Submitted on October 18, 2006
Revised on April 30, 2007
Accepted on May 7, 2007
Interaction of high density lipoprotein particles with membranes containing cholesterol
Susana A. Sanchez, Maria A. Tricerri, and Enrico Gratton
Biomedical Engineering, University of California at Irvine, Irvine, California 92697-2715
Corresponding Author: susanas{at}uci.edu
In this study, cholesterol (FC) efflux mediated by human high-density lipoproteins (HDL) was investigated using fluorescence methodologies. The accessibility of FC to HDL may depend on whether it is located in regions rich in unsaturated phospholipids or in domains containing high levels of FC and sphingomyelin, known as “lipid-rafts”. LAURDAN Generalized Polarization and two-photon microscopy was 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). 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. Through these experiments we concluded that rHDL preferentially removes 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.
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