CCL2 and obesity due to melanocortin 4 receptor deficiency: Genetic and lifestyle factors can lead to obesity, insulin resistance, and disorders of lipid metabolism, resulting in the accumulation of free fatty acids in the liver and, as a consequence, mitochondrial dysfunction with oxidative stress, endoplasmic reticulum (ER) stress, hepatocyte cell death, and the production of inflammatory chemokines and cytokines, such as monocyte chemotactic protein-1 (MCP-1) and tumor necrosis factor (TNF-α).