Isolation and assay of the Ac-LDL receptor

This chapter discusses various isolation and assay of the Ac-LDL receptor. To effectively study the scavenger cell pathway receptor, one needs a convenient source of receptor, a means for purification of the receptor, and methods for assay of receptor function. An alternative pathway for lipoprotein metabolism has been described in macrophages and endothelial cells from a variety of species. This pathway in the macrophage has been termed the scavenger cell pathway. The macrophages are incubated in vitro with chemically modified lipoproteins such as acetylated low-density lipoprotein (LDL), massive accumulation of cholesteryl esters results. Cells treated in this manner deposit the accumulated lipid as free droplets in the cytoplasm, taking on the appearance of the foam cells of atherosclerotic lesions. Isolated foam cells from atherosclerotic lesions of rabbits readily metabolize acet acetylated LDL through this receptor. The endothelial cells of the liver rapidly clear any modified lipoproteins injected into the circulation. The uptake of the modified lipoproteins is mediated by a specific membrane protein. A variety of lipoprotein ligands, and at least one non lipoprotein ligand, compete for binding to the receptor.