Cell-Like Mechanical Response in Passive Plasma Membrane Vesicles

Abstract

Giant plasma membrane vesicles (GPMVs) which are isolated from adherent cells are an emerging model system for the study of lipid-lipid and lipid-protein interactions. The membrane composition of GPMVs closely resembles the plasma membrane lipidome and proteome, but lacks active remodeling and cytoskeletal support. In addition to the complex composition, GPMVs are expected to retain the plasma membrane structural characteristics, thus allowing access to material parameters otherwise concealed in the active cellular system. Here, we report bending rigidity values for GPMVs at varying GPMV isolation conditions. Further, we correlate them with the membrane viscosity and order assessed from Laurdan general polarization and fluorescent lifetimes of molecular rotors. When aspirated in micropipettes, GPMVs show unexpected mechanical properties, which are not found in simple lipid bilayers. GPMVs exhibit droplet-like instabilities upon increasing aspiration pressures. We find that the apparent elastic modulus matches closely reported values of cellular cortical tension. To understand how the passive GPMV membrane gives rise to cell-like responses, we employed fluorescent lipid analogs, nanotube pulling experiments and electron microscopy. We detect membrane reservoirs exhibiting lipid sorting and investigate their role in the observed soft elastic response. Additionally, fluorescent lifetime imaging of a membrane order sensitive dye helps to clarify the GPMV membrane structural response to mechanical tension. The results contribute to the understanding of the plasma membrane structure and enable synthetic reconstitution of plasma membrane like comportments.