The hexanucleotide repeat expansion (HRE) GGGGCC (G4C2) in C9orf72 is the most common cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Recent studies support an HRE RNA ...gain-of-function mechanism of neurotoxicity, and we previously identified protein interactors for the G4C2 RNA including RanGAP1. A candidate-based genetic screen in Drosophila expressing 30 G4C2 repeats identified RanGAP (Drosophila orthologue of human RanGAP1), a key regulator of nucleocytoplasmic transport, as a potent suppressor of neurodegeneration. Enhancing nuclear import or suppressing nuclear export of proteins also suppresses neurodegeneration. RanGAP physically interacts with HRE RNA and is mislocalized in HRE-expressing flies, neurons from C9orf72 ALS patient-derived induced pluripotent stem cells (iPSC-derived neurons), and in C9orf72 ALS patient brain tissue. Nuclear import is impaired as a result of HRE expression in the fly model and in C9orf72 iPSC-derived neurons, and these deficits are rescued by small molecules and antisense oligonucleotides targeting the HRE G-quadruplexes. Nucleocytoplasmic transport defects may be a fundamental pathway for ALS and FTD that is amenable to pharmacotherapeutic intervention.
Neurons are markedly compartmentalized, which makes them reliant on axonal transport to maintain their health. Axonal transport is important for anterograde delivery of newly synthesized ...macromolecules and organelles from the cell body to the synapse and for the retrograde delivery of signaling endosomes and autophagosomes for degradation. Dysregulation of axonal transport occurs early in neurodegenerative diseases and plays a key role in axonal degeneration. Here, we provide an overview of mechanisms for regulation of axonal transport; discuss how these mechanisms are disrupted in neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Huntington's disease, hereditary spastic paraplegia, amyotrophic lateral sclerosis, and Charcot-Marie-Tooth disease; and discuss therapeutic approaches targeting axonal transport.
A dominant histopathological feature in neuromuscular diseases, including amyotrophic lateral sclerosis and inclusion body myopathy, is cytoplasmic aggregation of the RNA-binding protein TDP-43. ...Although rare mutations in TARDBP-the gene that encodes TDP-43-that lead to protein misfolding often cause protein aggregation, most patients do not have any mutations in TARDBP. Therefore, aggregates of wild-type TDP-43 arise in most patients by an unknown mechanism. Here we show that TDP-43 is an essential protein for normal skeletal muscle formation that unexpectedly forms cytoplasmic, amyloid-like oligomeric assemblies, which we call myo-granules, during regeneration of skeletal muscle in mice and humans. Myo-granules bind to mRNAs that encode sarcomeric proteins and are cleared as myofibres mature. Although myo-granules occur during normal skeletal-muscle regeneration, myo-granules can seed TDP-43 amyloid fibrils in vitro and are increased in a mouse model of inclusion body myopathy. Therefore, increased assembly or decreased clearance of functionally normal myo-granules could be the source of cytoplasmic TDP-43 aggregates that commonly occur in neuromuscular disease.
Macroautophagy/autophagy is a major pathway for the clearance of protein aggregates and damaged organelles, and multiple intracellular organelles participate in the process of autophagy, from ...autophagosome formation to maturation and degradation. Dysregulation of the autophagy pathway has been implicated in the pathogenesis of neurodegenerative diseases including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), however the mechanisms underlying autophagy impairment in these diseases are incompletely understood. Since the expansion of GGGGCC (G
4
C
2
) repeats in the first intron of the C9orf72 gene is the most common inherited cause of both ALS and FTD (C9-ALS-FTD), we investigated autophagosome dynamics in Drosophila motor neurons expressing 30 G
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C
2
repeats (30 R). In vivo imaging demonstrates that expression of expanded G
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repeats markedly impairs biogenesis of autophagosomes at synaptic termini, whereas trafficking and maturation of axonal autophagosomes are unaffected. Motor neurons expressing 30 R display marked disruption in endoplasmic reticulum (ER) structure and dynamics in the soma, axons, and synapses. Disruption of ER morphology with mutations in Rtnl1 (Reticulon-like 1) or atl (atlastin) also impairs autophagosome formation in motor neurons, suggesting that ER integrity is critical for autophagosome formation. Furthermore, live imaging demonstrates that autophagosomes are generated from dynamic ER tubules at synaptic boutons, and this process fails to occur in a C9-ALS-FTD model. Together, these findings suggest that dynamic ER tubules are required for formation of autophagosomes at the neuromuscular junction, and that this process is disrupted by expanded G
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C
2
repeats that cause ALS-FTD.
3R: UAS construct expressing 3 G
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repeats (used as control); 3WJ: three-way junction; 12R: UAS construct expressing leader sequence and 12 G
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repeats; 30R: UAS construct expressing 30 G
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repeats; 36R: UAS construct expressing 36 G
4
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repeats; 44R: UAS construct expressing leader sequence and 44 G
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C
2
repeats; ALS: amyotrophic lateral sclerosis; Atg: autophagy related; atl: atlastin; C9-ALS-FTD: ALS or FTD caused by hexanuleotide repeat expansion in C9orf72; ER: endoplasmic reticulum; FTD: frontotemporal dementia; HRE: GGGGCC hexanucleotide repeat expansion; HSP: hereditary spastic paraplegia; Lamp1: lysosomal associated membrane protein 1; MT: microtubule; NMJ: neuromuscular junction; Rab: Ras-associated binding GTPase; RAN: repeat associated non-AUG (RAN) translation; RO-36: UAS construct expression "RNA-only" version of 36 G
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C
2
repeats in which stop codons in all six reading frames are inserted.; Rtnl1: Reticulon-like 1; SN: segmental nerve; TFEB/Mitf: transcription factor EB/microphthalmia associated transcription factor (Drosophila ortholog of TFEB); TrpA1: transient receptor potential cation channel A1; VAPB: VAMP associated protein B and C; VNC: ventral nerve cord (spinal cord in Drosophila larvae)
How the circadian clock regulates the timing of sleep is poorly understood. Here, we identify a Drosophila mutant, wide awake (wake), that exhibits a marked delay in sleep onset at dusk. Loss of WAKE ...in a set of arousal-promoting clock neurons, the large ventrolateral neurons (l-LNvs), impairs sleep onset. WAKE levels cycle, peaking near dusk, and the expression of WAKE in l-LNvs is Clock dependent. Strikingly, Clock and cycle mutants also exhibit a profound delay in sleep onset, which can be rescued by restoring WAKE expression in LNvs. WAKE interacts with the GABAA receptor Resistant to Dieldrin (RDL), upregulating its levels and promoting its localization to the plasma membrane. In wake mutant l-LNvs, GABA sensitivity is decreased and excitability is increased at dusk. We propose that WAKE acts as a clock output molecule specifically for sleep, inhibiting LNvs at dusk to promote the transition from wake to sleep.
A GGGGCC (G4C2) repeat expansion in the C9orf72 gene is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Although disruptions in axonal ...transport are implicated in the pathogenesis of multiple neurodegenerative diseases, the underlying mechanisms causing these defects remain unclear. Here, we performed live imaging of Drosophila motor neurons expressing expanded G4C2 repeats in third‐instar larvae and investigated the axonal transport of multiple organelles in vivo. Expression of expanded G4C2 repeats causes an increase in static axonal lysosomes, while it impairs trafficking of late endosomes (LEs) and dense core vesicles (DCVs). Surprisingly, however, axonal transport of mitochondria is unaffected in motor axons expressing expanded G4C2 repeats. Thus, our data indicate that expanded G4C2 repeat expression differentially impacts axonal transport of vesicular organelles and mitochondria in Drosophila models of C9orf72‐associated ALS/FTD.
Synopsis
Axonal transport is an indispensable cellular process responsible for movement of cargos along the axon in order to maintain the long‐distance communication between soma and synapses. For decades, it has been reported that axonal transport defects are observed in motor neuron diseases, including ALS. In this study, we report that Drosophila motor neurons expressing expanded GGGGCC repeats to model C9orf72‐associated ALS show specific disruptions in organelle transport for endo‐lysosomes and dense core vesicles, but not for mitochondria.
The expansion of GGGGCC repeats in C9orf72 is the most common genetic cause of amyotrophic lateral sclerosis and FTD. Here, we performed live imaging of Drosophila larval motor neurons expressing GGGGCC repeats, and investigated axonal transport of multiple organelles in vivo. We have identified that the affected motor neurons show specific disruptions in organelle trafficking for endo‐lysosomes and dense core vesicles, but not for mitochondria. Image was generated using bioRENDER
Brain imaging can be used to study how individuals' brains are aging, compared against population norms. This can inform on aspects of brain health; for example, smoking and blood pressure can be ...seen to accelerate brain aging. Typically, a single 'brain age' is estimated per subject, whereas here we identified 62 modes of subject variability, from 21,407 subjects' multimodal brain imaging data in UK Biobank. The modes represent different aspects of brain aging, showing distinct patterns of functional and structural brain change, and distinct patterns of association with genetics, lifestyle, cognition, physical measures and disease. While conventional brain-age modelling found no genetic associations, 34 modes had genetic associations. We suggest that it is important not to treat brain aging as a single homogeneous process, and that modelling of distinct patterns of structural and functional change will reveal more biologically meaningful markers of brain aging in health and disease.
Huntington’s disease (HD) is caused by an expanded CAG repeat in the Huntingtin (HTT) gene. The mechanism(s) by which mutant HTT (mHTT) causes disease is unclear. Nucleocytoplasmic transport, the ...trafficking of macromolecules between the nucleus and cytoplasm, is tightly regulated by nuclear pore complexes (NPCs) made up of nucleoporins (NUPs). Previous studies offered clues that mHTT may disrupt nucleocytoplasmic transport and a mutation of an NUP can cause HD-like pathology. Therefore, we evaluated the NPC and nucleocytoplasmic transport in multiple models of HD, including mouse and fly models, neurons transfected with mHTT, HD iPSC-derived neurons, and human HD brain regions. These studies revealed severe mislocalization and aggregation of NUPs and defective nucleocytoplasmic transport. HD repeat-associated non-ATG (RAN) translation proteins also disrupted nucleocytoplasmic transport. Additionally, overexpression of NUPs and treatment with drugs that prevent aberrant NUP biology also mitigated this transport defect and neurotoxicity, providing future novel therapy targets.
•HD human and mouse brain share profound nuclear pore complex pathology•HD iPS neurons mirror dysregulated HD human brain nuclear pore complex pathology•Aberrant nucleocytoplasmic transport is identified in various in vitro HD models•HD neurotoxicity can be mitigated with rescue of nucleocytoplasmic transport defects
Grima et al. describe a new fundamental defect in nucleocytoplasmic transport in Huntington’s disease using multiple model systems and independent lines of evidence. This defect can be mitigated with agents that alter nuclear pore complex O-GlcNAcylation and/or transport functions.
Activation of the type 1 interferon (IFN1) pathway is a prominent feature of dermatomyositis (DM) muscle and may play a role in the pathogenesis of this disease. However, the relevance of the IFN1 ...pathway in patients with other types of myositis such as the antisynthetase syndrome (AS), immune-mediated necrotizing myopathy (IMNM), and inclusion body myositis (IBM) is largely unknown. Moreover, the activation of the type 2 interferon (IFN2) pathway has not been comprehensively explored in myositis. In this cross-sectional study, our objective was to determine whether IFN1 and IFN2 pathways are differentially activated in different types of myositis by performing RNA sequencing on muscle biopsy samples from 119 patients with DM, IMNM, AS, or IBM and on 20 normal muscle biopsies.
The expression of IFN1- and IFN2-inducible genes was compared between the different groups.
The expression of IFN1-inducible genes was high in DM, moderate in AS, and low in IMNM and IBM. In contrast, the expression of IFN2-inducible genes was high in DM, IBM, and AS but low in IMNM. The expression of IFN-inducible genes correlated with the expression of genes associated with inflammation and muscle regeneration. Of note,
expression levels alone performed as well as composite scores relying on multiple genes to monitor activation of the IFN1 pathway in myositis muscle biopsies.
IFN1 and IFN2 pathways are differentially activated in different forms of myositis. This observation may have therapeutic implications because immunosuppressive medications may preferentially target each of these pathways.
Neurotransmission requires anterograde axonal transport of dense core vesicles (DCVs) containing neuropeptides and active zone components from the soma to nerve terminals. However, it is puzzling how ...one-way traffic could uniformly supply sequential release sites called en passant boutons. Here, Drosophila neuropeptide-containing DCVs are tracked in vivo for minutes with a new method called simultaneous photobleaching and imaging (SPAIM). Surprisingly, anterograde DCVs typically bypass proximal boutons to accumulate initially in the most distal bouton. Then, excess distal DCVs undergo dynactin-dependent retrograde transport back through proximal boutons into the axon. Just before re-entering the soma, DCVs again reverse for another round of anterograde axonal transport. While circulating over long distances, both anterograde and retrograde DCVs are captured sporadically in en passant boutons. Therefore, vesicle circulation, which includes long-range retrograde transport and inefficient bidirectional capture, overcomes the limitations of one-way anterograde transport to uniformly supply release sites with DCVs.
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► A new imaging method (SPAIM) tracks synaptic delivery of neuropeptide vesicles ► Vesicles circulate between the proximal axon and the ends of nerve terminals ► En route sporadic bidirectional capture uniformly supplies release sites
Vesicles containing neuropeptides circulate continuously and bi-directionally along axons. En route, they are sporadically captured at synaptic boutons along the length of the axon, ensuring that all release sites are supplied with neurotransmitters.
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