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

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.

Superoxide dismutase: a key target for the neuroprotective effects of curcumin

Over the past few years, the prevalence of neurodegenerative diseases (NDD) has increased dramatically. The community health system is burdened by the high healthcare costs associated with NDD. Superoxide dismutase (SOD) is a type of metalloenzyme that possesses a distinct characteristic of protecting the body from oxidative stress through antioxidants. In this way, SOD supplementation may activate the endogenous antioxidant mechanism in various pathological conditions and could be used to neutralize free radical excess. Several factors are responsible for damaging DNA and RNA in the body, including the overproduction of reactive species, particularly reactive oxygen species (ROS) and reactive nitrogen species (RNS). Excessive ROS/RNS have deleterious effects on mitochondria and their metabolic processes, mainly through increased mitochondrial proteins, lipids and DNA oxidation. Studies have shown that oxidative stress is implicated in the etiology of many diseases, including NDD. It is thought that anti-inflammatory compounds, particularly phytochemicals, can interfere with these pathways and regulate inflammation. Extensive experimental and clinical research has proven that curcumin (Cur) has anti-inflammatory and anti-neurologic properties. In this review, we have compiled the available data on Cur's anti-inflammatory properties, paying special attention to its therapeutic impact on NDD through SOD.

Intracellular spatially-targeted chemical chaperones increase native state stability of mutant SOD1 barrel

Amyotrophic lateral sclerosis (ALS) is a progressive neurological disorder with currently no cure. Central to the cellular dysfunction associated with this fatal proteinopathy is the accumulation of unfolded/misfolded superoxide dismutase 1 (SOD1) in various subcellular locations. The molecular mechanism driving the formation of SOD1 aggregates is not fully understood but numerous studies suggest that aberrant aggregation escalates with folding instability of mutant apoSOD1. Recent advances on combining organelle-targeting therapies with the anti-aggregation capacity of chemical chaperones have successfully reduce the subcellular load of misfolded/aggregated SOD1 as well as their downstream anomalous cellular processes at low concentrations (micromolar range). Nevertheless, if such local aggregate reduction directly correlates with increased folding stability remains to be explored. To fill this gap, we synthesized and tested here the effect of 9 ER-, mitochondria- and lysosome-targeted chemical chaperones on the folding stability of truncated monomeric SOD1 (SOD1bar) mutants directed to those organelles. We found that compound ER-15 specifically increased the native state stability of ER-SOD1bar-A4V, while scaffold compound FDA-approved 4-phenylbutyric acid (PBA) decreased it. Furthermore, our results suggested that ER15 mechanism of action is distinct from that of PBA, opening new therapeutic perspectives of this novel chemical chaperone on ALS treatment.

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.

Tryptophan residue 32 in human Cu-Zn superoxide dismutase modulates prion-like propagation and strain selection

Mutations in Cu/Zn superoxide dismutase 1 (SOD1) associated with familial amyotrophic lateral sclerosis cause the protein to aggregate via a prion-like process in which soluble molecules are recruited to aggregates by conformational templating. These misfolded SOD1 proteins can propagate aggregation-inducing conformations across cellular membranes. Prior studies demonstrated that mutation of a Trp (W) residue at position 32 to Ser (S) suppresses the propagation of misfolded conformations between cells, whereas other studies have shown that mutation of Trp 32 to Phe (F), or Cys 111 to Ser, can act in cis to attenuate aggregation of mutant SOD1. By expressing mutant SOD1 fused with yellow fluorescent protein (YFP), we compared the relative ability of these mutations to modulate the formation of inclusions by ALS-mutant SOD1 (G93A and G85R). Only mutation of Trp 32 to Ser persistently reduced the formation of the amorphous inclusions that form in these cells, consistent with the idea that a Ser at position 32 inhibits templated propagation of aggregation prone conformations. To further test this idea, we produced aggregated fibrils of recombinant SOD1-W32S in vitro and injected them into the spinal cords of newborn mice expressing G85R-SOD1: YFP. The injected mice developed an earlier onset paralysis with a frequency similar to mice injected with WT SOD1 fibrils, generating a strain of misfolded SOD1 that produced highly fibrillar inclusion pathology. These findings suggest that the effect of Trp 32 in modulating the propagation of misfolded SOD1 conformations may be dependent upon the “strain” of the conformer that is propagating.

AAV2/9-mediated overexpression of MIF inhibits SOD1 misfolding, delays disease onset, and extends survival in mouse models of ALS

Mutations in superoxide dismutase (SOD1) cause amyotrophic lateral sclerosis (ALS), a neurodegenerative disease characterized by the loss of upper and lower motor neurons. Transgenic mice that overexpress mutant SOD1 develop paralysis and accumulate misfolded SOD1 onto the cytoplasmic faces of intracellular organelles, including mitochondria and endoplasmic reticulum (ER). Recently, macrophage migration inhibitory factor (MIF) was shown to directly inhibit mutant SOD1 misfolding and binding to intracellular membranes. In addition, complete elimination of endogenous MIF accelerated disease onset and late disease progression, as well as shortened the lifespan of mutant SOD1 mice with higher amounts of misfolded SOD1 detected within the spinal cord. Based on these findings, we used adeno-associated viral (AAV) vectors to overexpress MIF in the spinal cord of mutant SOD1^G93A and loxSOD1^G37R mice. Our data show that MIF mRNA and protein levels were increased in the spinal cords of AAV2/9-MIF-injected mice. Furthermore, mutant SOD1^G93A and loxSOD1^G37R mice injected with AAV2/9-MIF demonstrated a significant delay in disease onset and prolonged survival compared with their AAV2/9-GFP-injected or noninjected littermates. Moreover, these mice accumulated reduced amounts of misfolded SOD1 in their spinal cords, with no observed effect on glial overactivation as a result of MIF up-regulation. Our findings indicate that MIF plays a significant role in SOD1 folding and misfolding mechanisms and strengthen the hypothesis that MIF acts as a chaperone for misfolded SOD1 in vivo and may have further implications regarding the therapeutic potential role of up-regulation of MIF in modulating the specific accumulation of misfolded SOD1.

Experimental Mutations in Superoxide Dismutase 1 Provide Insight into Potential Mechanisms Involved in Aberrant Aggregation in Familial Amyotrophic Lateral Sclerosis

Mutations in more than 80 different positions in superoxide dismutase 1 (SOD1) have been associated with amyotrophic lateral sclerosis (fALS). There is substantial evidence that a common consequence of these mutations is to induce the protein to misfold and aggregate. How these mutations perturb native structure to heighten the propensity to misfold and aggregate is unclear. In the present study, we have mutagenized Glu residues at positions 40 and 133 that are involved in stabilizing the β-barrel structure of the native protein and a critical Zn binding domain, respectively, to examine how specific mutations may cause SOD1 misfolding and aggregation. Mutations associated with ALS as well as experimental mutations were introduced into these positions. We used an assay in which mutant SOD1 was fused to yellow fluorescent protein (SOD1:YFP) to visualize the formation of cytosolic inclusions by mutant SOD1. We then used existing structural data on SOD1, to predict how different mutations might alter local 3D conformation. Our findings reveal an association between mutant SOD1 aggregation and amino acid substitutions that are predicted to introduce steric strain, sometimes subtly, in the 3D conformation of the peptide backbone.

Atypical Familial Amyotrophic Lateral Sclerosis with Slowly Progressing Lower Extremities-predominant Late-onset Muscular Weakness and Atrophy

Objective Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disease characterized by the progressive loss of the upper and lower motor neurons that progresses to paralysis of almost all skeletal muscles of the extremities, bulbar, and respiratory system. Although most ALS cases are sporadic, about 10% are dominantly inherited. We herein report an atypical phenotype of familial ALS (fALS). To elucidate the phenotype-genotype correlation of this atypical phenotype of fALS, clinical and genetic investigations were performed. Methods and Patients Five sibling patients (three men, two women) from a Japanese family and one healthy sibling (a woman) were clinically interviewed and examined. Genetic analyses, including genome-wide linkage analyses and whole-exome sequencing, were performed using genomic DNA extracted from the peripheral blood samples of these siblings. Results The clinical features of fALS are characterized by slow progression (mean duration of the disease±standard deviation [SD]: 19.6±3.9 years) and lower extremities-predominant late-onset muscular weakness (mean onset of muscular weakness±SD: 52.8±2.6 years). Genetic analyses revealed novel heterozygous missense mutations of c.2668C>T, p.R890C in the PLEC gene and c.421G>C, p.V141L in the ST3GAL6 gene in all affected siblings. Conclusion A new atypical fALS family with a benign clinical course is herein reported. We identified two candidate gene mutations of PLEC and ST3GAL6 linked to this phenotype.

Loss of charge mutations in solvent exposed Lys residues of superoxide dismutase 1 do not induce inclusion formation in cultured cell models

Mutations in superoxide dismutase 1 (SOD1) associated with familial amyotrophic lateral sclerosis (fALS) induce the protein to misfold and aggregate. Missense mutations at more than 80 different amino acid positions have been associated with disease. How these mutations heighten the propensity of SOD1 to misfold and aggregate is unclear. With so many mutations, it is possible that more than one mechanism of aggregation may be involved. Of many possible mechanisms to explain heightened aggregation, one that has been suggested is that mutations that eliminate charged amino acids could diminish repulsive forces that would inhibit aberrant protein:protein interactions. Mutations at twenty-one charged residues in SOD1 have been associated with fALS, but of the 11 Lys residues in the protein, only 1 has been identified as mutated in ALS patients. Here, we examined whether loss of positively charged surface Lys residues in SOD1 would induce misfolding and formation of intracellular inclusions. We mutated four different Lys residues (K30, K36, K75, K91) in SOD1 that are not particularly well conserved, and expressed these variants as fusion proteins with yellow fluorescent protein (YFP) to assess inclusion formation. We also assessed whether these mutations induced binding to a conformation-restricted SOD1 antibody, designated C4F6, which recognizes non-natively folded protein. Although we observed some mutations to cause enhanced C4F6 binding, we did not observe that mutations that reduce charge at these positions caused the protein to form intracellular inclusions. Our findings may have implications for the low frequency of mutations at Lys residues SOD1 in ALS patients.

A copper-deficient form of mutant Cu/Zn-superoxide dismutase as an early pathological species in amyotrophic lateral sclerosis

Dominant mutations in the gene encoding copper and zinc-binding superoxide dismutase (SOD1) cause amyotrophic lateral sclerosis (ALS). Abnormal accumulation of misfolded SOD1 proteins in spinal motoneurons is a major pathological hallmark in SOD1-related ALS. Dissociation of copper and/or zinc ions from SOD1 has been shown to trigger the protein aggregation/oligomerization in vitro, but the pathological contribution of such metal dissociation to the SOD1 misfolding still remains obscure. Here, we tested the relevance of the metal-deficient SOD1 in the misfolding in vivo by developing a novel antibody (anti-apoSOD), which exclusively recognized mutant SOD1 deficient in metal ions at its copper-binding site. Notably, anti-apoSOD-reactive species were detected specifically in the spinal cords of the ALS model mice only at their early pre-symptomatic stages but not at the end stage of the disease. The cerebrospinal fluid as well as the spinal cord homogenate of one SOD1-ALS patient also contained the anti-apoSOD-reactive species. Our results thus suggest that metal-deficiency in mutant SOD1 at its copper-binding site is one of the earliest pathological features in SOD1-ALS.

MIF inhibits the formation and toxicity of misfolded SOD1 amyloid aggregates: implications for familial ALS

Mutations in superoxide dismutase (SOD1) cause amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease caused by the progressive loss of motor neurons in the brain and spinal cord. It has been suggested that toxicity of mutant SOD1 results from its misfolding, however, it is yet unclear why misfolded SOD1 accumulates specifically within motor neurons. We recently demonstrated that macrophage migration inhibitory factor (MIF)-a multifunctional protein with cytokine/chemokine activity and cytosolic chaperone-like properties-inhibits the accumulation of misfolded SOD1. Here, we show that MIF inhibits mutant SOD1 nuclear clearance when overexpressed in motor neuron-like NSC-34 cells. In addition, MIF alters the typical SOD1 amyloid aggregation pathway in vitro, and, instead, promotes the formation of disordered aggregates, as measured by Thioflavin T (ThT) assay and transmission electron microscopy (TEM) imaging. Moreover, we report that MIF reduces the toxicity of misfolded SOD1 by directly interacting with it, and that the chaperone function and protective effect of MIF in neuronal cultures do not require its intrinsic catalytic activities. Importantly, we report that the locked-trimeric MIF^N110C mutant, which exhibits strongly impaired CD74-mediated cytokine functions, has strong chaperone activity, dissociating, for the first time, these two cellular functions. Altogether, our study implicates MIF as a potential therapeutic candidate in the treatment of ALS.

Modulating the Effects of the Bacterial Chaperonin GroEL on Fibrillogenic Polypeptides through Modification of Domain Hinge Architecture

The isolated apical domain of the Escherichia coli GroEL subunit displays the ability to suppress the irreversible fibrillation of numerous amyloid-forming polypeptides. In previous experiments, we have shown that mutating Gly-192 (located at hinge II that connects the apical domain and the intermediate domain) to a tryptophan results in an inactive chaperonin whose apical domain is disoriented. In this study, we have utilized this disruptive effect of Gly-192 mutation to our advantage, by substituting this residue with amino acid residues of varying van der Waals volumes with the intent to modulate the affinity of GroEL toward fibrillogenic peptides. The affinities of GroEL toward fibrillogenic polypeptides such as Aβ(1-40) (amyloid-β(1-40)) peptide and α-synuclein increased in accordance to the larger van der Waals volume of the substituent amino acid side chain in the G192X mutants. When we compared the effects of wild-type GroEL and selected GroEL G192X mutants on α-synuclein fibril formation, we found that the effects of the chaperonin on α-synuclein fibrillation were different; the wild-type chaperonin caused changes in both the initial lag phase and the rate of fibril extension, whereas the effects of the G192X mutants were more specific toward the nucleus-forming lag phase. The chaperonins also displayed differential effects on α-synuclein fibril morphology, suggesting that through mutation of Gly-192, we may induce changes to the intermolecular affinities between GroEL and α-synuclein, leading to more efficient fibril suppression, and in specific cases, modulation of fibril morphology.

Suppression of amyloid fibrils using the GroEL apical domain

In E. coli cells, rescue of non-native proteins and promotion of native state structure is assisted by the chaperonin GroEL. An important key to this activity lies in the structure of the apical domain of GroEL (GroEL-AD) (residue 191–376), which recognizes and binds non-native protein molecules through hydrophobic interactions. In this study, we investigated the effects of GroEL-AD on the aggregation of various client proteins (α-Synuclein, Aβ42, and GroES) that lead to the formation of distinct protein fibrils in vitro. We found that GroEL-AD effectively inhibited the fibril formation of these three proteins when added at concentrations above a critical threshold; the specific ratio differed for each client protein, reflecting the relative affinities. The effect of GroEL-AD in all three cases was to decrease the concentration of aggregate-forming unfolded client protein or its early intermediates in solution, thereby preventing aggregation and fibrillation. Binding affinity assays revealed some differences in the binding mechanisms of GroEL-AD toward each client. Our findings suggest a possible applicability of this minimal functioning derivative of the chaperonins (the “minichaperones”) as protein fibrillation modulators and detectors.

Familial amyotrophic lateral sclerosis with an I104F mutation in the SOD1 gene: Multisystem degeneration with neurofilamentous aggregates and SOD1 inclusions

We previously reported familial amyotrophic lateral sclerosis (FALS) of 11 years duration in a 57-year-old woman, who received artificial ventilation for 5 years prior to death and exhibited widespread multisystem degeneration and neurofilamentous aggregates, so-called conglomerate inclusions (CIs). In the present study, we re-evaluated this autopsied patient (proband) with further immunohistochemical observation as well as mutational analysis of the superoxide dismutase 1 (SOD1) gene. A review of the clinical features of the proband's family revealed five affected members (including the proband) over two successive generations who showed marked variability in clinical presentation, such as the age at onset. The proband was found to harbor a heterozygous missense mutation in exon 4 (I104F) of the SOD1 gene. In the brain and spinal cord, SOD1-positive neuronal cytoplasmic inclusions (NCIs) were found to be more widely distributed than CIs, the latter being weakly positive for SOD1. No Lewy body-like hyaline inclusions were found. This is considered to be the first description of an autopsy case of FALS with an I104F SOD1 gene mutation, suggesting that combination of marked intra-familial clinical variability and multisystem degeneration with occurrence of CIs and SOD1-positive NCIs is a characteristic feature of FALS with this SOD1 gene mutation.

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.

Curcumin binds to the pre-fibrillar aggregates of Cu/Zn superoxide dismutase (SOD1) and alters its amyloidogenic pathway resulting in reduced cytotoxicity

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease that affects motor neurons. Unfortunately, effective therapeutics against this disease is still not available. Almost 20% of familial ALS (fALS) is suggested to be associated with pathological deposition of superoxide dismutase (SOD1). Evidences suggest that SOD1-containing pathological inclusions in ALS exhibit amyloid like properties. An effective strategy to combat ALS may be to inhibit amyloid formation of SOD1 using small molecules. In the present study, we observed the fibrillation of one of the premature forms of SOD1 (SOD1 with reduced disulfide) in the presence of curcumin. Using ThT binding assay, AFM, TEM images and FTIR, we demonstrate that curcumin inhibits the DTT-induced fibrillation of SOD1 and favors the formation of smaller and disordered aggregates of SOD1. The enhancement in curcumin fluorescence on the addition of oligomers and pre-fibrillar aggregates of SOD1 suggests binding of these species to curcumin. Docking studies indicate that putative binding site of curcumin may be the amyloidogenic regions of SOD1. Further, there is a significant increase in SOD1 mediated toxicity in the regime of pre-fibrillar and fibrillar aggregates which is not evident in curcumin containing samples. All these data suggest that curcumin reduces toxicity by binding to the amyloidogenic regions of the species on the aggregation pathway and blocking the formation of the toxic species. Nanoparticles of curcumin with higher aqueous solubility show similar aggregation control as that of curcumin bulk. This suggests a potential role for curcumin in the treatment of ALS.

Aggregation-triggering segments of SOD1 fibril formation support a common pathway for familial and sporadic ALS

ALS is a terminal disease of motor neurons that is characterized by accumulation of proteinaceous deposits in affected cells. Pathological deposition of mutated Cu/Zn superoxide dismutase (SOD1) accounts for ∼20% of the familial ALS (fALS) cases. However, understanding the molecular link between mutation and disease has been difficult, given that more than 140 different SOD1 mutants have been observed in fALS patients. In addition, the molecular origin of sporadic ALS (sALS) is unclear. By dissecting the amino acid sequence of SOD1, we identified four short segments with a high propensity for amyloid fibril formation. We find that fALS mutations in these segments do not reduce their propensity to form fibrils. The atomic structures of two fibril-forming segments from the C terminus, (101)DSVISLS(107) and (147)GVIGIAQ(153), reveal tightly packed β-sheets with steric zipper interfaces characteristic of the amyloid state. Based on these structures, we conclude that both C-terminal segments are likely to form aggregates if available for interaction. Proline substitutions in (101)DSVISLS(107) and (147)GVIGIAQ(153) impaired nucleation and fibril growth of full-length protein, confirming that these segments participate in aggregate formation. Our hypothesis is that improper protein maturation and incompletely folded states that render these aggregation-prone segments available for interaction offer a common molecular pathway for sALS and fALS.

Distinctive clinicopathological features of 2 large families with amyotrophic lateral sclerosis having L106V mutation in SOD1 gene

A clinicopathological study of 2 families with familial amyotrophic lateral sclerosis was previously reported [1]. The present study continues to investigate these families, with detailed clinical, genetic, and neuropathological studies performed on 24 patients, including 5 autopsy cases of the families. A point mutation at codon 106 (L106V) in the copper/zinc superoxide dismutase-1 (SOD1) gene was identified in the families. Average age at onset was 52.0 ± 9.4 years, and initial symptoms were weakness and atrophy in the distal muscles of the lower extremities in most patients. Half of the patients showed neurogenic bladder (overactive bladder) and sensory impairment. The neurophysiological study showed peripheral/central conduction delay. Neuropathological examination revealed severe motor neuron loss with many bizarre reactive astrocytes in the spinal anterior horn. SOD1-immunopositive Lewy body-like hyaline inclusions and aggregation of neurofilaments were observed in the surviving anterior horn cells. Degeneration of the corticospinal tract was relatively minor. In addition, slight but diffuse gliosis was identified in the hypothalamus and medial nucleus of thalamus. Neurogenic bladder, sensory impairment, and degeneration of the hypothalamus and thalamus might be specific features in patients with familial amyotrophic lateral sclerosis with L106V mutation in the SOD1 gene.

Exposure of hydrophobic surfaces initiates aggregation of diverse ALS-causing superoxide dismutase-1 mutants

The copper-zinc superoxide dismutase-1 (SOD1) is a highly structured protein and, a priori, one of the least likely proteins to be involved in a misfolding disease. However, more than 140, mostly missense, mutations in the SOD1 gene cause aggregation of the affected protein in familial forms of amyotrophic lateral sclerosis (ALS). The remarkable diversity of the effects of these mutations on SOD1 properties has suggested that they promote aggregation by a variety of mechanisms. Experimental assessment of surface hydrophobicity using a sensitive fluorescent-based assay, revealed that diverse ALS-causing mutations provoke SOD1 aggregation by increasing their propensity to expose hydrophobic surfaces. These findings could not be anticipated from analysis of the amino acid sequence. Our results uncover the biochemical nature of the misfolded aggregation-prone intermediate and reconcile the seemingly diverse effects of ALS-causing mutations into a unifying mechanism. Furthermore, the method we describe here will be useful for investigating and interfering with aggregation of various proteins and thereby provide insight into the molecular mechanisms underlying many neurodegenerative diseases.

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.

Immature copper-zinc superoxide dismutase and familial amyotrophic lateral sclerosis

Mutations in human copper-zinc superoxide dismutase (SOD1) cause an inherited form of amyotrophic lateral sclerosis (ALS, Lou Gehrig's disease, motor neuron disease). Insoluble forms of mutant SOD1 accumulate in neural tissues of human ALS patients and in spinal cords of transgenic mice expressing these polypeptides, suggesting that SOD1-linked ALS is a protein misfolding disorder. Understanding the molecular basis for how the pathogenic mutations give rise to SOD1 folding intermediates, which may themselves be toxic, is therefore of keen interest. A critical step on the SOD1 folding pathway occurs when the copper chaperone for SOD1 (CCS) modifies the nascent SOD1 polypeptide by inserting the catalytic copper cofactor and oxidizing its intrasubunit disulfide bond. Recent studies reveal that pathogenic SOD1 proteins coming from cultured cells and from the spinal cords of transgenic mice tend to be metal-deficient and/or lacking the disulfide bond, raising the possibility that the disease-causing mutations may enhance levels of SOD1-folding intermediates by preventing or hindering CCS-mediated SOD1 maturation. This mini-review explores this hypothesis by highlighting the structural and biophysical properties of the pathogenic SOD1 mutants in the context of what is currently known about CCS structure and action. Other hypotheses as to the nature of toxicity inherent in pathogenic SOD1 proteins are not covered.

Structural and dynamic aspects related to oligomerization of apo SOD1 and its mutants

The structural and dynamical properties of the metal-free form of WT human superoxide dismutase 1 (SOD1) and its familial amyotrophic lateral sclerosis (fALS)-related mutants, T54R and I113T, were characterized both in solution, through NMR, and in the crystal, through X-ray diffraction. We found that all 3 X-ray structures show significant structural disorder in 2 loop regions that are, at variance, well defined in the fully-metalated structures. Interestingly, the apo state crystallizes only at low temperatures, whereas all 3 proteins in the metalated form crystallize at any temperature, suggesting that crystallization selects one of the most stable conformations among the manifold adopted by the apo form in solution. Indeed, NMR experiments show that the protein in solution is highly disordered, sampling a large range of conformations. The large conformational variability of the apo state allows the free reduced cysteine Cys-6 to become highly solvent accessible in solution, whereas it is essentially buried in the metalated state and the crystal structures. Such solvent accessibility, together with that of Cys-111, accounts for the tendency to oligomerization of the metal-free state. The present results suggest that the investigation of the solution state coupled with that of the crystal state can provide major insights into SOD1 pathway toward oligomerization in relation to fALS.

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.

Protein aggregation and protein instability govern familial amyotrophic lateral sclerosis patient survival

The nature of the "toxic gain of function" that results from amyotrophic lateral sclerosis (ALS)-, Parkinson-, and Alzheimer-related mutations is a matter of debate. As a result no adequate model of any neurodegenerative disease etiology exists. We demonstrate that two synergistic properties, namely, increased protein aggregation propensity (increased likelihood that an unfolded protein will aggregate) and decreased protein stability (increased likelihood that a protein will unfold), are central to ALS etiology. Taken together these properties account for 69% of the variability in mutant Cu/Zn-superoxide-dismutase-linked familial ALS patient survival times. Aggregation is a concentration-dependent process, and spinal cord motor neurons have higher concentrations of Cu/Zn-superoxide dismutase than the surrounding cells. Protein aggregation therefore is expected to contribute to the selective vulnerability of motor neurons in familial ALS.

Interaction of amyotrophic lateral sclerosis (ALS)-related mutant copper-zinc superoxide dismutase with the dynein-dynactin complex contributes to inclusion formation

An important consequence of protein misfolding related to neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), is the formation of proteinaceous inclusions or aggregates within the central nervous system. We have previously shown that several familial ALS-linked copper-zinc superoxide dismutase (SOD1) mutants (A4V, G85R, and G93A) interact and co-localize with the dynein-dynactin complex in cultured cells and affected tissues of ALS mice. In this study, we report that the interaction between mutant SOD1 and the dynein motor plays a critical role in the formation of large inclusions containing mutant SOD1. Disruption of the motor by overexpression of the p50 subunit of dynactin in neuronal and non-neuronal cell cultures abolished the association between aggregation-prone SOD1 mutants and the dynein-dynactin complex. The p50 overexpression also prevented mutant SOD1 inclusion formation and improved the survival of cells expressing A4V SOD1. Furthermore, we observed that two ALS-linked SOD1 mutants, H46R and H48Q, which showed a lower propensity to interact with the dynein motor, also produced less aggregation and fewer large inclusions. Overall, these data suggest that formation of large inclusions depends upon association of the abnormal SOD1s with the dynein motor. Whether the misfolded SOD1s directly perturb axonal transport or impair other functional properties of the dynein motor, this interaction could propagate a toxic effect that ultimately causes motor neuron death in ALS.

SOD1 and amyotrophic lateral sclerosis: mutations and oligomerization

There are about 100 single point mutations of copper, zinc superoxide dismutase 1 (SOD1) which are reported (http://alsod.iop.kcl.ac.uk/Als/index.aspx) to be related to the familial form (fALS) of amyotrophic lateral sclerosis (ALS). These mutations are spread all over the protein. It is well documented that fALS produces protein aggregates in the motor neurons of fALS patients, which have been found to be associated to mitochondria. We selected eleven SOD1 mutants, most of them reported as pathological, and characterized them investigating their propensity to aggregation using different techniques, from circular dichroism spectra to ThT-binding fluorescence, size-exclusion chromatography and light scattering spectroscopy. We show here that these eleven SOD1 mutants, only when they are in the metal-free form, undergo the same general mechanism of oligomerization as found for the WT metal-free protein. The rates of oligomerization are different but eventually they give rise to the same type of soluble oligomeric species. These oligomers are formed through oxidation of the two free cysteines of SOD1 (6 and 111) and stabilized by hydrogen bonds, between beta strands, thus forming amyloid-like structures. SOD1 enters the mitochondria as demetallated and mitochondria are loci where oxidative stress may easily occur. The soluble oligomeric species, formed by the apo form of both WT SOD1 and its mutants through an oxidative process, might represent the precursor toxic species, whose existence would also suggest a common mechanism for ALS and fALS. The mechanism here proposed for SOD1 mutant oligomerization is absolutely general and it provides a common unique picture for the behaviors of the many SOD1 mutants, of different nature and distributed all over the protein.

Amyotrophic lateral sclerosis models and human neuropathology: similarities and differences

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that primarily involves the motor neuron system. The author initially summarizes the principal features of human ALS neuropathology, and subsequently describes in detail ALS animal models mainly from the viewpoint of pathological similarities and differences. ALS animal models in this review include strains of rodents that are transgenic for superoxide dismutase 1 (SOD1), ALS2 knockout mice, and mice that are transgenic for cytoskeletal abnormalities. Although the neuropathological results obtained from human ALS autopsy cases are valuable and important, almost all of such cases represent only the terminal stage. This makes it difficult to clarify how and why ALS motor neurons are impaired at each clinical stage from disease onset to death, and as a consequence, human autopsy cases alone yield little insight into potential therapies for ALS. Although ALS animal models cannot replicate human ALS, in order to compensate for the shortcomings of studies using human ALS autopsy samples, researchers must inevitably rely on ALS animal models that can yield very important information for clarifying the pathogenesis of ALS in humans and for the establishment of reliable therapy. Of course, human ALS and all ALS animal models share one most important similarity in that both exhibit motor neuron degeneration/death. This important point of similarity has shed much light on the pathomechanisms of the motor neuron degeneration/death at the cellular and molecular levels that would not have been appreciated if only human ALS autopsy samples had been available. On the basis of the aspects covered in this review, it can be concluded that ALS animal models can yield very important information for clarifying the pathogenesis of ALS in humans and for the establishment of reliable therapy only in combination with detailed neuropathological data obtained from human ALS autopsy cases.