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.
|Raguz, Marija; Mainali, Laxman; O'Brien, William J et al. (2014) Lipid-protein interactions in plasma membranes of fiber cells isolated from the human eye lens. Exp Eye Res 120:138-51|
|Widomska, Justyna; Subczynski, Witold K (2014) Why has Nature Chosen Lutein and Zeaxanthin to Protect the Retina? J Clin Exp Ophthalmol 5:326|
|Mainali, Laxman; Sidabras, Jason W; Camenisch, Theodore G et al. (2014) Spin-label W-band EPR with seven-loop-six-gap resonator: Application to lens membranes derived from eyes of a single donor. Appl Magn Reson 45:1343-1358|
|Plesnar, Elzbieta; Subczynski, Witold K; Pasenkiewicz-Gierula, Marta (2013) Comparative computer simulation study of cholesterol in hydrated unary and binary lipid bilayers and in an anhydrous crystal. J Phys Chem B 117:8758-69|
|Mainali, Laxman; Raguz, Marija; Subczynski, Witold K (2013) Formation of cholesterol bilayer domains precedes formation of cholesterol crystals in cholesterol/dimyristoylphosphatidylcholine membranes: EPR and DSC studies. J Phys Chem B 117:8994-9003|
|Mainali, Laxman; Hyde, James S; Subczynski, Witold K (2013) Using spin-label W-band EPR to study membrane fluidity profiles in samples of small volume. J Magn Reson 226:35-44|
|Mainali, Laxman; Raguz, Marija; O'Brien, William J et al. (2013) Properties of membranes derived from the total lipids extracted from the human lens cortex and nucleus. Biochim Biophys Acta 1828:1432-40|
|Subczynski, Witold K; Wisniewska-Becker, Anna; Widomska, Justyna (2012) Can macular xanthophylls replace cholesterol in formation of the liquid-ordered phase in lipid-bilayer membranes? Acta Biochim Pol 59:109-14|
|Wisniewska-Becker, Anna; Nawrocki, Grzegorz; Duda, Mariusz et al. (2012) Structural aspects of the antioxidant activity of lutein in a model of photoreceptor membranes. Acta Biochim Pol 59:119-24|
|Subczynski, Witold K; Raguz, Marija; Widomska, Justyna et al. (2012) Functions of cholesterol and the cholesterol bilayer domain specific to the fiber-cell plasma membrane of the eye lens. J Membr Biol 245:51-68|
Showing the most recent 10 out of 35 publications