Retinol binding protein 4 and fatty liver: A direct link?

Abstract

Retinol-binding protein 4 (RBP4) is a 21-kDa protein that facilitates the transport of retinol through the circulation to peripheral tissues. The principal source of RBP4 in the body is the liver. Hepatocytes are the primary producers of RBP4; they use the protein to contribute to total-body retinol homeostasis by complexing it with dietary retinol and secreting the retinol-RBP4 holoprotein into the circulation.1 Although hepatocytes are clearly a dominant source of RBP4, cells from other tissues also synthesize the protein. An important secondary source is the adipocyte. Under lean conditions, adipocytes express about one-fifth as much RBP4 mRNA as a hepatocyte;2 in obesity, this expression increases substantially.3