Investigating how apolipoprotein E genotypes modify fatty acid metabolism

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OVERALL AIM OF THE PROGRAM: To elucidate the role(s) of apolipoprotein E (APOE) genotypes on long chain polyunsaturated fatty acids (LC-PUFA) metabolism.BACKGROUND: The plasma LC-PUFA pool is critical to bring LC-PUFA to the brain and it is dynamic, constantly exchanging FA with organs and tissues. One third of the fatty acids composing brain membranes are arachidonic acid (ARA) and docosahexaenoic acid (DHA): two LC-PUFAs provided almost exclusively by the diet. Previous studies suggested that there is an adipose-liver-brain FA axis. The APOE gene has three existing isoforms in human (E2, E3 and E4). In our previous NSERC-discovery grant (DG), we have shown that there are APOE-genotype specific dysregulation in LC-PUFA homeostasis in the liver, the adipose tissue, the plasma and the brain. Using in situ intracerebral perfusion, my collaborator Frederic Calon and I showed lower brain uptake of 14C-DHA in 4- and 13-month-old hAPOE4 mice compared to uptake in hAPOE2 mice fed a deficient diet in n-3 LC-PUFA. This intriguing result suggests that LC-PUFA homeostasis deregulation starts early in life in hAPOE4 mice. Therefore, the hypothesis for this NSERC-DG program is that, at a young age, APOE genotype interacts with dietary fatty acids to modulate the fatty acid profile, their transport proteins and their levels of gene expression in the adipose-liver-brain axis.SPECIFIC OBJECTIVES FOR THE NEXT FIVE YEARS: 1. To investigate the fatty acid homeostasis of the adipose-liver-brain axis by APOE genotype and dietary fat intake. 2. To evaluate brain ARA and DHA uptake with respect to the different APOE genotypes and diets using in situ brain perfusion.EXPERIMENTAL APPROACHIn the current research program, we propose to use transgenic mouse strains expressing either humans APOE2, APOE3 or APOE4 and C57BL6 / 129SV mice as control (same genetic background than the transgenic mice). Three different diets will be used to alter the fatty acid profile of tissues and organs: A) a control diet, B) a diet enriched with DHA and C) a diet deprived in n-3 LC-PUFA. Mice will be fed these diets for 16 weeks. We will quantify ARA and DHA, the expression of fatty acid transporters genes as well as their respective proteins in each organs and tissues. We will develop lipididomics methodology with our new LC-MS-MS instrument. The brain uptake of ARA and DHA will be evaluated by APOE genotype and dietary fat intake using in situ cerebral perfusion with the collaboration of Frederic Calon at Université Laval. NOVELTY AND EXPECTED SIGNIFICANCE: Studying the adipose-liver-brain axis is something novel as we use an integrative approach instead of an organ targeted approach. Investigating multi-organ LC-PUFA homeostasis in relation to APOE genotype is important considering the regulatory role of LC-PUFA for organs and tissues and the role of apoe in lipid transport and homeostasis.