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

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. Articular cartilage was obtained from 18 month old bovines. 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. Cartilage PG content was measured in papain digests using the dimethylmethylene blue assay. PG synthesis was measured by incorporation of 35S labeled sulfate. OP-1 blocked damage and restored PG in damaged cartilage, apparently due to enhanced PG synthesis. However, TGF-beta1 alone decreased PG content. 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.