Expression of insulin-like growth factor I (IGF-I)mRNA and IGF-I protein was studied in human osteoarthritic and young articular cartilage by in situ hybridisation and immunohistochemistry. In situ hybridisation showed that relatively low amounts of IGF-I mRNA signal were present in anatomically normal regions of osteoarthritic and young cartilage. In fibrillated osteoarthritic cartilage, however, the signal intensity was significantly higher than in non-fibrillated cartilage. Particularly high levels of IGF-I mRNA were present in the surface cell clones of more advanced lesions, the amount of signal being about four to five times greater than in anatomically normal cartilage. The amount of message varied with cartilage depth. In young cartilage there was less IGF-I mRNA in the superficial zone than in the middle and deep zones. In fibrillated regions of osteoarthritic joints the amount of message in surface cells was greater than in deeper regions. A specific human IGF-I antibody was used to show the presence intracellularly of IGF-I protein in osteoarthritic and young cartilage. Raised levels of IGF-I message in osteoarthritic chondrocytes may represent an attempt at increased matrix repair, operating by an autocrine/paracrine mechanism.
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