The gene encoding alsin, a protein with three guanine-nucleotide exchange factor domains, is mutated in a form of recessive amyotrophic lateral sclerosis

Clinical Trials in Amyotrophic Lateral Sclerosis: The Tenuous Past and the Promising Future

The past decade of research in amyotrophic lateral sclerosis has contributed to a greater understanding of the disease process, the development of relevant animal models, and the identification of several therapeutic approaches that may delay disease progression. Completed and ongoing clinical trials and the process of selecting drugs for clinical trials are presented.

The changing scene of amyotrophic lateral sclerosis

Several recent breakthroughs have provided notable insights into the pathogenesis of amyotrophic lateral sclerosis (ALS), with some even shifting our thinking about this neurodegenerative disease and raising the question as to whether this disorder is a proteinopathy, a ribonucleopathy or both. In addition, these breakthroughs have revealed mechanistic links between ALS and frontotemporal dementia, as well as between ALS and other neurodegenerative diseases, such as the cerebellar atrophies, myotonic dystrophy and inclusion body myositis. Here, we summarize the new findings in ALS research, discuss what they have taught us about this disease and examine issues that are still outstanding.

The small heat shock proteins αB-crystallin and Hsp27 suppress SOD1 aggregation in vitro

Amyotrophic lateral sclerosis is a devastating neurodegenerative disease. The mechanism that underlies amyotrophic lateral sclerosis (ALS) pathology remains unclear, but protein inclusions are associated with all forms of the disease. Apart from pathogenic proteins, such as TDP-43 and SOD1, other proteins are associated with ALS inclusions including small heat shock proteins. However, whether small heat shock proteins have a direct effect on SOD1 aggregation remains unknown. In this study, we have examined the ability of small heat shock proteins αB-crystallin and Hsp27 to inhibit the aggregation of SOD1 in vitro. We show that these chaperone proteins suppress the increase in thioflavin T fluorescence associated with SOD1 aggregation, primarily through inhibiting aggregate growth, not the lag phase in which nuclei are formed. αB-crystallin forms high molecular mass complexes with SOD1 and binds directly to SOD1 aggregates. Our data are consistent with an overload of proteostasis systems being associated with pathology in ALS.

Redox regulation in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that results from the death of upper and lower motor neurons. Due to a lack of effective treatment, it is imperative to understand the underlying mechanisms and processes involved in disease progression. Regulations in cellular reduction/oxidation (redox) processes are being increasingly implicated in disease. Here we discuss the possible involvement of redox dysregulation in the pathophysiology of ALS, either as a cause of cellular abnormalities or a consequence. We focus on its possible role in oxidative stress, protein misfolding, glutamate excitotoxicity, lipid peroxidation and cholesterol esterification, mitochondrial dysfunction, impaired axonal transport and neurofilament aggregation, autophagic stress, and endoplasmic reticulum (ER) stress. We also speculate that an ER chaperone protein disulphide isomerase (PDI) could play a key role in this dysregulation. PDI is essential for normal protein folding by oxidation and reduction of disulphide bonds, and hence any disruption to this process may have consequences for motor neurons. Addressing the mechanism underlying redox regulation and dysregulation may therefore help to unravel the molecular mechanism involved in ALS.

Rabex-5 protein regulates dendritic localization of small GTPase Rab17 and neurite morphogenesis in hippocampal neurons

Small GTPase Rab17 has recently been shown to regulate dendritic morphogenesis of mouse hippocampal neurons; however, the exact molecular mechanism of Rab17-mediated dendritogenesis remained to be determined, because no guanine nucleotide exchange factor (GEF) for Rab17 had been identified. In this study we screened for the Rab17-GEF by performing yeast two-hybrid assays with a GDP-locked Rab17 mutant as bait and found that Rabex-5 and ALS2, both of which were originally described as Rab5-GEFs, interact with Rab17. We also found that expression of Rabex-5, but not of ALS2, promotes translocation of Rab17 from the cell body to the dendrites of developing mouse hippocampal neurons. The shRNA-mediated knockdown of Rabex-5 or its known downstream target Rab5 in hippocampal neurons inhibited morphogenesis of both axons and dendrites, whereas knockdown of Rab17 affected dendrite morphogenesis alone. Based on these findings, we propose that Rabex-5 regulates neurite morphogenesis of hippocampal neurons by activating at least two downstream targets, Rab5, which is localized in both axons and dendrites, and Rab17, which is localized in dendrites alone.

Protein SUMOylation, an emerging pathway in amyotrophic lateral sclerosis

The covalent attachment of SUMO proteins (small ubiquitin-like modifier) to specific proteins or SUMOylation regulates their functional properties in the nucleus and cytoplasm of neurons. Recent studies reported dysfunction of the SUMO pathway in molecular and cellular abnormalities associated with amyotrophic lateral sclerosis (ALS). Furthermore, several observations support a direct role for SUMOylation in diverse pathogenic mechanisms involved in ALS, such as response to hypoxia, oxidative stress, glutamate excitotoxicity and proteasome impairment. Recent results also suggest that SUMO modifications of superoxide dismutase 1, transactive response DNA-binding protein 43, CTE (COOH terminus of EAAT2) (proteolytic C-terminal fragment of the glutamate transporter excitatory amino acid transporter 2, EAAT2) and proteins regulating the turnover of ALS-related proteins can participate in the pathogenesis of ALS. Moreover, the fused in sarcoma (FUS) gene, mutated in ALS, encodes a protein with a SUMO E3 ligase activity. In this review, we summarize the functioning of the SUMO pathway in normal conditions and in response to stresses, its action on ALS-related proteins and discuss the need for further research on this pathway in ALS.

Impacts of massively parallel sequencing for genetic diagnosis of neuromuscular disorders

Neuromuscular disorders (NMD) such as neuropathy or myopathy are rare and often severe inherited disorders, affecting muscle and/or nerves with neonatal, childhood or adulthood onset, with considerable burden for the patients, their families and public health systems. Genetic and clinical heterogeneity, unspecific clinical features, unidentified genes and the implication of large and/or several genes requiring complementary methods are the main drawbacks in routine molecular diagnosis, leading to increased turnaround time and delay in the molecular validation of the diagnosis. The application of massively parallel sequencing, also called next generation sequencing, as a routine diagnostic strategy could lead to a rapid screening and fast identification of mutations in rare genetic disorders like NMD. This review aims to summarize and to discuss recent advances in the genetic diagnosis of neuromuscular disorders, and more generally monogenic diseases, fostered by massively parallel sequencing. We remind the challenges and benefit of obtaining an accurate genetic diagnosis, introduce the massively parallel sequencing technology and its novel applications in diagnosis of patients, prenatal diagnosis and carrier detection, and discuss the limitations and necessary improvements. Massively parallel sequencing synergizes with clinical and pathological investigations into an integrated diagnosis approach. Clinicians and pathologists are crucial in patient selection and interpretation of data, and persons trained in data management and analysis need to be integrated to the diagnosis pipeline. Massively parallel sequencing for mutation identification is expected to greatly improve diagnosis, genetic counseling and patient management.

Understanding ALS: new therapeutic approaches

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease associated with motor neuron degeneration, muscle atrophy and paralysis. Although numerous pathological mechanisms have been elucidated, ALS remains an invariably fatal disease in the absence of any effective therapy. The heterogeneity of the disease and the failure to develop satisfactory therapeutic protocols reinforce the view that ALS is a multi-factorial and multi-systemic disease. Thus, a better understanding of the pathogenic mechanisms and study of the potential pathological relationship between the various cellular processes is required to ensure efficacious therapy. The pathogenic mechanisms associated with ALS are reviewed, and the strengths and limitations of some new therapeutic approaches are discussed.

Loss of ERLIN2 function leads to juvenile primary lateral sclerosis

OBJECTIVE

Primary lateral sclerosis (PLS) is a motor neuron disorder that exclusively affects upper motor neurons leading to their degeneration. Mutations in the ALS2 gene encoding the protein Alsin have been described previously in the juvenile form of the disease. In this study, we identify mutation of the ERLIN2 gene in juvenile PLS patients and describe an in vitro model for loss of ERLIN2 function.

METHODS

Single nucleotide polymorphism arrays were used for homozygosity mapping. DNA sequencing of candidate genes was used to detect the underlying mutation. Level of ERLIN2 mRNA was measured by quantitative real time polymerase chain reaction. Knocking down ERLIN2 in NSC34 cells was accomplished by short-hairpin RNA interference.

RESULTS

We identified a splice junction mutation in the ERLIN2 gene-a component of the endoplasmic reticulum (ER) lipid rafts-that resulted in abnormal splicing of ERLIN2 transcript and nonsense-mediated decay of ERLIN2 mRNA. Knocking down ERLIN2 in NSC34 cells suppressed their growth in culture.

INTERPRETATION

Recently, we found that mutation of SIGMAR1, a component of ER lipid rafts, leads to juvenile amyotrophic lateral sclerosis. The identification of mutation in another component of the ER lipid rafts in juvenile PLS patients emphasizes their role in motor neuron function. Furthermore, the discovered effect of ERLIN2 loss on cell growth may advance understanding of the mechanism behind motor neuron degeneration in PLS.

Role of the N-methyl-d-aspartate receptors complex in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult onset neurodegenerative disease pathologically characterized by the massive loss of motor neurons in the spinal cord, brain stem and cerebral cortex. There is a consensus in the field that ALS is a multifactorial pathology and a number of possible mechanisms have been suggested. Among the proposed hypothesis, glutamate toxicity has been one of the most investigated. Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor mediated cell death and impairment of the glutamate-transport system have been suggested to play a central role in the glutamate-mediated motor neuron degeneration. In this context, the role played by the N-methyl-d-aspartate (NMDA) receptor has received considerable less attention notwithstanding its high Ca(2+) permeability, expression in motor neurons and its importance in excitotoxicity. This review overviews the critical role of NMDA-mediated toxicity in ALS, with a particular emphasis on the endogenous modulators of the NMDAR.

Amyotrophic lateral sclerosis: new insights into underlying molecular mechanisms and opportunities for therapeutic intervention

Recent years have witnessed a renewed interest in the pathogenic mechanisms of amyotrophic lateral sclerosis (ALS), a late-onset progressive degeneration of motor neurons. The discovery of new genes associated with the familial form of the disease, along with a deeper insight into pathways already described for this disease, has led scientists to reconsider previous postulates. While protein misfolding, mitochondrial dysfunction, oxidative damage, defective axonal transport, and excitotoxicity have not been dismissed, they need to be re-examined as contributors to the onset or progression of ALS in the light of the current knowledge that the mutations of proteins involved in RNA processing, apparently unrelated to the previous "old partners," are causative of the same phenotype. Thus, newly envisaged models and tools may offer unforeseen clues on the etiology of this disease and hopefully provide the key to treatment.

Genome-wide epigenetic regulation by early-life trauma

CONTEXT

Our genome adapts to environmental influences, in part through epigenetic mechanisms, including DNA methylation. Variations in the quality of the early environment are associated with alterations in DNA methylation in rodents, and recent data suggest similar processes in humans in response to early-life adversity.

OBJECTIVE

To determine genome-wide DNA methylation alterations induced by early-life trauma.

DESIGN

Genome-wide study of promoter methylation in individuals with severe abuse during childhood. PATIENTS, SETTING, AND MAIN OUTCOME MEASURES: Promoter DNA methylation levels were profiled using methylated DNA immunoprecipitation followed by microarray hybridization in hippocampal tissue from 41 French-Canadian men (25 with a history of severe childhood abuse and 16 control subjects). Methylation profiles were compared with corresponding genome-wide gene expression profiles obtained by messenger RNA microarrays. Methylation differences between groups were validated on neuronal and nonneuronal DNA fractions isolated by fluorescence-assisted cell sorting. Functional consequences of site-specific promoter methylation were assessed by luciferase assays.

RESULTS

We identified 362 differentially methylated promoters in individuals with a history of abuse compared with controls. Among these promoters, 248 showed hypermethylation and 114 demonstrated hypomethylation. Validation and site-specific quantification of DNA methylation in the 5 most hypermethylated gene promoters indicated that methylation differences occurred mainly in the neuronal cellular fraction. Genes involved in cellular/neuronal plasticity were among the most significantly differentially methylated, and, among these, Alsin (ALS2) was the most significant finding. Methylated ALS2 constructs mimicking the methylation state in samples from abused suicide completers showed decreased promoter transcriptional activity associated with decreased hippocampal expression of ALS2 variants.

CONCLUSION

Childhood adversity is associated with epigenetic alterations in the promoters of several genes in hippocampal neurons.

Are alsin and spartin novel interaction partners?

Mutations in ALS2 gene/alsin are associated with recessive forms of motor neuron disorders including Juvenile Amyotrophic Lateral Sclerosis (JALS), Infantile-onset Ascending Hereditary Spastic Paraplegia (IAHSP) and Juvenile Primary Lateral Sclerosis (JPLS). In this study, we show that alsin and another MND-linked protein, spartin are related to each other both at mRNA and protein levels in Neuro2a cells. We observed significant alterations in spartin expression in alsin knock-down conditions. We further found that both proteins colocalize in N2a cells and spartin isoform-a precipitates with alsin in the same protein complex. In the light of these results we suggest that alsin and spartin may interact each other physically.

The genetics and neuropathology of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease of motor neurons leading to death from respiratory failure within about 3 years of symptom onset. A family history of ALS is obtained in about 5 % but the distinction between familial and apparently sporadic ALS is artificial and genetic factors play a role in all types. For several years, only one gene was known to have a role in ALS pathogenesis, SOD1. In the last few years there has been a rapid advance in our genetic knowledge of the causes of ALS, and the relationship of the genetic subtypes with pathological subtypes and clinical phenotype. Mutations in the gene for TDP-43 protein, TARDBP, highlight this, with pathology mimicking closely that found in other types of ALS, and a phenotypic spectrum that includes frontotemporal dementia. Mutations in the FUS gene, closely related to TDP-43, lead to a similar clinical phenotype but distinct pathology, so that the three pathological groups represented by SOD1, TARDBP, and FUS are distinct. In this review, we explore the genetic architecture of ALS, highlight some of the genes implicated in pathogenesis, and describe their phenotypic range and overlap with other diseases.

Neuromuscular effects of G93A-SOD1 expression in zebrafish

Background

Amyotrophic lateral sclerosis (ALS) is a fatal disorder involving the degeneration and loss of motor neurons. The mechanisms of motor neuron loss in ALS are unknown and there are no effective treatments. Defects in the distal axon and at the neuromuscular junction are early events in the disease course, and zebrafish provide a promising in vivo system to examine cellular mechanisms and treatments for these events in ALS pathogenesis.

Results

We demonstrate that transient genetic manipulation of zebrafish to express G93A-SOD1, a mutation associated with familial ALS, results in early defects in motor neuron outgrowth and axonal branching. This is consistent with previous reports on motor neuron axonal defects associated with familial ALS genes following knockdown or mutant protein overexpression. We also demonstrate that upregulation of growth factor signaling is capable of rescuing these early defects, validating the potential of the model for therapeutic discovery. We generated stable transgenic zebrafish lines expressing G93A-SOD1 to further characterize the consequences of G93A-SOD1 expression on neuromuscular pathology and disease progression. Behavioral monitoring reveals evidence of motor dysfunction and decreased activity in transgenic ALS zebrafish. Examination of neuromuscular and neuronal pathology throughout the disease course reveals a loss of neuromuscular junctions and alterations in motor neuron innervations patterns with disease progression. Finally, motor neuron cell loss is evident later in the disease.

Conclusions

This sequence of events reflects the stepwise mechanisms of degeneration in ALS, and provides a novel model for mechanistic discovery and therapeutic development for neuromuscular degeneration in ALS.

[Nonsense-mediated mRNA decay and human monogenic disease]

Nonsense-mediated mRNA decay (NMD) is a widespread quality control mechanism in eukaryotic cells. It can recognize and degrade aberrant transcripts harbouring a premature translational termination codon (PTC), and thereby prevent the production of C-terminally truncated proteins which might be deleterious. Approximately, 30% of human genetic diseases are caused by transcripts containing PTCs. These transcripts are potential targets of NMD. As for monogenic diseases, NMD has effects on the phenotype or mode of inheritance. Here, we explain the mechanism of this surveillance pathway, and take several neuromuscular disorders as examples to discuss its influence for human monogenic diseases. The deeper understanding for NMD will shed light on the nosogenesis and therapies of monogenic diseases.

The complex molecular biology of amyotrophic lateral sclerosis (ALS)

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disorder that causes selective death of motor neurons followed by paralysis and death. A subset of ALS cases is caused by mutations in the gene for Cu, Zn superoxide dismutase (SOD1), which impart a toxic gain of function to this antioxidant enzyme. This neurotoxic property is widely believed to stem from an increased propensity to misfold and aggregate caused by decreased stability of the native homodimer or a tendency to lose stabilizing posttranslational modifications. Study of the molecular mechanisms of SOD1-related ALS has revealed a complex array of interconnected pathological processes, including glutamate excitotoxicity, dysregulation of neurotrophic factors and axon guidance proteins, axonal transport defects, mitochondrial dysfunction, deficient protein quality control, and aberrant RNA processing. Many of these pathologies are directly exacerbated by misfolded and aggregated SOD1 and/or cytosolic calcium overload, suggesting the primacy of these events in disease etiology and their potential as targets for therapeutic intervention.

Neurogenetics of slow axonal transport: from cells to animals

Slow axonal transport is a multivariate phenomenon implicated in several neurodegenerative disorders. Recent reports have unraveled the molecular basis of the transport of certain slow component proteins, such as the neurofilament subunits, tubulin, and certain soluble enzymes such as Ca(2+)/calmodulin-dependent protein kinase IIa (CaM kinase IIa), etc., in tissue cultured neurons. In addition, genetic analyses also implicate microtubule-dependent motors and other housekeeping proteins in this process. However, the biological relevance of this phenomenon is not so well understood. Here, the authors have discussed the possibility of adopting neurogenetic analyses in multiple model organisms to correlate molecular level measurements of the slow transport phenomenon to animal behavior, thus facilitating the investigation of its biological efficacy.

Dysregulation of the autophagy-endolysosomal system in amyotrophic lateral sclerosis and related motor neuron diseases

Amyotrophic lateral sclerosis (ALS) is a heterogeneous group of incurable motor neuron diseases (MNDs) characterized by a selective loss of upper and lower motor neurons in the brain and spinal cord. Most cases of ALS are sporadic, while approximately 5–10% cases are familial. More than 16 causative genes for ALS/MNDs have been identified and their underlying pathogenesis, including oxidative stress, endoplasmic reticulum stress, excitotoxicity, mitochondrial dysfunction, neural inflammation, protein misfolding and accumulation, dysfunctional intracellular trafficking, abnormal RNA processing, and noncell-autonomous damage, has begun to emerge. It is currently believed that a complex interplay of multiple toxicity pathways is implicated in disease onset and progression. Among such mechanisms, ones that are associated with disturbances of protein homeostasis, the ubiquitin-proteasome system and autophagy, have recently been highlighted. Although it remains to be determined whether disease-associated protein aggregates have a toxic or protective role in the pathogenesis, the formation of them results from the imbalance between generation and degradation of misfolded proteins within neuronal cells. In this paper, we focus on the autophagy-lysosomal and endocytic degradation systems and implication of their dysfunction to the pathogenesis of ALS/MNDs. The autophagy-endolysosomal pathway could be a major target for the development of therapeutic agents for ALS/MNDs.

Association of UBQLN1 mutation with Brown-Vialetto-Van Laere syndrome but not typical ALS

Genetic variants in UBQLN1 gene have been linked to neurodegeneration and mutations in UBQLN2 have recently been identified as a rare cause of amyotrophic lateral sclerosis (ALS).

OBJECTIVE

To test if genetic variants in UBQLN1 are involved in ALS.

METHODS

102 and 94 unrelated patients with familial and sporadic forms of ALS were screened for UBQLN1 gene mutations. Single nucleotide variants were further screened in a larger set of sporadic ALS (SALS) patients and unrelated control subjects using high-throughput Taqman genotyping; variants were further assessed for novelty using the 1000Genomes and NHLBI databases. In vitro studies tested the effect of UBQLN1 variants on the ubiquitin-proteasome system (UPS).

RESULTS

Only two UBQLN1 coding variants were detected in the familial and sporadic ALS DNA set; one, the missense mutation p.E54D, was identified in a single patient with atypical motor neuron disease consistent with Brown-Vialetto-Van Laere syndrome (BVVLS), for whom c20orf54 mutations had been excluded. Functional studies revealed that UBQLN1E54D protein forms cytosolic aggregates that contain mislocalized TDP-43 and impairs degradation of ubiquitinated proteins through the proteasome.

CONCLUSIONS

Genetic variants in UBQLN1 are not commonly associated with ALS. A novel UBQLN1 mutation (E45D) detected in a patient with BVVLS altered nuclear TDP-43 localization in vitro, suggesting that UPS dysfunction may also underlie the pathogenesis of this condition.

Identification of pharmacological targets in amyotrophic lateral sclerosis through genomic analysis of deregulated genes and pathways

Amyotrophic Lateral Sclerosis (ALS) is a progressive and disabling neurodegenerative disorder characterized by upper and lower motor neuron loss, leading to respiratory insufficiency and death after 3-5 years. Riluzole is currently the only FDA approved drug for ALS, but it has only modest effects on survival. The majority of ALS cases are sporadic and probably associated to a multifactorial etiology. With the completion of genome sequencing in humans and model organisms, together with the advent of DNA microarray technology, the transcriptional cascades and networks underlying neurodegeneration in ALS are being elucidated providing new potential pharmacological targets. The main challenge now is the effective screening of the myriad of targets to identify those with the most therapeutic utility. The present review will illustrate how the identification, prioritization and validation of preclinical therapeutics can be achieved through genomic analysis of critical pathways and networks deregulated in ALS pathology.

Rodent models of TDP-43: recent advances

Recently, missense mutations in the gene TARDBP encoding TDP-43 have been linked to familial ALS. The discovery of genes encoding these RNA binding proteins, such as TDP-43 and FUS/TLS, raised the notion that altered RNA metabolism is a major factor underlying the pathogenesis of ALS. To begin to unravel how mutations in TDP-43 cause dysfunction and death of motor neurons, investigators have employed both gain- and loss-of-function studies in rodent model systems. Here, we will summarize major findings from the initial sets of TDP-43 transgenic and knockout rodent models, identify their limitations, and point to future directions toward clarification of disease mechanism(s) and testing of therapeutic strategies that ultimately may lead to novel therapy for this devastating disease. This article is part of a Special Issue entitled RNA-Binding Proteins.

Iron and ER stress in neurodegenerative disease

Neurodegenerative disease is a condition in which subpopulations of neuronal cells of the brain and spinal cord are selectively lost. A common event in many neurodegenerative diseases is the increased level of endoplasmic reticulum (ER) stress caused by accumulation and deposits of inclusion bodies that contain abnormal aggregated proteins. However, the basis of how ER stress contributes to the selective neuronal vulnerability and degeneration remain elusive. Iron accumulation in the central nerve system is consistently present in many neurodegenerative diseases. In the past 5 years we have begun to show a relationship between polymorphisms in the HFE (high iron) gene and the risk of neurodegenerative disorders. Recent findings have suggested a connection between ER stress and iron metabolism and neurodegeneration. Here we review how the different levels of chronic ER stress contribute to the different fates of neurons, namely the adaptive response and neuronal death. And, we discuss the roles of iron and HFE genotype in selective neuronal vulnerability and degeneration through modifying the ER stress level.

Endocytosis and signaling: cell logistics shape the eukaryotic cell plan

Our understanding of endocytosis has evolved remarkably in little more than a decade. This is the result not only of advances in our knowledge of its molecular and biological workings, but also of a true paradigm shift in our understanding of what really constitutes endocytosis and of its role in homeostasis. Although endocytosis was initially discovered and studied as a relatively simple process to transport molecules across the plasma membrane, it was subsequently found to be inextricably linked with almost all aspects of cellular signaling. This led to the notion that endocytosis is actually the master organizer of cellular signaling, providing the cell with understandable messages that have been resolved in space and time. In essence, endocytosis provides the communications and supply routes (the logistics) of the cell. Although this may seem revolutionary, it is still likely to be only a small part of the entire story. A wealth of new evidence is uncovering the surprisingly pervasive nature of endocytosis in essentially all aspects of cellular regulation. In addition, many newly discovered functions of endocytic proteins are not immediately interpretable within the classical view of endocytosis. A possible framework, to rationalize all this new knowledge, requires us to "upgrade" our vision of endocytosis. By combining the analysis of biochemical, biological, and evolutionary evidence, we propose herein that endocytosis constitutes one of the major enabling conditions that in the history of life permitted the development of a higher level of organization, leading to the actuation of the eukaryotic cell plan.

Reduced expression of BTBD10, an Akt activator, leads to motor neuron death

BTBD10, an Akt interactor, activates Akt by decreasing the protein phosphatase 2A-mediated dephosphorylation and inactivation of Akt. Overexpression of BTBD10 suppresses motor neuron death that is induced by a familial amyotrophic lateral sclerosis (ALS)-linked superoxide dismutase 1 (SOD1) mutant, G93A-SOD1 in vitro. In this study, we further investigated the BTBD10-mediated suppression of motor neuron death. We found that the small interfering RNA-mediated inhibition of BTBD10 expression led to the death of cultured motor neurons. In Caenorhabditis elegans (C. elegans), disruption of the btbd-10 gene caused not only loss of neurons, including both motor and touch-receptor neurons, but also a locomotion defect. In addition, we found that the expression of BTBD10 was generally decreased in the motor neurons from patients of sporadic ALS and transgenic mice overexpressing G93A-SOD1 (G93A-SOD1-transgenic mice). Collectively, these results suggest that the reduced expression of BTBD10 leads to motor neuron death both in vitro and in vivo.

Molecular pathways of motor neuron injury in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a genetically diverse disease. At least 15 ALS-associated gene loci have so far been identified, and the causative gene is known in approximately 30% of familial ALS cases. Less is known about the factors underlying the sporadic form of the disease. The molecular mechanisms of motor neuron degeneration are best understood in the subtype of disease caused by mutations in superoxide dismutase 1, with a current consensus that motor neuron injury is caused by a complex interplay between multiple pathogenic processes. A key recent finding is that mutated TAR DNA-binding protein 43 is a major constituent of the ubiquitinated protein inclusions in ALS, providing a possible link between the genetic mutation and the cellular pathology. New insights have also indicated the importance of dysregulated glial cell-motor neuron crosstalk, and have highlighted the vulnerability of the distal axonal compartment early in the disease course. In addition, recent studies have suggested that disordered RNA processing is likely to represent a major contributing factor to motor neuron disease. Ongoing research on the cellular pathways highlighted in this Review is predicted to open the door to new therapeutic interventions to slow disease progression in ALS.

Clinical aspects of amyotrophic lateral sclerosis in Rio de Janeiro/Brazil

OBJECTIVE

The clinical and epidemiological profile of sporadic amyotrophic lateral sclerosis (ALS), a chronic, degenerative, progressive motor neuron disease of unknown etiology, was described and evaluated in the city of Rio de Janeiro.

METHOD

Patients with a diagnosis definite of ALS according to the revised criteria of the El Escorial World Federation of Neurology were included in this retrospective, descriptive study (n=227). Demographic data, clinical variables, mortality and survival of these patients were assessed.

RESULTS

Of the 227 included cases, 143 (63%) were male and 84 (37%) were female, resulting in a male/female ratio of 1.7:1. Mean age at onset of the disease was 53.6 ± 12.1 years, overall median survival time was 49 months (95%CI: 42.4-55.5) and the majority of patients (71.4%) were white, black patients 15.9% and mulattos 12.8%. The most common forms of the disease were classic and bulbar ALS.

CONCLUSION

Taking classic and bulbar ALS together, the disease was more common in white, male patients of 50 to 70 years of age. When analyzed separately, the bulbar form was more common in women and in older patients. Survival of patients with bulbar ALS was shorter compared to that of patients with classic ALS.

FUS-related proteinopathies: lessons from animal models

The recent identification of ALS-linked mutations in FUS and TDP-43 has led to a major shift in our thinking in regard to the potential molecular mechanisms of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). RNA-mediated proteinopathy is increasingly being recognized as a potential cause of neurodegenerative disorders. FUS and TDP-43 are structurally and functionally similar proteins. FUS is a DNA/RNA binding protein that may regulate aspects of RNA metabolism, including splicing, mRNA processing, and micro RNA biogenesis. It is unclear how ALS-linked mutations perturb the functions of FUS. This review highlights recent advances in understanding the functions of FUS and discusses findings from FUS animal models that provide several key insights into understanding the molecular mechanisms that might contribute to ALS pathogenesis.

Caenorhabditis elegans RNA-processing protein TDP-1 regulates protein homeostasis and life span

Transactive response DNA-binding protein (TARDBP/TDP-43), a heterogeneous nuclear ribonucleoprotein (hnRNP) with diverse activities, is a common denominator in several neurodegenerative disorders, including amyotrophic lateral sclerosis and frontotemporal lobar degeneration. Orthologs of TDP-43 exist in animals ranging from mammals to invertebrates. Here, we systematically studied mutant Caenorhabditis elegans lacking the nematode TDP-43 ortholog, TDP-1. Heterologous expression of human TDP-43 rescued the defects in C. elegans lacking TDP-1, suggesting their functions are conserved. Although the tdp-1 mutants exhibited deficits in fertility, growth, and locomotion, loss of tdp-1 attenuated defects in several C. elegans models of proteotoxicity. Loss of tdp-1 suppressed defects in transgenic C. elegans expressing TDP-43 or CuZn superoxide dismutase, both of which are associated with proteotoxicity in neurodegenerative diseases. Loss of tdp-1 also reduced defects in mutant animals lacking the heat shock factor HSF-1. Transcriptional profiling demonstrated that the loss of TDP-1 altered expression of genes functioning in RNA processing and protein folding. Furthermore, the absence of tdp-1 extended the life span in C. elegans. The life span extension required a FOXO transcriptional factor DAF-16 but not HSF-1. These results suggest that the C. elegans TDP-1 has a role in the regulation of protein homeostasis and aging.

Molecular motor proteins and amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder affecting motor neurons in the brain, brainstem and spinal cord, which is characterized by motor dysfunction, muscle dystrophy and progressive paralysis. Both inherited and sporadic forms of ALS share common pathological features, however, the initial trigger of neurodegeneration remains unknown. Motor neurons are uniquely targeted by ubiquitously expressed proteins in ALS but the reason for this selectively vulnerability is unclear. However motor neurons have unique characteristics such as very long axons, large cell bodies and high energetic metabolism, therefore placing high demands on cellular transport processes. Defects in cellular trafficking are now widely reported in ALS, including dysfunction to the molecular motors dynein and kinesin. Abnormalities to dynein in particular are linked to ALS, and defects in dynein-mediated axonal transport processes have been reported as one of the earliest pathologies in transgenic SOD1 mice. Furthermore, dynein is very highly expressed in neurons and neurons are particularly sensitive to dynein dysfunction. Hence, unravelling cellular transport processes mediated by molecular motor proteins may help shed light on motor neuron loss in ALS.

Molecular pathology and genetic advances in amyotrophic lateral sclerosis: an emerging molecular pathway and the significance of glial pathology

Research into amyotrophic lateral sclerosis (ALS) has been stimulated by a series of genetic and molecular pathology discoveries. The hallmark neuronal cytoplasmic inclusions of sporadic ALS (sALS) predominantly comprise a nuclear RNA processing protein, TDP-43 encoded by the gene TARDBP, a discovery that emerged from high throughput analysis of human brain tissue from patients with frontotemporal dementia (FTD) who share a common molecular pathology with ALS. The link between RNA processing and ALS was further strengthened by the discovery that another genetic locus linking familial ALS (fALS) and FTD was due to mutation of the fused in sarcoma (FUS) gene. Of potentially even greater importance it emerges that TDP-43 accumulation and inclusion formation characterises not only most sALS cases but also those that arise from mutations in several genes including TARDBP (predominantly ALS cases) itself, C9ORF72 (ALS and FTD cases), progranulin (predominantly FTD phenotypes), VAPB (predominantly ALS cases) and in some ALS cases with rare genetic variants of uncertain pathogenicity (CHMP2B). "TDP-proteinopathy" therefore now represents a final common pathology associated with changes in multiple genes and opens the possibility of research by triangulation towards key common upstream molecular events. It also delivers final proof of the hypothesis that ALS and most FTD cases are disorders within a common pathology expressed as a clinico-anatomical spectrum. The emergence of TDP-proteinopathy also confirms the view that glial pathology is a crucial facet in this class of neurodegeneration, adding to the established view of non-nerve cell autonomous degeneration of the motor system from previous research on SOD1 fALS. Future research into the mechanisms of TDP-43 and FUS-related neurodegeneration, taking into account the major component of glial pathology now revealed in those disorders will significantly accelerate new discoveries in this field, including target identification for new therapy.

A mutation in sigma-1 receptor causes juvenile amyotrophic lateral sclerosis

OBJECTIVE

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by loss of motor neurons in the brain and spinal cord, leading to muscle weakness and eventually death from respiratory failure. ALS is familial in about 10% of cases, with SOD1 mutations accounting for 20% of familial cases. Here we describe a consanguineous family segregating juvenile ALS in an autosomal recessive pattern and describe the genetic variant responsible for the disorder.

METHODS

We performed homozygosity mapping and direct sequencing to detect the genetic variant and tested the effect of this variant on a motor neuron-like cell line model (NSC34) expressing the wild-type or mutant gene.

RESULTS

We identified a shared homozygosity region in affected individuals that spans ~120 kbp on chromosome 9p13.3 containing 9 RefSeq genes. Sequencing the SIGMAR1 gene revealed a mutation affecting a highly conserved amino acid located in the transmembrane domain of the encoded protein, sigma-1 receptor. The mutated protein showed an aberrant subcellular distribution in NSC34 cells. Furthermore, cells expressing the mutant protein were less resistant to apoptosis induced by endoplasmic reticulum stress.

INTERPRETATION

Sigma-1 receptors are known to have neuroprotective properties, and recently Sigmar1 knockout mice have been described to have motor deficiency. Our findings emphasize the role of sigma-1 receptors in motor neuron function and disease.

The evolving biology of cell reprogramming

Modern stem cell biology has achieved a transformation that was thought by many to be every bit as unattainable as the ancient alchemists' dream of transforming base metals into gold. Exciting opportunities arise from the process known as 'cellular reprogramming' in which cells can be reliably changed from one tissue type to another. This is enabling novel approaches to more deeply investigate the fundamental basis of cell identity. In addition, new opportunities have also been created to study (perhaps even to treat) human genetic and degenerative diseases. Specific cell types that are affected in inherited disease can now be generated from easily accessible cells from the patient and compared with equivalent cells from healthy donors. The differences in cellular phenotype between the two may then be identified, and assays developed to establish therapies that prevent the development or progression of disease symptoms. Cellular reprogramming also has the potential to create new cells to replace those whose death or dysfunction causes disease symptoms. For patients suffering from inherited cases of degenerative diseases like Parkinson's disease or amyotrophic lateral sclerosis (also known as motor neuron disease), the future realization of such cell-based therapies would truly be worth its weight in gold. However, before this enormous potential can become a reality, several significant biological and technical challenges must be overcome. Furthermore, to maintain the credibility of the scientific community with the general public, it is important that hope-inspiring advances are not over-hyped. The papers in this issue of the Philosophical Transactions of the Royal Society B: Biological Sciences cover many areas relevant to this topic. In this Introduction, we provide an overall context in which to consider these individual papers.

Differential involvement of optineurin in amyotrophic lateral sclerosis with or without SOD1 mutations

BACKGROUND

Mutations in optineurin have recently been linked to amyotrophic lateral sclerosis (ALS).

OBJECTIVE

To determine whether optineurin-positive skeinlike inclusions are a common pathologic feature in ALS, including SOD1 -linked ALS.

DESIGN

Clinical case series.

SETTING

Academic referral center.

SUBJECTS

We analyzed spinal cord sections from 46 clinically and pathologically diagnosed ALS cases and ALS transgenic mouse models overexpressing ALS-linked SOD1 mutations G93A or L126Z.

RESULTS

We observed optineurin-immunoreactive skeinlike inclusions in all the sporadic ALS and familial ALS cases without SOD1 mutation, but not in cases with SOD1 mutations or in transgenic mice overexpressing the ALS-linked SOD1 mutations G93A or L126Z.

CONCLUSION

The data from this study provide evidence that optineurin is involved in the pathogenesis of sporadic ALS and non- SOD1 familial ALS, thus supporting the hypothesis that these forms of ALS share a pathway that is distinct from that of SOD1-linked ALS.

Lack of effect of methylene blue in the SOD1 G93A mouse model of amyotrophic lateral sclerosis

Background

Methylene blue (MB) is a drug with a long history and good safety profile, and with recently-described features desirable in a treatment for ALS.

Methodology/Principal Findings

We tested oral MB in inbred high-copy number SOD1 G93A mice, at 25 mg/kg/day beginning at 45 days of age. We measured disease onset, progression, and survival. There was no difference in disease onset between MB-treated mice and controls, although subgroup analysis showed a modest but statistically significant delay in disease onset in MB-treated female mice only (control 122±10.2 versus MB 129±10.0 days). MB-treated mice of both sexes spent more time in less severe stages of disease, and less time in later, more severe stages of disease. There was a non-significant trend to longer survival in MB-treated animals (control males reached endpoint at 161±14.1 days, versus 166±10.0 days for MB-treated animals, and control females reached endpoint at 171±6.2 days versus 173±13.4 days for MB-treated animals).

Conclusions/Significance

In spite of a strong theoretical rationale, MB had no significant effects on onset or survival in the inbred SOD1 G93A mouse model of ALS.

New considerations in the design of clinical trials for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a devastating neurodegenerative disease caused by loss of motor neurons. Its pathophysiology remains unknown, but progress has been made in understanding its genetic and biochemical basis. Clinical trialists are working to translate basic science successes into human trials with more efficiency, in the hope of finding successful treatments. In the future, new preclinical models, including patient-derived stem cells may augment transgenic animal models as preclinical tools. Biomarker discovery projects aim to identify markers of disease onset and progression for use in clinical trials. New trial designs are reducing study time, improving efficiency and helping to keep pace with the increasing rate of basic and translational discoveries. Ongoing trials with novel designs are paving the way for amyotrophic lateral sclerosis clinical research.

Alsin and SOD1(G93A) proteins regulate endosomal reactive oxygen species production by glial cells and proinflammatory pathways responsible for neurotoxicity

Recent studies have implicated enhanced Nox2-mediated reactive oxygen species (ROS) by microglia in the pathogenesis of motor neuron death observed in familial amyotrophic lateral sclerosis (ALS). In this context, ALS mutant forms of SOD1 enhance Rac1 activation, leading to increased Nox2-dependent microglial ROS production and neuron cell death in mice. It remains unclear if other genetic mutations that cause ALS also function through similar Nox-dependent pathways to enhance ROS-mediate motor neuron death. In the present study, we sought to understand whether alsin, which is mutated in an inherited juvenile form of ALS, functionally converges on Rac1-dependent pathways acted upon by SOD1(G93A) to regulate Nox-dependent ROS production. Our studies demonstrate that glial cell expression of SOD1(G93A) or wild type alsin induces ROS production, Rac1 activation, secretion of TNFα, and activation of NFκB, leading to decreased motor neuron survival in co-culture. Interestingly, coexpression of alsin, or shRNA against Nox2, with SOD1(G93A) in glial cells attenuated these proinflammatory indicators and protected motor neurons in co-culture, although shRNAs against Nox1 and Nox4 had little effect. SOD1(G93A) expression dramatically enhanced TNFα-mediated endosomal ROS in glial cells in a Rac1-dependent manner and alsin overexpression inhibited SOD1(G93A)-induced endosomal ROS and Rac1 activation. SOD1(G93A) expression enhanced recruitment of alsin to the endomembrane compartment in glial cells, suggesting that these two proteins act to modulate Nox2-dependent endosomal ROS and proinflammatory signals that modulate NFκB. These studies suggest that glial proinflammatory signals regulated by endosomal ROS are influenced by two gene products known to cause ALS.

Making connections: pathology and genetics link amyotrophic lateral sclerosis with frontotemporal lobe dementia

Over the last couple of decades, there has been a growing body of clinical, genetic, and histopathological evidence that similar pathological processes underlie amyotrophic lateral sclerosis (ALS) and some types of frontotemporal lobe dementia (FTD). Even though there is great diversity in the genetic causes of these disorders, there is a high degree of overlap in their histopathology. Genes linked to rare cases of familial ALS and/or FTD, like FUS, TARDBP, OPTN, and UBQLN2 may converge onto a unifying pathogenic pathway and thereby provide novel therapeutic targets common to a spectrum of etiologically diverse forms of ALS and ALS-FTD. Additionally, there are major loci for ALS-FTD on chromosomes 9p and 15q. Identification of causative genetic alterations at those loci will be an important step in understanding the pathogenesis of juvenile- and adult-onset ALS and ALS-FTD. Interactions between TDP-43, FUS, optineurin, and ubiquilin 2 need to be studied to understand their common molecular pathways. Future efforts should also be directed towards generation and characterization of in vivo models to dissect the pathogenic mechanisms of these diseases. Such efforts will rapidly accelerate the discovery of new drugs that regulate accumulation of pathogenic proteins and their downstream consequences.

Alfa-class prefoldin protein UXT is a novel interacting partner of Amyotrophic Lateral Sclerosis 2 (Als2) protein

Mutations in Als2 gene cause several autosomal recessive forms of motor neuron diseases including Juvenile Amyotrophic Lateral Sclerosis (JALS), Juvenile Primary Lateral Sclerosis (PLSJ) and Infantile-onset Ascending Hereditary Spastic Paralysis (IAHSP). To find novel protein-protein interactions of Als2 protein we performed a yeast two hybrid screen and fished out the Ubiquitously Expressed Transcript (UXT) protein. UXT is a novel gene encoding for an α-class prefoldin type chaperone which acts as a co-activator for various transcriptional factors such as Nf-κB and AR. The interaction between Als2 and UXT was confirmed by co-immunoprecipitation. Co-localization between endogenous Als2 and UXT was mainly found in the cytoplasm of neuronal Neuro2a cells with immunofluorescence microscopy. Cell cycle arrest of Neuro2a cells showed that Als2 and Uxt transcriptional levels are synchronously changing. Our results suggest that Als2 is a binding partner of Uxt and Als2/Uxt interaction could be important for the activation of Nf-κB pathway. These results provides basis for future research to investigate the role of Nf-κB pathway in the development of motor neuron diseases.

Mitochondrial redox signalling by p66Shc mediates ALS-like disease through Rac1 inactivation

Increased oxidative stress and mitochondrial damage are among the mechanisms whereby mutant SOD1 (mutSOD1) associated with familial forms of amyotrophic lateral sclerosis (ALS) induces motoneuronal death. The 66 kDa isoform of the growth factor adapter Shc (p66Shc) is known to be central in the control of mitochondria-dependent oxidative balance. Here we report that expression of mutSOD1s induces the activation of p66Shc in neuronal cells and that the overexpression of inactive p66Shc mutants protects cells from mutSOD1-induced mitochondrial damage. Most importantly, deletion of p66Shc ameliorates mitochondrial function, delays onset, improves motor performance and prolongs survival in transgenic mice modelling ALS. We also show that p66Shc activation by mutSOD1 causes a strong decrease in the activity of the small GTPase Rac1 through a redox-sensitive regulation. Our results provide new insight into the potential mechanisms of mutSOD1-mediated mitochondrial dysfunction.

Mitochondrial dysfunction in ALS

In the present article, we review the many facets of mitochondrial dysfunction in amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease due to loss of upper motor neurons in cerebral cortex and lower motor neurons in brainstem and spinal cord. Accumulating evidence from recent studies suggests that the many, interconnected facets of mitochondrial dysfunction may play a more significant role in the etiopathogenesis of this disorder than previously thought. This notion stems from our expanding knowledge of the complex physiology of mitochondria and of alteration of their properties that might confer an intrinsic susceptibility to long-lived, post-mitotic motor neurons to energy deficit, calcium mishandling and oxidative stress. The wealth of evidence implicating mitochondrial dysfunction as a major event in the pathology of ALS has prompted new studies aimed to the development of new mitochondria-targeted therapies. However, it is now clear that drugs targeting more than one aspect of mitochondrial dysfunction are needed to fight this devastating disease.

SOD1 and TDP-43 animal models of amyotrophic lateral sclerosis: recent advances in understanding disease toward the development of clinical treatments

Amyotrophic lateral sclerosis (ALS) is a fatal motor neuron disease with no cure. Breakthroughs in understanding ALS pathogenesis came with the discovery of dominant mutations in the superoxide dismutase 1 gene (SOD1) and other genes, including the gene encoding transactivating response element DNA binding protein-43 (TDP-43). This has led to the creation of animal models to further our understanding of the disease and identify a number of ALS-causing mechanisms, including mitochondrial dysfunction, protein misfolding and aggregation, oxidative damage, neuronal excitotoxicity, non-cell autonomous effects and neuroinflammation, axonal transport defects, neurotrophin depletion, effects from extracellular mutant SOD1, and aberrant RNA processing. Here we summarise the SOD1 and TDP-43 animal models created to date, report on recent findings supporting the potential mechanisms of ALS pathogenesis, and correlate this understanding with current developments in the clinic.

Adenylyl cyclase type 3, a marker of primary cilia, is reduced in primary cell culture and in lumbar spinal cord in situ in G93A SOD1 mice

Background

The primary cilium is a solitary organelle important in cellular signaling, that projects from the cell surface of most growth-arrested or post-mitotic cells including neurons in the central nervous system. We hypothesized that primary cilial dysfunction might play a role in the pathogenesis of Amyotrophic Lateral Sclerosis (ALS), and as a first step, report on the prevalence of primary cilial markers on cultured motor neurons from the lumbar spinal cord of embryonic wildtype (WT) and transgenic G93A SOD1 mice, and on motor neurons in situ in the lumbar spinal cord.

Results

At 7 days in culture there is no difference in the proportion of G93A SOD1 and WT motor neurons staining for the cilial marker ACIII. However, at 21 days there is a large relative drop in the proportion of ciliated G93A SOD1 motor neurons. In situ, at 40 days there was a slight relative drop in the proportion of ciliated motor neurons in G93A SOD1 mice. At 98 days of age there was no change in motor neuron ciliation in WT mice, but there was motor neuron loss and a large reduction in the proportion of surviving motor neurons bearing a primary cilium in G93A SOD1 mice.

Conclusions

In primary culture and in situ in G93A SOD1 mice there is a large reduction in the proportion of motor neurons bearing a primary cilium.