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.

Mutant TDP-43 within motor neurons drives disease onset but not progression in amyotrophic lateral sclerosis

“…A convergence of recent evidence has implicated errors in nucleo/cytoplasmic transport as a component of normal aging [11] as well as several neurodegenerative disorders [13], including ALS/FTD [8, 49], Huntington’s disease (Cleveland and Lagier-Tourenne, personal communication) [35, 43, 68], and other repeat expansion models [38, 51]. Studies in yeast [27] and flies [61] have identified components of nuclear transport as modifiers of toxicity in models expressing mutant TDP-43, or the C9orf72 hexanucleotide repeat expansion [17, 71].…”

Polyglutamine-Expanded Huntingtin Exacerbates Age-Related Disruption of Nuclear Integrity and Nucleocytoplasmic Transport

“…Indeed, impaired nucleocytoplasmic transport and nuclear integrity have been identified as hallmarks of aged neurons (Fifkova et al, 1987, Mertens et al, 2015). A flurry of recent reports has indicated that nucleocytoplasmic compartmentalization is also markedly impaired in several models of repeat expansion disorders (Chapple et al, 2008, Mapelli et al, 2012, Freibaum et al, 2015, Jovicic et al, 2015, Kaneb et al, 2015, Liu et al, 2015, Rodriguez et al, 2015, Zhang et al, 2015, Da Cruz and Cleveland, 2016, Lee et al, 2016, Nekrasov et al, 2016, Woerner et al, 2016, Zhang et al, 2016, Shi et al, 2017). Furthermore, apparent disruption of the nuclear envelope or disrupted nucleocytoplasmic transport has been reported in postmortem tissues from ALS (Kinoshita et al, 2009), Parkinson’s (Liu et al, 2012) and Alzheimer’s disease patients (Sheffield et al, 2006), and in cells expressing aggregation-prone proteins (Frost et al, 2016, Woerner et al, 2016).…”

The ataxin-1 interactome reveals direct connection with multiple disrupted nuclear transport pathways

“…The nuclear pore complex (NPC) is the regulated gateway for trafficking between the cell cytosol and nucleus, and is a potential target of mutant polyQ-huntingtin protein in HD 10 , where progressive disruption of nuclear envelope morphology has been observed in aging mice expressing the polyQ-huntingtin protein 9 . Post-mortem samples from patients with ALS 52 also show disruptions to the nuclear envelope, whereas polyQ-ataxin-1 may also decrease nuclear membrane instability 53 . Among the nucleoporins, the main components of NPC, NUP98 has the most conserved FG-dipeptide motif domain and is a major contributor to the NPC permeability barrier 54 .…”