Abstract
Purpose :
Age-related changes in plasma membranes of human eye lens fiber cells are much greater than age-related changes in the cell membranes of other organs and tissues. In the fiber cell membranes, the content of sphingolipids increases with age and the content of phosphatidylcholine decreases. However, the most characteristic change is the increase in cholesterol (Chol) content, which leads to the formation of pure Chol bilayer domains (CBDs) and even Chol crystals. All of these major changes occur in the normal lens without extensive compromise of lens transparency. Thus, it is intriguing to learn how the changes in phospholipid (PL) composition and Chol content affect the organization and dynamics of membrane lipids and proteins and how these changes are related to eye lens function.
Methods :
Continuous wave and saturation-recovery electron paramagnetic resonance (EPR) spin-labeling methods have been developed and applied to discriminate lipid domains in intact fiber cell membranes, quantify lipid domains, and obtain information about the heterogeneity of the membrane structure and dynamics. Confocal microscopy with fluorescent PL and Chol analogs was used to study the structure of the CBD. Molecular dynamics simulation was used to obtain information that cannot be obtained through EPR spin-labeling and fluorescence methods.
Results :
At the saturating Chol content, the physical properties of PL bilayers are very similar and independent of the PL composition. This is also true for lens lipid membranes; changes in the PL composition that occur with age do not affect membrane physical properties. However, recently we showed that, the PL composition affects the Chol content at which CBDs and Chol crystals start to form.
Conclusions :
High Chol content and the presence of CBDs play a significant role in maintaining the homeostasis of the fiber-cell membrane, fiber cell itself, and whole lens, and thus in the maintaining lens transparency. Recently obtained results support our hypothesis that the delicate balance between changes in the lens-membrane PL composition and in the Chol content form an uninvestigated mechanism through which Chol-dependent processes in the eye lens membrane can be regulated.
Acknowledgements: This work was supported by Grants EY015526, EB001980, and EY001931 from the NIH, USA, and by the Polish National Science Center 2016/22/M/NZ1/0187.
This is a 2020 ARVO Annual Meeting abstract.