Is Cholesterol Crystalline Domain a Barrier to Oxygen Transport in the Eye Lens?

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DESCRIPTION (provided by applicant): This research will be done primarily in Krakow, Poland, at the Jagiellonian University in collaboration with Dr. Marta Pasenkiewicz-Gierula as an extension of NIH Grant No. R01-EY015526. Cholesterol, the most prominent sterol of mammalian cells, is located predominantly in the plasma membrane, where it comprises 40-45 mol% of the total lipids. However, in membranes of fiber cells, the cholesterol level is extremely high, showing cholesterol-to-phospholipids mole ratios from 1 to 2 in the cortex of the lens to as high as 3 to 4 in the lens nucleus, which leads to the formation of immiscible cholesterol crystalline domains within this membrane. The long-term objective of this proposal is to achieve a greater understanding of the function of cholesterol in membranes of the eye lens, including the effect on the transport of metabolites, particularly oxygen, within the lens. It is proposed to (1) build computer models of selected domains of the fiber cell membrane, with special attention paid to its cholesterol crystalline domain, which can occupy as much as 50% of the cell surface in the lens nucleus, and (2) calculate the oxygen permeability coefficient across membrane domains arising from an oxygen concentration gradient across the membrane. This will allow testing of the hypothesis that the rigid cholesterol crystalline domain can be a barrier to oxygen transport, which, if true, should help to maintain low oxygen concentration in the eye-lens interior. Finally, it is proposed to (3) calculate profiles of both oxygen concentration and the oxygen translational diffusion coefficient across membrane domains and, based on these profiles, determine their oxygen permeability coefficients. Two methods of evaluation of the oxygen permeability coefficient will be compared, namely one that is based on oxygen flux in an oxygen concentration gradient, and one that depends on the details of oxygen self-diffusion in a membrane at equilibrium. Computer experiments will be performed using molecular dynamics (MD) membrane simulations to provide information that is not available from experimental studies about oxygen permeability, structure, and the dynamics of the cholesterol crystalline domain. When possible, the results of MD simulations will be compared with experimental data acquired by the PI under support of the Parent Grant. 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 an increase in oxygen concentration in the lens interior can lead to the development of cataracts. The proposed studies will generate important fundamental information about the contribution of cholesterol to the process of oxygen transport within the eye lens, which should increase our understanding of the role cholesterol plays and, in turn, help contribute to the prevention of age-related nuclear cataracts.