Minor apolipoprotein mainly associated with HDL and to a lesser extent with VLDL. May also be associated with chylomicrons. Important determinant of plasma triglyceride (TG) levels by both being a potent stimulator of apo-CII lipoprotein lipase (LPL) TG hydrolysis and an inhibitor of the hepatic VLDL-TG production rate (without affecting the VLDL-apoB production rate) (By similarity). Activates poorly lecithin:cholesterol acyltransferase (LCAT) and does not enhance efflux of cholesterol from macrophages. Binds heparin (PubMed:17326667). Interacts with GPIHBP1 (PubMed:17997385). Interacts with SORL1; this interaction leads to APOA5 internalization and sorting either to lysosomes and degradation, or to the trans-Golgi network (PubMed:17326667, PubMed:18603531). In the presence of SORL1, internalized to early endosomes, sorted in a retrograde fashion to late endosomes, from which a portion is sent to lysosomes and degradation, another portion is sorted to the trans-Golgi network. Liver and plasma. Up-regulated by PPARA agonists, which are used clinically to lower serum TG (such as fibrates). Phosphorylated by FAM20C in the extracellular medium. Three common alleles are known: allele APOA5*1, APOA5*2 and APOA5*3. The APOA5*2 haplotype, which consists of 3 non-coding SNPs, is present in approximately 16% of Caucasians and is associated with increased plasma triglyceride concentrations. APOA5*3 haplotype is defined by the rare Ser-19-Trp substitution. Together, the APOA5*2 and APOA5*3 haplotypes are found in 25 to 50% of African Americans, Hispanics, and Caucasians. Disease susceptibility is associated with variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Induced in early phase of liver regeneration. Belongs to the apolipoprotein A1/A4/E family. It is uncertain whether Met-1 or Met-4 is the initiator. Truncated C-terminus.