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Apolipoprotein E
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<p>Apolipoprotein E (Apo-E) is a protein involved in the metabolism of fats in the body of mammals. A subtype is implicated in <a href="/facts/Alzheimer%27s_disease/w7Ad6tdg">Alzheimer's disease</a> and <a href="/facts/Cardiovascular_disease/HD420nMv">cardiovascular diseases</a>. It is encoded in humans by the <a href="/facts/Gene/e1swwPY6">gene</a> <i>APOE</i>. </p><p>Apo-E belongs to a family of fat-binding proteins called <a href="/facts/Apolipoprotein/ATjKr0lz">apolipoproteins</a>. In the circulation, it is present as part of several classes of lipoprotein particles, including <a href="/facts/Chylomicron_remnants/YPkGLpI6">chylomicron remnants</a>, <a href="/facts/VLDL/uoQTgwX4">VLDL</a>, <a href="/facts/Intermediate-density_lipoprotein/Kg2DnhPQ">IDL</a>, and some <a href="/facts/High-density_lipoprotein/x7cs1ys9">HDL</a>. Apo-E interacts significantly with the <a href="/facts/LDL_receptor/zsSjTYyb">low-density lipoprotein receptor (LDLR)</a>, which is essential for the normal processing (<a href="/facts/Catabolism/CFWUdphX">catabolism</a>) of <a href="/facts/Triglyceride/BQmjv4A0">triglyceride</a>-rich lipoproteins. In peripheral tissues, Apo-E is primarily produced by the <a href="/facts/Liver/Rtp4Fk2b">liver</a> and <a href="/facts/Macrophages/z7hkQu3o">macrophages</a>, and mediates <a href="/facts/Cholesterol/TnfPlYc1">cholesterol</a> metabolism. In the <a href="/facts/Central_nervous_system/k8I6To97">central nervous system</a>, Apo-E is mainly produced by <a href="/facts/Astrocytes/PBUuHKzS">astrocytes</a> and transports <a href="/facts/Cholesterol/TnfPlYc1">cholesterol</a> to <a href="/facts/Neurons/G7CyTVdH">neurons</a> via Apo-E receptors, which are members of the <a href="/facts/Low_density_lipoprotein_receptor_gene_family/eRGYxfgx">low density lipoprotein receptor gene family</a>. Apo-E is the principal cholesterol carrier in the brain. Apo-E qualifies as a <a href="/facts/Checkpoint_inhibitor/lWqFxuz8">checkpoint inhibitor</a> of the <a href="/facts/Classical_complement_pathway/wtB1DPJn">classical complement pathway</a> by complex formation with activated <a href="/facts/Complement_component_1q/6aDcmcQ3">C1q</a>. </p>