Cholesterol homeostasis in neurons and glial cells.

Cholesterol is highly enriched in the brain compared to other tissues. Essentially all cholesterol in the brain is synthesized endogenously since plasma lipoproteins are unable to cross the blood-brain barrier. Cholesterol is transported within the central nervous system in the form of apolipoprotein E-containing lipoprotein particles that are secreted mainly by glial cells. Cholesterol is excreted from the brain in the form of 24-hydroxycholesterol. Apolipoprotein E and cholesterol have been implicated in the formation of amyloid plaques in Alzheimer's disease. In addition, the progressive neurodegenerative disorder Niemann-Pick C disease is characterized by defects in intracellular trafficking of cholesterol.