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

M. SOLEDAD JAUREGUIBERRY; SUSANA A. SANCHEZ; OMAR J. RIMOLDI; MARINA C. GONZALEZ; M. ALEJANDRA TRICERRI

Mar del Plata, Buenos Aires, Argentina

Congreso; 43 th Annual meeting- XLIII Reunión anual; 2007

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

  We previously showed that overexpression of rat Stearoyl CoA Desaturase gene (SCD) in CHO-K1 cells induced a decrease in cholesterol (Chol) removal mediated by human apolipoproteinA-I, compared to control cells (SAIB 2006). Here we observed a differential activity of cellular acyl-CoA cholesterol acyl-transferase (ACAT) both in SCD and control cells. Furthermore, we enlarged our studies on Chol solubilization by measuring Laurdan General Polarization (GP) under two-Photon Fluorescence Microscopy. The GP value of SCD cells was similar to that of control cells, suggesting that the increase in membrane fluidity due to higher 16:1/16:0 and 18:1/18:0 ratios in phospholipids fatty acids composition, might be compensated by higher contents of membrane-ordering lipids, probably Chol. However, when Chol is removed from the membrane the GP of control cells increases, while it decreases in SCD cells. 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 decreased when Chol was removed from more fluid domains, but it increased when Chol was removed from ordered domains. Data suggest that Chol could be solubilized preferentially from liquid-ordered domains in control cells, and from more fluid domains in SCD-cells. Results are discussed in terms of lateral phase separation.