Paradoxical impact of cholesterol on lipid packing and cell stiffness.

Cell stiffness or deformability is a fundamental property that is expected to play a major role in multiple cellular functions. It is well known that cell stiffness is dominated by the intracellular cytoskeleton that, together with the plasma membrane, forms a membrane-cytoskeleton envelope. However, our understanding of how lipid composition of plasma membrane regulates physical properties of the underlying cytoskeleton is only starting to emerge. In this review, we first briefly describe the impact of cholesterol on the physical properties of lipid bilayers in model membranes and in living cells, with the dominant effect of increasing the order of membrane lipids and decreasing membrane fluidity. Then, we discuss accumulating evidence that removal of cholesterol, paradoxically, decreases the mobility of membrane proteins and increases cellular stiffness, with both effects being dependent on the integrity of the cytoskeleton. Finally, we discuss emerging evidence that oxidized modifications of low-density lipoproteins (oxLDL) have the same effects on endothelial biomechanical properties as cholesterol depletion, an effect that is mediated by the incorporation of oxysterols into the membrane.