TNF and obesity due to melanocortin 4 receptor deficiency: Under obesity-associated mechanical stress, adipose and joint components such as chondrocytes and the infrapatellar fat pad are capable of producing multiple proinflammatory cytokines, including interleukin-1 (IL-1), IL-6, IL-10, IL-17, and tumor necrosis factor-α (TNF-α), to induce low-grade inflammation and promote cartilage matrix degradation leading to OA development [8, 9].