. The modulation of IGFBP-3, -4, -5 and -6 expression in the condylar cartilage in response to the propulsive appliance suggests that those peptides are involved in the mandibular adaptation during this therapy.