Du et al. (2020) studied the effect of high-fat diet (60% kcal fat) on TMJ of C57BL/6 mice. Less cartilage matrix, thinner condylar cartilage, and vertical clefts were observed in overweight mice after 12 weeks of high-fat feeding. Additionally, they found that the expression of IL-1β, MMP-3 and leptin were upregulated in condylar cartilage of high-fat-fed mice. Patients with knee OA have increased level of serum leptin and the abnormal leptin level in synovial fluid. Leptins are one of the increased proinflammatory factors in individuals with obesity (Conde et al., 2013). Here, LEP is linked to obesity due to melanocortin 4 receptor deficiency.