BNIP3 and osteoarthritis: We established an in vitro hypoxia model to explore the different responses of fibroblast-like synovial cells in patients with osteoarthritis (OA-FLSs) and RA-FLSs to hypoxia in terms of proliferation, apoptosis and mitophagy, and to explore whether BNIP3 mediated the different adaptive responses of OA-FLSs and RA-FLSs.