title: The Stress-Induced Atf3-Gelsolin Cascade Underlies Dendritic Spine Deficits in Neuronal Models of Tuberous Sclerosis Complex.
abstract: Hyperactivation of the mechanistic target of rapamycin (mTOR) kinase, as a result of loss-of-function mutations in tuberous sclerosis complex 1 (TSC1) or TSC2 genes, causes protein synthesis dysregulation, increased cell size, and aberrant neuronal connectivity. Dysregulated synthesis of synaptic proteins has been implicated in the pathophysiology of autism spectrum disorder (ASD) associated with TSC and fragile X syndrome. However, cell type-specific translational profiles in these disease models remain to be investigated. Here, we used high-fidelity and unbiased Translating Ribosome Affinity Purification (TRAP) methodology to purify ribosome-associated mRNAs and identified translational alterations in a rat neuronal culture model of TSC. We find that expression of many stress and/or activity-dependent proteins is highly induced while some synaptic proteins are repressed. Importantly, transcripts for the activating transcription factor-3 (Atf3) and mitochondrial uncoupling protein-2 (Ucp2) are highly induced in Tsc2-deficient neurons, as well as in a neuron-specific Tsc1 conditional knock-out mouse model, and show differential responses to the mTOR inhibitor rapamycin. Gelsolin, a known target of Atf3 transcriptional activity, is also upregulated. shRNA-mediated block of Atf3 induction suppresses expression of gelsolin, an actin-severing protein, and rescues spine deficits found in Tsc2-deficient neurons. Together, our data demonstrate that a cell-autonomous program consisting of a stress-induced Atf3-gelsolin cascade affects the change in dendritic spine morphology following mTOR hyperactivation. This previously unidentified molecular cascade could be a therapeutic target for treating mTORopathies.
  
  
  CONCLUSIONS
  Tuberous sclerosis complex (TSC) is a genetic disease associated with epilepsy and autism. Dysregulated protein synthesis has been implicated as a cause of this disease. However, cell type-specific translational profiles that are aberrant in this disease are unknown. Here we show that expression of many stress and/or activity-dependent proteins is highly induced while some synaptic proteins are repressed in neurons missing the Tsc2 gene expression. Identification of genes whose translation is abnormal in TSC may provide insights to previously unidentified therapeutic targets.
authors.affiliation: F.M. Kirby Neurobiology Center, Department of Neurology, Children's Hospital Boston, Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: Duyu
authors.identifier: http://orcid.org/0000-0002-4280-6956
authors.initials: D
authors.lastname: Nie
authors.affiliation: Broad Institute of Massachusetts Institute of Technology and Harvard, Cambridge, Massachusetts 02142, and.
authors.forename: Zehua
authors.identifier: http://orcid.org/0000-0001-6799-3500
authors.initials: Z
authors.lastname: Chen
authors.affiliation: F.M. Kirby Neurobiology Center, Department of Neurology, Children's Hospital Boston, Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: Darius
authors.identifier: http://orcid.org/0000-0002-0026-4714
authors.initials: D
authors.lastname: Ebrahimi-Fakhari
authors.affiliation: F.M. Kirby Neurobiology Center, Department of Neurology, Children's Hospital Boston, Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: Alessia
authors.initials: A
authors.lastname: Di Nardo
authors.affiliation: F.M. Kirby Neurobiology Center, Department of Neurology, Children's Hospital Boston, Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: Kristina
authors.initials: K
authors.lastname: Julich
authors.affiliation: F.M. Kirby Neurobiology Center, Department of Neurology, Children's Hospital Boston, Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: Victoria K
authors.identifier: http://orcid.org/0000-0003-1825-0035
authors.initials: VK
authors.lastname: Robson
authors.affiliation: F.M. Kirby Neurobiology Center, Department of Neurology, Children's Hospital Boston, Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: Yung-Chih
authors.initials: YC
authors.lastname: Cheng
authors.affiliation: F.M. Kirby Neurobiology Center, Department of Neurology, Children's Hospital Boston, Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: Clifford J
authors.identifier: http://orcid.org/0000-0002-6636-3897
authors.initials: CJ
authors.lastname: Woolf
authors.affiliation: Broad Institute of Massachusetts Institute of Technology and Harvard, Cambridge, Massachusetts 02142, and Massachusetts Institute of Technology Department of Brain and Cognitive Sciences and the Picower Institute for Learning and Memory, Cambridge, Massachusetts 02139.
authors.forename: Myriam
authors.initials: M
authors.lastname: Heiman
authors.affiliation: F.M. Kirby Neurobiology Center, Department of Neurology, Children's Hospital Boston, Harvard Medical School, Boston, Massachusetts 02115, mustafa.sahin@childrens.harvard.edu.
authors.forename: Mustafa
authors.identifier: http://orcid.org/0000-0001-7044-2953
authors.initials: M
authors.lastname: Sahin
mesh_terms: D051700:Activating Transcription Factor 3 / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D049229:Dendritic Spines / Q000378:metabolism* / Q000473:pathology*; D004195:Disease Models, Animal; D005260:Female; D018260:Gelsolin / Q000378:metabolism*; D006624:Hippocampus / Q000378:metabolism / Q000473:pathology; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D008817:Mice, Mutant Strains; D020411:Oligonucleotide Array Sequence Analysis; D034741:RNA, Small Interfering; D051381:Rats; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D059467:Transcriptome; D014162:Transfection; D014402:Tuberous Sclerosis / Q000378:metabolism* / Q000473:pathology
chemical_list: D051700:Activating Transcription Factor 3; D018260:Gelsolin; D034741:RNA, Small Interfering; D058570:TOR Serine-Threonine Kinases
keywords: autism; dendiritic spines; mTOR; protein synthesis; translation