The ins and outs of lipid rafts: Functions in intracellular cholesterol homeostasis, microparticles, and cell membranes

Cellular membranes are not homogenous mixtures of proteins; rather, they are segregated into microdomains on the basis of preferential association between specific lipids and proteins. These microdomains, called lipid rafts, are well known for their role in receptor signaling on the plasma membrane and are essential to such cellular functions as signal transduction and spatial organization of the plasma membrane. A number of disease states, including atherosclerosis and other cardiovascular disorders, may be caused by dysfunctional maintenance of lipid rafts. Lipid rafts do not occur only in the plasma membrane but also have been found in intracellular membranes and extracellular vesicles. Here, we focus on discussing newly discovered functions of lipid rafts and microdomains in intracellular membranes-including lipid and protein trafficking from the endoplasmic reticulum, Golgi bodies, and endosomes to the plasma membrane-and we examine lipid raft involvement in the production and composition of extracellular vesicles. Because lipid rafts are small and transient, visualization remains challenging. Future work with advanced techniques will continue to expand our knowledge about the roles of lipid rafts in cellular functioning.