Our current results suggest that RA-triggering factors, such as IL-1β and HIF-2α, enhance the expression of several chemokines in chondrocytes, including Cxcl1, Cxcl2, Cxcl5, Cxcl10, Ccl2, Ccl5, and Ccl7. These HIF-2α-induced chemokines in chondrocytes stimulate migration and invasion of FLS, leading to pannus expansion adjacent to cartilage tissue of RA joints. This evidence concerns the gene EPAS1 and rheumatoid arthritis.