Exosomal lipids from membrane organization to biomarkers: Focus on an endolysosomal-specific lipid

The term extracellular vesicles (EVs) has been recommended to describe various membrane-bound vesicles secreted by most living cells and found in various biological fluids. They gained growing interest as mediators of cell-cell communication and for their roles in different patho-physiological processes. In addition, they were recently considered as disease biomarkers and new drug delivery systems. However, it is still difficult to link a biological function to a specific EV population among the heterogenous EV mixture secreted in the extracellular space due to limitations of optimal isolation methods. EV classification according to their size as small (\textless200 nm) and large (\textgreater200 nm) vesicles is also completed by the identification of selected proteins, nucleic acids and lipids. In this review, we summarized briefly knowledge about the composition and role of EV lipids that received less attention compared to their protein and nucleic acid content. Lipids are not only essential structural components of EVs, but can give important information on their biogenesis. Especially, we discussed our recent data showing the utility of bis(monoacylglycero)phosphate (BMP), a specific endolysosomal lipid marker, that could sign the endosomal origin of small EVs, classically named as exosomes.