Human Apolipoprotein D (APOD) Protein

Background

Apolipoprotein D (APOD) is a unique member of the apolipoprotein family, functioning as a lipid transporter in the plasma and extracellular fluids. Unlike other apolipoproteins, APOD is not synthesized in the liver but is predominantly produced in the central nervous system (CNS), liver, kidneys, and mammary glands. APOD associates with high-density lipoprotein (HDL) and contributes to cholesterol transport, as well as lipid metabolism. Structurally, APOD is classified as a member of the lipocalin family, which binds small hydrophobic molecules, such as arachidonic acid and cholesterol. It has a prominent role in antioxidant defense by neutralizing reactive oxygen species (ROS) and reducing oxidative stress, particularly in the CNS. APOD is upregulated during injury and neurodegenerative conditions, including Alzheimer’s disease, Parkinson’s disease, and stroke, indicating its neuroprotective function. Elevated levels of APOD are also found in cancer, cardiovascular disease, and diabetes, suggesting its role in cellular stress responses. APOD may regulate inflammation, cellular lipid homeostasis, and signal transduction, making it a promising biomarker and therapeutic target in age-related disorders, metabolic syndromes, and neurological diseases.