BNIP3 and rheumatoid arthritis: When BNIP3 was low expressed in RA-FLSs by siRNA transfection, the proliferative activity of RA FLSs was decreased (Fig. 5A–D) and apoptosis was increased (Fig. 5E–H), which further confirmed the protective effect of BNIP3 on RA-FLSs under hypoxia.