Apolipoprotein D (ApoD)

Apolipoprotein D is a 29-kDa glycoprotein, encoded by the APOD gene, and structurally classified as a member of the lipocalin family. Unlike most canonical apolipoproteins, which are produced in the liver, ApoD is found primarily in the brain, testes, and other tissues, and is a major component of high-density lipoprotein (HDL) in plasma. Its characteristic eight-stranded β-barrel fold forms a hydrophobic pocket capable of binding a diverse range of small hydrophobic ligands, including steroid hormones, bilirubin, arachidonic acid, retinoic acid, cholesterol, and sphingolipids. ApoD exerts antioxidant effects by directly neutralizing lipid hydroperoxides and is implicated in lipid transport and remodeling, modulation of oxidative stress, neural maintenance and repair, and protection against age-related and metabolic diseases. Increased expression or deposition of ApoD is observed in atherosclerotic plaques, neurodegenerative diseases (such as Alzheimer’s), aging brains, and diverse tumors, positioning ApoD both as a functional molecule in metabolism and homeostasis, and as a potential biomarker for pathological states. There are currently no approved drugs that directly target ApoD as a primary mechanism of action.

Other names

Apolipoprotein DAPODApo-DApoDapo-Dapolipoprotein D

ApoD exerts an antioxidant effect on lipids, particularly through its methionine residues (e.g., Met93) which react with lipid hydroperoxides, thereby protecting lipoproteins and membranes from oxidative damage. It is also involved in lipid transport and binding, transporting small hydrophobic ligands like steroid hormones, arachidonic acid, bilirubin, cholesterol, and sphingomyelin. This transport modulates local signaling and lipid homeostasis, contributing to intracellular and extracellular lipid management at cellular and tissue levels.