ALS-associated FUS mutation reshapes the RNA and protein composition and dynamic of Stress Granules.
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ABSTRACT: Stress Granules (SG) formation is a cellular protection mechanism in harmful conditions, constituting a storage for untranslated mRNAs and RNA-binding proteins (RBPs); however, these condensates can turn into pathological aggregates, that in neurons are related to the onset of neurodegenerative diseases, like Amyotrophic Lateral Sclerosis (ALS). Mutations in the RBP FUS, leading to its cytoplasmic mis-localization, are causatively linked to ALS, since they mediate its accumulation in SGs, triggering their transition towards cytotoxic inclusions. Here, we describe the SG transcriptome in a neural context and compare with datasets from other systems, identifying both common rules and diversifying characteristics for SG recruitment of transcripts. We demonstrate that SG dynamics and RNA content are strongly modified by the incorporation of aberrantly localized mutant FUS, switching to a more unstructured, AU-rich SG transcriptome and losing a wide population of GC-rich, structured RNAs. We show that these alterations mainly depend on mutant FUS which favors the SG incorporation of its protein interactors and in turn of their target RNAs. Our data give a comprehensive view of the molecular differences between physiological and pathological SG in ALS conditions, showing how a single mutation is sufficient to impact the RNA and protein population of these condensates.
Project description:FUS is a primarily nuclear RNA-binding protein with important roles in RNA processing and transport. FUS mutations disrupting its nuclear localization characterize a subset of amyotrophic lateral sclerosis (ALS-FUS) patients, through an unidentified pathological mechanism. FUS regulates nuclear RNA, but its role at the synapse is poorly understood. Here, we used super-resolution imaging to determine the physiological localization of extranuclear, neuronal FUS and found it predominantly near the vesicle reserve pool of presynaptic sites. Using CLIP-seq on synaptoneurosome preparations, we identified synaptic RNA targets of FUS that are associated with synapse organization and plasticity. Synaptic FUS was significantly increased in a knock-in mouse model of ALS-FUS, at presymptomatic stages. Despite apparently unaltered synaptic organization, RNA-seq of synaptoneurosomes highlighted age-dependent dysregulation of glutamatergic and GABAergic synapses. Our study indicates that FUS relocalization to the synapse in early stages of ALS-FUS results in synaptic impairment, potentially representing an initial trigger of neurodegeneration.
Project description:FUS is a primarily nuclear RNA-binding protein with important roles in RNA processing and transport. FUS mutations disrupting its nuclear localization characterize a subset of amyotrophic lateral sclerosis (ALS-FUS) patients, through an unidentified pathological mechanism. FUS regulates nuclear RNA, but its role at the synapse is poorly understood. Here, we used super-resolution imaging to determine the physiological localization of extranuclear, neuronal FUS and found it predominantly near the vesicle reserve pool of presynaptic sites. Using CLIP-seq on synaptoneurosome preparations, we identified synaptic RNA targets of FUS that are associated with synapse organization and plasticity. Synaptic FUS was significantly increased in a knock-in mouse model of ALS-FUS, at presymptomatic stages. Despite apparently unaltered synaptic organization, RNA-seq of synaptoneurosomes highlighted age-dependent dysregulation of glutamatergic and GABAergic synapses. Our study indicates that FUS relocalization to the synapse in early stages of ALS-FUS results in synaptic impairment, potentially representing an initial trigger of neurodegeneration.
Project description:FUS is a primarily nuclear RNA-binding protein with important roles in RNA processing and transport. FUS mutations disrupting its nuclear localization characterize a subset of amyotrophic lateral sclerosis (ALS-FUS) patients, through an unidentified pathological mechanism. FUS regulates nuclear RNA, but its role at the synapse is poorly understood. Here, we used super-resolution imaging to determine the physiological localization of extranuclear, neuronal FUS and found it predominantly near the vesicle reserve pool of presynaptic sites. Using CLIP-seq on synaptoneurosome preparations, we identified synaptic RNA targets of FUS that are associated with synapse organization and plasticity. Synaptic FUS was significantly increased in a knock-in mouse model of ALS-FUS, at presymptomatic stages. Despite apparently unaltered synaptic organization, RNA-seq of synaptoneurosomes highlighted age-dependent dysregulation of glutamatergic and GABAergic synapses. Our study indicates that FUS relocalization to the synapse in early stages of ALS-FUS results in synaptic impairment, potentially representing an initial trigger of neurodegeneration.
Project description:Mutations in the RNA-binding protein FUS have been genetically linked to Amyotrophic Lateral Sclerosis (ALS), a neurodegenerative disease caused by the death of motoneurons (MNs). FUS is a ubiquitous protein and the mechanisms leading to selective MN loss downstream of FUS mutations are still largely unknown. We report the first transcriptome analysis of human purified MNs, obtained from isogenic induced Pluripotent Stem Cells (iPSCs) with a FUS wild-type or mutant genetic background. Gene ontology analysis of differentially expressed genes identified significant enrichment of pathways previously associated to other neurological diseases and non-FUS ALS, suggesting a common pathological mechanism. We also found several microRNAs deregulated in FUS mutant MNs and focused on miR-375 and miR-125b. Notably, miR-125b is a neural-enriched microRNA with multiple functions in the nervous system and miR-375 had been previously associated to MN survival. We report that relevant targets of both microRNAs, including the neural RNA-binding protein ELAVL4 and apoptosis factors such as p53, are aberrantly increased in FUS mutant MNs. Characterization of FUS RNA targets in the cell type primarily affected by the disease contributes to the definition of the pathogenic mechanisms of FUS-linked ALS.
Project description:FUS, an RNA binding protein was recently implicated in Amyotrophic Lateral Sclerosis (ALS). ALS is a fatal neurodegenerative disease. We report the identification of the conserved neuronal RNA targets of FUS and the assessment of the impact of FUS depletion on the neuronal transcriptome. We identified that FUS regulates splicing of conserved intron containing transcripts. FUS retains or excludes the conserved intron by binding to them. Identification of FUS neuronal targets using normal human brain samples and mouse neurons
Project description:This SuperSeries is composed of the following subset Series: GSE40649: Divergent roles of ALS-linked proteins FUS/TLS and TDP-43 intersect in processing long pre-mRNAs (microarray) GSE40651: Divergent roles of ALS-linked proteins FUS/TLS and TDP-43 intersect in processing long pre-mRNAs (CLIP-Seq) GSE40652: Divergent roles of ALS-linked proteins FUS/TLS and TDP-43 intersect in processing long pre-mRNAs (RNA-Seq) Refer to individual Series
Project description:The RNA-binding protein FUS/TLS, mutation in which is causative of the fatal motor neuron disease ALS, is demonstrated to directly bind to the U1-snRNP and SMN complexes. ALS-causative mutations in FUS/TLS are shown to abnormally enhance their interaction with SMN and reduce interaction with U1-snRNP. Correspondingly, global RNA analysis reveals a mutant-dependent loss of splicing activity, with ALS-linked mutants failing to reverse changes caused by loss of wild-type FUS/TLS. Furthermore, a common FUS/TLS mutant-associated RNA splicing signature is identified in ALS patient fibroblasts. Taken together, our studies establish potentially converging disease mechanisms in ALS and spinal muscular atrophy, with ALS-causative mutants acquiring properties representing both gain (dysregulation of SMN) and loss (reduced RNA processing mediated by U1-snRNP) of function. RNA-mediated oligonucleotide Annealing, Selection, and Ligation with Next-Generation sequencing (RASL-seq) method was used for analyzing alternative splicing changes. Oligonucleotide probes are designed to anneal to the exon-exon junctions. The probe library was assembled to assess 5530 unique alternative splicing events, most of which were exon inclusion or skipping, with a minority for alternative 5’- or 3’- splice sites. The splicing changes were compared among groups of reducing FUS/TLS or SMN levels, or expressing various FUS mutations to determine the loss versus gain of FUS/TLS function on splicing regulation.
Project description:Amyotrophic lateral sclerosis (ALS) is a progressive motor neuron (MN) degenerative disease with a major pathological feature of cytoplasmic TDP-43 aggregation. However, the mechanisms underlying TDP-43 proteinopathy are still largely unknown. We performed in vitro differentiation of ALS-induced pluripotent stem cells (ALS-iPSCs; carrying the TDP-43M337V mutation) and isogenic controls and found upregulation of paraspeckle-associated lncRNA NEAT1 isoforms in the ALS-iPSC-derived MNs (ALS-iPSC-MNs). Intriguingly, the upregulated NEAT1 isoforms were mislocalized to the cytoplasm of ALS-iPSC-MNs, and the cytoplasmic NEAT1 provoked TDP-43 and TDP-43M337V liquid-liquid phase separation, generating long-lived protein condensates. These condensates had reduced mobility and were converted into aggregates, finally co-aggregating with phospho-TDP-43. Disruption of NEAT1 expression reduced its cytoplasmic levels and also reduced the levels of TDP-43/TDP-43M337V condensates. In 3D neuromuscular organoids with the TDP-43M337V mutation, treatment with NEAT1-antisense oligonucleotides (NEAT1-ASO) promoted neuromuscular junction formation and function, as well as muscle contractility. Furthermore, treatment of TDP-43Q331K mice with Neat1-ASO attenuated TDP-43 pathology in spinal cord and preserved motor function. These findings suggest that NEAT1 plays an important role in TDP-43-associated pathology, and NEAT1-ASO may attenuate pathological TDP-43 aggregation to prevent motor neuron degeneration and muscle weakness in ALS.
Project description:Pathological FUS inclusions are found in 10% of patients with frontotemporal dementia (FTD) and those with amyotrophic lateral sclerosis (ALS) carrying FUS mutations. Current work indicates that FUS mutations may incur gain-of-toxic functions to drive ALS pathogenesis. However, how FUS dysfunction may affect cognition remains elusive. Using a mouse model expressing wild-type human FUS mimicking the endogenous expression pattern and level within the central nervous system, we found that they developed hippocampus-mediated cognitive deficits accompanied by an age-dependent reduction in spine density and long-term potentiation (LTP) in their hippocampus. However, there were no apparent FUS aggregates, nuclear envelope defects and cytosolic FUS accumulation. These suggest that these proposed pathogenic mechanisms may not be the underlying causes for the observed cognitive deficits. Unbiased transcriptomic analysis identified expression changes in a small set of genes with preferential expression in the neurons and oligodendrocyte lineage cells. Of these, we focused on Sema5a, a gene involved in axon guidance, spine dynamics, Parkinson’s disease and autism spectrum disorders. Critically, FUS binds directly to Sema5a mRNA and regulates Sema5a expression in a FUS-dose-dependent manner. Taken together, our data suggest that FUS-driven Sema5a deregulation may underlie the cognitive deficits in FUS transgenic mice.
Project description:FUS ALS seems to preferentially affect sMNs, and cognitive dysfunction in FUS ALS is rare. Considering this, we wanted to analyze if cortical neurons behave differently than spinal motor neurons in response to FUS mutations. For this, we used cortical neurons derived from isogenic human induced pluripotent stem cells (hiPSCs) in which either WT or NLS mutant FUS P525L was tagged with eGFP using CRISPR/Cas9 and systematically compared them to sMNs of the identical iPSCs. Phenotypically, mutant FUS cortical neurons showed less impairment of FUS recruitment to DNA damage sites compared to mutant sMNs and less signs of DNA damage, which were similarly found in post mortem tissue. To advance our understanding of finding different molecular mechanisms and pathways related to FUS mutations in ALS disease, we have performed RNA sequencing of FUS ALS cortical and spinal motor neurons and our results revealed basic differences in their transcriptomes. Alternative splicing events in spinal motor neurons were different from cortical neurons also pointing towards DNA damage in FUS ALS.