Mast cell- and dendritic cell-derived exosomes display a specific lipid composition and an unusual membrane organization

Abstract

Exosomes are small vesicles secreted from multivesicular bodies, which are able to stimulate the immune system leading to tumour cell eradication. We have analysed lipids of exosomes secreted either upon stimulation from rat mast cells (RBL-2H3 cells), or constitutively from human dendritic cells. As compared with parent cells, exosomes displayed an enrichment in sphingomyelin, but not in cholesterol. Phosphatidylcholine content was decreased, but an enrichment was noted in disaturated molecular species as in phosphatidylethanolamines. Lyso(bis)phosphatidic acid was not enriched in exosomes as compared with cells. Fluorescence anisotropy demonstrated an increase in exosome-membrane rigidity from pH 5 to 7, suggesting their membrane reorganization between the acidic multivesicular body compartment and the neutral outer cell medium. NMR analysis established a bilayer organization of exosome membrane, and ESR studies using 16-doxyl stearic acid demonstrated a higher flip-flop of lipids between the two leaflets as compared with plasma membrane. In addition, the exosome membrane exhibited no asymmetrical distribution of phosphatidylethanolamines. Therefore exosome membrane displays a similar content of the major phospholipids and cholesterol, and is organized as a lipid bilayer with a random distribution of phosphatidylethanolamines. In addition, we observed tight lipid packing at neutral pH and a rapid flip-flop between the two leaflets of exosome membranes. These parameters could be used as a hallmark of exosomes.

Exosomes as intercellular signalosomes and pharmacological effectors

“…Subsequently, the repartition of proteins between the two leaflets of the plasma membrane should be maintained in the ILVs, which progressively accumulate during endosome maturation. However phospholipid asymmetry may be not preserved during ILV formation since exosomes appear to have a similar lipid composition between the two membrane leaflet [8], consistent with the presence of a phospholipid scramblase [9].Thus, late endosomes can accumulate up to hundred intraluminal vesicles (ILVs) [10]. Similar conclusion can be drawn from observations performed in the mast cell line RBL-2H3 [9].…”

“…However LBPA by itself when added to a lipid mixture mimicking the composition of the MVB membrane can induce internal budding of small vesicles from large liposomes [14]. Exosomes appeared not to be enriched in LBPA as compared with parental cells [8,25]. By remaining on the MVB membrane, LBPA might reach the critical concentration allowing its fusogenic properties [26] with subsequent fission of the nascent intralumenal vesicle (ILV).…”

“…A common feature is an enrichment in sphingomyelins ranging from 1.3 times (erythrocytes) to 2.3 times (B lymphocytes) [49]. Cholesterol is enriched only in Blymphocyte-derived exosomes and phosphatidylserine only in dendritic cell-derived exosomes [49], whereas mast cell-derived exosomes are enriched in lysophosphatidylcholine [8]. The phosphatidylcholines and phosphatidylethanolamines present in exosomes are enriched in saturated fatty acids comparatively to the parent cell.…”

Cell-Cell Communication Via Extracellular Membrane Vesicles and Its Role in the Immune Response

“…The disparity between inside and outside leaflets in the phospholipid composition is, however, less distinct in the exosomal membrane. The flipping of phospholipids from inside to outside (and vice versa) takes place frequently and the asymmetry of the membrane exhibited by the plasma membrane is not restored (Laulagnier et al, 2004). The exosomal membrane is enriched in sphingomyelin, phosphatidylserine, glycolipid GM3 and phosphoethanolamine.…”

Therapeutic biomaterials based on extracellular vesicles: classification of bio‐engineering and mimetic preparation routes

“…that self-assemble in higher-order structures with tunable composition (bottom-up nanotechnology). Top-down products differ from natural EVs in terms of micro-structure and biochemical composition, since they are formed from cell fragments: the characteristic membrane microdomains [24] (lipid rafts) and associated pools of surface markers (especially tetraspanins) are absent, and the minimal cytoskeleton is not present.…”