EPAS1 and rheumatoid arthritis: Both HIF-1α and HIF-2α have been shown to be significantly overexpressed in cytoplasmic and nuclear of synovial lining and stromal cells derived from rheumatoid arthritis (RA) and OA human patients relative to cells from normal nonarthritic cases [55] and our regression analysis results also demonstrated a significant positive correlation of HIF-α isoforms expression in response to IL-1 (S2 Fig).