11 The best characterized
microdomain to date is the lipid raft that is enriched in cholesterol and saturated lipids such as sphingolipids. Another microdomain is the caveolae that are specialized uncoated cell surface invaginations. Caveolae are generally viewed as a specialized subtype of lipid rafts. These lipid raft microdomains are organized by the lipid constituents, namely, cholesterol and sphingolipids. Nonlipid raft microdomains have been reported and these appeared to be organized by proteins eg, the actin cytoskeleton, galectin-1, K- and H-ras. The compartmentalization of the plasma membrane into microdomains with specialized structures Proteasome inhibitor and functions suggest that the biogenesis
of each class of membrane vesicles from the plasma membrane is microdomain-specific. Therefore, the membrane lipids of circulating vesicles could reflect the microdomain from which they were derived and may determine their composition and functions. Indeed, membrane of exosomes that originated from endosomes is reportedly enriched in cholesterol and GM1 gangliosides, and this enrichment appears to distinguish exosomes from other membrane vesicles.8 Cholesterol- and GM1 ganglioside-rich membranes are reflective INK1197 manufacturer of lipid rafts that represent the major sites of endocytosis. Exposed phosphatidylserine has been reported to be present on membrane of several extracellular vesicles including exosomes.8
Although monocytes and macrophages DNA ligase endothelial cells are known to secrete vesicles with exposed phosphatidylserines during inflammation, circulating vesicles with exposed phosphatidylserine in a healthy individual is thought to originate primarily from platelets.12 Together, the studies on membrane lipids of circulating vesicles suggest that circulating vesicles could be differentiated by their membrane phospholipid composition, specifically GM1 gangliosides and phosphatidylserines. As these 2 phospholipids are known to bind cholera toxin B chain (CTB) and annexin V (AV), respectively, CTB and AV are potentially ligands for extracting different populations of circulating vesicles. In this study, we tested if circulating plasma membrane vesicles could be fractionated according to their affinity for CTB and AV, and if these fractionated vesicles could be used for discovery of PE biomarkers. The recruitment and enrollment of third trimester PE and matched healthy pregnant women by KK Women’s & Children’s Hospital were approved by the Singhealth Centralized Institutional Review Board (ref no: CIRB 2011/476/D).