Components of the IGF-system in the aging mouse temporomandibular joint

Objectives: The insulin-like growth factor (IGF) system plays an important role in articular cartilage physiology but is also involved in the pathogenesis of osteoarthrosis. In the temporo-mandibular joint (TMJ), IGFs contribute to growth processes, but their role in age related or pathological changes is unknown. In this study, the distribution of the IGF components in the TMJ of old mice was determined to obtain basic data for further research in this animal model. Methods: Sections of decalcified and paraffin embedded TMJs including condyle, fossa and discus of 3 male and female NMRI mice each aged between 3 and 18 months were investigated with H.E., alcian blue staining and immunohistochemistry using antibodies against the ligands IGF-I and -II, the IGF receptor 1 (IGF1R) and IGF binding proteins (IGFBP)s-1 to –6. Results: Early signs of degenerative cartilage changes, e.g. reduced alcianophilia, could be observed already in 3 months old animals. In later age stages, degenerative changes were more severe and could be characterized as osteoarthrotic, especially for the condylar cartilage, but there was no clear age correlation. Pathological changes were only mild in the fossa and discus. All components of the IGF system could be detected. Strong immunoreactivity could be found especially in cells and/or matrix of anterior and posterior regions of the condyle and also the fossa. IGF1R immunostaining was obvious in all specimens investigated, even in chondrocytes of arthrotic lesions. Most IGFBPs showed moderate immunoreactivities. In osteoarthrotic lesions, strong immunostaining for all IGF components was visible. Conclusion: The IGF system may play an important role during the development of TMJ osteoarthrosis and adaptive changes in old mice, especially in the condylar fibrocartilage. Spatial distribution patterns may be related to biomechanical influences. Upregulation of IGF components in severe arthrotic lesions can be discussed in relation to probable reparative processes.