Ultrastructural studies on the effect of transforming growth factor-β1 on rat articular cartilage

The destruction of articular cartilage in degenerative and inflammatory joint disease reflects an imbalance between synthesis and degradation of the structural components of the tissue. In previous, mainly in vitro studies, TGF-beta has been shown not only to play a role in controlling the synthesis of matrix components such as collagen and proteoglycans but also to influence their degradation. To elucidate the effect of local administration of TGF-beta on unloaded articular cartilage in growing rats, three animals were given intraarticular injections of TGF-beta for three consecutive days and sacrificed on the fourth. Perfusion fixation was combined with qualitative and quantitative evaluation (stereology) both at the light and electron microscopic level. Local administration of TGF-beta resulted in a decrease in height of the hypertrophic zone. Furthermore, the volume density of cells decreased and cells with a distinct morphology designated stellate cells appeared in this zone. In the same compartment, TGF-beta administration resulted in decreased pericellular collagen volume density while the volume density increased in the intermediate zone. The results of our investigation support and extend previous observations: TGF-beta does not only modulate the metabolism of articular cartilage in general, but the effect is targeted to specific subcompartments of the matrix. However, the result of this acute effect on the long-term function of the tissue remains to be elucidated.