Regulation of Glycosaminoglycan Metabolism by Bone Morphogenetic Protein-2 in Equine Cartilage Explant Cultures

Objective: To investigate whether recombinant human bone morphogenetic protein-2 (rhBMP-2) regulates glycosaminoglycan (GAG) synthesis and release from equine articular cartilage explant cultures.

Design: Equine articular cartilage explants were maintained in vitro for 7 days in the presence of 0 (control), 1, 10, or 100 ng of rhBMP-2/ml. Synthesis and release of GAG were assessed as measures of production and degradation of the extracellular matrix, respectively.

Animals: 6 horses (age range, 2 to 25 years old) without clinically detectable musculoskeletal abnormalities.

Procedure: Rate of synthesis of GAG was assessed by incorporation of [36S]sulfate during the final 24 hours of the 7-day incubation period. Release of GAG was assessed on days 3, 6, and 7, using 1,9-dimethylmethylene blue.

Results: Explants from all 6 horses had a significant (P = 0.05) increase in release of GAG in response to incubation with 100 ng of rhBMP-2/ml. There was a significant (P = 0.05) decrease in GAG synthesis in explants from only 2 of the 6 horses at the same concentration of rhBMP-2. There was no significant age correlation between responsive and nonresponsive horses.

Conclusions: A concentration of 100 ng of rhBMP-2/ml stimulates GAG release from explant cultures of equine articular cartilage. The data suggest that bone morphogenetic proteins may be potential regulators of equine cartilage degradation and repair.

Clinical Relevance: Surgical procedures that damage subchondral bone may stimulate generation of improved cartilage-like tissue. It is, therefore, crucial to understand how bone-derived factors may influence cartilage metabolism in horses.