ISOPRENOID METABOLISM IN THE RETINA
FLIESLER, STEVEN J. Principal Investigator
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DESCRIPTION (provided by applicant): The long-range goal of this project is to elucidate the biological functions of cholesterol and related molecules in the retina. The RSH/Smith-Lemli-Opitz Syndrome (SLOS), involves defective conversion of 7- dehydrocholesterol (7DHC) to cholesterol. The first discovered in a series of multiple congential anomalies (MCA) syndromes and anabolic cholesterol pathway defects, it is estimated to be the fourth most common human recessive disease. SLOS has an associated retinal degeneration, discovered only recently, but the mechanism underlying the degeneration is unknown. Initial studies suggest the involvement of oxidized lipids and proteins, as well as 'metabolic cross-talk' between sterol metabolism and other pathways, likely via transcriptional regulation. Treating rats with a selective inhibitor (AY9944) of the same enzyme that is defective in SLOS affords an animal model that exhibits a progressive retinal degeneration affecting both rods and cones. Using this model, in comparison with age- and sex-matched control rats, we will employ three different, complimentary approaches to elucidating the disease mechanism: 1) Microarray analysis (genomics) will reveal differential gene expression patterns in SLOS rat vs: control retinas, confirming targets by real-time PCR and biochemical methods. 2) Lipidomics will reveal quantitative differences in the steady-state levels of normal and oxidized lipids, while 3) proteomics will identify differences in the amounts and types of specific oxidative modifications of retinal proteins in retinas of these animals. In addition, the mechanism of photoreceptor cell death will be assessed using standard methods relevant to apoptosis. The ability of biologically compatible antioxidants (alpha-lipoic acid and EPC-K1) to block lipid and protein oxidation and to partially ameliorate the retinal degenerationln in SLOS rats will be assessed, under both normal and 'light-damage' conditions. In this way, fundamental new insights into the mechanism of retinal degeneration associated with SLOS will be obtained. These studies also may provide support for the use of antioxidants as adjuncts to cholesterol supplementation, the current (if imperfect) therapeutic strategy for SLOS patient management. The latter has been shown to improve photoreceptor function in the SLOS rat model. As such, this project supports the NEI's mission of developing sight-saving treatments, reducing visual impairment and blindness, and improving the quality of life for people of all ages.