Osteogenic protein-1 (OP-1) blocks cartilage damage caused by fibronectin fragments and promotes repair by enhancing proteoglycan synthesis.

Objective and Design: The abilities of osteogenic protein-1 (OP-1) and TGF-beta1 to affect cartilage damage caused by fibronectin fragments (Fn-fs) that are known to greatly enhance cartilage proteoglycan (PG) degradation were compared.
Material: Articular cartilage was obtained from 18 month old bovines.
Treatment: To test blocking of damage, cartilage was cultured with or without OP-1 or TGF-beta in the presence of 100 nM Fn-fs. To test restoration of PG, cartilage was first cultured with Fn-fs and the cartilage then treated with factors.
Methods: Cartilage PG content was measured in papain digests using the dimethylmethylene blue assay. PG synthesis was measured by incorporation of 35S labeled sulfate.
Results: OP-1 blocked damage and restored PG in damaged cartilage, apparently due to enhanced PG synthesis. However, TGF-beta1 alone decreased PG content.
Conclusions: These results clearly demonstrate differences between OP-1 and TGF-beta1, both members of the TGF-beta superfamily and illustrate the efficacy of OP- in blocking Fn-f mediated damage.