A research group led by Designated Assistant Professor Tomokazu Yasuda of Osaka University Graduate School, in collaboration with Gifu University and Tohoku University Graduate School, has discovered that lipid membranes that wrap microvesicles (exosomes) with a diameter of about 100 nm produced from cells have different physical properties. This is the first time in the world that it is composed of an asymmetric bilayer and that there are regions where fluctuations are suppressed, such as lipid rafts, which are responsible for signal transduction in the cell membrane.
Exosomes secreted from cells circulate in the body and carry the message substances they contain to target tissues.It is attracting attention as a carrier of intercellular communication in various life phenomena such as determination of cancer metastasis destination, fertilization, and aging.However, there are many unclear points about the mechanism by which target cells are selected from a myriad of cells, and research is currently underway around the world.
In this study, the research group precisely analyzed fluorescence information (fluorescence anisotropy, fluorescence lifetime, etc.) obtained by incorporating fluorescent molecules into the lipid membrane of exosomes.As a result, it was found that up to about half of the outer surface of the lipid bilayer surrounding exosomes is a lipid raft-like region (a small area where proteins, glycolipids, etc. aggregate) that supports signal transduction in cells.In addition, the bilayer lipid membrane that wraps the exosomes, contrary to previous expectations, had an "asymmetry" in which the physical properties of the front and back surfaces of the lipid bilayer differed.We believe that this asymmetry may determine the in vivo activity and lifespan of exosomes.
In the future, these findings will facilitate the elucidation of the mechanism by which exosomes select target cells. It is expected to develop into exosome creation and drug treatment targeting cancer metastasis.
Paper information:[Langmuir] Fluorescence spectroscopic analysis of lateral and trans-bilayer fluidity of exosome membranes
