Dataset Information

ALS-linked FUS exerts a gain of toxic function involving aberrant p38 MAPK activation.

ABSTRACT: Mutations in Fused in Sarcoma/Translocated in Liposarcoma (FUS) cause familial forms of amyotrophic lateral sclerosis (ALS), a neurodegenerative disease characterized by progressive axonal degeneration mainly affecting motor neurons. Evidence from transgenic mouse models suggests mutant forms of FUS exert an unknown gain-of-toxic function in motor neurons, but mechanisms underlying this effect remain unknown. Towards this end, we studied the effect of wild type FUS (FUS WT) and three ALS-linked variants (G230C, R521G and R495X) on fast axonal transport (FAT), a cellular process critical for appropriate maintenance of axonal connectivity. All ALS-FUS variants impaired anterograde and retrograde FAT in squid axoplasm, whereas FUS WT had no effect. Misfolding of mutant FUS is implicated in this process, as the molecular chaperone Hsp110 mitigated these toxic effects. Interestingly, mutant FUS-induced impairment of FAT in squid axoplasm and of axonal outgrowth in mammalian primary motor neurons involved aberrant activation of the p38 MAPK pathway, as also reported for ALS-linked forms of Cu, Zn superoxide dismutase (SOD1). Accordingly, increased levels of active p38 MAPK were detected in post-mortem human ALS-FUS brain tissues. These data provide evidence for a novel gain-of-toxic function for ALS-linked FUS involving p38 MAPK activation.

SUBMITTER: Sama RR

PROVIDER: S-EPMC5428330 | biostudies-literature | 2017 Mar

REPOSITORIES: biostudies-literature

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ALS-linked FUS exerts a gain of toxic function involving aberrant p38 MAPK activation.

Sama Reddy Ranjith K RR Fallini Claudia C Gatto Rodolfo R McKeon Jeanne E JE Song Yuyu Y Rotunno Melissa S MS Penaranda Saul S Abdurakhmanov Izrail I Landers John E JE Morfini Gerardo G Brady Scott T ST Bosco Daryl A DA

Scientific reports 20170308 1

Mutations in Fused in Sarcoma/Translocated in Liposarcoma (FUS) cause familial forms of amyotrophic lateral sclerosis (ALS), a neurodegenerative disease characterized by progressive axonal degeneration mainly affecting motor neurons. Evidence from transgenic mouse models suggests mutant forms of FUS exert an unknown gain-of-toxic function in motor neurons, but mechanisms underlying this effect remain unknown. Towards this end, we studied the effect of wild type FUS (FUS WT) and three ALS-linked ...[more]

PMID: 28273913

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Project description:BackgroundThe characteristic structure of motor neurons (MNs), particularly of the long axons, becomes damaged in the early stages of amyotrophic lateral sclerosis (ALS). However, the molecular pathophysiology of axonal degeneration remains to be fully elucidated.MethodTwo sets of isogenic human-induced pluripotent stem cell (hiPSCs)-derived MNs possessing the single amino acid difference (p.H517D) in the fused in sarcoma (FUS) were constructed. By combining MN reporter lentivirus, MN specific phenotype was analyzed. Moreover, RNA profiling of isolated axons were conducted by applying the microfluidic devices that enable axon bundles to be produced for omics analysis. The relationship between the target gene, which was identified as a pathological candidate in ALS with RNA-sequencing, and the MN phenotype was confirmed by intervention with si-RNA or overexpression to hiPSCs-derived MNs and even in vivo. The commonality was further confirmed with other ALS-causative mutant hiPSCs-derived MNs and human pathology.FindingsWe identified aberrant increasing of axon branchings in FUS-mutant hiPSCs-derived MN axons compared with isogenic controls as a novel phenotype. We identified increased level of Fos-B mRNA, the binding target of FUS, in FUS-mutant MNs. While Fos-B reduction using si-RNA or an inhibitor ameliorated the observed aberrant axon branching, Fos-B overexpression resulted in aberrant axon branching even in vivo. The commonality of those phenotypes was further confirmed with other ALS causative mutation than FUS.InterpretationAnalyzing the axonal fraction of hiPSC-derived MNs using microfluidic devices revealed that Fos-B is a key regulator of FUS-mutant axon branching. FUND: Japan Agency for Medical Research and development; Japanese Ministry of Education, Culture, Sports, Science and Technology Clinical Research, Innovation and Education Center, Tohoku University Hospital; Japan Intractable Diseases (Nanbyo) Research Foundation; the Kanae Foundation for the Promotion of Medical Science; and "Inochi-no-Iro" ALS research grant.

Project description:Formation of cytoplasmic RNA-protein structures called stress granules (SGs) is a highly conserved cellular response to stress. Abnormal metabolism of SGs may contribute to the pathogenesis of (neuro)degenerative diseases such as amyotrophic lateral sclerosis (ALS). Many SG proteins are affected by mutations causative of these conditions, including fused in sarcoma (FUS). Mutant FUS variants have high affinity to SGs and also spontaneously form de novo cytoplasmic RNA granules. Mutant FUS-containing assemblies (mFAs), often called "pathological SGs", are proposed to play a role in ALS-FUS pathogenesis. However, structural differences between mFAs and physiological SGs remain largely unknown therefore it is unclear whether mFAs can functionally substitute for SGs and how they affect cellular stress responses. Here we used affinity purification to isolate mFAs and physiological SGs and compare their protein composition. We found that proteins within mFAs form significantly more physical interactions than those in SGs however mFAs fail to recruit many factors involved in signal transduction. Furthermore, we found that proteasome subunits and certain nucleocytoplasmic transport factors are depleted from mFAs, whereas translation elongation, mRNA surveillance and splicing factors as well as mitochondrial proteins are enriched in mFAs, as compared to SGs. Validation experiments for a mFA-specific protein, hnRNPA3, confirmed its RNA-dependent interaction with FUS and its sequestration into FUS inclusions in cultured cells and in a FUS transgenic mouse model. Silencing of the Drosophila hnRNPA3 ortholog was deleterious and potentiated human FUS toxicity in the retina of transgenic flies. In conclusion, we show that SG-like structures formed by mutant FUS are structurally distinct from SGs, prone to persistence, likely cannot functionally replace SGs, and affect a spectrum of cellular pathways in stressed cells. Results of our study support a pathogenic role for cytoplasmic FUS assemblies in ALS-FUS.

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ALS-linked FUS exerts a gain of toxic function involving aberrant p38 MAPK activation.

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ALS-linked FUS exerts a gain of toxic function involving aberrant p38 MAPK activation.

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