title: Cholesterol strongly affects the organization of lipid monolayers studied as models of the milk fat globule membrane: Condensing effect and change in the lipid domain morphology.
abstract: The biological membrane that surrounds the milk fat globules exhibits phase separation of polar lipids that is poorly known. The objective of this study was to investigate the role played by cholesterol in the organization of monolayers prepared as models of the milk fat globule membrane (MFGM). Differential scanning calorimetry and X-ray diffraction experiments allowed characterization of the gel to liquid crystalline phase transition temperature of lipids, Tm ~35°C, in vesicles prepared with a MFGM lipid extract. For temperature below Tm, atomic force microscopy revealed phase separation of lipids at 30 mN·m(-1) in Langmuir-Blodgett monolayers of the MFGM lipid extract. The high Tm lipids form liquid condensed (LC) domains that protrude by about 1.5 nm from the continuous liquid expanded (LE) phase. Cholesterol was added to the MFGM extract up to 30% of polar lipids (cholesterol/milk sphingomyelin (MSM) molar ratio of 50/50). Compression isotherms evidenced the condensing effect of the cholesterol onto the MFGM lipid monolayers. Topography of the monolayers showed a decrease in the area of the LC domains and in the height difference H between the LC domains and the continuous LE phase, as the cholesterol content increased in the MFGM lipid monolayers. These results were interpreted in terms of nucleation effects of cholesterol and decrease of the line tension between LC domains and LE phase in the MFGM lipid monolayers. This study revealed the major structural role of cholesterol in the MFGM that could be involved in biological functions of this interface (e.g. mechanisms of milk fat globule digestion).
authors.affiliation: INRA, UMR 1253 Science et Technologie du Lait et de l'Œuf, 35042 Rennes, France; AGROCAMPUS OUEST, UMR 1253 Science et Technologie du Lait et de l'Œuf, 35042 Rennes, France.
authors.forename: Appala Venkata Ramana
authors.initials: AV
authors.lastname: Murthy
authors.affiliation: INRA, UMR 1253 Science et Technologie du Lait et de l'Œuf, 35042 Rennes, France; AGROCAMPUS OUEST, UMR 1253 Science et Technologie du Lait et de l'Œuf, 35042 Rennes, France.
authors.forename: Fanny
authors.initials: F
authors.lastname: Guyomarc'h
authors.affiliation: Université de Rennes 1, Institut de Physique de Rennes, UMR 6251, CNRS, 35042 Rennes, France.
authors.forename: Gilles
authors.initials: G
authors.lastname: Paboeuf
authors.affiliation: Université de Rennes 1, Institut de Physique de Rennes, UMR 6251, CNRS, 35042 Rennes, France.
authors.forename: Véronique
authors.initials: V
authors.lastname: Vié
authors.affiliation: INRA, UMR 1253 Science et Technologie du Lait et de l'Œuf, 35042 Rennes, France; AGROCAMPUS OUEST, UMR 1253 Science et Technologie du Lait et de l'Œuf, 35042 Rennes, France. Electronic address: Christelle.Lopez@rennes.inra.fr.
authors.forename: Christelle
authors.initials: C
authors.lastname: Lopez
mesh_terms: D040761:Biomimetic Materials / Q000737:chemistry*; D002784:Cholesterol / Q000737:chemistry*; D006017:Glycolipids / Q000737:chemistry*; D006023:Glycoproteins / Q000737:chemistry* / Q000648:ultrastructure; D066292:Lipid Droplets; D008560:Membrane Fluidity; D021962:Membrane Microdomains / Q000737:chemistry* / Q000648:ultrastructure; D044367:Phase Transition; D053835:Unilamellar Liposomes / Q000737:chemistry*
chemical_list: D006017:Glycolipids; D006023:Glycoproteins; D053835:Unilamellar Liposomes; C110367:milk fat globule; D002784:Cholesterol
keywords: Atomic force microscopy; Langmuir film; Membrane topography; Milk fat globule membrane; Milk sphingomyelin; Phase separation