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

描述（由申请人提供）：本研究将主要在波兰克拉科夫的雅盖隆大学与玛尔塔博士合作进行，作为NIH批准号R 01-EY 015526的扩展。胆固醇是哺乳动物细胞中最重要的固醇，主要位于质膜中，占总脂质的40-45 mol%。然而，在纤维细胞的膜中，胆固醇水平极高，显示胆固醇与磷脂的摩尔比在透镜的皮质中为1至2，而在透镜核中高达3至4，这导致在该膜内形成不混溶的胆固醇结晶域。该提案的长期目标是更好地了解胆固醇在眼透镜膜中的功能，包括对代谢物（特别是氧气）在透镜内运输的影响。建议（1）建立纤维细胞膜的选定区域的计算机模型，特别注意其胆固醇结晶区域，其可以占据透镜核中多达50%的细胞表面，和（2）计算由跨膜的氧浓度梯度引起的跨膜区域的氧渗透系数。这将允许测试刚性胆固醇晶体结构域可以是氧转运的障碍的假设，如果是真的，这将有助于维持眼睛晶状体内部的低氧浓度。最后，建议（3）计算跨膜区域的氧浓度和氧平移扩散系数的分布，并基于这些分布确定它们的氧渗透系数。将比较两种评价氧渗透系数的方法，即一种是基于氧浓度梯度中的氧通量，另一种是取决于平衡时膜中氧自扩散的细节。将使用分子动力学（MD）膜模拟进行计算机实验，以提供有关氧渗透性，结构和胆固醇结晶结构域的动力学的实验研究中无法获得的信息。在可能的情况下，MD模拟的结果将与PI在父母资助下获得的实验数据进行比较。公共卫生相关性：在发展中国家，与糖尿病相关的白内障是致盲的主要原因。白内障发病的原因尚不清楚，但大量证据表明，透镜内部氧浓度的增加可导致白内障的发展。拟议的研究将产生关于胆固醇对眼睛透镜内氧气运输过程的贡献的重要基本信息，这将增加我们对胆固醇所起作用的理解，从而有助于预防与年龄相关的核性白内障。

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.