Growth factors in experimental osteoarthritis: transforming growth factor beta pathogenic?

Osteoarthritis (OA) is characterized by focal cartilage destruction and osteophyte formation. Triple injections of transforming growth factor beta (TGF beta) in normal murine knee joints revealed that this growth factor can elicit osteophytes at sites characteristic for OA. Moreover, enhanced cartilage proteoglycan synthesis is induced and cartilage proteoglycan content is increased. Exuberant repair reactions may be pathogenic and indeed focal cartilage proteoglycan loss and disorganized chondrocyte spacing is noted in the tibial plateau after 1 month. Although TGF beta is immunosuppressive and can counteract interleukin 1 induced cartilage damage, suggesting potential therapeutic application in joint inflammation, it should probably be viewed as a pathogenic factor in OA.