Reversal of apoE4-driven brain pathology and behavioral deficits by bexarotene.
Apolipoprotein E4 (apoE4), the most prevalent genetic risk factor for Alzheimer's disease (AD), is less lipidated than its corresponding AD-benign form, apoE3, and it has been suggested that the pathological effects of apoE4 are mediated by lipid-related mechanisms. ATP-binding cassette transporters A1 and G1 (ABCA1 and ABCG1, respectively) are the most important apoE-lipidating proteins. The expression of these proteins, as well as that of apoE, is controlled by the transcription regulation retinoid X receptor (RXR)-liver X receptor (LXR) system. In the present study, we investigated the effects of the RXR agonist bexarotene on mRNA and protein levels of apoE, ABCA1, and ABCG1 in young, naive apoE3- and apoE4-targeted replacement mice and assessed the extent to which this reverses the apoE4-driven pathological phenotype. This investigation reveled that bexarotene increases the mRNA and protein levels of ABCA1 and ABCG1 in hippocampal neurons, but has no effect on the corresponding levels of apoE. These findings were associated with reversal of the lipidation deficiency of apoE4 and of the cognitive impairments of apoE4 mice in several tests. Furthermore, bexarotene reversed the apoE4-driven accumulation of Aβ42 and hyperphosphorylated tau in hippocampal neurons, as well as the apoE4-induced reduction in the levels of the presynaptic marker vesicular glutamatergic transporter 1 (VGluT1). In conclusion, the results show that treatment of apoE4 mice with the RXR agonist bexarotene reverses the apoE4-induced cognitive and neuronal impairments in vivo and suggest that this is due to reversal of the lipidation deficiency of apoE4. This puts forward the possibility that RXR activation and increased levels of ABCA1 and ABCG1 could be useful in the treatment of human apoE4 carriers.
Department of the Neurobiology, The George S. Wise Faculty of Life Sciences, The Sagol School of Neuroscience, Tel Aviv University, Tel Aviv 69978, Israel.
Anat
A
Boehm-Cagan
Department of the Neurobiology, The George S. Wise Faculty of Life Sciences, The Sagol School of Neuroscience, Tel Aviv University, Tel Aviv 69978, Israel dmichael@post.tau.ac.il.
Daniel M
DM
Michaelson
D064286:ATP Binding Cassette Transporter 1 / Q000235:genetics / Q000378:metabolism; D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D016229:Amyloid beta-Peptides / Q000378:metabolism; D000818:Animals; D016588:Anticarcinogenic Agents / Q000494:pharmacology / Q000627:therapeutic use*; D001057:Apolipoproteins E / Q000235:genetics / Q000378:metabolism*; D000077610:Bexarotene; D001921:Brain / Q000187:drug effects* / Q000473:pathology; D004195:Disease Models, Animal; D005106:Exploratory Behavior / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D008074:Lipoproteins / Q000235:genetics / Q000378:metabolism; D018782:Maze Learning / Q000187:drug effects; D001523:Mental Disorders / Q000188:drug therapy / Q000235:genetics / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D010446:Peptide Fragments / Q000378:metabolism; D021641:Recognition, Psychology / Q000187:drug effects; D013764:Tetrahydronaphthalenes / Q000494:pharmacology / Q000627:therapeutic use*; D013997:Time Factors
C487540:ABCG1 protein, mouse; D064286:ATP Binding Cassette Transporter 1; D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters; D016229:Amyloid beta-Peptides; D016588:Anticarcinogenic Agents; D001057:Apolipoproteins E; D008074:Lipoproteins; D010446:Peptide Fragments; D013764:Tetrahydronaphthalenes; C075222:amyloid beta-protein (1-42); D000077610:Bexarotene
ABCA1; ABCG1; Alzheimer's disease; ApoE4; apoE-targeted mice; bexarotene