A novel strategy for the treatment of osteoarthritis by restoring joint homeostasis using natural antagonists

Undesirable chondrocyte hypertrophy and terminal differentiation cause matrix degeneration and calcification and are characteristics of osteoarthritis. Maintaining the chondrogenic phenotype and avoiding hypertrophy remain a big challenge in cell-based therapeutic strategies. Targeting signalling pathways holds great potential for the development of therapies for OA. However, we need to gain insight in the regulation of those signalling pathways in the early stages of OA development. WNT pathway antagonists DKK1 and FRZB have been identified as possible key factors in the onset of osteoarthritis. In this study, we investigated the role of DKK1 and FRZB in the onset of osteoarthritis in bovine osteochondral plugs with specifically designed variable domain of single chain heavy chain only antibodies (VHH). To accomplish this, an experimental set-up has been established and the biological activity and binding characteristics of the VHHs was determined. It was revealed that isolated bChs can be used as a control cell line, bovine osteochondral plugs can be cultured stably for at least 28 days and Kristensen’s is the best decalcification technique. It was also found that in OA typically the cartilage thickness decreases, the cell density increases, the cellular diameter increases and the pericellular matrix of collagen I and II increases. Unfortunately, the VHHs were not able to neutralize DKK1 and FRZB, possibly because the VHH’s lost their biological activity due to long-term storage. To conclude, this research provides a platform to gain insight in the cellular mechanism involved in the onset of osteoarthritis. With the characterization of fresh VHHs, research can be continued. It sets the stage for the development of knowledge which can lead future therapies that are able to halt the development of osteoarthritis.