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1.
Nat Commun ; 12(1): 4908, 2021 08 13.
Artigo em Inglês | MEDLINE | ID: mdl-34389711

RESUMO

C9ORF72 hexanucleotide GGGGCC repeat expansion is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Repeat-containing RNA mediates toxicity through nuclear granules and dipeptide repeat (DPR) proteins produced by repeat-associated non-AUG translation. However, it remains unclear how the intron-localized repeats are exported and translated in the cytoplasm. We use single molecule imaging approach to examine the molecular identity and spatiotemporal dynamics of the repeat RNA. We demonstrate that the spliced intron with G-rich repeats is stabilized in a circular form due to defective lariat debranching. The spliced circular intron, instead of pre-mRNA, serves as the translation template. The NXF1-NXT1 pathway plays an important role in the nuclear export of the circular intron and modulates toxic DPR production. This study reveals an uncharacterized disease-causing RNA species mediated by repeat expansion and demonstrates the importance of RNA spatial localization to understand disease etiology.


Assuntos
Proteína C9orf72/genética , Núcleo Celular/metabolismo , Íntrons/genética , Biossíntese de Proteínas/genética , RNA/genética , Transporte Ativo do Núcleo Celular/genética , Esclerose Amiotrófica Lateral/genética , Esclerose Amiotrófica Lateral/metabolismo , Proteína C9orf72/metabolismo , Linhagem Celular Tumoral , Núcleo Celular/genética , Expansão das Repetições de DNA/genética , Dipeptídeos/genética , Dipeptídeos/metabolismo , Demência Frontotemporal/genética , Demência Frontotemporal/metabolismo , Predisposição Genética para Doença/genética , Células HEK293 , Humanos , Microscopia de Fluorescência , Proteínas de Transporte Nucleocitoplasmático/genética , Proteínas de Transporte Nucleocitoplasmático/metabolismo , RNA/metabolismo , Proteínas de Ligação a RNA/genética , Proteínas de Ligação a RNA/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Transdução de Sinais/genética
2.
J Vis Exp ; (173)2021 07 09.
Artigo em Inglês | MEDLINE | ID: mdl-34309603

RESUMO

Disruption of nucleocytoplasmic transport is increasingly implicated in the pathogenesis of neurodegenerative diseases. Moreover, there is a growing recognition of cell-specific differences in nuclear pore complex structure, prompting a need to adapt nuclear transport methods for use in neurons. Permeabilized cell assays, in which the plasma membrane is selectively perforated by digitonin, are widely used to study passive and active nuclear transport in immortalized cell lines but have not been applied to neuronal cultures. In our initial attempts, we observed the rapid loss of nuclear membrane integrity in primary mouse cortical neurons exposed to even low concentrations of digitonin. We hypothesized that neuronal nuclear membranes may be uniquely vulnerable to the loss of cytoplasmic support. After testing multiple approaches to improve nuclear stability, we observed optimal nuclear integrity following hypotonic lysis in the presence of a concentrated bovine serum albumin cushion. Neuronal nuclei prepared by this approach reliably import recombinant fluorescent cargo in an energy-dependent manner, facilitating analysis of nuclear import by high content microscopy with automated analysis. We anticipate that this method will be broadly applicable to studies of passive and active nuclear transport in primary neurons.

3.
J Am Chem Soc ; 143(19): 7368-7379, 2021 05 19.
Artigo em Inglês | MEDLINE | ID: mdl-33855846

RESUMO

The expansion of a hexanucleotide repeat GGGGCC (G4C2) in the C9orf72 gene is the most common cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The G4C2 expansion leads to repeat-associated non-AUG (RAN) translation and the production of toxic dipeptide repeat (DPR) proteins, but the mechanisms of RAN translation remain enigmatic. Here, we report that the RNA helicase DHX36 is a robust positive regulator of C9orf72 RAN translation. DHX36 has a high affinity for the G4C2 repeat RNA, preferentially binds to the repeat RNA's G-quadruplex conformation, and efficiently unwinds the G4C2 G-quadruplex structures. Native DHX36 interacts with the G4C2 repeat RNA and is essential for effective RAN translation in the cell. In induced pluripotent stem cells and differentiated motor neurons derived from C9orf72-linked ALS patients, reducing DHX36 significantly decreased the levels of endogenous DPR proteins. DHX36 is also aberrantly upregulated in tissues of C9orf72-linked ALS patients. These results indicate that DHX36 facilitates C9orf72 RAN translation by resolving repeat RNA G-quadruplex structures and may be a potential target for therapeutic intervention.

4.
Cell Rep ; 34(13): 108925, 2021 03 30.
Artigo em Inglês | MEDLINE | ID: mdl-33789100

RESUMO

Multiple cellular pathways have been suggested to be altered by the C9orf72 GGGGCC (G4C2) hexanucleotide repeat expansion (HRE), including aspects of RNA regulation such as nonsense-mediated decay (NMD). Here, we investigate the role that overexpression of UPF1, a protein involved in NMD, plays in mitigating neurotoxicity in multiple models of C9orf72 ALS/FTD. First, we show that NMD is not altered in our endogenous induced pluripotent stem cell (iPSC)-derived spinal neuron (iPSN) model of C9orf72 ALS (C9-ALS) or postmortem motor cortex tissue from C9-ALS patients. Unexpectedly, we find that UPF1 overexpression significantly reduces the severity of known neurodegenerative phenotypes without altering NMD function itself. UPF1 overexpression reduces poly(GP) abundance without altering the amount of repeat RNA, providing a potential mechanism by which UPF1 reduces dipeptide repeat (DPR) protein-mediated toxicity. Together, these findings indicate that UPF1 is neuroprotective in the context of C9-ALS, albeit independent of known UPF1-mediated NMD pathways.

6.
Elife ; 92020 03 02.
Artigo em Inglês | MEDLINE | ID: mdl-32119645

RESUMO

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 ß 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 ß, disrupt its cargo loading, and inhibit nuclear import of importin ß, importin α/ß, and transportin cargoes 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 nucleocytoplasmic transport protein sequestration, nor blockade of the phenylalanine-glycine (FG)-rich nuclear pore complex. Our results support a model in which R-DPRs interfere with cargo loading on karyopherins.


Assuntos
Arginina/metabolismo , Proteína C9orf72/metabolismo , Dipeptídeos/metabolismo , Carioferinas/metabolismo , Transporte Ativo do Núcleo Celular , Esclerose Amiotrófica Lateral/metabolismo , Animais , Proteína C9orf72/química , Humanos , Camundongos , Ligação Proteica , beta Carioferinas/metabolismo
7.
Neuron ; 104(5): 885-898.e8, 2019 12 04.
Artigo em Inglês | MEDLINE | ID: mdl-31587919

RESUMO

Hexanucleotide GGGGCC repeat expansion in C9ORF72 is the most prevalent genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). One pathogenic mechanism is the aberrant accumulation of dipeptide repeat (DPR) proteins produced by the unconventional translation of expanded RNA repeats. Here, we performed genome-wide CRISPR-Cas9 screens for modifiers of DPR protein production in human cells. We found that DDX3X, an RNA helicase, suppresses the repeat-associated non-AUG translation of GGGGCC repeats. DDX3X directly binds to (GGGGCC)n RNAs but not antisense (CCCCGG)n RNAs. Its helicase activity is essential for the translation repression. Reduction of DDX3X increases DPR levels in C9ORF72-ALS/FTD patient cells and enhances (GGGGCC)n-mediated toxicity in Drosophila. Elevating DDX3X expression is sufficient to decrease DPR levels, rescue nucleocytoplasmic transport abnormalities, and improve survival of patient iPSC-differentiated neurons. This work identifies genetic modifiers of DPR protein production and provides potential therapeutic targets for C9ORF72-ALS/FTD.


Assuntos
Esclerose Amiotrófica Lateral/metabolismo , Proteína C9orf72/biossíntese , RNA Helicases DEAD-box/metabolismo , Demência Frontotemporal/metabolismo , Animais , Sistemas CRISPR-Cas , Drosophila , Humanos , Biossíntese de Proteínas/fisiologia , Sequências Repetitivas de Ácido Nucleico
8.
Exp Neurol ; 318: 251-257, 2019 08.
Artigo em Inglês | MEDLINE | ID: mdl-31082391

RESUMO

Impairment of mitochondrial transport has long been implicated in the pathogenesis of neuropathy and neurodegeneration. However, the role of mitochondria in stabilizing motor nerve terminals at neuromuscular junction (NMJ) remains unclear. We previously demonstrated that mice lacking the antioxidant enzyme, superoxide dismutase-1 (Sod1-/-), develop progressive NMJ denervation. This was rescued by expression of SOD1 exclusively in the mitochondrial intermembrane space (MitoSOD1/Sod1-/-), suggesting that oxidative stress within mitochondria drives denervation in these animals. However, we also observed reduced mitochondrial density in Sod1-/- motor axons in vitro. To investigate the relationship between mitochondrial density and NMJ innervation in vivo, we crossed Sod1-/- mice with the fluorescent reporter strains Thy1-YFP and Thy1-mitoCFP. We identified an age-dependent loss of mitochondria at motor nerve terminals in Sod1-/- mice, that closely correlated with NMJ denervation, and was rescued by MitoSOD1 expression. To test whether augmenting mitochondrial transport rescues Sod1-/- axons, we generated transgenic mice overexpressing the mitochondrial cargo adaptor, Miro1. This led to a partial rescue of mitochondrial density at motor nerve terminals by 12 months of age, but was insufficient to prevent denervation. These findings suggest that loss of mitochondria in the distal motor axon may contribute to denervation in Sod1-/- mice, perhaps via loss of key mitochondrial functions such as calcium buffering and/or energy production.


Assuntos
Mitocôndrias/patologia , Junção Neuromuscular/patologia , Superóxido Dismutase-1/metabolismo , Animais , Humanos , Camundongos , Camundongos Knockout , Camundongos Transgênicos , Proteínas Mitocondriais/metabolismo , Músculo Esquelético/inervação , Proteínas rho de Ligação ao GTP/metabolismo
9.
Nat Commun ; 9(1): 51, 2018 01 04.
Artigo em Inglês | MEDLINE | ID: mdl-29302060

RESUMO

Hexanucleotide repeat expansion in C9ORF72 is the most frequent cause of both amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Here we demonstrate that the repeat-associated non-AUG (RAN) translation of (GGGGCC) n -containing RNAs into poly-dipeptides can initiate in vivo without a 5'-cap. The primary RNA substrate for RAN translation of C9ORF72 sense repeats is shown to be the spliced first intron, following its excision from the initial pre-mRNA and transport to the cytoplasm. Cap-independent RAN translation is shown to be upregulated by various stress stimuli through phosphorylation of the α subunit of eukaryotic initiation factor-2 (eIF2α), the core event of an integrated stress response (ISR). Compounds inhibiting phospho-eIF2α-signaling pathways are shown to suppress RAN translation. Since the poly-dipeptides can themselves induce stress, these findings support a feedforward loop with initial repeat-mediated toxicity enhancing RAN translation and subsequent production of additional poly-dipeptides through ISR, thereby promoting progressive disease.


Assuntos
Proteína C9orf72/genética , Fator de Iniciação 2 em Eucariotos/metabolismo , Estresse Fisiológico/genética , Esclerose Amiotrófica Lateral/genética , Proteína C9orf72/metabolismo , Expansão das Repetições de DNA , Dipeptídeos , Retroalimentação Fisiológica , Demência Frontotemporal/genética , Células HeLa , Humanos , Íntrons , Peptídeos , Fosforilação , Biossíntese de Proteínas , Splicing de RNA , Regulação para Cima
10.
Sci Transl Med ; 9(383)2017 03 29.
Artigo em Inglês | MEDLINE | ID: mdl-28356511

RESUMO

There is no effective treatment for amyotrophic lateral sclerosis (ALS), a devastating motor neuron disease. However, discovery of a G4C2 repeat expansion in the C9ORF72 gene as the most common genetic cause of ALS has opened up new avenues for therapeutic intervention for this form of ALS. G4C2 repeat expansion RNAs and proteins of repeating dipeptides synthesized from these transcripts are believed to play a key role in C9ORF72-associated ALS (c9ALS). Therapeutics that target G4C2 RNA, such as antisense oligonucleotides (ASOs) and small molecules, are thus being actively investigated. A limitation in moving such treatments from bench to bedside is a lack of pharmacodynamic markers for use in clinical trials. We explored whether poly(GP) proteins translated from G4C2 RNA could serve such a purpose. Poly(GP) proteins were detected in cerebrospinal fluid (CSF) and in peripheral blood mononuclear cells from c9ALS patients and, notably, from asymptomatic C9ORF72 mutation carriers. Moreover, CSF poly(GP) proteins remained relatively constant over time, boding well for their use in gauging biochemical responses to potential treatments. Treating c9ALS patient cells or a mouse model of c9ALS with ASOs that target G4C2 RNA resulted in decreased intracellular and extracellular poly(GP) proteins. This decrease paralleled reductions in G4C2 RNA and downstream G4C2 RNA-mediated events. These findings indicate that tracking poly(GP) proteins in CSF could provide a means to assess target engagement of G4C2 RNA-based therapies in symptomatic C9ORF72 repeat expansion carriers and presymptomatic individuals who are expected to benefit from early therapeutic intervention.


Assuntos
Esclerose Amiotrófica Lateral/genética , Biomarcadores/metabolismo , Proteína C9orf72/genética , Repetições de Dinucleotídeos/genética , Adulto , Idoso , Esclerose Amiotrófica Lateral/líquido cefalorraquidiano , Esclerose Amiotrófica Lateral/patologia , Animais , Encéfalo/metabolismo , Encéfalo/patologia , Linhagem Celular , Humanos , Células-Tronco Pluripotentes Induzidas/efeitos dos fármacos , Células-Tronco Pluripotentes Induzidas/metabolismo , Leucócitos Mononucleares/efeitos dos fármacos , Leucócitos Mononucleares/metabolismo , Estudos Longitudinais , Camundongos , Pessoa de Meia-Idade , Neurônios/metabolismo , Oligonucleotídeos Antissenso/farmacologia , Prognóstico , RNA/genética
11.
Neuron ; 90(3): 427-31, 2016 05 04.
Artigo em Inglês | MEDLINE | ID: mdl-27151634

RESUMO

For five years, since the landmark discovery of the C9ORF72 hexanucleotide repeat expansion in ALS/FTD, a transgenic mouse model has remained elusive. Now, two laboratories (Liu et al., 2016; Jiang et al., 2016) report the development of BAC transgenic mice that recapitulate features of the human disease.


Assuntos
Esclerose Amiotrófica Lateral/genética , Expansão das Repetições de DNA/genética , Demência Frontotemporal/genética , Fatores de Troca do Nucleotídeo Guanina/genética , Animais , Proteína C9orf72 , Modelos Animais de Doenças , Humanos
12.
Exp Neurol ; 246: 6-13, 2013 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-23664960

RESUMO

Axons are the anatomical link between neuronal cell bodies and their target organs, and thus axonal degeneration is the pathological substrate that underlies neurological dysfunction in a large number of neurological conditions. Recent advances in the field of axonal biology demonstrate that axons possess programs for survival and degeneration that are distinct from those of the cell body, indicating that therapeutic strategies must consider protection of both the cell body and the axon. This review discusses axonal degeneration in the peripheral nervous system (PNS) with a focus on amyotrophic lateral sclerosis, examining both the underlying mechanisms, and the cellular and disease models of axonal degeneration that relate to disease pathogenesis.


Assuntos
Esclerose Amiotrófica Lateral/etiologia , Axônios/patologia , Modelos Animais de Doenças , Degeneração Neural/etiologia , Esclerose Amiotrófica Lateral/metabolismo , Esclerose Amiotrófica Lateral/patologia , Animais , Axônios/metabolismo , Humanos , Degeneração Neural/metabolismo , Degeneração Neural/patologia
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