EPAS1 and arthropathy: Since the establishment of experimental mouse models with surgically induced knee joint instability, a large number of studies have revealed the major molecules or signalling pathways responsible for OA, such as a disintegrin-like and metallopeptidase with a thrombospondin type 1 motif 5 (Adamts5), matrix metalloproteinase-13 (Mmp13), hedgehog signalling, syndecan-4, Wnt signalling, and hypoxia-inducible factor 2-alpha (HIF-2α)1–13.