Fiber-cell membranes of the human eye lens are saturated with cholesterol (showing cholesterol-to- phospholipid mole ratios from 1 in the cortex to as high as 4 in the nucleus), which leads to the formation of immiscible cholesterol crystalline domains (CCDs) within these membranes. At the highest cholesterol content, up to 50% of the cell-membrane surface can be occupied by CCDs. These conditions exist in the lens nucleus, where the cholesterol content can significantly exceed the solubility threshold of the membrane. The appearance of CCDs is usually a sign of pathology;however, only in the eye lens can CCDs play a positive physiological function, maintaining lens transparency and possibly protecting against cataract formation. The long-term objective of this proposal is to achieve a greater understanding of cholesterol's function in fiber-cell membranes. In the short-term, we will (i) examine how high cholesterol content affects the lateral organization of phospholipid lens membranes, with special attention paid to the formation of CCDs, and (ii) test the hypothesis that the presence of CCDs determines the properties of the surrounding bulk phospholipid- cholesterol membranes. (iii) Additionally, experiments will reveal if the phospholipid composition of the lens membrane affects the formation, size, and stability of CCDs. (iv) Finally, the methodology developed and tested in model-membrane systems will be applied to detect and characterize coexisting cholesterol crystalline and bulk phospholipid-cholesterol domains in lens fiber-cell membranes during maturation, aging, and cataract formation. For studies of coexisting domains in membranes isolated from the eye lens, as well as in models of fiber-cell membranes, the discrimination by oxygen transport (DOT) method will be used. The DOT method, which is based on electron paramagnetic resonance (EPR) spin-labeling techniques, permits discrimination of different membrane domains and gives information about structure and molecular dynamics as a function of the membrane depth in coexisting domains without the need for their separation. It also allows information about oxygen transport within and across membrane domains to be obtained.
Age-related cataracts are a major cause of blindness in developing countries. The reason for the onset of cataracts is unknown, but a great deal of evidence suggests that the presence of the cholesterol crystalline domain in the eye lens helps to maintain transparency and prevent cataract formation. The proposed studies will generate important fundamental information about topographical and age-related differences in cholesterol- membrane interactions in the eye lens that will increase our understanding of the role cholesterol plays and, in turn, help contribute to the prevention of age-related nuclear cataracts.
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| Mainali, Laxman; O'Brien, William J; Subczynski, Witold K (2018) Detection of cholesterol bilayer domains in intact biological membranes: Methodology development and its application to studies of eye lens fiber cell plasma membranes. Exp Eye Res 178:72-81 |
| Subczynski, Witold Karol; Widomska, Justyna; Mainali, Laxman (2017) Factors Determining the Oxygen Permeability of Biological Membranes: Oxygen Transport Across Eye Lens Fiber-Cell Plasma Membranes. Adv Exp Med Biol 977:27-34 |
| Mainali, Laxman; Raguz, Marija; O'Brien, William J et al. (2017) Changes in the Properties and Organization of Human Lens Lipid Membranes Occurring with Age. Curr Eye Res 42:721-731 |
| Subczynski, Witold K; Mainali, Laxman; Raguz, Marija et al. (2017) Organization of lipids in fiber-cell plasma membranes of the eye lens. Exp Eye Res 156:79-86 |
| Mainali, Laxman; Camenisch, Theodore G; Hyde, James S et al. (2017) Saturation recovery EPR spin-labeling method for quantification of lipids in biological membrane domains. Appl Magn Reson 48:1355-1373 |
| Strangeway, Robert A; Hyde, James S; Camenisch, Theodore G et al. (2017) Broadband W-band Rapid Frequency Sweep Considerations for Fourier Transform EPR. Cell Biochem Biophys 75:259-273 |
| Subczynski, Witold K; Pasenkiewicz-Gierula, Marta; Widomska, Justyna et al. (2017) High Cholesterol/Low Cholesterol: Effects in Biological Membranes: A Review. Cell Biochem Biophys 75:369-385 |
| Widomska, Justyna; Subczynski, Witold K; Mainali, Laxman et al. (2017) Cholesterol Bilayer Domains in the Eye Lens Health: A Review. Cell Biochem Biophys 75:387-398 |
| Zareba, M; Widomska, J; Burke, J M et al. (2016) Nitroxide free radicals protect macular carotenoids against chemical destruction (bleaching) during lipid peroxidation. Free Radic Biol Med 101:446-454 |
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