Dataset Information

C9orf72 arginine-rich dipeptide repeat proteins disrupt importin beta-mediated nuclear import

ABSTRACT: Disruption of nucleocytoplasmic transport (NCT), including mislocalization of the importin beta cargo, TDP-43, is a hallmark of amyotrophic lateral sclerosis (ALS), including ALS caused by a hexanucleotide repeat expansion in C9orf72. However, the mechanism(s) remain unclear. Importin beta and its cargo adaptors have been shown to co-precipitate with the C9orf72-arginine-containing dipeptide repeat proteins (R-DPRs), poly-glycine arginine (GR) and poly-proline arginine (PR), and are protective in genetic modifier screens. Here, we show that R-DPRs interact with importin beta, disrupt its cargo loading, and inhibit nuclear import in permeabilized mouse neurons and HeLa cells, in a manner that can be rescued by RNA. Although R-DPRs induce widespread protein aggregation in this in vitro system, transport disruption is not due to NCT protein sequestration, nor blockade of the phenylalanine-glycine (FG)-rich nuclear pore complex. Our results support a model in which R-DPRs interfere with nuclear transport receptors in the vicinity of the nuclear envelope.

INSTRUMENT(S): Q Exactive

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Epithelial Cell, Cell Culture

DISEASE(S): Amyotrophic Lateral Sclerosis

SUBMITTER: Lindsey Hayes

LAB HEAD: Lindsey Hayes

PROVIDER: PXD015656 | Pride | 2020-05-20

REPOSITORIES: Pride

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Publications

C9orf72 arginine-rich dipeptide repeat proteins disrupt karyopherin-mediated nuclear import.

Hayes Lindsey R LR Duan Lauren L Bowen Kelly K Kalab Petr P Rothstein Jeffrey D JD

eLife 20200302

Disruption of nucleocytoplasmic transport is increasingly implicated in the pathogenesis of neurodegenerative diseases, including ALS caused by a C9orf72 hexanucleotide repeat expansion. However, the mechanism(s) remain unclear. Karyopherins, including importin β and its cargo adaptors, have been shown to co-precipitate with the C9orf72 arginine-containing dipeptide repeat proteins (R-DPRs), poly-glycine arginine (GR) and poly-proline arginine (PR), and are protective in genetic mo ...[more]

PMID: 32119645

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Project description:Amyotrophic lateral sclerosis (ALS) is a deleterious neurodegenerative disease without effective treatment options. Recent studies have indicated the involvement of the dysregulation of RNA metabolism in the pathogenesis of ALS. Among the various RNA regulatory machineries, nonsense-mediated mRNA decay (NMD) is a stress responsive cellular surveillance system that degrades selected mRNA substrates to prevent the translation of defective or harmful proteins. Whether this pathway is affected in neurodegenerative diseases is unclear. Here we report that the NMD pathway is inhibited in ALS patients with C9orf72 hexanucleotide repeat expansion (HRE), the most common cause of familial ALS. Bioinformatic analysis of multiple transcriptome profiles revealed significant overlap of upregulated genes in NMD-defective cells with those in the brain tissues, micro-dissected motor neurons, or induced pluripotent stem cell-derived motor neurons from ALS patients carrying C9orf72 HRE, suggesting the suppression of NMD pathway in these patients. In contrast, there are few overlapping upregulated genes in brain tissues from sporadic ALS patients with those in NMD-defective cells. Using Drosophila models expressing various C9orf72 HRE products, we have validated the suppression of the NMD pathway by C9orf72 HRE and identified arginine-rich dipeptide repeats (DPRs) generated from HRE as the main culprits of NMD inhibition. Furthermore, in human SH-SY5Y neuroblastoma cells and in mouse brains, expression of arginine-rich DPRs was sufficient to cause NMD inhibition. Remarkably, expression of UPF1, a core gene in the NMD pathway, efficiently blocked neurotoxicity caused by arginine-rich DPRs in both cellular and Drosophila models. Although not as effective as UPF1, expression of another NMD gene UPF2 also ameliorated the degenerative phenotypes in DPR-expressing flies, indicating neuroprotection by genetically reactivating the NMD pathway. Finally, after validating Tranilast as an NMD-activating drug, we demonstrated its therapeutic potential in cellular and Drosophila models of C9orf72 DPR neurotoxicity. Therefore, our study has revealed the suppression of NMD in C9orf72 ALS and has suggested that the restoration of the NMD pathway by Tranilast, an asthma drug with solid safety record, could be a promising therapeutic strategy for ALS.

Project description:Introduction: The mechanisms governing synaptonuclear transport, and the transcriptional pathways that are at the core of neuronal disorders are poorly understood. The importin family of nuclear import factors has pivotal roles in such pathways, due to their involvement in intracellular transport from both synapse to soma and cytoplasm to nucleus. Mammals express six different isoforms of importin α, which bind an Importin β to form transport complexes for specific cargoes. Methods: We addressed the roles of importin α isoforms in mammalian CNS by evaluation of a systematic series of importin α knockout mice. A comprehensive battery of behavioral tests was used to investigate spontaneous and novelty-induced locomotion, basal ganglia function, motor coordination, neuromuscular integration, anxiety-related behaviors and memory. Subsequent analyses using acute-brain slice electrophysiology, RNA-seq, bioinformatics, imaging and pharmacology was used in order to delineate the contribution of genes and signaling pathways involved in the identified phenotype and screen for new therapeutic approaches. Results and Discussion: During the course of comprehensive behavioral profiling of importin α mouse mutants, we identified an importin α knockout (KO) mouse with significantly reduced anxiety levels. Electrophysiological recordings in acute hippocampal slices showed a reduced short-term and presynaptic plasticity (paired-pulse facilitation deficit, lower PTP), while LTP was not affected in these mutants. We then performed transcriptional profiling (RNA-seq) from hippocampal extracts of wild type versus mutant animals after exposure to an anxiogenic drug. Computational analysis revealed differences in the expression of genes and the involvement of transcription factors. Drugs that activate LXR or the Sphingosine 1 phosphate receptor have robust anxiolytic effects, while a Sphk1 blocker reverses anxiolysis in the importin α5 knockout mouse. Thus, importin α5 influences anxiety by regulating nuclear import in neurons.

Dataset Information

C9orf72 arginine-rich dipeptide repeat proteins disrupt importin beta-mediated nuclear import

Publications

<i>C9orf72</i> arginine-rich dipeptide repeat proteins disrupt karyopherin-mediated nuclear import.

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