Fig. 1

Schematic representation of microparticle physiology. A. Membrane asymmetry in an unstimulated cell: The plasma membrane lipid bilayer harbors, transmembrane proteins, integrins, and ion channels. The membrane proteins are segregated laterally in lipid rafts. In the unstimulated state, the outer layer of plasma membrane is enriched with phosphatidyl choline (PC) and sphingomyelin (SM) whereas the inner layer is enriched by phosphatidyl ethanolamine (PE) and phosphatidyl serine (PS). The inward directed phosholipid pump flippase is active at this stage and maintains membrane asymmetry of the lipid bilayer. B. Disruption of cytoskeleton and plasma membrane vesiculation. Membrane vesiculation occurs as a response to various stimuli and as a result of cytoskeletal disruption during membrane remodelling. An influx of calcium ions in the cytosol activates cytosolic enzyme calpain disrupting the cytoskeleton, switches on floppase (outward phospholipid pump) and scramblase disrupting the (bidirectional) on the membrane. Floppase redirect PS to the outer leaflet causing exposure of PS—a hallmark of MPs. MPs package cytoskeletal elements, nucleic acids, proteins, lipids and carry the surface markers from the cell of origin resulting in cell shrinkage. Segregation of lipids and proteins into lipid rafts enable specific packaging of contents while membrane vesiculation resulting in diversity in MPs even if the origin is same. C. Diagrammatic representation of a microparticle. Microparticles (MPs) on the surface carries the hallmark of their cells of origin, membrane transporters, tissue factors and exposed phosphatidyl serine (PS). On the inside, MPs harbour selectively packaged cellular contents such as bioactive proteins, lipids and nucleic acids