title: Two-step activation of FOXO3 by AMPK generates a coherent feed-forward loop determining excitotoxic cell fate.
abstract: Cerebral ischemia and excitotoxic injury induce transient or permanent bioenergetic failure, and may result in neuronal apoptosis or necrosis. We have previously shown that ATP depletion and activation of AMP-activated protein kinase (AMPK) during excitotoxic injury induces neuronal apoptosis by transcription of the pro-apoptotic BH3-only protein, Bim. AMPK, however, also exerts pro-survival functions in neurons. The molecular switches that determine these differential outcomes are not well understood. Using an approach combining biochemistry, single-cell imaging and computational modeling, we here demonstrate that excitotoxic injury activated the bim promoter in a FOXO3-dependent manner. The activation of AMPK reduced AKT activation, and led to dephosphorylation and nuclear translocation of FOXO3. Subsequent mutation studies indicated that bim gene activation during excitotoxic injury required direct FOXO3 phosphorylation by AMPK in the nucleus as a second activation step. Inhibition of this phosphorylation prevented Bim expression and protected neurons against excitotoxic and oxygen/glucose deprivation-induced injury. Systems analysis and computational modeling revealed that these two activation steps defined a coherent feed-forward loop; a network motif capable of filtering any effects of short-term AMPK activation on bim gene induction. This may prevent unwanted AMPK-mediated Bim expression and apoptosis during transient or physiological bioenergetic stress.
authors.affiliation: Centre for the Study of Neurological Disorders, Royal College of Surgeons in Ireland, Dublin, Ireland.
authors.forename: D
authors.initials: D
authors.lastname: Davila
authors.forename: N M C
authors.initials: NM
authors.lastname: Connolly
authors.forename: H
authors.initials: H
authors.lastname: Bonner
authors.forename: P
authors.initials: P
authors.lastname: Weisová
authors.forename: H
authors.initials: H
authors.lastname: Dussmann
authors.forename: C G
authors.initials: CG
authors.lastname: Concannon
authors.forename: H J
authors.initials: HJ
authors.lastname: Huber
authors.forename: J H M
authors.initials: JH
authors.lastname: Prehn
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D000072224:Bcl-2-Like Protein 11; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D015536:Down-Regulation; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; C000606776:Bcl2l11 protein, mouse; C000606778:Bcl2l11 protein, rat; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; C474033:FoxO3 protein, mouse; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D018808:Transcription Factor AP-1; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D005947:Glucose