Understanding plasma membrane organization and cellular homeostasis relationship

SANCHEZ, S. A.; JAUREGUIBERRY, M. S.; RIMOLDI. O. J.; FINARELLI, G. S.; TRICERRI, M. A.

San Diego, California

Congreso; 56th Annual Meeting of the Biophysical Society; 2012

US Biophysical Society

Plasma membrane (PM) is a dynamic barrier which translates the outside signals to the cell. We are interested in how changes in the PM (composition, organization etc) influence cell homeostasis and vice versa. For this purpose we constructed two permanent Chinese Hamster Ovary (CHO KI) cell lines with permanent modifications in the PM lipid composition. The first line (SCD), over expressing Stearoyl CoA desaturase resulted in an increase of monounsaturated fatty acids at the PM phospholipids. The second cell line over expressing both Δ5 and Δ 6 desaturases (Δ 5/ Δ 6-cells), turned into a rise of poly unsaturated fatty acids and lower ratio cholesterol/ phospholipids. Laurdan Generalized Polarization (Laurdan GP) microscopy and two-photon excitation, used to measure membrane packing (fluidity) in the PM of alive cells, showed for the SCD similar fluidity than control cells, indicating a metabolic compensation due to a relative increase in cholesterol content induced by the mutation. For the second cell line (Δ5/Δ6-cells) this compensation process did not occurred and the membrane fluidity increased compared with the control. The MTT (3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyl tetrazolium bromide) reduction assay showed an increased viability in the two mutant cells as compared with the control. Cholesterol removal mediated by apolipoprotein A-I was measured by scintillation counting and showed to be reduced both cell lines. Together, our results indicate that PM lipid composition determines cholesterol partition, the feasibility of cholesterol to be exported and thus regulates its toxicity and homeostasis.