Tissue-factor–bearing microvesicles arise from lipid rafts and fuse with activated platelets to initiate coagulation

Abstract

Tissue factor (TF) circulates in plasma, largely on monocyte/macrophage-derived microvesicles that can bind activated platelets through a mechanism involving P-selectin glycoprotein ligand-1 (PSGL-1) on the microvesicles and P-selectin on the platelets. We found these mi-crovesicles to be selectively enriched in both TF and PSGL-1, and deficient in CD45, suggesting that they arise from distinct membrane microdomains. We investigated the possibility that mi-crovesicles arise from cholesterol-rich lipid rafts and found that both TF and PSGL-1, but not CD45, localize to lipid rafts in blood monocytes and in the mono-cytic cell line THP-1. Consistent with a raft origin of TF-bearing microvesicles, their shedding was significantly reduced with depletion of membrane cholesterol. We also evaluated the interaction between TF-bearing microvesicles and plate-lets. Microvesicles bound only activated platelets, and required PSGL-1 to do so. The microvesicles not only bound the activated platelets, they fused with them, transferring both proteins and lipid to the platelet membrane. Fusion was blocked by either annexin V or an antibody to PSGL-1 and had an important functional consequence: increasing the proteolytic activity of the TF-VIIa complex. These findings suggest a mechanism by which all of the membrane-bound reactions of the coagulation system can be localized to the surface of activated platelets.

Microglia convert aggregated amyloid-β into neurotoxic forms through the shedding of microvesicles

“…Notably, MVs have a distinct repertoire of lipids not only compared with exosomes (our unpublished data) 41 but also to the plasma membrane of origin. Indeed, MVs are enriched in cholesterol, sphingomyelin and ceramide, and contain lipid raft elements, 28 including GM1 and GM3 gangliosides and flotillin-2. 42 Accordingly, artificial liposomes, composed of the main phospholipids of the plasma membrane, neither induce fibril solubilization nor promote Ab neurotoxicity.…”

“…This sorting mechanism may be consistent with the proposed role of lipid rafts in setting up platforms to concentrate into MVs proteins destined to secretion. 28,56 Finally, processing of Ab 1-42 to Ab 1-40 may even proceed within MVs. Indeed, previous evidence showed that neuron-derived EMVs contain some components of the gsecretase complex, 57 whereas the insulin-degrading enzyme, which proteolyzes Ab 1-42 and Ab 1-40, has been detected among cargo proteins of microglial EMVs.…”

“…MVs are shed by microglia upon ATP activation 27 and originate from lipid rafts, 28 where the ATP receptor P2X 7 is localized. 29 Shed MVs selectively accumulate various cellular components, including soluble and integral proteins, lipids and nucleic acids and their composition reflects the activation state of donor microglia.…”

Microvesicles released from Giardia intestinalis disturb host-pathogen response in vitro

“…We investigated whether the disruption of lipid rafts from trophozoite plasma membranes affected MV formation, as it was defined previously (Del Conde et al, 2005). To assess this effect, we treated trophozoite Results are representative of two independent experiments.…”

“…Different reports have shown that cholesterol should influence the lipid raft microdomains on the membrane that participate in MV formation. An interesting report by Del Conde et al (2005), demonstrated that the coagulation process is dependent of the transference of tissue factors released from monocyte-MVs to platelets. This release is dependent of lipid raft microdomains.…”