Cholesterol is essential for life in mammals. Yet, chronic excess of cholesterol is a risk factor for cardiovascular and Alzheimer's diseases and likely age-related macular degeneration (AMD). Cholesterol and other lipids accumulate with age between the retinal pigment epithelium and Bruch's membrane, but in people with AMD this accumulation is more prominent suggesting defects in cholesterol removal. Cholesterol removal always involves two mechanisms, lipoprotein-mediated transport and catabolism to oxysterols by cytochrome P450 enzymes (CYP) including CYPs 27A1 and 46A1. While recent genetic studies revealed an association between AMD and genes affecting the formation of high density lipoproteins, the significance of the enzymatic cholesterol removal from the retina is still unknown. We only know that in humans, ocular manifestations of CYP27A1 deficiency include premature retinal senescence and cholesterol deposition, and that inhibition of CYP46A1 with voriconazole causes visual disturbances. To begin to gain insight into cholesterol catabolism in the retina, we analyzed cadaveric human eyes and established that retinal cholesterol is mainly metabolized by CYP27A1 while the other P450 isoform, CYP46A1, plays a lesser role. We also found that retinal levels of the CYP27A1 protein do not correlate with the levels of its metabolite 5-cholestenoic acid and ascertained the basis for this discrepancy. We demonstrated that CYP27A1 is subjected to a deleterious post-translational modification by isolevuglandins generated from arachidonic acid. We also found that mice lacking one (CYP27A1) or two (CYPs 27A1 and 46A1) cholesterol-catabolizing enzymes have structural retinal pathologies, altered blood flow and pathologic retinal vascularization. These findings confirm that enzymatic cholesterol elimination is an important contributor to the normal function of the retina. In this competing renewal, we propose to further explore our findings.
The Specific Aims of this application are: 1) to characterize the ocular phenotype of mice with impaired cholesterol catabolism;2) to identify the major mechanisms regulating retinal CHO levels;and 3) to examine the isoLG-adduction in the retina. Advanced diagnostic instrumentation, state-of-the-art mass spectrometry methodologies, biochemical and molecular biology analyses of human and mouse specimens, as well as dietary and pharmacological interventions in mice will be used to address the goals of the project. The data obtained will significantly advance our understanding of the role of cholesterol in vision and the mechanisms for pathologic vascularization in the retina. These studies may lead to the identification of therapeutic targets for prevention and treatment of neovascular AMD.

National Institute of Health (NIH)
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Special Emphasis Panel (ZRG1)
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Shen, Grace L
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Case Western Reserve University
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Pikuleva, Irina A; Curcio, Christine A (2014) Cholesterol in the retina: the best is yet to come. Prog Retin Eye Res 41:64-89
Saadane, Aicha; Mast, Natalia; Charvet, Casey D et al. (2014) Retinal and nonocular abnormalities in Cyp27a1(-/-)Cyp46a1(-/-) mice with dysfunctional metabolism of cholesterol. Am J Pathol 184:2403-19
Chen, Junjun; Pikuleva, Irina A; Turko, Illarion V (2013) Mass spectrometry quantification of PICALM and AP180 in human frontal cortex and neural retina. Anal Biochem 442:253-8
Charvet, Casey D; Saadane, Aicha; Wang, Meiyao et al. (2013) Pretreatment with pyridoxamine mitigates isolevuglandin-associated retinal effects in mice exposed to bright light. J Biol Chem 288:29267-80
Charvet, Casey D; Laird, James; Xu, Yunfeng et al. (2013) Posttranslational modification by an isolevuglandin diminishes activity of the mitochondrial cytochrome P450 27A1. J Lipid Res 54:1421-9
Liao, Wei-Li; Heo, Gun-Young; Dodder, Nathan G et al. (2011) Quantification of cholesterol-metabolizing P450s CYP27A1 and CYP46A1 in neural tissues reveals a lack of enzyme-product correlations in human retina but not human brain. J Proteome Res 10:241-8
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Charvet, Casey; Liao, Wei-Li; Heo, Gun-Young et al. (2011) Isolevuglandins and mitochondrial enzymes in the retina: mass spectrometry detection of post-translational modification of sterol-metabolizing CYP27A1. J Biol Chem 286:20413-22
Liao, Wei-Li; Heo, Gun-Young; Dodder, Nathan G et al. (2010) Optimizing the conditions of a multiple reaction monitoring assay for membrane proteins: quantification of cytochrome P450 11A1 and adrenodoxin reductase in bovine adrenal cortex and retina. Anal Chem 82:5760-7

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