Human Lipoproteins at Model Cell Membranes: Effect of Lipoprotein Class on Lipid Exchange

Abstract

High and low density lipoproteins (HDL and LDL) are thought to play vital roles in the onset and development of atherosclerosis; the biggest killer in the western world. Key issues of initial lipoprotein (LP) interactions at cellular membranes need to be addressed including LP deposition and lipid exchange. Here we present a protocol for monitoring the in situ kinetics of lipoprotein deposition and lipid exchange/removal at model cellular membranes using the non-invasive, surface sensitive methods of neutron reflection and quartz crystal microbalance with dissipation. For neutron reflection, lipid exchange and lipid removal can be distinguished thanks to the combined use of hydrogenated and tail-deuterated lipids. Both HDL and LDL remove lipids from the bilayer and deposit hydrogenated material into the lipid bilayer, however, the extent of removal and exchange depends on LP type. These results support the notion of HDL acting as the ‘good’ cholesterol, removing lipid material from lipid-loaded cells, whereas LDL acts as the ‘bad’ cholesterol, depositing lipid material into the vascular wall.

Brain metastases-derived extracellular vesicles induce binding and aggregation of low-density lipoprotein

“…3 g–i), indicating substantial aggregation. The ability of Br-EVs to induce LDL aggregation may be due to distinct lipid bilayer characteristics, as lipoproteins are thought to display dynamic interactions with cell membranes, including lipid exchange and removal [ 48 , 49 ]. Removal of lipids from the LDL surface may alter hydrophobic interactions, causing lipoprotein aggregation and fusion [ 50 ].…”

Time-resolved small-angle neutron scattering as a probe for the dynamics of lipid exchange between human lipoproteins and naturally derived membranes

“…Neutron reflectometry has previously been used to gather information on the structure and composition of the membrane itself after interactions with human lipoprotein particles. These studies show that LDL and HDL have differing interaction modes when tested with synthetic, saturated membranes 27,28 . Interestingly, the presence of negatively charged lipids in the synthetic membranes enhanced the uptake of lipids by both lipoproteins, whereas the lipid deposition remained the same 28 .…”

The Production of Matchout-Deuterated Cholesterol and the Study of Bilayer-Cholesterol Interactions

“…The lipids films required for NR were further hydrated in Milli-Q water to a concentration of 0.2 mg/mL and bath sonicated for 1 h. The lipid solutions were then tip sonicated for 5 min, at 10% power 5 sec on, 5 sec off, just before use. For optimum vesicle fusion, a 0.1 mg/mL solution of lipids in the presence of 2 mM CaCl 2 was used 15 , by mixing equal volumes of the tip sonicated lipids with a 4 mM CaCl 2 solution 26,41 . The sample was then introduced into the flow cell by a syringe injection and left to incubate at 37 °C for 20 min before rinsing the excess off in water followed by Tris buffer (50 mM Tris-HCl, 150 mM NaCl).…”