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Witold Karol Subczynski, Laxman Mainali, Marija Raguz, William J O'Brien; Functions of the lipid bilayer portion of the fiber cell plasma membranes in the maintaining lens homeostasis. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5737.
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© ARVO (1962-2015); The Authors (2016-present)
The plasma membrane together with the cytoskeleton forms the only supramolecular structure of the matured fiber cell which accounts for mostly all fiber cell lipids. We will focus on the organization and properties of the lipid bilayer portion of the fiber cell membrane and discuss the significant functions which this lipid bilayer plays in maintaining homeostasis of the fiber-cell plasma membrane, the fiber cell itself, and the whole lens.
Results presented here were obtained using EPR spin labeling methods and differential scanning calorimetry. Intact fiber cell plasma membranes from cortical and nuclear regions of human lenses as well as lens lipid membranes (made of the total lipid extracts from intact membranes) were investigated.
(1) The extremely high (saturating) content of cholesterol (Chol) in the fiber-cell membrane keeps the bulk physical properties of the lipid-bilayer portion of the membrane consistent and independent of changes in the phospholipid composition. The Chol bilayer domain (CBD) provides buffering capacity for Chol concentration in the surrounding phospholipid bilayer, keeping it at a constant saturating level. (2) The high Chol content in fiber-cell plasma membranes ensure that the lipid bilayer portion of these membranes forms the high hydrophobic barrier for permeation of polar molecules. (3) The lipid bilayer portion of lens membranes, with its unique lipid composition and structure, forms significant barriers to oxygen transport into the lens interior.
(1) The saturating Chol content and the CBD play a crucial role in maintaining homeostasis of the lens membrane by providing stability and consistency of physical properties of lipid bilayer surrounding membrane integral proteins, independent of changes in phospholipid composition. (2) The lipid bilayer portion of the intact fiber cell membrane provides high hydrophobic barrier which protect against uncontrolled leaking of small polar molecules. Thus, in human lenses, transport of polar molecules from fiber cell to fiber cell is tightly controlled by aquaporin-0 and connexins. (3) In clear lenses age-related changes in the lens lipid and protein composition and organization are orchestrated in a way that increases the fiber cell plasma membrane’s resistance to oxygen permeation helping to maintain lens transparency and protecting against cataract formation.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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