Oxidative stress is defined as the imbalance between reactive species such as free radicals and oxidants and the antioxidant defenses. Free radicals are molecules with one or more unpaired electrons, while oxidants are molecules with a high potential for taking electrons from other molecules. The more recognized reactive species are the reactive oxygen species (ROS), which include oxygen and its reduction products superoxide, hydrogen peroxide and hydroxyl radical, and the reactive nitrogen species (RNS) such as the free radical nitric oxide and its by-products, including the powerful oxidant peroxynitrite and the sub-product of peroxynitrite decomposition nitrogen dioxide.
As part of the antioxidant defense system, superoxide dismutase 1 (SOD1) is an abundant and highly conserved cytosolic enzyme responsible for the disproportionation of superoxide to molecular oxygen and hydrogen peroxide (McCord and Fridovich, 1969). SOD1 is a relatively small protein of 153 amino acids that works as a tight homodimer and requires a high stability for fast catalysis (Perry et al., 2010; Trumbull and Beckman, 2009). The stability is conferred by the quaternary structure of the protein, an eight-strand beta-barrel, as well as the binding of Cu and Zn, two metal ions with catalytic roles positioned in the active site channel (Perry et al., 2010; Trumbull and Beckman, 2009). The disproportionation of superoxide is a two-step oxidation-reduction reaction that involves the cycling of the copper atom in SOD1 from Cu2+ to Cu+ and back to Cu+2.
The zinc does not participate in this reaction but is essential for the structure of the active site. In addition, the formation of an intrasubunit disulfide bridge stabilizes the enzyme and plays an important role in preventing aggregation of metal-deficient SOD (Getzoff et al., 1989).
Mutations in the gene codifying for SOD1 were linked to familial ALS almost 20 years ago. Currently, over 130 point mutations on more than 70 sites on SOD1 have been described, most of these being missense single residue mutations located in critical positions that affect the stability and folding of the enzyme (Beckman et al., 2001; Perry et al., 2010; Roberts et al., 2007). The goal of this chapter is to review recent advances in our understanding of the role of oxidative stress on the gain of a toxic function associated with mutations in the gene of the copper/zinc superoxide dismutase.
2. Zn-deficient SOD1
The first proposed mechanisms linking mutations of SOD1 with ALS were based on the loss of dismutase activity (Beckman et al., 1993; Deng et al., 1993a). However, the SOD1 mutants G37R and G93A remain fully active and were linked to familial ALS (Borchelt et al., 1994; Yim et al., 1996). In addition, the mouse knockout for SOD1 developed normally and did not show signs of motor neuron deficit, although the motor neurons were more susceptible to cell death upon axonal injury (Reaume et al., 1996). This evidence indicated that a gain-of-function rather than the loss of function was responsible for motor neuron degeneration in ALS, and that the gain-of-function could be related to the redox properties of SOD1.
The discovery that mutations on the gene for an antioxidant enzyme such as SOD1 were associated with a population of familial ALS patients led to speculate on the role of oxidative stress in the pathogenesis of ALS (Beckman et al., 1993; Deng et al., 1993b; Rosen et al., 1993). From this original discovery to the present the interest on oxidative stress in ALS has been a rollercoaster. Several different groups described the presence of a variety of markers for oxidative stress in human samples and animal models of ALS, including elevated protein carbonyl and nitrotyrosine levels as well as lipid and DNA oxidation. Oxidation of proteins, lipids, and DNA was also found in transgenic mice and cell culture models (Barber and Shaw, 2010). On the other hand, other groups failed to find markers of oxidative damage in animal models of ALS, casting doubt on the relevance of oxidative stress in the pathogenesis of the disease (Barber and Shaw, 2010). Currently, a role for oxidative stress in ALS is generally accepted but whether oxidative stress is responsible for the mutant SOD1 gain-of-function is still controversial.
2.1. Mutant SOD1 aggregation and Zn-deficiency
Mutant SOD1s have a tendency to aggregate when expressed in bacterial systems and transfected cells, and the presence of mutant and wild type SOD1-containing aggregates has been described in animal models of ALS (Bruijn and Cleveland, 1996; Watanabe et al., 2001). The formation of aggregates clogging the proteasome and containing other relevant proteins along with mutant SOD1 is one of the possible explanations for SOD1 toxic gain-of-function. However, in mice expressing the SOD1A4V mutant, the most common mutation linked to familial ALS in humans, the mutant is expressed at high levels and forms protein aggregates but does not cause disease (Gurney et al., 1994). Alternatively, other groups proposed a hypothesis in which the formation of aggregates is a protective mechanism rather than cause of toxicity.
The link between the gain-of-function and the redox activity of soluble mutant SOD1 as a source of oxidative stress is based on the presence of the copper atom in the active site of the enzyme as well as the loss of zinc. The requirement for copper was challenged by genetic experiments in which the chaperone that delivers the copper metal to SOD1 was deleted. The ablation of the chaperone in the G93A, G85R, or G73R-SOD1 mutant mice decreased the activity of the enzyme but had no effect on the progression of the disease (Subramaniam et al., 2002), although it may be possible for SOD1 to acquire copper from an alternative source (Beckman et al., 2002). The transgenic expression of a SOD1 with mutations that eliminate the copper-binding site still produced disease (Prudencio et al., 2012; Wang et al., 2003). In contrast, another study showed that the mutant enzymes A4V, G85R, and G93A had a higher affinity for copper than the wild type protein, and that this aberrant copper binding was mediated by cysteine 111 (Watanabe et al., 2007), implying that the enzyme binds copper in an alternate site (Figure 1A).
Some SOD1 mutants bind copper and zinc and are fully active (Borchelt et al., 1994; Marklund et al., 1997) but many mutations affect the binding of zinc while copper remains tightly bound, thus favoring the formation of Zn-deficient SOD. In the SOD1G93A mouse model of ALS, the dietary depletion of zinc accelerates the progression of the disease while moderate supplement of zinc provides protection (Ermilova et al., 2005). Indeed, a peak corresponding to one-metal SOD1 was detected
ALS-linked mutant SOD1s have 5-50 fold less affinity for zinc than the wild type protein (Crow et al., 1997a; Lyons et al., 1996). The loss of zinc disorganizes the structure of the active site leaving the copper metal more expose and accessible to substrates other than superoxide, decreasing the normal activity of the enzyme. When replete with zinc, SOD1 mutants can generally fulfill the antioxidant activity of wild type SOD (Crow et al., 1997a). Early studies showed that mutant SOD1 has an aberrant chemistry and is reduced abnormally fast which allows the reaction with oxidants such as hydrogen peroxide and peroxynitrite (Crow et al., 1997a; Crow et al., 1997b; Lyons et al., 1996; Wiedau-Pazos et al., 1996), thus turning the antioxidant enzyme into a catalyst for oxidation. The conversion of SOD1 from antioxidant to pro-oxidant due to the loss of zinc is a simple explanation for the gain-of-function attributed to the ALS-linked SOD mutants, but is still highly controversial.
2.2. Formation of hydroxyl radical from hydrogen peroxide
In normal conditions SOD1 catalyzes the disproportionation of superoxide to hydrogen peroxide, but due to changes in mutant SOD1 conformation, the mutant enzyme can catalyze the production of hydroxyl radical from hydrogen peroxide
The aberrant chemistry of mutant SOD1 was shown to inactivate the glutamate transporter EAAT2 by oxidative reactions catalyzed by the A4V and I113T-SOD1 mutants and triggered by hydrogen peroxide (Trotti et al., 1999; Trotti et al., 1996). The function of this transporter is down regulated in human patients and animal models of ALS and its inactivation results in neuronal degeneration (Rothstein et al., 2005; Tanaka et al., 1997). Moreover, the aberrant SOD1 chemistry increases the vulnerability of a variety of cells in culture to hydrogen peroxide, with an increased susceptibility to inhibition by copper chelators. The G37R, G41D, and G85R-SOD1 mutants induce activation of caspase 1 and promoted apoptosis in N2a cells and tissue expressing mutant SOD1 when exposed to hydrogen peroxide. In NSC34 cells, a motor neuron model, mutant SOD1 induces cell death upon exposure of the cells to hydrogen peroxide (Pasinelli et al., 1998; Wiedau-Pazos et al., 1996). These findings suggest that the ALS phenotype may require both, the genetic background and an additional oxidative challenge.
2.3. Production of peroxynitrite
Nitric oxide alone is not toxic to normal motor neurons (Estévez et al., 1999), but when superoxide is also produced it can react with nitric oxide to form the powerful oxidant peroxynitrite, responsible for the induction of cell death. Overexpression of mutant SOD1 makes motor neurons vulnerable to exogenous and endogenous production of nitric oxide. The increased vulnerability is linked to the activation of the Fas death pathways (Raoul et al., 2002). More recently it was shown that motor neurons from mutant SOD1 transgenic animals have lower levels of a calcium-binding ER chaperone calreticulin. A decrease in the expression of this protein is necessary and sufficient to activate the Fas/NO pathways in motor neurons. Further evidence
2.4. Catalysis of tyrosine nitration
Cu,Zn-SOD1 is not only responsible for the production of peroxynitrite but it can also catalyze tyrosine nitration
3. Regulation of NADPH oxidase activity by mutant SOD1
Several lines of evidence support the role of oxidative stress in mutant SOD1 toxicity, but some evidence suggest that interactions other than the redox properties of the enzyme stimulate oxidative stress by different mechanisms. Mutant SOD1 can induce oxidative stress by disruption of the redox-sensitive regulation of NADPH oxidase (Nox) in microglial cells. Noxs are transmembrane proteins that catalyze the reduction of oxygen to superoxide using NADPH as an electron donor (Brown and Griendling, 2009). Superoxide is then converted to hydrogen peroxide by SOD1. Under reducing conditions, SOD1 regulates Nox2 activation by binding and stabilizing Rac1. The oxidation of Rac1 by hydrogen peroxide disrupts the complex with SOD1 and inactivates Nox2. Upon expression of certain ALS SOD1 mutants, the dissociation of Rac1 from SOD1 is impaired and Nox2 remains active (Figure 1C). In addition, the expression of Nox2 is upregulated in the SOD1G93A mouse model and in ALS patients. In fact, gene deletion of Nox1 or Nox2 provides the larger protection to date in animal models of ALS (Harraz et al., 2008; Marden et al., 2007).
4. Mutant SOD1 translocation to mitochondria
Mitochondria are one of the major sources of cellular ROS formed as by-products of oxidative phosphorylation. Abnormalities in the mitochondrial structure, localization and number as well as altered activity of the electron transport chain have been described in both, sporadic and familial ALS (Manfredi and Xu, 2005). The mitochondrial electron transport chain and ATP synthesis are severely impaired at disease onset in spinal cord and brain of SOD1G93A transgenic mice (Lin and Beal, 2006). Both, wild type and mutant SOD localize in mitochondria in the central nervous system (Higgins et al., 2002). Mutant human SOD1 was found in the mitochondrial outer membrane, intermembrane space and matrix in transgenic mice, while inactive mutant SOD1 accumulates and forms aggregates in the mitochondrial matrix in the brain (Vijayvergiya et al., 2005). Aggregates of the mutant enzyme are also selectively found in the mitochondrial outer membrane in spinal cord from mouse models of ALS (Liu et al., 2004). Interestingly, the anti-apoptotic protein Bcl-2 binds to mutant SOD1 and aggregates in spinal cord mitochondria from patients and a mouse model of ALS, suggesting that mutant SOD1 may be toxic by depleting motor neurons of this anti-apoptotic protein (Pasinelli et al., 2004). Mutant SOD1 targeted to the mitochondrial intermembrane space in NSC34 cells induces cell death upon exposure of the cells to hydrogen peroxide (Magrane et al., 2009). In addition, the increase in carbonylated proteins and lipid hydroperoxides in mitochondria, as well as the abnormally high rates of production of hydrogen peroxide in SOD1G93A transgenic mice (Mattiazzi et al., 2002; Panov et al., 2011) support the mutant SOD1 aberrant catalytic gain-of-function. Indeed, it was shown that metal-deficient SOD1s are prone to mitochondrial translocation and are found in the mitochondrial intermembrane space (Okado-Matsumoto and Fridovich, 2002). The mitochondria contain the majority of the cellular copper because is required by the oxygen-consuming proteins. The insertion of copper into the translocated metal-deficient SOD would result in the formation of Zn-deficient SOD inside the mitochondria (Figure 1A). This could explain why the mitochondria are affected early in the onset of the disease (Beckman et al., 2002). The ROS-linked toxic gain-of-function of mutant SOD1 would produce hydroxyl radical from H2O2 as well as peroxynitrite in the mitochondria. The mutant enzyme could then catalyze the nitration of mitochondrial proteins such as cyclophilin D and the adenine nucleotide translocator (Martin, 2010). Due to these toxic effects of mutant SOD1 on mitochondria, it has been proposed that the abnormal activity of the mitochondria in ALS may account for the initiation and progression of the disease. However, whether the mitochondrial localization of mutant SOD1 is cause or a consequence of pathology needs to be established.
5. Expression of mutant SOD1 in motor neurons and neighboring cells
A new mechanism integrating the autonomous and non-autonomous induction of motor neuron death in ALS is emerging. In this scenario, the role of motor neurons and surrounding cells in the onset and progression of ALS is temporally determined. Several studies were conducted where mutant SOD1 was selectively expressed
5.1. Expression of mutant SOD1 in motor neurons
ALS is a motor neuron disease characterized by the gradual and selective loss of both, upper and lower motor neurons. Expression of mutant SOD1 in spinal motor neurons and interneurons of chimeric mice is enough to induce neuronal degeneration (Boillee et al., 2006; Wang et al., 2008). The mice do not develop clinical ALS but the motor neurons expressing mutant SOD1 exhibit pathological and immunohistochemical abnormalities, while motor neurons negative for mutant SOD1 expression do not. These observations indicate that in the chimeric mice the degeneration of motor neurons can be cell-autonomous. The fact that only some of the motor neurons express mutant SOD1 in this model may explain why the animals do not develop the disease (Wang et al., 2008). Indeed, normal motor neurons can prevent or delay the degeneration of mutant SOD1-expressing motor neurons (Clement et al., 2003). In addition, decreased expression of mutant SOD1 in motor neurons has a modest effect on the duration of the disease but significantly delay the onset and early phase of the disease progression (Wang et al., 2008). Similar results were observed in culture, where primary spinal motor neurons as well as embryonic stem cell-derived motor neurons expressing mutant SOD1 showed changes characteristic of neurodegeneration (Di Giorgio et al., 2007; Raoul et al., 2002). Primary embryonic motor neurons from SOD1G93A and SOD1G85R transgenic animals exposed to endogenously produced or exogenously added nitric oxide show an increased susceptibility to cell death in culture (Raoul et al., 2002). Thus, motor neurons expressing mutant SOD1 are susceptible to cell death stimulated by oxidative stress.
5.2. Expression of mutant SOD1 in glial cells
Neighboring cells also seem to play a role in mutant SOD1 toxicity. Normal motor neurons in the context of a mutant SOD1-expressing chimera show signs of neurodegeneration, while non-neuronal cells negative for mutant SOD1 expression delay neuronal degeneration and significantly extend survival of mutant-expressing motor neurons (Clement et al., 2003). In the last few years, a role for microglia and astrocytes in the induction of motor neuron death has become evident.
5.2.1. Role of microglia in the induction of motor neuron death
Activated microglia is found in the spinal cord of SOD1G93A transgenic mice, suggesting that it may play a role in the neurodegeneration of neighboring motor neurons (Beers et al., 2006). Reducing the expression of mutant SOD1 in microglia and peripheral macrophages in chimeric mice leads to a delay in the late progression of ALS but has little effect on the onset and early disease progression (Boillee et al., 2006). Likewise, in the PU.1(-/-)/SOD1G93A mice unable to synthesize myeloid cells, the replacement of microglia, monocyte, and macrophage lineages with genotypically identical wild type cells slows disease progression and extends overall survival (Beers et al., 2006), suggesting that non cell-autonomous effects contribute to ALS progression independently of disease onset. Comparable findings were observed in co-culture studies where glial cells expressing mutant-SOD1 had a direct adverse effect on motor neuron survival (Di Giorgio et al., 2007). Microglia expressing G93A-SOD1 is toxic to primary motor neurons
5.2.2. Role of astrocytes in the induction of motor neuron death
Astrocytes are the most abundant non-neuronal cells in the nervous system. The co-culture of normal primary embryonic or stem cell-derived motor neurons with astrocytes expressing mutant SOD1 result in motor neuron death. The death pathway is triggered by a toxic factor released by the astrocytes (Aebischer et al., 2011; Nagai et al., 2007). A population of phenotypically aberrant astrocytes was recently described in the SOD1G93A mouse model of ALS (Diaz-Amarilla et al., 2011). These astrocytes, referred to as “AbA cells”, have an increased proliferative capacity and secrete soluble factors that are 10 times more potent than neonatal SOD1G93A astrocytes for the induction of motor neuron death. AbA cells are present in degenerating spinal cord of SODG93A rats surrounding affected motor neurons, and their number increases dramatically after disease onset, highlighting the importance of this finding. Interestingly, the levels of interferon-γ (IFNγ) are significantly increased in mutant SOD1-expressing astrocytes, and IFNγ induces motor neuron death (Aebischer et al., 2011), suggesting that this cytokine may be one of the toxic factors mediating induction of cell death (Figure 2). The role of astrocytes in the induction of motor neuron death was recently confirmed in astrocytes generated from post-mortem tissue of familial and sporadic ALS patients, additionally providing an
In summary, the mechanism of mutant SOD1 toxicity is unknown and highly controversial but there is strong evidence suggesting that the mutant SOD1 toxic gain-of-function is related to an alteration of its redox properties and the induction of oxidative stress. In this scenario, the aberrant chemistry of mutant SOD1 turns the enzyme from antioxidant to pro-oxidant. Zn-deficient SOD1 reacts with hydrogen peroxide, produces superoxide and peroxynitrite, and is able to catalyze tyrosine nitration, altering the cellular redox balance. In addition, although not related to the redox properties of the enzyme, the interaction of mutant SOD1 with mitochondria and Nox, the two major sources of cellular ROS, further support the involvement of oxidative stress in the toxic gain-of-function. The cell type affected by mutant SOD1 is also controversial. A picture in which several cell types are affected and play a role at different stages of the disease seems to be emerging. In this context, during onset and early stages of the disease SOD1-expressing motor neurons undergo neurodegeneration and cell death by cell-autonomous processes. The activation of microglia and astrocytes may work as an amplification mechanism in the induction of motor neuron death in the late progression of the disease (Figure 2).
Aebischer J P Cassina B Otsmane A Moumen D Seilhean V Meininger L Barbeito and B Pettmann C Raoul 2011IFNgamma triggers a LIGHT-dependent selective death of motoneurons contributing to the non-cell-autonomous effects of mutant SOD1. Cell death and differentiation 18 754 768
and Barber S. C P. J Shaw 2010Oxidative stress in ALS: key role in motor neuron injury and therapeutic target. Free radical biology & medicine 48 629 641
Beal M. F L. J Ferrante S. E Browne R. T Matthews and N. W Kowall R. H Brown 1997Increased 3-nitrotyrosine in both sporadic and familial amyotrophic lateral sclerosis. Ann Neurol 42 644 654
Beckman J. S M Carson and C. D Smith W. H Koppenol 1993ALS, SOD and peroxynitrite. Nature364:584.
Beckman J. S A. G Estévez and L Barbeito J. P Crow 2002CCS knockout mice establish an alternative source of copper for SOD in ALS. Free Rad. Biol. Med. 33 1433 1435
Beckman J. S A. G Estevez and J. P Crow L Barbeito 2001Superoxide dismutase and the death of motoneurons in ALS. Trends in neurosciences24:S 15 20
Beers D. R J. S Henkel Q Xiao W Zhao J Wang A. A Yen L Siklos and S. R Mckercher S. H Appel 2006Wild-type microglia extend survival in PU.1 knockout mice with familial amyotrophic lateral sclerosis. Proceedings of the National Academy of Sciences of the United States of America 103 16021 16026
Bernard-marissal N A Moumen C Sunyach C Pellegrino K Dudley C. E Henderson and C Raoul B Pettmann 2012Reduced Calreticulin Levels Link Endoplasmic Reticulum Stress and Fas-Triggered Cell Death in Motoneurons Vulnerable to ALS. The Journal of neuroscience : the official journal of the Society for Neuroscience 32 4901 4912
Boillee S K Yamanaka C. S Lobsiger N. G Copeland N. A Jenkins G Kassiotis and G Kollias D. W Cleveland 2006Onset and progression in inherited ALS determined by motor neurons and microglia. Science 312 1389 1392
Cleveland. Borchelt D. R M. K Lee H. S Slunt M Guarnieri Z. S Xu P. C Wong R. H Brown Jr D. L Price S. S Sisodiaand D. W 1994Superoxide dismutase 1 with mutations linked to familial amyotrophic lateral sclerosis possesses significant activity. Proceedings of the National Academy of Sciences of the United States of America 91 8292 8296
and Brown D. I K. K Griendling 2009Nox proteins in signal transduction. Free radical biology & medicine 47 1239 1253
and Bruijn L. I D. W Cleveland 1996Mechanisms of selective motor neuron death in ALS: insights from transgenic mouse models of motor neuron disease. Neuropathology and applied neurobiology 22 373 387
Cleveland. Clement A. M M. D Nguyen E. A Roberts M. L Garcia S Boillee M Rule A. P Mcmahon W Doucette D Siwek R. J Ferrante R. H Brown Jr J. P Julien L. S Goldsteinand D. W 2003Wild-type nonneuronal cells extend survival of SOD1 mutant motor neurons in ALS mice. Science 302 113 117
Crow J. P J. B Sampson Y Zhuang and J. A Thompson J. S Beckman 1997aDecreased zinc affinity of amyotrophic lateral sclerosis-associated superoxide dismutase mutants leads to enhanced catalysis of tyrosine nitration by peroxynitrite. J. Neurochem. 69 1936 1944
Crow J. P M. J Strong Y Zhuang and Y Ye J. S Beckman 1997bSuperoxide dimutase catalyzes nitration of tyrosines by peroxinitrite in the rod and head domains of neurofilament L. J Neurochem 69 1945 1953
M.C. Dal Canto, T.V. O’Halloran, and T. Siddique. Deng H X. , Y Shi Y Furukawa H Zhai R Fu E Liu G. H Gorrie M. S Khan W. -Y Hung E. H Bigio T Lukas 2006Conversion to the amyotrophic lateral sclerosis phenotype is associated with intermolecular linked insoluble aggregates of SOD1 in mitochondria. PNAS 103 7142 7147
Deng H. X A Hentati J. A Tainer Z Iqbal A Cayabyab W. Y Hung E. D Getzoff P Hu B Herzfeldt and R. P Roos et al 1993aAmyotrophic lateral sclerosis and structural defects in Cu,Zn superoxide dismutase. Science 261 1047 1051
Deng H. X A Hentati J. A Tainer Z Iqbal A Cayabyab W. Y Hung E. D Getzoff P Hu B Herzfeldt R. P Roos C Warner G Deng E Soriano C Smyth H. E Parge A Ahmed A. D Roses R. A Hallewell and M. A Prericak-vance T Siddique 1993bAmyotrophic lateral sclerosis and structural defects in Cu,Zn superoxide dismutase. Science 261 1047 1051
Di GiorgioF.P., M.A. Carrasco, M.C. Siao, T. Maniatis, and K. Eggan. 2007Non-cell autonomous effect of glia on motor neurons in an embryonic stem cell-based ALS model. Nature neuroscience 10 608 614
Diaz-amarilla P S Olivera-bravo E Trias A Cragnolini L Martinez-palma P Cassina and J Beckman L Barbeito 2011Phenotypically aberrant astrocytes that promote motoneuron damage in a model of inherited amyotrophic lateral sclerosis. Proceedings of the National Academy of Sciences of the United States of America 108 18126 18131
Ermilova I. P V. B Ermilov M Levy E Ho and C Pereira J. S Beckman 2005Protection by dietary zinc in ALS mutant G93A SOD transgenic mice. Neuroscience letters 379 42 46
Estévez A. G J. P Crow J. B Sampson C Reiter Y. -X Zhuang G. J Richardson M. M Tarpey and L Barbeito J. S Beckman 1999Induction of nitric oxide-dependent apoptosis in motor neurons by zinc-deficient superoxide dismutase. Science 286 2498 2500
Ferrante R. J L. A Shinobu J. B Schulz R. T Mathews C. E Thomas N. W Kowall and M. E Gurney M. F Beal 1997Increased 3-nitrotyrosine and oxidative damage in mice with a human copper/zinc superoxide dismutase mutation. Ann Neurol 42 326 334
and Franco M. C A. G Estévez 2011Reactive Nitrogen Species in Motor Neuron Apoptosis. In: Amyotrophic Lateral Sclerosis, edited by Martin H. Mauer. InTech, Rijeka, Croatia. 313 334pp.
Fukada K S Nagano M Satoh C Tohyama T Nakanishi A Shimizu and T Yanagihara S Sakoda 2001Stabilization of mutant Cu/Zn superoxide dismutase (SOD1) protein by coexpressed wild SOD1 protein accelerates the disease progression in familial amyotrophic lateral sclerosis mice. Eur J Neurosci 14 2032 2036
Furukawa Y R Fu H. -X Deng and T Siddique T. V. O Halloran 2006From the Cover: Disulfide cross-linked protein represents a significant fraction of ALS-associated Cu, Zn-superoxide dismutase aggregates in spinal cords of model mice. PNAS 103 7148 7153
Getzoff E. D J. A Tainer M. M Stempien and G. I Bell R. A Hallewell 1989Evolution of CuZn superoxide dismutase and the Greek key beta-barrel structural motif. Proteins 5 322 336
Gurney M. E H Pu A. Y Chiu M. C. D Canto C. Y Polchow D. D Alexander J Caliendo A Hentati Y. W Kwon H. -X Deng W Chen P Zhai and R. L Sufit T Siddique 1994Motor neuron degeneration in mice that express a human Cu,Zn superoxide dismutase mutation. Science 264 1772 1775
Haidet-phillips A. M M. E Hester C. J Miranda K Meyer L Braun A Frakes S Song S Likhite M. J Murtha K. D Foust M Rao A Eagle A Kammesheidt A Christensen J. R Mendell and A. H Burghes B. K Kaspar 2011Astrocytes from familial and sporadic ALS patients are toxic to motor neurons. Nature biotechnology 29 824 828
Harraz M. M J. J Marden W Zhou Y Zhang A Williams V. S Sharov K Nelson M Luo H Paulson and C Schoneich J. F Engelhardt 2008SOD1 mutations disrupt redox-sensitive Rac regulation of NADPH oxidase in a familial ALS model. J Clin Invest 118 659 670
Higgins C. M C Jung and H Ding Z Xu 2002Mutant Cu, Zn superoxide dismutase that causes motoneuron degeneration is present in mitochondria in the CNS. The Journal of neuroscience : the official journal of the Society for Neuroscience22:RC215.
Ischiropoulos H L Zhu J Chen M Tsai J. C Martin and C. D Smith J. S Beckman 1992Peroxynitrite-mediated tyrosine nitration catalyzed by superoxide dismutase. Archives of Biochemistry and Biophysics 298 431 437
and Lin M. T M. F Beal 2006Mitochondrial dysfunction and oxidative stress in neurodegenerative diseases. Nature 443 787 795
Liu D J Wen and J Liu L Li 1999The roles of free radicals in amyotrophic lateral sclerosis: reactive oxygen species and elevated oxidation of protein, DNA, and membrane phospholipids. FASEB journal : official publication of the Federation of American Societies for Experimental Biology 13 2318 2328
Liu J C Lillo P. A Jonsson C. V Velde C. M Ward T. M Miller J. R Subramaniam J. D Rothstein S Marklund P. M Andersen T Brannstrom O Gredal P. C Wong and D. S Williams D. W Cleveland 2004Toxicity of Familial ALS-Linked SOD1 Mutants from Selective Recruitment to Spinal Mitochondria. Neuron 43 5 17
Lyons T. J H Liu J. J Goto A Nersissian J. A Roe J. A Graden C Cafe L. M Ellerby D. E Bredesen and E. B Gralla J. S Valentine 1996Mutations in copper-zinc superoxide dismutase that cause amyotrophic lateral sclerosis alter the zinc binding site and the redox behavior of the protein. Proceedings of the National Academy of Sciences of the United States of America 93 12240 12244
Magrane J I Hervias M. S Henning M Damiano and H Kawamata G Manfredi 2009Mutant SOD1 in neuronal mitochondria causes toxicity and mitochondrial dynamics abnormalities. Hum Mol Genet 18 4552 4564
and Manfredi G Z Xu 2005Mitochondrial dysfunction and its role in motor neuron degeneration in ALS. Mitochondrion 5 77 87
Marden J. J M. M Harraz A. J Williams K Nelson M Luo and H Paulson J. F Engelhardt 2007Redox modifier genes in amyotrophic lateral sclerosis in mice. J Clin Invest 117 2913 2919
Marklund S. L P. M Andersen L Forsgren P Nilsson P. I Ohlsson and G Wikander A Oberg 1997Normal binding and reactivity of copper in mutant superoxide dimutase isolated from amyotrophic lateral sclerosis patients. J Neurochem 69 675 681
Martin L. J 2010The mitochondrial permeability transition pore: a molecular target for amyotrophic lateral sclerosis therapy. Biochimica et biophysica acta 1802 186 197
Mattiazzi M M. D Aurelio C. D Gajewski K Martushova M Kiaei and M. F Beal G Manfredi 2002Mutated human SOD1 causes dysfunction of oxidative phosphorylation in mitochondria of transgenic mice. The Journal of biological chemistry 277 29626 29633
and Mccord J. M I Fridovich 1969Superoxide dismutase. An enzymic function for erythrocuprein (hemocuprein). The Journal of biological chemistry 244 6049 6055
Nagai M D. B Re T Nagata A Chalazonitis T. M Jessell and H Wichterle S Przedborski 2007Astrocytes expressing ALS-linked mutated SOD1 release factors selectively toxic to motor neurons. Nature neuroscience 10 615 622
and Nauser T W. H Koppenol 2002The rate constant of the reaction of superoxide with nitrogen monoxide: Approaching the diffusion limit. J Phys Chem A 106 4084 4086
and Okado-matsumoto A I Fridovich 2002Amyotrophic lateral sclerosis: a proposed mechanism. Proceedings of the National Academy of Sciences of the United States of America 99 9010 9014
Panov A N Kubalik N Zinchenko R Hemendinger and S Dikalov H. L Bonkovsky 2011Respiration and ROS production in brain and spinal cord mitochondria of transgenic rats with mutant G93a Cu/Zn-superoxide dismutase gene. Neurobiol Dis 44 53 62
Jr. Pasinelli P M. E Belford N Lennon B. J Bacskai B. T Hyman and D Trotti R. H Brown 2004Amyotrophic lateral sclerosis-associated SOD1 mutant proteins bind and aggregate with Bcl-2 in spinal cord mitochondria. Neuron 43 19 30
and R.H. Brown Jr. Pasinelli P D. R Borchelt M. K Houseweart D. W Cleveland 1998Caspase-1 is activated in neural cells and tissue with amyotrophic lateral sclerosis-associated mutations in copper-zinc superoxide dismutase. Proc Natl Acad Sci USA 95 15763 15768
Perry J. J D. S Shin and E. D Getzoff J. A Tainer 2010The structural biochemistry of the superoxide dismutases. Biochimica et biophysica acta 1804 245 262
Prudencio M A Durazo and J. P Whitelegge D. R Borchelt 2009Modulation of Mutant Superoxide Dismutase 1 Aggregation by Co-Expression of Wild-Type Enzyme. J Neurochem 108 1009 1018
Prudencio M H Lelie H. H Brown J. P Whitelegge and J. S Valentine D. R Borchelt 2012A novel variant of human superoxide dismutase 1 harboring amyotrophic lateral sclerosis-associated and experimental mutations in metal-binding residues and free cysteines lacks toxicity in vivo. Journal of neurochemistry 121 475 485
Raoul C A. G Estévez H Nishimune D. W Cleveland O Delapeyrière C. E Henderson and G Haase B Pettmann 2002Motoneuron death triggered by a specific pathway downstream of Fas: potentiation by ALS-linked SOD1 mutations. Neuron 35 1067 1083
Snider. Reaume A. G J. L Elliott E. K Hoffman N. W Kowall R. J Ferrante D. F Siwek H. M Wilcox D. G Flood M. F Beal R. H Brown Jr R. W Scottand W. D 1996Motor neurons in Cu/Zn superoxide dismutase-deficient mice develop normally but exhibit enhanced cell death after axonal injury. Nature genetics 13 43 47
Rhoads T. W N. I Lopez D. R Zollinger J. T Morre B. L Arbogast C. S Maier and L Denoyer J. S Beckman 2011Measuring copper and zinc superoxide dismutase from spinal cord tissue using electrospray mass spectrometry. Analytical biochemistry 415 52 58
Roberts B. R J. A Tainer E. D Getzoff D. A Malencik S. R Anderson V. C Bomben K. R Meyers and P. A Karplus J. S Beckman 2007Structural characterization of zinc-deficient human superoxide dismutase and implications for ALS. Journal of molecular biology 373 877 890
Rosen D. R T Siddique D Patterson D. A Figlewicz P Sapp A Hentati D Donaldson J Goto J. P. O Regan H. -X Deng Z Rahmani A Krizus D Mckenna-yasek A Cayabyab S. M Gaston R Berger R. E Tanszi J. J Halperin B Herzfeldt R. V. d Bergh W. -Y Hung T Bird G Deng D. W Mulder C Smyth N. G Lang E Soriana M. A Pericak-vance J Haines G. A Rouleau J. S Gusella and H. R Horvitz R. H. J Brown 1993Mutations in Cu/Zn superoxide dimutase gene are associated with familial amyotrophic lateral sclerosis. Nature 362 59 62
Gupta, and P.B. Fisher. Rothstein J. D S Patel M. R Regan C Haenggeli Y. H Huang D. E Bergles L Jin M Dykes Hoberg S Vidensky D. S Chung S. V Toan L. I Bruijn Z. Z Su P 2005Beta-lactam antibiotics offer neuroprotection by increasing glutamate transporter expression. Nature 433 73 77
Sahawneh M. A K. C Ricart B. R Roberts V. C Bomben M Basso Y Ye J Sahawneh M. C Franco and J. S Beckman A. G Estevez 2010Cu,Zn superoxide dismutase (SOD) increases toxicity of mutant and Zn-deficient superoxide dismutase by enhancing protein stability. The Journal of biological chemistry 285 33885 33897
Subramaniam J. R W. E Lyons J Liu T. B Bartnikas J Rothstein D. L Price D. W Cleveland and J. D Gitlin P. C Wong 2002Mutant SOD1 causes motor neuron disease independent of copper chaperone-mediated copper loading. Nature Neurosci 5 301 307
Tanaka K K Watase T Manabe K Yamada M Watanabe K Takahashi H Iwama T Nishikawa N Ichihara T Kikuchi S Okuyama N Kawashima S Hori and M Takimoto K Wada 1997Epilepsy and exacerbation of brain injury in mice lacking the glutamate transporter GLT-1. Science 276 1699 1702
Trotti D A Rolfs N. C Danbolt and R. H. J Brown M. A Hediger 1999SOD 1 mutants linked to amyotrophic lateral sclerosis selectivity inactivate a glial glutamate transporter. Nature Neurosci 2 427 433
Trotti D D Rossi O Gjesdal L. M Levy G Racagni and N. C Danbolt A Volterra 1996Peroxynitrite inhibits glutamate transporter subtypes. J Biol. Chem. 271 5976 5979
and Trumbull K. A J. S Beckman 2009A role for copper in the toxicity of zinc-deficient superoxide dismutase to motor neurons in amyotrophic lateral sclerosis. Antioxidants & redox signaling 11 1627 1639
Vijayvergiya C M. F Beal and J Buck G Manfredi 2005Mutant superoxide dismutase 1 forms aggregates in the brain mitochondrial matrix of amyotrophic lateral sclerosis mice. The Journal of neuroscience : the official journal of the Society for Neuroscience 25 2463 2470
Wang H and Z Ying G Wang 2012Ataxin-3 Regulates Aggresome Formation of Copper-Zinc Superoxide Dismutase (SOD1) by Editing K63-linked Polyubiquitin Chains. The Journal of biological chemistry 287 28576 28585
Wang J. J H. H Slunt V. V Gonzales D. D Fromholt M. M Coonfield N. G. N. G Copeland and N. A. N. A Jenkins D. R. D. R Borchelt 2003Copper-binding-site-null SOD1 causes ALS in transgenic mice: aggregates of non-native SOD1 delineate a common feature. Human molecular genetics12:2753.
Wang L H. X Deng G Grisotti H Zhai and T Siddique R. P Roos 2009Wild-type SOD1 overexpression accelerates disease onset of a G85R SOD1 mouse. Hum Mol Genet 18 1642 1651
Wang L K Sharma H. X Deng T Siddique G Grisotti and E Liu R. P Roos 2008Restricted expression of mutant SOD1 in spinal motor neurons and interneurons induces motor neuron pathology. Neurobiol Dis 29 400 408
Watanabe M M Dykes-hoberg V. C Culotta D. L Price and P. C Wong J. D Rothstein 2001Histological evidence of protein aggregation in mutant SOD1 transgenic mice and in amyotrophic lateral sclerosis neural tissues. Neurobiol Dis 8 933 941
Watanabe S S Nagano J Duce M Kiaei Q. -X Li S. M Tucker A Tiwari J. R. H Brown M. F Beal L. J Hayward V. C Culotta S Yoshihara and S Sakoda A. I Bush 2007Increased affinity for copper mediated by cysteine 111 in forms of mutant superoxide dismutase 1 linked to amyotrophic lateral sclerosis. Free Radical Biology and Medicine 42 1534 1542
Wiedau-pazos M J. J Gato S Rabizadeh E. B Gralla B Roe C. K Lee and J. S Valentine D. E Bredesen 1996Alterd reactivity of superoxide dismutase in familial amyotrophic lateral sclerosis. Science 271 515 518
Witan H P Gorlovoy A. M Kaya I Koziollek-drechsler H Neumann and C Behl A. M Clement 2009Wild-type Cu/Zn superoxide dismutase (SOD1) does not facilitate, but impedes the formation of protein aggregates of amyotrophic lateral sclerosis causing mutant SOD1. Neurobiol Dis 36 331 342
Yim M. B and P. B Chock E. R Stadtman 1990Copper, zinc superoxide dismutase catalyzes hydroxyl radical production from hydrogen peroxide. Proceedings of the National Academy of Sciences of the United States of America 87 5006 5010
function of an amyotrophic lateral sclerosis-associated Cu,Zn-superoxide dismutase mutant: An enhancement of free radical formation due to a decrease in Km for hydrogen peroxide. Yim M. B J. H Kang H. S Yim H. S Kwak and P. B Chock E. R Stadtman 1996 A Gain-of Proceedings of the National Academy of Sciences of the United States of America 93 5709 5714