Increased number and differentiation of neural precursor cells in the brainstem of superoxide dismutase 1(G93A) (G1H) transgenic mouse model of amyotrophic lateral sclerosis

The superoxide dismutase 1(G93A G1H) (SOD1(G93A G1H)) transgenic mouse is a model of familial human amyotrophic lateral sclerosis (ALS) that has progressive neurodegeneration within the spinal cord and brainstem. In this study, we investigated the number and differentiation of neural precursor cells (NPCs). Nestin-positive NPCs were rarely seen in the nervous system of wild type controls or pre-disease mice at post-natal days 30 and 60. With disease onset on post-natal day 90, nestin labeled NPCs proliferated preferentially in the brainstem with maximal number and density at post-natal day 120. NPCs did not double-label with CNPase or O(4) markers of oligodendrocytes. The majority of the NPCs co-labeled with the astrocyte maker glial fibrillary acidic protein (GFAP) and a small number with the neuronal marker NeuN. At disease onset, 73 and 10% of NPCs co-expressed GFAP and NeuN respectively while at severe disease stage, 80 and 8% of the NPCs co-expressed GFAP and NeuN. Proliferating cell nuclear antigen (PCNA) was used to confirm that at least some of these cells undergo mitosis. Future studies could be directed at controlling the differentiation of these endogenous NPCs into neurons and astrocytes in order to ameliorate the degeneration within the brainstem of the ALS mouse.

Clinical characteristics of familial amyotrophic lateral sclerosis with a Phe20Cys mutation in the SOD1 gene in a Korean family

Familial ALS (FALS) is mostly inherited as an age-dependent autosomal dominant trait. Since the discovery of mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1), testing for SOD1 gene mutations has become a routine part of the investigation into ALS patients with a family history. This study reports the results of mutation evaluation and clinical features examination in a Korean family with ALS. The clinical symptoms, signs and neurological findings of a four-generation pedigree with 34 members were collected. Five exons of the Cu/Zn SOD gene were analyzed by polymerase chain reaction. The clinical signs and symptoms of ALS patients began in the lower extremities and spread to the upper extremities and bulbar muscles. The mode of transmission was determined to be autosomal dominant, and low penetrance was seen in females. The age at onset varied from 37 to 77 years. ALSFRS-R testing showed variability in the clinical progression of the disease. A point mutation in exon 1 of the SOD1 gene, resulting in an amino acid change from phenylalanine 20 to cysteine (F20C), was identified. This is the first report of clinical features resulting from the Phe20Cys mutation in the SOD1 gene.

Mutant SOD1(G93A) microglia are more neurotoxic relative to wild-type microglia

Recent studies suggest that microglia over-expressing mutant human superoxide dismutase (mSOD1(G93A)) may contribute to motoneuron death in a transgenic mouse model of familial amyotrophic lateral sclerosis. To further assess the relative neurotoxicity of wild-type microglia, mSOD1(G93A) microglia, and microglia over-expressing wild-type human SOD1, we used primary cultures of microglia and motoneurons in the presence and absence of lipopolysaccharide stimulation. Following activation with lipopolysaccharide, mSOD1(G93A) microglia released more nitric oxide, more superoxide, and less insulin-like growth factor-1 than wild-type microglia. In microglia/motoneuron co-cultures, mSOD1(G93A) microglia induced more motoneuron death and decreased neurite numbers and length compared with wild-type microglia. Mutant SOD1(G93A) microglia also induced more motoneuron injury than microglia over-expressing wild-type human SOD1 in microglia/motoneuron co-cultures. Motoneuron survival was inversely correlated with nitrate + nitrite concentrations in mSOD1(G93A) co-cultures, suggesting the important role of nitric oxide in microglia-induced motoneuron injury. Thus, relative to wild-type microglia, mSOD1(G93A) microglia were more neurotoxic and induced more motoneuron injury than similarly treated wild-type microglia.

Interaction between Familial Amyotrophic Lateral Sclerosis (ALS)-linked SOD1 Mutants and the Dynein Complex

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by progressive motor neuron death. More than 90 mutations in the copper-zinc superoxide dismutase (SOD1) gene cause a subset of familial ALS. Toxic properties have been proposed for the ALS-linked SOD1 mutants, but the nature of the toxicity has not been clearly specified. Cytoplasmic inclusion bodies containing mutant SOD1 and a number of other proteins are a pathological hallmark of mutant SOD1-mediated familial ALS, but whether such aggregates are toxic to motor neurons remains unclear. In this study, we identified a dynein subunit as a component of the mutant SOD1-containing high molecular weight complexes using proteomic techniques. We further demonstrated interaction and colocalization between dynein and mutant SOD1, but not normal SOD1, in cultured cells and also in G93A and G85R transgenic rodent tissues. Moreover, the interaction occurred early, prior to the onset of symptoms in the ALS animal models and increased over the disease progression. Motor neurons with long axons are particularly susceptible to defects in axonal transport. Our results demonstrate a direct "gain-of-interaction" between mutant SOD1 and dynein, which may provide insights into the mechanism by which mutant SOD1 could contribute to a defect in retrograde axonal transport or other dynein functions. The aberrant interaction is potentially critical to the formation of mutant SOD1 aggregates as well as the toxic cascades leading to motor neuron degeneration in ALS.

Increased affinity for copper mediated by cysteine 111 in forms of mutant superoxide dismutase 1 linked to amyotrophic lateral sclerosis

Mutations in Cu,Zn-superoxide dismutase (SOD1) cause familial amyotrophic lateral sclerosis (ALS). It has been proposed that neuronal cell death might occur due to inappropriately increased Cu interaction with mutant SOD1. Using Cu immobilized metal-affinity chromatography (IMAC), we showed that mutant SOD1 (A4V, G85R, and G93A) expressed in transfected COS7 cells, transgenic mouse spinal cord tissue, and transformed yeast possessed higher affinity for Cu than wild-type SOD1. Serine substitution for cysteine at the Cys111 residue in mutant SOD1 abolished the Cu interaction on IMAC. C111S substitution reversed the accelerated degradation of mutant SOD1 in transfected cells, suggesting that the Cys111 residue is critical for the stability of mutant SOD1. Aberrant Cu binding at the Cys111 residue may be a significant factor in altering mutant SOD1 behavior and may explain the benefit of controlling Cu access to mutant SOD1 in models of familial ALS.

An immunological epitope selective for pathological monomer-misfolded SOD1 in ALS

Misfolding of Cu/Zn-superoxide dismutase (SOD1) is emerging as a mechanism underlying motor neuron degeneration in individuals with amyotrophic lateral sclerosis (ALS) who carry a mutant SOD1 gene (SOD1 ALS). Here we describe a structure-guided approach to developing an antibody that specifically recognizes monomer-misfolded forms of SOD1. We raised this antibody to an epitope that is normally buried in the SOD1 native homodimer interface. The SOD1 exposed dimer interface (SEDI) antibody recognizes only those SOD1 conformations in which the native dimer is disrupted or misfolded and thereby exposes the hydrophobic dimer interface. Using the SEDI antibody, we established the presence of monomer-misfolded SOD1 in three ALS mouse models, with G37R, G85R and G93A SOD1 mutations, and in a human individual with an A4V SOD1 mutation. Despite ubiquitous expression, misfolded SOD1 was found primarily within degenerating motor neurons. Misfolded SOD1 appeared before the onset of symptoms and decreased at the end stage of the disease, concomitant with motor neuron loss.

Inhibition of p38 mitogen activated protein kinase activation and mutant SOD1G93A-induced motor neuron death

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by the selective loss of motor neurons. Stress activated protein kinases (SAPK) have been suggested to play a role in the pathogenesis of ALS. We studied the relevance of p38 MAPK for motor neuron degeneration in the mutant SOD1 mouse. Increased levels of phospho-p38 MAPK were present in the motor neurons and microglia of the ventral spinal cord. The p38 MAPK-inhibitor, SB203580, completely inhibited mutant SOD1-induced apoptosis of motor neurons and blocked LPS-induced activation of microglia. Semapimod, a p38 MAPK inhibitor suitable for clinical use, prolonged survival of mutant SOD1 mice to a limited extent, but largely protected motor neurons and proximal axons from mutant SOD1-induced degeneration. Our data confirm the abnormal activation of p38 MAPK in mutant SOD1 mice and the involvement of p38 MAPK in mutant SOD1-induced motor neuron death. We demonstrate the effect of p38 MAPK inhibition on survival of mutant SOD1 mice and reveal a dissociation between the effect on survival of motor neurons and that on survival of the animal, the latter likely depending on the integrity of the entire motor axon.

Toxicity from different SOD1 mutants dysregulates the complement system and the neuronal regenerative response in ALS motor neurons

Global, age-dependent changes in gene expression from rodent models of inherited ALS caused by dominant mutations in superoxide-dismutase 1 (SOD1) were identified by using gene arrays and RNAs isolated from purified embryonic and adult motor neurons. Comparison of embryonic motor neurons expressing a dismutase active ALS-linked mutant SOD1 with those expressing comparable levels of wild-type SOD1 revealed the absence of mutant-induced mRNA changes. An age-dependent mRNA change that developed presymptomatically in adult motor neurons collected by laser microdissection from mice expressing dismutase active ALS-linked mutants was dysregulation of the d/l-serine biosynthetic pathway, previously linked to both excitotoxic and neurotrophic effects. An unexpected dysregulation common to motor neurons expressing either dismutase active or inactive mutants was induction of neuronally derived components of the classic complement system and the regenerative/injury response. Alteration of these mutant SOD1-induced pathways identified a set of targets for therapies for inherited ALS.

Binding of a single zinc ion to one subunit of copper-zinc superoxide dismutase apoprotein substantially influences the structure and stability of the entire homodimeric protein

The thermodynamics of zinc binding to metal-free (apo) human and bovine copper-zinc superoxide dismutases (SOD1) were measured using isothermal titration calorimetry. The apparent thermodynamics of zinc binding to the apoproteins were favorable (Ka > 108 M-1), with an observed stoichiometry of one zinc per homodimer. The change in heat capacity for the one-zinc binding event was large and negative (approximately -650 cal mol-1 K-1), suggestive of significant structural changes to the protein upon zinc binding. We further characterized the one-zinc derivative by circular dichroism and determined that this derivative had nearly the same secondary structure as the two-zinc derivative and that both are structurally distinct from the metal-free protein. In addition, we monitored the effect of zinc binding on hydrogen-deuterium exchange and accessibility of histidyl residues to modification by diethyl pyrocarbonate and observed that more than 50% protection was afforded by the binding of one zinc in both assays. Differential scanning calorimetry on the human SOD1 zinc derivatives also showed increased thermostability of the protein due to zinc binding. Further, the melting transitions observed for the one-zinc derivative closely resembled those of the two-zinc derivative. Finally, we observed that the quaternary structure of the protein is stabilized upon binding of one and two zinc ions in analytical ultracentrifugation experiments. Combined, these results suggest communication between the two monomers of SOD1 such that the binding of one zinc ion per homodimer has a more profound effect on the homodimeric protein structure than the binding of subsequent metal ions. The relevance of these findings to amyotrophic lateral sclerosis is discussed.

Evidence for astrocytosis in ALS demonstrated by [11C](L)-deprenyl-D2 PET

OBJECTIVE

To use deuterium-substituted [11C](L)-deprenyl PET to depict astrocytosis in vivo in patients with amyotrophic lateral sclerosis (ALS).

BACKGROUND

In human brain, the enzyme MAO-B is primarily located in astrocytes. L-deprenyl binds to MAO-B and autoradiography with 3H-L-deprenyl has been used to map astrocytosis in vitro. Motor neuron loss in ALS is accompanied by astrocytosis and astrocytes may play an active role in the neurodegenerative process. Deuterium-substituted [11C](L)-deprenyl PET provides an opportunity to localize astrocytosis in vivo in the brain of patients with ALS.

METHODS

Deuterium-substituted [11C](L)-deprenyl PET was performed in seven patients with ALS and seven healthy control subjects.

RESULTS

Increased uptake rate of [11C](L)-deprenyl was demonstrated in ALS in pons and white matter.

CONCLUSION

This study provides evidence that astrocytosis may be detected in vivo in ALS by the use of deuterium-substituted [11C](L)-deprenyl PET though further studies are needed to determine whether deuterium-substituted [11C](L)-deprenyl binding tracks disease progression and reflects astrocytosis.

Dysequilibrium between caspases and their inhibitors in a mouse model for amyotrophic lateral sclerosis

Mutations in copper/zinc superoxide dismutase (SOD1) have been implicated in the pathogenesis of familial amyotrophic lateral sclerosis (ALS). Mutant SOD1 protein likely gains a novel cytotoxic property, leading to the death of motor neurons. We therefore investigated whether caspase-mediated apoptosis is associated with novel cytotoxic properties in a rodent model for familial ALS (G93A SOD1 transgenic mice). Caspase-9 (an effecter in the mitochondrial apoptotic pathway), caspase-8 (an effecter in the Fas apoptotic pathway), and caspase-3 (an executioner of both pathways) proteins were all present in nonactive forms in the spinal cords of wild-type mice during the early stage of the disease (8 weeks), at which time the mice had not yet exhibited motor paralysis. In transgenic mice, however, these proteins were present in their active forms, and their mRNA levels were significantly upregulated in the represent to this conversion from nonactive to active forms. During the advanced stage of the disease (16 weeks), when paralysis was evident, the active caspase levels were further elevated. On the other hand, the mRNA and protein levels of survivin, a counteraction protein against caspases, were significantly suppressed during the early stage, and sharply increased during the advanced stage. Although the mRNA and protein levels of X-linked inhibitor of apoptosis protein (XIAP) remained at the same levels as those seen in the control (wild-type mice) during the early stage, they were significantly depressed at an age of 16 weeks. These findings were observed exclusively in the spinal cord, the region responsible for the disease, and not in the cerebellum, a non-responsible region. We conclude that conditions facilitating the apoptotic process during the early stage of the disease play causative roles in the pathogenesis of ALS and that the suppression of XIAP levels during the advanced stage could contribute to disease expression and/or progression.

Identification of a novel D109Y mutation in Cu/Zn superoxide dismutase (sod1) gene associated with amyotrophic lateral sclerosis

We report a novel missense mutation (Asp109Tyr) in exon 4 of the Cu/Zn superoxide dismutase (sod1) gene in a woman with apparently sporadic amyotrophic lateral sclerosis (SALS). Signs of motor deficit appeared at the age of 51 years which progressed over the next 6 years to upper and lower motor neuron disease and death occurred by the age of 57 years. In this mutation, the base change of guanine to thymine at codon 109 of sod1 gene leads to the replacement of aspartic by tyrosine in the protein. This amino acid change in the protein however, did not alter the catalytic activity of the SOD1 enzyme as there was no change in the enzymatic activity of purified SOD1 from the patient's erythrocytes compared to control.

Motor neuron disease in mice expressing the wild type-like D90A mutant superoxide dismutase-1

Mutant human CuZn-superoxide dismutases (hSOD1s) cause amyotrophic lateral sclerosis (ALS). The most common mutation is the wild type-like D90A and to explore its properties, transgenic mice were generated and compared with mice expressing wild-type hSOD1. D90A hSOD1 was both in vivo in mice and in vitro under denaturing conditions nearly as stable as the wild-type human enzyme. It appeared less toxic than other tested mutants, but mice homozygous for the transgene insertion developed a fatal motor neuron disease. In these mice, the disease progression was slow and there were bladder disturbances similar to what is found in human ALS cases homozygous for the D90A mutation. The homozygous D90A mice accumulated detergent-resistant hSOD1 aggregates in spinal cords, and abundant hSOD1 inclusions and vacuoles were seen in the ventral horns. Mice expressing wild-type hSOD1 at a comparable rate showed similar pathologic changes but less and later. Hemizygous D90A mice showed even milder alterations. At 600 days, the wild-type hSOD1 transgenic mice had lost more ventral horn neurons than hemizygous D90A mice (38% vs 31% p < 0.01). Thus, wild-type hSOD1 shows a significant neurotoxicity in the spinal cord, that is less than equal but more than half as large as that of D90A mutant enzyme.

siRNAs meet their match

A new study addresses how to design highly specific small interfering RNAs (siRNAs) capable of distinguishing between similar variants of the same gene.

Structure, folding, and misfolding of Cu,Zn superoxide dismutase in amyotrophic lateral sclerosis

Fourteen years after the discovery that mutations in Cu, Zn superoxide dismutase (SOD1) cause a subset of familial amyotrophic lateral sclerosis (fALS), the mechanism by which mutant SOD1 exerts toxicity remains unknown. The two principle hypotheses are (a) oxidative damage stemming from aberrant SOD1 redox chemistry, and (b) misfolding of the mutant protein. Here we review the structure and function of wild-type SOD1, as well as the changes to the structure and function in mutant SOD1. The relative merits of the two hypotheses are compared and a common unifying principle is outlined. Lastly, the potential for therapies targeting SOD1 misfolding is discussed.

Red cell superoxide dismutase activity in sporadic amyotrophic lateral sclerosis

Specific biologic markers are not available for definitive diagnosis and monitoring of disease progression in sporadic amyotrophic lateral sclerosis (SALS). Oxidative stress plays a role in ALS pathogenesis. The purpose of this study was to determine the association between Cu/Zn superoxide dismutase (SOD1) activity, diagnosis and prognosis. The present study included 25 SALS patients (SALS group; age 51+/-12 years) and 10 healthy subjects (age 45+/-5 years) as a control group. Patients were divided into groups representing four levels of diagnostic certainty of ALS in accordance with the El Escorial Revisited criteria. The disease state was determined using the modified ALS health state scale of Riviere et al. (Arch Neurol 1998:55;526-8). Red-cell SOD1 activity was determined by spectrophotometry. SOD1 activity in red cells was compared statistically with diagnostic criteria and disease state. Red cell SOD1 activity was high in all SALS patients, but there was no significant association between enzyme activity and diagnostic criteria and disease state. In this preliminary study, we did not find any correlation between SOD1 activity level and diagnosis or prognosis. Measured SOD1 activity sometimes supports ALS diagnosis, but it is neither a specific nor a prognostic factor.

Cell culture models to investigate the selective vulnerability of motoneuronal mitochondria to familial ALS-linked G93ASOD1

Mitochondrial damage induced by superoxide dismutase (SOD1) mutants has been proposed to have a causative role in the selective degeneration of motoneurons in amyotrophic lateral sclerosis (ALS). In order to investigate the basis of the tissue specificity of mutant SOD1 we compared the effect of the continuous expression of wild-type or mutant (G93A) human SOD1 on mitochondrial morphology in the NSC-34 motoneuronal-like, the N18TG2 neuroblastoma and the non-neuronal Madin-Darby Canine Kidney (MDCK) cell lines. Morphological alterations of mitochondria were observed in NSC-34 expressing the G93A mutant (NSC-G93A) but not the wild-type SOD1, whereas a ten-fold greater level of total expression of the mutant had no effect on mitochondria of non-motoneuronal cell lines. Fragmented network, swelling and cristae remodelling but not vacuolization of mitochondria or other intracellular organelles were observed only in NSC-G93A cells. The mitochondrial alterations were not explained by a preferential localization of the mutant within NSC-G93A mitochondria, as a higher amount of the mutant SOD1 was found in mitochondria of MDCK-G93A cells. Our results suggest that mitochondrial vulnerability of motoneurons to G93ASOD1 is recapitulated in NSC-34 cells, and that peculiar features in network dynamics may account for the selective alterations of motoneuronal mitochondria.

Mutant SOD1 instability: implications for toxicity in amyotrophic lateral sclerosis

The biological basis of preferential motor neuron degeneration in amyotrophic lateral sclerosis (ALS) remains incompletely understood, and effective therapies to prevent the lethal consequences of this disorder are not yet available. Since 1993, more than 100 mutant variants of the antioxidant enzyme Cu/Zn superoxide dismutase (SOD1) have been identified in familial ALS. Many studies have sought to distinguish abnormal properties shared by these proteins that may contribute to their toxic effects and cause age-dependent motor neuron loss. Complex networks of cellular interactions and changes associated with aging may link mutant SOD1s and other stresses to motor neuron death in ALS. Our laboratory and collaborators have compared physicochemical properties of biologically metallated wild-type and mutant SOD1 proteins to discern specific vulnerabilities that may be relevant to the mutant toxicity in vivo. X-ray crystal structures obtained from metallated 'wild-type-like' (WTL) SOD1 mutants, which retain the ability to bind copper and zinc and exhibit normal specific activity, indicate a native-like structure with only subtle changes to the backbone fold. In contrast, a group of 'metal-binding region' (MBR) SOD1 mutants that are deficient in copper and zinc exhibit severe thermal destabilization and structural disorder of conserved loops near the metal-binding sites. A growing body of evidence highlights specific stresses in vivo that may perturb well-folded, metallated SOD1 variants and thereby favor an increased burden of partially unfolded, metal-deficient species. For example, WTL SOD1 mutants are more susceptible than wild-type SOD1 to reduction of the intrasubunit disulfide bond between Cys-57 and Cys-146 at physiological pH and temperature. This bond anchors the disulfide loop to the SOD1 beta-barrel and helps to maintain the dimeric configuration of the protein. Cleavage of the disulfide linkage renders the well-folded WTL mutants vulnerable to metal loss and monomerization such that they may resemble the destabilized and locally misfolded MBR mutant species. SOD1 proteins with disordered loops or monomeric structure are expected to be more susceptible to aberrant self-association or detrimental interactions with other cellular constituents. The challenge for future investigations is to relate these abnormal properties of partially unfolded SOD1 to specific mechanisms of toxicity in motor neurons, supporting cells, or target tissues.

Deficiency in the ALS2 gene does not affect the motor neuron degeneration in SOD1(G93A) transgenic mice

Dysfunction of the ALS2 gene has been linked to one form of juvenile onset autosomal recessive amyotrophic lateral sclerosis (ALS). Previous in vitro studies suggest that over-expression of ALS2 protects cells from mutant Cu/Zn superoxide dismutase (SOD1)-induced cytotoxicity. To test whether ALS2 plays a protective role against mutant SOD1-mediated motor neuron degeneration in vivo, we examined the progression of motor neuron disease in SOD1(G93A) mice on an ALS2 null background. Our data suggest that deficiency in the ALS2 gene does not affect the pathogenesis of SOD1(G93A) mice.

Identification of three mutations in the Cu,Zn-superoxide dismutase (Cu,Zn-SOD) gene with familial amyotrophic lateral sclerosis: transduction of human Cu,Zn-SOD into PC12 cells by HIV-1 TAT protein basic domain

The most frequent genetic causes of amyotrophic lateral sclerosis (ALS) determined so far are mutations occurring in the gene coding for copper/zinc superoxide dismutase (Cu,Zn-SOD). The mechanism may involve the formation of hydroxyl radicals or malfunctioning of the SOD protein. Wild-type SOD1 was constructed into a transcription-translation expression vector to examine the SOD1 production in vitro. Wild-type SOD1 was highly expressed in Escherichia coli. Active SOD1 was expressed in a metal-dependent manner. To investigate the possible roles of genetic causes of ALS, a human Cu,Zn-SOD gene was fused with a gene fragment encoding the nine amino acid transactivator of transcription (Tat) protein transduction domain (RKKRRQRRR) of human immunodeficiency virus type 1 in a bacterial expression vector to produce a genetic in-frame Tat-SOD1 fusion protein. The expressed and purified Tat-SOD1 fusion proteins in E. coli can enter PC12 neural cells to observe the cellular consequences. Denatured Tat-SOD1 was successfully transduced into PC12 cells and retained its activity via protein refolding. Three point mutations, E21K, D90V, and D101G, were cloned by site-directed mutagenesis and showed lower SOD1 activity. In undifferentiated PC12 cells, wild-type Tat-SOD1 could prevent DNA fragmentation due to superoxide anion attacks generated by 35 mM paraquat, whereas mutant Tat-D101G enhanced cell death. Our results demonstrate that exogenous human Cu,Zn-SOD fused with Tat protein can be directly transduced into cells, and the delivered enzymatically active Tat-SOD exhibits a cellular protective function against oxidative stress.

Familial ALS-superoxide dismutases associate with mitochondria and shift their redox potentials

Recent studies suggest that the toxicity of familial amyotrophic lateral sclerosis mutant Cu, Zn superoxide dismutase (SOD1) arises from its selective recruitment to mitochondria. Here we demonstrate that each of 12 different familial ALS-mutant SOD1s with widely differing biophysical properties are associated with mitochondria of motoneuronal cells to a much greater extent than wild-type SOD1, and that this effect may depend on the oxidation of Cys residues. We demonstrate further that mutant SOD1 proteins associated with the mitochondria tend to form cross-linked oligomers and that their presence causes a shift in the redox state of these organelles and results in impairment of respiratory complexes. The observation that such a diverse set of mutant SOD1 proteins behave so similarly in mitochondria of motoneuronal cells and so differently from wild-type SOD1 suggests that this behavior may explain the toxicity of ALS-mutant SOD1 proteins, which causes motor neurons to die.

Two approaches to drug discovery in SOD1-mediated ALS

Familial amyotrophic lateral sclerosis (ALS) accounts for 10% of all ALS cases; approximately 25% of these cases are due to mutations in the Cu/Zn superoxide dismutase gene (SOD1). To date, 105 different mutations spanning all 5 exons have been identified in the SOD1 gene. Mutant SOD1-associated ALS is caused by a toxic gain of function of the mutated protein. Therefore, regardless of the specific mechanism whereby mutant SOD1 initiates motor neuron death, the authors hypothesize that measures that decrease levels of mutant SOD1 protein should ameliorate the phenotype in transgenic mice and potentially in patients with SOD1-mediated disease. They have designed 2 cell-based screening assays to identify small, brain-permeant molecules that inactivate expression of the SOD1 gene or increase the degradation of the SOD1 protein. Here they describe the development and optimization of these assays and the results of high-throughput screening using a variety of compound libraries, including a total of more than 116,000 compounds. The majority of the hit compounds identified that down-regulated SOD1 were shown to be toxic in a cell-based viability assay or were nonselective transcription inhibitors, but work is continuing on a number of nonspecific inhibitors of SOD1 expression. Ultimately, the authors believe that these 2 cell-based assays will provide powerful strategies to identify novel therapies for the treatment of inherited SOD1-associated forms of ALS.

The adult neural stem and progenitor cell niche is altered in amyotrophic lateral sclerosis mouse brain

Amyotrophic lateral sclerosis (ALS) is a fatal adult human disease caused by motor neuron degeneration. Stem cell therapy might be a treatment for ALS. The adult mammalian forebrain has neural stem cells (NSCs) and neural progenitor cells (NPCs) in the anterior subventricular zone (SVZa), rostral migratory stream (RMS), olfactory bulb (OB) core, and dentate gyrus (DG). These cells could be used to rescue or replace degenerating upper and lower motor neurons through endogenous recruitment or autologous/allogenic transplantation. We evaluated the competency of forebrain NSCs and NPCs in transgenic (tg) mice harboring human mutant superoxide dismutase-1 (mSOD1), a model of ALS. Tg human wild-type SOD1 (wtSOD1) mice and non-tg mice were controls. Bromodeoxyuridine (BrdU) labeling of cells, a marker for cell proliferation and other events, was reduced in a niche-specific pattern in presymptomatic and symptomatic mice, with the SVZa having greater reductions than the RMS, OB, and DG. Different NSC and NPC complements were evaluated by localizing nestin, neural cell adhesion molecule, distalless-2 transcription factor, vimentin, and glial fibrillary acidic protein. In symptomatic mice, NSC markers were reduced, whereas NPC markers were unchanged or elevated. Neurogenesis was preserved in symptomatic mSOD1 mice. NSC/NPC competence assessment in vitro revealed that mSOD1 SVZa cells had the ability to proliferate and form neurospheres but had an impaired response to mitogen stimulation. We conclude that adult mSOD1 ALS mice have abnormalities in forebrain NSCs, but the essential features of NSC/NPCs remained in presymptomatic and symptomatic mice.