Model of demyelination on a molecular scale at physiological and pathological conditions
Myelin is multibilayered, dominantly lipid sheath that enwraps axons and ensures proper transmission of neural impulses. Loss of myelin integrity in terms of redundant unwrapping, vacuole formation and swelling of the bilayer sheaths is referred as demyelination and is related to multiple sclerosis. In vivo studies reported that the amounts of representative lipids, including phosphatidylethanolamines (PEs), are significantly changed in diseased compared to healthy animals, and are further accompanied by reduced adhesive activity of myelin basic protein (MBP). The impact of the amount of PE in mixed model lipid membranes on the transition temperature between lamellar (La) to inverse hexagonal (HII) phase, where the latter shares structural features with vacuole formation, is significant but rather elusive issue. The aim of this proposal is to establish a link between this temperature change and the size and arrangement of PE domains in mixed model lipid membranes in the presence and absence of MBP. Model myelin membranes will be prepared from representative myelin lipids according to their ratios found in normal and diseased species. La to HII phase transitions of PE domains will be studied by probing different surroundings of PE domains within the bilayer, along with the variations in the hydrating medium regarding the presence of MBP and ionic content. A detailed molecular picture of these events will be provided by combining temperature-dependent IR spectroscopy and computational chemistry; structural changes of PE domain during this phase transition will be identified together with the interactions between PE, MBP and neighboring domains. As a result, the parameters considered as the most critical in reduction of La to HII phase transition temperature will be revealed. Aside of understanding demyelination at the molecular level, obtained results will help in suggesting possible solutions in lipid composition regulation by medications and appropriate nutrition.