Essi F Biyong1, Cyntia Tremblay2, Manon Leclerc2, Vicky Caron2, Serge Alfos3, Jean-Christophe Helbling3, Léa Rodriguez4, Vincent Pernet4, David A Bennett5, Véronique Pallet6, Frédéric Calon7. 1. Univ. Bordeaux, INRAE, Bordeaux INP, NutriNeuro, UMR 1286, F-33000 Bordeaux, France; Faculté de pharmacie, Université Laval, Québec, Québec, Canada; Centre de recherche du CHU de Québec-Université Laval (CHUL), Axe Neurosciences, 2705 Boulevard Laurier, Québec, Québec, Canada; Institut sur la Nutrition et les Aliments Fonctionnels (INAF), Québec, Québec, Canada; LIA OptiNutriBrain - Laboratoire International Associé (NutriNeuro France-INAF Canada), Canada. 2. Faculté de pharmacie, Université Laval, Québec, Québec, Canada; Centre de recherche du CHU de Québec-Université Laval (CHUL), Axe Neurosciences, 2705 Boulevard Laurier, Québec, Québec, Canada. 3. Univ. Bordeaux, INRAE, Bordeaux INP, NutriNeuro, UMR 1286, F-33000 Bordeaux, France. 4. CUO-Recherche, Centre de Recherche du CHU de Québec, Québec, QC, Canada; Département d'ophtalmologie, Faculté de Médecine, Université Laval, Québec, QC, Canada. 5. Rush Alzheimer's Disease Center, Rush University Medical Center, Chicago, IL, USA. 6. Univ. Bordeaux, INRAE, Bordeaux INP, NutriNeuro, UMR 1286, F-33000 Bordeaux, France; LIA OptiNutriBrain - Laboratoire International Associé (NutriNeuro France-INAF Canada), Canada. 7. Faculté de pharmacie, Université Laval, Québec, Québec, Canada; Centre de recherche du CHU de Québec-Université Laval (CHUL), Axe Neurosciences, 2705 Boulevard Laurier, Québec, Québec, Canada; Institut sur la Nutrition et les Aliments Fonctionnels (INAF), Québec, Québec, Canada; LIA OptiNutriBrain - Laboratoire International Associé (NutriNeuro France-INAF Canada), Canada. Electronic address: frederic.calon@crchudequebec.ulaval.ca.
Abstract
BACKGROUND: Vitamin A (VitA), via its active metabolite retinoic acid (RA), is critical for the maintenance of memory function with advancing age. Although its role in Alzheimer's disease (AD) is not well understood, data suggest that impaired brain VitA signaling is associated with the accumulation of β-amyloid peptides (Aβ), and could thus contribute to the onset of AD. METHODS: We evaluated the protective action of a six-month-long dietary VitA-supplementation (20 IU/g), starting at 8 months of age, on the memory and the neuropathology of the 3xTg-AD mouse model of AD (n = 11-14/group; including 4-6 females and 7-8 males). We also measured protein levels of Retinoic Acid Receptor β (RARβ) and Retinoid X Receptor γ (RXRγ) in homogenates from the inferior parietal cortex of 60 participants of the Religious Orders study (ROS) divided in three groups: no cognitive impairment (NCI) (n = 20), mild cognitive impairment (MCI) (n = 20) and AD (n = 20). RESULTS: The VitA-enriched diet preserved spatial memory of 3xTg-AD mice in the Y maze. VitA-supplementation affected hippocampal RXR expression in an opposite way according to sex by tending to increase in males and decrease in females their mRNA expression. VitA-enriched diet also reduced the amount of hippocampal Aβ40 and Aβ42, as well as the phosphorylation of tau protein at sites Ser396/Ser404 (PHF-1) in males. VitA-supplementation had no effect on tau phosphorylation in females but worsened their hippocampal Aβ load. However, the expression of Rxr-β in the hippocampus was negatively correlated with the amount of both soluble and insoluble Aβ in both males and females. Western immunoblotting in the human cortical samples of the ROS study did not reveal differences in RARβ levels. However, it evidenced a switch from a 60-kDa-RXRγ to a 55-kDa-RXRγ in AD, correlating with ante mortem cognitive decline and the accumulation of neuritic plaques in the brain cortex. CONCLUSION: Our data suggest that (i) an altered expression of RXRs receptors is a contributor to β-amyloid pathology in both humans and 3xTg-AD mice, (ii) a chronic exposure of 3xTg-AD mice to a VitA-enriched diet may be protective in males, but not in females.
BACKGROUND: Vitamin A (VitA), via its active metabolite retinoic acid (RA), is critical for the maintenance of memory function with advancing age. Although its role in Alzheimer's disease (AD) is not well understood, data suggest that impaired brain VitA signaling is associated with the accumulation of β-amyloid peptides (Aβ), and could thus contribute to the onset of AD. METHODS: We evaluated the protective action of a six-month-long dietary VitA-supplementation (20 IU/g), starting at 8 months of age, on the memory and the neuropathology of the 3xTg-AD mouse model of AD (n = 11-14/group; including 4-6 females and 7-8 males). We also measured protein levels of Retinoic Acid Receptor β (RARβ) and Retinoid X Receptor γ (RXRγ) in homogenates from the inferior parietal cortex of 60 participants of the Religious Orders study (ROS) divided in three groups: no cognitive impairment (NCI) (n = 20), mild cognitive impairment (MCI) (n = 20) and AD (n = 20). RESULTS: The VitA-enriched diet preserved spatial memory of 3xTg-AD mice in the Y maze. VitA-supplementation affected hippocampal RXR expression in an opposite way according to sex by tending to increase in males and decrease in females their mRNA expression. VitA-enriched diet also reduced the amount of hippocampal Aβ40 and Aβ42, as well as the phosphorylation of tau protein at sites Ser396/Ser404 (PHF-1) in males. VitA-supplementation had no effect on tau phosphorylation in females but worsened their hippocampal Aβ load. However, the expression of Rxr-β in the hippocampus was negatively correlated with the amount of both soluble and insoluble Aβ in both males and females. Western immunoblotting in the human cortical samples of the ROS study did not reveal differences in RARβ levels. However, it evidenced a switch from a 60-kDa-RXRγ to a 55-kDa-RXRγ in AD, correlating with ante mortem cognitive decline and the accumulation of neuritic plaques in the brain cortex. CONCLUSION: Our data suggest that (i) an altered expression of RXRs receptors is a contributor to β-amyloid pathology in both humans and 3xTg-AD mice, (ii) a chronic exposure of 3xTg-AD mice to a VitA-enriched diet may be protective in males, but not in females.
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