Oxidative stress causes abnormal accumulation of familial amyotrophic lateral sclerosis-related mutant SOD1 in transgenic Caenorhabditis elegans

Mutations in the Cu/Zn superoxide dismutase (SOD1) genes are present in approximately 20% of families suffering from familial amyotrophic lateral sclerosis (FALS). Results from several transgenic studies in which FALS-related SOD1 mutations have been expressed have suggested that mutant SOD1 proteins induce cytotoxicity through a toxic gain of function, although the specific mechanism of this has not been fully clarified. To investigate the mechanism of toxicity induced by the mutant SOD1 associated with FALS, we generated transgenic Caenorhabditis elegans strains that contain wild-type and mutant human A4V, G37R and G93A SOD1 recombinant plasmids. The transgenic strains expressing mutant human SOD1 showed greater vulnerability to oxidative stress induced by 0.2 mM paraquat than a control that contained the wild-type human SOD1. In the absence of oxidative stress, mutant human SOD1 proteins were degraded more rapidly than the wild-type human SOD1 protein in C.elegans. In the presence of oxidative stress, however, this rapid degradation was inhibited, and the transgenic C.elegans co-expressing mutant human SOD1 and green fluorescent proteins (GFPs) in muscle tissues demonstrated discrete aggregates in the adult stage. These results suggest that oxidative damage inhibits the degradation of FALS-related mutant human SOD1 proteins, resulting in an aberrant accumulation of mutant proteins that might contribute to the cytotoxicity.

Superoxide dismutase mutations of familial amyotrophic lateral sclerosis and the oxidative inactivation of calcineurin

Approximately 10% of all familial cases of amyotrophic lateral sclerosis (fALS) are linked to mutations in the SOD1 gene, which encodes the copper/zinc superoxide dismutase (CuZnSOD). Recently, wild-type CuZnSOD was shown to protect calcineurin, a calcium/calmodulin-regulated phosphoprotein phosphatase, from inactivation by reactive oxygen species. We asked whether the protective effect of CuZnSOD on calcineurin is affected by mutations associated with fALS. For this, we monitored calcineurin activity in the presence of mutant and wild-type SOD. We found that the degree of protection against inactivation of calcineurin by different SOD mutants correlates with the severity of the phenotype associated with the different mutations, suggesting a potential role for calcineurin-SOD1 interaction in the etiology of fALS.

Zinc and copper in the pathogenesis of amyotrophic lateral sclerosis

1. Missense mutations in the gene encoding Cu,Zn superoxide dismutase (SOD1) are responsible for causing one form of familial amyotrophic lateral sclerosis (FALS) linked to chromosome 21q. 2. Mutant SOD1-induced disease is clearly related to a toxic gain of function for the abnormal enzyme, and recent work has begun to investigate the mechanisms underlying this toxicity. In addition to its well known and likely beneficial dismutase activity, wild type SOD1 also possesses the ability to participate in other enzymatic reactions that may be injurious to cells including peroxidation or nitration. 3. Many of the SOD1 mutations associated with FALS appear to increase the likelihood that the enzyme will perform either one of these potentially harmful functions resulting in increased hydroxyl radical formation or the addition of nitro groups to tyrosine residues within cellular proteins.

Hydrogen peroxide damages the zinc-binding site of zinc-deficient Cu,Zn superoxide dismutase

Mutations in Cu,Zn superoxide dismutase (Cu,Zn SOD) account for approximately 20% of cases of familial amyotrophic lateral sclerosis (ALS), a late-onset neurodegenerative disease affecting motor neurons. These mutations decrease protein stability and lower zinc affinity. Zinc-deficient SOD (Cu,E SOD) has altered redox activities and is toxic to motor neurons in vitro. Using bovine SOD, we studied the effects of hydrogen peroxide (H(2)O(2)) on Cu,E SOD and Cu,Zn SOD. Hydrogen peroxide treatment of Cu,E SOD inactivated zinc binding activity six times faster than superoxide dismutase activity, whereas inactivation of dismutase activity occurred at the same rate for both Cu,Zn SOD and Cu,E SOD. Zinc binding by Cu,E SOD was also damaged by simultaneous generation of superoxide and hydrogen peroxide by xanthine oxidase plus xanthine. Although urate, xanthine, and ascorbate can protect superoxide dismutase activity of Cu,Zn SOD from inactivation, they were not effective at protecting Cu,E SOD. Hydrogen peroxide induced subtle changes in the tertiary structure but not the secondary structure of Cu,E SOD as detected by near and far UV circular dichroism. Our results suggest that low levels of hydrogen peroxide could potentially enhance the toxicity of zinc deficient SOD to motor neurons in ALS by rendering zinc loss from SOD irreversible.

Superoxide dismutase in CSF from amyotrophic lateral sclerosis patients with and without CuZn-superoxide dismutase mutations

Mutations in CuZn-superoxide dismutase (CuZn-SOD) have been linked to familial amyotrophic lateral sclerosis (ALS), and motor neurone death is caused by the gain of a toxic property of the mutant protein. Here we determined amounts, activity and molecular forms of CuZn-SOD in CSF from ALS patients carrying the D90A and other CuZn-SOD mutations and patients without such mutations. There were no differences in amount of protein and enzymic activities of CuZn-SOD between 37 neurological controls, 54 sporadic and 12 familial ALS cases, and 10 cases homozygous for the D90A mutation. Three cases heterozygous for the A89V, S105L and G114A CuZn-SOD mutations showed low amounts of CuZn-SOD. There was no evidence for accumulation of inactive protein in any of the groups. Immunoblots showed no evidence for the presence of any precipitates or other molecular forms of CuZn-SOD with higher molecular weight in the groups. About 25% of the CuZn-SOD subunits in CSF from controls shows an N-terminal truncation. This truncated portion does not differ between controls and ALS groups not carrying CuZn-SOD mutations, but is 70% larger in samples from D90A homozygous ALS patients. The findings suggest an essentially normal amount and activity of D90A mutant CuZn-SOD in CNS tissues of ALS cases. The increased occurrence of N-terminally truncated mutant subunits may indicate a difference in degradation routes compared with the wild-type enzyme, resistance against subsequent proteolytic steps and/or a compromised downstream proteolytic machinery. Molecular fragments accumulated to a greater extent from the D90A mutant enzyme might contribute to the motor neurone degeneration. We also determined the other SOD isoenzymes: in the controls, CuZn-SOD contributed 75%, extracellular SOD 25% and Mn-SOD <5% of the total SOD activity. There was no difference in the amount of extracellular SOD between any of the groups.

Caspase inhibition: a potential therapeutic strategy in neurological diseases

Caspases are intracellular proteases that participate in apoptotic pathways in mammalian cells, including neurons. Here we review evidence that caspase inhibition, through pharmacological or molecular means, may inhibit neuronal cell death in a number of in vitro and in vivo models of neurological disease. It has recently become clear that, at least in most cell culture models, caspase inhibition offers only transient protection, and that a caspase-independent death eventually occurs. This may be due to irreversible caspase-independent alterations at the level of the mitochondria. Despite concerns that targeting caspases alone may prove insufficient to truly reverse the effects of various death stimuli, in vivo studies indicate that caspase inhibition promotes survival and functional outcome in a variety of neurological disease models. In addition, studies of human post-mortem material suggest that caspases are activated in certain human neurological diseases. Caspase inhibition may therefore provide a novel strategy for the treatment of such disorders. Caspases, through the generation of toxic fragments of critical protein substrates, may also be involved in earlier steps of neuronal dysfunction, such as protein aggregation in Huntington's and Alzheimer's disease, and therefore caspase inhibition may be of additional value in the treatment of these particular disorders.

The geographical and ethnic distribution of the D90A CuZn-SOD mutation in the Russian Federation

INTRODUCTION

Mutations in the gene encoding the free radical scavenging enzyme CuZn-superoxide dismutase have been associated with amyotrophic lateral sclerosis (ALS). Ninety-eight mutations have been found worldwide in patients with ALS, all but one showing a dominant pattern of inheritance. The exception is the D90A mutation which in Finland, northern Norway and northern Sweden exists with an allele frequency of 1-2.5% and is in these regions associated with ALS inherited as a recessive trait.

METHODS AND RESULTS

In this study we searched for the D90A CuZn-SOD mutation in different ethnic populations of the Russian Federation and found the D90A mutation not only in locations close to the Scandinavian peninsula but also in remote populations in Asia.

CONCLUSION

The finding makes the D90A mutation the most prevalent CuZn-SOD mutation globally and has implications for interpreting the recent reports of D90A-heterozygous ALS patients in North America and Europe.

Increased expression of neuronal nitric oxide synthase spliced variants in reactive astrocytes of amyotrophic lateral sclerosis human spinal cord

The expression of three different neuronal nitric oxide synthase (nNOS) spliced variants, named nNOSalpha, nNOSbeta, and nNOSgamma, was investigated in the spinal cord of control and both familiar and sporadic amyotrophic lateral sclerosis (FALS and SALS) patients. Western blot analysis showed a consistent increase in nNOS expression in six SALS patients compared with controls when antibodies recognizing both nNOSalpha and nNOSbeta, or nNOSalpha, nNOSbeta, and nNOSgamma were used, whereas no change was observed when a selective anti-nNOSalpha antibody was used. Immunoreactivity signal for nNOSalpha-beta-gamma and nNOSalpha-beta was equally present in ventral horn neurons of control and ALS spinal cord but was dramatically increased in reactive astrocytes of the ventral horn and white matter in both FALS and SALS. nNOSalpha signal was equally expressed in motor neurons of normal and ALS spinal cord but was not evident in astrocytes. This finding indicates that nNOSbeta and nNOSgamma spliced variants are upregulated in reactive astrocytes in ALS. This may contribute to the peroxynitrite-mediated oxidative damage involved in the pathogenesis of both FALS and SALS.

Mutations in the lysyl oxidase gene are not associated with amyotrophic lateral sclerosis

BACKGROUND

There is an urgent need to identify genes involved in familial ALS (FALS), as mutations in the CuZn superoxide dismutase (SOD1) gene can account for 20% of FALS cases. The mechanisms by which the many mutations in the SOD1 gene lead to motoneuron degeneration are unknown, although current experimental evidence supports a toxic gain of function, possibly through copper-induced cytotoxicity. Copper is an integral component of a number of enzymes as well as SOD1. Since abnormalities in connective tissue cross-linking have been reported in ALS patients, an enzyme of possible relevance is lysyl oxidase (LOX), a copper-containing enzyme which catalyses the crosslinking of collagens and elastin. The aim of this study was to investigate the hypothesis that allelic variants or mutants of LOX gene result in altered function of LOX in ALS patients.

METHODS

The coding regions of the LOX gene were screened for polymorphism and mutations in a cohort of sporadic and familial ALS patients.

RESULTS

A novel polymorphism, Pro159Gln, was identified in eight individuals with sporadic ALS (5.0%) and five controls (3.6%). The previously identified Arg158Gln polymorphism was also detected in ALS patients and controls. These polymorphisms were genotyped in 192 ALS patients, including 31 unrelated familial cases and 138 controls, and no association was found between any of these polymorphisms and amyotrophic lateral sclerosis or its phenotype.

CONCLUSION

Mutations in the LOX gene are unlikely to be directly causative of ALS.

Nitrotyrosination contributes minimally to toxicity of mutant SOD1 associated with ALS

Enhanced production of nitrotyrosine and subsequent protein nitration has been proposed as the mechanism by which mutant SOD1 causes death of motor neurons in a familial form of amyotrophic lateral sclerosis (FALS-1). We have tested this hypothesis in a primary culture model in which mutant human SOD1 was expressed in motor neurons of dissociated spinal cord cultures. Preventing formation of nitrotyrosine by inhibiting nitric oxide synthase rescued cultured motor neurons from excitotoxic death induced by adding glutamate to the culture medium, but failed to significantly delay death of motor neurons expressing the G93A mutant SOD1. The results do not support generation of nitrotyrosine being the predominant lethal gain of function conferred by mutations in SOD1.

Deregulation of Cdk5 in a mouse model of ALS: toxicity alleviated by perikaryal neurofilament inclusions

Recent studies suggest that increased activity of cyclin-dependent kinase 5 (Cdk5) may contribute to neuronal death and cytoskeletal abnormalities in Alzheimer's disease. We report here such deregulation of Cdk5 activity associated with the hyperphosphorylation of tau and neurofilament (NF) proteins in mice expressing a mutant superoxide dismutase (SOD1(G37R)) linked to amyotrophic lateral sclerosis (ALS). A Cdk5 involvement in motor neuron degeneration is supported by our analysis of three SOD1(G37R) mouse lines exhibiting perikaryal inclusions of NF proteins. Our results suggest that perikaryal accumulations of NF proteins in motor neurons may alleviate ALS pathogenesis by acting as a phosphorylation sink for Cdk5 activity, thereby reducing the detrimental hyperphosphorylation of tau and other neuronal substrates.

Transgenic mouse model for familial amyotrophic lateral sclerosis with superoxide dismutase-1 mutation

Familial amyotrophic lateral sclerosis (ALS) with mutations in the gene for superoxide dismutase-1 (SOD1) is clinicopathologically reproduced by transgenic mice expressing mutant forms of SOD1 detectable in familial ALS patients. Motor neuron degeneration associated with SOD1 mutation has been thought to result from a novel neurotoxicity of mutant SOD1, but not from a reduction in activity of this enzyme, based on autosomal dominant transmission of SOD1 mutant familial ALS and its transgenic mouse model, clinical severity of the ALS patients independent to enzyme activity, no ALS-like disease in SOD1 knockout or wild-type SOD1-overexpressing mice, and clinicopathological severity of mutant SOD1 transgenic mice dependent on transgene copy numbers. Proposed mechanisms of motor neuron degeneration such as oxidative injury, peroxynitrite toxicity, cytoskeletal disorganization, glutamate excitotoxicity, disrupted calcium homeostasis, SOD1 aggregation, carbonyl stress and apoptosis have been discussed. Intracytoplasmic vacuoles, indicative of increased oxidative damage to the mitochondria and endoplasmic reticulum, in the neuropil and motor neurons appear in high expressors of mutant SOD1 transgenic mice but not in low expressors of the mice or familial ALS patients, suggesting that overexpression of mutant SOD1 in mice may enhance oxidative stress generation from this enzyme. Thus, transgenic mice carrying small transgene copy numbers of mutant SOD1 would provide a beneficial animal model for SOD1 mutant familial ALS. Such a model would contribute to elucidating the pathomechanism of this disease and establishing new therapeutic agents.

[Superoxide dismutase-1 (SOD-1) gene mutation-dependent mechanisms of neural degeneration in amyotrophic lateral sclerosis]

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease involving motor neuron degeneration, occurring in sporadic and familial forms. Mutations in Cu/Zn superoxide dismutase gene (SOD-1) play a key role in the pathogenesis of the familial form in which it is present in about 20%. The mechanisms by which the mutated enzyme produces the disease are not sufficiently know. The following hypothesis are considered: oxidative damage, disorganization of neurofilaments, toxic action of intracellular aggregates, disturbed mechanisms of protein synthesis or degradation, and increased glutamic acid toxicity due to damage of EAAT 2 mRNA, transporter of this acid. It is supposed that motor neuron death is due to various mechanisms caused by SOD-1 enzyme mutations. Pathological changes suggest that biochemical processes leading to neurodegeneration in familial ALS form related or unrelated to SOD-1 mutation, and in sporadic form may be very similar.

Increased expression of the pro-inflammatory enzyme cyclooxygenase-2 in amyotrophic lateral sclerosis

Mutations in the copper/zinc superoxide dismutase (mSOD1) gene are associated with a familial form of amyotrophic lateral sclerosis (ALS), and their expression in transgenic mice produces an ALS-like syndrome. Recent observations suggest a role for inflammatory-related events in the progression and propagation of the neurodegenerative process in ALS. Consistent with this view, the present study demonstrates that, during the course of the disease, the expression of cyclooxygenase type 2 (Cox-2), a key enzyme in the synthesis of prostanoids, which are potent mediators of inflammation, is dramatically increased. In both early symptomatic and end-stage transgenic mSOD1 mice, neurons and, to a lesser extent, glial cells in the anterior horn of the spinal cord exhibit robust Cox-2 immunoreactivity. Cox-2 mRNA and protein levels and catalytic activity are also significantly increased in the spinal cord of the transgenic mSOD1 mice. The time course of the spinal cord Cox-2 upregulation parallels that of motor neuronal loss in transgenic mSOD1 mice. We also show that Cox-2 activity is dramatically increased in postmortem spinal cord samples from sporadic ALS patients. We speculate that Cox-2 upregulation, through its pivotal role in inflammation, is instrumental in the ALS neurodegenerative process and that Cox-2 inhibition may be a valuable therapeutic avenue for the treatment of ALS.

The physiological basis of conduction slowing in ALS patients homozygous for the D90A CuZn-SOD mutation

Familial amyotrophic lateral sclerosis (ALS) with the autosomal-recessively inherited D90A CuZn-superoxide dismutase (CuZn-SOD) mutation is characterized by a stereotypic slowly progressive, distinctive phenotype and very slow central motor conduction. To determine the basis of this slowing, we assessed corticomotoneuronal function using peristimulus time histograms (PSTHs) in 8 ALS patients homozygous for the D90A CuZn-SOD mutation. The results were compared with findings in 10 patients with multiple sclerosis (MS), in which slowing of central motor conduction is common, and 11 healthy subjects. PSTHs were constructed from 3-7 different, voluntarily recruited motor units recorded in each patient from the extensor digitorum communis muscle (EDC). In D90A and MS patients, the stimulus threshold, onset latency, number of excess bins, duration, amplitude, and synchrony of the primary peak differed significantly from controls (P < 0.0004). The mean onset latency of the primary peak in D90A patients was 35.3 ms, compared to 23.6 ms for MS patients and 19.3 ms for normal subjects (P < 0.0001). In the D90A patients, the onset latencies of the primary peak had a bimodal distribution, whereas in MS the distribution showed a continuum. Loss of synchrony was similar in D90A and MS patients, but the threshold, number of excess bins, and duration differed significantly (P < 0.0057), which suggests that either axonal loss or demyelination can result in delayed and desynchronized primary peaks. We propose that conduction slowing in the D90A homozygotes results from selective loss of fast-conducting large pyramidal cells with preservation of slow-conducting mono- or polysynaptic corticomotoneuronal connections.

Delaying caspase activation by Bcl-2: A clue to disease retardation in a transgenic mouse model of amyotrophic lateral sclerosis

Molecular mechanisms of apoptosis may participate in motor neuron degeneration produced by mutant copper/zinc superoxide dismutase (mSOD1), the only proven cause of amyotrophic lateral sclerosis (ALS). Consistent with this, herein we show that the spinal cord of transgenic mSOD1 mice is the site of the sequential activation of caspase-1 and caspase-3. Activated caspase-3 and its produced beta-actin cleavage fragments are found in apoptotic neurons in the anterior horn of the spinal cord of affected transgenic mSOD1 mice; although such neurons are few, their scarcity should not undermine the potential importance of apoptosis in the overall mSOD1-related neurodegeneration. Overexpression of the anti-apoptotic protein Bcl-2 attenuates neurodegeneration and delays activation of the caspases and fragmentation of beta-actin. These data demonstrate that caspase activation occurs in this mouse model of ALS during neurodegeneration. Our study also suggests that modulation of caspase activity may provide protective benefit in the treatment of ALS, a view that is consistent with our recent demonstration of caspase inhibition extending the survival of transgenic mSOD1 mice.

Enhanced oxidative damage by the familial amyotrophic lateral sclerosis-associated Cu,Zn-superoxide dismutase mutants

Some cases of familial amyotrophic lateral sclerosis (FALS), a degenerative disorder of motor neurons, is associated with mutation in the Cu,Zn-superoxide dismutase (SOD) gene SOD1. The purified FALS mutant and wild-type Cu,Zn-SODs expressed in Escherichia coli cells have identical dismutation activity whereas the hydroxyl radical formation of FALS mutants was enhanced relative to that of the wild-type enzyme. These higher free radical-generating activities of mutants facilitated the release of copper ions from their own molecules. The reaction of the mutants with hydrogen peroxide enhanced DNA strand breaks and lipid peroxidation. The results suggested that the enhanced oxidative damage of macromolecules is mediated in the Cu,Zn-SOD mutants and hydrogen peroxide system via the generation of hydroxyl radicals by a combination of the higher free radical-generating activities of mutants and a Fenton-like reaction of copper ions released from oxidatively damaged Cu,Zn-SODs. Carnosine has been proposed to act as antioxidant in vivo. We investigated whether carnosine could protect the oxidative damage induced by FALS mutants. Carnosine effectively inhibited the DNA cleavage and lipid peroxidation. These results suggest that the higher free radical-generating function of FALS mutants can lead to increased oxidative damage of macromolecules which further implicates free radical-mediated motor neuronal injury in the pathogenesis of FALS and carnosine may be explored as potential therapeutic agents for FALS patients.

Caspase-1 and -3 are sequentially activated in motor neuron death in Cu,Zn superoxide dismutase-mediated familial amyotrophic lateral sclerosis

Familial amyotrophic lateral sclerosis-linked mutations in copper-zinc superoxide dismutase cause motor neuron death through one or more acquired toxic properties. An early event in the mechanism of toxicity from such mutants is now demonstrated to be activation of caspase-1. Neuronal death, however, follows only after months of chronic caspase-1 activation concomitantly with activation of the executioner caspase-3 as the final step in the toxic cascade. Thus, a common toxicity of mutant SOD1 is a sequential activation of at least two caspases, caspase-1 that acts slowly as a chronic initiator and caspase-3 acting as the final effector of cell death.

Human Cu/Zn superoxide dismutase (SOD1) overexpression in mice causes mitochondrial vacuolization, axonal degeneration, and premature motoneuron death and accelerates motoneuron disease in mice expressing a familial amyotrophic lateral sclerosis mutant SOD1

Cytosolic Cu/Zn superoxide dismutase (SOD1) is a ubiquitous small cytosolic metalloenzyme that catalyzes the conversion of superoxide anion to hydrogen peroxide (H(2)O(2)). Mutations in the SOD1 gene cause a familial form of amyotrophic lateral sclerosis (fALS). The mechanism by which mutant SOD1s causes ALS is not understood. Transgenic mice expressing multiple copies of fALS-mutant SOD1s develop an ALS-like motoneuron disease resembling ALS. Here we report that transgenic mice expressing a high concentration of wild-type human SOD1 (hSOD1(WT)) develop an array of neurodegenerative changes consisting of (1) swelling and vacuolization of mitochondria, predominantly in axons in the spinal cord, brain stem, and subiculum; (2) axonal degeneration in a number of long fiber tracts, predominantly the spinocerebellar tracts; and (3) at 2 years of age, a moderate loss of spinal motoneurons. Parallel to the development of neurodegenerative changes, hSOD1(WT) mice also develop mild motor abnormalities. Interestingly, mitochondrial vacuolization was associated with accumulation of hSOD1 immunoreactivity, suggesting that the development of mitochondrial pathology is associated with disturbed SOD1 turnover. In this study we also crossed hSOD1(WT) mice with a line of fALS-mutant SOD1 mice (hSOD1(G93A)) to generate "double" transgenic mice that express high levels of both wild-type and G93A mutant hSOD1. The "double" transgenic mice show accelerated motoneuron death, earlier onset of paresis, and earlier death as compared with hSOD1(G93A) littermates. Thus in vivo expression of high levels of wild-type hSOD1 is not only harmful to neurons in itself, but also increases or facilitates the deleterious action of a fALS-mutant SOD1. Our data indicate that it is important for motoneurons to control the SOD1 concentration throughout their processes, and that events that lead to improper synthesis, transport, or breakdown of SOD1 causing its accumulation are potentially dangerous.

Advanced glycation endproduct-modified superoxide dismutase-1 (SOD1)-positive inclusions are common to familial amyotrophic lateral sclerosis patients with SOD1 gene mutations and transgenic mice expressing human SOD1 with a G85R mutation

To clarify the biological significance of the neuronal Lewy body-like hyaline inclusions and astrocytic hyaline inclusions characteristically found in patients with familial amyotrophic lateral sclerosis with superoxide dismutase-1 (SOD1) gene mutations and in transgenic mice expressing human SOD1 with G85R mutation, the detailed protein composition in both types of inclusions was immunohistochemically analyzed using 45 different antibodies. Both types of inclusions had very strong immunoreactivity for SOD1. The SOD1-positive inclusions in both cell types were also immunoreactive for the insoluble advanced glycation endproducts (AGEs) such as Nepsilon-(carboxymethyl)lysine (CML), pyrraline and pentosidine: both inclusions in both conditions were ultrastructurally composed of the granule-coated fibrils that had immunoreactivities to CML and pyrraline. Both types of inclusions were negative for stress-response proteins (SRPs), 4-hydroxy-2-nonenal (HNE), acrolein, nitric oxide synthases (NOSs) and nitrotyrosine as representative markers of oxidative stress. The neurons and astrocytes of the normal individuals and non-transgenic mice showed no significant immunoreactivity for SOD1, AGEs, SRPs, HNE, acrolein, NOSs or nitrotyrosine. Our results suggest that a portion of the SOD1 composing both type of inclusions, probably toxic mutant SOD1, is modified by the AGEs, and that the formation of the AGE-modified SOD1 is one of the mechanisms responsible for the aggregation involving no significant oxidative mechanisms.

Apoptosis in the nervous system

Neuronal apoptosis sculpts the developing brain and has a potentially important role in neurodegenerative diseases. The principal molecular components of the apoptosis programme in neurons include Apaf-1 (apoptotic protease-activating factor 1) and proteins of the Bcl-2 and caspase families. Neurotrophins regulate neuronal apoptosis through the action of critical protein kinase cascades, such as the phosphoinositide 3-kinase/Akt and mitogen-activated protein kinase pathways. Similar cell-death-signalling pathways might be activated in neurodegenerative diseases by abnormal protein structures, such as amyloid fibrils in Alzheimer's disease. Elucidation of the cell death machinery in neurons promises to provide multiple points of therapeutic intervention in neurodegenerative diseases.

Copper, ceruloplasmin and superoxide dismutase (SOD) in amyotrophic lateral sclerosis

In two previous studies we found copper dyshomeostasis in patients with Alzheimer's disease and in patients with Parkinson's disease. In this study, the levels of copper in plasma, of ceruloplasmin in serum, ceruloplasmin oxidative activity, ceruloplasmin specific oxidative activity (activity related to mass) as well as superoxide dismutase (SOD) activity in erythrocytes have been determined in 14 patients with amyotrophic lateral sclerosis and their healthy age- and gender-matched controls. Three of the patients had a familial form of the disease or were suspected of having it. The mean values of all parameters were found not to differ significantly between the patients and their controls (Student's t-test; P>0.05). By testing the equality of variances (F distribution) we found that the variances of individual results for ceruloplasmin specific oxidative activity and SOD activity differed significantly between the patients group and the controls group (P= 0.021 and P=0.003), but the individual results of these two activities were not correlated (P>0.05). We conclude that disturbances in ceruloplasmin specific oxidative activity and SOD activity could contribute to motor neurone death in amyotrophic lateral sclerosis, and since the two enzyme activities are not correlated it is uncertain which one is more closely related to the pathology of the disease.

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.