ATP-binding cassette A1 protein and HDL homeostasis.

For three decades, low-density lipoprotein (LDL) dominated research into cholesterol metabolism and atherosclerosis, whereas scant attention was paid to high-density lipoprotein (HDL), an equally important risk factor for cardiovascular disease. This low interest reflected the lack of knowledge about physiological HDL receptors. As a result, our understanding of HDL-cell interactions failed to develop alongside that of LDL, and mechanisms through which atheroprotective HDL promoted clearance of cholesterol from peripheral cells remained poorly-defined. Interest was kindled with the recognition that scavenger receptor class B, type I is the cell-surface protein in hepatocytes and steroidogenic tissues which selectively extracts cholesteryl esters from HDL. Greater impetus still was given by the discovery that mutations in the gene encoding the ATP-binding cassette transporter, class A1 (ABCA1) are the cause of Tangier disease, a rare recessive disorder with near-absent plasma HDL. The ABCA1 transmembrane protein is crucial for efficient efflux of cellular cholesterol and HDL maturation and has emerged as a promising therapeutic target for cardiovascular disease. The hope is that new drugs, regulating ABCA1 activity and HDL homeostasis, will accelerate cholesterol efflux from lipid-laden foam cells and thus promote regression of atherosclerotic lesions.