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Amyotrophic lateral sclerosis (ALS) is the most frequent motor neuron disease. Cytoplasmic fused in sarcoma (FUS) aggregates are pathological hallmarks of FUS-ALS. Proper shuttling between the nucleus and cytoplasm is essential for physiological cell function. However, the initial event in the pathophysiology of FUS-ALS remains enigmatic. Using human induced pluripotent stem cell (hiPSCs)-derived motor neurons (MNs), we show that impairment of poly(ADP-ribose) polymerase (PARP)-dependent DNA damage response (DDR) signaling due to mutations in the FUS nuclear localization sequence (NLS) induces additional cytoplasmic FUS mislocalization which in turn results in neurodegeneration and FUS aggregate formation. Our work suggests that a key pathophysiologic event in ALS is upstream of aggregate formation. Targeting DDR signaling could lead to novel therapeutic routes for ameliorating ALS. Abnormal cytoplasmic aggregates of FUS are a hallmark of some forms of amyotrophic lateral sclerosis (ALS). Here, using neurons derived from patients with FUS-ALS, the authors demonstrate that impairment of PARP-dependent DNA damage signaling is an event that occurs upstream of neurodegeneration and cytoplasmic aggregate formation in FUS-ALS.

ObjectiveThe only identified cause of amyotrophic lateral sclerosis (ALS) are mutations in a number of genes found in familial cases but also in sporadic cases. De novo mutations occurring in a parental gonadal cell, in the zygote or postzygotic during embryonal development can result in an apparently sporadic/isolated case of ALS later in life. We searched for de novo mutations in SOD1 as a cause of ALS.MethodsWe analysed peripheral-blood exome, genome and Sanger sequencing to identify deleterious mutations in SOD1 in 4000 ALS patients from Germany, South Korea and Sweden. Parental kinship was confirmed using highly polymorphic microsatellite markers across the genome. Medical genealogical and clinical data were reviewed and compared with the literature.ResultsWe identified four sporadic ALS cases with de novo mutations in SOD1. They aggregate in hot-spot codons earlier found mutated in familial cases. Their phenotypes match closely what has earlier been reported in familial cases with pathogenic mutations in SOD1. We also encountered familial cases where de novo mutational events in recent generations may have been involved.ConclusionsDe novo mutations are a cause of sporadic ALS and may also be underpinning smaller families with few affected ALS cases. It was not possible to ascertain if the origin of the de novo mutations was parental germline, zygotic or postzygotic during embryonal development. All ALS patients should be offered genetic counselling and genetic screening, the challenges of variant interpretation do not outweigh the potential benefits including earlier confirmed diagnosis and possible bespoken therapy.

Members of the fragile X protein (FXP) family (FMR1, FXR1 and FXR2) are differentially expressed in most types of cancer and major neurodegenerative diseases. While increased expression of FXR1 in cancer has been linked to senescence evasion and consequently tumor initiation and progression, decreased expression of FXPs in neurodegeneration may contribute to pathogenic protein aggregation and death of vulnerable neurons. However, due the causal role in fragile x syndrome, most data are available about loss of FMR1 in neurons while functions of FXR1 and especially FXR2 remain largely unexplored. To address this knowledge gap, and to directly compare functions of the FXPs, we used proteomics of CRISPR/Cas9 edited HAP1 cells carrying knockouts of the individual FXPs for identification of cellular mechanisms associated with these proteins. Further exploration of proteomic findings suggests roles of the FXPs in ribosome biogenesis, autophagy and mitochondrial health linked to organismal aging, and cellular senescence. Validation of FXP induced defects relevant for neurodegenerative diseases in neuroblastoma cell line SH-SY5Y upon FXP knockdown revealed high cell type specificity of individual FXP functions. Overall, we provide a comprehensive overview and comparison of cellular mechanisms related to the individual FXPs, as well as starting points for further studying this protein family in respective cell types of FXP associated diseases, and in aging in general.

The fragile X protein (FXP) family comprises the multifunctional RNA-binding proteins FMR1, FXR1, and FXR2 that play an important role in RNA metabolism and regulation of translation, but also in DNA damage and cellular stress responses, mitochondrial organization, and more. FMR1 is well known for its implication in neurodevelopmental diseases. Recent evidence suggests substantial contribution of this protein family to amyotrophic lateral sclerosis (ALS) pathogenesis. ALS is a highly heterogeneous neurodegenerative disease with multiple genetic and unclear environmental causes and very limited treatment options. The loss of motoneurons in ALS is still poorly understood, especially because pathogenic mechanisms are often restricted to patients with mutations in specific causative genes. Identification of converging disease mechanisms evident in most patients and suitable for therapeutic intervention is therefore of high importance. Recently, deregulation of the FXPs has been linked to pathogenic processes in different types of ALS. Strikingly, in many cases, available data points towards loss of expression and/or function of the FXPs early in the disease, or even at the presymptomatic state. In this review, we briefly introduce the FXPs and summarize available data about these proteins in ALS. This includes their relation to TDP-43, FUS, and ALS-related miRNAs, as well as their possible contribution to pathogenic protein aggregation and defective RNA editing. Furthermore, open questions that need to be addressed before definitively judging suitability of these proteins as novel therapeutic targets are discussed.

Amyotrophic lateral sclerosis (ALS) has substantial heritability, in part shared with fronto-temporal dementia (FTD). We show that ALS heritability is enriched in splicing variants and in binding sites of 6 RNA-binding proteins including TDP-43 and FUS. A transcriptome wide association study (TWAS) identified 6 loci associated with ALS, including in NUP50 encoding for the nucleopore basket protein NUP50. Independently, rare variants in NUP50 were associated with ALS risk ( P  = 3.71.10 −03 ; odds ratio = 3.29; 95%CI, 1.37 to 7.87) in a cohort of 9,390 ALS/FTD patients and 4,594 controls. Cells from one patient carrying a NUP50 frameshift mutation displayed a decreased level of NUP50. Loss of NUP50 leads to death of cultured neurons, and motor defects in Drosophila and zebrafish. Thus, our study identifies alterations in splicing in neurons as critical in ALS and provides genetic evidence linking nuclear pore defects to ALS. ALS is somewhat heritable, but the genetic basis is not completely understood. Here, the authors identify alterations in splicing in neurons associated with amyotrophic lateral sclerosis and uncover several associated genetic loci, with a potential link to nuclear pore defects.

Amyotrophic lateral sclerosis (ALS) is a devastating progressive neurodegenerative disease affecting primarily the upper and lower motor neurons. A common feature of all ALS cases is a well-characterized neuroinflammatory reaction within the central nervous system (CNS). However, much less is known about the role of the peripheral immune system and its interplay with CNS resident immune cells in motor neuron degeneration. Here, we characterized peripheral monocytes in both temporal and spatial dimensions of ALS pathogenesis. We found the circulating monocytes to be deregulated in ALS regarding subtype constitution, function and gene expression. Moreover, we show that CNS infiltration of peripheral monocytes correlates with improved motor neuron survival in a genetic ALS mouse model. Furthermore, application of human immunoglobulins or fusion proteins containing only the human Fc, but not the Fab antibody fragment, increased CNS invasion of peripheral monocytes and delayed the disease onset. Our results underline the importance of peripheral monocytes in ALS pathogenesis and are in agreement with a protective role of monocytes in the early phase of the disease. The possibility to boost this beneficial function of peripheral monocytes by application of human immunoglobulins should be evaluated in clinical trials.

Amyotrophic lateral sclerosis (ALS) is a fatal, adult-onset disease marked by a progressive degeneration of motor neurons (MNs) present in the spinal cord, brain stem and motor cortex. Death in most patients usually occurs within 2–4 years after symptoms onset. Despite promising progress in delineating underlying mechanisms, such as disturbed proteostasis, DNA/RNA metabolism, splicing or proper nucleocytoplasmic shuttling, there are no effective therapies for the vast majority of cases. A reason for this might be the disease heterogeneity and lack of substantial clinical and molecular biomarkers. The identification and validation of such pathophysiology driven biomarkers could be useful for early diagnosis and treatment stratification. Recent advances in next generation RNA-sequencing approaches have provided important insights to identify key changes of non-coding RNAs (ncRNAs) implicated with ALS disease. Especially, microRNAs (miRNAs) have emerged as key post-transcriptional regulators of gene expression to target several genes/pathways by degrading messenger RNAs (mRNAs) or repressing levels of gene expression. In this study, we expand our previous work to identify top-regulated differentially expressed (DE)-miRNAs by combining different normalizations to search for important and generalisable pathomechanistic dysregulations in ALS as putative novel biomarkers of the disease. For this we performed a consensus pipeline of existing datasets to investigate the transcriptomic profile (mRNAs and miRNAs) of MN cell lines from iPSC-derived SOD1 - and TARDBP (TDP-43 protein)-mutant-ALS patients and healthy controls to identify potential signatures and their related pathways associated with neurodegeneration. Transcriptional profiling of miRNA–mRNA interactions from MN cell lines in ALS patients revealed differential expression of genes showed greater vulnerability to KEAP1-NRF2 stress response pathway, sharing a common molecular denominator linked to both disease conditions. We also reported that mutations in above genes led to significant upregulation of the top candidate miR-10b-5p, which we could validate in immortalized lymphoblast cell lines (LCLs) derived from sporadic and familial ALS patients and postmortem tissues of familial ALS patients. Collectively, our findings suggest that miRNA analysis simultaneously performed in various human biological samples may reveal shared miRNA profiles potentially useful as a biomarker of the disease.

Mutations in FUS and TBK1 often cause aggressive early-onset amyotrophic lateral sclerosis (ALS) or a late-onset ALS and/or frontotemporal dementia (FTD) phenotype, respectively. Co-occurrence of mutations in two or more Mendelian ALS/FTD genes has been repeatedly reported. However, little is known how two pathogenic ALS/FTD mutations in the same patient interact to shape the final phenotype. We screened 28 ALS patients with a known FUS mutation by whole-exome sequencing and targeted evaluation for mutations in other known ALS genes followed by genotype–phenotype correlation analysis of FUS/TBK1 double-mutant patients. We report on new and summarize previously published FUS and TBK1 double-mutant ALS/FTD patients and their families. We found that, within a family, mutations in FUS cause ALS while TBK1 single mutations are observed in FTD patients. FUS/TBK1 double mutations manifested as ALS and without a manifest difference regarding age at onset and disease duration when compared to FUS single-mutant individuals. In conclusion, TBK1 and FUS variants do not seem to interact in a simple additive way. Rather, the phenotype of FUS/TBK1 double-mutant patients appears to be dominated by the FUS mutation.