The ins and outs of lipid rafts: functions in intracellular cholesterol homeostasis, microparticles, and cell membranes: Thematic Review Series: Biology of Lipid Rafts

Abstract

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 (PM) and are essential to such cellular functions as signal transduction and spatial organization of the PM. 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 PM but also have been found in intracellular membranes and extracellular vesicles (EVs). Here, we focus on discussing newly discovered functions of lipid rafts and microdomains in intracellular membranes, including lipid and protein trafficking from the ER, Golgi bodies, and endosomes to the PM, and we examine lipid raft involvement in the production and composition of EVs. 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.

Keywords: cholesterol trafficking; exosomes; extracellular vesicles; microdomains.

Fig. 1.

Ins and outs of cellular cholesterol transport. EN, endosomes; EX, exosome; LE, late endosome; LY, lysosome; MVE, multivesicular endosome; NUC; nucleus; SE, sorting endosome; TG, trans-Golgi; SREBP-NE, SREBP-nuclear element. Cholesterol movement (solid arrows); activation (solid arrows with black dots); SREBP movement (dashed arrow).