Genetic epidemiology of amyotrophic lateral sclerosis

PAK4 suppresses motor neuron degeneration in hSOD1G93A -linked amyotrophic lateral sclerosis cell and rat models

OBJECTIVES

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the progressive loss of motor neurons (MN). CREB pathway-mediated inhibition of apoptosis contributes to neuron protection, and PAK4 activates CREB signalling in diverse cell types. This study aimed to investigate PAK4's effect and mechanism of action in ALS.

METHODS

We analysed RNA levels by qRT-PCR, protein levels by immunofluorescence and Western blotting, and apoptosis by flow cytometry and TUNEL staining. Cell transfection was performed for in vitro experiment. Mice were injected intraspinally to evaluate PAK4 function in vivo experiment. Rotarod test was performed to measure motor function.

RESULTS

The expression and activation of PAK4 significantly decreased in the cell and mouse models of ALS as the disease progressed, which was caused by the negative regulation of miR-9-5p. Silencing of PAK4 increased the apoptosis of MN by inhibiting CREB-mediated neuroprotection, whereas overexpression of PAK4 protected MN from hSOD1^G93A -induced degeneration by activating CREB signalling. The neuroprotective effect of PAK4 was markedly inhibited by CREB inhibitor. In ALS models, the PAK4/CREB pathway was inhibited, and cell apoptosis increased. In vivo experiments revealed that PAK4 overexpression in the spinal neurons of hSOD1^G93A mice suppressed MN degeneration, prolonged survival and promoted the CREB pathway.

CONCLUSIONS

PAK4 protects MN from degeneration by activating the anti-apoptotic effects of CREB signalling, suggesting it may be a therapeutic target in ALS.

TDP-43 proteinopathies: a new wave of neurodegenerative diseases

Inclusions of pathogenic deposits containing TAR DNA-binding protein 43 (TDP-43) are evident in the brain and spinal cord of patients that present across a spectrum of neurodegenerative diseases. For instance, the majority of patients with sporadic amyotrophic lateral sclerosis (up to 97%) and a substantial proportion of patients with frontotemporal lobar degeneration (~45%) exhibit TDP-43 positive neuronal inclusions, suggesting a role for this protein in disease pathogenesis. In addition, TDP-43 inclusions are evident in familial ALS phenotypes linked to multiple gene mutations including the TDP-43 gene coding (TARDBP) and unrelated genes (eg, C9orf72). While TDP-43 is an essential RNA/DNA binding protein critical for RNA-related metabolism, determining the pathophysiological mechanisms through which TDP-43 mediates neurodegeneration appears complex, and unravelling these molecular processes seems critical for the development of effective therapies. This review highlights the key physiological functions of the TDP-43 protein, while considering an expanding spectrum of neurodegenerative diseases associated with pathogenic TDP-43 deposition, and dissecting key molecular pathways through which TDP-43 may mediate neurodegeneration.

Modulating ALS-Related Amyloidogenic TDP-43307-319 Oligomeric Aggregates with Computationally Derived Therapeutic Molecules

TDP-43 aggregates are a salient feature of amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and a variety of other neurodegenerative diseases, including Alzheimer's disease (AD). With an anticipated growth in the most susceptible demographic, projections predict neurodegenerative diseases will potentially affect 15 million people in the United States by 2050. Currently, there are no cures for ALS, FTD, or AD. Previous studies of the amyloidogenic core of TDP-43 have demonstrated that oligomers greater than a trimer are associated with toxicity. Utilizing a joint pharmacophore space (JPS) method, potential drugs have been designed specifically for amyloid-related diseases. These molecules were generated on the basis of key chemical features necessary for blood-brain barrier permeability, low adverse side effects, and target selectivity. Combining ion-mobility mass spectrometry and atomic force microscopy with the JPS computational method allows us to more efficiently evaluate a potential drug's efficacy in disrupting the development of putative toxic species. Our results demonstrate the dissociation of higher-order oligomers in the presence of these novel JPS-generated inhibitors into smaller oligomer species. Additionally, drugs approved by the Food and Drug Administration for the treatment of ALS were also evaluated and demonstrated to maintain higher-order oligomeric assemblies. Possible mechanisms for the observed action of the JPS molecules are discussed.

Characterization of the activity, aggregation, and toxicity of heterodimers of WT and ALS-associated mutant Sod1

Aggregation of the antioxidant enzyme Sod1 represents common factors of both familial (fALS) and sporadic cases of ALS, a fatal neurodegenerative disease. Although many ALS studies have focused on Sod1 homodimers/homomers, the investigation of Sod1 heterodimers/heteromers remains controversial and has mostly been performed with recombinant proteins in vitro, in the absence of a cellular environment. By using living cells, this study sheds light into a critical issue in the context of fALS, the high toxicity of the WT–mutant heteromeric inclusions, especially WT–A4V heteromers which accumulate both in human cells as well as in chronologically aged yeast cells. Besides the aggregation, we proposed that an inefficient heteromer response against oxidative conditions might contribute to fALS-linked mutant hSod1 toxicity.

Mutations in Cu/Zn superoxide dismutase (Sod1) have been reported in both familial and sporadic amyotrophic lateral sclerosis (ALS). In this study, we investigated the behavior of heteromeric combinations of wild-type (WT) and mutant Sod1 proteins A4V, L38V, G93A, and G93C in human cells. We showed that both WT and mutant Sod1 formed dimers and oligomers, but only mutant Sod1 accumulated in intracellular inclusions. Coexpression of WT and hSod1 mutants resulted in the formation of a larger number of intracellular inclusions per cell than that observed in cells coexpressing WT or mutant hSod1. The number of inclusions was greater in cells expressing A4V hSod1. To eliminate the contribution of endogenous Sod1, and better evaluate the effect of ALS-associated mutant Sod1 expression, we expressed human Sod1 WT and mutants in human cells knocked down for endogenous Sod1 (Sod1-KD), and in sod1Δ yeast cells. Using Sod1-KD cells we found that the WT–A4V heteromers formed higher molecular weight species compared with A4V and WT homomers. Using the yeast model, in conditions of chronological aging, we concluded that cells expressing Sod1 heterodimers showed decreased antioxidant activity, increased oxidative damage, reduced longevity, and oxidative stress-induced mutant Sod1 aggregation. In addition, we also found that ALS-associated Sod1 mutations reduced nuclear localization and, consequently, impaired the antioxidant response, suggesting this change in localization may contribute to disease in familial ALS. Overall, our study provides insight into the molecular underpinnings of ALS and may open avenues for the design of future therapeutic strategies.

Wild-type p53-induced phosphatase 1 down-regulation promotes apoptosis by activating the DNA damage-response pathway in amyotrophic lateral sclerosis

Accumulation of DNA damage has been detected in the spinal cord of patients as well as in the G93A mouse model of amyotrophic lateral sclerosis (ALS). Wild-type p53-induced phosphatase 1 (Wip1) is a p53-inducible serine/threonine phosphatase that terminates DNA-damage responses via dephosphorylation of DNA-damage response proteins, namely ataxia-telangiectasia mutated (ATM) kinase, checkpoint kinase 2, and p53, thus enhancing cell proliferation. However, the role of Wip1, DNA-damage responses, and their interaction in ALS development remains to be elucidated. Here, we showed that Wip1 expression levels were substantially decreased in ALS motor neurons compared with wild-type controls both in vivo and in vitro. The DNA-damage response was activated in superoxide dismutase 1 (SOD1) ^G93A-transfected cells. However, increased expression of Wip1 improved cell viability and inhibited the DNA-damage response in mutated SOD1^G93A cells. Further studies demonstrated that decreased Wip1 expression reduced cell viability and further activated the DNA-damage response in chronic H₂O₂-treated NSC34 cells. In contrast, Wip1 promoted cell survival and suppressed DNA damage-induced apoptosis during persistent DNA damage conditions. Over-expression of Wip1 in the central nervous system (CNS) can delay the onset of disease symptoms, extended the survival, decreased MN loss improved motor function and inhibit the DNA-damage response in SOD1 G93A mice. Furthermore, homeodomain-interacting protein kinase 2 (HIPK2) promoted the degradation of Wip1 via the ubiquitin-proteasome system during chronic stress. These findings indicate that persistent accumulation of DNA damage and subsequent chronic activation of the downstream DNA damage-response ATM and p53 pro-apoptotic signaling pathways may trigger neuronal dysfunction and neuronal death in ALS. Wip1 may play a protective role by targeting the DNA-damage response in ALS motor neurons. Importantly, these findings provide a novel direction for therapeutic options for patients with ALS.

Characterizing TDP-43307-319 Oligomeric Assembly: Mechanistic and Structural Implications Involved in the Etiology of Amyotrophic Lateral Sclerosis

Aggregation of TAR DNA-binding protein of 43 kDa (TDP-43) is a salient feature of amyotrophic lateral sclerosis (ALS), a debilitating neurodegenerative disorder affecting over 200 000 people worldwide. The protein undergoes both functional and pathogenic aggregation; the latter is irreversible and hypothesized to produce soluble oligomers that are toxic to neurons in addition to inclusions made of stable fibrous deposits. Despite progress made toward identifying disease-related proteins, the underlying pathogenic mechanism associated with these toxic oligomers remains elusive. Utilizing a multimodal approach that combines several measurement techniques (circular dichroism (CD), thioflavin T spectroscopy (ThT), Fourier transform infrared spectroscopy (FTIR)) and high spatial resolution imaging tools (electron microscopy (EM) and atomic force microscopy (AFM)), with soft ion mobility mass spectrometry (IM-MS) and atomistic molecular dynamics (MD) simulations, we explore the oligomerization mechanisms, structures, and assembly pathways of TDP-43_307-319. This fragment is both amyloidogenic and toxic and is within the glycine-rich C-terminal domain essential for both toxicity and aggregation of the full-length protein. In addition to the wild-type peptide, two ALS-related mutants (A315T and A315E) and a non-axon-toxic mutant (G314V) were investigated to determine how mutations affect the oligomerization of TDP-43_307-319 and structures of toxic oligomers. The results of our study provide new insights into how ALS-related mutants, A315T and A315E, accelerate or alter the pathogenic mechanism and highlight the role of an internal glycine, G314, in maintaining efficient packing known to be critical for functional oligomer assembly. More importantly, our data demonstrate that G314 plays a vital role in TDP-43 assembly and prevents cytotoxicity via its unique aversion to oligomers larger than trimer. Our observation is consistent with previous studies showing that G314V mutation of the full-length TDP-43 induced remediation of both axonotoxicity and neuronal apoptosis. Our findings reveal a distinct aggregation mechanism for each peptide and elucidate oligomeric species and possible structures that may be involved in the pathology of ALS.

Adipsin, MIP-1b, and IL-8 as CSF Biomarker Panels for ALS Diagnosis

Amyotrophic lateral sclerosis (ALS) is an aggressive neurodegenerative disorder that selectively attacks motor neurons in the brain and spinal cord. Despite important advances in the knowledge of the etiology and progression of the disease, there are still no solid grounds in which a clinician could make an early objective and reliable diagnosis from which patients could benefit. Diagnosis is difficult and basically made by clinical rating scales (ALSRs and El Escorial). The possible finding of biomarkers to aid in the early diagnosis and rate of disease progression could serve for future innovative therapeutic approaches. Recently, it has been suggested that ALS has an important immune component that could represent either the cause or the consequence of the disease. In this report, we analyzed 19 different cytokines and growth factors in the cerebrospinal fluid of 77 ALS patients and 13 controls by decision tree and PanelomiX program. Results showed an increase of Adipsin, MIP-1b, and IL-6, associated with a decrease of IL-8 thresholds, related with ALS patients. This biomarker panel analysis could represent an important aid for diagnosis of ALS alongside the clinical and neurophysiological criteria.

Antisense oligonucleotides in neurological disorders

The introduction of genetics revolutionized the field of neurodegenerative and neuromuscular diseases and has provided considerable insight into the underlying pathomechanisms. Nevertheless, effective treatment options have been limited. This changed recently when antisense oligonucleotides (ASOs) could be translated from in vitro and experimental animal studies into clinical practice. In 2016, two ASOs were approved by the United States US Food and Drug Administration (FDA) and demonstrated remarkable efficacy in Duchenne muscular dystrophy (DMD) and spinal muscular atrophy (SMA). ASOs are synthetic single-stranded strings of nucleic acids. They selectively bind to specific premessenger ribonucleic acid (pre-mRNA)/mRNA sequences and alter protein synthesis by several mechanisms of action. Thus, apart from gene replacement, ASOs may therefore provide the most direct therapeutic strategy for influencing gene expression. In this review, we shall discuss basic mechanisms of ASO action, the role of chemical modifications needed to improve the pharmacodynamic and pharmacokinetic properties of ASOs, and we shall then focus on several ASOs developed for the treatment of neurodegenerative and neuromuscular disorders, including SMA, DMD, myotonic dystrophies, Huntington's disease, amyotrophic lateral sclerosis and Alzheimer's disease.

A novel D90_K91insN mutation in exon 4 of the SOD1 gene caused familial amyotrophic lateral sclerosis in a Chinese pedigree

We reported a novel heterozygous duplication mutation (c.272_274dupACA, D90_K91insN) in exon 4 of the SOD1 gene in a Chinese pedigree. This pedigree demonstrates an autosomal dominant pattern of inheritance, with potentially reduced penetrance. The clinical phenotype was rather uniform with a distal lower extremity onset, predominant involvement of lower motor neurons (LMNs), and a relatively short survival time (mean 2.6 years) compared with other mutations in the loop V structure of SOD1. We also detected that the average SOD1 activity in D90_K91insN mutation carriers is 68.5% of wild-type controls. In conclusion, we identified the first non-frameshift duplication mutation in loop V of the human SOD1 in the Chinese population, suggesting the importance of the loop V structure in the pathogenicity of FALS.

Quercitrin and quercetin 3-β-d-glucoside as chemical chaperones for the A4V SOD1 ALS-causing mutant

In many cases of familial amyotrophic lateral sclerosis (ALS), mutant forms of the Cu,Zn superoxide dismutase protein (SOD1) misfold and aggregate in motor neurons. Monomers of the normally homodimeric SOD1 have been found in patient tissue, presymptomatic mouse models of ALS, and in vitro misfolding assays which suggests that monomerization might be an early step in the pathological SOD1 misfolding pathway. In this study, we targeted the dimer interface with small molecules that might act as chemical chaperones to stabilize the native dimer and prevent downstream misfolding and aggregation. We performed a computational screen with a library of ~4400 drugs and natural compounds that were docked to two pockets around the SOD1 dimer interface. Of the resultant hits, seven were tested for misfolding and aggregation inhibition activity with A4V mutant SOD1. Quercitrin, quercetin-3-β-d-glucoside (Q3BDG), and, to a markedly lesser extent, epigallocatechin gallate (EGCG) were found to combat misfolding and aggregation induced by hydrogen peroxide, a physiologically relevant stress, as assessed by a gel-based assay and 8-anilinonaphthalene-1-suflonic acid (ANS) fluorescence. Isothermal titration calorimetry (ITC) and a colourimetric assay determined that these molecules directly bind A4V SOD1. Based on these findings, we speculate that quercitrin and Q3BDG may be potential therapeutic inhibitors of misfolding and aggregation in SOD1-associated ALS.

Neuroinflammation and ALS: Transcriptomic Insights into Molecular Disease Mechanisms and Therapeutic Targets

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease affecting the motor nervous system. Despite the mechanism underlying motor neuron death is not yet clarified, multiple pathogenic processes have been proposed to account for ALS. Among these, inflammatory/immune responses have recently gained particular interest, although there are conflicting reports on the role of these processes in ALS pathogenesis and treatment. This apparent discrepancy may be due to the absence of an effective stratification of ALS patients into subgroups with markedly different clinical, biological, and molecular features. Our research group recently described genome-wide characterization of motor cortex samples from sporadic ALS (SALS) patients, revealing the existence of molecular and functional heterogeneity in SALS. Here, we reexamine data coming from our previous work, focusing on transcriptomic changes of inflammatory-related genes, in order to investigate their potential contribution in ALS. A total of 1573 inflammatory genes were identified as differentially expressed between SALS patients and controls, characterizing distinct topological pathways and networks, suggestive of specific inflammatory molecular signatures for different patient subgroups. Besides providing promising insights into the intricate relationship between inflammation and ALS, this paper represents a starting point for the rationale design and development of novel and more effective diagnostic and therapeutic applications.

Improving the Delivery of SOD1 Antisense Oligonucleotides to Motor Neurons Using Calcium Phosphate-Lipid Nanoparticles

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease affecting the upper and lower motor neurons in the motor cortex and spinal cord. Abnormal accumulation of mutant superoxide dismutase I (SOD1) in motor neurons is a pathological hallmark of some forms of the disease. We have shown that the orderly progression of the disease may be explained by misfolded SOD1 cell-to-cell propagation, which is reliant upon its active endogenous synthesis. Reducing the levels of SOD1 is therefore a promising therapeutic approach. Antisense oligonucleotides (ASOs) can efficiently silence proteins with gain-of-function mutations. However, naked ASOs have a short circulation half-life and are unable to cross the blood brain barrier (BBB) warranting the use of a drug carrier for effective delivery. In this study, calcium phosphate lipid coated nanoparticles (CaP-lipid NPs) were developed for delivery of SOD1 ASO to motor neurons. The most promising nanoparticle formulation (Ca/P ratio of 100:1), had a uniform spherical core-shell morphology with an average size of 30 nm, and surface charge (ζ-potential) of -4.86 mV. The encapsulation efficiency of ASO was 48% and stability studies found the particle to be stable over a period of 20 days. In vitro experiments demonstrated that the negatively charged ASO-loaded CaP-lipid NPs could effectively deliver SOD1-targeted ASO into a mouse motor neuron-like cell line (NSC-34) through endocytosis and significantly down-regulated SOD1 expression in HEK293 cells. The CaP-lipid NPs exhibited a pH-dependant dissociation, suggesting that that the acidification of lysosomes is the likely mechanism responsible for facilitating intracellular ASO release. To demonstrate tissue specific delivery and localization of these NPs we performed in vivo microinjections into zebrafish. Successful delivery of these NPs was confirmed for the zebrafish brain, the blood stream, and the spinal cord. These results suggest that CaP-lipid NPs could be an effective and safe delivery system for the improved delivery of SOD1 ASOs to motor neurons. Further in vivo evaluation in transgenic mouse models of SOD1 ALS are therefore warranted.

Inflammatory role of dendritic cells in Amyotrophic Lateral Sclerosis revealed by an analysis of patients' peripheral blood

Chronic inflammation is one of the causes of neurodegeneration in Amyotrophic lateral sclerosis (ALS). Here we examined whether circulating dendritic cells (DCs) can contribute to disease progression. We found ALS patients show a significant reduction in the number of circulating DCs. Also, patients' DCs present an increased expression of CD62L and a tendency to overexpress CCR2 compared with healthy donors. Moreover, DCs derived from a subpopulation of ALS patients produced higher levels of IL-8 and CCL-2 upon lipopolysaccharide (LPS)-stimulation. Finally, we found a significant inverse correlation between the time from onset of the pathology to its diagnosis and the levels of IL-6 secretion induced by LPS. Our data support the hypothesis, in a subpopulation of patients, DCs recruited at the diseased tissue produce high levels of CCL-2 and IL-8 and contribute to the inflammatory process promoting the recruitment of other inflammatory cells. An increased efficiency of IL-6 production may accelerate only the initial phases of disease progression. Blood DC analysis can be used to identify ALS patients with an altered course of inflammatory cell recruitment at the diseased central nervous system (CNS). The high levels of CD62L expression suggests this molecule could be a target for treatment of CNS inflammation.

Downregulation of MicroRNA-193b-3p Promotes Autophagy and Cell Survival by Targeting TSC1/mTOR Signaling in NSC-34 Cells

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the death of upper and lower motor neurons. MicroRNAs (miRNAs) are reported to be closely related to the development of ALS. However, the precise functions of miRNAs in the pathogenesis of ALS remain largely unknown. In previous studies, we determined that miRNA-193b-3p was significantly downregulated in patients with sporadic ALS (sALS). Here, we observed that miRNA-193b-3p was downregulated in the SOD1^G93A mouse model of ALS and promoted cell death in NSC-34 cells. We further found that miR-193b-3p directly targeted tuberous sclerosis 1 (TSC1) to regulate mechanistic target of rapamycin complex 1 (mTORC1) activity. Downregulation of miR-193b-3p led to TSC1 increase accompanied with mTORC1 inactivation, and vice versa. Moreover, downregulation of miR-193b-3p promoted protective autophagy and cell survival in NSC-34 cells. In contrast, upregulation of miR-193b-3p activated mTORC1 signaling, leading to inhibition of autophagy and promotion of cell death. Taken together, our study suggests that downregulation of miR-193b-3p is required for cell survival by targeting TSC1/mTOR signaling in NSC-34 cells and provides a novel target for improving the clinical therapy of ALS.

Phase to Phase with TDP-43

TDP-43 is a dimeric nuclear protein that plays a central role in RNA metabolism. In recent years, this protein has become a focal point of research in the amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD) disease spectrum, as pathognomonic inclusions within affected neurons contain post-translationally modified TDP-43. A key question in TDP-43 research involves determining the mechanisms and triggers that cause TDP-43 to form pathological aggregates. This review gives a brief overview of the physiological and pathological roles of TDP-43 and focuses on the structural features of its protein domains and how they may contribute to normal protein function and to disease. A special emphasis is placed on the C-terminal prion-like region thought to be implicated in pathology, as it is where nearly all ALS/FTD-associated mutations reside. Recent structural studies of this domain revealed its crucial role in the formation of phase-separated liquid droplets through a partially populated α-helix. This new discovery provides further support for the theory that liquid droplets such as stress granules may be precursors to pathological aggregates, linking environmental effects such as stress to the potential etiology of the disease. The transition of TDP-43 among soluble, droplet, and aggregate phases and the implications of these transitions for pathological aggregation are summarized and discussed.

Profilin1 biology and its mutation, actin(g) in disease

Profilins were discovered in the 1970s and were extensively studied for their significant physiological roles. Profilin1 is the most prominent isoform and has drawn special attention due to its role in the cytoskeleton, cell signaling, and its link to conditions such as cancer and vascular hypertrophy. Recently, multiple mutations in the profilin1 gene were linked to amyotrophic lateral sclerosis (ALS). In this review, we will discuss the physiological and pathological roles of profilin1. We will further highlight the cytoskeletal function and dysfunction caused by profilin1 dysregulation. Finally, we will discuss the implications of mutant profilin1 in various diseases with an emphasis on its contribution to the pathogenesis of ALS.

CHCHD10 is not a frequent causative gene in Chinese ALS patients

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disorder characterized by the death of motor neurons. Recently, mutations in CHCHD10 have been reported to cause ALS in Western populations. In the present study, direct DNA sequencing has been performed on CHCHD10 in a cohort of 294 ALS patients of Chinese Han origin. No mutations were identified in CHCHD10 in ALS cases of Chinese ancestry. We propose CHCHD10 might not be a frequent causal gene among Chinese with ALS.

A 50 bp deletion in the SOD1 promoter lowers enzyme expression but is not associated with ALS in Sweden

Mutations in the superoxide dismutase (SOD1) gene have been linked to amyotrophic lateral sclerosis (ALS). A 50 base pair (bp) deletion of SOD1 has been suggested to reduce transcription and to be associated with later disease onset in ALS. This study was aimed to reveal if the 50 bp deletion influenced SOD1 enzymatic activity, occurrence and phenotype of the disease in a Swedish ALS/control cohort. Blood samples from 512 Swedish ALS patients and 354 Swedish controls without coding SOD1 mutations were analysed for the 50 bp deletion allele. The enzymatic activity of SOD1 in erythrocytes was analysed and genotype-phenotype correlations were assessed. Results demonstrated that the genotype frequencies of the 50 bp deletion were all found to be in Hardy-Weinberg equilibrium. No significant differences were found for age of onset, disease duration or site of onset. SOD1 enzymatic activity showed a statistically significant decreasing trend in the control group, in which the allele was associated with a 5% reduction in SOD1 activity. The results suggest that the 50 bp deletion has a moderate reducing effect on SOD1 synthesis. No modulating effects, however, were found on ALS onset, phenotype and survival in the Swedish population.

Mitochondrial oxidative metabolism and uncoupling proteins in the failing heart

Despite significant progress in cardiovascular medicine, myocardial ischemia and infarction, progressing eventually to the final end point heart failure (HF), remain the leading cause of morbidity and mortality in the USA. HF is a complex syndrome that results from any structural or functional impairment in ventricular filling or blood ejection. Ultimately, the heart's inability to supply the body's tissues with enough blood may lead to death. Mechanistically, the hallmarks of the failing heart include abnormal energy metabolism, increased production of reactive oxygen species (ROS) and defects in excitation-contraction coupling. HF is a highly dynamic pathological process, and observed alterations in cardiac metabolism and function depend on the disease progression. In the early stages, cardiac remodeling characterized by normal or slightly increased fatty acid (FA) oxidation plays a compensatory, cardioprotective role. However, upon progression of HF, FA oxidation and mitochondrial oxidative activity are decreased, resulting in a significant drop in cardiac ATP levels. In HF, as a compensatory response to decreased oxidative metabolism, glucose uptake and glycolysis are upregulated, but this upregulation is not sufficient to compensate for a drop in ATP production. Elevated mitochondrial ROS generation and ROS-mediated damage, when they overwhelm the cellular antioxidant defense system, induce heart injury and contribute to the progression of HF. Mitochondrial uncoupling proteins (UCPs), which promote proton leak across the inner mitochondrial membrane, have emerged as essential regulators of mitochondrial membrane potential, respiratory activity and ROS generation. Although the physiological role of UCP2 and UCP3, expressed in the heart, has not been clearly established, increasing evidence suggests that these proteins by promoting mild uncoupling could reduce mitochondrial ROS generation and cardiomyocyte apoptosis and ameliorate thereby myocardial function. Further investigation on the alterations in cardiac UCP activity and regulation will advance our understanding of their physiological roles in the healthy and diseased heart and also may facilitate the development of novel and more efficient therapies.

Binding of TDP-43 to the 3'UTR of its cognate mRNA enhances its solubility

TAR DNA binding protein of 43 kDa (TDP-43) has been implicated in the pathogenesis of a broad range of neurodegenerative diseases termed TDP-43 proteinopathies, which encompass a spectrum of diseases ranging from amyotrophic lateral sclerosis to frontotemporal dementia. Pathologically misfolded and aggregated forms of TDP-43 are found in cytoplasmic inclusion bodies of affected neurons in these diseases. The mechanism by which TDP-43 misfolding causes disease is not well-understood. Current hypotheses postulate that the TDP-43 aggregation process plays a major role in pathogenesis. We amplify that hypothesis and suggest that binding of cognate ligands to TDP-43 can stabilize the native functional state of the protein and ameliorate aggregation. We expressed recombinant TDP-43 containing an N-terminal Venus yellow fluorescent protein tag in Escherichia coli and induced its aggregation by altering solvent salt concentrations and examined the extent to which various oligonucleotide molecules affect its aggregation in vitro using aggregation-induced turbidity assays. We show that vYFP-TDP-43 binding to its naturally occurring RNA target that comprises a sequence on the 3'UTR region of its mRNA improves its solubility, suggesting interplay among TDP-43 solubility, oligonucleotide binding, and TDP-43 autoregulation.

Searching for a link between the L-BMAA neurotoxin and amyotrophic lateral sclerosis: a study protocol of the French BMAALS programme

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is the most common motor neurone disease. It occurs in two forms: (1) familial cases, for which several genes have been identified and (2) sporadic cases, for which various hypotheses have been formulated. Notably, the β-N-methylamino-L-alanine (L-BMAA) toxin has been postulated to be involved in the occurrence of sporadic ALS. The objective of the French BMAALS programme is to study the putative link between L-BMAA and ALS.

METHODS AND ANALYSIS

The programme covers the period from 1 January 2003 to 31 December 2011. Using multiple sources of ascertainment, all the incident ALS cases diagnosed during this period in the area under study (10 counties spread over three French regions) were collected. First, the standardised incidence ratio will be calculated for each municipality under concern. Then, by applying spatial clustering techniques, overincidence and underincidence zones of ALS will be sought. A case-control study, in the subpopulation living in the identified areas, will gather information about patients' occupations, leisure activities and lifestyle habits in order to assess potential risk factors to which they are or have been exposed. Specimens of drinking water, food and biological material (brain tissue) will be examined to assess the presence of L-BMAA in the environment and tissues of ALS cases and controls.

ETHICS AND DISSEMINATION

The study has been reviewed and approved by the French ethical committee of the CPP SOOM IV (Comité de Protection des Personnes Sud-Ouest & Outre-Mer IV). The results will be published in peer-reviewed journals and presented at national and international conferences.

The ubiquitin proteasome system in glia and its role in neurodegenerative diseases

The ubiquitin proteasome system (UPS) is crucial for intracellular protein homeostasis and for degradation of aberrant and damaged proteins. The accumulation of ubiquitinated proteins is a hallmark of many neurodegenerative diseases, including amyotrophic lateral sclerosis, Alzheimer’s, Parkinson’s, and Huntington’s disease, leading to the hypothesis that proteasomal impairment is contributing to these diseases. So far, most research related to the UPS in neurodegenerative diseases has been focused on neurons, while glial cells have been largely disregarded in this respect. However, glial cells are essential for proper neuronal function and adopt a reactive phenotype in neurodegenerative diseases, thereby contributing to an inflammatory response. This process is called reactive gliosis, which in turn affects UPS function in glial cells. In many neurodegenerative diseases, mostly neurons show accumulation and aggregation of ubiquitinated proteins, suggesting that glial cells may be better equipped to maintain proper protein homeostasis. During an inflammatory reaction, the immunoproteasome is induced in glia, which may contribute to a more efficient degradation of disease-related proteins. Here we review the role of the UPS in glial cells in various neurodegenerative diseases, and we discuss how studying glial cell function might provide essential information in unraveling mechanisms of neurodegenerative diseases.

Biomarkers for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is the most common form of motor neuron disease. ALS is a fatal neurodegenerative disease and clinical diagnosis typically takes many months to complete. Early disease diagnosis through the use of biomarkers may aid in correct clinical management of patients and possibly delay time to ventilator and morbidity. This review explores the progress of biomarker discovery efforts for ALS and the many challenges that remain. Included are different technologies utilized in biomarker discovery efforts (proteomic, genomic and metabolomic) and putative biomarkers uncovered using these techniques. These studies have discovered genetic mutations leading to familial forms of ALS, and specific protein alterations that occur in biological fluids (cerebrospinal fluid and blood) and/or tissues of ALS subjects. More recent high-throughput technologies have revealed panels of proteomic or metabolic biomarkers that can discriminate between ALS and control groups. The identification of disease-specific biomarkers will provide opportunities to develop early diagnostic measures as well as surrogate markers to monitor disease progression and test drug efficacy in clinical trials.

Techniques for Monitoring Protein Misfolding and Aggregation in Vitro and in Living Cells

Protein misfolding and aggregation have been considered important in understanding many neurodegenerative diseases and recombinant biopharmaceutical production. Therefore, various traditional and modern techniques have been utilized to monitor protein aggregation in vitro and in living cells. Fibril formation, morphology and secondary structure content of amyloidogenic proteins in vitro have been monitored by molecular probes, TEM/AFM, and CD/FTIR analyses, respectively. Protein aggregation in living cells has been qualitatively or quantitatively monitored by numerous molecular folding reporters based on either fluorescent protein or enzyme. Aggregation of a target protein is directly correlated to the changes in fluorescence or enzyme activity of the folding reporter fused to the target protein, which allows non-invasive monitoring aggregation of the target protein in living cells. Advances in the techniques used to monitor protein aggregation in vitro and in living cells have greatly facilitated the understanding of the molecular mechanism of amyloidogenic protein aggregation associated with neurodegenerative diseases, optimizing culture conditions to reduce aggregation of biopharmaceuticals expressed in living cells, and screening of small molecule libraries in the search for protein aggregation inhibitors.

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.

Walking the oxidative stress tightrope: a perspective from the naked mole-rat, the longest-living rodent

Reactive oxygen species (ROS), by-products of aerobic metabolism, cause oxidative damage to cells and tissue and not surprisingly many theories have arisen to link ROS-induced oxidative stress to aging and health. While studies clearly link ROS to a plethora of divergent diseases, their role in aging is still debatable. Genetic knock-down manipulations of antioxidants alter the levels of accrued oxidative damage, however, the resultant effect of increased oxidative stress on lifespan are equivocal. Similarly the impact of elevating antioxidant levels through transgenic manipulations yield inconsistent effects on longevity. Furthermore, comparative data from a wide range of endotherms with disparate longevity remain inconclusive. Many long-living species such as birds, bats and mole-rats exhibit high-levels of oxidative damage, evident already at young ages. Clearly, neither the amount of ROS per se nor the sensitivity in neutralizing ROS are as important as whether or not the accrued oxidative stress leads to oxidative-damage-linked age-associated diseases. In this review we examine the literature on ROS, its relation to disease and the lessons gleaned from a comparative approach based upon species with widely divergent responses. We specifically focus on the longest lived rodent, the naked mole-rat, which maintains good health and provides novel insights into the paradox of maintaining both an extended healthspan and lifespan despite high oxidative stress from a young age.

Does α-amino-β-methylaminopropionic acid (BMAA) play a role in neurodegeneration?

The association of α-amino-β-methylaminopropionic acid (BMAA) with elevated incidence of amyotrophic lateral sclerosis/Parkinson’s disease complex (ALS/PDC) was first identified on the island of Guam. BMAA has been shown to be produced across the cyanobacterial order and its detection has been reported in a variety of aquatic and terrestrial environments worldwide, suggesting that it is ubiquitous. Various in vivo studies on rats, mice, chicks and monkeys have shown that it can cause neurodegenerative symptoms such as ataxia and convulsions. Zebrafish research has also shown disruption to neural development after BMAA exposure. In vitro studies on mice, rats and leeches have shown that BMAA acts predominantly on motor neurons. Observed increases in the generation of reactive oxygen species (ROS) and Ca²⁺ influx, coupled with disruption to mitochondrial activity and general neuronal death, indicate that the main mode of activity is via excitotoxic mechanisms. The current review pertaining to the neurotoxicity of BMAA clearly demonstrates its ability to adversely affect neural tissues, and implicates it as a potentially significant compound in the aetiology of neurodegenerative disease. When considering the potential adverse health effects upon exposure to this compound, further research to better understand the modes of toxicity of BMAA and the environmental exposure limits is essential.

[SOD1-N196 mutation in a family with amyotrophic lateral sclerosis]

INTRODUCTION

N19S mutation is produced by substitution in the 139 position of SOD1 and was described by Mayeux in a patient with amyotrophic lateral sclerosis (ALS). He suggested that it did not have a causal effect as it was found in asymptomatic and sporadic cases. Other authors in later articles did not agree.

MATERIAL AND METHODS

We describe a family with 4 members with ALS patients and attempt to find the carrier of the N19S mutation of the propositus. Molecular studies were performed on 15 members of the family of a different order.

RESULTS

The ALS cases were found in the maternal line of the propositus. The presence of the mutation was detected in 3 people, the other two were asymptomatic. One of patients with ALS in the family, who died previously, did not have the mutation. Two of the sons of this case and another of the other case did not show it. On the other hand, N19S mutation was only present in paternal branch of the propositus, where there were no cases.

CONCLUSION

The described family supports the hypothesis by Mayeux and against that mutation N19S has pathological consequences, since mutation is only in the family line where there are no cases with ALS. In consequence, although the described case is included as a familiar form, it cannot be attributed to the mutation, and its relationship with N19S should be considered as casual.

ALS-causing SOD1 mutations promote production of copper-deficient misfolded species

Point mutations scattered throughout the sequence of Cu,Zn superoxide dismutase (SOD1) cause a subset of amyotrophic lateral sclerosis (ALS) cases. SOD1 is a homodimer in which each subunit binds one copper atom and one zinc atom. Inclusions containing misfolded SOD1 are seen in motor neurons of SOD1-associated ALS cases. The mechanism by which these diverse mutations cause misfolding and converge on the same disease is still not well understood. Previously, we developed several time-resolved techniques to monitor structural changes in SOD1 as it unfolds in guanidine hydrochloride. By measuring the rates of Cu and Zn release using an absorbance-based assay, dimer dissociation through chemical cross-linking, and β-barrel conformation changes by tryptophan fluorescence, we established that wild-type SOD1 unfolds by a branched pathway involving a Zn-deficient monomer as the dominant intermediate of the major pathway, and with various metal-loaded and Cu-deficient dimers populated along the minor pathway. We have now compared the unfolding pathway of wild-type SOD1 with those of A4V, G37R, G85R, G93A, and I113T ALS-associated mutant SOD1. The kinetics of unfolding of the mutants were generally much faster than those of wild type. However, all of the mutants utilize the minority pathway to a greater extent than the wild-type protein, leading to greater populations of Cu-deficient intermediates and decreases in Zn-deficient intermediates relative to the wild-type protein. The greater propensity of the mutants to populate Cu-deficient states potentially implicates these species as a pathogenic form of SOD1 in SOD1-associated ALS and provides a novel target for therapeutic intervention.

Effect of genetic background on phenotype variability in transgenic mouse models of amyotrophic lateral sclerosis: a window of opportunity in the search for genetic modifiers

Transgenic (Tg) mouse models of FALS containing mutant human SOD1 genes (G37R, G85R, D90A, or G93A missense mutations or truncated SOD1) exhibit progressive neurodegeneration of the motor system that bears a striking resemblance to ALS, both clinically and pathologically. The most utilized and best characterized Tg mice are the G93A mutant hSOD1 (Tg(hSOD1-G93A)1GUR mice), abbreviated G93A. In this review we highlight what is known about background-dependent differences in disease phenotype in transgenic mice that carry mutated human or mouse SOD1. Expression of G93A-hSOD1Tg in congenic lines with ALR, NOD.Rag1KO, SJL or C3H backgrounds show a more severe phenotype than in the mixed (B6xSJL) hSOD1Tg mice, whereas a milder phenotype is observed in B6, B10, BALB/c and DBA inbred lines. We hypothesize that the background differences are due to disease-modifying genes. Identification of modifier genes can highlight intracellular pathways already suspected to be involved in motor neuron degeneration; it may also point to new pathways and processes that have not yet been considered. Most importantly, identified modifier genes provide new targets for the development of therapies.

Role and treatment of mitochondrial DNA-related mitochondrial dysfunction in sporadic neurodegenerative diseases

Several sporadic neurodegenerative diseases display phenomena that directly or indirectly relate to mitochondrial function. Data suggesting altered mitochondrial function in these diseases could arise from mitochondrial DNA (mtDNA) are reviewed. Approaches for manipulating mitochondrial function and minimizing the downstream consequences of mitochondrial dysfunction are discussed.

TDP-43 proteinopathy and motor neuron disease in chronic traumatic encephalopathy

Epidemiological evidence suggests that the incidence of amyotrophic lateral sclerosis is increased in association with head injury. Repetitive head injury is also associated with the development of chronic traumatic encephalopathy (CTE), a tauopathy characterized by neurofibrillary tangles throughout the brain in the relative absence of β-amyloid deposits. We examined 12 cases of CTE and, in 10, found a widespread TAR DNA-binding protein of approximately 43kd (TDP-43) proteinopathy affecting the frontal and temporal cortices, medial temporal lobe, basal ganglia, diencephalon, and brainstem. Three athletes with CTE also developed a progressive motor neuron disease with profound weakness, atrophy, spasticity, and fasciculations several years before death. In these 3 cases, there were abundant TDP-43-positive inclusions and neurites in the spinal cord in addition to tau neurofibrillary changes, motor neuron loss, and corticospinal tract degeneration. The TDP-43 proteinopathy associated with CTE is similar to that found in frontotemporal lobar degeneration with TDP-43 inclusions, in that widespread regions of the brain are affected. Akin to frontotemporal lobar degeneration with TDP-43 inclusions, in some individuals with CTE, the TDP-43 proteinopathy extends to involve the spinal cord and is associated with motor neuron disease. This is the first pathological evidence that repetitive head trauma experienced in collision sports might be associated with the development of a motor neuron disease.

The structural biochemistry of the superoxide dismutases

The discovery of superoxide dismutases (SODs), which convert superoxide radicals to molecular oxygen and hydrogen peroxide, has been termed the most important discovery of modern biology never to win a Nobel Prize. Here, we review the reasons this discovery has been underappreciated, as well as discuss the robust results supporting its premier biological importance and utility for current research. We highlight our understanding of SOD function gained through structural biology analyses, which reveal important hydrogen-bonding schemes and metal-binding motifs. These structural features create remarkable enzymes that promote catalysis at faster than diffusion-limited rates by using electrostatic guidance. These architectures additionally alter the redox potential of the active site metal center to a range suitable for the superoxide disproportionation reaction and protect against inhibition of catalysis by molecules such as phosphate. SOD structures may also control their enzymatic activity through product inhibition; manipulation of these product inhibition levels has the potential to generate therapeutic forms of SOD. Markedly, structural destabilization of the SOD architecture can lead to disease, as mutations in Cu,ZnSOD may result in familial amyotrophic lateral sclerosis, a relatively common, rapidly progressing and fatal neurodegenerative disorder. We describe our current understanding of how these Cu,ZnSOD mutations may lead to aggregation/fibril formation, as a detailed understanding of these mechanisms provides new avenues for the development of therapeutics against this so far untreatable neurodegenerative pathology.

No evidence of association of FLJ10986 and ITPR2 with ALS in a large German cohort

A recent genome-wide association study (GWAS) found significant association of six single nucleotide polymorphisms (SNPs) in the gene FLJ10986 with sporadic amyotrophic lateral sclerosis (SALS). Another independent GWAS reported significant association of one SNP in the gene inositol 1,4,5-triphosphate receptor 2 (ITPR2) with SALS. These studies provided conflicting results. We examined the six most significant SNPs in FLJ10986 and one SNP in ITPR2 in a large cohort consisting of 595 SALS cases and 681 controls ascertained from Germany. Our results did not provide evidence for the association of these SNPs with SALS, suggesting a possible population-specific effect for FLJ10986 and ITPR2 that do not modulate the risk for SALS in the German population.

A novel form of juvenile recessive ALS maps to loci on 6p25 and 21q22

We describe a novel form of juvenile recessive ALS (JRALS) affecting four of six offspring from a consanguineous first cousin marriage. The syndrome is characterized by early and prominent upper motor neuron signs, along with striking amyotrophy of the upper and lower limbs and bulbar involvement. After excluding linkage to loci with known association to ALS and other motor neuron diseases, we used a homozygosity mapping approach to identify loci on chromosomes 6p25 and 21q22, each with an equal probability of linkage to the trait (with a LOD score=3.1, the maximum possible given the family structure). Mutation analysis of seven candidate genes that are expressed in the CNS or have roles in neuronal function did not reveal any pathogenic mutations. Identification of additional families will help to distinguish between which of the two autosomal loci contains the disease-causing gene, or whether this is a digenic trait.

Destabilizing protein polymorphisms in the genetic background direct phenotypic expression of mutant SOD1 toxicity

Genetic background exerts a strong modulatory effect on the toxicity of aggregation-prone proteins in conformational diseases. In addition to influencing the misfolding and aggregation behavior of the mutant proteins, polymorphisms in putative modifier genes may affect the molecular processes leading to the disease phenotype. Mutations in SOD1 in a subset of familial amyotrophic lateral sclerosis (ALS) cases confer dominant but clinically variable toxicity, thought to be mediated by misfolding and aggregation of mutant SOD1 protein. While the mechanism of toxicity remains unknown, both the nature of the SOD1 mutation and the genetic background in which it is expressed appear important. To address this, we established a Caenorhabditis elegans model to systematically examine the aggregation behavior and genetic interactions of mutant forms of SOD1. Expression of three structurally distinct SOD1 mutants in C. elegans muscle cells resulted in the appearance of heterogeneous populations of aggregates and was associated with only mild cellular dysfunction. However, introduction of destabilizing temperature-sensitive mutations into the genetic background strongly enhanced the toxicity of SOD1 mutants, resulting in exposure of several deleterious phenotypes at permissive conditions in a manner dependent on the specific SOD1 mutation. The nature of the observed phenotype was dependent on the temperature-sensitive mutation present, while its penetrance reflected the specific combination of temperature-sensitive and SOD1 mutations. Thus, the specific toxic phenotypes of conformational disease may not be simply due to misfolding/aggregation toxicity of the causative mutant proteins, but may be defined by their genetic interactions with cellular pathways harboring mildly destabilizing missense alleles.

Correct folding and stability are essential for protein function. In cells, a network of molecular chaperones and degradative enzymes facilitate folding, prevent aggregation and ensure degradation of the misfolded proteins, thus maintaining protein homeostasis. In many diseases, including Amyotrophic Lateral Sclerosis (ALS), expression of a single mutant protein that misfolds and aggregates causes cellular toxicity that is strongly dependent on the genetic background. To address the influence of genetic background on the toxicity of aggregation-prone proteins, we established a C. elegans model of misfolding and aggregation of several distinct ALS-related mutants of superoxide dismutase 1 (SOD1). In one wild type genetic background (N2), these proteins exhibited only mild cellular toxicity despite strong, mutant-specific aggregation phenotypes. However, when SOD1 mutants were expressed in the background of mildly destabilized protein polymorphisms, their toxicity was enhanced and a number of distinct phenotypes were exposed. These synthetic phenotypes reflected the loss-of-function of the destabilized polymorphic proteins. Furthermore, the degree to which each of these phenotypes was exposed depended on the nature of the SOD1 mutation. These data suggest that the presence of mildly destabilizing polymorphisms in the genetic background may modulate and direct the specific toxic phenotypes in protein aggregation diseases.

Superoxide dismutase from the eukaryotic thermophile Alvinella pompejana: structures, stability, mechanism, and insights into amyotrophic lateral sclerosis

Prokaryotic thermophiles supply stable human protein homologs for structural biology; yet, eukaryotic thermophiles would provide more similar macromolecules plus those missing in microbes. Alvinella pompejana is a deep-sea hydrothermal-vent worm that has been found in temperatures averaging as high as 68 degrees C, with spikes up to 84 degrees C. Here, we used Cu,Zn superoxide dismutase (SOD) to test if this eukaryotic thermophile can provide insights into macromolecular mechanisms and stability by supplying better stable mammalian homologs for structural biology and other biophysical characterizations than those from prokaryotic thermophiles. Identification, cloning, characterization, X-ray scattering (small-angle X-ray scattering, SAXS), and crystal structure determinations show that A. pompejana SOD (ApSOD) is superstable, homologous, and informative. SAXS solution analyses identify the human-like ApSOD dimer. The crystal structure shows the active site at 0.99 A resolution plus anchoring interaction motifs in loops and termini accounting for enhanced stability of ApSOD versus human SOD. Such stabilizing features may reduce movements that promote inappropriate intermolecular interactions, such as amyloid-like filaments found in SOD mutants causing the neurodegenerative disease familial amyotrophic lateral sclerosis or Lou Gehrig's disease. ApSOD further provides the structure of a long-sought SOD product complex at 1.35 A resolution, suggesting a unified inner-sphere mechanism for catalysis involving metal ion movement. Notably, this proposed mechanism resolves apparent paradoxes regarding electron transfer. These results extend knowledge of SOD stability and catalysis and suggest that the eukaryote A. pompejana provides macromolecules highly similar to those from humans, but with enhanced stability more suitable for scientific and medical applications.