Inborn errors in cholesterol (Chol) biosynthesis comprise a group of severe, often lethal, metabolic disorders, of which the Smith-Lemli-Opitz Syndrome (SLOS) -the fourth most prevalent recessive human disease - is the most well-known. Prior work has established a SLOS rat model, which exhibits a progressive retinal degeneration in which photoreceptors seem more susceptible than RPE cells or Muller glia. While the exact disease mechanism is not yet known, the initial biochemical defect involves inefficient conversion of 7- dehydrocholesterol (7DHC) to Chol, which is catalyzed by DHCR7 (3b-hydroxysterol-D7-reductase, the DHCR7 gene product). We have proposed that this leads to multiple sequelae, including altered gene expression, lipid and protein oxidation, caspase activation, and perturbed membrane structure, which then result in progressive cellular dysfunction and demise. 7DHC is the most oxygen-labile lipid known, and readily forms "oxysterols" (some of which are extraordinarily toxic to cells), and 7DHC-derived oxysterols tend to be more cytotoxic than are Chol-derived oxysterols. The native environment of the retina (high oxygen tension, iron, and incident light) presents ideal conditions for oxysterol formation. We hypothesize that the demonstrable rise in retina/RPE 7DHC levels with blockade of DHCR7 leads to in situ oxysterol formation, resulting in progressive dysfunction and death of photoreceptors, while RPE and Muller glia are relatively spared. Preliminary data strongly support this hypothesis, which we will test further via three Specific Aims: 1) Using transformed, retina-derived cell lines, we will examine whether 7DHC-derived oxysterols differentially alter gene expression and viability of photoreceptors, vs. RPE and Muller glia, in culture, and also will examine the protective effects of antioxidants;2) We will examine whether photoreceptors are more sensitive to intravitreally injected 7DHC- vs. Chol-derived oxysterols compared to other retinal cell types in vivo;and 3) We will examine the impact of cell-type specific disruption of cholesterol biosynthesis on retinal structure and function in vivo, selectively knocking out Dhcr7 in rods, RPE, or Muller glia. This will markedly advance our understanding of the SLOS-associated retinal degeneration mechanism, as well as provide new insights into the development of more effective therapeutic interventions for such diseases.
The proposed studies will provide a mechanistic basis for understanding the pathobiology of retinal degeneration associated with the Smith-Lemli-Opitz syndrome (SLOS) and, by inference, allied cholesterol deficiency disorders, for which there currently are no cures and only partially effective treatments. If the hypothesis proves correct, blocking the formation of cytotoxic oxysterols (e.g., with a suitable antioxidant regimen) in conjunction with cholesterol supplementation would likely provide a markedly improved therapeutic intervention for such diseases.
|Aslebagh, Roshanak; Pfeffer, Bruce A; Fliesler, Steven J et al. (2016) Mass spectrometry-based proteomics of oxidative stress: Identification of 4-hydroxy-2-nonenal (HNE) adducts of amino acids using lysozyme and bovine serum albumin as model proteins. Electrophoresis 37:2615-2623|
|Pfeffer, Bruce A; Xu, Libin; Porter, Ned A et al. (2016) Differential cytotoxic effects of 7-dehydrocholesterol-derived oxysterols on cultured retina-derived cells: Dependence on sterol structure, cell type, and density. Exp Eye Res 145:297-316|
|Zhang, Sarah X; Ma, Jacey H; Bhatta, Maulasri et al. (2015) The unfolded protein response in retinal vascular diseases: implications and therapeutic potential beyond protein folding. Prog Retin Eye Res 45:111-31|
|Fliesler, Steven J (2015) Cholesterol homeostasis in the retina: seeing is believing. J Lipid Res 56:1-4|
|Murray, Anne R; Vuong, Linda; Brobst, Daniel et al. (2015) Glycosylation of rhodopsin is necessary for its stability and incorporation into photoreceptor outer segment discs. Hum Mol Genet 24:2709-23|
|Sapkota, Darshan; Chintala, Hemabindu; Wu, Fuguo et al. (2014) Onecut1 and Onecut2 redundantly regulate early retinal cell fates during development. Proc Natl Acad Sci U S A 111:E4086-95|
|Rowan, Sheldon; Weikel, Karen; Chang, Min-Lee et al. (2014) Cfh genotype interacts with dietary glycemic index to modulate age-related macular degeneration-like features in mice. Invest Ophthalmol Vis Sci 55:492-501|
|Zhang, Sarah X; Sanders, Emily; Fliesler, Steven J et al. (2014) Endoplasmic reticulum stress and the unfolded protein responses in retinal degeneration. Exp Eye Res 125:30-40|
|Conley, Shannon M; Stuck, Michael W; Burnett, Justin L et al. (2014) Insights into the mechanisms of macular degeneration associated with the R172W mutation in RDS. Hum Mol Genet 23:3102-14|
|Tu, Chengjian; Li, Jun; Jiang, Xiaosheng et al. (2013) Ion-current-based proteomic profiling of the retina in a rat model of Smith-Lemli-Opitz syndrome. Mol Cell Proteomics 12:3583-98|
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