Scavenger receptor BI: A multi-purpose player in cholesterol and steroid metabolism

Figure 1 Schematic representation of the scavenger receptor class B type I protein. Structural elements include a heavily N-glycosylated and fatty-acylated protein backbone that contains a large extracellular loop, two transmembrane domains, and short intracellular N-terminal and C-terminal domains.

Figure 2 Overview of the diverse role of scavenger receptor class B type I in cholesterol and steroid metabolism in mice. (1) In liver, scavenger receptor class B type I (SR-BI) mediates the selective uptake of cholesterol (C; yellow) from high-density lipoprotein (HDL) that is subsequently converted to bile acids (BA; green) for biliary excretion; (2) HDL-associated cholesteryl esters are taken up via SR-BI in adrenocortical cells, which is efficiently coupled to the synthesis and subsequent secretion of glucocorticoids (GC; blue) into plasma; (3) SR-BI binds apolipoprotein (apo)B-containing lipoproteins, i.e. chylomicrons and very low density lipoprotein (VLDL), in liver and macrophages, which contributes to macrophage foam cell formation; (4) SR-BI is able to efflux cholesterol from macrophages to small HDL particles, which inhibits foam cell formation; and (5) HDL can interact with platelets, in part via the direct action of SR-BI, to modulate platelet aggregation and susceptibility to thrombosis.