Apolipoprotein AIV, Human Plasma

Apolipoprotein AIV (Apo AIV) is a glycoprotein synthesized by the human intestine. Synthesis appears to be stimulated by the absorption of high density lipoproteins that are rich in triglycerides rather than by the uptake or re-esterification of fatty acids. The formation of chylomicrons acts as a signal for the induction of Apo AIV synthesis a signal enhanced by a factor from the ileum, probably PYY. Apo AIV alters the activity of the key enzymes (LPL and LCAT) of lipoprotein metabolism and cholesterol efflux from extra hepatic tissues. Also, since stimulation of intestinal synthesis and secretion by lipid absorption are rapid, Apo AIV likely plays a role in the short-term regulation of food intake. Other evidence suggests involvement in the long-term regulation of both food intake and body weight. Chronic ingestion of high-fat diet blunts the intestinal Apo AIV response to lipid feeding and, consequently, may explain why the chronic ingestion of a high-fat diet predisposes both animals and humans to obesity. It is required for efficient activation of lipoprotein lipase by ApoC-II and is a potent activator of LCAT. Apo AIV is an amphipathic protein that can emulsify lipids and has been linked to protective roles against cardiovascular disease and obesity.