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.

Public Health Relevance

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.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Research Project (R01)
Project #
5R01EY015526-07
Application #
7994801
Study Section
Anterior Eye Disease Study Section (AED)
Program Officer
Araj, Houmam H
Project Start
2004-04-01
Project End
2014-11-30
Budget Start
2010-12-01
Budget End
2011-11-30
Support Year
7
Fiscal Year
2011
Total Cost
$328,320
Indirect Cost
Name
Medical College of Wisconsin
Department
Biophysics
Type
Schools of Medicine
DUNS #
937639060
City
Milwaukee
State
WI
Country
United States
Zip Code
53226
Mainali, Laxman; Raguz, Marija; O'Brien, William J et al. (2016) Changes in the Properties and Organization of Human Lens Lipid Membranes Occurring with Age. Curr Eye Res :1-11
Widomska, Justyna; Zareba, Mariusz; Subczynski, Witold Karol (2016) Can Xanthophyll-Membrane Interactions Explain Their Selective Presence in the Retina and Brain? Foods 5:
Subczynski, Witold K; Mainali, Laxman; Raguz, Marija et al. (2016) Organization of lipids in fiber-cell plasma membranes of the eye lens. Exp Eye Res :
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
Raguz, Marija; Mainali, Laxman; O'Brien, William J et al. (2015) Lipid domains in intact fiber-cell plasma membranes isolated from cortical and nuclear regions of human eye lenses of donors from different age groups. Exp Eye Res 132:78-90
Raguz, Marija; Mainali, Laxman; O'Brien, William J et al. (2015) Amounts of phospholipids and cholesterol in lipid domains formed in intact lens membranes: Methodology development and its application to studies of porcine lens membranes. Exp Eye Res 140:179-86
Mainali, Laxman; Vasquez-Vivar, Jeannette; Hyde, James S et al. (2015) Spin-labeled small unilamellar vesicles with the T 1-sensitive saturation-recovery EPR display as an oxygen sensitive analyte for measurement of cellular respiration. Appl Magn Reson 46:885-895
Mainali, Laxman; Raguz, Marija; O'Brien, William J et al. (2015) Properties of membranes derived from the total lipids extracted from clear and cataractous lenses of 61-70-year-old human donors. Eur Biophys J 44:91-102
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
Widomska, Justyna; Subczynski, Witold K (2014) Why has Nature Chosen Lutein and Zeaxanthin to Protect the Retina? J Clin Exp Ophthalmol 5:326

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