Cholesterol removal by High Density Lipoprotein particles depends on membrane lipids lateral organization

SANCHEZ, S. A.; TRICERRI, M. A.; GRATTON, E.

Monteveo, Uruguay

Congreso; 5to Congreso de Biofísica del Cono Sur.; 2007

Sociedad Biofisica del Cono Sur

Extensive epidemiological research supports a key role of human high density lipoproteins (HDL) and their major apolipoprotein A-I (apoA-I) in the prevention of Cardiovascular Disease. An excess of free cholesterol (FC) is toxic to cells, and therefore several mechanisms triggering its clearance have been addressed. One of them involves cholesterol removal mediated by HDL. Accessibility of FC to HDL may depend on the domains it is located at the plasma membrane, either in regions rich in unsaturated phospholipids or in domains containing high amounts of FC and sphingomyelin, known as “lipid-rafts”. In this report Laurdan Generalized Polarization and two-photon microscopy were used to quantify FC removal from different pools in the bilayer of Giant Unilamellar Vesicles (GUVs).  GUVs made of POPC and FC were observed after incubation with reconstituted particles containing apolipoprotein A-I and POPC (78Å diameter rHDL). At the same time, Fluorescence Correlation Spectroscopy (FCS) data show an increase in the rHDL size during the incubation period. GUVs made of two “raft-like” mixtures (DOPC:DPPC:FC 1:1:1 and POPC:SPM:FC 6:1:1) were used to model liquidordered/ liquiddisordered phase coexistence. We conclude that rHDL preferentially remove cholesterol from the more fluid phases. These data and their extrapolation to in vivo systems show the significant role phase separation plays in the regulation of cholesterol homeostasis.