Zeinab Wehbe MSc, Khaled Alatibi BSc, Ute Spiekerkoetter MD, Sara Tucci* PhD
Laboratory of Clinical Biochemistry and Metabolism, Center for Pediatric and Adolescent Medicine, Medical Center- University of Freiburg, Faculty of Medicine, University of Freiburg, Germany
*email: email@example.com; phone: +49 761 270 43700
BACKGROUND: VLCAD deficiency is the most common disorder of mitochondrial long-chain fatty acid β- oxidation with an incidence of 1:50,000 in newborns. The clinical phenotype is very heterogeneous involving organs and tissues that mostly rely on fatty acid β-oxidation for energy production. The official treatment recommendations include a fat-restricted and -modified diet in which long-chain fatty acids are fully or in part replaced by medium-chain triglycerides (MCT). Our studies on the VLCAD-/- mouse have shown that a long-term application of MCT results in a severe metabolic syndrome in female mice whereas males are protected. Our aim is to explore the sexually dimorphic response to defective mitochondrial β-oxidation as well as the effects of MCT on signaling pathways downstream mTOR which are involved in lipogenesis and adipogenesis.
METHODS: We performed in vivo metabolic phenotyping of untreated and with MCT treated fibroblasts by measuring cellular energetics, oxygen consumption, ATP production and proton efflux using Seahorse Technology. Regulation of mTOR pathway was investigated by Western Blot analysis. SILAC-based proteomic analysis was performed to quantify protein expression under normal conditions and under MCT diet.
RESULTS: Cellular respiration was significantly reduced in both sexes, however, male showed a better compensatory ability for defective β-oxidation than females. We detected a clear difference in the phosphorylation degree expressed as the ratio mTOR-P/ mTOR between male and female VLCAD-/- mice. Permanent incubation with MCT resulted to a significant reduction of mTOR phosphorylation degree in fibroblasts from male VLCAD-/- mice. In contrast, we observed a marked increase in the ratio mTOR-P/ mTOR in fibroblasts from female VLCAD-/- mice on MCT.
CONCLUSIONS: Our results showed for the first time the mechanisms of sex-specific difference in the metabolic regulation of cells with a β-oxidation defect in response to MCT treatment. The clinical relevance of this finding is under investigation.
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