Phosphorylation of C-terminal tyrosine residue 526 in FUS impairs its nuclear import

Aberrant cytoplasmic aggregation of FUS, which is caused by mutations primarily in the C-terminal nuclear localisation signal, is associated with 3% of cases of familial amyotrophic lateral sclerosis (ALS). FUS aggregates are also pathognomonic for 10% of all frontotemporal lobar degeneration (FTLD) cases; however, these cases are not associated with mutations in the gene encoding FUS. This suggests that there are differences in the mechanisms that drive inclusion formation of FUS in ALS and FTLD. Here, we show that the C-terminal tyrosine residue at position 526 of FUS is crucial for normal nuclear import. This tyrosine is subjected to phosphorylation, which reduces interaction with transportin 1 and might consequentially affect the transport of FUS into the nucleus. Furthermore, we show that this phosphorylation can occur through the activity of the Src family of kinases. Our study implicates phosphorylation as an additional mechanism by which nuclear transport of FUS might be regulated and potentially perturbed in ALS and FTLD.

Establishing the UK DNA Bank for motor neuron disease (MND)

In 2003 the Motor Neurone Disease (MND) Association, together with The Wellcome Trust, funded the creation of a national DNA Bank specific for MND. It was anticipated that the DNA Bank would constitute an important resource to researchers worldwide and significantly increase activity in MND genetic research. The DNA Bank houses over 3000 high quality DNA samples, all of which were donated by people living with MND, family members and non-related controls, accompanied by clinical phenotype data about the patients. Today the primary focus of the UK MND DNA Bank still remains to identify causative and disease modifying factors for this devastating disease.

Wild type human TDP-43 potentiates ALS-linked mutant TDP-43 driven progressive motor and cortical neuron degeneration with pathological features of ALS

Introduction

Amyotrophic lateral sclerosis (ALS) is a relentlessly progressive neurodegenerative disorder, and cytoplasmic inclusions containing transactive response (TAR) DNA binding protein (TDP-43) are present in ~90 % of cases. Here we report detailed pathology in human TDP-43 transgenic mice that recapitulate key features of TDP-43-linked ALS.

Results

Expression of human wild-type TDP-43 (TDP-43^WT) caused no clinical or pathological phenotype, while expression of Q331K mutant (TDP-43^Q331K) resulted in a non-lethal age-dependent motor phenotype, accompanied by cytoplasmic TDP-43 aggregation, mild neuronal loss, with astroglial and microglial activation in the motor cortex and spinal cord at 24 months. However, co-expression of WT and Q331K mutant (TDP-43^WTxQ331K) resulted in an extremely aggressive motor phenotype with tremor from 3 weeks and progressive hind-limb paralysis necessitating euthanasia by 8–10 weeks of age. Neuronal loss and reactive gliosis was observed in the spinal cord and layer V region of the cortex, with TDP-43, ubiquitin and p62 cytoplasmic inclusions and an increase in insoluble TDP-43. Nuclear clearance of TDP-43 was not observed in TDP-43^Q331K mice but was seen in 65 % of aggregate containing spinal cord motor neurons in TDP-43^WTxQ331K mice.

Conclusions

We hypothesise that cytoplasmic TDP-43^Q331K aggregates facilitate the recruitment of WT protein in compound animals, which dramatically accelerates neurodegeneration and disease progression. The exploration of disease mechanisms in slow and rapid disease models of TDP-43 proteinopathy will help elucidate novel drug targets and provide a more informative platform for preclinical trials.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-015-0212-4) contains supplementary material, which is available to authorized users.

Dipeptide repeat protein inclusions are rare in the spinal cord and almost absent from motor neurons in C9ORF72 mutant amyotrophic lateral sclerosis and are unlikely to cause their degeneration

Introduction

Cytoplasmic TDP-43 inclusions are the pathological hallmark of amyotrophic lateral sclerosis (ALS) and tau-negative frontotemporal lobar dementia (FTLD). The G₄C₂ repeat mutation in C9ORF72 is the most common cause of ALS and FTLD in which, in addition to TDP-43 inclusions, five different di-peptide repeat (DPR) proteins have been identified. Di-peptide repeat proteins are translated in a non-canonical fashion from sense and antisense transcripts of the G₄C₂ repeat (GP, GA, GR, PA, PR). DPR inclusions are abundant in the cerebellum, as well as in the frontal and temporal lobes of ALS and FTLD patients and some are neurotoxic in a range of cellular and animal models, implying that DPR aggregation directly contributes to disease pathogenesis. Here we sought to quantify inclusions for each DPR and TDP-43 in ALS cases with and without the C9ORF72 mutation. We characterised the abundance of DPRs and their cellular location and compared this to cytoplasmic TDP-43 inclusions in order to explore the role of each inclusion in lower motor neuron degeneration.

Results

Spinal cord sections from ten cases positive for the C9ORF72 repeat expansion (ALS-C9+ve) and five cases that were not were probed by double immunofluorescence staining for individual DPRs and TDP-43. Inclusions immunoreactive for each of the DPRs were present in the spinal cord but they were rare or very rare in abundance (in descending order of frequency: GA, GP, GR, PA and PR). TDP-43 cytoplasmic inclusions were 45- to 750-fold more frequent than any DPR, and fewer than 4 % of DPR inclusions colocalized with TDP-43 inclusions. In motor neurons, a single cytoplasmic DPR inclusion was detected (0.1 %) in contrast to the 34 % of motor neurons that contained cytoplasmic TDP-43 inclusions. Furthermore, the number of TDP-43 inclusions in ALS cases with and without the C9ORF72 mutation was nearly identical.

Conclusions

For all other neurodegenerative diseases, the neurotoxic protein aggregates are detected in the affected population of neurons. TDP-43 cytoplasmic aggregation is the dominant feature of ALS spinal cord pathology irrespective of C9ORF72 mutation status. The near absence of DPR inclusions in spinal cord motor neurons challenges their contribution to lower motor neuron degeneration in ALS-C9+ve cases.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-015-0218-y) contains supplementary material, which is available to authorized users.

The role of TREM2 R47H as a risk factor for Alzheimer's disease, frontotemporal lobar degeneration, amyotrophic lateral sclerosis, and Parkinson's disease

A rare variant in TREM2 (p.R47H, rs75932628) was recently reported to increase the risk of Alzheimer's disease (AD) and, subsequently, other neurodegenerative diseases, i.e. frontotemporal lobar degeneration (FTLD), amyotrophic lateral sclerosis (ALS), and Parkinson's disease (PD). Here we comprehensively assessed TREM2 rs75932628 for association with these diseases in a total of 19,940 previously untyped subjects of European descent. These data were combined with those from 28 published data sets by meta-analysis. Furthermore, we tested whether rs75932628 shows association with amyloid beta (Aβ42) and total-tau protein levels in the cerebrospinal fluid (CSF) of 828 individuals with AD or mild cognitive impairment. Our data show that rs75932628 is highly significantly associated with the risk of AD across 24,086 AD cases and 148,993 controls of European descent (odds ratio or OR = 2.71, P = 4.67 × 10(-25)). No consistent evidence for association was found between this marker and the risk of FTLD (OR = 2.24, P = .0113 across 2673 cases/9283 controls), PD (OR = 1.36, P = .0767 across 8311 cases/79,938 controls) and ALS (OR = 1.41, P = .198 across 5544 cases/7072 controls). Furthermore, carriers of the rs75932628 risk allele showed significantly increased levels of CSF-total-tau (P = .0110) but not Aβ42 suggesting that TREM2's role in AD may involve tau dysfunction.

TDP-43 Proteinopathy and ALS: Insights into Disease Mechanisms and Therapeutic Targets

Therapeutic options for patients with amyotrophic lateral sclerosis (ALS) are currently limited. However, recent studies show that almost all cases of ALS, as well as tau-negative frontotemporal dementia (FTD), share a common neuropathology characterized by the deposition of TAR-DNA binding protein (TDP)-43-positive protein inclusions, offering an attractive target for the design and testing of novel therapeutics. Here we demonstrate how diverse environmental stressors linked to stress granule formation, as well as mutations in genes encoding RNA processing proteins and protein degradation adaptors, initiate ALS pathogenesis via TDP-43. We review the progressive development of TDP-43 proteinopathy from cytoplasmic mislocalization and misfolding through to macroaggregation and the addition of phosphate and ubiquitin moieties. Drawing from cellular and animal studies, we explore the feasibility of therapeutics that act at each point in pathogenesis, from mitigating genetic risk using antisense oligonucleotides to modulating TDP-43 proteinopathy itself using small molecule activators of autophagy, the ubiquitin-proteasome system, or the chaperone network. We present the case that preventing the misfolding of TDP-43 and/or enhancing its clearance represents the most important target for effectively treating ALS and frontotemporal dementia.

U1 snRNP is mislocalized in ALS patient fibroblasts bearing NLS mutations in FUS and is required for motor neuron outgrowth in zebrafish

Mutations in FUS cause amyotrophic lateral sclerosis (ALS), but the molecular pathways leading to neurodegeneration remain obscure. We previously found that U1 snRNP is the most abundant FUS interactor. Here, we report that components of the U1 snRNP core particle (Sm proteins and U1 snRNA), but not the mature U1 snRNP-specific proteins (U1-70K, U1A and U1C), co-mislocalize with FUS to the cytoplasm in ALS patient fibroblasts harboring mutations in the FUS nuclear localization signal (NLS). Similar results were obtained in HeLa cells expressing the ALS-causing FUS R495X NLS mutation, and mislocalization of Sm proteins is RRM-dependent. Moreover, as observed with FUS, knockdown of any of the U1 snRNP-specific proteins results in a dramatic loss of SMN-containing Gems. Significantly, knockdown of U1 snRNP in zebrafish results in motor axon truncations, a phenotype also observed with FUS, SMN and TDP-43 knockdowns. Our observations linking U1 snRNP to ALS patient cells with FUS mutations, SMN-containing Gems, and motor neurons indicate that U1 snRNP is a component of a molecular pathway associated with motor neuron disease. Linking an essential canonical splicing factor (U1 snRNP) to this pathway provides strong new evidence that splicing defects may be involved in pathogenesis and that this pathway is a potential therapeutic target.

Exome sequencing in amyotrophic lateral sclerosis identifies risk genes and pathways

Amyotrophic lateral sclerosis (ALS) is a devastating neurological disease with no effective treatment. We report the results of a moderate-scale sequencing study aimed at increasing the number of genes known to contribute to predisposition for ALS. We performed whole-exome sequencing of 2869 ALS patients and 6405 controls. Several known ALS genes were found to be associated, and TBK1 (the gene encoding TANK-binding kinase 1) was identified as an ALS gene. TBK1 is known to bind to and phosphorylate a number of proteins involved in innate immunity and autophagy, including optineurin (OPTN) and p62 (SQSTM1/sequestosome), both of which have also been implicated in ALS. These observations reveal a key role of the autophagic pathway in ALS and suggest specific targets for therapeutic intervention.

Stratified gene expression analysis identifies major amyotrophic lateral sclerosis genes

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease of motor neurons resulting in progressive paralysis. Gene expression studies of ALS only rarely identify the same gene pathways as gene association studies. We hypothesized that analyzing tissues by matching on degree of disease severity would identify different patterns of gene expression from a traditional case-control comparison. We analyzed gene expression changes in 4 postmortem central nervous system regions, stratified by severity of motor neuron loss. An overall comparison of cases (n = 6) and controls (n = 3) identified known ALS gene, SOX5, as showing differential expression (log2 fold change = 0.09, p = 5.5 × 10(-5)). Analyses stratified by disease severity identified expression changes in C9orf72 (p = 2.77 × 10(-3)), MATR3 (p = 3.46 × 10(-3)), and VEGFA (p = 8.21 × 10(-4)), all implicated in ALS through genetic studies, and changes in other genes in pathways involving RNA processing and immune response. These findings suggest that analysis of gene expression stratified by disease severity can identify major ALS genes and may be more efficient than traditional case-control comparison.

Human iPSC-derived motoneurons harbouring TARDBP or C9ORF72 ALS mutations are dysfunctional despite maintaining viability

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease for which a greater understanding of early disease mechanisms is needed to reveal novel therapeutic targets. We report the use of human induced pluripotent stem cell (iPSC)-derived motoneurons (MNs) to study the pathophysiology of ALS. We demonstrate that MNs derived from iPSCs obtained from healthy individuals or patients harbouring TARDBP or C9ORF72 ALS-causing mutations are able to develop appropriate physiological properties. However, patient iPSC-derived MNs, independent of genotype, display an initial hyperexcitability followed by progressive loss of action potential output and synaptic activity. This loss of functional output reflects a progressive decrease in voltage-activated Na(+) and K(+) currents, which occurs in the absence of overt changes in cell viability. These data implicate early dysfunction or loss of ion channels as a convergent point that may contribute to the initiation of downstream degenerative pathways that ultimately lead to MN loss in ALS.

Autosomal dominant inheritance of rapidly progressive amyotrophic lateral sclerosis due to a truncation mutation in the fused in sarcoma (FUS) gene

Mutations in the gene encoding the RNA-binding protein fused in sarcoma (FUS) account for 4 - 5% of familial cases of amyotrophic lateral sclerosis (ALS). We describe the identification and in vitro cellular characterization of a genetic mutation in a family in which the index case, and subsequently her two children, each developed rapidly progressive ALS at a young age and died within a year of onset. Exome capture and sequencing revealed a mutation in the FUS gene consisting of a 2-bp deletion, c.1509_1510delAG, resulting in a predicted truncated protein, p.G504Wfs * 12, lacking the nuclear localization signal. Expression of this mutation in HEK293 and NSC-34 cells demonstrated severe cytoplasmic mislocalization of mutant FUS, and colocalization with stress granules when compared to wild-type, R521C and P525L mutant FUS. This study provides further evidence of a broad correlation between clinical severity of FUS-related ALS and mislocalization of the protein to the cytoplasm.

The evaluation of pain in amyotrophic lateral sclerosis: a case controlled observational study

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder leading to progressive paralysis. ALS is complicated by a number of non-motor symptoms including pain. Pain in ALS has been poorly studied and poorly managed. This study aimed to collate information regarding pain in ALS using standardized pain questionnaires. Forty-two patients with ALS participated in the study. Control subjects included 41 age-matched healthy volunteers and 42 age-matched patients with neurological conditions other than ALS. Data on pain were collected using the The Brief Pain Inventory and The painDetect Questionnaire. Eighty-five percent of subjects with ALS reported pain versus 50% of neurology clinic controls and 35% of healthy controls (p < 0.01). Pain in ALS included cramping, aching, tiring, sharp and tender, and was non-neuropathic. Pain impacted significantly on mood, general activity, relationships and general enjoyment of life. Fifty-four percent of people with painful ALS used regular analgesia and 29% regular opioids. Other non-motor symptoms suffered included tiredness, constipation, urinary problems, itching and drowsiness. In conclusion, these data support the fact that pain is a significant symptom in ALS which impacts on quality of life. These data can be used to educate clinicians and patients to promote better multidisciplinary management of ALS symptoms and a better quality of life.

Exome-wide rare variant analysis identifies TUBA4A mutations associated with familial ALS

Exome sequencing is an effective strategy for identifying human disease genes. However, this methodology is difficult in late-onset diseases where limited availability of DNA from informative family members prohibits comprehensive segregation analysis. To overcome this limitation, we performed an exome-wide rare variant burden analysis of 363 index cases with familial ALS (FALS). The results revealed an excess of patient variants within TUBA4A, the gene encoding the Tubulin, Alpha 4A protein. Analysis of a further 272 FALS cases and 5,510 internal controls confirmed the overrepresentation as statistically significant and replicable. Functional analyses revealed that TUBA4A mutants destabilize the microtubule network, diminishing its repolymerization capability. These results further emphasize the role of cytoskeletal defects in ALS and demonstrate the power of gene-based rare variant analyses in situations where causal genes cannot be identified through traditional segregation analysis.

Analysis of amyotrophic lateral sclerosis as a multistep process: a population-based modelling study

Background

Amyotrophic lateral sclerosis shares characteristics with some cancers, such as onset being more common in later life, progression usually being rapid, the disease affecting a particular cell type, and showing complex inheritance. We used a model originally applied to cancer epidemiology to investigate the hypothesis that amyotrophic lateral sclerosis is a multistep process.

Methods

We generated incidence data by age and sex from amyotrophic lateral sclerosis population registers in Ireland (registration dates 1995–2012), the Netherlands (2006–12), Italy (1995–2004), Scotland (1989–98), and England (2002–09), and calculated age and sex-adjusted incidences for each register. We regressed the log of age-specific incidence against the log of age with least squares regression. We did the analyses within each register, and also did a combined analysis, adjusting for register.

Findings

We identified 6274 cases of amyotrophic lateral sclerosis from a catchment population of about 34 million people. We noted a linear relationship between log incidence and log age in all five registers: England r²=0·95, Ireland r²=0·99, Italy r²=0·95, the Netherlands r²=0·99, and Scotland r²=0·97; overall r²=0·99. All five registers gave similar estimates of the linear slope ranging from 4·5 to 5·1, with overlapping confidence intervals. The combination of all five registers gave an overall slope of 4·8 (95% CI 4·5–5·0), with similar estimates for men (4·6, 4·3–4·9) and women (5·0, 4·5–5·5).

Interpretation

A linear relationship between the log incidence and log age of onset of amyotrophic lateral sclerosis is consistent with a multistage model of disease. The slope estimate suggests that amyotrophic lateral sclerosis is a six-step process. Identification of these steps could lead to preventive and therapeutic avenues.

Funding

UK Medical Research Council; UK Economic and Social Research Council; Ireland Health Research Board; The Netherlands Organisation for Health Research and Development (ZonMw); the Ministry of Health and Ministry of Education, University, and Research in Italy; the Motor Neurone Disease Association of England, Wales, and Northern Ireland; and the European Commission (Seventh Framework Programme).

Psychological as well as illness factors influence acceptance of non-invasive ventilation (NIV) and gastrostomy in amyotrophic lateral sclerosis (ALS): a prospective population study

Our objective was to identify factors associated with acceptance of non-invasive ventilation (NIV) and gastrostomy in an exploratory population-based study. Seventy-eight people with ALS at least six months post-diagnosis, and 50 caregivers, were recruited from the South-East ALS Register. Baseline physical, cognitive and psychological measures were obtained. Three-monthly follow-ups monitored whether patients had accepted or refused NIV or gastrostomy. Following an intervention decision, post-decision interviews repeated baseline measures and included further intervention-specific questionnaires. Results showed that 32 people with ALS made at least one intervention decision and of these 10 decided about both NIV and gastrostomy. While illness factors predicted those needing to make an intervention decision, cognitive and education status, and level of executive dysfunction were associated with decision-making and acceptance or refusal of interventions. Patients' understanding of their illness, their early approach to considering interventions and carer-related factors were also associated with treatment decisions. In conclusion, our findings highlight the complexity of decision-making and provide a platform for designing further studies. Cognitive and psychosocial factors may assume a greater role in palliative care decisions for people with ALS than has been explicitly recognized. Future work must clarify how to ensure patients are not inadvertently being denied suitable interventions.

C9orf72 and UNC13A are shared risk loci for amyotrophic lateral sclerosis and frontotemporal dementia: a genome-wide meta-analysis

OBJECTIVE

Substantial clinical, pathological, and genetic overlap exists between amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). TDP-43 inclusions have been found in both ALS and FTD cases (FTD-TDP). Recently, a repeat expansion in C9orf72 was identified as the causal variant in a proportion of ALS and FTD cases. We sought to identify additional evidence for a common genetic basis for the spectrum of ALS-FTD.

METHODS

We used published genome-wide association studies data for 4,377 ALS patients and 13,017 controls, and 435 pathology-proven FTD-TDP cases and 1,414 controls for genotype imputation. Data were analyzed in a joint meta-analysis, by replicating topmost associated hits of one disease in the other, and by using a conservative rank products analysis, allocating equal weight to ALS and FTD-TDP sample sizes.

RESULTS

Meta-analysis identified 19 genome-wide significant single nucleotide polymorphisms (SNPs) in C9orf72 on chromosome 9p21.2 (lowest p = 2.6 × 10(-12) ) and 1 SNP in UNC13A on chromosome 19p13.11 (p = 1.0 × 10(-11) ) as shared susceptibility loci for ALS and FTD-TDP. Conditioning on the 9p21.2 genotype increased statistical significance at UNC13A. A third signal, on chromosome 8q24.13 at the SPG8 locus coding for strumpellin (p = 3.91 × 10(-7) ) was replicated in an independent cohort of 4,056 ALS patients and 3,958 controls (p = 0.026; combined analysis p = 1.01 × 10(-7) ).

INTERPRETATION

We identified common genetic variants in C9orf72, but in addition in UNC13A that are shared between ALS and FTD. UNC13A provides a novel link between ALS and FTD-TDP, and identifies changes in neurotransmitter release and synaptic function as a converging mechanism in the pathogenesis of ALS and FTD-TDP.

ER-mitochondria associations are regulated by the VAPB-PTPIP51 interaction and are disrupted by ALS/FTD-associated TDP-43

Mitochondria and the endoplasmic reticulum (ER) form tight structural associations and these facilitate a number of cellular functions. However, the mechanisms by which regions of the ER become tethered to mitochondria are not properly known. Understanding these mechanisms is not just important for comprehending fundamental physiological processes but also for understanding pathogenic processes in some disease states. In particular, disruption to ER-mitochondria associations is linked to some neurodegenerative diseases. Here we show that the ER-resident protein VAPB interacts with the mitochondrial protein tyrosine phosphatase-interacting protein-51 (PTPIP51) to regulate ER-mitochondria associations. Moreover, we demonstrate that TDP-43, a protein pathologically linked to amyotrophic lateral sclerosis and fronto-temporal dementia perturbs ER-mitochondria interactions and that this is associated with disruption to the VAPB-PTPIP51 interaction and cellular Ca(2+) homeostasis. Finally, we show that overexpression of TDP-43 leads to activation of glycogen synthase kinase-3β (GSK-3β) and that GSK-3β regulates the VAPB-PTPIP51 interaction. Our results describe a new pathogenic mechanism for TDP-43.

Estimating clinical stage of amyotrophic lateral sclerosis from the ALS Functional Rating Scale

ALS is a progressive neurodegenerative disease. The stage of disease reached can be described using a simple system based on the number of central nervous system regions involved. Historically, datasets have not attempted to record clinical stage, but being able to re-analyse the data by stage would have several advantages. We therefore explored the possibility of using an algorithm based on the revised ALS Functional Rating Scale (ALSFRS-R), which is commonly used in clinical practice, to estimate clinical stage. We devised an algorithm to convert ALSFRS-R score into clinical stage. ALSFRS-R domains were mapped to equivalent CNS regions. Stage 4 is reached when gastrostomy or non- invasive ventilation is needed, but as a proxy we used provision. We collected ALSFRS-R from clinic visits, and compared the estimation of clinical stage from the ALSFRS-R with the actual stage. Results showed that the agreement between staging by the two methods was excellent with an intraclass correlation coefficient of 0.92 (95% confidence interval 0.88-0.94). There was no systematic bias towards over-staging or under-staging using the algorithm. In conclusion, we have shown that clinical stage in ALS can be reliably estimated using the ALSFRS-R in historical data and in current data where stage has not been recorded.

Evidence of an environmental effect on survival in ALS

Amyotrophic lateral sclerosis (ALS, motor neuron disease) is a neurodegenerative disorder of motor neurons leading to paralysis and eventual death by respiratory failure. Median survival is 2-3 years. Susceptibility genes, environmental triggers and disease related prognostic factors have been established, but environmental effects on survival are yet to be investigated. We analysed survival in the South-East England ALS register (SEALS register). Kaplan-Meier and Cox regression analyses were used to investigate survival in London, coastal and rural areas according to postcode at diagnosis. Results showed that there were 933 cases of ALS identified in the catchment area during the study period (1994-January 2012). Cox regression demonstrated a highly significant model for survival with significant protective variables: coastal residency, riluzole use and younger age at onset. Significantly worse survival was associated with London residency, older age as well as definite and probable El Escorial classifications. In conclusion, these findings suggest the possibility of an environmental effect on survival in ALS.