Cholesterol removal by human apolipoprotein A-I depends on membrane lipid organization

JAUREGUIBERRY, M. S.; SANCHEZ, S. A.; RIMOLDI. O. J.; GONZALEZ, MARINA CECILIA; TRICERRI, M. A.

Mar del Plata

Congreso; XLIII Congreso Nacional de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2007

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

We previously showed that overexpression of rat Stearoyl CoA Desaturase gen in CHO-K1 cells (SCD) induced a decrease in cholesterol removal mediated by human apolipoproteinA-I compared to control cells (SAIB 2006). We observed here a differential activity of cellular acyl-Coa Cholesterol acyl-transferase in both cells, and expanded our studies on cholesterol solubilization by measuring Laurdan General Polarization measurements (GP) under two-Photon Fluorescence Microscopy. GP value of SCD cells is similar to control, suggesting that the increase in membrane fluidity due to a higher ratio 16:1/16:0 and 18:1/18:0 in phospholipids fatty acids composition, could be compensated by higher contents of membrane-ordering lipids, probably by cholesterol (Chol). Instead, when Chol is removed from the membrane, the GP of control cells increase, while GP of SCD- overexpressing cells decreased. In order to interpret these results, we analyzed GP changes when Chol is removed from Giant Unilamellar Vesicles showing lipid coexistence. In this case, GP decrease when Chol is removed from liquid-ordered domains and increase when Chol is removed from ordered domains. Data suggest that this lipid could be solubilized preferentially from liquid-ordered domains in the control cells, and from more fluid domains in SCD-cells. Results are discussed in terms of lateral phase separation.