Understanding the role of cholesterol in cellular biomechanics and regulation of vesicular trafficking: The power of imaging

Cholesterol is an important component of cell plasma membrane. Due to its chemical composition (long rigid hydrophobic chain and a small polar hydroxyl group), it fits most of its structure into the lipid bilayer, where its steroid rings are in close proximity and attracted to the hydrocarbon chains of neighboring lipids. This gives a condensing effect on the packing of lipids in cell membranes creating cholesterol-enriched regions called membrane rafts, which also congregate a lot of specific proteins. Membrane rafts have been shown to work as platforms involved with signaling in diverse cellular processes, such as immune regulation, cell cycle control, membrane trafficking and fusion events. A series of studies in the last two decades have linked many of these functions with the effects of membrane cholesterol content and rafts integrity on actin cytoskeleton organization, as well as its consequences in cellular biomechanics. This was possible by using microscopy techniques before and after manipulation of cholesterol content from cell plasma membrane, using agents that are able to sequester these molecules, such as cyclodextrins. In this review we'll give a personal perspective on these studies and how microscopy techniques were important to unravel the effects of cholesterol on actin and cellular mechanics. We will also discuss how actin and cholesterol contributes to control cell secretion and vesicular trafficking.