Superoxide dismutase is an abundant component in cell bodies, dendrites, and axons of motor neurons and in a subset of other neurons

Neurodegeneration in amyotrophic lateral sclerosis: the role of oxidative stress and altered homeostasis of metals

Amyotrophic lateral sclerosis is one of the most common neurodegenerative disorders, with an incidence of about 1/100,000. One of the typical features of this progressive, lethal disease, occurring both sporadically and as a familial disorder, is degeneration of cortical and spinal motor neurones. Present evidence indicates that loss of neurones in patients results from a complex interplay among oxidative injury, excitotoxic stimulation, dysfunction of critical proteins and genetic factors. This review focuses on existing evidence that oxidative stress is a major culprit in the pathogenesis of amyotrophic lateral sclerosis. An increase in reactive oxygen species and in products of oxidation has been observed both in post-mortem samples and in experimental models for ALS. This increase may be consequent to altered metabolism of copper and iron ions, that share the property to undergo redox cycling and generate reactive oxygen species. Metal-mediated oxidative stress would lead to several intracellular alterations and contribute to the induction of cell death pathways.

Human embryonic germ cell derivatives facilitate motor recovery of rats with diffuse motor neuron injury

We have investigated the potential of human pluripotent cells to restore function in rats paralyzed with a virus-induced motor neuronopathy. Cells derived from embryonic germ cells, termed embryoid body-derived (EBD) cells, introduced into the CSF were distributed extensively over the rostrocaudal length of the spinal cord and migrated into the spinal cord parenchyma in paralyzed, but not uninjured, animals. Some of the transplanted human cells expressed the neuroglial progenitor marker nestin, whereas others expressed immunohistochemical markers characteristic of astrocytes or mature neurons. Rare transplanted cells developed immunoreactivity to choline acetyltransferase (ChAT) and sent axons into the sciatic nerve as detected by retrograde labeling. Paralyzed animals transplanted with EBD cells partially recovered motor function 12 and 24 weeks after transplantation, whereas control animals remained paralyzed. Semi-quantitative analysis revealed that the efficiency of neuronal differentiation and extension of neurites could not account for the functional recovery. Rather, transplanted EBD cells protected host neurons from death and facilitated reafferentation of motor neuron cell bodies. In vitro, EBD cells secrete transforming growth factor-alpha (TGF-alpha) and brain-derived neurotrophic factor (BDNF). Neutralizing antibodies to TGF-alpha and to BDNF abrogated the ability of EBD-conditioned media to sustain motor neuron survival in culture, whereas neutralizing antibodies to BDNF eliminated the axonal outgrowth from spinal organotypics observed with direct coculture of EBD cells. We conclude that cells derived from human pluripotent stem cells have the capacity to restore neurologic function in animals with diffuse motor neuron disease via enhancement of host neuron survival and function.

ALS-associated mutant SOD1G93A causes mitochondrial vacuolation by expansion of the intermembrane space and by involvement of SOD1 aggregation and peroxisomes

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is an age-dependent neurodegenerative disease that causes motor neuron degeneration, paralysis and death. Mutations in Cu, Zn superoxide dismutase (SOD1) are one cause for the familial form of this disease. Transgenic mice expressing mutant SOD1 develop age-dependent motor neuron degeneration, skeletal muscle weakness, paralysis and death similar to humans. The mechanism whereby mutant SOD1 induces motor neuron degeneration is not understood but widespread mitochondrial vacuolation has been observed during early phases of motor neuron degeneration. How this vacuolation develops is not clear, but could involve autophagic vacuolation, mitochondrial permeability transition (MPT) or uncharacterized mechanisms. To determine which of these possibilities are true, we examined the vacuolar patterns in detail in transgenic mice expressing mutant SOD1G93A.

RESULTS

Vacuolar patterns revealed by electron microscopy (EM) suggest that vacuoles originate from the expansion of the mitochondrial intermembrane space and extension of the outer mitochondrial membrane. Immunofluorescence microscopy and immuno-gold electron microscopy reveal that vacuoles are bounded by SOD1 and mitochondrial outer membrane markers, but the inner mitochondrial membrane marker is located in focal areas inside the vacuoles. Small vacuoles contain cytochrome c while large vacuoles are porous and lack cytochrome c. Vacuoles lack lysosomal signal but contain abundant peroxisomes and SOD1 aggregates.

CONCLUSION

These findings demonstrate that mutant SOD1, possibly by toxicity associated with its aggregation, causes mitochondrial degeneration by inducing extension and leakage of the outer mitochondrial membrane, and expansion of the intermembrane space. This could release the pro-cell death molecules normally residing in the intermembrane space and initiate motor neuron degeneration. This Mitochondrial Vacuolation by Intermembrane Space Expansion (MVISE) fits neither MPT nor autophagic vacuolation mechanisms, and thus, is a previously uncharacterized mechanism of mitochondrial degeneration in mammalian CNS.

Altered long-term corticostriatal synaptic plasticity in transgenic mice overexpressing human CU/ZN superoxide dismutase (GLY(93)-->ALA) mutation

Apart from the extensive loss of motor neurons, degeneration of midbrain dopaminergic cells has been described in both familial and sporadic forms of amyotrophic lateral sclerosis (ALS). Mice overexpressing the mutant human Cu/Zn superoxide dismutase (SOD1) show an ALS-like phenotype in that they show a progressive death of motor neurons accompanied by degeneration of dopaminergic cells. To describe the functional alterations specifically associated with this dopaminergic dysfunction, we have investigated the corticostriatal synaptic plasticity in mice overexpressing the human SOD1 (SOD1+) and the mutated (Gly(93)-->Ala) form (G93A+) of the same enzyme. We show that repetitive stimulation of the corticostriatal pathway generates long-term depression (LTD) in SOD1+ mice and in control (G93A-/SOD1-) animals, whereas in G93A+ mice the same stimulation generates an N-methyl-D-aspartic acid receptor-dependent long-term potentiation. No significant alterations were found in the intrinsic membrane properties of striatal medium spiny neurons and basal corticostriatal synaptic transmission of G93A+ mice. Bath perfusion of dopamine or the D(2) dopamine receptor agonist quinpirole restored LTD in G93A+ mice. Consistent with these in vitro results, habituation of locomotor activity and striatal-dependent active avoidance learning were impaired in G93A+ mice. Thus, degeneration of dopaminergic neurons in the substantia nigra of G93A+ mice causes substantial modifications in striatal synaptic plasticity and related behaviors, and may be a cellular substrate of the extrapyramidal motor and cognitive disorders observed in familial and sporadic ALS.

Human embryonic germ cell derivatives facilitate motor recovery of rats with diffuse motor neuron injury

We have investigated the potential of human pluripotent cells to restore function in rats paralyzed with a virus-induced motor neuronopathy. Cells derived from embryonic germ cells, termed embryoid body-derived (EBD) cells, introduced into the CSF were distributed extensively over the rostrocaudal length of the spinal cord and migrated into the spinal cord parenchyma in paralyzed, but not uninjured, animals. Some of the transplanted human cells expressed the neuroglial progenitor marker nestin, whereas others expressed immunohistochemical markers characteristic of astrocytes or mature neurons. Rare transplanted cells developed immunoreactivity to choline acetyltransferase (ChAT) and sent axons into the sciatic nerve as detected by retrograde labeling. Paralyzed animals transplanted with EBD cells partially recovered motor function 12 and 24 weeks after transplantation, whereas control animals remained paralyzed. Semi-quantitative analysis revealed that the efficiency of neuronal differentiation and extension of neurites could not account for the functional recovery. Rather, transplanted EBD cells protected host neurons from death and facilitated reafferentation of motor neuron cell bodies. In vitro, EBD cells secrete transforming growth factor-alpha (TGF-alpha) and brain-derived neurotrophic factor (BDNF). Neutralizing antibodies to TGF-alpha and to BDNF abrogated the ability of EBD-conditioned media to sustain motor neuron survival in culture, whereas neutralizing antibodies to BDNF eliminated the axonal outgrowth from spinal organotypics observed with direct coculture of EBD cells. We conclude that cells derived from human pluripotent stem cells have the capacity to restore neurologic function in animals with diffuse motor neuron disease via enhancement of host neuron survival and function.

Age-related changes in peroxisomal membrane protein 70 and superoxide dismutase 1 in transgenic G93A mice

Peroxisomal membrane protein 70 (PMP70) and Cu/Zn superoxide dismutase (SOD1) were examined in the spinal cords of transgenic (Tg) mice expressing a human mutant SOD1 protein (G93A) and their age-matched controls at 8, 20 and 32 weeks by immunohistochemistry. At pre-symptomatic 20 weeks and symptomatic 32 weeks, PMP70 was reduced in the cytoplasm of motor neurons in Tg animals and increased in glial cells in anterior horn at late age. SOD1 showed a progressive increase of dot-like deposits in the neuropil of anterior horn of Tg mice, and a late decrease of signal intensity in the white matter and motor neurons at 32 weeks. It is conceivable that reduction of PMP70 might underlie decrease in peroxisomal functions and increase in oxidative stress that is well documented in this animal model.

The structure of holo and metal-deficient wild-type human Cu, Zn superoxide dismutase and its relevance to familial amyotrophic lateral sclerosis

Cu, Zn superoxide dismutase (SOD1) forms a crucial component of the cellular defence against oxidative stress. Zn-deficient wild-type and mutant human SOD1 have been implicated in the disease familial amyotrophic lateral sclerosis (FALS). We present here the crystal structures of holo and metal-deficient (apo) wild-type protein at 1.8A resolution. The P21 wild-type holo enzyme structure has nine independently refined dimers and these combine to form a "trimer of dimers" packing motif in each asymmetric unit. There is no significant asymmetry between the monomers in these dimers, in contrast to the subunit structures of the FALS G37R mutant of human SOD1 and in bovine Cu,Zn SOD. Metal-deficient apo SOD1 crystallizes with two dimers in the asymmetric unit and shows changes in the metal-binding sites and disorder in the Zn binding and electrostatic loops of one dimer, which is devoid of metals. The second dimer lacks Cu but has approximately 20% occupancy of the Zn site and remains structurally similar to wild-type SOD1. The apo protein forms a continuous, extended arrangement of beta-barrels stacked up along the short crystallographic b-axis, while perpendicular to this axis, the constituent beta-strands form a zig-zag array of filaments, the overall arrangement of which has a similarity to the common structure associated with amyloid-like fibrils.

Genetic defects in copper metabolism

Genetic defects in copper metabolism highlight the delicate balance mammalian systems have developed to maintain normal copper homeostasis. Menkes disease, the mottled mouse, the Atox-1-deficient mouse and the ctr1 knockout mouse reveal the importance of adequate copper intake during embryogenesis and early development, especially in the central nervous system. The toxicity associated with excess copper as manifest in Wilson disease, the toxic milk mouse, the LEC rat and copper toxicosis in the Bedlington terrier demonstrate the profound cellular susceptibility to copper overload, in particular, in the brain and liver. Ceruloplasmin (Cp) contains 95% of the copper found in human serum, and inherited loss of this protein results in diabetes, retinal degeneration and neurodegeneration. Despite normal copper metabolism, aceruloplasminemic patients and the Cp knockout mouse have disturbed iron homeostasis and mild hepatic copper retention. These genetic disorders of copper metabolism provide valuable insight into the mechanisms regulating copper homeostasis and models to further dissect the role of this essential metal in health and disease.

Alterations in m-RNA expression for Cu,Zn-superoxide dismutase and glutathione peroxidase in the basal ganglia of MPTP-treated marmosets and patients with Parkinson's disease

Alterations occurring in the antioxidant enzymes, copper, zinc-dependent superoxide dismutase (Cu,Zn-SOD) and glutathione peroxidase (GPX) following nigral dopaminergic denervation are unclear. We now report on the distribution and levels of m-RNA for Cu,Zn-SOD and GPX in basal ganglia of normal and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated common marmosets, and in normal individuals and patients with Parkinson's disease (PD) using in situ hybridization histochemistry and oligodeoxynucleotide (single-stranded DNA) probes. Cu,Zn-SOD and GPX m-RNA was present throughout basal ganglia (nucleus accumbens, caudate-putamen, globus pallidus, substantia nigra) in the common marmoset, with the highest levels being in substantia nigra (SN). Following MPTP induced nigral cell loss, Cu,Zn-SOD m-RNA levels were decreased in all areas but the SNr, and particularly in SNc (71%, P<0.001). MPTP-treatment had no effect on GPX m-RNA expression in any area of basal ganglia. Cu,Zn-SOD and GPX m-RNA was also present in the normal human SN. In PD, however, Cu,Zn-SOD m-RNA was significantly decreased (89%, P<0.005) in SNc, and there was a near-complete loss of GPX m-RNA in both SNc (100%, P<0.005) and SNr (88%, P<0.005). The loss of Cu,Zn-SOD m-RNA in SNc in MPTP-treated marmosets and patients with PD suggests that it is primarily located in dopaminergic neuronal cell bodies. The loss of GPX m-RNA in SNc in PD also suggests a localisation to dopaminergic cell bodies, but the similar change in SNr may indicate its presence in dopaminergic neurites. In contrast, the absence of change in GPX m-RNA in MPTP-treated primates appears to rule out its presence in dopaminergic cells in this species, but this may only be apparent and may reflect increased expression in glial cells following acute toxin treatment.

Oxidation-induced misfolding and aggregation of superoxide dismutase and its implications for amyotrophic lateral sclerosis

The presence of intracellular aggregates that contain Cu/Zn superoxide dismutase (SOD1) in spinal cord motor neurons is a pathological hallmark of amyotrophic lateral sclerosis (ALS). Although SOD1 is abundant in all cells, its half-life in motor neurons far exceeds that in any other cell type. On the basis of the premise that the long half-life of the protein increases the potential for oxidative damage, we investigated the effects of oxidation on misfolding/aggregation of SOD1 and ALS-associated SOD1 mutants. Zinc-deficient wild-type SOD1 and SOD1 mutants were extremely prone to form visible aggregates upon oxidation as compared with wild-type holo-protein. Oxidation of select histidine residues that bind metals in the active site mediates SOD1 aggregation. Our results provide a plausible model to explain the accumulation of SOD1 aggregates in motor neurons affected in ALS.

Change in superoxide dismutase 1 protein localization towards mitochondria: an immunohistochemical study in transgenic G93A mice

Localization of superoxide dismutase1 (SOD1) and mitochondrial glucose-regulated protein 75 (Grp75), were examined in the spinal cords of transgenic (Tg) mice expressing human mutant SOD1 protein (G93A) and wild-type (Wt) controls at 8, 20 and 32 weeks. SOD1 showed a progressive increase of dot-like deposits in the neuropil of anterior horn of Tg mice, and a late decrease of signal intensity in the white matter and motor neurons. Colocalization of Grp75 and SOD1 signals was demonstrated in Wt and presymptomatic Tg animals, while it was lost in Tg mice at a symptomatic age. The present results suggest that loss of SOD1 protein from mitochondria could contribute to motor neuron damage.

Defective neurite outgrowth in aphidicolin/cAMP-induced motor neurons expressing mutant Cu/Zn superoxide dismutase

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder characterized by motor neuron involvement. Mutations in the human Cu/Zn superoxide dismutase (SOD1) gene are found in some cases of familial ALS. Many studies have reported SOD1 mutation-related neurodegeneration. However, whether or not a mutant SOD1 affects neural development has not been demonstrated. We developed motor neuron-neuroblastoma hybrid cells that expressed a mutant (G93A) or the wild type (WT) SOD1. Cells were differentiated by dibutyryl cAMP and aphidicolin. The mutant showed a defect in neurite outgrowth and had decreased viability. Cytochrome c released and nuclear fragmentation were observed. Western blot analysis showed that the amount of neurofilament and microtubule associated proteins-2 (MAP-2) decreased during differentiation. These results suggest that the defect in neurite outgrowth of mutant SOD1 cells is a cytoskeletal defect and is associated with neuronal death.

Accumulation of SOD1 mutants in postnatal motoneurons does not cause motoneuron pathology or motoneuron disease

Transgenic mice expressing high levels of familial amyotrophic lateral sclerosis (FALS)-associated mutant superoxide dismutase 1 (SOD1) under the control of a human SOD1 minigene (hMg) accumulate mutant protein ubiquitously and develop motoneuron disease. However, restricted expression of SOD1 mutants in neurons apparently does not cause motor impairments in mice. Here, we investigated the possible pathogenic roles of mutant SOD1 accumulation in motoneurons. First, we used a Thy1 expression cassette to drive high constitutive expression of transgene in postnatal mouse neurons, including upper and lower motoneurons. Second, we expressed human (h) SOD1(G93A) and hSOD1(G85R) as transgenes (i.e., two SOD1 mutants with aggressive pathogenic properties in inducing FALS). Third, in addition to clinical signs of disease, we monitored early signs of disease onset and pathogenesis, including muscle innervation, astrogliosis in the spinal cord, and accumulation of ubiquitinated deposits in motoneurons and astrocytes. We report that high-level expression and accumulation of the mutant proteins in neurons failed to produce any detectable sign of pathology or disease in these transgenic mice. Crossing hMg-SOD1(G93A) mice (Gurney et al., 1994) with Thy1-SOD1(G93A) mice produced double-transgenic mice with spinal cord SOD1(G93A) levels that were approximately twofold higher than in the hMg-SOD1(G93A) single transgenics but did not affect the onset or progression of pathology or motoneuron disease. The accumulation of mutant SOD1 in postnatal motoneurons is thus not sufficient and probably also not critical to induce or accelerate motoneuron disease in FALS mice. The pathogenic process in FALS may involve non-neuronal cells, and selective vulnerability of motoneurons to this process may lead to motoneuron pathology and disease.

Amyotrophic lateral sclerosis: a proposed mechanism

Missense mutations in Cu,Zn-superoxide dismutase (SOD1) account for approximately 20% of familial amyotrophic lateral sclerosis (FALS) through some, as yet undefined, toxic gain of function that leads to gradual death of motor neurons. Mitochondrial swelling and vacuolization are early signs of incipient motor neuron death in FALS. We previously reported that SOD1 exists in the intermembrane space of mitochondria. Herein, we demonstrate that the entry of SOD1 into mitochondria depends on demetallation and that heat shock proteins (Hsp70, Hsp27, or Hsp25) block the uptake of the FALS-associated mutant SOD1 (G37R, G41D, or G93A), while having no effect on wild-type SOD1. The binding of mutant SOD1 to Hsps in the extract of neuroblastoma cells leads to formation of sedimentable aggregates. Many antiapoptotic effects of Hsps have been reported. We now propose that this binding of Hsps to mutant forms of a protein abundant in motor neurons, such as SOD1, makes Hsps unavailable for their antiapoptotic functions and leads ultimately to motor neuron death. It also appears that the Hsp-SOD1 complex recruits other proteins present in the neuroblastoma cell and presumably in motor neurons to form sedimentable aggregates.

Accumulation of SOD1 mutants in postnatal motoneurons does not cause motoneuron pathology or motoneuron disease

Transgenic mice expressing high levels of familial amyotrophic lateral sclerosis (FALS)-associated mutant superoxide dismutase 1 (SOD1) under the control of a human SOD1 minigene (hMg) accumulate mutant protein ubiquitously and develop motoneuron disease. However, restricted expression of SOD1 mutants in neurons apparently does not cause motor impairments in mice. Here, we investigated the possible pathogenic roles of mutant SOD1 accumulation in motoneurons. First, we used a Thy1 expression cassette to drive high constitutive expression of transgene in postnatal mouse neurons, including upper and lower motoneurons. Second, we expressed human (h) SOD1(G93A) and hSOD1(G85R) as transgenes (i.e., two SOD1 mutants with aggressive pathogenic properties in inducing FALS). Third, in addition to clinical signs of disease, we monitored early signs of disease onset and pathogenesis, including muscle innervation, astrogliosis in the spinal cord, and accumulation of ubiquitinated deposits in motoneurons and astrocytes. We report that high-level expression and accumulation of the mutant proteins in neurons failed to produce any detectable sign of pathology or disease in these transgenic mice. Crossing hMg-SOD1(G93A) mice (Gurney et al., 1994) with Thy1-SOD1(G93A) mice produced double-transgenic mice with spinal cord SOD1(G93A) levels that were approximately twofold higher than in the hMg-SOD1(G93A) single transgenics but did not affect the onset or progression of pathology or motoneuron disease. The accumulation of mutant SOD1 in postnatal motoneurons is thus not sufficient and probably also not critical to induce or accelerate motoneuron disease in FALS mice. The pathogenic process in FALS may involve non-neuronal cells, and selective vulnerability of motoneurons to this process may lead to motoneuron pathology and disease.

Spatial and temporal correlation of nitric oxide synthase expression with CuZn-superoxide dismutase reduction in motor neurons following axotomy

Axotomized neurons expressing neuronal nitric oxide synthase (nNOS) may use nitric oxide (NO), known for its antioxidant activities and ability to scavenge free radicals, to protect against oxidative stress. This hypothesis was tested by immunohistochemical examination of superoxide dismutase (SOD) in neurons of the hypoglossal nucleus (HGN) and dorsal motor nucleus of the vagus nerve (DMV) one day to ten weeks after unilateral hypoglossal nerve crush or avulsion combined with vagus nerve crush in adult rats, and also in neurons of the anterior horn (AH) one week after unilateral sciatic nerve crush or avulsion. In the HGN, emergence of nNOS coincided temporally with reduction of CuZn-SOD immunoreactivity (ir), and the level of reduction correlated with that of nNOS induction, differing only in magnitude between nerve crush and nerve avulsion. The two nerve lesion models further revealed the concurrence of nNOS abatement with recovery of CuZn-SOD ir, and absence of nNOS abatement with persistent low CuZn-SOD ir. In the AH, reduced CuZn-SOD ir was localized in the segments containing nNOS positive neurons as a result of sciatic nerve avulsion. CuZn-SOD ir was unchanged in the absence of nNOS induction following sciatic nerve crush. DMV neurons were devoid of CuZn-SOD ir. However, increased Mn-SOD ir one and two weeks post crush was similar to that in HGN neurons. DMV neurons lacked both nNOS abatement and CuZn-SOD ir, which may explain their particular vulnerability to cell death from axotomy in comparison with other peripheral neurons. These data suggest that axotomy-induced nNOS expression is causally linked to oxidative stress, and that NO is neuroprotective, but can become neurodestructive when produced in excess.

The distribution of copper, zinc- and manganese-superoxide dismutase, and glutathione peroxidase messenger ribonucleic acid in rat basal ganglia

Oxidative stress may contribute to the progression of Parkinson's disease, and while the status of antioxidant enzymes is thus important, little data on their regional distribution in basal ganglia exist. We now report on the distribution and levels of messenger ribonucleic acid (m-RNA) for the antioxidant enzymes copper, zinc-superoxide dismutase (Cu,Zn-SOD), manganese-superoxide dismutase (Mn-SOD), and glutathione peroxidase in rat basal ganglia using in situ hybridisation histochemistry with complementary deoxyribonucleic acid probes specific for these enzymes. The m-RNA for Cu,Zn-SOD, Mn-SOD, and glutathione peroxidase was expressed throughout basal ganglia. Levels of m-RNA were significantly higher in substantia nigra pars compacta than in all other regions of basal ganglia for both Cu,Zn-SOD (53-62%, P<0.001) and Mn-SOD (37-45%, P<0.05). Mn-SOD m-RNA levels were also significantly higher in SN pars reticulata than in the nucleus accumbens (10%, P<0.05) and striatum (12%, P<0.01). In contrast, glutathione peroxidase m-RNA levels were only significantly higher in SN pars compacta when compared with SN pars reticulata (23%, P<0.05), and in the striatum when compared with the nucleus accumbens (21%, P<0.05). The data suggest that SN pars compacta may be vulnerable to oxidative stress and thus dependent on the high antioxidant capacity provided by these cytoprotective enzymes. In conclusion, this study demonstrates the relative distribution of antioxidant enzymes in rat basal ganglia and forms the basis for further study in rodent models of Parkinson's disease.

Expression and activity of antioxidants in the brain in progressive supranuclear palsy

Recent evidence implicates oxidative stress in the pathophysiology of progressive supranuclear palsy (PSP). Thus, we undertook a study of the activity and localization of two essential antioxidant systems (superoxide dismutase [SOD] enzymes and total glutathione) in the human post-mortem PSP and control brain. Marked increases in SOD1 (Cu/ZnSOD) activity and glutathione levels were measured within most PSP brain regions examined, whereas, only the subthalamic nucleus exhibited a significant increase (+68%) in SOD2 (MnSOD) activity. Two additional cases with mild pathological abnormalities were studied. The first (case A) may represent an example of an asymptomatic PSP case, while the second (case B) had mild pathological abnormalities consistent with typical PSP. In case A, only the STN had elevated levels of SOD activity, in the absence of an increase in tissue glutathione content. In case B, SOD activities and tissue glutathione content were elevated in several regions. Immunolocalization of the SOD1 and SOD2 proteins in paraffin-embedded tissue sections revealed a marked increase in the density of SOD immunopositive profiles (particularly glia) in the typical PSP brain, particularly within the white matter. Together, our data argues strongly in favor of the involvement of oxidative stress in the etiology and progression of PSP, and suggests that deficit in SOD or glutathione metabolism are not causative.

Focal loss of the glutamate transporter EAAT2 in a transgenic rat model of SOD1 mutant-mediated amyotrophic lateral sclerosis (ALS)

Transgenic overexpression of Cu(+2)/Zn(+2) superoxide dismutase 1 (SOD1) harboring an amyotrophic lateral sclerosis (ALS)-linked familial genetic mutation (SOD1(G93A)) in a Sprague-Dawley rat results in ALS-like motor neuron disease. Motor neuron disease in these rats depended on high levels of mutant SOD1 expression, increasing from 8-fold over endogenous SOD1 in the spinal cord of young presymptomatic rats to 16-fold in end-stage animals. Disease onset in these rats was early, approximately 115 days, and disease progression was very rapid thereafter with affected rats reaching end stage on average within 11 days. Pathological abnormalities included vacuoles initially in the lumbar spinal cord and subsequently in more cervical areas, along with inclusion bodies that stained for SOD1, Hsp70, neurofilaments, and ubiquitin. Vacuolization and gliosis were evident before clinical onset of disease and before motor neuron death in the spinal cord and brainstem. Focal loss of the EAAT2 glutamate transporter in the ventral horn of the spinal cord coincided with gliosis, but appeared before motor neuron/axon degeneration. At end-stage disease, gliosis increased and EAAT2 loss in the ventral horn exceeded 90%, suggesting a role for this protein in the events leading to cell death in ALS. These transgenic rats provide a valuable resource to pursue experimentation and therapeutic development, currently difficult or impossible to perform with existing ALS transgenic mice.

6-Hydroxydopamine-lesioning of the nigrostriatal pathway in rats alters basal ganglia mRNA for copper, zinc- and manganese-superoxide dismutase, but not glutathione peroxidase

The effects of nigrostriatal pathway destruction on the mRNA levels of copper, zinc-dependent superoxide dismutase (Cu,Zn-SOD), manganese-dependent superoxide dismutase (Mn-SOD), and glutathione peroxidase in basal ganglia of adult rat were investigated using in situ hybridization histochemistry and oligodeoxynucleotide (single-stranded complementary DNA) probes. The 6-hydroxydopamine (6-OHDA)-induced destruction of the nigrostriatal pathway resulted in contralateral rotation to apomorphine and a marked loss of specific [(3)H]mazindol binding in the striatum (93%; P<0.05) and of tyrosine hydroxylase mRNA in substantia nigra pars compacta (SC) (93%; P<0.05) compared with control rats. Levels of Cu,Zn-SOD mRNA were decreased in the striatum, globus pallidus, and SC on the lesioned side of 6-OHDA-lesioned rats compared with sham-lesioned rats (P<0.05). Levels of Mn-SOD mRNA were increased in the nucleus accumbens (P<0.05), but decreased in the SC (P<0.05) on the lesioned side of 6-OHDA-treated rats compared with sham-lesioned rats. Lesioning with 6-OHDA had no effect on glutathione peroxidase mRNA levels in any region of basal ganglia examined. The significant changes in Cu,Zn-SOD and Mn-SOD mRNA indicate that SOD is primarily expressed by dopaminergic neurons of the nigrostriatal pathway, and that the Mn-SOD gene appears to be inducible in rat basal ganglia in response to both physical and chemical damage 5 weeks after 6-OHDA-lesioning. These findings may clarify the status of antioxidant enzymes, particularly Mn-SOD, in patients with Parkinson's disease and their relevance to disease pathogenesis.

Histological evidence of protein aggregation in mutant SOD1 transgenic mice and in amyotrophic lateral sclerosis neural tissues

The mechanisms leading to neurodegeneration in ALS (amyotrophic lateral sclerosis) are not well understood, but cytosolic protein aggregates appear to be common in sporadic and familial ALS as well as transgenic mouse models expressing mutant Cu/Zn superoxide dismutase (SOD1). In this study, we systematically evaluated the presence of these aggregates in three different mouse models (G93A, G85R, and G37R SOD1) and compared these aggregates to those seen in cases of sporadic and familial ALS. Inclusions and loss of motor neurons were observed in spinal cords of all of these three mutant transgenic lines. Since a copper-mediated toxicity hypothesis has been proposed to explain the cytotoxic gain-of-function of mutant SOD1, we sought to determine the involvement of the copper chaperone for SOD1 (CCS) in the formation of protein aggregates. Although all aggregates contained CCS, SOD1 was not uniformly found in the inclusions. Similarly, CCS-positive skein-like inclusions were rarely seen in ALS neurons. These studies do not provide strong evidence for a causal role of CCS in aggregate formation, but they do suggest that protein aggregation is a common event in all animal models of the disease. Selected proteins, such as the glutamate transporter GLT-1, were not typically observed within the inclusions. Most inclusions were positively stained with antibodies recognizing ubiquitin, proteasome, Hsc70 in transgenic lines, and some Hsc70-positive inclusions were detected in sporadic ALS cases. Overall, these observations suggest that inclusions might be sequestered into ubiquitin-proteasome pathway and some chaperone proteins such as Hsc70 may be involved in formation and/or degradation of these inclusions.

Disease mechanisms revealed by transcription profiling in SOD1-G93A transgenic mouse spinal cord

Mutations of copper,zinc-superoxide dismutase (cu,zn SOD) are found in patients with a familial form of amyotrophic lateral sclerosis. When expressed in transgenic mice, mutant human cu,zn SOD causes progressive loss of motor neurons with consequent paralysis and death. Expression profiling of gene expression in SOD1-G93A transgenic mouse spinal cords indicates extensive glial activation coincident with the onset of paralysis at 3 months of age. This is followed by activation of genes involved in metal ion regulation (metallothionein-I, metallothionein-III, ferritin-H, and ferritin-L) at 4 months of age just prior to end-stage disease, perhaps as an adaptive response to the mitochondrial destruction caused by the mutant protein. Induction of ferritin-H and -L gene expression may also limit iron catalyzed hydroxyl radical formation and consequent oxidative damage to lipids, proteins, and nucleic acids. Thus, glial activation and adaptive responses to metal ion dysregulation are features of disease in this transgenic model of familial amyotrophic lateral sclerosis.

Presymptomatic motor neuron loss and reactive astrocytosis in the SOD1 mouse model of amyotrophic lateral sclerosis

In familial amyotrophic lateral sclerosis (fALS), there is a need to establish more precisely the progression of the disease, particularly whether there is gradual presymptomatic neuronal loss or an abrupt loss coinciding with the symptomatic stage. To elucidate this, we investigated the progression of motor neuron loss through morphological techniques, reactive astrocytosis, and expression of ubiquitin and neurofilament proteins, by immunohistochemistry, in SOD1 G93A mice with a protracted disease course and control mice. Loss of motor neurons in SOD1 G93A mice followed a biphasic progression, with an initial loss at 126 days of age, followed by a gradual loss from onset of symptoms through to end-stage disease. Reactive astrocytosis was first observed at 70 days of age and showed a gradual increase through to end-stage disease. This suggests that there is a need for early detection of fALS cases, and potential therapeutic treatments may be more beneficial if administered at an early stage.

Accelerated s-nitrosothiol breakdown by amyotrophic lateral sclerosis mutant copper,zinc-superoxide dismutase

Mutations in copper,zinc-superoxide dismutase (SOD) have been implicated in familial amyotrophic lateral sclerosis (FALS). We have investigated the breakdown of S-nitrosothiols by wild-type (WT) SOD and two common FALS mutants, alanine-4 valine (A4V) SOD and glycine-37 arginine (G37R) SOD. In the presence of glutathione, A4V SOD and G37R SOD catalyzed S-nitrosoglutathione breakdown three times more efficiently than WT SOD. Indeed, A4V SOD catabolized GSNO more efficiently than WT SOD throughout the physiological range of GSH concentrations. Moreover, a variety of additional S-nitrosothiols were catabolized more readily by A4V SOD than by WT SOD. Initial rate data for fully reduced WT SOD and A4V SOD, and data using ascorbic acid as the reductant, suggest that FALS mutations in SOD may influence the efficiency of reduction of the copper center by glutathione. We have identified a potentially toxic gain of function of two common FALS mutations that may contribute to neurodegeneration in FALS.

Kennedy's disease: a triplet repeat disorder or a motor neuron disease?

Two definite genetic causes of adult motor neuron degeneration have been identified to date: CAG repeat expansion in the androgen receptor gene in Kennedy's disease and point mutations in the SOD1 gene, encoding the enzyme, Cu/Zn superoxide dismutase, in some familial forms of amyotrophic lateral sclerosis. Although both have unrelated genetic causes, Kennedy's disease and SOD1-linked amyotrophic lateral sclerosis share several pathogenic features. First, expanded androgen receptor and mutant Cu/Zn superoxide dismutase have a propensity to aggregate into insoluble complexes and form inclusion bodies in affected neurons. Deposits of mutant proteins could be detrimental to neuronal viability by interfering with the normal housekeeping functions of chaperones and of the ubiquitin/proteasome system. Secondly, cytoskeletal function may be impaired in both diseases as decreased transactivational activity of expanded androgen receptor may cause an abnormal pattern of tubulin expression in motor neurons in Kennedy's disease and disruption of neurofilament organisation is a hallmark of amyotrophic lateral sclerosis. The concept of activation of overlapping cell death cascades by two distinct genetic defects could help elucidating downstream pathogenic processes and may provide novel targets for pharmacological intervention or gene therapy for the treatment of motor neuron disorders.

Chronic and cyclical neuronal loss in hippocampal slice cultures following transient inhibition of the type 1 isoform of superoxide dismutase

Increased oxidative stress contributes to chronic neurodegenerative diseases, yet the underlying mechanisms are poorly understood. Hippocampal slice cultures prepared from 20-30-day-old mice or rats were used to model chronic neuronal loss following oxidative stress. Neuronal loss was initiated by inhibition of the antioxidant enzyme, superoxide dismutase type 1 (SOD1), using the copper chelator diethyldithiocarbamate (DDC). Continuous DDC treatment of slice cultures induced delayed neuronal loss beginning at 9 days of treatment that lasted for over 4 weeks. Neuronal loss was not uniform, rather it was cyclic: peaking at days 9-13 and at days 19-21 after DDC exposure. Neuronal loss was significantly attenuated in slice cultures that overexpress SOD1, suggesting that SOD1 inhibition was responsible. Inhibitors of nitric oxide synthase also attenuated DDC-induced neuronal loss. Chronic neuronal loss, however, did not require continuous SOD1 inhibition. Application of DDC for 13 days resulted in loss of SOD1 activity. Removal of DDC restored SOD1 activity, yet the cycles of cell loss continued until no neurons remained. Astrocyte activation was observed following the second peak of neuronal loss. Media conditioned by cultures following DDC removal induced neuronal loss and microglial activation in recipient cultures. These data suggest that slice cultures released soluble neurotoxic factor(s) following DDC removal. These data also suggest that a transient reduction of SOD1 activity leads to chronic loss of hippocampal neurons. This neuronal loss may be mediated by soluble neurotoxic factor(s) and microglial activation. Cyclical neuronal loss may also underlie chronic neurodegeneration in vivo.

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.

Oxidative stress, human genetic variation, and disease

Oxidative stress has been implicated in numerous pathophysiological conditions and also aging. The tools for studying oxidative stress are now expanding as a result of the human genome effort and, in particular, expanding knowledge on human genetic variation. A few genetic variants, mostly in the form of single nucleotide polymorphisms of relevance to oxidative stress are already studied by a molecular epidemiologic approach. A review of the current knowledge on variant human genes that are directly implicated in human protection against oxidative stress is presented.

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.

Loss of oxidation-reduction specificity in amyotrophic lateral sclerosis-associated CuZnSOD mutants

Both transgenic mouse and cell culture models of familial amyotrophic lateral sclerosis (FALS) support a gain-of-function effect for the mutations in copper-zinc superoxide dismutase (CuZnSOD) associated with FALS, but the nature of the function gained remains incompletely characterized. We previously reported an enhanced peroxidase activity for FALS-associated CuZnSOD mutants. Because one of the targets of such activity is CuZnSOD itself, we examined peroxide-mediated inactivation of wild-type and mutant CuZnSODs, and found that the mutants are more readily inactivated. Inactivation of the mutants was associated with fragmentation, which did not occur in the wild-type enzyme under these conditions. Furthermore, the reduction of the FALS-associated mutants by ascorbate was enhanced markedly when compared to the wild-type enzyme. The visible spectra of the mutants showed a consistent blue shift of the peak at 680 nm in the wild-type enzyme, suggesting an alteration in copper-site geometry. These results extend previous studies demonstrating enhanced peroxidase activity in the mutants, and suggest that the toxic function that leads to motor neuron degeneration may result from a loss of specificity of the redox reactions catalyzed by CuZnSOD.

Immunohistochemistry of advanced glycation end products in neurofilamentous axonal spheroids induced by beta-beta'-iminodipropionitrile in lower motor neurons of rat

Chronic parenteral administration of beta-beta'-iminodipropionitrile (IDPN) in adult female rats induces large neurofilament-rich axonal spheroids (AXS) in spinal motor neurons closely resembling those AXS in early phases of amyotrophic lateral sclerosis. Immunohistochemistry of advanced glycosylation end-products (AGEs) in axonal spheroids was performed in the present study. Anti-AGE and anti-neurofilament antibodies strongly co-labeled IDPN-induced axonal spheroids, whereas motor neuron soma showed little AGE immunoreactivity. In an attempt to modify and intensify glycosylation, another group of IDPN rats was made hyperglycemic with streptozotocin after IDPN intoxication. These hyperglycemic rats showed AXS with striking AGE immunoreactivity. An additional group of rats made hyperglycemic before IDPN intoxication showed markedly diminished AXS formation, with a few small AGE-positive AXS in anterior horns. Findings suggest that AGEs are involved in neurofilament crosslinking as well as disassembly of neurofilament induced by IDPN with or without hyperglycemia. Hyperglycemia did not intensify neurofilament aggregation. Additional immunohistochemistry revealed not only aberrant phosphorylation, but also intense local production of Cu/Zn superoxide dismutase and nitrotyrosine in axonal spheroids, probably secondary to superoxide generation as a consequence of AGE production at neurofilament protein, impeding its assembly as hypothesized in motoneuron diseases.

Detection of 8-oxoG DNA glycosylase activity and OGG1 transcripts in the rat CNS

The oxoguanine DNA glycosylase (Ogg1) is a DNA repair enzyme that excises 7,8-dihydro-8-oxoguanine present in DNA damaged by oxidative stress. We have investigated the expression of the OGG1 gene in different regions of the rat CNS. Biochemical studies on brain homogenates of adult rats have shown that Ogg1 nicking activity is present at relatively similar levels in the cerebral cortex, the hypothalamus, the pons and the cerebellum. Following in situ hybridization with radiolabeled OGG1 cDNA or specific antisense oligonucleotides, OGG1 transcripts showed a widespread but heterogeneous distribution pattern among distinct brain regions of adult rats: high levels of this transcript were detected in the CA1-CA3 layers and the gyrus dentate of the hippocampal formation, the piriform cortex, the supraoptic nuclei, the olivary complex as well as in the pyramidal cells of layer V of the cortex and the Purkinje cells of the cerebellum. In peripheral organs such as the lungs, the stomach and the spleen, OGG1 transcript is however expressed in specific subpopulations of cells. Using a semi-quantitative reverse transcription - polymerase chain reaction assay on total mRNA from the frontal cortex, OGG1 mRNA was determined to be expressed with relatively the same levels in 1-day-old and 7-day-old rats as well as in adult rats. These results provide evidence for the widespread expression of the OGG1 gene in developing and adult brains.

Copper chaperone for superoxide dismutase is essential to activate mammalian Cu/Zn superoxide dismutase

Recent studies in Saccharomyces cerevisiae suggest that the delivery of copper to Cu/Zn superoxide dismutase (SOD1) is mediated by a cytosolic protein termed the copper chaperone for superoxide dismutase (CCS). To determine the role of CCS in mammalian copper homeostasis, we generated mice with targeted disruption of CCS alleles (CCS(-/-) mice). Although CCS(-/-) mice are viable and possess normal levels of SOD1 protein, they reveal marked reductions in SOD1 activity when compared with control littermates. Metabolic labeling with (64)Cu demonstrated that the reduction of SOD1 activity in CCS(-/-) mice is the direct result of impaired Cu incorporation into SOD1 and that this effect was specific because no abnormalities were observed in Cu uptake, distribution, or incorporation into other cuproenzymes. Consistent with this loss of SOD1 activity, CCS(-/-) mice showed increased sensitivity to paraquat and reduced female fertility, phenotypes that are characteristic of SOD1-deficient mice. These results demonstrate the essential role of any mammalian copper chaperone and have important implications for the development of novel therapeutic strategies in familial amyotrophic lateral sclerosis.

Molecular factors underlying selective vulnerability of motor neurons to neurodegeneration in amyotrophic lateral sclerosis

Current research evidence suggests that genetic factors, oxidative stress and glutamatergic toxicity, with damage to critical target proteins and organelles, may be important contributory factors to motor neuron injury in amyotrophic lateral sclerosis (ALS). Various molecular and neurochemical features of human motor neurons may render this cell group differentially vulnerable to such insults. Motor neurons are large cells with long axonal processes which lead to requirements for a high level of mitochondrial activity and a high neurofilament content compared to other neuronal groups. The lack of calcium buffering proteins parvalbumin and calbindin D28k and the low expression of the GluR2 AMPA receptor subunit may render human motor neurons particularly vulnerable to calcium toxicity following glutamate receptor activation. Motor neurons also have a high perisomatic expression of the glutamate transporter protein EAAT2 and a very high expression of the cytosolic free radical scavenging enzyme Cu/Zn superoxide dismutase (SOD1) which may render this cell group vulnerable in the face of genetic or post-translational alterations interfering with the function of these proteins. More detailed characterisation of the molecular features of human motor neurons in the future may allow the strategic development of better neuroprotective therapies for the benefit of patients afflicted by ALS.

Cellular distribution of superoxide dismutases in the rat CNS

Superoxide dismutase (SOD) is considered to be a major factor in protection of nervous tissue against excitotoxic and ischemic/hypoxic lesion. Controversial reports about the localization of SOD after such an insult prompted us to re-investigate immunocytochemically the localization of the enzyme in the brain and spinal cord using specific antibodies against the manganese (Mn-SOD) and copper/zinc (Cu/Zn-SOD) containing isoenzyme in combination with cell type specific markers. CNS tissue sections were analyzed by confocal laser scanning microscopy and digital photo imaging. Cu/Zn-SOD immunoreactivity was found to be located predominantly in astrocytes throughout the CNS. The staining was found in the cytoplasm, in cellular processes and, less intensive, in the nucleus sparing the nucleolus. At a lower level the enzyme was also detectable in neuronal perikarya and in structures of the neuropil. Motoneurons of the spinal cord displayed an enhanced Cu/Zn-SOD staining intensity, when compared to brain neurons. In contrast the Mn-containing isoenzyme was predominantly localized to neurons and their processes throughout the brain and the spinal cord. Confirming the mitochondrial localization of the enzyme, a granular staining pattern sparing the nucleus was observed. Mn-SOD stained mitochondria were also seen in astroglial cells but the staining intensity was, on the whole, much lower compared to neurons, and often hardly detectable. It seems reasonable to conclude that differences in the basal content of SOD-isoenzymes may contribute to different cellular susceptibilities in neurodegenerative processes that are accompanied by oxidative stress.

Induction of nitric oxide-dependent apoptosis in motor neurons by zinc-deficient superoxide dismutase

Mutations in copper, zinc superoxide dismutase (SOD) have been implicated in the selective death of motor neurons in 2 percent of amyotrophic lateral sclerosis (ALS) patients. The loss of zinc from either wild-type or ALS-mutant SODs was sufficient to induce apoptosis in cultured motor neurons. Toxicity required that copper be bound to SOD and depended on endogenous production of nitric oxide. When replete with zinc, neither ALS-mutant nor wild-type copper, zinc SODs were toxic, and both protected motor neurons from trophic factor withdrawal. Thus, zinc-deficient SOD may participate in both sporadic and familial ALS by an oxidative mechanism involving nitric oxide.

The roles of free radicals in amyotrophic lateral sclerosis: reactive oxygen species and elevated oxidation of protein, DNA, and membrane phospholipids

To explore whether reactive oxygen species (ROS) play a role in the pathogenesis of amyotrophic lateral sclerosis (ALS), a unique microdialysis or microcannula sampling technique was used in mice transfected with a mutant Cu,Zn-superoxide dismutase (SOD1) gene from humans with familial ALS, mice transfected with the normal human SOD1 gene, and normal mice. We demonstrate for the first time that the levels of hydrogen peroxide (H(2)O(2)) and the hydroxyl radical ((.)OH) are significantly higher, and the level of the superoxide anion (O(2)(.-)) is significantly lower in ALS mutant mice than in controls, supporting by in vivo evidence the hypothesis that the mutant enzyme catalyzes (.)OH formation by the sequence: O(2)(.-) --> H(2)O(2) --> (.)OH. This removes doubts regarding the relevance of elevated ROS in FALS raised by in vitro experiments. The levels of oxidation products are also significantly higher in the mutant mice than in controls, consistent with some previous reports. Only the superoxide concentration differs between two controls among all the measurements. Our findings correlate in vivo a gene mutation to both elevated H(2)O(2) and (.)OH and increased oxidation of cellular constituents. The elevated H(2)O(2) in mutant mice indicates impairment of its detoxification pathways, perhaps by changed interactions between SOD1 and H(2)O(2) detoxification enzymes.-Liu, D., Wen, J., Liu, J., Li, L. The roles of free radicals in amyotrophic lateral sclerosis: reactive oxygen species and elevated oxidation of protein, DNA, and membrane phospholipids.

A receptor for advanced glycosylation endproducts (AGEs) is colocalized with neurofilament-bound AGEs and SOD1 in motoneurons of ALS: immunohistochemical study

Neurofilament (NF)-bound AGEs colocalize immunochemically with SOD1 in the motoneurons of patients with ALS. Among three types of AGE receptors reported in the human brain, AGE-R1 (oligosaccharyltransferase family) and AGE-R2 (substrate of protein kinase C) have been found in neurons, while AGE-R3 is restricted to glia. The present study investigates which of these receptors may be responsible for binding AGEs in the NF conglomerates of motoneurons. Immunostaining of paraffin sections from eight ALS patients (five sporadic and three familial) and three control cases was performed with antibodies directed against R1 and R2, in parallel with those against AGEs and SOD1. The sites of AGE-R1 immunoreactivity (IR) in motoneurons were in conformity to those of NF-associated AGE and SOD1 IRs. By contrast, the IR of R2 was negative in NF conglomerates. Negative R2 IR for NF conglomerates was outlined by surrounding coarse R2 immunopositive granules in the perikaryon. No IR for R1 or R2 was found in hyaline or Bunina inclusions. There was no extraneuronal expression of IR for AGE-R1 or AGEs in microglia or astroglia around the NF accumulation. The colocalization of AGE, AGE-R1, and SOD1 at NF conglomerates in motoneurons supports the notion that AGE-mediated oxidative stress and protein aggregation may be implicated in NF conglomeration and ALS pathogenesis.

Peripheral axotomy slows motoneuron degeneration in a transgenic mouse line expressing mutant SOD1 G93A

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder that involves motoneuron degeneration, paralysis, and death. Mutations in Cu, Zn superoxide dismutase (SOD1) are one cause of this disease. It has been a puzzle as to why mutations in SOD1, an enzyme expressed in many neuronal types, selectively kill motoneurons. To begin to explore the factors that determine this selectivity, we carried out peripheral axotomy in mice expressing a mutant SOD1 (G93A mice) and controls (nontransgenic mice and mice expressing wild-type human SOD1). Axotomy in controls induced a predicted axonal atrophy and a small degree of axon loss. The axonal atrophy led to an increase in the number of small axons and a decrease in the number of large axons. In contrast to the controls, axotomy in G93A mice reduced the extent of axon degeneration at the end stage of the disease, leading to an increase in the number of surviving motor axons. Interestingly, all of the increased surviving axons were in the axon group with diameters smaller than 4.5 microm. This result suggests an apparent threshold of vulnerability that is correlated with axon size.

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

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

Hindlimb motor neurons require Cu/Zn superoxide dismutase for maintenance of neuromuscular junctions

The role of oxidative damage in neurodegenerative disease was investigated in mice lacking cytoplasmic Cu/Zn superoxide dismutase (SOD), created by deletion of the SOD1 gene (SOD1(-/-)). SOD1(-/-) mice developed a chronic peripheral hindlimb axonopathy. Mild denervation of muscle was detected at 2 months, and behavioral and physiological motor deficits were present at 5-7 months of age. Ventral root axons were shrunken but were normal in number. The somatosensory system in SOD1(-/-) mice was mildly affected. SOD1(-/-) mice expressing Cu/Zn SOD only in brain and spinal cord were generated using transgenic mice expressing mouse SOD1 driven by the neuron-specific synapsin promoter. Neuron-specific expression of Cu/Zn SOD in SOD1(-/-) mice rescued motor neurons from the neuropathy. Therefore, Cu/Zn SOD is not required for normal motor neuron survival, but is necessary for the maintenance of normal neuromuscular junctions by hindlimb motor neurons.

Lack of involvement of neuronal nitric oxide synthase in the pathogenesis of a transgenic mouse model of familial amyotrophic lateral sclerosis

A subset of familial cases of amyotrophic lateral sclerosis are linked to missense mutations in copper/zinc superoxide dismutase type 1. Patients with missense mutations in copper/zinc superoxide dismutase type 1 develop a paralytic disease indistinguishable from sporadic amyotrophic lateral sclerosis through an unknown toxic gain of function. Nitric oxide reacts with the superoxide anion to form the strong oxidant, peroxynitrite, which participates in neuronal injury in a variety of model systems. Peroxynitrite is an alternate substrate for copper/zinc superoxide dismutase type 1, causing catalytic nitration of tyrosine residues in other proteins. Mutations in copper/zinc superoxide dismutase type 1 may disrupt the active site of the enzyme and permit greater access of peroxynitrite to copper, leading to increased nitration by peroxynitrite of critical cellular targets. To investigate whether neuronal-derived nitric oxide plays a role in the pathogenesis of familial amyotrophic lateral sclerosis, we examined the effects of three different nitric oxide synthase inhibitors: a non-selective nitric oxide synthase inhibitor, nitro-L-arginine methyl ester; a relatively selective inhibitor of neuronal nitric oxide synthase, 7-nitroindazole; and a novel highly selective neuronal nitric oxide synthase inhibitor, AR-R 17,477, in transgenic mice expressing a familial amyotrophic lateral sclerosis-linked mutant human copper/zinc superoxide dismutase type 1 (Gly-->Ala at position 93; G93A) containing a high transgene copy number and a low transgene copy number. AR-R 17,477, but not nitro-L-arginine methyl ester or 7-nitroindazole, significantly prolonged survival in both the high and low transgene transgenic mice. To determine whether neuronal nitric oxide synthase is involved in the pathogenesis resulting from the familial amyotrophic lateral sclerosis copper/zinc superoxide dismutase type 1 mutation, we produced mice with the copper/zinc superoxide dismutase type 1 mutation which lack the neuronal nitric oxide synthase gene. The transgenic mice expressing a familial amyotrophic lateral sclerosis-linked mutant human copper/zinc superoxide dismutase type 1 on neuronal nitric oxide synthase null background do not live significantly longer than transgenic mice expressing a familial amyotrophic lateral sclerosis-linked mutant human copper/zinc superoxide dismutase type 1. Western blot analysis indicates the presence of two neuronal nitric oxide synthase-like immunoreactive bands in spinal cord homogenates of the neuronal nitric oxide synthase null mice, and residual neuronal nitric oxide synthase catalytic activity ( > 7%) is detected in the spinal cord of the transgenic mice expressing a familial amyotrophic lateral sclerosis-linked mutant human copper/zinc superoxide dismutase type 1 on neuronal nitric oxide synthase null background. This amount of residual activity probably does not account for lack of protection afforded by the disrupted neuronal nitric oxide synthase gene in the familial amyotrophic lateral sclerosis-linked mutant human copper/zinc superoxide dismutase type 1 mice. Immunological nitric oxide synthase is not detected in the copper/zinc superoxide dismutase type 1 mutant mice at several different ages, thus excluding immunological nitric oxide synthase as a contributor to the pathogenesis of familial amyotrophic lateral sclerosis. Levels of neuronal nitric oxide synthase as well as Ca2+-dependent nitric oxide synthase catalytic activity in the copper/zinc superoxide dismutase type 1 mutant mice do not differ from wild type mice. Endothelial nitric oxide synthase levels may be decreased in the copper/zinc superoxide dismutase type 1 mutant mice. Together, these results do not support a significant role for neuronal-derived nitric oxide in the pathogenesis of familial amyotrophic lateral sclerosis transgenic mice.

Distribution and kinetics of ethanol metabolism in rat brain

It was found that the accumulation of acetaldehyde produced from 50 mM ethanol in rat brain homogenates takes place in all major brain regions. The velocity varied between 3.5 to 7.1 nmol/mg of protein/hr. The rate increased in the following order: brain hemispheres, striatum, brainstem, hypothalamus, and cerebellum. Significant regional differences in this process were found: in the initial period of incubation (5 min), acetaldehyde accumulation was maximal in the brain hemispheres; but, in the 30- to 60-min period, it became significantly higher in the cerebellum. Inhibition of this process by the catalase inhibitor, 3-amino-1,2,4-triazole (8 mM), was minimal in the brainstem (27%) and maximal (57%) in the cerebellum, despite nearly complete inhibition of catalase. This would indicate that processes other than catalase activity must contribute to acetaldehyde accumulation.

Slowing of axonal transport is a very early event in the toxicity of ALS-linked SOD1 mutants to motor neurons

Mutations in copper/zinc superoxide dismutase 1 (SOD1), primary causes of human amyotrophic lateral sclerosis (ALS), provoke motor neuron death through an unidentified toxic property. The known neurofilament-dependent slowing of axonal transport, combined with the prominent misaccumulation of neurofilaments in ALS, suggests that an important aspect of toxicity may arise from damage to transport. Here we verify this hypothesis for two SOD1 mutations linked to familial ALS. Reduced transport of selective cargoes of slow transport, especially tubulin, arises months before neurodegeneration. For one mutant, this represents the earliest detectable abnormality. Thus, damage to the cargoes or machinery of slow transport is an early feature of toxicity mediated by mutant SOD1.

Amyotrophic lateral sclerosis associated with mutations in superoxide dismutase: a putative mechanism of degeneration

Amyotrophic lateral sclerosis (ALS) is a devastating neurologic disease that rapidly progresses from mild motor symptoms to severe motor paralysis and premature death. Until recently, there were few substantive studies conducted on the pathogenesis of the disease. With the genetic linkage of mutations in the superoxide dismutase (SOD-1) gene with familial ALS patients, new avenues for study have become available including transgenic mice and culture models. Although not yet providing a complete picture of the disease mechanism, studies utilizing these model systems have greatly advanced our understanding of the mechanism of degeneration and should eventually lead to putative therapeutic agents. In this review, we will present the important findings from these model systems, provide a framework in which to evaluate these findings, and speculate on the mechanism of degeneration initiated by the mutations in SOD-1.

Oxidative stress and motor neurone disease

The effects of oxidative stress within post mitotic cells such as neurones may be cumulative, and injury by free radical species is a major potential cause of the age-related deterioration in neuronal function seen in several neurodegenerative diseases. There is strong evidence that oxidative stress plays an important role in the pathogenesis of motor neurone disease (MND). Point mutations in the antioxidant enzyme Cu,Zn superoxide dismutase (SOD1) are found in some pedigrees with the familial form of MND. How mutations in this ubiquitous enzyme cause the relatively selective cell death of specific groups of motor neurones is not clear, although a number of hypotheses have been forwarded. These include (1) the formation of hydroxyl radicals, (2) the catalysis of reactions of the nitrogen centred oxidant species peroxynitrite, (3) toxicity of copper or zinc and (4) protein aggregation. Some experimental support for these different hypotheses has been produced by manipulating cells in culture to express the mutant SOD1 proteins and by generating transgenic mice which over-express mutant SOD1. Observations in these model systems are, in some cases at least, supported by observations made on pathological material from patients with similar SOD1 mutations. Furthermore, there are reports of evidence of free radical mediated damage to neurones in the sporadic form of MND. Several lines of evidence suggest that alterations in the glutamatergic neurotransmitter system may also play a key role in the injury to motor neurones in sporadic MND. There are several important subcellular targets, which may be preferentially impaired within motor neurones, including neurofilament proteins and mitochondria. Future research will need to identify the aspects of the molecular and physiological phenotype of human motor neurones that makes them susceptible to degeneration in MND, and to identify those genetic and environmental factors which combine to cause this disease in individuals and in familial pedigrees.

The copper chaperone CCS is abundant in neurons and astrocytes in human and rodent brain

Copper trafficking in mammalian cells is highly regulated. CCS is a copper chaperone that donates copper to the antioxidant enzyme copper/zinc superoxide dismutase 1 (SOD 1). Mutations of SOD1 are responsible for approximately 20% of familial amyotrophic lateral sclerosis (FALS). Monospecific antibodies were generated to evaluate the localization and cellular distribution of this copper chaperone in human and mouse brain as well as other organs. CCS is found to be ubiquitously expressed by multiple tissues and is present in particularly high concentrations in kidney and liver. In brain and spinal cord, CCS was found throughout the neuropil, with expression largely confined to neurons and some astrocytes. Like SOD1, CCS immunoreactivity was intense in Purkinje cells, deep cerebellar neurons, and pyramidal cortical neurons, whereas in spinal cord, CCS was highly expressed in motor neurons. In cortical neurons, CCS was present in the soma and proximal dendrites, as well as some axons. Although the distribution of CCS paralleled that of SOD1, there was a 12-30-fold molar excess of SOD1 over CCS. That both SOD1 and CCS are present, together, in cells that degenerate in ALS also emphasizes the potential role of CCS in mutant SOD1-mediated toxicity.