title: Toxic effects of expanded ataxin-1 involve mechanical instability of the nuclear membrane.
abstract: Ataxin 1 (ATXN1) is the protein involved in spinocerebellar ataxia type 1, one of nine dominantly inherited neurodegenerative diseases triggered by polyglutamine expansion. One of the isolated polyglutamine tracts properties is to interact with lipid bilayers. Here we used a multidisciplinary approach to test whether one of the mechanisms responsible for neuronal degeneration involves the destabilization of the nuclear membrane. We thus analyzed the interaction between ATXN1 and lipid membranes, both on cellular models and on artificial lipid bilayers, comparing pathological expanded polyglutamine and histidine interrupted non-harmful polyglutamine tracts of the same length. The toxicity of the different constructs was tested in transiently transfected COS1 cells. Cells expressing pathological ATXN1 presented a significantly higher frequency of anomalous nuclei with respect to those expressing non-harmful ATXN1. Immunofluorescence and electron microscopy showed severe damage in the nuclear membrane of cells expressing the pathological protein. Atomic force microscopy on artificial membranes containing interrupted and non-interrupted partial ATXN1 peptides revealed a different arrangement of the peptides within the lipid bilayer. Force-distance measurements indicated that membrane fragility increases with the lengthening of the uninterrupted glutamine. Transmembrane electrical measurements were performed on artificial bilayers and on the inner nuclear membrane of ATXN1 full length transfected cells. Both artificial lipid bilayers and cellular models demonstrated the dynamic appearance of ionic pathways. Uninterrupted polyglutamines showed not only a larger ionic flow, but also an increase in the single event conductance. Collectively, our results suggest that expanded ATXN1 may induce unregulated ionic pathways in the nuclear membrane, causing severe damage to the cell.
authors.affiliation: Department of Biomolecular Science and Biotechnology, University of Milan, Italy.
authors.forename: Lisa
authors.initials: L
authors.lastname: Mapelli
authors.forename: Claudio
authors.initials: C
authors.lastname: Canale
authors.forename: Daniela
authors.initials: D
authors.lastname: Pesci
authors.forename: Stefania
authors.initials: S
authors.lastname: Averaimo
authors.forename: Fabiana
authors.initials: F
authors.lastname: Guizzardi
authors.forename: Valentina
authors.initials: V
authors.lastname: Fortunati
authors.forename: Laura
authors.initials: L
authors.lastname: Falasca
authors.forename: Mauro
authors.initials: M
authors.lastname: Piacentini
authors.forename: Alessandra
authors.initials: A
authors.lastname: Gliozzi
authors.forename: Annalisa
authors.initials: A
authors.lastname: Relini
authors.forename: Michele
authors.initials: M
authors.lastname: Mazzanti
authors.forename: Carla
authors.initials: C
authors.lastname: Jodice
mesh_terms: D000818:Animals; D000067528:Ataxins; D019556:COS Cells; D002467:Cell Nucleus / Q000648:ultrastructure*; D002522:Chlorocebus aethiops; D006639:Histidine / Q000378:metabolism; D008051:Lipid Bilayers / Q000032:analysis*; D018625:Microscopy, Atomic Force; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000378:metabolism*; D009685:Nuclear Envelope / Q000502:physiology*; D009687:Nuclear Proteins / Q000737:chemistry* / Q000378:metabolism*; D010455:Peptides / Q000737:chemistry; D020754:Spinocerebellar Ataxias / Q000473:pathology
chemical_list: D000067528:Ataxins; D008051:Lipid Bilayers; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010455:Peptides; C097188:polyglutamine; D006639:Histidine