Article révisé par les pairs
Résumé : Adequate membrane fluidity is required for a variety of key cellular processes and in particular for proper function of membrane proteins. In most eukaryotic cells membrane fluidity is known to be regulated by fatty acids desaturation and cholesterol although some cells, such insect cells, are almost devoid of sterols synthesis. We show here that insect and mammalian cells present similar microviscosity at their respective physiological temperature. In order to investigate how both sterols and phospholipids control fluidity homeostasis we quantified the lipidic composition of insect SF9b and mammalian HEK 293T cells under normal or sterol-modified condition. As expected, insect cells show minimal sterols compared to mammalian cells. A major difference is also observed in phospholipid content as the ratio of phosphatidylethanolamine (PE) to phosphatidylcholine (PC) is inverted (four times higher in SF9 cells). In vitro studies in liposomes confirm that both cholesterol and PE can increase rigidity of the bilayer, suggesting that both can be used by cells to maintain membrane fluidity. We then show that exogenously increasing the cholesterol amount in SF9 membranes leads to a significant decrease in PE/PC ratio while decreasing cholesterol in HEK 293T cells using statin treatment leads to an increase in the PE/PC ratio. In all cases the membrane fluidity is maintained, indicating that both cell types combine regulation by sterols and phospholipids to control proper membrane fluidity.