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进行，与Marta Pasenkiewicz-Gierula博士合作，作为NIH拨款号的延伸。R01-EY015526。胆固醇是哺乳动物细胞中最重要的固醇，主要存在于质膜中，占总脂质的40- 45mol %。然而，在纤维细胞的膜中，胆固醇水平非常高，在晶状体皮层显示胆固醇与磷脂的摩尔比从1:2到晶状体核高达3:4，这导致在膜内形成不混溶的胆固醇结晶结构域。这项建议的长期目标是更好地了解胆固醇在晶状体膜中的功能，包括对晶状体内代谢物（尤其是氧气）运输的影响。建议(1)建立纤维细胞膜的选定结构域的计算机模型，特别关注其胆固醇结晶结构域，它可以占据晶状体核中多达50%的细胞表面；(2)计算由膜上氧浓度梯度引起的膜上氧渗透系数。这将允许测试假设，即刚性胆固醇结晶区域可以成为氧气运输的障碍，如果这是真的，应该有助于维持眼球晶状体内部的低氧浓度。最后，建议(3)计算氧浓度和氧跨膜域的平移扩散系数分布，并根据这些分布确定它们的氧渗透系数。将比较两种评估氧渗透系数的方法，即基于氧浓度梯度中的氧通量的方法和依赖于平衡状态下膜中氧自扩散的细节的方法。计算机实验将使用分子动力学（MD）膜模拟来提供有关氧渗透性，结构和胆固醇结晶域动力学的实验研究无法获得的信息。在可能的情况下，研究小组会在“父母资助”的支持下，将MD模拟的结果与实验数据进行比较。公共卫生相关性：与年龄有关的白内障是发展中国家致盲的一个主要原因。白内障发生的原因尚不清楚，但大量证据表明，晶状体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晶状体内氧运输过程的贡献的重要基础信息，这将增加我们对胆固醇所起作用的理解，反过来，有助于预防与年龄有关的核性白内障。

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.