STAT3 and obesity due to melanocortin 4 receptor deficiency: The accumulation of fat in the liver (hepatic steatosis) is a feature of obesity.159 This process is regulated in part through JAK/STAT signaling pathway by growth factors and cytokines.160,161 Studies have consistently suggested that hepatocyte-specific deficiency of STAT3 leads to insulin resistance and increased expression of gluconeogenic genes.162–164 Conversely, STAT3 activation in hepatocytes may prevent steatosis.