The unprecedented membrane deformation of the human nuclear envelope, in a magnetic field, indicates formation of nuclear membrane invaginations

Abstract

AbstractHuman nuclear membrane (hNM) invaginations are thought to be crucial in fusion, fission and remodeling of cells and present in many human diseases. There is however little knowledge, if any, about their lipid composition and dynamics. We therefore isolated nuclear envelope lipids from human kidney cells, analyzed their composition and determined the membrane dynamics after resuspension in buffer. The hNM lipid extract was composed of a complex mixture of phospholipids, with high amounts of phosphatidylcholines, phosphatidylinositols (PI) and cholesterol. hNM dynamics was determined by solid-state NMR and revealed that the lamellar gel-to-fluid phase transition occurs below 0 °C, reflecting the presence of elevated amounts of unsaturated fatty acid chains. Fluidity was higher than the plasma membrane, illustrating the dual action of Cholesterol (ordering) and PI lipids (disordering). The most striking result was the large magnetic field-induced membrane deformation allowing to determine the membrane bending elasticity, a property related to hydrodynamics of cells and organelles. Human Nuclear Lipid Membranes were at least two orders of magnitude more elastic than the classical plasma membrane suggesting a physical explanation for the formation of nuclear membrane invaginations.