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Expression of Insulin-Like Growth Factor I Messenger Ribonucleic Acid in Developing Osteophytes in Murine Experimental Osteoarthritis and in Rats Inoculated with Growth Hormone-Secreting Tumor

Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, 3–1-1 Maidashi, Higashi-ku, Fukuoka; the Department of Nature Medicine, Atomic Bomb Disease Institute (A.O., S.Y.), and the Department of Anatomy I, Nagasaki University School of Medicine (K.A.), 1-7-1, Sakamoto, Nagasaki, Japan 852-8501; and the Department of Pathology, Osaka University Medical School (S.N.), 2-2, Yamadaoka Suita, Osaka, Japan 565-0871

Address all correspondence and requests for reprints to: Seiya Jingushi M.D., Ph.D., Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, 3–1-1 Maidashi, Higashi-ku, Fukuoka, Japan. E-mail: jingushi{at}ortho.med.kyushu-u.ac.jp

Osteophytes are one of the characteristic features of osteoarthritis and are often found in acromegalic arthropathy. The aim of this study was to investigate insulin-like growth factor I (IGF-I) involvement in osteophyte formation. One percent collagenase solution was injected into murine knee joints as an osteoarthritis model. In a different animal group, GH-secreting tumor cells were inoculated sc to the rat thigh as an acromegaly model. A series of osteophyte formation was examined histologically. IGF-I messenger RNA was detected using the in situ hybridization method. Type I IGF receptors were detected immunohistochemically. In the osteoarthritis model, osteophyte formation appeared as synovial or perichondral cell proliferation adjacent to the articular cartilage on day 5, followed by cartilage formation on day 7 and endochondral ossification on day 14. In the acromegaly model, synovial or perichondral cell proliferation was observed 4 weeks after inoculation, followed by osteophyte formation at 8 weeks. In both models, IGF-I messenger RNA and type I IGF receptor were coexpressed by proliferating synovial or perichondral cells, proliferating chondrocytes, and osteoblasts within the developing osteophytes. These results suggest that IGF-I regulated the initiation and development of osteophyte formation in both models in an autocrine and/or paracrine fashion.