The molecular mechanisms of HDL and associated vesicular trafficking mechanisms to mediate cellular lipid homeostasis.

HDL functions mainly as a cholesterol scavenger, facilitating transport of cholesterol to the liver for conversion to bile acids and secretion into the bile for elimination or recycling in the enterohepatic bile acid cycle. Because of its major function in cholesterol clearance, HDL is in general considered to be atheroprotective. From cell cholesterol can be removed by efflux especially to apoA-I and HDL as extracellular acceptors which transport the cholesterol to the liver for excretion. This process is called reverse cholesterol transport. In this context the ATP binding cassette transporter protein ABCA1 facilitates cellular cholesterol and phospholipid release to apoA-I-containing HDL precursors. In addition ABCA1 plays a role in vesicular lipid transport mechanisms required for HDL particle formation. In general to maintain intracellular lipid homeostasis, sterols and associated lipids move between cellular compartments by vesicular and nonvesicular pathways. However, cholesterol sorting on vesicle formation is poorly understood. This review summarizes the current knowledge of the molecular mechanisms of HDL and associated vesicular trafficking mechanisms to mediate cellular lipid homeostasis.