Fig. 1. Cholesterol metabolism in the brain and alteration in PD. Cholesterol is produced at higher rates in astrocytes than in neurons. Astrocytes are responsible for most of lipoprotein production (HDL-like particles) and these lipoproteins are matured in the brain. Some cholesterol remodeling enzymes such as LCAT, CETP, and PLTP were also found in the brain. ApoE and ApoA-I are major forms of apolipoprotein found in the brain. ApoE is mainly produced in astrocytes. ApoA-I is not synthesized in the brain, but transported from plasma HDL through SR-BI-mediated uptake. LRP1 and LDLR are the major receptors related to ApoE-containing lipoproteins carrying cholesterol between neurons and glia. Cholesterol can be hydroxylated to 24-HC by cholesterol 24-hydroxylase and this form of oxysterol pass lipophilic membranes, such as BBB. Cholesterol is also excreted from neurons through ABC transporters. Neurons express more ABC transporters than astrocytes. The cholesterols released via ABC transporters connect to the ApoA-I-containing lipoproteins present in the CSF, and then removed through LRP1 or SR-BI, which is expressed in brain capillary endothelial cells. CETP, cholesteryl ester transfer protein; LCAT, lecithin:cholesterol acyltransferase; PLTP, phospholipid transfer protein. The schematic art pieces used in this figure were provided by Servier Medical art (). Servier Medical Art by Servier is licensed under a Creative Commons Attribution 3.0 Unported License.
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