Apolipoprotein A4 (APOA4) is a secreted protein that belongs to the apolipoprotein A1/A4/E family. Apoa-IV is a major component of HDL and chylomicrons. APOA4 is secreted into circulation on the surface of newly synthesized chylomicron particles. APOA4 play a role in the regulation of appetite and satiety in rodent models. APOA4 involved in chylomicrons and VLDL secretion and catabolism and required for efficient activation of lipoprotein lipase by ApoC-II. In addition, APOA4 is a potent activator of lecithin-cholesterol acyltransferase in vitro.