Familial amyotrophic lateral sclerosis (ALS) in Japan associated with H46R mutation in Cu/Zn superoxide dismutase gene: a possible new subtype of familial ALS

Clinical characterization and founder effect analysis in Chinese amyotrophic lateral sclerosis patients with SOD1 common variants

OBJECTIVE

In the Asian population, SOD1 variants are the most common cause of amyotrophic lateral sclerosis (ALS). To date, more than 200 variants have been reported in SOD1. This study aimed to summarize the genotype-phenotype correlation and determine whether the patients carrying common variants derive from a common ancestor.

METHODS

A total of 103 sporadic ALS (SALS) and 11 familial ALS (FALS) probands were included and variants were screened by whole exome sequencing. Functional analyses were performed on fibroblasts derived from patients with SOD1 p.V48A and control. Haplotype analysis was performed in the probands with p.H47R or p.V48A and their familial members.

RESULTS

A total of 25 SOD1 variants were identified in 44 probands, in which p.H47R, p.V48A and p.C112Y variants were the most common variants. 94.3% and 60% of patients with p.H47R or p.V48A had lower limb onset with predominant lower motor neurons (LMNs) involvement. Patients with p.H47R had a slow progression and prolonged survival time, while patients with p.V48A exhibited a duration of 2-5 years. Patients with p.C112Y variant showed remarkable phenotypic variation in age at onset and disease course. SOD1V48A fibroblasts showed mutant SOD1 aggregate formation, enhanced intracellular reactive oxygen species level, and decreased mitochondrial membrane potential compared to the control fibroblast. Haplotype analysis showed that seven families had two different haplotypes. p.H47R and p.V48A variants did not originate from a common founder.

CONCLUSIONS

Our study expanded the understanding of the genotype-phenotype correlation of ALS with SOD1 variants and revealed that the common p.H47R or p.V48A variant did not have a founder effect.

Updated Genetic Analysis of Japanese Familial ALS Patients Carrying SOD1 Variants Revealed Phenotypic Differences for Common Variants

Background and Objectives

Amyotrophic lateral sclerosis (ALS) is an adult-onset progressive neurodegenerative disease. Approximately 10% of ALS cases are familial, and more than 20 causative genes have been identified. As we have previously reported, SOD1 variants are the most common causes of familial ALS in Japan. Because antisense oligonucleotides for SOD1-linked ALS are being used in practical applications, the types of variants and the clinical features of patients need to be updated.

Methods

We consecutively recruited 160 families with familial ALS in Japan. We performed genetic analyses, focusing on SOD1-linked ALS as the most common in our cohort, updated their genotypes, and characterized clinical phenotypes.

Results

A total of 26 SOD1 variants in 56 patients and 49 families (30.6%) were collected, with the 3 most common (p.His47Arg [the conventional numbering; H46R], p.Leu127Ser [L126S], p.Asn87Ser [N86S]) accounting for 38.8% of all families. We also identified 2 novel variants (p.Ile36Phe [I35F] and p.Asn132Argfs*3 [N131Rfs*3]). The mean age at onset was 48.9 ± 12.2 (mean ± SD) years for all patients with SOD1-linked ALS. Lower limb onset comprised 70% of cases. The mean disease duration was 64.7 ± 82 months, and the median survival was 71.5 months. Some variants led to a relatively homogeneous phenotype, although clinical characteristics differed among types of variants and families. Patients with p.His47Arg (H46R) showed slower progression with lower limb onset and a predominance of lower motor neuron involvement. The p.Leu127Ser (L126S) variant led to varying degrees of progression in heterozygous or homozygous states and presented incomplete penetrance. Intrafamilial phenotypic differences were observed in families carrying p.Asn87Ser (N86S). Four variants (p.Cys7Gly [C6G], p.His44Arg [H43R], p.Leu85Val [L84V], and p.Cys147Arg [C146R]) were found to be associated with rapid disease progression.

Discussion

The genetic basis of familial ALS, at least for SOD1 variants, still differed by geographic and ethnic background. Understanding these clinical profiles will help optimize evaluation in targeted gene therapy worldwide and benefit efficient diagnosis, leading to precise application in clinical practice.

Axonopathy Underlying Amyotrophic Lateral Sclerosis: Unraveling Complex Pathways and Therapeutic Insights

Amyotrophic Lateral Sclerosis (ALS) is a complex neurodegenerative disorder characterized by progressive axonopathy, jointly leading to the dying back of the motor neuron, disrupting both nerve signaling and motor control. In this review, we highlight the roles of axonopathy in ALS progression, driven by the interplay of multiple factors including defective trafficking machinery, protein aggregation, and mitochondrial dysfunction. Dysfunctional intracellular transport, caused by disruptions in microtubules, molecular motors, and adaptors, has been identified as a key contributor to disease progression. Aberrant protein aggregation involving TDP-43, FUS, SOD1, and dipeptide repeat proteins further amplifies neuronal toxicity. Mitochondrial defects lead to ATP depletion, oxidative stress, and Ca2+ imbalance, which are regarded as key factors underlying the loss of neuromuscular junctions and axonopathy. Mitigating these defects through interventions including neurotrophic treatments offers therapeutic potential. Collaborative research efforts aim to unravel ALS complexities, opening avenues for holistic interventions that target diverse pathological mechanisms.

Another de novo mutation in the SOD1 gene: the first Turkish patient with SOD1-His47Arg, a case report

Amyotrophic lateral sclerosis (ALS) is a fatal, progressive neurodegenerative disease of motor neurons. Most ALS cases are considered sporadic due to the presence of a combination of environmental and complex genetic risk factors, while approximately 10% of cases have a family history. Pathogenic variants in the SOD1 gene are the second most frequent causative factor of genetics-based ALS worldwide, after C9ORF72 hexanucleotide repeat expansion. The De novo occurrence of pathogenic mutations in ALS-associated genes and its effect on disease progression have been studied previously, especially in the FUS gene. Recent studies have shown that a very small portion of SOD1 cases occurred de novo. Here, we present the first de novo case of the SOD1 His47Arg mutation in a young female patient with mild symptoms and, currently, a slow progression for 7 years.

Advantages of routine next-generation sequencing over standard genetic testing in the amyotrophic lateral sclerosis clinic

BACKGROUND

Next-generation sequencing has enhanced our understanding of amyotrophic lateral sclerosis (ALS) and its genetic epidemiology. Outside the research setting, testing is often restricted to those who report a family history. The aim of this study was to explore the added benefit of offering routine genetic testing to all patients in a regional ALS centre.

METHODS

C9ORF72 expansion testing and exome sequencing was offered to consecutive patients (150 with ALS and 12 with primary lateral sclerosis [PLS]) attending the Oxford Motor Neuron Disease Clinic within a defined time period.

RESULTS

A total of 17 (11.3%) highly penetrant pathogenic variants in C9ORF72, SOD1, TARDBP, FUS and TBK1 were detected, of which 10 were also found through standard clinical genetic testing pathways. The systematic approach resulted in five additional diagnoses of a C9ORF72 expansion (number needed to test [NNT] = 28), and two further missense variants in TARDBP and SOD1 (NNT = 69). Additionally, 3 patients were found to carry pathogenic risk variants in NEK1, and 13 patients harboured common missense variants in CFAP410 and KIF5A, also associated with an increased risk of ALS. We report two novel non-coding loss-of-function splice variants in TBK1 and OPTN. No relevant variants were found in the PLS patients. Patients were offered double-blinded participation, but >80% requested disclosure of the results.

CONCLUSIONS

This study provides evidence that expanding genetic testing to all patients with a clinical diagnosis of ALS enhances the potential for recruitment to clinical trials, but will have direct resource implications for genetic counselling.

Structure of a superoxide dismutase from a tardigrade: Ramazzottius varieornatus strain YOKOZUNA-1

Superoxide dismutase (SOD) is an essential and ubiquitous antioxidant protein that is widely present in biological systems. The anhydrobiotic tardigrades are some of the toughest micro-animals. They have an expanded set of genes for antioxidant proteins such as SODs. These proteins are thought to play an essential role in oxidative stress resistance in critical situations such as desiccation, although their functions at the molecular level have yet to be explored. Here, crystal structures of a copper/zinc-containing SOD (RvSOD15) from an anhydrobiotic tardigrade, Ramazzottius varieornatus strain YOKOZUNA-1, are reported. In RvSOD15, one of the histidine ligands of the catalytic copper center is replaced by a valine (Val87). The crystal structures of the wild type and the V87H mutant show that even though a histidine is placed at position 87, a nearby flexible loop can destabilize the coordination of His87 to the Cu atom. Model structures of other RvSODs were investigated and it was found that some of them are also unusual SODs, with features such as deletion of the electrostatic loop or β3 sheet and unusual metal-binding residues. These studies show that RvSOD15 and some other RvSODs may have evolved to lose the SOD function, suggesting that gene duplications of antioxidant proteins do not solely explain the high stress tolerance of anhydrobiotic tardigrades.

Genetics of amyotrophic lateral sclerosis: seeking therapeutic targets in the era of gene therapy

Amyotrophic lateral sclerosis (ALS) is an intractable disease that causes respiratory failure leading to mortality. The main locus of ALS is motor neurons. The success of antisense oligonucleotide (ASO) therapy in spinal muscular atrophy (SMA), a motor neuron disease, has triggered a paradigm shift in developing ALS therapies. The causative genes of ALS and disease-modifying genes, including those of sporadic ALS, have been identified one after another. Thus, the freedom of target choice for gene therapy has expanded by ASO strategy, leading to new avenues for therapeutic development. Tofersen for superoxide dismutase 1 (SOD1) was a pioneer in developing ASO for ALS. Improving protocols and devising early interventions for the disease are vital. In this review, we updated the knowledge of causative genes in ALS. We summarized the genetic mutations identified in familial ALS and their clinical features, focusing on SOD1, fused in sarcoma (FUS), and transacting response DNA-binding protein. The frequency of the C9ORF72 mutation is low in Japan, unlike in Europe and the United States, while SOD1 and FUS are more common, indicating that the target mutations for gene therapy vary by ethnicity. A genome-wide association study has revealed disease-modifying genes, which could be the novel target of gene therapy. The current status and prospects of gene therapy development were discussed, including ethical issues. Furthermore, we discussed the potential of axonal pathology as new therapeutic targets of ALS from the perspective of early intervention, including intra-axonal transcription factors, neuromuscular junction disconnection, dysregulated local translation, abnormal protein degradation, mitochondrial pathology, impaired axonal transport, aberrant cytoskeleton, and axon branching. We simultaneously discuss important pathological states of cell bodies: persistent stress granules, disrupted nucleocytoplasmic transport, and cryptic splicing. The development of gene therapy based on the elucidation of disease-modifying genes and early intervention in molecular pathology is expected to become an important therapeutic strategy in ALS.

Common mutations of interest in the diagnosis of amyotrophic lateral sclerosis: how common are common mutations in ALS genes?

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is a complex neurodegenerative disease predominantly affecting upper and lower motor neurons. Diagnosis of this devastating pathology is very difficult because the high degree of clinical heterogeneity with which it occurs and until now, no truly effective treatment exists.

AREAS COVERED

Molecular diagnosis may be a valuable tool for dissecting out ALS complex heterogeneity and for identifying new molecular mechanisms underlying the characteristic selective degeneration and death of motor neurons. To date, pathogenic variants in ALS genes are known to be present in up to 70% of familial and 10% of apparently sporadic ALS cases and can be associated with risks for ALS only or risks for other neurodegenerative diseases. This paper shows the procedure currently used in diagnostic laboratories to investigate most frequent mutations in ALS and evaluating the utility of involved molecular techniques as potential tools to discriminate 'common mutations' in ALS patients.

EXPERT OPINION

Genetic testing may allow for establishing an accurate pathological diagnosis and a more precise stratification of patient groups in future drug trials.

Enhancement of Oxidative Reaction by the Intramolecular Electron Transfer between the Coordinated Redox-Active Metal Ions in SOD1

The denatured Cu, Zn superoxide dismutase (SOD1) has the pro-oxidant activity that is suggested to be related with the pathogenesis of amyotrophic lateral sclerosis (ALS). We showed from the changes in the coordinated metal ions that the Cu ion in the Cu-binding site is the catalytic site of the pro-oxidant activity, and a redox-active metal ion in the Zn-binding site has the auxiliary function to enhance the pro-oxidant activity. The auxiliary function is suggested to arise from the intramolecular electron transfer between the coordinated metal ions in the denatured SOD1. The oxidation/reduction cycle of Cu in the Cu-binding site is assisted with changing the oxidation state of a metal ion in the Zn-binding site. The magnitude of the toxicity of the denatured SOD1 is discussed based on the ability of the auxiliary function.

Evolutionary Analyses of Sequence and Structure Space Unravel the Structural Facets of SOD1

Superoxide dismutase (SOD) is the primary enzyme of the cellular antioxidant defense cascade. Misfolding, concomitant oligomerization, and higher order aggregation of human cytosolic SOD are linked to amyotrophic lateral sclerosis (ALS). Although, with two metal ion cofactors SOD1 is extremely robust, the de-metallated apo form is intrinsically disordered. Since the rise of oxygen-based metabolism and antioxidant defense systems are evolutionary coupled, SOD is an interesting protein with a deep evolutionary history. We deployed statistical analysis of sequence space to decode evolutionarily co-varying residues in this protein. These were validated by applying graph theoretical modelling to understand the impact of the presence of metal ion co-factors in dictating the disordered (apo) to hidden disordered (wild-type SOD1) transition. Contact maps were generated for different variants, and the selected significant residues were mapped on separate structure networks. Sequence space analysis coupled with structure networks helped us to map the evolutionarily coupled co-varying patches in the SOD1 and its metal-depleted variants. In addition, using structure network analysis, the residues with a major impact on the internal dynamics of the protein structure were investigated. Our results reveal that the bulk of these evolutionarily co-varying residues are localized in the loop regions and positioned differentially depending upon the metal residence and concomitant steric restrictions of the loops.

From animal models to human disease: a genetic approach for personalized medicine in ALS

Amyotrophic Lateral Sclerosis (ALS) is the most frequent motor neuron disease in adults. Classical ALS is characterized by the death of upper and lower motor neurons leading to progressive paralysis. Approximately 10 % of ALS patients have familial form of the disease. Numerous different gene mutations have been found in familial cases of ALS, such as mutations in superoxide dismutase 1 (SOD1), TAR DNA-binding protein 43 (TDP-43), fused in sarcoma (FUS), C9ORF72, ubiquilin-2 (UBQLN2), optineurin (OPTN) and others. Multiple animal models were generated to mimic the disease and to test future treatments. However, no animal model fully replicates the spectrum of phenotypes in the human disease and it is difficult to assess how a therapeutic effect in disease models can predict efficacy in humans. Importantly, the genetic and phenotypic heterogeneity of ALS leads to a variety of responses to similar treatment regimens. From this has emerged the concept of personalized medicine (PM), which is a medical scheme that combines study of genetic, environmental and clinical diagnostic testing, including biomarkers, to individualized patient care. In this perspective, we used subgroups of specific ALS-linked gene mutations to go through existing animal models and to provide a comprehensive profile of the differences and similarities between animal models of disease and human disease. Finally, we reviewed application of biomarkers and gene therapies relevant in personalized medicine approach. For instance, this includes viral delivering of antisense oligonucleotide and small interfering RNA in SOD1, TDP-43 and C9orf72 mice models. Promising gene therapies raised possibilities for treating differently the major mutations in familial ALS cases.

H46R SOD1 mutation is consistently associated with a relatively benign form of amyotrophic lateral sclerosis with slow progression

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease caused by progressive loss of motor neurons in the motor cortex, brainstem, and spinal cord. Over 60% of patients die from respiratory failure within three years of presentation. We report two ALS patients carrying the p.H46R missense mutation in the SOD1 gene presented with a characteristic clinical phenotype of very slow progression. We also reviewed the 13 pedigrees harbouring the p.H46R mutation reported previously. SOD1 p.H46R mutation is consistently associated with a specific phenotype, i.e. lower limb onset with rare bulbar involvement, and a slow progression with longer survival. It is important to recognize the typical clinical picture of the SOD1 p.H46R mutation, and SOD1 sequencing may be necessary to give the patient correct diagnosis and prognosis.

Slowly progressing lower motor neuron disease caused by a novel duplication mutation in exon 1 of the SOD1 gene

Familial amyotrophic lateral sclerosis accounts for about 5% of all cases of the neurodegenerative disorder amyotrophic lateral sclerosis. Genetic mutations in Cu/Zn superoxide dismutase (SOD1) have been associated with one kind of familial amyotrophic lateral sclerosis (ALS1). We identified a novel duplication mutation in exon 1 of the SOD1 gene in a Japanese family whose members had lower motor neuron diseases. The patients showed slow disease progression, with the onset of lower limb muscle weakness and exertional dyspnea. Some patients had mild motor and sensory neuropathy and/or bladder dysfunction, which is further evidence that SOD1 mutation results in a predominantly lower motor neuron phenotype.

Finding inhibitors of mutant superoxide dismutase-1 for amyotrophic lateral sclerosis therapy from traditional chinese medicine

Superoxide dismutase type 1 (SOD1) mutations cause protein aggregation and decrease protein stability, which are linked to amyotrophic lateral sclerosis (ALS) disease. This research utilizes the world's largest traditional Chinese medicine (TCM) database to search novel inhibitors of mutant SOD1, and molecular dynamics (MD) simulations were used to analyze the stability of protein that interacted with docked ligands. Docking results show that hesperidin and 2,3,5,4'-tetrahydroxystilbene-2-O- β -D-glucoside (THSG) have high affinity to mutant SOD1 and then dopamine. For MD simulation analysis, hesperidin and THSG displayed similar value of RMSD with dopamine, and the migration analysis reveals stable fluctuation at the end of MD simulation time. Interestingly, distance between the protein and ligand has distinct difference, and hesperidin changes the position from initial binding site to the other place. In flexibility of residues analysis, the secondary structure among all complexes does not change, indicating that the structure are not affect ligand binding. The binding poses of hesperidin and THSG are similar to dopamine after molecular simulation. Our result indicated that hesperidin and THSG might be potential lead compound to design inhibitors of mutant SOD1 for ALS therapy.

Dimerization, oligomerization, and aggregation of human amyotrophic lateral sclerosis copper/zinc superoxide dismutase 1 protein mutant forms in live cells

More than 100 copper/zinc superoxide dismutase 1 (SOD1) genetic mutations have been characterized. These mutations lead to the death of motor neurons in ALS. In its native form, the SOD1 protein is expressed as a homodimer in the cytosol. In vitro studies have shown that SOD1 mutations impair the dimerization kinetics of the protein, and in vivo studies have shown that SOD1 forms aggregates in patients with familial forms of ALS. In this study, we analyzed WT SOD1 and 9 mutant (mt) forms of the protein by non-invasive fluorescence techniques. Using microscopic techniques such as fluorescence resonance energy transfer, fluorescence complementation, image-based quantification, and fluorescence correlation spectroscopy, we studied SOD1 dimerization, oligomerization, and aggregation. Our results indicate that SOD1 mutations lead to an impairment in SOD1 dimerization and, subsequently, affect protein aggregation. We also show that SOD1 WT and mt proteins can dimerize. However, aggregates are predominantly composed of SOD1 mt proteins.

A clinical variance in familial amyotrophic lateral sclerosis with a point mutation in Cu/Zn superoxide dismutase gene

We report here a novel point mutation in exon 5 of the Cu/Zn superoxide dismutase (SOD) gene resulting in an amino acid substitution of valine(148) by isoleucine (V148I) in a Japanese family with amyotrophic lateral sclerosis (FALS). In this family, the age at onset was young (28.0 ± 3.8 years old, mean ± SD, n = 4) and the disease progression was rapid (22.0 ± 5.9 months, n = 3) with low Cu/Zn SOD activity (56.3 and 59.0% of the controls, n = 2). It is interesting that the clinical features of ALS varied very much among the affected members. One case had weakness of the lower extremities at first, and died without bulbar paresis. The second case first noticed wasting of the upper limbs with bulbar symptoms, but the third had weakness of upper extremities without developing dysarthria nor dysphagia until death. The living remainder first developed fasciculation of the tongue without weakness of extremities. The valine(148) is conserved among different species, and V148I mutation might destabilize dimer formation with another SOD subunit, leading to decrease enzymatic activity. These results suggested that there could be considerable clinical variance among the patients of FALS within one family, carrying the same Cu/Zn SOD mutation such as V148I.

Different human copper-zinc superoxide dismutase mutants, SOD1G93A and SOD1H46R, exert distinct harmful effects on gross phenotype in mice

Amyotrophic lateral sclerosis (ALS) is a heterogeneous group of fatal neurodegenerative diseases characterized by a selective loss of motor neurons in the brain and spinal cord. Creation of transgenic mice expressing mutant Cu/Zn superoxide dismutase (SOD1), as ALS models, has made an enormous impact on progress of the ALS studies. Recently, it has been recognized that genetic background and gender affect many physiological and pathological phenotypes. However, no systematic studies focusing on such effects using ALS models other than SOD1^G93A mice have been conducted. To clarify the effects of genetic background and gender on gross phenotypes among different ALS models, we here conducted a comparative analysis of growth curves and lifespans using congenic lines of SOD1^G93A and SOD1^H46R mice on two different genetic backgrounds; C57BL/6N (B6) and FVB/N (FVB). Copy number of the transgene and their expression between SOD1^G93A and SOD1^H46R lines were comparable. B6 congenic mutant SOD1 transgenic lines irrespective of their mutation and gender differences lived longer than corresponding FVB lines. Notably, the G93A mutation caused severer disease phenotypes than did the H46R mutation, where SOD1^G93A mice, particularly on a FVB background, showed more extensive body weight loss and earlier death. Gender effect on survival also solely emerged in FVB congenic SOD1^G93A mice. Conversely, consistent with our previous study using B6 lines, lack of Als2, a murine homolog for the recessive juvenile ALS causative gene, in FVB congenic SOD1^H46R, but not SOD1^G93A, mice resulted in an earlier death, implying a genetic background-independent but mutation-dependent phenotypic modification. These results indicate that SOD1^G93A- and SOD1^H46R-mediated toxicity and their associated pathogenic pathways are not identical. Further, distinctive injurious effects resulted from different SOD1 mutations, which are associated with genetic background and/or gender, suggests the presence of several genetic modifiers of disease expression in the mouse genome.

Peripheral markers in neurodegenerative patients and their first-degree relatives

We have determined various biomarkers in the peripheral blood of Alzheimer, Parkinson and vascular dementia patients by comparing the samples with those of first-degree relatives and control subjects. Our results, together with correlation studies using data from the Mini-Mental State Examination (MMSE), suggest that the clinical evaluation of the nitrite (NOx) concentration in Alzheimer patients should be complemented by assays of protein carbonyls (PCs) levels, the ratio of reduced to oxidized glutathione (GSH/GSSG) in plasma, PCs in erythrocytes and PCs and calcium content in leukocytes. For Parkinson patients it would be useful to determine NOx, thiobarbituric-acid reactive substances (TBARS) and PCs in erythrocytes, and NOx and TBARS en leukocytes. For vascular-demented (VD) patients, determination of NOx, Cu, and GSH/GSSG in plasma and TBARS, and PCs in erythrocytes together with PCs in leukocytes should be assayed. Relatives of Alzheimer patients showed alterations in plasma Se and Zn concentrations, catalase (CAT) activity in erythrocytes and calcium content in leukocytes as possible predictive markers of the disease. Relatives of Parkinson patients showed elevated levels of NOx in leukocytes. In the case of vascular-demented patients we suggest NOx, GSH/GSSG and α-tocopherol in plasma, the CAT/superoxide dismutase ratio in erythrocytes and TBARS, GSSG and glutathione reductase in leukocytes as predictive markers. Large-scale longitudinal population-based studies using these suggested biomarkers are necessary in order to assess their level of reliability and specificity in clinical practice.

Loss of glial fibrillary acidic protein marginally accelerates disease progression in a SOD1(H46R) transgenic mouse model of ALS

Glial fibrillary acidic protein (GFAP) is an intermediate filament protein that is highly expressed in reactive astrocytes. Increased production of GFAP is a hallmark of astrogliosis in neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS). However, the physiological and pathological roles of GFAP, particularly in chronic neurodegenerative conditions, remain unclear. To address this issue, we here investigate whether absence of GFAP affects the phenotypic expression of motor neuron disease (MND) using an H46R mutant Cu/Zn superoxide dismutase-expressing mouse model of ALS (SOD1(H46R)). GFAP deficient SOD1(H46R) mice showed a significant shorter lifespan than SOD1(H46R) littermates. Further, at the end stage of disease, loss of GFAP resulted in increased levels of Vim and Aif1 mRNAs, encoding vimentin and allograft inflammatory factor 1 (AIF1), respectively, in the spinal cord, although no discernible differences in the levels and distribution of these proteins between SOD1(H46R) and GFAP-deficient SOD1(H46R) mice were observed. These results suggest that loss of GFAP in SOD1(H46R) mice marginally accelerates the disease progression by moderately enhancing glial cell activation. Our findings in a mouse model of ALS may have implication that GFAP is not necessary for the initiation of disease, but it rather plays some modulatory roles in the progression of ALS/MND.

Familial amyotrophic lateral sclerosis with a novel G85S mutation of superoxide dismutase 1 gene: clinical features of lower motor neuron disease

Amyotrophic lateral sclerosis (ALS) is a devastating disease characterized by upper and lower motor neuron damage. Mutations of Cu/Zn superoxide dismutase gene (SOD1) account for 20% of familial ALS (FALS). We report a unique clinicogenotype of a Japanese family with a novel SOD 1 mutation. A 37-year-old woman (the proband) noticed muscle weakness in the left lower limb. Her mother had developed progressive lower motor neuron signs in four extremities at 38 years of age. Subsequently she was diagnosed as ALS and died of respiratory failure at 15 months after clinical onset. Neurological examination of the proband showed absent muscle stretch reflexes in the left knee and the left ankle without Babinski signs. Mild to moderate degree of muscle weakness existed in the left lower extremity. Muscle atrophy was presented in the left thigh. Initial pulmonary function revealed forced vital capacity of 91.1%. Electromyography disclosed ongoing denervation muscle potentials in the left lower extremity. SOD1 analysis demonstrated amino acid substitution of glycine by serine at codon 85 (G85S) in exon 4. Six months later, marked muscle weakness and atrophy expanded to four extremities. All muscle stretch reflexes were absent. Three months later, ventilator support with a tracheostomy was needed. The patient died at 18 months after clinical onset. Clinical hallmarks of this FALS family indicate that G85S mutation of SOD1 may cause rapidly progressive form of pure lower motor neuron signs.

Pseudopolyneuritic form of ALS revisited: clinical and pathological heterogeneity

Pseudopolyneuritic form of ALS is a subtype of ALS characterized by distal weakness of the unilateral lower limb and absence of Achilles tendon reflex (ATR) at disease onset. Recognition of this form of ALS is important for clinicians because the combination of distal weakness of the lower limb and absence of ATR usually suggests peripheral neuropathy. We reviewed the clinical records of 42 autopsy-proven sporadic ALS cases and found three cases that showed onset of weakness of the unilateral lower limb with distal dominance and absence of ATR. The disease duration in the three cases was 2, 3 and 19 years, respectively. The clinical features of the patient with a course of 19 years had been restricted to lower motor neuron signs. Histopathologically, consistent findings in the three cases were severe motor neuron loss throughout the whole spinal cord, with relative preservation of the hypoglossal nucleus. Reflecting this finding, TDP-43-positive neuronal cytoplasmic inclusions in the spinal cord were sparse in two cases, and absent in a third. In the patient showing a clinical course of 19 years, mild corticospinal tract degeneration appeared to correspond to the absence of upper motor neuron signs and prolonged disease duration. In this case only, Bunina bodies were not demonstrated. In this study, we clarified the clinical and pathological heterogeneity of this form of ALS.

[Amyotrophic lateral sclerosis with the SOD1 mutations]

Mutations in Cu/Zn superoxide dismutase (SOD1) have been linked to some familial cases of amyotrophic lateral sclerosis (ALS). In familial ALS kinders with mutations in the SOD1 gene, the age of onset of weakness varies greatly but the duration of illness appears to be characteristic to each mutation. For example, in patients with the L84V mutation, the average life expectancy is less than 1.5 year after the onset of symptoms, whereas patients harboring the H46R mutation have an average life expectancy of 18 years after the disease onset. In view of the evidence supporting the idea that familial ALS variants of SOD1 enzymes acquire toxic properties, the variations in the duration of illness in the different kinders might arise because each mutation imparts different degrees of toxicity to the mutant protein. We developed rats that express a human SOD1 transgene with two different ALS-associated mutations (G93A and H46R) develop striking motor neuron degeneration and paralysis. The larger size of this rat model as compared with the ALS mice will facilitate studies involving manipulations of spinal fluid (implantation of intrathecal catheters for chronic therapeutic studies; CSF sampling) and spinal cord (e.g., direct administration of viral- and cell-mediated therapies). Hepatocyte growth factor (HGF) is one of the most potent survival-promoting factors for motor neurons. To examine its both protective effect on motor neurons and therapeutic potential, we administered human recombinant HGF (hrHGF) by continuous intrathecal delivery to G93A transgenic (Tg) rats at onset of paralysis for 4 weeks. Intrathecal administration of hrHGF attenuates motor neuron degeneration and prolonged the duration of the disease by 63%. Our results indicated the therapeutic efficacy of continuous intrathecal administration of hrHGF in Tg rats. The results should prompt further clinical trials in ALS using continuous intrathecal administration of hrHGF.

Flexor-dominant myopathic phenotype in patients with His46Arg substitution in the Cu/Zn superoxide dismutase gene

We present the cases of 3 patients with a histidine-to-arginine substitution at position 46 of the Cu/Zn superoxide dismutase gene. Consistent with previous reports, the initial symptom in each patient was unilateral weakness in the distal leg muscles. Remarkably, muscular atrophy in these patients during the early stage of the disease was more specific to the flexor muscle group, with the extensor muscle group remaining intact over long-term observation. More interestingly, biopsy of the affected muscle in the early stage of the disease revealed necrotic and regenerative myofibers with infiltration of lymphocytes, resembling inflammatory myopathy. These novel findings might provide further insights into the pathophysiology of familial amyotrophic lateral sclerosis.

[Massive bleeding from tracheoarterial fistula in an amyotrophic lateral sclerosis patient treated with long-term invasive ventilation: an autopsy case report]

We report a 43-year-old woman with familial amyotrophic lateral sclerosis (FALS) who died of massive bleeding from a tracheoarterial fistula. Four years after the onset of the disease, she received invasive ventilation by tracheostomy because of respiratory failure. Four years and 7 months later, she showed an abrupt hemorrhage from the tracheostomy and died. The postmortem examination revealed a fistulous tract between the tracheal mucosal ulcer and the brachiocephalic trunk. The ulcer was in close proximity to the tracheostomy tube. In order to avoid such unexpected complications, we should observe the contact site between the tracheal mucosa and the tracheal tube in chronic tracheostomy patients.

Motor neuron disease in transgenic mice with an H46R mutant SOD1 gene

Human familial amyotrophic lateral sclerosis with an H46R mutant Cu/Zn superoxide dismutase (SOD1) gene is characterized by initial muscle weakness and atrophy in the legs and a very long-term clinical course (approximately 15 years). Transgenic mice with this mutation generated in our laboratory occasionally showed aggregates in the anterior horns and axonal degeneration in all white matter sections of the spinal cord on plastic sections at the presymptomatic stages (12 and 16 weeks old), although conventional staining revealed no pathologic changes. At the symptomatic stages (20 and 24 weeks), loss of anterior horn neurons was observed. On plastic sections, aggregates were frequently seen not only in the anterior horns but also in the posterior horns and in all sections of white matter. Degenerated fibers were observed in the anterior and posterior roots as well as in white matter. Electron and immunoelectron microscopic observation revealed human SOD1- and ubiquitin-positive aggregates consisting of intermediate filaments in the anterior horn even from an early presymptomatic stage. Thus, H46R mutant SOD1 transgenic mice are characterized by widespread pathologic changes of the spinal cord that extend beyond the motor system, including many aggregates lacking vacuoles. The close pathologic similarity makes this animal model suitable for the investigation of human familial amyotrophic lateral sclerosis with the mutation.

Activation of the Nrf2-ARE pathway in muscle and spinal cord during ALS-like pathology in mice expressing mutant SOD1

Oxidative stress plays a key role in the neuronal loss exhibited in amyotrophic lateral sclerosis (ALS), an event precipitating irreversible muscle atrophy. By crossing ALS mouse models (SOD(G93A) and SOD(H46RH48Q)) with an antioxidant response element (ARE) reporter mouse, we identified activation characteristics of the ARE system throughout the timecourse of motor neuron disease. Surprisingly, the earliest and most significant activation of this genetic sensor of oxidative stress occurred in the distal muscles of mutant SOD mice. The resultant data supports existing hypotheses that the muscle is somehow implicated during the initial pathology of these mice. Subsequently, Nrf2-ARE activation appears to progress in a retrograde fashion along the motor pathway. These data provide timely information concerning the contributions of the Nrf2-ARE pathway in ALS disease progression.

Disease-associated mutations at copper ligand histidine residues of superoxide dismutase 1 diminish the binding of copper and compromise dimer stability

A subset of superoxide dismutase 1 (Cu/Zn-SOD1) mutants that cause familial amyotrophic lateral sclerosis (FALS) have heightened reactivity with (-)ONOO and H(2)O(2) in vitro. This reactivity requires a copper ion bound in the active site and is a suggested mechanism of motor neuron injury. However, we have found that transgenic mice that express SOD1-H46R/H48Q, which combines natural FALS mutations at ligands for copper and which is inactive, develop motor neuron disease. Using a direct radioactive copper incorporation assay in transfected cells and the established tools of single crystal x-ray diffraction, we now demonstrate that this variant does not stably bind copper. We find that single mutations at copper ligands, including H46R, H48Q, and a quadruple mutant H46R/H48Q/H63G/H120G, also diminish the binding of radioactive copper. Further, using native polyacrylamide gel electrophoresis and a yeast two-hybrid assay, the binding of copper was found to be related to the formation of the stable dimeric enzyme. Collectively, our data demonstrate a relationship between copper and assembly of SOD1 into stable dimers and also define disease-causing SOD1 mutants that are unlikely to robustly produce toxic radicals via copper-mediated chemistry.

Identification of a Mutation in SLC30A2 (ZnT-2) in Women with Low Milk Zinc Concentration That Results in Transient Neonatal Zinc Deficiency

Breast milk normally contains adequate zinc to meet infant requirements up to six months of age; however, transient neonatal zinc deficiency has been documented in exclusively breastfed infants of women with low milk zinc concentration. This condition is not corrected by maternal zinc supplementation, supporting the speculation that it results from an inherited genetic condition. We identified a family in which two exclusively breast-fed infants developed zinc deficiency that was associated with low milk zinc concentration in both women. Sequencing of genomic DNA detected a mis-sense mutation (Ade-->Gua) that substitutes a conserved histidine at amino acid 54 with arginine (H54R) in SLC30A2 (ZnT-2) that is present in both affected subjects and several other siblings. Gene knockdown of SLC30A2 in mammary epithelial cells reduced zinc secretion, illustrating the role of ZnT-2 in zinc secretion from this cell type. Expression of the H54R mutant in human embryonic kidney-293 cells resulted in reduced zinc secretion as a consequence of perinuclear, aggresomal accumulation, whereas co-expression of the H54R mutant and wild-type ZnT-2 did not abrogate increased zinc secretion in cells overexpressing wild-type ZnT-2 alone. Together, these data provide evidence that low milk zinc concentration in some women is a consequence of a genetic disorder resulting from a mutation in SLC30A2 and can result in neonatal zinc deficiency if unrecognized. Further studies are needed to evaluate the incidence and penetrance of this mutation in the human population.

Development of a rat model of amyotrophic lateral sclerosis expressing a human SOD1 transgene

Mutations in copper-zinc superoxide dismutase gene (SOD1) have been linked to some familial cases of ALS. We report here that rats that express a human SOD1 transgene with two different ALS-associated mutations (G93A and H46R) develop striking motor neuron degeneration and paralysis. By comparing the two transgenic rats with different SOD1 mutations, we demonstrate that the time course in these rats was similar to human SOD1-mediated familial ALS. As in the human disease and transgenic ALS mice, pathological analysis shows selective loss of motor neurons in the spinal cords of these transgenic rats. In addition, typical neuronal Lewy body-like hyaline inclusions as well as astrocytic hyaline inclusions identical to those in human familial ALS are observed in the spinal cords. The larger size of this rat model as compared with the ALS mice will facilitate studies involving manipulations of spinal fluid (implantation of intrathecal catheters for chronic therapeutic studies; CSF sampling) and spinal cord (e.g., direct administration of viral- and cell-mediated therapies).

Oxidative state in platelets and erythrocytes in aging and Alzheimer's disease

Several studies have shown involvement of peroxynitrite anion, a potent oxidative agent, in Alzheimer's disease (AD) neuropathology. Herein, we assessed in platelets and erythrocytes of AD patients, age-matched and young adults controls: thiobarbituric acid-reactive substances (TBARS) production; superoxide dismutase (SOD), nitric oxide synthase (NOS) and Na,K-ATPase activities; cyclic GMP (cGMP) content, both basal and after sodium nitroprusside (SNP) stimulation. Aging was associated with an increase in TBARS production and NOS activity, a decrease in basal cGMP content and no change in SOD and Na,K-ATPase activities. AD patients, compared to aged controls, have: increase in TBARS production and in NOS, SOD and Na,K-ATPase activities but no alteration in basal cGMP content. SNP increased cGMP platelets production in all groups. In conclusion, we demonstrated in platelets and erythrocytes a disruption in systemic modulation of oxidative stress in aging and with more intensity in AD.

Structural consequences of the familial amyotrophic lateral sclerosis SOD1 mutant His46Arg

The His46Arg (H46R) mutant of human copper-zinc superoxide dismutase (SOD1) is associated with an unusual, slowly progressing form of familial amyotrophic lateral sclerosis (FALS). Here we describe in detail the crystal structures of pathogenic H46R SOD1 in the Zn-loaded (Zn-H46R) and metal-free (apo-H46R) forms. The Zn-H46R structure demonstrates a novel zinc coordination that involves only three of the usual four liganding residues, His 63, His 80, and Asp 83 together with a water molecule. In addition, the Asp 124 "secondary bridge" between the copper- and zinc-binding sites is disrupted, and the "electrostatic loop" and "zinc loop" elements are largely disordered. The apo-H46R structure exhibits partial disorder in the electrostatic and zinc loop elements in three of the four dimers in the asymmetric unit, while the fourth has ordered loops due to crystal packing interactions. In both structures, nonnative SOD1-SOD1 interactions lead to the formation of higher-order filamentous arrays. The disordered loop elements may increase the likelihood of protein aggregation in vivo, either with other H46R molecules or with other critical cellular components. Importantly, the binding of zinc is not sufficient to prevent the formation of nonnative interactions between pathogenic H46R molecules. The increased tendency to aggregate, even in the presence of Zn, arising from the loss of the secondary bridge is consistent with the observation of an increased abundance of hyaline inclusions in spinal motor neurons and supporting cells in H46R SOD1 transgenic rats.

Familial amyotrophic lateral sclerosis with His46Arg mutation in Cu/Zn superoxide dismutase presenting characteristic clinical features and Lewy body-like hyaline inclusions

We evaluated the characteristic clinical features of one family of familial amyotrophic sclerosis (FALS) with a His46Arg mutation in the enzyme Cu/Zn superoxide dismutase (SOD1). Codon 46 encodes the binding site for copper and the His46Arg mutation may result in decreased copper binding and copper toxicity. The disease duration of this family was 17.8+/-13.2 years (mean+/-S.D.) with the age at onset being 42.9+/-4.7 years old (mean+/-S.D.). The initial sign was distal weakness of the unilateral lower limb, extending to the other lower limb. An autopsy was performed on a 62-year-old female member of the family who had the mutation. Her disease duration was 23 years, and she died of tonsillar herniation caused by metastasis of colon cancer in the cerebellum. Neuropathological findings showed marked loss of large anterior horn cells and very mild degeneration of corticospinal tracts as well as posterior columns. The number of nuclei of Clark's column was reduced. Lewy body-like hyaline inclusion bodies (LBHIs) were frequently seen in the remaining anterior horn cells. Astrocytic hyaline inclusions (Ast-HIs) were also seen. This is the first autopsy report of FALS with a His46Arg mutation presenting neuronal LBHIs and Ast-HIs. The formation of LBHIs and Ast-HIs may be dependent on the phenotype of the preferential lower motor neuron involvement in FALS with a SOD mutation and long disease duration.

Motoneuron degeneration after facial nerve avulsion is exacerbated in presymptomatic transgenic rats expressing human mutant Cu/Zn superoxide dismutase

We investigated motoneuron degeneration after proximal nerve injury in presymptomatic transgenic (tg) rats expressing human mutant Cu/Zn superoxide dismutase (SOD1). The right facial nerves of presymptomatic tg rats expressing human H46R or G93A SOD1 and their non-tg littermates were avulsed, and facial nuclei were examined at 2 weeks postoperation. Nissl-stained cell counts revealed that facial motoneuron loss after avulsion was exacerbated in H46R- and G93A-tg rats compared with their non-tg littermates. The loss of motoneurons in G93A-tg rats after avulsion was significantly greater than that in H46R-tg rats. Intense cytoplasmic immunolabeling for SOD1 in injured motoneurons after avulsion was demonstrated in H46R- and G93A-tg rats but not in their littermates. Facial axotomy did not induce significant motoneuron loss nor enhance SOD1 immunoreactivity in these tg rats and non-tg littermates at 2 weeks postoperation, although both axotomy and avulsion elicited intense immunolabeling for activating transcription factor-3, phosphorylated c-Jun, and phosphorylated heat shock protein 27 in injured motoneurons of all these animals. The present data indicate the increased vulnerability of injured motoneurons after avulsion in the presymptomatic mutant SOD1-tg rats.

MCI-186 prevents spinal cord damage and affects enzyme levels of nitric oxide synthase and Cu/Zn superoxide dismutase after transient ischemia in rabbits

OBJECTIVE

The mechanism of spinal cord injury is believed to be related to the vulnerability of spinal motor neuron cells against ischemia. We tested whether MCI-186, which is useful for treating ischemic damage in the brain, can protect against ischemic spinal cord damage.

METHODS

After induction of ischemia, MCI-186 or vehicle was injected intravenously. Cell damage was analyzed by observing the function of the lower limbs and by counting the number of motor neurons. To investigate the mechanism by which MCI-186 prevents ischemic spinal cord damage, we observed the immunoreactivity of Cu/Zn superoxide dismutase, neuronal nitric oxide synthase, and endothelial nitric oxide synthase.

RESULTS

MCI-186 eased the functional deficits and increased the number of motor neurons after ischemia. The induction of neuronal nitric oxide synthase was significantly reduced by the treatment with MCI-186. Furthermore, the increase in the induction of endothelial nitric oxide synthase and Cu/Zn superoxide dismutase was more pronounced.

CONCLUSION

These results indicate that MCI-186 may protect motor neurons from ischemic injury by reducing neuronal nitric oxide synthase and increasing endothelial nitric oxide synthase. MCI-186 may be a strong candidate for use as a therapeutic agent in the treatment of ischemic spinal cord injury.

Clinical features and neuropathological findings of familial amyotrophic lateral sclerosis with a His46Arg mutation in Cu/Zn superoxide dismutase

We examined the characteristic clinical features of one family of familial amyotrophic lateral sclerosis (FALS) with a His46Arg mutation in the enzyme Cu/Zn superoxide dismutase-1 (SOD1). The disease duration for this family was 18.1 +/- 13.2 (mean +/- S.D.) years, with the age at onset being 39.7 +/- 10.5 years old (mean +/- S.D.). The initial sign was distal weakness of the unilateral lower limb, extending to the lower limb of the other side. A wheel chair became necessary at 9.8 +/- 3.2 years after the onset. Upper limb weakness started at 15.5 +/- 8.9 years following from the onset. An autopsy was performed on a 71-year-old woman of the family with the mutation. Her disease duration was 47 years, and she died of pneumonia. She had no clear upper motor neuron involvement. Bulbar sign and respiratory muscle weakness had developed 2 years before her death. Neuropathological findings showed degeneration of corticospinal tracts, anterior/posterior spinocerebellar tracts, posterior columns, and Clarke's columns. There were few anterior horn cells in the lumbar spinal cord and no Lewy body-like hyaline inclusion bodies in these remaining anterior horn neurons. This is the first autopsy report of FALS with a His46Arg mutation in the SOD1 enzyme.

The solution structure of reduced dimeric copper zinc superoxide dismutase. The structural effects of dimerization

The solution structure of homodimeric Cu2Zn2 superoxide dismutase (SOD) of 306 aminoacids was determined on a 13C, 15N and 70% 2H labeled sample. Two-thousand eight-hundred and five meaningful NOEs were used, of which 96 intersubunit, and 115 dihedral angles provided a family of 30 conformers with an rmsd from the average of 0.78 +/- 0.11 and 1.15 +/- 0.09 A for the backbone and heavy atoms, respectively. When the rmsd is calculated for each subunit, the values drop to 0.65 +/- 0.09 and 1.08 +/- 0.11 A for the backbone and heavy atoms, respectively. The two subunits are identical on the NMR time scale, at variance with the X-ray structures that show structural differences between the two subunits as well as between different molecules in the unit cell. The elements of secondary structure, i.e. eight beta sheets, are the same as in the X-ray structures and are well defined. The odd loops (I, III and V) are well resolved as well as loop II located at the subunit interface. On the contrary, loops IV and VI show some disorder. The residues of the active cavity are well defined whereas within the various subunits of the X-ray structure some are disordered or display different orientation in different X-ray structure determinations. The copper(I) ion and its ligands are well defined. This structure thus represents a well defined model in solution relevant for structure-function analysis of the protein. The comparison between the solution structure of monomeric mutants and the present structure shows that the subunit-subunit interactions increase the order in loop II. This has the consequences of inducing the structural and dynamic properties that are optimal for the enzymatic function of the wild-type enzyme. The regions 37-43 and 89-95, constituting loops III and V and the initial part of the beta barrel and showing several mutations in familial amyotrophis lateral sclerosis (FALS)-related proteins have a quite extensive network of H-bonds that may account for their low mobility. Finally, the conformation of the key Arg143 residue is compared to that in the other dimeric and monomeric structures as well as in the recently reported structure of the CCS-superoxide dismutase (SOD) complex.

Rats expressing human cytosolic copper-zinc superoxide dismutase transgenes with amyotrophic lateral sclerosis: associated mutations develop motor neuron disease

Some cases of familial amyotrophic lateral sclerosis (ALS) are caused by mutations in the gene encoding cytosolic, copper-zinc superoxide dismutase (SOD1). We report here that rats that express a human SOD1 transgene with two different ALS-associated mutations (G93A and H46R) develop striking motor neuron degeneration and paralysis. As in the human disease and transgenic ALS mice, pathological analysis demonstrates selective loss of motor neurons in the spinal cords of these transgenic rats. In spinal cord tissues, this is accompanied by activation of apoptotic genes known to be activated by mutant SOD1 protein in vitro and in vivo. These animals provide additional support for the proposition that motor neuron death in SOD1-related ALS reflects one or more acquired, neurotoxic properties of the mutant SOD1 protein. The larger size of this rat model as compared with the ALS mice will facilitate studies involving manipulations of spinal fluid (implantation of intrathecal catheters for chronic therapeutic studies; CSF sampling) and spinal cord (e.g., direct administration of viral- and cell-mediated therapies).

Marked reduction of the Cu/Zn superoxide dismutase polypeptide in a case of familial amyotrophic lateral sclerosis with the homozygous mutation

We identified a missense mutation of the Cu/Zn superoxide dismutase (SOD) gene (Leu126Ser) in a Japanese family with ALS that included a patient with the homozygous mutation. The content of the Cu/Zn SOD polypeptide in erythrocytes was markedly reduced in the case with the homozygous mutation compared to those with the heterozygous mutation. We speculated that this reduction of the mutant Cu/Zn SOD molecule might be related to the severe clinical phenotype of the case.

Copper(2+) binding to the surface residue cysteine 111 of His46Arg human copper-zinc superoxide dismutase, a familial amyotrophic lateral sclerosis mutant

Mutations in copper-zinc superoxide dismutase (CuZnSOD) cause 25% of familial amyotrophic lateral sclerosis (FALS) cases. This paper examines one such mutant, H46R, which has no superoxide dismutase activity yet presumably retains the gain-of-function activity that leads to disease. We demonstrate that Cu(2+) does not bind to the copper-specific catalytic site of H46R CuZnSOD and that Cu(2+) competes with other metals for the zinc binding site. Most importantly, Cu(2+) was found to bind strongly to a surface residue near the dimer interface of H46R CuZnSOD. Cysteine was identified as the new binding site on the basis of multiple criteria including UV-vis spectroscopy, RR spectroscopy, and chemical derivatization. Cysteine 111 was pinpointed as the position of the reactive ligand by tryptic digestion of the modified protein and by mutational analysis. This solvent-exposed residue may play a role in the toxicity of this and other FALS CuZnSOD mutations. Furthermore, we propose that the two cysteine 111 residues, found on opposing subunits of the same dimeric enzyme, may provide a docking location for initial metal insertion during biosynthesis of wild-type CuZnSOD in vivo.

Variation in the biochemical/biophysical properties of mutant superoxide dismutase 1 enzymes and the rate of disease progression in familial amyotrophic lateral sclerosis kindreds

Mutations in superoxide dismutase 1 (SOD1) polypeptides cause a form of familial amyotrophic lateral sclerosis (FALS). In different kindreds, harboring different mutations, the duration of illness tends to be similar for a given mutation. For example, patients inheriting a substitution of valine for alanine at position four (A4V) average a 1.5 year life expectancy after the onset of symptoms, whereas patients harboring a substitution of arginine for histidine at position 46 (H46R) average an 18 year life expectancy after disease onset. Here, we examine a number of biochemical and biophysical properties of nine different FALS variants of SOD1 polypeptides, including enzymatic activity (which relates indirectly to the affinity of the enzyme for copper), polypeptide half-life, resistance to proteolytic degradation and solubility, in an effort to determine whether a specific property of these enzymes correlates with clinical progression. We find that although all the mutants tested appear to be soluble, the different mutants show a remarkable degree of variation with respect to activity, polypeptide half-life and resistance to proteolysis. However, these variables do not stratify in a manner that correlates with clinical progression. We conclude that the basis for the different life expectancies of patients in different kindreds of sod1-linked FALS may result from an as yet unidentified property of these mutant enzymes.

Selective impairment of fast anterograde axonal transport in the peripheral nerves of asymptomatic transgenic mice with a G93A mutant SOD1 gene

Transgenic mice that express a mutant Cu/Zn superoxide dismutase (SOD1) gene have been provided a valuable model for human amyotrophic lateral sclerosis (ALS). We studied a possible impairment of fast axonal transport in transgenic mice carrying a Gly93-->Ala (G93A) mutant SOD1 gene found in human familial ALS (FALS). Left sciatic nerve was ligated for 6 h in transgenic (Tg) and age-matched wild-type (WT) mice. Immunohistochemical analyses were performed for accumulations of kinesin and cytoplasmic dynein on both sides of the ligation site. Clinical function and histology in the spinal cords, sciatic nerves and gastrocnemius muscles were also assessed. The mice were examined at an early asymptomatic stage (aged 19 weeks) and a late stage (30 weeks) just before the development of the symptoms. WT mice showed an apparent increase in immunoreactivities for kinesin and cytoplasmic dynein at proximal and distal of the ligation, respectively. In contrast, the young Tg mice showed a selective decrease of kinesin accumulation in the proximal of the ligation. The mice were asymptomatic with a mild histological change only in muscles. The old Tg mice showed a marked reduction of the immunoreactivity for kinesin and cytoplasmic dynein on both sides of the ligation. They had a significant loss of spinal motor neurons, relatively small myelinated fiber densities of sciatic nerves, and severe muscular changes. These results provide direct evidence that the SOD1 mutation leads to impaired fast axonal transport, particularly in the anterograde direction at an early, asymptomatic stage preceding loss of spinal motor neurons and peripheral axons. This impairment may contribute to subsequent selective motor neuron death in the present model implicated for human FALS.

Molecular analyses of the Cu/Zn superoxide dismutase gene in patients with familial amyotrophic lateral sclerosis (ALS) in Japan

1. Amyotrophic lateral sclerosis (ALS) is a degenerative disorder characterized by selective damage to the neural system that mediates voluntary movement. Although the pathophysiologic process of ALS remains unknown, about 5 to 10% of cases are familial. According to genetic linkage studies, the familial ALS (FALS) gene has been mapped on chromosome 21 in some families and recent work identified some different missense mutations in the Cu/Zn superoxide dismutase gene in FALS families. 2. We recently identified five mutations in six FALS families. The mutations identified in our FALS families are H46R, L84V, I104F, S134N, and V148I. The H46R mutation that locates in the active site of Cu/Zn SOD gene is associated with two Japanese families with very slow progression of ALS. On the other hand, the L84V mutation associated with a rapidly progressive loss of motor function with predominant lower motor neuron manifestations. 3. In the family with the V148I, the phenotype of the patient varied very much among the affected members. One case had weakness of the lower extremities at first and died without bulbar paresis. The second case first noticed wasting of the upper limbs with bulbar symptoms, but the third had weakness of upper extremities without developing dysarthria nor dysphagia until death. These mutations account for 50% of all FALS families screened, although Cu/Zn SOD gene mutations are responsible for less than about 13-21% in the Western population. 4. Our results indicate that the progression of disease with mutations of Cu/Zn SOD is well correlated with each mutation. The exact mechanism by which the abnormal Cu/Zn SOD molecules selectively affect the function of motor neurons is still unknown.