Transient caloric restriction in early adulthood hastens disease endpoint in male, but not female, Cu/Zn-SOD mutant G93A mice

Long-term caloric restriction (CR) prolongs the lifespan in healthy insects, rodents, and nonhuman primates. We previously reported that long-term CR improves motor performance but hastens clinical onset of disease in an animal model of amyotrophic lateral sclerosis (G93A mice). G93A mice overexpress the mutant human Cu/Zn-SOD gene and show progressive lower motor neuron weakness and increased oxidative stress. To study short-term (15 days) CR in the same animal model, we investigated the effect of transient caloric restriction (TCR) on paw grip endurance, clinical onset, disease progression (time from clinical onset to endpoint), and lifespan. Starting at age 40 days, 32 separately caged G93A mice were randomly divided into two groups: ad libitum (AL, n = 17; 10 females, 7 males) and TCR (n = 15; 6 females, 9 males) with a diet equal to 60% of AL. When the TCR mice lost 30% of their weight they were offered food AL until endpoint, otherwise all TCR mice were provided food AL from age 55 days until endpoint (i.e., range of TCR = 13-15 days). Paw grip endurance started to decrease significantly at age 96 days compared with baseline values for all the groups. TCR males reached clinical onset 5 days sooner than TCR females. Disease progression was 8 days faster in TCR mice than AL mice and 6 days faster in male mice than female mice. The probability of survival was significantly different between the groups, with the TCR males having a faster rate of reaching endpoint than TCR females, AL males, and AL females. We conclude that TCR hastens clinical onset of disease and shortens the lifespan in male, but not female, G93A mice. Moreover, TCR hastens progress of disease but has no effect on paw grip endurance. The female sex is protective against the detrimental effects of short-term CR in G93A mice. Assuming we can extrapolate these results to humans, short-term CR should be avoided in patients with amyotrophic lateral sclerosis, especially men.

Lymphopenia and spontaneous autorosette formation in SOD1 mouse model of ALS

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by motoneuron degeneration. Increasing evidence suggests immune system involvement in ALS pathogenesis but information about peripheral blood characteristics has been lacking. We evaluated hematological and morphological parameters in peripheral blood of G93A SOD1 mice. A significant decrease in white blood cells was found at the end stage of disease. The lymphocyte reduction may suggest immunodeficiency in ALS. Spontaneously forming rosettes with autologous erythrocytes were noted in approximately 28% of lymphocytes in SOD1 mice. To our knowledge, this is the first study characterizing hematology and revealing autorosettes in the SOD1 mouse model of ALS at the terminal phase of disease.

Chromogranin-mediated secretion of mutant superoxide dismutase proteins linked to amyotrophic lateral sclerosis

Here we report that chromogranins, components of neurosecretory vesicles, interact with mutant forms of superoxide dismutase (SOD1) that are linked to amyotrophic lateral sclerosis (ALS), but not with wild-type SOD1. This interaction was confirmed by yeast two-hybrid screen and by co-immunoprecipitation assays using either lysates from Neuro2a cells coexpressing chromogranins and SOD1 mutants or lysates from spinal cord of ALS mice. Confocal and immunoelectron microscopy revealed a partial colocalization of mutant SOD1 with chromogranins in spinal cord of ALS mice. Mutant SOD1 was also found in immuno-isolated trans-Golgi network and in microsome preparations, suggesting that it can be secreted. Indeed we report evidence that chromogranins may act as chaperone-like proteins to promote secretion of SOD1 mutants. From these results, and our finding that extracellular mutant SOD1 can trigger microgliosis and neuronal death, we propose a new ALS pathogenic model based on the toxicity of secreted SOD1 mutants.

Disulphide-reduced superoxide dismutase-1 in CNS of transgenic amyotrophic lateral sclerosis models

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease afflicting the voluntary motor system. More than 100 different mutations in the ubiquitously expressed enzyme superoxide dismutase-1 (SOD1) have been associated with the disease. To search for the nature of the cytotoxicity of mutant SOD1s, amounts, enzymic activities and structural properties of the protein as well as the CNS histopathology were examined in multiple transgenic murine models. In order to generate the ALS phenotype within the short lifespan of the mouse, more than 20-fold increased rates of synthesis of mutant SOD1s appear to be required. The organs of transgenic mice expressing human wild-type SOD1 or either of the G93A and D90A mutant proteins showed high steady-state protein levels. The major proportion of these SOD1s in the CNS were inactive due to insufficient Cu charging and all contained subfractions with a reduced C57-C146 intrasubunit disulphide bond. Both G85R and the truncated G127insTGGG mutant showed low steady-state protein levels, lacked enzyme activity and had no C57-C146 disulphide bond. These mutants were also enriched in the CNS relative to other organs, suggesting inefficient recognition and degradation of misfolded disulphide-reduced SOD1 in susceptible tissues. In end-stage disease, despite 35-fold differences in levels of mutant SOD1s, similar amounts of detergent-resistant aggregates accumulated in the spinal cord. Small granular as well as larger more diffuse human SOD1 (hSOD1)-inclusions developed in all strains, the latter more pronounced in those with high hSOD1 levels. Widespread vacuolizations were seen in the strains with high levels of hSOD1 but not those with low, suggesting these alterations to be artefacts related to high hSOD1 levels and not to the ALS-causing cytotoxicity. The findings suggest that the motoneuron degeneration could be due to long-term exposure to misfolded aggregation-prone disulphide-reduced SOD1, which constitutes minute subfractions of the stable mutants and larger proportions of the unstable mutants.

Coincident thresholds of mutant protein for paralytic disease and protein aggregation caused by restrictively expressed superoxide dismutase cDNA

Familial amyotrophic lateral sclerosis (FALS) has been modeled in transgenic mice by introducing mutated versions of human genomic DNA encompassing the entire gene for Cu,Zn superoxide dismutase (SOD1). In this setting, the transgene is expressed throughout the body and results in mice that faithfully recapitulate many pathological and behavioral aspects of FALS. By contrast, transgenic mice made by introducing recombinant vectors, encoding cDNA genes, that target mutant SOD1 expression to motor neurons, only, or astrocytes, only, do not develop disease. Here, we report that mice transgenic for human SOD1 cDNA with the G37R mutation, driven by the mouse prion promoter, develop motor neuron disease. In this model, expression of the transgene is highest in CNS (both neurons and astrocytes) and muscle. The gene was not expressed in cells of the macrophage lineage. Although the highest expressing hemizygous transgenic mice fail to develop disease by 20 months of age, mice homozygous for the transgene show typical ALS-like phenotypes as early as 7 months of age. Spinal cords and brain stems from homozygous animals with motor neuron disease were found to contain aggregated species of mutant SOD1. The establishment of this SOD1-G37R cDNA transgenic model indicates that expression of mutant SOD1 proteins in the neuromuscular unit is sufficient to cause motor neuron disease. The expression levels required to induce disease coincide with the levels required to induce the formation of SOD1 aggregates.

Structural properties and neuronal toxicity of amyotrophic lateral sclerosis-associated Cu/Zn superoxide dismutase 1 aggregates

The appearance of protein aggregates is a characteristic of protein misfolding disorders including familial amyotrophic lateral sclerosis, a neurodegenerative disease caused by inherited mutations in Cu/Zn superoxide dismutase 1 (SOD1). Here, we use live cell imaging of neuronal and nonneuronal cells to show that SOD1 mutants (G85R and G93A) form an aggregate structure consisting of immobile scaffolds, through which noninteracting cellular proteins can diffuse. Hsp70 transiently interacts, in a chaperone activity-dependent manner, with these mutant SOD1 aggregate structures. In contrast, the proteasome is sequestered within the aggregate structure, an event associated with decreased degradation of a proteasomal substrate. Through the use of time-lapse microscopy of individual cells, we show that nearly all (90%) aggregate-containing cells express higher levels of mutant SOD1 and died within 48 h, whereas 70% of cells expressing a soluble mutant SOD1 survived. Our results demonstrate that SOD1 G85R and G93A mutants form a distinct class of aggregate structures in cells destined for neuronal cell death.

Regional and temporal alterations of ODC/polyamine system during ALS-like neurodegenerative motor syndrome in G93A transgenic mice

Natural polyamines (putrescine, spermidine and spermine) are ubiquitous molecules known to regulate a number of physiological processes and suspected to play a role also in various pathological conditions. Changes in polyamine levels and in their biosynthetic enzymes have been described for some neurodegenerative diseases but the available data are incomplete and somewhat contradictory. We report here alterations of the key enzyme of the polyamine pathway, ornithine decarboxylase (ODC) catalytic activity and polyamine levels in different CNS areas from SOD1 G39A transgenic mice, an animal model for amyotrophic lateral sclerosis (ALS). ODC catalytic activity, was found significantly increased both in the cervical and lumbar spinal cord and, to a lesser extent in the brain stem of transgenic mice at a symptomatic stage of the disease (125-day-old mice), while no differences were present at a pre-symptomatic stage (55-day-old mice). In parallel with the increase of ODC activity putrescine levels were several times increased in both cervical and lumbar spinal cord and in the brain stem of 125-day-old SOD1 G39A mice. Higher order polyamines were not increased except for a significant increase of spermidine in the cervical spinal cord. The present data demonstrate considerable alterations of the ODC/polyamine system in a reliable animal model of ASL, consistent with their role in neurodegeneration and in particular in motor neuron diseases.

Phosphatidylinositol 3-kinase activator reduces motor neuronal cell death induced by G93A or A4V mutant SOD1 gene

The primary pathogenic mechanism of amyotrophic lateral sclerosis (ALS) remains largely unclear. We recently observed that motoneuron cell death mediated by G93A or A4V mutant SOD1, causing familial ALS, was related with decrease of survival signals, such as phosphatidylinositol 3-kinase (PI3-K) and Akt, which play a pivotal role in neuronal survival. Using a G93A or A4V mutant SOD1 transfected VSC4.1 motoneuron cells (G93A or A4V cells, respectively), we presently investigated whether PI3-K activator could reduce mutant SOD1-mediated motoneuron cell death. To investigate the effect of PI3-K activator on viability of G93A and A4V cells, these cells were treated with 10, 50 or 100ng/ml PI3-K activator for 24h and viability and intracellular signals, including Akt, glycogen synthase kinase-3 (GSK-3), heat shock transcription factor-1 (HSTF-1), cytosolic cytochrome c, caspase-3 and poly(ADP-ribose) polymerase (PARP), were compared with those without treatment (control). Compared with non-treated control G93A or A4V cells, the PI3-K activator treatment increased their viability by enhancing the survival signals, including pAkt, pGSK-3, and by inhibiting the death signals, including caspase-3 activation and PARP cleavage. These results suggest that PI3-K activator protects G93A or A4V cells from mutant SOD1-mediated motoneuron cell death by both activating survival signals and inactivating death signals.

Copper-zinc superoxide dismutase and amyotrophic lateral sclerosis

Copper-zinc superoxide dismutase (CuZnSOD, SOD1 protein) is an abundant copper- and zinc-containing protein that is present in the cytosol, nucleus, peroxisomes, and mitochondrial intermembrane space of human cells. Its primary function is to act as an antioxidant enzyme, lowering the steady-state concentration of superoxide, but when mutated, it can also cause disease. Over 100 different mutations have been identified in the sod1 genes of patients diagnosed with the familial form of amyotrophic lateral sclerosis (fALS). These mutations result in a highly diverse group of mutant proteins, some of them very similar to and others enormously different from wild-type SOD1. Despite their differences in properties, each member of this diverse set of mutant proteins causes the same clinical disease, presenting a challenge in formulating hypotheses as to what causes SOD1-associated fALS. In this review, we draw together and summarize information from many laboratories about the characteristics of the individual mutant SOD1 proteins in vivo and in vitro in the hope that it will aid investigators in their search for the cause(s) of SOD1-associated fALS.

Activity and expression of glutathione S-transferase pi in patients with amyotrophic lateral sclerosis

Glutathione S-transferase (GST, EC 2.5.1.18) is an enzyme responsible for inactivation of a large variety of toxic, electrophilic compounds and organic peroxides. GST activity and GST pi expression were studied in patients with amyotrophic lateral sclerosis (ALS). Studies were conducted on cerebrospinal fluid (CSF), blood serum and peripheral blood mononuclear cells (PBMC) obtained from 40 ALS patients. CSF from 30 subjects without neurological diseases and blood from 40 healthy blood donors were used as controls. GST activity assayed with 1-chloro-2,4-dinitrobenzene (substrate for transferase activity) and cumene peroxide (substrate for peroxidase activity) was significantly decreased in PBMC of ALS patients, as well as the GST pi expression on both mRNA and protein level. The mean peroxidase activity was however significantly increased in CSF and serum of ALS patients with the specificity of 80% and 73%, and the sensitivity of 78% and 85%, respectively. It can thus be concluded that the protective barrier formed by GST is originally affected in peripheral blood of ALS patients, and may increase their vulnerability to toxic effects of electrophilic compounds and organic peroxides. Studies on a larger group are needed to answer the question whether GSH-Px determination may be implicated in the diagnosis of ALS.

The cellular mRNA expression of GABA and glutamate receptors in spinal motor neurons of SOD1 mice

ALS is a fatal neurodegenerative disorder characterized by a selective loss of upper motor neurons in the motor cortex and lower motor neurons in the brain stem and spinal cord. About 10% of ALS cases are familial, in 10-20% of these, mutations in the gene coding for superoxide dismutase 1 (SOD1) can be detected. Overexpression of mutated SOD1 in mice created animal models which clinically resemble ALS. Abnormalities in glutamatergic and GABAergic neurotransmission presumably contribute to the selective motor neuron damage in ALS. By in situ hybridization histochemistry (ISH), we investigated the spinal mRNA expression of the GABAA and AMPA type glutamate receptor subunits at different disease stages on spinal cord sections of mutant SOD1 mice and control animals overexpressing wild-type SOD1 aged 40, 80, 120 days and at disease end-stage, i.e. around 140 days) (n=5, respectively). We detected a slight but statistically significant decrease of the AMPA receptor subunits GluR3 and GluR4 only in end stage disease animals.

Aberrantly Increased Hydrophobicity Shared by Mutants of Cu,Zn-Superoxide Dismutase in Familial Amyotrophic Lateral Sclerosis

More than 100 different mutations in the gene encoding Cu,Zn-superoxide dismutase (SOD1) cause preferential motor neuron degeneration in familial amyotrophic lateral sclerosis (ALS). Although the cellular target(s) of mutant SOD1 toxicity have not been precisely specified, evidence to date supports the hypothesis that ALS-related mutations may increase the burden of partially unfolded SOD1 species. Influences that may destabilize SOD1 in vivo include impaired metal ion binding, reduction of the intrasubunit disulfide bond, or oxidative modification. In this study, we observed that metal-deficient as-isolated SOD1 mutants (H46R, G85R, D124V, D125H, and S134N) with disordered electrostatic and zinc-binding loops exhibited aberrant binding to hydrophobic beads in the absence of other destabilizing agents. Other purified ALS-related mutants that can biologically incorporate nearly normal amounts of stabilizing zinc ions (A4V, L38V, G41S, D90A, and G93A) exhibited maximal hydrophobic behavior after exposure to both a disulfide reducing agent and a metal chelator, while normal SOD1 was more resistant to these agents. Moreover, we detected hydrophobic SOD1 species in lysates from affected tissues in G85R and G93A mutant but not wildtype SOD1 transgenic mice. These findings suggest that a susceptibility to the cellular disulfide reducing environment and zinc loss may convert otherwise stable SOD1 mutants into metal-deficient forms with locally destabilized electrostatic and zinc-binding loops. These abnormally hydrophobic SOD1 species may promote aberrant interactions of the enzyme with itself or with other cellular constituents to produce toxicity in familial ALS.

Low levels of ALS-linked Cu/Zn superoxide dismutase increase the production of reactive oxygen species and cause mitochondrial damage and death in motor neuron-like cells

Mutations of Cu/Zn superoxide dismutase (SOD1) are found in patients with familial amyotrophic lateral sclerosis (FALS). A cellular model of FALS was developed by stably transfecting the motor neuron-like cell line NSC-34 with human wild type (wt) or mutant (G93A) SOD1. Expression levels of G93ASOD1 were close to those seen in the human disease. The presence of G93ASOD1 did not alter cell proliferation but toxicity was evident when the cells were in the growth plateau phase. Flow cytometry analysis indicated that, in this phase, G93ASOD1 significantly lowered viability and that the level of reactive oxygen species was significantly higher in living G93ASOD1 cells compared to wt SOD1 cells. Biparametric analysis of mitochondrial membrane potential and viability of transfected cells highlighted a peculiar population of damaged cells with strong mitochondrial depolarization in the G93ASOD1 cells. Mitochondrial function seemed related to the level of the mutant protein since MTT conversion decreased when expression of G93ASOD1 doubled after treating cells with sodium butyrate. The mutant protein rendered G93ASOD1 cells more sensitive to mitochondrial dysfunction induced by stimuli that alter cellular free radical homeostasis, like serum withdrawal, depletion of glutathione by ethacrynic acid or rotenone-mediated inhibition of complex I of the mitochondrial electron transport chain. In conclusion, even a small amount of mutant SOD1 put motor neurons in a condition of oxidative stress and mitochondrial damage that causes cell vulnerability and death.

Association between CYP1A2 activity and riluzole clearance in patients with amyotrophic lateral sclerosis

AIMS

Riluzole is used in a fixed dosing schedule of 50 mg twice daily to treat patients with amyotropic lateral sclerosis (ALS), one form of motor neurone disease. The large variability in the pharmacokinetics of riluzole may be a factor contributing to its limited therapeutic benefit. Riluzole is assumed to be mainly metabolized by the cytochrome P450 enzyme 1A2 (CYP1A2). The aim of the study was to investigate the relationship between CYP1A2 activity and riluzole clearance with a view to optimize drug treatment.

METHODS

A group of 30 ALS patients participated in the study. In each patient the CYP1A2 activity was determined using caffeine as a metabolic probe. Riluzole clearance was estimated from serum drug concentration measurements followed by Bayesian fitting.

RESULTS

Riluzole clearance and the serum paraxanthine : caffeine (P/C) ratio showed a positive correlation (r = 0.693; P = 0.0002). Linear regression analysis identified the P/C ratio (beta: 1.16) and height (beta: 0.027) as independent predictors of riluzole clearance (adjusted r2 = 0.369).

CONCLUSIONS

The P/C ratio, used as measure of CYP1A2 activity, significantly correlated with the riluzole clearance, although only 37% of the observed variability could be explained.

An RNAi strategy for treatment of amyotrophic lateral sclerosis caused by mutant Cu,Zn superoxide dismutase

Amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease) is a neurodegenerative disease characterized by motor neuron degeneration, paralysis and death. One cause of this disease is mutations in the Cu,Zn superoxide dismutase (SOD1) gene. As mutant SOD1 acquires a toxic property that kills motor neurons, by reducing the mutant protein the disease progression may be slowed or prevented. While mutant SOD1 is toxic, the wild-type SOD1 is indispensable for motor neuron health. Therefore, the ideal therapeutic strategy would be to inhibit selectively the mutant protein expression. Previously we have demonstrated that RNA interference (RNAi) can selectively inhibit some mutant SOD1 expression. However, more than 100 SOD1 mutants can cause ALS and all mutants cannot be inhibited selectively by RNAi. To overcome this obstacle, we have designed a replacement RNAi strategy. Using this strategy, all mutants and wild-type genes are inhibited by RNAi. The wild-type SOD1 function is then replaced by designed wild-type SOD1 genes that are resistant to the RNAi. Here we demonstrate the concept of this strategy.

The effect of peripheral nerve injury on disease progression in the SOD1(G93A) mouse model of amyotrophic lateral sclerosis

Around 20% of familial cases of amyotrophic lateral sclerosis have been shown to carry mutations in Cu/Zn superoxide dismutase 1 (Cu/Zn SOD1). Transgenic mice over-expressing human mutant SOD1 genes have been developed and in this study we examined the effect of nerve injury on disease progression in these mice. Firstly, disease progression in uninjured mice was characterised using physiological methods. Muscle force, contractile characteristics and motor unit survival was established at 90 days, an early symptomatic stage and also at the end-stage of the disease, at 130 days. In addition, muscle histochemistry was examined and the extent of motoneuron survival established morphologically. By 90 days of age, there is a significant reduction in muscle force, and nearly 40% of motoneurons within the sciatic motor pool have already died. By 130 days, the muscles are significantly weaker, and there is a dramatic change in the phenotype of extensor digitorum longus (EDL), which changes from a fast fatigable muscle, to a fatigue resistant muscle with a high oxidative capacity. By this stage of the disease, only 40% of motor units in EDL survive, with only 29% of motoneurons surviving within the sciatic motor pool. Following injury to the sciatic nerve in SOD1(G93A) mice, there is an acceleration in disease progression so that 90 day old mice show deficits that are only seen at the end stage in uninjured SOD1(G93A) mice. It is therefore possible that mutant SOD1 toxicity increases the vulnerability of motoneurons and muscles to stressful stimuli such as nerve injury.

Inhibition of Chaperone Activity Is a Shared Property of Several Cu,Zn-Superoxide Dismutase Mutants That Cause Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive motor neuron degeneration, paralysis, and death. Mutant Cu,Zn-superoxide dismutase (SOD1) causes a subset of ALS by an unidentified toxic property. Increasing evidence suggests that chaperone dysfunction plays a role in motor neuron degeneration in ALS. To investigate the relationship between mutant SOD1 expression and chaperone dysfunction, we measured chaperone function in central nervous system tissue lysates from normal mice and transgenic mice expressing human SOD1 variants. We observed a significant decrease in chaperone activity in tissues from mice expressing ALS-linked mutant SOD1 but not control mice expressing human wild type SOD1. This decrease was detected only in the spinal cord, became apparent by 60 days of age (before the onset of muscle weakness and significant motor neuron loss), and persisted throughout the late stages. In addition, this impairment of chaperone activity occurred only in cytosolic but not in mitochondrial and nuclear fractions. Furthermore, multiple recombinant human SOD1 mutants with differing biochemical and biophysical properties inhibited chaperone function in a cell-free extract of normal mouse spinal cords. Thus, mutant SOD1 proteins may impair chaperone function independent of gene expression in vivo, and this inhibition may be a shared property of ALS-linked mutant SOD1 proteins.

Activation of the stress-activated MAP kinase, p38, but not JNK in cortical motor neurons during early presymptomatic stages of amyotrophic lateral sclerosis in transgenic mice

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder, characterized by the degeneration of upper and lower motor neurons (MNs). Central nervous system features include a loss of Betz cells and other pyramidal cells from sensorimotor cortex. The intrinsic mechanism underlying this selective motor neuron loss has not been identified. A recent in vitro study has provided evidence of a novel programmed cell death (PCD) pathway that is unique to spinal cord MNs and is exacerbated by superoxide dismutase (SOD) mutations. This PCD pathway is triggered through the Fas receptor and involves the apoptosis signal-regulating kinase 1 (ASK1), the p38 MAP kinase, and the neuronal form of nitric oxide synthase (nNOS). Previously, we found significant increases in the numbers of ventral horn MNs immunopositive for these enzymes in the spinal cords of mutant SOD transgenic (G93A) mice as early as 60 days of age, suggesting that this pathway may be active in vivo. Since the upper MNs of ALS patients and G93A mice are also known to degenerate, the purpose of the present study was to investigate the possible activation of this PCD pathway in the MNs of the sensorimotor cortex of G93A transgenic mice. Compared to non-transgenic littermates, the G93A mice showed significant increases in the numbers of MNs immunopositive for the active (phosphorylated) forms of ASK1, p38, MKK3/6 (the known activator of p38), and also active caspase-3, as early as 60 days of age. Another stress-activated protein kinase, c-Jun N-terminal kinase (JNK), commonly activated in other neurodegenerative disorders such as Alzheimer's disease, showed no increases in G93A mice at any age. These results suggest that, not only has a PCD pathway been activated in the cortical MNs, but one that may be unique to ALS. Moreover, these findings suggest that earlier diagnosis and therapeutic intervention may be possible for successful treatment of ALS. Consequently, these enzymes may provide the biochemical markers to enable earlier diagnosis of ALS and molecular targets for the development of new therapeutic compounds.

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.

The metabolic hypothesis in amyotrophic lateral sclerosis: insights from mutant Cu/Zn-superoxide dismutase mice

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by selective loss of motor neurons and progressive muscle atrophy. A subset of patients harbors point mutations in the gene encoding Cu/Zn-superoxide dismutase (SOD1), which allowed the generation of transgenic mice that express different SOD1 mutations and develop an ALS-like pathology. Recently, we reported in these mice the occurrence of a characteristic defect in energy homeostasis and the beneficial effect on the course of the disease of a high-energy fat-enriched diet. In this review, we discuss the implication of these findings in the light of classical clinical observations concerning metabolic alterations in human ALS.

Distinct cerebral lesions in sporadic and 'D90A' SOD1 ALS: studies with [11C]flumazenil PET

Five to ten percent of amyotrophic lateral sclerosis (ALS) cases are associated with mutations of the superoxide dismutase-1 (SOD1) gene, and the 'D90A' mutation is associated with a unique phenotype and markedly slower disease progression (mean survival time 14 years). Relative sparing of inhibitory cortical neuronal circuits might be one mechanism contributing to the slower progression in patients homozygous for the D90A mutation (homD90A). The GABA(A) receptor PET ligand [11C]flumazenil has demonstrated motor and extra-motor cortical changes in sporadic ALS. In this study, we used [11C]flumazenil PET to explore differences in the pattern of cortical involvement between sporadic and genetically homogeneous ALS groups. Twenty-four sporadic ALS (sALS) and 10 homD90A patients underwent [11C]flumazenil PET of the brain. In addition, two subjects homozygous for the D90A mutation, but without symptoms or signs ('pre-symptomatic', psD90A), also underwent imaging. Results for each group were compared with those for 24 healthy controls of similar age. Decreases in the binding of [11C]flumazenil in the sALS group were found within premotor regions, motor cortex and posterior motor association areas. In the homD90A group of ALS patients, however, decreases were concentrated in the left fronto-temporal junction and anterior cingulate gyrus. In the two psD90A subjects, a small focus of reduced [11C]flumazenil binding at the left fronto-temporal junction was seen, similar to the pattern seen in the clinically affected patients. Within the sALS group, there was no statistically significant association between decreases in cortical [11C]flumazenil binding and revised ALS functional rating scale (ALSFRS-R score), whereas the upper motor neuron (UMN) score correlated with widespread and marked cortical decreases over the dominant hemisphere. In the homD90A group, there was a stronger statistical association between reduced cortical [11C]flumazenil binding and the ALSFRS-R, rather than the UMN, score, and also with disease duration. This study provides evidence for differences in the distribution of reduced cortical [11C]flumazenil binding in homD90A compared with sALS patients. We hypothesize that this might reflect differences in cortical neuronal vulnerability.

Genetically decreased spinal cord copper concentration prolongs life in a transgenic mouse model of amyotrophic lateral sclerosis

Mutations in the Cu/Zn superoxide dismutase (SOD1) gene cause familial amyotrophic lateral sclerosis (FALS) by gain of an aberrant function that is not yet well understood. The role of Cu(2+) in mediating the toxicity of mutant SOD1 has been earnestly contested. We tested the in vivo effects of genetically induced copper deprivation on the ALS phenotype of transgenic mice expressing G86R mutant mouse SOD1, a protein that fails to incorporate Cu(2+) in its active site. Genetically copper-deficient SOD1(G86R) transgenic mice were produced by mating SOD1(G86R) males to female carriers of the X-linked mottled/brindled (Mobr) mutation. We found that the Mobr allele causes a severe ( approximately 60%) depletion of spinal cord copper levels; however, despite the burden of double genetic lesions, it lengthens the lives of SOD1(G86R) transgenic mice by 9%. These findings provide evidence supporting a role for copper in the pathogenesis of FALS linked to SOD1 mutations.

Unsaturated fatty acids induce cytotoxic aggregate formation of amyotrophic lateral sclerosis-linked superoxide dismutase 1 mutants

Formation of misfolded protein aggregates is a remarkable hallmark of various neurodegenerative diseases including Alzheimer disease, Parkinson disease, Huntington disease, prion encephalopathies, and amyotrophic lateral sclerosis (ALS). Superoxide dismutase 1 (SOD1) immunoreactive inclusions have been found in the spinal cord of ALS animal models and patients, implicating the close involvement of SOD1 aggregates in ALS pathogenesis. Here we examined the molecular mechanism of aggregate formation of ALS-related SOD1 mutants in vitro. We found that long-chain unsaturated fatty acids (FAs) promoted aggregate formation of SOD1 mutants in both dose- and time-dependent manners. Metal-deficient SOD1s, wild-type, and mutants were highly oligomerized compared with holo-SOD1s by incubation in the presence of unsaturated FAs. Oligomerization of SOD1 is closely associated with its structural instability. Heat-treated holo-SOD1 mutants were readily oligomerized by the addition of unsaturated FAs, whereas wild-type SOD1 was not. The monounsaturated FA, oleic acid, directly bound to SOD1 and was characterized by a solid-phase FA binding assay using oleate-Sepharose. The FA binding characteristics were closely correlated with the oligomerization propensity of SOD1 proteins, which indicates that FA binding may change SOD1 conformation in a way that favors the formation of aggregates. High molecular mass aggregates of SOD1 induced by FAs have a granular morphology and show significant cytotoxicity. These findings suggest that SOD1 mutants gain FA binding abilities based on their structural instability and form cytotoxic granular aggregates.

Integrative role of cPLA2with COX-2 and the effect of non-steriodal anti-inflammatory drugs in a transgenic mouse model of amyotrophic lateral sclerosis

Cyclooxygenase-2 (COX-2) is a key molecule in the inflammatory pathway in amyotrophic lateral sclerosis (ALS). Cytosolic phospholipase A (cPLA2) is an important enzyme providing substrate for cyclooxygenases. We therefore examined cPLA2 expression in human ALS and mutant Cu/Zn superoxide dismutase (SOD1) transgenic mice and its relation to COX-2. Immunohistochemistry and real-time RT-PCR revealed elevated cPLA2 protein and its mRNA levels in the lumbar spinal cord of mutant SOD1 mice. COX-2 immunoreactivity was increased in lumbar spinal cord sections from both familial ALS (FALS) and sporadic ALS (SALS) as compared to controls, and cPLA2 immunoreactivity was increased in a patient with FALS. Oral administration of the non-selective cyclooxygenase (COX) inhibitor, sulindac, extended the survival (by 10%) of G93A SOD1 mice as compared to littermate controls. Sulindac, as well as the selective COX-2 inhibitors, rofecoxib and celecoxib reduced cPLA2 immunoreactivity in the lumbar spinal cord of G93A transgenic mice. Sulindac treatment preserved motor neurons, and reduced microglial activation and astrocytosis, in the spinal cord of G93A SOD1 transgenic mice. These results suggest that cPLA2 plays an important role in supplying arachidonic acid to the COX-2 driven inflammatory pathway in ALS associated with SOD1 mutations.

Role of matrix metalloproteinase-9 in a mouse model for amyotrophic lateral sclerosis

The pathogenesis of amyotrophic lateral sclerosis remains poorly understood, but microglial and astroglial activation are thought to contribute to motor neuron death. Evidence suggests that matrix metalloproteinase-9 (MMP-9) is a mediator of this deleterious effect. In this study, we evaluated the effect of MMP-9 on the pathogenesis of amyotrophic lateral sclerosis. Although marked microglial and astroglial proliferation was seen in the spinal cord and in-vitro studies proved MMP-9 to be produced by these cells, deletion of the MMP-9 gene in SOD1(G93A) mice accelerated rather than delayed the motor neuron disease and significantly reduced survival. Our results suggest that the effect of MMP-9 on mutant superoxide dismutase-1 (SOD1)-induced motor neuron disease is protective rather than hazardous. Therefore, the effect of pharmacological inhibition of MMP-9 activity is unlikely to be of therapeutical benefit in amyotrophic lateral sclerosis.

Radio-sensitivity of the cells from amyotrophic lateral sclerosis model mice transfected with human mutant SOD1

In order to clarify the possible involvement of oxidative damage induced by ionizing radiation in the onset and/or progression of familial amyotrophic lateral sclerosis (ALS), we studied radio-sensitivity in primary cells derived from ALS model mice expressing human mutant SOD1. The primary mouse cells expressed both mouse and the mutant human SOD1. The cell survival of the transgenic mice (with mutant SOD1), determined by counting cell numbers at a scheduled time after X-irradiation, is very similar to that of cells from wild type animals. The induction and repair of DNA damage in the transgenic cells, measured by single cell gel electrophoresis and pulsed field gel electrophoresis, are also similar to those of wild type cells. These results indicate that the human mutant SOD1 gene does not seem to contribute to the alteration of radio-sensitivity, at least in the fibroblastic cells used here. Although it is necessary to consider the difference in cell types between fibroblastic and neuronal cells, the present results may suggest that ionizing radiation is not primarily responsible for the onset of familial ALS with the SOD1 mutation, and that the excess risks are probably not a concern for radiation diagnosis and therapy in familial ALS patients.

Small-molecule-mediated stabilization of familial amyotrophic lateral sclerosis-linked superoxide dismutase mutants against unfolding and aggregation

Familial amyotrophic lateral sclerosis (FALS) is a fatal motor neuron disease that is caused by mutations in the gene encoding superoxide dismutase-type 1 (SOD1). The affected regions of the FALS brain are characterized by aggregated SOD1, and the mutations that destabilize SOD1 appear to promote its aggregation in vitro. Because dissociation of the native SOD1 dimer is required for its in vitro aggregation, we initiated an in silico screening program to find drug-like molecules that would stabilize the SOD1 dimer. A potential binding site for such molecules at the SOD1 dimer interface was identified, and its importance was validated by mutagenesis. About 1.5 million molecules from commercial databases were docked at the dimer interface. Of the 100 molecules with the highest predicted binding affinity, 15 significantly inhibited in vitro aggregation and denaturation of A4V, a FALS-linked variant of SOD1. In the presence of several of these molecules, A4V and other FALS-linked SOD1 mutants such as G93A and G85R behaved similarly to wild-type SOD1, suggesting that these compounds could be leads toward effective therapeutics against FALS.

[Sporadic amyotrophic lateral sclerosis associated with Asp90Ala CuZn-superoxide dismutase mutations in Russia]

16 blood samples from Russian patients (Moscow) with idiopathic motor neuron disease were analysed for mutations in the CuZn-superoxide dismutase gene. Two patients (12.5%) with amyotrophic lateral sclerosis (ALS) were found to have a disease related mutation. One patient appears to have autosomal recessive adult-onset ALS associated with homozygosity for Asp90Ala and presents the characteristic phenotype of very slowly ascending paresis with both lower and upper motor neuron signs. The other patient heterozygous for Asp90Ala presents ALS with lumbar onset and rapid progression. Both of cases are apparently sporadic.

Aberrant δPKC activation in the spinal cord of Wobbler mouse: a model of motor neuron disease

Protein kinase C (PKC) was suggested to play a role in the pathology of amyotrophic lateral sclerosis (ALS) patients. Activation of PKC delta (deltaPKC) modulates mitochondrially induced apoptosis. The goal of the present study was to define whether deltaPKC activation occurs in Wobbler mouse spinal cord (a model of motor neuron disease). The level of deltaPKC in the soluble fraction was significantly decreased in the spinal cord of Wobbler mice, which was associated with a significant increase in deltaPKC cleavage. Since caspase-3 is known to cleave deltaPKC, we determined caspase-3 activation in the Wobbler mice spinal cord, immunohistochemically. The results demonstrated intense immunoreactivity for activated caspase-3 in corticospinal tract motor neurons of Wobbler mice spinal cord. We hypothesize from these results that caspase-3 activation cleaves deltaPKC, which in turn promotes an aberrant signal transduction pathway in the Wobbler spinal cord.

Widespread increased expression of the DNA repair enzyme PARP in brain in ALS

Expression of the DNA repair enzyme poly(ADP-ribose) polymerase (PARP) is a known response to oxidative damage of DNA. In ALS brain, PARP expression by western analyses was increased in the motor cortex, parietal cortex, and cerebellum. PARP immunostaining in the motor cortex was increased in ALS neurons and subcortical glia and macrophages. Importantly, there was widespread increased PARP expression in neurons in the parietal cortex and cerebellum, regions that are typically clinically unaffected in ALS, suggesting widespread oxidative stress.

Impaired extracellular secretion of mutant superoxide dismutase 1 associates with neurotoxicity in familial amyotrophic lateral sclerosis

Mutations in the intracellular metalloenzyme superoxide dismutase 1 (SOD1) are linked to neurotoxicity in familial amyotrophic lateral sclerosis (ALS) by an unclear mechanism. Golgi fragmentation and endoplasmic reticulum stress are early hallmarks of spinal motor neuron pathology in transgenic mice overexpressing mutant SOD1, suggesting that dysfunction of the neuronal secretory pathway may contribute to ALS pathogenesis. We therefore proposed that mutant SOD1 directly engages and modulates the secretory pathway based on recent evidence of SOD1 secretion in diverse human cell lines. Here, we demonstrate that a fraction of active endogenous SOD1 is secreted by NSC-34 motor neuron-like cells via a brefeldin-A (BFA)-sensitive pathway. Expression of enhanced green fluorescent protein-tagged mutant human SOD1 (hSOD1-EGFP) in NSC-34 cells induced frequent cytoplasmic inclusions and protein insolubility that correlated with toxicity. In contrast, transfection of non-neuronal COS-7 cells resulted in mutant hSOD1-EGFP cytoplasmic inclusions, oligomerization, and fragmentation without detectable toxicity. Importantly, impaired secretion of hSOD1-EGFP was common to all 10 SOD1 mutants tested relative to wild-type protein in NSC-34 cells. Treatment with BFA inhibited hSOD1-EGFP secretion with pronounced BFA-induced toxicity in mutant cells. Extracellular targeting of mutant hSOD1-EGFP via SOD3 signal peptide fusion attenuated cytoplasmic inclusion formation and toxicity. The effect of elevated extracellular SOD1 was then evaluated in a transgenic rat model of ALS. Chronic intraspinal infusion of exogenous wild-type hSOD1 significantly delayed disease progression and endpoint in transgenic SOD1(G93A) rats. Collectively, these results suggest novel extracellular roles for SOD1 in ALS and support a causal relationship between mutant SOD1 secretion and intraneuronal toxicity.

Mice with the deleted neurofilament of low molecular weight (Nefl) gene: 2. Effects on motor functions and spatial orientation

Mice with a null mutation of the Nefl gene were compared with normal controls in tests of motor activity, equilibrium, and spatial orientation. Despite a normal capacity to ambulate, NFL -/- mice had fewer rears in an open field, crossed fewer segments on stationary beams, and fell more frequently when suspended on a horizontal bar. In addition, the distance swum before reaching the escape platform was greater in NFL -/- mice than in controls during acquisition of place learning in the Morris water maze at the start of training. The motor impairments were linearly correlated with increased cytochrome oxidase activity seen in cerebellum and brainstem. These results indicate that, as early as 6 months, depletion of the NFL protein is sufficient to cause mild sensorimotor dysfunctions and spatial deficits, but without overt signs of paresis.

RNAi knockdown of Par-4 inhibits neurosynaptic degeneration in ALS-linked mice

Evidence from human amyotrophic lateral sclerosis (ALS) patients and ALS-linked Cu/Zn superoxide dismutase (Cu/Zn-SOD) transgenic mice bearing the mutation of glycine to alanine at position 93 (G93A) suggests that the pro-apoptotic protein prostate apoptosis response-4 (Par-4) might be a critical link in the chain of events leading to motor neuron degeneration. We now report that Par-4 is enriched in synaptosomes and post-synaptic density from the ventral horn of the spinal cord. Levels of Par-4 in synaptic compartments increased significantly during rapid and slow declining stages of muscle strength in hSOD1 G93A mutant mice. In the pre-muscle weakness stage, hSOD1 G93A mutation sensitized synaptosomes from the ventral horn of the spinal cord to increased levels of Par-4 expression following excitotoxic and apoptotic insults. In ventral spinal synaptosomes, Par-4-mediated production of pro-apoptotic cytosolic factor(s) was significantly enhanced by the hSOD1 G93A mutation. RNA interference (RNAi) knockdown of Par-4 inhibited mitochondrial dysfunction and caspase-3 activation induced by G93A mutation in synaptosomes from the ventral horn of the spinal cord, and protected spinal motor neurons from apoptosis. These results identify the synapse as a crucial cellular site for the cell death promoting actions of Par-4 in motor neurons, and suggest that targeted inhibition of Par-4 by RNAi may prove to be a neuroprotective strategy for motor neuron degeneration.

Caloric restriction transiently improves motor performance but hastens clinical onset of disease in the Cu/Zn-superoxide dismutase mutant G93A mouse

Caloric restriction (CR) prolongs lifespan in insects, rodents, and nonhuman primates, a process attributed to a reduction in oxidative stress. Transgenic mice that overexpress the mutant human Cu/Zn-superoxide dismutase (SOD1) gene (G93A mice) are an animal model of amyotrophic lateral sclerosis showing progressively lower motor neuron weakness and increased oxidative stress. We investigated the effect of CR on motor performance, clinical onset, disease progression, and lifespan in G93A mice. Starting at 40 days of age, 14 separately caged G93A mice were randomly divided into two groups: ad libitum (AL; n = 6) and calorie-restricted (CR; n = 8) with a diet equal to 60% of AL. The CR mice (mean +/- SEM: 14.0 +/- 0.7 g) weighed 31% less than the AL mice (20.3 +/- 1.0 g) (P = 0.0002). From 74 to 93 days of age, the CR mice performed better on the rotarod than the AL mice: fall time, P = 0.039; fall speed, P = 0.009. The CR mice had a faster rate of reaching clinical onset than the AL mice (hazard ratio = 4.3, P = 0.0006). The CR and AL mice reached clinical onset of disease at age 99 +/- 1 and 110 +/- 2 days, respectively (P = 0.0003), with no significant difference in disease progression. The CR mice tended to reach endpoint sooner than the AL mice (age-specific death: 125 +/- 3 vs. 133 +/- 3 days, respectively, P = 0.09). We conclude that CR diet transiently improves motor performance but hastens clinical onset of disease in G93A mice. These results suggest that CR diet is not a protective strategy for patients with amyotrophic lateral sclerosis (ALS) and hence is contraindicated.

Mice with the deleted neurofilament of low-molecular-weight (Nefl) gene: 1. Effects on regional brain metabolism

Neuronal intermediate filaments consist of the NFL subunit linked with NFM and NFH, and their alterations have been proposed as a pathogenesic cause in motor neuron diseases. Depletion of the Nefl gene in mice mimicks the reduced NFL mRNA levels seen in amyotrophic lateral sclerosis and causes perikaryal accumulation of neurofilament proteins and axonal hypotrophy in motoneurons. NFL -/- mice were evaluated for regional brain metabolism by means of quantitative histochemical estimation of cytochrome oxidase (COx) activity. The NFL null mice displayed enzymatic activity alterations in numerous hindbrain regions, mainly the cerebellum, connected regions of the brainstem (red nucleus, vestibular nuclei, and reticular formation), and cranial nerve nuclei. All of the affected regions presented elevated COx activity, except for the Purkinje cells of the cerebellum and the magnocellular red nucleus, where enzymatic activity was lower. NFL-disrupted mice displayed functional alterations in brainstem sensorimotor regions affected in amyotrophic lateral sclerosis.

Impairment of glutamate transport and increased vulnerability to oxidative stress in neuroblastoma SH-SY5Y cells expressing a Cu,Zn superoxide dismutase typical of familial amyotrophic lateral sclerosis

Human neuroblastoma SH-SY5Y cells transfected with either familial amyotrophic lateral sclerosis-typical G93A mutant or wild-type copper/zinc superoxide dismutase were compared to untransfected cells in term of glutamate transport. Vmax of glutamate uptake was reduced in mutant cells, with no change in Km. No difference in EAAT1, EAAT2 and EAAT3 glutamate transporter mRNAs and immunoreactive proteins was found, suggesting that one or more transporters are functionally inactivated, possibly due to increased oxidative stress induced by the G93A mutation. Mutant cells showed a marked sensitivity to oxidants, resulting in a more pronounced reduction of glutamate uptake. Short-term antioxidant treatment did not reverse the impairment of glutamate uptake in G93A cells. Interestlingly, N-acetylcysteine was partially effective in preventing glutamate uptake reduction due to exogenous oxidative insults. Since the inhibition of the EAAT2 transporter subtype had no effect on glutamate re-uptake in this model, our study suggests an impaired function of the EAAT1/3 transporter subtypes, possibly due to oxidative inactivation, in the presence of mutant copper/zinc superoxide dismutase. Therefore, this model might prove to be a valuable tool to study the effects of mutant copper/zinc superoxide dismutase associated with amyotrophic lateral sclerosis on glutamate transport in neuronal cells, without the specific contribution of glial cells. These findings might lead to the identification of new therapeutic strategies aimed at preventing the damage associated with ALS.

Expression of a familial amyotrophic lateral sclerosis-associated mutant human superoxide dismutase in yeast leads to decreased mitochondrial electron transport

Strains of Saccharomyces cerevisiae that express either the wild type or the amyotrophic lateral sclerosis-associated mutant human copper-zinc superoxide dismutase (SOD1) proteins A4V and G93A, respectively, in a yeast SOD1-deficient parent strain were used to investigate the hypothesis that expression of a mutant SOD1 protein causes deficient mitochondrial electron transport as a possible mechanism for disease induction. Mitochondria isolated from the wild type SOD1-expressing yeast were identical to mitochondria from the parent strain in heme content and activities of complexes II, III, and IV. Mitochondria isolated from the A4V-expressing yeast had decreased rates of electron transport in complexes II+III, III, and IV and corresponding decreases in hemes b, c-c1, and a-a3 content compared to mitochondria from wild type human SOD1-expressing yeast. Mitochondria isolated from G93A-expressing yeast had decreased rates of electron transport in complex IV and probably in complex II with a corresponding decrease in heme a-a3 content. These results suggest that mutant SOD1-expression causes defective electron transport complex assembly and that the yeast system will provide an excellent model for the study of the mechanism of mutant SOD1-induced mitochondrial electron transport defects.

Folding of human superoxide dismutase: disulfide reduction prevents dimerization and produces marginally stable monomers

The molecular mechanism by which the homodimeric enzyme Cu/Zn superoxide dismutase (SOD) causes neural damage in amytrophic lateral sclerosis is yet poorly understood. A striking, as well as an unusual, feature of SOD is that it maintains intrasubunit disulfide bonds in the reducing environment of the cytosol. Here, we investigate the role of these disulfide bonds in folding and assembly of the SOD apo protein (apoSOD) homodimer through extensive protein engineering. The results show that apoSOD folds in a simple three-state process by means of two kinetic barriers: 2D<==>2M<==>M(2). The early predominant barrier represents folding of the monomers (M), and the late barrier the assembly of the dimer (M(2)). Unique for this mechanism is a dependence of protein concentration on the unfolding rate constant under physiological conditions, which disappears above 6 M Urea where the transition state for unfolding shifts to first-order dissociation of the dimer in accordance with Hammond-postulate behavior. Although reduction of the intrasubunit disulfide bond C57-C146 is not critical for folding of the apoSOD monomer, it has a pronounced effect on its stability and abolishes subsequent dimerization. Thus, impaired ability to form, or retain, the C57-C146 bond in vivo is predicted to increase the cellular load of marginally stable apoSOD monomers, which may have implications for the amytrophic lateral sclerosis neuropathology.

The pro and the active form of matrix metalloproteinase-9 is increased in serum of patients with amyotrophic lateral sclerosis

Pro and active-matrix metalloproteinase-9 (MMP-9) was measured in sera from patients with amyotrophic lateral sclerosis (ALS), Guillain-Barre syndome (GBS), and healthy subjects. Both forms of MMP-9 were elevated in sera of ALS and GBS patients, compared with healthy controls. It has been postulated that elevated MMP-9 reflects damage to peripheral nerve and muscle. This possibility was investigated in sera, and tissue extracts of sciatic nerves and muscle from mice 5 and 12 days after axotomy of the sciatic nerve. Pro-MMP-9 was elevated in sera and extracts of damaged nerve and muscle, suggesting such damage may be followed by elevated pro-MM9-9 in sera. Active MMP-9 was only elevated in the sera. However, in situ activation of MMP-9 is tightly regulated and localised, and probably difficult to demonstrate by ELISA, resulting in a short half-life active MMP-9, implying any active MMP-9 in the serum may have a more immediate origin than injured muscle or nerve, for example circulating blood cells.

The rate and equilibrium constants for a multistep reaction sequence for the aggregation of superoxide dismutase in amyotrophic lateral sclerosis

Mutation-induced aggregation of the dimeric enzyme Cu, Zn superoxide dismutase 1 (SOD1) has been implicated in the familial form of the disease amyotrophic lateral sclerosis, but the mechanism of aggregation is not known. Here, we show that in vitro SOD1 aggregation is a multistep reaction that minimally consists of dimer dissociation, metal loss from the monomers, and oligomerization of the apo-monomers: [reaction: see text], where D(holo), M(holo), M(apo), and A are the holo-dimer, holo-monomer, apo-monomer, and aggregate, respectively. Under aggregation-promoting conditions (pH 3.5), the rate and equilibrium constants corresponding to each step are: (i) dimer dissociation, Kd approximately 1 microM; k(off) approximately 1 x 10(-3) s(-1), k(on) approximately 1 x 10(3) M(-1).s(-1); (ii) metal loss, Km approximately 0.1 microM, km- approximately 1 x 10(-3)s(-1), km+ approximately 1 x 10(4) M(-1).s(-1); and (iii) assembly (rate-limiting step), k(agg) approximately 1 x 10(3) M(-1).s(-1). In contrast, under near-physiological conditions (pH 7.8), where aggregation is drastically reduced, dimer dissociation is less thermodynamically favorable: Kd approximately 0.1 nM, and extremely slow: k(off) approximately 3 x 10(-5) s(-1), k(on) approximately 3 x 10(5) M(-1).s(-1). Our results suggest that familial amyotrophic lateral sclerosis-linked SOD1 aggregation occurs by a mutation-induced increase in dimer dissociation and/or increase in apomonomer formation.

Antisense peptide nucleic acid targeting GluR3 delays disease onset and progression in the SOD1 G93A mouse model of familial ALS

Glutamate excitotoxicity is strongly implicated as a major contributing factor in motor neuron degeneration in amyotrophic lateral sclerosis (ALS). Excitotoxicity results from elevated intracellular calcium ion (Ca(2+)) levels, which in turn recruit cell death signaling pathways. Recent evidence suggests that alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor subunit (GluR) stoichiometry is a dominant factor leading to excess Ca(2+) loading in neurodegeneration. In particular, the Ca(2+) permeable glutamate receptor subunit 3 (GluR3) has been implicated in several neurologic conditions such as bipolar disorder and epilepsy. Recent proteomic analysis within our group on the copper zinc superoxide dismutase (SOD1)(G93A) transgenic mouse model of familial ALS (FALS) reveals a potentially deleterious upregulation of GluR3 in spinal cord compared to that in wild-type littermates. Based on this finding we designed a 12mer antisense peptide nucleic acid (PNA) directed against GluR3. This sequence significantly reduced levels of GluR3 protein and protected neuroblastoma x spinal cord (NSC-34) cells against death induced by the AMPA receptor-specific agonist (S)-5-fluorowillardiine. We subsequently treated SOD1(G93A) mice thrice weekly with intraperitoneal injections of the antisense PNA (2.5 mg/kg) commencing at postnatal day 50. Mice treated with the antisense sequence had significantly extended survival compared to mice injected with a nonsense sequence. Western blot analysis, however, did not reveal a significant reduction in GluR3 protein levels in whole extracts of the lumbar spinal cord. These results suggest that interference with the GluR3 component of the AMPA receptor assembly may be a novel strategy for controlling excitotoxic destruction of motor neurons and may lead to new therapeutic opportunities for the treatment of human ALS.

Induction of cyclooxygenase-2 in reactive glial cells by the CD40 pathway: relevance to amyotrophic lateral sclerosis

An inflammatory process in association with reactive gliosis has been suggested to play an important role in the pathogenesis of amyotrophic lateral sclerosis (ALS). One of the key findings is a marked increase in the level of cyclooxygenase-2 (COX-2), a therapeutic target of ALS. We investigated the expression of CD40 in the spinal cord of a transgenic mouse model of ALS (G93A mice), and its relevance to COX-2 upregulation. CD40 was predominantly expressed in neurons in normal spinal cord and upregulated in reactive glial cells in spinal cord injury. In the spinal cord of G93A mice, the expression of CD40 was increased in both reactive microglia and astrocytes, where COX-2 was especially increased. The level of COX-2 was upregulated in microglia and astrocytes by CD40 stimulation in vitro. CD40 stimulation in primary spinal cord cultures caused motor neuron loss that was protected by selective COX-2 inhibitor. These results suggest that CD40, which is upregulated in reactive glial cells in ALS, participates in motor neuron loss via induction of COX-2.

Rasagiline alone and in combination with riluzole prolongs survival in an ALS mouse model

Rasagiline is an antiapoptotic compound with neuroprotective potential. We examined its neuroprotective effect alone and in combination with the putative glutamate release blocker riluzole in the G93A model of familial amyotrophic lateral sclerosis (fALS). Endpoints of experimental treatment were survival and motor activity. The drug had a significant dose-dependent therapeutic effect on both preclinical and clinical motor function and survival of the animals. We also found that the combination of rasagiline with riluzole is safe and increases survival by about 20 % in a dose-dependent manner. Therefore, we conclude that the combination of rasagiline and riluzole is a promising clinical combination for the improvement of current neuroprotective treatment strategies of ALS.

CHIP promotes proteasomal degradation of familial ALS-linked mutant SOD1 by ubiquitinating Hsp/Hsc70

Over 100 mutants in superoxide dismutase 1 (SOD1) are reported in familial amyotrophic lateral sclerosis (ALS). However, the precise mechanism by which they are degraded through a ubiquitin-proteasomal pathway (UPP) remains unclear. Here, we report that heat-shock protein (Hsp) or heat-shock cognate (Hsc)70, and the carboxyl terminus of the Hsc70-interacting protein (CHIP), are involved in proteasomal degradation of mutant SOD1. Only mutant SOD1 interacted with Hsp/Hsc70 in vivo, and in vitro experiments revealed that Hsp/Hsc70 preferentially interacted with apo-SOD1 or dithiothreitol (DTT)-treated holo-SOD1, compared with metallated or oxidized forms. CHIP, a binding partner of Hsp/Hsc70, interacted only with mutant SOD1 and promoted its degradation. Both Hsp70 and CHIP promoted polyubiquitination of mutant SOD1-associated molecules, but not of mutant SOD1, indicating that mutant SOD1 is not a substrate of CHIP. Moreover, mutant SOD1-associated Hsp/Hsc70, a known substrate of CHIP, was polyubiquitinated in vivo, and polyubiquitinated Hsc70 by CHIP interacted with the S5a subunit of the 26S proteasome in vitro. Furthermore, CHIP was predominantly expressed in spinal neurons, and ubiquitinated inclusions in the spinal motor neurons of hSOD1(G93A) transgenic mice were CHIP-immunoreactive. Taken together, we propose a novel pathway in which ubiquitinated Hsp/Hsc70 might deliver mutant SOD1 to, and facilitate its degradation, at the proteasome.

Calcium-permeable AMPA receptors promote misfolding of mutant SOD1 protein and development of amyotrophic lateral sclerosis in a transgenic mouse model

Mutant Cu/Zn-superoxide dismutase (SOD1) protein aggregation has been suggested as responsible for amyotrophic lateral sclerosis (ALS), although the operative mediating factors are as yet unestablished. To evaluate the contribution of motoneuronal Ca2+-permeable (GluR2 subunit-lacking) alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-type glutamate receptors to SOD1-related motoneuronal death, we generated chat-GluR2 transgenic mice with significantly reduced Ca2+-permeability of these receptors in spinal motoneurons. Crossbreeding of the hSOD1G93A transgenic mouse model of ALS with chat-GluR2 mice led to marked delay of disease onset (19.5%), mortality (14.3%) and the pathological hallmarks such as release of cytochrome c from mitochondria, induction of cox2 and astrogliosis. Subcellular fractionation analysis revealed that unusual SOD1 species first accumulated in two fractions dense with neurofilaments/glial fibrillary acidic protein/nuclei and mitochondria long time before disease onset, and then concentrated into the former fraction by disease onset. All these processes for unusual SOD1 accumulation were considerably delayed by GluR2 overexpression. Ca2+-influx through atypical motoneuronal AMPA receptors thus promotes a misfolding of mutant SOD1 protein and eventual death of these neurons.