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The cytoplasmic mislocalization and aggregation of TAR DNA-binding protein-43 (TDP-43) is a common histopathological hallmark of the amyotrophic lateral sclerosis and frontotemporal dementia disease spectrum (ALS/FTD). However, the composition of aggregates and their contribution to the disease process remain unknown. Here we used proximity-dependent biotin identification (BioID) to interrogate the interactome of detergent-insoluble TDP-43 aggregates and found them enriched for components of the nuclear pore complex and nucleocytoplasmic transport machinery. Aggregated and disease-linked mutant TDP-43 triggered the sequestration and/or mislocalization of nucleoporins and transport factors, and interfered with nuclear protein import and RNA export in mouse primary cortical neurons, human fibroblasts and induced pluripotent stem cell–derived neurons. Nuclear pore pathology is present in brain tissue in cases of sporadic ALS and those involving genetic mutations in TARDBP and C9orf72. Our data strongly implicate TDP-43-mediated nucleocytoplasmic transport defects as a common disease mechanism in ALS/FTD.

Nuclear loss and cytoplasmic buildup of the RNA-binding protein TDP-43 is a hallmark of ALS and related disorders. While studies using artificial TDP-43 depletion in neurons have revealed changes in gene expression and splicing, their relevance to actual patients remained unclear. Induced pluripotent stem cell (iPSC)-derived neurons (iPSNs) from 180 individuals, including controls, C9orf72 ALS/FTD, and sporadic ALS (sALS) patients were used to generate and analyze ~32,500 qRT-PCR data points across 20 genes which identified variable, time-dependent signatures of TDP-43 loss of function in individual lines. Notably, the same changes were also seen in postmortem brain tissue from the same patients, confirming that iPSNs accurately model disease. Inducing damage to the nuclear pore complex, specifically by reducing the nucleoporin POM121 in healthy iPSNs, was enough to replicate the molecular changes associated with ALS/FTD TDP-43 dysfunction. This directly links nuclear pore integrity to TDP-43-related pathology. Encouragingly, repairing nuclear pore injury in sALS iPSNs restored normal gene processing disrupted by TDP-43 loss. This study (1) provides a valuable population-scale resource for studying TDP-43 dysfunction in ALS, (2) confirms that patient-derived iPSNs closely reflect disease processes seen in the brain, and (3) demonstrates that targeting nuclear pore injury may offer a promising therapeutic strategy in ALS. In this study, the authors analyzed iPSC-derived neurons from 180 ALS patients and controls, finding that TDP-43 dysfunction is variable and mirrors changes seen in postmortem brain and repairing nuclear pore damage is sufficient to reverse TDP-43 proteinopathy.

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are neurodegenerative diseases with overlap in clinical presentation, neuropathology, and genetic underpinnings. The molecular basis for the overlap of these disorders is not well established. We performed a comparative unbiased mass spectrometry‐based proteomic analysis of frontal cortical tissues from postmortem cases clinically defined as ALS, FTD, ALS and FTD (ALS/FTD), and controls. We also included a subset of patients with the C9orf72 expansion mutation, the most common genetic cause of both ALS and FTD. Our systems‐level analysis of the brain proteome integrated both differential expression and co‐expression approaches to assess the relationship of these differences to clinical and pathological phenotypes. Weighted co‐expression network analysis revealed 15 modules of co‐expressed proteins, eight of which were significantly different across the ALS‐FTD disease spectrum. These included modules associated with RNA binding proteins, synaptic transmission, and inflammation with cell‐type specificity that showed correlation with TDP‐43 pathology and cognitive dysfunction. Modules were also examined for their overlap with TDP‐43 protein–protein interactions, revealing one module enriched with RNA‐binding proteins and other causal ALS genes that increased in FTD/ALS and FTD cases. A module enriched with astrocyte and microglia proteins was significantly increased in ALS cases carrying the C9orf72 mutation compared to sporadic ALS cases, suggesting that the genetic expansion is associated with inflammation in the brain even without clinical evidence of dementia. Together, these findings highlight the utility of integrative systems‐level proteomic approaches to resolve clinical phenotypes and genetic mechanisms underlying the ALS‐FTD disease spectrum in human brain. Synopsis A systems‐level quantitative analysis of the brain proteome reveals pathways and cell types underlying clinicopathological phenotypes across the amyotrophic lateral sclerosis and frontotemporal dementia (ALS‐FTD) disease spectrum, further linking the C9orf72 mutation to neuroinflammation. Human brain protein expression has a molecular signature distinguishing clinical phenotype along the ALS‐FTD disease spectrum. Co‐expression revealed modules associated with RNA binding proteins, synaptic transmission, and inflammation with strong correlation to TDP‐43 pathology and cognitive dysfunction. A module enriched with microglial markers, TDP‐43 protein–protein interactions, and causal ALS gene products implicates novel drivers of disease. An astrocyte and microglia module differentiates ALS cases with the C9orf72 mutation from sporadic ALS cases, linking the genetic expansion with neuroinflammation. Graphical Abstract A systems‐level quantitative analysis of the brain proteome reveals pathways and cell types underlying clinicopathological phenotypes across the amyotrophic lateral sclerosis and frontotemporal dementia (ALS‐FTD) disease spectrum, further linking the C9orf72 mutation to neuroinflammation.

Maintaining the connections between nerve cells and muscle could help to slow the progression of amyotrophic lateral sclerosis.Maintaining the connections between nerve cells and muscle could help to slow the progression of amyotrophic lateral sclerosis.

ImportanceUnderstanding the natural history of familial amyotrophic lateral sclerosis (ALS) caused by SOD1 mutations (ALSSOD1) will provide key information for optimising clinical trials in this patient population.ObjectiveTo establish an updated natural history of ALSSOD1.Design, setting and participantsRetrospective cohort study from 15 medical centres in North America evaluated records from 175 patients with ALS with genetically confirmed SOD1 mutations, cared for after the year 2000.Main outcomes and measuresAge of onset, survival, ALS Functional Rating Scale (ALS-FRS) scores and respiratory function were analysed. Patients with the A4V (Ala-Val) SOD1 mutation (SOD1A4V), the largest mutation population in North America with an aggressive disease progression, were distinguished from other SOD1 mutation patients (SOD1non-A4V) for analysis.ResultsMean age of disease onset was 49.7±12.3 years (mean±SD) for all SOD1 patients, with no statistical significance between SOD1A4V and SOD1non-A4V (p=0.72, Kruskal-Wallis). Total SOD1 patient median survival was 2.7 years. Mean disease duration for all SOD1 was 4.6±6.0 and 1.4±0.7 years for SOD1A4V. SOD1A4V survival probability (median survival 1.2 years) was significantly decreased compared with SOD1non-A4V (median survival 6.8 years; p<0.0001, log-rank). A statistically significant increase in ALS-FRS decline in SOD1A4V compared with SOD1non-A4V participants (p=0.02) was observed, as well as a statistically significant increase in ALS-forced vital capacity decline in SOD1A4V compared with SOD1non-A4V (p=0.02).Conclusions and relevanceSOD1A4V is an aggressive, but relatively homogeneous form of ALS. These SOD1-specific ALS natural history data will be important for the design and implementation of clinical trials in the ALSSOD1 patient population.

Objective To investigate neurodegenerative and inflammatory biomarkers in people with amyotrophic lateral sclerosis (PALS), evaluate their predictive value for ALS progression rates, and assess their utility as pharmacodynamic biomarkers for monitoring treatment effects. Methods De‐identified, longitudinal plasma, and cerebrospinal fluid (CSF) samples from PALS (n = 108; 85 with samples from ≥2 visits) and controls without neurological disease (n = 41) were obtained from the Northeast ALS Consortium (NEALS) Biofluid Repository. Seventeen of 108 PALS had familial ALS, of whom 10 had C9orf72 mutations. Additional healthy control CSF samples (n = 35) were obtained from multiple sources. We stratified PALS into fast‐ and slow‐progression subgroups using the ALS Functional Rating Scale‐Revised change rate. We compared cytokines/chemokines and neurofilament (NF) levels between PALS and controls, among progression subgroups, and in those with C9orf72 mutations. Results We found significant elevations of cytokines, including MCP‐1, IL‐18, and neurofilaments (NFs), indicators of neurodegeneration, in PALS versus controls. Among PALS, these cytokines and NFs were significantly higher in fast‐progression and C9orf72 mutation subgroups versus slow progressors. Analyte levels were generally stable over time, a key feature for monitoring treatment effects. We demonstrated that CSF/plasma neurofilament light chain (NFL) levels may predict disease progression, and stratification by NFL levels can enrich for more homogeneous patient groups. Interpretation Longitudinal stability of cytokines and NFs in PALS support their use for monitoring responses to immunomodulatory and neuroprotective treatments. NFs also have prognostic value for fast‐progression patients and may be used to select similar patient subsets in clinical trials.

Evidence of misfolded wild-type superoxide dismutase 1 (SOD1) has been detected in spinal cords of sporadic ALS (sALS) patients, suggesting an etiological relationship to SOD1-associated familial ALS (fALS). Given that there are currently a number of promising therapies under development that target SOD1, it is of critical importance to better understand the role of misfolded SOD1 in sALS. We previously demonstrated the permissiveness of the G85R-SOD1:YFP mouse model for MND induction following injection with tissue homogenates from paralyzed transgenic mice expressing SOD1 mutations. This prompted us to examine whether WT SOD1 can self-propagate misfolding of the G85R-SOD1:YFP protein akin to what has been observed with mutant SOD1. Using the G85R-SOD1:YFP mice, we demonstrate that misfolded conformers of recombinant WT SOD1, produced in vitro, induce MND with a distinct inclusion pathology. Furthermore, the distinct pathology remains upon successive passages in the G85R-SOD1:YFP mice, strongly supporting the notion for conformation-dependent templated propagation and SOD1 strains. To determine the presence of a similar misfolded WT SOD1 conformer in sALS tissue, we screened homogenates from patients diagnosed with sALS, fALS, and non-ALS disease in an organotypic spinal cord slice culture assay. Slice cultures from G85R-SOD1:YFP mice exposed to spinal homogenates from patients diagnosed with ALS caused by the A4V mutation in SOD1 developed robust inclusion pathology, whereas spinal homogenates from more than 30 sALS cases and various controls failed. These findings suggest that mutant SOD1 has prion-like attributes that do not extend to SOD1 in sALS tissues.

Mutations in the gene encoding superoxide dismutase 1 (SOD1) account for about 20% of the cases of familial amyotrophic lateral sclerosis (fALS). It is not known how the mutant protein causes disease, or why only a subset of cell types (motor neurons) are targeted. The aggregation and misfolding of mutant SOD1 are implicated in disease pathogenesis in both animal models and humans. We used a monoclonal antibody, C4F6, which specifically reacts with mutant and/or \"misfolded\" SOD1, to investigate the regional distribution of mutant SOD1 protein in rodent and human tissues. C4F6 reacted only with mutant SOD1 and showed remarkable selectivity for disease-affected tissues and cells. Tissue not affected by disease but containing high levels of mutant protein (sensory neurons) did not stain with C4F6. Additionally, C4F6 intensely stained some motor neurons while leaving adjacent motor neurons unstained. Although C4F6 was generated against the G93A SOD1 mutant, it also recognized other SOD1 mutants. In human autopsy tissues from patients carrying SOD1 mutations, C4F6 identified skein-like intracellular inclusions in motor neurons, similar to those seen in rodents, and again stained only a subset of motor neurons. In spinal cords from patients with sporadic ALS, other neurodegenerative diseases, and normal controls, C4F6-immunoreactive inclusions were not detected, but the antibody did reveal diffuse immunostaining of some spinal motor neurons. The ability of C4F6 to differentiate pathologically affected tissue in mutant SOD1 ALS rodent models and humans, specifically motor neuron populations, suggests that this antibody may recognize a \"toxic\" form of the mutant SOD1 protein.

Background The objective of this study was to investigate cellular bioenergetics in primary skin fibroblasts derived from patients with amyotrophic lateral sclerosis (ALS) and to determine if they can be used as classifiers for patient stratification. Methods We assembled a collection of unprecedented size of fibroblasts from patients with sporadic ALS (sALS, n  = 171), primary lateral sclerosis (PLS, n  = 34), ALS/PLS with C9orf72 mutations ( n  = 13), and healthy controls ( n  = 91). In search for novel ALS classifiers, we performed extensive studies of fibroblast bioenergetics, including mitochondrial membrane potential, respiration, glycolysis, and ATP content. Next, we developed a machine learning approach to determine whether fibroblast bioenergetic features could be used to stratify patients. Results Compared to controls, sALS and PLS fibroblasts had higher average mitochondrial membrane potential, respiration, and glycolysis, suggesting that they were in a hypermetabolic state. Only membrane potential was elevated in C9Orf72 lines. ATP steady state levels did not correlate with respiration and glycolysis in sALS and PLS lines. Based on bioenergetic profiles, a support vector machine (SVM) was trained to classify sALS and PLS with 99% specificity and 70% sensitivity. Conclusions sALS, PLS, and C9Orf72 fibroblasts share hypermetabolic features, while presenting differences of bioenergetics. The absence of correlation between energy metabolism activation and ATP levels in sALS and PLS fibroblasts suggests that in these cells hypermetabolism is a mechanism to adapt to energy dissipation. Results from SVM support the use of metabolic characteristics of ALS fibroblasts and multivariate analysis to develop classifiers for patient stratification.

Mutations in superoxide dismutase 1 (SOD1) account for ~ 10% of familial amyotrophic lateral sclerosis (fALS) cases. Most SOD1 ALS cases show a 2–5 year clinical course, but a subset of patients exhibit a slowly progressing illness lasting 10–20 years. Substantial evidence indicates that disease-causing mutations in SOD1 promote misfolding and aggregation. Spinal tissue homogenates from paralyzed transgenic mice containing misfolded mutant SOD1 accelerate paralysis when injected into the spine or sciatic nerve of young mutant SOD1 transgenic mice. Using this prion-like seeding model in G85R-SOD1:YFP transgenic mice to initiate the disease process, we show that human SOD1 variants associated with rapidly progressing ALS produce SOD1-ALS strains that cause paralysis earlier than mutations associated with slowly progressing disease. Our findings suggest that the heterogeneous clinical presentations of different SOD1 mutations in ALS could be linked to prion-like strain attributes that govern the templating and propagation kinetics of misfolded SOD1.