Previous work has shown that potentially important changes in the lipid composition of brain myelin occur during experimental allergic encephalomyelitis (EAE), an established animal model of Multiple Sclerosis. The organization (structure) of normal and EAE lipids are different for both the cytoplasmic and extracellular monolayers. These differences in 'phase behavior' contribute to the differences in the interaction forces between myelin membranes that we have observed using the Surface Forces Apparatus (SFA), which appear to be related to the delamination of the myelin sheath. We hypothesize that the interactions between the cytoplasmic sides of the membranes are due primarily to myelin basic protein (MBP) that couples to the lipid composition, with the anionic lipid and protein isoform content being especially important. The interactions between the extracellular sides of the membrane are due exclusively to the lipids as there are no known adhesive proteins on this side. The adhesion between the extracellular surfaces is therefore likely due to non-specific interactions such as electrostatic and van der Waals forces, which should also be strongly influenced by alterations in the phase behavior and distribution of the lipids in EAE membranes. The SFA will be used to study the complete force vs distance curves of normal and EAE myelin to relate the composition and phase behavior variations to the interaction forces that hold the extracellular and cytoplasmic sides of the myelin sheath together. In addition to variations in lipid composition, the effects of different MBP isoforms (C1, C3, C8) on the membrane adhesion will be determined with the SFA to show how these isoforms couple to the lipid distribution. We will use Langmuir isotherms and fluorescence microscopy of model cytoplasmic and extracellular monolayers and bilayers to determine the relationship between lipid composition and lateral phase separation. We are especially interested in cholesterol, the anionic lipids phosphatdylserine and sphingomyelin, and the neutral lipid phosphatidylcholine, which show the greatest differences between control and EAE myelin. Atomic force microscopy (AFM) will be used in parallel to study the distribution of lipids and MBP and its isoforms at the nanometer scale. We hypothesize that polyethylene glycol (PEG) and poloxamers, non-toxic and FDA-approved polymers, recently used to treat spinal cord injuries in animals, might act to heal the myelin sheath via adding an attractive osmotic 'depletion' force to provide a similar effect that we have recently observed for MBP. This work will provide insights into the role of membrane-composition and organization on the interactions that lead to MS, as well as basic advances in understanding the relationships between lipid phase behavior, protein localization and function, and membrane demyelination. ? ? ?

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM076709-02
Application #
7448559
Study Section
Biochemistry and Biophysics of Membranes Study Section (BBM)
Program Officer
Chin, Jean
Project Start
2007-07-01
Project End
2011-06-30
Budget Start
2008-07-01
Budget End
2009-06-30
Support Year
2
Fiscal Year
2008
Total Cost
$271,905
Indirect Cost
Name
University of California Santa Barbara
Department
Engineering (All Types)
Type
Schools of Engineering
DUNS #
094878394
City
Santa Barbara
State
CA
Country
United States
Zip Code
93106
Lee, Dong Woog; Banquy, Xavier; Kristiansen, Kai et al. (2015) Adsorption mechanism of myelin basic protein on model substrates and its bridging interaction between the two surfaces. Langmuir 31:3159-66
Lee, Dong Woog; Banquy, Xavier; Kristiansen, Kai et al. (2014) Lipid domains control myelin basic protein adsorption and membrane interactions between model myelin lipid bilayers. Proc Natl Acad Sci U S A 111:E768-75
Dhar, Prajnaparamita; Eck, Elizabeth; Israelachvili, Jacob N et al. (2012) Lipid-protein interactions alter line tensions and domain size distributions in lung surfactant monolayers. Biophys J 102:56-65
Banquy, Xavier; Kristiansen, Kai; Lee, Dong Woog et al. (2012) Adhesion and hemifusion of cytoplasmic myelin lipid membranes are highly dependent on the lipid composition. Biochim Biophys Acta 1818:402-10
Donaldson Jr, Stephen H; Lee Jr, C Ted; Chmelka, Bradley F et al. (2011) General hydrophobic interaction potential for surfactant/lipid bilayers from direct force measurements between light-modulated bilayers. Proc Natl Acad Sci U S A 108:15699-704
Lee, Dong Woog; Min, Younjin; Dhar, Prajnaparamitra et al. (2011) Relating domain size distribution to line tension and molecular dipole density in model cytoplasmic myelin lipid monolayers. Proc Natl Acad Sci U S A 108:9425-30
Choi, S Q; Steltenkamp, S; Zasadzinski, J A et al. (2011) Active microrheology and simultaneous visualization of sheared phospholipid monolayers. Nat Commun 2:312
Ramachandran, Arun; Anderson, Travers H; Leal, L Gary et al. (2011) Adhesive interactions between vesicles in the strong adhesion limit. Langmuir 27:59-73
Min, Y; Alig, T F; Lee, D W et al. (2011) Critical and off-critical miscibility transitions in model extracellular and cytoplasmic myelin lipid monolayers. Biophys J 100:1490-8
Hammer, Malte U; Anderson, Travers H; Chaimovich, Aviel et al. (2010) The search for the hydrophobic force law. Faraday Discuss 146:299-308; discussion 367-93, 395

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