The Ways Of Ectosomes Release And Their Sources Of Membrane In Glia Cells

The phospholipids of inner and outer leaflets of the plasma membrane is asymmetric.Phosphatidylserine is almost exclusively present on the inner leaflet of the plasma membrane.In contrast,phosphatidylserine is almost exclusively present on the outer leaflet of the intracellular membrane system such as endoplasmic reticulum,Golgi complex,and vesicles.Since each of the pro-proteins of secretive molecules has a signal peptide,growth factors and hormones are located in the lumen of the intracellular membrane(such as vesicles)after synthesis.The ectosome is thought to be released by outward budding from the plasma membrane and contains a small portion of the plasma membrane and cytoplasm.Some exosomes have a high level of phosphatidylserine on the surface of the membrane and contain growth factors in the lumen,which are consistent with intracellular vesicles.The reason why the plasma membrane derivative has the same composition and characteristics as intracellular vesicles is still unknown.Using primary cultured glial cells and cytoskeletal depolymerization drugs,we have studied the real-time release of exosomes using live cell dynamic observation techniques.We have found that there are at least three different ways of ectosomes release in glia cells: the first is that multiple ectosomes emerge almost at same time and are released by outward budding from the plasma membrane,the release process is relatively slow,and the vesicles are bigger at the beginning;the second is several ectosomes pumping out one by one from the same site of the plasma membrane rapidly;the third is many ectosomes shedding from the whole surface of a cell at the same time,in which the total vesicle area is estimated to be larger than the plasma membrane.The formation of the latter two types of ectosomes appears to be the extrusion of the inner membrane through a fixed point on the plasma membrane.The outer leaflet of this type of ectosome membrane will have a different composition of phospholipids from that of the plasma membrane-derived ectosomes and contain growth factors in the lumen just as the intracellular vesicles.We have got further evidences to show that intracellular membrane can directly get out of the plasma membrane by dynamic visualizing our ER-tracker labeled cells.Therefore,ectosomes can be divided into two major groups: one is derived from the plasma membrane with phosphatidylserine on the inner leaflet of the membrane,and a part of cytoplasm as the content;the other is derived from the intracellular membrane with phosphatidylserine on the outer leaflet of the membrane,and growth factors as the content.Our results demonstrate a new way of exosomes release and reasonably explain why the ectosomes including microsomes,microparticles,and apoptotic bodies have the characteristics and the contents that are inconsistent with the plasma membrane.