Mutations in the FUS/TLS gene on chromosome 16 cause familial amyotrophic lateral sclerosis

Frequency of ubiquitin and FUS-positive, TDP-43-negative frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) is a clinically, genetically and pathologically heterogeneous disorder. Within FTLD with ubiquitin-positive inclusions (FTLD-U), a new pathological subtype named FTLD-FUS was recently found with fused in sarcoma (FUS) positive, TDP-43-negative inclusions, and striking atrophy of the caudate nucleus. The aim of this study was to determine the frequency of FTLD-FUS in our pathological FTLD series, and to describe the clinical, neuroimaging and neuropathological features of FTLD-FUS, especially caudate atrophy. Demographic and clinical data collected prospectively from 387 patients with frontotemporal dementia (FTD) yielded 74 brain specimens. Immunostaining was carried out using a panel of antibodies, including AT-8, ubiquitin, p62, FUS, and TDP-43. Cortical and caudate atrophy on MRI (n = 136) was rated as normal, mild-moderate or severe. Of the 37 FTLD-U cases, 33 were reclassified as FTLD-TDP and four (0.11, 95%: 0.00-0.21) as FTLD-FUS, with ubiquitin and FUS-positive, p62 and TDP-43-negative neuronal intranuclear inclusions (NII). All four FTLD-FUS cases had a negative family history, behavioural variant FTD (bvFTD), and three had an age at onset <or=40 years. MRI revealed mild-moderate or severe caudate atrophy in all, with a mean duration from onset till MRI of 63 months (range 16-119 months). In our total clinical FTD cohort, we found 11 patients (0.03; 95% CI: 0.01-0.05) with bvFTD, negative family history, and age at onset <or=40 years. Caudate atrophy was present in 10 out of 136 MRIs, and included all four FUS-cases. The newly identified FTLD-FUS has a frequency of 11% in FTLD-U, and an estimated frequency of three percent in our clinical FTD cohort. The existence of this pathological subtype can be predicted with reasonable certainty by age at onset <or=40 years, negative family history, bvFTD and caudate atrophy on MRI.

Epigenetic mechanisms in neurological diseases: genes, syndromes, and therapies

Epigenetic mechanisms such as DNA methylation and modifications to histone proteins regulate high-order DNA structure and gene expression. Aberrant epigenetic mechanisms are involved in the development of many diseases, including cancer. The neurological disorder most intensely studied with regard to epigenetic changes is Rett syndrome; patients with Rett syndrome have neurodevelopmental defects associated with mutations in MeCP2, which encodes the methyl CpG binding protein 2, that binds to methylated DNA. Other mental retardation disorders are also linked to the disruption of genes involved in epigenetic mechanisms; such disorders include alpha thalassaemia/mental retardation X-linked syndrome, Rubinstein-Taybi syndrome, and Coffin-Lowry syndrome. Moreover, aberrant DNA methylation and histone modification profiles of discrete DNA sequences, and those at a genome-wide level, have just begun to be described for neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, and Huntington's disease, and in other neurological disorders such as multiple sclerosis, epilepsy, and amyotrophic lateral sclerosis. In this Review, we describe epigenetic changes present in neurological diseases and discuss the therapeutic potential of epigenetic drugs, such as histone deacetylase inhibitors.

The heritability and genetics of frontotemporal lobar degeneration

BACKGROUND

Frontotemporal lobar degeneration (FTLD) is a genetically and pathologically heterogeneous neurodegenerative disorder.

METHODS

We collected blood samples from a cohort of 225 patients with a diagnosis within the FTLD spectrum and examined the heritability of FTLD by giving each patient a family history score, from 1 (a clear autosomal dominant history of FTLD) through to 4 (no family history of dementia). We also looked for mutations in each of the 5 disease-causing genes (MAPT, GRN, VCP, CHMP2B, and TARDP) and the FUS gene, known to cause motor neuron disease.

RESULTS

A total of 41.8% of patients had some family history (score of 1, 2, 3, or 3.5), although only 10.2% had a clear autosomal dominant history (score of 1). Heritability varied across the different clinical subtypes of FTLD with the behavioral variant being the most heritable and frontotemporal dementia-motor neuron disease and the language syndromes (particularly semantic dementia) the least heritable. Mutations were found in MAPT (8.9% of the cohort) and GRN (8.4%) but not in any of the other genes. Of the remaining patients without mutations but with a strong family history, 7 had pathologic confirmation, falling into 2 groups: type 3 FTLD-TDP without GRN mutations (6) and FTLD-UPS (1).

CONCLUSION

These findings show that frontotemporal lobar degeneration (FTLD) is a highly heritable disorder but heritability varies between the different syndromes. Furthermore, while MAPT and GRN mutations account for a substantial proportion of familial cases, there are other genes yet to be discovered, particularly in patients with type 3 FTLD-TDP without a GRN mutation.

The occurrence of mutations in FUS in a Belgian cohort of patients with familial ALS

BACKGROUND AND PURPOSE

Mutations in fused in sarcoma (FUS) were recently identified as a cause of familial amyotrophic lateral sclerosis (ALS). The frequency of occurrence of mutations in FUS in sets of patients with familial ALS remains to be established.

METHODS

We sequenced the FUS gene in a cohort of patients with familial ALS seen at the neuromuscular clinic in Leuven. A total of 28 patients with SOD1-negative ALS from 22 families were analyzed.

RESULTS

We identified a R521H mutation in 4 patients, belonging to a kindred of dominantly inherited classical ALS. The mutation segregated with disease. Mutations in FUS were observed in 2.9% of ALS pedigrees in our cohort.

CONCLUSIONS

These results show that mutations in FUS are also a significant cause of familial ALS in Belgium.

Knockdown of transactive response DNA-binding protein (TDP-43) downregulates histone deacetylase 6

TDP-43 is an RNA/DNA-binding protein implicated in transcriptional repression and mRNA processing. Inclusions of TDP-43 are hallmarks of frontotemporal dementia and amyotrophic lateral sclerosis. Besides aggregation of TDP-43, loss of nuclear localization is observed in disease. To identify relevant targets of TDP-43, we performed expression profiling. Thereby, histone deacetylase 6 (HDAC6) downregulation was discovered on TDP-43 silencing and confirmed at the mRNA and protein level in human embryonic kidney HEK293E and neuronal SH-SY5Y cells. This was accompanied by accumulation of the major HDAC6 substrate, acetyl-tubulin. HDAC6 levels were restored by re-expression of TDP-43, dependent on RNA binding and the C-terminal protein interaction domains. Moreover, TDP-43 bound specifically to HDAC6 mRNA arguing for a direct functional interaction. Importantly, in vivo validation in TDP-43 knockout Drosophila melanogaster confirmed the specific downregulation of HDAC6. HDAC6 is necessary for protein aggregate formation and degradation. Indeed, HDAC6-dependent reduction of cellular aggregate formation and increased cytotoxicity of polyQ-expanded ataxin-3 were found in TDP-43 silenced cells. In conclusion, loss of functional TDP-43 causes HDAC6 downregulation and might thereby contribute to pathogenesis.

Applying proteomics to the diagnosis and treatment of ALS and related diseases

Protein-based biomarkers for amyotrophic lateral sclerosis (ALS) and other motor neuron diseases (MNDs) have many potential clinical utilities, including diagnostic, prognostic, and drug development indications. During the past decade a number of potential protein biomarkers have been proposed for MNDs. Further verification studies, followed by large validation and qualification studies, are required to advance these initial discoveries toward clinical use. Study of additional patient populations, including disease mimics, is required during the validation phase of biomarker development. Important regulatory issues are discussed that will affect the timing and strategy for biomarker assay development in ALS and other MNDs. The continued development of protein biomarkers for MNDs requires extensive collaboration between academic clinicians and scientists in conjunction with the biotechnology and pharmaceutical industries.

[Development of motor neuron restorative therapy in amyotrophic lateral sclerosis using hepatocyte growth factor]

Amyotrophic lateral sclerosis (ALS) is an adult onset neurodegenerative disorder characterized by the death of upper and lower motor neurons. Approximately 20% of familial ALS cases are caused by mutations in the superoxide dismutase 1 (SOD1) gene. Mutations in the fused in sarcoma/translated in liposarcoma (FUS/TLS) gene have been recently discovered to be associated with familial ALS. We found FUS/TLS mutations in familial ALS cases in Japan. Even in Asian races, ALS with FUS/TLS mutations may have common characteristics of early onset, rapid progress, high penerence trait. We developed rats that express a human SOD1 transgene with two different ALS-associated mutations (G93A and H46R) develop striking motor neuron degeneration and paralysis. The larger size of this rat model as compared with the ALS mice will facilitate studies involving manipulations of spinal fluid (implantation of intrathecal catheters for chronic therapeutic studies; CSF sampling) and spinal cord (e.g., direct administration of viral- and cell-mediated therapies). Hepatocyte growth factor (HGF) is one of the most potent survival-promoting factors for motor neurons. To examine its both protective effect on motor neurons and therapeutic potential, we administered human recombinant HGF (hrHGF) by continuous intrathecal delivery to G93A transgenic rats at onset of paralysis for 4 weeks. Intrathecal administration of hrHGF attenuates motor neuron degeneration and prolonged the duration of the disease by 63%. Our results indicated the therapeutic efficacy of continuous intrathecal administration of hrHGF in ALS rats. In addition, HGF is capable of reducing astrocytosis and microglial accumulation, and thus supports the attention of a glial-dependent mechanism of ALS progression. These results should prompt further clinical trials in ALS using continuous intrathecal administration of hrHGF.

Abundant FUS-immunoreactive pathology in neuronal intermediate filament inclusion disease

Neuronal intermediate filament inclusion disease (NIFID) is an uncommon neurodegenerative condition that typically presents as early-onset, sporadic frontotemporal dementia (FTD), associated with a pyramidal and/or extrapyramidal movement disorder. The neuropathology is characterized by frontotemporal lobar degeneration with neuronal inclusions that are immunoreactive for all class IV intermediate filaments (IF), light, medium and heavy neurofilament subunits and alpha-internexin. However, not all the inclusions in NIFID are IF-positive and the primary molecular defect remains uncertain. Mutations in the gene encoding the fused in sarcoma (FUS) protein have recently been identified as a cause of familial amyotrophic lateral sclerosis (ALS). Because of the recognized clinical, genetic and pathological overlap between FTD and ALS, we investigated the possible role of FUS in NIFID. We found abnormal intracellular accumulation of FUS to be a consistent feature of our NIFID cases (n = 5). More neuronal inclusions were labeled using FUS immunohistochemistry than for IF. Several types of inclusions were consistently FUS-positive but IF-negative, including neuronal intranuclear inclusions and glial cytoplasmic inclusions. Double-label immunofluorescence confirmed that many cells had only FUS-positive inclusions and that all cells with IF-positive inclusions also contained pathological FUS. No mutation in the FUS gene was identified in a single case with DNA available. These findings suggest that FUS may play an important role in the pathogenesis of NIFID.

FUS pathology in basophilic inclusion body disease

Basophilic Inclusion Body Disease (BIBD) is a tau-negative form of frontotemporal lobar degeneration (FTLD), characterized by neuronal cytoplasmic inclusions (NCI) that are visible on hematoxylin and eosin stain (HE), contain RNA, and are inconsistently ubiquitin-immunoreactive (ir). The normal nuclear expression of TDP-43 is not altered. Here we investigate whether the distribution of the structurally and functionally related protein fused in sarcoma (FUS) is altered in BIBD. Mutations in the FUS gene have recently been identified as a cause of familial amyotrophic lateral sclerosis (ALS). In addition to these familial ALS cases, FUS protein has recently been demonstrated in NCI in a subset of FTLD with ubiquitinated inclusions (atypical FTLD-U) and in neuronal intermediate filament inclusion disease (NIFID). We examined seven BIBD brains of patients with average age at onset 46 (range 29-57) and average duration of disease 8 years (range 5-12). Three cases presented with the behavioural variant of fronto-temporal dementia (FTD-bv) and one with FTD-bv combined with severe dysarthria. All four developed motor neuron disease/ALS syndrome (MND/ALS) several years later. In the other three cases, presentation was predominantly with motor symptoms, construed as MND/ALS in two, and progressive supranuclear palsy (PSP) in one. Severity of cortical degeneration varied, but all cases shared severe nigrostriatal atrophy and lower motor neuron pathology. In spared areas of cortex, FUS antibodies showed intense labelling of neuronal nuclei and weak positivity of cytoplasm, whereas, in affected areas, intense labelling of NCI was accompanied by reduction or disappearance of the normal IR pattern. The number of FUS-ir NCI was much greater than the number detected by HE or with ubiquitin or P62 immunohistochemistry. FUS-ir glial cytoplasmic inclusions (GCI) were abundant in the grey and white matter in all cases, whereas neuronal intranuclear inclusions were rare and only seen in 2/7 cases. Thus, BIBD shares with atypical FTLD-U and NIFID the presence of FUS-ir NCI and GCI, and together comprise a new biochemical category of neurodegenerative disease (FUS proteinopathies). The consistent involvement of motorneurons in BIBD indicates that the association of FTLD and MND/ALS can occur on a FUS or TDP-43 pathological substrate.

Sporadic ALS has compartment-specific aberrant exon splicing and altered cell-matrix adhesion biology

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive weakness from loss of motor neurons. The fundamental pathogenic mechanisms are unknown and recent evidence is implicating a significant role for abnormal exon splicing and RNA processing. Using new comprehensive genomic technologies, we studied exon splicing directly in 12 sporadic ALS and 10 control lumbar spinal cords acquired by a rapid autopsy system that processed nervous systems specifically for genomic studies. ALS patients had rostral onset and caudally advancing disease and abundant residual motor neurons in this region. We created two RNA pools, one from motor neurons collected by laser capture microdissection and one from the surrounding anterior horns. From each, we isolated RNA, amplified mRNA, profiled whole-genome exon splicing, and applied advanced bioinformatics. We employed rigorous quality control measures at all steps and validated findings by qPCR. In the motor neuron enriched mRNA pool, we found two distinct cohorts of mRNA signals, most of which were up-regulated: 148 differentially expressed genes (P ≤ 10⁻³) and 411 aberrantly spliced genes (P ≤ 10⁻⁵). The aberrantly spliced genes were highly enriched in cell adhesion (P ≤ 10⁻⁵⁷), especially cell–matrix as opposed to cell–cell adhesion. Most of the enriching genes encode transmembrane or secreted as opposed to nuclear or cytoplasmic proteins. The differentially expressed genes were not biologically enriched. In the anterior horn enriched mRNA pool, we could not clearly identify mRNA signals or biological enrichment. These findings, perturbed and up-regulated cell–matrix adhesion, suggest possible mechanisms for the contiguously progressive nature of motor neuron degeneration. Data deposition: GeneChip raw data (CEL-files) have been deposited for public access in the Gene Expression Omnibus (GEO), www.ncbi.nlm.nih.gov/geo, accession number GSE18920.

The evidence for altered RNA metabolism in amyotrophic lateral sclerosis (ALS)

In this review, the role of aberrant RNA metabolism in ALS is examined, including the evidence that a majority of the genetic mutations observed in familial ALS (including mutations in TDP-43, FUS/TLS, SOD1, angiogenin (ANG) and senataxin (SETX)) can impact directly on either gene transcription, pre-mRNA splicing, ribonucleoprotein complex formation, transport, RNA translation or degradation. The evidence that perturbed expression or function of RNA binding proteins is causally related to the selective suppression of the low molecular weight subunit protein (NFL) steady state mRNA levels in degenerating motor neurons in ALS is examined. The discovery that mtSOD1, TDP-43 and 14-3-3 proteins, all of which form cytosolic aggregates in ALS, can each modulate the stability of NFL mRNA, suggests that a fundamental alteration in the interaction of mRNA species with key trans-acting binding factors has occurred in ALS. These observations lead directly to the hypothesis that ALS can be viewed as a disorder of RNA metabolism, thus providing a novel pathway for the development of molecular pharmacotherapies.

Rare missense variants of neuronal nicotinic acetylcholine receptor altering receptor function are associated with sporadic amyotrophic lateral sclerosis

Sporadic amyotrophic lateral sclerosis (SALS) is a motor neuron degenerative disease of unknown etiology. Current thinking on SALS is that multiple genetic and environmental factors contribute to disease liability. Since neuronal acetylcholine receptors (nAChRs) are part of the glutamatergic pathway, we searched for sequence variants in CHRNA3, CHRNA4 and CHRNB4 genes, encoding neuronal nicotinic AChR subunits, in 245 SALS patients and in 450 controls. We characterized missense variants by in vitro mutagenesis, cell transfection and electrophysiology. Sequencing the regions encoding the intracellular loop of AChRs subunits disclosed 15 missense variants (6.1%) in 14 patients compared with only six variants (1.3%) in controls (P = 0.001; OR 4.48, 95% CI 1.7-11.8). The frequency of variants in exons encoding extracellular and transmembrane domains and in intronic regions did not differ. NAChRs formed by mutant alpha3 and alpha4 and wild-type (WT) beta4 subunits exhibited altered affinity for nicotine (Nic), reduced use-dependent rundown of Nic-activated currents (I(Nic)) and reduced desensitization leading to sustained intracellular Ca(2+) concentration, in comparison with WT-nAChR. The cellular loop has a crucial importance for receptor trafficking and regulating ion channel properties. Missense variants in this domain are significantly over-represented in SALS patients and alter functional properties of nAChR in vitro, resulting in increased Ca(2+) entry into the cells. We suggest that these gain-of-function variants might contribute to disease liability in a subset of SALS because Ca(2+) signals mediate nAChR's neuromodulatory effects, including regulation of glutamate release and control of cell survival.

TDP-43 mutant transgenic mice develop features of ALS and frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS) are neurodegenerative diseases that show considerable clinical and pathologic overlap, with no effective treatments available. Mutations in the RNA binding protein TDP-43 were recently identified in patients with familial amyotrophic lateral sclerosis (ALS), and TDP-43 aggregates are found in both ALS and FTLD-U (FTLD with ubiquitin aggregates), suggesting a common underlying mechanism. We report that mice expressing a mutant form of human TDP-43 develop a progressive and fatal neurodegenerative disease reminiscent of both ALS and FTLD-U. Despite universal transgene expression throughout the nervous system, pathologic aggregates of ubiquitinated proteins accumulate only in specific neuronal populations, including layer 5 pyramidal neurons in frontal cortex, as well as spinal motor neurons, recapitulating the phenomenon of selective vulnerability seen in patients with FTLD-U and ALS. Surprisingly, cytoplasmic TDP-43 aggregates are not present, and hence are not required for TDP-43-induced neurodegeneration. These results indicate that the cellular and molecular substrates for selective vulnerability in FTLD-U and ALS are shared between mice and humans, and suggest that altered DNA/RNA-binding protein function, rather than toxic aggregation, is central to TDP-43-related neurodegeneration.

Axonal transport defects in neurodegenerative diseases

Adult-onset neurodegenerative diseases (AONDs) comprise a heterogeneous group of neurological disorders characterized by a progressive, age-dependent decline in neuronal function and loss of selected neuronal populations. Alterations in synaptic function and axonal connectivity represent early and critical pathogenic events in AONDs, but molecular mechanisms underlying these defects remain elusive. The large size and complex subcellular architecture of neurons render them uniquely vulnerable to alterations in axonal transport (AT). Accordingly, deficits in AT have been documented in most AONDs, suggesting a common defect acquired through different pathogenic pathways. These observations suggest that many AONDs can be categorized as dysferopathies, diseases in which alterations in AT represent a critical component in pathogenesis. Topics here address various molecular mechanisms underlying alterations in AT in several AONDs. Illumination of such mechanisms provides a framework for the development of novel therapeutic strategies aimed to prevent axonal and synaptic dysfunction in several major AONDs.

The RNA-binding protein FUS/TLS is a common aggregate-interacting protein in polyglutamine diseases

Neuronal intranuclear inclusions (NIIs) are the pathological hallmark of polyglutamine (polyQ) diseases. We previously found that the RNA-binding protein FUS/TLS is the major component of nuclear polyQ aggregates of a cellular model of Huntington disease. In this study, we revealed that FUS/TLS binds to NIIs in the human brains from patients with spinocerebellar ataxia type 1, 2, 3, and dentatorubral-pallidoluysian atrophy. Recent reports have revealed that mutations in FUS/TLS gene are responsible for familial amyotrophic lateral sclerosis 6 (ALS6). Our results indicated that changing FUS/TLS to an insoluble form may be a common process in polyQ diseases and ALS6.

Accumulation of TDP-43 and alpha-actin in an amyotrophic lateral sclerosis patient with the K17I ANG mutation

A K17I mutation in the ANG gene encoding angiogenin has been identified in a case that we previously published as ALS with neuronal intranuclear protein inclusions (Seilhean et al. in Acta Neuropathol 108:81-87, 2004). These inclusions were immunoreactive for smooth muscle alpha-actin but not for angiogenin. Moreover, they were not labeled by anti-TDP-43 antibodies, while numerous cytoplasmic inclusions immunoreactive for ubiquitin, p62 and TDP-43 were detected in both oligodendrocytes and neurons in various regions of the central nervous system. In addition, expression of smooth muscle alpha-actin was increased in the liver where severe steatosis was observed. This is the first neuropathological description of a case with an ANG mutation. Angiogenin is known to interact with actin. Like other proteins involved in ALS pathogenesis, such as senataxin, TDP-43 and FUS/TLS, it plays a role in RNA maturation.

The TET family of proteins: functions and roles in disease

Translocated in liposarcoma, Ewing's sarcoma and TATA-binding protein-associated factor 15 constitute an interesting and important family of proteins known as the TET proteins. The proteins function in several aspects of cell growth control, including multiple different steps in gene expression, and they are also found mutated in a number of specific diseases. For example, all contain domains for binding nucleic acids and have been shown to function in both RNA polymerase II-mediated transcription and pre-mRNA splicing, possibly connecting these two processes. Chromosomal translocations in human sarcomas result in a fusion of the amino terminus of these proteins, which contains a transcription activation domain, to the DNA-binding domain of a transcription factor. Although the fusion proteins have been characterized in a clinical environment, the function of the cognate full-length protein in normal cells is a more recent topic of study. The first part of this review will describe the TET proteins, followed by detailed descriptions of their multiple roles in cells. The final sections will examine changes that occur in gene regulation in cells expressing the fusion proteins. The clinical implications and treatment of sarcomas will not be addressed but have recently been reviewed.

TDP-43 is recruited to stress granules in conditions of oxidative insult

Transactive response DNA-binding protein 43 (TDP-43) forms abnormal ubiquitinated and phosphorylated inclusions in brain tissues from patients with amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration. TDP-43 is a DNA/RNA-binding protein involved in RNA processing, such as transcription, pre-mRNA splicing, mRNA stabilization and transport to dendrites. We found that in response to oxidative stress and to environmental insults of different types TDP-43 is capable to assemble into stress granules (SGs), ribonucleoprotein complexes where protein synthesis is temporarily arrested. We demonstrated that a specific aminoacidic interval (216-315) in the C-terminal region and the RNA-recognition motif 1 domain are both implicated in TDP-43 participation in SGs as their deletion prevented the recruitment of TDP-43 into SGs. Our data show that TDP-43 is a specific component of SGs and not of processing bodies, although we proved that TDP-43 is not necessary for SG formation, and its gene silencing does not impair cell survival during stress. The analysis of spinal cord tissue from ALS patients showed that SG markers are not entrapped in TDP-43 pathological inclusions. Although SGs were not evident in ALS brains, we speculate that an altered control of mRNA translation in stressful conditions may trigger motor neuron degeneration at early stages of the disease.

Mutations in FUS cause FALS and SALS in French and French Canadian populations

BACKGROUND

The identification of mutations in the TARDBP and more recently the identification of mutations in the FUS gene as the cause of amyotrophic lateral sclerosis (ALS) is providing the field with new insight about the mechanisms involved in this severe neurodegenerative disease.

METHODS

To extend these recent genetic reports, we screened the entire gene in a cohort of 200 patients with ALS. An additional 285 patients with sporadic ALS were screened for variants in exon 15 for which mutations were previously reported.

RESULTS

In total, 3 different mutations were identified in 4 different patients, including 1 3-bp deletion in exon 3 of a patient with sporadic ALS and 2 missense mutations in exon 15 of 1 patient with familial ALS and 2 patients with sporadic ALS.

CONCLUSIONS

Our study identified sporadic patients with mutations in the FUS gene. The accumulation and description of different genes and mutations helps to develop a more comprehensive picture of the genetic events underlying amyotrophic lateral sclerosis.

Analysis of FUS gene mutation in familial amyotrophic lateral sclerosis within an Italian cohort

OBJECTIVE

Mutations in the FUS gene on chromosome 16 have been recently discovered as a cause of familial amyotrophic lateral sclerosis (FALS). This study determined the frequency and identities of FUS gene mutations in a cohort of Italian patients with FALS.

METHODS

We screened all 15 coding exons of FUS for mutations in 94 Italian patients with FALS.

RESULTS

We identified 4 distinct missense mutations in 5 patients; 2 were novel. The mutations were not present in 376 healthy Italian controls and thus are likely to be pathogenic.

CONCLUSIONS

Our results demonstrate that FUS mutations cause approximately 4% of familial amyotrophic lateral sclerosis cases in the Italian population.

Weighted gene co-expression network analysis of the peripheral blood from Amyotrophic Lateral Sclerosis patients

Background

Amyotrophic Lateral Sclerosis (ALS) is a lethal disorder characterized by progressive degeneration of motor neurons in the brain and spinal cord. Diagnosis is mainly based on clinical symptoms, and there is currently no therapy to stop the disease or slow its progression. Since access to spinal cord tissue is not possible at disease onset, we investigated changes in gene expression profiles in whole blood of ALS patients.

Results

Our transcriptional study showed dramatic changes in blood of ALS patients; 2,300 probes (9.4%) showed significant differential expression in a discovery dataset consisting of 30 ALS patients and 30 healthy controls. Weighted gene co-expression network analysis (WGCNA) was used to find disease-related networks (modules) and disease related hub genes. Two large co-expression modules were found to be associated with ALS. Our findings were replicated in a second (30 patients and 30 controls) and third dataset (63 patients and 63 controls), thereby demonstrating a highly significant and consistent association of two large co-expression modules with ALS disease status. Ingenuity Pathway Analysis of the ALS related module genes implicates enrichment of functional categories related to genetic disorders, neurodegeneration of the nervous system and inflammatory disease. The ALS related modules contain a number of candidate genes possibly involved in pathogenesis of ALS.

Conclusion

This first large-scale blood gene expression study in ALS observed distinct patterns between cases and controls which may provide opportunities for biomarker development as well as new insights into the molecular mechanisms of the disease.

Genetic variants in the promoter of TARDBP in sporadic amyotrophic lateral sclerosis

All patients with sporadic amyotrophic lateral sclerosis (SALS) have TDP-43 inclusions in their motor neurons, suggesting this protein plays a major role in the disease. Coding mutations in the gene for TDP-43, TARDBP, have been found in only a few patients with SALS. However, the non-coding regulatory regions of TARDBP have not yet been examined in SALS. We therefore sequenced both coding and non-coding regions of TARDBP in 46 tissue-banked SALS brains (brain DNA was used to detect somatic mutations). Non-coding variants (in the promoter or intron 1) were detected in 16 patients (35%) and coding variants in 4 (9%). Two known promoter variants were found more frequently in SALS patients than in controls. Two other variants, found in one patient each but not in controls, have potential regulatory functions. In addition, a novel exon 2 change with predicted functional effects was found in one patient. In summary, variants in the promoter and other non-coding regions of TARDBP may disturb the regulation of this gene in some patients with SALS.

A new subtype of frontotemporal lobar degeneration with FUS pathology

Frontotemporal dementia (FTD) is a clinical syndrome with a heterogeneous molecular basis. The neuropathology associated with most FTD is characterized by abnormal cellular aggregates of either transactive response DNA-binding protein with Mr 43 kDa (TDP-43) or tau protein. However, we recently described a subgroup of FTD patients, representing around 10%, with an unusual clinical phenotype and pathology characterized by frontotemporal lobar degeneration with neuronal inclusions composed of an unidentified ubiquitinated protein (atypical FTLD-U; aFTLD-U). All cases were sporadic and had early-onset FTD with severe progressive behavioural and personality changes in the absence of aphasia or significant motor features. Mutations in the fused in sarcoma (FUS) gene have recently been identified as a cause of familial amyotrophic lateral sclerosis, with these cases reported to have abnormal cellular accumulations of FUS protein. Because of the recognized clinical, genetic and pathological overlap between FTD and amyotrophic lateral sclerosis, we investigated whether FUS might also be the pathological protein in aFTLD-U. In all our aFTLD-U cases (n = 15), FUS immunohistochemistry labelled all the neuronal inclusions and also demonstrated previously unrecognized glial pathology. Immunoblot analysis of protein extracted from post-mortem aFTLD-U brain tissue demonstrated increased levels of insoluble FUS. No mutations in the FUS gene were identified in any of our patients. These findings suggest that FUS is the pathological protein in a significant subgroup of sporadic FTD and reinforce the concept that FTD and amyotrophic lateral sclerosis are closely related conditions.

Two Italian kindreds with familial amyotrophic lateral sclerosis due to FUS mutation

Recently, fused in sarcoma/translated in liposarcoma (FUS/TLS) gene, located on chromosome 16p11.2, has been identified as a disease gene in familial amyotrophic lateral sclerosis (FALS). We have analyzed FUS/TLS in a cohort of 52 index cases from seven Italian regions with non-SOD1 and non-TARDBP FALS. We identified a heterozygous c.G1542C missense mutation in a family of northern Italian origin, and a heterozygous c.C1574T missense mutation in a family of Sicilian origin. Both variants are located in exon 15 encoding the RNA-recognition motif, and result in a substitution of an arginine with a serine in position 514 (p.R514S) and substitution of a proline with a leucine at position 525 (p.P525L), respectively. Overall, the two mutations accounted for 3.8% of 52 non-SOD1 and non-TDP43 index cases of FALS. The clinical phenotype was similar within each of the families, with a predominantly upper limb onset in the family carrying the p.R514S mutation and bulbar onset, with very young age and a rapid course in the family carrying the p.P525L mutation.

The pathogenic mechanisms of polyglutamine diseases and current therapeutic strategies

Expansion of CAG trinucleotide repeat within the coding region of several genes results in the production of proteins with expanded polyglutamine (PolyQ) stretch. The expression of these pathogenic proteins leads to PolyQ diseases, such as Huntington's disease or several types of spinocerebellar ataxias. This family of neurodegenerative disorders is characterized by constant progression of the symptoms and molecularly, by the accumulation of mutant proteins inside neurons causing their dysfunction and eventually death. So far, no effective therapy actually preventing the physical and/or mental decline has been developed. Experimental therapeutic strategies either target the levels or processing of mutant proteins in an attempt to prevent cellular deterioration, or they are aimed at the downstream pathologic effects to reverse or ameliorate the caused damages. Certain pathomechanistic aspects of PolyQ disorders are discussed here. Relevance of disease models and recent knowledge of therapeutic possibilities is reviewed and updated.

Experimental models for the study of neurodegeneration in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease of unknown cause, characterized by the selective and progressive death of both upper and lower motoneurons, leading to a progressive paralysis. Experimental animal models of the disease may provide knowledge of the pathophysiological mechanisms and allow the design and testing of therapeutic strategies, provided that they mimic as close as possible the symptoms and temporal progression of the human disease. The principal hypotheses proposed to explain the mechanisms of motoneuron degeneration have been studied mostly in models in vitro, such as primary cultures of fetal motoneurons, organotypic cultures of spinal cord sections from postnatal rodents and the motoneuron-like hybridoma cell line NSC-34. However, these models are flawed in the sense that they do not allow a direct correlation between motoneuron death and its physical consequences like paralysis. In vivo, the most widely used model is the transgenic mouse that bears a human mutant superoxide dismutase 1, the only known cause of ALS. The major disadvantage of this model is that it represents about 2%-3% of human ALS. In addition, there is a growing concern on the accuracy of these transgenic models and the extrapolations of the findings made in these animals to the clinics. Models of spontaneous motoneuron disease, like the wobbler and pmn mice, have been used aiming to understand the basic cellular mechanisms of motoneuron diseases, but these abnormalities are probably different from those occurring in ALS. Therefore, the design and testing of in vivo models of sporadic ALS, which accounts for >90% of the disease, is necessary. The main models of this type are based on the excitotoxic death of spinal motoneurons and might be useful even when there is no definitive demonstration that excitotoxicity is a cause of human ALS. Despite their difficulties, these models offer the best possibility to establish valid correlations between cellular alterations and motor behavior, although improvements are still necessary in order to produce a reliable and integrative model that accurately reproduces the cellular mechanisms of motoneuron degeneration in ALS.

Development of immunization approaches to amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disease characterized by loss of motor neurons in the brain and spinal cord. Mutations in the gene encoding superoxide dismutase (SOD1) remain the major known genetic causes associated with ALS. Evidence suggests that the toxicity of SOD1 mutations is related to the abnormal misfolding and aggregation of mutant SOD1 proteins. The discovery of a secretion pathway for mutant SOD1 increased the possibility of using immunization approaches to reduce or neutralize the burden of toxic SOD1 species in the nervous system. Both active and passive immunization protocols were successful in delaying the onset of disease and mortality in transgenic mice expressing mutant SOD1. Owing to the potential adverse immune responses, immunization strategies need to be considered cautiously before being tested in human clinical trials. Critical issues for development of human immunotherapy will be discussed including the routes and methods of antibody delivery, the specificity of antibodies and immune responses, the penetration through the BBB and the time to start treatment. Prophylactic immunotherapy may become a conceivable approach for SOD1-linked ALS patients providing that the treatment is not overly invasive and can be implemented at reasonable cost. This article reviews how innate and adaptive immunity can affect the pathogenesis of ALS and how harnessing the immune system through immunization approaches might offer promising future therapeutic avenues.

CD 4+ T cells in the pathobiology of neurodegenerative disorders

CD4+ T cells orchestrate innate and adaptive immunity. In the central nervous system they modulate immune responses including cell trafficking and glial neuroregulatory functions through an array of soluble molecules cell-cell interactions affecting tissue homeostasis. During disease their roles evolve to an auto-aggressive or, alternatively, protective phenotype. How such a balance is struck in the setting of neurodegenerative disorders may reflect a dichotomy between regulatory T cell, anti-inflammatory and neuroprotective activities versus effector T cell inflammation and neurodegeneration. Interestingly, such roles may show commonalities amongst neurodegenerative diseases. Herein we focus on strategies to modulate such CD4+ T cell responses for therapeutic gain.

A protein-protein interaction of stress-responsive myosin VI endowed to inhibit neural progenitor self-replication with RNA binding protein, TLS, in murine hippocampus

We have shown preferential expression of both mRNA and corresponding protein for myosin VI (Myo6) in the murine hippocampus within 24 h after the extreme traumatic experience, water-immersion restraint stress (WIRS), prior to a drastic decrease in neural progenitor proliferation in the dentate gyrus. Myosin (Myo6) protein levels were significantly increased in hippocampus within 24 h after flashback experience in mice previously exposed to WIRS. Myo6 protein was ubiquitously distributed in discrete mouse brain regions with exceptionally high expression in olfactory bulb, whereas Myo6 protein was expressed in cultured rat astroglia and neurons, in addition to Myo6 mRNA expression by cultured neural progenitors. In mouse embryonal carcinoma P19 cells endowed to proliferate and differentiate, Myo6 protein was expressed in line with astroglial marker protein expression. Transient over-expression of Myo6 induced a significant decrease in the size of clustered aggregates as an index of self-replication in P19 cells. Immunoprecipitation analysis revealed the interaction between Myo6 and the RNA-binding protein, translocated in liposarcoma (TLS), while TLS was predominantly expressed by neurons in the cortex, striatum, cerebellum, and hippocampus. These results suggest that Myo6 may play a pivotal role in the mechanism underlying the suppressed adult neurogenesis after traumatic stress in association with TLS.

Recent advances in the genetics of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disorder with a low survival rate beyond 5 years from symptom onset. Although the genes that cause most cases of ALS are still unknown, several important genetic discoveries have been made recently that will bring substantial insight into some of the mechanisms involved in ALS. Mutations in two genes with related functions were recently reported in patients with familial ALS: the FUS/TLS gene at the ALS6 locus on chromosome 16 and the TARDBP gene at the ALS10 locus on chromosome 1. In addition, the first wave of genomewide association studies in ALS has been published. While these studies clearly show that there is no definitive and common highly penetrant allele that causes ALS, some interesting candidate genes emerged from these studies. The findings help to better delineate the types of genes and genetic variants that are involved in ALS and provide substantial material for future research.

Reduced expression of the Kinesin-Associated Protein 3 (KIFAP3) gene increases survival in sporadic amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a degenerative disorder of motor neurons that typically develops in the 6th decade and is uniformly fatal, usually within 5 years. To identify genetic variants associated with susceptibility and phenotypes in sporadic ALS, we performed a genome-wide SNP analysis in sporadic ALS cases and controls. A total of 288,357 SNPs were screened in a set of 1,821 sporadic ALS cases and 2,258 controls from the U.S. and Europe. Survival analysis was performed using 1,014 deceased sporadic cases. Top results for susceptibility were further screened in an independent sample set of 538 ALS cases and 556 controls. SNP rs1541160 within the KIFAP3 gene (encoding a kinesin-associated protein) yielded a genome-wide significant result (P = 1.84 x 10(-8)) that withstood Bonferroni correction for association with survival. Homozygosity for the favorable allele (CC) conferred a 14.0 months survival advantage. Sequence, genotypic and functional analyses revealed that there is linkage disequilibrium between rs1541160 and SNP rs522444 within the KIFAP3 promoter and that the favorable alleles of rs1541160 and rs522444 correlate with reduced KIFAP3 expression. No SNPs were associated with risk of sporadic ALS, site of onset, or age of onset. We have identified a variant within the KIFAP3 gene that is associated with decreased KIFAP3 expression and increased survival in sporadic ALS. These findings support the view that genetic factors modify phenotypes in this disease and that cellular motor proteins are determinants of motor neuron viability.

SNP haplotype mapping in a small ALS family

The identification of genes for monogenic disorders has proven to be highly effective for understanding disease mechanisms, pathways and gene function in humans. Nevertheless, while thousands of Mendelian disorders have not yet been mapped there has been a trend away from studying single-gene disorders. In part, this is due to the fact that many of the remaining single-gene families are not large enough to map the disease locus to a single site in the genome. New tools and approaches are needed to allow researchers to effectively tap into this genetic gold-mine. Towards this goal, we have used haploid cell lines to experimentally validate the use of high-density single nucleotide polymorphism (SNP) arrays to define genome-wide haplotypes and candidate regions, using a small amyotrophic lateral sclerosis (ALS) family as a prototype. Specifically, we used haploid-cell lines to determine if high-density SNP arrays accurately predict haplotypes across entire chromosomes and show that haplotype information significantly enhances the genetic information in small families. Panels of haploid-cell lines were generated and a 5 centimorgan (cM) short tandem repeat polymorphism (STRP) genome scan was performed. Experimentally derived haplotypes for entire chromosomes were used to directly identify regions of the genome identical-by-descent in 5 affected individuals. Comparisons between experimentally determined and in silico haplotypes predicted from SNP arrays demonstrate that SNP analysis of diploid DNA accurately predicted chromosomal haplotypes. These methods precisely identified 12 candidate intervals, which are shared by all 5 affected individuals. Our study illustrates how genetic information can be maximized using readily available tools as a first step in mapping single-gene disorders in small families.

Rethinking ALS: the FUS about TDP-43

Mutations in TDP-43, a DNA/RNA-binding protein, cause an inherited form of the neurodegenerative disease amyotrophic lateral sclerosis (ALS). Two recent studies (Kwiatkowski et al., 2009; Vance et al., 2009) now report that mutations in FUS/TLS, another DNA/RNA-binding protein, also trigger premature degeneration of motor neurons. TDP-43 and FUS/TLS have striking structural and functional similarities, implicating alterations in RNA processing as a key event in ALS pathogenesis.

Biochemical and genetic evidence for a role of IGHMBP2 in the translational machinery

The human motor neuron degenerative disease spinal muscular atrophy with respiratory distress type 1 (SMARD1) is caused by loss of function mutations of immunoglobulin mu-binding protein 2 (IGHMBP2), a protein of unknown function that contains DNA/RNA helicase and nucleic acid-binding domains. Reduced IGHMBP2 protein levels in neuromuscular degeneration (nmd) mice, the mouse model of SMARD1, lead to motor neuron degeneration. We report the biochemical characterization of IGHMBP2 and the isolation of a modifier locus that rescues the phenotype and motor neuron degeneration of nmd mice. We find that a 166 kb BAC transgene derived from CAST/EiJ mice and containing tRNA genes and activator of basal transcription 1 (Abt1), a protein-coding gene that is required for ribosome biogenesis, contains the genetic modifier responsible for motor neuron rescue. Our biochemical investigations show that IGHMBP2 associates physically with tRNAs and in particular with tRNA(Tyr), which are present in the modifier and with the ABT1 protein. We find that transcription factor IIIC-220 kDa (TFIIIC220), an essential factor required for tRNA transcription, and the helicases Reptin and Pontin, which function in transcription and in ribosome biogenesis, are also part of IGHMBP2-containing complexes. Our findings strongly suggest that IGHMBP2 is a component of the translational machinery and that these components can be manipulated genetically to suppress motor neuron degeneration.

Treatment for familial amyotrophic lateral sclerosis/motor neuron disease

BACKGROUND

Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND), is a rare neurodegenerative disease. Approximately 5% to 7% of ALS/MND patients report a family history of a similarly affected relative. Superoxide dismutase-1 gene mutations are the cause in about 20% of familial cases. In those with non-familial (sporadic) ALS/MND the cause is unknown. Also unknown is whether patients with familial and sporadic ALS/MND respond differently to treatment.

OBJECTIVES

To systematically review the literature and to answer the specific question: 'Is there a difference in the response to treatment between patients with sporadic and familial forms of ALS?'

SEARCH STRATEGY

In May 2006 we searched the Cochrane Neuromuscular Disease Group Trials Register, MEDLINE (January 1966 to May 2006) and EMBASE (January 1980 to May 2006) for randomized controlled trials (RCTs). Two review authors read the titles and abstracts of all articles and reviewed the full text of all possibly relevant articles. We scanned references of all included trials to identify additional relevant articles. For all trials eligible for inclusion we contacted the authors to request the necessary raw data.

SELECTION CRITERIA

Studies had to meet two criteria: (a) randomized controlled study design, and (b) inclusion of patients with both familial and sporadic ALS/MND.

DATA COLLECTION AND ANALYSIS

We attempted to contact authors of all trials that met inclusion criteria. We obtained data regarding ALS/MND type (sporadic versus familial), treatment assignment (active versus placebo), survival and ALS Functional Rating Scale scores for four large RCTs that included 822 sporadic and 41 familial ALS patients. We could not obtain data from 25 potentially eligible studies (17 trial authors could not be contacted and eight were unwilling to provide data).

MAIN RESULTS

There was no statistical evidence for a different response to treatment in patients with familial ALS/MND compared to those with sporadic ALS/MND. The pooled estimate of the hazard ratio for the interaction term (treatment x familial ALS) suggested a more beneficial response with respect to survival among patients with familial ALS/MND, but the result was not statistically significant. Estimates of the rate of decline on the ALS Functional Rating Scale also suggested a slightly better response to treatment among those with familial ALS/MND, but the result was not statistically significant.

AUTHORS' CONCLUSIONS

Future RCTs should document whether patients with familial ALS/MND are included and the presence or absence of a mutation in the superoxide dismutase-1 gene amongst those with familial ALS/MND.

The molecular links between TDP-43 dysfunction and neurodegeneration

TDP-43 nuclear protein is involved in several major neurodegenerative diseases that include frontotemporal lobar degeneration with ubiquitin (FTLD-U) bodies and amyotrophic lateral sclerosis (ALS). As a consequence, the role played by this protein in both normal and diseased cellular metabolism has come under very close scrutiny. In the neuronal tissues of affected individuals TDP-43 undergoes aberrant localization to the cytoplasm to form insoluble aggregates. Furthermore, it is subject to degradation, ubiquitination, and phosphorylation. Understanding the pathways that lead to these changes will be crucial to define the functional role played by this protein in disease. Several recent biochemical and molecular studies have provided new information regarding the potential physiological consequences of these modifications. Moreover, the discovery of TDP-43 mutations associated with disease in a limited number of cases and the data from existing animal models have strengthened the proposed links between this protein and disease. In this review we will discuss the available data regarding the biochemical and functional changes that transform the wild-type endogenous TDP-43 in its pathological form. Furthermore, we will concentrate on examining the potential pathological mechanisms mediated by TDP-43 in different gain- versus loss-of-function scenarios. In the near future, this knowledge will hopefully increase our knowledge on disease progression and development. Moreover, it will allow the design of innovative therapeutic strategies for these pathologies based on the specific molecular defects causing the disease.