| Abstrakt: |
Mammalian somatic cells do not catabolize cholesterol and therefore must export it to maintain sterol homeostasis at the levels of cells and whole body. This mechanism may reduce intracellular cholesterol accumulated in excess, and thereby contribute to prevention or cure of atherosclerotic vascular lesions. High-density lipoprotein (HDL) plays a central role in this reaction by removing cholesterol from cells and transporting it to the liver, the major cholesterol catabolic site to bile acids. Two independent mechanisms are identified for the cellular cholesterol release. One is non-specific diffusion-mediated 'efflux' of cell cholesterol that is trapped by various extracellular acceptors including lipoproteins. Cholesterol acyl esterification on HDL provides a driving force for net outflow of cell cholesterol in this pathway, and some cellular factors may also enhance this reaction. The other is apolipoprotein-mediated process to generate new HDL particles by removing cellular phospholipid and cholesterol. This reaction is mediated with a membrane protein, ATP binding cassette transporter (ABC) A1, and helical apolipoproteins recruit cellular phospholipid and cholesterol to assemble HDL particles. The reaction is composed of two elements: assembly of HDL particles with phospholipid by apolipoprotein, and cholesterol enrichment in this HDL. ABCA1 is essential for the former step, and apolipoproteins are dissociated from HDL or secreted from cells and interact with ABCA1 in their free form. The latter step requires other cellular factors, such that ABCA1 mediates production of cholesterol-rich and cholesterol-poor HDL while ABCA7 produces only cholesterol-poor HDL. [ABSTRACT FROM AUTHOR] |
