TNF and obesity due to melanocortin 4 receptor deficiency: In the liver, increased expression of osteopontin, an ECM glycoprotein that plays a vital role in the development of hepatic steatosis and insulin resistance, is linked to increased expression of TNF-α and the macrophage markers F4/80 and CD68 in the liver as well as abdominal subcutaneous adipose tissue in obesity [51, 52].