Metabolic pathways modulate the neuronal toxicity associated with fragile X-associated tremor/ataxia syndrome.

Fragile X-associated tremor/ataxia syndrome (FXTAS) is an adult-onset neurodegenerative disorder that affects premutation carriers (55-200 CGG repeats) of the fragile X mental retardation 1 (FMR1) gene. Much remains unknown regarding the metabolic alterations associated with FXTAS, especially in the brain, and the most affected region, the cerebellum. Investigating the metabolic changes in FXTAS will aid in the identification of biomarkers as well as in understanding the pathogenesis of disease. To identify the metabolic alterations associated with FXTAS, we took advantage of our FXTAS mouse model that expresses 90 CGG repeats in cerebellar Purkinje neurons and exhibits the key phenotypic features of FXTAS. We performed untargeted global metabolic profiling of age-matched control and FXTAS mice cerebella at 16-20 weeks and 55 weeks. Out of 506 metabolites measured in cerebellum, we identified 186 metabolites that demonstrate significant perturbations due to the (CGG)90 repeat (P<0.05) and found that these differences increase dramatically with age. To identify key metabolic changes in FXTAS pathogenesis, we performed a genetic screen using a Drosophila model of FXTAS. Out of 28 genes that we tested in the fly, 8 genes showed significant enhanced neuronal toxicity associated with CGG repeats, such as Schlank (ceramide synthase), Sk2 (sphingosine kinase) and Ras (IMP dehydrogenase). By combining metabolic profiling with a Drosophila genetic screen to identify genetic modifiers of FXTAS, we demonstrate an effective method for functional validation of high-throughput metabolic data and show that sphingolipid and purine metabolism are significantly perturbed in FXTAS pathogenesis.
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