Lamellar Phases Composed of Phospholipid, Cholesterol, and Ceramide, as Studied by 2H NMR

Reza Siavashi; Tejas Phaterpekar; Sherry S W Leung; Alicia Alonso; Félix M Goñi; Jenifer L Thewalt

doi:10.1016/j.bpj.2019.05.027

Lamellar Phases Composed of Phospholipid, Cholesterol, and Ceramide, as Studied by ²H NMR

Biophys J. 2019 Jul 23;117(2):296-306. doi: 10.1016/j.bpj.2019.05.027. Epub 2019 Jun 19.

Authors

Reza Siavashi¹, Tejas Phaterpekar¹, Sherry S W Leung¹, Alicia Alonso², Félix M Goñi², Jenifer L Thewalt³

Affiliations

¹ Department of Physics, Simon Fraser University, Burnaby, British Columbia, Canada.
² Instituto Biofisika, University of the Basque Country/Spanish National Research Council (CSIC), Leioa, Spain; Department of Biochemistry and Molecular Biology, University of the Basque Country, Leioa, Spain.
³ Department of Physics, Simon Fraser University, Burnaby, British Columbia, Canada; Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada. Electronic address: jthewalt@sfu.ca.

Abstract

Sphingolipids constitute a significant fraction of cellular plasma membrane lipid content. Among sphingolipids, ceramide levels are usually very low. However, in some cell processes like apoptosis, cell membrane ceramide levels increase markedly because of the activation of enzymes like acid sphingomyelinase. This increase can change the physical state of the membrane by promoting molecular order and inducing solid-ordered (S_o) phase domains. This effect has been observed in a previous ²H NMR study on membranes consisting of palmitoyl sphingomyelin (PSM) and palmitoyl ceramide (PCer). Cholesterol (Chol), too, is present at high concentrations in mammalian plasma membranes and has a favorable interaction with sphingomyelin (SM), together forming domains in the liquid-ordered phase in model membranes. There are reports that Chol is able to displace ceramide (Cer) in SM bilayers and abolish the S_o phase domains formed by SM:Cer. This ability of Chol appears to be concentration dependent; in membranes with low Chol and high Cer contents, S_o phase domains rich in Cer coexist with the continuous fluid phase of the membrane. Here, we studied the effect of increasing PCer concentration in PSM:Chol bilayers, using ²H NMR. Chol:PCer mole ratios were 3:1, 3:2, and 3:3, at a fixed 7:3 phospholipid:cholesterol mol ratio. Both PSM and PCer were monitored in separate samples for changes in their physical state by introducing a perdeuterated palmitoyl chain in either molecule. Moreover, the effect of replacing PSM with DPPC was investigated to test the impact on membrane phase behavior of replacing the sphingosine with a palmitoylated glycerol backbone. We found that PCer can increase acyl chain order in both PSM:Chol and DPPC:Chol bilayers. Especially in bilayers with Chol:PCer 1:1 molar ratios, PCer induces highly stable S_o phase domains in both PSM and DPPC bilayers near 37°C. However, PCer has a more pronounced ordering effect on PSM compared to DPPC bilayers.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Ceramides / chemistry*
Cholesterol / chemistry*
Deuterium / chemistry*
Magnetic Resonance Spectroscopy*
Phospholipids / chemistry*
Temperature

Substances

Ceramides
Phospholipids
Cholesterol
Deuterium