Members of this family promote cholesterol efflux from macrophage cells. They are present in various lipoprotein complexes, including HDL, LDL and VLDL. The apoprotein is secreted by a microsomal triglyceride transfer protein (MTTP)-dependent mechanism, probably as a VLDL-associated protein that is subsequently transferred to HDL [1].

1: ApoO, a novel apolipoprotein, is an original glycoprotein up-regulated by diabetes in human heart. Lamant M, Smih F, Harmancey R, Philip-Couderc P, Pathak A, Roncalli J, Galinier M, Collet X, Massabuau P, Senard JM, Rouet P; J Biol Chem. 2006;281:36289-36302. PMID:16956892