A decade of intense investigation has established a central role for lipoprotein receptors in regulating plasma cholesterol traffic. These receptors bind cholesterol-carrying lipoproteins and transport them into cells by receptor-mediated endocytosis. The receptor for low density lipoprotein (LDL) was the first discovered; it has been purified and its structure characterized. The LDL receptor was described in cultured human fibroblasts; identical receptors are now known to function in liver as well as in extrahepatic tissues. Operationally, the LDL/LDL receptor system can be considered the primary transport mechanism for endogenous cholesterol. Dietary cholesterol, on the other hand, is transported from the intestine in chylomicron remnants, which enter hepatocytes via distinct chylomicron remnant receptors. The chylomicron remnant/remnant receptor system is to exogenous cholesterol transport as the LDL/LDL receptor system is to endogenous cholesterol transport. In this article, we review recent developments in this rapidly advancing field.
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