Lipoproteins carry cholesterol, triglycerides and other lipids through the blood. Apolipoproteins such as APOB, APOA1 and APOE organize lipoprotein particles (chylomicrons, VLDL, LDL and HDL) and mediate their binding to receptors including LDLR, LRP1, VLDLR and the HDL receptor SCARB1. Lipoprotein metabolism is regulated by enzymes such as lipoprotein lipase (LPL), LCAT and CETP, by PCSK9, and by ABCA1 mediated cholesterol efflux. Disrupted lipoprotein signaling leads to high LDL cholesterol and atherosclerosis and is also linked to Alzheimer's disease through APOE.