title: Forkhead transcription factor FOXO3a levels are increased in Huntington disease because of overactivated positive autofeedback loop.
abstract: Huntington disease (HD) is a fatal autosomal dominant neurodegenerative disorder caused by an increased number of CAG repeats in the HTT gene coding for huntingtin. Decreased neurotrophic support and increased mitochondrial and excitotoxic stress have been reported in HD striatal and cortical neurons. The members of the class O forkhead (FOXO) transcription factor family, including FOXO3a, act as sensor proteins that are activated upon decreased survival signals and/or increased cellular stress. Using immunocytochemical screening in mouse striatal Hdh(7/7) (wild type), Hdh(7/109) (heterozygous for HD mutation), and Hdh(109/109) (homozygous for HD mutation) cells, we identified FOXO3a as a differentially regulated transcription factor in HD. We report increased nuclear FOXO3a levels in mutant Hdh cells. Additionally, we show that treatment with mitochondrial toxin 3-nitropropionic acid results in enhanced nuclear localization of FOXO3a in wild type Hdh(7/7) cells and in rat primary cortical neurons. Furthermore, mRNA levels of Foxo3a are increased in mutant Hdh cells compared with wild type cells and in 3-nitropropionic acid-treated primary neurons compared with untreated neurons. A similar increase was observed in the cortex of R6/2 mice and HD patient post-mortem caudate tissue compared with controls. Using chromatin immunoprecipitation and reporter assays, we demonstrate that FOXO3a regulates its own transcription by binding to the conserved response element in Foxo3a promoter. Altogether, the findings of this study suggest that FOXO3a levels are increased in HD cells as a result of overactive positive feedback loop.
authors.affiliation: From the Department of Gene Technology, Tallinn University of Technology, Tallinn 12618, Estonia and.
authors.forename: Kaja
authors.initials: K
authors.lastname: Kannike
authors.affiliation: From the Department of Gene Technology, Tallinn University of Technology, Tallinn 12618, Estonia and.
authors.forename: Mari
authors.initials: M
authors.lastname: Sepp
authors.affiliation: the Department of Pharmacological Sciences and Center for Stem Cell Research, University of Milan, Milano 20133, Italy.
authors.forename: Chiara
authors.initials: C
authors.lastname: Zuccato
authors.affiliation: the Department of Pharmacological Sciences and Center for Stem Cell Research, University of Milan, Milano 20133, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Cattaneo
authors.affiliation: From the Department of Gene Technology, Tallinn University of Technology, Tallinn 12618, Estonia and tonis.timmusk@ttu.ee.
authors.forename: Tõnis
authors.initials: T
authors.lastname: Timmusk
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D003342:Corpus Striatum / Q000166:cytology / Q000378:metabolism; D025461:Feedback, Physiological; D005260:Female; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D057809:HEK293 Cells; D006801:Humans; D006816:Huntington Disease / Q000235:genetics / Q000378:metabolism*; D007150:Immunohistochemistry; D008297:Male; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D009154:Mutation; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D009574:Nitro Compounds / Q000494:pharmacology; D011401:Promoter Regions, Genetic / Q000235:genetics; D011422:Propionates / Q000494:pharmacology; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050486:Serotonin Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C499517:FOXO3 protein, human; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; C474033:FoxO3 protein, mouse; D009574:Nitro Compounds; D011422:Propionates; D050486:Serotonin Plasma Membrane Transport Proteins; C493231:Slc6a4 protein, mouse; C015392:3-nitropropionic acid
keywords: 3-Nitropropionic Acid (3-NP); Akt PKB; Autoregulation; Chromatin Immunoprecipitation (ChIP); FOXO; Hdh Cell Line; Huntington Disease; Neurons; Nuclear Translocation; R6/2 Mice, Post-mortem Brain Tissue