The leading-edge subset (core genes) of the cytokine activity pathway included the upregulation of SPP1 (osteopontin), several members of interleukin families 1 and 6 (CRLF1, IL1RN, IL36G, IL11, IL1B) and members of the tumor necrosis factor family (TNFSF18, TNFSF8) indicating inflammation driven by mainly IL-1 and IL-6 cytokine families in osteoarthritis cartilage. Here, SPP1 is linked to osteoarthritis.