LDL R (Low Density Lipoprotein Receptor) is a widely expressed cell surface scavenger receptor. LDL R binds ApoB and ApoE, the apolipoproteins of low- and very low-density lipoproteins (LDL and VLDL), respectively. Hepatocyte LDL R is responsible for endocytosis and clearing of most plasma LDL cholesterol. At the low pH of the endocytic vesicle, it dissociates, allowing degradation of LDL and recycling of LDL R to the cell surface. Lack of LDL R expression or function causes familial hypercholesterolemia (FH). The protease PCSK9 can also cause increased plasma cholesterol by promoting LDL R degradation rather than recycling to the cell surface.