Mediates the binding, internalization, and catabolism of lipoprotein particles. It can serve as a ligand for the LDL (apo B/E) receptor and for the specific apo-E receptor (chylomicron remnant) of hepatic tissues. Defects in APOE are a cause of hyperlipoproteinemia type 3 (HLPP3); also known as familial dysbetalipoproteinemia. Individuals with HLPP3 are clinically characterized by xanthomas, yellowish lipid deposits in the palmar crease, or less specific on tendons and on elbows. The disorder rarely manifests before the third decade in men. In women, it is usually expressed only after the menopause. The vast majority of the patients are homozygous for APOE*2 alleles. More severe cases of HLPP3 have also been observed in individuals heterozygous for rare APOE variants. The influence of APOE on lipid levels is often suggested to have major implications for the risk of coronary artery disease (CAD). Individuals carrying the common APOE*4 variant are at higher risk of CAD. Genetic variations in APOE are associated with Alzheimer disease type 2 (AD2). It is a late-onset neurodegenerative disorder characterized by progressive dementia, loss of cognitive abilities, and deposition of fibrillar amyloid proteins as intraneuronal neurofibrillary tangles, extracellular amyloid plaques and vascular amyloid deposits. The major constituent of these plaques is the neurotoxic amyloid-beta-APP 40-42 peptide (s), derived proteolytically from the transmembrane precursor protein APP by sequential secretase processing. The cytotoxic C-terminal fragments (CTFs) and the caspase-cleaved products such as C31 derived from APP, are also implicated in neuronal death. The APOE*4 allele is genetically associated with the common late onset familial and sporadic forms of Alzheimer disease. Risk for AD increased from 20% to 90% and mean age at onset decreased from 84 to 68 years with increasing number of APOE*4 alleles in 42 families with late onset AD. Thus APOE*4 gene dose is a major risk factor for late onset AD and, in these families, homozygosity for APOE*4 was virtually sufficient to cause AD by age 80. The mechanism by which APOE*4 participates in pathogenesis is not known. Defects in APOE are a cause of sea-blue histiocyte disease (SBHD); also known as sea-blue histiocytosis. This disorder is characterized by splenomegaly, mild thrombocytopenia and, in the bone marrow, numerous histiocytes containing cytoplasmic granules which stain bright blue with the usual hematologic stains. The syndrome is the consequence of an inherited metabolic defect analogous to Gaucher disease and other sphingolipidoses. Defects in APOE are a cause of lipoprotein glomerulopathy (LPG). LPG is an uncommon kidney disease characterized by proteinuria, progressive kidney failure, and distinctive lipoprotein thrombi in glomerular capillaries. It mainly affects people of Japanese and Chinese origin. The disorder has rarely been described in Caucasians. Belongs to the apolipoprotein A1/A4/E family. Note: This description may include information from UniProtKB.
Protein type: Secreted, signal peptide; Secreted; Lipid binding protein
Chromosomal Location of Human Ortholog: 19q13.2
Cellular Component: Golgi apparatus; extracellular space; dendrite; early endosome; extracellular region; chylomicron; extrinsic to external side of plasma membrane; membrane; cell soma; cytoplasm; late endosome; plasma membrane; nucleus
Molecular Function: antioxidant activity; lipid transporter activity; heparin binding; identical protein binding; protein binding; protein homodimerization activity; low-density lipoprotein receptor binding; metal chelating activity; cholesterol transporter activity; hydroxyapatite binding; beta-amyloid binding; phospholipid binding; lipid binding; tau protein binding
Biological Process: phototransduction, visible light; negative regulation of MAP kinase activity; lipoprotein catabolic process; cGMP-mediated signaling; positive regulation of axon extension; positive regulation of membrane protein ectodomain proteolysis; axon regeneration in the peripheral nervous system; synaptic transmission, cholinergic; intracellular transport; oligodendrocyte differentiation; negative regulation of neuron apoptosis; cholesterol catabolic process; long-chain fatty acid transport; cholesterol metabolic process; regulation of Cdc42 protein signal transduction; positive regulation of nitric-oxide synthase activity; negative regulation of blood coagulation; lipoprotein metabolic process; positive regulation of lipid biosynthetic process; regulation of axon extension; negative regulation of blood vessel endothelial cell migration; maintenance of cellular localization; response to reactive oxygen species; cholesterol homeostasis; response to ethanol; positive regulation of cGMP biosynthetic process; lipoprotein biosynthetic process; negative regulation of endothelial cell proliferation; protein import; nitric oxide mediated signal transduction; regulation of neuronal synaptic plasticity; cell death; response to dietary excess; vasodilation; response to insulin stimulus; positive regulation of low-density lipoprotein receptor catabolic process; phospholipid efflux; retinoid metabolic process; negative regulation of cholesterol biosynthetic process; aging; receptor-mediated endocytosis; response to retinoic acid; negative regulation of lipid biosynthetic process; cholesterol efflux; cytoskeleton organization and biogenesis; cellular calcium ion homeostasis; G-protein coupled receptor protein signaling pathway; triacylglycerol metabolic process; reverse cholesterol transport; fatty acid homeostasis; negative regulation of inflammatory response; artery morphogenesis
SS: The number of records in which this modification site was determined using site-specific methods. SS methods include amino acid sequencing, site-directed mutagenesis, modification site-specific antibodies, specific MS strategies, etc.