To examine the impact of prolonged TGF-beta exposure on cartilage and ligamentous joint structures in vivo, to investigate involvement of TGF-beta in osteoarthritis pathology.
TGF-beta was injected into murine knee joints once or repeatedly, whereafter articular cartilage proteoglycan (PG) synthesis and content, and histological changes in knee joints were studied over a 2-month period.
A single injection of TGF-beta stimulated patellar cartilage PG synthesis for 3 weeks and PG content for 2 weeks. Triple TGF-beta injections prolonged the increase in PG content to 3 weeks. Patellar cartilage showed no histological abnormalities at 1 and 2 months after the last injection. In contrast, 2 months after triple TGF-beta injections the superficial layer of tibial cartilage still had an increased proteoglycan content, while severe PG depletion was found in deeper layers of the posterior part of the lateral tibia in particular. Eventually, lesions occurred at the level of the tide-mark, exactly the site where cartilage is torn off in experimental and spontaneous osteoarthritis in mice. Additionally, multiple TGF-beta injections induced formation of chondroid structures along the margins of articular cartilage. These chondroid structures were transformed into osteophytes via endochondral ossification. Formation of chondroid tissue was also observed in collateral ligaments.
Multiple intra-articular injections of TGF-beta induce changes in articular cartilage and surrounding tissues that have strong resemblance to features of experimental and spontaneous osteoarthritis in mice, suggesting a role for TGF-beta in the OA process.